Forskolin-mediated induction of CYP3A1 mRNA expression in primary rat hepatocytes is independent of elevated intracellular cyclic AMP.
Previously, we demonstrated that elevated levels of cyclic AMP (cAMP) repressed phenobarbital (PB)-inducible cytochrome P450 (CYP)2B gene expression in primary rat hepatocyte cultures. Although CYP3A1 induction by PB was similarly repressed by most of the cAMP-enhancing strategies, forskolin additions in particular resulted in marked stimulation of CYP3A1 expression. Here we examined whether this effect was due to forskolin's ability to activate adenylate cyclase. By using a specific ELISA for assessment of intracellular cAMP levels, we determined that forskolin and a water-soluble analog (L858051; 7 beta-desacetyl-7 beta-(N-methylpiperazine)) were equipotent in stimulating adenylate cyclase activity. However, only forskolin and its inactive 1,9-dideoxy analog were active as inducers of CYP3A1. In comparative studies, both dexamethasone and PB were ineffective in stimulating production of intracellular cAMP. Furthermore, treatment of hepatocytes with glucagon, dibutyryl-cAMP, or N6O2'-dibutyryl-cyclic GMP, resulted in no detectable enhancement of CYP3A1 gene expression. These results demonstrated that CYP3A1 induction by forskolin is independent of cAMP, and instead is likely to involve a direct chemical effect of forskolin on the CYP3A1 activation pathway.
Sidhu
J S
JS
Department of Environmental Health, University of Washington, Seattle, USA.
Omiecinski
C J
CJ
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000096:biosynthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000235:genetics; D051381:Rats; D013268:Stimulation, Chemical
D010726:Phosphodiesterase Inhibitors; D012333:RNA, Messenger; D005576:Colforsin; D003577:Cytochrome P-450 Enzyme System; D000242:Cyclic AMP; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C104464:CYP3A protein, human; C465138:Cyp3a23-3a1 protein, rat; D051544:Cytochrome P-450 CYP3A