Abstract 1578: Distinct expression and biological functions of PMEPA1 isoforms in prostate cancer
Authors: Sharad Shashwat , Li Hua , Dillman Allissa , Srinivasan Alagarsamy , Dobi Albert , Srivastava Shiv 
Published: July 2017

Introduction and Objectives: The androgen receptor (AR) and TGF-β dysfunctions contribute to prostate cancer (CaP) development and progression. Our laboratory since the discovery of PMEPA1, has established PMEPA1/NEDD4 and AR negative feedback loop and its role in AR regulation in prostate cancer. PMEPA1 gene has also identified as a TGF-β responsive gene and inhibits TGF-β signaling via a negative feedback loop. Five isoforms are transcribed from distinct promoters within the PMEPA1 locus. PMEPA1 isoforms were shown to have variations at the N-terminus of the protein. Our previous study has shown the differential correlations of 2 PMEPA isoforms (PMEPA1 and STAG1) in context of AR expression in CaP. This study focuses on understanding of the expression and biological functions of PMEPA1 isoforms in CaP.

Methods: RNA-Seq data from LNCaP and VCaP cells, and from The Cancer Genome Atlas (TCGA) dataset, were used to evaluate the expression levels of PMEPA1 isoforms. LNCaP cells were treated with R1881 (0, 0.1, 1.0 nM) and DU-145 and PC-3 cells were treated with TGF-β (0, 5 and 25 ng/ml) for 24 hours. PMEPA1 isoform specific plasmids and siRNAs were transfected into LNCaP, DU-145 and PC-3 cells individually. Cell growth was analyzed by cell counting and BrdU incorporation assay. The protein levels of PMEPA1 isoforms and AR were detected by immunoblotting, and the transcript levels were evaluated by QRT-PCR.

Results: Since the annotation of PMEPA1/TMEPA1 isoforms has been empirical in the literature, here we propose a new structure/expression based nomenclature: PMEPA1 (reading frame of 252 amino acids (aa)); PMEPA2 (344aa); PMEPA3 (287aa; STAG1); PMEPA4 (259aa); and PMEPA5 (237aa). Expression of PMEPA1 and PMEPA2 was restricted to androgen responsive prostate cancer cells in comparison to broader expression pattern of other isoforms (PMEPA3-5). The expression of PMEPA1-2 was androgen regulated, whereas expression of PMEPA 3-5 was regulated by TGF-β. Only PMEPA1 inhibited cell growth of LNCaP, DU-145 and PC-3 cells. In contrast, PMEPA2-4 promoted cell growth of DU-145 and PC-3 cells. Of all the isoforms only PMEPA1 mediated AR protein degradation in CaP.

Conclusions: The PMEPA isforms appear to underscore distinct biological functions in the context of androgen and TGF-β signaling. Widely studied PMEPA1 was specific for AR degradation in prostate cancer cells and was consistent with previous observations of association of AR upregulation with loss of PMEPA1 in prostate cancer. The roles of PMEPA isoforms need to be better defined in prostate cancer and other cancers.

Funding: This study was supported by CPDR, USUHS, HU0001-10-2-0002 to DGM.

Citation Format: Shashwat Sharad, Hua Li, Allissa Dillman, Alagarsamy Srinivasan, Albert Dobi, Shiv Srivastava. Distinct expression and biological functions of PMEPA1 isoforms in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1578. doi:10.1158/1538-7445.AM2017-1578