Loss of disialyl Lewis(a), the ligand for lymphocyte inhibitory receptor sialic acid-binding immunoglobulin-like lectin-7 (Siglec-7) associated with increased sialyl Lewis(a) expression on human colon cancers

Siglec-7 as a Novel Biomarker to Predict Mortality in Decompensated Cirrhosis and Acute Kidney Injury

BACKGROUND

Patients with decompensated cirrhosis have high morbidity and are commonly hospitalized with acute kidney injury.

AIMS

We examined serum levels of Siglec-7, a transmembrane receptor that regulates immune activity, as a biomarker for mortality in patients with cirrhosis and acute kidney injury.

METHODS

Serum Siglec-7 was measured in hospitalized patients with cirrhosis and acute kidney injury, as well as in reference groups with acute liver injury/acute kidney injury, cirrhosis without acute kidney injury, and sepsis without liver disease. Clinical characteristics and subsequent outcomes were examined using univariate and multivariable analyses according to initial Siglec-7 levels. Primary outcome was death by 90 days.

RESULTS

One hundred twenty-eight subjects were included, 92 of which had cirrhosis and acute kidney injury and were used in the primary analysis. Average Model for End-Stage Liver Disease (MELD) score was 24 [95 % CI 23, 26], and serum creatinine was 2.5 [2.2, 2.8] mg/dL at the time Siglec-7 was measured. After adjusting for age and MELD score, high serum Siglec-7 level predicted mortality with a hazard ratio of 1.96 [1.04, 3.69; p = 0.04]. There was no difference in Siglec-7 levels by etiology of AKI (p = 0.24). Addition of serum Siglec-7 to MELD score improved discrimination for 90-day mortality [category-free net reclassification index = 0.38 (p = 0.04); integrated discrimination increment = 0.043 (p = 0.04)].

CONCLUSION

Serum Siglec-7 was associated with increased mortality among hospitalized patients with cirrhosis and acute kidney injury. Addition of Siglec-7 to MELD score may increase discrimination to predict 90-day mortality.

Unexpected distribution of CA19.9 and other type 1 chain Lewis antigens in normal and cancer tissues of colon and pancreas: Importance of the detection method and role of glycosyltransferase regulation

BACKGROUND

CA19.9 antigen has been assumed as an abundant product of cancer cells, due to the reactivity found by immunohistochemical staining of cancer tissues with anti-CA19.9 antibody.

METHODS

Expression and biosynthesis of type 1 chain Lewis antigens in the colon and the pancreas were studied by immunodetection in tissue sections and lysates, quantification of glycosyltransferase transcripts, bisulfite sequencing, and chromatin immunoprecipitation assays.

RESULTS

CA19.9 was poorly detectable in normal colon mucosa and almost undetectable in colon cancer, while it was easily detected in the pancreatic ducts, together with Lewis b antigen, under both normal and cancer conditions. B3GALT5 transcripts were down-regulated in colon cancer, while they remained expressed in pancreatic cancer. Even ST3GAL3 transcript appeared well expressed in the pancreas but poorly in the colon, irrespective of normal or cancer conditions. CpG islands flanking B3GALT5 native promoter presented an extremely low degree of methylation in pancreatic cancer with respect to colon cancer. In a DNA region about 1kb away from the B3GALT5 retroviral promoter, a stretch of CG dinucleotides presented a methylation pattern potentially associated with transcription. Such a DNA region and the transcription factor binding site provided overlapping results by chromatin immunoprecipitation assays, corroborating the hypothesis.

CONCLUSIONS

CA19.9 appears as a physiological product whose synthesis strongly depends on the tissue specific and epigenetically-regulated expression of B3GALT5 and ST3GAL3.

GENERAL SIGNIFICANCE

CA19.9 and other Lewis antigens acquire tumor marker properties in the pancreas due to mechanisms giving rise to reabsorption into vessels and elevation in circulating levels.

CA 19-9: Biochemical and Clinical Aspects

CA19-9 (carbohydrate antigen 19-9, also called cancer antigen 19-9 or sialylated Lewis a antigen) is the most commonly used and best validated serum tumor marker for pancreatic cancer diagnosis in symptomatic patients and for monitoring therapy in patients with pancreatic adenocarcinoma. Normally synthesized by normal human pancreatic and biliary ductal cells and by gastric, colon, endometrial and salivary epithelia, CA 19-9 is present in small amounts in serum, and can be over expressed in several benign gastrointestinal disorders. Importantly, it exhibits a dramatic increase in its plasmatic levels during neoplastic disease. However, several critical aspects for its clinical use, such as false negative results in subjects with Lewis (a-b-) genotype and false positive elevation, occasional and transient, in patients with benign diseases, together with its poor positive predictive value (72.3 %), do not make it a good cancer-specific marker and renders it impotent as a screening tool. In the last years a large number of putative biomarkers for pancreatic cancer have been proposed, most of which is lacking of large scale validation. In addition, none of these has showed to possess the requisite sensitivity/specificity to be introduced in clinical use. Therefore, although with important limitations we well-know, CA 19-9 continues being the only pancreatic cancer marker actually in clinical use.

Pathobiological implications of mucin glycans in cancer: Sweet poison and novel targets

Mucins are large glycoproteins expressed on the epithelia that provide a protective barrier against harsh insults from toxins and pathogenic microbes. These glycoproteins are classified primarily as being secreted and membrane-bound; both forms are involved in pathophysiological functions including inflammation and cancer. The high molecular weight of mucins is attributed to their large polypeptide backbone that is extensively covered by glycan moieties that modulate the function of mucins and, hence, play an important role in physiological functions. Deregulation of glycosylation machinery during malignant transformation results in altered mucin glycosylation. This review describes the functional implications and pathobiological significance of altered mucin glycosylation in cancer. Further, this review delineates various factors such as glycosyltransferases and tumor microenvironment that contribute to dysregulation of mucin glycosylation during cancer. Finally, this review discusses the scope of mucin glycan epitopes as potential diagnostic and therapeutic targets.

Epigenetic regulation of protein glycosylation

Protein N-glycosylation is an ancient metabolic pathway that still exists in all three domains of life (Archaea, Bacteria and Eukarya). The covalent addition of one or more complex oligosaccharides (glycans) to protein backbones greatly diversifies their structures and makes the glycoproteome several orders of magnitude more complex than the proteome itself. Contrary to polypeptides, which are defined by a sequence of nucleotides in the corresponding genes, the glycan part of glycoproteins are encoded in a complex dynamic network of hundreds of proteins, whereby activity is defined by both genetic sequence and the regulation of gene expression. Owing to the complex nature of their biosynthesis, glycans are particularly versatile and apparently a large part of human variation derives from differences in protein glycosylation. Composition of the individual glycome appears to be rather stable, and thus differences in the pattern of glycan synthesis between individuals could originate either from genetic polymorphisms or from stable epigenetic regulation of gene expression in different individuals. Studies of epigenetic modification of genes involved in protein glycosylation are still scarce, but their results indicate that this process might be very important for the regulation of protein glycosylation.

Significance of β-Galactoside α2,6 Sialyltranferase 1 in Cancers

Altered glycosylation is a common feature of cancer cells. It takes a variety of forms, which includes loss of expression or excessive expression of some structures, the accumulation of precursors, the appearance of novel structures, etc. Notably, these changes in glycan structure do not occur as a random consequence of disorder biology. Only a limited subset of oligosaccharides is found frequently enriched on the tumor cell surface and implicated in different tumor phenotypes. Among these, altered sialylation has long been associated with metastatic cell behaviors such as invasion and enhanced cell survival and accumulating evidence points to the alteration occurring in the sialic acid linkage to other sugars, which normally exists in three main configurations: α2,3, α2,6, and α2,8, catalyzed by a group of sialyltransferases. The aberrant expression of all three configurations has been described in cancer progression. However, the increased α2,6 sialylation catalyzed by β-galactoside α2,6 sialyltranferase 1 (ST6Gal I) is frequently observed in many types of the cancers. In this review, we describe the findings on the role of ST6Gal I in cancer progression, and highlight in particular the knowledge of how ST6Gal I-mediated α2,6 sialylated glycans or sialylated carrier proteins regulate cell signaling to promote the malignant phenotype of human carcinoma.

Cancer intelligence acquired (CIA): tumor glycosylation and sialylation codes dismantling antitumor defense

Aberrant glycosylation is a key feature of malignant transformation and reflects epigenetic and genetic anomalies among the multitude of molecules involved in glycan biosynthesis. Although glycan biosynthesis is not template bound, altered tumor glycosylation is not random, but associated with common glycosylation patterns. Evidence suggests that acquisition of distinct glycosylation patterns evolves from a 'microevolutionary' process conferring advantages in terms of tumor growth, tumor dissemination, and immune escape. Such glycosylation modifications also involve xeno- and hypersialylation. Xeno-autoantigens such as Neu5Gc-gangliosides provide potential targets for immunotherapy. Hypersialylation may display 'enhanced self' to escape immunosurveillance and involves several not mutually exclusive inhibitory pathways that all rely on protein-glycan interactions. A better understanding of tumor 'glycan codes' as deciphered by lectins, such as siglecs, selectins, C-type lectins and galectins, may lead to novel treatment strategies, not only in cancer, but also in autoimmune disease or transplantation.

Glycosylation characteristics of colorectal cancer

Glycans on proteins and lipids are known to alter with malignant transformation. The study of these may contribute to the discovery of biomarkers and treatment targets as well as understanding of cancer biology. We here describe the change of glycosylation specifically defining colorectal cancer with view on N-glycans, O-glycans, and glycosphingolipid glycans in colorectal cancer cells and tissues as well as patient sera. Glycan alterations observed in colon cancer include increased β1,6-branching and correlating higher abundance of (poly-)N-acetyllactosamine extensions of N-glycans as well as an increase in (truncated) high-mannose type glycans, while bisected structures decrease. Colorectal cancer-associated O-glycan changes are predominated by reduced expression of core 3 and 4 glycans, whereas higher levels of core 1 glycans, (sialyl) T-antigen, (sialyl) Tn-antigen, and a generally higher density of O-glycans are observed. Specific changes for glycosphingolipid glycans are lower abundances of disialylated structures as well as globo-type glycosphingolipid glycans with exception of Gb3. In general, alterations affecting all discussed glycan types are increased sialylation, fucosylation as well as (sialyl) Lewis-type antigens and type-2 chain glycans. As a consequence, interactions with glycan-binding proteins can be affected and the biological function and cellular consequences of the altered glycosylation with regard to tumorigenesis, metastasis, modulation of immunity, and resistance to antitumor therapy will be discussed. Finally, analytical approaches aiding in the field of glycomics will be reviewed with focus on binding assays and mass spectrometry.

Control of Glycosylation-Related Genes by DNA Methylation: the Intriguing Case of the B3GALT5 Gene and Its Distinct Promoters

Glycosylation is a metabolic pathway consisting of the enzymatic modification of proteins and lipids through the stepwise addition of sugars that gives rise to glycoconjugates. To determine the full complement of glycoconjugates that cells produce (the glycome), a variety of genes are involved, many of which are regulated by DNA methylation. The aim of the present review is to briefly describe some relevant examples of glycosylation-related genes whose DNA methylation has been implicated in their regulation and to focus on the intriguing case of a glycosyltransferase gene (B3GALT5). Aberrant promoter methylation is frequently at the basis of their modulation in cancer, but in the case of B3GALT5, at least two promoters are involved in regulation, and a complex interplay is reported to occur between transcription factors, chromatin remodelling and DNA methylation of typical CpG islands or even of other CpG dinucleotides. Transcription of the B3GALT5 gene underwent a particular evolutionary fate, so that promoter hypermethylation, acting on one transcript, and hypomethylation of other sequences, acting on the other, cooperate on one gene to obtain full cancer-associated silencing. The findings may also help in unravelling the complex origin of serum CA19.9 antigen circulating in some patients.

Clinicopathological utility of sialoglycoconjugates in diagnosing and treating colorectal cancer

Aberrant expression of glycoconjugates occurs during malignant transformation of cancer cells. Overexpression of sialoglycoconjugates in particular may play an important role in the progression, i.e., invasion or metastasis, of cancer. Various types of sialoglycoconjugates have been investigated to clarify their biological significance and clinical utility in diagnosing and treating colorectal cancer. This review focuses specifically on expression of mucin (MUC) 1 and it suggests that MUC1 with the specific structure of a sialo-oligosaccharide has biological significance in determining the metastatic potential of colorectal cancer cells and clinicopathological utility in evaluating the effectiveness of treatments and the prognosis for patients with colorectal cancer. Further studies are expected to contribute to the expanded use of cancer-associated sialoglycoconjugates in cancer diagnosis and therapy.

Altered tumor-cell glycosylation promotes metastasis

Malignant transformation of cells is associated with aberrant glycosylation presented on the cell-surface. Commonly observed changes in glycan structures during malignancy encompass aberrant expression and glycosylation of mucins; abnormal branching of N-glycans; and increased presence of sialic acid on proteins and glycolipids. Accumulating evidence supports the notion that the presence of certain glycan structures correlates with cancer progression by affecting tumor-cell invasiveness, ability to disseminate through the blood circulation and to metastasize in distant organs. During metastasis tumor-cell-derived glycans enable binding to cells in their microenvironment including endothelium and blood constituents through glycan-binding receptors – lectins. In this review, we will discuss current concepts how tumor-cell-derived glycans contribute to metastasis with the focus on three types of lectins: siglecs, galectins, and selectins. Siglecs are present on virtually all hematopoietic cells and usually negatively regulate immune responses. Galectins are mostly expressed by tumor cells and support tumor-cell survival. Selectins are vascular adhesion receptors that promote tumor-cell dissemination. All lectins facilitate interactions within the tumor microenvironment and thereby promote cancer progression. The identification of mechanisms how tumor glycans contribute to metastasis may help to improve diagnosis, prognosis, and aid to develop clinical strategies to prevent metastasis.

Carbohydrate-containing molecules as potential biomarkers in colon cancer

Glycans play a critical role in physiological and pathological processes through interaction with a variety of ligands. Altered expression and dysregulation of these molecules can cause aberrant cellular function such as malignancy. Glycomics provide information of the structure and function of glycans, glycolipids, and glycoproteins such as proteoglycans, and may help to predict cancer development and progression as biomarkers. In this report, we compared the expression of proteoglycans, the content and structure of glycosaminoglycans and glycolipids between patient-matched normal and cancer tissues obtained from colon cancer patients. Tumor-related proteoglycans, glypican-3, and syndecan-1 showed downregulation in cancer tissues compared to normal tissues. In cancer tissue, the total amount of chondroitin sulfate (CS)/dermatan sulfate and heparan sulfate were lower and, interestingly, the level of disaccharide units of both 4S6S (CS-E) and 6S (CS-C) were higher compared to normal tissue. Also, overall lipids including glycolipids, a major glycomics target, were analyzed by hydrophilic interaction liquid chromatography mass spectrometry. Increase of lyso-phosphatidylcholine (phospholipid), sphingomyelin (sphigolipid), and four types of glycolipids (glucosylceramide, lactosylceramide, monosialic acid ganglioside, and globoside 4) in cancer tissue showed the possibility as potential biomarkers in colon cancer. While requiring the need for careful interpretation, this type of broad investigation gives us a better understanding of pathophysiological roles on glycosaminoglycans and glycolipids and might be a powerful tool for colon cancer diagnosis.

Suppression of B3GNT7 gene expression in colon adenocarcinoma and its potential effect in the metastasis of colon cancer cells

The cell surface sialyl Lewis a (sLe(a)) and sialyl Lewis x (sLe(x)) antigens, which are built on the terminals of glyco-structures called poly-N-acetyllactosamine (LacNAc) chains, have been shown to play a critical role in the metastasis of colon cancer. In the present investigation, expression of the B3GNT7 gene, which encodes a β-1,3-N-acetylglucosaminyltransferase that mainly acts on and extends sulfated poly-LacNAc chains, was found to be markedly suppressed during the oncogenetic processes associated with colon cancer. DNA methylation in the promoter region of the B3GNT7 gene was found to play a significant role in the suppression of the B3GNT7 gene in colon cancer cells. The results obtained from Transwell experiments and the nude mice xenograft model demonstrated that ectopic expression of the B3GNT7 gene in colon cancer cells diminished the migration capability and the liver-metastasis potential, respectively, of colon cancer cells. Flow cytometric analysis showed that expression of cell surface sLe(a) and sLe(x) antigens was decreased in colon cancer cells when the B3GNT7 gene was ectopically expressed. Taken together, the results of the present investigation suggest a link between suppression of B3GNT7 gene expression and elevation of sLe(a)/sLe(x) antigen expressions on the surface of cells and that this consequently promotes the metastasis potential of cancer cells as part of the colon cancer oncogenetic process.

Fucosylated TGF-β receptors transduces a signal for epithelial-mesenchymal transition in colorectal cancer cells

Background:

Transforming growth factor-β (TGF-β) is a major inducer of epithelial–mesenchymal transition (EMT) in different cell types. TGF-β-mediated EMT is thought to contribute to tumour cell spread and metastasis. Sialyl Lewis antigens synthesised by fucosyltransferase (FUT) 3 and FUT6 are highly expressed in patients with metastatic colorectal cancer (CRC) and are utilised as tumour markers for cancer detection and evaluation of treatment efficacy. However, the role of FUT3 and FUT6 in augmenting the malignant potential of CRC induced by TGF-β is unclear.

Methods:

Colorectal cancer cell lines were transfected with siRNAs for FUT3/6 and were examined by cell proliferation, invasion and migration assays. The expression and phosphorylation status of TGF-β downstream molecules were analysed by western blot. Fucosylation of TGF-β receptor (TβR) was examined by lectin blot analysis.

Results:

Inhibition of FUT3/6 expression by siRNAs suppressed the fucosylation of type I TβR and phosphorylation of the downstream molecules, thereby inhibiting the invasion and migration of CRC cells by EMT.

Conclusion:

Fucosyltransferase 3/6 has an essential role in cancer cell adhesion to endothelial cells by upregulation of sialyl Lewis antigens and also by enhancement of cancer cell migration through TGF-β-mediated EMT.

Investigations on aberrant glycosylation of glycosphingolipids in colorectal cancer tissues using liquid chromatography and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS)

Cancer is a leading cause of death and alterations of glycosylation are characteristic features of malignant cells. Colorectal cancer is one of the most common cancers and its exact causes and biology are not yet well understood. Here, we compared glycosylation profiles of colorectal tumor tissues and corresponding control tissues of 13 colorectal cancer patients to contribute to the understanding of this cancer. Using MALDI-TOF(/TOF)-MS and 2-dimensional LC-MS/MS we characterized enzymatically released and 2-aminobenzoic acid labeled glycans from glycosphingolipids. Multivariate data analysis revealed significant differences between tumor and corresponding control tissues. Main discriminators were obtained, which represent the overall alteration in glycosylation of glycosphingolipids during colorectal cancer progression, and these were found to be characterized by (1) increased fucosylation, (2) decreased acetylation, (3) decreased sulfation, (4) reduced expression of globo-type glycans, as well as (5) disialyl gangliosides. The findings of our current research confirm former reports, and in addition expand the knowledge of glycosphingolipid glycosylation in colorectal cancer by revealing new glycans with discriminative power and characteristic, cancer-associated glycosylation alterations. The obtained discriminating glycans can contribute to progress the discovery of biomarkers to improve diagnostics and patient treatment.

Epigenetic regulation of glycosylation is the quantum mechanics of biology

BACKGROUND

Most proteins are glycosylated, with glycans being integral structural and functional components of a glycoprotein. In contrast to polypeptides, which are fully encoded by the corresponding gene, glycans result from a dynamic interaction between the environment and a network of hundreds of genes.

SCOPE OF REVIEW

Recent developments in glycomics, genomics and epigenomics are discussed in the context of an evolutionary advantage for higher eukaryotes over microorganisms, conferred by the complexity and adaptability which glycosylation adds to their proteome.

MAJOR CONCLUSIONS

Inter-individual variation of glycome composition in human population is large; glycome composition is affected by both genes and environment; epigenetic regulation of "glyco-genes" has been demonstrated; and several mechanisms for transgenerational inheritance of epigenetic marks have been documented.

GENERAL SIGNIFICANCE

Epigenetic recording of acquired characteristics and their transgenerational inheritance could be important mechanisms used by higher organisms to compete or collaborate with microorganisms.

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.

The interaction between Siglec-15 and tumor-associated sialyl-Tn antigen enhances TGF-β secretion from monocytes/macrophages through the DAP12-Syk pathway

We previously demonstrated that Siglec-15, a member of the Siglec family of glycan-recognition proteins, is expressed on a subset of macrophages and preferentially recognizes the sialyl-Tn (sTn) antigen, a tumor-associated glycan structure. In this study, we report on the biological significance of the Siglec-15-mediated interaction between monocytes/macrophages and cancer cells. Siglec-15 is expressed on tumor-associated macrophages (TAMs) in various human tumor tissues. We further demonstrated that its expression is substantially elevated in macrophage colony-stimulating factor-induced M2-like macrophages, which produced more transforming growth factor-β (TGF-β) in response to sTn-positive cells than to negative cells. We designed a co-culture model of THP-1 (human monocytic leukemia) cells and H157 (human lung carcinoma) cells mimicking the interaction between monocytes/macrophages and cancer cells that recapitulated the enhanced TGF-β production in Siglec-15 expressing THP-1 cells by the cellular interaction with sTn expressing H157 cells. The enhanced TGF-β production required a direct interaction between the two cell lines through sialic acids. Siglec-15 associates with adaptor protein DNAX activation protein of 12 kDa (DAP12) at the binding determinant Lys(274) in the transmembrane domain and transduces a signal to spleen tyrosine kinase (Syk). The enhanced TGF-β secretion was significantly attenuated by Syk inhibitor treatment of THP-1 cells or by substitution of the Siglec-15 Lys(274) to Ala, which disrupts the molecular interaction between Siglec15 and DAP12. These findings indicate that Siglec-15 recognizes the tumoral sTn antigen and transduces a signal for enhanced TGF-β secretion in TAMs and further suggest that Siglec-15 on macrophages may contribute to tumor progression by the TGF-β-mediated modulation of intratumoral microenvironments.

Targeting anticancer drug delivery to pancreatic cancer cells using a fucose-bound nanoparticle approach

Owing to its aggressiveness and the lack of effective therapies, pancreatic ductal adenocarcinoma has a dismal prognosis. New strategies to improve treatment and survival are therefore urgently required. Numerous fucosylated antigens in sera serve as tumor markers for cancer detection and evaluation of treatment efficacy. Increased expression of fucosyltransferases has also been reported for pancreatic cancer. These enzymes accelerate malignant transformation through fucosylation of sialylated precursors, suggesting a crucial requirement for fucose by pancreatic cancer cells. With this in mind, we developed fucose-bound nanoparticles as vehicles for delivery of anticancer drugs specifically to cancer cells. L-fucose-bound liposomes containing Cy5.5 or Cisplatin were effectively delivered into CA19-9 expressing pancreatic cancer cells. Excess L-fucose decreased the efficiency of Cy5.5 introduction by L-fucose-bound liposomes, suggesting L-fucose-receptor-mediated delivery. Intravenously injected L-fucose-bound liposomes carrying Cisplatin were successfully delivered to pancreatic cancer cells, mediating efficient tumor growth inhibition as well as prolonging survival in mouse xenograft models. This modality represents a new strategy for pancreatic cancer cell-targeting therapy.

Transcription factors c-Myc and CDX2 mediate E-selectin ligand expression in colon cancer cells undergoing EGF/bFGF-induced epithelial-mesenchymal transition

Sialyl Lewis x (sLe(x)) and sialyl Lewis a (sLe(a)) glycans are expressed on highly metastatic colon cancer cells. They promote extravasation of cancer cells and tumor angiogenesis via interacting with E-selectin on endothelial cells. Recently, epithelial-mesenchymal transition (EMT) has been noted as a critical phenotypic alteration in metastatic cancer cells. To address the association between sLe(x/a) expression and EMT, we assessed whether sLe(x/a) are highly expressed on colon cancer cells undergoing EMT. Treatment of HT29 and DLD-1 cells with EGF and/or basic FGF (bFGF) induced EMT and significantly increased sLe(x/a) expression resulting in enhanced E-selectin binding activity. The transcript levels of the glycosyltransferase genes ST3GAL1/3/4 and FUT3 were significantly elevated and that of FUT2 was significantly suppressed by the treatment. We provide evidence that ST3GAL1/3/4 and FUT3 are transcriptionally up-regulated by c-Myc with probable involvement of Ser62 phosphorylation, and that FUT2 is transcriptionally down-regulated through the attenuation of CDX2. The contribution of c-Myc and CDX2 to the sLe(x/a) induction was proved to be significant by knockdown or forced expression experiments. Interestingly, the cells undergoing EMT exhibited significantly increased VEGF secretion, which can promote tumor angiogenesis in cooperation with sLe(x/a). Finally, immunohistological study indicated high E-selectin ligand expression on cancer cells undergoing EMT in vivo, supporting their coexistence observed in vitro. These results suggest a significant link between sLe(x/a) expression and EMT in colon cancer cells and a pivotal role of c-Myc and CDX2 in regulating sLe(x/a) expression during EMT.

Colonic epithelial cells express specific ligands for mucosal macrophage immunosuppressive receptors siglec-7 and -9

Immune cells are known to express specific recognition molecules for cell surface glycans. However, mechanisms involved in glycan-mediated cell-cell interactions in mucosal immunity have largely been left unaccounted for. We found that several glycans preferentially expressed in nonmalignant colonic epithelial cells serve as ligands for sialic acid-binding Ig-like lectins (siglecs), the immunosuppressive carbohydrate-recognition receptors carried by immune cells. The siglec ligand glycans in normal colonic epithelial cells included disialyl Lewis(a), which was found to have binding activity to both siglec-7 and -9, and sialyl 6-sulfo Lewis(x), which exhibited significant binding to siglec-7. Expression of these siglec-7/-9 ligands was impaired upon carcinogenesis, and they were replaced by cancer-associated glycans sialyl Lewis(a) and sialyl Lewis(x), which have no siglec ligand activity. When we characterized immune cells expressing siglecs in colonic lamina propriae by flow cytometry and confocal microscopy, the majority of colonic stromal immune cells expressing siglec-7/-9 turned out to be resident macrophages characterized by low expression of CD14/CD89 and high expression of CD68/CD163. A minor subpopulation of CD8(+) T lymphocytes also expressed siglec-7/-9. Siglec-7/-9 ligation suppressed LPS-induced cyclooxygenase-2 expression and PGE(2) production by macrophages. These results suggest that normal glycans of epithelial cells exert a suppressive effect on cyclooxygenase-2 expression by resident macrophages, thus maintaining immunological homeostasis in colonic mucosal membranes. Our results also imply that loss of immunosuppressive glycans by impaired glycosylation during colonic carcinogenesis enhances inflammatory mediator production.

The immunomodulating roles of glycoproteins in epithelial ovarian cancer

The complexity of the immune system demands an intricate defense mechanism by tumors. Ovarian and other tumors employ specific glycoproteins and the associated glycan sequences to modulate immune responses. Glycoproteins enable tumor cells that express or secrete these molecules to evade immune cell attack and induce the immune system to promote tumor growth. This review focuses first on the immune environment in ovarian cancer, and the mechanisms of activation and inhibition that immune cells undergo in order to either attack or ignore a target cell. Next we illustrate the immunomodulatory roles of ovarian cancer-associated glycans and glycoproteins in 1. preventing immune synapse formation, 2. serving as ligands of immune cell receptors, 3. scavenging cytokines and chemokines, and 4. participating in the formation of autoantibodies against the tumor. The importance of these immunomodulating strategies from the view points of understanding the tumor immunology of ovarian tumors, potential origin of such mechanisms, and specific strategies to circumvent the glycoconjugate-mediated suppression of immune responses is discussed in this review.

Advances in biomarker research for pancreatic cancer

Pancreatic cancer (PC) is a leading cause of cancer related deaths in United States. The lack of early symptoms results in latestage detection and a high mortality rate. Currently, the only potentially curative approach for PC is surgical resection, which is often unsuccessful because the invasive and metastatic nature of the tumor masses makes their complete removal difficult. Consequently, patients suffer relapses from remaining cancer stem cells or drug resistance that eventually lead to death. To improve the survival rate, the early detection of PC is critical. Current biomarker research in PC indicates that a serum carbohydrate antigen, CA 19-9, is the only available biomarker with approximately 90% specificity to PC. However, the efficacy of CA 19-9 for assessing prognosis and monitoring patients with PC remains contentious. Thus, advances in technology and the detection of new biomarkers with high specificity to PC are needed to reduce the mortality rate of pancreatic cancer.

Evolutional and clinical implications of the epigenetic regulation of protein glycosylation

Protein N glycosylation is an ancient posttranslational modification that enriches protein structure and function. The addition of one or more complex oligosaccharides (glycans) to the backbones of the majority of eukaryotic proteins makes the glycoproteome several orders of magnitude more complex than the proteome itself. Contrary to polypeptides, which are defined by a sequence of nucleotides in the corresponding genes, glycan parts of glycoproteins are synthesized by the activity of hundreds of factors forming a complex dynamic network. These are defined by both the DNA sequence and the modes of regulating gene expression levels of all the genes involved in N glycosylation. Due to the absence of a direct genetic template, glycans are particularly versatile and apparently a large part of human variation derives from differences in protein glycosylation. However, composition of the individual glycome is temporally very constant, indicating the existence of stable regulatory mechanisms. Studies of epigenetic mechanisms involved in protein glycosylation are still scarce, but the results suggest that they might not only be important for the maintenance of a particular glycophenotype through cell division and potentially across generations but also for the introduction of changes during the adaptive evolution.

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.

Sialylation of 3-methylcholanthrene-induced fibrosarcoma determines antitumor immune responses during immunoediting

Sialylation of tumor cells is involved in various aspects of their malignancy (proliferation, motility, invasion, and metastasis); however, its effect on the process of immunoediting that affects tumor cell immunogenicity has not been studied. We have shown that in mice with impaired immunoediting, such as in IL-1α(-/-) and IFNγ(-/-) mice, 3-methylcholanthrene-induced fibrosarcoma cells are immunogenic and concomitantly bear low levels of surface sialylation, whereas tumor cells derived from wild type mice are nonimmunogenic and bear higher levels of surface sialylation. To study immune mechanisms whose interaction with tumor cells involves surface sialic acid residues, we used highly sialylated 3-methylcholanthrene-induced nonimmunogenic fibrosarcoma cell lines from wild type mice, which were treated with sialidase to mimic immunogenic tumor cell variants. In vivo and in vitro experiments revealed that desialylation of tumor cells reduced their growth and induced cytotoxicity by NK cells. Moreover, sialidase-treated tumor cells better activated NK cells for IFN-γ secretion. The NKG2D-activating receptor on NK cells was shown to be involved in interactions with desialylated ligands on tumor cells, the nature of which is still not known. Thus, the degree of sialylation on tumor cells, which is selected during the process of immunoediting, has possibly evolved as an important mechanism of tumor cells with low intrinsic immunogenicity or select for tumor cells that can evade the immune system or subvert its function. When immunoediting is impaired, such as in IFN-γ(-/-) and IL-1α(-/-) mice, the overt tumor consists of desialylayed tumor cells that interact better with immunosurveillance cells.

Ganglioside DSGb5, preferred ligand for Siglec-7, inhibits NK cell cytotoxicity against renal cell carcinoma cells

In renal cell carcinoma (RCC), the presence of higher gangliosides correlates with systematic metastasis. Disialosyl globopentaosylceramide (DSGb5) was identified previously as one of the major gangliosides from RCC tissues. Siglec-7 (sialic acid-binding Ig-like lectin-7), expressed on natural killer (NK) cells as an inhibitory receptor, has a striking preference for internally branched α2,6-linked disialic gangliosides such as DSGb5. To clarify the functional role of DSGb5 in RCC metastases, we have investigated whether DSGb5 expressed on RCC cells can modulate NK cell cytotoxicity in a Siglec-7-dependent manner. The binding activity of RCC cells to Siglec-7-Fc fusion protein was specifically inhibited by anti-DSGb5 monoclonal antibody and transfection of siRNA for ST6GalNAcVI (synthetase of DSGb5). These observations showed that Siglec-7-Fc fusion protein specifically bound to DSGb5 expressed on RCC cells. In contrast, the sialic acid-binding site of Siglec-7 on NK cells was masked by cis interactions with endogenous sialoconjugates at the cell surface, but it could be unmasked by sialidase treatment of the NK cells. Following sialidase treatment of NK cells, NK cell cytotoxicity against RCC cells with high DSGb5 expression was significantly decreased relative to cells with low DSGb5 expression. These findings indicate that such NK cell cytotoxicity against RCC cells could be inhibited by the interaction between Siglec-7 on effecter cells and DSGb5 on target cells. The results of the present study suggest that DSGb5 expressed on RCC cells can downregulate NK cell cytotoxicity in a DSGb5-Siglec-7-dependent manner and that RCC cells with DSGb5 create favorable circumstance for their own survival and metastases.

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

Colon cancer cells express the carbohydrate determinant sialyl Lewis(x), while they exhibit markedly decreased the expression of its sulfated derivative, sialyl 6-sulfo Lewis(x). In contrast, normal colonic epithelial cells strongly express sialyl 6-sulfo Lewis(x), but they virtually do not express sialyl Lewis(x). Impaired sulfation was therefore suggested to occur during the course of malignant transformation of colonic epithelial cells and was assumed to be responsible for the increased sialyl Lewis(x) expression in cancers. To elucidate the molecular biological background of the impaired sulfation in cancers, we studied the expression levels of mRNA for 6-O-sulfotransferase isoenzymes, PAPS synthases and transporters, and a cell membrane sulfate transporter, DTDST, in cancer tissues. The most striking decrease in cancer cells compared with nonmalignant epithelial cells was noted in the transcription of the DTDST gene (P = 0.0000014; n = 20). Most cultured colon cancer cells had a diminished DTDST transcription, which was restored when cultured with histone deacetylase inhibitors. Suppression of DTDST transcription under the control of a tet-off inducible promoter resulted in increased sialyl Lewis(x) expression and reduced sialyl 6-sulfo Lewis(x) expression. Unexpectedly, the growth rate of the cancer cells was markedly enhanced when transcription of DTDST was suppressed. These results show that the decrease in the transcription of the sulfate transporter gene is the major cause of decreased expression of sialyl 6-sulfo Lewis(x) and increased expression of sialyl Lewis(x) in colon cancers. The results also suggest that the diminished DTDST expression is closely related to enhanced proliferation of cancer cells.

Fucosylation and gastrointestinal cancer

Fucose (6-deoxy-L-galactose) is a monosaccharide that is found on glycoproteins and glycolipids in verte-brates, invertebrates, plants, and bacteria. Fucosylation, which comprises the transfer of a fucose residue to oligosaccharides and proteins, is regulated by many kinds of molecules, including fucosyltransferases, GDP-fucose synthetic enzymes, and GDP-fucose transporter(s). Dramatic changes in the expression of fucosylated oligosaccharides have been observed in cancer and inflammation. Thus, monoclonal antibodies and lectins recognizing cancer-associated fucosylated oligosaccharides have been clinically used as tumor markers for the last few decades. Recent advanced glycomic approaches allow us to identify novel fucosylation-related tumor markers. Moreover, a growing body of evidence supports the functional significance of fucosylation at various pathophysiological steps of carcinogenesis and tumor progression. This review highlights the biological and medical significance of fucosylation in gastrointestinal cancer.

Altered expression of glycan genes in cancers induced by epigenetic silencing and tumor hypoxia: clues in the ongoing search for new tumor markers

The glycan molecules that preferentially appear in cancers are clinically utilized as serum tumor markers. The exact reason, however, why glycans are useful as tumor markers remain elusive. Here, we will summarize lessons learned from well-established cancer-associated glycans, and propose strategies to develop new cancer markers. Our recent results on cancer-associated glycans, sialyl Lewis A and sialyl Lewis X, indicated that the repressed transcription of some glycan genes by epigenetic silencing during early carcinogenesis, and the transcriptional induction of some other glycan genes by tumor hypoxia accompanying cancer progression at locally advanced stages, are two major factors determining cancer-associated glycan expression. Multiple genes are involved in glycan synthesis, and epigenetic silencing of a part of such genes leads to accumulation of glycans having truncated incomplete structures, which are readily detected by specific antibodies. Glycans are very unique and advantageous as marker molecules because they are capable of reflecting epigenetic silencing in their structures. Transcriptional induction of some glycan genes by tumor hypoxia at the later stages produces further glycan modifications, such as an unusual increase of the N-glycolyl sialic acid residues in the glycan molecules. The entire process of malignant transformation thus creates abnormal glycans, whose structures reveal the effects of both epigenetic silencing and tumor hypoxia. The second advantage of a glycan marker over a proteinous marker is that they can reflect the plurality of genetic anomalies in a singular molecule, as it is synthesized by the cooperative action of multiple genes. Glycans are sometimes covalently bound to well-known cancer-associated proteins, such as CD44v, and this eventually contributes to a high cancer specificity and functional relevancy in cancer progression.

Siglec-7 mediates nonapoptotic cell death independently of its immunoreceptor tyrosine-based inhibitory motifs in monocytic cell line U937

Siglec-7, a sialic acid binding immunoglobulin-like lectin, predominantly transduces inhibitory signals through cytosolic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Here, we report that clustering of Siglec-7 with a specific F(ab')(2) elicited cell death. Interestingly, a truncated Siglec-7 lacking the cytosolic ITIM domain still induced the cell death, suggesting that the ITIMs are not essential for the death signaling. Further analyses of the death signaling revealed that an oxygen radical scavenger, N-acetyl cysteine, completely inhibited the cell death, whereas a pancaspase inhibitor did not. In addition, caspase-3 activation, DNA ladder formation, and nuclear condensation were not detected during the death process, suggesting that the cell death is nonapoptotic. To identify the critical region for the death signaling, we prepared a series of shuffling chimeras between Siglec-7 and Siglec-9, the latter of which did not transduce a death signal. The critical region was mapped to the middle of the membrane-proximal C2-set domain, which contained only six amino acid differences between Siglec-7 and Siglec-9. Point mutation analyses of each of these six amino acids revealed that four of the six amino acids were critical for the death signal. A computer-assisted 3D modeling revealed that these four amino acids were proximally located on the surface of the C2-set domain. In conclusion, Siglec-7 induces nonapoptotic cell death, the signal for which is transduced by an extracellular C2-set domain.

Effect of Neem (Azadirchta indica) on serum glycoprotein contents of rats administered 1,2 dimethylhydrazine

The present study was designed to investigate the effects of aqueous Azadirchta Indica leaf extract (AAILE) on serum glycoprotein contents and tumor incidence rate in colon of rats subjected to Dimethylhydrazine (DMH) treatment. Forty rats were divided equally and randomly into four groups viz., Group I (normal control), Group II (DMH-treated), Group III (AAILE) and Group IV (DMH + AAILE treated). Group II and IV animals were injected subcutaneously every week with DMH (30 mg/kg b.wt.) for two durations of 10 and 20 weeks. AAILE was given orally three times a week on alternate days (100 mg/kg b.wt.) to animals belonging to groups III and IV. Blood samples were drawn from all the animals by ocular vein puncture every month for the estimation of Total Sialic Acid (TSA) and Lipid Bound Sialic Acid (LSA), which served as markers for the cancer. No incidence of tumor was recorded in the animals given DMH treatment for 10 weeks. However, DMH treatment for 20 weeks showed 100% tumor incidence. Animals treated with DMH for both the time durations showed a significant increase in the levels of TSA in comparison to normal control, which however were decreased significantly following AAILE supplementation. There was no significant difference between LSA levels of DMH-treated animals and normal controls. The present study suggested that supplementation of AAILE in cancer-bearing animals attenuates considerably the molecular events that initiate the development of tumors.

Altered sphingolipid metabolism induced by tumor hypoxia - new vistas in glycolipid tumor markers

Uncontrolled growth of malignant cells produces hypoxic regions in locally advanced tumors. Recently we showed that tumor hypoxia-induced transcription of multiple genes involved in glycan synthesis, leading to expression of useful glycolipid tumor markers, such as gangliosides having N-glycolyl sialic acid. Our subsequent studies indicated that the ceramide portion of glycolipids, as well as their glycan moiety, was also significantly affected by hypoxia. Tumor hypoxia-induced marked accumulation of sphinganine (dihydrosphingosine) long-chain base, and significant reduction of unsaturated very long-chain fatty acids in the ceramide moiety. Mass-spectrometry, which yields information on both glycan- and ceramide moieties, is expected to be clinically useful in detecting such distinct molecular species of cancer-associated glycolipids having combined alteration in both glycan- and ceramide moieties.

High expression of alpha 2, 3-linked sialic acid residues is associated with the metastatic potential of human gastric cancer

BACKGROUND

Sialic acid, as a terminal saccharide residue on cell surface glycoconjugates, plays an important role in a variety of biological processes. However, the precise nature of the molecules in gastric cancers has not been unveiled nor documented to be of clinical relevance. Herein, we measured the expression of alpha 2, 3-linked sialic acid residues by using a specific lectin as well as the potential of invasion and metastasis of gastric cancer was analyzed.

METHODS

The expression of alpha 2, 3-linked sialic acid residues in 100 cases of gastric cancer samples was evaluated using Maackia amurensis leukoagglutinin (MAL) histochemical staining analysis. The assays of cytochemical staining and flow cytometry were employed to determine the MAL positive cells in the gastric cancer cell lines. The activities of invasion and migration were evaluated using the assays of cell adhesion and transwell chamber.

RESULTS

The staining of MAL in gastric cancer tissues showed that high levels of alpha 2, 3-linked sialic acid residues were closely associated with the invasive depth (P=0.0003) and lymph node metastasis (P=0.0441). In gastric adenocarcinoma cell lines, SGC-7901, the highly metastatic cell line, displayed the most positive reaction with MAL among the selected cell lines. The potential of invasion and migration was confirmed using the assays of adhesion and transwell chamber that SGC-7901 exhibited the high activity of adhesion to extracellular matrix (ECM) and penetration to Matrigel.

CONCLUSION

These results suggested that high level of alpha 2, 3-linked sialic acid residues was associated with metastatic potential of gastric cancer cells.

Natural killer cell receptors

Natural killer (NK) cells are an important arm of the innate immune response that are directly involved in the recognition and lysis of virus-infected and tumor cells. Such function is under the control of a complex array of germline-encoded receptors able to deliver either inhibitory or activating signals. The majority of inhibitory receptors expressed by NK cells are major histocompatibility complex (MHC) class I-specific and display clonal and stochastic distribution on the cell surface. Thus, a given NK cell expresses at least one self class I inhibitory receptor. Under normal conditions, the strength of inhibitory signals delivered by multiple interactions always overrides the activating signals, resulting in NK cell self-tolerance. Under certain pathological conditions, such as viral infections or tumor transformation, the delicate balance of inhibition versus activation is broken, resulting in downregulation or loss of MHC class I expression. In general, the degree of inhibition induced by class I-specific receptors is proportional to the amount of these molecules on the cell surface. Thus, in transformed cells, this inhibition can be overridden by the triggering signal cascades, leading to cell activation. The majority of triggering receptors expressed by NK cells belong to the multichain immune recognition receptor (MIRR) family and use separate signal-transducing polypeptides similar to those used by other immune receptors such as the T-cell antigen receptor, the B-cell antigen receptor and other receptors expressed by myeloid cells. Inhibitory receptors are not members of the MIRR family but they are relevant for a better understanding the exquisite equilibrium and regulatory crosstalk between positive and negative signals.

Clinical application of functional glycoproteomics - dissection of glycotopes carried by soluble CD44 variants in sera of patients with cancers

We provide here an example of clinical application of functional glycoproteomics for cancer diagnosis. Sialyl Lewis a and sialyl Lewis x glycotopes, which are the specific ligands for selectins, and variant forms of CD44, which are the adhesion molecules recognizing hyaluronate, are both implicated in cancer metastasis. The CD44 variants modified by the sialyl Lewis a and sialyl Lewis x glycotopes are expected to have dual functions, serving as ligands for vascular selectins, and simultaneously having binding activity to vascular bed hyaluronate, and are expected to figure heavily in cancer metastasis. We developed a heterogeneous sandwich assay system to detect soluble CD44v specifically modified by the cancer-associated sialyl Lewis a/x glycotopes, using the extracellular domain of CD44v cleaved by the metalloproteinase ADAM10 as standard molecules. We also developed the assay system for CD44v modified by normal epithelial glycotopes including disialyl Lewis a and sialyl 6-sulfo Lewis x. The results indicated that serum levels of soluble CD44v modified by cancer-associated glycotopes were frequently increased in patients with cancers, while those of CD44v modified by the nonmalignant glycotopes tended to be elevated in patients with benign disorders.

Design, synthesis, and structure-affinity relationships of novel series of sialosides as CD22-specific inhibitors

Sialosides incorporating substituted amides or amines at 9-position of sialic acid moiety have been synthesized and evaluated as CD22 inhibitors. Several derivatives exhibited inhibitory potency in sub- to low micromolar range (e. g., 8o, 9d, 9g, and 9k showed IC 50 values 0.40, 0.47, 0.24, and 0.23 microM, respectively, for hCD22, while 8p, 8q, and 9f, showed IC 50 values 1.70, 2.90, and 4.10 microM, respectively, for mCD22). The most significant result was the strongly enhanced affinity of 9g and 9k containing 9-(2' or 4'-hydroxy-4-biphenyl) methylamino substituents (600-fold more potent for hCD22 than the corresponding 9-hydroxy derivative; 7a). Molecular modeling study was carried out to get some insights into the molecular basis of CD22 inhibition. To the best of our knowledge, this is the first systematic structure-affinity relationship study on inhibition of CD22.

Protein-glycan interactions in the control of innate and adaptive immune responses

The importance of protein glycosylation in the migration of immune cells throughout the body has been extensively appreciated. However, our awareness of the impact of glycosylation on the regulation of innate and adaptive immune responses is relatively new. An increasing number of studies reveal the relevance of glycosylation to pathogen recognition, to the modulation of the innate immune system and to the control of immune cell homeostasis and inflammation. Similarly important is the effect of glycan-containing 'information' in the development of autoimmune diseases and cancer. In this review, we provide an overview of these new directions and their impact in the field of glycoimmunology.

DNA hypermethylation contributes to incomplete synthesis of carbohydrate determinants in gastrointestinal cancer

BACKGROUND & AIMS

It has long been known that malignant transformation is associated with abnormal expression of carbohydrate determinants. The aim of this study was to clarify the cause of cancer-associated abnormal glycosylation in gastrointestinal (GI) cancers.

METHODS

We compared the expression levels of "glyco-genes," including glycosyltransferases and glycosidases, in normal GI mucosa and in gastric and colorectal cancer cells. To examine the possibility that DNA hypermethylation contributed to the down-regulation of these genes, we treated GI cancer cells with 5-aza-2'-deoxycytidine (5-aza-dC), an inhibitor of DNA methyltransferase.

RESULTS

The silencing of some of these glyco-genes, but not up-regulation of certain molecules, was observed. The Sd(a) carbohydrate was abundantly expressed in the normal GI mucosa, but its expression was significantly decreased in cancer tissues. When human colon and gastric cancer cells were treated with 5-aza-dC, cell surface expression of Sd(a) and the transcription of B4GALNT2, which catalyzes the synthesis of the Sd(a), were induced. The promoter region of the human B4GALNT2 gene was heavily hypermethylated in many of the GI cancer cell lines examined as well as in gastric cancer tissues (39 out of 78 cases). In addition, aberrant methylation of the B4GALNT2 gene was strongly correlated with Epstein-Barr virus-associated gastric carcinomas and occurred coincidentally with hypermethylation of the ST3GAL6 gene.

CONCLUSIONS

Epigenetic changes in a group of glycosyltransferases including B4GALNT2 and ST3GAL6 represent a malignant phenotype of gastric cancer caused by silencing of the activity of these enzymes, which action may eventually induce aberrant glycosylation and expression of cancer-associated carbohydrate antigens.

Increased bisecting and core-fucosylated N-glycans on mutant human amyloid precursor proteins

Alteration of glycoprotein glycans often changes various properties of the glycoprotein. To understand the significance of N-glycosylation in the pathogenesis of early-onset familial Alzheimer's disease (AD) and in beta-amyloid (Abeta) production, we examined whether the mutations in the amyloid precursor protein (APP) gene found in familial AD affect the N-glycans on APP. We purified the secreted forms of wild-type and mutant human APPs (both the Swedish type and the London type) produced by transfected C17 cells and determined the N-glycan structures of these three recombinant APPs. Although the major N-glycan species of the three APPs were similar, both mutant APPs contained higher contents of bisecting N-acetylglucosamine and core-fucose residues as compared to wild-type APP. These results demonstrate that familial AD mutations in the polypeptide backbone of APP can affect processing of the attached N-glycans; however, whether these changes in N-glycosylation affect Abeta production remains to be established.