A Major Glucocorticoid-Inducible P450 in Rat Liver Is Not P450 3A11

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Abstract
A new P450 3A cDNA (RL33) has been cloned from a liver cDNA library of untreated male rat. RL33 is 2032 nucleotides in length and has an open reading frame of 502 amino acid residues. The nucleotide sequence of its 5'-noncoding region is completely identical with that of a genomic clone of P450 3A1 isolated by Burger et al. [Proc. Natl. Acad. Sci. USA 89, 2145–2149 (1992)]. Compared with rat P450 3A1, P450 RL33 showed 98 and 97% identities in the nucleotide and deduced amino acid sequences, respectively, with the deletion of 2 amino acids and substitution of 12 amino acids. These residues were localized around amino acids 107–230. Recently Kirita and Matsubara have isolated the same P450 3A cDNA (cDEX) from dexamethasone (DEX)-treated rat liver [Arch. Biochenu Biophys. 307, 253–258 (1993)]. Northern blot analysis using an oligonucleotide probe specific for P450 RL33/ cDEX revealed that P450 RL33/cDEX mRNA was induced strongly by pregnenolone 16 a-carbonitrile and DEX and weakly by phenobarbital (PB) and triacetyloleandomycin. We constructed a P450 3A cDNA library by the reverse transcriptase-polymerase chain reaction using common primers to P450 RL33/cDEX, 3A1, and 3A2, and subcloned the cDNAs into pUC119. The expression level of P450 RL33/cDEX mRNA was investigated by identifying each clone with the above oligonucleotide probe. P450 RL33/cDEX mRNA represented over 70% of the total P450 3A mRNA from untreated, PB-, and DEX-treated rat liver. These results indicated that the major DEX-inducible form of P450 3A is P450 RL33/ cDEX and not P450 3A1.

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