Abstract 1806: Distinct PMEPA1 gene isoforms regulate androgen-responsive or TGF-β-responsive prostate cancers
Authors: Li Hua , Sharad Shashwat , Ravindranath Lakshmi , Petrovics Gyorgy , Chen Yongmei , Rosner Inger L. , Dobi Albert , Srivastava Shiv 
Published: August 2018

Introduction: PMEPA1 gene has been defined as androgen and TGF-β responsive gene to inhibit AR and TGF-β signaling via negative feedback loops. Our previous studies identified five PMEPA1 isoforms (PMEPA1-252, PMEPA1-287, PMEPA1-237, PMEPA1-259 and PMEPA1-344) in prostate cancer (CaP) cell lines and CaP RNA-Seq data. PMEPA1-252 decreased androgen receptor (AR) protein levels, suppressed AR signaling and inhibited CaP cell growth. In contrast, PMEPA1-287 and PMEPA1-259 inhibited the transcript levels of TGF-β responsive genes and promoted CaP cell growth. Previous studies showed that knockdown of PMEPA1 gene in PC-3 cells facilitated bone metastasis via activating TGF-β signaling and increasing bone metastasis associated genes. In this study, we further study the roles of PMEPA1 isoforms in the context androgen resistance and bone metastasis process in CaP.

Methods: The expression vectors harboring PMEPA1 isoforms were transfected into DU-145 and PC-3 cells. The protein levels of PMEPA1 isoforms, TGF-β receptor I, SMAD2 and 3 were detected by immunoblotting. The TGF-β signaling activity was measured by SMAD reported dual-luciferase assay in DU-145 and PC-3 cells. The transcript levels of PMEPA1 isoforms and AR or TGF-β responsive genes including KLK3 (PSA), THBS1, NEDD9, bone metastasis associated genes, such as SPARC, CTGF, IL11 and PTHRP were assessed by quantitative PCR (Q-PCR).

Results: PMEPA1-287 and PMEPA1-259 inhibited SMAD reporter activity in DU-145 and PC-3 cells. No PMEPA1 isoform was found to down-regulate the protein levels of TGF-β receptor I and SMAD2 and 3. Increased TGF-β signaling was detected in androgen independent LAPC4-AI and C4-2B cells. In contrast, AR signaling and PMEPA1-252 increased in C4 cells, but not in C4-2 and C4-2B cells. Decreased transcript level of PMEPA1-259 was detected in C4-2 and C4-2B cells, while PMEPA1-287 was found to decrease in C4-2 cells but increase in C4-2B and LAPC4-AI cells. No significant changes of transcript levels of PMEPA1-344 and PMEPA1-237 were detected. In 120 matched human benign and malignant frozen prostate tissues, only PMEPA1-252 associated with SPARC showing inverse correlation. The expression of SPARC was not responsive to either androgen or TGF-β in CaP cells, but increase significantly in C4-2B cells compared to LNCaP cells. These findings suggested PMEPA1 isoforms drive bone metastasis and androgen resistance development via interrupting AR/TGF-β signaling and bone metastasis associated genes.

Conclusions: Our results provide a plausible explanation for the dual function of PMEPA1 gene through its alternative isoforms in the process of prostate cancer progression from androgen dependent to TGF-β dependent/androgen resistant stages of the disease. These findings may lead to new therapeutic opportunities in standard hormone ablation and TGF-β targeted therapies of CaP.

Citation Format: Hua Li, Shashwat Sharad, Lakshmi Ravindranath, Gyorgy Petrovics, Yongmei Chen, Inger L. Rosner, Albert Dobi, Shiv Srivastava. Distinct PMEPA1 gene isoforms regulate androgen-responsive or TGF-β-responsive prostate cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1806.