DNMT3A epigenetically regulates key microRNAs involved in epithelial-to-mesenchymal transition in prostate cancer

Epithelial-to-Mesenchymal Transition (EMT) is involved in prostate cancer metastatic progression and its plasticity suggests epigenetic implications. Deregulation of UHRF1/DNMT1, DNMT3A and miRNAs play a role in EMT, but their interplay has not been clarified yet. Here, we identify miR-720 and miR-1260a as new DNMT3A regulators through miRNA microarray performed on UHRF1 silenced Androgen Receptor (AR) non-responsive (PC3) cell extracts, and subsequent target validation and functional overexpression and downregulation in PC3 and AR responsive LNCaP cells, respectively. These miRNAs inversely correlated with DNMT3A in our ex-vivo model of EMT in PC3 but not in LNCaP cells, induced with conditioned media from patient-derived Cancer-Associated Fibroblasts (CM-CAF). miR-720 and miR-1260a were expressed in very few patients from the PRAD TCGA data set expressing an EMT or MET (Mesenchymal-to-Epitelial Transition) signature; miR-200 family (miR-200a/b, -141, -429), along with miR-205 and miR-203, were downregulated in EMT patients as they modulate key EMT factors. These latter miRNAs resulted hyper-methylated at their promoters in our ex-vivo EMT prostate cancer model, while in the EMT PRAD TCGA data set only miR200c and miR141 promoters displayed a diffused hyper-methylated pattern inversely correlated with their transcriptional expression. Chromatin immunoprecipitation experiments performed on CM-CAF induced PC3 cells extracts showed that DNMT3A gets recruited onto the promoters of the latter two miRNAs, coupled with a marked increase of H3K27me3 and H3K9me3 and/or the decrease of H3K4me3 and H3K36me3. Altogether, our results point to a DNMT3A regulatory role of key miRNAs for EMT in prostate cancer.