Human Estrogen Sulfotransferase Research Articles

Interaction of Native- and Oxidized-Low-Density Lipoprotein with Human Estrogen Sulfotransferase.

Cytosolic estrogen sulfotransferase (SULT1E) mainly catalyzes the sulfate conjugation of estrogens, which decrease atherosclerosis progression. Recently we reported that a YKEG sequence in human SULT1E1 (hSULT1E1) corresponding to residues 61-64 can bind specifically to oxidized low-density lipoprotein (Ox-LDL), which plays a major role in the pathogenesis of atherosclerosis; its major oxidative lipid component lysophosphatidylcholine (LPC), and its structurally similar lipid, platelet-activating factor (PAF). In this study, we investigated the effect of Ox-LDL on the sulfating activity of hSULT1E1. In vivo experiments using a mouse model of atherosclerosis showed that the protein expression of SULT1E1 was higher in the aorta of mice with atherosclerosis compared with that in control animals. Results from a sulfating activity assay of hSULT1E1 using 1-hydroxypyrene as the substrate demonstrated that Ox-LDL, LPC, and PAF markedly decreased the sulfating activity of hSULT1E1, whereas native LDL and 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC) as one of the oxidized phosphatidylcholines showed the opposite effect. The sulfating activity greatly changed in the presence of LPC, PAF, and POVPC in their concentration-dependen manner (especially above their critical micelle concentrations). Moreover, Ox-LDL specifically recognized dimeric hSULT1E1. These results suggest that the effects of Ox-LDL and native LDL on the sulfating activity of hSULT1E1 might be helpful in elucidating the novel mechanism underlying the pathogenesis of atherosclerosis, involving the relationship between estrogen metabolism, LDL, and Ox-LDL.

The molecular basis of OH-PCB estrogen receptor activation

Polychlorinated bisphenols (PCBs) continue to contaminate food chains globally where they concentrate in tissues and disrupt the endocrine systems of species throughout the ecosphere. Hydroxylated PCBs (OH-PCBs) are major PCB metabolites and high-affinity inhibitors of human estrogen sulfotransferase (SULT1E1), which sulfonates estrogens and thus prevents them from binding to and activating their receptors. OH-PCB inhibition of SULT1E1 is believed to contribute significantly to PCB-based endocrine disruption. Here, for the first time, the molecular basis of OH-PCB inhibition of SULT1E1 is revealed in a structure of SULT1E1 in complex with OH-PCB1 (4ʹ-OH-2,6-dichlorobiphenol) and its substrates, estradiol (E2), and PAP (3’-phosphoadenosine-5-phosphosulfate). OH-PCB1 prevents catalysis by intercalating between E2 and catalytic residues and establishes a new E2-binding site whose E2 affinity and positioning are greater than and competitive with those of the reactive-binding pocket. Such complexes have not been observed previously and offer a novel template for the design of high-affinity inhibitors. Mutating residues in direct contact with OH-PCB weaken its affinity without compromising the enzyme’s catalytic parameters. These OH-PCB resistant mutants were used in stable transfectant studies to demonstrate that OH-PCBs regulate estrogen receptors in cultured human cell lines by binding the OH-PCB binding pocket of SULT1E1.

Human estrogen sulfotransferase and its related fluorescently labeled decapeptides specifically interact with oxidized low-density lipoprotein.

Estrogen sulfotransferase (SULT1E) mainly catalyzes the sulfation of estrogens, which are known to prevent the pathogenesis of atherosclerosis. Recently, we found that peptides with a YKDG sequence specifically bind to oxidized low-density lipoprotein (Ox-LDL), which plays a major role in the pathogenesis of atherosclerosis. Here, we investigated the interaction between human SULT1E1 (hSULT1E1), which has a YKEG sequence (residues 61-64) unlike other human SULTs, and Ox-LDL. Results from polyacrylamide gel electrophoresis and western blotting demonstrated that hSULT1E1 specifically binds to Ox-LDL and its major lipid component (lysophosphatidylcholine; LPC), and platelet-activating factor (PAF), which bears a marked resemblance to LPC in terms of structure and activity. Moreover, an N-terminally fluorescein isothiocyanate (FITC)-labeled decapeptide (MIYKEGDVEK; FITC-hSULT1E1-P10) corresponding to residues 59-68 of hSULT1E1 specifically binds to Ox-LDL, LPC, and PAF. Unveiling the specific interaction between hSULT1E1 and Ox-LDL, LPC, and PAF provides important information regarding the mechanisms underlying various diseases caused by Ox-LDL, LPC, and PAF, such as atherosclerosis. In addition, FITC-hSULT1E1-P10 could be used as an efficient fluorescent probe for the detection of Ox-LDL, LPC, and PAF, which could facilitate the mechanistic study, identification, diagnosis, prevention, and treatment of atherosclerosis.

Dependence between estrogen sulfotransferase (SULT1E1) and nuclear transcription factor Nrf-2 regulations via oxidative stress in breast cancer

Human estrogen sulfotransferase (SULT1E1) and nuclear factor erythroid 2-related factor 2 (Nrf-2) expression influences each other in advanced human breast carcinogenesis. The difference in the metabolism of estradiol (E2) in pre- and post-menopausal women remains to be connected with post-menopausal breast cancer. A synergism between ROS production and E2 generation has been demonstrated. No definite mechanism for simultaneous functions of Nrf2, oxidative stress E2 regulating enzymes (SULT1E1) has been yet clarified. Our present review demonstrates that ROS dependent regulation of Nrf-2 is one of the most important determinants of E2 regulation by altering SULT1E1 expression. This study also focuses the idea that estrogen receptor cased subtypes of cancer may have different molecular environments which has an impact on the therapeutic efficacy.

Hydroxylated and sulfated metabolites of commonly occurring airborne polychlorinated biphenyls inhibit human steroid sulfotransferases SULT1E1 and SULT2A1

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that are associated with varied adverse health effects. Lower chlorinated PCBs are prevalent in indoor and outdoor air and can be metabolized to their hydroxylated derivatives (OH-PCBs) followed by sulfation to form PCB sulfates. Sulfation is also a means of signal termination for steroid hormones. The human estrogen sulfotransferase (SULT1E1) and alcohol/hydroxysteroid sulfotransferase (SULT2A1) catalyze the formation of steroid sulfates that are inactive at steroid hormone receptors. We investigated the inhibition of SULT1E1 (IC50s ranging from 7.2 nM to greater than 10 μM) and SULT2A1 (IC50s from 1.3 μM to over 100 μM) by five lower-chlorinated OH-PCBs and their corresponding PCB sulfates relevant to airborne PCB-exposure. Several congeners of lower chlorinated OH-PCBs relevant to airborne PCB exposures were potent inhibitors of SULT1E1 and SULT2A1 and thus have the potential to disrupt regulation of intracellular concentrations of the receptor-active steroid substrates for these enzymes.

Biotransformation of Endocrine Disrupting Compounds by Selected Phase I and Phase II Enzymes – Formation of Estrogenic and Chemically Reactive Metabolites by Cytochromes P450 and Sulfotransferases

The endocrine system is a major communication system in the body and is involved in maintenance of the reproductive system, fetal development, growth, maturation, energy production, and metabolism,. The endocrine system responds to the needs of an organism by secreting a wide variety of hormones that enable the body to maintain homeostasis, to respond to external stimuli, and to follow various developmental programs. This occurs through complex signalling cascades,with multiple sites at which the signals can be regulated. Endocrine disrupting compounds (EDCs) affect the endocrine system by simulating the action of the naturally produced hormones, by inhibiting the action of natural hormones, by changing the function and synthesis of hormone receptors, or by altering the synthesis, transport, metabolism, and elimination of hormones. It has been established that exposure to environmental EDCs is a risk factor for disruption of reproductive development and oncogenesis in both humans and wildlife. For accurate risk assessment of EDCs, the possibility of bioactivation through biotransformation processes needs to be included since neglecting these mechanisms may lead to undervaluation of adverse effects on human health caused by EDCs and/or their metabolites. This accurate risk assessment should include: (1) possibility of EDCs to be bioactivated into metabolites with enhanced endocrine disruption (ED) effects, and (2) possibility of EDCs to be biotransformed into reactive metabolites that may cause DNA damage. Here, we present an overview of different metabolic enzymes that are involved in the biotransformation of EDCs. In addition, we describe how biotransformation by Cytochromes P450 (CYPs), human estrogen sulfotransferase 1E1 (SULT1E1) and selected other phase II enzymes, can lead to the formation of bioactive metabolites. This review mainly focuses on CYP- and SULT-mediated bioactivation of estrogenic EDCs and summarizes our views on this topic while also showing the importance of including bioactivation and biotransformation processes for improved risk assessment strategies.

The Transition of Human Estrogen Sulfotransferase from Generalist to Specialist Using Directed Enzyme Evolution

Broad specificity is believed to be a property of primordial enzymes that diverged during natural protein evolution to produce highly specific and efficient enzymes. Human estrogen sulfotransferase (SULT1E1) is a broad-specificity enzyme that detoxifies a variety of chemicals, including estrogens, by the transfer of sulfate. To study the molecular basis for the broad specificity of this enzyme and to investigate the process of SULT1E1 specialization, we have adopted a directed enzyme evolution approach. Using two iterative rounds of evolution, we generated SULT1E1 mutants with increased thermostability and narrower specificity from the broadly specific wild-type enzyme. To identify mutants with enhanced specificity, we developed an unbiased screening assay to assess sulfate transfer to three different acceptors in parallel. Such an assay enabled the isolation of SULT1E1 mutants with enhanced or wild-type activity toward an estrogen acceptor and significantly reduced activity for phenol or coumarin type of acceptors, leading to up to 3 orders of magnitude increase in specificity. We found that mutations conferring novel specificity are located in the vicinity of the active site and thus may play a direct role in reshaping the acceptor-binding site. Finally, such mutations resulted in reduced SULT1E1 thermostability, revealing a trade-off between SULT1E1 thermostability and acquisition of novel function.

Comparison of murine and human estrogen sulfotransferase inhibition in vitro and in silico—Implications for differences in activity, subunit dimerization and substrate inhibition

It is well established that various endocrine disrupting compounds (EDCs) can inhibit human estrogen sulfotransferase (SULT1E1). In this study, we investigate murine SULT1E1 inhibition in vitro and in silico and compare this to data for the human enzyme. 34 potential EDCs were screened for their ability to inhibit both murine and human SULT1E1 and IC 50 values were determined for 14 of the inhibitory EDCs. Only estrone, dienestrol and enterolactone showed significant differences in affinity between the human and murine SULT1E1. Extensive molecular modelling was performed using molecular dynamics (MD) simulations. During the MD simulations the ligands moved away from the catalytically active position, something which was not observed when simulating the unit cell of the crystal structure. This finding suggests that catalytically inactive binding modes, other than the one observed in the crystal structures, are possible in SULT1E1. The ligands stayed longer in the catalytically active position in mSULT1E1, which is likely a result of simultaneous hydrogen bond formation on both sides of the binding pocket, which does not seem to be possible in hSULT1E1. The ligands in the human protein moved to a sub-pocket near the entrance of the active site, which offers hydrogen bond formation possibilities with Asp22 and Lys85 as well as favourable hydrophobic interactions. The ligands moved more randomly in mSULT1E1. These observations offer a possible explanation for the substrate inhibition only observed in hSULT1E1.

DNA microarray analysis suggests a regulatory role of human estrogen sulfotransferase SULT1E1 in the expression of signal transduction‐related genes in human prostate cancer CA‐HPV‐10 cells

Human estrogen sulfotransferase catalyzes the sulfation of estrogen at the 3-hydroxyl position. Studying the roles of estrogen sulfotransferase in the regulation of estrogenic action in human cells could provide valuable information for the treatment and prevention of human estrogen-associated diseases such as prostate cancer. The main purpose of this work is to elucidate the regulatory role of human estrogen sulfotransferase SULT1E1 in the signal transduction-related gene expression in human prostate cancer CA-HPV-10 cells. Expression of intracellular signal transduction-related genes in CA-HPV-10 cells following SULT1E1 transfection was investigated by DNA microarray analysis. Notable changes were observed in transcriptional expression of TFRC, a cell membrane transferrin receptor related gene, and PMEPA1, a gene encoding a steroid-dependent protein product. Expression of TFRC was down-regulated while expression of PMEPA1 was up-regulated by SULT1E1 transfection in CA-HPV-10 cells. The DNA microarray results were further confirmed by real-time RT-PCR analysis. These results indicated a regulatory role of SULT1E1 in expression of signal transduction-related genes in CA-HPV-10 cells. Future studies will focus on the molecular mechanism underlying the observed effects of SULT1E1.

Regulation of human hepatic estrogen sulfotransferase (SULT1E1) expression by xenobiotics and lipid intermediates.

Estrogens regulate hepatobiliary lipid metabolism, and estrogen sulfotransferase (SULT1E1) plays a key role as an estrogen-inactivating enzyme in the liver and other estrogen target tissues. In this study, the effects of pharmacological activation of xenobiotic- or lipid-sensing pathways on SULT1E1 expression were investigated in primary cultured human hepatocytes by TaqMan RT-PCR. Treatment with the pregnane X receptor (PXR) ligand, rifampicin (5x10−5M), suppressed SULT1E1 mRNA content by ~90% relative to control. Treatment with either of the aryl hydrocarbon receptor (AhR) ligands, β-naphthoflavone (10−5M) or 2,3,7,8-TCDD (10−8M), suppressed SULT1E1 transcript levels by ~70%, while the non-AhR binding 1,3,7,8-TCDD analog had no effect on SULT1E1 mRNA content. The activation of lipid-sensing nuclear receptors, such as the peroxisome proliferator activated receptor α by ciprofibrate (10−4M) and the liver X receptor by 24,25(S)-epoxycholesterol (3x10−5M), increased SULT1E1 mRNA content ~3-fold relative to control. These results suggest that human hepatic SULT1E1 expression is repressed by xenobiotic activators of the PXR and AhR, but induced by metabolic intermediates of lipid metabolism. Supported by ES05823 (M.R.M.), HL50710 (T.A.K.) and ES06636.

Redox regulation of human estrogen sulfotransferase (hSULT1E1)

Sulfotransferases (SULTs) are enzymes that catalyze the sulfation of hydroxyl-containing compounds. Sulfation regulates hormone activities and detoxifies xenobiotics. Human estrogen sulfotransferase (hSULT1E1) catalyzes the sulfation of estrogens and regulates estrogen bioactivities. Oxidative regulation provides a biological mechanism for regulating enzyme activities in vivo. The oxidative regulation of human SULTs has not been reported. In this study, we used amino acid modification, manipulation of intracellular redox state, and site-directed mutagenesis to study the redox regulation of human SULTs and specifically the mechanism of hSULT1E1 inhibitory regulation by oxidized glutathione (GSSG). Of the four major human SULTs, hSULT1A1, hSULT1A3, and hSULT2A1 do not undergo redox regulation; hSULT1E1, on the other hand, can be redox regulated. GSSG inactivated hSULT1E1 activity in an efficient, time- and concentration-dependant manner. The co-enzyme adenosine 3′-phosphate 5′-phosphosulfate protected hSULT1E1 from GSSG-associated inactivation. A reduced glutathione (GSH) inducer (N-acetyl cysteine) significantly increased while a GSH depletor (buthionine sulfoxamine) significantly decreased hSULT1E1 activity, but both failed to affect the amount of hSULT1E1 protein in human hepatocyte carcinoma Hep G2 cells. Crystal structure suggested that no Cys residues exist near the active sites of hSULT1A1, hSULT1A3, and hSULT2A1, but Cys residues do exist within the active site of hSULT1E1. Site-directed mutagenesis demonstrated that Cys83 is critical for the redox regulation of hSULT1E1. This first report on the redox regulation of human SULTs suggests that the redox regulation of hSULT1E1 may interrupt the regulation and function of estrogens under various physiological and pathological conditions.

Inhibition of Human Phenol and Estrogen Sulfotransferase by Certain Non-Steroidal Anti-Inflammatory Agents

We hypothesized that aryl acetate- and aryl carboxylate-containing drugs would inhibit human phenol sulfotransferase (SULT1A1), and that selectivity would depend upon the interaction of the aryl portion of the molecule with the sulfotransferase acceptor binding site. This hypothesis was based on results with the rat orthologue showing that oxidation of phenolic substrates to carboxylate derivatives resulted in competitive inhibition of rat phenol sulfotransferase. We chose nine structurally representative non-steroidal anti-inflammatory agents and determined their inhibitory potency and selectivity toward SULT1A1 and expressed human estrogen sulfotransferase (SULT1E1). The results show that the tested agents reversibly inhibit SULT1A1 activity with IC(50) ranging from 0.1 microM to 3800 microM. These agents also inhibited SULT1E1 (IC(50) = 6 microM to 9000 microM). The agents were clearly isoform selective, with IC(50) ratios (1E1/1A1) ranging from 0.01 to 200. Nimesulide, meclofenamate, and piroxicam were more selective towards SULT1A1 inhibition, while sulindac and ibuprofen were more selective towards SULT1E1 inhibition. Sulfotransferase inhibition was maintained after substituting the carboxylate with enolate (nimesulide) or methylsulfonamide (piroxicam). Kinetic studies determined the type of inhibition of SULT1A1 for three agents (meclofenamate, nimesulide, aspirin) to be non-competitive or partial non-competitive versus both substrate (p-nitrophenol) and cofactor (PAPS). This inhibition mechanism indicates that meclofenamate, nimesulide and aspirin bind near enough to the substrate binding site to prevent catalysis but not affect dissociation of the substrate-enzyme complex. The inhibition of SULT1A1 by meclofenamate, nimesulide, salicylate and aspirin may be clinically relevant based on ratio of inhibition constant to predicted in vivo inhibitor concentration ([I]/IC(50) > 1).

Development and validation of a fluorescence HPLC-based screening assay for inhibition of human estrogen sulfotransferase

Human estrogen sulfotransferase (SULT1E1) is involved in the regulation of 17β-estradiol responsiveness and is believed to protect peripheral tissues from excessive estrogenic effects. Several assays already have been developed to investigate the inhibitory effect of endocrine-disrupting compounds (EDCs) on SULT1E1. However, most of these assays make use of the radiolabeled cofactor [ 35S]3′-phosphoadenosine 5′-phosphosulfate (PAPS) or radiolabeled substrate [ 3H]estradiol. In this article, we describe the development and validation of an assay for the inhibition of human SULT1E1 that is rapid and simple and that uses the nonradioactive and noncarcinogenic 1-hydroxypyrene. A gradient HPLC separation of 15 min using a C18-RP column was developed to detect 1-hydroxypyrene and its metabolite pyrene 1-sulfate fluorescently. Time- and protein-dependent formation of pyrene 1-sulfate was investigated, and enzyme kinetics was determined ( K m = 6.4 ± 0.8 nM and V max = 158 ± 19 pmol/min/μg SULT1E1). At higher 1-hydroxypyrene concentrations, the assay displayed non-Michaelis–Menten kinetics involving substrate inhibition. IC 50 values have been determined for eight known SULT1E1 inhibitors or competing substrates (17β-estradiol, 17α-estradiol, genistein, 17α-ethynylestradiol, estrone, diethylstilbestrol, estriol, and hexestrol) and two previously unknown SULT1E1 inhibitors (zearalenone and dienestrol). The method was demonstrated to be easy, feasible, and highly reproducible for SULT1E1 screening assay inhibition studies.

Effects of inhibitors of Ras signaling on the expression of human estrogen sulfotransferase (SULT1E1) in the MCF10AT1 breast epithelial cell line

The MCF10A cell line was derived from a patient with benign proliferative breast disease. The stable transfection of MCF10A cells with the mutant T24 c-Ha-ras oncogene led to the production of a derivative cell line MCF10AT1, which is tumorigenic in immunodeficient mice. Estrogen sulfotransferase (SULT1E1) is a major estrogen inactivating enzyme in breast tissue. Previous studies suggested that SULT1E1 is differentially expressed in MCF10A relative to MCF10AT1 cells. To determine if modulations in Ras oncoprotein activity may affect the expression of SULT1E1 in MCF10AT1 cells, pre-confluent cultures of MCF10AT1 cells were treated for 48h with inhibitors of Ras signaling. Relative to vehicle-treated controls (DMSO 0.1%), treatment with the farnesyl transferase inhibitor FTI-277 (10μM) produced a ~2.4 fold increase in SULT1E1 mRNA expression. Co-treatments with FTI (10μM) and the HMG-CoA reductase inhibitor lovastatin (at 0.3 μM, 1 μM, or 3 μM), significantly induced SULT1E1 mRNA levels by ~2.8, 2.4 and 1.3 fold, respectively, relative to vehicle-treated controls. Thus, treatment with disruptors of Ras signaling in MCF10AT1 cells, induces the expression of SULT1E1. These results have implications for SULT1E1-mediated estrogen inactivation during breast epithelial neoplastic progression. Supported by NIH Grants ES05823, S11 ES11182, and ES06639.

Searching for the minimum energy path in the sulfuryl transfer reaction catalyzed by human estrogen sulfotransferase: Role of enzyme dynamics

AbstractThe enzymatic transfer of a sulfuryl group from the ubiquitous biological source of sulfate 3′‐phosphoadenosine 5′‐phosphosulfate (PAPS) to estrogen is investigated by the pseudo‐bond quantum mechanical/molecular mechanical method (QM/MM) method. Calculations of the reaction path are performed starting with models based on two crystal structures, which differ in information about the cofactor and substrates. In addition, a subsequent relaxation of the enzyme was performed with the found transition state frozen, followed by redetermination of the path. An activation barrier of 22 kcal/mol is estimated. The reaction mechanism features a proton transfer from the estrogen to a catalytic histidine followed by the rate determining SO3 transfer. The mechanism found is largely dissociative. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Bioactivation of Dibrominated Biphenyls by Cytochrome P450 Activity to Metabolites with Estrogenic Activity and Estrogen Sulfotransferase Inhibition Capacity

Exposure of humans and wildlife to xenobiotics, such as halogenated biphenyls, that interfere with the endogenous estrogen balance may lead to endocrine disruption. Such compounds may either mimic or block estradiol's action by agonistic or antagonistic action, respectively. They may also affect endogenous estradiol concentrations by induction or inhibition of enzymes that metabolize estradiol. In the present study, we demonstrate that estrogenic metabolites of two brominated biphenyls, 2,2'-dibromobiphenyl (2,2'-DBB) and 4,4'-dibromobiphenyl (4,4'-DBB), are formed by rat liver microsomal cytochrome P450 (CYP) activity. Bioactivation of 2,2'-DBB and 4,4'-DBB yielded various mono- and dihydroxylated bromobiphenyl metabolites, which were collected by preparative HPLC and analyzed by LC/MS. Several of the metabolites bound to the estrogen receptor (ER) activated the ER and inhibited human estrogen sulfotransferase (hEST). Seven monohydroxylated metabolites were positively identified using synthetic monohydroxylated reference compounds. These synthetic monohydroxylated bromobiphenyls also bound to and activated the ER and inhibited hEST. The highest ER affinity was observed for 4-OH-2,2'-DBB, with an EC50 of 6.6 nM. The highest ER activation was observed for 4-OH-3,4'-DBB (EC50 of 74 nM) while 4-OH-4'-MBB and 4-OH-2,2'-DBB induced a supramaximal (as compared to estradiol) ER activation. The strongest hEST inhibition was found with 4-OH-3,4'-DBB (EC50 = 40 nM). In conclusion, we show that two dibrominated biphenyls are bioactivated by CYP activity into very potent estrogenic metabolites and inhibitors of hEST. These findings are of vital importance for accurate risk assessment of exposure to environmental contaminants, such as halogenated biphenyls. Neglecting bioactivation through biotransformation will lead to underestimation of health risks of this class of xenobiotics.

Methotrexate induction of human sulfotransferases in Hep G2 and Caco-2 cells

Methotrexate (MTX) was the first antifolate drug developed for the treatment of cancer. It is also effective in treating inflammatory and autoimmune diseases. Sulfotransferases are phase II drug-metabolizing enzymes and their induction by hormones and endogenous molecules is relatively well known, although xenobiotic drug induction of sulfotransferases has not been well studied. In the present investigation, MTX is shown to be a xenobiotic inducer of human sulfotransferases in transformed human liver (Hep G2) and intestinal (Caco-2) cells. Following MTX treatment, various sulfotransferases were induced in both cell lines. Enzyme assay, Western blot and reverse-transcription polymerase chain reaction (RT-PCR) results demonstrated that protein and mRNA expressions of human simple phenol sulfotransferase (P-PST), human monoamine sulfotransferase (M-PST), human dehydroepiandrosterone sulfotransferase (DHEA-ST) and human estrogen sulfotransferase (EST) were induced in Hep G2 cells; M-PST and DHEA-ST were induced in Caco-2 cells. Inductions in both cell lines were dose dependent. Enzyme activity and Western blot results were in good agreement with RT-PCR results, suggesting that the induction is at the gene transcription level. Folic acid had a significantly lesser effect on sulfotransferases compared with MTX. Interestingly, the induction of different sulfotransferases by MTX was inhibited by high doses of folic acid at both protein and mRNA levels in Hep G2 cells. Methotrexate is the first antifolate and apoptosis-inducing drug to show induction of sulfotransferases in Hep G2 cells and Caco-2 cells. The inhibition by folic acid suggests a possible mechanism for MTX induction.

Biocides, tributyltin and triphenyltin, as possible inhibitors of the human sulfotransferase involved in the estrogen homeostasis

This work using purified recombinant human estrogen sulfotransferase (hSULT1E1) aimed to investigate the mechanism of the inhibition of estrogen sulfation by organotin compounds. Tributyltin (TBT) inhibited the sulfation of estrone (E1) and 17 β-estradiol (E2) by hSULT1E1 competitively, with IC 50 values of, respectively, 3 and 12 μM. The sulfation of E1 and E2 was also inhibited competitively by triphenyltin (TPT), with IC 50 of, respectively, 10 and 5 μM. These data strongly suggested that His 107 residue might act as a ligand to establish a coordination bond with organotins at estrogen binding site in hSULT1E1. A more surprising finding was that TBT competed with 3′-phosphoadenosine 5′-phosphosulfate (PAPS), indicating that TBT may coordinate with certain amino acid residue such as Lys 47 at the PAPS binding site of hSULT1E1. Taken together, these data provided clear evidence that TBT and TPT have a capacity to disrupt endocrine-mediated events by inhibiting hSULT1E1 involved in the metabolism of sex steroids.

Inhibition of human liver and duodenum sulfotransferases by drugs and dietary chemicals: a review of the literature.

Sulfotransferase catalyzes the transfer of sulfate, donated by 3'-phosphoadenosine-5'-phosphosulfate, to an acceptor substrate that may be a hydroxy group or an amine group. Man is exposed daily to drugs and dietary chemicals that can inhibit sulfotransferase activity. The aim of this study was to review the literature concerning the inhibition of sulfotransferases by drugs and dietary chemicals in the human liver and duodenum. The IC50 value of mefenamic acid for human liver phenol sulfotransferase (SULT 1A1) was 0.02 microM and for human liver catechol sulfotransferase (SULT1A3) 76 microM with a SULT 1A3/SULT1A1 ratio for the IC50 of 3,800. Mefenamic acid is therefore a potent and selective inhibitor of human liver SULT1A1. The IC50 values of mefenamic acid for the sulfation rates of (-)-salbutamol and (-)-apomorphine were 4 orders of magnitude greater in the human duodenum than in the liver. Salicylic acid inhibited the sulfation of (-)-apomorphine in human liver with an IC50 of 54 gM but did not inhibit the sulfation of (-)-apomorphine in human duodenum. Quercetin, a flavonoid present in edible fruit, vegetable and wine, was a potent inhibitor of human liver SULT1A1 and estrogen sulfotransferase (EST) activities and the sulfation of resveratrol. Quercetin inhibited the sulfation of dopamine, (-)-salbutamol, minoxidil and paracetamol and the IC50 values were 1 - 2 orders of magnitude greater in human duodenum than in the liver. In conclusion, mefenamic acid, salicylic acid and quercetin inhibit SULT1A1 whereas SULT1A3 is relatively resistant to the inhibition by these compounds. Under particular circumstances, human duodenum sulfotransferase is more resistant than liver sulfotransferase to the inhibition by mefenamic acid, salicylic acid and quercetin.

Crystallographic analysis of a hydroxylated polychlorinated biphenyl (OH-PCB) bound to the catalytic estrogen binding site of human estrogen sulfotransferase.

Certain hydroxylated polychlorinated biphenyls (OH-PCBs) inhibit the human estrogen sulfotransferase (hEST) at subnanomolar concentrations, suggesting a possible pathway for PCB toxicity due to environmental exposure in humans. To address the structural basis of the inhibition, we have determined the crystal structure of hEST in the presence of the sulfuryl donor product 3 -phosphoadenosine 5 -phosphate and the OH-PCB 4,4 -OH 3,5,3,5 -tetraCB. The OH-PCB binds in the estrogen binding site with the position of the first phenolic ring in an orientation similar to the phenolic ring of 17 beta-estradiol. Interestingly, the OH-PCB does not bind in a planar conformation, but rather with a 30-degree twist between the phenyl rings. The crystal structure of hEST with the OH-PCB bound gives physical evidence that certain OH-PCBs can mimic binding of estrogenic compounds in biological systems.