Academic Appointments


Honors & Awards


  • Teaching Honor Roll, Tau Beta Pi Stanford (2019-2020)
  • Terman Award - Stanford Advisor, School of Engineering (2019-2020)

All Publications


  • A long lost key opens an ancient lock: Drosophila Myb causes a synthetic multivulval phenotype in nematodes. Biology open Vorster, P. J., Goetsch, P., Wijeratne, T. U., Guiley, K. Z., Andrejka, L., Tripathi, S., Larson, B. J., Rubin, S. M., Strome, S., Lipsick, J. S. 2020

    Abstract

    The five-protein MuvB core complex is highly conserved in animals. This nuclear complex interacts with RB family tumor suppressor proteins and E2F-DP transcription factors to form DREAM complexes that repress genes that regulate cell cycle progression and cell fate. The MuvB core complex also interacts with proteins Myb family oncoproteins to form the Myb-MuvB complexes that activate many of the same genes. We show that animal-type Myb genes are present in Bilateria, Cnidaria, and Placozoa, the latter including the simplest known animal species. However, bilaterian nematode worms lost their animal-type Myb genes hundreds of millions of years ago. Nevertheless, amino acids in the LIN9 and LIN52 proteins that directly interact with the MuvB-binding domains of human B-Myb and Drosophila Myb are conserved in C. elegans Here we show that, despite greater than 500 million years since their last common ancestor, the Drosophila melanogaster Myb protein can bind to the nematode LIN9-LIN52 proteins in vitro and can cause a synthetic multivulval (synMuv) phenotype in vivo This phenotype is similar to that caused by loss-of-function mutations in C. elegans synMuvB class genes including those that encode homologs of the MuvB core, RB, E2F, and DP. Furthermore, amino acid substitutions in the MuvB-binding domain of Drosophila Myb that disrupt its functions in vitro and in vivo also disrupt these activities in C. elegans We speculate that nematodes and other animals may contain another protein that can bind to LIN9 and LIN52 in order to activate transcription of genes repressed by DREAM complexes.

    View details for DOI 10.1242/bio.051508

    View details for PubMedID 32295830

  • The Drosophila LIN54 homolog Mip120 controls two aspects of oogenesis. Biology open Cheng, M. H., Andrejka, L., Vorster, P. J., Hinman, A., Lipsick, J. S. 2017

    Abstract

    The conserved multi-protein MuvB core associates with the Myb oncoproteins and with the RB-E2F-DP tumor suppressor proteins in complexes that regulate cell proliferation, differentiation, and apoptosis. Drosophila Mip120, a homolog of LIN54, is a sequence-specific DNA-binding protein within the MuvB core. A mutant of Drosophila mip120 was previously shown to cause female and male sterility. We now show that Mip120 regulates two different aspects of oogenesis. First, in the absence of the Mip120 protein, egg chambers arrest during the transition from stage 7 to 8 with a failure of the normal program of chromosomal dynamics in the ovarian nurse cells. Specifically, the decondensation, disassembly and dispersion of the endoreplicated polytene chromosomes fail to occur without Mip120. The conserved carboxy-terminal DNA-binding and protein-protein interaction domains of Mip120 are necessary but are not sufficient for this process. Second, we show that a lack of Mip120 causes a dramatic increase in the expression of benign gonial cell neoplasm (bgcn), a gene that is normally expressed in only a small number of cells within the ovary including the germline stem cells.

    View details for PubMedID 28522430

  • A Dichotomy in Cortical Actin and Chemotactic Actin Activity between Human Memory and Naive T Cells Contributes to Their Differential Susceptibility to HIV-1 Infection JOURNAL OF BIOLOGICAL CHEMISTRY Wang, W., Guo, J., Yu, D., Vorster, P. J., Chen, W., Wu, Y. 2012; 287 (42): 35455-35469

    Abstract

    Human memory and naive CD4 T cells can mainly be identified by the reciprocal expression of the CD45RO or CD45RA isoforms. In HIV-1 infection, blood CD45RO memory CD4 T cells are preferentially infected and serve as a major viral reservoir. The molecular mechanism dictating this differential susceptibility to HIV-1 remains largely obscure. Here, we report that the different susceptibility of memory and naive T cells to HIV is not determined by restriction factors such as Apobec3G or BST2. However, we observed a phenotypic distinction between human CD45RO and CD45RA resting CD4 T cells in their cortical actin density and actin dynamics. CD45RO CD4 T cells possess a higher cortical actin density and can be distinguished as CD45RO(+)Actin(high). In contrast, CD45RA T cells are phenotypically CD45RA(+)Actin(low). In addition, the cortical actin in CD45RO memory CD4 T cells is more dynamic and can respond to low dosages of chemotactic induction by SDF-1, whereas that of naive cells cannot, despite a similar level of the chemokine receptor CXCR4 present on both cells. We further demonstrate that this difference in the cortical actin contributes to their differential susceptibility to HIV-1; resting memory but not naive T cells are highly responsive to HIV-mediated actin dynamics that promote higher levels of viral entry and early DNA synthesis in resting memory CD4 T cells. Furthermore, transient induction of actin dynamics in resting naive T cells rescues HIV latent infection following CD3/CD28 stimulation. These results suggest a key role of chemotactic actin activity in facilitating HIV-1 latent infection of these T cell subsets.

    View details for DOI 10.1074/jbc.M112.362400

    View details for Web of Science ID 000309968000055

    View details for PubMedID 22879601

  • Involvement of LIM kinase 1 in actin polarization in human CD4 T cells. Communicative & integrative biology Xu, X., Guo, J., Vorster, P., Wu, Y. 2012; 5 (4): 381-383

    Abstract

    Chemokine binding to cognate receptors induces actin dynamics that are a major driving force for T cell migration and chemotactic motility. HIV-1 binding to the chemokine coreceptor CXCR4 initiates chemotactic signaling, mimicking chemokine-induced actin dynamics to facilitate infection processes such as entry, early DNA synthesis, and nuclear migration. Recently, we identified that HIV-triggered early actin polymerization is mediated through the Rac1-PAK1/2-LIMK1-cofilin pathway. Inhibition of LIMK1 (LIM domain kinase 1), a kinase phosphorylating cofilin, through shRNA knockdown decreases actin polymerization and T cell chemotaxis toward SDF-1. The LIMK1 knockdown T cells also supported lower viral entry, DNA synthesis and nuclear migration, suggesting a critical role of LIMK1-mediated actin dynamics in the initiation of HIV-1 infection. Surprisingly, LIMK1 knockdown in CEM-SS T cells did not lead to an overall change in the ratio of phospho-cofilin to total cofilin although there was a measurable decrease in the amount of actin filaments in cells. The decrease in filamentous actin in LIMK1 knockdown cells was found to mainly occur in polarized cap region rich in F-actin. These results suggest that LIMK1 may be involved in spontaneous actin polarization in transformed T cells. The inhibition of T cell chemotaxis by LIMK1 knockdown likely result from inhibition of localized LIMK1 activation and cofilin phosphorylation that are required for polarized actin polymerization for directional cell migration. The inhibition of HIV-1 infection by LIMK1 knockdown may also result from the decrease of actin-rich membrane protrusions that may be preferred viral entry sites in T cells.

    View details for DOI 10.4161/cib.20165

    View details for PubMedID 23060964

  • Genetic Dissection of Acute Ethanol Responsive Gene Networks in Prefrontal Cortex: Functional and Mechanistic Implications PLOS ONE Wolen, A. R., Phillips, C. A., Langston, M. A., Putman, A. H., Vorster, P. J., Bruce, N. A., York, T. P., Williams, R. W., Miles, M. F. 2012; 7 (4)

    Abstract

    Individual differences in initial sensitivity to ethanol are strongly related to the heritable risk of alcoholism in humans. To elucidate key molecular networks that modulate ethanol sensitivity we performed the first systems genetics analysis of ethanol-responsive gene expression in brain regions of the mesocorticolimbic reward circuit (prefrontal cortex, nucleus accumbens, and ventral midbrain) across a highly diverse family of 27 isogenic mouse strains (BXD panel) before and after treatment with ethanol.Acute ethanol altered the expression of ~2,750 genes in one or more regions and 400 transcripts were jointly modulated in all three. Ethanol-responsive gene networks were extracted with a powerful graph theoretical method that efficiently summarized ethanol's effects. These networks correlated with acute behavioral responses to ethanol and other drugs of abuse. As predicted, networks were heavily populated by genes controlling synaptic transmission and neuroplasticity. Several of the most densely interconnected network hubs, including Kcnma1 and Gsk3β, are known to influence behavioral or physiological responses to ethanol, validating our overall approach. Other major hub genes like Grm3, Pten and Nrg3 represent novel targets of ethanol effects. Networks were under strong genetic control by variants that we mapped to a small number of chromosomal loci. Using a novel combination of genetic, bioinformatic and network-based approaches, we identified high priority cis-regulatory candidate genes, including Scn1b, Gria1, Sncb and Nell2.The ethanol-responsive gene networks identified here represent a previously uncharacterized intermediate phenotype between DNA variation and ethanol sensitivity in mice. Networks involved in synaptic transmission were strongly regulated by ethanol and could contribute to behavioral plasticity seen with chronic ethanol. Our novel finding that hub genes and a small number of loci exert major influence over the ethanol response of gene networks could have important implications for future studies regarding the mechanisms and treatment of alcohol use disorders.

    View details for DOI 10.1371/journal.pone.0033575

    View details for Web of Science ID 000305338600010

    View details for PubMedID 22511924

  • LIM Kinase 1 Modulates Cortical Actin and CXCR4 Cycling and Is Activated by HIV-1 to Initiate Viral Infection JOURNAL OF BIOLOGICAL CHEMISTRY Vorster, P. J., Guo, J., Yoder, A., Wang, W., Zheng, Y., Xu, X., Yu, D., Spear, M., Wu, Y. 2011; 286 (14)

    Abstract

    Almost all viral pathogens utilize a cytoskeleton for their entry and intracellular transport. In HIV-1 infection, binding of the virus to blood resting CD4 T cells initiates a temporal course of cortical actin polymerization and depolymerization, a process mimicking the chemotactic response initiated from chemokine receptors. The actin depolymerization has been suggested to promote viral intracellular migration through cofilin-mediated actin treadmilling. However, the role of the virus-mediated actin polymerization in HIV infection is unknown, and the signaling molecules involved remain unidentified. Here we describe a pathogenic mechanism for triggering early actin polymerization through HIV-1 envelope-mediated transient activation of the LIM domain kinase (LIMK), a protein that phosphorylates cofilin. We demonstrate that HIV-mediated LIMK activation is through gp120-triggered transient activation of the Rack-PAK-LIMK pathway, and that knockdown of LIMK through siRNA decreases filamentous actin, increases CXCR4 trafficking, and diminishes viral DNA synthesis. These results suggest that HIV-mediated early actin polymerization may directly regulate the CXCR4 receptor during viral entry and is involved in viral DNA synthesis. Furthermore, we also demonstrate that in resting CD4 T cells, actin polymerization can be triggered through transient treatment with a pharmacological agent, okadaic acid, that activates LIMK and promotes HIV latent infection of resting CD4 T cells. Taken together, our results suggest that HIV hijacks LIMK to control the cortical actin dynamics for the initiation of viral infection of CD4 T cells.

    View details for DOI 10.1074/jbc.M110.182238

    View details for Web of Science ID 000289077500068

    View details for PubMedID 21321123

    View details for PubMedCentralID PMC3069457

  • Synthesis and characterization of hydrogel particles containing Cibacron Blue F3G-A. Colloids and surfaces. A, Physicochemical and engineering aspects Patanarut, A., Luchini, A., Botterell, P. J., Mohan, A., Longo, C., Vorster, P., Petricoin, E. F., Liotta, L. A., Bishop, B. 2010; 362 (1-3): 8–19

    Abstract

    The analysis of low abundance and low molecular weight biomolecules is challenging due to their labile nature and the presence of high abundance, high molecular weight species such as serum albumin, which can hinder their detection. Functionalized hydrogel particles have proven to be ideally suited for this application. We here report the synthesis of hydrogel core and core-shell particles with incorporated Cibacron Blue F3G-A, and analysis of their harvesting properties. Hydrogel particle scaffolds consisting of cross-linked N-isopropylacrylamide and allylamine copolymers were synthesized via surfactant-free precipitation polymerization, with the blue dye subsequently affixed via a nucleophilic substitution reaction. The dye-functionalized core and core-shell particles were found to efficiently harvest and sequester dilute low molecular weight peptides and proteins from solution, with the core-shell particles more effectively excluding larger proteins. Moreover, proteins bound by core and core-shell particles containing blue dye were protected from tryptic degradation. These findings suggest that core and core-shell hydrogel particles containing Cibacron Blue F3G-A constitute promising new tools for peptide/protein biomarker harvesting applications.

    View details for DOI 10.1016/j.colsurfa.2010.03.023

    View details for PubMedID 20871782

    View details for PubMedCentralID PMC2943629

  • HIV envelope-CXCR4 signaling activates cofilin to overcome cortical actin restriction in resting CD4 T cells CELL Yoder, A., Yu, D., Dong, L., Iyer, S. R., Xu, X., Kelly, J., Liu, J., Wang, W., Vorster, P. J., Agulto, L., Stephany, D. A., Cooper, J. N., Marsh, J. W., Wu, Y. 2008; 134 (5): 782-792

    Abstract

    Binding of the HIV envelope to the chemokine coreceptors triggers membrane fusion and signal transduction. The fusion process has been well characterized, yet the role of coreceptor signaling remains elusive. Here, we describe a critical function of the chemokine coreceptor signaling in facilitating HIV infection of resting CD4 T cells. We find that static cortical actin in resting T cells represents a restriction and that HIV utilizes the Galphai-dependent signaling from the chemokine coreceptor CXCR4 to activate a cellular actin-depolymerizing factor, cofilin, to overcome this restriction. HIV envelope-mediated cofilin activation and actin dynamics are important for a postentry process that leads to viral nuclear localization. Inhibition of HIV-mediated actin rearrangement markedly diminishes viral latent infection of resting T cells. Conversely, induction of active cofilin greatly facilitates it. These findings shed light on viral exploitation of cellular machinery in resting T cells, where chemokine receptor signaling becomes obligatory.

    View details for DOI 10.1016/j.cell.2008.06.036

    View details for Web of Science ID 000258947500018

    View details for PubMedID 18775311