Abstract 1324: PMEPA1 enhances the prostate cancer cell growth inhibitory effect of MDV3100 and bicalutamide.

Abstract Introduction and Objective: PMEPA1 is a highly androgen-inducible gene in prostate cancer cells, recruits the NEDD4-1, an E3 ubiquitin ligase, to degrade AR. We hypothesize that the frequently (65%) observed decrease or loss of PMPEA1 expression in human prostate tumors may lead to enhanced AR functions and accelerated prostate tumorigenesis. Therefore, we investigated the growth and survival of prostate cancer cells in the presence of AR inhibitors in response to PMEPA1 knockdown. Methods: PMEPA1 was silenced by PMEPA1 Mission shRNA lentivirus infection and puromycin selection in LNCaP and VCaP cells respectively. The PMEPA1 deficient LNCaP and VCaP cells were treated with the AR inhibitors (MDV3100 and bicalutamide), as well as the artificial synthesized androgen R1881. Ectopic NEDD4-1 was expressed by pCMV-XL4-NEDD4-1 eukaryotic expression vector. Cell growth was monitored by cell counting assay, BrdU incorporation assay and colony plating efficiency assay. Cell cycle was analyzed with propidium iodide staining based flowcytometry assay. Protein levels of AR, PMEPA1, PSA and NEDD4-1 were assessed by immunoblot assays. Results: PMEPA1 silenced LNCaP and VCaP cells had higher AR, PSA protein levels, suggesting activated AR signaling. Consistent with this observation, inhibition of PMEPA1-1 by shRNA resulted in increased cell growth, stronger BrdU incorporation ability and higher colony plating efficiency in both LNCaP and VCaP cells. Cell cycle assay showed more S-phase cells in PMEPA1 deficient LNCaP and VCaP cells in regular medium or R1881 supplemented charcoal-striped medium. Ectopic expression of NEDD4-1 could not inhibit cell growth in PMEPA1 silenced LNCaP cells. More interestingly, the PMEPA1 deficient CaP cells (both LNCaP and VCaP cells) demonstrated more resistance to the growth inhibitory effects of MDV3100 and bicalutamide. Conclusions: The frequently observed decreased expression of PMEPA1 results in elevated AR protein levels and activated AR signaling, which in turn promotes cell growth in androgen responsive prostate cancer cells. The PMEPA1 deficient cells develop more resistance to AR inhibitors. Our findings further suggest the important role of decreased PMEPA1 in AR related prostate tumorigenesis. These data highlight that PMEPA1 deficiency may confer resistance to AR inhibitors during CaP progression. This study is supported by the NIH grant (R01CA106653) to SS. Citation Format: Hua E. Li, Daniel Heidenberg, Albert Dobi, Shiv Srivastava. PMEPA1 enhances the prostate cancer cell growth inhibitory effect of MDV3100 and bicalutamide. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1324. doi:10.1158/1538-7445.AM2013-1324