PHENOBARBITAL INDUCTION AND TISSUE-SPECIFIC EXPRESSION OF THE RAT CYP2B2 GENE IN TRANSGENIC MICE

To investigate molecular events regulating the transcription of genes inducible by phenobarbital, transgenic mouse strains were developed in corporating rat cytochrome P450 2B2 (CYP2B2) genes. Expression in mous e tissues was analyzed for two series of rat CYP2B2 gene constructs, o f 19 and-39 kilobase pairs total length, each containing the entire co ding region, introns, and 3'-flanking sequences of CYP2B2, but differi ng in the respective lengths of 5'-flanking sequence. One group of mic e, whose transgene included the complete 2B2 gene but only 800 base pa irs of 5'-proximal sequence, were not phenobarbital-inducible in mouse liver or in any extrahepatic tissue; rather, these genes were express ed at very high levels constitutively and selectively in only kidney a nd liver. A second group of mice with an identical transgene, except f or the presence of an additional 19 kilobase pairs of 5'-flanking sequ ence, expressed 2B2 only in the liver and at high levels only after ph enobarbital treatment, analogous to the expression pattern observed fo r the endogenous CYP2B2 gene in the rat. These results demonstrate tha t, in vivo, phenobarbital induction and tissue-specific control requir es interaction of regulatory elements far upstream of the core CYP2B2 promoter region and upstream of motifs indicated previously as determi nants of phenobarbital responsiveness.