Abstract 2101: PMEPA1 co-operates with the androgen responsive gene, NEDD4-1, to control the androgen receptor levels in human prostate cancer cells

Abstract

Abstract Androgen receptor (AR) is a male hormone receptor and a nuclear transcriptional factor that plays central role in the differentiation and growth of the prostate gland and alterations of the AR network contribute to prostate tumorigenesis. The stability of the AR protein has been known to be regulated by the MDM2 E3 ubiquitin ligase. Recent investigations from our group suggest the role of PMEPA1-NEDD4-1 negative feedback loop in the regulation of AR protein levels in prostate cancer cells. In the PMEPA1-NEDD4-1 feedback loop, AR transcriptionally activates PMEPA1, which in turn provides a docking platform to recruit NEDD4-1 E3 ubiquitin ligase, to facilitate the proteasome dependent degradation of the AR. We hypothesize that decreased or absent PMPEA1 expression observed in more than 65% for prostate tumors may lead to the gain of AR functions which contribute to prostate tumorigenesis. Here we further investigate how PMEPA1 recruits NEDD4-1 to alter AR protein levels and AR signaling in prostate cancer cells. Androgen receptor positive prostate cancer cells lines, LNCaP and VCaP, were treated with synthetic androgen R1881 for 24 hours. The androgen receptor, PMEPA1 and NEDD4-1 were knocked down with specific small interfering RNA (siRNA) molecules. Wild-type AR and mt AR (T877A) were ectopically expressed in LNCaP cells with adenoviral expression vectors. Protein levels of AR, PMEPA1, NEDD4-1, as well as AR responsive gene PSA were assessed by immunoblot assays. Our new observations revealed that that NEDD4-1 was androgen inducible in both LNCaP and VCaP cells. Over-expression of wild-type and mutant AR (T877A) resulted in the upregulation of NEDD4-1 in LNCaP cells. Consistent with these findings, inhibition of AR by siRNA lead to down-regulation of NEDD4-1. As expected, loss of PMEPA1 in LNCaP cells induced up-regulation of AR and NEDD4-1 in an androgen dose-dependent manner. Knockdown of NEDD4-1, rather than NEDD4-2, resulted in elevation of androgen receptor levels and decreases of PMEPA1 expression in LNCaP cells. Our data suggest that NEDD4-1 is an androgen inducible gene and a complex inter-relationship between PMEPA1, NEDD4-1 and AR. Intriguingly, the AR degradation function of NEDD4-1 depends on the availability of PMEPA1. Thus PMEPA1-NEDD4-1 co-operation is critical for the regulation of androgen receptor protein levels. In conclusion, loss of PMEPA1 in human prostate cancer may also lead to the activation of NEDD4-1 through elevated AR signaling, representing a feed-forward event in tumorigenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2101. doi:10.1158/1538-7445.AM2011-2101