N-acetylglucosaminyltransferase III in human serum, and liver and hepatoma tissues: increased activity in liver cirrhosis and hepatoma patients

Serum N-glycan fingerprint nomogram predicts liver fibrosis: a multicenter study

OBJECTIVES

Liver cirrhosis (LC) is the end-stage of fibrosis in chronic liver diseases, non-invasive early detection of liver fibrosis (LF) is particularly essential for therapeutic decision. Aberrant glycosylation of glycoproteins has been demonstrated to be closely related to liver abnormalities.

METHODS

This study was designed to enroll a total of 1,565 participants with LC/LF, chronic hepatitis virus (CHB) and healthy controls. Fibrosis was confirmed by liver biopsy. Using capillary electrophoresis N-glycan fingerprint (NGFP) analysis, we developed a nomogram algorithm (FIB-G) to discriminate LC from non-cirrhotic subjects.

RESULTS

The FIB-G demonstrated good diagnostic performances in identifying LC with the area under the curve (AUC) 0.895 (95%CI: 0.857-0.915). Furthermore, the diagnostic efficiencies of FIB-G were superior to that of log (P2/P8), procollagen III N-terminal (PIIINP), type IV collage (IV-C), laminin (LN), hyaluronic acid (HA), aspartate transaminase to platelets ratio index (APRI), and FIB-4 when detecting significant fibrosis (S0-1 vs. S2-4, AUC: 0.787, 95%CI: 0.701-0.873), severe fibrosis (S0-2 vs. S3-4, AUC: 0.844, 95%CI: 0.763-0.924), and LC (S0-3 vs. S4, AUC: 0.773, 95%CI: 0.667-0.880). Besides, changes of FIB-G were associated well with the regression of fibrosis and liver function Child-Pugh classification.

CONCLUSIONS

FIB-G is an accurate multivariant N-glycomic algorithm for LC prediction and fibrosis progression/regression monitoring. The high throughput feasible NGFP using only 2 μL of serum could help physicians make the more precise non-invasive staging of LF or cirrhosis and reduce the need for invasive liver biopsy.

A Potential Serum N-glycan Biomarker for Hepatitis C Virus-Related Early-Stage Hepatocellular Carcinoma with Liver Cirrhosis

Detection of early-stage hepatocellular carcinoma (HCC) is beneficial for prolonging patient survival. However, the serum markers currently used show limited ability to identify early-stage HCC. In this study, we explored human serum N-glycans as sensitive markers to diagnose HCC in patients with cirrhosis. Using a simplified fluorescence-labeled N-glycan preparation method, we examined non-sialylated and sialylated N-glycan profiles from 71 healthy controls and 111 patients with hepatitis and/or liver cirrhosis (LC) with or without HCC. We found that the level of serum N-glycan A2G1(6)FB, a biantennary N-glycan containing core fucose and bisecting GlcNAc residues, was significantly higher in hepatitis C virus (HCV)-infected cirrhotic patients with HCC than in those without HCC. In addition, A2G1(6)FB was detectable in HCV-infected patients with early-stage HCC and could be a more accurate marker than alpha-fetoprotein (AFP) or protein induced by vitamin K absence or antagonists-II (PIVKA-II). Moreover, there was no apparent correlation between the levels of A2G1(6)FB and those of AFP or PIVKA-II. Thus, simultaneous use of A2G1(6)FB and traditional biomarkers could improve the accuracy of HCC diagnosis in HCV-infected patients with LC, suggesting that A2G1(6)FB may be a reliable biomarker for early-stage HCC patients.

Advances in the discovery of novel biomarkers for cancer: spotlight on protein N-glycosylation

Progress on glycosylation and tumor markers has not been extensively reported. Glycosylation plays an important part in post-translational modification. Previous research on glycosylation-modified biomarkers has lagged behind due to insufficient understanding of glycosylation-related regulations. However, some new methods and ideas illustrated in recent research may provide new inspirations in the field. This article aims to review current advances in revealing relationship between tumors and abnormal N-glycosylation and discuss leading-edge applications of N-glycosylation in developing novel tumor biomarkers.

Title: Human Serum/Plasma Glycoprotein Analysis by 1H-NMR, an Emerging Method of Inflammatory Assessment

Several studies suggest that variations in the concentration of plasma glycoproteins can influence cellular changes in a large number of diseases. In recent years, proton nuclear magnetic resonance (1H-NMR) has played a major role as an analytical tool for serum and plasma samples. In recent years, there is an increasing interest in the characterization of glycoproteins through 1H-NMR in order to search for reliable and robust biomarkers of disease. The objective of this review was to examine the existing studies in the literature related to the study of glycoproteins from an analytical and clinical point of view. There are currently several techniques to characterize circulating glycoproteins in serum or plasma, but in this review, we focus on 1H-NMR due to its great robustness and recent interest in its translation to the clinical setting. In fact, there is already a marker in H-NMR representing the acetyl groups of the glycoproteins, GlycA, which has been increasingly studied in clinical studies. A broad search of the literature was performed showing a general consensus that GlycA is a robust marker of systemic inflammation. The results also suggested that GlycA better captures systemic inflammation even more than C-reactive protein (CRP), a widely used classical inflammatory marker. The applications reviewed here demonstrated that GlycA was potentially a key biomarker in a wide range of diseases such as cancer, metabolic diseases, cardiovascular risk, and chronic inflammatory diseases among others. The profiling of glycoproteins through 1H-NMR launches an encouraging new paradigm for its future incorporation in clinical diagnosis.

Protein Glycosylation as a Diagnostic and Prognostic Marker of Chronic Inflammatory Gastrointestinal and Liver Diseases

Glycans are sequences of carbohydrates that are added to proteins or lipids to modulate their structure and function. Glycans modify proteins required for regulation of immune cells, and alterations have been associated with inflammatory conditions. For example, specific glycans regulate T-cell activation, structures, and functions of immunoglobulins; interactions between microbes and immune and epithelial cells; and malignant transformation in the intestine and liver. We review the effects of protein glycosylation in regulation of gastrointestinal and liver functions, and how alterations in glycosylation serve as diagnostic or prognostic factors, or as targets for therapy.

A Glycomics-Based Test Predicts the Development of Hepatocellular Carcinoma in Cirrhosis

Purpose: Cirrhosis is a major risk factor for the development of hepatocellular carcinoma but remains underdiagnosed in the compensated stage. Fibrosis progression and cirrhosis are associated with changes in blood serum glycomic profiles. Previously, the serum glycomics-based GlycoCirrhoTest was shown to identify 50% to 70% of compensated cirrhosis cases in chronic liver disease cohorts, at >90% specificity. This study assessed GlycoCirrhoTest for the risk of hepatocellular carcinoma development in compensated cirrhosis.Experimental Design: Serum glycomics were analyzed in sera of 133 patients, with compensated cirrhosis collected between 1995 and 2005 in a surveillance protocol for hepatocellular carcinoma using an optimized glycomic technology on a DNA sequencer.Results: Baseline GlycoCirrhoTest values were significantly increased in patients who developed hepatocellular carcinoma after a median follow-up of 6.4 years as compared with patients who did not. For patients with a baseline GlycoCirrhoTest exceeding 0.2, the HR for hepatocellular carcinoma development over the entire study (Cox regression) was 5.1 [95% confidence interval (CI), 2.2-11.7; P < 0.001], and the HR for hepatocellular carcinoma development within 7 years was 12.1 (95% CI, 2.8-51.6; P = 0.01) based on the cut-off value optimized in the same cohort. An absolute increase in GlycoCirrhoTest of 0.2 was associated with an HR of 10.29 (95% CI, 3.37-31.43; P < 0.001) for developing hepatocellular carcinoma. In comparison, the HR for the development of hepatocellular carcinoma within 7 years for AFP levels above the optimal cutoff in this study (5.75 ng/mL) was 4.65 (95% CI, 1.59-13.61).Conclusions: This prognostic study suggests that GlycoCirrhoTest is a serum biomarker that identifies compensated cirrhotic patients at risk for developing hepatocellular carcinoma. Screening strategies could be guided by a positive test on GlycoCirrhoTest. Clin Cancer Res; 23(11); 2750-8. ©2016 AACR.

Sialoglycoproteins and N-glycans from secreted exosomes of ovarian carcinoma cells

Exosomes consist of vesicles that are secreted by several human cells, including tumor cells and neurons, and they are found in several biological fluids. Exosomes have characteristic protein and lipid composition, however, the results concerning glycoprotein composition and glycosylation are scarce. Here, protein glycosylation of exosomes from ovarian carcinoma SKOV3 cells has been studied by lectin blotting, NP-HPLC analysis of 2-aminobenzamide labeled glycans and mass spectrometry. An abundant sialoglycoprotein was found enriched in exosomes and it was identified by peptide mass fingerprinting and immunoblot as the galectin-3-binding protein (LGALS3BP). Exosomes were found to contain predominantly complex glycans of the di-, tri-, and tetraantennary type with or without proximal fucose and also high mannose glycans. Diantennary glycans containing bisecting N-acetylglucosamine were also detected. This work provides detailed information about glycoprotein and N-glycan composition of exosomes from ovarian cancer cells, furthermore it opens novel perspectives to further explore the functional role of glycans in the biology of exosomes.

All-trans-retinoic acid modulates ICAM-1 N-glycan composition by influencing GnT-III levels and inhibits cell adhesion and trans-endothelial migration

Changes in the expression of glycosyltransferases directly influence the oligosaccharide structures and conformations of cell surface glycoproteins and consequently cellular phenotype transitions and biological behaviors. In the present study, we show that all-trans-retinoic acid (ATRA) modulates the N-glycan composition of intercellular adhesion molecule-1 (ICAM-1) by manipulating the expression of two N-acetylglucosaminyltransferases, GnT-III and GnT-V, via the ERK signaling pathway. Exposure of various cells to ATRA caused a remarkable gel mobility down-shift of ICAM-1. Treatment with PNGase F confirmed that the reduction of the ICAM-1 molecular mass is attributed to the decreased complexity of N-glycans. We noticed that the expression of the mRNA encoding GnT-III, which stops branching, was significantly enhanced following ATRA exposure. In contrast, the level of the mRNA encoding GnT-V, which promotes branching, was reduced following ATRA exposure. Silencing of GnT-III prevented the molecular mass shift of ICAM-1. Moreover, ATRA induction greatly inhibited the adhesion of SW480 and U937 cells to the HUVEC monolayer, whereas knock-down of GnT-III expression effectively restored cell adhesion function. Treatment with ATRA also dramatically reduced the trans-endothelial migration of U937 cells. These data indicate that the alteration of ICAM-1 N-glycan composition by ATRA-induced GnT-III activities hindered cell adhesion and cell migration functions simultaneously, pinpointing a unique regulatory role of specific glycosyltransferases in the biological behaviors of tumor cells and a novel function of ATRA in the modulation of ICAM-1 N-glycan composition.

Alterations of glycan branching and differential expression of sialic acid on alpha fetoprotein among hepatitis patients

The level of serum glycoproteins and their glycosylation pattern change in liver diseases including hepatocellular carcinoma (HCC). Some of them, especially alpha fetoprotein (AFP), serve as useful biomarkers for HCC. The present investigation showed high level of AFP in hepatitis B cirrhosis (HBV-LC) and hepatitis C cirrhosis (HCV-LC) patients. However, increase of AFP level was not significantly high in chronic hepatitis B (HBV-CH) as determined by ELISA using monoclonal anti-human AFP (mAb-AFP). The differential expression of sialic acid linkage was observed in HBV-CH and HCV-LC by ELISA; the former bound strongly with Sambucus nigra agglutinin (SNA), which has exclusive binding specificity for NeuAcα2-6-, whereas HCV-LC reacted preferably with Maackia amurensis agglutinin (MAA) which recognizes NeuAcα2-3-. There was significantly high glycan branching in HBV-LC and HCV-LC in comparison to controls as illustrated by concanavalin A. This was further confirmed by Phaseolus vulgaris erythroagglutinin (E-PHA) and Datura stramonium agglutinin (DSA). Enhanced fucosylation of AFP was observed in HBV-LC, HCV-LC and HCC patients by ELISA using fucose binding Aleuria aurantia lectin; however, maximum binding was found in HCC. Fucosylation with α1-6 linkage was further confirmed by Lens culinaris agglutinin (LCA). From the above results it is concluded that the changes in concentration of AFP, differential expression of sialic acid, increase of glycan branching and fucosylation have a prognostic value of hepatitis and it could be possible that lectin-based assay with AFP can aid in diagnosis of hepatitis diseases besides clinical examination and routine laboratory investigation.

GlycoFibroTest is a highly performant liver fibrosis biomarker derived from DNA sequencer-based serum protein glycomics

Liver fibrosis is currently assessed by liver biopsy, a costly and rather cumbersome procedure that is unsuitable for frequent patient monitoring, which drives research into biomarkers for this purpose. To investigate whether the serum N-glycome contains information suitable for this goal, we developed a 96-well plate-based serum N-glycomics sample preparation protocol that only involves fluid transfer steps and incubations in a PCR thermocycler yielding 8-aminopyrene-1,3,6-trisulfonic acid-labeled N-glycans. These N-glycans are then ready for analysis on the capillary electrophoresis-based DNA sequencers that are the current standard in clinical genetics laboratories worldwide. Subsequently we performed a multicenter, blinded study of 376 consecutive chronic hepatitis C virus patients for which liver biopsies and extensive serum biochemistry data were available. Among patients, the METAVIR fibrosis stage distribution was as follows: 10.6% F0, 44.4% F1, 20.5% F2, 18.4% F3, and 6.1% F4. We found that the ratio of two N-glycans, here called GlycoFibroTest, correlates with the histological fibrosis stage equally well as FibroTest (rho = 0.4-0.5 in F1-F4), which is used in the clinic today. Finally using affinity chromatography we depleted sera of immunoglobulin G, and this resulted in a complete removal of the undergalactosylated biantennary glycans from the N-glycome, which are partially determining GlycoFibroTest.

GlycoFibroTest is a highly performant liver fibrosis biomarker derived from DNA sequencer-based serum protein glycomics

Liver fibrosis is currently assessed by liver biopsy, a costly and rather cumbersome procedure that is unsuitable for frequent patient monitoring, which drives research into biomarkers for this purpose. To investigate whether the serum N-glycome contains information suitable for this goal, we developed a 96-well plate-based serum N-glycomics sample preparation protocol that only involves fluid transfer steps and incubations in a PCR thermocycler yielding 8-aminopyrene-1,3,6-trisulfonic acid-labeled N-glycans. These N-glycans are then ready for analysis on the capillary electrophoresis-based DNA sequencers that are the current standard in clinical genetics laboratories worldwide. Subsequently we performed a multicenter, blinded study of 376 consecutive chronic hepatitis C virus patients for which liver biopsies and extensive serum biochemistry data were available. Among patients, the METAVIR fibrosis stage distribution was as follows: 10.6% F0, 44.4% F1, 20.5% F2, 18.4% F3, and 6.1% F4. We found that the ratio of two N-glycans, here called GlycoFibroTest, correlates with the histological fibrosis stage equally well as FibroTest (rho = 0.4-0.5 in F1-F4), which is used in the clinic today. Finally using affinity chromatography we depleted sera of immunoglobulin G, and this resulted in a complete removal of the undergalactosylated biantennary glycans from the N-glycome, which are partially determining GlycoFibroTest.

Focused glycomic analysis of the N-linked glycan biosynthetic pathway in ovarian cancer

Epithelial ovarian cancer is the deadliest female reproductive tract malignancy in Western countries. Less than 25% of cases are diagnosed when the cancer is confined, however, pointing to the critical need for early diagnostics for ovarian cancer. Identifying the changes that occur in the glycome of ovarian cancer cells may provide an avenue to develop a new generation of potential biomarkers for early detection of this disease. We performed a glycotranscriptomic analysis of endometrioid ovarian carcinoma using human tissue, as well as a newly developed mouse model that mimics this disease. Our results show that the N-linked glycans expressed in both nondiseased mouse and human ovarian tissues are similar; moreover, malignant changes in the expression of N-linked glycans in both mouse and human endometrioid ovarian carcinoma are qualitatively similar. Lectin reactivity was used as a means for rapid validation of glycan structural changes in the carcinomas that were predicted by the glycotranscriptome analysis. Among several changes in glycan expression noted, the increase of bisected N-linked glycans and the transcripts of the enzyme responsible for its biosynthesis, GnT-III, was the most significant. This study provides evidence that glycotranscriptome analysis can be an important tool in identifying potential cancer biomarkers.

Elevated expression of bisecting N-acetylglucosaminyltransferase-III gene in a human fetal hepatocyte cell line by hepatitis B virus

BACKGROUND AND AIM

UDP-N-acetylglucosamine: alpha-D-mannoside beta-1,4 N-acetylglucosaminyltransferase III (GnT-III) is a key enzyme in N-glycan biosynthesis. Human GnT-III enzyme activity was found to be elevated in the serum of patients with hepatomas and liver cirrhosis and in hepatocellular carcinoma tissues. Therefore, to understand the relationship between the elevation in GnT-III activity and hepatitis B viral (HBV) hepartocarcinogenesis, we investigated GnT-III gene expression in the HBV-infected cells.

METHODS

A cell line, HFH-T1, producing HBV was produced by natural infection of human fetal hepatocytes. A 170-bp band corresponding to the pre-S1 region of HBV was detected in the culture medium by polymerase chain reaction. Virions were also isolated from the culture medium by sucrose density gradient centrifugation. The synthesis of both alpha-fetoprotein and albumin as an indicator that these cells were functional hepatocytes and the extent of differentiation was examined. Polymerase chain reaction and Western blot analysis using a monoclonal antibody, GT273, which was prepared using human aglycosyl recombinant GnT-III were used for HBV DNA and GnT-III detection.

RESULTS

Two types of HBV-related particles were secreted into the culture medium; one was a Dane particle (40 nm in size) containing HBV DNA and the other was a subviral hepatitis B surface antigen particle (20 nm in size) that did not contain the viral genome. The secretion from the cell line was diminished by the number of passages and, thus, this cell was renamed as HFH-T2. A decreased level of the HBV was secreted from the cells after a rest period. HFH-T2 cells showed a weak staining for alpha-fetoprotein and a moderate staining for albumin in the cytoplasm around the nucleus. High levels of a 0.7 kb DNA fragment originating from GnT-III DNA were detected in HFH-T2 cells. Western blot analysis using a monoclonal antibody, GT273, which was prepared using human aglycosyl recombinant GnT-III showed a single band, corresponding to Mr 63 kDa, whereas aglycosyl GnT-III showed a band at Mr 53 kDa, with a molecular weight difference of about 10 kDa. This indicates that HFH-T2 cells express glycosylated GnT-III. GnT-III activities were 347.2 +/- 53.6 pmol/mg of protein/h in HFH-T2, 276 +/- 26.3 in Hep3B, 252.5 +/- 23.3 in HepG2 and 30.7 +/- 3.4 in NIH-3T3. GnT-III activity was higher in HFH-T2 cells than in the hepatoma cell lines, Hep3B and HepG2.

CONCLUSION

A human fetal hepatocyte cell line was transformed by infection with HBV and the cell line expressed high levels of GnT-III as the levels of secretion of HBV decreased. The decrease in HBV secretion from HFH-T2 cells could be due to a high level of expression of GnT-III. Such a cell line could be used to investigate relationships between HBV infection and glycosyltransferase gene expression. Furthermore, this cell line will be useful in future studies on the effect of the expression of GnT-III on other glycosyltransferase.

Determination of UDP-N-acetylglucosamine: beta-D-mannoside-1,4-N-acetylglucosaminyltransferase-III in patients sera with chronic hepatitis and liver cirrhosis using a monoclonal antibody

The glycoprotein UDP-N-acetylglucosamine: beta-D-mannoside-1,4-N-acetylglucosaminyltransferase-III (GnT-III) catalyzes the addition of N-acetylglucosamine via a beta-1, 4-linkage to the beta-linked mannose of the trimannosyl core of N-linked glycans. It has been reported that the expression of GnT-III increases in many oncogenically transformed cells and human hepatocellular carcinoma (HCC) tissues, and GnT-III enzyme activity in serum can be used for the detection and monitoring of primary hepatomas and hepatocellular carcinomas. A solid-phase enzyme-linked immunosorbent sandwich assay in which a polyclonal antibody (PAb) to aglycosylrecombinant GnT-III (AGR-GnT-III) and a monoclonal antibody (mAb) are employed as a capture protein and probe protein, respectively, is described. The sensitivity of the PAb-mAb sandwich assay, as determined by the dose-response effect for AGR-GnT-III, was 10 ng/ml. This assay was specific for GnT-III and did not detect beta-1, 6-N-acetylglucosaminyltrasferase-V (GnT-V). AGR-GnT-III concentrations in 377 serum specimens were determined by the PAb-mAb sandwich assay and the results were analyzed based on the disease category, using 1.99 microg/mL (AGR-GnT-III) as a cut-off value. The AGR-GnT-III level of 61 normal serum samples was 0.57 +/- 0.71 microg/ml (mean +/- SD). The results revealed an elevation in serum AGR-GnT-III levels in 60 of 86 patients (3.03 +/- 2.04 microg/ml) with liver cirrhosis (LC) and 86 of 91 patients (2.73 +/- 0.59 microg/ml) with chronic hepatitis (CH). By contrast, 3 of 61 normal subjects, 9 of 34 patients (1.02 +/- 1.03 microg/ml) with acute hepatitis and 8 of 38 patients (1.79 +/- 0.56 microg/ml) with a variety of non-hepatic diseases exhibited a slight increase above the cut-off value. These results indicate that serum AGR-GnT-III levels are elevated predominantly in LC or CH cases. Serum AGR-GnT-III concentration, as measured by the developed PAb-mAb sandwich assay, may be a useful differential marker as a diagnostic aid for CH and/or LC and warrants further investigations with expanded serum panels.

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.

Hyperexpression of N-acetylglucosaminyltransferase-III in liver tissues of transgenic mice causes fatty body and obesity through severe accumulation of Apo A-I and Apo B

N-Acetylglucosaminyltransferase (GnT)-III catalyzes the attachment of an N-acetylglucosamine (GlcNAc) residue to mannose in beta(1-4) configuration in the region of N-glycans and forms a bisecting GlcNAc. To investigate the pathophysiological role of dysregulated glycosylation mediated by aberrantly expressed GnT-III, we generated transgenic mice hyperexpressing the human GnT-III in the liver by introducing human GnT-III cDNA under the control of mouse albumin enhancer/promoter. Total five transgenic founder mice (pGnTSVTpA-10, -14, -20, -25, and -51) expressed the human GnT-III in their livers and were characterized by molecular genetic means. The copy number of transgene integrated into the genome of these mice ranged between 1 and 3 copies per haploid genome. Northern and Western blot analyses showed that the transgene is specifically expressed in the liver but not in any other tissues tested. The triglyceride level in GnT-III transgenic mice was significantly decreased, however, no significant differences in the levels of glucose, cholesterol, or albumin were observed between transgenic and nontransgenic mice. Although glutamate oxaloacetic transaminase and glutamic pyruvic transaminase activities of transgenic mice were also higher than those of nontransgenic mice, no differences in total bililubin and total protein were observed between the two animal lines. Large amounts of apolipoprotein (Apo) A-I and Apo B were specifically detected in the intracellular liver of transgenic mice. The accumulation of Apo A-I in hepatocytes may be due to aberrant glycosylation, since glycosylated Apo A-I was not observed in transgenic mice. However, the accumulated Apo B was severely glycosylated. Therefore, it is suggested that highly expressed transgenic GnT-III allowed unknown target proteins to be glycosylated in large amounts, and the resulting target protein(s) disrupted in assembly formation of Apo A-I in the hepatocytes and cause a decrease in the release of lipoproteins and accumulations of Apo A-I and Apo B in the liver. The transgenic mice showed aberrant glycosylation by GnT-III, resulting in numerous lipid droplets in liver tissues and the obesity. These mice showed microvesicular fatty changes with abnormal lipid accumulation in the hepatocytes. Our study provides the basis for future analysis of the role of glycosylation in hepatic pathogenesis. In the transgenic mice, Apo A-I and Apo B were significantly increased compared with levels in nontransgenic liver tissues.

Noninvasive diagnosis of liver cirrhosis using DNA sequencer-based total serum protein glycomics

We applied our 'clinical glycomics' technology, based on DNA sequencer/fragment analyzers, to generate profiles of serum protein N-glycans of liver disease patients. This technology yielded a biomarker that distinguished compensated cirrhotic from noncirrhotic chronic liver disease patients, with 79% sensitivity and 86% specificity (100% sensitivity and specificity for decompensated cirrhosis). In combination with the clinical chemistry-based Fibrotest biomarker, compensated cirrhosis was detected with 100% specificity and 75% sensitivity. The current 'gold standard' for liver cirrhosis detection is an invasive, costly, often painful liver biopsy. Consequently, the highly specific set of biomarkers presented could obviate biopsy in many cirrhosis patients. This biomarker combination could eventually be used in follow-up examinations of chronic liver disease patients, to yield a warning that cirrhosis has developed and that the risk of complications (such as hepatocellular carcinoma) has increased considerably. Our clinical glycomics technique can easily be implemented in existing molecular diagnostics laboratories.

The hepatitis B virus X protein inhibits secretion of apolipoprotein B by enhancing the expression of N-acetylglucosaminyltransferase III

The X protein of hepatitis B virus (HBx) plays a major role on hepatocellular carcinoma (HCC). Apolipoprotein B (apoB) in the liver is an important glycoprotein for transportation of very low density lipoproteins and low density lipoproteins. Although lipid accumulation in the liver is known as one of the factors for the HCC, the relationship between HBx and apoB during the HCC development is poorly understood. To better understand the biological significance of HBx in HCC, liver Chang cells that specifically express HBx were established and characterized. In this study we demonstrate that overexpression of HBx significantly up-regulates the expression of UDP-N-acetylglucosamine:beta-d-mannoside-1,4-N-acetylglucosaminyltransferase-III (GnT-III), an enzyme that functions as a bisecting-N-acetylglucosamine (GlcNAc) transferase in apoB, and increases GnT-III promoter activity in a chloramphenicol acetyltransferase assay. GnT-III expression levels of HBx-transfected cells appeared to be higher than that of hepatocarcinoma cells as well as GnT-III-transfected cells, indicating that HBx may has a strong GnT-III promotor-enhancing activity. Intracellular levels of apoBs, which contained the increased bisecting GlcNAc, were accumulated in HBx-transfected liver cells. These cells as well as GnT-III-transfected liver cells revealed the inhibition of apoB secretion and the increased accumulation of intracellular triglyceride and cholesterol compared with vector-transfected cells. Moreover, overexpression of GnT-III and HBx in liver cells was shown to down-regulate the transcriptional level of microsomal triglyceride transfer protein, which regulates the assembly and secretion of apoB. Therefore, our study strongly suggested that the HBx increase in intracellular accumulation of aberrantly glycosylated apoB resulted in inhibition of secretion of apoB as well as intracellular lipid accumulation by elevating the expression of GnT-III.

Biological consequences of overexpressing or eliminating N-acetylglucosaminyltransferase-TIII in the mouse

N-acetylglucosaminyltransferase III (GlcNAc-TIII), a product of the human MGAT3 gene, was discovered as a glycosyltransferase activity in hen oviduct. GlcNAc-TIII transfers GlcNAc in beta4-linkage to the core Man of complex or hybrid N-glycans, and thereby alters not only the composition, but also the conformation of the N-glycan. The dramatic consequences of the addition of this bisecting GlcNAc residue are reflected in the altered binding of lectins that recognize Gal residues on N-glycans. Changes in GlcNAc-TIII expression correlate with hepatoma and leukemia in rodents and humans, and the bisecting GlcNAc on Asn 297 of human IgG antibodies enhances their effector functions. Overexpression of a cDNA encoding GlcNAc-TIII alters growth control and cell-cell interactions in cultured cells, and in transgenic mice. While mice lacking GlcNAc-TIII are viable and fertile, they exhibit retarded progression of diethylnitrosamine (DEN)-induced liver tumors. Further biological functions of GlcNAc-TIII are expected to be uncovered as mice with a null mutation in the Mgat3 gene are challenged.

Truncated, inactive N-acetylglucosaminyltransferase III (GlcNAc-TIII) induces neurological and other traits absent in mice that lack GlcNAc-TIII

N-Acetylglucosaminyltransferase III (GlcNAc-TIII), the product of the Mgat3 gene, transfers the bisecting GlcNAc to the core mannose of complex N-glycans. The addition of this residue is regulated during development and has functional consequences for receptor signaling, cell adhesion, and tumor progression. Mice homozygous for a null mutation at the Mgat3 locus (Mgat3(Delta)) or for a targeted mutation in the Mgat3 gene (previously called Mgat3(neo), but herein renamed Mgat3(T37) because the allele generates inactive GlcNAc-TIII of approximately 37 kDa) were found to exhibit retarded progression of liver tumors. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of neutral N-glycans from kidneys revealed no significant differences, and both mutants showed the expected lack of N-glycan species with an additional GlcNAc. However, the two mutants differed in several biological traits. Mgat3(T37/T37) homozygotes in a mixed or 129(SvJ) background were retarded in growth rate and exhibited an altered leg clasp reflex, an altered gait, and defective nursing behavior. Pups abandoned by Mgat3(T37/T37) mothers were rescued by wild-type foster mothers. None of these Mgat3(T37/T37) traits were exhibited by Mgat3(Delta/Delta) mice or by heterozygous mice carrying the Mgat3(T37) mutation. Similarly, no dominant-negative effect was observed in Chinese hamster ovary cells expressing truncated GlcNAc-TIII in the presence of wild-type GlcNAc-TIII. However, compound heterozygotes carrying both the Mgat3(T37) and Mgat3(Delta) mutations exhibited a marked leg clasp reflex, indicating that in the absence of wild-type GlcNAc-TIII, truncated GlcNAc-TIII causes this phenotype. The Mgat3 gene was expressed in brain at embryonic day 10.5 and thereafter and in neurons of adult cerebellum. The mutant Mgat3 gene was also highly expressed in Mgat3(T37/T37) brain. This may be the basis of the unexpected neurological phenotype induced by truncated, inactive GlcNAc-TIII in the mouse.

Expression of bisecting N-acetylglucosaminyltransferase-III in human hepatocarcinoma tissues, fetal liver tissues, and hepatoma cell lines of Hep3B and HepG2

In this paper, uridine diphosphate (UDP)-N-acetylglucosamine/beta-D-mannoside beta-1,4 N-acetylglucosaminyltransferase III (GlcNAc-transferase-III C 2.4.1.144) activity was determined in human hepatoma cell lines of Hep3B and HepG2, and also compared with those of normal liver tissues and primary hepatocytes. GlcNAc-transferase-III enzymes of Hep3B and HepG2 were mainly detected in the membrane fraction. When GlcN,GlcN-biant-PA and UDP-GlcNAc were used as substrates, the Km values (4.7 mM for UDP-GlcNAc and 1.1 mM for GlcN, GlcN-biant-PA) of Hep3B GlcNAc-transferase-III were distinguishable from those of HepG2 GlcNAc-transferase-III (6.8 mM for UDP-GlcNAc and 3.4 mM for GlcN,GlcN-biant-PA). Furthermore, Hep3B enzyme in membrane fraction showed about 1.5-fold higher specific activity (1423 pmol/hr/mg) than that of HepG2 (1066 pmol/hr/mg). Normal liver cells and primary adult hepatocytes are characterized by a very low level of GlcNAc-transferase-III activity, whereas human hepatoma cells exhibited high activities. These data were supported by reverse transcription-polymerase chain reaction results, showing that expression of the GlcNAc-transferase-III mRNA increased in proportion to the enzymatic activities. Although the mechanism underlying the induction of this enzyme is unknown, lectin blot analysis showed that oligosaccharides in many glycoproteins were observed in hepatoma cells. By treating hepatocarcinoma cultures that express GlcNAc-transferase-III with inhibitors (tunicamycin, deoxymannojirimycin, and swainsonine) of different steps of the glycosylation, we provide evidence that expression of GlcNAc-transferase-III mRNA is dependent on glycosylation of cellular proteins.

N-Acetylglucosaminyltransferase V as a possible aid for the evaluation of tumor invasiveness in patients with hepatocellular carcinoma

BACKGROUND

A close relationship has been shown to exist between the metastatic potential and beta1-6 branched oligosaccharides in human and rodent cells. N-acetylglucosaminyltransferase V (GnT-V) catalyzes this process. Although this phenomenon has been reported, little is known about the clinical usefulness of the determination of GnT-V in the evaluations of tumor invasiveness in hepatocellular carcinoma (HCC). In this study, we measured the GnT-V activity in serum of patients with HCC, together with its activity and gene expression in HCC tissues, and elucidated the clinical usefulness of the GnT-V level in evaluating tumor invasiveness.

METHODS

Seventy-three serum samples from 38 patients with HCC, 11 with chronic hepatitis, eight with hepatic cirrhosis and 16 healthy controls were used. Twenty-one liver tissues were obtained by surgical resection from 17 patients with HCC, three with colorectal cancers and one with gallbladder cancer metastatic to the liver. The GnT-V activity was determined by using high performance liquid chromatography. The GnT-V mRNA was quantified by using competitive RT-PCR.

RESULTS

There were statistically significant correlations between GnT-V activity in sera of HCC, and GnT-V activity and GnT-V mRNA expression in tumor tissue. The mean GnT-V activity in the sera of patients with HCC increased in accordance with the degree of tumor invasion. The HCC group with intrahepatic and extrahepatic metastases showed the highest serum GnT-V-value.

CONCLUSIONS

The present study demonstrated that there was a close association between tumor invasiveness and GnT-V activity in sera, and that the measurement of GnT-V may improve prognostic estimates and therapeutic outcomes for patients with HCC.

The joys of HexNAc. The synthesis and function of N- and O-glycan branches

This review covers discoveries made over the past 30-35 years that were important to our understanding of the synthetic pathway required for initiation of the antennae or branches on complex N-glycans and O-glycans. The review deals primarily with the author's contributions but the relevant work of other laboratories is also discussed. The focus of the review is almost entirely on the glycosyltransferases involved in the process. The following topics are discussed. (1) The localization of the synthesis of complex N-glycan antennae to the Golgi apparatus. (2) The "evolutionary boundary" at the stage in N-glycan processing where there is a change from oligomannose to complex N-glycans; this switch correlates with the appearance of multicellular organisms. (3) The discovery of the three enzymes which play a key role in this switch, N-acetylglucosaminyltransferases I and II and mannosidase II. (4) The "yellow brick road" which leads from oligomannose to highly branched complex N-glycans with emphasis on the enzymes involved in the process and the factors which control the routes of synthesis. (5) A short discussion of the characteristics of the enzymes involved and of the genes that encode them. (6) The role of complex N-glycans in mammalian and Caenorhabditis elegans development. (7) The crystal structure of N-acetylglucosaminyltransferase I. (8) The discovery of the enzymes which synthesize O-glycan cores 1, 2, 3 and 4 and their elongation.

Serum N-acetylglucosaminyltransferase III activities in hepatocellular carcinoma

N-Acetylglucosaminyltransferase III (GnT III) catalyses the addition of N-acetylglucosamine through a beta 1-4 linkage to the mannose of the trimannosyl core, resulting in conversion of the concanavalin A (Con A)-reactive glycan into a non-reactive state. In this study, we measured GnT III activity to evaluate its diagnostic efficacy and its therapeutic effect on hepatocellular carcinoma (HCC). Concanavalin A-non-reactive fraction of serum transferrin (Tf) was also determined since the sugar chains of Tf are one of the possible candidates for the product of GnT III. Serum samples (159) were used from patients with HCC (89), liver cirrhosis (30), chronic hepatitis (19), alpha-fetoprotein (AFP) producing gastric carcinoma metastatic to the liver (five) and healthy controls (16). N-Acetylglucosaminyltransferase III activity was determined by high performance liquid chromatography. The reactivity of serum Tf to Con A was also analysed in 21 paired HCC samples before and after treatment by crossed immuno-affinoelectrophoresis. N-Acetylglucosaminyltransferase III activity from the HCC group (153 +/- 72pmol/mL/h) was significantly higher than that from liver cirrhosis (99 +/- 67 pmol/mL per h), chronic hepatitis (84 +/- 39 pmol/mL per h) and the normal controls (62 +/- 16 pmol/mL per h). N-Acetylglucosaminyltransferase III activity of 21 patients with HCC was significantly reduced after treatment such as transcatheter arterial chemoembolization and/or percutaneous ethanol infection therapy, (123 +/- 77 to 100 +/- 60 pmol/mL per h). Commensurate decreases of AFP and des-gamma-carboxy prothrombin with GnT III activity were also observed after treatment. The Con A-non-reactive fraction (n = 21; 6.4 +/- 2.3%) in patients with HCC after treatment was significantly lower than before (8.2 +/- 2.4%). The present study suggests that GnT III activity is a possible aid in the diagnosis and evaluation of HCC, especially when other tumour markers are negative.

Bisecting GlcNAc structures act as negative sorting signals for cell surface glycoproteins in forskolin-treated rat hepatoma cells

The bisecting N-acetylglucosamine residue is formed by UDP-N-acetylglucosamine:beta-D-mannoside-beta-1, 4-N-acetylglucosaminyltransferase III (GnT-III), a key branching enzyme for N-glycans. We found that forskolin, an adenylyl cyclase activator, markedly enhanced GnT-III at the transcriptional level in various hepatoma cells and hepatocytes, resulting in an increase of bisecting GlcNAc residues in various glycoproteins, as judged from the lectin binding to erythroagglutinating phytohemagglutinin (E-PHA). In whole cell lysates, the E-PHA binding was increased, and leukoagglutinating phytohemagglutinin (L-PHA) binding was decreased at 12 h after forskolin treatment, by time, both GnT-III activity and mRNA had reached the maximum levels. In contrast, the binding capacity as to E-PHA, determined by fluorescence-activated cell sorting on the cell surface, was decreased, suggesting that bisecting GlcNAc structures in certain glycoproteins changed the expression levels of glycoproteins and decreased their sorting on the cell surface. Fractionated organelles of M31 cells showed that the binding capacity as to E-PHA was mainly localized in Golgi membranes and lysosomes. This was also supported by a fluorescence microscopy. In order to determine whether or not the bisecting GlcNAc residue acts as a sorting signal for glycoproteins, N-oligosaccharide structures of lysosomal-associated membrane glycoprotein 1 and beta-glucuronidase, gamma-glutamyltranspeptidase, and secretory glycoproteins such as ceruloplasmin and alpha-fetoprotein were measured by E-PHA and L-PHA blotting after immunoprecipitation. The expression levels of lysosomal membrane glycoprotein 1 and gamma-glutamyltranspeptidase on the cell surface were decreased at 12 h after forskolin treatment, indicating that the bisecting GlcNAc structure may act as a negative sorting signal for the cell surface glycoproteins and may alter the characteristics of hepatoma cells. This is the first report on glycoprotein sorting related to a specific structure of oligosaccharides, bisecting GlcNAc.

Human N-acetylglucosaminyltransferase III gene is transcribed from multiple promoters

We have isolated cDNA clones for the human N-acetylglucosaminyltransferase III (GlcNAc-transferase III) gene. Two of them, H15 and H20, contain 5' non-coding regions that are totally different from each other except for 8 bp adjacent to the putative initiation codon. Analysis of one of the genomic cosmid clones containing the GlcNAc-transferase III coding region, Hug3, revealed the 5' non-coding regions of H15 and H20 contain two and one exons, respectively, in addition to the exon containing the coding region (exon 1). These have arisen as the result of alternative splicing. The transcription-initiation sites were determined by primer-extension analysis and 5'-rapid amplification of cDNA ends (RACe). Both H15-specific and H20-specific primers gave cDNAs longer than those expected from the lengths of H15 and H20, and a primer complementary to the region around the intron/exon junction near the putative initiation codon also gave distinct signals. Promoter activities of the 5'-flanking regions of H15, H20 and exon 1 were measured in a human hepatoblastoma cell line, HuH-6 cells by luciferase assays. The 5'-flanking region of exon 1 was the most active, whilst that of H15 was several times less active, and that of H20 was inactive. Our study suggests that multiple promoters of the GlcNAc-transferase III gene contribute to the complex regulation of this gene.

Transfection of N-acetylglucosaminyltransferase III gene suppresses expression of hepatitis B virus in a human hepatoma cell line, HB611

beta-D-mannoside beta-1,4-N-acetylglucosaminyltransferase III (GnT-III) catalyzes the addition of N-acetylglucosamine in beta 1-4 linkage to the beta-linked mannose of the trimannosyl core of N-linked oligosaccharides and forms a bisecting GlcNAc structure. Although the biological meaning of the bisecting GlcNAc structure remains unclear, it is known that the attachment of a bisecting GlcNAc inhibits further processing of oligosaccharides by other glycosyltransferases. To investigate whether or not structural changes of oligosaccharides affect secretion and gene expression of hepatitis B virus (HBV), we introduced the GnT-III gene into a human hepatoma cell line, HB611, which secreted HBV-related proteins into the medium. Positive transfectants were cloned by hygromycin resistant selection. Three clones have high activities of GnT-III and secreted lower levels of HBV-related proteins into the medium in comparison with other clones. These clones showed marked suppression of HBV-related mRNAs and an increased binding with E-PHA as judged by lectin blot. Expression of beta actin, alpha fetoprotein, albumin, and prealubmin was not correlated with GnT-III activity in all the seven clones. Treatment of these cells with tunicamycin or swainsonine resulted in enhanced expression of HBV-related mRNA. These results indicate that some glycoproteins whose oligosaccharide structures are changed by over-expression of GnT-III suppress HBV gene expression.

Increased plasma alpha (1 --> 3)-L-fucosyltransferase activities in patients with hepatocellular carcinoma

Alpha (1 --> 3)-L-fucosyltransferase (alpha 1,3FT) activity was determined in plasma of patients with chronic liver diseases, namely, chronic hepatitis (CH), liver cirrhosis (LC) and hepatocellular carcinoma (HCC), The plasma alpha 1,3FT activity was significantly higher (p < 0.01) in chronic liver diseases than that in normal controls. The enzyme activity in plasma of patients with HCC was also significantly higher than that in LC (p < 0.05) or that in CH (p < 0.01). However, no significant difference was observed in the enzyme activity between LC and CH. Plasma alpha 1,3FT activity in patients with HCC was not significantly changed before and after transcatheter arterial embolization. In addition, the enzyme activity in the homogenate of the cirrhotic liver tissue was higher than that in the preparation of the hepatoma tissue in the same patient. These results suggest that the increased plasma alpha 1,3FT activity in patients with HCC reflects mainly the enzyme activity of cirrhotic liver tissue, not that of hepatoma tissue. The significance of the elevated levels of plasma alpha 1,3FT and its decreased hepatoma tissue activity in patients with HCC, compared with that in LC, remains to be clarified.

Synthesis of a di-O-methylated pentasaccharide for use in the assay of N-acetylglucosaminyltransferase III activity

The biantennary oligosaccharide analogue beta-D-Glc pNAc-(1-->2)-alpha-D-Man p-(1-->3)-[beta-D-Glc pNAc-(1-->2)-alpha- D-Man p-(1-->6)]-beta-D-man p-O(CH2)8COOMe (3) is a potential substrate for N-acetylglucosaminyltransferases (GlcNAcTs) III-V which are present in mammalian cells. The di-O-methylated analogue of 3, beta-D-Glc pNAc-(1-->2)-[4-O-methyl-alpha-D-Man p]-(1-->3)-[beta-D-Glc pNAc-(1-->2)-[6-O-methyl-alpha-D-Man p]-(1-->6)]-beta-D-Man p-O-(CH2)8COOMe (5), was prepared by a block synthesis approach involving sequential addition of two O-methylated disaccharide donors to a protected central beta-D-Man residue. The OH groups acted on by GlcNAcT-IV and -V are protected from glycosylation in 5 since they are present as their methyl ethers. Pentasaccharide 5 was found to be an excellent substrate for GlcNAcT-III (EC 2.4.1.144) from rat kidney with Km = 0.15 mM. The product formed by incubation of 5 with a rat kidney extract, in the presence of UDP-GlcNAc, was isolated, structurally characterized by NMR spectroscopy and confirmed to be the expected di-O-methyl hexasaccharide where a beta-D-Glc pNAc residue had been added to OH-4 of the central beta-D-Man p unit.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

The metastatic potential of rat prostate tumor variant R3327-MatLyLu is correlated with an increased activity of N-acetylglucosaminyl transferase III and V

Enzyme activities of N-acetylglucosaminyltransferase (GlcNAc-Tase) I-V involved in N-linked complex-type carbohydrate synthesis were determined in a non-metastatic hormone-dependent rat prostate tumor (R3327-H) and a related, hormone-independent variant metastasizing to lymph nodes and lungs (R3327-MatLyLu). In the metastasizing variant a significantly increased activity of both GlcNAc-Tase III and GlcNAc-Tase V was observed, whereas the activities of GlcNAc-Tase I and II were essentially unchanged. The increase in activity of GlcNAc-Tase III is particularly noteworthy since it indicates that elevated expression of this enzyme cannot be considered as an exclusive marker of hepatic malignancy.

N-glycosylation of serum proteins in disease and its investigation using lectins

The majority of serum proteins are glycosylated. When disease is present, subtle changes occur in this glycosylation. These changes could provide the basis for more sensitive and more discriminative clinical tests. In order to address this possibility, a review is given of serum protein glycosylation in liver disease, inflammation and cancer. It is concluded that liver disease is accompanied by reduced sialylation and increased glycan branching; whereas cancer is accompanied by increased sialylation and increased fucosylation. In inflammation, the type of glycosylation change observed seems to depend upon the disease studied. Glycoprotein analysis can already be used for diagnosis in a few clinical situations; however, further studies are required in most diseases to provide a more detailed picture of the glycosylation changes that are occurring. This situation will change with the increasing availability of simpler techniques for glycoprotein analysis. One such group of techniques are lectin-based methods. The usefulness of these methods for glycoprotein analysis and the suitability for analysing clinical specimens are discussed in detail.

Enzymatic basis of sugar structures of alpha-fetoprotein in hepatoma and hepatoblastoma cell lines: correlation with activities of alpha 1-6 fucosyltransferase and N-acetylglucosaminyltransferases III and V

alpha-Fetoproteins (AFPs) were purified from 2 hepatoma cell lines (Hep G2 and HuH-7) and a hepatoblastoma cell line (HuH-6), and the structures of pyridylaminated (PA) derivatives of their sugar chains were analyzed by HPLC. Simultaneously, the activities of alpha 1-6 fucosyltransferase (alpha 1-6FT) and N-acetylglucosaminyltransferase III (GnT-III), IV (GnT-IV) and V (GnT-V) were assayed in these cell lines. For all 3 cell lines the major sugar chain detected was a fucosylated biantennary structure. Hep G2 cells contained a high level of GnT-V, which catalyzes the formation of a tri'-antennary structure, and in fact a substantial percentage of the AFP sugar chains in these cells had the tri'-antennary structure. alpha 1-6FT was also high, and fucosylated tri' structures were detected, which suggests that high activities of transferases affect the AFP sugar chains. In HuH-6 cells, GnT-III, which catalyzes the formation of bisecting GlcNAc, was elevated. Correspondingly, a fucosylated, bisected biantennary structure was found as a major sugar chain. In the HuH-7 cell line, the contents of bisecting GlcNAc and tri' structure were low and neither GnT-III nor GnT-V was elevated. These data indicate that the sugar structures of AFP in these cell lines correlate well with the activities of alpha 1-6 FT, GnT-III and GnT-V.

Discrimination of liver cirrhosis from chronic hepatitis by analysis of serum cholinesterase isozymes using affinity electrophoresis with concanavalin A or wheat germ agglutinin

Isozymic alteration of serum cholinesterase (ChE) was investigated in patients with chronic liver diseases using affinity electrophoresis with concanavalin A (Con A) or wheat germ agglutinin (WGA). On Con A-containing agarose gel electrophoresis, three bands with enzyme activity (named bands I to III, from the anodic side to the cathodic) were observed in sera of normal controls. Disappearance of band II was observed in 50% (15/30) of cirrhotic patients, but only one of 20 patients with chronic hepatitis lacked band II of the serum ChE isozymes. Meanwhile, WGA-containing agarose gel electrophoresis revealed that normal controls had four ChE isozymes (named bands I to IV from the anodic side to the cathodic). These four isozymes were also observed in patients with chronic hepatitis. However approximately 67% (20/30) of cirrhotic patients lacked band II of ChE isozymes. When these two affinity electrophoreses were used in combination, 22 (73%) of 30 cirrhotic patients had isozymic alteration of their serum ChE on either Con A-containing or WGA-containing agarose gel electrophoresis, or both. Thus, affinity electrophoreses with Con A and WGA seemed to be useful methods in differentiating liver cirrhosis from chronic hepatitis.

Modulation of N-acetylglucosaminyltransferase III, IV and V activities and alteration of the surface oligosaccharide structure of a myeloma cell line by interleukin 6

The activity of N-acetylglucosaminyltransferase (GnT) III, IV and V on a myeloma cell line, OPM-1, was examined after incubation with interleukin 6 (IL-6). While augmenting cell proliferation, IL-6 resulted in a decrease of GnT III activity and an increase of GnT IV and V activities. Consistent with this, OPM-1 cultured with IL-6 showed an increased affinity to Datura stramonium lectin, which recognizes asialo-tri- and asialo-tetraantenary N-linked oligosaccharides. These results indicate that IL-6 modulates glycosyltransferase activity and the oligosaccharide structure of target cells.