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

Sulfotransferase 1A1 (SULT1A1) gene expression is regulated by members of the NFI transcription factors in human breast cancer cells

Background

Sulfotransferase 1A1 (SULT1A1) gene expression is tissue specific, with little to no expression in normal breast epithelia. Expression in breast tumors has been documented, but the transcriptional regulation of SULT1A1 in human breast tissue is poorly understood. We identified Nuclear Factor I (NFI) as a transcription factor family involved in the regulation of SULT1A1 expression.

Methods

Transcription Factor Activation Profiling Plate Array assay was used to identify the possible transcription factors that regulate the gene expression of SULT1A1in normal breast MCF-10A cells and breast cancer ZR-75-1 cells. Expression levels of NFI-C and SULT1A1 were determined by real-time RT-PCR using total RNA isolated from 84 human liver samples. Expression levels of SULT1A1, NFI-A, NFI-B, NFI-C, and NFI-X were also determined in different human breast cancer cell lines (MCF-7, T-47D, ZR-75-1, and MDA-MB-231), in the transformed human epithelial cell line MCF-10A, and in ZR-75-1 cells that were transfected with siRNAs directed against NFI-A, NFI-B, NFI-C, or NFI-X for 48 h. The copy numbers of SULT1A1 in cell lines ZR-75-1, MCF-7, T-47D, MDA-MB-231, and MCF-10A were determined using a pre-designed Custom Plus TaqMan^® Copy Number kit from Life Technologies.

Results

In normal human liver samples, SULT1A1 mRNA level was positively associated with NFI-C. In different human breast cancer and normal epithelial cell lines, SULT1A1 expression was positively correlated with NFI-B and NFI-C. SULT1A1 expression was decreased 41% and 61% in ZR-75-1 cells treated with siRNAs against NFI-A and NFI-C respectively. SULT1A1 gene expression was higher in cells containing more than one SULT1A1 copy numbers.

Conclusions

Our data suggests that SULT1A1 expression is regulated by NFI, as well as SULT1A1 copy number variation in human breast cancer cell lines. These data provide a mechanistic basis for the differential expression of SULT1A1 in different tissues and different physiological states of disease.

Proteomic analysis of chronic restraint stress-induced Gan (肝)-stagnancy syndrome in rats

OBJECTIVE

To analyze the proteomic characteristics of Gan (肝)-stagnancy syndrome (GSS) by seeking the differential protein in blood and tissues of GSS model rats.

METHODS

GSS model rats were established by chronic restraint stress, keeping rats in restrain chamber for 6 h every day for 21 successive days. Their blood and liver samples were collected at the end of experiment for differential protein detection with methods of isoelectrofocusing and polyacrylamide SDS-PAGE, silver staining, and scanning. The gel images were analyzed with Imagemaster 2D Elite software, and the excavated differential protein spots were identified with matrix assistant laser resolving TOF mass spectrometry, Western blot, ELISA, and RT-PCR, respectively.

RESULTS

A method for isolating the protein in blood serum and tissues by two-dimensional gel electrophoresis was established and optimized. Six serum proteins and three liver proteins that differentially expressed were identified. The down-regulated differential proteins in serum of GSS model rats were serum albumin precursor, beta 1 globin, antibody against muscle acetylcholine receptor, Ig lambda-2 C region, and transthyretin (TTR), and those in liver tissue were aryl sulfotransferase, enoyl-CoA hydratase, and TTR. TTR down-regulation was found in both serum and liver. Preliminary biological information analysis showed that these differential proteins involved in immune, neuroendocrine, nutrition, and substance metabolism.

CONCLUSION

Proteomic analysis of differential proteins showed that TTR, aryl sulfotransferase, and enoyl-CoA hydratase expressions are downregulated in the GSS model rats, suggesting that the susceptibility of cancer could be enhanced by chronic stress.

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.

Identification and localization of soluble sulfotransferases in the human gastrointestinal tract

Soluble SULTs (sulfotransferases) are important in the regulation of messenger molecules and the elimination of xenobiotics. However, sulfo-conjugation of various substrates can also lead to the formation of reactive metabolites that may induce cancer and cause other damage. The aim of the present study was to identify the SULT forms expressed in the human gastrointestinal tract, especially the colon and rectum (common sites for cancer), and to determine their cellular localization. Normal colonic or rectal tissue, resected with tumours, was obtained from 39 subjects. For comparison, we additionally studied one to four samples from stomach, jejunum, ileum, cecum and liver. SULTs were detected by immunoblotting, immunohistochemistry and measurement of enzyme activities. SULT1A1, 1A3 and 1B1 were found in all parts of the gastrointestinal tract, often exceeding levels in liver (where these forms were present at high, undetectable and low levels respectively). They were predominantly localized in differentiated enterocytes. SULT1E1 and 2A1 were only detected in liver, jejunum, ileum and cecum. SULT1C1 was readily found in stomach, but was negligible elsewhere. SULT1A2 was present at low levels in individual samples. The remaining forms were not detected with the limitation that only high levels could be recognized with the antisera used. In conclusion, SULTs are abundant in the gastrointestinal tract of man. We suspect that they are involved in the presystemic elimination of bioactive food-borne components, including aglycones released by gut microbiota, as well as the bioactivation of some procarcinogens.

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.

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.

Enzyme polymorphisms influencing the metabolism of heterocyclic aromatic amines

Heterocyclic aromatic amines are dietary carcinogens possibly involved in human carcinogenesis, DNA-adduct formation being an obligatory step in this multistage process. Heterocyclic amine binding to DNA largely depends on the balance between metabolic activation and detoxification pathways and DNA repair efficiency. Several genes coding for metabolic enzymes are polymorphic, which affects gene expression and/or enzyme activity. This paper briefly reviews the effect of polymorphisms of activating/detoxifying enzymes on the metabolism of heterocyclic amines. Despite some epidemiological evidence of an association between genetic polymorphisms and susceptibility to cancer possibly resulting from dietary exposure to heterocyclic aromatic amines (HA), the genetic polymorphisms had only slight effects on biomarker levels, suggesting the existence of further unknown factors.

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.

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.