Primary structures and properties of two related forms of aryl sulfotransferases in human liver

Journey in the Polyphenol Research World with Ragai Ibrahim

Dr. Ragai K. Ibrahim, Professor Emeritus at Concordia University, Montréal, Canada, passed away on the November 19, 2017 at the age of 88 years. Dr. Ibrahim dedicated his entire professional life to polyphenols and spent most of his academic career (1967-1997) at the Department of Biology of Concordia University in Montréal. He has been an active member of the Groupe Polyphénols since the beginning. This paper is a tribute to Dr. Ibrahim from some of his former students. An overview of the evolution of polyphenol research since the late 1950s and the outstanding contribution that Dr. Ibrahim had to this topic is given. The input of Dr. Ibrahim's research to the enzymology and genetics of polyphenol biosynthesis is discussed. Furthermore, the links between Dr. Ibrahim's work and some aspects of modern studies on the health benefits of polyphenols are presented.

Δ4-3-ketosteroids as a new class of substrates for the cytosolic sulfotransferases

Cytosolic sulfotransferase (SULT)-mediated sulfation is generally known to involve the transfer of a sulfonate group from the active sulfate, 3'-phosphoadenosine 5'-phosphosulfate (PAPS), to a hydroxyl group or an amino group of a substrate compound. We report here that human SULT2A1, in addition to being able to sulfate dehydroepiandrosterone (DHEA) and other hydroxysteroids, could also catalyze the sulfation of Δ⁴-3-ketosteroids, which carry no hydroxyl groups in their chemical structure. Among a panel of Δ⁴-3-ketosteroids tested as substrates, 4-androstene-3,17-dione and progesterone were found to be sulfated by SULT2A1. Mass spectrometry analysis and structural modeling supported a reaction mechanism which involves the isomerization of Δ⁴-3-ketosteroids from the keto form to an enol form, prior to being subjected to sulfation. Results derived from this study suggested a potential role of SULT2A1 as a Δ⁴-3-ketosteroid sulfotransferase in steroid metabolism.

Single nucleotide polymorphisms in SULT1A1 and SULT1A2 in a Korean population

SULT1A1 and SULT1A2 are encoded on the same chromatid, and exhibit a 96% amino acid similarity. To screen for genetic variants in these two closely related genes, SULT1A1 and SULT1A2 were directly sequenced in 50 healthy Koreans. A total of 30 variations were identified in SULT1A1: eight in exons, thirteen in introns, and nine in the 5'-untranslated region. With regard to SULT1A2, 21 variants were identified, comprising seven in exons, five in introns, and nine in the 5'-untranslated region. Among these 51 variations, one in SULT1A1 and eight in SULT1A2 were previously unidentified, which include three coding variants (SULT1A2 R37Q, 110G>A; SULT1A2 G50S, 148G>A; SULT1A2 F286L, 3819C>A) and one null allele (SULT1A2 E217Stop, 3542G>T). Two LD blocks, major haplotype structures, and 7 haplotype-tagging SNPs were determined together for SULT1A1 and SULT1A2 as a single set. Frequencies of common functional variants were compared among ethnic groups. Since these two SULT enzymes are on the same chromatid in a parallel direction with overlapping substrate specificities, a combined analysis using LD and haplotype-tagging single-nucleotide polymorphisms (SNPs) will facilitate understanding of the variations in the sulfation reactions of a wide range of substrates, as compared with analysis of individual genes.

Enzymatic sulfation of tocopherols and tocopherol metabolites by human cytosolic sulfotransferases

Tocopherols are essential micronutrients for mammals widely known as potent lipid-soluble antioxidants that are present in cell membranes. Recent studies have demonstrated that most of the carboxychromanol (CEHC), a tocopherol metabolite, in the plasma exists primarily in sulfate- and glucuronide-conjugated forms. To gain insight into the enzymatic sulfation of tocopherols and their metabolites, a systematic investigation was performed using all 14 known human cytosolic sulfotransferases (SULTs). The results showed that the members of the SULT1 family displayed stronger sulfating activities toward tocopherols and their metabolites. These enzymes showed a substrate preference for γ-tocopherol over α-tocopherol and for γ-CEHC over other CEHCs. Using A549 human lung epithelial cells in a metabolic labeling study, a similar trend in the sulfation of tocopherols and CEHCs was observed. Collectively, the results obtained indicate that SULT-mediated enzymatic sulfation of tocopherols and their metabolites is a significant pathway for regulation of the homeostasis and physiological functions of these important compounds.

Induction of human sulfotransferase 1A3 (SULT1A3) by glucocorticoids

Sulfotransferases (SULTs) play an important role in the detoxification and bioactivation of endogenous compounds and xenobiotics. Studies on rat sulfotransferases had shown that SULT genes, like cytochrome P450 genes, can be regulated by ligands that bind nuclear receptors. For human SULT genes, the regulation of human SULT2A1 expression is currently the best characterized. In this study, we systematically examined the regulation of human SULT1A genes by glucocorticoids. Treatment of the human hepatocellular carcinoma derived HepG2 cells with 10(-7) M dexamethasone did not affect the SULT1A1 activity toward p-nitrophenol. In contrast, SULT1A3 activity toward dopamine was significantly induced. Transient transfection of the SULT1A3 5'-flanking region/luciferase reporter construct showed that SULT1A3 was responsive to dexamethasone and prednisolone in a concentration-dependent manner with maximal induction at 10(-7) M dexamethasone or 1 microM prednisolone. In addition, induction by dexamethasone was dependent on the level of expression of the glucocorticoid receptor. Analysis of the 5'-flanking region led to the identification of a putative glucocorticoid response element at position (-1211 to -1193) upstream of the transcription start site and deletion or mutation of this element resulted in a loss of response. In summary, the data from this study shows that the human SULT1A3 gene is inducible by glucocorticoids through a glucocorticoid receptor-mediated mechanism and the glucocorticoid response element at position (-1211 to -1193) is necessary for this induction.

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 polymorphisms and linkage disequilibrium of sulfotransferase SULT1A1 and SULT1A2 in a Korean population: comparison of other ethnic groups

AIMS

To determine the allele frequencies of sulfotransferases (SULTs) 1A1 and 1A2 and their linkage disequilibrium in a Korean population and compare them with those of other ethnic groups.

METHODS

Genotypes of the SULT1A1*1, *2, and *3 and SULT1A2*1, *2, and *3 allelic variants were determined in 234 Korean subjects using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) methods.

RESULTS

Allele frequencies for SULT1A1*1 and *2 were 0.876 [95% confidence interval (CI), 0.843-0.905] and 0.124 (95% CI, 0.096-0.157), respectively. Similarly, those for SULT1A2*1 and *2 were 0.885 (95% CI, 0.852-0.912) and 0.115 (95% CI, 0.088-0.150), respectively. However, no subject with SULT1A1*3 or SULT1A2*3 was detected. These genotype distributions are similar to those of Asian populations including the Chinese and Japanese, but quite different from other ethnic groups such as African-Americans and Caucasians. The expected allelic frequencies of SULT1A1 and SULT1A2 at Hardy-Weinberg equilibrium are quite similar to the observed distributions in the population. SULT1A1*2 and SULT1A2*2, the most common variant alleles of these two genes, are strongly and positively linked in the Korean population (D' = 0.8919, chi2 = 343.24, P = 0.0034).

CONCLUSIONS

SULT1A1*2 and SULT1A2*2 are the major allelic variants in the Korean population, whereas the SULT1A1*3 and SULT1A2*3 alleles were not found. SULT1A1*2 and SULT1A2*2 are strongly linked.

Phylogenomic approaches to common problems encountered in the analysis of low copy repeats: the sulfotransferase 1A gene family example

Background

Blocks of duplicated genomic DNA sequence longer than 1000 base pairs are known as low copy repeats (LCRs). Identified by their sequence similarity, LCRs are abundant in the human genome, and are interesting because they may represent recent adaptive events, or potential future adaptive opportunities within the human lineage. Sequence analysis tools are needed, however, to decide whether these interpretations are likely, whether a particular set of LCRs represents nearly neutral drift creating junk DNA, or whether the appearance of LCRs reflects assembly error. Here we investigate an LCR family containing the sulfotransferase (SULT) 1A genes involved in drug metabolism, cancer, hormone regulation, and neurotransmitter biology as a first step for defining the problems that those tools must manage.

Results

Sequence analysis here identified a fourth sulfotransferase gene, which may be transcriptionally active, located on human chromosome 16. Four regions of genomic sequence containing the four human SULT1A paralogs defined a new LCR family. The stem hominoid SULT1A progenitor locus was identified by comparative genomics involving complete human and rodent genomes, and a draft chimpanzee genome. SULT1A expansion in hominoid genomes was followed by positive selection acting on specific protein sites. This episode of adaptive evolution appears to be responsible for the dopamine sulfonation function of some SULT enzymes. Each of the conclusions that this bioinformatic analysis generated using data that has uncertain reliability (such as that from the chimpanzee genome sequencing project) has been confirmed experimentally or by a "finished" chromosome 16 assembly, both of which were published after the submission of this manuscript.

Conclusion

SULT1A genes expanded from one to four copies in hominoids during intra-chromosomal LCR duplications, including (apparently) one after the divergence of chimpanzees and humans. Thus, LCRs may provide a means for amplifying genes (and other genetic elements) that are adaptively useful. Being located on and among LCRs, however, could make the human SULT1A genes susceptible to further duplications or deletions resulting in 'genomic diseases' for some individuals. Pharmacogenomic studies of SULT1Asingle nucleotide polymorphisms, therefore, should also consider examining SULT1A copy number variability when searching for genotype-phenotype associations. The latest duplication is, however, only a substantiated hypothesis; an alternative explanation, disfavored by the majority of evidence, is that the duplication is an artifact of incorrect genome assembly.

Involvement of SULT1A3 in elevated sulfation of 4-hydroxypropranolol in Hep G2 cells pretreated with β-naphthoflavone

Pretreatment of Hep G2 cells with beta-naphthoflavone (BNF 1-25microM) significantly increased cytosolic sulfation activities of 4-hydroxypropranolol (4-OH-PL) racemate. The profile was similar to those of sulfations towards dopamine and triiodothyronine in the same cytosolic fractions. Kinetic studies of 4-OH-PL sulfation in Hep G2 cytosolic fractions revealed that V(max) values increased but apparent K(m) values remained unchanged following the BNF pretreatment. Among five recombinant human SULT isoforms (SULT1A1, -1A3, -1B1, -1E1 and -2A1) examined, only SULT2A1 did not show 4-OH-PL sulfation activities under the conditions used. SULT1A3 and -1E1 exhibited an enantioselectivity of 4-OH-R-PL sulfation>4-OH-S-PL sulfation, which agreed with that of BNF-pretreated Hep G2 cells as well as of nontreated cells, whereas SULT1A1 and -1B1 showed a reversed enantioselectivity (R<S). In kinetic studies of 4-OH-PL sulfations by four kinds of human SULT isoforms, apparent K(m) values for SULT1A3 were the lowest, and the parameters were close to those of Hep G2 cytosolic fractions. Real time RT-PCR using TaqMan probes demonstrated that the mRNA levels of SULT1A3 increased following BNF pretreatment, which paralleled the results from Western blotting showing the elevated levels of SULT1A3 proteins. These results suggest that the induction of SULT1A3 is mainly responsible for the elevated 4-OH-PL sulfation activities following the pretreatment of Hep G2 cells with BNF.

Human SULT1A Genes: Cloning and Activity Assays of the SULT1A Promoters

The three human SULT1A sulfotransferase enzymes are closely related in amino acid sequence (>90%), yet differ in their substrate preference and tissue distribution. SULT1A1 has a broad tissue distribution and metabolizes a range of xenobiotics as well as endogenous substrates such as estrogens and iodothyronines. While the localization of SULT1A2 is poorly understood, it has been shown to metabolize a number of aromatic amines. SULT1A3 is the major catecholamine sulfonating form, which is consistent with it being expressed principally in the gastrointestinal tract. SULT1A proteins are encoded by three separate genes, located in close proximity to each other on chromosome 16. The presence of differential 5'-untranslated regions identified upon cloning of the SULT1A cDNAs suggested the utilization of differential transcriptional start sites and/or differential splicing. This chapter describes the methods utilized by our laboratory to clone and assay the activity of the promoters flanking these different untranslated regions found on SULT1A genes. These techniques will assist investigators in further elucidating the differential mechanisms that control regulation of the human SULT1A genes. They will also help reveal how different cellular environments and polymorphisms affect the activity of SULT1A gene promoters.

The human sulfotransferase SULT1A1 gene is regulated in a synergistic manner by Sp1 and GA binding protein

Human sulfotransferase SULT1A1 is an important phase II xenobiotic metabolizing enzyme that is highly expressed in the liver and mediates the sulfonation of drugs, carcinogens, and steroids. Until this study, the transcriptional regulation of the SULT1A subfamily had been largely unexplored. Preliminary experiments in primary human hepatocytes showed that SULT1A mRNA levels were not changed in response to nuclear receptor activators, such as dexamethasone and 3-methylcolanthrene, unlike other metabolizing enzymes. Using HepG2 cells, the high activity of the TATA-less SULT1A1 promoter was shown to be dependent on the presence of Sp1 and Ets transcription factor binding sites (EBS), located within -112 nucleotides from the transcriptional start site. The homologous promoter of the closely related SULT1A3 catecholamine sulfotransferase, which is expressed at negligible levels in the adult liver, displayed 70% less activity than SULT1A1. This was shown to be caused by a two-base pair difference in the EBS. The Ets transcription factor GA binding protein (GABP) was shown to bind the SULT1A1 EBS and could transactivate the SULT1A1 promoter in Drosophila melanogaster S2 cells. Cotransfection of Sp1 could synergistically enhance GABP-mediated activation by 10-fold. Although Sp1 and GABP alone could induce SULT1A3 promoter activity, the lack of the EBS on this promoter prevented a synergistic interaction between the two factors. This study reports the first insight into the transcriptional regulation of the SULT1A1 gene and identifies a crucial difference in regulation of the closely related SULT1A3 gene, which accounts for the two enzymes' differential expression patterns observed in the adult liver.

A proposed nomenclature system for the cytosolic sulfotransferase (SULT) superfamily

A nomenclature system for the cytosolic sulfotransferase (SULT) superfamily has been developed. The nomenclature guidelines were applied to 65 SULT cDNAs and 18 SULT genes that were characterized from eukaryotic organisms. SULT cDNA and gene sequences were identified by querying the GenBank databases and from published reports of their identification and characterization. These sequences were evaluated and named on the basis of encoded amino acid sequence identity and, in a few cases, a necessity to maintain historical naming convention. Family members share at least 45% amino acid sequence identity whereas subfamily members are at least 60% identical. cDNAs which encode amino acid sequences of at least 97% identity to each other were assigned identical isoform names. We also attempted to categorize orthologous enzymes between various species, where these have been identified, and the nomenclature includes a species descriptor. We present recommendations for the naming of allelic variants of SULT genes and their derived allozymes arising from single nucleotide polymorphisms and other genetic variation. The superfamily currently comprises 47 mammalian SULT isoforms, one insect isoform and eight plant enzymes, and collectively these sequences represent nine separate SULT families and 14 subfamilies. It is hoped that this nomenclature system will be widely adopted and that, as novel SULTs are identified and characterized, investigators will name their discoveries according to these guidelines.

Regioselective Monosulfation and Disulfation of the Phytoestrogens Daidzein and Genistein by Human Liver Sulfotransferases

Regioselective sulfation of the phytoestrogens daidzein (DZ, 7,4'-dihydroxyisoflavone) and genistein (GS, 5,7,4'-trihydroxyisoflavone) was investigated using human liver cytosol and purified recombinant human sulfotransferase (SULT) isoforms, SULT1A1, SULT1A3, SULT2A1, and SULT1E1. 7-Position-preferential sulfation of DZ and GS was observed in human hepatic cytosols from 3 male and 3 female subjects. Average ratios for 7- to 4'-sulfate formation were 4.5:1 from DZ and 8.4:1 from GS in these human liver cytosols. Apparent K(m) values for the 7- and 4'-sulfation of DZ and GS by these cytosols were similar and in a range from 0.46 to 0.66 microM. All recombinant human SULTs had activity for 7- and 4'-sulfation of these phytoestrogens except for 7-sulfating activity of SULT1A3. SULT1A1 and SULT1E1 exhibited much higher catalytic efficiency, k(cat)/K(m), for 7- and 4'-sulfation of these substrates than did the other two, SULT1A3 and SULT2A1. SULT1A1 showed K(m) values of 0.47 and 0.52 microM for the mono-sulfation of DZ and GS, respectively, which were very similar to those of human cytosol. The observed k(cat)/K(m) indicated that SULT1A1 catalyzed 7-sulfation of DZ and GS at rates 4.4- and 8.8-fold higher, respectively, than such 4'-sulfation. However, with SULT1E1, catalytic efficiency was very similar for the sulfation of both positions. These data strongly suggest that SULT1A1 plays a major role in monosulfation of the phytoestrogens and determines the regioselectivity of sulfation in human hepatic cytosol. A kinetic study for 7,4'-disulfate formation of DZ and GS from their 7- and 4'-monosulfates indicated that SULT1E1 most efficiently catalyzed both reactions among human SULTs.

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.

Reverse geometrical selectivity in glucuronidation and sulfation of cis- and trans-4-hydroxytamoxifens by human liver UDP-glucuronosyltransferases and sulfotransferases

The phenolic active metabolites, cis-4-hydroxytamoxifen (cis-HO-TAM) and trans-4-hydroxytamoxifen (trans-HO-TAM), of the anti-breast-cancer drug, trans-tamoxifen (TAM), were geometrically selectively glucuronidated in the manner of cis>>trans by microsomes and sulfated in the manner of trans>>cis by cytosol from the liver of 10 human subjects (7 females and 3 males). There was a large individual difference in the microsomal glucuronidation of cis-HO-TAM, which correlated well with glucuronidation of 4-hydroxybiphenyl by human liver microsomes. However, there was only a slight correlation between the glucuronidation of cis-HO-TAM and trans-HO-TAM or 4-nitrophenol (NP). A small individual difference was observed for the human liver cytosolic sulfation of trans-HO-TAM, which correlated well with the sulfation of NP. Recombinant human UDP-glucuronosyltransferase (UGT)2B15 catalyzed the cis-selective glucuronidation of geometrical isomers of HO-TAM. UGTs1A1, 1A4, 1A9 and 2B7 had weak activity toward HO-TAMs with a much smaller cis-selectivity than did UGT2B15. UGTs1A3 and 1A6 had no detectable activity toward these substrates. Among the four known major sulfotransferases (SULTs) occurring in the human liver, SULT1A1 was strongly suggested to play the most important role in the hepatic cytosolic trans-selective sulfation of HO-TAM isomers. A good correlation was observed between the hepatic cytosolic sulfation of trans-HO-TAM and NP, a standard substrate for SULT1A1. SULT1E1 had slight activity toward the HO-TAMs. SULTs1A3 and 2A1 had no detectable activity toward HO-TAMs.

Canine sulfotransferase SULT1A1: molecular cloning, expression, and characterization

Sulfotransferases (SULTs) are involved in detoxification and activation of various endogenous and exogenous compounds including important drugs and hormones. SULT1A, the phenol-SULT subfamily, is the most prominent subfamily in xenobiotic metabolism and has been found in several species, e.g., human, rat, and mouse. We have cloned a phenol-sulfating phenol SULT from dog (cSULT1A1) and expressed it in Escherichia coli for characterization. cSULT1A1 showed 85.8, 82.7, 76.3, and 73.6% identities to human P-PST, human M-PST, rat PST-1, and mouse STp1, respectively. It consists of 295 amino acids, which is in agreement with the human ortholog and sulfate substrates typical for the SULT1A family, i.e., p-nitrophenol (PNP), alpha-naphthol, and dopamine. The K(m) for PNP was found to be within the nanomolar range. It also sulfates minoxidil and beta-estradiol but not dehydroepiandrosterone. Western blot analysis indicated that this newly cloned enzyme was found to be ubiquitously expressed in canine tissues with highest expression in male and female liver.

Human cytosolic sulphotransferases: genetics, characteristics, toxicological aspects

Cytosolic sulphotransferases transfer the sulpho moiety from the cofactor 5'-phosphoadenosine-3'-phosphosulphate (PAPS) to nucleophilic groups of xenobiotics and small endogenous compounds (such as hormones and neurotransmitters). This reaction often leads to products that can be excreted readily. However, other sulpho conjugates are strong electrophiles and may covalently bind with DNA and proteins. All known cytosolic sulphotransferases are members of an enzyme/gene superfamily termed SULT. In humans, 10 SULT genes are known. One of these genes encodes two different enzyme forms due to the use of alternative first exons. Different SULT forms substantially differ in their substrate specificity and tissue distribution. Genetic polymorphisms have been described for three human SULTs. Several allelic variants differ in functional properties, including the activation of promutagens. Only initial results are available from the analysis of SULT allele frequencies in different population groups, e.g. subjects suffering from specific diseases and corresponding controls.

Molecular cloning, expression, and characterization of a canine sulfotransferase that is a human ST1B2 ortholog

Sulfation is an important conjugation pathway in deactivating thyroid hormones, keeping the proper hormonal balance, and increasing the rate of thyroid hormone metabolism. We have identified, cloned, and characterized a sulfotransferase (SULT) that is capable of thyroid hormone conjugation in the dog. This enzyme, designated cSULT1B1, displays a strong identity (>84%) to the human ST1B2 enzyme. However, cSULT1B1 displays less identity, about 73%, to mouse and rat orthologs. In addition, the canine enzyme is three amino acids shorter than the rodent ones but has the same length as the human ortholog, 296 amino acids. The bacterial expressed and partial purified cSULT1B1 enzyme sulfates p-nitrophenol and 1-naphtol, but not dopamine. The thyroid hormones 3,3'-diiodothyronine and 3,5,3'-triiodothyronine are efficiently sulfated. 3,3',5'-Triiodothyronine is sulfated to lesser degree while sulfation of 3,5'-diiodothyronine and 3,3',5,5'-tetraiodothyronine cannot be detected. The cSULT1B1 is found in the colon (highest level), kidney and small intestine in dogs, but surprisingly not in the male dog liver although low levels of immunoreactivity were detected in the female dog liver. The male dog expresses more of SULT1B1 enzyme in the lower part of the small intestine while the female dog displays an opposite pattern of expression. These results describe the cloning and characterization of a canine thyroid hormone sulfating enzyme that is more closely related to the human ortholog than to the rodent thyroid sulfating enzymes.

Identification of a new subfamily of sulphotransferases: cloning and characterization of canine SULT1D1

Sulphation is an important conjugation pathway in drug metabolism that has been studied in several species including humans. However, few studies have been performed using the dog as a subject. In this report we describe the cloning and characterization of a canine cytosolic sulphotransferase (SULT). The overall primary structure of this enzyme is very similar to that of a rat phenol-sulphating enzyme found in the EMBL Database and to a mouse SULT termed amine-N-sulphotransferase (81% identity). The expressed canine SULT conjugates small phenols and aromatic amines such as dopamine, minoxidil, p-nitrophenol and 5-hydroxytryptamine, but not dehydroepiandrosterone or beta-oestradiol. These results are in agreement with the results reported for the mouse SULT. In contrast with the mouse enzyme, the canine SULT does not conjugate eicosanoid compounds, i.e. prostaglandins, thromboxane B(2) or leukotriene E(4). The canine SULT is expressed at high levels in the colon of both genders; it is also expressed in the small intestine, kidney and liver. Furthermore, because the canine, mouse and rat SULT forms exhibit significant sequence identity (more than 80%), they seem to represent a distinct group in the SULT family tree. This suggestion is strengthened by the low identity with other SULTs. The subfamily that is most similar to this new group is SULT1A, with approx. 60% similarity. However, the mouse and canine enzymes are not characterized by the efficient sulphation of p-nitrophenol, dopamine, beta-oestradiol or oestrone. Thus these results seem to exclude them from the SULT1A subfamily. We therefore propose a new subfamily in the phenol SULT family, designated SULT1D, and consequently the canine enzyme is termed SULT1D1.

Sulfation pharmacogenetics: SULT1A1 and SULT1A2 allele frequencies in Caucasian, Chinese and African-American subjects

Sulfotransferase (SULT) enzymes catalyze the sulfate conjugation of drugs, other xenobiotics, neurotransmitters and hormones. The genes for SULT1A1 and SULT1A2 contain common genetic polymorphisms that are associated with individual variations in levels of enzyme activity as well as variations in biochemical and physical properties. We set out to compare the frequencies of common SULT1A1 and SULT1A2 alleles in Caucasian, Chinese and African-American subjects. Allele frequencies for SULT1A1*1, *2 and *3 in 242 Caucasian subjects were 0.656, 0.332 and 0.012, respectively. Frequencies of those same alleles were significantly different in 290 Chinese subjects: 0.914, 0.080 and 0.006, respectively, as were frequencies in 70 African-American subjects: 0.477, 0.294 and 0.229, respectively. Ethnic variation in allele frequencies was also observed for SULT1A2, with frequencies in Caucasian subjects for SULT1A2*1, *2 and *3 of 0.507, 0.389 and 0.104; frequencies in Chinese of 0.924 and 0.076 with no *3 alleles observed; and, finally, in African-Americans frequencies of 0.637, 0.249 and 0.114, respectively. We also found that SULT1A1*2 and SULT1A2*2, the most common variant alleles for these two genes, were in positive linkage disequilibrium in all three populations studied, with D' values of 0.776 in Caucasian (P < 0.001), 0.915 in Chinese (P < 0.001) and 0.864 in African-American subjects (P < 0.001). These observations represent a step towards determining the possible functional implications for individual variations in sulfate conjugation of common genetic polymorphisms for SULT1A1 and SULT1A2.

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.

Site-directed mutagenesis of the substrate-binding cleft of human estrogen sulfotransferase

The sulfonation of estrogens by human estrogen sulfotransferase (humSULT1E1) plays a vital role in controlling the active levels of these hormones in the body. To understand more fully the structural and functional characteristics of humSULT1E1, we have carried out site-directed mutagenesis of critical amino acids found in the substrate-binding cleft. Three single amino acid mutations of humSULT1E1 (V145E, H107A, and K85A) were created in this study. Kinetic studies were used to provide information about the importance of these residues in substrate specificity and catalysis, using a variety of substrates. Lysine at position 85 has been proposed to be within hydrogen bonding distance to the 3alpha-phenol group of beta-estradiol, thereby stabilising the substrate in the active site. However, substitution to a neutral alanine at this position improved substrate specificity of humSULT1E1 for beta-estradiol, estrone, and dehydroepiandrosterone (DHEA). The exchange of valine 145 for negatively charged glutamic acid markedly improved the ability of humSULT1E1 to sulfonate dopamine, but caused a reduction in specificity constants toward steroids tested, in particular DHEA. The presence of a histidine residue at position 107 was shown to be essential for the production of a functional protein, as substitution of this amino acid to alanine resulted in complete loss of activity of humSULT1E1 towards all substrates tested.

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.

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).

Sulfation of "estrogenic" alkylphenols and 17beta-estradiol by human platelet phenol sulfotransferases

We have investigated the ability of alkylphenols to act as substrates and/or inhibitors of phenol sulfotransferase enzymes in human platelet cytosolic fractions. Our results indicate: (i) straight chain alkylphenols do not interact with the monoamine-sulfating phenol sulfotransferase (SULT1A3); (ii) short chain 4-n-alkylphenols (C < 8) are substrates for the phenol-sulfating enzymes (SULT1A1/2), which exhibit two activity maxima against substrates with alkyl chain lengths of C1-2 and C4-5; (iii) long chain 4-n-substituted alkylphenols (C >/= 8) are poor substrates and act as inhibitors of SULT1A1/2; (iv) human platelets contain two activities, of low and high affinity, capable of sulfating 17beta-estradiol, and 4-n-nonylphenol is a partial mixed inhibitor of the low affinity form of this activity. We conclude that by acting either as substrates or inhibitors of SULT1A1/2, alkylphenols may influence the sulfation, and hence the excretion, of estrogens and other phenol sulfotransferase substrates in humans.

Human phenol sulfotransferases SULT1A2 and SULT1A1: genetic polymorphisms, allozyme properties, and human liver genotype-phenotype correlations

Phenol sulfotransferases (PSTs or phenol SULTs) catalyze the sulfate conjugation of phenolic drugs, xenobiotics, and monoamines. Two human PST isoforms have been defined biochemically, a thermostable (TS), or phenol-preferring, and a thermolabile (TL), or monoamine-preferring form. Pharmacogenetic studies showed that levels of both TS PST activity and TS PST thermal stability (an indirect measure of variation in amino acid sequence) in the platelet were regulated by genetic polymorphisms. Subsequent molecular genetic experiments revealed the existence of three human PST genes, two of which, SULT1A1 and SULT1A2, encode proteins with "TS PST-like" activity. We recently reported common nucleotide polymorphisms for SULT1A1 that are associated with variations in platelet TS PST activity and thermal stability. In the present experiments, we set out to determine whether functionally significant DNA polymorphisms also might exist for SULT1A2, to compare the biochemical properties of all common allozymes encoded by SULT1A2 and SULT1A1, and to study phenol SULT genotype-phenotype correlations in the human liver. We phenotyped 61 human liver biopsy samples for TS PST thermal stability and activity. The open reading frames of SULT1A2 and SULT1A1 then were amplified with the polymerase chain reaction and sequenced for each of these hepatic tissue samples. We observed 13 SULT1A2 alleles that encoded 6 allozymes. These alleles were in linkage disequilibrium with alleles for SULT1A1. Biochemical characterization of common allozymes encoded by both genes suggested that SULT1A1 was primarily responsible for "TS PST phenotype" in the human liver. In summary, both SULT1A2 and SULT1A1 have a series of common alleles encoding enzymes that differ functionally and are associated with individual differences in phenol SULT properties in the liver.

Characterization of human iodothyronine sulfotransferases

Sulfation is an important pathway of thyroid hormone metabolism that facilitates the degradation of the hormone by the type I iodothyronine deiodinase, but little is known about which human sulfotransferase isoenzymes are involved. We have investigated the sulfation of the prohormone T4, the active hormone T3, and the metabolites rT3 and 3,3'-diiodothyronine (3,3'-T2) by human liver and kidney cytosol as well as by recombinant human SULT1A1 and SULT1A3, previously known as phenol-preferring and monoamine-preferring phenol sulfotransferase, respectively. In all cases, the substrate preference was 3,3'-T2 >> rT3 > T3 > T4. The apparent Km values of 3,3'-T2 and T3 [at 50 micromol/L 3'-phosphoadenosine-5'-phosphosulfate (PAPS)] were 1.02 and 54.9 micromol/L for liver cytosol, 0.64 and 27.8 micromol/L for kidney cytosol, 0.14 and 29.1 micromol/L for SULT1A1, and 33 and 112 micromol/L for SULT1A3, respectively. The apparent Km of PAPS (at 0.1 micromol/L 3,3'-T2) was 6.0 micromol/L for liver cytosol, 9.0 micromol/L for kidney cytosol, 0.65 micromol/L for SULT1A1, and 2.7 micromol/L for SULT1A3. The sulfation of 3,3'-T2 was inhibited by the other iodothyronines in a concentration-dependent manner. The inhibition profiles of the 3,3'-T2 sulfotransferase activities of liver and kidney cytosol obtained by addition of 10 micromol/L of the various analogs were better correlated with the inhibition profile of SULT1A1 than with that of SULT1A3. These results indicate similar substrate specificities for iodothyronine sulfation by native human liver and kidney sulfotransferases and recombinant SULT1A1 and SULT1A3. Of the latter, SULT1A1 clearly shows the highest affinity for both iodothyronines and PAPS, but it remains to be established whether it is the prominent isoenzyme for sulfation of thyroid hormone in human liver and kidney.

Phenol sulphotransferase SULT1A1 polymorphism: molecular diagnosis and allele frequencies in Caucasian and African populations

Sulphation, catalysed by members of the sulphotransferase (SULT) enzyme family, is an important component of the body's chemical defence mechanism, but also acts to bioactivate mutagens such as hydroxylated aryl and heterocyclic amines. A major human sulphotransferase, SULT1A1 (P-PST), metabolizes and/or bioactivates many drugs, iodothyronines and hydroxylated aromatic amines. The enzyme activity varies widely within the population and is under genetic control. We have developed an assay detecting a G-->A transition in SULT1A1 that causes an Arg213-->His substitution associated with low SULT activity and altered enzyme properties, and have used it to assess the SULT1A1 genotype in Caucasian (n=293) and African (Nigerian, n=52) populations. We show that the mutant SULT1A1*2 allele is present at frequencies of 0.321 and 0.269 in the Caucasian and African populations respectively. We also demonstrate a significant age-related difference in SULT1A1 genotype within our Caucasian population, with increasing incidence of SULT1A1*1 homozygosity and decreasing incidence of SULT1A1*2 homozygosity with increasing age, indicating a potential association of SULT1A1*1 allozyme(s) with protection against cell and/or tissue damage during aging.

A single amino acid, glu146, governs the substrate specificity of a human dopamine sulfotransferase, SULT1A3

Sulfation, catalyzed by members of the sulfotransferase (SULT) superfamily, exerts considerable influence over the biological activity of numerous endogenous and xenobiotic chemicals. In humans, catecholamines such as dopamine are extensively sulfated, and a SULT isoform (SULT1A3 or the monoamine-sulfating form of phenolsulfotransferase) has evolved with considerable selectivity for dopamine and other biogenic amines. To investigate the molecular basis for this selectivity, we identified a region of SULT1A3, which, we hypothesized, contributes to its preference for biogenic amines, and mutated two amino acids within this domain to the corresponding residues in a closely related but functionally distinct phenol sulfotransferase, SULT1A1 (H143Y and E146A). The change of a single amino acid, E146A, was sufficient to transform the catalytic properties and substrate preference of SULT1A3, such that they closely resembled those of SULT1A1. These experiments confirm the functional role of Glu146 in the selectivity of SULT1A3 for biogenic amines and suggest that this region is a key determinant of sulfotransferase substrate specificity.

Human hydroxysteroid sulfotransferase SULT2B1: two enzymes encoded by a single chromosome 19 gene

We have cloned and characterized cDNAs that encode two human hydroxysteroid sulfotransferase (SULT) enzymes, SULT2B1a and SULT2B1b, as well as the single gene that encodes both of these enzymes. The two cDNAs differed at their 5'-termini and had 1050- and 1095-bp open reading frames that encoded 350 and 365 amino acids, respectively. The amino acid sequences encoded by these cDNAs included "signature sequences" that are conserved in all known cytosolic SULTs. Both cDNAs appeared, on the basis of amino acid sequence analysis, to be members of the hydroxysteroid SULT "family, " SULT2, but they were only 48% identical in amino acid sequence with the single known member of that family in humans, SULT2A1 (also referred to as DHEA ST). Northern blot analysis demonstrated the presence of SULT2B1 mRNA species approximately 1.4 kb in length in human placenta, prostate, and trachea and-faintly-in small intestine and lung. Expression of the two human SULT2B1 cDNAs in COS-1 cells showed that both of the encoded proteins catalyzed sulfation of the prototypic hydroxysteroid SULT substrate, dehydroepiandrosterone, but both failed to catalyze the sulfate conjugation of 4-nitrophenol or 17beta-estradiol, prototypic substrates for the phenol and estrogen SULT subfamilies. Both of these cDNAs were encoded by a single gene, SULT2B1. The locations of most exon-intron splice junctions in SULT2B1 were identical to those of the only other known human hydroxysteroid SULT gene SULT2A1 (previously STD). The divergence in 5'-terminal sequences of the two SULT2B1 cDNAs resulted from alternative transcription initiation prior to different 5' exons, combined with alternative splicing. SULT2B1 mapped to human chromosome band 19q13.3, approximately 500 kb telomeric to the location of SULT2A1.

Localization and functional analysis of the substrate specificity/catalytic domains of human M-form and P-form phenol sulfotransferases

Human monoamine (M)-form and simple phenol (P)-form phenol sulfotransferases (PSTs), which are greater than 93% identical in their primary sequences, were used as models for investigating the structural determinants responsible for their distinct substrate specificity and other enzymatic properties. A series of chimeric PSTs were constructed by reciprocal exchanges of DNA segments between cDNAs encoding M-form and P-form PSTs. Functional characterization of the recombinant wild-type M-form, P-form, and chimeric PSTs expressed in Escherichia coli and purified to homogeneity revealed that internal domain-spanning amino acid residues 84-148 contain the structural determinants for the substrate specificity of either M-form or P-form PST. Data on the kinetic constants (Km, Vmax, and Vmax/Km) further showed the differential roles of the two highly variable regions (Region I spanning amino acid residues 84-89 and Region II spanning amino acid residues 143-148) in substrate binding, catalysis, and sensitivity to the inhibition by 2,6-dichloro-4-nitrophenol. In contrast to the differential sulfotransferase activities of M-form and P-form PSTs toward dopamine and p-nitrophenol, the Dopa/tyrosine sulfotransferase activities were found to be restricted to M-form, but not P-form, PST. Furthermore, the variable Region II of M-form PST appeared to play a predominant role in determining the Dopa/tyrosine sulfotransferase activities of chimeric PSTs. Kinetic studies indicated the role of manganese ions in dramatically enhancing the binding of D-p-tyrosine to wild-type M-form PST. Taken together, these results pinpoint unequivocally the sequence encompassing amino acid residues 84-148 to be the substrate specificity/catalytic domain of both M-form and P-form PSTs and indicate the importance of the variable Regions I and II in determining their distinct enzymatic properties.

Biology and function of the reversible sulfation pathway catalysed by human sulfotransferases and sulfatases

Sulfation and sulfate conjugate hydrolysis play an important role in metabolism, and are catalysed by members of the sulfotransferase and sulfatase enzyme super-families. In general, sulfation is a deactivating, detoxication pathway, but for some chemicals the sulfate conjugates are much more reactive than the parent compound. The range of compounds which are sulfated is enormous, yet we still understand relatively little of the function of this pathway. This review summarises current knowledge of the sulfation system and the enzymes involved, and illustrates how heterologous expression of sulfotransferases (SULTs) and sulfatases is aiding our appreciation of the properties of these important proteins. The role of sulfation in the bioactivation of procarcinogens and promutagens is discussed, and new data on the inhibition of the sulfotransferase(s) involved by common dietary components such as tea and coffee are presented. The genetic and environmental factors which are known to influence the activity and expression of human SULTs and sulfatases are also reviewed.

Novel sulfotransferases cloned by RT-PCR: real proteins or PCR artifacts?

During studies designed to subclone human phenol sulfotransferase (STP and STM) sequences for use in heterologous E. coli-based expression systems, we designed two oligonucleotide primers that would allow for the simultaneous PCR amplification of expression cassettes containing the coding regions of the STP1, STP2 and STM cDNAs. Following total RNA isolation from human liver, reverse transcription of cDNA, PCR amplification under standard conditions, plasmid subcloning and restriction analysis to select for suitable ST recombinants, we recovered plasmids containing inserts corresponding to STP1, STP2 and STM. However, ten additional, closely related but apparently novel ST sequences were also isolated. Alignments of the three known ST sequences (and one published allelic variant) with these new clones revealed that each one appears to be a PCR-generated modular chimera possessing a combination of DNA segments derived from STP1, STP2 and STM. This observation should serve as an alert to the potential pitfalls of using PCR techniques for the cloning of highly related genes and their cDNA products, especially when PCR primer design allows for the amplification of multiple products in a single reaction.

Genetic polymorphisms in human liver phenol sulfotransferases involved in the bioactivation of N-hydroxy derivatives of carcinogenic arylamines and heterocyclic amines

Three related forms of phenol sulfotransferase (PSULT), thermostable ST1A2 (SULT1A2hum) and ST1A3 (SULT1A1hum) and a thermolabile TL-PST (SULT1A3hum), are known to exist in human livers. Thermostable forms, whose activities are polymorphically distributed, have been shown to mediate the bioactivation of carcinogenic N-hydroxy arylamines and heterocyclic amines. To clarify the nature of the sulfation polymorphism, the study compared the expressed levels of ST1A2, ST1A3 and TL-PST mRNAs in human livers by the method of reverse-transcriptase polymerase chain reaction (RT-PCR), utilizing HindIII, BamHI and SnaBI sites which were unique to the above PSULT cDNAs, respectively. Of the PCR products derived from human liver (n = 26), 43-89, < 1-29 and < 1-21% showed the restriction pattern characteristic for ST1A3, ST1A2 and TL-PST cDNAs, respectively, thus indicating that ST1A3 mRNA is the major transcript. Hepatic p-nitrophenol and dopamine sulfation rates ranged from 440-2670 and < 5-460 pmol/min per mg protein in the 26 individuals, respectively. The observed differences in the ST1A3 and TL-PST mRNA levels were consistent with the differences in p-nitrophenol and dopamine sulfations. Relative levels of hepatic ST1A3 mRNA were non-normally distributed and correlated significantly with p-nitrophenol sulfation. In addition, variant forms of ST1A3 mRNA encoding Arg213His and Met223Val were detected in human livers. With regard to Arg213His, 28 individuals who had homozygous 213Arg alleles, 15 individuals who were heterozygotes and nine homozygous 213His individuals were found by a newly established genotyping method among 52 human liver samples. Frequency of 223Val allele was apparently lower than that of 213His allele, as no homozygous 223Val individual and only three individuals who were heterozygotes (223Met/Val) were observed among 52 individuals. These results suggest that regulation of p-nitrophenol sulfation occurs at the level of gene transcription of ST1A3 which is the major transcript of the three PSULT mRNAs and that a polygenic basis for the apparent genetic polymorphism of sulfation was likely because of the existence of ST1A3 variants.

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

Phenol sulfotransferases (PST) catalyze the sulfonation of catecholamines, thyroid hormones and phenolic drugs. At least two major forms of human PST enzyme have been characterized biochemically from liver, platelets and other tissues, the phenol-preferring PST (P-PST) and the monoamine neurotransmitter-preferring PST (M-PST). Molecular cloning efforts worldwide over the past 7 years have resulted in the identification of numerous PST cDNA isolates representing alleles of three human PST gene loci termed as STP1, STP2 and STM. All three genes have been mapped precisely to a small region on human chromosome 16p12.1-p11.2 (homologous to mouse chromosome 7), using somatic cell hybrids and cosmid clones. The two most closely related genes, STP1 and STP2, encoding P-PST isozymes have been mapped to a single cosmid clone and are, therefore, in close proximity to one another. STP1 and STP2 are approximately 96% identical at the amino acid sequence level, whereas, the STM gene (encoding M-PST) exhibits a lower level of identity (approximately 93-90.5%) relative to STP1 and STP2. STM is located at a distance of ca. 100 Kb from the STP1 and STP2 doublet. One may speculate that the three genes arose by gene duplication and/or gene conversion in humans. Genomic clones have been sequenced to determine the genomic organization for each of the three highly-related genes. All contain seven coding exons, with conserved intron exon boundaries. Sequencing of individual cDNA isolates of STP1 and STM from various tissues has revealed significant heterogeneity in the 5' nontranslated region, likely due to alternative splicing and/or tissue-specific promoter utilization. DNA polymorphisms have been detected in these genes in the human population and may be useful for molecular genetic studies of the metabolism of endogenous and xenobiotic phenolic molecules. Recent advances in the molecular biology of the human PST gene family are summarized.

Arylamine activating sulfotransferase in liver

Carcinogenic N-hydroxy-arylamines and -arylamides undergo metabolic activation by several enzymes in mammals to cause the DNA damage. Cytosolic sulfotransferases in rat and human livers, which belong to the ST1 (SULT1) family, have been studied to assess their properties to mediate the metabolic activation. A human orthologue of rat ST1C1 from, which catalyzes sulfation of N-hydroxy-2-acetylaminofluorene, was screened in a EMBL genomic library with ST1C1 cDNA [Nagata, K., S. Ozawa, M. Miyata, M. Shimada, D.-W. Gong, Y. Yamazoe and R. Kato (1993) J. Biol. Chem., 268, 24720-24725]. Sequencing of the hybridized clones indicate that at least 3'-terminal region of human ST1C1 orthologue contains sequence highly homologus to rat ST1C1 at both nucleotide and deduced amino acid levels. The experiments using anti-rat ST1C1 antibody and nucleotide probes for human ST1C1 showed no detectable band in Western blots and an mRNA-detecting method with polymerase chain reaction, respectively, in human liver samples.

Cloning, structural organization, and chromosomal mapping of the human phenol sulfotransferase STP2 gene

Phenol- and monoamine-metabolizing sulfotransferases (STP and STM, respectively) are members of a superfamily of enzymes that add sulfate to a variety of xenobiotics and endobiotics containing hydroxyl or amino functional groups. To characterize related sulfotransferase genes further, we used extra-long PCR (XL-PCR) to generate three distinct sizes of amplification products from human genomic DNA or from genomic phage library clones, each of which contained sulfotransferase gene sequences. One of the PCR fragments contained a new sulfotransferase gene, STP2, corresponding to a recently published cDNA clone that encodes a sulfotransferase with catalytic specificity distinct from that of the previously described STP1 and STM. Additional upstream sequence information was obtained using a second STP2-specific XL-PCR-based approach. The STP2 gene is composed of eight exons and seven introns, with exon sizes ranging from 95 to 181 bp. Protein-coding exon lengths and locations of the splice junctions were identical to those in both the STM gene and an STP2 gene published independently by another group recently. The STP2 gene maps to a chromosomal location (16p11.2-p12) that is the same as that previously determined for both STP1 and STM. The characterization of the STP2 gene provides further insight into the organization, regulation, and multiplicity of the sulfotransferase supergene family.

Human dehydroepiandrosterone sulfotransferase pharmacogenetics: quantitative Western analysis and gene sequence polymorphisms

Dehydroepiandrosterone sulfotransferase (DHEA ST) catalyzes the sulfation of DHEA and other hydroxysteroids. DHEA ST enzymatic activity in individual human liver biopsy samples has been shown to vary over a five-fold range, and frequency distribution histograms are bimodal, with approximately 25% of subjects included in a high activity subgroup. We set out to characterize the molecular basis for variation in human liver DHEA ST activity. The first step involved performing quantitative Western analysis of cytosol preparations from 92 human liver samples that had been phenotyped with regard to level of DHEA ST enzymatic activity. There was a highly significant correlation (r(s) = 0.635, P < 0.0001) between levels of DHEA ST activity and immunoreactive protein. We next attempted to determine whether the expression of DHEA ST might be controlled, in part, by a genetic polymorphism. DNA was isolated from three "low" and three "high" DHEA ST activity liver samples. Exons and the 5'-flanking region of the DHEA ST gene (STD) were amplified for each of these samples with the polymerase chain reaction (PCR). When compared with "wild type" STD sequence, some of the samples contained a T --> C transition at DHEA ST cDNA nucleotide 170, located within exon 2, resulting in a Met 57 --> Thr change in amino acid. Other samples contained an A --> T transversion at nucleotide 557 within STD exon 4 that resulted in a Glu 186 --> Val change. STD exons 2 and 4 were then sequenced for DNA isolated from an additional 87 liver samples that had been phenotyped with regard to level of DHEA ST enzymatic activity. The allele frequency for the exon 2 polymorphism in these samples was 0.027, whereas that for the exon 4 polymorphism was 0.038, but neither polymorphism was systematically related to the level of enzyme activity in these samples. Transient expression in COS-1 cells of cDNA that contained the nucleotide 170 and 557 polymorphisms, either separately or together, resulted in decreased expression of both DHEA ST enzymatic activity and level of immunoreactive protein, but only when the nucleotide 557 variant was present. Identification of common genetic polymorphisms within STD will now make it possible to test the hypothesis that those polymorphisms might alter in vivo expression and/or function of this important human steroid-metabolizing enzyme.