Phenolsulphotransferase: localization in kidney during human embryonic and fetal development

Interaction of the Brain-Selective Sulfotransferase SULT4A1 with Other Cytosolic Sulfotransferases: Effects on Protein Expression and Function

Sulfotransferase (SULT) 4A1 is a brain-selective sulfotransferase-like protein that has recently been shown to be essential for normal neuronal development in mice. In the present study, SULT4A1 was found to colocalize with SULT1A1/3 in human brain neurons. Using immunoprecipitation, SULT4A1 was shown to interact with both SULT1A1 and SULT1A3 when expressed in human cells. Mutation of the conserved dimerization motif located in the C terminus of the sulfotransferases prevented this interaction. Both ectopically expressed and endogenous SULT4A1 decreased SULT1A1/3 protein levels in neuronal cells, and this was also prevented by mutation of the dimerization motif. During differentiation of neuronal SH-SY5Y cells, there was a loss in SULT1A1/3 protein but an increase in SULT4A1 protein. This resulted in an increase in the toxicity of dopamine, a substrate for SULT1A3. Inhibition of SULT4A1 using small interference RNA abrogated the loss in SULT1A1/3 and reversed dopamine toxicity. These results show a reciprocal relationship between SULT4A1 and the other sulfotransferases, suggesting that it may act as a chaperone to control the expression of SULT1A1/3 in neuronal cells. SIGNIFICANCE STATEMENT: The catalytically inactive sulfotransferase (SULT) 4A1 may regulate the function of other SULTs by interacting with them via a conserved dimerization motif. In neuron-like cells, SULT4A1 is able to modulate dopamine toxicity by interacting with SULT1A3, potentially decreasing the metabolism of dopamine.

Human sulphotransferases are involved in the activation of aristolochic acids and are expressed in renal target tissue

Use of herbal preparations containing Aristolochia species has led to progressive nephropathy and urothelial cancer in humans. Analysis of DNA adducts formed in human target tissues and studies in animal models have pointed out a major role of the secondary plant metabolites, aristolochic acids, in these effects. Only a minority of the users of Aristolochia-containing products developed nephropathy and cancer, suggesting differences in individual susceptibility. Differences in metabolic activation and inactivation frequently affect the susceptibility towards chemicals. Others have shown that the activation of aristolochic acids to DNA-reactive and mutagenic metabolites requires reduction of their aryl nitro group. The biological activity of numerous nitro- and aminoarenes, after appropriate phase I metabolism, is strongly enhanced in the presence of acetyltransferases or sulphotransferases (SULTs). In the present study, we demonstrate that expression of human SULTs in bacterial and mammalian target cells reinforces the mutagenic activity of aristolochic acids. Using Salmonella typhimurium TA1538 as the recipient organism, we identified the expression of all 12 human SULT forms. SULT1A1 led to the strongest increase in the mutagenicity of aristolochic acids. Some activation was also observed with SULT1B1, but not with the remaining forms. The role of SULT1A1 in the activation of aristolochic acids was corroborated using S. typhimurium TA100- and Chinese hamster V79-derived target cells engineered for expression of human SULT1A1 when compared with control cells. Furthermore, pentachlorophenol, an inhibitor of SULT1A1, strongly reduced the mutagenic effect of aristolochic acids in V79-hCYP2E1-hSULT1A1 cells. Moreover, we demonstrate that SULT1A1 and SULT1B1 are expressed in human kidney using immunoblot analysis, but their levels are substantially lower than in liver. Finally, we discuss the possibility that reactive sulphuric acid conjugates produced in other tissues are transferred to kidney and ureter.

Expression profiling of human fetal cytosolic sulfotransferases involved in steroid and thyroid hormone metabolism and in detoxification

Protection against chemical insult is essential for normal development of the fetus, however many detoxification enzymes are poorly expressed during fetal development. A major exception is the sulfotransferase (SULT) family, which appears to be widely expressed in the developing human. These enzymes also play a key role in biosynthesis and homeostasis of a number of hormones, including estrogens and iodothyronines. We therefore examined the enzyme activity, protein and mRNA expression of SULT 1A, 1B, 1C, 1E and 2A families in a variety of human fetal and adult tissues. Our results show that these SULTs are expressed in the human fetus, with most present at levels equivalent to or higher than the adult. As there are no isoform-selective substrates for SULTs 1B1 and 1C2 we used immunoblot analysis to show for the first time expression of SULT1B1 at high levels in fetal small intestine, and expression of SULT1C2 in fetal liver, kidney and small intestine. SULT1C2 was not expressed in adult liver or colon. Sulfotransferase expression in the developing fetus is therefore more widespread than in the adult, and this has significant implication for our understanding of human developmental physiology.

Sulfation through the looking glass--recent advances in sulfotransferase research for the curious

Members of the cytosolic sulfotransferase (SULT) superfamily catalyse the sulfation of a multitude of xenobiotics, hormones and neurotransmitters. Humans have at least 10 functional SULT genes, and a number of recent advances reviewed here have furthered our understanding of SULT function. Analysis of expression patterns has shown that sulfotransferases are highly expressed in the fetus, and SULTs may in fact be a major detoxification enzyme system in the developing human. The X-ray crystal structures of three SULTs have been solved and combined with mutagenesis experiments and molecular modelling, they have provided the first clues as to the factors that govern the unique substrate specificities of some of these enzymes. In the future these and other studies will facilitate prediction of the fate of chemicals metabolised by sulfation. Variation in sulfation capacity may be important in determining an individual's response to xenobiotics, and there has been an explosion in information on sulfotransferase polymorphisms and their functional consequences, including the influence of SULT1A1 genotype on susceptibility to colorectal and breast cancer. Finally, the first gene knockout experiments with SULTs have recently been described, with the generation of estrogen sulfotransferase deficient mice in which reproductive capacity is compromised. Our improved understanding of these enzymes will have significant benefits in such diverse areas as drug design and development, cancer susceptibility, reproduction and development.

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.

A novel hypothesis for the mechanism of action of P-glycoprotein as a multidrug transporter

For years, P-glycoprotein (P-gp) has been purported to be a membrane transporter capable of selectively transporting many (but not all) lipophilic anticancer drugs with diverse chemical structures. Because the alleged functions of P-gp provide a straightforward, near-perfect explanation for the molecular mechanism of multidrug resistance associated with P-gp overexpression. However, the exact molecular mechanism for P-gp's purported function has never been clearly understood since its initial discovery some 20 yr ago. In this paper, I develop a novel working hypothesis regarding the mechanism of P-gp's action and suggest that P-gp is an energy-dependent efflux pump only for certain conjugated metabolites (probably sulfates) of the lipophilic anticancer drugs but not for the parent compounds, as was always claimed. According to this hypothesis, P-gp overexpression in most cases is not the "culprit" but instead an "accomplice" in P-gp-associated multidrug resistance. The culprit is probably the enhanced function of the metabolizing enzymes for the lipophilic anticancer drugs. This hypothesis also predicts that one of the important physiological functions of P-gp is to be part of an intracellular machinery (together with the phase I and II metabolizing enzymes) for the metabolism, detoxification, and disposition of lipophilic endogenous chemicals as well as xenobiotics, including cytotoxic anticancer drugs. There exists a considerable body of circumstantial evidence in the literature that lends strong support to this mechanistic hypothesis of P-gp's action as well as to the predicted physiological functions of P-gp. It will be of considerable interest to examine this novel hypothesis experimentally.

Localisation of aryl sulfotransferase expression in human tissues using hybridisation histochemistry and immunohistochemistry

To date, the laboratory has cloned seven unique human sulfotransferases; five aryl sulfotransferases (HAST1, HAST2, HAST3, HAST4 and HAST4v), an estrogen sulfotransferase and a dehydroepiandrosterone sulfotransferase. The cellular distribution of human aryl sulfotransferases in human hepatic and extrahepatic tissues has been determined using the techniques of hybridization histochemistry and immunohistochemistry. Human aryl sulfotransferase expression was detected in liver, epithelial cells of the gastrointestinal mucosal layer, epithelial cells lining bronchioles and in mammary duct epithelial cells.

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.

Differential expression and immunohistochemical localisation of the phenol and hydroxysteroid sulphotransferase enzyme families in the developing lung

Reversible sulphation, catalysed by sulphotransferases and sulphatases, of biologically active compounds such as androgens and oestrogens is a sensitive mechanism for regulating their bioavailability, and we have previously hypothesised that this process plays a significant role in the regulation of human fetal lung development. Sulphation is also a major detoxification reaction, contributing significantly to the body's chemical defence mechanism. We have used qualitative and semiquantitative immunological studies to determine the temporal expression and localisation of phenol and hydroxysteroid sulphotransferases during human lung development. Our results show that in the early fetal lung, phenol sulphotransferase expression is at its highest, and is most widely distributed throughout the developing respiratory epithelium. With later development, expression levels decrease and become predominantly restricted to the more proximal airways. In contrast, hydroxysteroid sulphotransferase is present only at very low levels in the early-gestation lung but expression increases rapidly through gestation to reach an apparent peak by 1 year postnatal age. The proximal-to-distal gradients of phenol and hydroxysteroid sulphotransferase expression were similar in mature respiratory epithelium, with immunoreactivity in ciliated cells, non-ciliated secretory cells and basal cells, but with no apparent expression in mucus-secreting cells. These studies provide supporting evidence for the hypothesis that hydroxysteroid sulphotransferase, an androgen-inactivating enzyme, contributes to the role of androgens in retarding the maturation of human lung in utero.