MiR-27a-3p: An AR-modulatory microRNA with a distinct role in prostate cancer progression and therapy

193 Background: Prostate cancer (PCa) is an androgen dependent malignancy. PCa patients initially respond to androgen ablation but eventually the disease becomes castrate resistant. MicroRNAs (miRs) are considered to be master regulators of gene expression and could be potential biomarkers and therapeutic targets for PCa. We previously showed miR-27a-3p to be an androgen receptor (AR)-modulatory oncomiR, with a role in PCa progression. Methods: RNA sequencing was carried out on xenograft tumours treated with an inhibitory antisense oligonucleotide for miR-27a (ASO-27a), or control. Differentially expressed genes were cross-referenced with publicly available patient tissue datasets. ASO-27a was transfected in a panel of PCa cell lines mirroring disease progression, to verify changes in transcriptional and translational levels. Immunohistochemical analysis of encoded proteins was undertaken in a cohort of 46 PCa patients with Gleason 3+4 or 4+3 disease and compared with normal tissue-control. Results: Putative target genes tested included the tumour suppressor HIP2, the oncogenes SRC3, YAP, and PAX3, which can act both as oncogene and tumour suppressor. MRNA or protein levels of the majority of those genes tested were upregulated after ASO-27a treatment of PCa cell lines. In 22Rv1 cells, HIPK2 mRNA levels were significantly upregulated with ASO-27a (p = 0.0137), while protein levels were downregulated . PAX3 mRNA levels were significantly reduced by ASO-27a in 22Rv1 cells (p = 0.0364), while protein levels were significantly increased (p = 0.0112). Immunohistochemically, PAX3 protein was lower in Gleason 7 tumours than in normal tissue, while YAP expression was higher in patients with Gleason 4+3, relative to those with 3+4. SRC3 immunostaining was slightly, but not significantly, higher in patients with 3+4 compared to 4+3. Conclusions: MiR-27a-3p is an AR-modulatory oncomiR in PCa, with potential as a therapeutic target. MiR-27a interaction with its target genes and especially HIPK2, YAP, SRC3 and PAX3 could provide the basis for therapeutic advance in screening and in the treatment of castrate resistant disease, through ASO-27a inhibition.