THE 4S BENZO(A)PYRENE-BINDING PROTEIN IS NOT A TRANSCRIPTIONAL ACTIVATOR OF CYP1A1 GENE IN AH RECEPTOR-DEFICIENT (AHR - -) TRANSGENIC MICE/

In an effort to better understand the role of the 4S benzo(a)pyrene-bi nding protein in the induction of CYP1A1 by PAHs, we used a geneticall y engineered mouse line deficient in Ah receptor (AHR -/-). First, we demonstrated through binding experiments analyzed by sucrose gradient sedimentation and gel permeation chromatography that AHR -/- mice have no detectable AHR protein. In contrast, this AHR-deficient line expre ssed a 4S protein which efficiently binds BP as it does in hepatic cyt osol from C57BL/6 mice. In vivo BP exposure in AHR-deficient mice prov ed the inability to sustain any CYP1A1 mRNA or CYP1A1 protein inductio n. These findings demonstrate the requirement of an active AHR to sust ain the transactivation pathway leading to CYP1A1 induction. Surprisin gly, the 45 BP-binding protein, which was previously characterized as the glycine N-methyltransferase, was completely devoid of such an enzy matic activity after purification by Sephacryl gel permeation chromato graphy. Moreover, sedimentation and chromatographic experiments, under nondenaturing conditions, do not support the assumption of 45 protein as a subunit of a multimeric protein (GNMT) displaying a molecular ma ss of 150 kDa. (C) 1998 Academic Press.