Cis-acting sequences from the rat cytochrome P450 2B1 gene confer pulmonary and phenobarbital-inducible expression in transgenic mice.

Specific cytochrome P450 enzymes show tissue-specific induction, and different regulatory units for expression of these enzymes have been identified. The regulation of the phenobarbital (PB)-inducible P450 genes has been relatively well characterized in terms of PB induction, but less so with regard to tissue-specific expression. CYP2B2 is not expressed in the rat lung, whereas cytochrome P450 2B1 (CYP2B1) is a dominating enzyme in the same tissue. The constitutive expression of CYP2B1 and CYP2B2 in liver is low, but inducible by PB, whereas the pulmonary expression of CYP2B1 is not induced by PB. This indicates utilization of different regulating mechanisms in the two organs. A gene construct consisting of the structural gene for LacZ coupled to a 1.3-kb 5' fragment of the rat CYP2B1 gene was used to generate transgenic mice in order to further elucidate the mechanism behind tissue-specific expression and PB induction of the CYP2B1 gene. Using reverse transcriptase-polymerase chain reaction on total RNA extracted from lung and liver tissue, a lung-specific transcription of the transgene was observed. Transcription of the construct was also observed in livers from PB-treated transgenic animals. By histochemical staining of lung sections with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal), we demonstrated expression at the protein level in bronchiolar cells. In conclusion, our results revealed that the region extending to -1. 3 kb in the 5' flanking region of the CYP2B1 gene included sequences that could partly account for the lung-specific transcription of CYP2B1 and the hepatic induction of CYP2B1 transcription by PB.