Abstract 4679: Silencing of PMEPA1, a NEDD4 E3 ubiquitin ligase binding protein, stabilizes androgen receptor and confers resistance to AR inhibitors
Authors: Li Hua , Umeda Elizabeth , Song Yingjie , Young Denise , Ravindranath Lakshmi , Mohamed Ahmed , Sharad Shashwat , Petrovics Gyorgy , McLeod David , Sesterhenn Isabell , Sreenath Taduru , Dobi Albert , Srivastava Shiv 
Published: August 2015

INTRODUCTION: The androgen receptor (AR) dysfunctions contribute to prostate cancer (CaP) development and progression. Earlier we defined the regulation of AR protein levels by a negative feed-back loop between AR and the androgen regulated PMEPA1, a NEDD4 E3 ubiquitin ligase binding protein. Our data also revealed decreased or absent PMEPA1 transcripts in 65% prostate tumors. This study focuses on the relationship of PMEPA1 protein with AR and its transcriptional targets (PSA) in human CaP, as well as the impact of PMEPA1 silencing on growth of PMEPA1-shRNA LNCaP cells derived tumors in naïve and castrated nude mice.

METHODS: Ten weeks old athymic Ncr-nu/nu mice were evaluated for the growth of tumor xenografts derived from PMPEA1-shRNA LNCaP (N = 20) and control-shRNA LNCaP cells (N = 20). Each mouse received 4×106 cells by subcutaneous injection to right flank side. The mice with tumors were castrated at 9th week post-injection. The tumor sizes were monitored twice per week until 16th week post-injection. The xenograft tissues were assayed by immunohistochemical (IHC) staining for PMEPA1, AR and PSA protein levels. The AR, PMEPA1 and PSA expressions in whole mount human prostate specimens were evaluated by IHC staining and QRT-PCR.

RESULTS: The PMEPA1 shRNA-LNCaP and control shRNA-LNCaP cells started to form subcutaneous tumors at 4 weeks after injections. However, the growth rate of PMEPA1 shRNA-LNCaP derived tumors was significantly faster than control derived tumors (P&lt;0.05). PMEPA1 shRNA-LNCaP tumors expressed higher levels of AR and PSA proteins as assessed by IHC. At 7 weeks after castration the tumor sizes increased by 69% in the control group in contrast to 304% in the PMEPA1-shRNA harboring xenografts (P&lt;0.05). In human CaP, decreased PMEPA1 mRNA expression significantly correlated with increased levels of AR transcription target PSA, as a surrogate for elevated AR. Focally increased PSA and AR protein levels were detected in a subset of low PMEPA1 expressing tumors.CONCLUSIONS: PMEPA1 silencing in CaP cells leads to gain of AR, increased tumor growth with potential to induce resistance to AR inhibition targeted therapy. Decreased PMEPA1 in human CaP correlated with increased AR activity. Thus, monitoring PMEPA1 expression in CaP cells offers new opportunities in therapeutic stratification of CaP. Further, restoring PMEPA1 in CaP cells may provide a new strategy for AR degradation focused therapy.

Citation Format: Hua Li, Elizabeth Umeda, Yingjie Song, Denise Young, Lakshmi Ravindranath, Ahmed Mohamed, Shashwat Sharad, Gyorgy Petrovics, David McLeod, Isabell Sesterhenn, Taduru Sreenath, Albert Dobi, Shiv Srivastava. Silencing of PMEPA1, a NEDD4 E3 ubiquitin ligase binding protein, stabilizes androgen receptor and confers resistance to AR inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4679. doi:10.1158/1538-7445.AM2015-4679