Cell-Cell Interaction-dependent Regulation of N-Acetylglucosaminyltransferase III and the Bisected N-Glycans in GE11 Epithelial Cells

Expression of GnT-III decreases chemoresistance via negatively regulating P-glycoprotein expression: Involvement of the TNFR2-NF-κB signaling pathway

The phenomenon of multidrug resistance (MDR) is called chemoresistance with respect to the treatment of cancer, and it continues to be a major challenge. The role of N-glycosylation in chemoresistance, however, remains poorly understood. Here, we established a traditional model for adriamycin resistance in K562 cells, which are also known as K562/adriamycin-resistant (ADR) cells. Lectin blot, mass spectrometry, and RT-PCR analysis showed that the expression levels of N-acetylglucosaminyltransferase III (GnT-III) mRNA and its products, bisected N-glycans, are significantly decreased in K562/ADR cells, compared with the levels in parent K562 cells. By contrast, the expression levels of both P-glycoprotein (P-gp) and its intracellular key regulator, NF-κB signaling, are significantly increased in K562/ADR cells. These upregulations were sufficiently suppressed by the overexpression of GnT-III in K562/ADR cells. We found that the expression of GnT-III consistently decreased chemoresistance for doxorubicin and dasatinib, as well as activation of the NF-κB pathway by tumor necrosis factor (TNF) α, which binds to two structurally distinct glycoproteins, TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2), on the cell surface. Interestingly, our immunoprecipitation analysis revealed that only TNFR2, but not TNFR1, contains bisected N-glycans. The lack of GnT-III strongly induced TNFR2's autotrimerization without ligand stimulation, which was rescued by the overexpression of GnT-III in K562/ADR cells. Furthermore, the deficiency of TNFR2 suppressed P-gp expression while it increased GnT-III expression. Taken together, these results clearly show that GnT-III negatively regulates chemoresistance via the suppression of P-gp expression, which is regulated by the TNFR2-NF/κB signaling pathway.

Aberrant N-glycosylation in cancer: MGAT5 and β1,6-GlcNAc branched N-glycans as critical regulators of tumor development and progression

BACKGROUND

Changes in protein glycosylation are widely observed in tumor cells. N-glycan branching through adding β1,6-linked N-acetylglucosamine (β1,6-GlcNAc) to an α1,6-linked mannose, which is catalyzed by the N-acetylglucosaminyltransferase V (MGAT5 or GnT-V), is one of the most frequently observed tumor-associated glycan structure formed. Increased levels of this branching structure play a pro-tumoral role in various ways, for example, through the stabilization of growth factor receptors, the destabilization of intercellular adhesion, or the acquisition of a migratory phenotype.

CONCLUSION

In this review, we provide an updated and comprehensive summary of the physiological and pathophysiological roles of MGAT5 and β1,6-GlcNAc branched N-glycans, including their regulatory mechanisms. Specific emphasis is given to the role of MGAT5 and β1,6-GlcNAc branched N-glycans in cellular mechanisms that contribute to the development and progression of solid tumors. We also provide insight into possible future clinical implications, such as the use of MGAT5 as a prognostic biomarker.

Disruption of ZNF334 promotes triple-negative breast carcinoma malignancy through the SFRP1/ Wnt/β-catenin signaling axis

Zinc-finger proteins (ZNFs) constitute the largest transcription factor family in the human genome. The family functions in many important biological processes involved in tumorigenesis. In our research, we identified ZNF334 as a novel tumor suppressor of triple-negative breast cancer (TNBC). ZNF334 expression was usually reduced in breast cancerv (BrCa) tissues and TNBC cell lines MDA-MB-231 (MB231) and YCCB1. We observed that promoter hypermethylation of ZNF334 was common in BrCa cell lines and tissues, which was likely responsible for its reduced expression. Ectopic expression of ZNF334 in TNBC cell lines MB231 and YCCB1 could suppress their growth and metastatic capacity both in vitro and in vivo, and as well induce cell cycle arrest at S phase and cell apoptosis. Moreover, re-expression of ZNF334 in TNBC cell lines could rescue Epithelial-Mesenchymal Transition (EMT) process and restrain stemness, due to up-regulation of SFRP1, which is an antagonist of Wnt/β-catenin signaling. In conclusion, we verified that ZNF334 had a suppressive function of TNBC cell lines by targeting the SFRP1/Wnt/β-catenin signaling axis, which might have the potentials to become a new biomarker for diagnosis and treatment of TNBC patients.

Bisecting-GlcNAc on Asn388 is characteristic to ERC/mesothelin expressed on epithelioid mesothelioma cells

Mesothelioma is a highly aggressive tumour associated with asbestos exposure and is histologically classified into three types: epithelioid-type, sarcomatoid-type and biphasic-type. The prognosis of mesothelioma patients is poor and there is no effective molecular-targeting therapy as yet. ERC/mesothelin is a glycoprotein that is highly expressed on several types of cancers including epithelioid mesothelioma, but also expressed on normal mesothelial cells. This is a predicted reason why there is no clinically approved therapeutic antibody targeting ERC/mesothelin. In the present study, we focussed on the differential glycosylation between ERC/mesothelin present on epithelioid mesothelioma and that on normal mesothelial cells and aimed to reveal a distinct feature of epithelioid mesothelioma cells. Lectin microarray analysis of ERC/mesothelin using cells and patient specimens showed significantly stronger binding of PHA-E₄ lectin, which recognizes complex-type N-glycans having a so-called bisecting-GlcNAc structure, to ERC/mesothelin from epithelioid mesothelioma cells than that from normal mesothelial cells. Further, liquid chromatography/mass spectrometry analysis on ERC/mesothelin from epithelioid mesothelioma cells confirmed the presence of a bisecting-GlcNAc attached to Asn388 of ERC/mesothelin. These results suggest that this glycoproteome could serve as a potential target for the generation of a highly selective and safe therapeutic antibody for epithelioid mesothelioma.

Bisecting N-Acetylglucosamine Structures Inhibit Hypoxia-Induced Epithelial-Mesenchymal Transition in Breast Cancer Cells

The epithelial-mesenchymal transition (EMT) process plays a key role in many biological processes, including tissue fibrosis, metastatic diseases, and cancer progression. EMT can be induced by certain factors, notably hypoxia, in the tumor microenvironment. Aberrant levels of certain N-glycans is associated with cancer progression. We used an integrated strategy (mass spectrometry in combination with lectin microarray analysis) to elucidate aberrant glycosylation in a hypoxia-induced EMT model using breast cancer cell lines MCF7 and MDA-MB-231. The model showed reduced levels of bisecting GlcNAc structures, and downregulated expression of the corresponding glycosyltransferase MGAT3. MGAT3 overexpression in MCF7 suppressed cell migration, proliferation, colony formation, expression of EMT markers, and AKT signaling pathway, whereas MGAT3 knockdown (shRNA silencing) had opposite effects. Our findings clearly demonstrate the functional role (and effects of dysregulation) of bisecting GlcNAc structures in hypoxia-induced EMT, and provide a useful basis for further detailed studies of physiological functions of these structures in breast cancer.

Bisecting GlcNAc restricts conformations of branches in model N-glycans with GlcNAc termini

Bisected N-glycans play significant roles in tumor migration and Alzheimer's disease through modulating the action and localization of their carrier proteins. Such biological functions are often discussed in terms of the conformation of the attached N-glycans with or without bisecting GlcNAc. To obtain insights into the effects of bisecting GlcNAc on glycan conformation, a systematic NMR structural analysis was performed on two pairs of synthetic N-glycans, with and without bisecting GlcNAc. The analysis reveals that terminal GlcNAcs and bisecting GlcNAc cooperate to restrict the conformations of both the α1-3 and α1-6 branches of N-glycans. ¹H and ¹³C chemical shift comparisons suggest that bisecting GlcNAc directly modulates local conformation. Unique NOE correlations between core-mannose and the α1-3 branch mannose as well as the ³J_C-H constant of the glycoside linkage indicate that bisecting GlcNAc restricts the conformation of the 1-3 branch. The angles of the glycosidic bonds between core-mannose and α1-6 branch mannose derived from ³J_C-H and ³J_H-H coupling constants show that terminal GlcNAcs restrict the distribution of the ψ angle to 180° and the bisecting GlcNAc increases the distribution of the ω angle +60° in the presence of terminal GlcNAcs. It is feasible that restriction of branch conformations by bisecting GlcNAc has important consequences for protein-glycan interplay and following biological events.

Cadherins Glycans in Cancer: Sweet Players in a Bitter Process

Cadherins are key components in tissue morphogenesis and architecture, contributing to the establishment of cohesive cell adhesion. Reduced cellular adhesiveness as a result of cadherin dysfunction is a defining feature of cancer. During tumor development and progression, major changes in the glycan repertoire of cancer cells take place, affecting the stability, trafficking, and cell-adhesion properties of cadherins. Importantly, the different glycoforms of cadherins are promising biomarkers, with potential clinical application to improve the management of patients, and constitute targets for the development of new therapies. This review discusses the most recent insights on the impact of glycan structure on the regulation of cadherin function in cancer, and provides a perspective on how cadherin glycans constitute tumor biomarkers and potential therapeutic targets.

On the trail of the glycan codes stored in cancer-related cell adhesion proteins

Changes in the profile of protein glycosylation are a hallmark of ongoing neoplastic transformation. A unique set of tumor-associated carbohydrate antigens expressed on the surface of malignant cells may serve as powerful diagnostic and therapeutic targets. Cell-surface proteins with altered glycosylation affect the growth, proliferation and survival of those cells, and contribute to their acquisition of the ability to migrate and invade. They may also facilitate tumor-induced immunosuppression and the formation of distant metastases. Deciphering the information encoded in these particular glycan portions of glycoconjugates may shed light on the mechanisms of cancer progression and metastasis. A majority of the related review papers have focused on overall changes in the patterns of cell-surface glycans in various cancers, without pinpointing the molecular carriers of these glycan structures. The present review highlights the ways in which particular tumor-associated glycan(s) coupled with a given membrane-bound protein influence neoplastic cell behavior during the development and progression of cancer. We focus on altered glycosylated cell-adhesion molecules belonging to the cadherin, integrin and immunoglobulin-like superfamilies, examined in the context of molecular interactions.

Enzymes for N-Glycan Branching and Their Genetic and Nongenetic Regulation in Cancer

N-glycan, a fundamental and versatile protein modification in mammals, plays critical roles in various physiological and pathological events including cancer progression. The formation of N-glycan branches catalyzed by specific N-acetylglucosaminyltransferases [GnT-III, GnT-IVs, GnT-V, GnT-IX (Vb)] and a fucosyltransferase, Fut8, provides functionally diverse N-glycosylated proteins. Aberrations of these branches are often found in cancer cells and are profoundly involved in cancer growth, invasion and metastasis. In this review, we focus on the GlcNAc and fucose branches of N-glycans and describe how their expression is dysregulated in cancer by genetic and nongenetic mechanisms including epigenetics and nucleotide sugar metabolisms. We also survey the roles that these N-glycans play in cancer progression and therapeutics. Finally, we discuss possible applications of our knowledge on basic glycobiology to the development of medicine and biomarkers for cancer therapy.

Chitooligomer-Immobilized Biointerfaces with Micropatterned Geometries for Unidirectional Alignment of Myoblast Cells

Skeletal muscle possesses a robust capacity to regenerate functional architectures with a unidirectional orientation. In this study, we successfully arranged skeletal myoblast (C2C12) cells along micropatterned gold strips on which chitohexaose was deposited via a vectorial chain immobilization approach. Hexa-N-acetyl-d-glucosamine (GlcNAc6) was site-selectively modified at its reducing end with thiosemicarbazide, then immobilized on a gold substrate in striped micropatterns via S–Au chemisorption. Gold micropatterns ranged from 100 to 1000 µm in width. Effects of patterning geometries on C2C12 cell alignment, morphology, and gene expression were investigated. Unidirectional alignment of C2C12 cells having GlcNAc6 receptors was clearly observed along the micropatterns. Decreasing striped pattern width increased cell attachment and proliferation, suggesting that the fixed GlcNAc6 and micropatterns impacted cell function. Possibly, interactions between nonreducing end groups of fixed GlcNAc6 and cell surface receptors initiated cellular alignment. Our technique for mimicking native tissue organization should advance applications in tissue engineering.

Biosynthetic Machinery Involved in Aberrant Glycosylation: Promising Targets for Developing of Drugs Against Cancer

Cancer cells depend on altered metabolism and nutrient uptake to generate and keep the malignant phenotype. The hexosamine biosynthetic pathway is a branch of glucose metabolism that produces UDP-GlcNAc and its derivatives, UDP-GalNAc and CMP-Neu5Ac and donor substrates used in the production of glycoproteins and glycolipids. Growing evidence demonstrates that alteration of the pool of activated substrates might lead to different glycosylation and cell signaling. It is already well established that aberrant glycosylation can modulate tumor growth and malignant transformation in different cancer types. Therefore, biosynthetic machinery involved in the assembly of aberrant glycans are becoming prominent targets for anti-tumor drugs. This review describes three classes of glycosylation, O-GlcNAcylation, N-linked, and mucin type O-linked glycosylation, involved in tumor progression, their biosynthesis and highlights the available inhibitors as potential anti-tumor drugs.

Glycans and cancer: role of N-glycans in cancer biomarker, progression and metastasis, and therapeutics

Glycosylation is catalyzed by various glycosyltransferase enzymes which are mostly located in the Golgi apparatus in cells. These enzymes glycosylate various complex carbohydrates such as glycoproteins, glycolipids, and proteoglycans. The enzyme activity of glycosyltransferases and their gene expression are altered in various pathophysiological situations including cancer. Furthermore, the activity of glycosyltransferases is controlled by various factors such as the levels of nucleotide sugars, acceptor substrates, nucleotide sugar transporters, chaperons, and endogenous lectin in cancer cells. The glycosylation results in various functional changes of glycoproteins including cell surface receptors and adhesion molecules such as E-cadherin and integrins. These changes confer the unique characteristic phenotypes associated with cancer cells. Therefore, glycans play key roles in cancer progression and treatment. This review focuses on glycan structures, their biosynthetic glycosyltransferases, and their genes in relation to their biological significance and involvement in cancer, especially cancer biomarkers, epithelial-mesenchymal transition, cancer progression and metastasis, and therapeutics. Major N-glycan branching structures which are directly related to cancer are β1,6-GlcNAc branching, bisecting GlcNAc, and core fucose. These structures are enzymatic products of glycosyltransferases, GnT-V, GnT-III, and Fut8, respectively. The genes encoding these enzymes are designated as MGAT5 (Mgat5), MGAT3 (Mgat3), and FUT8 (Fut8) in humans (mice in parenthesis), respectively. GnT-V is highly associated with cancer metastasis, whereas GnT-III is associated with cancer suppression. Fut8 is involved in expression of cancer biomarker as well as in the treatment of cancer. In addition to these enzymes, GnT-IV and GnT-IX (GnT-Vb) will be also discussed in relation to cancer.

Quantitative glycomics monitoring of induced pluripotent- and embryonic stem cells during neuronal differentiation

Alterations in the structure of cell surface glycoforms occurring during the stages of stem cell differentiation remain unclear. We describe a rapid glycoblotting-based cellular glycomics method for quantitatively evaluating changes in glycoform expression and structure during neuronal differentiation of murine induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs). Our results show that changes in the expression of cellular N-glycans are comparable during the differentiation of iPSCs and ESCs. The expression of bisect-type N-glycans was significantly up-regulated in neurons that differentiated from both iPSCs and ESCs. From a glycobiological standpoint, iPSCs are an alternative neural cell source in addition to ESCs.

Synthesis of N-glycan units for assessment of substrate structural requirements of N-acetylglucosaminyltransferase III

N-Acetylglucosaminyltransferase (GnT) III is a glycosyltransferase which produces bisected N-glycans by transferring GlcNAc to the 4-position of core mannose. Bisected N-glycans are involved in physiological and pathological processes through the functional regulation of their carrier proteins. An understanding of the biological functions of bisected glycans will be greatly accelerated by use of specific inhibitors of GnT-III. Thus far, however, such inhibitors have not been developed and even the substrate-binding mode of GnT-III is not fully understood. To gain insight into structural features required of the substrate, we systematically synthesized four N-glycan units, the branching parts of the bisected and non-bisected N-glycans. The series of syntheses were achieved from a common core trimannose, giving bisected tetra- and hexasaccharides as well as non-bisected tri- and pentasaccharides. A competitive GnT-III inhibition assay using the synthetic substrates revealed a vital role for the Manβ(1-4)GlcNAc moiety. In keeping with previous reports, GlcNAc at the α1,3-branch is also involved in the interaction. The structural requirements of GnT-III elucidated in this study will provide a basis for rational inhibitor design.

The absence of core fucose up-regulates GnT-III and Wnt target genes: a possible mechanism for an adaptive response in terms of glycan function

Glycans play key roles in a variety of protein functions under normal and pathological conditions, but several glycosyltransferase-deficient mice exhibit no or only mild phenotypes due to redundancy or compensation of glycan functions. However, we have only a limited understanding of the underlying mechanism for these observations. Our previous studies indicated that 70% of Fut8-deficient (Fut8(-/-)) mice that lack core fucose structure die within 3 days after birth, but the remainder survive for up to several weeks although they show growth retardation as well as emphysema. In this study, we show that, in mouse embryonic fibroblasts (MEFs) from Fut8(-/-) mice, another N-glycan branching structure, bisecting GlcNAc, is specifically up-regulated by enhanced gene expression of the responsible enzyme N-acetylglucosaminyltransferase III (GnT-III). As candidate target glycoproteins for bisecting GlcNAc modification, we confirmed that level of bisecting GlcNAc on β1-integrin and N-cadherin was increased in Fut8(-/-) MEFs. Moreover using mass spectrometry, glycan analysis of IgG1 in Fut8(-/-) mouse serum demonstrated that bisecting GlcNAc contents were also increased by Fut8 deficiency in vivo. As an underlying mechanism, we found that in Fut8(-/-) MEFs Wnt/β-catenin signaling is up-regulated, and an inhibitor against Wnt signaling was found to abrogate GnT-III expression, indicating that Wnt/β-catenin is involved in GnT-III up-regulation. Furthermore, various oxidative stress-related genes were also increased in Fut8(-/-) MEFs. These data suggest that Fut8(-/-) mice adapted to oxidative stress, both ex vivo and in vivo, by inducing various genes including GnT-III, which may compensate for the loss of core fucose functions.

Intermediate filament proteins expression and carbohydrate moieties in trophoblast and decidual cells of mature cat placenta

The aim of this study was to characterize cytoskeletal intermediate filament proteins and glycoconjugates of syncytiotrophoblast, cytotrophoblast and decidual cells of feline endotheliochorial placenta. Samples from 12 normal pregnant female cats, after 45 ± 5 days of gestation, were obtained removing the uterine horns by hysterectomy. Sections were processed for routine observation and for immunohistochemistry using anticytokeratin, antivimentin and antidesmin antibodies. In addition, lectin histochemistry was performed using a panel of several biotinylated lectins to characterize glycosides expression profile. Cytotrophoblast and syncytiotrophoblast showed immunoreactivity only with acidic and basic cytokeratins. Decidual cells were only positive to vimentin, consistent with their origin from endometrial fibroblasts. Trophoblast expressed a broad population of glycans, highly exposing terminal N-acetyl glucosamine residues and non-sialylated galactose and N-acetyl galactosamine oligomers. Oligosaccharides bound by Phaseolus vulgaris erythroagglutinin were the only highly branched N-linked residues evidenced in cats, and they were restricted to the syncytium. Unlike results reported on humans, mice and rats on lectin affinity of decidual cells, sialid acids and complex N-linked oligosaccharides were not demonstrated in cats. Glycosylation of proteins determines many of their final properties, thus becoming essential for the embryo-maternal dialogue during implantation and placentation. Changes in glycosylation pattern have been related to pathological pregnancies in other species. Hence, the knowledge about glycosylation profile of the normal cat placenta may lead to a better understanding of both normal and pathological reproductive events.

Insulin/IGF-I signaling pathways enhances tumor cell invasion through bisecting GlcNAc N-glycans modulation. an interplay with E-cadherin

Changes in glycosylation are considered a hallmark of cancer, and one of the key targets of glycosylation modifications is E-cadherin. We and others have previously demonstrated that E-cadherin has a role in the regulation of bisecting GlcNAc N-glycans expression, remaining to be determined the E-cadherin-dependent signaling pathway involved in this N-glycans expression regulation. In this study, we analysed the impact of E-cadherin expression in the activation profile of receptor tyrosine kinases such as insulin receptor (IR) and IGF-I receptor (IGF-IR). We demonstrated that exogenous E-cadherin expression inhibits IR, IGF-IR and ERK 1/2 phosphorylation. Stimulation with insulin and IGF-I in MDA-MD-435 cancer cells overexpressing E-cadherin induces a decrease of bisecting GlcNAc N-glycans that was accompanied with alterations on E-cadherin cellular localization. Concomitantly, IR/IGF-IR signaling activation induced a mesenchymal-like phenotype of cancer cells together with an increased tumor cell invasion capability. Altogether, these results demonstrate an interplay between E-cadherin and IR/IGF-IR signaling as major networking players in the regulation of bisecting N-glycans expression, with important effects in the modulation of epithelial characteristics and tumor cell invasion. Here we provide new insights into the role that Insulin/IGF-I signaling play during cancer progression through glycosylation modifications.

Epithelial E- and P-cadherins: role and clinical significance in cancer

E-cadherin and P-cadherin are major contributors to cell-cell adhesion in epithelial tissues, playing pivotal roles in important morphogenetic and differentiation processes during development, and in maintaining integrity and homeostasis in adult tissues. It is now generally accepted that alterations in these two molecules are observed during tumour progression of most carcinomas. Genetic or epigenetic alterations in E- and P-cadherin-encoding genes (CDH1 and CDH3, respectively), or alterations in their proteins expression, often result in tissue disorder, cellular de-differentiation, increased invasiveness of tumour cells and ultimately in metastasis. In this review, we will discuss the major properties of E- and P-cadherin molecules, its regulation in normal tissue, and their alterations and role in cancer, with a specific focus on gastric and breast cancer models.

The Na-K-ATPase α₁β₁ heterodimer as a cell adhesion molecule in epithelia

The ion gradients generated by the Na-K-ATPase play a critical role in epithelia by driving transepithelial transport of various solutes. The efficiency of this Na-K-ATPase-driven vectorial transport depends on the integrity of epithelial junctions that maintain polar distribution of membrane transporters, including the basolateral sodium pump, and restrict paracellular diffusion of solutes. The review summarizes the data showing that, in addition to pumping ions, the Na-K-ATPase located at the sites of cell-cell junction acts as a cell adhesion molecule by interacting with the Na-K-ATPase of the adjacent cell in the intercellular space accompanied by anchoring to the cytoskeleton in the cytoplasm. The review also discusses the experimental evidence on the importance of a specific amino acid region in the extracellular domain of the Na-K-ATPase β(1) subunit for the Na-K-ATPase trans-dimerization and intercellular adhesion. Furthermore, a possible role of N-glycans linked to the Na-K-ATPase β(1) subunit in regulation of epithelial junctions by modulating β(1)-β(1) interactions is discussed.

Roles of N-acetylglucosaminyltransferase III in epithelial-to-mesenchymal transition induced by transforming growth factor β1 (TGF-β1) in epithelial cell lines

The epithelial-to-mesenchymal transition (EMT) plays crucial roles in embryonic development, wound healing, tissue repair, and cancer progression. Results of this study show how transforming growth factor β1 (TGF-β1) down-regulates expression of N-acetylglucosaminyltransferase III (GnT-III) during EMT-like changes. Treatment with TGF-β1 resulted in a decrease in E-cadherin expression and GnT-III expression, as well as its product, the bisected N-glycans, which was confirmed by erythro-agglutinating phytohemagglutinin lectin blot and HPLC analysis in human MCF-10A and mouse GE11 cells. In contrast with GnT-III, the expression of N-acetylglucosaminyltransferase V was slightly enhanced by TGF-β1 treatment. Changes in the N-glycan patterns on α3β1 integrin, one of the target proteins for GnT-III, were also confirmed by lectin blot analysis. To understand the roles of GnT-III expression in EMT-like changes, the MCF-10A cell was stably transfected with GnT-III. It is of particular interest that overexpression of GnT-III influenced EMT-like changes induced by TGF-β1, which was confirmed by cell morphological changes of phase contrast, immunochemical staining patterns of E-cadherin, and actin. In addition, GnT-III modified E-cadherin, which served to prolong E-cadherin turnover on the cell surface examined by biotinylation and pulse-chase experiments. GnT-III expression consistently inhibited β-catenin translocation from cell-cell contact into the cytoplasm and nucleus. Furthermore, the transwell assay showed that GnT-III expression suppressed TGF-β1-induced cell motility. Taken together, these observations are the first to clearly demonstrate that GnT-III affects cell properties, which in turn influence EMT-like changes, and to explain a molecular mechanism for the inhibitory effects of GnT-III on cancer metastasis.

Loss and recovery of Mgat3 and GnT-III Mediated E-cadherin N-glycosylation is a mechanism involved in epithelial-mesenchymal-epithelial transitions

Background

N-acetylglucosaminyltransferase-III (GnT-III) is a glycosyltransferase encoded by Mgat3 that catalyzes the addition of β1,4-bisecting-N-acetylglucosamine on N-glycans. GnT-III has been pointed as a metastases suppressor having varying effects on cell adhesion and migration. We have previously described the existence of a functional feedback loop between E-cadherin expression and GnT-III-mediated glycosylation. The effects of GnT-III-mediated glycosylation on E-cadherin expression and cellular phenotype lead us to evaluate Mgat3 and GnT-III-glycosylation role during Epithelial-Mesenchymal-Transition (EMT) and the reverted process, Mesenchymal-Epithelial-Transition (MET).

Methodology/Principal Findings

We analyzed the expression profile and genetic mechanism controlling Mgat3 expression as well as GnT-III-mediated glycosylation, in general and specifically on E-cadherin, during EMT/MET. We found that during EMT, Mgat3 expression was dramatically decreased and later recovered when cells returned to an epithelial-like phenotype. We further identified that Mgat3 promoter methylation/demethylation is involved in this expression regulation. The impact of Mgat3 expression variation, along EMT/MET, leads to a variation in the expression levels of the enzymatic product of GnT-III (bisecting GlcNAc structures), and more importantly, to the specific modification of E-cadherin glycosylation with bisecting GlcNAc structures.

Conclusions/Significance

Altogether, this work identifies for the first time Mgat3 glycogene expression and GnT-III-mediated glycosylation, specifically on E-cadherin, as a novel and major component of the EMT/MET mechanism signature, supporting its role during EMT/MET.

Engagement of I-branching {beta}-1, 6-N-acetylglucosaminyltransferase 2 in breast cancer metastasis and TGF-{beta} signaling

In this study, we have showed that GCNT2, a gene-encoding glucosaminyl (N-acetyl) transferase 2, I-branching enzyme, is overexpressed in highly metastatic breast cancer cell lines of human and mouse origin and basal-like breast tumor samples. GCNT2 expression is also significantly correlated to the metastatic phenotype in breast tumor samples. Functional studies showed that ectopic expression of GCNT2 enhances cell detachment, adhesion to endothelial cells, cell migration and invasion in vitro, and lung metastasis of breast cancer cells in vivo. Knockdown of GCNT2 expression decreases cell migration and invasion in vitro and lung metastasis in vivo. We have further shown the involvement of GCNT2 in the epithelial-to-mesenchymal transition (EMT). Specifically, the expression of E-cadherin is significantly changed upon GCNT2 expression at the protein level but not at the RNA level. Moreover, we have shown that GCNT2 is a direct target of the TGF-β-smad pathway and that change in GCNT2 expression modulates EMT induced by TGF-β1 treatment. Finally, we have shown that diminution of the glycosyltransferase activity of I-branching β-1, 6-N-acetylglucosaminyl transferase 2 (GCNT2) abrogates its cell migration and invasion-promoting function and synergistic effect with TGF-β to induce EMT. Our study for the first time showed that GCNT2 is a novel gene contributing to breast cancer metastasis with preferential expression in basal-like breast cancer. Moreover, we discovered that involvement of GCNT2 in EMT and TGF-β signaling, and further glycosylation modification of E-cadherin by GCNT2, are the underlying integrative mechanisms for breast cancer metastasis, implying that blocking TGF-β/GCNT2 signaling is a promising approach for targeting metastatic breast cancer.

Modulation of E-cadherin function and dysfunction by N-glycosylation

Several mechanisms have been proposed to explain the E-cadherin dysfunction in cancer, including genetic and epigenetic alterations. Nevertheless, a significant number of human carcinomas have been seen that show E-cadherin dysfunction that cannot be explained at the genetic/epigenetic level. A substantial body of evidence has appeared recently that supports the view that other mechanisms operating at the post-translational level may also affect E-cadherin function. The present review addresses molecular aspects related to E-cadherin N-glycosylation and evidence is presented showing that the modification of N-linked glycans on E-cadherin can affect the adhesive function of this adhesion molecule. The role of glycosyltransferases involved in the remodeling of N-glycans on E-cadherin, including N-acetylglucosaminyltransferase III (GnT-III), N-acetylglucosaminyltransferase V (GnT-V), and the α1,6 fucosyltransferase (FUT8) enzyme, is also discussed. Finally, this review discusses an alternative functional regulatory mechanism for E-cadherin operating at the post-translational level, N-glycosylation, that may underlie the E-cadherin dysfunction in some carcinomas.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Wnt/beta-catenin signaling down-regulates N-acetylglucosaminyltransferase III expression: the implications of two mutually exclusive pathways for regulation

In previous studies, we reported that N-acetylglucosaminyltransferase III (GnT-III) activity and the enzyme product, bisected N-glycans, both were induced in cells cultured under dense conditions in an E-cadherin-dependent manner (Iijima, J., Zhao, Y., Isaji, T., Kameyama, A., Nakaya, S., Wang, X., Ihara, H., Cheng, X., Nakagawa, T., Miyoshi, E., Kondo, A., Narimatsu, H., Taniguchi, N., and Gu, J. (2006) J. Biol. Chem. 281, 13038-13046). Furthermore, we found that α-catenin, a component of the E-cadherin-catenin complex, was also required for this induction (Akama, R., Sato, Y., Kariya, Y., Isaji, T., Fukuda, T., Lu, L., Taniguchi, N., Ozawa, M., and Gu, J. (2008) Proteomics 8, 3221-3228). To further explore the molecular mechanism of this regulation, the roles of β-catenin, an essential molecule in both cadherin-mediated cell adhesion and canonical Wnt signaling, were investigated. Unexpectedly, shRNA knockdown of β-catenin resulted in a dramatic increase in GnT-III expression and its product, the bisected N-glycans, which was confirmed by RT-PCR and GnT-III activity and by E4-PHA lectin blot analysis. The induction of GnT-III expression increased bisecting GlcNAc residues on β1 integrin, which led to down-regulation of integrin-mediated cell adhesion and cell migration. Immunostaining showed that nuclear localization of β-catenin was greatly suppressed; intriguingly, the knockdown of β-catenin in the nuclei was more effective than that in cell-cell contacts in the knockdown cells, which was also confirmed by Western blot analysis. Stimulation of the Wnt signaling pathway by the addition of exogenous Wnt3a or BIO, a GSK-3β inhibitor, consistently and significantly inhibited GnT-III expression and its products. Conversely, the inhibition of β-catenin translocation into the nuclei increased GnT-III activation. Taken together, the results of the present study are the first to clearly demonstrate that GnT-III expression may be precisely regulated by the interplay of E-cadherin-catenin complex-mediated cell-cell adhesion and Wnt/β-catenin signaling, which are both crucial in the process of epithelial-mesenchymal transitions in physiological and pathological conditions.

The bisecting GlcNAc on N-glycans inhibits growth factor signaling and retards mammary tumor progression

The branching of complex N-glycans attached to growth factor receptors promotes tumor progression by prolonging growth factor signaling. The addition of the bisecting GlcNAc to complex N-glycans by Mgat3 has varying effects on cell adhesion, cell migration, and hepatoma formation. Here, we show that Chinese hamster ovary cells expressing Mgat3 and the polyoma middle T (PyMT) antigen have reduced cell proliferation and growth factor signaling dependent on a galectin lattice. The Mgat3 gene is not expressed in virgin mammary gland but is upregulated during lactation and is expressed in mouse mammary tumor virus (MMTV)/PyMT tumors. Mice lacking Mgat3 that cannot transfer the bisecting GlcNAc to N-glycans acquire PyMT-induced mammary tumors more rapidly and have an increased tumor burden, increased migration of tumor cells, and increased early metastasis to lung. Tumors and tumor-derived cells lacking Mgat3 exhibit enhanced signaling through the Ras pathway and reduced amounts of functionally glycosylated alpha-dystroglycan. Constitutive overexpression of an MMTV/Mgat3 transgene inhibits early mammary tumor development and tumor cell migration. Thus, the addition of the bisecting GlcNAc to complex N-glycans of mammary tumor cell glycoprotein receptors is a cell autonomous mechanism serving to retard tumor progression by reducing growth factor signaling.

Functional roles of the bisecting GlcNAc in integrin-mediated cell adhesion

N-acetylglucosaminyltransferase III (GnT-III) transfers N-acetylglucosamine (GlcNAc) from UDP-GlcNAc to core mannose with a beta1,4 linkage, so-called bisecting GlcNAc, in N-glycans. The bisecting GlcNAc is found in various hybrid and complex N-glycans. GnT-III is generally regarded as a key glycosyltransferase in N-glycan biosynthetic pathways. Introduction of a bisecting GlcNAc suppresses further processing and elongation of N-glycans catalyzed by other GlcNAc transferases to form branching structures, such as N-acetylglucosaminyltransferase V (GnT-V), since GnT-V cannot utilize the bisected oligosaccharide as a substrate. Considering that expression of the enzyme leads to a remarkable structural alteration of the N-glycans on cell surface, it has been postulated that the enzyme is associated with various biological events such as cell adhesion, migration, cell growth, cell differentiation, and tumor invasion. Integrin is a major carrier of N-glycans. In fact, overexpression of GnT-III reduced the beta1,6 GlcNAc branching structures, in conjunction with the increase in the bisected N-glycans on integrins, and resulted in an inhibition of integrin-mediated cell spreading and migration, and the cellular phosphorylation levels. Conversely, knockdown of endogenous GnT-III expression resulted in increased cell migration, concomitant with an increase in beta1,6 GlcNAc-branched N-glycans on integrins. Thus, N-glycan could be considered as either a positive or negative regulator for biological functions of integrin.

Glycan gene expression signatures in normal and malignant breast tissue; possible role in diagnosis and progression

Glycosylation is the stepwise procedure of covalent attachment of oligosaccharide chains to proteins or lipids, and alterations in this process have been associated with malignant transformation. Simultaneous analysis of the expression of all glycan-related genes clearly gives the advantage of enabling a comprehensive view of the genetic background of the glycobiological changes in cancer cells. Studies focusing on the expression of the whole glycome have now become possible, which prompted us to review the present knowledge on glycosylation in relation to breast cancer diagnosis and progression, in the light of available expression data from tumors and breast tissue of healthy individuals. We used various data resources to select a set of 419 functionally relevant genes involved in synthesis, degradation and binding of N-linked and O-linked glycans, Lewis antigens, glycosaminoglycans (chondroitin, heparin and keratan sulfate in addition to hyaluronan) and glycosphingolipids. Such glycans are involved in a number of processes relevant to carcinogenesis, including regulation of growth factors/growth factor receptors, cell-cell adhesion and motility as well as immune system modulation. Expression analysis of these glycan-related genes revealed that mRNA levels for many of them differ significantly between normal and malignant breast tissue. An associative analysis of these genes in the context of current knowledge of their function in protein glycosylation and connection(s) to cancer indicated that synthesis, degradation and adhesion mediated by glycans may be altered drastically in mammary carcinomas. Although further analysis is needed to assess how changes in mRNA levels of glycan genes influence a cell's glycome and the precise role that such altered glycan structures play in the pathogenesis of the disease, lessons drawn from this study may help in determining directions for future research in the rapidly-developing field of glycobiology.

Bisecting GlcNAc residues on laminin-332 down-regulate galectin-3-dependent keratinocyte motility

Laminin-332 (Lm332; formerly laminin-5) is a basement membrane protein in the skin, which promotes cell motility in wound healing and cancer invasion. In a previous study, we reported that the introduction of bisecting GlcNAc into Lm332 (GnT-III-Lm332), catalyzed by N-acetylglucosaminyltransferase III (GnT-III), reduced cell migration (Kariya, Y., Kato, R., Itoh, S., Fukuda, T., Shibukawa, Y., Sanzen, N., Sekiguchi, K., Wada, Y., Kawasaki, N., and Gu, J. (2008) J. Biol. Chem. 283, 33036-33045). However, the underlying molecular mechanism by which GnT-III-Lm332 suppresses the normal biological functions of Lm332 remains to be elucidated. In this study, we show that galectin-3, which is a beta-galactoside-binding protein, strongly bound to unmodified Lm332 but not to GnT-III-Lm332 and that binding of galectin-3 was completely blocked by lactose. Exogenous galectin-3 significantly enhanced keratinocyte cell motility on control Lm332 but not on GnT-III-Lm332. A functional blocking antibody against galectin-3 inhibited Lm332-induced alpha3beta1 and alpha6beta4 integrin clustering and focal contact formation. Co-immunoprecipitation revealed that galectin-3 associated with both beta4 integrin and epidermal growth factor receptor, thereby cross-linking the two molecules. The associations were inhibited by either the presence of lactose or expression of GnT-III. Moreover, galectin-3 consistently enhanced ERK activation. Taken together, the results of this study are the first to clearly identify the molecular mechanism responsible for the inhibitory effects of GnT-III on extracellular matrix-integrin-meditated cell adhesion, migration, and signal transduction. The findings presented herein shed light on the importance of N-glycosylation-mediated supramolecular complex formation on the cell surface.

Core fucosylation of E-cadherin enhances cell-cell adhesion in human colon carcinoma WiDr cells

Alpha1,6-fucosyltransferase (Fut8), an enzyme that catalyzes the introduction of alpha1,6 core fucose to the innermost N-acetylglucosamine residue of the N-glycan, has been implicated in the development, immune system, and tumorigenesis. We found that alpha1,6-fucosyltransferase and E-cadherin expression levels are significantly elevated in primary colorectal cancer samples. Interestingly, low molecular weight population of E-cadherin appeared as well as normal sized E-cadherin in cancer samples. To investigate the correlation between alpha1,6-fucosyltransferase and E-cadherin expression, we introduced alpha1,6-fucosyltransferase in WiDr human colon carcinoma cells. It was revealed that the low molecular weight population of E-cadherin was significantly increased in alpha1,6-fucosyltransferase-transfected WiDr cells in dense culture, which resulted in an enhancement in cell-cell adhesion. The transfection of mutated alpha1,6-fucosyltransferase with no enzymatic activity had no effect on E-cadherin expression, indicating that core fucosylation is involved in the phenomena. In alpha1,6-fucosyltransferase knock down mouse pancreatic acinar cell carcinoma TGP49 cells, the expression of E-cadherin and E-cadherin dependent cell-cell adhesion was decreased. The introduction of alpha1,6-fucosyltransferase into kidney epithelial cells from alpha1,6-fucosyltransferase(-/-) mice restored the expression of E-cadherin and E-cadherin-dependent cell-cell adhesion. Based on the results of lectin blotting, peptide N-glycosidase F treatment, and pulse-chase studies, it was demonstrated that the low molecular weight population of E-cadherin contains peptide N-glycosidase F insensitive sugar chains, and the turnover rate of E-cadherin was reduced in alpha1,6-Fucosyltransferase transfectants. Thus, it was suggested that core fucosylation regulates the processing of oligosaccharides and turnover of E-cadherin. These results suggest a possible role of core fucosylation in the regulation of cell-cell adhesion in cancer.

The role of N-acetylglucosaminyltransferase III and V in the post-transcriptional modifications of E-cadherin

It has long been recognized that E-cadherin dysfunction is a major cause of epithelial cell invasion. However, very little is known about the post-transcriptional modifications of E-cadherin and its role in E-cadherin mediated tumor progression. N-acetylglucosaminyltransferase III (GnT-III) catalyzes the formation of a bisecting GlcNAc structure in N-glycans, and has been pointed as a metastasis suppressor. N-acetylglucosaminyltransferase V (GnT-V) catalyzes the addition of beta1,6 GlcNAc branching of N-glycans, and has been associated to increase metastasis. The regulatory mechanism between E-cadherin expression and the remodeling of its oligosaccharides structures by GnT-III and GnT-V were explored in this study. We have demonstrated that wild-type E-cadherin regulates MGAT3 gene transcription resulting in increased GnT-III expression. We also showed that GnT-III and GnT-V competitively modified E-cadherin N-glycans. The GnT-III knockdown cells revealed a membrane de-localization of E-cadherin leading to its cytoplasmic accumulation. Further, the GnT-III knockdown cells also caused modifications of E-cadherin N-glycans catalyzed by GnT-III and GnT-V. Altogether our results have clarified the existence of a bidirectional crosstalk between E-cadherin and GnT-III/GnT-V that was, for the first time, reproduced in an in vivo model. This study opens new insights into the post-transcriptional modifications of E-cadherin in its biological function, in a tumor context.

A mutual regulation between cell-cell adhesion and N-glycosylation: implication of the bisecting GlcNAc for biological functions

Changes in oligosaccharide structures are associated with numerous physiological and pathological events. E-cadherin-mediated cell-cell adhesion is believed to be both temporally and spatially regulated during development, and represents a key step in the acquisition of the invasive phenotype for many tumors. Here, we focus mainly on a mutual regulation between E-cadherin-mediated cell-cell adhesion and N-acetylglucosaminyltransferase III (GnT-III) expression, and discuss its implications for biological functions.

Potential of N-glycan in cell adhesion and migration as either a positive or negative regulator

Glycosylation is one of the most abundant posttranslational modification reactions, and nearly half of all known proteins in eukaryotes are glycosylated. In fact, changes in oligosaccharide structure (glycan) are associated with many physiological and pathological events, including cell adhesion, migration, cell growth, cell differentiation and tumor invasion. Glycosylation reactions are catalyzed by the action of glycosyltransferases, which add sugar chains to various complex carbohydrates such as glycoproteins, glycolipids and proteoglycans. Functional glycomics, which uses sugar remodeling by glycosyltransferases, is a promising tool for the characterization of glycan functions. Here, we will focus on the positive and negative regulation of biological functions of integrins by the remodeling of N-glycans with N-acetylglucosaminyltransferase III (GnT-III) and N-acetylglucosaminyltransferase V (GnT-V), which catalyze branched N-glycan formations, bisecting GlcNAc and beta1,6 GlcNAc, respectively. Typically, integrins are modified by GnT-III, which inhibits cell migration and cancer metastasis. In contrast, integrins modified by GnT-V promote cell migration and cancer invasion.

Functional roles of N-glycans in cell signaling and cell adhesion in cancer

Glycosylation is one of the most common post-translational modification reactions and nearly half of all known proteins in eukaryotes are glycosylated. In fact, changes in oligosaccharide structures are associated with many physiological and pathological events, including cell growth, migration, differentiation, tumor invasion, host-pathogen interactions, cell trafficking, and transmembrane signaling. Emerging roles of glycan functions have been highly attractive to scientists in various fields of life science as they open a field, "Functional Glycomics", that is a comprehensive study of the glycan structures in relation to functions. In particular, the N-glycans of signaling molecules including receptors or adhesion molecules are considered to be involved in cellular functions. This review will focus on the roles of glycosyltransferases involved in the biosynthesis of N-glycan branching and identification of cell surface receptors as their target proteins. We also suggest that the modulation of N-glycans of those receptors alters their important functions such as cell signaling and cell adhesion which are implicated in cancer invasion and metastasis.

Branched N-glycans regulate the biological functions of integrins and cadherins

Glycosylation is one of the most common post-translational modifications, and approximately 50% of all proteins are presumed to be glycosylated in eukaryotes. Branched N-glycans, such as bisecting GlcNAc, beta-1,6-GlcNAc and core fucose (alpha-1,6-fucose), are enzymatic products of N-acetylglucosaminyltransferase III, N-acetylglucosaminyltransferase V and alpha-1,6-fucosyltransferase, respectively. These branched structures are highly associated with various biological functions of cell adhesion molecules, including cell adhesion and cancer metastasis. E-cadherin and integrins, bearing N-glycans, are representative adhesion molecules. Typically, both are glycosylated by N-acetylglucosaminyltransferase III, which inhibits cell migration. In contrast, integrins glycosylated by N-acetylglucosaminyltransferase V promote cell migration. Core fucosylation is essential for integrin-mediated cell migration and signal transduction. Collectively, N-glycans on adhesion molecules, especially those on E-cadherin and integrins, play key roles in cell-cell and cell-extracellular matrix interactions, thereby affecting cancer metastasis.

Inverse correlation between the extent of N-glycan branching and intercellular adhesion in epithelia. Contribution of the Na,K-ATPase beta1 subunit

The majority of cell adhesion molecules are N-glycosylated, but the role of N-glycans in intercellular adhesion in epithelia remains ill-defined. Reducing N-glycan branching of cellular glycoproteins by swainsonine, the inhibitor of N-glycan processing, tightens and stabilizes cell-cell junctions as detected by a 3-fold decrease in the paracellular permeability and a 2-3-fold increase in the resistance of the adherens junction proteins to extraction by non-ionic detergent. In addition, exposure of cells to swainsonine inhibits motility of MDCK cells. Mutagenic removal of N-glycosylation sites from the Na,K-ATPase beta(1) subunit impairs cell-cell adhesion and decreases the effect of swainsonine on the paracellular permeability of the cell monolayer and also on detergent resistance of adherens junction proteins, indicating that the extent of N-glycan branching of this subunit is important for intercellular adhesion. The N-glycans of the Na,K-ATPase beta(1) subunit and E-cadherin are less complex in tight renal epithelia than in the leakier intestinal epithelium. The complexity of the N-glycans linked to these proteins gradually decreases upon the formation of a tight monolayer from dispersed MDCK cells. This correlates with a cell-cell adhesion-induced increase in expression of GnT-III (stops N-glycan branching) and a decrease in expression of GnTs IVC and V (promote N-glycan branching) as detected by real-time quantitative PCR. Consistent with these results, partial silencing of the gene encoding GnT-III increases branching of N-glycans linked to the Na,K-ATPase beta(1) subunit and other glycoproteins and results in a 2-fold increase in the paracellular permeability of MDCK cell monolayers. These results suggest epithelial cells can regulate tightness of cell junctions via remodeling of N-glycans, including those linked to the Na,K-ATPase beta(1)-subunit.

Beta1,6-branched oligosaccharides regulate melanin content and motility in macrophage-melanoma fusion hybrids

In previous studies, fusion of peritoneal macrophages or blood monocytes with mouse melanoma cells produced hybrids with upregulated expression of the glycosyltransferase beta1,6-N-acetylglucosaminyltransferase V (GnT-V) and its enzymatic product, beta1,6-branched oligosaccharides. This correlated with marked increases in motility, metastatic potential and, surprisingly, melanin content. This study was designed to establish direct roles for beta1,6-branched oligosaccharides in melanogenesis and motility. The levels of beta1,6-branched oligosaccharides were lowered by transfecting beta1,4-N-acetylglucosaminyltransferase III, a competitive inhibitor of GnT-V. beta1,4-N-acetylglucosaminyltransferase III transfection virtually eliminated melanin production and markedly decreased chemotactic motility. This implied that the metastatic and melanogenic phenotypes in hybrids were each upregulated by beta1,6-branched oligosaccharides. Although roles for beta1,6-branched oligosaccharides in motility and metastasis have been reported previously, this is the first study to directly implicate these structures in melanogenesis. Although drawn from experimental models, the findings might explain the well known hypermelanotic regions of human cutaneous malignant melanoma as hypermelanotic cutaneous malignant melanoma cells are rich in beta1,6-branched oligosaccharides. They might also explain why melanogenesis pathways differ between malignant and normal melanocytes as GnT-V is a myeloid-associated enzyme that is aberrantly expressed in melanoma cells but not in normal melanocytes.

Regulation of Integrin Functions by N-glycans

Integrins are cell surface transmembrane glycoproteins that function as adhesion receptors in cell-ECM interactions and link matrix proteins to the cytoskeleton. Integrins play an important role in cytoskeleton organization and in the transduction of intracellular signals, regulating various processes such as proliferation, differentiation, apoptosis, and cell migration. Although integrin-mediated adhesion is based on the binding of alpha and beta subunits to a defined peptide sequence, the strength of this binding is modulated by various factors including the status of glycosylation of integrin. Glycosylation reactions are catalyzed by the catalytic action of glycosyltransferases, such as N-acetylglucosaminyltransferase III, V and alpha1,6 fucosyltransferase, etc., which catalyze the formation of glycosidic bonds. In this talk we will briefly overview the N-glycan structures of integrins, such as alpha3beta1 and alpha5beta1, and their related functions arising from recent studies, which provide insight into some long-standing questions concerning N-glycosylation functions.