Regulation of CYP 2 A 5 induction by porphyrinogenic agents in mouse primary hepatocytes.
All cytochrome P450 (CYP) enzymes contain heme as a prosthetic group. In contrast to other CYP enzymes, murine CYP 2 A 5 is upregulated in vivo by several agents that disturb cellular heme balance. To test the hypothesis that porphyrinogenic agents have the common feature of being able to increase CYP 2 A 5 expression, mouse liver primary hepatocytes were exposed to various porphyrinogenic chemicals and changes in CYP 2 A 5 catalytic activity and levels of mRNA were monitored. Phenobarbital increased hepatic CYP 2 A 5-mediated coumarin 7-hydroxylase (COH) activity (13.2-fold) and the amount of CYP 2 A 5 steady-state mRNA (10.6-fold). Hepatocyte COH activity was increased also by the ferrochelatase inhibitor griseofulvin and the protoporphyrinogen oxidase inhibitor acifluorfen (about 9-fold induction). Of these inducers, only phenobarbital affected CYP 1 A 12 and CYP 2 B 10 expression. In contrast, many other porphyrinogenic agents such as cobalt, 2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ), 1-[4-(3-acetyl-2,4,6-trimethylphenyl)-2,6-cyclohexanedionyl]-O-eth yl propionaldehyde oxime (ATMP), aminotriazole, and thioacetamide either decreased or had no effect on CYP 2 A 5. The increases in COH activity and CYP 2 A 5 mRNA were unaffected by combined treatment with the inducers and heme arginate, suggesting that heme is not a regulator of CYP 2 A 5 induction. Treatment with actinomycin D totally abolished both constitutive CYP 2 A 5 expression and its inducibility, suggesting that a transcriptional component is involved. These data suggest that, in mouse primary hepatocytes, CYP 2 A 5 induction is not a universal response to disturbed cellular heme biosynthesis.
Salonpää
P
P
Department of Pharmacology and Toxicology, University of Oulu, Finland.
Kottari
S
S
Pelkonen
O
O
Raunio
H
H
D000818:Animals; D001120:Arginine / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases; D002478:Cells, Cultured; D065637:Cytochrome P-450 CYP2A6; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D003609:Dactinomycin / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D006118:Griseofulvin / Q000494:pharmacology*; D006418:Heme / Q000494:pharmacology; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D006899:Mixed Function Oxygenases / Q000096:biosynthesis* / Q000235:genetics; D009579:Nitrobenzoates / Q000494:pharmacology*; D010634:Phenobarbital / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis
D009579:Nitrobenzoates; D012333:RNA, Messenger; D003609:Dactinomycin; D006118:Griseofulvin; D006418:Heme; D003577:Cytochrome P-450 Enzyme System; D001120:Arginine; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6; C018425:acifluorfen; C048849:heme arginate; D010634:Phenobarbital