VDR regulation of microRNA differs across prostate cell models suggesting extremely flexible control of transcription

The Vitamin D Receptor (VDR) is a member of the nuclear receptor superfamily and is of therapeutic interest in cancer and other settings. Regulation of microRNA (miRNA) by the VDR appears to be important to mediate its actions, for example, to control cell growth. To identify if and to what extent VDR-regulated miRNA patterns change in prostate cancer progression, we undertook miRNA microarray analyses in 7 cell models representing non-malignant and malignant prostate cells (RWPE-1, RWPE-2, HPr1, HPr1AR, LNCaP, LNCaP-C4-2, and PC-3). To focus on primary VDR regulatory events, we undertook expression analyses after 30 minutes treatment with 1α,25(OH)2D3. Across all models, 111 miRNAs were significantly modulated by 1α,25(OH)2D3 treatment. Of these, only 5 miRNAs were modulated in more than one cell model, and of these, only 3 miRNAs were modulated in the same direction. The patterns of miRNA regulation, and the networks they targeted, significantly distinguished the different cell types. Integration of 1α,25(OH)2D3-regulated miRNAs with published VDR ChIP-seq data showed significant enrichment of VDR peaks in flanking regions of miRNAs. Furthermore, mRNA and miRNA expression analyses in non-malignant RWPE-1 cells revealed patterns of miRNA and mRNA co-regulation; specifically, 13 significant reciprocal patterns were identified and these patterns were also observed in TCGA prostate cancer data. Lastly, motif search analysis revealed differential motif enrichment within VDR peaks flanking mRNA compared to miRNA genes. Together, this study revealed that miRNAs are rapidly regulated in a highly cell-type specific manner, and are significantly co-integrated with mRNA regulation.