About

Bryce M. Paschal is a professor in the Department of Biochemistry and Molecular Genetics at the University of Virginia School of Medicine. He holds a BA in Biology from the University of North Carolina, Chapel Hill, and a PhD in Medical Science from the University of Massachusetts Medical School. He completed a postdoctoral fellowship in Cell Biology at The Scripps Research Institute in La Jolla, California. His laboratory studies how nuclear transport and signal transduction control the compartmentalization and activity of transcription factors, with a particular focus on prostate cancer. A major research interest is the androgen receptor (AR), a steroid hormone receptor critical for prostate cell growth. His work investigates the mechanisms of AR translocation through the nuclear pore complex, including the roles of nuclear import/export signals, transport receptors, and RanGTPase-dependent complex assembly and disassembly. His research explores the signals that specify nuclear import and export of AR, the receptors mediating AR translocation, and the role of RanGTPase in AR transport. Dr. Paschal's studies also examine the regulation of AR activity, including the significance of AR translocation to the cytoplasm for its nuclear activity, and the phospho-regulation of AR via kinase pathways. His team has identified a novel mechanism for loading protein phosphatase 2A (PP2A) onto AR, involving the small T antigen encoded by SV40. His research employs biochemical, cell biological, and animal model approaches, and benefits from collaborations with experts in mass spectrometry, pathology, and prostate cancer.

Research topics

• Biology
• Cell biology
• Biochemistry
• Chemistry
• Genetics
• Endocrinology
• Computational biology

Selected publications

• Characterizing the clinical and genomic features of androgen indifferent prostate cancer.

  Journal of Clinical Oncology · 2025-02-10

  article

  222 Background: Androgen indifferent prostate cancer (AIPC) is increasingly common and particularly lethal. Data describing these tumors are sparse and AIPC remains a poorly understood malignancy. This study aims to characterize the clinical and genomic features of AIPC. Our work ultimately seeks to identify biomarkers with diagnostic and therapeutic potential. Methods: Utilizing the Oncology Research Information Exchange Network (ORIEN) database, we queried all prostate cancer (PC) patients, identified metastatic castrate resistant prostate cancer (MCRPC) samples, and aimed to enrich for tumors with features of AIPC using previously described characteristics. Our AIPC cohort included three subgroups: aggressive variant prostate cancer (AVPC) defined as having alterations in at least two of TP53, RB1, PTEN; neuroendocrine PC (NEPC) defined as small cell histology or NEPC signature score ≥ 0.25 (1); and double-negative PC (DNPC), defined as non-NEPC patients with low AR expression/AR signaling score. We compared clinical characteristics and genomic analysis of AIPC vs non-AIPC samples in patients who developed MCRPC. Clinical analysis was done using Wilcoxon rank sum test or Fisher's exact test. Gene expression analysis was performed using DESeq2 and GSEA. Results: Of 1,496 total PC patients available for analysis, we identified 323 (22%) as MCRPC. Of those, 39 (12%) met AIPC criteria (17 AVPC, 13 NEPC, 9 DNPC) and 284 (88%) were non-AIPC. Median age at diagnosis for AIPC was 62 years and 85% were white, compared to 62 years and 87% for non-AIPC. Fifty-seven percent of AIPC patients had ECOG ≥1 at diagnosis vs 16% of non-AIPC. Forty-three percent of AIPC patients had de novo metastatic disease vs 15% for non-AIPC (p=0.003). TMPRSS2-ERG gene fusions were found in a significantly higher proportion of AIPC samples vs non-AIPC (38.5% vs 16%, p=0.014). Homologous recombination deficiency (HRD) and tumor mutational burden (TMB) did not differ between cohorts, but microsatellite instability scores (MSI) were significantly higher in AIPC (p=0.019). Using Gene Set Enrichment Analysis (GSEA), we found that genes defining response to androgens and genes involved in oxidative phosphorylation were the most downregulated, whereas genes involved in epithelial mesenchymal transition (EMT), interferon response, and angiogenesis were significantly upregulated in AIPC vs non-AIPC samples. Conclusions: There was a significantly higher rate of de novo metastasis in the AIPC cohort. The downregulated androgen response and upregulated EMT pathways in AIPC suggest enrichment for androgen indifference with our methodology. Upregulated immune signaling and angiogenesis as well as higher MSI suggest opportunities for therapeutic investigation. Future directions include more focused in vitro and in vivo analysis to identify actionable targets. 1. Beltran H, et al. Nat Med . 2016;22(3):298-305. doi:10.1038/nm.4045.

  PublisherDOI

• Clinical and Genomic Features of Androgen Indifferent Prostate Cancer

  International Journal of Molecular Sciences · 2025-01-15 · 4 citations

  articleOpen access

  Androgen-indifferent prostate cancer (AIPC) is increasingly common and particularly lethal. Data describing these tumors are sparse, and AIPC remains a poorly understood malignancy. Utilizing the Oncology Research Information Exchange Network (ORIEN) database, we enriched for tumors with features of AIPC using previously described characteristics. Our AIPC cohort included three subgroups: aggressive variant prostate cancer (AVPC), neuroendocrine PC (NEPC), and double-negative PC (DNPC). Of 1496 total PC patients available for analysis, we identified 323 (22%) as MCRPC. Of those, 39 (12%) met AIPC criteria (17 AVPC, 13 NEPC, 9 DNPC) and 284 (88%) were non-AIPC. Forty-three percent of AIPC patients had de novo metastatic disease vs. 15% for non-AIPC (p = 0.003). Homologous recombination deficiency (HRD) and tumor mutational burden (TMB) did not differ between cohorts, but microsatellite instability scores (MSI) were significantly higher in AIPC (p = 0.019). Using Gene Set Enrichment Analysis (GSEA), we found that genes defining response to androgens and genes involved in oxidative phosphorylation were the most downregulated, whereas genes involved in epithelial–mesenchymal transition (EMT) and immune signaling were significantly upregulated in AIPC vs. non-AIPC. Our study demonstrates the potential for predefined criteria that aim to enrich for AIPC and suggests opportunities for therapeutic investigation.

  PublisherOA PDFDOI

• Parp7 generates an ADP-ribosyl degron that controls negative feedback of androgen signaling

  The EMBO Journal · 2025-07-18 · 7 citations

  articleOpen accessSenior author

  The androgen receptor (AR) transduces the effects of circulating and tumor-derived androgens to the nucleus through ligand-induced changes in protein conformation, localization, and chromatin engagement. Defining how these events are integrated with signal transduction is critical to understand how AR drives prostate cancer and unveil pathway features that are potentially amenable to therapeutic intervention. We describe a novel post-transcriptional mechanism that controls AR levels on chromatin and gene output based on highly selective, inducible degradation. We find that the mono-ADP-ribosyltransferase PARP7 generates an ADP-ribosyl degron in the DNA-binding domain of AR, which is recognized by the ADP-ribose reader domain in the ubiquitin E3 ligase DTX2 and degraded by the proteasome. Mathematical modeling of the pathway suggested that PARP7 ADP-ribosylates chromatin-bound AR, a prediction that was validated in cells using an AR DNA-binding mutant. Non-conventional ubiquitin conjugation to ADP-ribosyl-cysteine and degradation by the proteasome forms the basis of a negative feedback loop that regulates modules of AR target genes. Our data expand the repertoire of mono-ADP-ribosyltransferases to include gene regulation via highly selective protein degradation.

  PublisherDOI

• Parp7 generates an ADP-ribosyl degron that controls negative feedback of androgen signaling

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-12-22

  preprintOpen accessSenior authorCorresponding

  Abstract The androgen receptor (AR) tranduces the effects of circulating and tumor-derived androgens to the nucleus through ligand-induced changes in protein conformation, localization, and engagement with chromatin binding sites. Understanding these events and their integration with signal transduction is critical for defining how AR drives prostate cancer and unveiling pathway features that are amenable to therapeutic intervention. Here, we describe a novel post-transcriptional mechanism that controls AR protein levels on chromatin and associated gene output which is based on a highly selective, inducible degradation mechanism. We find that the mono-ADP-ribosyltransferase PARP7 generates an ADP-ribosyl degron on a single cysteine within the DNA binding domain of AR, which is then recognized by the ADP- ribose reader domain in the ubiquitin E3 ligase DTX2 and degraded by the proteasome. Mathematical modeling of the pathway suggested that PARP7 ADP-ribosylates chromatin-bound AR, a prediction that was validated in cells using an AR mutant that undergoes nuclear import but fails to bind DNA. Lysine- independent, non-conventional ubiquitin conjugation to ADP-ribosyl-cysteine and AR degradation by the proteasome forms the basis of a negative feedback loop that regulates specific modules of AR target genes. Our data expand the repertoire of mono-ADP-ribosyltransferase enzymes to include gene regulation based on highly selective protein degradation. One Sentence Summary PARP7 mono-ADP-ribosylates the androgen receptor on Cys620 to mark the androgen receptor for ubiquitin conjugation by an E3 ligase with ADP-ribose reader function, resulting in in negative feedback of AR-dependent gene expression.

  PublisherDOI

• Oligomerization mediated by the D2 domain of DTX3L is critical for DTX3L‐PARP9 reading function of mono‐ADP‐ribosylated androgen receptor

  Protein Science · 2024-03-21 · 10 citations

  articleOpen accessCorresponding

  Abstract Deltex proteins are a family of E3 ubiquitin ligases that encode C‐terminal RING and DTC domains that mediate interactions with E2 ubiquitin‐conjugating enzymes and recognize ubiquitination substrates. DTX3L is unique among the Deltex proteins based on its N‐terminal domain architecture. The N‐terminal D1 and D2 domains of DTX3L mediate homo‐oligomerization, and the D3 domain interacts with PARP9, a protein that contains tandem macrodomains with ADP‐ribose reader function. While DTX3L and PARP9 are known to heterodimerize, and assemble into a high molecular weight oligomeric complex, the nature of the oligomeric structure, including whether this contributes to the ADP‐ribose reader function is unknown. Here, we report a crystal structure of the DTX3L N‐terminal D2 domain and show that it forms a tetramer with, conveniently, D2 symmetry. We identified two interfaces in the structure: a major, conserved interface with a surface of 973 Å 2 and a smaller one of 415 Å 2 . Using native mass spectrometry, we observed molecular species that correspond to monomers, dimers and tetramers of the D2 domain. Reconstitution of DTX3L knockout cells with a D1‐D2 deletion mutant showed the domain is dispensable for DTX3L‐PARP9 heterodimer formation, but necessary to assemble an oligomeric complex with efficient reader function for ADP‐ribosylated androgen receptor. Our results suggest that homo‐oligomerization of DTX3L is important for the DTX3L‐PARP9 complex to read mono‐ADP‐ribosylation on a ligand‐regulated transcription factor.

  PublisherOA PDFDOI

• Synthetic Dual Cysteine-ADP Ribosylated Peptides from the Androgen Receptor are Recognized by the DTX3L/PARP9 Complex

  ACS Chemical Biology · 2023-11-08 · 13 citations

  articleOpen accessCorresponding

  Androgen signaling in prostate cancer cells involves multisite cysteine ADP-ribosylation of the androgen receptor (AR) by PARP7. The AR modification is read by ADP-ribosyl binding macrodomains in PARP9, but the reason that multiple cysteines are modified is unknown. Here, we use synthetic peptides to show that dual ADP-ribosylation of closely spaced cysteines mediates recognition by the DTX3L/PARP9 complex. Mono and dual ADP-ribosylated cysteine peptides were prepared using a novel solid-phase synthetic strategy utilizing a key, Boc-protected, ribofuranosylcysteine building block. This synthetic strategy allowed us to synthesize fluorescently labeled peptides containing a dual ADP-ribosylation motif. It was found that the DTX3L/PARP9 complex recognizes the dual ADP-ribosylated AR peptide (Kd = 80.5 nM) with significantly higher affinity than peptides with a single ADP-ribose. Moreover, oligomerization of the DTX3L/PARP9 complex proved crucial for ADP-ribosyl-peptide interaction since a deletion mutant of the complex that prevents its oligomer formation dramatically reduced peptide binding. Our data show that features of the substrate modification and the reader contribute to the efficiency of the interaction and imply that multivalent interactions are important for AR-DTX3L/PARP9 assembly.

  PublisherOA PDFDOI

• Data from Induction of PARP7 Creates a Vulnerability for Growth Inhibition by RBN2397 in Prostate Cancer Cells

  2023-04-17

  preprintOpen accessSenior author

  <div><p>The ADP-ribosyltransferase PARP7 modulates protein function by conjugating ADP-ribose to the side chains of acceptor amino acids. PARP7 has been shown to affect gene expression in prostate cancer cells and certain other cell types by mechanisms that include transcription factor ADP-ribosylation. Here, we use a recently developed catalytic inhibitor to PARP7, RBN2397, to study the effects of PARP7 inhibition in androgen receptor (AR)-positive and AR-negative prostate cancer cells. We find that RBN2397 has nanomolar potency for inhibiting androgen-induced ADP-ribosylation of the AR. RBN2397 inhibits the growth of prostate cancer cells in culture when cells are treated with ligands that activate the AR, or the aryl hydrocarbon receptor, and induce PARP7 expression. We show that the growth-inhibitory effects of RBN2397 are distinct from its enhancement of IFN signaling recently shown to promote tumor immunogenicity. RBN2397 treatment also induces trapping of PARP7 in a detergent-resistant fraction within the nucleus, which is reminiscent of how inhibitors such as talazoparib affect PARP1 compartmentalization. Because PARP7 is expressed in AR-negative metastatic tumors and RBN2397 can affect cancer cells through multiple mechanisms, PARP7 may be an actionable target in advanced prostate cancer.</p>Significance:<p>RBN2397 is a potent and selective inhibitor of PARP7 that reduces the growth of prostate cancer cells, including a model for treatment-emergent neuroendocrine prostate cancer. RBN2397 induces PARP7 trapping on chromatin, suggesting its mechanism of action might be similar to clinically used PARP1 inhibitors.</p></div>

  PublisherDOI

• Supplementary Figure 1 from Induction of PARP7 Creates a Vulnerability for Growth Inhibition by RBN2397 in Prostate Cancer Cells

  2023-04-17

  preprintOpen accessSenior author

  <p>Cell cycle distributions of cell lines treated with RBN2397 plus androgen or plus AHR agonist</p>

  PublisherDOI

• Abstract B072: Induction of PARP7 creates a vulnerability for growth inhibition by RBN2397 in prostate cancer cells

  Cancer Research · 2023-06-02

  articleSenior author

  Abstract The ADP-ribosyltransferase PARP7 modulates protein function by conjugating ADP-ribose to the side chains of acceptor amino acids. PARP7 has been shown to affect gene expression in prostate cancer cells and certain other cell types by mechanisms that include transcription factor ADP-ribosylation. Here, we use a recently developed catalytic inhibitor to PARP7, RBN2397 (NCT04053673), to study the effects of PARP7 inhibition in androgen receptor-positive (AR+) and androgen receptor-negative (AR-) prostate cancer cells. Ribon Therapeutics developed RBN2397 as a first-in-class mono-ADP-ribosyltransferase inhibitor, and showed that it blocks PARP7 negative regulation of TBK1 [1]. We find that RBN2397 has nanomolar potency for inhibiting androgen-induced ADP-ribosylation of the androgen receptor. RBN2397 inhibits the growth of prostate cancer cells in culture when cells are treated with ligands that activate the androgen receptor (PC3-AR, VCaP, CWR22Rv1), or the aryl hydrocarbon receptor (PC3, DU145, NCI-H660), and induce PARP7 expression. We show that the growth inhibitory effects of RBN2397 are distinct from its enhancement of interferon signaling recently shown to promote tumor immunogenicity in lung cancer models [1]. Chemical inhibitors to PARP1 exert effects on cells by blocking enzyme function, but also via cytotoxic effects attributed to stabilizing PARP1-chromatin interactions in a process termed trapping [2]. Drug-induced trapping of PARP1 can be detected biochemically by immunoblotting the detergent-resistant chromatin fraction. We found that RBN2397 treatment of AR+ and AR- prostate cancer cells induces biochemical trapping of PARP7 within the nucleus, which was also detected by confocal microscopy. Potential therapeutic benefits of RBN2397 are likely to depend on the level of PARP7 expression, given its induction is necessary for growth inhibitory effects of RBN2397 in cell culture. As a first step towards evaluating whether PARP7 levels in human prostate cancer may be actionable with RBN2397, we used computational methods to analyze PARP7 gene expression data from primary prostate tumors and metastatic AR+ and AR- prostate tumors. To assess PARP7 mRNA levels, we used data from the online resource recount3, which uniformly reprocesses publicly available RNA-seq datasets using a Monorail analysis pipeline. Using the level of PARP7 expression in VCaP cells that confers sensitivity to RBN2397 as a threshold, 50% of primary tumors, 41% of metastatic AR- and 11% of AR+ tumors are predicted to have PARP7 expression levels that are sufficient for a response to RBN2397. Because RBN2397 can inhibit the growth of castration-resistant and neuroendocrine prostate cancer cells, PARP7 may be an actionable target in advanced prostate cancer. 1. Gozgit, J.M., et al., PARP7 negatively regulates the Type I interferon response in cancer cells and its inhibition triggers antitumor immunity. Cancer Cell, 2021. 39(9): p. 1214-1226 e10 2. Murai, J., et al., Trapping of PARP1 and PARP2 by Clinical PARP Inhibitors. Cancer Res, 2012. 72(21): p. 5588-99. Citation Format: Chunsong Yang, Krzysztof Wierbilowicz, Natalia M. Dworak, Song Yi Bae, Sachi B. Tengse, Nicki Abianeh, Justin M. Drake, Tarek Abbas, Aakrosh Ratan, David Wotton, Bryce M. Paschal. Induction of PARP7 creates a vulnerability for growth inhibition by RBN2397 in prostate cancer cells [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B072.

  PublisherDOI

• Supplementary Table 1 from Induction of PARP7 Creates a Vulnerability for Growth Inhibition by RBN2397 in Prostate Cancer Cells

  2023-04-17

  supplementary-materialsOpen accessSenior author

  <p>Supplementary Table 1: RBN2397 growth effects in prostate cencer cell lines</p>

  PublisherDOI

Recent grants

• Project 2

  NIH · $26.2M · 2005–2017

• NIH Grant R01AG040162

  NIH · $1.6M · 2018

• Parp Function in Prostate Cancer

  NIH · $3.6M · 2017–2028

• NIH Grant R01GM058639

  NIH · $2.2M · 2011

Frequent coauthors

• Chunsong Yang

  Sheng Jing Hospital

  66 shared

• Aakrosh Ratan

  University of Virginia

  42 shared

• David Wotton

  Oregon State University

  36 shared

• Natalia M. Dworak

  University of Virginia

  35 shared

• Tarek Abbas

  University of Virginia

  30 shared

• Nicki Abianeh

  University of Virginia

  30 shared

• Sachi B. Tengse

  University of Minnesota

  30 shared

• Krzysztof Wierbiłowicz

  30 shared