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 and N6,O2'-dibutyryl cAMP in hepatocyte cultures. At 100 microM, forskolin significantly inhibited both the phenobarbital-induced CYP3A31 mRNAs expression and the testosterone 6beta-hydroxylation activity related to the CYP3A subfamily in rats, whereas 0.1 microM forskolin potentiated the phenobarbital induction of CYP3A31 mRNA and the testosterone 6beta-hydroxylation activity. Treatment with N6,O2'-dibutyryl cAMP resulted in an inhibition of phenobarbital-induced CYP3A31 gene expression and testosterone 6beta-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 that in vitro induction of CYP3A31 by phenobarbital in Syrian hamster hepatocytes is regulated by a cAMP-dependent pathway.