Cloning of the human phenol sulfotransferase gene family: three genes implicated in the metabolism of catecholamines, thyroid hormones and drugs

Impact of SULT1A3/SULT1A4 genetic polymorphisms on the sulfation of phenylephrine and salbutamol by human SULT1A3 allozymes

OBJECTIVES

Phenylephrine and salbutamol are drugs that are used widely to treat diseases/disorders, such as nasal congestion, hypotension, and asthma, in individuals of different age groups. Human cytosolic sulfotransferase (SULT) SULT1A3 has been shown to be critically involved in the metabolism of these therapeutic agents. This study was carried out to investigate the effects of single nucleotide polymorphisms of human SULT1A3 and SULT1A4 genes on the sulfation of phenylephrine and salbutamol by SULT1A3 allozymes.

MATERIALS AND METHODS

Wild-type and SULT1A3 allozymes, prepared previously by site-directed mutagenesis in conjunction with bacterial expression and affinity purification, were analyzed for sulfating activity using an established assay procedure.

RESULTS

Purified SULT1A3 allozymes, in comparison with the wild-type enzyme, showed differential sulfating activities toward phenylephrine and salbutamol. Kinetic studies showed further significant variations in their substrate-binding affinity and catalytic activity toward phenylephrine and salbutamol.

CONCLUSION

The results obtained showed clearly the differential enzymatic characteristics of SULT1A3 allozymes in mediating the sulfation of phenylephrine and salbutamol. This information may contribute toward a better understanding of the pharmacokinetics of these two drugs in individuals with distinct SULT1A3 and/or SULT1A4 genotypes.

Effects of human SULT1A3/SULT1A4 genetic polymorphisms on the sulfation of acetaminophen and opioid drugs by the cytosolic sulfotransferase SULT1A3

Sulfoconjugation has been shown to be critically involved in the metabolism of acetaminophen (APAP), morphine, tapentadol and O-desmethyl tramadol (O-DMT). The objective of this study was to investigate the effects of single nucleotide polymorphisms (SNPs) of human SULT1A3 and SULT1A4 genes on the sulfating activity of SULT1A3 allozymes toward these analgesic compounds. Twelve non-synonymous coding SNPs (cSNPs) of SULT1A3/SULT1A4 were investigated, and the corresponding cDNAs were generated by site-directed mutagenesis. SULT1A3 allozymes, bacterially expressed and purified, exhibited differential sulfating activity toward each of the four analgesic compounds tested as substrates. Kinetic analyses of SULT1A3 allozymes further revealed significant differences in binding affinity and catalytic activity toward the four analgesic compounds. Collectively, the results derived from the current study showed clearly the impact of cSNPs of the coding genes, SULT1A3 and SULT1A4, on the sulfating activity of the coded SULT1A3 allozymes toward the tested analgesic compounds. These findings may have implications in the pharmacokinetics as well as the toxicity profiles of these analgesics administered in individuals with distinct SULT1A3 and/or SULT1A4 genotypes.

Sulfation of catecholamines and serotonin by SULT1A3 allozymes

Previous studies have demonstrated the involvement of sulfoconjugation in the metabolism of catecholamines and serotonin. The current study aimed to clarify the effects of single nucleotide polymorphisms (SNPs) of human SULT1A3 and SULT1A4 genes on the enzymatic characteristics of the sulfation of dopamine, epinephrine, norepinephrine and serotonin by SULT1A3 allozymes. Following a comprehensive search of different SULT1A3 and SULT1A4 genotypes, twelve non-synonymous (missense) coding SNPs (cSNPs) of SULT1A3/SULT1A4 were identified. cDNAs encoding the corresponding SULT1A3 allozymes, packaged in pGEX-2T vector were generated by site-directed mutagenesis. SULT1A3 allozymes were expressed, and purified. Purified SULT1A3 allozymes exhibited differential sulfating activity toward catecholamines and serotonin. Kinetic analyses demonstrated differences in both substrate affinity and catalytic efficiency of the SULT1A3 allozymes. Collectively, these findings provide useful information relevant to the differential metabolism of dopamine, epinephrine, norepinephrine and serotonin through sulfoconjugation in individuals having different SULT1A3/SULT1A4 genotypes.

Depigmentation of melanocytes by isopanduratin A and 4-hydroxypanduratin A isolated from Kaempferia pandurata ROXB

This study was carried out to investigate the in vitro effects of isopanduratin A and 4-hydroxypanduratin A isolated from Kaempferia pandurata ROXB. on melanin biosynthesis and tyrosinase activity. Two chalcone compounds, isopanduratin A and 4-hydroxypanduratin A, were isolated from the ethyl acetate fraction of ethanol extract as the active principles. Compared with phenylthiourea (IC(50)=34.3 microM) as a positive control, the depigmentation IC(50) values for isopanduratin A and 4-hydroxypanduratin A were 10.6 microM and 23.2 microM, respectively. The compounds also significantly inhibited the activity of tyrosinase, the enzyme that converts DOPA (3,4-dihydroxyphenylalanine) to dopachrome in the biosynthetic process of melanin. The IC(50) values of isopanduratin A and 4-hydroxypanduratin A for tyrosinase were 10.5 microM and >30 microM, respectively, while that of phenylthiourea was 47.6 microM. The tyrosinase protein level was also significantly decreased by isopanduratin A and 4-hydroxypanduratin A. The results indicate that isopanduratin A and 4-hydroxypanduratin A isolated from K. pandurata ROXB. are promising compounds that could be useful for treating hyperpigmentation as skin-whitening agents.

Structural and chemical profiling of the human cytosolic sulfotransferases

The human cytosolic sulfotransfases (hSULTs) comprise a family of 12 phase II enzymes involved in the metabolism of drugs and hormones, the bioactivation of carcinogens, and the detoxification of xenobiotics. Knowledge of the structural and mechanistic basis of substrate specificity and activity is crucial for understanding steroid and hormone metabolism, drug sensitivity, pharmacogenomics, and response to environmental toxins. We have determined the crystal structures of five hSULTs for which structural information was lacking, and screened nine of the 12 hSULTs for binding and activity toward a panel of potential substrates and inhibitors, revealing unique "chemical fingerprints" for each protein. The family-wide analysis of the screening and structural data provides a comprehensive, high-level view of the determinants of substrate binding, the mechanisms of inhibition by substrates and environmental toxins, and the functions of the orphan family members SULT1C3 and SULT4A1. Evidence is provided for structural "priming" of the enzyme active site by cofactor binding, which influences the spectrum of small molecules that can bind to each enzyme. The data help explain substrate promiscuity in this family and, at the same time, reveal new similarities between hSULT family members that were previously unrecognized by sequence or structure comparison alone.

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.

Human Sulfotransferases and Their Role in Chemical Metabolism

Sulfonation is an important reaction in the metabolism of numerous xenobiotics, drugs, and endogenous compounds. A supergene family of enzymes called sulfotransferases (SULTs) catalyze this reaction. In most cases, the addition of a sulfonate moiety to a compound increases its water solubility and decreases its biological activity. However, many of these enzymes are also capable of bioactivating procarcinogens to reactive electrophiles. In humans three SULT families, SULT1, SULT2, and SULT4, have been identified that contain at least thirteen distinct members. SULTs have a wide tissue distribution and act as a major detoxification enzyme system in adult and the developing human fetus. Nine crystal structures of human cytosolic SULTs have now been determined, and together with site-directed mutagenesis experiments and molecular modeling, we are now beginning to understand the factors that govern distinct but overlapping substrate specificities. These studies have also provided insight into the enzyme kinetics and inhibition characteristics of these enzymes. The regulation of human SULTs remains as one of the least explored areas of research in the field, though there have been some recent advances on the molecular transcription mechanism controlling the individual SULT promoters. Interindividual variation in sulfonation capacity may be important in determining an individual's response to xenobiotics, and recent studies have begun to suggest roles for SULT polymorphism in disease susceptibility. This review aims to provide a summary of our present understanding of the function of human cytosolic sulfotransferases.

Genetic Variants of the Sulfotransferase 1A1 and Breast Cancer Risk

Sulfotransferase 1A1 (SULT1A1), also designated as phenol-preferring sulfotransferase, is involved in the bioactivation and detoxification of a variety of potential carcinogens, including iodothyronines, hydroxylated aromatic amines, and phenolic xenobiotics. A common arginine (R) to histidine (H) polymorphism at amino acid position 213 influences SULT1A1 activity and has been suggested as risk factor for a different types of cancers. To investigate the role of this polymorphism for breast cancer risk, SULT1A1 genotype was determined in 500 women with clinically verified breast cancer and 500 female age-matched healthy control subjects. Frequencies of heterozygous (controls: 42.5% patients: 50.2%) or homozygous (controls: 12.6%; patients: 9.4%) carriers of the 213H variant were not significantly different between groups. The SULT1A1 genotype was furthermore not associated with tumor size, histological grading, estrogen or progesterone receptor status and age at diagnosis. The SULT1A1 213H variant was associated with the presence of lymph node metastases (p = 0.002). We conclude that the SULT1A1 R213H polymorphism is not a general risk factor for breast cancer, but may be involved in lymph node metastazing in breast cancer patients.

Synergistic effect of antioxidant phenolic acids on human phenolsulfotransferase activity

Sulfate conjugation by phenolsulfotransferases (PSTs) is an important process in the detoxification of xenobiotics and endogenous compounds. There are two forms of PSTs for the sulfation of small phenols (PST-P) and monoamines (PST-M). Phenolic acids are known to increase the activities of PST-P and PST-M. The purpose of this study is to investigate the synergistic effect of the combinations of phenolic acids on human PSTs activities. The combinations of p-hydroxybenzoic acid, gentisic acid, ferulic acid, gallic acid, and coumaric acid in a random order for their effects on PSTs activities were evaluated at concentrations of 2.5, 5.0, and 7.5 microM. The PST-M activity was significantly increased when gentisic acid was combined with each of the other phenolic acids. When p-hydroxybenzoic acid was combined with each of the other phenolic acids, a synergistic effect with respect to the promotion of PST-P activity was obtained. A potential synergistic effect for the PST-P activity was also found in the following combination: p-hydroxybenzoic acid + gallic acid + gentisic acid, p-hydroxybenzoic acid + gallic acid + m-coumaric acid, p-hydroxybenzoic acid + o-coumaric acid + p-coumaric acid, p-hydroxybenzoic acid + o-coumaric acid + m-coumaric acid, gallic acid + gentisic acid + p-coumaric acid, and gallic acid + o-coumaric acid + m-coumaric acid. Therefore, the activities of both forms of PSTs can be promoted by all of these combinations of phenolic acids. These results provide a better understanding regarding the effect of phenolic acids on human PSTs activities, as well as more information on the intake of antioxidant phenolic acids for human health.

Differential activation of promutagens by alloenzymes of human sulfotransferase 1A2 expressed in Salmonella typhimurium

Various enzymatically formed sulfuric acid esters are chemically reactive and mutagenic. This metabolic activation pathway is not detected in standard in-vitro mutagenicity test systems. We describe the construction of Salmonella typhimurium TA1538-derived strains expressing alloenzymes *1, *2, *3, *5, *6 of human sulfotransferase 1A2 (SULT1A2). The reference compounds, 1-hydroxymethylpyrene (1-HMP), N-hydroxy-2-acetylaminofluorene (OH-AAF) and 2-hydroxylamino-5-phenylpyridine (OH-APP), were activated to mutagens in these strains. Their activity differed 7- to 16-fold between strains expressing various alloenzymes. It was strongest and weakest in the strains expressing the common alloenzymes, *1 and *2, respectively. The SULT1A2 protein expression levels, and the V(max) and K(m) values with the reference substrate 4-nitrophenol, varied 2.5-, 4-, and 110-fold, respectively, in cytosolic preparations from strains TA1538-SULT1A2*1 and *2. Strains with varying protein levels were constructed via insertion of silent mutations in the 5'-part of the cDNA. TA1538-SULT1A2*1Z and TA1538-SULT1A2*2Y showed equal expression levels of alloenzymes *1 and *2, respectively, which were 3 times above those of TA1538-SULT1A2*1. The mutagenicity of OH-AAF and OH-APP was unchanged in strain TA1538-SULT1A2*1Z versus *1, and moderately increased in TA1538-SULT1A2*2Y versus *2. The influence of the protein level was stronger with 1-HMP. Nevertheless, mutagenic activity of 1-HMP was still 11 times higher in TA1538-SULT1A2*1Z than in TA1538-SULT1A2*2Y. Thus, differences in the properties between alloenzymes can lead to differences in the activation of promutagens. The model compounds were also tested in strains expressing the other ten human SULTs identified. Whereas OH-AAF and OH-APP showed the highest mutagenic activities in strains expressing SULT1A2, 1-HMP was more potent in strains expressing other SULT forms. With the limitation that little is known about the tissue distribution and regulation of SULT1A2, the findings suggest that its polymorphism may affect the individual susceptibility towards procarcinogens, in particular certain aromatic amines and amides.

Sulfonation and molecular action

The sulfonation of endogenous molecules is a pervasive biological phenomenon that is not always easily understood, and although it is increasingly recognized as a function of fundamental importance, there remain areas in which significant cognizance is still lacking or at most minimal. This is particularly true in the field of endocrinology, in which the sulfoconjugation of hormones is a widespread occurrence that is only partially, if at all, appreciated. In the realm of steroid/sterol sulfoconjugation, the discovery of a novel gene that utilizes an alternative exon 1 to encode for two sulfotransferase isoforms, one of which sulfonates cholesterol and the other pregnenolone, has been an important advance. This is significant because cholesterol sulfate plays a crucial role in physiological systems such as keratinocyte differentiation and development of the skin barrier, and pregnenolone sulfate is now acknowledged as an important neurosteroid. The sulfonation of thyroglobulin and thyroid hormones has been extensively investigated and, although this transformation is better understood, there remain areas of incomplete comprehension. The sulfonation of catecholamines is a prevalent modification that has been extensively studied but, unfortunately, remains poorly understood. The sulfonation of pituitary glycoprotein hormones, especially LH and TSH, does not affect binding to their cognate receptors; however, sulfonation does play an important role in their plasma clearance, which indirectly has a significant effect on biological activity. On the other hand, the sulfonation of distinct neuroendocrine peptides does have a profound influence on receptor binding and, thus, a direct effect on biological activity. The sulfonation of specific extracellular structures plays an essential role in the binding and signaling of a large family of extracellular growth factors. In summary, sulfonation is a ubiquitous posttranslational modification of hormones and extracellular components that can lead to dramatic structural changes in affected molecules, the biological significance of which is now beginning to be appreciated.

Cardiac gene expression profile and lipid accumulation in response to starvation

Starvation induces many biochemical and histological changes in the heart; however, the molecular events underlying these changes have not been fully elucidated. To explore the molecular response of the heart to starvation, microarray analysis was performed together with biochemical and histological investigations. Serum free fatty acids increased twofold in both 16- and 48-h-fasted mice, and cardiac triglyceride content increased threefold and sixfold in 16- and 48-h-fasted mice, respectively. Electron microscopy showed numerous lipid droplets in hearts of 48-h-fasted mice, whereas fewer numbers of droplets were seen in hearts from 16-h-fasted mice. Expression of 11,000 cardiac genes was screened by microarrays. More than 50 and 150 known genes were detected by differential expression analysis after 16- and 48-h-fasts, respectively. Genes for fatty acid oxidation and gluconeogenesis were increased, and genes for glycolysis were decreased. Many other genes for metabolism, signaling/cell cycle, cytoskeleton, and tissue antigens were affected by fasting. These data provide a broad perspective of the molecular events occurring physiologically in the heart in response to starvation.

Structure and localization of the human SULT1B1 gene: neighborhood to SULT1E1 and a SULT1D pseudogene

The soluble sulfotransferases are involved in the elimination of xenobiotics, the activation of procarcinogens, and the regulation of hormones. They comprise a gene superfamily (SULT). The structure and chromosomal location of nine human SULT genes are known. We have characterized a further gene, SULT1B1. Its structure is similar to that of other SULT1 genes. However, the total length of its eight exons and the introns (33.6 kb) is larger than that of other human SULT1 genes (4 to 21 kb). The SULT1B1 gene sequence is part of a sequence entry in the unfinished High-Throughput Genomic Sequences (HTGS) division of GenBank. However, the order and orientation of the SULT1B1 exons are not correct in this entry. SULT1B1 is located on chromosome 4q13.1, nearly 100 kb downstream of SULT1E1 on the same strand. The intervening sequence contains a SULT-like structure showing substantial homology to the mouse SULT1D1 cDNA recently described. However, in humans this structure represents a pseudogene (SULT1D1P) because of mutated splice donors/acceptors and in-frame stop codons in the sequence corresponding to exon II. This SULT gene cluster is located on the minus strand of chromosome 4 with SULT1B1 being closest to the centromer.

Expression profiling of human sulfotransferase and sulfatase gene superfamilies in epithelial tissues and cultured cells

The bioavailability of drugs administered topically or orally depends on their metabolism by epithelial enzymes such as the cytosolic sulfotransferases (SULT). Reverse transcriptase-polymerase chain reaction (RT-PCR) methods were established to detect expression of 8 SULT genes and 4 arylsulfatase (ARS) genes in human tissues of epithelial origin and in cultures of normal and transformed (cancer) cells. The results indicate: (i) SULT 1A1, 1A3, ARSC, and ARSD genes are ubiquitously expressed; (ii) expression is frequently similar between cell lines and corresponding tissues; (iii) SULT gene expression in normal cultured cells is generally comparable to the expression in associated transformed (cancer) cell lines; (iv) SULT 1A1 promoter usage is mainly tissue specific; however, both promoters are frequently used in SULT 1A3 expression; and (v) the expression profile of SULT 1A1, 1A3, 1E1, and 2B1a/b suggests that one or more of these isoforms may be involved in the cutaneous sulfoconjugation of minoxidil and cholesterol.

Pharmacogenetics of sulfotransferase

Cytosolic sulfotransferase catalyzes sulfoconjugation of relatively small lipophilic endobiotics and xenobiotics. At least 44 cytosolic sulfotransferases have been identified from mammals, and based on their amino acid sequences, these forms are shown to constitute five different families. In humans, 10 sulfotransferase genes have been identified and shown to localize on at least five different chromosomes. The enzymatic properties characterized in the recombinant forms indicate the association of their substrate specificity with metabolisms of such nonpeptide hormones as estrogen, corticoid, and thyroxine, although most forms are also active on the sulfation of various xenobiotics. Genetic polymorphisms are observed on such human sulfotransferases as ST1A2, ST1A3, and ST2A3.

Purification and characterization of hepatic and intestinal phenol sulfotransferase with high affinity for benzo[a]pyrene phenols from channel catfish, Ictalurus punctatus

Cytosol from channel catfish liver and intestinal mucosa has high sulfotransferase activity with low concentrations of 3-, 7-, or 9-hydroxybenzo[a]pyrene. To further investigate this conjugation pathway, sulfotransferase activity toward 9-hydroxybenzo[a]pyrene was isolated from catfish intestinal and hepatic cytosol by chromatography on anion exchange and PAP-agarose affinity columns. SDS-PAGE of the active fractions showed that one major band with molecular size of about 41,000 Da was isolated from intestine, while two bands of about 41,000 and 31,000 Da were obtained from liver. Antibodies against human phenol-sulfating sulfotransferase cross-reacted strongly with the 41,000-Da bands from liver and intestine, but weakly with the hepatic 31,000-Da protein. N-Terminal sequence information could not be obtained from the pure proteins. Following digestion, an internal sequence of 20 amino acid residues was obtained from the hepatic 41,000-Da protein, which matched a sequence found in several mammalian sulfotransferases. No fish sulfotransferase sequences were available for comparison. The identity of the hepatic 31,000-Da protein was not established. The purified 41,000-Da proteins had very high activities with 3-, 7-, or 9-hydroxybenzo[a]pyrene, with K(m) values in the 40-100 nM range and V(max) 125-300 nmol/min/mg of protein. Substrate inhibition was observed when the concentrations of hydroxylated benzo[a]pyrenes were above 0.5 microM. As well as benzo[a]pyrene phenols, the purified 41,000-Da sulfotransferases catalyzed sulfation of 2-naphthol, 4-nitrophenol, 4-methylumbelliferone, 7-(hydroxymethyl)-12-methylbenz[a]anthracene, dehydroepiandrosterone, estrone, and 17beta-estradiol. Phenolic compounds were the preferred substrates for the purified enzymes.

Association between functional genetic polymorphisms of human sulfotransferases 1A1 and 1A2

Three human phenol sulfotransferases, provisionally named SULT1A1, 1A2 and 1A3, show 91-96% homology of their amino acid sequences and are encoded by neighbouring gene loci. Functional genetic polymorphisms are known for two of these sulfotransferases. In SULT1A1, a G to A transition leads to an Arg213 to His exchange and eliminates a Bsp143II restriction site. SULT1A1*His shows lower enzyme activity and thermostability than SULT1A1*Arg. In SULT1A2, an A to C transversion causes an Asn235 to Thr exchange and introduces a BpiI restriction site. Enzyme SULT1A2*Thr is less active than SULT1A2*Asn. These substitutions were detected by restriction fragment length polymorphism analyses of genomic sequences amplified by polymerase chain reaction. Despite the high similarity between the different human SULT1A genes, it was possible to amplify specifically the polymorphic parts of either SULT1A1 or 1A2, but not the homologous sequences of the other SULT, by setting the forward primer into intron 6. DNA from 300 adult male Caucasian subjects was analysed. Allele frequencies were 0.63 and 0.37 for SULT1A1*Arg and *His, and 0.62 and 0.38 for SULT1A2*Asn and *Thr, respectively. The frequency of the haplotype SULT1A1*Arg/SULT1A2*Asn (0.61) was nearly as high as the allele frequencies of its components. The same was observed for the haplotype SULT1A1*His/SULT1A2*Thr, whose frequency was 0.35. In contrast, haplotypes 1A1*Arg/1A2*Thr and 1A1*His/1A2*Asn were very rare. Their frequencies (0.02 each) were less than 10% of the figures expected in an independent distribution. The results demonstrate a strong association of the alleles producing the more active enzyme variants (SULT1A1*Arg and SULT1A2*Asn) and of those encoding the less active variants (SULT1A1*His and SULT1A2*Thr).

Control of sulfatase and sulfotransferase activities by medrogestone in the hormone-dependent MCF-7 and T-47D human breast cancer cell lines

In the present study, we explored the effect of the progestin medrogestone on the sulfatase and sulfotransferase activities in the hormone-dependent MCF-7 and T-47D human breast cancer cell lines. After 24 h incubation at 37 degrees C of physiological concentrations of estrone sulfate ([3H]-E1S: 5x10(-9) mol/l), it was observed that this estrogen was converted in a great proportion to E2 in both cell lines. Medrogestone significantly inhibits this transformation, at all the concentrations tested (5x10(-8) to 5x10(-5) mol/l), in both cell lines. The IC50 values were 1.93 micromol/l and 0.21 micromol/l in MCF-7 and T-47D cells, respectively. In another series of studies, after 24 h incubation at 37 degrees C of physiological concentrations of estrone ([3H]-E1: 5x10(-9) mol/l), the sulfotransferase activity was detectable in both cell lines. Estrogen sulfates (ES) are found exclusively in the culture medium, which suggests that as soon as they are formed they are excreted into the medium. Medrogestone has a biphasic effect on sulfotransferase activity in both cell lines. At low doses: 5x10(-8) and 5x10(-7) mol/l, this compound stimulates the enzyme by +73.5 and 52.7%, respectively, in MCF-7, and by 84.5 and 62.6% in T-47D cells. At high concentrations: 5x10(-6) and 5x10(-5) mol/l, medrogestone has no effect on MCF-7 cells, but inhibits the sulfotransferase activity in T-47D cells by -31.4% at 5x10(-5) mol/l. In conclusion, the inhibitory effect provoked by medrogestone on the enzyme involved in the biosynthesis of E2 (sulfatase pathway) in estrogen-dependent breast cancer, as well as the stimulatory effect on the formation of the inactive ES, support a probable anti-proliferative effect of this progestin in breast tissue. Clinical applications of these findings can open new therapeutic possibilities for this disease.