INDUCTION OF CYTOCHROME-P450 1B1 AND CATECHOL ESTROGEN METABOLISM IN ACHN HUMAN RENAL ADENOCARCINOMA CELLS

The catechol estrogen metabolites of 17 beta-estradiol (E-2), 2-hydrox yestradiol (OHE2) and 4-OHE2, differ in hormonal properties and carcin ogenic potential. In Syrian hamster kidney, 4-OHE2 induces clear-cell carcinoma whereas 2-OHE2 does not, and an E-2 4-hydroxylase appears to be involved in E-2-induced carcinogenesis in these animals. Specific E-2 4-hydroxylase activity has been observed in extrahepatic tissues f rom several species. In humans, cytochrome P450 1B1 (CYP1B1) appears t o be an extrahepatic E-2 4-hydroxylase under the regulatory control of the aromatic hydrocarbon receptor (AhR). As an initial approach to in vestigating CYP1B1 expression and E-2 4-hydroxylase activity in human kidney, we used the ACHN cell line, derived from a human renal adenoca rcinoma. In untreated ACHN cells, a very low level of CYP1B1 mRNA expr ession was observed and CYP1B1 protein could not be detected; however, in ACHN cells exposed to the high-affinity AhR ligand, 2,3,7,8-tetrac hlorodibenzo-p-dioxin (TCDD), CYP1B1 mRNA levels were elevated 28-fold , and the CYP1B1 protein was detected by immunoblot analysis. Exposure of ACHN cells to TCDD resulted in minimal induction of the CYP1A1 mRN A, and the CYP1A1 protein was not detectable prior to or after exposur e to TCDD. E-2 hydroxylase activity could not be detected with microso mes from untreated ACHN cells, although activities at C-4 and, to a le sser extent, at C-2 of E-2 were observed with microsomes from TCDD-tre ated ACHN cells. In experiments with intact ACHN cells, elevated rates of formation of 4-methoxyestradiol (MeOE2) and 2-MeOE2 were observed in response to treatment with TCDD. The EC50 for induction of the CYP1 B1 mRNA was 1.5 nM TCDD; EC(50)s for the stimulation of 2- and 4-MeOE2 formation were 0.68 and 1.1 nM TCDD. These results indicate that the ACHN cell line may be a useful in vitro model system to study the regu lation of CYP1B1 expression and the cytotoxic effects associated with E-2 4-hydroxylation. (C) 1997 Elsevier Science Ltd.