MiR-21 Is Induced by Hypoxia and Down-Regulates RHOB in Prostate Cancer

Simple Summary: A low level of oxygen (hypoxia) is a common feature of many solid tumours. Tumour hypoxia is a contributing factor to prostate cancer progression and is known to cause the abnormal expression of many important genes, including microRNAs. In this study, we investigate the link between hypoxia and microRNA-21 (miR-21) in prostate cancer cells. We use in vitro and in vivo models to show that miR-21 expression is induced by hypoxia in prostate cells, which we propose explains why miR-21 up-regulation is a feature of prostate tumours. We demonstrate that miR-21 up-regulation can alter the behaviour of normal prostate cells and we further show for the first time in prostate cancer that it down-regulates RHOB, a tumour suppressor gene. We finish by presenting data to suggest miR-21 has considerable potential as a biomarker of hypoxia that can aid in the diagnosis and prognosis of prostate cancer. Abstract: Tumour hypoxia is a well-established contributor to prostate cancer progression and is also known to alter the expression of several microRNAs. The over-expression of microRNA-21 (miR-21) has been consistently linked with many cancers, but its role in the hypoxic prostate tumour environment has not been well studied. In this paper, the link between hypoxia and miR-21 in prostate cancer is investigated. A bioinformatic analysis of The Cancer Genome Atlas (TCGA) prostate biopsy datasets shows the up-regulation of miR-21 is significantly associated with prostate cancer and clinical markers of disease progression. This up-regulation of miR-21 expression was shown to be caused by hypoxia in the LNCaP prostate cancer cell line in vitro and in an in vivo prostate tumour xenograft model. A functional enrichment analysis also revealed a significant association of miR-21 and its target genes with processes related to cellular hypoxia. The over-expression of miR-21 increased the migration and colony-forming ability of RWPE-1 normal prostate cells. In vitro and in silico analyses demonstrated that miR-21 down-regulates the tumour suppressor gene Ras Homolog Family Member B (RHOB) in prostate cancer. Further a TCGA analysis illustrated that miR-21 can distinguish between different patient outcomes following therapy. This study presents evidence that hypoxia is a key contributor to the over-expression of miR-21 in prostate tumours, which can subsequently promote prostate cancer progression by suppressing RHOB expression. We propose that miR-21 has good potential as a clinically useful diagnostic and prognostic biomarker of hypoxia and prostate cancer.