Regulation of CYP1A and CYP3A mRNAs by ascorbic acid in guinea pigs

In previous studies, we found that the ascorbic acid (AsA) deficiency caused changes in the amounts of the various forms of cytochrome P450 (P450) in liver microsomes from guinea pigs in a form-specific manner. Thus, the aim of this study was to clarify whether the changes seen in the protein contents of the various forms of P450 were associated with the levels of the expression of their mRNAs. Prior to determining the mRNA level, we isolated four cDNA clones, encoding CYP1A2, CYP3A14, CYP3A15, and CYP3A17, from guinea pig liver cDNA libraries to use them as probes in further experiments. The amino acid sequence of the guinea pig CYP1A2 showed identity ranging from 73 to 77% with those of other mammalian P450s. The amino acid sequences among guinea pig CYP3As had about 94% identities with each other. The AsA deficiency apparently decreased the expression of mRNA for CYP1A1 and CYP1A2. These results were in agreement with the decrease in the content of CYP1A1 and CYP1A2 proteins. The amount of P450 protein(s) immunochemically cross-reactive with antibodies to human CYP3A4 was likely unaffected while that of human CYP3A7 tended to be decreased by the AsA deficiency. It suggested that the expression of each CYP3A isozyme was regulated differently by AsA. In fact, the level of mRNA for CYP3A14 was unaffected by the AsA deficiency, while those for CYP3A15 and CYP3A17 were significantly decreased by the AsA deficiency, clearly indicating that the expression of each isozyme within the CYP3A subfamily is differently regulated by AsA. These results support the idea that the transcription of P450 is regulated by AsA in guinea pigs.