Analysis of PMEPA1 Isoforms (a and b) as Selective Inhibitors of Androgen and TGF-β Signaling Reveals Distinct Biological and Prognostic Features in Prostate Cancer

Abstract

Dysfunctions of androgen/TGF-β signaling play important roles in prostate tumorigenesis. Prostate Transmembrane Protein Androgen Induced 1 (PMEPA1) inhibits androgen and TGF-β signaling via a negative feedback loop. The loss of PMEPA1 confers resistance to androgen signaling inhibitors and promotes bone metastasis. Conflicting reports on the expression and biological functions of PMEPA1 in prostate and other cancers propelled us to investigate isoform specific functions in prostate cancer (PCa). One hundred and twenty laser capture micro-dissection matched normal prostate and prostate tumor tissues were analyzed for correlations between quantitative expression of PMEPA1 isoforms and clinical outcomes with Q-RT-PCR, and further validated with a The Cancer Genome Atlas (TCGA) RNA-Seq dataset of 499 PCa. Cell proliferation was assessed with cell counting, plating efficiency and soft agar assay in androgen responsive LNCaP and TGF-β responsive PC3 cells. TGF-β signaling was measured by SMAD dual-luciferase reporter assay. Higher PMEPA1-a mRNA levels indicated biochemical recurrence (p = 0.0183) and lower PMEPA1-b expression associated with metastasis (p = 0.0173). Further, lower PMEPA1-b and a higher ratio of PMEPA1-a vs. -b were correlated to higher Gleason scores and lower progression free survival rate (p < 0.01). TGF-β-responsive PMEPA1-a promoted PCa cell growth, and androgen-responsive PMEPA1-b inhibited cancer cell proliferation. PMEPA1 isoforms -a and -b were shown to be promising candidate biomarkers indicating PCa aggressiveness including earlier biochemical relapse and lower disease specific life expectancy via interrupting androgen/TGF-β signaling.

PMEPA1 Gene Isoforms: A Potential Biomarker and Therapeutic Target in Prostate Cancer

“…The analysis of predicted structural features of PMEPA1 protein contains the following three domains: (i) Luminal (N-terminal domain), (ii) Membrane spanning (Transmembrane domain), and (iii) Cytoplasmic. N-terminal domain shows length polymorphisms among the isoforms [ 11 ]. The transmembrane and cytoplasmic domains show highly conservative amino acid sequences.…”

“…Assessments of relative expression of each isoform indicated that PMEPA1-a was most abundant followed by PMEPA1-b and PMEPA1-c in prostate cancer cell lines and human prostate tumor tissues which are defined as major isoforms [ 1 , 11 ]. PMEPA1-d and PMEPA1-e isoforms are marked as minor isoforms with lower transcript levels detected [ 1 ].…”

“…The transcripts of PMEPA1-a , PMEPA1-d , and PMEPA1-c were detected in both AR positive and negative cell lines. In contrast, the expression levels of PMEPA1-b and PMEPA1-e isoforms were found only in AR positive cell lines such as LNCaP, VCaP, LAPC4, CWR22v1 and C4-2B cells but not in AR negative PC-3 and DU-145 cells [ 1 , 11 ]. All of these finding implicated that these isoforms are more associated with androgen or TGF-β regulation in prostate cancer context and their expression levels detected by Q-PCR were showed in Table 3 .…”

“…As a TGF-β responsive gene, PMEPA1 (isoform -a and - d ) also inhibits TGF-β signaling via a negative feedback loop. Additionally, it has been shown that PMEPA1 gene drive tumorigenesis through interference with other signaling cascades such as EGF, Wnt, mutated p53, and Hippo signaling [ 1 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. The elucidation of PMEPA1/STAG1/TMEPAI gene sequences at the mRNA level reveals multiple isoforms.…”

“…The elucidation of PMEPA1/STAG1/TMEPAI gene sequences at the mRNA level reveals multiple isoforms. Currently, 5 PMEPA1 isoforms ( a , b , c , d , and e ) are identified with distinct expression and function pattern in prostate cancer [ 1 , 11 ]. This review highlights the pleiotropic nature of PMEPA1 gene isoforms in the context of molecular structures and cancer biology, especially androgen and TGF-β signaling.…”