Evidence for Involvement of cAMP-Dependent Pathway in the Phenobarbital-Induced Expression of a Novel Hamster Cytochrome P450, CYP3A31

Recently, we isolated a novel Syrian hamster cDNA clone that encodes a protein which has been named CYP3A31. In primary hepatocyte cultures, CYP3A31 is dramatically induced by phenobarbital. To elucidate the mechanism of this induction, we first studied the effects of cAMP on phenobarbital-induced CYP3A31 expression using forskolin andN6,O2′-dibutyryl cAMP in hepatocyte cultures. At 100 μM, forskolin significantly inhibited both the phenobarbital-induced CYP3A31 mRNAs expression and the testosterone 6β-hydroxylation activity related to the CYP3A subfamily in rats, whereas 0.1 μM forskolin potentiated the phenobarbital induction of CYP3A31 mRNA and the testosterone 6β-hydroxylation activity. Treatment withN6,O2′-dibutyryl cAMP resulted in an inhibition of phenobarbital-inducedCYP3A31gene expression and testosterone 6β-hydroxylation activity. Increasing amounts of transfected cAMP-response element binding proteins (CREB) or CREB-binding proteins in hamster hepatocytes reduced the phenobarbital-induction of CYP3A31 mRNAs expression. These results suggest thatin vitroinduction of CYP3A31 by phenobarbital in Syrian hamster hepatocytes is regulated by a cAMP-dependent pathway.