Epigenetic silencing of the sulfate transporter gene DTDST induces sialyl Lewisx expression and accelerates proliferation of colon cancer cells

Guanine nucleotides differentially modulate backbone dynamics of the STAS domain of the SulP/SLC26 transport protein Rv1739c of Mycobacterium tuberculosis

Enzymatic catalysis and protein signaling are dynamic processes that involve local and/or global conformational changes occurring across a broad range of time scales. (1) H-(15) N relaxation NMR provides a comprehensive understanding of protein backbone dynamics both in the apo (unliganded) and ligand-bound conformations, enabling both fast and slow internal motions of individual amino acid residues to be observed. We recently reported the structure and nucleotide binding properties of the sulfate transporter and anti-sigma factor antagonist (STAS) domain of Rv1739c, a SulP anion transporter protein of Mycobacterium tuberculosis. In the present study, we report (1) H-(15) N NMR backbone dynamics measurements [longitudinal (T(1) ), transverse (T(2) ) and steady-state ({(1) H}-(15) N) heteronuclear NOE] of the Rv1739c STAS domain, in the absence and presence of saturating concentrations of GTP and GDP. Analysis of measured relaxation data and estimated dynamic parameters indicated distinct features differentiating the binding of GTP and GDP to Rv1739c STAS. The 9.55 ns overall rotational correlation time of Rv1739c STAS increased to 10.48 ns in the presence of GTP, and to 13.25 ns in the presence of GDP, indicating significant nucleotide-induced conformational changes. These conformational changes were accompanied by slow time scale (μs to ms) motions in discrete regions of the protein, as reflected by guanine nucleotide-induced changes in relaxation parameters. The observed nucleotide-specific alterations in the relaxation properties of individual STAS residues reflect an increased molecular anisotropy and/or the emergence of conformational equilibria governing functional properties of the STAS domain.

Transcriptional regulation of the pendrin gene

Pendrin (SLC26A4), a Cl(-)/anion exchanger encoded by the gene PDS, is highly expressed in the kidney, thyroid and inner ear epithelia and is essential for bicarbonate secretion/chloride reabsorption, iodide accumulation and endolymph ion balance, respectively. The molecular mechanisms controlling pendrin activity in renal, thyroid and inner ear epithelia have been the subject of recent studies. The effects of ambient pH, the hormone aldosterone and the peptide uroguanylin (UGN; the "intestinal natriuretic hormone"), known modulators of electrolyte balance, on transcription of the pendrin gene, have been investigated. Luciferase reporter plasmids containing different length fragments of the human PDS (hPDS) promoter were transfected into renal HEK293, thyroid LA2, and inner ear VOT36 epithelial cells. Acidic pH decreased and alkaline pH increased hPDS promoter activity in transfected HEK293 and VOT36, but not in LA2 cells. Aldosterone reduced hPDS promoter activity in HEK293 but had no effect in LA2 and VOT36 cells. These pH and aldosterone-induced effects on the hPDS promoter occurred within 96-bp and 89-bp regions, respectively, which likely contain distinct response elements to these modulators. Injection of UGN into mice resulted in decreased pendrin mRNA and protein expression in the kidney. Exposure of transfected HEK293 to UGN decreased hPDS promoter activity. The findings provided evidence for the presence of a UGN response element within the 96-bp region overlapping with the pH response element on the hPDS promoter. Pendrin is also expressed in airway epithelium. The cytokins interleukin 4 (IL-4) and interleukin-13 (IL-13), known regulators of airway surface function, have been shown to increase hPDS promoter activity by a STAT6-dependent mechanism. In conclusion, systemic pH, the hormone aldosterone, and the peptide UGN influence renal tubular pendrin gene expression and, perhaps, pendrin-mediated Cl(-)/HCO(3)(-) exchange at the transcriptional level. Pendrin-driven anion transport in the endolymph and at the airway surface may be regulated transcriptionally by systemic pH and IL-3/IL-4, respectively. The distinct response elements and the corresponding transcription factors mediating the effect of these modulators on the PDS promoter remain to be identified and characterized.

Butyrate induces expression of 17β-hydroxysteroid dehydrogenase type 1 in HT29 and SW707 colorectal cancer cells

Epidemiological studies have revealed that butyrate and 17β-estradiol (E2) may decrease the incidence of colorectal cancer (CRC). In peripheral tissue, E2 can be produced locally by 17β-hydroxysteroid dehydrogenase 1 (HSD17B1) estrone (E1) reduction. Using quantitative real-time polymerase chain reaction and western blotting analysis, we found that sodium butyrate significantly upregulates HSD17B1 long and short transcripts and protein levels in HT29 and SW707 CRC cells. Chromatin immunoprecipitation analysis showed that upregulation of these transcript levels correlated with an increase in binding of Polymerase II to proximal and distal promoters of HSD17B1. Moreover, we observed that upregulation of HSD17B1 protein levels was associated with increased conversion of E1 to E2 in HT29 and SW707 CRC cells. Since sodium butyrate increases the conversion of E1 to E2, our findings may support the validity of butyrate in the prophylaxis of CRC incidence.

Regulation of sialyl Lewis antigen expression in colon cancer cells by sialidase NEU4

Sialyl Lewis antigens, sialyl Lewis a and sialyl Lewis x, are utilized as tumor markers, and their increase in cancer is associated with tumor progression by enhancement of cancer cell adhesion to endothelial E-selectin. However, regulation mechanisms are not fully understood. We previously demonstrated that NEU4 is the only sialidase efficiently acting on mucins and it is down-regulated in colon cancer. To elucidate the significance of NEU4 down-regulation, we investigated sialyl Lewis antigens as endogenous substrates for the sialidase. NEU4 was found to hydrolyze the antigens in vitro and decrease cell surface levels much more effectively than other sialidases. Western blot, thin layer chromatography, and metabolic inhibition studies of desialylation products revealed NEU4 to preferentially catalyze sialyl Lewis antigens expressed on O-glycans. Cell adhesion to and motility and growth on E-selectin were significantly reduced by NEU4. E-selectin stimulation of colon cancer cells enhanced cell motility through activation of the p38/Hsp27/actin reorganization pathway, whereas NEU4 attenuated the signaling. On immunocytochemical analysis, some NEU4 molecules were localized at cell surfaces. Under hypoxia conditions whereby the antigens were increased concomitantly with several sialyl- and fucosyltransferases, NEU4 expression was markedly decreased. These results suggest that NEU4 plays an important role in control of sialyl Lewis antigen expression and its impairment in colon cancer.

Expression and the role of 3'-phosphoadenosine 5'-phosphosulfate transporters in human colorectal carcinoma

Sulfation represents an essential modification for various molecules and regulates many biological processes. The sulfation of glycans requires a specific transporter for 3'-phosphoadenosine 5'-phosphosulfate (PAPS) on the Golgi apparatus. This study investigated the expression of PAPS transporter genes in colorectal carcinomas and the significance of Golgi-specific sulfation in the proliferation of colorectal carcinoma cells. The relative amount of PAPST1 transcripts was found to be higher than those of PAPST2 in colorectal cancerous tissues. Immunohistochemically, the enhanced expression of PAPST1 was observed in fibroblasts in the vicinity of invasive cancer cells, whereas the expression of PAPST2 was decreased in the epithelial cells. RNA interference of either of the two PAPS transporter genes reduced the extent of sulfation of cellular proteins and cellular proliferation of DLD-1 human colorectal carcinoma cells. Silencing the PAPS transporter genes reduced fibroblast growth factor signaling in DLD-1 cells. These findings indicate that PAPS transporters play a role in the proliferation of colorectal carcinoma cells themselves and take part in a desmoplastic reaction to support cancer growth by controlling their sulfation status.

Glycan changes: cancer metastasis and anti-cancer vaccines

Complex carbohydrates, which are major components of the cell membrane, perform important functions in cell-cell and cell-extracellular matrix interactions, as well as in signal transduction. They comprise three kinds of biomolecules: glycoproteins, proteoglycans and glycosphingolipids. Recent studies have also shown that glycan changes in malignant cells take a variety of forms and mediate key pathophysiological events during the various stages of tumour progression. Glycosylation changes are universal hallmarks of malignant transformation and tumour progression in human cancer, which take place on the whole cells or some specific molecules. Accordingly, those changes make them prominent candidates for cancer biomarkers in the meantime. This review mainly focuses on the correlation between glycosylation and the metastasis potential of tumour cells from comprehensive aspects to further address the vital roles of glycans in oncogenesising. Moreover, utilizing these glycosylation changes to ward off tumour metastasis by means of anti-adhesion approach or devising anti-cancer vaccine is one of promising targets of future study.

The biosynthesis of the selectin-ligand sialyl Lewis x in colorectal cancer tissues is regulated by fucosyltransferase VI and can be inhibited by an RNA interference-based approach

Sialyl Lewis x (sLex) is a selectin ligand whose overexpression in epithelial cancers mediates metastasis formation. The molecular basis of sLex biosynthesis in colon cancer tissues is still unclear. The prerequisite for therapeutic approaches aimed at sLex down-regulation in cancer, is the identification of rate-limiting steps in its biosynthesis. We have studied the role of α1,3-fucosyltransferases (Fuc-Ts) potentially involved in sLex biosynthesis in specimens of normal and cancer colon as well as in experimental systems. We found that: (i) in colon cancer, but not in normal mucosa where the antigen was poorly expressed, sLex correlated with a Fuc-T which, like Fuc-TVI, was active on 3'sialyllactosamine at a low concentration (Fuc-T(SLN)); (ii) competitive RT-PCR analysis revealed that the level of Fuc-T mRNA expression in both normal and cancer colon was Fuc-TVI>Fuc-TIII>Fuc-TIV; Fuc-TV and Fuc-TVII expression was negligible; (iii) sLex was expressed only by the gastrointestinal cell lines displaying both Fuc-TVI mRNA and Fuc-T(SLN) activity, but not by those expressing only Fuc-TIII mRNA; (iv) transfection with Fuc-TVI cDNA, but not with Fuc-TIII cDNA, induced sLex expression in gastrointestinal cell lines; (v) Fuc-TVI knock-down with specific siRNA induced down-regulation of Fuc-TVI mRNA and Fuc-T(SLN) activity and a dramatic inhibition of sLex expression. These data indicate that in colon cancer tissues Fuc-TVI is a key regulator of sLex biosynthesis which can be the target of RNA-interference-based gene knock-down approaches.