BS, Stanford University, Biological Sciences (2008)
MPhil, University of Cambridge, Computational Biology (2010)
PhD, University of Washington, Molecular and Cellular Biology (2017)
MD, University of Washington (2019)
Howard Chang, Postdoctoral Research Mentor
Suppression of unwanted CRISPR-Cas9 editing by co-administration of catalytically inactivating truncated guide RNAs.
2020; 11 (1): 2697
CRISPR-Cas9 nucleases are powerful genome engineering tools, but unwanted cleavage at off-target and previously edited sites remains a major concern. Numerous strategies to reduce unwanted cleavage have been devised, but all are imperfect. Here, we report thatoff-target sites can be shielded from the active Cas9single guide RNA (sgRNA) complex through the co-administration of dead-RNAs (dRNAs), truncated guide RNAs that direct Cas9 binding but not cleavage. dRNAs can effectively suppress a wide-range of off-targets with minimal optimization while preserving on-target editing, and they can be multiplexed to suppress several off-targets simultaneously. dRNAs can be combined with high-specificity Cas9 variants, which often do not eliminate all unwanted editing. Moreover, dRNAs can prevent cleavage of homology-directed repair (HDR)-corrected sites, facilitating scarless editing by eliminating the need for blocking mutations. Thus, we enable precise genome editing by establishing a flexible approach for suppressing unwanted editing of both off-targets and HDR-corrected sites.
View details for DOI 10.1038/s41467-020-16542-9
View details for PubMedID 32483117
Rapidly inducible Cas9 and DSB-ddPCR to probe editing kinetics
2017; 14 (9): 891-+
We developed a chemically inducible Cas9 (ciCas9) and a droplet digital PCR assay for double-strand breaks (DSB-ddPCR) to investigate the kinetics of Cas9-mediated generation and repair of DSBs in cells. ciCas9 is a rapidly activated, single-component Cas9 variant engineered by replacing the protein's REC2 domain with the BCL-xL protein and fusing an interacting BH3 peptide to the C terminus. ciCas9 can be tunably activated by a compound that disrupts the BCL-xL-BH3 interaction within minutes. DSB-ddPCR demonstrates time-resolved, highly quantitative, and targeted measurement of DSBs. Combining these tools facilitated an unprecedented exploration of the kinetics of Cas9-mediated DNA cleavage and repair. We find that sgRNAs targeting different sites generally induce cleavage within minutes and repair within 1 or 2 h. However, we observe distinct kinetic profiles, even for proximal sites, and this suggests that target sequence and chromatin state modulate cleavage and repair kinetics.
View details for DOI 10.1038/NMETH.4368
View details for Web of Science ID 000408776400018
View details for PubMedID 28737741
View details for PubMedCentralID PMC5730411
A computationally engineered RAS rheostat reveals RAS-ERK signaling dynamics
NATURE CHEMICAL BIOLOGY
2017; 13 (1): 119-126
Synthetic protein switches controlled with user-defined inputs are powerful tools for studying and controlling dynamic cellular processes. To date, these approaches have relied primarily on intermolecular regulation. Here we report a computationally guided framework for engineering intramolecular regulation of protein function. We utilize this framework to develop chemically inducible activator of RAS (CIAR), a single-component RAS rheostat that directly activates endogenous RAS in response to a small molecule. Using CIAR, we show that direct RAS activation elicits markedly different RAS-ERK signaling dynamics from growth factor stimulation, and that these dynamics differ among cell types. We also found that the clinically approved RAF inhibitor vemurafenib potently primes cells to respond to direct wild-type RAS activation. These results demonstrate the utility of CIAR for quantitatively interrogating RAS signaling. Finally, we demonstrate the general utility of our approach in design of intramolecularly regulated protein tools by applying it to the Rho family of guanine nucleotide exchange factors.
View details for DOI 10.1038/NGHEMBIO.2244
View details for Web of Science ID 000393267200022
View details for PubMedID 27870838
View details for PubMedCentralID PMC5161653
ecDNA hubs drive cooperative intermolecular oncogene expression.
Extrachromosomal DNA (ecDNA) is prevalent in human cancers and mediates high expression of oncogenes through gene amplification and altered gene regulation1. Gene induction typically involves cis-regulatory elements that contact and activate genes on the same chromosome2,3. Here we show that ecDNA hubs-clusters of around 10-100 ecDNAs within the nucleus-enable intermolecular enhancer-gene interactions to promote oncogene overexpression. ecDNAs that encode multiple distinct oncogenes form hubs in diverse cancer cell types and primary tumours. Each ecDNA is more likely to transcribe the oncogene when spatially clustered with additional ecDNAs. ecDNA hubs are tethered by the bromodomain and extraterminal domain (BET) protein BRD4 in a MYC-amplified colorectal cancer cell line. The BET inhibitor JQ1 disperses ecDNA hubs and preferentially inhibits ecDNA-derived-oncogene transcription. The BRD4-bound PVT1 promoter is ectopically fused to MYC and duplicated in ecDNA, receiving promiscuous enhancer input to drive potent expression of MYC. Furthermore, the PVT1 promoter on an exogenous episome suffices to mediate gene activation in trans by ecDNA hubs in a JQ1-sensitive manner. Systematic silencing of ecDNA enhancers by CRISPR interference reveals intermolecular enhancer-gene activation among multiple oncogene loci that are amplified on distinct ecDNAs. Thus, protein-tethered ecDNA hubs enable intermolecular transcriptional regulation and may serve as units of oncogene function and cooperative evolution and as potential targets for cancer therapy.
View details for DOI 10.1038/s41586-021-04116-8
View details for PubMedID 34819668
DIFFERENTIAL LOCALIZATION OF AN ENGINEERED RAS RHEOSTAT REVEALS UNIQUE RAS-ERK SIGNALING DYNAMICS
WILEY. 2019: 158–59
View details for Web of Science ID 000488134600288
A Chemically Disrupted Proximity System for Controlling Dynamic Cellular Processes
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2019; 141 (8): 3352–55
Chemical methods that allow the spatial proximity of proteins to be temporally modulated are powerful tools for studying biology and engineering synthetic cellular behaviors. Here, we describe a new chemically controlled method for rapidly disrupting the interaction between two basally colocalized protein binding partners. Our chemically disrupted proximity (CDP) system is based on the interaction between the hepatitis C virus protease (HCVp) NS3a and a genetically encoded peptide inhibitor. Using clinically approved antiviral inhibitors as chemical disrupters of the NS3a/peptide interaction, we demonstrate that our CDP system can be used to confer temporal control over diverse intracellular processes. This NS3a-based CDP system represents a new modality for engineering chemical control over intracellular protein function that is complementary to currently available techniques.
View details for DOI 10.1021/jacs.8b12382
View details for Web of Science ID 000460200100004
View details for PubMedID 30735038
View details for PubMedCentralID PMC6492022
"Examining RAS pathway rewiring with a chemically inducible activator of RAS".
RAS signaling pathways govern diverse cellular processes, are dynamic, and exhibit marked plasticity. Yet, these features also present a considerable obstacle to their study. Here, we report the use of a recently described RAS rheostat, Chemically Inducible Activator of RAS (CIAR), to study two poorly understood phenomena in RAS biology. First, we show that short-term activation of wild type endogenous RAS can desensitize cells to EGF stimulation. Second, we examine the phenomena of paradoxical activation of RAS/ERK signaling by RAF inhibitors. Specifically, we characterize the effects on RAS/ERK signaling kinetics of four RAF inhibitors, which stabilize distinct ATP-binding site conformations. These results demonstrate the utility of CIAR in conducting quantitative studies of complex features of RAS biology.
View details for DOI 10.1080/21541248.2018.1446697
View details for PubMedID 29634387
PAZOPANIB-INDUCED RHABDOMYOLYSIS IN THE SETTING OF HYPOTHYROIDISM
SPRINGER. 2018: S585
View details for Web of Science ID 000442641403099
Rheostatic Control of Cas9-Mediated DNA Double Strand Break (DSB) Generation and Genome Editing
ACS CHEMICAL BIOLOGY
2018; 13 (2): 438–42
We recently reported two novel tools for precisely controlling and quantifying Cas9 activity: a chemically inducible Cas9 variant (ciCas9) that can be rapidly activated by small molecules and a ddPCR assay for time-resolved measurement of DNA double strand breaks (DSB-ddPCR). Here, we further demonstrate the potential of ciCas9 to function as a tunable rheostat for Cas9 function. We show that a new highly potent and selective small molecule activator paired with a more tightly regulated ciCas9 variant expands the range of accessible Cas9 activity levels. We subsequently demonstrate that ciCas9 activity levels can be dose-dependently tuned with a small molecule activator, facilitating rheostatic time-course experiments. These studies provide the first insight into how Cas9-mediated DSB levels correlate with overall editing efficiency. Thus, we demonstrate that ciCas9 and our DSB-ddPCR assay permit the time-resolved study of Cas9 DSB generation and genome editing kinetics at a wide range of Cas9 activity levels.
View details for DOI 10.1021/acschembio.7b00652
View details for Web of Science ID 000426012800020
View details for PubMedID 28895730
View details for PubMedCentralID PMC5821106
Principles of Systems Biology, No. 14
2017; 4 (2): 140–43
This month: sage advice from phage to their offspring; systematic analyses of protein quality control, mitochondrial respiration, and woody biomass; a continental-scale experiment; and engineered protein tools galore.
View details for Web of Science ID 000395786100002
View details for PubMedID 28231445
Mechanisms of resistance to cabazitaxel.
Molecular cancer therapeutics
2015; 14 (1): 193-201
We studied mechanisms of resistance to the novel taxane cabazitaxel in established cellular models of taxane resistance. We also developed cabazitaxel-resistant variants from MCF-7 breast cancer cells by stepwise selection in drug alone (MCF-7/CTAX) or drug plus the transport inhibitor PSC-833 (MCF-7/CTAX-P). Among multidrug-resistant (MDR) variants, cabazitaxel was relatively less cross-resistant than paclitaxel and docetaxel (15- vs. 200-fold in MES-SA/Dx5 and 9- vs. 60-fold in MCF-7/TxT50, respectively). MCF-7/TxTP50 cells that were negative for MDR but had 9-fold resistance to paclitaxel were also 9-fold resistant to cabazitaxel. Selection with cabazitaxel alone (MCF-7/CTAX) yielded 33-fold resistance to cabazitaxel, 52-fold resistance to paclitaxel, activation of ABCB1, and 3-fold residual resistance to cabazitaxel with MDR inhibition. The MCF-7/CTAX-P variant did not express ABCB1, nor did it efflux rhodamine-123, BODIPY-labeled paclitaxel, and [(3)H]-docetaxel. These cells are hypersensitive to depolymerizing agents (vinca alkaloids and colchicine), have reduced baseline levels of stabilized microtubules, and impaired tubulin polymerization in response to taxanes (cabazitaxel or docetaxel) relative to MCF-7 parental cells. Class III β-tubulin (TUBB3) RNA and protein were elevated in both MCF-7/CTAX and MCF-7/CTAX-P. Decreased BRCA1 and altered epithelial-mesenchymal transition (EMT) markers are also associated with cabazitaxel resistance in these MCF-7 variants, and may serve as predictive biomarkers for its activity in the clinical setting. In summary, cabazitaxel resistance mechanisms include MDR (although at a lower level than paclitaxel and docetaxel), and alterations in microtubule dynamicity, as manifested by higher expression of TUBB3, decreased BRCA1, and by the induction of EMT. Mol Cancer Ther; 14(1); 193-201. ©2014 AACR.
View details for DOI 10.1158/1535-7163.MCT-14-0155
View details for PubMedID 25416788
HTSanalyzeR: an R/Bioconductor package for integrated network analysis of high-throughput screens
2011; 27 (6): 879–80
High-throughput screens (HTS) by RNAi or small molecules are among the most promising tools in functional genomics. They enable researchers to observe detailed reactions to experimental perturbations on a genome-wide scale. While there is a core set of computational approaches used in many publications to analyze these data, a specialized software combining them and making them easily accessible has so far been missing.Here we describe HTSanalyzeR, a flexible software to build integrated analysis pipelines for HTS data that contains over-representation analysis, gene set enrichment analysis, comparative gene set analysis and rich sub-network identification. HTSanalyzeR interfaces with commonly used pre-processing packages for HTS data and presents its results as HTML pages and network plots.Our software is written in the R language and freely available via the Bioconductor project at http://www.bioconductor.org.
View details for DOI 10.1093/bioinformatics/btr028
View details for Web of Science ID 000288277300025
View details for PubMedID 21258062
View details for PubMedCentralID PMC3051329
The expression of activator protein 2 (AP-2) transcription factors in MDR1(+) and MDR1(-) taxane resistant human breast carcinoma variants.
AMER ASSOC CANCER RESEARCH. 2009
View details for Web of Science ID 000209701803019