USP22 Functions as an Oncogenic Driver in Prostate Cancer by Regulating Cell Proliferation and DNA Repair.

Emerging evidence indicates the deubiquitinase USP22 regulates transcriptional activation and modification of target substrates to promote pro-oncogenic phenotypes. Here, in vivo characterization of tumor-associated USP22 upregulation and unbiased interrogation of USP22-regulated functions in vitro demonstrated critical roles for USP22 in prostate cancer. Specifically, clinical datasets validated that USP22 expression is elevated in prostate cancer, and a novel murine model demonstrated a hyperproliferative phenotype with prostate-specific USP22 overexpression. Accordingly, upon overexpression or depletion of USP22, enrichment of cell-cycle and DNA repair pathways was observed in the USP22-sensitive transcriptome and ubiquitylome using prostate cancer models of clinical relevance. Depletion of USP22 sensitized cells to genotoxic insult, and the role of USP22 in response to genotoxic insult was further confirmed using mouse adult fibroblasts from the novel murine model of USP22 expression. As it was hypothesized that USP22 deubiquitylates target substrates to promote protumorigenic phenotypes, analysis of the USP22-sensitive ubiquitylome identified the nucleotide excision repair protein, XPC, as a critical mediator of the USP22-mediated response to genotoxic insult. Thus, XPC undergoes deubiquitylation as a result of USP22 function and promotes USP22-mediated survival to DNA damage. Combined, these findings reveal unexpected functions of USP22 as a driver of protumorigenic phenotypes and have significant implications for the role of USP22 in therapeutic outcomes. SIGNIFICANCE: The studies herein present a novel mouse model of tumor-associated USP22 overexpression and implicate USP22 in modulation of cellular survival and DNA repair, in part through regulation of XPC.

Sigma1 Targeting to Suppress Aberrant Androgen Receptor Signaling in Prostate Cancer.

Suppression of androgen receptor (AR) activity in prostate cancer by androgen depletion or direct AR antagonist treatment, although initially effective, leads to incurable castration-resistant prostate cancer (CRPC) via compensatory mechanisms including resurgence of AR and AR splice variant (ARV) signaling. Emerging evidence suggests that Sigma1 (also known as sigma-1 receptor) is a unique chaperone or scaffolding protein that contributes to cellular protein homeostasis. We reported previously that some Sigma1-selective small molecules can be used to pharmacologically modulate protein homeostasis pathways. We hypothesized that these Sigma1-mediated responses could be exploited to suppress AR protein levels and activity. Here we demonstrate that treatment with a small-molecule Sigma1 inhibitor prevented 5α- dihydrotestosterone-mediated nuclear translocation of AR and induced proteasomal degradation of AR and ARV, suppressing the transcriptional activity and protein levels of both full-length and splice-variant AR. Consistent with these data, RNAi knockdown of Sigma1 resulted in decreased AR levels and transcriptional activity. Furthermore, Sigma1 physically associated with ARV7 and ARv567es as well as full-length AR. Treatment of mice xenografted with ARV-driven CRPC tumors with a drug-like small-molecule Sigma1 inhibitor significantly inhibited tumor growth associated with elimination of AR and ARV7 in responsive tumors. Together, our data show that Sigma1 modulators can be used to suppress AR/ARV-driven prostate cancer cells via regulation of pharmacologically responsive Sigma1-AR/ARV interactions, both in vitro and in vivoCancer Res; 77(9); 2439-52. ©2017 AACR.

Aberrant BAF57 signaling facilitates prometastatic phenotypes.

PURPOSE: BAF57, a component of the switching-defective and sucrose nonfermenting (SWI/SNF) chromatin-remodeling complex conglomerate, modulates androgen receptor activity to promote prostate cancer. However, the molecular consequences of tumor-associated BAF57 expression have remained undefined in advanced disease such as castration-resistant prostate cancer and/or metastasis. EXPERIMENTAL DESIGN: Clinical human specimens of primary and metastatic prostate cancer were immunohistochemically examined for tumor-grade association of BAF57 expression. Global gene expression analyses were conducted in models mimicking tumor-associated BAF57 expression. Aberrant BAF57-dependent gene expression changes, bypass of androgen-mediated signaling, and chromatin-specific SWI/SNF complex alterations with respect to cytoskeletal remodelers such as integrins were validated. Cell migration assays were used to profile the biologic phenotypes conferred under conditions simulating tumor-derived BAF57 expression. RESULTS: Immunohistochemical quantitation of primary human specimens revealed that BAF57 was significantly and aberrantly elevated as a function of tumor grade. Critically, gene expression analyses showed that BAF57 deregulation circumvented androgen-mediated signaling, elicited α2 integrin upregulation, and altered other SWI/SNF complex components at the α2 integrin locus. BAF57-dependent α2 integrin induction conferred a prometastatic migratory advantage, which was attenuated by anti-α2 integrin antibody blockade. Furthermore, BAF57 was found to be markedly upregulated in human prostate cancer metastases of the lung, lymph node, and dura. CONCLUSION: The findings herein, identifying tumor-associated BAF57 perturbation as a means to bypass androgen-signaling events that facilitate novel prometastatic phenotypes, link BAF57 upregulation to tumor dissemination. These data thereby establish BAF57 as a putative marker of metastatic potential that could be leveraged for therapeutic intervention.