SUMO-3 Enhances Androgen Receptor Transcriptional Activity through a Sumoylation-independent Mechanism in Prostate Cancer Cells

Abstract

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 androgendependent 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.The physiological functions of the androgens testosterone and 5␣-dihydrotestosterone (DHT) 4 are mediated by the androgen receptor (AR) (reviewed in Ref. 1), a member of the nuclear receptor superfamily (reviewed in Refs. 2-6). Through the regulation of target genes, androgens and AR play an essential role in male sexual development and the proper development and function of male reproductive organs, such as prostate and epididymis (7). Patients with 5␣-reductase II deficiency, which results in low levels of DHT, have ambiguous external genitalia and a highly underdeveloped and impalpable prostate (8, 9). Reduction or loss of AR activity in males results in androgen insensitivity syndrome (10). In addition to normal prostate development, AR is essential for the initiation and progression of prostate cancer. The best demonstration of this is the effectiveness of anti-androgen and androgen ablation therapy in inhibiting the development of prostate cancer in the early stage of the disease (11). However, local recurrences and metastases will eventually develop in most, if not all, patients after therapy, and prostat...

Small Ubiquitin-like Modifier (SUMO) Modification of the Androgen Receptor Attenuates Polyglutamine-mediated Aggregation

“…3). This behavior is similar to what has been observed for AR bearing a normal Gln tract (64) and likely reflects alterations in transcriptional components other than AR itself. These observations indicate that the reduced aggregation afforded by enhanced SUMOylation is unlikely to be a consequence of altered AR transcriptional activity.…”

Regulation of the androgen receptor by post-translational modifications

“…This differs from their effect on AR activity in primary prostate epithelial cells, where SUMO3 has a weak negative effect on AR activity, suggesting that effects are dependent on cell type and the cellular background. Interestingly, the sites of AR-Su and the ligase activity were found to be independent for the effects (Zheng et al 2006).…”

“…When SUMO1 is present, AR activity is repressed, but in the absence of SUMO1, PIASxa and to a lesser extent PIAS1 can activate the AR (Zheng et al 2006).…”

c-Jun enhancement of androgen receptor transactivation is associated with prostate cancer cell proliferation

“…The coactivator p300 is implicated in ligand-independent AR activation (Debes et al, 2002). SUMO-3 can enhance AR transcriptional activity independent of its sumoylation activity (Zheng et al, 2006). LSD1 is a histone demethylase that recently was shown to act on the AR and be overexpressed in prostate cancer (Metzger et al, 2005).…”