Sequence analyses of CYP2B genes and catalytic profiles for P450s in Qdj:Sprague-dawley rats that lack response to the phenobarbital-mediated induction of CYP2B2.
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 16beta-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 16beta-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.
Yamada
H
H
Graduate School of Pharmaceutical Sciences, Kyushu University 62, Fukuoka, Japan.
Matsunaga
H
H
Tsuji
K
K
Matsumoto
S
S
Yamamoto
M
M
Ishii
Y
Y
Omiecinski
C J
CJ
Oguri
K
K
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D002384:Catalysis; D019362:Cytochrome P-450 CYP2B1 / Q000096:biosynthesis / Q000235:genetics*; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000235:genetics*; D004790:Enzyme Induction / Q000187:drug effects; D008297:Male; D010634:Phenobarbital / Q000494:pharmacology*; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D013250:Steroid Hydroxylases / Q000096:biosynthesis / Q000235:genetics*
D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1; C025619:steroid 16-beta-hydroxylase; D010634:Phenobarbital