Academic Appointments


Professional Education


  • Postdoctoral Fellow, University of California, San Francisco, Cellular and Molecular Pharmacology (2013)
  • Ph.D., Harvard University, Biological and Biomedical Sciences (2005)
  • B.S., University of Wisconsin, Madison, Biochemistry and Molecular Biology (1996)

Current Research and Scholarly Interests


We are an interdisciplinary lab focused on two major areas:(1) we seek to understand mechanisms of cancer growth and drug resistance in order to find new therapeutic targets(2) we study mechanisms by which macrophages and other cells take up diverse materials by endocytosis and phagocytosis; these substrates range from bacteria, viruses, and cancer cells to drugs and protein toxins.
 
In each case, the processes we study represent both fascinating basic problems in cell biology and important therapeutic targets. A complementary interest is in the characterization of novel small molecule drugs and identification of synergistic drug interactions, with the aim of finding new treatments for diseases such as cancer and neurodegeneration.
 
To accomplish these goals, we develop and use new technologies for high-throughput functional genomics. These include ultra-complex CRISPR/Cas9 and RNAi-based libraries for genome-wide screens, systematic pairwise genetic interaction maps, and strategies for targeted mutagenesis. We combine these techniques with microscopy, biochemistry, cell biology, and bioinformatics, tailored to each problem. Together with collaborators, we use these tools to annotate the genome in health and disease states.

2023-24 Courses


Stanford Advisees


Graduate and Fellowship Programs


All Publications


  • Inter-cellular CRISPR screens reveal regulators of cancer cell phagocytosis. Nature Kamber, R. A., Nishiga, Y., Morton, B., Banuelos, A. M., Barkal, A. A., Vences-Catalan, F., Gu, M., Fernandez, D., Seoane, J. A., Yao, D., Liu, K., Lin, S., Spees, K., Curtis, C., Jerby-Arnon, L., Weissman, I. L., Sage, J., Bassik, M. C. 2021

    Abstract

    Monoclonal antibody therapies targeting tumour antigens drive cancer cell elimination in large part by triggering macrophage phagocytosis of cancer cells1-7. However, cancer cells evade phagocytosis using mechanisms that are incompletely understood. Here we develop a platform for unbiased identification of factors that impede antibody-dependent cellular phagocytosis (ADCP) using complementary genome-wide CRISPR knockout and overexpression screens in both cancer cells and macrophages. In cancer cells, beyond known factors such as CD47, we identify many regulators of susceptibility to ADCP, including the poorly characterized enzyme adipocyte plasma membrane-associated protein (APMAP). We find that loss of APMAP synergizes with tumour antigen-targeting monoclonal antibodies and/or CD47-blocking monoclonal antibodies to drive markedly increased phagocytosis across a wide range of cancer cell types, including those that are otherwise resistant to ADCP. Additionally, we show that APMAP loss synergizes with several different tumour-targeting monoclonal antibodies to inhibit tumour growth in mice. Using genome-wide counterscreens in macrophages, we find that the G-protein-coupled receptor GPR84 mediates enhanced phagocytosis of APMAP-deficient cancer cells. This work reveals a cancer-intrinsic regulator of susceptibility to antibody-driven phagocytosis and, more broadly, expands our knowledge of the mechanisms governing cancer resistance to macrophage phagocytosis.

    View details for DOI 10.1038/s41586-021-03879-4

    View details for PubMedID 34497417

  • CRISPR screens in cancer spheroids identify 3D growth-specific vulnerabilities. Nature Han, K., Pierce, S. E., Li, A., Spees, K., Anderson, G. R., Seoane, J. A., Lo, Y. H., Dubreuil, M., Olivas, M., Kamber, R. A., Wainberg, M., Kostyrko, K., Kelly, M. R., Yousefi, M., Simpkins, S. W., Yao, D., Lee, K., Kuo, C. J., Jackson, P. K., Sweet-Cordero, A., Kundaje, A., Gentles, A. J., Curtis, C., Winslow, M. M., Bassik, M. C. 2020; 580 (7801): 136-141

    Abstract

    Cancer genomics studies have identified thousands of putative cancer driver genes1. Development of high-throughput and accurate models to define the functions of these genes is a major challenge. Here we devised a scalable cancer-spheroid model and performed genome-wide CRISPR screens in 2D monolayers and 3D lung-cancer spheroids. CRISPR phenotypes in 3D more accurately recapitulated those of in vivo tumours, and genes with differential sensitivities between 2D and 3D conditions were highly enriched for genes that are mutated in lung cancers. These analyses also revealed drivers that are essential for cancer growth in 3D and in vivo, but not in 2D. Notably, we found that carboxypeptidase D is responsible for removal of a C-terminal RKRR motif2 from the α-chain of the insulin-like growth factor 1 receptor that is critical for receptor activity. Carboxypeptidase D expression correlates with patient outcomes in patients with lung cancer, and loss of carboxypeptidase D reduced tumour growth. Our results reveal key differences between 2D and 3D cancer models, and establish a generalizable strategy for performing CRISPR screens in spheroids to reveal cancer vulnerabilities.

    View details for DOI 10.1038/s41586-020-2099-x

    View details for PubMedID 32238925

  • High-Throughput Discovery and Characterization of Human Transcriptional Effectors. Cell Tycko, J. n., DelRosso, N. n., Hess, G. T., Aradhana, n. n., Banerjee, A. n., Mukund, A. n., Van, M. V., Ego, B. K., Yao, D. n., Spees, K. n., Suzuki, P. n., Marinov, G. K., Kundaje, A. n., Bassik, M. C., Bintu, L. n. 2020

    Abstract

    Thousands of proteins localize to the nucleus; however, it remains unclear which contain transcriptional effectors. Here, we develop HT-recruit, a pooled assay where protein libraries are recruited to a reporter, and their transcriptional effects are measured by sequencing. Using this approach, we measure gene silencing and activation for thousands of domains. We find a relationship between repressor function and evolutionary age for the KRAB domains, discover that Homeodomain repressor strength is collinear with Hox genetic organization, and identify activities for several domains of unknown function. Deep mutational scanning of the CRISPRi KRAB maps the co-repressor binding surface and identifies substitutions that improve stability/silencing. By tiling 238 proteins, we find repressors as short as ten amino acids. Finally, we report new activator domains, including a divergent KRAB. These results provide a resource of 600 human proteins containing effectors and demonstrate a scalable strategy for assigning functions to protein domains.

    View details for DOI 10.1016/j.cell.2020.11.024

    View details for PubMedID 33326746

  • Retro-2 protects cells from ricin toxicity by inhibiting ASNA1-mediated ER targeting and insertion of tail-anchored proteins. eLife Morgens, D. W., Chan, C., Kane, A. J., Weir, N. R., Li, A., Dubreuil, M. M., Tsui, C. K., Hess, G. T., Lavertu, A., Han, K., Polyakov, N., Zhou, J., Handy, E. L., Alabi, P., Dombroski, A., Yao, D., Altman, R. B., Sello, J. K., Denic, V., Bassik, M. C. 2019; 8

    Abstract

    The small molecule Retro-2 prevents ricin toxicity through a poorly-defined mechanism of action (MOA), which involves halting retrograde vesicle transport to the endoplasmic reticulum (ER). CRISPRi genetic interaction analysis revealed Retro-2 activity resembles disruption of the transmembrane domain recognition complex (TRC) pathway, which mediates post-translational ER-targeting and insertion of tail-anchored (TA) proteins, including SNAREs required for retrograde transport. Cell-based and in vitro assays show that Retro-2 blocks delivery of newly-synthesized TA-proteins to the ER-targeting factor ASNA1 (TRC40). An ASNA1 point mutant identified using CRISPR-mediated mutagenesis abolishes both the cytoprotective effect of Retro-2 against ricin and its inhibitory effect on ASNA1-mediated ER-targeting. Together, our work explains how Retro-2 prevents retrograde trafficking of toxins by inhibiting TA-protein targeting, describes a general CRISPR strategy for predicting the MOA of small molecules, and paves the way for drugging the TRC pathway to treat broad classes of viruses known to be inhibited by Retro-2.

    View details for DOI 10.7554/eLife.48434

    View details for PubMedID 31674906

  • CRISPR-Cas9 screens identify regulators of antibody-drug conjugate toxicity. Nature chemical biology Tsui, C. K., Barfield, R. M., Fischer, C. R., Morgens, D. W., Li, A., Smith, B. A., Gray, M. A., Bertozzi, C. R., Rabuka, D., Bassik, M. C. 2019

    Abstract

    Antibody-drug conjugates (ADCs) selectively deliver chemotherapeutic agents to target cells and are important cancer therapeutics. However, the mechanisms by which ADCs are internalized and activated remain unclear. Using CRISPR-Cas9 screens, we uncover many known and novel endolysosomal regulators as modulators of ADC toxicity. We identify and characterize C18ORF8/RMC1 as a regulator of ADC toxicity through its role in endosomal maturation. Through comparative analysis of screens with ADCs bearing different linkers, we show that a subset of late endolysosomal regulators selectively influence toxicity of noncleavable linker ADCs. Surprisingly, we find cleavable valine-citrulline linkers can be processed rapidly after internalization without lysosomal delivery. Lastly, we show that sialic acid depletion enhances ADC lysosomal delivery and killing in diverse cancer cell types, including with FDA (US Food and Drug Administration)-approved trastuzumab emtansine (T-DM1) in Her2-positive breast cancer cells. Together, these results reveal new regulators of endolysosomal trafficking, provide important insights for ADC design and identify candidate combination therapy targets.

    View details for DOI 10.1038/s41589-019-0342-2

    View details for PubMedID 31451760

  • Identification of phagocytosis regulators using magnetic genome-wide CRISPR screens. Nature genetics Haney, M. S., Bohlen, C. J., Morgens, D. W., Ousey, J. A., Barkal, A. A., Tsui, C. K., Ego, B. K., Levin, R., Kamber, R. A., Collins, H., Tucker, A., Li, A., Vorselen, D., Labitigan, L., Crane, E., Boyle, E., Jiang, L., Chan, J., Rincon, E., Greenleaf, W. J., Li, B., Snyder, M. P., Weissman, I. L., Theriot, J. A., Collins, S. R., Barres, B. A., Bassik, M. C. 2018

    Abstract

    Phagocytosis is required for a broad range of physiological functions, from pathogen defense to tissue homeostasis, but the mechanisms required for phagocytosis of diverse substrates remain incompletely understood. Here, we developed a rapid magnet-based phenotypic screening strategy, and performed eight genome-wide CRISPR screens in human cells to identify genes regulating phagocytosis of distinct substrates. After validating select hits in focused miniscreens, orthogonal assays and primary human macrophages, we show that (1) the previously uncharacterized gene NHLRC2 is a central player in phagocytosis, regulating RhoA-Rac1 signaling cascades that control actin polymerization and filopodia formation, (2) very-long-chain fatty acids are essential for efficient phagocytosis of certain substrates and (3) the previously uncharacterized Alzheimer's disease-associated gene TM2D3 can preferentially influence uptake of amyloid-beta aggregates. These findings illuminate new regulators and core principles of phagocytosis, and more generally establish an efficient method for unbiased identification of cellular uptake mechanisms across diverse physiological and pathological contexts.

    View details for PubMedID 30397336

  • Pathways for macrophage uptake of cell-free circular RNAs. Molecular cell Amaya, L., Abe, B., Liu, J., Zhao, F., Zhang, W. L., Chen, R., Li, R., Wang, S., Kamber, R. A., Tsai, M. C., Bassik, M. C., Majeti, R., Chang, H. Y. 2024

    Abstract

    Circular RNAs (circRNAs) are stable RNAs present in cell-free RNA, which may comprise cellular debris and pathogen genomes. Here, we investigate the phenomenon and mechanism of cellular uptake and intracellular fate of exogenous circRNAs. Human myeloid cells and B cells selectively internalize extracellular circRNAs. Macrophage uptake of circRNA is rapid, energy dependent, and saturable. CircRNA uptake can lead to translation of encoded sequences and antigen presentation. The route of internalization influences immune activation after circRNA uptake, with distinct gene expression programs depending on the route of RNA delivery. Genome-scale CRISPR screens and chemical inhibitor studies nominate macrophage scavenger receptor MSR1, Toll-like receptors, and mTOR signaling as key regulators of receptor-mediated phagocytosis of circRNAs, a dominant pathway to internalize circRNAs in parallel to macropinocytosis. These results suggest that cell-free circRNA serves as an "eat me" signal and danger-associated molecular pattern, indicating orderly pathways of recognition and disposal.

    View details for DOI 10.1016/j.molcel.2024.04.022

    View details for PubMedID 38761795

  • Multicenter integrated analysis of noncoding CRISPRi screens. Nature methods Yao, D., Tycko, J., Oh, J. W., Bounds, L. R., Gosai, S. J., Lataniotis, L., Mackay-Smith, A., Doughty, B. R., Gabdank, I., Schmidt, H., Guerrero-Altamirano, T., Siklenka, K., Guo, K., White, A. D., Youngworth, I., Andreeva, K., Ren, X., Barrera, A., Luo, Y., Yardımcı, G. G., Tewhey, R., Kundaje, A., Greenleaf, W. J., Sabeti, P. C., Leslie, C., Pritykin, Y., Moore, J. E., Beer, M. A., Gersbach, C. A., Reddy, T. E., Shen, Y., Engreitz, J. M., Bassik, M. C., Reilly, S. K. 2024

    Abstract

    The ENCODE Consortium's efforts to annotate noncoding cis-regulatory elements (CREs) have advanced our understanding of gene regulatory landscapes. Pooled, noncoding CRISPR screens offer a systematic approach to investigate cis-regulatory mechanisms. The ENCODE4 Functional Characterization Centers conducted 108 screens in human cell lines, comprising >540,000 perturbations across 24.85 megabases of the genome. Using 332 functionally confirmed CRE-gene links in K562 cells, we established guidelines for screening endogenous noncoding elements with CRISPR interference (CRISPRi), including accurate detection of CREs that exhibit variable, often low, transcriptional effects. Benchmarking five screen analysis tools, we find that CASA produces the most conservative CRE calls and is robust to artifacts of low-specificity single guide RNAs. We uncover a subtle DNA strand bias for CRISPRi in transcribed regions with implications for screen design and analysis. Together, we provide an accessible data resource, predesigned single guide RNAs for targeting 3,275,697 ENCODE SCREEN candidate CREs with CRISPRi and screening guidelines to accelerate functional characterization of the noncoding genome.

    View details for DOI 10.1038/s41592-024-02216-7

    View details for PubMedID 38504114

    View details for PubMedCentralID 3771521

  • A Lectin-Drug Conjugate CRISPR Screen Identifies Sortilin as the Lysosomal Trafficking Receptor for Galectin-1 Donnelly, J., Kamber, R., Wisnovsky, S., Roberts, D., Peltan, E., Bassik, M. OXFORD UNIV PRESS INC. 2023: 1055
  • Cell volume expansion and local contractility drive collective invasion of the basement membrane in breast cancer. Nature materials Chang, J., Saraswathibhatla, A., Song, Z., Varma, S., Sanchez, C., Alyafei, N. H., Indana, D., Slyman, R., Srivastava, S., Liu, K., Bassik, M. C., Marinkovich, M. P., Hodgson, L., Shenoy, V., West, R. B., Chaudhuri, O. 2023

    Abstract

    Breast cancer becomes invasive when carcinoma cells invade through the basement membrane (BM)-a nanoporous layer of matrix that physically separates the primary tumour from the stroma. Single cells can invade through nanoporous three-dimensional matrices due to protease-mediated degradation or force-mediated widening of pores via invadopodial protrusions. However, how multiple cells collectively invade through the physiological BM, as they do during breast cancer progression, remains unclear. Here we developed a three-dimensional in vitro model of collective invasion of the BM during breast cancer. We show that cells utilize both proteases and forces-but not invadopodia-to breach the BM. Forces are generated from a combination of global cell volume expansion, which stretches the BM, and local contractile forces that act in the plane of the BM to breach it, allowing invasion. These results uncover a mechanism by which cells collectively interact to overcome a critical barrier to metastasis.

    View details for DOI 10.1038/s41563-023-01716-9

    View details for PubMedID 37957268

  • An encyclopedia of enhancer-gene regulatory interactions in the human genome. bioRxiv : the preprint server for biology Gschwind, A. R., Mualim, K. S., Karbalayghareh, A., Sheth, M. U., Dey, K. K., Jagoda, E., Nurtdinov, R. N., Xi, W., Tan, A. S., Jones, H., Ma, X. R., Yao, D., Nasser, J., Avsec, Ž., James, B. T., Shamim, M. S., Durand, N. C., Rao, S. S., Mahajan, R., Doughty, B. R., Andreeva, K., Ulirsch, J. C., Fan, K., Perez, E. M., Nguyen, T. C., Kelley, D. R., Finucane, H. K., Moore, J. E., Weng, Z., Kellis, M., Bassik, M. C., Price, A. L., Beer, M. A., Guigó, R., Stamatoyannopoulos, J. A., Lieberman Aiden, E., Greenleaf, W. J., Leslie, C. S., Steinmetz, L. M., Kundaje, A., Engreitz, J. M. 2023

    Abstract

    Identifying transcriptional enhancers and their target genes is essential for understanding gene regulation and the impact of human genetic variation on disease1-6. Here we create and evaluate a resource of >13 million enhancer-gene regulatory interactions across 352 cell types and tissues, by integrating predictive models, measurements of chromatin state and 3D contacts, and largescale genetic perturbations generated by the ENCODE Consortium7. We first create a systematic benchmarking pipeline to compare predictive models, assembling a dataset of 10,411 elementgene pairs measured in CRISPR perturbation experiments, >30,000 fine-mapped eQTLs, and 569 fine-mapped GWAS variants linked to a likely causal gene. Using this framework, we develop a new predictive model, ENCODE-rE2G, that achieves state-of-the-art performance across multiple prediction tasks, demonstrating a strategy involving iterative perturbations and supervised machine learning to build increasingly accurate predictive models of enhancer regulation. Using the ENCODE-rE2G model, we build an encyclopedia of enhancer-gene regulatory interactions in the human genome, which reveals global properties of enhancer networks, identifies differences in the functions of genes that have more or less complex regulatory landscapes, and improves analyses to link noncoding variants to target genes and cell types for common, complex diseases. By interpreting the model, we find evidence that, beyond enhancer activity and 3D enhancer-promoter contacts, additional features guide enhancerpromoter communication including promoter class and enhancer-enhancer synergy. Altogether, these genome-wide maps of enhancer-gene regulatory interactions, benchmarking software, predictive models, and insights about enhancer function provide a valuable resource for future studies of gene regulation and human genetics.

    View details for DOI 10.1101/2023.11.09.563812

    View details for PubMedID 38014075

    View details for PubMedCentralID PMC10680627

  • Elucidating the cellular determinants of targeted membrane protein degradation by lysosome-targeting chimeras. Science (New York, N.Y.) Ahn, G., Riley, N. M., Kamber, R. A., Wisnovsky, S., Moncayo von Hase, S., Bassik, M. C., Banik, S. M., Bertozzi, C. R. 2023; 382 (6668): eadf6249

    Abstract

    Targeted protein degradation can provide advantages over inhibition approaches in the development of therapeutic strategies. Lysosome-targeting chimeras (LYTACs) harness receptors, such as the cation-independent mannose 6-phosphate receptor (CI-M6PR), to direct extracellular proteins to lysosomes. In this work, we used a genome-wide CRISPR knockout approach to identify modulators of LYTAC-mediated membrane protein degradation in human cells. We found that disrupting retromer genes improved target degradation by reducing LYTAC recycling to the plasma membrane. Neddylated cullin-3 facilitated LYTAC-complex lysosomal maturation and was a predictive marker for LYTAC efficacy. A substantial fraction of cell surface CI-M6PR remains occupied by endogenous M6P-modified glycoproteins. Thus, inhibition of M6P biosynthesis increased the internalization of LYTAC-target complexes. Our findings inform design strategies for next-generation LYTACs and elucidate aspects of cell surface receptor occupancy and trafficking.

    View details for DOI 10.1126/science.adf6249

    View details for PubMedID 37856615

  • Assembloid CRISPR screens reveal impact of disease genes in human neurodevelopment. Nature Meng, X., Yao, D., Imaizumi, K., Chen, X., Kelley, K. W., Reis, N., Thete, M. V., Arjun McKinney, A., Kulkarni, S., Panagiotakos, G., Bassik, M. C., Pașca, S. P. 2023

    Abstract

    The assembly of cortical circuits involves the generation and migration of interneurons from the ventral to the dorsal forebrain1-3, which has been challenging to study at inaccessible stages of late gestation and early postnatal human development4. Autism spectrum disorder and other neurodevelopmental disorders (NDDs) have been associated with abnormal cortical interneuron development5, but which of these NDD genes affect interneuron generation and migration, and how they mediate these effects remains unknown. We previously developed a platform to study interneuron development and migration in subpallial organoids and forebrain assembloids6. Here we integrate assembloids with CRISPR screening to investigate the involvement of 425 NDD genes in human interneuron development. The first screen aimed at interneuron generation revealed 13 candidate genes, including CSDE1 and SMAD4. We subsequently conducted an interneuron migration screen in more than 1,000 forebrain assembloids that identified 33 candidate genes, including cytoskeleton-related genes and the endoplasmic reticulum-related gene LNPK. We discovered that, during interneuron migration, the endoplasmic reticulum is displaced along the leading neuronal branch before nuclear translocation. LNPK deletion interfered with this endoplasmic reticulum displacement and resulted in abnormal migration. These results highlight the power of this CRISPR-assembloid platform to systematically map NDD genes onto human development and reveal disease mechanisms.

    View details for DOI 10.1038/s41586-023-06564-w

    View details for PubMedID 37758944

    View details for PubMedCentralID 4349583

  • Single-molecule imaging reveals distinct elongation and frameshifting dynamics between frames of expanded RNA repeats in C9ORF72-ALS/FTD. Nature communications Latallo, M. J., Wang, S., Dong, D., Nelson, B., Livingston, N. M., Wu, R., Zhao, N., Stasevich, T. J., Bassik, M. C., Sun, S., Wu, B. 2023; 14 (1): 5581

    Abstract

    C9ORF72 hexanucleotide repeat expansion is the most common genetic cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). One pathogenic mechanism is the accumulation of toxic dipeptide repeat (DPR) proteins like poly-GA, GP and GR, produced by the noncanonical translation of the expanded RNA repeats. However, how different DPRs are synthesized remains elusive. Here, we use single-molecule imaging techniques to directly measure the translation dynamics of different DPRs. Besides initiation, translation elongation rates vary drastically between different frames, with GP slower than GA and GR the slowest. We directly visualize frameshift events using a two-color single-molecule translation assay. The repeat expansion enhances frameshifting, but the overall frequency is low. There is a higher chance of GR-to-GA shift than in the reversed direction. Finally, the ribosome-associated protein quality control (RQC) factors ZNF598 and Pelota modulate the translation dynamics, and the repeat RNA sequence is important for invoking the RQC pathway. This study reveals that multiple translation steps modulate the final DPR production. Understanding repeat RNA translation is critically important to decipher the DPR-mediated pathogenesis and identify potential therapeutic targets in C9ORF72-ALS/FTD.

    View details for DOI 10.1038/s41467-023-41339-x

    View details for PubMedID 37696852

    View details for PubMedCentralID PMC10495369

  • Death-seq identifies regulators of cell death and senolytic therapies. Cell metabolism Colville, A., Liu, J. Y., Rodriguez-Mateo, C., Thomas, S., Ishak, H. D., Zhou, R., Klein, J. D., Morgens, D. W., Goshayeshi, A., Salvi, J. S., Yao, D., Spees, K., Dixon, S. J., Liu, C., Rhee, J. W., Lai, C., Wu, J. C., Bassik, M. C., Rando, T. A. 2023

    Abstract

    Selectively ablating damaged cells is an evolving therapeutic approach for age-related disease. Current methods for genome-wide screens to identify genes whose deletion might promote the death of damaged or senescent cells are generally underpowered because of the short timescales of cell death as well as the difficulty of scaling non-dividing cells. Here, we establish "Death-seq," a positive-selection CRISPR screen optimized to identify enhancers and mechanisms of cell death. Our screens identified synergistic enhancers of cell death induced by the known senolytic ABT-263. The screen also identified inducers of cell death and senescent cell clearance in models of age-related diseases by a related compound, ABT-199, which alone is not senolytic but exhibits less toxicity than ABT-263. Death-seq enables the systematic screening of cell death pathways to uncover molecular mechanisms of regulated cell death subroutines and identifies drug targets for the treatment of diverse pathological states such as senescence, cancer, and fibrosis.

    View details for DOI 10.1016/j.cmet.2023.08.008

    View details for PubMedID 37699398

  • A genome-wide genetic screen uncovers determinants of human pigmentation. Science (New York, N.Y.) Bajpai, V. K., Swigut, T., Mohammed, J., Naqvi, S., Arreola, M., Tycko, J., Kim, T. C., Pritchard, J. K., Bassik, M. C., Wysocka, J. 2023; 381 (6658): eade6289

    Abstract

    Skin color, one of the most diverse human traits, is determined by the quantity, type, and distribution of melanin. In this study, we leveraged the light-scattering properties of melanin to conduct a genome-wide screen for regulators of melanogenesis. We identified 169 functionally diverse genes that converge on melanosome biogenesis, endosomal transport, and gene regulation, of which 135 represented previously unknown associations with pigmentation. In agreement with their melanin-promoting function, the majority of screen hits were up-regulated in melanocytes from darkly pigmented individuals. We further unraveled functions of KLF6 as a transcription factor that regulates melanosome maturation and pigmentation in vivo, and of the endosomal trafficking protein COMMD3 in modulating melanosomal pH. Our study reveals a plethora of melanin-promoting genes, with broad implications for human variation, cell biology, and medicine.

    View details for DOI 10.1126/science.ade6289

    View details for PubMedID 37561850

  • High-throughput functional characterization of combinations of transcriptional activators and repressors. Cell systems Mukund, A. X., Tycko, J., Allen, S. J., Robinson, S. A., Andrews, C., Sinha, J., Ludwig, C. H., Spees, K., Bassik, M. C., Bintu, L. 2023

    Abstract

    Despite growing knowledge of the functions of individual human transcriptional effector domains, much less is understood about how multiple effector domains within the same protein combine to regulate gene expression. Here, we measure transcriptional activity for 8,400 effector domain combinations by recruiting them to reporter genes in human cells. In our assay, weak and moderate activation domains synergize to drive strong gene expression, whereas combining strong activators often results in weaker activation. In contrast, repressors combine linearly and produce full gene silencing, and repressor domains often overpower activation domains. We use this information to build a synthetic transcription factor whose function can be tuned between repression and activation independent of recruitment to target genes by using a small-molecule drug. Altogether, we outline the basic principles of how effector domains combine to regulate gene expression and demonstrate their value in building precise and flexible synthetic biology tools. A record of this paper's transparent peer review process is included in the supplemental information.

    View details for DOI 10.1016/j.cels.2023.07.001

    View details for PubMedID 37543039

  • Parallel CRISPR-Cas9 screens identify mechanisms of PLIN2 and lipid droplet regulation. Developmental cell Roberts, M. A., Deol, K. K., Mathiowetz, A. J., Lange, M., Leto, D. E., Stevenson, J., Hashemi, S. H., Morgens, D. W., Easter, E., Heydari, K., Nalls, M. A., Bassik, M. C., Kampmann, M., Kopito, R. R., Faghri, F., Olzmann, J. A. 2023

    Abstract

    Despite the key roles of perilipin-2 (PLIN2) in governing lipid droplet (LD) metabolism, the mechanisms that regulate PLIN2 levels remain incompletely understood. Here, we leverage a set of genome-edited human PLIN2 reporter cell lines in a series of CRISPR-Cas9 loss-of-function screens, identifying genetic modifiers that influence PLIN2 expression and post-translational stability under different metabolic conditions and in different cell types. These regulators include canonical genes that control lipid metabolism as well as genes involved in ubiquitination, transcription, and mitochondrial function. We further demonstrate a role for the E3 ligase MARCH6 in regulating triacylglycerol biosynthesis, thereby influencing LD abundance and PLIN2 stability. Finally, our CRISPR screens and several published screens provide the foundation for CRISPRlipid (http://crisprlipid.org), an online data commons for lipid-related functional genomics data. Our study identifies mechanisms of PLIN2 and LD regulation and provides an extensive resource for the exploration of LD biology and lipid metabolism.

    View details for DOI 10.1016/j.devcel.2023.07.001

    View details for PubMedID 37494933

  • Direct mapping of ligandable tyrosines and lysines in cells with chiral sulfonyl fluoride probes. Nature chemistry Chen, Y., Craven, G. B., Kamber, R. A., Cuesta, A., Zhersh, S., Moroz, Y. S., Bassik, M. C., Taunton, J. 2023

    Abstract

    Advances in chemoproteomic technology have revealed covalent interactions between small molecules and protein nucleophiles, primarily cysteine, on a proteome-wide scale. Most chemoproteomic screening approaches are indirect, relying on competition between electrophilic fragments and a minimalist electrophilic probe with inherently limited proteome coverage. Here we develop a chemoproteomic platform for direct electrophile-site identification based on enantiomeric pairs of clickable arylsulfonyl fluoride probes. Using stereoselective site modification as a proxy for ligandability in intact cells, we identify 634 tyrosines and lysines within functionally diverse protein sites, liganded by structurally diverse probes. Among multiple validated sites, we discover a chiral probe that modifies Y228 in the MYC binding site of the epigenetic regulator WDR5, as revealed by a high-resolution crystal structure. A distinct chiral probe stimulates tumour cell phagocytosis by covalently modifying Y387 in the recently discovered immuno-oncology target APMAP. Our work provides a deep resource of ligandable tyrosines and lysines for the development of covalent chemical probes.

    View details for DOI 10.1038/s41557-023-01281-3

    View details for PubMedID 37460812

  • High-throughput discovery and characterization of viral transcriptional effectors in human cells. Cell systems Ludwig, C. H., Thurm, A. R., Morgens, D. W., Yang, K. J., Tycko, J., Bassik, M. C., Glaunsinger, B. A., Bintu, L. 2023; 14 (6): 482

    Abstract

    Viruses encode transcriptional regulatory proteins critical for controlling viral and host gene expression. Given their multifunctional nature and high sequence divergence, it is unclear which viral proteins can affect transcription and which specific sequences contribute to this function. Using a high-throughput assay, we measured the transcriptional regulatory potential of over 60,000 protein tiles across 1,500 proteins from 11 coronaviruses and all nine human herpesviruses. We discovered hundreds of transcriptional effector domains, including a conserved repression domain in all coronavirus Spike homologs, dual activation-repression domains in viral interferon regulatory factors (VIRFs), and an activation domain in six herpesvirus homologs of the single-stranded DNA-binding protein that we show is important for viral replication and late gene expression in Kaposi's sarcoma-associated herpesvirus (KSHV). For the effector domains we identified, we investigated their mechanisms via high-throughput sequence and chemical perturbations, pinpointing sequence motifs essential for function. This work massively expands viral protein annotations, serving as a springboard for studying their biological and health implications and providing new candidates for compact gene regulation tools.

    View details for DOI 10.1016/j.cels.2023.05.008

    View details for PubMedID 37348463

  • Co-transcriptional genome surveillance by HUSH is coupled to termination machinery. Molecular cell Spencley, A. L., Bar, S., Swigut, T., Flynn, R. A., Lee, C. H., Chen, L., Bassik, M. C., Wysocka, J. 2023

    Abstract

    The HUSH complex recognizes and silences foreign DNA such as viruses, transposons, and transgenes without prior exposure to its targets. Here, we show that endogenous targets of the HUSH complex fall into two distinct classes based on the presence or absence of H3K9me3. These classes are further distinguished by their transposon content and differential response to the loss of HUSH. A de novo genomic rearrangement at the Sox2 locus induces a switch from H3K9me3-independent to H3K9me3-associated HUSH targeting, resulting in silencing. We further demonstrate that HUSH interacts with the termination factor WDR82 and-via its component MPP8-with nascent RNA. HUSH accumulates at sites of high RNAPII occupancy including long exons and transcription termination sites in a manner dependent on WDR82 and CPSF. Together, our results uncover the functional diversity of HUSH targets and show that this vertebrate-specific complex exploits evolutionarily ancient transcription termination machinery for co-transcriptional chromatin targeting and genome surveillance.

    View details for DOI 10.1016/j.molcel.2023.04.014

    View details for PubMedID 37164018

  • CasKAS: direct profiling of genome-wide dCas9 and Cas9 specificity using ssDNA mapping. Genome biology Marinov, G. K., Kim, S. H., Bagdatli, S. T., Higashino, S. I., Trevino, A. E., Tycko, J., Wu, T., Bintu, L., Bassik, M. C., He, C., Kundaje, A., Greenleaf, W. J. 2023; 24 (1): 85

    Abstract

    Detecting and mitigating off-target activity is critical to the practical application of CRISPR-mediated genome and epigenome editing. While numerous methods have been developed to map Cas9 binding specificity genome-wide, they are generally time-consuming and/or expensive, and not applicable to catalytically dead CRISPR enzymes. We have developed CasKAS, a rapid, inexpensive, and facile assay for identifying off-target CRISPR enzyme binding and cleavage by chemically mapping the unwound single-stranded DNA structures formed upon binding of a sgRNA-loaded Cas9 protein. We demonstrate this method in both in vitro and in vivo contexts.

    View details for DOI 10.1186/s13059-023-02930-z

    View details for PubMedID 37085898

    View details for PubMedCentralID PMC10120127

  • An SPNS1-dependent lysosomal lipid transport pathway that enables cell survival under choline limitation. Science advances Scharenberg, S. G., Dong, W., Ghoochani, A., Nyame, K., Levin-Konigsberg, R., Krishnan, A. R., Rawat, E. S., Spees, K., Bassik, M. C., Abu-Remaileh, M. 2023; 9 (16): eadf8966

    Abstract

    Lysosomes degrade macromolecules and recycle their nutrient content to support cell function and survival. However, the machineries involved in lysosomal recycling of many nutrients remain to be discovered, with a notable example being choline, an essential metabolite liberated via lipid degradation. Here, we engineered metabolic dependency on lysosome-derived choline in pancreatic cancer cells to perform an endolysosome-focused CRISPR-Cas9 screen for genes mediating lysosomal choline recycling. We identified the orphan lysosomal transmembrane protein SPNS1 as critical for cell survival under choline limitation. SPNS1 loss leads to intralysosomal accumulation of lysophosphatidylcholine (LPC) and lysophosphatidylethanolamine (LPE). Mechanistically, we reveal that SPNS1 is a proton gradient-dependent transporter of LPC species from the lysosome for their re-esterification into phosphatidylcholine in the cytosol. Last, we establish that LPC efflux by SPNS1 is required for cell survival under choline limitation. Collectively, our work defines a lysosomal phospholipid salvage pathway that is essential under nutrient limitation and, more broadly, provides a robust platform to deorphan lysosomal gene function.

    View details for DOI 10.1126/sciadv.adf8966

    View details for PubMedID 37075117

    View details for PubMedCentralID PMC10115416

  • Large-scale mapping and mutagenesis of human transcriptional effector domains. Nature DelRosso, N., Tycko, J., Suzuki, P., Andrews, C., Mukund, A., Liongson, I., Ludwig, C., Spees, K., Fordyce, P., Bassik, M. C., Bintu, L. 2023

    Abstract

    Human gene expression is regulated by more than 2,000 transcription factors and chromatin regulators1,2. Effector domains within these proteins can activate or repress transcription. However, for many of these regulators we do not know what type of effector domains they contain, their location in the protein, their activation and repression strengths, and the sequences that are necessary for their functions. Here, we systematically measure the effector activity of more than 100,000 protein fragments tiling across most chromatin regulators and transcription factors in human cells (2,047 proteins). By testing the effect they have when recruited at reporter genes, we annotate 374 activation domains and 715 repression domains, roughly 80% of which are new and have not been previously annotated3-5. Rational mutagenesis and deletion scans across all the effector domains reveal aromatic and/or leucine residues interspersed with acidic, proline, serine and/or glutamine residues are necessary for activation domain activity. Furthermore, most repression domain sequences contain sites for small ubiquitin-like modifier (SUMO)ylation, short interaction motifs for recruiting corepressors or are structured binding domains for recruiting other repressive proteins. We discover bifunctional domains that can both activate and repress, some of which dynamically split a cell population into high- and low-expression subpopulations. Our systematic annotation and characterization of effector domains provide a rich resource for understanding the function of human transcription factors and chromatin regulators, engineering compact tools for controlling gene expression and refining predictive models of effector domain function.

    View details for DOI 10.1038/s41586-023-05906-y

    View details for PubMedID 37020022

    View details for PubMedCentralID 4494013

  • A novel ammonium transporter functions as a lysosomal detoxifier Konigsberg, R., Nigam, A., Mitra, K., Spees, K., Hivare, P., Krishnan, Y., Bassik, M. C. AMER SOC CELL BIOLOGY. 2023: 1112-1113
  • A BORC-dependent molecular pathway for vesiculation of cell corpse phagolysosomes. Current biology : CB Fazeli, G., Levin-Konigsberg, R., Bassik, M. C., Stigloher, C., Wehman, A. M. 2023

    Abstract

    Phagocytic clearance is important to provide cells with metabolites and regulate immune responses, but little is known about how phagolysosomes finally resolve their phagocytic cargo of cell corpses, cell debris, and pathogens. While studying the phagocytic clearance of non-apoptotic polar bodies in C.elegans, we previously discovered that phagolysosomes tubulate into small vesicles to facilitate corpse clearance within 1.5 h. Here, we show that phagolysosome vesiculation depends on amino acid export by the solute transporter SLC-36.1 and the activation of TORC1. We demonstrate that downstream of TORC1, BLOC-1-related complex (BORC) is de-repressed by Ragulator through the BORC subunit BLOS-7. In addition, the BORC subunit SAM-4 is needed continuously to recruit the small GTPase ARL-8 to the phagolysosome for tubulation. We find that disrupting the regulated GTP-GDP cycle of ARL-8 reduces tubulation by kinesin-1, delays corpse clearance, and mislocalizes ARL-8 away from lysosomes. We also demonstrate that mammalian phagocytes use BORC to promote phagolysosomal degradation, confirming the conserved importance of TOR and BORC. Finally, we show that HOPS is required after tubulation for the rapid degradation of cargo in small phagolysosomal vesicles, suggesting that additional rounds of lysosome fusion occur. Thus, by observing single phagolysosomes over time, we identified the molecular pathway regulating phagolysosome vesiculation that promotes efficient resolution of phagocytosed cargos.

    View details for DOI 10.1016/j.cub.2022.12.041

    View details for PubMedID 36652947

  • Niclosamide Inhibits Proliferation of Leukemia Cells and Synergizes with Chemotherapy Mark, K., Robbins, M., Gamble, A., Chae, H., Bassik, M., Han, K., Sakamoto, K. M. AMER SOC HEMATOLOGY. 2022: 8870-8871
  • A conserved megaprotein-based molecular bridge critical for lipid trafficking and cold resilience. Nature communications Wang, C., Wang, B., Pandey, T., Long, Y., Zhang, J., Oh, F., Sima, J., Guo, R., Liu, Y., Zhang, C., Mukherjee, S., Bassik, M., Lin, W., Deng, H., Vale, G., McDonald, J. G., Shen, K., Ma, D. K. 2022; 13 (1): 6805

    Abstract

    Cells adapt to cold by increasing levels of unsaturated phospholipids and membrane fluidity through conserved homeostatic mechanisms. Here we report an exceptionally large and evolutionarily conserved protein LPD-3 in C. elegans that mediates lipid trafficking to confer cold resilience. We identify lpd-3 mutants in a mutagenesis screen for genetic suppressors of the lipid desaturase FAT-7. LPD-3 bridges the endoplasmic reticulum (ER) and plasma membranes (PM), forming a structurally predicted hydrophobic tunnel for lipid trafficking. lpd-3 mutants exhibit abnormal phospholipid distribution, diminished FAT-7 abundance, organismic vulnerability to cold, and are rescued by Lecithin comprising unsaturated phospholipids. Deficient lpd-3 homologues in Zebrafish and mammalian cells cause defects similar to those observed in C. elegans. As mutations in BLTP1, the human orthologue of lpd-3, cause Alkuraya-Kucinskas syndrome, LPD-3 family proteins may serve as evolutionarily conserved highway bridges critical for ER-associated non-vesicular lipid trafficking and resilience to cold stress in eukaryotic cells.

    View details for DOI 10.1038/s41467-022-34450-y

    View details for PubMedID 36357390

  • The N6-methyladenosine methyltransferase METTL16 enables erythropoiesis through safeguarding genome integrity. Nature communications Yoshinaga, M., Han, K., Morgens, D. W., Horii, T., Kobayashi, R., Tsuruyama, T., Hia, F., Yasukura, S., Kajiya, A., Cai, T., Cruz, P. H., Vandenbon, A., Suzuki, Y., Kawahara, Y., Hatada, I., Bassik, M. C., Takeuchi, O. 2022; 13 (1): 6435

    Abstract

    During erythroid differentiation, the maintenance of genome integrity is key for the success of multiple rounds of cell division. However, molecular mechanisms coordinating the expression of DNA repair machinery in erythroid progenitors are poorly understood. Here, we discover that an RNA N6-methyladenosine (m6A) methyltransferase, METTL16, plays an essential role in proper erythropoiesis by safeguarding genome integrity via the control of DNA-repair-related genes. METTL16-deficient erythroblasts exhibit defective differentiation capacity, DNA damage and activation of the apoptotic program. Mechanistically, METTL16 controls m6A deposition at the structured motifs in DNA-repair-related transcripts including Brca2 and Fancm mRNAs, thereby upregulating their expression. Furthermore, a pairwise CRISPRi screen revealed that the MTR4-nuclear RNA exosome complex is involved in the regulation of METTL16 substrate mRNAs in erythroblasts. Collectively, our study uncovers that METTL16 and the MTR4-nuclear RNA exosome act as essential regulatory machinery to maintain genome integrity and erythropoiesis.

    View details for DOI 10.1038/s41467-022-34078-y

    View details for PubMedID 36307435

  • Genome-wide CRISPR screen reveals v-ATPase as a drug target to lower levels of ALS protein ataxin-2. Cell reports Kim, G., Nakayama, L., Blum, J. A., Akiyama, T., Boeynaems, S., Chakraborty, M., Couthouis, J., Tassoni-Tsuchida, E., Rodriguez, C. M., Bassik, M. C., Gitler, A. D. 2022; 41 (4): 111508

    Abstract

    Mutations in the ataxin-2 gene (ATXN2) cause the neurodegenerative disorders amyotrophic lateral sclerosis (ALS) and spinocerebellar ataxia type 2 (SCA2). A therapeutic strategy using antisense oligonucleotides targeting ATXN2 has entered clinical trial in humans. Additional ways to decrease ataxin-2 levels could lead to cheaper or less invasive therapies and elucidate how ataxin-2 is normally regulated. Here, we perform a genome-wide fluorescence-activated cell sorting (FACS)-based CRISPR-Cas9 screen in human cells and identify genes encoding components of the lysosomal vacuolar ATPase (v-ATPase) as modifiers of endogenous ataxin-2 protein levels. Multiple FDA-approved small molecule v-ATPase inhibitors lower ataxin-2 protein levels in mouse and human neurons, and oral administration of at least one of these drugs-etidronate-is sufficient to decrease ataxin-2 in the brains of mice. Together, we propose v-ATPase as a drug target for ALS and SCA2 and demonstrate the value of FACS-based screens in identifying genetic-and potentially druggable-modifiers of human disease proteins.

    View details for DOI 10.1016/j.celrep.2022.111508

    View details for PubMedID 36288714

  • Spatial epitope barcoding reveals clonal tumor patch behaviors. Cancer cell Rovira-Clave, X., Drainas, A. P., Jiang, S., Bai, Y., Baron, M., Zhu, B., Dallas, A. E., Lee, M. C., Chu, T. P., Holzem, A., Ayyagari, R., Bhattacharya, D., McCaffrey, E. F., Greenwald, N. F., Markovic, M., Coles, G. L., Angelo, M., Bassik, M. C., Sage, J., Nolan, G. P. 2022

    Abstract

    Intratumoral heterogeneity is a seminal feature of human tumors contributing to tumor progression and response to treatment. Current technologies are still largely unsuitable to accurately track phenotypes and clonal evolution within tumors, especially in response to genetic manipulations. Here, we developed epitopes for imaging using combinatorial tagging (EpicTags), which we coupled to multiplexed ion beam imaging (EpicMIBI) for in situ tracking of barcodes within tissue microenvironments. Using EpicMIBI, we dissected the spatial component of cell lineages and phenotypes in xenograft models of small cell lung cancer. We observed emergent properties from mixed clones leading to the preferential expansion of clonal patches for both neuroendocrine and non-neuroendocrine cancer cell states in these models. In a tumor model harboring a fraction of PTEN-deficient cancer cells, we observed a non-autonomous increase of clonal patch size in PTEN wild-type cancer cells. EpicMIBI facilitates in situ interrogation of cell-intrinsic and cell-extrinsic processes involved in intratumoral heterogeneity.

    View details for DOI 10.1016/j.ccell.2022.09.014

    View details for PubMedID 36240778

  • Systematic discovery of recombinases for efficient integration of large DNA sequences into the human genome. Nature biotechnology Durrant, M. G., Fanton, A., Tycko, J., Hinks, M., Chandrasekaran, S. S., Perry, N. T., Schaepe, J., Du, P. P., Lotfy, P., Bassik, M. C., Bintu, L., Bhatt, A. S., Hsu, P. D. 2022

    Abstract

    Large serine recombinases (LSRs) are DNA integrases that facilitate the site-specific integration of mobile genetic elements into bacterial genomes. Only a few LSRs, such as Bxb1 and PhiC31, have been characterized to date, with limited efficiency as tools for DNA integration in human cells. In this study, we developed a computational approach to identify thousands of LSRs and their DNA attachment sites, expanding known LSR diversity by >100-fold and enabling the prediction of their insertion site specificities. We tested their recombination activity in human cells, classifying them as landing pad, genome-targeting or multi-targeting LSRs. Overall, we achieved up to seven-fold higher recombination than Bxb1 and genome integration efficiencies of 40-75% with cargo sizes over 7kb. We also demonstrate virus-free, direct integration of plasmid or amplicon libraries for improved functional genomics applications. This systematic discovery of recombinases directly from microbial sequencing data provides a resource of over 60 LSRs experimentally characterized in human cells for large-payload genome insertion without exposed DNA double-stranded breaks.

    View details for DOI 10.1038/s41587-022-01494-w

    View details for PubMedID 36217031

  • Identification of orphan ligand-receptor relationships using a cell-based CRISPRa enrichment screening platform. eLife Siepe, D. H., Henneberg, L. T., Wilson, S. C., Hess, G. T., Bassik, M. C., Zinn, K., Garcia, K. C. 2022; 11

    Abstract

    Secreted proteins, which include cytokines, hormones and growth factors, are extracellular ligands that control key signaling pathways mediating cell-cell communication within and between tissues and organs. Many drugs target secreted ligands and their cell-surface receptors. Still, there are hundreds of secreted human proteins that either have no identified receptors ('orphans') and are likely to act through cell surface receptors that have not yet been characterized. Discovery of secreted ligand-receptor interactions by high-throughput screening has been problematic, because the most commonly used high-throughput methods for protein-protein interaction (PPI) screening do not work well for extracellular interactions. Cell-based screening is a promising technology for definition of new ligand-receptor interactions, because multimerized ligands can enrich for cells expressing low affinity cell-surface receptors, and such methods do not require purification of receptor extracellular domains. Here, we present a proteo-genomic cell-based CRISPR activation (CRISPRa) enrichment screening platform employing customized pooled cell surface receptor sgRNA libraries in combination with a magnetic bead selection-based enrichment workflow for rapid, parallel ligand-receptor deorphanization. We curated 80 potentially high value orphan secreted proteins and ultimately screened 20 secreted ligands against two cell sgRNA libraries with targeted expression of all single-pass (TM1) or multi-pass (TM2+) receptors by CRISPRa. We identified previously unknown interactions in 12 of these screens, and validated several of them using surface plasmon resonance and/or cell binding. The newly deorphanized ligands include three receptor tyrosine phosphatase (RPTP) ligands and a chemokine like protein that binds to killer cell inhibitory receptors (KIR's). These new interactions provide a resource for future investigations of interactions between the human secreted and membrane proteomes.

    View details for DOI 10.7554/eLife.81398

    View details for PubMedID 36178190

  • Genome-scale CRISPR screening reveals that C3aR signaling is critical for rapid capture of fungi by macrophages. PLoS pathogens Cohen, A., Jeng, E. E., Voorhies, M., Symington, J., Ali, N., Rodriguez, R. A., Bassik, M. C., Sil, A. 2022; 18 (9): e1010237

    Abstract

    The fungal pathogen Histoplasma capsulatum (Hc) invades, replicates within, and destroys macrophages. To interrogate the molecular mechanisms underlying this interaction, we conducted a host-directed CRISPR-Cas9 screen and identified 361 genes that modify macrophage susceptibility to Hc infection, greatly expanding our understanding of host gene networks targeted by Hc. We identified pathways that have not been previously implicated in Hc interaction with macrophages, including the ragulator complex (involved in nutrient stress sensing), glycosylation enzymes, protein degradation machinery, mitochondrial respiration genes, solute transporters, and the ER membrane complex (EMC). The highest scoring protective hits included the complement C3a receptor (C3aR), a G-protein coupled receptor (GPCR) that recognizes the complement fragment C3a. Although it is known that complement components react with the fungal surface, leading to opsonization and release of small peptide fragments such as C3a, a role for C3aR in macrophage interactions with fungi has not been elucidated. We demonstrated that whereas C3aR is dispensable for macrophage phagocytosis of bacteria and latex beads, it is critical for optimal macrophage capture of pathogenic fungi, including Hc, the ubiquitous fungal pathogen Candida albicans, and the causative agent of Valley Fever Coccidioides posadasii. We showed that C3aR localizes to the early phagosome during Hc infection where it coordinates the formation of actin-rich membrane protrusions that promote Hc capture. We also showed that the EMC promotes surface expression of C3aR, likely explaining its identification in our screen. Taken together, our results provide new insight into host processes that affect Hc-macrophage interactions and uncover a novel and specific role for C3aR in macrophage recognition of fungi.

    View details for DOI 10.1371/journal.ppat.1010237

    View details for PubMedID 36174103

  • Functional characterization of the PI3K/AKT/MTOR signaling pathway for targeted therapy in B-precursor acute lymphoblastic leukemia. Cancer gene therapy Gruninger, P. K., Uhl, F., Herzog, H., Gentile, G., Andrade-Martinez, M., Schmidt, T., Han, K., Morgens, D. W., Bassik, M. C., Cleary, M. L., Gorka, O., Zeiser, R., GroSS, O., Duque-Afonso, J. 2022

    Abstract

    B-cell precursor acute lymphoblastic leukemias (B-ALL) are characterized by the activation of signaling pathways, which are involved in survival and proliferation of leukemia cells. Using an unbiased shRNA library screen enriched for targeting signaling pathways, we identified MTOR as the key gene on which human B-ALL E2A-PBX1+ RCH-ACV cells are dependent. Using genetic and pharmacologic approaches, we investigated whether B-ALL cells depend on MTOR upstream signaling pathways including PI3K/AKT and the complexes MTORC1 or MTORC2 for proliferation and survival in vitro and in vivo. Notably, the combined inhibition of MTOR and AKT shows a synergistic effect on decreased cell proliferation in B-ALL with different karyotypes. Hence, B-ALL cells were more dependent on MTORC2 rather than MTORC1 complex in genetic assays. Using cell metabolomics, we identified changes in mitochondrial fuel oxidation after shRNA-mediated knockdown or pharmacological inhibition of MTOR. Dependence of the cells on fatty acid metabolism for their energy production was increased upon inhibition of MTOR and associated upstream signaling pathways, disclosing a possible target for a combination therapy. In conclusion, B-ALL are dependent on the PI3K/AKT/MTOR signaling pathway and the combination of specific small molecules targeting this pathway appears to be promising for the treatment of B-ALL patients.

    View details for DOI 10.1038/s41417-022-00491-0

    View details for PubMedID 35794338

  • Ribosome stalling during selenoprotein translation exposes a ferroptosis vulnerability. Nature chemical biology Li, Z., Ferguson, L., Deol, K. K., Roberts, M. A., Magtanong, L., Hendricks, J. M., Mousa, G. A., Kilinc, S., Schaefer, K., Wells, J. A., Bassik, M. C., Goga, A., Dixon, S. J., Ingolia, N. T., Olzmann, J. A. 2022

    Abstract

    The selenoprotein glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting lipid peroxides into nontoxic lipid alcohols. GPX4 has emerged as a promising therapeutic target for cancer treatment, but some cancer cells are resistant to ferroptosis triggered by GPX4 inhibition. Using a chemical-genetic screen, we identify LRP8 (also known as ApoER2) as a ferroptosis resistance factor that is upregulated in cancer. Loss of LRP8 decreases cellular selenium levels and the expression of a subset of selenoproteins. Counter to the canonical hierarchical selenoprotein regulatory program, GPX4 levels are strongly reduced due to impaired translation. Mechanistically, low selenium levels result in ribosome stalling at the inefficiently decoded GPX4 selenocysteine UGA codon, leading to ribosome collisions, early translation termination and proteasomal clearance of the N-terminal GPX4 fragment. These findings reveal rewiring of the selenoprotein hierarchy in cancer cells and identify ribosome stalling and collisions during GPX4 translation as ferroptosis vulnerabilities in cancer.

    View details for DOI 10.1038/s41589-022-01033-3

    View details for PubMedID 35637349

  • Pathogenic or benign? Nature biotechnology Du, P. P., Liu, K., Bassik, M. C., Hess, G. T. 2022

    View details for DOI 10.1038/s41587-022-01333-y

    View details for PubMedID 35578021

  • Small molecule C381 targets the lysosome to reduce inflammation and ameliorate disease in models of neurodegeneration. Proceedings of the National Academy of Sciences of the United States of America Vest, R. T., Chou, C. C., Zhang, H., Haney, M. S., Li, L., Laqtom, N. N., Chang, B., Shuken, S., Nguyen, A., Yerra, L., Yang, A. C., Green, C., Tanga, M., Abu-Remaileh, M., Bassik, M. C., Frydman, J., Luo, J., Wyss-Coray, T. 2022; 119 (11): e2121609119

    Abstract

    SignificanceNeurodegenerative diseases are poorly understood and difficult to treat. One common hallmark is lysosomal dysfunction leading to the accumulation of aggregates and other undegradable materials, which cause damage to brain resident cells. Lysosomes are acidic organelles responsible for breaking down biomolecules and recycling their constitutive parts. In this work, we find that the antiinflammatory and neuroprotective compound, discovered via a phenotypic screen, imparts its beneficial effects by targeting the lysosome and restoring its function. This is established using a genome-wide CRISPRi target identification screen and then confirmed using a variety of lysosome-targeted studies. The resulting small molecule from this study represents a potential treatment for neurodegenerative diseases as well as a research tool for the study of lysosomes in disease.

    View details for DOI 10.1073/pnas.2121609119

    View details for PubMedID 35259016

  • Small molecule C381 targets the lysosome to reduce inflammation and ameliorate disease in models of neurodegeneration Proc Natl Acad Sci U S A . Vest*, R. T., Chou*, C., Zhang, H., Haney, M. S., Li, L., Laqtom, N. N., Chang, B., Shuken, S., Nguyen, A., Yerra, L., Yang, A. C., Green, C., Tanga, M., Abu-Remaileh, M., Bassik, M. C., Frydman, J., Luo, J., Wyss-Coray, T. 2022; 119 (11): e2121609119

    View details for DOI 10.1073/pnas.2121609119

  • Genome-Wide CRISPR screens reveal specific ligands for glycan-binding immune checkpoint receptors Wisnovsky, S., Mockl, L., Malaker, S. A., Pedram, K., Hess, G. T., Riley, N. M., Gray, M. A., Smith, B. H., Bassik, M. C., Moerner, W. E., Bertozzi, C. R. OXFORD UNIV PRESS INC. 2021: 1682-1683
  • An engineered transcriptional reporter of protein localization identifies regulators of mitochondrial and ER membrane protein trafficking in high-throughput CRISPRi screens. eLife Coukos, R. W., Yao, D., Sanchez, M. L., Strand, E. T., Olive, M. E., Udeshi, N. D., Weissman, J. S., Carr, S. A., Bassik, M. C., Ting, A. Y. 2021; 10

    Abstract

    The trafficking of specific protein cohorts to correct subcellular locations at correct times is essential for every signaling and regulatory process in biology. Gene perturbation screens could provide a powerful approach to probe the molecular mechanisms of protein trafficking, but only if protein localization or mislocalization can be tied to a simple and robust phenotype for cell selection, such as cell proliferation or fluorescence-activated cell sorting (FACS). To empower the study of protein trafficking processes with gene perturbation, we developed a genetically-encoded molecular tool named HiLITR. HiLITR converts protein colocalization into proteolytic release of a membrane-anchored transcription factor, which drives the expression of a chosen reporter gene. Using HiLITR in combination with FACS-based CRISPRi screening in human cell lines, we identified genes that influence the trafficking of mitochondrial and ER tail-anchored proteins. We show that loss of the SUMO E1 component SAE1 results in mislocalization and destabilization of many mitochondrial tail-anchored proteins. We also demonstrate a distinct regulatory role for EMC10 in the ER membrane complex, opposing the transmembrane-domain insertion activity of the complex. Through transcriptional integration of complex cellular functions, HiLITR expands the scope of biological processes that can be studied by genetic perturbation screening technologies.

    View details for DOI 10.7554/eLife.69142

    View details for PubMedID 34414886

  • LKB1 inactivation modulates chromatin accessibility to drive metastatic progression. Nature cell biology Pierce, S. E., Granja, J. M., Corces, M. R., Brady, J. J., Tsai, M. K., Pierce, A. B., Tang, R., Chu, P., Feldser, D. M., Chang, H. Y., Bassik, M. C., Greenleaf, W. J., Winslow, M. M. 2021

    Abstract

    Metastasis is the leading cause of cancer-related deaths and enables cancer cells to compromise organ function by expanding in secondary sites. Since primary tumours and metastases often share the same constellation of driver mutations, the mechanisms that drive their distinct phenotypes are unclear. Here we show that inactivation of the frequently mutated tumour suppressor gene LKB1 (encoding liver kinase B1) has evolving effects throughout the progression of lung cancer, which leads to the differential epigenetic re-programming of early-stage primary tumours compared with late-stage metastases. By integrating genome-scale CRISPR-Cas9 screening with bulk and single-cell multi-omic analyses, we unexpectedly identify LKB1 as a master regulator of chromatin accessibility in lung adenocarcinoma primary tumours. Using an in vivo model of metastatic progression, we further show that loss of LKB1 activates the early endoderm transcription factor SOX17 in metastases and a metastatic-like sub-population of cancer cells within primary tumours. The expression of SOX17 is necessary and sufficient to drive a second wave of epigenetic changes in LKB1-deficient cells that enhances metastatic ability. Overall, our study demonstrates how the downstream effects of an individual driver mutation can change throughout cancer development, with implications for stage-specific therapeutic resistance mechanisms and the gene regulatory underpinnings of metastatic evolution.

    View details for DOI 10.1038/s41556-021-00728-4

    View details for PubMedID 34341533

  • A genome-wide atlas of co-essential modules assigns function to uncharacterized genes. Nature genetics Wainberg, M., Kamber, R. A., Balsubramani, A., Meyers, R. M., Sinnott-Armstrong, N., Hornburg, D., Jiang, L., Chan, J., Jian, R., Gu, M., Shcherbina, A., Dubreuil, M. M., Spees, K., Meuleman, W., Snyder, M. P., Bassik, M. C., Kundaje, A. 2021

    Abstract

    A central question in the post-genomic era is how genes interact to form biological pathways. Measurements of gene dependency across hundreds of cell lines have been used to cluster genes into 'co-essential' pathways, but this approach has been limited by ubiquitous false positives. In the present study, we develop a statistical method that enables robust identification of gene co-essentiality and yields a genome-wide set of functional modules. This atlas recapitulates diverse pathways and protein complexes, and predicts the functions of 108 uncharacterized genes. Validating top predictions, we show that TMEM189 encodes plasmanylethanolamine desaturase, a key enzyme for plasmalogen synthesis. We also show that C15orf57 encodes a protein that binds the AP2 complex, localizes to clathrin-coated pits and enables efficient transferrin uptake. Finally, we provide an interactive webtool for the community to explore our results, which establish co-essentiality profiling as a powerful resource for biological pathway identification and discovery of new gene functions.

    View details for DOI 10.1038/s41588-021-00840-z

    View details for PubMedID 33859415

  • The AMBRA1 E3 ligase adaptor regulates the stability of cyclinD. Nature Chaikovsky, A. C., Li, C., Jeng, E. E., Loebell, S., Lee, M. C., Murray, C. W., Cheng, R., Demeter, J., Swaney, D. L., Chen, S., Newton, B. W., Johnson, J. R., Drainas, A. P., Shue, Y. T., Seoane, J. A., Srinivasan, P., He, A., Yoshida, A., Hipkins, S. Q., McCrea, E., Poltorack, C. D., Krogan, N. J., Diehl, J. A., Kong, C., Jackson, P. K., Curtis, C., Petrov, D. A., Bassik, M. C., Winslow, M. M., Sage, J. 2021

    Abstract

    The initiation of cell division integrates a large number of intra- and extracellular inputs. D-type cyclins (hereafter, cyclinD) couple these inputs to the initiation of DNA replication1. Increased levels of cyclinD promote cell division by activating cyclin-dependent kinases4 and 6 (hereafter, CDK4/6), which in turn phosphorylate and inactivate the retinoblastoma tumour suppressor. Accordingly, increased levels and activity of cyclinD-CDK4/6 complexes are strongly linked to unchecked cell proliferation and cancer2,3. However, the mechanisms that regulate levels of cyclinD are incompletely understood4,5. Here we show that autophagy and beclin1 regulator1 (AMBRA1) is the main regulator of the degradation of cyclinD. We identified AMBRA1 in a genome-wide screen to investigate the genetic basis of the response to CDK4/6 inhibition. Loss of AMBRA1 results in high levels of cyclinD in cells and in mice, which promotes proliferation and decreases sensitivity to CDK4/6 inhibition. Mechanistically, AMBRA1 mediates ubiquitylation and proteasomal degradation of cyclinD as a substrate receptor for the cullin4 E3 ligase complex. Loss of AMBRA1 enhances the growth of lung adenocarcinoma in a mouse model, and low levels of AMBRA1 correlate with worse survival in patients with lung adenocarcinoma. Thus, AMBRA1 regulates cellular levels of cyclinD, and contributes to cancer development and the response of cancer cells to CDK4/6 inhibitors.

    View details for DOI 10.1038/s41586-021-03474-7

    View details for PubMedID 33854239

  • An expanded universe of cancer targets. Cell Hahn, W. C., Bader, J. S., Braun, T. P., Califano, A., Clemons, P. A., Druker, B. J., Ewald, A. J., Fu, H., Jagu, S., Kemp, C. J., Kim, W., Kuo, C. J., McManus, M., B Mills, G., Mo, X., Sahni, N., Schreiber, S. L., Talamas, J. A., Tamayo, P., Tyner, J. W., Wagner, B. K., Weiss, W. A., Gerhard, D. S., Cancer Target Discovery and Development Network, Dancik, V., Gill, S., Hua, B., Sharifnia, T., Viswanathan, V., Zou, Y., Dela Cruz, F., Kung, A., Stockwell, B., Boehm, J., Dempster, J., Manguso, R., Vazquez, F., Cooper, L. A., Du, Y., Ivanov, A., Lonial, S., Moreno, C. S., Niu, Q., Owonikoko, T., Ramalingam, S., Reyna, M., Zhou, W., Grandori, C., Shmulevich, I., Swisher, E., Cai, J., Chan, I. S., Dunworth, M., Ge, Y., Georgess, D., Grasset, E. M., Henriet, E., Knutsdottir, H., Lerner, M. G., Padmanaban, V., Perrone, M. C., Suhail, Y., Tsehay, Y., Warrier, M., Morrow, Q., Nechiporuk, T., Long, N., Saultz, J., Kaempf, A., Minnier, J., Tognon, C. E., Kurtz, S. E., Agarwal, A., Brown, J., Watanabe-Smith, K., Vu, T. Q., Jacob, T., Yan, Y., Robinson, B., Lind, E. F., Kosaka, Y., Demir, E., Estabrook, J., Grzadkowski, M., Nikolova, O., Chen, K., Deneen, B., Liang, H., Bassik, M. C., Bhattacharya, A., Brennan, K., Curtis, C., Gevaert, O., Ji, H. P., Karlsson, K. A., Karagyozova, K., Lo, Y., Liu, K., Nakano, M., Sathe, A., Smith, A. R., Spees, K., Wong, W. H., Yuki, K., Hangauer, M., Kaufman, D. S., Balmain, A., Bollam, S. R., Chen, W., Fan, Q., Kersten, K., Krummel, M., Li, Y. R., Menard, M., Nasholm, N., Schmidt, C., Serwas, N. K., Yoda, H. 2021; 184 (5): 1142–55

    Abstract

    The characterization of cancer genomes has provided insight into somatically altered genes across tumors, transformed our understanding of cancer biology, and enabled tailoring of therapeutic strategies. However, the function of most cancer alleles remains mysterious, and many cancer features transcend their genomes. Consequently, tumor genomic characterization does not influence therapy for most patients. Approaches to understand the function and circuitry of cancer genes provide complementary approaches to elucidate both oncogene and non-oncogene dependencies. Emerging work indicates that the diversity of therapeutic targets engendered by non-oncogene dependencies is much larger than the list of recurrently mutated genes. Here we describe a framework for this expanded list of cancer targets, providing novel opportunities for clinical translation.

    View details for DOI 10.1016/j.cell.2021.02.020

    View details for PubMedID 33667368

  • Genome-wide CRISPR screens reveal a specific ligand for the glycan-binding immune checkpoint receptor Siglec-7. Proceedings of the National Academy of Sciences of the United States of America Wisnovsky, S., Mockl, L., Malaker, S. A., Pedram, K., Hess, G. T., Riley, N. M., Gray, M. A., Smith, B. A., Bassik, M. C., Moerner, W. E., Bertozzi, C. R. 2021; 118 (5)

    Abstract

    Glyco-immune checkpoint receptors, molecules that inhibit immune cell activity following binding to glycosylated cell-surface antigens, are emerging as attractive targets for cancer immunotherapy. Defining biologically relevant ligands that bind and activate such receptors, however, has historically been a significant challenge. Here, we present a CRISPRi genomic screening strategy that allowed unbiased identification of the key genes required for cell-surface presentation of glycan ligands on leukemia cells that bind the glyco-immune checkpoint receptors Siglec-7 and Siglec-9. This approach revealed a selective interaction between Siglec-7 and the mucin-type glycoprotein CD43. Further work identified a specific N-terminal glycopeptide region of CD43 containing clusters of disialylated O-glycan tetrasaccharides that form specific Siglec-7 binding motifs. Knockout or blockade of CD43 in leukemia cells relieves Siglec-7-mediated inhibition of immune killing activity. This work identifies a potential target for immune checkpoint blockade therapy and represents a generalizable approach to dissection of glycan-receptor interactions in living cells.

    View details for DOI 10.1073/pnas.2015024118

    View details for PubMedID 33495350

  • A New Paradigm in Catalase Research. Trends in cell biology Fujiki, Y., Bassik, M. C. 2021

    Abstract

    Recent findings provide evidence for dynamic and highly regulated dual subcellular localization of catalase, a hydrogen peroxide (H2O2)-metabolizing enzyme, in peroxisomes and the cytosol. These data suggest a number of important implications for the field of oxidative stress biology.

    View details for DOI 10.1016/j.tcb.2020.12.006

    View details for PubMedID 33422360

  • p53 is a central regulator driving neurodegeneration caused by C9orf72 poly(PR). Cell Maor-Nof, M. n., Shipony, Z. n., Lopez-Gonzalez, R. n., Nakayama, L. n., Zhang, Y. J., Couthouis, J. n., Blum, J. A., Castruita, P. A., Linares, G. R., Ruan, K. n., Ramaswami, G. n., Simon, D. J., Nof, A. n., Santana, M. n., Han, K. n., Sinnott-Armstrong, N. n., Bassik, M. C., Geschwind, D. H., Tessier-Lavigne, M. n., Attardi, L. D., Lloyd, T. E., Ichida, J. K., Gao, F. B., Greenleaf, W. J., Yokoyama, J. S., Petrucelli, L. n., Gitler, A. D. 2021

    Abstract

    The most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is a GGGGCC repeat expansion in the C9orf72 gene. We developed a platform to interrogate the chromatin accessibility landscape and transcriptional program within neurons during degeneration. We provide evidence that neurons expressing the dipeptide repeat protein poly(proline-arginine), translated from the C9orf72 repeat expansion, activate a highly specific transcriptional program, exemplified by a single transcription factor, p53. Ablating p53 in mice completely rescued neurons from degeneration and markedly increased survival in a C9orf72 mouse model. p53 reduction also rescued axonal degeneration caused by poly(glycine-arginine), increased survival of C9orf72 ALS/FTD-patient-induced pluripotent stem cell (iPSC)-derived motor neurons, and mitigated neurodegeneration in a C9orf72 fly model. We show that p53 activates a downstream transcriptional program, including Puma, which drives neurodegeneration. These data demonstrate a neurodegenerative mechanism dynamically regulated through transcription-factor-binding events and provide a framework to apply chromatin accessibility and transcription program profiles to neurodegeneration.

    View details for DOI 10.1016/j.cell.2020.12.025

    View details for PubMedID 33482083

  • Roadmap for the use of base editors to decipher drug mechanism of action. PloS one Aparicio-Prat, E., Yan, D., Mariotti, M., Bassik, M., Hess, G., Fortin, J., Weston, A., Xi, H. S., Stanton, R. 2021; 16 (9): e0257537

    Abstract

    CRISPR base editors are powerful tools for large-scale mutagenesis studies. This kind of approach can elucidate the mechanism of action of compounds, a key process in drug discovery. Here, we explore the utility of base editors in an early drug discovery context focusing on G-protein coupled receptors. A pooled mutagenesis screening framework was set up based on a modified version of the CRISPR-X base editor system. We determine optimized experimental conditions for mutagenesis where sgRNAs are delivered by cell transfection or viral infection over extended time periods (>14 days), resulting in high mutagenesis produced in a short region located at -4/+8 nucleotides with respect to the sgRNA match. The beta2 Adrenergic Receptor (B2AR) was targeted in this way employing a 6xCRE-mCherry reporter system to monitor its response to isoproterenol. The results of our screening indicate that residue 184 of B2AR is crucial for its activation. Based on our experience, we outline the crucial points to consider when designing and performing CRISPR-based pooled mutagenesis screening, including the typical technical hurdles encountered when studying compound pharmacology.

    View details for DOI 10.1371/journal.pone.0257537

    View details for PubMedID 34547052

  • Zmat3 Is a Key Splicing Regulator in the p53 Tumor Suppression Program. Molecular cell Bieging-Rolett, K. T., Kaiser, A. M., Morgens, D. W., Boutelle, A. M., Seoane, J. A., Van Nostrand, E. L., Zhu, C., Houlihan, S. L., Mello, S. S., Yee, B. A., McClendon, J., Pierce, S. E., Winters, I. P., Wang, M., Connolly, A. J., Lowe, S. W., Curtis, C., Yeo, G. W., Winslow, M. M., Bassik, M. C., Attardi, L. D. 2020; 80 (3): 452

    Abstract

    Although TP53 is the most commonly mutated gene in human cancers, the p53-dependent transcriptional programs mediating tumor suppression remain incompletely understood. Here, to uncover critical components downstream of p53 in tumor suppression, we perform unbiased RNAi and CRISPR-Cas9-based genetic screens invivo. These screens converge upon the p53-inducible gene Zmat3, encoding an RNA-binding protein, and we demonstrate that ZMAT3 is an important tumor suppressor downstream of p53 in mouse KrasG12D-driven lung and liver cancers and human carcinomas. Integrative analysis of the ZMAT3 RNA-binding landscape and transcriptomic profiling reveals that ZMAT3 directly modulates exon inclusion in transcripts encoding proteins of diverse functions, including the p53 inhibitors MDM4 and MDM2, splicing regulators, and components of varied cellular processes. Interestingly, these exons are enriched in NMD signals, and, accordingly, ZMAT3 broadly affects target transcript stability. Collectively, these studies reveal ZMAT3 as a novel RNA-splicing and homeostasis regulator and a key component of p53-mediated tumor suppression.

    View details for DOI 10.1016/j.molcel.2020.10.022

    View details for PubMedID 33157015

  • LRRC8A:C/E Heteromeric Channels Are Ubiquitous Transporters of cGAMP. Molecular cell Lahey, L. J., Mardjuki, R. E., Wen, X., Hess, G. T., Ritchie, C., Carozza, J. A., Bohnert, V., Maduke, M., Bassik, M. C., Li, L. 2020

    Abstract

    Extracellular 2'3'-cyclic-GMP-AMP (cGAMP) is an immunotransmitter exported by diseased cells and imported into host cells to activate the innate immune STING pathway. We previously identified SLC19A1 as a cGAMP importer, but its use across human cell lines is limited. Here, we identify LRRC8A heteromeric channels, better known as volume-regulated anion channels (VRAC), as widely expressed cGAMP transporters. LRRC8A forms complexes with LRRC8C and/or LRRC8E, depending on their expression levels, to transport cGAMP and other 2'3'-cyclic dinucleotides. In contrast, LRRC8D inhibits cGAMP transport. We demonstrate that cGAMP is effluxed or influxed via LRRC8 channels, as dictated by the cGAMP electrochemical gradient. Activation of LRRC8A channels, which can occur under diverse stresses, strongly potentiates cGAMP transport. We identify activator sphingosine 1-phosphate and inhibitor DCPIB as chemical tools to manipulate channel-mediated cGAMP transport. Finally, LRRC8A channels are key cGAMP transporters in resting primary human vasculature cells and universal human cGAMP transporters when activated.

    View details for DOI 10.1016/j.molcel.2020.10.021

    View details for PubMedID 33171122

  • Combined Proteomic and Genetic Interaction Mapping Reveals New RAS Effector Pathways and Susceptibilities. Cancer discovery Kelly, M. R., Kostyrko, K., Han, K., Mooney, N. A., Jeng, E. E., Spees, K., Dinh, P. T., Abbott, K. L., Gwinn, D. M., Sweet-Cordero, E. A., Bassik, M. C., Jackson, P. K. 2020

    Abstract

    Activating mutations in RAS GTPases drive many cancers, but limited understanding of less-studied RAS interactors, and of the specific roles of different RAS interactor paralogs, continues to limit target discovery. We developed a multistage discovery and screening process to systematically identify genes conferring RAS-related susceptibilities in lung adenocarcinoma. Using affinity purification mass spectrometry, we generated a protein-protein interaction map of RAS interactors and pathway components containing hundreds of interactions. From this network, we constructed a CRISPR dual knockout library targeting 119 RAS-related genes that we screened for KRAS-dependent genetic interactions (GIs). This approach identified new RAS effectors, including the adhesion controller RADIL and the endocytosis regulator RIN1, and >250 synthetic lethal GIs, including a potent KRAS-dependent interaction between RAP1GDS1 and RHOA. Many GIs link specific paralogs within and between gene families. These findings illustrate the power of multiomic approaches to uncover synthetic lethal combinations specific for hitherto untreatable cancer genotypes.

    View details for DOI 10.1158/2159-8290.CD-19-1274

    View details for PubMedID 32727735

  • Systematic Identification of Regulators of Oxidative Stress Reveals Non-canonical Roles for Peroxisomal Import and the Pentose Phosphate Pathway. Cell reports Dubreuil, M. M., Morgens, D. W., Okumoto, K., Honsho, M., Contrepois, K., Lee-McMullen, B., Traber, G. M., Sood, R. S., Dixon, S. J., Snyder, M. P., Fujiki, Y., Bassik, M. C. 2020; 30 (5): 1417

    Abstract

    Reactive oxygen species (ROS) play critical roles inmetabolism and disease, yet a comprehensive analysis of the cellular response to oxidative stress is lacking. To systematically identify regulators ofoxidative stress, we conducted genome-wide Cas9/CRISPR and shRNA screens. This revealed a detailed picture of diverse pathways that control oxidative stress response, ranging from the TCA cycle and DNA repair machineries to iron transport, trafficking, and metabolism. Paradoxically, disrupting the pentose phosphate pathway (PPP) at the level of phosphogluconate dehydrogenase (PGD) protects cells against ROS. This dramatically alters metabolites in the PPP, consistent with rewiring of upper glycolysis to promote antioxidant production. In addition, disruption of peroxisomal import unexpectedly increases resistance to oxidative stress by altering the localization of catalase. Together, these studies provide insights into the roles of peroxisomal matrix import and the PPP in redox biology and represent a rich resource for understanding the cellular response to oxidative stress.

    View details for DOI 10.1016/j.celrep.2020.01.013

    View details for PubMedID 32023459

  • Lipid-droplet-accumulating microglia represent a dysfunctional and proinflammatory state in the aging brain. Nature neuroscience Marschallinger, J., Iram, T., Zardeneta, M., Lee, S. E., Lehallier, B., Haney, M. S., Pluvinage, J. V., Mathur, V., Hahn, O., Morgens, D. W., Kim, J., Tevini, J., Felder, T. K., Wolinski, H., Bertozzi, C. R., Bassik, M. C., Aigner, L., Wyss-Coray, T. 2020

    Abstract

    Microglia become progressively activated and seemingly dysfunctional with age, and genetic studies have linked these cells to the pathogenesis of a growing number of neurodegenerative diseases. Here we report a striking buildup of lipid droplets in microglia with aging in mouse and human brains. These cells, which we call 'lipid-droplet-accumulating microglia' (LDAM), are defective in phagocytosis, produce high levels of reactive oxygen species and secrete proinflammatory cytokines. RNA-sequencing analysis of LDAM revealed a transcriptional profile driven by innate inflammation that is distinct from previously reported microglial states. An unbiased CRISPR-Cas9 screen identified genetic modifiers of lipid droplet formation; surprisingly, variants of several of these genes, including progranulin (GRN), are causes of autosomal-dominant forms of human neurodegenerative diseases. We therefore propose that LDAM contribute to age-related and genetic forms of neurodegeneration.

    View details for DOI 10.1038/s41593-019-0566-1

    View details for PubMedID 31959936

  • Genome-wide analysis of targets of macrolide antibiotics in mammalian cells. The Journal of biological chemistry Gupta, A., Okesli-Armlovich, A., Morgens, D., Bassik, M. C., Khosla, C. 2020

    Abstract

    Macrolide antibiotics, such as erythromycin and josamycin, are polyketide natural products harboring 14-16-membered macrocyclic lactone rings to which various sugars are attached. These antibiotics are extensively used in the clinic because of their ability to inhibit bacterial protein synthesis. More recently, some macrolides have been shown to also possess anti-inflammatory and other therapeutic activities in mammalian cells. To better understand the targets and effects of this drug class in mammalian cells, we used a genome-wide shRNA screen in K562 cancer cells to identify genes that modulate cellular sensitivity to josamycin. Among the most sensitizing hits were proteins involved in mitochondrial translation and the mitochondrial unfolded protein response, glycolysis and the mitogen-activated protein kinase signaling cascade. Further analysis revealed that cells treated with josamycin or other antibacterials exhibited impaired oxidative phosphorylation and metabolic shifts to glycolysis. Interestingly, we observed that knockdown of the mitogen-activated protein kinase kinase kinase 4 (MAP3K4) gene, which contributes to p38 MAPK signaling, sensitized cells to only josamycin but not to other antibacterials. There is a growing interest in better characterizing the therapeutic effects and toxicities of antibiotics in mammalian cells to guide new applications in both cellular and clinical studies. To our knowledge, this is the first report of an unbiased genome-wide screen to investigate the effects of a clinically used antibiotic on human cells.

    View details for DOI 10.1074/jbc.RA119.010770

    View details for PubMedID 31915244

  • Metabolic precision labeling enables selective probing of O-linked N-acetylgalactosamine glycosylation. Proceedings of the National Academy of Sciences of the United States of America Debets, M. F., Tastan, O. Y., Wisnovsky, S. P., Malaker, S. A., Angelis, N. n., Moeckl, L. K., Choi, J. n., Flynn, H. n., Wagner, L. J., Bineva-Todd, G. n., Antonopoulos, A. n., Cioce, A. n., Browne, W. M., Li, Z. n., Briggs, D. C., Douglas, H. L., Hess, G. T., Agbay, A. J., Roustan, C. n., Kjaer, S. n., Haslam, S. M., Snijders, A. P., Bassik, M. C., Moerner, W. E., Li, V. S., Bertozzi, C. R., Schumann, B. n. 2020

    Abstract

    Protein glycosylation events that happen early in the secretory pathway are often dysregulated during tumorigenesis. These events can be probed, in principle, by monosaccharides with bioorthogonal tags that would ideally be specific for distinct glycan subtypes. However, metabolic interconversion into other monosaccharides drastically reduces such specificity in the living cell. Here, we use a structure-based design process to develop the monosaccharide probe N-(S)-azidopropionylgalactosamine (GalNAzMe) that is specific for cancer-relevant Ser/Thr(O)-linked N-acetylgalactosamine (GalNAc) glycosylation. By virtue of a branched N-acylamide side chain, GalNAzMe is not interconverted by epimerization to the corresponding N-acetylglucosamine analog by the epimerase N-acetylgalactosamine-4-epimerase (GALE) like conventional GalNAc-based probes. GalNAzMe enters O-GalNAc glycosylation but does not enter other major cell surface glycan types including Asn(N)-linked glycans. We transfect cells with the engineered pyrophosphorylase mut-AGX1 to biosynthesize the nucleotide-sugar donor uridine diphosphate (UDP)-GalNAzMe from a sugar-1-phosphate precursor. Tagged with a bioorthogonal azide group, GalNAzMe serves as an O-glycan-specific reporter in superresolution microscopy, chemical glycoproteomics, a genome-wide CRISPR-knockout (CRISPR-KO) screen, and imaging of intestinal organoids. Additional ectopic expression of an engineered glycosyltransferase, "bump-and-hole" (BH)-GalNAc-T2, boosts labeling in a programmable fashion by increasing incorporation of GalNAzMe into the cell surface glycoproteome. Alleviating the need for GALE-KO cells in metabolic labeling experiments, GalNAzMe is a precision tool that allows a detailed view into the biology of a major type of cancer-relevant protein glycosylation.

    View details for DOI 10.1073/pnas.2007297117

    View details for PubMedID 32989128

  • Enhancing the Antiviral Efficacy of RNA-Dependent RNA Polymerase Inhibition by Combination with Modulators of Pyrimidine Metabolism. Cell chemical biology Liu, Q. n., Gupta, A. n., Okesli-Armlovich, A. n., Qiao, W. n., Fischer, C. R., Smith, M. n., Carette, J. E., Bassik, M. C., Khosla, C. n. 2020

    Abstract

    Genome-wide analysis of the mode of action of GSK983, a potent antiviral agent, led to the identification of dihydroorotate dehydrogenase as its target along with the discovery that genetic knockdown of pyrimidine salvage sensitized cells to GSK983. Because GSK983 is an ineffective antiviral in the presence of physiological uridine concentrations, we explored combining GSK983 with pyrimidine salvage inhibitors. We synthesized and evaluated analogs of cyclopentenyl uracil (CPU), an inhibitor of uridine salvage. We found that CPU was converted into its triphosphate in cells. When combined with GSK983, CPU resulted in large drops in cellular UTP and CTP pools. Consequently, CPU-GSK983 suppressed dengue virus replication in the presence of physiological concentrations of uridine. In addition, the CPU-GSK983 combination markedly enhanced the effect of RNA-dependent RNA polymerase (RdRp) inhibition on viral infection. Our findings highlight a new host-targeting strategy for potentiating the antiviral activity of RdRp inhibitors.

    View details for DOI 10.1016/j.chembiol.2020.05.002

    View details for PubMedID 32442424

    View details for PubMedCentralID PMC7241336

  • SETD5-Coordinated Chromatin Reprogramming Regulates Adaptive Resistance to Targeted Pancreatic Cancer Therapy. Cancer cell Wang, Z. n., Hausmann, S. n., Lyu, R. n., Li, T. M., Lofgren, S. M., Flores, N. M., Fuentes, M. E., Caporicci, M. n., Yang, Z. n., Meiners, M. J., Cheek, M. A., Howard, S. A., Zhang, L. n., Elias, J. E., Kim, M. P., Maitra, A. n., Wang, H. n., Bassik, M. C., Keogh, M. C., Sage, J. n., Gozani, O. n., Mazur, P. K. 2020

    Abstract

    Molecular mechanisms underlying adaptive targeted therapy resistance in pancreatic ductal adenocarcinoma (PDAC) are poorly understood. Here, we identify SETD5 as a major driver of PDAC resistance to MEK1/2 inhibition (MEKi). SETD5 is induced by MEKi resistance and its deletion restores refractory PDAC vulnerability to MEKi therapy in mouse models and patient-derived xenografts. SETD5 lacks histone methyltransferase activity but scaffolds a co-repressor complex, including HDAC3 and G9a. Gene silencing by the SETD5 complex regulates known drug resistance pathways to reprogram cellular responses to MEKi. Pharmacological co-targeting of MEK1/2, HDAC3, and G9a sustains PDAC tumor growth inhibition in vivo. Our work uncovers SETD5 as a key mediator of acquired MEKi therapy resistance in PDAC and suggests a context for advancing MEKi use in the clinic.

    View details for DOI 10.1016/j.ccell.2020.04.014

    View details for PubMedID 32442403

  • Transcriptomic signatures across human tissues identify functional rare genetic variation. Science (New York, N.Y.) Ferraro, N. M., Strober, B. J., Einson, J. n., Abell, N. S., Aguet, F. n., Barbeira, A. N., Brandt, M. n., Bucan, M. n., Castel, S. E., Davis, J. R., Greenwald, E. n., Hess, G. T., Hilliard, A. T., Kember, R. L., Kotis, B. n., Park, Y. n., Peloso, G. n., Ramdas, S. n., Scott, A. J., Smail, C. n., Tsang, E. K., Zekavat, S. M., Ziosi, M. n., Aradhana, n. n., Ardlie, K. G., Assimes, T. L., Bassik, M. C., Brown, C. D., Correa, A. n., Hall, I. n., Im, H. K., Li, X. n., Natarajan, P. n., Lappalainen, T. n., Mohammadi, P. n., Montgomery, S. B., Battle, A. n. 2020; 369 (6509)

    Abstract

    Rare genetic variants are abundant across the human genome, and identifying their function and phenotypic impact is a major challenge. Measuring aberrant gene expression has aided in identifying functional, large-effect rare variants (RVs). Here, we expanded detection of genetically driven transcriptome abnormalities by analyzing gene expression, allele-specific expression, and alternative splicing from multitissue RNA-sequencing data, and demonstrate that each signal informs unique classes of RVs. We developed Watershed, a probabilistic model that integrates multiple genomic and transcriptomic signals to predict variant function, validated these predictions in additional cohorts and through experimental assays, and used them to assess RVs in the UK Biobank, the Million Veterans Program, and the Jackson Heart Study. Our results link thousands of RVs to diverse molecular effects and provide evidence to associate RVs affecting the transcriptome with human traits.

    View details for DOI 10.1126/science.aaz5900

    View details for PubMedID 32913073

  • Genome-wide synthetic lethal CRISPR screen identifies FIS1 as a genetic interactor of ALS-linked C9ORF72. Brain research Chai, N., Haney, M. S., Couthouis, J., Morgens, D. W., Benjamin, A., Wu, K., Ousey, J., Fang, S., Finer, S., Bassik, M. C., Gitler, A. D. 2019: 146601

    Abstract

    Mutations in the C9ORF72 gene are the most common cause of amyotrophic lateral sclerosis (ALS). Both toxic gain of function and loss of function pathogenic mechanisms have been proposed. Accruing evidence from mouse knockout studies point to a role for C9ORF72 as a regulator of immune function. To provide further insight into its cellular function, we performed a genome-wide synthetic lethal CRISPR screen in human myeloid cells lacking C9ORF72. We discovered a strong synthetic lethal genetic interaction between C9ORF72 and FIS1, which encodes a mitochondrial membrane protein involved in mitochondrial fission and mitophagy. Mass spectrometry experiments revealed that in C9ORF72 knockout cells, FIS1 strongly bound to a class of immune regulators that activate the receptor for advanced glycation end (RAGE) products and trigger inflammatory cascades. These findings present a novel genetic interactor for C9ORF72 and suggest a compensatory role for FIS1 in suppressing inflammatory signaling in the absence of C9ORF72.

    View details for DOI 10.1016/j.brainres.2019.146601

    View details for PubMedID 31843624

  • The CoQ oxidoreductase FSP1 acts parallel to GPX4 to inhibit ferroptosis. Nature Bersuker, K., Hendricks, J., Li, Z., Magtanong, L., Ford, B., Tang, P. H., Roberts, M. A., Tong, B., Maimone, T. J., Zoncu, R., Bassik, M. C., Nomura, D. K., Dixon, S. J., Olzmann, J. A. 2019

    Abstract

    Ferroptosis is a form of regulated cell death that is caused by the iron-dependent peroxidation of lipids1,2. The glutathione-dependent lipid hydroperoxidase glutathione peroxidase 4 (GPX4) prevents ferroptosis by converting lipid hydroperoxides into non-toxic lipid alcohols3,4. Ferroptosis has been implicated in the cell death that underlies several degenerative conditions2, and induction of ferroptosis by inhibition of GPX4 has emerged as a therapeutic strategy to trigger cancer cell death5. However, sensitivity to GPX4 inhibitors varies greatly across cancer cell lines6, suggesting that additional factors govern resistance to ferroptosis. Here, using a synthetic lethal CRISPR-Cas9 screen, we identify ferroptosis suppressor protein 1 (FSP1) (previously known as apoptosis-inducing factor mitochondrial 2 (AIFM2)) as a potent ferroptosis resistance factor. Our data indicate that myristoylation recruits FSP1 to the plasma membrane where it functions as an oxidoreductase that reduces coenzyme Q10 (CoQ), generating a lipophilic radical-trapping antioxidant (RTA) that halts the propagation of lipid peroxides. We further find that FSP1 expression positively correlates with ferroptosis resistance across hundreds of cancer cell lines, and that FSP1 mediates resistance to ferroptosis in lung cancer cells in culture and in mouse tumor xenografts. Thus, our data identify FSP1 as a key component of a non-mitochondrial CoQ antioxidant system that acts in parallel to the canonical glutathione-based GPX4 pathway. These findings define a new ferroptosis suppression pathway and indicate that pharmacological inhibition of FSP1 may provide an effective strategy to sensitize cancer cells to ferroptosis-inducing chemotherapeutics.

    View details for DOI 10.1038/s41586-019-1705-2

    View details for PubMedID 31634900

  • A ZDHHC5-GOLGA7 Protein Acyltransferase Complex Promotes Nonapoptotic Cell Death. Cell chemical biology Ko, P., Woodrow, C., Dubreuil, M. M., Martin, B. R., Skouta, R., Bassik, M. C., Dixon, S. J. 2019

    Abstract

    Lethal small molecules are useful probes to discover and characterize novel cell death pathways and biochemical mechanisms. Here we report that the synthetic oxime-containing small molecule caspase-independent lethal 56 (CIL56) induces an unconventional form of nonapoptotic cell death distinct from necroptosis, ferroptosis, and other pathways. CIL56-induced cell death requires a catalytically active protein S-acyltransferase complex comprising the enzyme ZDHHC5 and an accessory subunit GOLGA7. The ZDHHC5-GOLGA7 complex is mutually stabilizing and localizes to the plasma membrane. CIL56 inhibits anterograde protein transport from the Golgi apparatus, which may be lethal in the context of ongoing ZDHHC5-GOLGA7 complex-dependent retrograde protein trafficking from the plasma membrane to internal sites. Other oxime-containing small molecules, structurally distinct from CIL56, may trigger cell death through the same pathway. These results define an unconventional form of nonapoptotic cell death regulated by protein S-acylation.

    View details for DOI 10.1016/j.chembiol.2019.09.014

    View details for PubMedID 31631010

  • Phagolysosome resolution requires contacts with the endoplasmic reticulum and phosphatidylinositol-4-phosphate signalling. Nature cell biology Levin-Konigsberg, R., Montano-Rendon, F., Keren-Kaplan, T., Li, R., Ego, B., Mylvaganam, S., DiCiccio, J. E., Trimble, W. S., Bassik, M. C., Bonifacino, J. S., Fairn, G. D., Grinstein, S. 2019

    Abstract

    Phosphoinositides have a pivotal role in the maturation of nascent phagosomes into microbicidal phagolysosomes. Following degradation of their contents, mature phagolysosomes undergo resolution, a process that remains largely uninvestigated. Here we studied the role of phosphoinositides in phagolysosome resolution. Phosphatidylinositol-4-phosphate (PtdIns(4)P), which is abundant in maturing phagolysosomes, was depleted as they tubulated and resorbed. Depletion was caused, in part, by transfer of phagolysosomal PtdIns(4)P to the endoplasmic reticulum, a process mediated by oxysterol-binding protein-related protein 1L (ORP1L), a RAB7 effector. ORP1L formed discrete tethers between the phagolysosome and the endoplasmic reticulum, resulting in distinct regions with alternating PtdIns(4)P depletion and enrichment. Tubules emerged from PtdIns(4)P-rich regions, where ADP-ribosylation factor-like protein 8B (ARL8B) and SifA- and kinesin-interacting protein/pleckstrin homology domain-containing family M member 2 (SKIP/PLEKHM2) accumulated. SKIP binds preferentially to monophosphorylated phosphoinositides, of which PtdIns(4)P is most abundant in phagolysosomes, contributing to their tubulation. Accordingly, premature hydrolysis of PtdIns(4)P impaired SKIP recruitment and phagosome resolution. Thus, resolution involves phosphoinositides and tethering of phagolysosomes to the endoplasmic reticulum.

    View details for DOI 10.1038/s41556-019-0394-2

    View details for PubMedID 31570833

  • CRISPR-Cas9 Screens Identify the RNA Helicase DDX3X as a Repressor of C9ORF72 (GGGGCC)n Repeat-Associated Non-AUG Translation. Neuron Cheng, W., Wang, S., Zhang, Z., Morgens, D. W., Hayes, L. R., Lee, S., Portz, B., Xie, Y., Nguyen, B. V., Haney, M. S., Yan, S., Dong, D., Coyne, A. N., Yang, J., Xian, F., Cleveland, D. W., Qiu, Z., Rothstein, J. D., Shorter, J., Gao, F., Bassik, M. C., Sun, S. 2019

    Abstract

    Hexanucleotide GGGGCC repeat expansion in C9ORF72 is the most prevalent genetic cause ofamyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). One pathogenic mechanism isthe aberrant accumulation of dipeptide repeat (DPR) proteins produced by the unconventional translation of expanded RNA repeats. Here, we performed genome-wide CRISPR-Cas9 screens for modifiers of DPR protein production in human cells.We found that DDX3X, an RNA helicase, suppresses the repeat-associated non-AUG translation of GGGGCC repeats. DDX3X directly binds to (GGGGCC)n RNAs but not antisense (CCCCGG)n RNAs. Its helicase activity is essential for the translation repression. Reduction of DDX3X increases DPR levels in C9ORF72-ALS/FTD patient cells and enhances (GGGGCC)n-mediated toxicity in Drosophila. Elevating DDX3X expression is sufficient to decrease DPR levels, rescue nucleocytoplasmic transport abnormalities, and improve survival of patient iPSC-differentiated neurons. This work identifies genetic modifiers of DPR protein production and provides potential therapeutic targets for C9ORF72-ALS/FTD.

    View details for DOI 10.1016/j.neuron.2019.09.003

    View details for PubMedID 31587919

  • Systematic Identification of Host Cell Regulators of Legionella pneumophila Pathogenesis Using a Genome-wide CRISPR Screen. Cell host & microbe Jeng, E. E., Bhadkamkar, V., Ibe, N. U., Gause, H., Jiang, L., Chan, J., Jian, R., Jimenez-Morales, D., Stevenson, E., Krogan, N. J., Swaney, D. L., Snyder, M. P., Mukherjee, S., Bassik, M. C. 2019

    Abstract

    During infection, Legionella pneumophila translocates over 300 effector proteins into the host cytosol, allowing the pathogen to establish an endoplasmic reticulum (ER)-like Legionella-containing vacuole (LCV) that supports bacterial replication. Here, we perform a genome-wide CRISPR-Cas9 screen and secondary targeted screens in U937 human monocyte/macrophage-like cells to systematically identify host factorsthat regulate killing by L.pneumophila. The screens reveal known host factors hijacked by L.pneumophila, as well as genes spanning diverse trafficking and signaling pathways previously not linked to L.pneumophila pathogenesis. We further characterize C1orf43 and KIAA1109 as regulators ofphagocytosis and show that RAB10 and its chaperone RABIF are required for optimal L.pneumophila replication and ER recruitment to the LCV. Finally, we show that Rab10 protein is recruited to the LCV and ubiquitinated by the effectors SidC/SdcA. Collectively, our results provide a wealth of previously undescribed insights into L.pneumophila pathogenesis and mammalian cell function.

    View details for DOI 10.1016/j.chom.2019.08.017

    View details for PubMedID 31540829

  • Discovery of small molecule inhibitors of human uridine-cytidine kinase 2 by high-throughput screening. Bioorganic & medicinal chemistry letters Okesli-Armlovich, A., Gupta, A., Jimenez, M., Auld, D., Liu, Q., Bassik, M. C., Khosla, C. 2019

    Abstract

    Clinically relevant inhibitors of dihydroorotate dehydrogenase (DHODH), a rate-limiting enzyme in mammalian de novo pyrimidine synthesis, have strong antiviral and anticancer activity in vitro. However, they are ineffective in vivo due to efficient uridine salvage by infected or rapidly dividing cells. The pyrimidine salvage enzyme uridine-cytidine kinase 2 (UCK2), a 29 kDa protein that forms a tetramer in its active state, is necessary for uridine salvage. Notwithstanding the pharmacological potential of this target, no medicinally tractable inhibitors of the human enzyme have been reported to date. We therefore established and miniaturized an in vitro assay for UCK2 activity and undertook a high-throughput screen against a 40,000-compound library to generate drug-like leads. The structures, activities, and modes of inhibition of the most promising hits are described. Notably, our screen yielded non-competitive UCK2 inhibitors which were able to suppress nucleoside salvage in cells both in the presence and absence of DHODH inhibitors.

    View details for DOI 10.1016/j.bmcl.2019.08.010

    View details for PubMedID 31420268

  • Astrocyte-to-astrocyte contact and a positive feedback loop of growth factor signaling regulate astrocyte maturation GLIA Li, J., Khankan, R. R., Caneda, C., Godoy, M., Haney, M. S., Krawczyk, M. C., Bassik, M. C., Sloan, S. A., Zhan, Y. 2019; 67 (8): 1571–97

    View details for DOI 10.1002/glia.23630

    View details for Web of Science ID 000470958100011

  • Kinetic analysis identifies determinants of sensitivity to MEK inhibitor-induced cell death Inde, Z., Han, K., Bassik, M. C., Dixon, S. J. AMER ASSOC CANCER RESEARCH. 2019
  • Neuronally Enriched RUFY3 Is Required for Caspase-Mediated Axon Degeneration. Neuron Hertz, N. T., Adams, E. L., Weber, R. A., Shen, R. J., O'Rourke, M. K., Simon, D. J., Zebroski, H., Olsen, O., Morgan, C. W., Mileur, T. R., Hitchcock, A. M., Sinnott Armstrong, N. A., Wainberg, M., Bassik, M. C., Molina, H., Wells, J. A., Tessier-Lavigne, M. 2019

    Abstract

    Selective synaptic and axonal degeneration are critical aspects of both brain development and neurodegenerative disease. Inhibition of caspase signaling in neurons is a potential therapeutic strategy for neurodegenerative disease, but no neuron-specific modulators of caspase signaling have been described. Using a mass spectrometry approach, we discovered that RUFY3, a neuronally enriched protein, is essential for caspase-mediated degeneration of TRKA+ sensory axons invitro and invivo. Deletion of Rufy3 protects axons from degeneration, even in the presence of activated CASP3 that is competent to cleave endogenous substrates. Dephosphorylation of RUFY3 at residue S34 appears required for axon degeneration, providing a potential mechanism for neurons to locally control caspase-driven degeneration. Neuronally enriched RUFY3 thus provides an entry pointfor understanding non-apoptotic functions of CASP3 and a potential target to modulate caspase signaling specifically in neurons for neurodegenerative disease.

    View details for DOI 10.1016/j.neuron.2019.05.030

    View details for PubMedID 31221560

  • SLC19A1 Is an Importer of the Immunotransmitter cGAMP. Molecular cell Ritchie, C., Cordova, A. F., Hess, G. T., Bassik, M. C., Li, L. 2019

    Abstract

    2'3'-cyclic-GMP-AMP (cGAMP) is a second messenger that activates the antiviral stimulator of interferon genes (STING) pathway. We recently identified a novel role for cGAMP as a soluble, extracellular immunotransmitter that is produced and secreted by cancer cells. Secreted cGAMP is then sensed by host cells, eliciting an antitumoral immune response. Due to the antitumoral effects of cGAMP, other CDN-based STING agonists are currently under investigation in clinical trials for metastatic solid tumors. However, it is unknown how cGAMP and other CDNs cross the cell membrane to activateintracellular STING. Using a genome-wide CRISPRscreen, we identified SLC19A1 as the first knownimporter of cGAMP and other CDNs, including theinvestigational new drug 2'3'-bisphosphosphothioate-cyclic-di-AMP (2'3'-CDAS). These discoveries will provide insight into cGAMP's role as an immunotransmitter and aid in the development of more targeted CDN-based cancer therapeutics.

    View details for DOI 10.1016/j.molcel.2019.05.006

    View details for PubMedID 31126740

  • Astrocyte-to-astrocyte contact and a positive feedback loop of growth factor signaling regulate astrocyte maturation. Glia Li, J., Khankan, R. R., Caneda, C., Godoy, M. I., Haney, M. S., Krawczyk, M. C., Bassik, M. C., Sloan, S. A., Zhang, Y. 2019

    Abstract

    Astrocytes are critical for the development and function of the central nervous system. In developing brains, immature astrocytes undergo morphological, molecular, cellular, and functional changes as they mature. Although the mechanisms that regulate the maturation of other major cell types in the central nervous system such as neurons and oligodendrocytes have been extensively studied, little is known about the cellular and molecular mechanisms that control astrocyte maturation. Here, we identified molecular markers of astrocyte maturation and established an in vitro assay for studying the mechanisms of astrocyte maturation. Maturing astrocytes in vitro exhibit similar molecular changes and represent multiple molecular subtypes of astrocytes found in vivo. Using this system, we found that astrocyte-to-astrocyte contact strongly promotes astrocyte maturation. In addition, secreted signals from microglia, oligodendrocyte precursor cells, or endothelial cells affect a small subset of astrocyte genes but do not consistently change astrocyte maturation. To identify molecular mechanisms underlying astrocyte maturation, we treated maturing astrocytes with molecules that affect the function of tumor-associated genes. We found that a positive feedback loop of heparin-binding epidermal growth factor-like growth factor (HBEGF) and epidermal growth factor receptor (EGFR) signaling regulates astrocytes maturation. Furthermore, HBEGF, EGFR, and tumor protein 53 (TP53) affect the expression of genes important for cilium development, the circadian clock, and synapse function. These results revealed cellular and molecular mechanisms underlying astrocytes maturation with implications for the understanding of glioblastoma.

    View details for PubMedID 31033049

  • CD22 blockade restores homeostatic microglial phagocytosis in ageing brains NATURE Pluvinage, J. V., Haney, M. S., Smith, B. H., Sun, J., Iram, T., Bonanno, L., Li, L., Lee, D. P., Morgens, D. W., Yang, A. C., Shuken, S. R., Gate, D., Scott, M., Khatri, P., Luo, J., Bertozzi, C. R., Bassik, M. C., Wyss-Coray, T. 2019; 568 (7751): 187-+
  • CD22 blockade restores homeostatic microglial phagocytosis in ageing brains. Nature Pluvinage, J. V., Haney, M. S., Smith, B. A., Sun, J., Iram, T., Bonanno, L., Li, L., Lee, D. P., Morgens, D. W., Yang, A. C., Shuken, S. R., Gate, D., Scott, M., Khatri, P., Luo, J., Bertozzi, C. R., Bassik, M. C., Wyss-Coray, T. 2019

    Abstract

    Microglia maintain homeostasis in the central nervous system through phagocytic clearance of protein aggregates and cellular debris. This function deteriorates during ageing and neurodegenerative disease, concomitant with cognitive decline. However, the mechanisms of impaired microglial homeostatic function and the cognitive effects of restoring this function remain unknown. We combined CRISPR-Cas9 knockout screens with RNAsequencing analysis to discover age-related genetic modifiers of microglial phagocytosis. These screens identified CD22, a canonical Bcell receptor, as a negative regulator of phagocytosis that is upregulated on aged microglia. CD22 mediates the anti-phagocytic effect of alpha2,6-linked sialic acid, and inhibition of CD22 promotes the clearance of myelin debris, amyloid-beta oligomers and alpha-synuclein fibrils in vivo. Long-term central nervous system delivery of an antibody that blocks CD22 function reprograms microglia towards a homeostatic transcriptional state and improves cognitive function in aged mice. These findings elucidate a mechanism of age-related microglial impairment and a strategy to restore homeostasis in the ageing brain.

    View details for PubMedID 30944478

  • METTL13 Methylation of eEF1A Increases Translational Output to Promote Tumorigenesis CELL Liu, S., Hausmann, S., Carlson, S., Fuentes, M., Francis, J., Pillai, R., Lofgren, S., Hulea, L., Tandoc, K., Lu, J., Li, A., Nicholas Dang Nguyen, Caporicci, M., Kim, M., Maitra, A., Wang, H., Wistuba, I., Porco, J., Bassik, M., Elias, J., Song, J., Topisirovic, I., Van Rechem, C., Mazur, P., Gozani, O. 2019; 176 (3): 491-+
  • Genome-wide CRISPR Analysis Identifies Substrate-Specific Conjugation Modules in ER-Associated Degradation MOLECULAR CELL Leto, D. E., Morgens, D. W., Zhang, L., Walczak, C. P., Elias, J. E., Bassik, M. C., Kopito, R. R. 2019; 73 (2): 377-+
  • Mitigation of off-target toxicity in CRISPR-Cas9 screens for essential non-coding elements. Nature communications Tycko, J. n., Wainberg, M. n., Marinov, G. K., Ursu, O. n., Hess, G. T., Ego, B. K., Aradhana, n. n., Li, A. n., Truong, A. n., Trevino, A. E., Spees, K. n., Yao, D. n., Kaplow, I. M., Greenside, P. G., Morgens, D. W., Phanstiel, D. H., Snyder, M. P., Bintu, L. n., Greenleaf, W. J., Kundaje, A. n., Bassik, M. C. 2019; 10 (1): 4063

    Abstract

    Pooled CRISPR-Cas9 screens are a powerful method for functionally characterizing regulatory elements in the non-coding genome, but off-target effects in these experiments have not been systematically evaluated. Here, we investigate Cas9, dCas9, and CRISPRi/a off-target activity in screens for essential regulatory elements. The sgRNAs with the largest effects in genome-scale screens for essential CTCF loop anchors in K562 cells were not single guide RNAs (sgRNAs) that disrupted gene expression near the on-target CTCF anchor. Rather, these sgRNAs had high off-target activity that, while only weakly correlated with absolute off-target site number, could be predicted by the recently developed GuideScan specificity score. Screens conducted in parallel with CRISPRi/a, which do not induce double-stranded DNA breaks, revealed that a distinct set of off-targets also cause strong confounding fitness effects with these epigenome-editing tools. Promisingly, filtering of CRISPRi libraries using GuideScan specificity scores removed these confounded sgRNAs and enabled identification of essential regulatory elements.

    View details for DOI 10.1038/s41467-019-11955-7

    View details for PubMedID 31492858

  • Targeted genomic CRISPR-Cas9 screen identifies MAP4K4 as essential for glioblastoma invasion. Scientific reports Prolo, L. M., Li, A. n., Owen, S. F., Parker, J. J., Foshay, K. n., Nitta, R. T., Morgens, D. W., Bolin, S. n., Wilson, C. M., Vega L, J. C., Luo, E. J., Nwagbo, G. n., Waziri, A. n., Li, G. n., Reimer, R. J., Bassik, M. C., Grant, G. A. 2019; 9 (1): 14020

    Abstract

    Among high-grade brain tumors, glioblastoma is particularly difficult to treat, in part due to its highly infiltrative nature which contributes to the malignant phenotype and high mortality in patients. In order to better understand the signaling pathways underlying glioblastoma invasion, we performed the first large-scale CRISPR-Cas9 loss of function screen specifically designed to identify genes that facilitate cell invasion. We tested 4,574 genes predicted to be involved in trafficking and motility. Using a transwell invasion assay, we discovered 33 genes essential for invasion. Of the 11 genes we selected for secondary testing using a wound healing assay, 6 demonstrated a significant decrease in migration. The strongest regulator of invasion was mitogen-activated protein kinase 4 (MAP4K4). Targeting of MAP4K4 with single guide RNAs or a MAP4K4 inhibitor reduced migration and invasion in vitro. This effect was consistent across three additional patient derived glioblastoma cell lines. Analysis of epithelial-mesenchymal transition markers in U138 cells with lack or inhibition of MAP4K4 demonstrated protein expression consistent with a non-invasive state. Importantly, MAP4K4 inhibition limited migration in a subset of human glioma organotypic slice cultures. Our results identify MAP4K4 as a novel potential therapeutic target to limit glioblastoma invasion.

    View details for DOI 10.1038/s41598-019-50160-w

    View details for PubMedID 31570734

  • Discovery of common and rare genetic risk variants for colorectal cancer NATURE GENETICS Huyghe, J. R., Bien, S. A., Harrison, T. A., Kang, H., Chen, S., Schmit, S. L., Conti, D. V., Qu, C., Jeon, J., Edlund, C. K., Greenside, P., Wainberg, M., Schumacher, F. R., Smith, J. D., Levine, D. M., Nelson, S. C., Sinnott-Armstrong, N. A., Albanes, D., Alonso, M., Anderson, K., Arnau-Collell, C., Arndt, V., Bamia, C., Banbury, B. L., Baron, J. A., Berndt, S. I., Bezieau, S., Bishop, D., Boehm, J., Boeing, H., Brenner, H., Brezina, S., Buch, S., Buchanan, D. D., Burnett-Hartman, A., Butterbach, K., Caan, B. J., Campbell, P. T., Carlson, C. S., Castellvi-Bel, S., Chan, A. T., Chang-Claude, J., Chanock, S. J., Chirlaque, M., Cho, S., Connolly, C. M., Cross, A. J., Cuk, K., Curtis, K. R., de la Chapelle, A., Doheny, K. F., Duggan, D., Easton, D. F., Elias, S. G., Elliott, F., English, D. R., Feskens, E. M., Figueiredo, J. C., Fischer, R., FitzGerald, L. M., Forman, D., Gala, M., Gallinger, S., Gauderman, W., Giles, G. G., Gillanders, E., Gong, J., Goodman, P. J., Grady, W. M., Grove, J. S., Gsur, A., Gunter, M. J., Haile, R. W., Hampe, J., Hampel, H., Harlid, S., Hayes, R. B., Hofer, P., Hoffmeister, M., Hopper, J. L., Hsu, W., Huang, W., Hudson, T. J., Hunter, D. J., Ibanez-Sanz, G., Idos, G. E., Ingersoll, R., Jackson, R. D., Jacobs, E. J., Jenkins, M. A., Joshi, A. D., Joshu, C. E., Keku, T. O., Key, T. J., Kim, H., Kobayashi, E., Kolonel, L. N., Kooperberg, C., Kuehn, T., Kury, S., Kweon, S., Larsson, S. C., Laurie, C. A., Le Marchand, L., Leal, S. M., Lee, S., Lejbkowicz, F., Lemire, M., Li, C. I., Li, L., Lieb, W., Lin, Y., Lindblom, A., Lindor, N. M., Ling, H., Louie, T. L., Mannisto, S., Markowitz, S. D., Martin, V., Masala, G., McNeil, C. E., Melas, M., Milne, R. L., Moreno, L., Murphy, N., Myte, R., Naccarati, A., Newcomb, P. A., Offit, K., Ogino, S., Onland-Moret, N., Pardini, B., Parfrey, P. S., Pearlman, R., Perduca, V., Pharoah, P. P., Pinchev, M., Platz, E. A., Prentice, R. L., Pugh, E., Raskin, L., Rennert, G., Rennert, H. S., Riboli, E., Rodriguez-Barranco, M., Romm, J., Sakoda, L. C., Schafmayer, C., Schoen, R. E., Seminara, D., Shah, M., Shelford, T., Shin, M., Shulman, K., Sieri, S., Slattery, M. L., Southey, M. C., Stadler, Z. K., Stegmaier, C., Su, Y., Tangen, C. M., Thibodeau, S. N., Thomas, D. C., Thomas, S. S., Toland, A. E., Trichopoulou, A., Ulrich, C. M., Van den Berg, D. J., van Duijnhoven, F. B., Van Guelpen, B., van Kranen, H., Vijai, J., Visvanathan, K., Vodicka, P., Vodickova, L., Vymetalkova, V., Weigl, K., Weinstein, S. J., White, E., Win, A., Wolf, C., Wolk, A., Woods, M. O., Wu, A. H., Zaidi, S. H., Zanke, B. W., Zhang, Q., Zheng, W., Scacheri, P. C., Potter, J. D., Bassik, M. C., Kundaje, A., Casey, G., Moreno, V., Abecasis, G. R., Nickerson, D. A., Gruber, S. B., Hsu, L., Peters, U. 2019; 51 (1): 76-+
  • METTL13 Methylation of eEF1A Increases Translational Output to Promote Tumorigenesis. Cell Liu, S., Hausmann, S., Carlson, S. M., Fuentes, M. E., Francis, J. W., Pillai, R., Lofgren, S. M., Hulea, L., Tandoc, K., Lu, J., Li, A., Nguyen, N. D., Caporicci, M., Kim, M. P., Maitra, A., Wang, H., Wistuba, I. I., Porco, J. A., Bassik, M. C., Elias, J. E., Song, J., Topisirovic, I., Van Rechem, C., Mazur, P. K., Gozani, O. 2018

    Abstract

    Increased protein synthesis plays an etiologic role in diverse cancers. Here, we demonstrate that METTL13 (methyltransferase-like 13) dimethylation of eEF1A (eukaryotic elongation factor 1A) lysine 55 (eEF1AK55me2) is utilized by Ras-driven cancers to increase translational output and promote tumorigenesis invivo. METTL13-catalyzed eEF1A methylation increases eEF1A's intrinsic GTPase activity invitro and protein production in cells. METTL13 and eEF1AK55me2 levels are upregulated in cancer and negatively correlate with pancreatic and lung cancer patient survival. METTL13 deletion and eEF1AK55me2 loss dramatically reduce Ras-driven neoplastic growth in mouse models and in patient-derived xenografts (PDXs) from primary pancreatic and lung tumors. Finally, METTL13 depletion renders PDX tumors hypersensitive to drugs thattarget growth-signaling pathways. Together, our work uncovers a mechanism by which lethal cancers become dependent on the METTL13-eEF1AK55me2 axis to meet their elevated protein synthesis requirement and suggests that METTL13 inhibition may constitute a targetable vulnerability of tumors driven by aberrant Ras signaling.

    View details for PubMedID 30612740

  • Genome-wide interrogation of extracellular vesicle biology using barcoded miRNAs. eLife Lu, A., Wawro, P., Morgens, D. W., Portela, F., Bassik, M. C., Pfeffer, S. R. 2018; 7

    Abstract

    Extracellular vesicles mediate transfer of biologically active molecules between neighboring or distant cells, and these vesicles may play important roles in normal physiology and the pathogenesis of multiple disease states including cancer. However, the underlying molecular mechanisms of their biogenesis and release remain unknown. We designed artificially barcoded, exosomal microRNAs (bEXOmiRs) to monitor extracellular vesicle release quantitatively using deep sequencing. We then expressed distinct pairs of CRISPR guide RNAs and bEXOmiRs, enabling identification of genes influencing bEXOmiR secretion from Cas9-edited cells. This approach uncovered genes with unrecognized roles in multivesicular endosome exocytosis, including critical roles for Wnt signaling in extracellular vesicle release regulation. Coupling bEXOmiR reporter analysis with CRISPR-Cas9 screening provides a powerful and unbiased means to study extracellular vesicle biology and for the first time, to associate a nucleic acid tag with individual membrane vesicles.

    View details for PubMedID 30556811

  • Genome-wide interrogation of extracellular vesicle biology using barcoded miRNAs ELIFE Lu, A., Wawro, P., Morgens, D. W., Portela, F., Bassik, M. C., Pfeffer, S. R. 2018; 7
  • Genome-wide CRISPR Analysis Identifies Substrate-Specific Conjugation Modules in ER-Associated Degradation. Molecular cell Leto, D. E., Morgens, D. W., Zhang, L., Walczak, C. P., Elias, J. E., Bassik, M. C., Kopito, R. R. 2018

    Abstract

    The ubiquitin proteasome system (UPS) maintains the integrity of the proteome by selectively degrading misfolded or mis-assembled proteins, but the rules that govern how conformationally defective proteins in the secretory pathway are selected from the structurally and topologically diverse constellation of correctly folded membrane and secretory proteins for efficient degradation by cytosolic proteasomes is not well understood. Here, we combine parallel pooled genome-wide CRISPR-Cas9 forward genetic screening with a highly quantitative and sensitive protein turnover assay to discover a previously undescribed collaboration between membrane-embedded cytoplasmic ubiquitin E3 ligases to conjugate heterotypic branched or mixed ubiquitin (Ub) chains on substrates of endoplasmic-reticulum-associated degradation (ERAD). These findings demonstrate that parallel CRISPR analysis can be used to deconvolve highly complex cell biological processes and identify new biochemical pathways in protein quality control.

    View details for PubMedID 30581143

  • Discovery of common and rare genetic risk variants for colorectal cancer. Nature genetics Huyghe, J. R., Bien, S. A., Harrison, T. A., Kang, H. M., Chen, S., Schmit, S. L., Conti, D. V., Qu, C., Jeon, J., Edlund, C. K., Greenside, P., Wainberg, M., Schumacher, F. R., Smith, J. D., Levine, D. M., Nelson, S. C., Sinnott-Armstrong, N. A., Albanes, D., Alonso, M. H., Anderson, K., Arnau-Collell, C., Arndt, V., Bamia, C., Banbury, B. L., Baron, J. A., Berndt, S. I., Bezieau, S., Bishop, D. T., Boehm, J., Boeing, H., Brenner, H., Brezina, S., Buch, S., Buchanan, D. D., Burnett-Hartman, A., Butterbach, K., Caan, B. J., Campbell, P. T., Carlson, C. S., Castellvi-Bel, S., Chan, A. T., Chang-Claude, J., Chanock, S. J., Chirlaque, M., Cho, S. H., Connolly, C. M., Cross, A. J., Cuk, K., Curtis, K. R., de la Chapelle, A., Doheny, K. F., Duggan, D., Easton, D. F., Elias, S. G., Elliott, F., English, D. R., Feskens, E. J., Figueiredo, J. C., Fischer, R., FitzGerald, L. M., Forman, D., Gala, M., Gallinger, S., Gauderman, W. J., Giles, G. G., Gillanders, E., Gong, J., Goodman, P. J., Grady, W. M., Grove, J. S., Gsur, A., Gunter, M. J., Haile, R. W., Hampe, J., Hampel, H., Harlid, S., Hayes, R. B., Hofer, P., Hoffmeister, M., Hopper, J. L., Hsu, W., Huang, W., Hudson, T. J., Hunter, D. J., Ibanez-Sanz, G., Idos, G. E., Ingersoll, R., Jackson, R. D., Jacobs, E. J., Jenkins, M. A., Joshi, A. D., Joshu, C. E., Keku, T. O., Key, T. J., Kim, H. R., Kobayashi, E., Kolonel, L. N., Kooperberg, C., Kuhn, T., Kury, S., Kweon, S., Larsson, S. C., Laurie, C. A., Le Marchand, L., Leal, S. M., Lee, S. C., Lejbkowicz, F., Lemire, M., Li, C. I., Li, L., Lieb, W., Lin, Y., Lindblom, A., Lindor, N. M., Ling, H., Louie, T. L., Mannisto, S., Markowitz, S. D., Martin, V., Masala, G., McNeil, C. E., Melas, M., Milne, R. L., Moreno, L., Murphy, N., Myte, R., Naccarati, A., Newcomb, P. A., Offit, K., Ogino, S., Onland-Moret, N. C., Pardini, B., Parfrey, P. S., Pearlman, R., Perduca, V., Pharoah, P. D., Pinchev, M., Platz, E. A., Prentice, R. L., Pugh, E., Raskin, L., Rennert, G., Rennert, H. S., Riboli, E., Rodriguez-Barranco, M., Romm, J., Sakoda, L. C., Schafmayer, C., Schoen, R. E., Seminara, D., Shah, M., Shelford, T., Shin, M., Shulman, K., Sieri, S., Slattery, M. L., Southey, M. C., Stadler, Z. K., Stegmaier, C., Su, Y., Tangen, C. M., Thibodeau, S. N., Thomas, D. C., Thomas, S. S., Toland, A. E., Trichopoulou, A., Ulrich, C. M., Van Den Berg, D. J., van Duijnhoven, F. J., Van Guelpen, B., van Kranen, H., Vijai, J., Visvanathan, K., Vodicka, P., Vodickova, L., Vymetalkova, V., Weigl, K., Weinstein, S. J., White, E., Win, A. K., Wolf, C. R., Wolk, A., Woods, M. O., Wu, A. H., Zaidi, S. H., Zanke, B. W., Zhang, Q., Zheng, W., Scacheri, P. C., Potter, J. D., Bassik, M. C., Kundaje, A., Casey, G., Moreno, V., Abecasis, G. R., Nickerson, D. A., Gruber, S. B., Hsu, L., Peters, U. 2018

    Abstract

    To further dissect the genetic architecture of colorectal cancer (CRC), we performed whole-genome sequencing of 1,439 cases and 720 controls, imputed discovered sequence variants and Haplotype Reference Consortium panel variants into genome-wide association study data, and tested for association in 34,869 cases and 29,051 controls. Findings were followed up in an additional 23,262 cases and 38,296 controls. We discovered a strongly protective 0.3% frequency variant signal at CHD1. In a combined meta-analysis of 125,478 individuals, we identified 40 new independent signals at P<5*10-8, bringing the number of known independent signals for CRC to ~100. New signals implicate lower-frequency variants, Kruppel-like factors, Hedgehog signaling, Hippo-YAP signaling, long noncoding RNAs and somatic drivers, and support a role for immune function. Heritability analyses suggest that CRC risk is highly polygenic, and larger, more comprehensive studies enabling rare variant analysis will improve understanding of biology underlying this risk and influence personalized screening strategies and drug development.

    View details for PubMedID 30510241

  • Identification of phagocytosis regulators using magnetic genome-wide CRISPR screens NATURE GENETICS Haney, M. S., Bohlen, C. J., Morgens, D. W., Ousey, J. A., Barkal, A. A., Tsui, C., Ego, B. K., Levin, R., Kamber, R. A., Collins, H., Tucker, A., Li, A., Vorselen, D., Labitigan, L., Crane, E., Boyle, E., Jiang, L., Chan, J., Rincon, E., Greenleaf, W. J., Li, B., Snyder, M. P., Weissman, I. L., Theriot, J. A., Collins, S. R., Barres, B. A., Bassik, M. C. 2018; 50 (12): 1716-+
  • CBP Modulates Sensitivity to Dasatinib in Pre-BCR+ Acute Lymphoblastic Leukemia CANCER RESEARCH Duque-Afonso, J., Lin, C., Han, K., Morgens, D. W., Jeng, E. E., Weng, Z., Jeong, J., Wong, S., Zhu, L., Wei, M. C., Chae, H., Schrappe, M., Cario, G., Duyster, J., Xiao, X., Sakamoto, K. M., Bassik, M. C., Cleary, M. L. 2018; 78 (22): 6497-6508
  • CBP modulates sensitivity to dasatinib in pre-BCR+ acute lymphoblastic leukemia. Cancer research Duque-Afonso, J., Lin, C., Han, K., Morgens, D. W., Jeng, E. E., Weng, Z., Jeong, J., Wong, S. H., Zhu, L., Wei, M. C., Chae, H., Schrappe, M., Cario, G., Duyster, J., Sakamoto, K. M., Bassik, M. C., Cleary, M. L. 2018

    Abstract

    Dasatinib is a multi-tyrosine kinase inhibitor approved for treatment of Ph+ acute lymphoblastic leukemia (ALL), but its efficacy is limited by resistance. Recent preclinical studies suggest that dasatinib may be a candidate therapy in additional ALL subtypes including pre-BCR+ ALL. Here we utilized shRNA library screening and global transcriptomic analysis to identify several novel genes and pathways that may enhance dasatinib efficacy or mitigate potential resistance in human pre-BCR+ ALL. Depletion of the transcriptional co-activator CBP increased dasatinib sensitivity by activating transcription of the pre-BCR signaling pathway previously associated with dasatinib sensitivity. Acquired resistance was due in part to upregulation of alternative pathways including WNT through a mechanism suggesting transcriptional plasticity. Small molecules that disrupt CBP interactions with the CREB KID domain or beta-catenin showed promising preclinical efficacy in combination with dasatinib. These findings highlight novel modulators of sensitivity to targeted therapies in human pre-BCR+ ALL, which can be reversed by small molecules inhibitors. They also identify promising therapeutic approaches to ameliorate dasatinib sensitivity and prevent resistance in ALL.

    View details for PubMedID 30262461

  • KIF15 nanomechanics and kinesin inhibitors, with implications for cancer chemotherapeutics PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Milic, B., Chakraborty, A., Han, K., Bassik, M. C., Block, S. M. 2018; 115 (20): E4613–E4622

    Abstract

    Eg5, a mitotic kinesin, has been a target for anticancer drug development. Clinical trials of small-molecule inhibitors of Eg5 have been stymied by the development of resistance, attributable to mitotic rescue by a different endogenous kinesin, KIF15. Compared with Eg5, relatively little is known about the properties of the KIF15 motor. Here, we employed single-molecule optical-trapping techniques to define the KIF15 mechanochemical cycle. We also studied the inhibitory effects of KIF15-IN-1, an uncharacterized, commercially available, small-molecule inhibitor, on KIF15 motility. To explore the complementary behaviors of KIF15 and Eg5, we also scored the effects of small-molecule inhibitors on admixtures of both motors, using both a microtubule (MT)-gliding assay and an assay for cancer cell viability. We found that (i) KIF15 motility differs significantly from Eg5; (ii) KIF15-IN-1 is a potent inhibitor of KIF15 motility; (iii) MT gliding powered by KIF15 and Eg5 only ceases when both motors are inhibited; and (iv) pairing KIF15-IN-1 with Eg5 inhibitors synergistically reduces cancer cell growth. Taken together, our results lend support to the notion that a combination drug therapy employing both inhibitors may be a viable strategy for overcoming chemotherapeutic resistance.

    View details for PubMedID 29703754

  • A CRISPR-based screen for Hedgehog signaling provides insights into ciliary function and ciliopathies. Nature genetics Breslow, D. K., Hoogendoorn, S., Kopp, A. R., Morgens, D. W., Vu, B. K., Kennedy, M. C., Han, K., Li, A., Hess, G. T., Bassik, M. C., Chen, J. K., Nachury, M. V. 2018; 50 (3): 460-471

    Abstract

    Primary cilia organize Hedgehog signaling and shape embryonic development, and their dysregulation is the unifying cause of ciliopathies. We conducted a functional genomic screen for Hedgehog signaling by engineering antibiotic-based selection of Hedgehog-responsive cells and applying genome-wide CRISPR-mediated gene disruption. The screen can robustly identify factors required for ciliary signaling with few false positives or false negatives. Characterization of hit genes uncovered novel components of several ciliary structures, including a protein complex that contains δ-tubulin and ε-tubulin and is required for centriole maintenance. The screen also provides an unbiased tool for classifying ciliopathies and showed that many congenital heart disorders are caused by loss of ciliary signaling. Collectively, our study enables a systematic analysis of ciliary function and of ciliopathies, and also defines a versatile platform for dissecting signaling pathways through CRISPR-based screening.

    View details for DOI 10.1038/s41588-018-0054-7

    View details for PubMedID 29459677

    View details for PubMedCentralID PMC5862771

  • A CRISPR-based screen for Hedgehog signaling provides insights into ciliary function and ciliopathies Nat. Genet. Breslow, D. K., Hoogendoorn, S., Kopp, A. R., Morgens, D. W., Vu, B. K., Han, K., Li, A., Hess, G. T., Bassik, M. C., Chen, J. K., V, N. M. 2018; Epub ahead of print: 460–71

    Abstract

    Primary cilia organize Hedgehog signaling and shape embryonic development, and their dysregulation is the unifying cause of ciliopathies. We conducted a functional genomic screen for Hedgehog signaling by engineering antibiotic-based selection of Hedgehog-responsive cells and applying genome-wide CRISPR-mediated gene disruption. The screen can robustly identify factors required for ciliary signaling with few false positives or false negatives. Characterization of hit genes uncovered novel components of several ciliary structures, including a protein complex that contains δ-tubulin and ε-tubulin and is required for centriole maintenance. The screen also provides an unbiased tool for classifying ciliopathies and showed that many congenital heart disorders are caused by loss of ciliary signaling. Collectively, our study enables a systematic analysis of ciliary function and of ciliopathies, and also defines a versatile platform for dissecting signaling pathways through CRISPR-based screening.

    View details for DOI 10.1038/s41588-018-0054-7

    View details for PubMedCentralID PMC5862771

  • CRISPR-Cas9 screens in human cells and primary neurons identify modifiers of C9ORF72 dipeptide-repeat-protein toxicity. Nature genetics Kramer, N. J., Haney, M. S., Morgens, D. W., Jovičić, A. n., Couthouis, J. n., Li, A. n., Ousey, J. n., Ma, R. n., Bieri, G. n., Tsui, C. K., Shi, Y. n., Hertz, N. T., Tessier-Lavigne, M. n., Ichida, J. K., Bassik, M. C., Gitler, A. D. 2018

    Abstract

    Hexanucleotide-repeat expansions in the C9ORF72 gene are the most common cause of amyotrophic lateral sclerosis and frontotemporal dementia (c9ALS/FTD). The nucleotide-repeat expansions are translated into dipeptide-repeat (DPR) proteins, which are aggregation prone and may contribute to neurodegeneration. We used the CRISPR-Cas9 system to perform genome-wide gene-knockout screens for suppressors and enhancers of C9ORF72 DPR toxicity in human cells. We validated hits by performing secondary CRISPR-Cas9 screens in primary mouse neurons. We uncovered potent modifiers of DPR toxicity whose gene products function in nucleocytoplasmic transport, the endoplasmic reticulum (ER), proteasome, RNA-processing pathways, and chromatin modification. One modifier, TMX2, modulated the ER-stress signature elicited by C9ORF72 DPRs in neurons and improved survival of human induced motor neurons from patients with C9ORF72 ALS. Together, our results demonstrate the promise of CRISPR-Cas9 screens in defining mechanisms of neurodegenerative diseases.

    View details for PubMedID 29507424

  • CMTM6 maintains the expression of PD-L1 and regulates anti-tumour immunity NATURE Burr, M. L., Sparbier, C. E., Chan, Y., Williamson, J. C., Woods, K., Beavis, P. A., Lam, E. N., Henderson, M. A., Bell, C. C., Stolzenburg, S., Gilan, O., Bloor, S., Noori, T., Morgens, D. W., Bassik, M. C., Neeson, P. J., Behren, A., Darcy, P. K., Dawson, S., Voskoboinik, I., Trapani, J. A., Cebon, J., Lehner, P. J., Dawson, M. A. 2017; 549 (7670): 101–5

    Abstract

    Cancer cells exploit the expression of the programmed death-1 (PD-1) ligand 1 (PD-L1) to subvert T-cell-mediated immunosurveillance. The success of therapies that disrupt PD-L1-mediated tumour tolerance has highlighted the need to understand the molecular regulation of PD-L1 expression. Here we identify the uncharacterized protein CMTM6 as a critical regulator of PD-L1 in a broad range of cancer cells, by using a genome-wide CRISPR-Cas9 screen. CMTM6 is a ubiquitously expressed protein that binds PD-L1 and maintains its cell surface expression. CMTM6 is not required for PD-L1 maturation but co-localizes with PD-L1 at the plasma membrane and in recycling endosomes, where it prevents PD-L1 from being targeted for lysosome-mediated degradation. Using a quantitative approach to profile the entire plasma membrane proteome, we find that CMTM6 displays specificity for PD-L1. Notably, CMTM6 depletion decreases PD-L1 without compromising cell surface expression of MHC class I. CMTM6 depletion, via the reduction of PD-L1, significantly alleviates the suppression of tumour-specific T cell activity in vitro and in vivo. These findings provide insights into the biology of PD-L1 regulation, identify a previously unrecognized master regulator of this critical immune checkpoint and highlight a potential therapeutic target to overcome immune evasion by tumour cells.

    View details for PubMedID 28813417

    View details for PubMedCentralID PMC5706633

  • Genome-scale measurement of off-target activity using Cas9 toxicity in high-throughput screens NATURE COMMUNICATIONS Morgens, D. W., Wainberg, M., Boyle, E. A., Ursu, O., Araya, C. L., Tsui, C. K., Haney, M. S., Hess, G. T., Han, K., Jeng, E. E., Li, A., Snyder, M. P., Greenleaf, W. J., Kundaje, A., Bassik, M. C. 2017; 8

    Abstract

    CRISPR-Cas9 screens are powerful tools for high-throughput interrogation of genome function, but can be confounded by nuclease-induced toxicity at both on- and off-target sites, likely due to DNA damage. Here, to test potential solutions to this issue, we design and analyse a CRISPR-Cas9 library with 10 variable-length guides per gene and thousands of negative controls targeting non-functional, non-genic regions (termed safe-targeting guides), in addition to non-targeting controls. We find this library has excellent performance in identifying genes affecting growth and sensitivity to the ricin toxin. The safe-targeting guides allow for proper control of toxicity from on-target DNA damage. Using this toxicity as a proxy to measure off-target cutting, we demonstrate with tens of thousands of guides both the nucleotide position-dependent sensitivity to single mismatches and the reduction of off-target cutting using truncated guides. Our results demonstrate a simple strategy for high-throughput evaluation of target specificity and nuclease toxicity in Cas9 screens.

    View details for DOI 10.1038/ncomms15178

    View details for PubMedID 28474669

  • Population- and individual- specific regulatory variation in Sardinia NATURE GENETICS Pala, M., Zappala, Z., Marongiu, M., Li, X., Davis, J. R., Cusano, R., Crobu, F., Kukurba, K. R., Gloudemans, M. J., Reinier, F., Berutti, R., Piras, M. G., Mulas, A., Zoledziewska, M., Marongiu, M., Sorokin, E. P., Hess, G. T., Smith, K. S., Busonero, F., Maschio, A., Steri, M., Sidore, C., Sanna, S., Fiorillo, E., Bassik, M. C., Sawcer, S. J., Battle, A., Novembre, J., Jones, C., Angius, A., Abecasis, G. R., Schlessinger, D., Cucca, F., Montgomery, S. B. 2017; 49 (5): 700-?

    Abstract

    Genetic studies of complex traits have mainly identified associations with noncoding variants. To further determine the contribution of regulatory variation, we combined whole-genome and transcriptome data for 624 individuals from Sardinia to identify common and rare variants that influence gene expression and splicing. We identified 21,183 expression quantitative trait loci (eQTLs) and 6,768 splicing quantitative trait loci (sQTLs), including 619 new QTLs. We identified high-frequency QTLs and found evidence of selection near genes involved in malarial resistance and increased multiple sclerosis risk, reflecting the epidemiological history of Sardinia. Using family relationships, we identified 809 segregating expression outliers (median z score of 2.97), averaging 13.3 genes per individual. Outlier genes were enriched for proximal rare variants, providing a new approach to study large-effect regulatory variants and their relevance to traits. Our results provide insight into the effects of regulatory variants and their relationship to population history and individual genetic risk.

    View details for DOI 10.1038/ng.3840

    View details for Web of Science ID 000400051400010

    View details for PubMedID 28394350

  • Synergistic drug combinations for cancer identified in a CRISPR screen for pairwise genetic interactions NATURE BIOTECHNOLOGY Han, K., Jeng, E. E., Hess, G. T., Morgens, D. W., Li, A., Bassik, M. C. 2017; 35 (5): 463-?

    Abstract

    Identification of effective combination therapies is critical to address the emergence of drug-resistant cancers, but direct screening of all possible drug combinations is infeasible. Here we introduce a CRISPR-based double knockout (CDKO) system that improves the efficiency of combinatorial genetic screening using an effective strategy for cloning and sequencing paired single guide RNA (sgRNA) libraries and a robust statistical scoring method for calculating genetic interactions (GIs) from CRISPR-deleted gene pairs. We applied CDKO to generate a large-scale human GI map, comprising 490,000 double-sgRNAs directed against 21,321 pairs of drug targets in K562 leukemia cells and identified synthetic lethal drug target pairs for which corresponding drugs exhibit synergistic killing. These included the BCL2L1 and MCL1 combination, which was also effective in imatinib-resistant cells. We further validated this system by identifying known and previously unidentified GIs between modifiers of ricin toxicity. This work provides an effective strategy to screen synergistic drug combinations in high-throughput and a CRISPR-based tool to dissect functional GI networks.

    View details for DOI 10.1038/nbt.3834

    View details for Web of Science ID 000400809800021

    View details for PubMedID 28319085

  • Human pyrimidine nucleotide biosynthesis as a target for antiviral chemotherapy. Current opinion in biotechnology Okesli, A., Khosla, C., Bassik, M. C. 2017; 48: 127-134

    Abstract

    The development of broad-spectrum, host-acting antiviral therapies remains an important but elusive goal in anti-infective drug discovery. To replicate efficiently, viruses not only depend on their hosts for an adequate supply of pyrimidine nucleotides, but also up-regulate pyrimidine nucleotide biosynthesis in infected cells. In this review, we outline our understanding of mammalian de novo and salvage metabolic pathways for pyrimidine nucleotide biosynthesis. The available spectrum of experimental and FDA-approved drugs that modulate individual steps in these metabolic pathways is also summarized. The logic of a host-acting combination antiviral therapy comprised of inhibitors of dihydroorotate dehydrogenase and uridine/cytidine kinase is discussed.

    View details for DOI 10.1016/j.copbio.2017.03.010

    View details for PubMedID 28458037

  • Methods and Applications of CRISPR-Mediated Base Editing in Eukaryotic Genomes. Molecular cell Hess, G. T., Tycko, J. n., Yao, D. n., Bassik, M. C. 2017; 68 (1): 26–43

    Abstract

    The past several years have seen an explosion in development of applications for the CRISPR-Cas9 system, from efficient genome editing, to high-throughput screening, to recruitment of a range of DNA and chromatin-modifying enzymes. While homology-directed repair (HDR) coupled with Cas9 nuclease cleavage has been used with great success to repair and re-write genomes, recently developed base-editing systems present a useful orthogonal strategy to engineer nucleotide substitutions. Base editing relies on recruitment of cytidine deaminases to introduce changes (rather than double-stranded breaks and donor templates) and offers potential improvements in efficiency while limiting damage and simplifying the delivery of editing machinery. At the same time, these systems enable novel mutagenesis strategies to introduce sequence diversity for engineering and discovery. Here, we review the different base-editing platforms, including their deaminase recruitment strategies and editing outcomes, and compare them to other CRISPR genome-editing technologies. Additionally, we discuss how these systems have been applied in therapeutic, engineering, and research settings. Lastly, we explore future directions of this emerging technology.

    View details for PubMedID 28985508

  • Static and Dynamic DNA Loops form AP-1-Bound Activation Hubs during Macrophage Development. Molecular cell Phanstiel, D. H., Van Bortle, K. n., Spacek, D. n., Hess, G. T., Shamim, M. S., Machol, I. n., Love, M. I., Aiden, E. L., Bassik, M. C., Snyder, M. P. 2017; 67 (6): 1037–48.e6

    Abstract

    The three-dimensional arrangement of the human genome comprises a complex network of structural and regulatory chromatin loops important for coordinating changes in transcription during human development. To better understand the mechanisms underlying context-specific 3D chromatin structure and transcription during cellular differentiation, we generated comprehensive in situ Hi-C maps of DNA loops in human monocytes and differentiated macrophages. We demonstrate that dynamic looping events are regulatory rather than structural in nature and uncover widespread coordination of dynamic enhancer activity at preformed and acquired DNA loops. Enhancer-bound loop formation and enhancer activation of preformed loops together form multi-loop activation hubs at key macrophage genes. Activation hubs connect 3.4 enhancers per promoter and exhibit a strong enrichment for activator protein 1 (AP-1)-binding events, suggesting that multi-loop activation hubs involving cell-type-specific transcription factors represent an important class of regulatory chromatin structures for the spatiotemporal control of transcription.

    View details for PubMedID 28890333

  • Finding host targets for HIV therapy. Nature genetics Tsui, C. K., Gupta, A. n., Bassik, M. C. 2017; 49 (2): 175–76

    Abstract

    A CRISPR screen conducted in a CD4+ T cell leukemia line has identified host factors required for HIV infection but dispensable for cellular survival. The results highlight sulfation on the HIV co-receptor CCR5 and cellular aggregation as potential targets for therapeutic intervention.

    View details for PubMedID 28138150

  • The impact of rare variation on gene expression across tissues. Nature Li, X. n., Kim, Y. n., Tsang, E. K., Davis, J. R., Damani, F. N., Chiang, C. n., Hess, G. T., Zappala, Z. n., Strober, B. J., Scott, A. J., Li, A. n., Ganna, A. n., Bassik, M. C., Merker, J. D., Hall, I. M., Battle, A. n., Montgomery, S. B. 2017; 550 (7675): 239–43

    Abstract

    Rare genetic variants are abundant in humans and are expected to contribute to individual disease risk. While genetic association studies have successfully identified common genetic variants associated with susceptibility, these studies are not practical for identifying rare variants. Efforts to distinguish pathogenic variants from benign rare variants have leveraged the genetic code to identify deleterious protein-coding alleles, but no analogous code exists for non-coding variants. Therefore, ascertaining which rare variants have phenotypic effects remains a major challenge. Rare non-coding variants have been associated with extreme gene expression in studies using single tissues, but their effects across tissues are unknown. Here we identify gene expression outliers, or individuals showing extreme expression levels for a particular gene, across 44 human tissues by using combined analyses of whole genomes and multi-tissue RNA-sequencing data from the Genotype-Tissue Expression (GTEx) project v6p release. We find that 58% of underexpression and 28% of overexpression outliers have nearby conserved rare variants compared to 8% of non-outliers. Additionally, we developed RIVER (RNA-informed variant effect on regulation), a Bayesian statistical model that incorporates expression data to predict a regulatory effect for rare variants with higher accuracy than models using genomic annotations alone. Overall, we demonstrate that rare variants contribute to large gene expression changes across tissues and provide an integrative method for interpretation of rare variants in individual genomes.

    View details for PubMedID 29022581

  • Selective silencing of euchromatic L1s revealed by genome-wide screens for L1 regulators. Nature Liu, N. n., Lee, C. H., Swigut, T. n., Grow, E. n., Gu, B. n., Bassik, M. n., Wysocka, J. n. 2017

    Abstract

    Transposable elements (TEs) are now recognized not only as parasitic DNA, whose spread in the genome must be controlled by the host, but also as major players in genome evolution and regulation1-6. Long INterspersed Element-1 (LINE-1 or L1), the only currently autonomous mobile transposon in humans, occupies 17% of the genome and continues to generate inter- and intra-individual genetic variation, in some cases resulting in disease1-7. Nonetheless, how L1 activity is controlled and what function L1s play in host gene regulation remain incompletely understood. Here, we use CRISPR/Cas9 screening strategies in two distinct human cell lines to provide the first genome-wide survey of genes involved in L1 retrotransposition control. We identified functionally diverse genes that either promote or restrict L1 retrotransposition. These genes, often associated with human diseases, control the L1 lifecycle at transcriptional or post-transcriptional levels and in a manner that can depend on the endogenous L1 sequence, underscoring the complexity of L1 regulation. We further investigated L1 restriction by MORC2 and human silencing hub (HUSH) complex subunits MPP8 and TASOR8. HUSH/MORC2 selectively bind evolutionarily young, full-length L1s located within transcriptionally permissive euchromatic environment, and promote H3K9me3 deposition for transcriptional silencing. Interestingly, these silencing events often occur within introns of transcriptionally active genes and lead to down-regulation of host gene expression in a HUSH/MORC2-dependent manner. Together, we provide a rich resource for studies of L1 retrotransposition, elucidate a novel L1 restriction pathway, and illustrate how epigenetic silencing of TEs rewires host gene expression programs.

    View details for PubMedID 29211708

  • The mTOR Complex Controls HIV Latency CELL HOST & MICROBE Besnard, E., Hakre, S., Kampmann, M., Lim, H. W., Hosmane, N. N., Martin, A., Bassik, M. C., Verschueren, E., Battivelli, E., Chan, J., Svensson, J. P., Gramatica, A., Conrad, R. J., Ott, M., Greene, W. C., Krogan, N. J., Siliciano, R. F., Weissman, J. S., Verdin, E. 2016; 20 (6): 785-797

    Abstract

    A population of CD4 T lymphocytes harboring latent HIV genomes can persist in patients on antiretroviral therapy, posing a barrier to HIV eradication. To examine cellular complexes controlling HIV latency, we conducted a genome-wide screen with a pooled ultracomplex shRNA library and in vitro system modeling HIV latency and identified the mTOR complex as a modulator of HIV latency. Knockdown of mTOR complex subunits or pharmacological inhibition of mTOR activity suppresses reversal of latency in various HIV-1 latency models and HIV-infected patient cells. mTOR inhibitors suppress HIV transcription both through the viral transactivator Tat and via Tat-independent mechanisms. This inhibition occurs at least in part via blocking the phosphorylation of CDK9, a p-TEFb complex member that serves as a cofactor for Tat-mediated transcription. The control of HIV latency by mTOR signaling identifies a pathway that may have significant therapeutic opportunities.

    View details for DOI 10.1016/j.chom.2016.11.001

    View details for Web of Science ID 000392843500014

    View details for PubMedID 27978436

    View details for PubMedCentralID PMC5354304

  • Directed evolution using dCas9-targeted somatic hypermutation in mammalian cells. Nature methods Hess, G. T., Frésard, L., Han, K., Lee, C. H., Li, A., Cimprich, K. A., Montgomery, S. B., Bassik, M. C. 2016

    Abstract

    Engineering and study of protein function by directed evolution has been limited by the technical requirement to use global mutagenesis or introduce DNA libraries. Here, we develop CRISPR-X, a strategy to repurpose the somatic hypermutation machinery for protein engineering in situ. Using catalytically inactive dCas9 to recruit variants of cytidine deaminase (AID) with MS2-modified sgRNAs, we can specifically mutagenize endogenous targets with limited off-target damage. This generates diverse libraries of localized point mutations and can target multiple genomic locations simultaneously. We mutagenize GFP and select for spectrum-shifted variants, including EGFP. Additionally, we mutate the target of the cancer therapeutic bortezomib, PSMB5, and identify known and novel mutations that confer bortezomib resistance. Finally, using a hyperactive AID variant, we mutagenize loci both upstream and downstream of transcriptional start sites. These experiments illustrate a powerful approach to create complex libraries of genetic variants in native context, which is broadly applicable to investigate and improve protein function.

    View details for DOI 10.1038/nmeth.4038

    View details for PubMedID 27798611

  • E2A-PBX1 remodels oncogenic signaling networks in B-cell precursor acute lymphoid leukemia. Cancer research Duque-Afonso, J., Lin, C., Han, K., Wei, M. C., Feng, J., Kurzer, J., Schneidawind, C., Wong, S. H., Bassik, M. C., Cleary, M. L. 2016

    Abstract

    There is limited understanding of how signaling pathways are altered by oncogenic fusion transcription factors that drive leukemogenesis. To address this, we interrogated activated signaling pathways in a comparative analysis of mouse and human leukemias expressing the fusion protein E2A-PBX1, which is present in 5%-7% of pediatric and 50% of pre-B-cell receptor (preBCR(+)) acute lymphocytic leukemia (ALL). In this study, we describe remodeling of signaling networks by E2A-PBX1 in pre-B-ALL, which results in hyperactivation of the key oncogenic effector enzyme PLCγ2. Depletion of PLCγ2 reduced proliferation of mouse and human ALLs, including E2A-PBX1 leukemias, and increased disease-free survival after secondary transplantation. Mechanistically, E2A-PBX1 bound promoter regulatory regions and activated the transcription of its key target genes ZAP70, SYK, and LCK, which encode kinases upstream of PLCγ2. Depletion of the respective upstream kinases decreased cell proliferation and phosphorylated levels of PLCγ2 (pPLCγ2). Pairwise silencing of ZAP70, SYK, or LCK showed additive effects on cell growth inhibition, providing a rationale for combination therapy with inhibitors of these kinases. Accordingly, inhibitors such as the SRC family kinase (SFK) inhibitor dasatinib reduced pPLCγ2 and inhibited proliferation of human and mouse preBCR(+)/E2A-PBX1(+) leukemias in vitro and in vivo Furthermore, combining small-molecule inhibition of SYK, LCK, and SFK showed synergistic interactions and preclinical efficacy in the same setting. Our results show how the oncogenic fusion protein E2A-PBX1 perturbs signaling pathways upstream of PLCγ2 and renders leukemias amenable to targeted therapeutic inhibition. Cancer Res; 76(23); 6937-49. ©2016 AACR.

    View details for PubMedID 27758892

  • Bithionol blocks pathogenicity of bacterial toxins, ricin, and Zika virus SCIENTIFIC REPORTS Leonardi, W., Zilbermintz, L., Cheng, L. W., Zozaya, J., Tran, S. H., Elliott, J. H., Polukhina, K., Manasherob, R., Li, A., Chi, X., Gharaibeh, D., Kenny, T., Zamani, R., Soloveva, V., Haddow, A. D., Nasar, F., Bavari, S., Bassik, M. C., Cohen, S. N., Levitin, A., Martchenko, M. 2016; 6

    Abstract

    Diverse pathogenic agents often utilize overlapping host networks, and hub proteins within these networks represent attractive targets for broad-spectrum drugs. Using bacterial toxins, we describe a new approach for discovering broad-spectrum therapies capable of inhibiting host proteins that mediate multiple pathogenic pathways. This approach can be widely used, as it combines genetic-based target identification with cell survival-based and protein function-based multiplex drug screens, and concurrently discovers therapeutic compounds and their protein targets. Using B-lymphoblastoid cells derived from the HapMap Project cohort of persons of African, European, and Asian ancestry we identified host caspases as hub proteins that mediate the lethality of multiple pathogenic agents. We discovered that an approved drug, Bithionol, inhibits host caspases and also reduces the detrimental effects of anthrax lethal toxin, diphtheria toxin, cholera toxin, Pseudomonas aeruginosa exotoxin A, Botulinum neurotoxin, ricin, and Zika virus. Our study reveals the practicality of identifying host proteins that mediate multiple disease pathways and discovering broad-spectrum therapies that target these hub proteins.

    View details for DOI 10.1038/srep34475

    View details for Web of Science ID 000384291100001

    View details for PubMedID 27686742

    View details for PubMedCentralID PMC5043268

  • Translation readthrough mitigation NATURE Arribere, J. A., Cenik, E. S., Jain, N., Hess, G. T., Lee, C. H., Bassik, M. C., Fire, A. Z. 2016; 534 (7609): 719-?

    Abstract

    A fraction of ribosomes engaged in translation will fail to terminate when reaching a stop codon, yielding nascent proteins inappropriately extended on their C termini. Although such extended proteins can interfere with normal cellular processes, known mechanisms of translational surveillance are insufficient to protect cells from potential dominant consequences. Here, through a combination of transgenics and CRISPR–Cas9 gene editing in Caenorhabditis elegans, we demonstrate a consistent ability of cells to block accumulation of C-terminal-extended proteins that result from failure to terminate at stop codons. Sequences encoded by the 3′ untranslated region (UTR) were sufficient to lower protein levels. Measurements of mRNA levels and translation suggested a co- or post-translational mechanism of action for these sequences in C. elegans. Similar mechanisms evidently operate in human cells, in which we observed a comparable tendency for translated human 3′ UTR sequences to reduce mature protein expression in tissue culture assays, including 3′ UTR sequences from the hypomorphic ‘Constant Spring’ haemoglobin stop codon variant. We suggest that 3′ UTRs may encode peptide sequences that destabilize the attached protein, providing mitigation of unwelcome and varied translation errors.

    View details for DOI 10.1038/nature18308

    View details for Web of Science ID 000378676000044

    View details for PubMedID 27281202

    View details for PubMedCentralID PMC5054982

  • Systematic comparison of CRISPR/Cas9 and RNAi screens for essential genes NATURE BIOTECHNOLOGY Morgens, D. W., Deans, R. M., Li, A., Bassik, M. C. 2016; 34 (6): 634-636

    Abstract

    We compared the ability of short hairpin RNA (shRNA) and CRISPR/Cas9 screens to identify essential genes in the human chronic myelogenous leukemia cell line K562. We found that the precision of the two libraries in detecting essential genes was similar and that combining data from both screens improved performance. Notably, results from the two screens showed little correlation, which can be partially explained by the identification of distinct essential biological processes with each technology.

    View details for DOI 10.1038/nbt.3567

    View details for Web of Science ID 000377846400030

    View details for PubMedID 27159373

    View details for PubMedCentralID PMC4900911

  • Parallel shRNA and CRISPR-Cas9 screens enable antiviral drug target identification NATURE CHEMICAL BIOLOGY Deans, R. M., Morgens, D. W., Okesli, A., Pillay, S., Horlbeck, M. A., Kampmann, M., Gilbert, L. A., Li, A., Mateo, R., Smith, M., Glenn, J. S., Carette, J. E., Khosla, C., Bassik, M. C. 2016; 12 (5): 361-?

    Abstract

    Broad-spectrum antiviral drugs targeting host processes could potentially treat a wide range of viruses while reducing the likelihood of emergent resistance. Despite great promise as therapeutics, such drugs remain largely elusive. Here we used parallel genome-wide high-coverage short hairpin RNA (shRNA) and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 screens to identify the cellular target and mechanism of action of GSK983, a potent broad-spectrum antiviral with unexplained cytotoxicity. We found that GSK983 blocked cell proliferation and dengue virus replication by inhibiting the pyrimidine biosynthesis enzyme dihydroorotate dehydrogenase (DHODH). Guided by mechanistic insights from both genomic screens, we found that exogenous deoxycytidine markedly reduced GSK983 cytotoxicity but not antiviral activity, providing an attractive new approach to improve the therapeutic window of DHODH inhibitors against RNA viruses. Our results highlight the distinct advantages and limitations of each screening method for identifying drug targets, and demonstrate the utility of parallel knockdown and knockout screens for comprehensive probing of drug activity.

    View details for DOI 10.1038/NCHEMBIO.2050

    View details for PubMedID 27018887

  • Weak base pairing in both seed and 3' regions reduces RNAi off-targets and enhances si/shRNA designs. Nucleic acids research Gu, S., Zhang, Y., Jin, L., Huang, Y., Zhang, F., Bassik, M. C., Kampmann, M., Kay, M. A. 2014; 42 (19): 12169-12176

    Abstract

    The use of RNA interference is becoming routine in scientific discovery and treatment of human disease. However, its applications are hampered by unwanted effects, particularly off-targeting through miRNA-like pathways. Recent studies suggest that the efficacy of such off-targeting might be dependent on binding stability. Here, by testing shRNAs and siRNAs of various GC content in different guide strand segments with reporter assays, we establish that weak base pairing in both seed and 3' regions is required to achieve minimal off-targeting while maintaining the intended on-target activity. The reduced off-targeting was confirmed by RNA-Seq analyses from mouse liver RNAs expressing various anti-HCV shRNAs. Finally, our protocol was validated on a large scale by analyzing results of a genome-wide shRNA screen. Compared with previously established work, the new algorithm was more effective in reducing off-targeting without jeopardizing on-target potency. These studies provide new rules that should significantly improve on siRNA/shRNA design.

    View details for DOI 10.1093/nar/gku854

    View details for PubMedID 25270879

    View details for PubMedCentralID PMC4231738

  • Functional genomics platform for pooled screening and generation of mammalian genetic interaction maps NATURE PROTOCOLS Kampmann, M., Bassik, M. C., Weissman, J. S. 2014; 9 (8): 1825-1847

    Abstract

    Systematic genetic interaction maps in microorganisms are powerful tools for identifying functional relationships between genes and for defining the function of uncharacterized genes. We have recently implemented this strategy in mammalian cells as a two-stage approach. First, genes of interest are robustly identified in a pooled genome-wide screen using complex shRNA libraries. Second, phenotypes for all pairwise combinations of 'hit' genes are measured in a double-shRNA screen and used to construct a genetic interaction map. Our protocol allows for rapid pooled screening under various conditions without a requirement for robotics, in contrast to arrayed approaches. Each round of screening can be implemented in ∼2 weeks, with additional time for analysis and generation of reagents. We discuss considerations for screen design, and we present complete experimental procedures, as well as a full computational analysis suite for the identification of hits in pooled screens and generation of genetic interaction maps. Although the protocol outlined here was developed for our original shRNA-based approach, it can be applied more generally, including to CRISPR-based approaches.

    View details for DOI 10.1038/nprot.2014.103

    View details for Web of Science ID 000340039700004

    View details for PubMedID 24992097

    View details for PubMedCentralID PMC4144868

  • Next-Generation NAMPT Inhibitors Identified by Sequential High-Throughput Phenotypic Chemical and Functional Genomic Screens. Chemistry & biology Matheny, C. J., Wei, M. C., Bassik, M. C., Donnelly, A. J., Kampmann, M., Iwasaki, M., Piloto, O., Solow-Cordero, D. E., Bouley, D. M., Rau, R., Brown, P., McManus, M. T., Weissman, J. S., Cleary, M. L. 2013; 20 (11): 1352-1363

    Abstract

    Phenotypic high-throughput chemical screens allow for discovery of small molecules that modulate complex phenotypes and provide lead compounds for novel therapies; however, identification of the mechanistically relevant targets remains a major experimental challenge. We report the application of sequential unbiased high-throughput chemical and ultracomplex small hairpin RNA (shRNA) screens to identify a distinctive class of inhibitors that target nicotinamide phosphoribosyl transferase (NAMPT), a rate-limiting enzyme in the biosynthesis of nicotinamide adenine dinucleotide, a crucial cofactor in many biochemical processes. The lead compound STF-118804 is a highly specific NAMPT inhibitor, improves survival in an orthotopic xenotransplant model of high-risk acute lymphoblastic leukemia, and targets leukemia stem cells. Tandem high-throughput screening using chemical and ultracomplex shRNA libraries, therefore, provides a rapid chemical genetics approach for seamless progression from small-molecule lead identification to target discovery and validation.

    View details for DOI 10.1016/j.chembiol.2013.09.014

    View details for PubMedID 24183972

  • A systematic mammalian genetic interaction map reveals pathways underlying ricin susceptibility. Cell Bassik, M. C., Kampmann, M., Lebbink, R. J., Wang, S., Hein, M. Y., Poser, I., Weibezahn, J., Horlbeck, M. A., Chen, S., Mann, M., Hyman, A. A., Leproust, E. M., McManus, M. T., Weissman, J. S. 2013; 152 (4): 909-22

    Abstract

    Genetic interaction (GI) maps, comprising pairwise measures of how strongly the function of one gene depends on the presence of a second, have enabled the systematic exploration of gene function in microorganisms. Here, we present a two-stage strategy to construct high-density GI maps in mammalian cells. First, we use ultracomplex pooled shRNA libraries (25 shRNAs/gene) to identify high-confidence hit genes for a given phenotype and effective shRNAs. We then construct double-shRNA libraries from these to systematically measure GIs between hits. A GI map focused on ricin susceptibility broadly recapitulates known pathways and provides many unexpected insights. These include a noncanonical role for COPI, a previously uncharacterized protein complex affecting toxin clearance, a specialized role for the ribosomal protein RPS25, and functionally distinct mammalian TRAPP complexes. The ability to rapidly generate mammalian GI maps provides a potentially transformative tool for defining gene function and designing combination therapies based on synergistic pairs.

    View details for DOI 10.1016/j.cell.2013.01.030

    View details for PubMedID 23394947

    View details for PubMedCentralID PMC3652613

  • Rapid creation and quantitative monitoring of high coverage shRNA libraries. Nature methods Bassik, M. C., Lebbink, R. J., Churchman, L. S., Ingolia, N. T., Patena, W., LeProust, E. M., Schuldiner, M., Weissman, J. S., McManus, M. T. 2009; 6 (6): 443-5

    Abstract

    Short hairpin RNA libraries are limited by low efficacy of many shRNAs and by off-target effects, which give rise to false negatives and false positives, respectively. Here we present a strategy for rapidly creating expanded shRNA pools (approximately 30 shRNAs per gene) that are analyzed by deep sequencing (EXPAND). This approach enables identification of multiple effective target-specific shRNAs from a complex pool, allowing a rigorous statistical evaluation of true hits.

    View details for DOI 10.1038/nmeth.1330

    View details for PubMedID 19448642

    View details for PubMedCentralID PMC2783737