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Prostate cancer starts as a treatable hormone-dependent disease, but often ends in a drug-resistant form called castration-resistant prostate cancer (CRPC). Despite the development of the antiandrogens enzalutamide and abiraterone for CRPC, which target the androgen receptor (AR), drug resistance usually develops within 6 months and metastatic CRPC (mCRPC) leads to lethality. EZH2, found with SUZ12, EED, and RbAP48 in Polycomb repressive complex 2 (PRC2), has emerged as an alternative target for the treatment of deadly mCRPC. Unfortunately, drugs targeting EZH2 have shown limited efficacy in mCRPC. To address these failures, we have developed novel, dual-acting peptide inhibitors of PRC2 that uniquely target the SUZ12 protein component, resulting in the inhibition of both PRC2 canonical and noncanonical functions in prostate cancer. These peptides were found to inhibit not only the EZH2 methylation activity, but also block its positive effect on AR gene expression in prostate cancer cells. Since the peptide effect on AR levels is transcriptional, the inhibitory peptides can block the expression of both full-length AR and its splicing variants including AR-V7, which plays a significant role in the development of drug resistance. This dual-mode action provides the peptides with the capability to kill enzalutamide-resistant CRPC cells. These peptides are also more cytotoxic to prostate cancer cells than the combination of enzalutamide and an EZH2 inhibitory drug, which was recently suggested to be an effective treatment of mCRPC disease. Our data show that such a dual-acting therapeutic approach can be more effective than the existing front-line drug therapies for treating deadly mCRPC. [ABSTRACT FROM AUTHOR]

Androgens are important for male sexual development, which depend on the cognate receptor, the androgen receptor. The transcriptional activity of the androgen receptor, like other nuclear receptors, is regulated by accessory proteins that can have either positive or negative effects. Through a yeast functional screen, we have identified SUMO-3 as a regulator of androgen receptor activity in prostate cancer cells. SUMO-3 is one of three eukaryotic proteins that become post-translationally conjugated to their target proteins in a manner analogous to the attachment of ubiquitin. In primary prostate epithelial cells, PrEC, and the prostate cancer cells, PC-3, SUMO-3 has a weak negative effect on androgen receptor transcriptional activity. In contrast, SUMO-3 and it close relative SUMO-2 strongly enhance transactivation by endogenous androgen receptor in LNCaP cells. This positive effect is observed in both androgen-dependent and androgen-independent LNCaP cells. Interestingly, SUMO-1, unlike SUMO-3 and SUMO-2, can inhibit, but not stimulate, androgen receptor activity. Mutational analysis of the androgen receptor and SUMO-3 demonstrates that the SUMO-3-positive activity does not depend on either the sumoylation sites of the androgen receptor or the sumoylation function of SUMO-3. Stable overexpression of SUMO-3 in LNCaP cells significantly enhances the androgen-dependent proliferation of these cells. Additionally, siRNA-mediated repression of SUMO-2 significantly inhibits the growth of both androgen-dependent and -independent LNCaP cells. Collectively, these results suggest (i) a novel mechanism for elevating AR activity through the switch of SUMO-3 from a weak negative regulator in normal prostate cells to a strong positive regulator in prostate cancer cells and (ii) a proliferative role for SUMO-3 and SUMO-2 in the growth of prostate cancer cells that is independent of sumoylation of the androgen receptor. [ABSTRACT FROM AUTHOR]

Kinases can phosphorylate and regulate androgen receptor activity during prostate cancer progression. In particular, we showed that glycogen synthase kinase-3 beta phosphorylates the androgen receptor, thereby inhibiting androgen receptor-driven transcription. Conversely, the glycogen synthase kinase-3 beta inhibitor lithium chloride suppressed the glycogen synthase kinase-3 beta-mediated phosphorylation of the androgen receptor, thereby enabling androgen receptor-driven transcription to occur. The androgen receptor hinge and ligand-binding domains were important for both the phosphorylation and the inhibition of transcriptional activity of the receptor by glycogen synthase kinase-3 beta. Furthermore, androgen receptor phosphorylation was augmented by LY294002, an indirect inhibitor of protein kinase B/Akt that inhibits glycogen synthase kinase-3 beta. We also showed that the mutation of various phosphorylation sites on glycogen synthase kinase-3 beta affected the ability of these mutants to co-distribute with the androgen receptor in the cell nucleus, also that both glycogen synthase kinase-3beta and androgen receptor proteins can be found in cell nuclei of prostate cancer tissue samples. Because glycogen synthase kinase-3 beta activity is suppressed after the enzyme is phosphorylated by protein kinase B/Akt and Akt activity frequently increases during the progression of prostate cancer, nullification of the glycogen synthase kinase-3 beta-mediated suppression of androgen receptor activity by Akt likely contributes to prostate cancer progression.