Do miRNAs play a role in androgen-induced phenotypic expression in prostate epithelial cells?

Abstract

Activation of the androgen receptor (AR) results in a phenotypic change in androgen-responsive cells; for example, in the human prostate carcinoma cell line LNCaP, androgens mediate proliferation. MicroRNAs (miRNA) are a class of short non-coding RNA that act as post-transcriptional regulators of gene expression; their role in the androgenic phenotype is yet to be fully explored. In the present study, I examined the hypothesis that androgen-mediated effects on gene expression and cellular proliferation are in part mediated through miRNAs. Therefore, exposure to a synthetic AR agonist (mibolerone), a physiological AR agonist (dihydrotestosterone) and a therapeutic AR antagonist (bicalutamide) was studied in LNCaP at four, eight, 24 and 120 hours. The cellular response to these compounds was assessed in terms of proliferation, prostate-specific antigen (PSA) expression and alteration of the miRNA profile. Microarray analysis revealed that a number of miRNAs were altered in a compound-specific and temporal manner. Of note, androgen-induced proliferation and PSA secretion were associated with repression of miR-221 and induction of miR-210. In silico methods identified putative targets of miR-221, such as the transcription factor IRX5. Immunoblotting and a luciferase reporter construct provided preliminary evidence that IRX5 is indeed a novel target of miR-221. Down-regulation of IRX5 is anti-proliferative and pro-apoptotic therefore androgen-mediated repression of miR-221 may contribute to growth. miR-210, a hypoxia-inducible miRNA, was induced under androgenic stimuli with concomitant repression of the Myc-inhibitor Mnt. Efforts were made to elucidate the mechanism of miR-210 induction outside the context of classical HIF1 activation, but further research is required. miR-720 had the highest expression of any individual miRNA in LNCaP cells. DNMT3A was identified as a potential target implicating miR-720 in androgen insensitivity. However, analysis of androgen-insensitive cell lines did not reveal differential expression and its role in prostate epithelial biology remains to be discovered. In summary, the research confirms the hypothesis that androgens can mediate phenotypic change through mechanisms that include miRNA-mediated responses. The data offers insights into androgen-induced processes and identifies new avenues for future research. [For supplementary files please contact author].