Differential expression of CYP1A1 and CYP1B1 in human breast epithelial cells and breast tumor cells

Abstract

Human cytochromes P450 1A1 (CYP1A1) and P450 1B1 (CYP1B1) catalyze the metabolic activation of a number of procarcinogens and the hydroxylation of 17beta-estradiol (E2) at the C-2 and C-4 positions, respectively. The aromatic hydrocarbon receptor (AhR) agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has a marked effect on estrogen metabolism in MCF-7 breast-tumor cells by induction of these two enzymes. To investigate whether induction of CYP1A1 and CYP1B1 by AhR agonists and the associated increase in E2 metabolism are common to all breast epithelial cells and breast-tumor cells, we determined the effects of TCDD on E2 metabolism, and CYP1A1 and CYP1B1 mRNA levels in a series of non-tumor-derived breast epithelial (184A1 and MCF-10A) and breast-tumor (MCF-7, T-47D, ZR-75-1, BT-20, MDA-MB-157, MDA-MB-231 and MDA-MB-436) cell lines. In 184A1 cells, which did not express detectable estrogen receptor (ER) alpha mRNA, CYP1A1 mRNA and activity were induced by TCDD, and enhanced E2 metabolism in TCDD-treated cells was predominantly E2 2-hydroxylation. In MCF-10A, MCF-7, T-47D, ZR-75-1 and BT-20 cells, which expressed varying levels of ER alpha mRNA, both CYP1A1 and CYP1B1 mRNA levels and rates of both E2 2- and 4-hydroxylation were highly elevated following exposure to TCDD. In MDA-MB-157, MDA-MB-231 and MDA-MB-436 cells, which did not express detectable ER alpha mRNA and generally displayed fibroblastic or mesenchymal rather than epithelial morphology, CYP1B1 induction was favored, and the rate of E2 4-hydroxylation exceeded that of 2-hydroxylation in TCDD-treated cells. These results show that breast epithelial cells and tumor cells vary widely with regard to AhR-mediated CYP1A1 and CYP1B1 induction, suggesting that factors in addition to the AhR regulate CYP1A1 and CYP1B1 gene expression. In these cell lines, significant CYP1A1 inducibility was restricted to cultures displaying epithelial morphology, whereas CYP1B1 inducibility was observed in cells of both epithelial and mesenchymal morphology.

Induction of Oxidative Stress Responses by Dioxin and other Ligands of the Aryl Hydrocarbon Receptor

“…In liver, TCDD increases the levels of CYP1A1 and CYP1A2 relative to CYP1B1 (Walker et al, 1999), hence 2-hydroxylation predominates over 4-hydroxylation. Similar results have been reported in several breast epithelial tumor and nontumor cell lines where TCDD strongly induced CYP1A1 activity with resultant 2-hydroxyestradiol formation as the major E 2 metabolite (Spink et al, 1998). In this regard, increased production of 2-hydroxyestradiol relative to 4-hydroxyestradiol and 16α-hydroxyestrone has been observed after exposure to indole 3-carbinol, a dietary micronutrient and AHR proligand.…”

Inhibition of catechol-O-methyltransferase increases estrogen–DNA adduct formation

“…Another important factor is excessive formation of 4-OHE 1 (E 2 ) as a major metabolite of E 1 (E 2 ), catalyzed by CYP1B1 [30][31][32]. Minimization of estrogen-DNA adduct formation occurs when COMT is present at high levels because methoxylation of 4-OHE 1 (E 2 ) is one of the key elements in reducing adduct formation.…”

“…In extrahepatic tissues, cytochrome P450 (CYP)1A1 and CYP1B1 predominantly metabolize the natural estrogens E 1 and E 2 to 2-and 4-catechol estrogens (CE), respectively [30][31][32], which can be competitively oxidized to their respective semiquinones and quinones. In general, the CE are inactivated by conjugating reactions, such as glucuronidation and sulfation.…”

Pharmacogenetics and Regulation of Human CytochromeP450 1B1: Implications in Hormone-Mediated Tumor Metabolism and a Novel Target for Therapeutic Intervention

“…CYP1B1 mRNA detection does not always correlate with CYP1B1 protein expression (67). RNA-PCR studies have shown that expression of CYP1B1 is equivalent in normal and tumor tissues, whereas immunohistochemical analysis and activity assays indicate that protein expression is increased in tumors (4,5,63,68).…”