Vol. 295, Issue 3, 986-993, December 2000

Sequence Analyses of CYP2B Genes and Catalytic Profiles for P450s in Qdj:Sprague-Dawley Rats That Lack Response to the Phenobarbital-Mediated Induction of CYP2B2¹

Hideyuki Yamada, Hiromi Matsunaga, Kazuhiro Tsuji, Sanae Matsumoto, Midori Yamamoto, Yuji Ishii, Curtis J. Omiecinski and Kazuta Oguri

Graduate School of Pharmaceutical Sciences, Kyushu University 62, Fukuoka, Japan (H.Y., H.M., K.T., S.M., M.Y., Y.I., K.O.); and Department of Environmental Health, University of Washington, Seattle, Washington (C.J.O.)

The Qdj:Sprague-Dawley (SD) rat is a mutant strain lacking in phenobarbital (PB)-mediated induction of CYP2B2. The presence of interindividual differences in the hepatic content of CYP2B proteins and testosterone 16-hydroxylase activity demonstrated that the breeding colony of Qdj:SD rats involves normal (+/+) and intermediate (+/) phenotypes as well as mutant (/)-type rats. Although PB-treated Qdj:SD (/) rats expressed CYP2B1 normally, testosterone 16-hydroxylase activity in these rats was quite low. Analysis of regioselective metabolism of testosterone and 4-hydroxybiphenyl glucuronidation demonstrated normal catalytic activities associated with other forms of cytochrome P450s, including CYP2A, -2C, and -3A, as well as PB-inducible UDP-glucuronosyltransferase in Qdj:SD (/) rats. There were no serious mutations in the exons of the CYP2B1 gene in Qdj:SD (/) rats, demonstrating that this gene codes a functional CYP2B1. These observations suggest that CYP2B1 needs the interaction with CYP2B2 to exert the full function. The CYP2B2 gene in Qdj:SD (/) rats was the same as that in wild-type (+/+) rats in its length of the region containing all exon/introns and 5'-upstream up to 2.3 kilobase pairs. Malignant mutation such as stop codon formation was not observed in the exons, and no mutation was detected in the region containing the PB-responsive unit. These results strongly suggest that impaired induction of CYP2B2 in Qdj:SD (/) rats is attributable either to mutation at the region different from PB-responsive unit and exons or to absence or lowered expression of trans-acting factor(s) necessary for gene regulation.