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 me chanism of this induction, we first studied the effects of cAMP on phe nobarbital-induced CYP3A31 expression using forskolin and N-6,O-2'-dib utyryl cAMP in hepatocyte cultures. At 100 mu M, forskolin significant ly inhibited both the phenobarbital-induced CYP3A31 mRNAs expression a nd the testosterone 6 beta-hydroxylation activity related to the CYP3A subfamily in rats, whereas 0.1 mu M forskolin potentiated the phenoba rbital induction of CYP3A31 mRNA and the testosterone 6 beta-hydroxyla tion activity. Treatment with N-6,O-2'-dibutyryl cAMP resulted in an i nhibition of phenobarbital-induced CYP3A31 gene expression and testost erone 6 beta-hydroxylation activity. Increasing amounts of transfected cAMP-response element binding proteins (CREB) or CREB-binding protein s in hamster hepatocytes reduced the phenobarbital-induction of CYP3A3 1 mRNAs expression. These results suggest that in vitro induction of C YP3A31 by phenobarbital in Syrian hamster hepatocytes is regulated by a cAMP-dependent pathway. (C) 1998 Academic Press.