Expression and induction of cytochrome P450s in rabbit parotid glands

Earlier, we isolated and purified five different P450 isoforms from rabbit kidney cortex microsomes, three of which are members of the CYP4A subfamily (CYP4A5, CYP4A6, and CYP4A7), with the others being CYP2B4 and CYP1A1. In contrast, P450s in parotid glands were unknown. The fact that the parotid glands bear a marked morphological and functional resemblance to kidney tissue prompted us to investigate P450s in these glands. The present study was undertaken to determine which P450 isoforms are expressed in this tissue. Microsomes from parotid glands of untreated rabbits were found to contain 42.3 pmol of P450/mg protein and to catalyze the omega-hydroxylation of laurate. Administration of di(2-ethylhexyl) phthalate (DEHP) resulted in a 7-fold increase of laurate omega-hydroxylation. This enzyme activity was greatly inhibited by pretreatment with antibodies against CYP4A5. Furthermore, parotid gland CYP4A5, CYP4A6, and CYP4A7 mRNAs were identified by RT-PCR. Moreover, the CYP4A enzymes were demonstrated immunohistochemically to be localized exclusively in the ducts of these glands. In addition to the CYP4A enzymes, immunoblot analysis revealed that CYP2B4 is constitutively present, and that CYP1A1 is induced in these glands by treatment with 3-methylcholanthrene. Taken together, we can conclude that the P450 isoforms expressed in rabbit kidney cortex and parotid glands are identical in composition.