Mechanism of induction of cytochrome P-450 by phenobarbital.
Treatment of rats with phenobarbital (PB) leads to a substantial increase in the hepatic levels of translatable polysomal poly(A) + cytochrome P-450 mRNA. An enriched fraction of P-450 mRNA was obtained by agarose gel electrophoresis and used to prepare a cDNA probe by differential hybridization to total mRNA from control and PB-treated rats. The majority of the sequences within the probe hybridized to recombinant DNA plasmids which contained a bona fide P-450 cDNA insert identified by positive hybridization selection and in vitro translation. The cDNA probe was used to demonstrate that PB treatment leads to a 30-fold increase in polysomal P-450 mRNA, which is not due to more efficient utilization of previously existing mRNA but to the appearance of new messenger in the cytoplasm. The induction of cytoplasmic P-450 mRNA by PB was rapid, with increases detected within 3 h of PB injection and steady state levels reached in approximately 20 h. The data suggest that the increase in cytoplasmic P-450 protein levels observed after PB treatment may be totally accounted for by an enhanced rate of synthesis resulting from translation of higher cytoplasmic levels of its specific mRNA. The P-450 mRNA was almost exclusively segregated into the membrane-bound polysome compartment was expected for an mRNA coding for an integral membrane protein of the endoplasmic reticulum.
D000818:Animals; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics*; D004274:DNA, Recombinant / Q000378:metabolism; D004790:Enzyme Induction; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology*; D011061:Poly A / Q000235:genetics; D011132:Polyribosomes / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats
D004274:DNA, Recombinant; D012333:RNA, Messenger; D011061:Poly A; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital