17 beta-estradiol hydroxylation catalyzed by human cytochrome P450 1B1.

Abstract

The 4-hydroxy metabolite of 178-estradiol (E2) has been implicated in the carcinogenicity of this hormone. Previous studies showed that aryl hydrocarbonreceptor agonists induced a cytochrome P450 that catalyzed the 4-hydroxylation of E2. This activity was associated with human P450 lBi. To determine the relationship of the human P450 lBl gene product and E2 4-hydroxylation, the protein was expressed in Saccharomyces cerevisiae. Microsomes from the transformed yeast catalyzed the 4-and 2-hydroxylation of E2 with Km values of 0.71 and 0.78 ,uM and turnover numbers of 1.39 and 0.27 nmol product min'l nmol P450-1, respectively. Treatment of MCF-7 human breast cancer cells with the aryl hydrocarbon-receptor ligand indolo[3,2-b]carbazole resulted in a concentration-dependent increase in P450 lBl and P450 lAl mRNA levels, and caused increased rates of 2-, 4-, 6c-, and 15a-hydroxylation of E2. At an E2 concentration of 10 nM, the increased rates of 2-and 4-hydroxylation were approximately equal, emphasizing the significance of the low Km P450 lBl-component of E2 metabolism. These studies demonstrate that human P450 lB1 is a catalytically efficient E2 4-hydroxylase that is likely to participate in endocrine regulation and the toxicity of estrogens.The importance of estrogens in the etiology of breast and uterine cancer is widely recognized (1-3). The carcinogenicity of estrogens has been primarily attributed to their action as agonists of the estrogen receptor, through which concerted gene regulation controls cellular growth and differentiation in estrogen responsive tissues. Increasing evidence of another mechanism of carcinogenicity has focused attention on the catechol estrogen metabolites, which are less potent estrogens than 17f3-estradiol (E2). The 2-and 4-hydroxylated metabolites of both E2 and estrone (E1) can directly or indirectly damage DNA, proteins, and lipids through the generation of reactive free radicals by the reductive-oxidative cycling of these catechol estrogens between their semiquinone and quinone forms (4-6).4-Hydroxylated metabolites represent only a small percentage of the total urinary catechol-estrogen content, and 4-hydroxylation was previously thought to be only a minor metabolic route (7). However, tissue-specific 4-hydroxylation of E2 may be significant in the metabolic control of estrogen homeostasis. In human (8) and mouse uteri (9), rat pituitary (10), and hamster kidney (11) the rate of E2 4-hydroxylation approaches or exceeds that of 2-hydroxylation. Interestingly, these organs are targets of estrogen-induced tumorigenesis (2, 12-14), and higher E2 4-hydroxylase activity has been measured in tumors of the human breast (15, 16) and uterus (8), each compared with normal tissue. Furthermore, in the male hamster kidney, the carcinogenic and DNA-damaging activity of 4-hydroxyestradiol (4-OHE2), and lack of activity of 2-hydroxyestradiol (2-OHE2), (17)(18)(19), implicate the 4-hydroxylated metabolites in estrogen-induced carcinogenesis. Pertinent to elucidating the contribution of 4...

Cytochrome P450 1B1 Contributes to the Development of Angiotensin II–Induced Aortic Aneurysm in Male Apoe−/− Mice

“…11 CYP1B1 can metabolize various substrates, including steroids, retinoic acid, and fatty acids. 48,50 In the present study, Ang IIeinduced AAA in Apoe À/À /Cyp1b1 þ/þ mice was associated with oxidative stress, as indicated by increased cardiac NADPH oxidase, production of ROSs in the lesion site in aortae, and increased plasma levels of 8-isoprostane, all of which were minimized by TMS or in Apoe À/À /Cyp1b1 À/À mice. Collectively, these observations suggest that the generation of oxidative stress and lipid peroxides by CYP1B1 contributes to the development of Ang IIeinduced AAA.…”

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.…”

Genetic polymorphisms of cytochrome P450 19 and 1B1, alcohol use, and breast cancer risk in Korean women

“…Polymeropulous et al, 1991;Sourdaine et al, 1994;Siegelmann-Danieli and Buetow, 1999;Healey et al, 2000;Miyoshi et al, 2000). One of these, a C-to-T variation in exon 7 resulting in an Arg 264 Cys amino-acid exchange, has been shown to be very common in Asians (Watanabe et al, 1997;Miyoshi et al, 2000) and could thus be an important modifier of breast cancer risk in this ethnic group.The CYP1B1 enzyme is known to be involved in the formation of 4-hydroxyoestradiol, which is a catechol metabolite of oestrogen (Hayes et al, 1996). A C-to-G variation in exon 3 of the CYP1B1 gene results in a Leu 432 Val amino-acid exchange.…”

“…The CYP1B1 enzyme is known to be involved in the formation of 4-hydroxyoestradiol, which is a catechol metabolite of oestrogen (Hayes et al, 1996). A C-to-G variation in exon 3 of the CYP1B1 gene results in a Leu 432 Val amino-acid exchange.…”