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Description
UDP-glucuronosyltransferases (UGTs) and cytochromes P450 (P450s, CYPs) are a family of enzymes that catalyze glucuronidation and oxidation. Although these are membrane proteins bound to the endoplasmic reticulum, their topologies are distinct. Therefore, these proteins are considered to function independently. Cumulative evidence suggests that protein¬¬–protein interactions exist between P450 and UGT. CYP3A4 modulates the catalytic properties of UGT isoforms. CYP3A4 is involved in the metabolism of 50% of all drugs. While we have previous knowledge of how P450 modulates UGT activity, UGT can also modulate P450 activity. To address this issue, we set up a system to co-express CYP3A4, NADPH-P450 reductase, and the major human UGT isoforms UGT2B7/UGT1A9 by utilizing a baculovirus–insect cell expression system. We compared CYP3A4 function in the presence and absence of co-expressed UGT2B7/UGT1A9. UGT1A9 and UGT2B7 attenuated CYP3A4 activity. Kinetic studies showed that both UGTs reduced the Vmax of CYP3A4 activity. Recently, we established Ugt2b1-knockout (KO) mice using the CRISPR-Cas9 method. The hepatic Cyp3a expression levels in these mice were comparable. Kinetic analysis revealed that Cyp3a activity under constitutive conditions was sigmoidal and was not markedly altered by Ugt2b1 deficiency. After phenobarbital (PB)treatment, Vmax of Cyp3a activity was significantly increased in both wild-type and Ugt2b1-KO mice. Furthermore, the S50 of Cyp3a activity was lower in the PB-treated Ugt2b1-KO mice. Taken together, these results suggest that Ugt2b1 negatively modulates hepatic Cyp3a activity in mice.
