EPIGENETIC REGULATION OF MICRORNA EXPRESSION IN PROSTATE CANCER

MicroRNAs are small, non-coding RNA species (19-25nts) which have been found to play a fundamental role in many molecular pathways including embryogenesis, cell differentiation, proliferation and apoptosis. Altered miRNA expression has been correlated with a wide range of disease states and pathologies, including cancer. Recently, there is an increasing body of evidence suggesting that epigenetic regulation of miRNAs via DNA methylation may be an important mechanism in contributing to their deregulation in cancer. We hypothesise that miRNAs with tumour suppressor function may be silenced by epigenetic modifications in prostate cancer (PCa).In this study we have carried out a screen for miRNAs showing altered expression in PCa cell lines. This identified three miRNAs (miR-205, miR-200c, miR-138) that are typically down-regulated in PCa cells and which may be controlled by methylation. We also show that the expression of these miRNAs is generally decreased in prostate tumour biopsy samples compared to matched normal tissue. We demonstrate that these miRNAs are up-regulated by the chemotherapy drug decitabine (5-aza-2’deoxycytidine), which alters DNA methylation levels, and also by reduction in DNA methyltransferase 1 (DNMT1) levels in PCa cells. Methylation levels in the loci of each candidate miRNA were examined in PCa cells and biopsy tissue. We propose that the relative expression of these miRNAs is related to their respective methylation status. In addition, the functionality of the miRNAs in PCa cells has been investigated by examining their effect on cell proliferation, and by measuring expression levels of known and novel target genes. Our findings provide further evidence that profiling of miRNA expression and methylation status has great potential as a basis for a novel biomarker in the diagnosis and prognosis of PCa.