Obstructing Androgen Receptor Activation in Prostate Cancer Cells through Posttranslational Modification by NEDD8

PUBLIC ABSTRACT

Androgen receptor (AR), a classic member of the steroid hormone receptor superfamily, is a well-established therapeutic target for treating prostate cancer as AR plays a pivotal role in regulating both normal physiology and disease progression of the prostate. The steroid hormones testosterone and its metabolite dihydrotestosterone are natural androgens that bind directly to AR to activate its transcriptional potential, causing stimulation of prostate tissue proliferation and cancer progression. Androgen ablation therapy effectively inhibits tumor growth at first; however, adapted tumor cells will develop alternative pathways to escape androgen ablation and evolve eventually into an androgen-independent prostate cancer. Therefore, it is of particular importance to explore regulatory mechanisms that modulate AR activity. Post-translational modification of proteins has marked impacts on gene expression. We have recently found evidence that AR may be post-translationally modified by NEDD8, a small ubiquitin-like modifier overexpressed in prostate cancer. NEDD8 modification appears to inhibit the transcriptional activity of AR. We have also identified potential enzymes that mediate the conjugation and deconjugation of NEDD8 to AR.

In this study, we hypothesize that AR is subject to covalent modification by NEDD8, and this modification (neddylation) may influence the transcriptional activity of AR, which in turn will affect prostate cancer cell growth and proliferation. We aim to: (1) Establish whether AR is indeed modified by Nedd8, (2) determine the effects of androgen on AR neddylation, (3) identify neddylation sites in AR, (4) determine the enzymes that catalyze AR neddylation and also de-neddylation, and (5) address the effects of neddylation on transcriptional activity of AR and prostate cancer cell growth and proliferation.

There is so far no reported evidence of AR being modified by NEDD8. Our evidence strongly suggests that AR is indeed modified by Nedd8. Nedd8 modification has been shown to play a critical role in modulating the activity of P53. In addition, connection between NEDD8 and prostate cancer has been reported. Therefore, this study represents a highly innovative project. If successful, the knowledge obtained from this study will have great impact on our understanding of regulation of prostate cancer control by AR through a new mechanism of post-translational modification. It may also provide a rationale target for treating prostate cancer.