Complementary DNA and protein sequences of ethanol-inducible rat and human cytochrome P-450s. Transcriptional and post-transcriptional regulation of the rat enzyme.

Abstract

The cDNAs encoding ethanol-inducible forms of rat and human cytochrome P-450s have been isolated, sequenced, and used to study the expression of this cytochrome P-450 during development and by various inducing agents. Polyclonal antibody against ethanol-inducible cytochrome P-450 was used to screen rat and human lambda gt11 cDNA expression libraries. The longest cDNAs obtained from each library were completely sequenced, and the deduced amino acid sequence of the rat cDNA was found to correspond to P450j based on the published amino-terminal sequence. The rat and human cytochrome P-450s both contained 493 amino acids and calculated molecular masses of 56,634 and 56,916 daltons, respectively. Human P450j shared 75% nucleotide and 78% amino acid similarities to the respective orthologous rat cDNA and deduced amino acid sequences. Amino acid alignment also revealed that P450j was 48% similar to P450b and P450e, the major phenobarbital-inducible forms, and 54% similar to P450PB1 and P450f, two developmentally regulated forms. Southern blot analyses of rat and human genomic DNAs verified that only a single gene shared extensive homology with P450j. The expression of P450j was found to be developmentally regulated. No immunodetectable protein or P450j mRNA was present in newborn rats; however, rapid increases in P450j mRNA and protein occurred within 1 week after birth in both male and female rats. The levels of P450j and its mRNA thereafter remained elevated up to 12 weeks of age in both sexes. The increases in both P450j and its mRNA paralleled the change in aniline hydroxylase activity during development. Run-on transcriptional analysis confirmed that these increases were due to transcriptional activation of the P450j gene. In contrast to transcriptional activation during development, induction of P450j by various agents such as pyrazole, 4-methylpyrazole, and acetone might be due to post-transcriptional events. A 4-fold elevation in both enzymatic activity and immunodetectable P450j was not accompanied by an increase in P450j mRNA level.