Cis-acting sequences from the rat cytochrome P4502B1 gene confer pulmonaryand phenobarbital-inducible expression in transgenic mice

Specific cytochrome P450 enzymes show tissue-specific induction, and differ ent regulatory units for expression of these enzymes have been identified. The regulation of the phenobarbital (PB)-inducible P450 genes has been rela tively well characterized in terms of PB induction, but less so with regard to tissue-specific expression. CYP2B2 is not expressed in the rat lung, wh ereas cytochrome P450 2B1 (CYP2B1) is a dominating enzyme in the same tissu e. The constitutive expression of CYP2B1 and CYP2B2 in liver is low, but in ducible by PB, whereas the pulmonary expression of CYP2B1 is not induced by PB. This indicates utilization of different regulating mechanisms in the t wo organs. A gene construct consisting of the structural gene for LacZ coup led to a 1.3-kb 5' fragment of the rat CYP2B1 gene was used to generate tra nsgenic mice in order to further elucidate the mechanism behind tissue-spec ific expression and PB induction of the CYP2B1 gene. Using reverse transcri ptase-polymerase chain reaction on total RNA extracted from lung and liver tissue: a lung-specific transcription of the transgene was observed. Transc ription of the construct was also observed in livers from PB-treated transg enic animals. By histochemical staining of lung sections with 5-bromo-4-chl oro-3-indolyl-beta-D-galactopyranoside (X-gal), we demonstrated expression at the protein level in bronchiolar cells. In conclusion, our results revea led that the region extending to -1.3 kb in the 5' flanking region of the C YP2B1 gene included sequences that could partly account for the lung-specif ic transcription of CYP2B1 and the hepatic induction of CYP2B1 transcriptio n by PB.