Person:
Paulk, Joshiawa

Profile Picture

Email Address

AA Acceptance Date

Birth Date

Research Projects

Organizational Units

Job Title

Last Name

Paulk

First Name

Joshiawa

Name

Paulk, Joshiawa
Author's Publications: search.filters.isAuthorOfPublication.e29db47b-2d63-4de3-b55e-53240a133026

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Publication
    An oncogenic Ezh2 mutation cooperates with particular genetic alterations to induce tumors in mice and redistributes H3K27 trimethylation throughout the genome
    (2016) Souroullas, George P.; Jeck, William R.; Parker, Joel S.; Simon, Jeremy M.; Liu, Jie-Yu; Paulk, Joshiawa; Xiong, Jessie; Clark, Kelly S.; Fedoriw, Yuri; Qi, Jun; Burd, Christin E.; Bradner, James E; Sharpless, Norman E.
    B-cell lymphoma and melanoma harbor recurrent mutations in the gene encoding the EZH2 histone methyltransferase, but the carcinogenic role of these mutations is unclear. Here we describe a mouse model in which the most common somatic EZH2 gain-of-function mutation (Y646F in human, Y641F in the mouse) can be conditionally expressed. Expression of Ezh2Y641F in mouse B-cells or melanocytes caused high-penetrance lymphoma or melanoma, respectively. Bcl2 overexpression or p53 loss, but not c-Myc overexpression, further accelerated lymphoma progression, and expression of mutant B-Raf but not mutant N-Ras further accelerated melanoma progression. Although expression of Ezh2Y641F increased abundance of global H3K27 trimethylation (H3K27me3), it also caused a widespread redistribution of this repressive mark, including a loss of H3K27me3 associated with increased transcription at many loci. These results suggest that Ezh2Y641F induces lymphoma and melanoma through a vast reorganization of chromatin structure inducing both repression and activation of polycomb-regulated loci.
  • Thumbnail Image
    Publication
    Modulators of Cellular and Biochemical PRC2 Activity
    (2014-10-21) Paulk, Joshiawa; Schreiber, Stuart L.; Golub, Todd; Phillips, Andrew; Bernstein, Bradley
    EZH2 is a SET domain-containing methyltransferase and the catalytic component of the multimeric Polycomb- group (PcG) protein complex, PRC2. When in complex with other PRC2 members (EED, SUZ12, AEBP2, and RBBP4), EZH2 catalyzes methylation of H3K27, a histone modification associated with transcriptional repression and developmental regulation. As several PRC2 components are upregulated or mutated in a variety of human cancers, efforts to discover small-molecule modulators of PRC2 and understand its regulation may yield therapeutic insights. Identification of small-molecule probes with distinct chemotypes, MOAs, and selectivity profiles are not only of great value, but necessary in establishing comprehensive probe sets capable of illuminating the various roles of EZH2 in oncogenesis. Here we describe efforts to identify and characterize small-molecule modulators of PRC2 and further understand its regulation. Chapter II outlines the expression and purification of 5-component PRC2 (EZH2-EED-SUZ12-AEBP2-RBBP4) and the establishment of biochemical and cellular HTS assays. These assays were used to screen a diverse set of small molecules (>120,000), identifying biochemical PRC2 inhibitors and activators (described in Chapter III). One biochemical PRC2 inhibitor, BRD1835, appeared to inhibit PRC2 activity through a novel artifactual mechanism involving interaction with peptide substrate, leading to apparent peptide-competitive behavior and putative cellular activity (described in Chapter IV). The characterization of novel biochemical PRC2 activators, BRD3934 and BRD8284, is discussed in Chapter V. Chapter VI describes the use of an HCS assay to identify known bioactive compounds that alter intracellular levels of H3K27me3 through modulating H3K27me3-connected regulatory nodes or by targeting PRC2 directly. These efforts led to the discovery that an antifungal agent, miconazole, is capable of activating PRC2 activity in vitro, while a mucolytic agent, bromhexine, selectively ablates cellular H3K27me3 levels through targeting an activity distinct from PRC2. Finally, Chapter VII discusses novel PRC2-connected crosstalk mechanisms identified through screening libraries of uniquely modified histone peptides for their ability to bind or support methylation by PRC2. These studies enhance our understanding of PRC2 regulation by revealing the effects of H3R26 and H3K23me1 modifications on enzymatic activity, implicating their respective methyltransferases in PRC2 regulation.
  • Thumbnail Image
    Publication
    An Unbiased Approach To Identify Endogenous Substrates of “Histone” Deacetylase 8
    (American Chemical Society, 2014) Olson, David E.; Udeshi, Namrata D.; Wolfson, Noah A.; Pitcairn, Carol Ann; Sullivan, Eric D.; Jaffe, Jacob D.; Svinkina, Tanya; Natoli, Ted; Lu, Xiaodong; Paulk, Joshiawa; McCarren, Patrick; Wagner, Florence F.; Barker, Doug; Howe, Eleanor; Lazzaro, Fanny; Gale, Jennifer P.; Zhang, Yan-Ling; Subramanian, Aravind; Fierke, Carol A.; Carr, Steven A.; Holson, Edward B.
    Despite being extensively characterized structurally and biochemically, the functional role of histone deacetylase 8 (HDAC8) has remained largely obscure due in part to a lack of known cellular substrates. Herein, we describe an unbiased approach using chemical tools in conjunction with sophisticated proteomics methods to identify novel non-histone nuclear substrates of HDAC8, including the tumor suppressor ARID1A. These newly discovered substrates of HDAC8 are involved in diverse biological processes including mitosis, transcription, chromatin remodeling, and RNA splicing and may help guide therapeutic strategies that target the function of HDAC8.
  • Thumbnail Image
    Publication
    A Small-Molecule Probe of the Histone Methyltransferase G9a Induces Cellular Senescence in Pancreatic Adenocarcinoma
    (American Chemical Society, 2012) Yuan, Yuan; Wang, Qiu; Paulk, Joshiawa; Kubicek, Stefan; Kemp, Melissa M.; Adams, Drew J.; Shamji, Alykhan; Wagner, Bridget K.; Schreiber, Stuart
    Post-translational modifications of histones alter chromatin structure and play key roles in gene expression and specification of cell states. Small molecules that target chromatin-modifying enzymes selectively are useful as probes and have promise as therapeutics, although very few are currently available. G9a (also named euchromatin histone methyltransferase 2 (EHMT2)) catalyzes methylation of lysine 9 on histone H3 (H3K9), a modification linked to aberrant silencing of tumor-suppressor genes, among others. Here, we report the discovery of a novel histone methyltransferase inhibitor, BRD4770. This compound reduced cellular levels of di- and trimethylated H3K9 without inducing apoptosis, induced senescence, and inhibited both anchorage-dependent and -independent proliferation in the pancreatic cancer cell line PANC-1. ATM-pathway activation, caused by either genetic or small-molecule inhibition of G9a, may mediate BRD4770-induced cell senescence. BRD4770 may be a useful tool to study G9a and its role in senescence and cancer cell biology.