Expression and inducibility of UDP-glucuronosyltransferases 1-naphthol in human cultured hepatocytes and hepatocarcinoma cell lines

The UDP-glucuronosyltransferase (UGTs) isoforms involved in the conjugation of 1-naphthol were characterized in human cultured hepatocytes and in two human hepatocarcinoma cell lines, KYN-2 and Mz-Hep-1 in terms of expression, kinetics and induction by drugs. Their properties were compared to those of UGT1∗6 stably expressed in the V79 cell line (V79UGT1∗6), which glucuronidates 1-naphthol preferentially. The determination of kinetic constants for glucuronidation of 1-naphthol revealed a two-site model in human hepatocytes, but a one-site model in the two hepatocarcinoma cell lines. Southern blot analysis of RT-PCR products, showed that the UGT1∗6 mRNA was expressed in KYN-2, but not in Mz-Hep-1 cells. However, a mRNA encoding a UGT different from UGT1∗6 was expressed in Mz-Hep-1 cells. The two inducers, β-naphthoflavone and rifampicin exerted a differential effect, depending on the cell lines considered. Altogether, the results suggest that, in hepatocytes, two UGT isoforms, which glucuronidate 1-naphthol are expressed and are differentialy regulated by inducers. Both KYN-2 and Mz-Hep-1 cells express one of the two different UGT isoforms found in hepatocytes. The UGT isoform present in KYN-2 cells corresponds to UGT1∗6, whereas in Mz-Hep-1 cells the UGT isoform present was different from UGT1∗6 and UGT1∗7.