INDUCTION OF CYP1A1, BUT NOT CYP1A2, IN ADRENALS OF 3,3'-METHYLCHOLANTHRENE-TREATED GUINEA-PIGS

To test the inducibility of CYP1A homologs in guinea pig adrenal, the effects of 3,3'-methylcholanthrene, an archetypal inducer of CYP1A, we re compared in guinea pig adrenal and liver. Western blot analysis sho wed that levels of both CYP1A1 (53 kDa) and CYP1A2 (56 kDa) increased in Liver microsomes of 3,3' -methylcholanthrene-treated guinea pigs. I n adrenals, an immunoreactive protein comigrating with liver CYP1A1 wa s detected only after 3,3'methylcholanthrene treatment. Protein comigr ating with CYP1A2 was never detected in adrenal microsomes. A third in ducible immunoreactive protein (57 kDa) was seen in Liver, but not adr enal, after 3,3'-methylcholanthrene treatment. Another immunoreactive protein (52 kDa), present constitutively in liver and adrenal microsom es, was not induced in either tissue by 3,3'-methylcholanthrene. The p recise identities of the inducible 57-kDa and the noninducible 52-kDa proteins remain to be determined. However, the identity of the 53-kDa protein in the adrenal as CYP1A1 was confirmed by RT-PCR, Northern blo t, and sequence analysis, Similar analyses demonstrated that, despite the fact that the 56-kDa protein was not detectable in adrenal microso mes, CYP1A2 mRNA was present in adrenals of control animals. Strikingl y, CYP1A2 mRNA decreased in adrenal, but increased in liver, following 3,3'-methylcholanthrene treatment, underscoring differences in the re gulation of CYP1A expression in the two tissues. Levels of ethoxyresor ufin and methyoxyresorufin metabolism correlated with levels of CYP1A1 and CYP1A2 protein, respectively. (C) 1998 Academic Press.