Formation of glucuronides of estradiol-17 beta by human mammary cancer cells

Enhanced UGT1A1 Gene and Protein Expression in Endometriotic Lesions

The cellular function in endometriosis lesions depends on a highly estrogenic milieu. Lately, it is becoming evident that, besides the circulating levels of estrogens, the balance of synthesis versus inactivation (metabolism) of estrogens by intralesion steroid-metabolizing enzymes also determines the local net estrogen availability. In order to extend the knowledge of the role of estrogen-metabolizing enzymes in endometriosis, we investigated the gene and protein expression of a key uridine diphospho-glucuronosyltransferase (UGT) for estrogen glucuronidation, UGT1A1, in eutopic endometrial samples obtained from nonaffected and endometriosis-affected women and also from endometriotic lesions. Although UGT1A1 messenger RNA (mRNA) expression was detected at similar frequencies in endometriotic lesions and in eutopic endometrial samples, the levels of mRNA expression were greater in deep-infiltrating endometriotic lesions and in non-deep-infiltrating lesions when compared with either control endometrium or eutopic endometrium from women with endometriosis. Overall, we observed that protein expression of UGT1A1 was significantly more frequent in samples from endometriotic lesions in comparison with endometria. In addition, expression of UGT1A1 protein was greater in deep-infiltrating than in non-deep-infiltrating endometriotic lesions. We suggest that the finding of increased expression of UGT1A1 in lesions versus endometria might be related to impairment of regulatory mechanisms, in response to a highly estrogenic milieu, and that this enzyme may be a new target for therapy.

Ciprofibrate regulation of rat hepatic bilirubin glucuronidation and UDP-glucuronosyltransferases expression

Synthetic fibrates are hypolipidemic drugs known to stimulate hepatic peroxisome proliferation and bilirubin glucuronidation. This study was designed to estimate the effects of ciprofibrate simultaneously on rat hepatic bilirubin glucuronoconjugation and on hepatic expression of UGT1A1, UGT1A2 and UGT1A5, all of which belong to the bilirubin cluster. Hepatic bilirubin glucuronidation activity and UDP-glucuronosyltransferase expression (RT-PCR and Western blotting) were measured after a single-dose ciprofibrate treatment (5 mg/kg by gastric intubation) in 36-h time course experiments. Ciprofibrate regulation of PPARα and UGT1A5 mRNA expression was also investigated in rat hepatocytes. Bilirubin conjugation activity was induced by ciprofibrate, reaching a maximum level (2.4×) 24 h after the treatment. UGT1A1 and UGT1A5 mRNA expression was induced 1.5 times by ciprofibrate, with UGT1A5 reaching the basal level of UGT1A1. Although UGT1A2 mRNA was induced approximately threefold by ciprofibrate, its expression level remained low in comparison with basal or induced levels of UGT1A1 and UGT1A5 mRNA. In the 36-h time course experiment, bilirubin conjugation activity as well as UGT1A5 and PPARα mRNA expression presented a biphasic induction profile. Although a similar level of induction was observed in primary cultured hepatocyte experiments, such biphasic variation was not observed for both UGT1A5 and PPARα, and the induction of UGT1A5 mRNA expression by ciprofibrate required de novo protein synthesis. A single dose of ciprofibrate significantly induces rat liver bilirubin conjugation as well as UGT1A1, UGT1A5 and PPARα expression. The induction mechanism may involve PPARα, at least regarding UGT1A5 regulation.

Estrogen regulation of the glucuronidation enzyme UGT2B15 in estrogen receptor-positive breast cancer cells

Estrogens and androgens influence many properties of breast cancer cells; hence, regulation of local estrogen and androgen levels by enzymes involved in steroid hormone biosynthesis and metabolism would impact signaling by these hormones in breast cancer cells. In this study, we show that the UDP-glucuronosyltransferase (UGT) enzyme UGT2B15, a member of the UGT family of phase II enzymes involved in the glucuronidation of steroids and xenobiotics, is a novel, estrogen-regulated gene in estrogen receptor (ER)-positive human breast cancer cells (MCF-7, BT474, T47D, and ZR-75). UGT2B15 is the only UGT2B enzyme up-regulated by estrogen, and marked estradiol stimulation of UGT2B15 mRNA levels is observed, in a time- and dose-dependent manner. UGT2B15 stimulation by estradiol is blocked by the antiestrogen ICI182,780, but not by the translational inhibitor cycloheximide, indicating that UGT2B15 is likely a primary transcriptional response mediated through the ER. UGT2B15 up-regulation is also evoked by other estrogens (propylpyrazoletriol, genistein) and by the androgen 5alpha-dihydrotestosterone working through the ER, but not by other steroid hormone receptor ligands. Western blot and immunocytochemical analyses with several UGT2B-specific antibodies we have designed and steroid glucuronidation assays indicate a large increase in both cellular UGT2B15 protein and enzyme activity after estrogen treatment. Due to the important role of UGT enzymes in forming conjugates between steroids and glucuronic acid, thereby inactivating them and targeting them for removal, the estrogen-induced up-regulation of UGT2B15 might have a significant moderating effect on estrogen and androgen concentrations, thereby reducing their signaling in breast cancer cells.

Formation of estrogenic metabolites of benzo[a]pyrene and chrysene by cytochrome P450 activity and their combined and supra-maximal estrogenic activity

Metabolism of polycyclic aromatic hydrocarbons (PAHs) has been studied intensively, and potential metabolites with estrogenic activity have been identified previously. However, little attention has been paid to the metabolic pathways in mammalians and to the combined effect of individual metabolites. Several hydroxylated metabolites of benzo[a]pyrene (BaP) and chrysene (CHN) were formed by rat liver microsomal cytochrome P450 (CYP) activity, some of which possess estrogenic activity. All mono- and several dihydroxylated metabolites of BaP and CHN were tested for ER affinity and estrogenic activity in a proliferation assay (E-screen) and in a reporter-gene assay (ER-CALUX). Twelve estrogenic metabolites were identified with EC50 values ranging from 40nM to 0.15mM. The combined effect of a mixture of seven PAH-metabolites was also studied in the ER binding assay. At concentrations that show little activity themselves, their joint action clearly exhibited significant estrogenic activity. BaP itself exhibited estrogenicity in the ER-CALUX assay due to bio-activation into estrogenic metabolites, probably via aryl hydrocarbon receptor (AhR) induced CYP activity. Furthermore, 2-hydroxy-CHN (2-OHCHN) induced supra-maximal (400%) estrogenic effects in the ER-CALUX assay. This effect was entirely ER-mediated, since the response was completely blocked with the ER-antagonist ICI182,780. We showed that 2-OHCHN increased ER-concentration, using ELISA techniques, which may explain the observed supra-maximal effects. Co-treatment with the AhR-antagonist 3',4'-dimethoxyflavone (DMF) enhanced ER-signaling, possibly via blockage of AhR-ER inhibitory cross-talk.

Quercetin and resveratrol potently reduce estrogen sulfotransferase activity in normal human mammary epithelial cells

Estrogen sulfotransferase (EST) is the sole sulfotransferase expressed in normal human breast epithelial cells and has an important function in determining free estrogen hormone levels in these cells. In the present study we examined the inhibitory effect of the dietary polyphenols quercetin and resveratrol on EST activity, i.e. 17beta-estradiol (E2) sulfation. Both the compounds potently inhibited recombinant human EST in a competitive fashion with K(i) values of about 1 microM. In fact, both polyphenols could serve as substrates for EST. In order to extend the studies to more physiologically relevant conditions, we examined whether inhibition of EST also occurred in the intact cultured human mammary epithelial (HME) cells. The mean baseline EST activity (E2 sulfate formation) in the HME cells was 4.4 pmol/h per mg protein. The IC(50) for resveratrol was very similar to that for recombinant EST, i.e. about 1 microM. Surprisingly, quercetin was 10 times more potent in the HME cells with an IC(50) of about 0.1 microM, a concentration that should be possible to achieve from the normal dietary content of this flavonoid.

Identification and cloning of a novel androgen-responsive gene, uridine diphosphoglucose dehydrogenase, in human breast cancer cells

Androgens inhibit the growth of breast cancer cells, but the mechanism of androgen-induced growth inhibition has not yet been elucidated, and few androgen-responsive genes have been identified. We, therefore, used differential display PCR to identify novel androgen-responsive genes in ZR-75-1 human breast cancer cells. The human UDP-glucose dehydrogenase gene (UDPGDH), which was not known to be androgen regulated, was detected and cloned by complementary DNA library screening. The UDPGDH open reading frame codes for a protein of 494 amino acids that migrates at an apparent molecular mass of approximately 54 kDa. Northern blot analysis revealed the existence of two messenger RNA species of approximately 3.5 and 2.7 kb in all of the human breast cancer cell lines examined. The major UDPGDH transcript was induced rapidly (within 6 h) by dihydrotestosterone in ZR-75-1 cells, and a maximal 13-fold induction was observed after 24 h of treatment. The increase in UDPGDH messenger RNA was completely prevented by coincubation with the pure antiandrogen hydroxyflutamide, but not by cycloheximide, indicating that UDPGDH is directly regulated by the androgen receptor. As UDPGDH is required for the production of uridine 5'-diphosphoglucuronic acid, a substrate for the steroid-conjugating uridine diphospho-glucuronosyltransferase enzymes, up-regulation of UDPGDH expression by androgens might play an important role in the control of sex steroid inactivation via glucuronidation in breast cancer cells.

The monkey and human uridine diphosphate-glucuronosyltransferase UGT1A9, expressed in steroid target tissues, are estrogen-conjugating enzymes

Considering the physiologic importance of the steroid response, which is regulated in part by steroid levels in a given tissue, relatively little is known about steroid glucuronidation, which is widely accepted as a major pathway involved in the catabolism and elimination of steroid hormones from the human body. In a previous study, it was ascertained that the monkey may be the most appropriate model in which to examine the role of steroid glucuronidation. Northern blot analysis of simian RNA, hybridized with human UGT complementary DNA (cDNA) probes demonstrate the similarity of the transcripts. The simian UGT1A09 cDNA isolated from a liver library is 2396 bp and contains an open reading frame encoding 530 amino acids. The predicted primary structure is most homologous to the human UGT1A9 (hUGT1A9) enzyme, which share 93% identity. Stable transfection of the monkey UGT1A09 (monUGT1A09) cDNA into HK293 cells, expresses a microsomal protein with an apparent molecular mass of 55 kDa. Of the more than 30 endogenous substrates tested, both proteins show the highest activity on 4-hydroxyestradiol and 4-hydroxyestrone, followed by 2-hydroxyestradiol and estradiol. RT-PCR analysis demonstrate that UGT1A9 transcript is expressed in several tissues, which include the prostate, testis, breast, ovary, and skin of the monkey and humans. The expression of UGT1A9 in extrahepatic estrogen-responsive tissues, and its high activity on estrogens is consistent with this enzyme having a role in estrogen metabolism.

Characterization of UDP-glucuronosyltransferases active on steroid hormones

In recent years, the enzymes which are involved in the formation of DHT in steroid target tissues have been well investigated, however, enzymes responsible for the catabolism and elimination of steroids in these tissues, in particular the uridine diphospho-glucuronosyltransferase (UGT) family of enzymes, have received much less attention. We have recently demonstrated that human and monkey are unique in having high plasma levels of C19 steroid glucuronides. These circulating conjugates have been proposed to reflect the peripheral conversion of adrenal and gonadal C19 steroids to potent androgens, especially DHT. In humans, the presence of steroid UGT activities is found in the liver and several extrahepatic tissues including the prostate, mammary gland and ovary. In addition, UGT activities were observed in breast and prostate tumor cell lines such as MCF-7 and LNCaP, respectively. In agreement with the presence of steroid conjugating enzymes in extrahepatic tissues, UGT cDNA clones, which encode steroid conjugating proteins, have been isolated from libraries constructed from human and monkey prostate mRNA. The presence of UGT transcripts and proteins in extrahepatic tissues in both species, as determined by Northern blot, ribonuclease protection, specific RT-PCR, in situ hybridization, Western blot and immunocytochemistry analysis, indicate the relevance of steroid glucuronidation in tissues other than the liver. Knowing that both the human prostate and the human prostate cancer LNCaP cell line express steroid metabolizing proteins, including UGT enzymes, regulation of UGT mRNA and protein levels, as well as promoter activity was studied in these cells. The results demonstrate a differential regulation between the two highly related isoforms UGT2B15 and UGT2B17, where only the expression of UGT2B17 was affected following treatments of LNCaP cells with androgens, growth factors or cytokines. Steroid conjugation by UGT enzymes is potentially involved in hormone inactivation in steroid target tissues, thus modifications in UGT expression levels may influence hormonal responses.

Isolation and characterization of a novel cDNA encoding a human UDP-glucuronosyltransferase active on C19 steroids

To isolate cDNA clones encoding novel UGT2B enzymes, human prostate and LNCaP cell cDNA libraries were screened using a pool of steroid-specific UGT2B cDNA probes. In approximately 10(6) recombinants, we isolated 3 cDNA clones of 2.1 kilobases that encode a novel UGT2B enzyme. UGT2B17 is 95% identical with UGT2B15 and 91% identical with UGT2B8. Primary structure analysis of UGT2B17 based on the nucleotide sequence revealed a putative amino-terminal membrane insertion signal peptide, a carboxyl-terminal membrane-spanning region, and three potential asparagine-linked glycosylation sites. UGT2B17 cloned in the pBK-CMV expression vector was transfected into HK293 cells to obtain a stable clonal cell line expressing a high level of the active 53-kDa UGT2B17 enzyme. Of the over 60 endogenous and exogenous substances tested, 25 compounds revealed reactivity. The major substrates are eugenol > 4-methylumbelliferone > dihydrotestosterone > androstane-3alpha, 17beta-diol (3alpha-diol) > testosterone > androsterone (ADT). The apparent Km values obtained with tritiated steroids in intact cells were 0.4 microM for ADT, 0.7 microM for dihydrotestosterone, 1.0 microM for 3alpha-diol, and 3.4 microM for testosterone. Southern blot analysis of reverse transcription-polymerase chain reaction products revealed expression of UGT2B17 mRNA in various tissues including the liver, kidney, testis, uterus, placenta, mammary gland, adrenal gland, skin, and prostate. UGT2B17 is the first human uridine diphosphoglucuronosyltransferase enzyme expressed in extrahepatic tissues to have a specificity for ADT as well as testosterone, dihydrotestosterone, and 3alpha-diol.

Expression of transcripts encoding steroid UDP-glucuronosyltransferases in human prostate hyperplastic tissue and the LNCaP cell line

The UDP-glucuronosyltransferase (EC 2.4.1.17) enzymes transform many lipophilic compounds to more water-soluble products via conjugation with glucuronic acid. This conversion is responsible for enhancing the excretion of endogenous aglycones such as steroids. To date, several distinct isoforms of steroid UDP-glucuronosyltransferases (UGTs) have been isolated in the human liver. Among these UGTs, UGT2B7 is specific for estriol and 3,4-catechol estrogens, UGT2B15 glucuronidates 17beta-hydroxy-C19 steroids while UGT2B10 has as yet an undescribed activity. To further demonstrate the presence of UGTs in peripheral tissues we studied the expression of these enzymes in human prostate hyperplastic tissue and the LNCaP cell line. Metabolism studies using intact LNCaP cells in culture indicate the presence of UGT activities involved in the glucuronidation of 3alpha-hydroxysteroids (androsterone) and 17beta-hydroxysteroids (testosterone and dihydrotestosterone). Northern blot analysis of poly(A+) RNA from LNCaP cells and prostate using a UGT2B15 cDNA probe revealed two bands of 2.0 and 2.3 kb. In order to identify more specifically the mRNAs detected in Northern blot analysis we used RNase protection and RT-PCR, although, these approaches did not allow detection of UGT2B7 transcripts. Our studies demonstrate the presence of two UGT activities and at least two types of UGT transcripts in both the human prostate and the LNCaP.

Stimulation of 17 beta-estradiol metabolism in MCF-7 cells by bromochloro- and chloromethyl-substituted dibenzo-p-dioxins and dibenzofurans: correlations with antiestrogenic activity

Mixed halo- and haloalkyl-substituted dibenzo-p-dioxins (DD) and dibenzofurans (DF) are known environmental contaminants, although there is limited information on the toxic effects of these compounds in human cells. In this study antiestrogenicity, a property of 2,3,7,8-Cl4-DD, was investigated with a series of bromochloro- and chloromethyl-substituted DDs and DFs. The effects of these compounds on the metabolism of 17 beta-estradiol (E2) and on the estrogen-dependent formation of multicellular foci in cultures of MCF-7 human breast cells were examined. Pretreatment of MCF-7 cells with 2,3,7,8-Cl4-DD induced pathways of E2 metabolism involving cytochrome P-450-catalyzed hydroxylation, methylation of the catechol estrogens, and conjugation. Several Br-Cl3-DD and Br2-Cl2-DD congeners with halogen substitution at the 2, 3, 7, and 8 positions also stimulated E2 metabolism with similar potency to that of 2,3,7,8-Cl4-DD; however, compounds with substitution of a methyl group for a halogen at any of these positions did not stimulate the metabolism of E2. For the series of compounds tested in MCF-7 cultures, a close correlation was observed between the antiestrogenicity as measured by the inhibition of estrogen-dependent postconfluent growth that results in focus formation and the efficacy with which the compounds stimulated the metabolism of E2. 2,3,7,8-TetrahaloDDs with one or two bromine atoms at these positions were highly antiestrogenic as determined by their inhibition of estrogen-dependent focus formation, whereas the methyl-substituted polychlorinated DDs and DFs investigated did not inhibit focus formation. These results indicate that the 2,3,7,8-substituted mixed halo-substituted DDs and DFs are of importance when the biologic effects of halogenated DD and DF congeners are considered, and provide additional evidence for the role of increased metabolism of E2 in the antiestrogenic effects of halogenated DDs and DFs.

Estrogen-stimulated glucuronidation of dihydrotestosterone in MCF-7 human breast cancer cells

The non-aromatizable androgen dihydrotestosterone (DHT) has been shown to exert a potent inhibitory effect on the proliferation of some human breast cancer cell lines. DHT, however, has little or no significant inhibition on MCF-7 cell proliferation in either the presence or absence of estradiol (E2). Since the metabolism of DHT into non-active compounds may be responsible for the observed lack of androgenic effect in this cell line, we have investigated the metabolic fate of labeled DHT in MCF-7 cells. A time course incubation was performed with 1 nM [3H]DHT and analysis of the various metabolites formed revealed a time-dependent increase in glucuronidated steroids which was stimulated more than 4-fold by 0.1 nM E2. The major glucuronidated steroid was androstane-3 alpha, 17 beta-diol in both control and E2-stimulated cells, comprising 22 +/- 1.2% and 30 +/- 0.6% of the total radioactivity in the medium, respectively. Other steroid glucuronides observed included DHT, androstane-3 beta,17 beta-diol, and androsterone, all of which were elevated in the E2-treated cells relative to control values. The present data show that E2 exerts a stimulatory effect on the glucuronidation of androgens and their metabolites in the estrogen-dependent breast cancer cell line MCF-7. Since glucuronidation is an effective means of cellular elimination of active steroids, such a pathway may be considered as a possible site of regulation of breast cancer cell growth by hormones.

Metabolism of the oral contraceptive steroids ethynylestradiol and norgestimate by normal (Huma 7) and malignant (MCF-7 and ZR-75-1) human breast cells in culture

Human breast cancer cells are used extensively for the study of steroid hormone action. It is known that in both receptor positive and receptor negative cell lines there is considerable metabolism of the natural estrogens, estradiol (E2) and estrone (E1) with interconversion of the two steroids and formation of sulphate and glucuronide conjugates. The aim of the present work was to see if the commonly used oral contraceptive steroids (OCS) ethynylestradiol (EE2) and norgestimate (Ngmate) were metabolized in human breast cancer cell lines (MCF-7 and ZR-75-1) and a normal breast cell line (Huma 7). MCF-7, ZR-75-1 and Huma 7 cells were maintained in Dulbeccos Modified Eagles Medium (DMEM) containing foetal calf serum (FCS) insulin and hydrocortisone. In addition, ZR-75-1 cells required epidermal growth factor (EGF) and E2 while MCF-7 cells required only EGF. On reaching confluence cells were transferred to DMEM containing charcoal-stripped FCS, insulin and hydrocortisone. 48 h later this medium was renewed, radiolabelled steroid ([3H]E1; [3H]E2; [3H]EE2, [3H]Ngmate; [3H]E1-SO4; 1 nM; 0.2 microCi) was added and incubation was for 24 or 48 h. Following incubation, the medium was removed and radioactive steroid extracted with ether. Metabolites were analysed by on-line radiometric HPLC. All the cell lines were able to interconvert E1 and E2; the equilibrium favouring the formation of E2 in MCF-7 and ZR-75-1 and E1 in Huma 7 cells. E1 and E2 also underwent phase II metabolism to form their respective estrogen sulphates, this activity being most marked in the Huma 7 cell line. In addition to sulphotransferase activity, the study with E1 sulphate demonstrated sulphatase activity in both normal and cancer cells. There appeared to be no difference in extent of hydrolysis, with both E1 and E2 formed. With EE2 as substrate there was no evidence of phase I metabolism in any of the cell lines but there was conversion to the presumed 3-sulphate conjugate. The percentage formation of this metabolite was very much greater in Human 7 cells (64.1 +/- 9.6% after 24 h) than in MCF-7 and ZR-75-1 cells (7.4 +/- 5.3% and 10.6 +/- 4.1%, respectively after 24 h). In all the cell lines deacetylation of the progestogen Ngmate to norgestrel oxime was complete within 24 h. In addition there was evidence of loss of the oxime moiety to give norgestrel.(ABSTRACT TRUNCATED AT 400 WORDS)

Steroid glucuronides: human circulatory levels and formation by LNCaP cells

We studied the relationship between circulating androsterone glucuronide, androstane-3 alpha, 17 beta-diol glucuronide and androstane-3 beta, 17 beta-diol glucuronide concentrations and adrenal as well as testicular C-19 steroids in men. Among the three 5 alpha-reduced steroid glucuronides, androsterone glucuronide is the predominant C-19 steroid glucuronide measured in plasma and its levels are markedly elevated compared to those of the non-conjugated steroid. The marked rise in testosterone during puberty was strongly correlated with the increase in both androsterone glucuronide and androstane-3 alpha, 17 beta-diol glucuronide, thus suggesting that testicular C-19 steroids are the main precursors of the steroid glucuronides. We also found that the presence of testicular androgen in plasma contributes to approx. 70% of plasma androsterone glucuronide and androstane-3 alpha, 17 beta-diol glucuronide. Our data suggest that the adrenal C-19 steroids remaining in circulation after castration in men are converted into potent androgen which are then glucuronidated by UDP-glucuronyltransferase. We also demonstrated that the human prostate cell line LNCaP is capable of converting to a large extent androstenedione into androsterone glucuronide. Our data further confirm that glucuronidation is a major pathway of steroid metabolism in steroid target tissues.