The human cytochrome P450 (CYP) 3A gene subfamily members, which are the major hepatic and intestinal CYPs, are known to biotransform a wide variety of therapeutic drugs. 1,2) In the known functional members which include CYP3A4, CYP3A5 and CYP3A7, 3) CYP3A4 expression is consistently observed in the adult liver, and the alteration of its encoded amino acids due to genetic polymorphisms has been reported. 4) On the other hand, CYP3A5 exhibits polymorphic expression in the human liver; namely, its mRNA and protein are detected in 10 to 30% of human adults. [5][6][7][8] Additionally, CYP3A7, a major human fetal liver form, 9,10) is not expressed in the adult liver. Because of the great personto-person variability in CYP3A expression, care must be exercised when administering therapeutic drugs that are CYP3A substrates.Using a probe drug midazolam, predicting the levels of CYP3A4 and CYP3A5 is possible. 11,12) In these reports, however, CYP3A4 activity was not enough to explain the hepatic metabolism of midazolam. Furthermore, a CYP3A5 specific metabolite of irinotecan was detected. 13) CYP3A5 was reported to be commonly expressed in the human intestine, where "first-pass" metabolism of orally administered therapeutic drugs took place. 1) These results indicate the important role of CYP3A5 in the evaluation of individual differences in drug metabolism.The molecular basis for CYP3A5 polymorphisms has not yet been clearly established. Polymorphisms in the 5Ј-flanking regions might be of general importance in explaining individual differences of CYP3A expression, since a number of gene regulatory elements have been reported. 14,15) Sequencing of the 5Ј-flanking region of the CYP3A5 gene would be beneficial in establishing possible differences in the nucleotide sequence, as no regulatory single nucleotide polymorphisms (SNPs) has been reported. The recently elucidated genomic structure of CYP3As revealed multiple CYP3A5-like sequences including CYP3AP1 as reported by Finta and Zaphiropoulos. 16) This observed sequence similarity made it extremely difficult to analyze the CYP3A5 promoter.In this paper, we constructed a series of primers that were able to distinguish between the CYP3A5 and the CYP3AP1. Furthermore, we sequenced the proximal promoter region of the CYP3A5 gene from 86 established cell lines derived from Japanese individuals as substitute for human samples in order to reveal putative SNPs affecting promoter activity.
MATERIALS AND METHODS
DNA PreparationEstablished cell lines derived from 86 different Japanese individuals were obtained from either the Health Science Research Resources Bank (Osaka, Japan) or the Japanese Collection of Research Bioresources, National Institute of Health Sciences (Tokyo, Japan). These included 82 tumor cell lines (10 leukemias , 8 lymphomas, 18 lung tumors, 6 brain tumors, 2 hepatomas, 14 gastro-intestinal tumors, 3 thyroid carcinomas, 5 reproductive organ tumors, 2 mammary carcinomas, 4 oral tumors, 4 skin tumors, 3 osteosarcomas, and 3 embryonic tumors) and 4 normal cell li...