MUTAGENIC ACTIVATION OF PROCARCINOGEN IN EXTRAHEPATIC TISSUES -CONTRIBUTION OF CYP4B1-

Abstract

A new P450 responsible for mutagenic activation of 3-methoxy-4-aminoazobenzene (3-MeO-AAB) which is a potent procarcinogen was purified from renal microsomes of male mice using an index of umu gene expression. The purified P450 had high bioactivation toward 2-aminofluorene (2-AF), 2-aminoanthracene (2-AA), and 3, 3'-dichlorobenzidine (DCB) as well as 3-MeO-AAB. The antibody against this P450 completely inhibited mutagenic activation of 3-MeO-AAB, 2-AF, 2-AA, and DCB by mouse renal microsomes. With immunoblotting, this form was present abundantly in renal microsomes of male mice but not in those of female mice. This P450 was also present in mouse pulmonary and bladder microsomes but not in hepatic microsomes. The NH2-terminal amino acid sequence analysis indicated that this form belonged to the CYP4B subfamily. Thus, mouse kidney cDNA library was screened with rat CYP4B1 probe. The cDNA-deduced amino acid sequence of isolated cDNA consisted of 511 amino acids and the NH2-terminal amino acid sequence of the purified renal P450 agreed with the cDNA-deduced amino acid sequence, indicating that renal P450 purified in this study is mouse CYP4B1. Human pulmonary and renal cDNA library were screened with mouse CYP4B1 cDNA probe. Two full-length cDNAs were isolated and they had two or three amino acid changes to human CYP4B1 reported previously.