CYTOCHROME P4502A5 EXPRESSION AND INDUCIBILITY BY PHENOBARBITAL IS MODULATED BY CAMP IN MOUSE PRIMARY HEPATOCYTES

Factors involved in CYP2A5 expression were studied in mouse liver prim ary hepatocytes in culture. CYP2A5-mediated coumarin 7-hydroxylase (CO H) activity was retained in simple culture conditions for at least 96 hours and the activity was inducible up to 33-fold by phenobarbital (P B). The constitutive activity and inducibility of COH was totally bloc ked by treatment of hepatocytes with actinomycin D, and short initial treatment with cycloheximide caused superinducibility when coadministe red with PB. Treatment of hepatocytes with inhibitors of protein kinas e C, tyrosine kinases and a generator of nitric oxide did not affect C OH basal activity or inducibility. Administration of dibutyryl cAMP, f orskolin, and 3-isobutyl-1-methyl-xanthine (IBMX) enhanced both basal and PB-induced COH activities and CYP2A5 mRNA levels, indicating that cAMP plays a major role in CYP2A5 expression. (C) 1994 Academic Press, Inc.