Effects of H-ras and v-sis overexpression on N-acetylglucosaminyltransferase V and metastasis-related phenotypes in human hepatocarcinoma cells

Selectin Ligands Sialyl-Lewis a and Sialyl-Lewis x in Gastrointestinal Cancers

The tetrasaccharide structures Siaα2,3Galβ1,3(Fucα1,4)GlcNAc and Siaα2,3Galβ1,4(Fucα1,3)GlcNAc constitute the epitopes of the carbohydrate antigens sialyl-Lewis a (sLe^a) and sialyl-Lewis x (sLe^x), respectively, and are the minimal requirement for selectin binding to their counter-receptors. Interaction of sLe^x expressed on the cell surface of leucocytes with E-selectin on endothelial cells allows their arrest and promotes their extravasation. Similarly, the rolling of cancer cells ectopically expressing the selectin ligands on endothelial cells is potentially a crucial step favoring the metastatic process. In this review, we focus on the biosynthetic steps giving rise to selectin ligand expression in cell lines and native tissues of gastrointestinal origin, trying to understand whether and how they are deregulated in cancer. We also discuss the use of such molecules in the diagnosis of gastrointestinal cancers, particularly in light of recent data questioning the ability of colon cancers to express sLe^a and the possible use of circulating sLe^x in the early detection of pancreatic cancer. Finally, we reviewed the data dealing with the mechanisms that link selectin ligand expression in gastrointestinal cells to cancer malignancy. This promising research field seems to require additional data on native patient tissues to reach more definitive conclusions.

Prognostic significance of β1,6-N-acetylglucosaminyltransferase V expression in patients with hepatocellular carcinoma

OBJECTIVE

Alterations to the N-glycans in glycoproteins have been suggested to play important roles in the proliferation, differentiation, invasion and metastasis of hepatocellular carcinoma (HCC). This study aims to evaluate the potential prognostic value of β1,6-N-acetylglucosaminyltransferase V (Mgat5) in hepatocellular carcinoma patients after surgical resection.

METHODS

We retrospectively enrolled 300 patients (156 in the training cohort and 144 in the validation cohort) with hepatocellular carcinoma undergoing hepatectomy at a single institution. Mgat5 intensities were assessed by immunohistochemistry in the specimens of patients. The Kaplan-Meier method was applied to compare survival curves. Cox regression models were used to analyze the impact of prognostic factors on overall survival and recurrence-free survival. The concordance index was calculated to assess predictive accuracy.

RESULTS

Intratumoral Mgat5 expression was significantly higher than non-tumoral tissues (P < 0.001). In both cohorts, elevated Mgat5 expression in tumor tissues positively correlated with vascular invasion and advanced tumor-node-metastasis stage. High Mgat5 expression indicated poor survival (P < 0.001 in the training cohort and P < 0.001 in the validation cohort) and recurrence (P < 0.001 in both cohorts, respectively) in patients with hepatocellular carcinoma, particularly with early-stage disease. Mgat5 expression was identified as an independent adverse prognostic factor for survival and recurrence. The predictive accuracy of tumor-node-metastasis and Barcelona Clinic Liver Cancer prognostic models was improved when Mgat5 expression was added.

CONCLUSION

Mgat5 expression is a potential independent adverse prognostic biomarker for recurrence and survival of patients with hepatocellular carcinoma after hepatectomy.

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.

Post-translational glycoprotein modifications regulate colon cancer stem cells and colon adenoma progression in Apc(min/+) mice through altered Wnt receptor signaling

Deletion of GnT-V (MGAT5), which synthesizes N-glycans with β(1,6)-branched glycans, reduced the compartment of cancer stem cells (CSC) in the her-2 mouse model of breast cancer, leading to delay of tumor onset. Because GnT-V levels are also commonly up-regulated in colon cancer, we investigated their regulation of colon CSC and adenoma development. Anchorage-independent cell growth and tumor formation induced by injection of colon tumor cells into NOD/SCID mice were positively associated with GnT-V levels, indicating regulation of proliferation and tumorigenicity. Using Apc(min/+) mice with different GnT-V backgrounds, knock-out of GnT-V had no significant effect on the number of adenoma/mouse, but adenoma size was significantly reduced and accompanied increased survival of Apc(min/+) mice with GnT-V deletion (p < 0.01), suggesting an inhibition in the progression of colon adenoma caused by deletion of GnT-V. Decreased expression levels of GnT-V down-regulated the population of colon (intestine) CSC, affecting their ability for self-renewal and tumorigenicity in NOD/SCID mice. Furthermore, altered nuclear translocation of β-catenin and expression of Wnt target genes were positively associated with expression levels of GnT-V, indicating the regulation of canonical Wnt/β-catenin signaling. By overexpressing the Wnt receptor, FZD-7, in colon cancer cells, we found that FZD-7 receptors expressed N-linked β(1,6) branching, indicating that FZD-7 can be modified by GnT-V. The aberrant Wnt signaling observed after modulating GnT-V levels is likely to result from altered N-linked β(1,6) branching on FZD-7, thereby affecting Wnt signaling, the compartment of CSC, and tumor progression.

Recent progress and new perspectives in lymphoma glycobiology

Glycosylation has recently become one of the most significant subjects in tumor biology, and cell surface glycosylation is closely associated with various biological phenomena in tumor cells. However, the biological significance of cell surface glycosylation and sialic acid linked to glycans in human malignant lymphoma is not well elucidated. We have determined that 1) sialylation or loss of N-glycosylation is closely associated with a worse prognosis in human diffuse large B-cell lymphoma (DLBCL), and 2) glycosylation or sialic acid on the surface of lymphoma cells plays significant roles in cell adhesion or invasion to the extracellular matrix, cell growth, apoptosis and cell death. In the present review, the biological functions of glycosylation or sialic acid in human malignant lymphoma are discussed.

The recognition of N-glycans by the lectin ArtinM mediates cell death of a human myeloid leukemia cell line

ArtinM, a d-mannose-binding lectin from Artocarpus heterophyllus (jackfruit), interacts with N-glycosylated receptors on the surface of several cells of hematopoietic origin, triggering cell migration, degranulation, and cytokine release. Because malignant transformation is often associated with altered expression of cell surface glycans, we evaluated the interaction of ArtinM with human myelocytic leukemia cells and investigated cellular responses to lectin binding. The intensity of ArtinM binding varied across 3 leukemia cell lines: NB4>K562>U937. The binding, which was directly related to cell growth suppression, was inhibited in the presence of Manα1-3(Manα1-6)Manβ1, and was reverted in underglycosylated NB4 cells. ArtinM interaction with NB4 cells induced cell death (IC₅₀ = 10 µg/mL), as indicated by cell surface exposure of phosphatidylserine and disruption of mitochondrial membrane potential unassociated with caspase activation or DNA fragmentation. Moreover, ArtinM treatment of NB4 cells strongly induced reactive oxygen species generation and autophagy, as indicated by the detection of acidic vesicular organelles in the treated cells. NB4 cell death was attributed to ArtinM recognition of the trimannosyl core of N-glycans containing a ß1,6-GlcNAc branch linked to α1,6-mannose. This modification correlated with higher levels of N-acetylglucosaminyltransferase V transcripts in NB4 cells than in K562 or U937 cells. Our results provide new insights into the potential of N-glycans containing a β1,6-GlcNAc branch linked to α1,6-mannose as a novel target for anti-leukemia treatment.

Glycans as Biomarkers: Status and Perspectives

Protein glycosylation is a ubiquitous and complex co- and post-translational modification leading to glycan formation, i.e. oligosaccharide chains covalently attached to peptide backbones. The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is widely recognized. Thus, glycans are considered as unique structures to diagnose, predict susceptibility to and monitor the progression of disease. In the »omics« era, the glycome, a glycan analogue of the proteome and genome, holds considerable promise as a source of new biomarkers. In the design of a strategy for biomarker discovery, new principles and platforms for the analysis of relatively small amounts of numerous glycoproteins are needed. Emerging glycomics technologies comprising different types of mass spectrometry and affinity-based arrays are next in line to deliver new analytical procedures in the field of biomarkers. Screening different types of glycomolecules, selection of differentially expressed components, their enrichment and purification or identification are the most challenging parts of experimental and clinical glycoproteomics. This requires large-scale technologies enabling high sensitivity, proper standardization and validation of the methods to be used. Further progress in the field of applied glycoscience requires an integrated systematic approach in order to explore properly all opportunities for disease diagnosis.

The effect of receptor protein tyrosine phosphatase kappa on the change of cell adhesion and proliferation induced by N-acetylglucosaminyltransferase V

N-acetylglucosaminyltransferase V (GnT-V) has been reported to be positively associated with tumor progression, but its mechanism still remains unknown. In the present study, we found that GnT-V overexpression not only changed the glycosylation of receptor protein tyrosine phosphatase kappa (RPTPkappa) but also decreased its protein level. Moreover, GnT-V overexpression decreased cell calcium-independent adhesion and increased the tyrosine phosphorylation level of beta-catenin, in which RPTPkappa played an important role. Since RPTPkappa has an RXKR motif, which is a favored cleavage site for furin, we used furin inhibitor to further explore the effect of RPTPkappa on the change of cell adhesion and beta-catenin signaling induced by GnT-V. Our results showed that preventing RPTPkappa cleavage rescued the above effects of GnT-V, suggesting that furin cleavage could be one of the factors for RPTPkappa to regulate cell adhesion and beta-catenin signaling in GnT-V overexpression cell lines. In addition, the increased tyrosine phosphorylation level of beta-catenin was associated with the increased nuclear level of beta-catenin and downstream signaling molecules such as c-myc and cyclin D1 that were associated with cell proliferation. Our results suggest that GnT-V could decrease human hepatoma SMMC-7721 cell adhesion and promote cell proliferation partially through RPTPkappa.

Glycans as a Target in the Detection of Reproductive Tract Cancers

The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is highly recognized. In this review we summarized literature data on the alteration of glycans in cancer, especially glycoforms of tumor markers of reproductive tract cancers: prostate-specific antigen (PSA) and cancer antigen 125 (CA125). We aimed to highlight the diagnostic potential and relevance of glycan microheterogeneity and to present some novel methods for cancer detection. A computerized search of articles published up to 2007 was performed through the PubMed database. Search terms utilized included prostate/ovarian cancer glycosylation, prostate/ovarian cancer detection, PSA/CA125 glycosylation. Additional sources were identified through cross-referencing and researching in available biomedical books. The comparative studies of sugar chain structures of the PSA and CA125 indicated specific structural alterations associated with malignant transformation, in relation to glycan branching, sialylation and fucosylation. These glycan modifications should be better in distinguishing between benign and malignant conditions than the measurement of marker concentrations alone, which is widely used in practice. Cancer-associated changes in the glycosylation could yield more sensitive and discriminative diagnostic tests for reproductive tract cancer detection, i.e. for improvement of the clinical utility of known tumor markers or the discovery of new ones.

Inhibition of a specific N-glycosylation activity results in attenuation of breast carcinoma cell invasiveness-related phenotypes: inhibition of epidermal growth factor-induced dephosphorylation of focal adhesion kinase

Changes in the expression of glycosyltransferases that branch N-linked glycans can alter the function of several types of cell surface receptors and a glucose transporter. To study in detail the mechanisms by which aberrant N-glycosylation caused by altered N-acetylglucosaminyltransferase V(GnT-V, GnT-Va, and Mgat5a) expression can regulate the invasiveness-related phenotypes found in some carcinomas, we utilized specific small interfering RNA (siRNA) to selectively knock down GnT-V expression in the highly metastatic and invasive human breast carcinoma cell line, MDA-MB231. Knockdown of GnT-V by siRNA expression had no effect on epidermal growth factor receptor expression levels but lowered expression of N-linked beta(1,6)-branching on epidermal growth factor receptor, as expected. Compared with control cells, knockdown of GnT-V caused significant inhibition of the morphological changes and cell detachment from matrix that is normally seen after stimulation with epidermal growth factor (EGF). Decreased expression of GnT-V caused a marked inhibition of EGF-induced dephosphorylation of focal adhesion kinase (FAK), consistent with the lack of cell morphology changes in the cells expressing GnT-V siRNA. The attenuation of EGF-mediated phosphorylation and activation of the tyrosine phosphatase SHP-2 was dramatically observed in GnT-V knockdown cells, and these effects could be rescued by reintroduction of GnT-V into these cells, indicating that reduced EGF-mediated activation of SHP-2 was GnT-V related. Concomitantly, knockdown of GnT-V caused reduced EGF-mediated ERK signaling and tumor cell invasiveness-related phenotypes, including effects on actin rearrangement and cell motility. No changes in EGF binding were observed, however, after knockdown of GnT-V. Our results demonstrate that decreased GnT-V activity due to siRNA expression in human breast carcinoma cells resulted in an inhibition of EGF-stimulated SHP-2 activation and, consequently, caused attenuation of the dephosphorylation of FAK induced by EGF. These effects suppressed EGF-mediated downstream signaling and invasiveness-related phenotypes and suggest GnT-V as a potential therapeutic target.

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.

Down regulation of N-acetylglucosaminyltransferase V facilitates all-transretinoic acid to induce apoptosis of human hepatocarcinoma cells

After N-acetylglucosaminyltransferase V (GnT-V) activity was down-regulated by the transfection of its antisense cDNA(GnTV-AS), apoptosis of H7721 cells was appeared and the apoptosis induced by 80 microM all-transretinoic acid (ATRA) was facilitated, while ATRA itself could not induce apparent apoptosis in mock cells transfected with the vector. In the study of the molecular mechanism of this phenomenon, it was found that GnTV-AS reduced the expressions of anti-apoptotic proteins, such as phosphorylated protein kinase B and phosphorylated Bad as well as Bcl-2 and Bcl-X (L), and elevated those of pro-apoptotic proteins, including Bax, full length caspase-3 and its activated fragments as well as anti-oncoprotein p53. In the contrast, ATRA up regulated the expressions of Bax and activated caspase-3 fragments only. After the GnTV-AS transfected cells were treated with ATRA, phosphorylated PKB and Bad were further decreased, while Bax and activated caspase-3 fragment were further increased, leading to the enhanced apoptosis in flow-cytometry analysis when compared with GnTV-AS cells not treated with ATRA. It was speculated that the decreased phospho-Bad resulted from the reduced phospho-PKB and the up regulation of p53 caused the elevated activity of Bax. The increased active caspase-3 was the consequence of the elevated Bax/ Bcl-2(Bcl-X(L)) activity ratio in the cells.

Tumour-cell fusion as a source of myeloid traits in cancer

Malignant cells express molecular pathways that are also expressed by myeloid cells. Such behaviour is associated with loss of homotypic adhesion between cells, changes in the cellular matrix, induction of angiogenesis, motility, chemotaxis, and several immune-signalling pathways. The overlap between malignant cells and myeloid cells could be explained by one mechanism: fusion of myeloid cells and tumour cells, as noted in animal studies and in two patients with renal-cell carcinoma who underwent bone-marrow transplantation. An overlapping trait in these cells is their glycosylation patterns: hybrids have high expression of N-terminal glycosylation and beta1,6-branched oligosaccharides. In macrophages and cancer cells, these structures have a role in motility and systemic migration; in cancer, they are associated with metastasis and poor prognosis. In addition to myeloid traits, fusion might contribute to aneuploidy and plasticity in cancer. Understanding metastatic cells as myeloid-tumour hybrids suggests new strategies for diagnosis, treatment, and prevention of malignant disease.

Altered glycosylation of proteins produced by malignant cells, and application for the diagnosis and immunotherapy of tumours

Most secretory and membrane-bound proteins produced by mammalian cells contain covalently linked sugar chains. Alterations of the sugar chain structures of glycoproteins have been found to occur in various tumours. Because the sugar chains of glycoproteins are essential for the maintenance of the ordered social behaviour of differentiated cells in multicellular organisms, alterations to the sugar chains are the molecular basis of abnormal social behaviours in tumour cells, such as invasion into the surrounding tissues and metastasis. In this review, the structure and enzymatic basis of typical alterations of the N-linked sugar chains, which are found in various tumours, are introduced. These data are useful for devising diagnostic methods and immunotherapies for the clinical treatment of tumours. Three beta-N-acetylglucosaminyltransferases, GnT-III, -IV and -V, play roles in the structural alteration of the complex-type sugar chains in various tumours. In addition, transcriptional changes in various glycosyltransferases, together with the transporters of sugar nucleotides and sulfate, which are responsible for the formation of the outer chain moieties of complex-type sugar chains, are the keys to inducing the alterations.

Alteration in N -acetylglucosaminyltransferase activities and glycan structure in tissue and bile glycoproteins from extrahepatic bile duct carcinoma

The activities of three N -acetylglucosaminyltransferases (GnT)-III, IV and V, as well as the structural alterations of N-glycans on the glycoproteins in cancer tissues and bile specimens from 28 cases of extrahepatic bile duct carcinoma (EBDC) were compared with those from 18 cases of benign biliary duct diseases (BBDD). GnT activities were determined with fluorescence-labeled substrate using a HPLC method. It was found that GnT-III and GnT-V activities in EBDC were increased to 3.14 and 15.96 times respectively of the mean BBDD values, but GnT-IV remained unchanged. The activity of GnT-V was correlated with the grade of differentiation and TMN stage of EBDC. The up-regulation of GnT-III resulted in the increased bisecting-GlcNAc on the N-glycans of glycoproteins in cancer tissues and a 201 kDa bile glycoprotein when analyzed with HRP-labeled E(4)-PHA. The increased GnT-V activity led to the elevation of the beta1,6GlcNAc branch (or antennary number) on the N-glycans in cancer tissue glycoproteins and 201, 163, 122 kDa proteins in the bile as probed with HRP-labeled DSA. These findings suggest that the alteration in GnT activities may be involved in the malignant transformation and development of EBDC, resulting in the aberrant glycosylation of some tissue and bile proteins. The latter was expected to be used in the clinical diagnosis and prognosis evaluation in EBDC patients.

Increased expression of N-acetylglucosaminyltransferase-V in human hepatoma cells by retinoic acid and 1alpha,25-dihydroxyvitamin D3

UDP-N-acetylglucosamine: alpha-6-D-mannoside beta-1,6N-acetylglucosaminyltransferase-V activities were determined in human hepatoma cell lines of Hep3B and HepG2, and also compared with those of normal liver tissues and primary hepatocytes. When GlcNAcbeta1-2Manalpha1-3(GlcNAcbeta1-2Manalpha1-4)(Manbeta1-4GlcNAc-2-amino pyridine (GlcN,GlcN-biant-PA) and UDP-GlcNAc were used as substrates, the enzymes displayed optimum temperatures of 50 degrees C, optimum pHs of 6.5 in each case, K(m) values for UDP-GlcNAc to be 5.8 (Hep3B) and 4.5 mM (HepG2) and K(m) values for GlcN,GlcN-biant-PA (mM) to be 1.28 (Hep3B) and 2.4 (HepG2). This indicates that values of Hep3B GlcNAc-transferase-V were distinguishable with HepG2 enzyme. Furthermore, Hep3B enzyme in membrane fraction showed about 1.5-fold higher specific activity (1.423 pmol/(h mg) than that (1.066 pmol/(h mg)) of HepG2. Normal hepatocytes are characterized by very low level of GlcNAc-transferase-V activity whereas hepatoma cells contained high activities. Treatment of hepatoma cells with retinoic acid and 1alpha,2,5-dihydroxyvitamin D(3) (Vit-D(3)) resulted in an increase in GlcNAc-transferase-V activity, while treatment with dimethyl sulfoxide and cytosine-arabinoside resulted in decrease in the enzyme activity. Although retinoic acid (RA) treated cells shows a changed GlcNAc-transferase-V mRNA expression, expression of marker proteins such as alpha-fetoprotein and albumin was not changed. This is the first demonstration of GlcNAc-transferase-V activity in RA and Vit-D(3)-treated hepatoma cell lines.

Forskolin up-regulates metastasis-related phenotypes and molecules via protein kinase B, but not PI-3K, in H7721 human hepato-carcinoma cell line

Forskolin (FSK) is known as an up-regulator of intracellular cAMP and inhibitor of cancer growth and metastasis. The effects of FSK on the metastasis potential and its mechanisms were studied using a human hepatocarcinoma cell line, H7721. It was found that FSK stimulated cell growth, increased cAMP in the cells, and enhanced the metastasis-related phenotypes, including adhesion to laminin (Ln) and human umbilical vein epithelial cells (HUVEC), chemotactic migration and invasion. These effects were supposed to result from the increase of the SLex expression induced by FSK, since only the monoclonal antibody of SLex showed a significant attenuation of the enhanced metastasis-associated phenotypes. Using H7721 cells transfected with the sense or antisense cDNA of protein kinase B (PKB) and some inhibitors of signal transduction, it was discovered that FSK up-regulated the expression of SLex via PKB, but it was independent of phosphotidylinositide-3-kinase (PI-3K). A subtype of atypical protein kinase C (a-PKC) might also participate in the up-regulation of SLex expression by FSK, and cAMP/PKA pathway is a negative regulator of SLex expression on H7721 cells. It can be concluded that FSK shows a metastasis-promoting effect ex vivo.

Effect of N-acetylglucosaminyltransferase V on the expressions of other glycosyltransferases

Transfection of sense cDNA of N-acetylglucosaminyltransferase V (GnTV) into H7721 human hepatocellular carcinoma cells resulted in the decreased expression of surface sialyl Lewis X (SLe(x)), a sialylated fucose-containing antigen. The enzymatic mechanisms were speculated to be the concomitantly decreased expression of alpha1,3-fucosyltransferase (FucT)-III, -VI, -VII and the branching enzyme of O-glycans, core 2-beta1,6-N-acetylglucosaminyltransferase (C2GnT)-I, -II. These two glycosyltransferase families were suggested to be the key enzymes in the synthesis of SLe(x). The expression of alpha2,3-sialyltransferase (ST3)-IV, but not ST3-I, -II and -III was elevated by sense GnTV. However, it did not cause the increase of SLe(x) synthesis. Transfection of antisense GnTV into H7721 cells showed entirely opposite effects on the expression of above-mentioned SLe(x) and glycosyltransferases as the sense GnTV.

Variant glycosylation: an underappreciated regulatory mechanism for β1 integrins

Although it has been known for many years that beta1 integrins undergo differential glycosylation in accordance with changes in cell phenotype, the potential role of N-glycosylation as a modulator of integrin function has received little attention. One reason for the relatively limited interest in this topic likely relates to the fact that much of the prior research was correlative in nature. However, new results now bolster the hypothesis that there is a causal relationship between variant glycosylation and altered integrin activity. In this review, the evidence for variant glycosylation as a regulatory mechanism for beta1 integrins are summarized, with particular emphasis on: (1). outlining the instances in which cell phenotypic variation is associated with differential beta1 glycosylation, (2). describing the specific alterations in glycan structure that accompany phenotypic changes and (3). presenting potential mechanisms by which variant glycosylation might regulate integrin function.

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

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

Mapping glycosylation changes related to cancer using the Multiplexed Proteomics technology: a protein differential display approach

The metastatic spread of tumor cells in malignant progression is known to be a major cause of cancer mortality. Protein glycosylation is increasingly being recognized as one of the most prominent biochemical alterations associated with malignant transformation and tumorigenesis. The Multiplexed Proteomics (MP) approach is a new technology that permits quantitative, multicolor fluorescence detection of proteins in two-dimensional (2-D) gels and on Western blots. This methodology allows the parallel determination of both altered glycosylation patterns and protein expression level changes within a single 2-D gel experiment. The linear responses of the fluorescent dyes utilized allow rigorous quantitation of changes in protein expression over a broad 3-log linear dynamic range. Global analysis of changes in protein glycosylation and total protein expression is followed by dichromatic, lectin-based profiling methods for rapidly categorizing glycan branching structures. The MP approach was applied to whole tissue extracts of normal and cancerous liver, so that altered glycosylation modification patterns and protein expression levels could be determined. One prominent glycoprotein determined to be up-regulated in the tumor tissue was haptoglobin, an acute-phase response protein. The detection methodologies associated with the MP technology radically increase the information content of 2-D gel experiments. This new information greatly enhances the applicability of these experiments in addressing fundamental questions associated with proteome-wide glycosylation changes related to cancer.

Alteration in the expression of early stage processing enzymes of N-glycan during myeloid and monocytoid differentiation of HL-60 cells

The expressions of the enzymes participating in the early stage of N-glycan processing, Golgi alpha-Mase-I, alpha-Mase-II and GnT-I, GnT-II, were studied before and after HL-60 cells were differentiated to myelocytes or monocytes induced by ATRA or PMA, respectively. It was found that alpha-Mase-I activity and GnT-I mRNA were decreased by both ATRA and PMA, while alpha-Mase-II and GnT-II were altered insignificantly. The down-regulation of alpha-Mase-I and GnT-I was cell specific, since ATRA up-regulated alpha-Mase-I and GnT-I in the H7721 hepatocarcinoma cell line. However, in H7721 cells, PMA also decreased alpha-Mase-I and GnT-I, and both ATRA and PMA also did not obviously change the expressions of alpha-Mase-II and GnT-II.

Alterations in metastatic properties of hepatocellular carcinoma cell following H-ras oncogene transfection

AIM: To demonstrate the relationship between H-ras oncogene and hepatocellular carcinoma (HCC) metastasis.

METHODS: Activated H-ras oncogene was transfected into SMMC 7721, a cell line derived from human HCC, by calcium phosphate transfection method. Some metastasis-related parameters were detected in vitro, including adhesion assay, migration assay, expression of collagenase IV (cIVase) and epidermal growth factor receptor (EGFR).

RESULTS: The abilities of H-ras-transfected cell clones in adhesion to laminin (LN) or fibronectin (FN), migration, cIVase secretion increased markedly, and the expression of EGFR elevated moderately. More importantly, these alterations were consistent positively with the expression of p21, the protein product of H-ras oncogene.

CONCLUSION: H-ras oncogene could induce the metastatic phenotype of HCC cell in vitro to raise its metastatic potential.

Transfection of the c-erbB2/neu gene upregulates the expression of sialyl Lewis X, alpha1,3-fucosyltransferase VII, and metastatic potential in a human hepatocarcinoma cell line

The pCMV4 plasmid containing the cancer-promoting gene, c-erbB2/neu, was cotransfected into the human hepatocarcinoma cell line 7721 with the pcDNA3 vector, which contains the 'neo' selectable marker. Several clones showing stable expression of c-erbB2/neu were established and characterized by determination of c-erbB2/neu mRNA and its encoded protein p185. Expression of Lewis antigens and alpha1,3-fucosyltransferases and the biological behavior of 7721 cells after c-erbB2/neu transfection were studied using mock cells transfected with the vectors pCMV4 and pcDNA3 as controls. SLe(x) expression on the surface of mock cells was high, whereas expression of SDLe(x), Lex and SLe(a) was absent or negligible. This is compatible with the abundant expression of alpha1,3-fucosyltransferase VII, very low expression of alphafucosyltransferase III/VI, and almost absent expression of alpha1,3-fucosyltransferase IV in the mock cells. After transfection of c-erbB2/neu, expression of SLe(x) and alpha1,3-fucosyltransferase VII were simultaneously elevated, but that of alphafucosyltransferase III/VI was not altered. The expression of both SLe(x) and alpha1,3-fucosyltransferase VII correlated positively with the expression of c-erbB2/neu in different clones, being highest in clone 13, medium in clone 6, and lowest in clone 7. In addition, the adhesion of 7721 cells to human umbilical vein endothelial cells (HUVECs) or P-selectin, as well as cell migration and invasion, were increased in c-erbB2/neu-transfected cells. These increases also correlated positively with the expression intensities of c-erbB2/neu, SLe(x) and alpha1,3-fucosyltransferase VII in the different clones, whereas cell adhesion to fibronectin correlated negatively with these variables. mAbs to SLe(x) (KM93) and SDLe(x) (FH6) significantly and slightly, respectively, abolished cell adhesion to HUVECs or P-selectin and cell migration and invasion. mAbs to SDLe(x) and SLe(a) did not suppress cell adhesion to HUVECs nor inhibit cell migration and invasion. Transfection of alpha1,3-fucosyltransferase VII cDNA into 7721 cells showed similar results to transfection of c-erbB2/neu, and the increased adhesion to HUVECs, cell migration, and invasion were also inhibited significantly by KM93 and slightly by FH6. These results indicate that expression of alpha1,3-fucosyltransferase VII and its specific product, SLe(x), and their capacity for cell adhesion, migration and invasion are closely related. Therefore, the c-erbB2/neu gene is proposed to be a metastasis-promoting gene, and its effects are at least partially mediated by the increased expression of alpha1,3-fucosyltransferase VII and SLe(x).

Down-regulation of N-acetylglucosaminyltransferase V by tumorigenesis- or metastasis-suppressor gene and its relation to metastatic potential of human hepatocarcinoma cells

The effects of transfection of the metastasis suppressor gene nm23-H1 and cell-cycle related tumor-suppressor gene p16 on the activity of N-acetylglucosaminyltransferase V (GnT-V) and their relations to cancer metastatic potential were investigated. After transfection of nm23-H1 into 7721 human hepatocarcinoma cells and A549 human lung cancer cells, the activities of GnT-V were decreased by 28%-42% in the cells. In contrast, when p16 was transfected into these two cell lines, the decrease of GnT-V activity was only observed in A549 cells. This was probably to be due to the obvious expression of p16 gene in parental 7721 cells and the deletion of p16 in A549 cells. The decrease of GnT-V mRNA was only observed in nm23-H1-transfected cells, but not in p16-transfected A549 cells, suggesting that these two genes regulated GnT-V via different mechanisms. Horseradish peroxidase (HRP)-lectin staining showed that the 7721 cells transfected with nm23-H1 or the A549 cells transfected with p16 displayed a decreased intensity with HRP-leucoagglutinating phytohemagglutinin and increased intensity with HRP-concanavalin A, indicating the decline of beta1,6 N-acetylglucosamine branching structure on the asparagine-linked glycans of cell-surface and intracellular glycoproteins. The nm23-H1 transfected 7721 cells also displayed some changes in metastasis-related phenotypes, including the increase in cell adhesion to fibronectin (Fn), the decline in cell adhesion to laminin (Ln), and the decreased cell migration and invasion through matrigel. Transfection of antisense GnT-V cDNA into 7721 cells resulted in a decrease of GnT-V activity, an increase of cell adhesion to Fn or Ln, and a decrease in cell migration and invasion through matrigel. These phenotypes bore similarity to those of the 7721 cells transfected with nm23-H1. Our findings indicate that the down-regulation of GnT-V by nm23-H1 contributes to the alterations in metastasis-related phenotypes, and is an important molecular mechanism of metastasis suppression mediated by nm23-H1.