Glucuronosyltransferase activity in human cancer cell line LNCaP

Testosterone accumulation in prostate cancer cells is enhanced by facilitated diffusion

BACKGROUND

Testosterone is a driver of prostate cancer (PC) growth via ligand-mediated activation of the androgen receptor (AR). Tumors that have escaped systemic androgen deprivation, castration-resistant prostate cancers (CRPC), have measurable intratumoral levels of testosterone, suggesting that a resistance mechanism still depends on androgen-simulated growth. However, AR activation requires an optimal intracellular concentration of androgens, a situation challenged by low circulating testosterone concentrations. Notably, PC cells may optimize their androgen levels by regulating the expression of steroid metabolism enzymes that convert androgen precursors into androgens. Here we propose that testosterone entry into the cell could be another control point.

METHODS

To determine whether testosterone enters cells via a transporter, we performed in vitro 3 H-testosterone uptake assays in androgen-dependent LNCaP and androgen and AR-independent PC3 cells. To determine if the uptake mechanism depended on a concentration gradient, we modified UGT2B17 levels in LNCaP cells and measured androgen levels by liquid-liquid extraction-mass spectrometry. We also analyzed CRPC metastases for expression of AKR1C3 to determine whether this enzyme that converts adrenal androgens to testosterone was present in the tumor stroma (microenvironment) in addition to its expression in the tumor epithelium.

RESULTS

Testosterone uptake followed a concentration gradient but unlike in passive diffusion, was saturable and temperature-dependent, thus suggesting facilitated transport. Suppression of UGT2B17 to abrogate a testosterone gradient reduced testosterone transport while overexpression of the enzyme enhanced it. The facilitated transport suggests a paracrine route of testosterone uptake for maintaining optimal intracellular levels. We found that AKR1C3 was expressed in the tumor microenvironment of CRPC metastases in addition to epithelial cells and the pattern of relative abundance of the enzyme in epithelium vs stroma varied substantially between the metastatic sites.

CONCLUSIONS

Our findings suggest that in addition to testosterone transport and metabolism by tumor epithelium, testosterone could also be produced by components of the tumor microenvironment. Facilitated testosterone uptake by tumor cells supports a cell nonautonomous mechanism for testosterone signaling in CRPC.

Profiling adrenal 11β-hydroxyandrostenedione metabolites in prostate cancer cells, tissue and plasma: UPC2-MS/MS quantification of 11β-hydroxytestosterone, 11keto-testosterone and 11keto-dihydrotestosterone

Adrenal C₁₉ steroids serve as precursors to active androgens in the prostate. Androstenedione (A4), 11β-hydroxyandrostenedione (11OHA4) and 11β-hydroxytestosterone (11OHT) are metabolised to potent androgen receptor (AR) agonists, dihydrotestosterone (DHT), 11-ketotestosterone (11KT) and 11-ketodihydrotestosterone (11KDHT). The identification of 11OHA4 metabolites, 11KT and 11KDHT, as active androgens has placed a new perspective on adrenal C11-oxy C₁₉ steroids and their contribution to prostate cancer (PCa). We investigated adrenal androgen metabolism in normal epithelial prostate (PNT2) cells and in androgen-dependent prostate cancer (LNCaP) cells. We also analysed steroid profiles in PCa tissue and plasma, determining the presence of the C₁₉ steroids and their derivatives using ultra-performance liquid chromatography (UHPLC)- and ultra-performance convergence chromatography tandem mass spectrometry (UPC²-MS/MS). In PNT2 cells, sixty percent A4 (60%) was primarily metabolised to 5α-androstanedione (5αDIONE) (40%), testosterone (T) (10%), and androsterone (AST) (10%). T (30%) was primarily metabolised to DHT (10%) while low levels of A4, 5αDIONE and 3αADIOL (≈20%) were detected. Conjugated steroids were not detected and downstream products were present at <0.05μM. Only 20% of 11OHA4 and 11OHT were metabolised with the former yielding 11keto-androstenedione (11KA4), 11KDHT and 11β-hydroxy-5α-androstanedione (11OH-5αDIONE) and the latter yielding 11OHA4, 11KT and 11KDHT with downstream products <0.03μM. In LNCaP cells, A4 (90%) was metabolised to AST-glucuronide via the alternative pathway while T was detected as T-glucuronide with negligible conversion to downstream products. 11OHA4 (80%) and 11OHT (60%) were predominantly metabolised to 11KA4 and 11KT and in both assays more than 50% of 11KT was detected in the unconjugated form. In tissue, we detected C11-oxy C₁₉ metabolites at significantly higher levels than the C₁₉ steroids, with unconjugated 11KDHT, 11KT and 11OHA4 levels ranging between 13 and 37.5ng/g. Analyses of total steroid levels in plasma showed significant levels of 11OHA4 (≈230-440nM), 11KT (≈250-390nM) and 11KDHT (≈19nM). DHT levels (<0.14nM) were significantly lower. In summary, 11β-hydroxysteroid dehydrogenase type 2 activity in PNT2 cells was substantially lower than in LNCaP cells, reflected in the conversion of 11OHA4 and 11OHT. Enzyme substrate preferences suggest that the alternate pathway is dominant in normal prostate cells. Glucuronidation activity was not detected in PNT2 cells and while all T derivatives were efficiently conjugated in LNCaP cells, 11KT was not. Substantial 11KT levels were also detected in both PCa tissue and plasma. 11OHA4 therefore presents a significant androgen precursor and its downstream metabolism to 11KT and 11KDHT as well as its presence in PCa tissue and plasma substantiate the importance of this adrenal androgen.

Validation of a sequential extraction and liquid chromatography-tandem mass spectrometric method for determination of dihydrotestosterone, androstanediol and androstanediol-glucuronide in prostate tissues

Androgens are key mediators of prostate development and function, a role that extends to the development of prostate diseases such as benign prostatic hyperplasia (BPH) and prostate cancer. In prostate, DHT is the major androgen and reduction and glucuronidation are the major metabolic pathways for DHT elimination. A streamlined method for quantitation of dihydrotestosterone (DHT), 5α-androstan-3α,17β-diol (3α-diol), and 3α-diol glucuronide (diol-gluc) was established and validated for use with archived prostate tissue specimens to facilitate examination of the roles of the underlying metabolism. This involved a sequential 70/30 hexane/ethyl acetate (hex/EtOAc) extraction of steroids, followed by an ethyl acetate extraction for diol-gluc. Derivatization of the hex/EtOAc fraction with2-fluoro-1-methylpyridinium p-toluene-4-sulfonate (FMP) was used to enhance sensitivity for hydroxyl steroids and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was utilized for analysis of both fractions. The method was validated with calibration standards followed by recovery assessment from spiked samples of BPH and normal prostate. Lower limits of quantitation (LLOQ) were 50 pg/g, 20 pg/g and 100 pg/g for DHT, 3α-diol and diol-gluc, respectively for extracts from 50mg equivalents of tissue. Prepared samples were stable for up to three weeks at 4 °C and 37 °C. The method provides excellent sensitivity and selectivity for determination of tissue levels of DHT, 3α-diol, and diol-gluc. Furthermore, this protocol can easily be extended to other hydroxyl steroids, is relatively straightforward to perform and is an effective tool for assessing steroid levels in archived clinical prostate samples.

Androgen-stimulated UDP-glucose dehydrogenase expression limits prostate androgen availability without impacting hyaluronan levels

UDP-glucose dehydrogenase (UGDH) oxidizes UDP-glucose to UDP-glucuronate, an essential precursor for production of hyaluronan (HA), proteoglycans, and xenobiotic glucuronides. High levels of HA turnover in prostate cancer are correlated with aggressive progression. UGDH expression is high in the normal prostate, although HA accumulation is virtually undetectable. Thus, its normal role in the prostate may be to provide precursors for glucuronosyltransferase enzymes, which inactivate and solubilize androgens by glucuronidation. In this report, we quantified androgen dependence of UGDH, glucuronosyltransferase, and HA synthase expression. Androgen-dependent and androgen-independent human prostate cancer cell lines were used to test the effects of UGDH manipulation on tumor cell growth, HA production, and androgen glucuronidation. Dihydrotestosterone (DHT) increased UGDH expression approximately 2.5-fold in androgen-dependent cells. However, up-regulation of UGDH did not affect HA synthase expression or enhance HA production. Mass spectrometric analysis showed that DHT was converted to a glucuronide, DHT-G, at a 6-fold higher level in androgen-dependent cells relative to androgen-independent cells. The increased solubilization and elimination of DHT corresponded to slower cellular growth kinetics, which could be reversed in androgen-dependent cells by treatment with a UDP-glucuronate scavenger. Collectively, these results suggest that dysregulated expression of UGDH could promote the development of androgen-independent tumor cell growth by increasing available levels of intracellular androgen.

UDP-glucuronosyltransferase 2B15 (UGT2B15) and UGT2B17 Enzymes Are Major Determinants of the Androgen Response in Prostate Cancer LNCaP Cells

Uridine diphosphate-glucuronosyltransferase 2 (UGT2)B15 and B17 enzymes conjugate dihydrotestosterone (DHT) and its metabolites androstane-3alpha, 17beta-diol (3alpha-DIOL) and androsterone (ADT). The presence of UGT2B15/B17 in the epithelial cells of the human prostate has been clearly demonstrated, and significant 3alpha-DIOL glucuronide and ADT-glucuronide concentrations have been detected in this tissue. The human androgen-dependent cancer cell line, LNCaP, expresses UGT2B15 and -B17 and is also capable of conjugating androgens. To assess the impact of these two genes in the inactivation of androgens in LNCaP cells, their expression was inhibited using RNA interference. The efficient inhibitory effects of a UGT2B15/B17 small interfering RNA (siRNA) probe was established by the 70% reduction of these UGT mRNA levels, which was further confirmed at the protein levels. The glucuronidation of dihydrotestosterone (DHT), 3alpha-DIOL, and ADT by LNCaP cell homogenates was reduced by more than 75% in UGT2B15/B17 siRNA-transfected LNCaP cells when compared with cells transfected with a non-target probe. In UGT2B15/B17-deficient LNCaP cells, we observe a stronger response to DHT than in control cells, as determined by cell proliferation and expression of eight known androgen-sensitive genes. As expected, the amounts of DHT in cell culture media from control cells were significantly lower than that from UGT2B15/B17 siRNA-treated cells, which was caused by a higher conversion to its corresponding glucuronide derivative. Taken together these data support the idea that UGT2B15 and -B17 are critical enzymes for the local inactivation of androgens and that glucuronidation is a major determinant of androgen action in prostate cells.

The liver X-receptor alpha controls hepatic expression of the human bile acid-glucuronidating UGT1A3 enzyme in human cells and transgenic mice

Glucuronidation, an important bile acid detoxification pathway, is catalyzed by enzymes belonging to the UDP-glucuronosyltransferase (UGT) family. Among UGT enzymes, UGT1A3 is considered the major human enzyme for the hepatic C24-glucuronidation of the primary chenodeoxycholic (CDCA) and secondary lithocholic (LCA) bile acids. We identify UGT1A3 as a positively regulated target gene of the oxysterol-activated nuclear receptor liver X-receptor alpha (LXRalpha). In human hepatic cells and human UGT1A transgenic mice, LXRalpha activators induce UGT1A3 mRNA levels and the formation of CDCA-24glucuronide (24G) and LCA-24G. Furthermore, a functional LXR response element (LXRE) was identified in the UGT1A3 promoter by site-directed mutagenesis, electrophoretic mobility shift assays and chromatin immunoprecipitation experiment. In addition, LXRalpha is found to interact with the SRC-1alpha and NCoR cofactors to regulate the UGT1A3 gene, but not with PGC-1beta. In conclusion, these observations establish LXRalpha as a crucial regulator of bile acid glucuronidation in humans and suggest that accumulation of oxysterols in hepatocytes during cholestasis favors bile acid detoxification as glucuronide conjugates. LXR agonists may be useful for stimulating both bile acid detoxification and cholesterol removal in cholestatic or hypercholesterolemic patients, respectively.

Human prostate cancer risk factors

Prostate cancer has the highest prevalence of any nonskin cancer in the human body, with similar likelihood of neoplastic foci found within the prostates of men around the world regardless of diet, occupation, lifestyle, or other factors. Essentially all men with circulating androgens will develop microscopic prostate cancer if they live long enough. This review is a contemporary and comprehensive, literature-based analysis of the putative risk factors for human prostate cancer, and the results were presented at a multidisciplinary consensus conference held in Crystal City, Virginia, in the fall of 2002. The objectives were to evaluate known environmental factors and mechanisms of prostatic carcinogenesis and to identify existing data gaps and future research needs. The review is divided into four sections, including 1) epidemiology (endogenous factors [family history, hormones, race, aging and oxidative stress] and exogenous factors [diet, environmental agents, occupation and other factors, including lifestyle factors]); 2) animal and cell culture models for prediction of human risk (rodent models, transgenic models, mouse reconstitution models, severe combined immunodeficiency syndrome mouse models, canine models, xenograft models, and cell culture models); 3) biomarkers in prostate cancer, most of which have been tested only as predictive factors for patient outcome after treatment rather than as risk factors; and 4) genotoxic and nongenotoxic mechanisms of carcinogenesis. The authors conclude that most of the data regarding risk relies, of necessity, on epidemiologic studies, but animal and cell culture models offer promise in confirming some important findings. The current understanding of biomarkers of disease and risk factors is limited. An understanding of the risk factors for prostate cancer has practical importance for public health research and policy, genetic and nutritional education and chemoprevention, and prevention strategies.

Adrenal steroids in human prostatic cancer cell lines

Adrenal androgens function as an androgen source within prostate and androgen target tissue. This study compares the ability of three human prostatic cancer cell lines to metabolize the adrenal androgens, dehydroepiandrosterone (DHEA), and androstenedione under living culture conditions. Androgen-independent cell lines PC-3 and DU145 and androgen-dependent cell line LNCaP were investigated. The effect of glucuronide and sulfate conjugates was also investigated. There was a strong tendency in PC-3 or DU145 to convert androstenedione to DHEA or DHEA-S reservoir. On the other hand, LNCaP was capable of converting DHEA into androstenedione and subsequently into dihydrotestosterone (DHT). Moreover, androgens were converted into a glucuronide conjugate in LNCaP, but not in PC-3 or DU145. As a result, the metabolism of the adrenal precursor shifted to androgen formation in LNCaP. This could be confirmed by means of reverse transcription-PCR of uridine diphosphoglucuronosyl-transferase (UGT) 2B15. Kinetic properties of UGT activity in LNCaP revealed DHT to be a better substrate than testosterone. In conclusion, the findings show that the adrenal precursor pool has the potential to contribute to the regulation of prostatic cells. Moreover, the presence of UGT activities in LNCaP may have a regulatory effect on the active androgen level in the intracellular environment.

Alteration of human UDP-glucuronosyltransferase UGT2B17 regio-specificity by a single amino acid substitution

The glucuronidation of steroid hormones is catalyzed by a family of UDP-glucuronosyltransferase (UGT) enzymes. Previously, two cDNA clones, UGT2B15 and UGT2B17, which encode UGT enzymes capable of glucuronidating C19steroids, were isolated and characterized. These proteins are 95% identical in primary structure; however, UGT2B17 is capable of conjugating C19steroid molecules at both the 3alpha and 17beta-OH positions, whereas UGT2B15 is only active at the 17beta-OH position. To identify the amino acid residue(s) which may account for this difference in substrate specificity, a comprehensive study on the role of 15 residues which differ between UGT2B15 and UGT2B17 was performed by site-directed mutagenesis. The stable expression of UGT2B17 mutant proteins into HK293 cells demonstrated that the mutation of isoleucine 125, valine 181 and valine 455 to the residues found in UGT2B15 did not alter enzyme activity nor substrate specificity. Furthermore, mutation of the variant residues in UGT2B15 (serine 124, asparagine 125, phenylalanine 165) to the amino acid residues found in UGT2B17 did not alter enzyme activity nor substrate specificity. However, mutation of the serine residue at position 121 of UGT2B17 to a tyrosine, as found in UGT2B15, abolished the ability of UGT2B17 to conjugate androsterone at the 3alpha position, but still retained activity for dihydrotestosterone and 5alpha-androstane-3alpha, 17beta-diol, which have an OH-group at the 17beta position. Interestingly, mutation of tyrosine 121 in UGT2B15 to a serine abolished activity for C19steroids. It is suggested that the serine residue at position 121 in UGT2B17 is required for activity towards the 3alpha and not for the 17beta position of C19steroids, whereas the tyrosine 121 in UGT2B15 is necessary for UGT activity. Despite the high homology between UGT2B15 and UGT2B17, it is apparent that different amino acid residues in the two proteins are required to confer conjugation of C19steroid molecules.

Expression of the androgen metabolizing enzyme UGT2B15 in adipose tissue and relative expression measurement using a competitive RT-PCR method

OBJECTIVES

We have demonstrated previously that obesity in men was significantly associated with low plasma testosterone levels and higher concentrations of the androgen metabolite androstane-3 alpha, 17 beta-diol glucuronide, suggesting that androgen metabolism and elimination is increased in this condition. The objective of the present study was to investigate whether adipose tissue was a site of expression of the androgen metabolizing enzymes UDP-glucuronosyltransferases (UGT) 2B15 and 2B17.

DESIGN AND PATIENTS

Subcutaneous and visceral adipose tissue was obtained from male patients subjected to various abdominal surgeries.

MEASUREMENTS AND RESULTS

By performing reverse transcriptase-PCR (RT-PCR) amplification of mRNA extracted from adipose tissue samples, UGT2B15 transcript was detected in both subcutaneous and omental adipose tissue while UGT2B17 transcript expression was very low, or undetectable. A quantitative, competitive RT-PCR method was established and used to quantify UGT2B15 messenger RNA. The level of UGT2B15 expression was also measured in other human tissues. Although the major sites of expression were the liver and the lung, expression in adipose tissue was similar to levels found in the prostate, testis and mammary gland.

CONCLUSIONS

These results demonstrate for the first time that both subcutaneous and visceral adipose tissue express androgen metabolizing enzyme UGT2B15 mRNA and further support the role of adipose tissue as a site of steroid 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.

Characterization and regulation of UDP-glucuronosyltransferases in steroid target tissues

Conjugation of compounds by glucuronidation is a pathway found in all vertebrates studied to date. Although, it is widely recognized that the liver is a major site of glucuronidation, it is now clear that extrahepatic tissues are also involved in the conjugation of compounds to which these tissues are exposed. High levels of androsterone glucuronide and androstane-3alpha,17beta-diol glucuronide found in the human prostate, breast cyst fluid and ovary follicular fluid suggest that glucuronidation of 5alpha-reduced C19 steroids occurs in these tissues. Recently, we have reported the tissue distribution of UGT2B15, which can conjugate steroids in several human extrahepatic steroid target tissues including the skin, breast and prostate. We have also isolated a new UGT2B cDNA encoding UGT2B17, that conjugates ADT which is the major 5alpha-reduced C19 steroid glucuronide in the circulation of humans. UGT2B17 is also widely distributed in several human steroid target tissues. This gene was mapped to human chromosome 4q13 and has an exon/intron structure similar to that of rat UGT2B1 and UGT2B2. Both UGT2B15 and UGT2B17, which are able to catalyze the glucuronidation of DHT, are expressed in LNCaP cells. Interestingly, glucuronidation of steroids is markedly regulated by several factors including androgens and growth factors. Treatment of LNCaP cells with dihydrotestosterone (DHT) and epidermal growth factor (EGF) caused a decrease of DHT glucuronidation and UGT2B mRNA levels. RNase protection assays showed a specific decrease of UGT2B17 transcript in LNCaP cells treated with DHT and EGF however, the level of UGT2B15 mRNA was not affected. As well, Western blot analysis demonstrated a diminution of UGT2B17 protein level in response to DHT and EGF. These results demonstrate a differential regulation of different isoforms of steroid conjugating UGTs present in human prostate LNCaP cells. In addition, UGT2B17 was shown to be more labile than UGT2B15 indicating that regulation of UGT2B17 expression would lead to a more rapid change in the level of glucuronidated steroids. Expression of exogenous UGT2B17 in LNCaP cells by gene transfer led to a significant decrease in the androgen response. This result indicates the ability of UGT enzymes to regulate the androgen response by conjugating androgens which abolishes their interaction with their receptor and facilitates their clearance from the cell. The glucuronidation of steroids by UGT enzymes is an important mechanism by which the levels of steroids is regulated in steroid target tissues.

Effect of fibroblastic growth factors (FGF) on steroid UDP-glucuronosyltransferase expression and activity in the LNCaP cell line

It is now widely accepted that factors other than androgens are crucial in the normal and abnormal growth of the prostate. In addition to hormones, many polypeptide growth factors, including the fibroblast growth factor family (FGF), can act as potent mitogens on cell proliferation. The FGF family of growth factors are essential factors for both normal and abnormal proliferation of prostate cells. To study the effect of FGFs on steroid glucuronidation, we used the human prostate cancer LNCaP cell line which is known to be stimulated by FGF resulting in increased cell proliferation. LNCaP cells express steroid metabolizing enzymes including uridine diphosphoglucuronosyltransferases (UGTs). In addition, LNCaP cells treated with dihydrotestosterone (DHT) and epidermal growth factor (EGF) express differential levels of the human UGT2B15 and UGT2B17 transcripts. In the present study, we examined the possible interaction between FGF and steroid UGT enzymes. Results show a dose dependent inhibition of DHT glucuronide (DHT-G) formation following treatment (6 days) with acidic FGF (aFGF) and basic FGF (bFGF). When cells were treated with 10 ng/ ml of FGFs, we observed 33 and 51% inhibition of glucuronidation activity using aFGF and bFGF respectively. Ribonuclease protection analyses revealed a 2 and 3 fold increase of UGT2B15 mRNA expression following treatment with aFGF (50 ng/ml) and bFGF (10 ng/ml) respectively. However, a slight decrease in UGT2B17 transcripts was observed, demonstrating a differential regulation. Since a reduction in the glucuronidation of DHT or its 5alpha-reduced metabolites may contribute to an increase in intraprostatic androgen levels, down-regulation of UGTs by growth factors such as FGFs may increase the proliferation of androgen-dependent tumors.

Expression and characterization of a novel UDP-glucuronosyltransferase, UGT2B9, from cynomolgus monkey

Uridine diphosphate glucuronosyltransferases (UGTs) are important phase II detoxification enzymes. Despite the expression of UGT proteins in many species, previous results have suggested that simians represent the most appropriate animal model to study the glucuronidation of steroids in extrahepatic steroid target tissues. Northern blot analysis using a pool of human UGT2B cDNA probes demonstrated the expression of homologous UGT2B transcripts in several tissues including the liver, kidney, adrenal, breast, testis, and prostate of the cynomolgus monkey (Macacafascicularis). Western blot analyses using a polyclonal antibody raised against human UGT2B17 protein also demonstrated expression of homologous UGT2B proteins in monkey tissues. cDNA libraries were constructed from monkey liver and prostate mRNA and a novel UGT2B cDNA, UGT2B9, was isolated from both libraries. The UGT2B cDNA from the prostate library is 2,648 bp in length and contains an open reading frame of 1,587 bp encoding a protein of 529 residues. In vitro transcription/translation of the cDNA clone produced a protein of 52 kD. The UGT2B9 cDNA clone was transfected into HK293 cells and a stable cell line expressing UGT2B9 protein was established. The activity of UGT2B9 was tested with over 60 compounds and was demonstrated to be active on C18, C19, and C21 steroids, bile acids, and several xenobiotics including eugenol, 1-naphthol, and p-nitrophenol. Kinetic analysis revealed that UGT2B9 glucuronidates steroids with high affinity and efficiency with Km values of 0.2, 3.2, 0.2, and 1.8 microM for dihydrotestosterone, testosterone, androsterone, and 1,3,5,10-estratrien-3,4-diol-17-one, respectively. It is apparent that this simian UGT2B enzyme is specific for more different classes of steroids than any other UGT enzyme characterized to date, and may be related to the high plasma levels of glucuronidated C19 steroids found in the cynomolgus monkey.

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.

Evidence for a role of glucuronosyltransferase in the regulation of androgen action in the human prostatic cancer cell line LNCaP

Androgens play an important role in the regulation of cell growth and specific protein synthesis in hormone-sensitive prostatic cancer. In this study, we have investigated the metabolism of androgens in LNCaP cells from low passage (LP) and high passage (HP) cultures which were previously shown to possess differential androgen responsiveness. When treated with dihydrotestosterone (DHT), cells showed the characteristic biphasic response of cell proliferation with an ED50 of 1 nM for both the LP and HP cells, but the maximal proliferative response was different with values of 2.65- and 4.29-fold over basal for LP and HP cells, respectively. Metabolism studies indicated no difference in 5alpha-reductase activity between LP and HP cells, while 3alpha-, 3beta- and 17beta-hydroxysteroid dehydrogenase activities were significantly higher in LP cultures. The formation of steroid glucuronides (-G), namely DHT-G, was higher in LP than in HP cells with values of 2.16 and 1.31 pmol of glucuronides formed/microgram DNA/3 h, respectively. Northern blot analysis with a UGT21B15 cDNA probe identified two bands corresponding to two or more UGT transcripts in both LNCaP cells and more transcript was observed in LP than in HP cells. Taken together these results indicate that DHT is deactivated more rapidly in the LP cells, which may explain in part the lower proliferative response to androgens of LP cells compared with HP cells.

Steroid-growth factor interaction in human prostate cancer. 2. Effects of transforming growth factors on androgen metabolism of prostate cancer cells

The ability of human prostate cancer cells to metabolize androgens was assessed through administration of physiological concentration (0.5-10 nM) of tritiated testosterone (T) as precursor and one-step analysis of both T degradation and products' formation by reverse-phase HPLC and on-line radioactive detection after either 24 h or 72 h incubation. Overall, different prostate cancer cells degraded T quite differently, favoring alternatively reductive or oxidative metabolic pathways. In particular, both LNCaP and DU145 cells retained high levels of unconverted T, with a limited production of androstenedione and its 17-keto derivatives and relatively high amounts of dihydrotestosterone (DHT) and 3 alpha-androstanediol (3 alpha-diol). In contrast, PC3 cells quickly degraded T and exhibited high formation rates of androstenedione and 17-keto metabolites, while neither dihydrotestosterone nor 3 alpha-diol were detected after short or longer incubation times. The effects of both TGF alpha (50 ng/mL) and TGF beta 1 (5 ng/mL) on rates and direction of T metabolism were also explored. In LNCaP cells TGF alpha induced a significant (P < 0.04) decrease of the reductive metabolism of T with a corresponding enhancement of the oxidative pathway (P < 0.002), while TGF beta 1 did not significantly affect T metabolism. On the other hand, both reductive and oxidative pathways were only partially influenced by either growth factor in DU145 and PC3 cells, although TGF alpha significantly raised 5 alpha-androstanedione formation and reduced androsterone production in DU145 cells. All the above evidence was confirmed at both 24 h and 72 h or using increasing doses of TGF alpha and TGF beta 1, a peak activity of 50 ng/mL and 5 ng/mL, respectively, being generally encountered. Overall, our data suggest that TGFs may have a role in the growth regulation of hormone-responsive prostate tumor cells through changes of the intracellular contents of biologically active androgen metabolites.

Specificity of glucuronosyltransferase activity in the human cancer cell line LNCaP, evidence for the presence of at least two glucuronosyltransferase enzymes

Recent findings obtained by our group showed that incubation of LNCaP cells with labeled steroids leads to the formation of 3- and 17-hydroxysteroid glucuronides. In this study, the specificity and the kinetic properties of 3-hydroxy-C19steroid uridine diphospho-glucuronosyltransferase (3-OH-UGT) and 17-hydroxy-C19steroid UGT (17-OH-UGT) activities in LNCaP cells were investigated. Results indicate that the UGT has a high affinity for testosterone, dihydrotestosterone (DHT), androsterone (ADT) and androstane-3 alpha, 17 beta-diol (3 alpha-DIOL), with Km values ranging from 0.25 to 0.68 microM. The Km values are approx. 10-fold higher for androst-5-ene-3 beta,17 beta-diol (5-ene-DIOL) and androstane-3 beta,17 beta-diol (3 beta-DIOL). The relative specificities (Vmax/Km) also showed higher turnover rates for testosterone, DHT, ADT and 3 alpha-DIOL with values ranging from 2.93 to 5.71, than for 3 beta-DIOL and 5-ene-DIOL with ratios of 0.41 and 1.10, respectively. Dixon plot and Cornish-Bowden analysis demonstrate that testosterone, DHT, ADT, and 3 alpha-DIOL inhibit the glucuronidation of DHT and ADT in a competitive fashion. In contrast, when the studies are performed with 3 beta-diol and 5-ene-DIOL the inhibition of ADT glucuronidation is uncompetitive while the glucuronidation of DHT is inhibited competitively, suggesting the presence of two UGT enzymes, one for glucuronidation of the 17 beta-OH group and a second for the 3 alpha-OH group. Further evidence for the presence of two UGTs in LNCaP cells was obtained by incubation with a variety of 3 beta-OH-C19 steroids which caused a marked inhibition of DHT-G formation but had no effect on the glucuronidation of ADT. In summary, our data demonstrate the presence of at least two UGTs in the human prostate cancer cell line LNCaP. The relative specificity of the 17-OH-UGT in LNCaP cells is 3 alpha-DIOL > DHT > testosterone, while ADT is glucuronidated by the 3-OH-UGT.

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.