Regulation of UDP-Glucuronosyltransferases UGT2B4 and UGT2B7 by MicroRNAs in Liver Cancer Cells

The transcriptional regulation of UDP-glucuronosyltransferases UGT2B4 and UGT2B7 has been well studied using liver cancer cell lines, and post-transcriptional regulation of these two UGTs by microRNA (miRNA/miR) miR-216b-5p was recently reported. This study describes novel miRNA-mediated regulation of UGT2B4 and UGT2B7 in liver cancer cells. Bioinformatic analyses identified a putative miR-3664-3p binding site in the UGT2B7 3'-untranslated region (UTR) and binding sites for both miR-135a-5p and miR-410-3p in the UGT2B4 3'-UTR. These sites were functionally characterized using miRNA mimics and reporter constructs. A miR-3664-3p mimic induced repression of a luciferase reporter carrying the UGT2B7 3'-UTR in liver cancer cell lines; mutation of the miR-3664-3p site abrogated the response of the reporter to the mimic. Similarly, mutation of the miR-135a-5p site or miR-410-3p site in a luciferase reporter bearing UGT2B4 39-UTR abrogated the ability of miR-135a-5p or miR-410-3p mimics to reduce reporter activity. Transfection of miR-3664-3p mimics in HepG2 liver cancer cells significantly reduced mRNA and protein levels of UGT2B7, and this led to reduced enzymatic activity. Transfection of miR-135a-5p or miR-410-3p mimics significantly decreased UGT2B4 mRNA levels in Huh7 liver cancer cells. The expression levels of miR-410-3p were inversely correlated with UGT2B4 mRNA levels in The Cancer Genome Atlas cohort of liver hepatocellular carcinoma (371 specimens) and a panel of ten normal human tissues. Similarly, there was an inverse correlation between miR-135a and UGT2B4 mRNA levels in a panel of 18 normal human liver tissues. Together, these data suggest that miR-135a and miR-410 control UGT2B4 and that miR-3664 controls UGT2B7 expression in liver cancer and/or normal liver cells.