Epigenetic regulation of steroid inactivating UDP-glucuronosyltransferases by microRNAs in prostate cancer

• UGT2B15 and UGT2B17 enzymes are involved in androgen inactivation in cancer cells.
• miR-376c represses UGT expression and DHT inactivation in prostate cancer cells.
• miR-376c is inversely linked to UGT2B15/17 in high-grade disease and in metastasis.

Androgens play a central role in prostate cancer progression. Systemic and local androgen bioavailability is controlled by UDP-glucuronosyltransferases conjugating enzymes (UGT), namely UGT2B15, UGT2B17 and UGT2B28. Reporter vector assays in HEK293 cells initially validated in silico-predicted regulatory potential of candidate miRNAs to target UGT transcripts, including miR-376c, miR-409 and miR-494 for UGT2B17, miR-331-5p and miR-376c for UGT2B15 while none were efficient for UGT2B28. miR-376c was shown as the most effective to downregulate UGT2B15 and UGT2B17 through interactions with a site conserved in both UGTs. Ectopic miR-376c expression in prostate cancer cells significantly reduced UGT2B15 and UGT2B17 expression (>32%; P < 0.005) with a consequent decrease in dihydrotestosterone glucuronidation (−37%; P < 0.001). Consistent with reduced androgen inactivation, ectopic expression of miR-376c changed expression of androgen responsive genes and enhanced cell proliferation with no effect on androgen receptor levels. Sustaining a role of miR-376c in the regulation of androgen-inactivating UGTs, its expression was significantly downregulated in prostatic tumors and further reduced in metastases (P < 0.0001), whereas the opposite was observed for UGT2B15/17 (P = 0.031). In high-grade tumors (Gleason ≥8), UGT2B15/17 and miR-376c were inversely correlated (r = −0.557; P = 0.048) with also a significant relationship in metastases (r = −0.747; P = 0.003). In line with a modification in androgen bioavailability, PSA mRNA levels were also negatively correlated to those of UGT2B15/17 (r = −0.573; P = 0.01) but positively linked to levels of miR-376c (r = 0.577; P = 0.039). This study reveals that the androgen-inactivating UGT2B15 and UGT2B17 genes are direct targets of miR-376c and thus may influence steroid metabolism during prostate cancer progression.