Human alpha (1,3)-fucosyltransferase IV (FUTIV) gene expression is regulated by elk-1 in the U937 cell line

Advances in molecular mechanisms of drugs affecting abnormal glycosylation and metastasis of breast cancer

Breast cancer remains the leading cause of cancer-related death among women worldwide, and its incidence is also increasing. High recurrence rate and metastasis rate are the key causes of poor prognosis and death. It is suggested that abnormal glycosylation plays an important role in the growth, invasion, metastasis and resistance to therapy of breast cancer cells. Meanwhile, it can be used as the biomarkers for the early detection and prognosis of breast cancer and the potential attractive targets for drug treatment. However, only a few attentions have been paid to the molecular mechanism of abnormal glycosylation in the epithelial-mesenchymal transition (EMT) of breast cancer cells and the related intervention of drugs. This manuscript thus investigated the relationship between abnormal glycosylation, the EMT, and breast cancer metastasis. Then, the process of abnormal glycosylation, the classification and their molecular regulatory mechanisms of breast cancer were analyzed in detail. Last, potential drugs are introduced in different categories, which are expected to reverse or intervene the abnormal glycosylation of breast cancer. This review is conducive to an in-depth understanding of the metastasis and drug resistance of breast cancer cells, which will provide new ideas for the clinical regulation of glycosylation and related drug treatments in breast cancer.

Dual Specificity Phosphatase 5, a Specific Negative Regulator of ERK Signaling, Is Induced by Serum Response Factor and Elk-1 Transcription Factor

Serum stimulation of mammalian cells induces, via the MAPK pathway, the nuclear protein DUSP5 (dual-specificity phosphatase 5), which specifically interacts with and inactivates the ERK1/2 MAP kinases. However, molecular mechanisms underlying DUSP5 induction are not well known. Here, we found that the DUSP5 mRNA induction depends on a transcriptional regulation by the MAPK pathway, without any modification of the mRNA stability. Two contiguous CArG boxes that bind serum response factor (SRF) were found in a 1 Kb promoter region, as well as several E twenty-six transcription factor family binding sites (EBS). These sites potentially bind Elk-1, a transcription factor activated by ERK1/2. Using wild type or mutated DUSP5 promoter reporters, we demonstrated that SRF plays a crucial role in serum induction of DUSP5 promoter activity, the proximal CArG box being important for SRF binding in vitro and in living cells. Moreover, in vitro and in vivo binding data of Elk-1 to the same promoter region further demonstrate a role for Elk-1 in the transcriptional regulation of DUSP5. SRF and Elk-1 form a ternary complex (Elk-1-SRF-DNA) on DUSP5 promoter, consequently providing a link to an important negative feedback tightly regulating phosphorylated ERK levels.

Transcriptional regulation of fucosyltransferase 1 gene expression in colon cancer cells

The α 1,2-fucosyltransferase I (FUT1) enzyme is important for the biosynthesis of H antigens, Lewis B, and Lewis Y. In this study, we clarified the transcriptional regulation of FUT1 in the DLD-1 colon cancer cell line, which has high expression of Lewis B and Lewis Y antigens, expresses the FUT1 gene, and shows α 1,2-fucosyltransferase (FUT) activity. 5'-rapid amplification of cDNA ends revealed a FUT1 transcriptional start site -10 nucleotides upstream of the site registered at NM_000148 in the DataBase of Human Transcription Start Sites (DBTSS). Using the dual luciferase assay, FUT1 gene expression was shown to be regulated at the region -91 to -81 nt to the transcriptional start site, which contains the Elk-1 binding site. Site-directed mutagenesis of this region revealed the Elk-1 binding site to be essential for FUT1 transcription. Furthermore, transfection of the dominant negative Elk-1 gene, and the chromatin immunoprecipitation (CHIp) assay, supported Elk-1-dependent transcriptional regulation of FUT1 gene expression in DLD-1 cells. These results suggest that a defined region in the 5'-flanking region of FUT1 is critical for FUT1 transcription and that constitutive gene expression of FUT1 is regulated by Elk-1 in DLD-1 cells.

Differential fucosyltransferase IV expression in squamous carcinoma cells is regulated by promoter methylation

Enhanced fucosyltransferase IV (FUT4) expression correlates with increased tumor malignancy in many carcinomas. However, little is known about the regulation of FUT4 expression, and whether FUT4 expression is influenced by the methylation status of the FUT4 promoter is unclear. In this study, we demonstrated that FUT4 expression is negatively correlated with the methylation degree of a CpG island in the FUT4 promoter, suggesting that the methylation status of FUT4 promoter regulates the expression of FUT4. The results indicate that manipulating the methylation status of the FUT4 promoter to regulate FUT4 expression may be a novel approach in the treatment of malignant tumors.

Genomics meets glycomics-the first GWAS study of human N-Glycome identifies HNF1α as a master regulator of plasma protein fucosylation

Over half of all proteins are glycosylated, and alterations in glycosylation have been observed in numerous physiological and pathological processes. Attached glycans significantly affect protein function; but, contrary to polypeptides, they are not directly encoded by genes, and the complex processes that regulate their assembly are poorly understood. A novel approach combining genome-wide association and high-throughput glycomics analysis of 2,705 individuals in three population cohorts showed that common variants in the Hepatocyte Nuclear Factor 1α (HNF1α) and fucosyltransferase genes FUT6 and FUT8 influence N-glycan levels in human plasma. We show that HNF1α and its downstream target HNF4α regulate the expression of key fucosyltransferase and fucose biosynthesis genes. Moreover, we show that HNF1α is both necessary and sufficient to drive the expression of these genes in hepatic cells. These results reveal a new role for HNF1α as a master transcriptional regulator of multiple stages in the fucosylation process. This mechanism has implications for the regulation of immunity, embryonic development, and protein folding, as well as for our understanding of the molecular mechanisms underlying cancer, coronary heart disease, and metabolic and inflammatory disorders.

By combining recently developed high-throughput glycan analysis with genome-wide association study, we performed the first comprehensive analysis of common genetic polymorphisms that affect protein glycosylation. Over half of all proteins are glycosylated; but, due to difficulties in glycan analysis and the absence of a genetic template for their synthesis, knowledge about the complex processes that regulate glycan assembly is still limited. We demonstrated that HNF1α regulates the expression of key fucosyltransferase and fucose biosynthesis genes and acts as a master regulator of plasma protein fucosylation. Proper protein fucosylation is essential in numerous processes including inflammation, cancer, and coronary heart disease, thus the identification of a master regulator of plasma protein fucosylation has important implications for understanding both normal biological functions and disease processes.

Negative-feedback regulation of FGF signalling by DUSP6/MKP-3 is driven by ERK1/2 and mediated by Ets factor binding to a conserved site within the DUSP6/MKP-3 gene promoter

DUSP6 (dual-specificity phosphatase 6), also known as MKP-3 [MAPK (mitogen-activated protein kinase) phosphatase-3] specifically inactivates ERK1/2 (extracellular-signal-regulated kinase 1/2) in vitro and in vivo. DUSP6/MKP-3 is inducible by FGF (fibroblast growth factor) signalling and acts as a negative regulator of ERK activity in key and discrete signalling centres that direct outgrowth and patterning in early vertebrate embryos. However, the molecular mechanism by which FGFs induce DUSP6/MKP-3 expression and hence help to set ERK1/2 signalling levels is unknown. In the present study, we demonstrate, using pharmacological inhibitors and analysis of the murine DUSP6/MKP-3 gene promoter, that the ERK pathway is critical for FGF-induced DUSP6/MKP-3 transcription. Furthermore, we show that this response is mediated by a conserved binding site for the Ets (E twenty-six) family of transcriptional regulators and that the Ets2 protein, a known target of ERK signalling, binds to the endogenous DUSP6/MKP-3 promoter. Finally, the murine DUSP6/MKP-3 promoter coupled to EGFP (enhanced green fluorescent protein) recapitulates the specific pattern of endogenous DUSP6/MKP-3 mRNA expression in the chicken neural plate, where its activity depends on FGFR (FGF receptor) and MAPK signalling and an intact Ets-binding site. These findings identify a conserved Ets-factor-dependent mechanism by which ERK signalling activates DUSP6/MKP-3 transcription to deliver ERK1/2-specific negative-feedback control of FGF signalling.

Expression and regulation of fucosyltransferase 4 in human endometrium

It has been suggested that selectin ligands expressed by the endometrial epithelium are essential for the initial adhesion of the blastocyst to the luminal epithelium of human endometrium. One of the enzymes responsible for the production of selectin ligands is fucosyltransferase 4 (FUT4), a member of α1,3 fucosyltransferases. The aims of the present study were to characterizeFUT4mRNA and protein in human endometrium during the menstrual cycle and to investigate the hormonal regulation ofFUT4whose mRNA expression was quantified by real-time PCR in fresh endometrial tissue from cycling women and protein expression was analyzed by immunohistochemistry and Western blotting. Hormonal regulation ofFUT4transcription was investigated using an endometrial explant system.FUT4mRNA was significantly upregulated in fresh tissues during early and mid-secretory phases when compared with other phases of the menstrual cycle. FUT4 protein was localized to glandular and luminal epithelium and the expression levels followed the same pattern as forFUT4mRNA. Our data also show that, in proliferative explants, progesterone significantly increasedFUT4transcription and translation after 24 h in culture. The inductive effect of progesterone onFUT4transcription was lost after 48 h of treatment. Estrogen did not have any significant effects. These data suggest that the upregulation of selectin ligands in the human endometrium at the time of implantation may be mediated, at least in part, by the regulation ofFUT4expression.

Sequential action of Ets-1 and Sp1 in the activation of the human beta-1,4-galactosyltransferase V gene involved in abnormal glycosylation characteristic of cancer cells

Malignant transformation is associated with increased gene expression of beta-1,4-galactosyltransferase (beta-1,4-GalT) V, which contributes to the biosynthesis of highly branched N-linked oligosaccharides characteristic of cancer cells. Our previous study showed that expression of the human beta-1,4-GalT V gene is regulated by Sp1 (Sato, T., and Furukawa, K. (2004) J. Biol. Chem. 279, 39574-39583), and a subsequent study showed that the gene expression is also activated by Ets-1, a product of the oncogene (Sato, T., and Furukawa, K. (2005) Glycoconj. J. 22, 365). Herein we report the mechanism of beta-1,4-GalT V gene activation by these transcription factors. The gene expression and promoter activity of beta-1,4-GalT V increased when the ets-1 cDNA was transfected into A549 cells, which contain a small amount of Ets-1, but decreased dramatically when the dominant-negative ets-1 cDNA was transfected into HepG2 cells, which contain a large amount of Ets-1. Luciferase assays using deletion constructs of the beta-1,4-GalT V gene promoter showed that promoter region -116 to +22 is critical for the transcriptional activation of the gene by Ets-1. Despite the presence of one Ets-1-binding site, which overlapped the Sp1-binding site, electrophoretic mobility shift assays showed that the region bound preferentially to Sp1 rather than to Ets-1. To solve this problem, we examined the transcriptional regulation of the human Sp1 gene by Ets-1 and found that the gene expression and promoter activity of Sp1 are regulated by Ets-1 in cancer cells. Functional analyses of two Ets-1-binding sites in the Sp1 gene promoter showed that only Ets-1-binding site -413 to -404 is involved in the activation of the gene by Ets-1. These results indicate that Ets-1 enhances expression of the beta-1,4-GalT V gene through activation of the Sp1 gene in cancer cells.

Increased expression of Lewis X and Y antigens on the cell surface and FUT 4 mRNA during granzyme B-induced Jurkat cell apoptosis

Cytotoxic T cells and natural killer cells play key roles in cell-mediated cytotoxicity and can induce apoptosis in virus-infected and malignant cells by releasing cytotoxic granules. In the current study, apoptosis was induced in Jurkat cells, a human T cell line, by delivering granzyme B into the cells using BioPORTER, a cationic lipid formulation. During granzyme B-induced apoptosis, there was an increase in the cell surface expression of Lewis X and Y antigens. To clarify the roles of initiator and executioner caspases in the expression of Lewis X and Y antigens, we treated Jurkat cells with granzyme B in the presence of caspase 3, 8, and 9 inhibitors. The results indicated that delivery of granzyme B into Jurkat cells induces apoptosis by activating caspase 3 and that caspase 3 but not caspase 8 and 9 plays a key role in enhancing the expression of Lewis X and Y antigens. Real-time PCR revealed that expression of the mRNAs for alpha1,3-fucosyltransferases FUT4 was increased at 3 h during granzyme B-induced apoptosis, while FUT9 mRNA expression gradually increased after 12 h. This increased expression of FUT4 mRNA occurred downstream of caspase 3 activation and resulted in the increased cell surface expression of Lewis X and Y antigens.

The ternary complex factor Net regulates cell migration through inhibition of PAI-1 expression

Net, Elk-1, and Sap-1 are members of the ternary complex factor (TCF) subfamily of Ets transcription factors. They form ternary complexes with serum response factor (SRF) on serum response elements of immediate early genes such as c-fos and egr-1 and mediate responses to growth factors and mitogen-activated protein kinase signaling. Although the TCFs have been extensively studied as intermediates in signaling cascades, surprisingly little is known about their different target genes and physiological functions. We report that Net homozygous mutant mouse embryonic fibroblasts have a defect in cell migration. This defect results at least in part from increased expression of plasminogen activator inhibitor type 1 (PAI-1), a serine protease inhibitor (serpin) that controls extracellular proteolysis and cell matrix adhesion. The defect in cell migration can be reverted by the addition of a PAI-1 blocking antibody. Net represses PAI-1 promoter activity and binds to a specific region of the promoter containing Ets binding sites in the absence of SRF. We conclude that Net is a negative regulator of PAI-1 expression and is thereby involved in cell migration.

Identification of biomarkers for tumor endothelial cell proliferation through gene expression profiling

Extensive efforts are under way to identify antiangiogenic therapies for the treatment of human cancers. Many proposed therapeutics target vascular endothelial growth factor (VEGF) or the kinase insert domain receptor (KDR/VEGF receptor-2/FLK-1), the mitogenic VEGF receptor tyrosine kinase expressed by endothelial cells. Inhibition of KDR catalytic activity blocks tumor neoangiogenesis, reduces vascular permeability, and, in animal models, inhibits tumor growth and metastasis. Using a gene expression profiling strategy in rat tumor models, we identified a set of six genes that are selectively overexpressed in tumor endothelial cells relative to tumor cells and whose pattern of expression correlates with the rate of tumor endothelial cell proliferation. In addition to being potential targets for antiangiogenesis tumor therapy, the expression patterns of these genes or their protein products may aid the development of pharmacodynamic assays for small molecule inhibitors of the KDR kinase in human tumors.

Molecular mechanism for cancer-associated induction of sialyl Lewis X and sialyl Lewis A expression-The Warburg effect revisited

Cell adhesion mediated by selectins and their carbohydrate ligands, sialyl Lewis X and sialyl Lewis A, figures heavily in cancer metastasis. Expression of these carbohydrate determinants is markedly enhanced in cancer cells, but the molecular mechanism that leads to cancer-associated expression of sialyl Lewis X/A has not been well understood. Results of recent studies indicated involvement of two principal mechanisms in the accelerated expression of sialyl Lewis X/A in cancers; 'incomplete synthesis' and ' neo synthesis.' As to 'incomplete synthesis,' we have recently found further modified forms of sialyl Lewis X and sialyl Lewis A in non-malignant colonic epithelium, which have additional 6-sulfation or 2 --> 6 sialylation. The impairment of GlcNAc 6-sulfation and 2 --> 6 sialylation upon malignant transformation leads to accumulation of sialyl Lewis X/A in colon cancer cells. Epigenetic changes such as DNA methylation and/or histone deacetylation are suggested to lie behind such incomplete synthesis. As to the mechanism called ' neo synthesis,' recent studies have indicated that cancer-associated alterations in the sugar transportation and intermediate carbohydrate metabolism play important roles. Cancer cells are known to exhibit a metabolic shift from oxidative to elevated anaerobic glycolysis (Warburg effect), which is correlated with the increased gene expression of sugar transporters and glycolytic enzymes induced by common cancer-specific genetic alterations. The increased sialyl Lewis X/A expression in cancer is a link in the chains of these events because our recent results indicated that these events accompany transcriptional induction of a set of genes closely related to its expression.

Ternary complex factor-serum response factor complex-regulated gene activity is required for cellular proliferation and inhibition of apoptotic cell death

Members of the ternary complex factor (TCF) subfamily of the ETS-domain transcription factors are activated through phosphorylation by mitogen-activated protein kinases (MAPKs) in response to a variety of mitogenic and stress stimuli. The TCFs bind and activate serum response elements (SREs) in the promoters of target genes in a ternary complex with a second transcription factor, serum response factor (SRF). The association of TCFs with SREs within immediate-early gene promoters is suggestive of a role for the ternary TCF-SRF complex in promoting cell cycle entry and proliferation in response to mitogenic signaling. Here we have investigated the downstream gene regulatory and phenotypic effects of inhibiting the activity of genes regulated by TCFs by expressing a dominantly acting repressive form of the TCF, Elk-1. Inhibition of ternary complex activity leads to the downregulation of several immediate-early genes. Furthermore, blocking TCF-mediated gene expression leads to growth arrest and triggers apoptosis. By using mutant Elk-1 alleles, we demonstrated that these effects are via an SRF-dependent mechanism. The antiapoptotic gene Mcl-1 is identified as a key target for the TCF-SRF complex in this system. Thus, our data confirm a role for TCF-SRF-regulated gene activity in regulating proliferation and provide further evidence to indicate a role in protecting cells from apoptotic cell death.

Expression of cell surface Lewis X and Y antigens and FUT4 mRNA is increased in Jurkat cells undergoing apoptosis

Cell surface molecules undergo specific changes during apoptosis, including the expression of phosphatidylserine (PS) and some proteins and alterations in sugar chains. Among the various sugar chains on the cell surface, Lewis X (Le(X)) and Lewis Y (Le(Y)) antigens are key determinants for a variety of biological processes. We studied the changes in Le(X) and Le(Y) expression in Jurkat cells, a human T cell line, during apoptosis. Flow cytometry showed that Le(X) and Le(Y) antigen expression was enhanced on the cell surface during apoptosis induced by anti-Fas antibody. To clarify the mechanism of enhanced Le(X) and Le(Y) expression, we assessed the expression levels of fucosyltransferase (FUT1, 2, 3-5-6, 4, and 9) mRNAs that are predominantly expressed in Jurkat cells and which are considered to form Le(X) and Le(Y). The expression of FUT4 mRNA was up-regulated after exposing cells to anti-Fas antibody. Moreover, the increase in Le(X) and Le(Y) antigen levels was significantly suppressed by caspase 3 or 8 inhibitors. These results indicated that the induction of FUT (mainly FUT4), the gene expression of which is mediated by signals downstream of caspase 3, increases Le(X) and Le(Y) expression in apoptotic cells.

Insulin/protein kinase B signalling pathway upregulates metastasis-related phenotypes and molecules in H7721 human hepatocarcinoma cell line

The effect of insulin on cancer metastatic potential was studied in a human hepatocarcinoma cell line, H7721. Cell adhesion to human umbilical vein endothelial cells (HUVECs) and laminin as well as chemotactic cell migration and invasion were selected as the indices of metastasis-related phenotypes for assessment of metastatic potential ex vivo. The results indicated that insulin enhanced all of these metastasis-related phenotypes. After the cells were treated with specific inhibitor of PI3K (LY294002) or transfected with antisense cDNA of PKB (AS-PKB), all of the above phenotypes were attenuated, and they could not be significantly stimulated by insulin, indicating that the insulin effect on metastatic potential was mediated by PI3K and PKB. Only the monoclonal antibody to the sialyl Lewis X (SLe(x)), but not antibodies to other Lewis antigens, significantly blocked the cell adhesion to HUVECs, cell migration and invasion, suggesting that SLe(x) played a crucial role in the metastatic potential of H7721 cells. The upregulation of cell surface SLe(x) and alpha-1,3-fucosyltransferase-VII (alpha-1,3 Fuc T-VII, enzyme for SLe(x) synthesis) was also mediated by PI3K and PKB, since LY294002 and AS-PKB also reduced the expressions of SLe(x) and alpha-1,3 FucT-VII, and attenuated the response to insulin. Furthermore, the alterations in the expressions of PKB protein and activity were correlated to the changes of metastatic phenotypes and SLe(x) expression. Taken together, the insulin/PKB signalling pathway participated in the enhancement of metastatic potential of H7721 cells, which was mediated by the upregulation of the expression of SLe(x) and alpha-1,3 FucT-VII.

Structure, organization, and function of glycosphingolipids in membrane

A large variety of glycosylation patterns in combination with different ceramide structures in glycosphingolipids provide a basis for cell type-specific glycosphingolipid pattern in membrane, which essentially reflects the composition of glycosphingolipid-enriched microdomains. Functions of glycosphingolipids as antigens, mediators of cell adhesion, and modulators of signal transduction are all based on such organization. Of particular importance is the assembly of glycosphingolipids with signal transducers and other membrane proteins to form a functional unit termed a, through which glycosylation-dependent cell adhesion coupled with signal transduction takes place. The microenvironment formed by interfacing glycosynapses of interacting cells plays a central role in defining phenotypic changes after cell adhesion, as occur in ontogenic development and cancer progression. These basic functional features of glycosphingolipids in membrane can also be considered roles of glycosphingolipids and gangliosides characteristic of neutrophils, myelocytes, and other blood cells. A series of sialyl fucosyl poly-N-acetylgalactosamine gangliosides without the sialyl-Le epitope, collectively termed, have been shown to mediate E-selectin-dependent rolling and tethering under dynamic flow with physiologic shear stress conditions. Functional roles of myeloglycan in neutrophils during inflammatory processes are discussed.

Regulatory roles of carbohydrate ligands for selectins in the homing of lymphocytes

Cell surface carbohydrate determinants figure heavily in the regulation of lymphocyte homing and the inflammatory recruitment of leukocytes. The recently described sulfated carbohydrate ligand for selectins, sialyl 6-sulfo Lewis x, is mainly involved in the routine homing of various subsets of lymphocytes, such as nai;ve helper T cells, and skin- and gut-homing helper memory T cells. The homing of lymphocytes is regulated by a unique post-translational modification of sialic acid moieties that occurs specifically in sulfated selectin ligands, whereby the sialic acid loses its N-acetyl group and is converted into a 1-5 cyclic derivative. By contrast, nonsulfated carbohydrate ligands of the selectins, such as sialyl Lewis x, are mainly involved in the recruitment of leukocytes during inflammation. The increment of sialyl Lewis x expression upon inflammatory stimuli is mediated by transcriptional induction of fucosyltransferase genes.

Characterization of the promoter for the mouse alpha 3 integrin gene

The alpha 3 beta 1 integrin is an adhesion receptor for extracellular matrix proteins including isoforms of laminin, and the changes of its expression level in various cancer cells are thought to cause their malignant phenotypes. We have cloned an approximately 4 kb DNA fragment of the 5'-flanking region of the murine alpha 3 integrin gene and analyzed its promoter activity. Transfection of MKN1 gastric carcinoma cells with serially truncated segments of the 5'-flanking region linked to a luciferase gene indicated that a 537-bp SalI/SacI fragment upstream of exon 1 was sufficient to promote high level gene expression. By 5'-rapid amplification of cDNA ends (5'-RACE) using a cap site-labeled cDNA library, we determined one major and one minor transcription start sites in this region. The murine alpha 3 integrin gene was found to contain a CCAAT box, but to lack a TATA box. Luciferase assay following transfection with a series of deletion constructs of the SalI/SacI fragment revealed that the sequence between positions -260 and -119 bp (relative to the major transcription start site) is required for efficient transcription in gastric carcinoma cells. The sequence analysis of this segment showed the presence of several consensus sequences for transcription factors including Ets, GATA and MyoD/E-box binding factors. The introduction of mutation in one of the Ets-binding sequences greatly decreased its promoter activity, suggesting that the transcription of the alpha 3 integrin gene in these cells is regulated by the Ets-family of transcription factors.

Fucosyltransferases: structure/function studies

Alpha3-fucosyltransferases (alpha3-FucTs) catalyze the final step in the synthesis of a range of important glycoconjugates that function in cell adhesion and lymphocyte recirculation. Six members of this family of enzymes have been cloned from the human genome, and their expression pattern has been shown to be highly regulated. Each enzyme has a unique acceptor substrate binding pattern, and each generates a unique range of fucosylated products. Results from a range of studies have provided information on amino acids in the FucT sequence that contribute to the differential acceptor specificity for the FucTs, and to the binding of the nucleotide sugar donor GDP-fucose. These results, in conjunction with results obtained from the analysis of the disulfide bond pattern, have provided useful clues about the spatial distribution of amino acids that influence or directly contribute to substrate binding. This information is reviewed here, and a molecular fold prediction is presented which has been constructed based on the available information and current modeling methodology.

Characterization of the functional domains of galactosylceramide expression factor 1 in MDCK cells

We previously reported that GalCer expression factor 1 (GEF-1), a rat homologue of hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), induced GalCer expression, morphological changes, and cell growth inhibition in COS-7 cells. In this study, we describe the characterization of GEF-1 in MDCK cells. Overexpression of GEF-1 in MDCK (MDCK/GEF-1) cells showed GalCer-derived sulfatide expression as well as dramatic morphological changes, but not cell growth suppression. The enzyme activity and the mRNA level of UDP-galactose:ceramide galactosyltransferase (CGT) increased significantly in MDCK/GEF-1 cells compared with control cells. GEF-1 molecule is composed of four domains; a zinc-finger (Z), a proline-rich (P), a coiled-coil (C), and a proline/glutamine-rich (Q) domain. MDCK cells transfected with various GEF-1 deletion mutants were examined for morphology and for glycolipid expression. MDCK cells transfected with Z-domain deletion mutant (MDCK/PCQ) and those with both Z- and P-domains deletion mutant (MDCK/CQ) were similar to those with a wild-type GEF-1 (MDCK/ZPCQ) in shape, exhibiting fibroblast-like cells, whereas those with the other deletion mutants showed no morphological changes, exhibiting typical epithelial-like cells. On the other hand, MDCK/ZPCQ, MDCK/PCQ, MDCK/CQ, and MDCK/Q cells expressed sulfatide, whereas those with the other deletion mutants that did not include the Q-domain showed neither GalCer nor sulfatide expression. Thus, the correlation between fibroblast-like cells in shape and the glycolipid expression was good in these deletion mutants except MDCK/Q cells, which showed epithelial-like cells, but expressed sulfatide. The glycolipid expression paralleled CGT mRNA levels. Taking these results together, it is suggested that only the Q-domain may be essential for the role of GEF-1 in inducing CGT mRNA, whereas the Q-domain together with the C-domain may be required for the induction of morphological changes in MDCK cells.

Traveling for the glycosphingolipid path

Our studies on glycosphingolipids (GSLs) were initiated through isolation and structural characterization of lacto-series type 1 and 2 GSLs, and globo-series GSLs. Lacto-series structures included histo-blood group ABH and I/i antigens. Our subsequent studies were focused on GSL changes associated with: (i) ontogenic development and differentiation; (ii) oncogenic transformation and tumor progression. Various novel types of GSLs such as extended globo-series, sialyl-Le(x) (SLe(x)), sialyl-dimeric-Le(x) (SLe(x)-Le(x)), dimeric-Le(x) (Le(x)-Le(x)), Le(y)-on-Le(x), dimeric-Le(a) (Le(a)-Le(a)), Le(b)-on-Le(a), etc. were identified as tumor-associated antigens. These studies provide an essential basis for up- or down-regulation of key glycosyltransferase genes controlling development, differentiation, and oncogenesis. GSL structures established in our laboratory are summarized in Table 1, and structural changes of GSLs associated with ontogenesis and oncogenesis are summarized in Sections 2 and 3. Based on these results, we endeavored to find out the cell biological significance of GSL changes, focused on (i) cell adhesion, e.g., the compaction process of preimplantation embryo in which Le(x)-to-Le(x), Gb4-to-GalGb4 or -nLc4 play major roles; and (ii) modulation of signal transduction through interaction of growth factor receptor tyrosine kinase with ganglioside, e.g., EGF receptor tyrosine kinase with GM3. Recent trends of studies on i and ii lead to the concept that GSL clusters (microdomains) are organized with various signal transducer molecules to form 'glycosignaling domains' (GSD). GSL-dependent adhesion occurs through clustered GSLs, and is coupled with activation of signal transducers (cSrc, Src family kinase, Rho A, etc.). Clustered GSLs involved in cell adhesion are recognized by GSLs on counterpart cells (carbohydrate-to-carbohydrate interaction), or by lectins (e.g., siglecs, selectins). Our major effort in utilization of GSLs in medical science has been for: (i) cancer diagnosis and treatment (vaccine development) based on tumor-associated GSLs and glycoepitopes; (ii) genetically defined phenotype for susceptibility to E. coli infection; (iii) clear identification of physiological E-selectin epitope (myeloglycan) expressed on neutrophils and myelocytes; (iv) characterization of sialyl poly-LacNAc epitopes recognized as male-specific antigens. Utilization of these GSLs or glycoepitopes in development of anti-adhesion approach to prevent tumor metastasis, infection, inflammation, or fertilization (i.e., contraceptive) is discussed. For each approach, development of mimetics of key GSLs or glycoepitopes is an important subject of future study.