Molecular characterization of a novel androgen receptor transgene responsive to MicroRNA mediated post-transcriptional control exerted via 3'-untranslated region.

Background: Androgen Receptor (AR) gene is associated with Prostate cancer (PCa) and hence targeting androgen-and AR-signaling axis remains the most promising primary therapeutic option to treat the disease. The AR mRNA has a 6.8 kb long 3'-untranslated region (UTR) which harbors several experimentally validated and numerous predicted miRNA binding sites. AR 3'-UTR is likely to positively or negatively regulate AR expression by interacting with miRNAs and possibly other trans-acting auxiliary factors including 3'-UTR RNA binding proteins. In this context, systematic understanding of the regulatory role of AR 3'-UTR in intrinsic post-transcriptional control of AR gene expression is of significance to understand AR related diseases including PCa.

Methods: In this study, we have constructed a heterologous reporter system in which Firefly luciferase and AR expression is experimentally influenced by the presence of AR 3'-UTR and its interactions with ectopically expressing miRNA.

Results: The expression of AR 3'-UTR containing reporters, including the Firefly luciferase and the AR open reading frame (ORF) were repressed by the overexpression of miR-488* mimics. In addition, the AR expressed from 3'-UTR containing expression vectors was fully functional in its transactivation function as determined by a prostate specific antigen (PSA) reporter assay. Further, by using confocal microscopy we also demonstrate that AR can translocate to the nucleus upon DHT activation confirming the functional ability of AR.

Conclusions: AR transgenes with AR 3'-UTR fragments closely resemble the endogenous AR expression than any other previously characterized AR expression constructs. The 3'-UTR containing AR expression system is amiable to post-transcriptional manipulations including miRNA mediated repression of AR expression. This AR reporter system has the potential to be used in determining specificity of AR targeting miRNAs and their role in AR functional regulatory networks. Prostate 76:834-844, 2016. © 2016 Wiley Periodicals, Inc.