Regulation of UGT2A1 by miR-196a-5p and miR-196b-5p

UDP-glucuronosyltransferase (UGT) 2A1 is an important enzyme in the detoxification of polycyclic aromatic hydrocarbons found in cigarette smoke. This enzyme is expressed in aerodigestive tract tissues including lung as both its wild-type and exon 4-deleted splice variant isoforms, with the latter acting as a negative regulator of wild-type UGT2A1 activity. UGT2A1 regulation may also be mediated by microRNA (miRNA). To identify miRNA important in the regulation of UGT2A1, expression analysis in tandem with in silico analysis suggested miR-196a-5p and miR-196b-5p as potential top candidates. Significant reductions in firefly luciferase activity were observed in human embryonic kidney cell line 293 cells cotransfected with the wild-type UGT2A1 3'-untranslated region (UTR)-containing luciferase plasmid and either miR-196a-5p (62%, P = 0.00080) or nniR-196b-5p (60%, P = 0.00030) mimics. In pull-down assays, there was a 3.4- and 5.2-fold increase in nniR-196a-5p (P = 0.054) and nniR-196b-5p (P = 0.035), respectively, using the UGT2A1 3'-UTR biotinylated mRNA probe as compared with the beta-actin coding region control mRNA probe. UGT2A1 mRNA was reduced by 25% (P = 0.058) and 35% (P = 0.023) in H146 and H1944 cells, respectively, after overexpression of the miR196a-5p mimic. A similar 32% (P = 0.030) and 41 % (P = 0.016) reduction was observed after over-expression of the nniR-196b-5p mimic. In H146 cells transfected with miRNA mimic together with a small interfering RNA (siRNA) specific for the UGT2A1 splice variant, a significant reduction in 3-hydroxy-benzo[a]pyrene-glucuronide formation was observed. The nniR-196a-5p- and nniR-196b-55p-treated cells exhibited reductions of 35% (P = 0.047) and 44% (P = 0.0063), respectively. These data suggest that miR196a-5p and nniR-196b-5p play an important role in UGT2A1 regulation within the lung and potentially other aerodigestive tract tissues.