Expression of UGT2B7, a UDP-Glucuronosyltransferase Implicated in the Metabolism of 4-Hydroxyestrone and All-Trans Retinoic Acid, in Normal Human Breast Parenchyma and in Invasive and in Situ Breast Cancers

Abstract

Glucuronidation, mediated by UDP-glucuronosyltransferases (UGTs), affects the actions and disposition of diverse endo-and xenobiotics. In the case of catecholestrogens (CEs), glucuronidation is likely to block their oxidation to quinone estrogens that are the putative mediators of CEs' actions as initiators of cancers. The goal of this study was to determine whether UGT2B7, the isoenzyme with a high affinity for 4-hydroxyestrone, is expressed in human breast parenchyma. Glucuronidation of 4-hydroxyestrone has relevance to breast carcinogenesis because quinone metabolites of 4-hydroxylated CEs can form potentially mutagenic depurinating DNA adducts, and because in breast tissue estrone is likely to be the predominant estrogen available for 4-hydroxylation. Using reverse transcriptase-polymerase chain reaction, immunocytochemistry, immunoblot analyses, and assays of glucuronidation of 4-hydroxyestrone, we show that UGT2B7 is expressed in human mammary epithelium, and that its expression is dramatically reduced in invasive breast cancers. In many in situ carcinomas, however, 4-hydroxyestrone immunostaining was not only preserved but even more intense than in normal mammary epithelium. The finding of reduced UGT2B7 protein and glucuronidation of 4-hydroxyestrone in invasive cancers suggests a tumor-suppressor function for the enzyme. Recent identification of all-trans retinoic acid as a substrate of UGT2B7 suggests that this function includes the generation of retinoyl-␤-glucuronide, a potent mediator of actions of retinoids important for maintaining epithelia in a differentiated state. Current knowledge does not provide any ready explanation for the apparent increase in UGT2B7 expression in carcinomas in situ. However, this finding, together with reduced immunostaining at loci showing breach of the basement membrane (microinvasion), suggests involvement of UGT2B7-catalyzed reaction(s) in protection against invasion of surrounding tissue by cancer cells.

Characterization of UDP-glucuronosyltransferase (UGT1A1) Promoter Polymorphisms and Gene Expression on Ethnicity, Stage of Disease, and Menopausal Status in Breast Cancer

“…In support of our findings, an epidemiological study, demonstrated that the presence of lower levels of UGT1A1 protein resulted in decreased production of estrogen glucuronides and consequently higher exposure to E 2 [17]. Furthermore, a study by Gestl et al demonstrated that UGT2B7 mRNA and protein was downregulated in breast tumors as compared to normal breast tissues [14], which is consistent with our results in this study. To further determine if UGT1A1 mRNA levels had an effect on clinicopathological and variable factors, we compared UGT1A1 mRNA expression levels to ethnicity, menopausal status, and stage of breast disease.…”

“…Estrogen metabolism by UGTs is the major drug-metabolic pathway that results in the complete inactivation of estrogens and their hydroxylated metabolites [9–12]. Alterations in UGTs, resulting in decreased UGT expression and glucuronidation activity towards estrogens and their metabolites, has been suggested to play a potential role in breast cancer risk [14–16]. Our previous published study demonstrated that several UGTs, including UGT1A1, are involved in the complete inactivation of both native estrogens and their oxidative metabolites, including the genotoxic 4-OH-E1 [12].…”

“…Thus, suggesting that UGTs play a protective role in the breast by terminating or attenuating the biological activities of estrogens and its metabolites. However, modifications in the glucuronidation metabolic pathway, through loss of UGT expression and activity, have been proposed to alter estrogen metabolism, resulting in an increased accumulation of genotoxic estrogen metabolites and risk of breast cancer development [14–16]. For instance, a genetic variant in UGT1A1, which is characterized by the number of TA repeats in the TATA box of the promoter region, has been associated with reduced transcriptional activity towards estrogens in vitro and increased breast cancer risk in several population-based studies [17–20].…”

Pharmacogenomics of human UDP-glucuronosyltransferase enzymes

“…Since high levels of estrogen-glucuronides have been observed in breast cyst fluid and the expression of UGTs confirmed in estrogen target cells, formation of glucuronides within the breast, ovary and uterine tissues is expected. 66,73 Unconditional logistic regression adjusted for the matching variables, and age at menarche, parity, age at first birth, BMI at age 18, weight gain since age 18, age at menopause, benign breast disease, firstdegree family history of breast cancer, and duration of postmenopausal hormone use. f Matched for all variables mentioned above ( d ) and for laboratory batch.…”

“…Recent findings suggest that metabolic alterations may actually determine the degree of exposure of an individual to toxic or carcinogenic substances over a long time period and may contribute to modify one's susceptibility to diseases such as cancer. [65][66][67][68][69][70][71][72][73] This review is focused on recent work in the area of the pharmacogenomics of human UGTs. The following topics will be covered: (i) overview of human UGT enzymes; (ii) description of polymorphic human UGT enzymes; (iii) pharmacogenomic phenomena involving polymorphic UGT enzymes in drug response and (iv) pharmacogenomic phenomena involving polymorphic UGT enzymes in cancer.…”