High expression of alpha-1-6 fucosyltransferase during rat hepatocarcinogenesis

Metabolic utilization and remodeling of glycan biosynthesis using fucose analogs

BACKGROUND

Fucose (Fuc), a monosaccharide present at the core or the termini of glycans, critically regulates various biological phenomena and is associated with various diseases. Specifically detecting Fuc residues or inhibiting the fucosylation pathway is pivotal in understanding the mechanisms of how fucosylated glycans are related to biological processes and diseases and in developing novel therapeutic agents.

SCOPE OF REVIEW

This review focuses on chemical biology approaches using Fuc analogs developed for metabolically labeling fucosylated glycans or inhibiting the biosynthesis of fucosylated glycans.

MAJOR CONCLUSIONS

Developed Fuc analogs have different potency, specificity and effects on protein and cellular functions. Developing highly enzyme-specific probes and inhibitors is desirable for future investigations.

GENERAL SIGNIFICANCE

Chemical glycobiology approaches using sugar analogs are useful for revealing novel mechanisms of inter-relationships among sugar metabolism pathways and manipulating glycan expression to develop new glycan-targeted therapies.

E-cadherin on epithelial-mesenchymal transition in thyroid cancer

Thyroid carcinoma is a common malignant tumor of endocrine system and head and neck. Recurrence, metastasis and high malignant expression after routine treatment are serious clinical problems, so it is of great significance to explore its mechanism and find action targets. Epithelial-mesenchymal transition (EMT) is associated with tumor malignancy and invasion. One key change in tumour EMT is low expression of E-cadherin. Therefore, this article reviews the expression of E-cadherin in thyroid cancers (TC), discuss the potential mechanisms involved, and outline opportunities to exploit E-cadherin on regulating the occurrence of EMT as a critical factor in cancer therapeutics.

Partial silencing of fucosyltransferase 8 gene expression inhibits proliferation of Ishikawa cells, a cell line of endometrial cancer

Endometrial cancer is the most common gynecologic malignancy and is associated with increased morbidity each year, including young people. However, its mechanisms of proliferation and progression are not fully elucidated. It is well known that abnormal glycosylation is involved in oncogenesis, and fucosylation is one of the most important types of glycosylation. In particular, fucosyltransferase 8 (FUT8) is the only FUT responsible for α1, 6-linked fucosylation (core fucosylation), and it is involved in various physiological as well as pathophysiological processes, including cancer biology. Therefore, we aimed to identify the expression of FUT8 in endometrial endometrioid carcinoma and investigate the effect of the partial silencing of the FUT8 gene on the cell proliferation of Ishikawa cells, an epithelial-like endometrial cancer cell line. Quantitative real-time PCR analysis showed that FUT8 gene expression was significantly elevated in the endometrial endometrioid carcinoma, compared to the normal endometrium. The immunostaining of FUT8 and Ulex europaeus Agglutinin 1 (UEA-1), a kind of lectin family specifically binding to fucose, was detected endometrial endometrioid carcinoma. The proliferation assay showed FUT8 partial knockdown by transfection of siRNA significantly suppressed the proliferation of Ishikawa cells, concomitant with the upregulation in the gene expressions associated with the interesting pathways associated with de-ubiquitination, aspirin trigger, mesenchymal-epithelial transition (MET) et al. It was suggested that the core fucosylation brought about by FUT8 might be involved in the proliferation of endometrial endometrioid carcinoma cells.

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Fucosyltransferase 8 gene expression is elevated in the tissues affected by endometrial endometrioid carcinoma.

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Fucosyltransferase 8 protein is specifically detected in the glands affected by endometrial endometrioid carcinoma.

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Silencing of fucosyltransferase 8 suppressed the proliferation of Ishikawa cells, an endometrial cancer cell line.

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These results suggest that fucosyltransferase 8 might be involved in the proliferation of endometrial endometrioid carcinoma.

Improving Immunotherapy Through Glycodesign

Immunotherapy is revolutionizing health care, with the majority of high impact "drugs" approved in the past decade falling into this category of therapy. Despite considerable success, glycosylation-a key design parameter that ensures safety, optimizes biological response, and influences the pharmacokinetic properties of an immunotherapeutic-has slowed the development of this class of drugs in the past and remains challenging at present. This article describes how optimizing glycosylation through a variety of glycoengineering strategies provides enticing opportunities to not only avoid past pitfalls, but also to substantially improve immunotherapies including antibodies and recombinant proteins, and cell-based therapies. We cover design principles important for early stage pre-clinical development and also discuss how various glycoengineering strategies can augment the biomanufacturing process to ensure the overall effectiveness of immunotherapeutics.

Prognostic role of FUT8 expression in relation to p53 status in stage II and III colorectal cancer

The expression of fucosyltransferase 8, an enzyme responsible for core fucosylation encoded by FUT8, influences tumor biology and correlates with patient prognosis in several solid cancers. We hypothesized that p53 alteration modifies prognostic associations of FUT8 expression in colorectal cancer (CRC), since FUT8 has recently been identified as a direct transcriptional target of wild-type p53. Utilizing multiple datasets of microarray and RNA sequence of CRC, FUT8 mRNA was found to be highly expressed in wild-type p53 tumors (n = 382) compared to those of mutant p53 (n = 437). Prognostic values of FUT8 expression in conjunction with the p53 status for disease-free survival (DFS) were analyzed using two independent cohorts of stage II and III CRC after curative surgery, including the immunohistochemistry (IHC) cohort (n = 123) and the microarray cohort (n = 357). In both cohorts, neither FUT8 expression nor the p53 status was associated with DFS. Strikingly, positive expression of FUT8 protein was significantly associated with better DFS only in tumors with negative p53, while it had no prognostic impact in tumors with positive p53 in the IHC cohort. Although not statistically significant, a similar prognostic trend was observed in the microarray cohort when patients were stratified by the p53 status. Our results suggest that the prognostic values of FUT8 expression on DFS may be modified by the p53 status, and the expression of FUT8 protein can be a prognostic biomarker for patients with stage II and III CRC.

Glycosylation Changes in Brain Cancer

Protein glycosylation is a posttranslational modification that affects more than half of all known proteins. Glycans covalently bound to biomolecules modulate their functions by both direct interactions, such as the recognition of glycan structures by binding partners, and indirect mechanisms that contribute to the control of protein conformation, stability, and turnover. The focus of this Review is the discussion of aberrant glycosylation related to brain cancer. Altered sialylation and fucosylation of N- and O-glycans play a role in the development and progression of brain cancer. Additionally, aberrant O-glycan expression has been implicated in brain cancer. This Review also addresses the clinical potential and applications of aberrant glycosylation for the detection and treatment of brain cancer. The viable roles glycans may play in the development of brain cancer therapeutics are addressed as well as cancer-glycoproteomics and personalized medicine. Glycoprotein alterations are considered as a hallmark of cancer while high expression in body fluids represents an opportunity for cancer assessment.

An Alkynyl-Fucose Halts Hepatoma Cell Migration and Invasion by Inhibiting GDP-Fucose-Synthesizing Enzyme FX, TSTA3

Fucosylation is a glycan modification critically involved in cancer and inflammation. Although potent fucosylation inhibitors are useful for basic and clinical research, only a few inhibitors have been developed. Here, we focus on a fucose analog with an alkyne group, 6-alkynyl-fucose (6-Alk-Fuc), which is used widely as a detection probe for fucosylated glycans, but is also suggested for use as a fucosylation inhibitor. Our glycan analysis using lectin and mass spectrometry demonstrated that 6-Alk-Fuc is a potent and general inhibitor of cellular fucosylation, with much higher potency than the existing inhibitor, 2-fluoro-fucose (2-F-Fuc). The action mechanism was shown to deplete cellular GDP-Fuc, and the direct target of 6-Alk-Fuc is FX (encoded by TSTA3), the bifunctional GDP-Fuc synthase. We also show that 6-Alk-Fuc halts hepatoma invasion. These results highlight the unappreciated role of 6-Alk-Fuc as a fucosylation inhibitor and its potential use for basic and clinical science.

Development of α1,6-fucosyltransferase inhibitors through the diversity-oriented syntheses of GDP-fucose mimics using the coupling between alkyne and sulfonyl azide

We developed α1,6-fucosyltransferase (FUT8) inhibitors through a diversity-oriented synthesis. The coupling reaction between the fucose unit containing alkyne and the guanine unit containing sulfonyl azide under various conditions afforded a series of Guanosine 5'-diphospho-β-l-fucose (GDP-fucose) analogs. The synthesized compounds displayed FUT8 inhibition activity. A docking study revealed that the binding mode of the inhibitor synthesized with FUT8 was similar to that of GDP-fucose.

Inhibiting post-translational core fucosylation prevents vascular calcification in the model of uremia

Vascular calcification (VC) is an independent risk factor for cardiovascular disease and mortality in uremia. Post-translational core fucosylation is implicated in a number of pathological processes. First, we investigated the role of core fucosylation and key TGF-β1 pathway receptors in calcified arteries in vivo. To determine whether blocking core fucosylation effectively inhibited VC and TGF-β/Smad signaling pathway, we established an in vitro model of phosphate-induced calcification in rat vascular smooth muscle cells (VSMCs) to assess the role of core fucosylation in VC. Core fucose could be detected at markedly higher levels in calcified VSMCs than control cells. Fut8 (α-1,6 fucosyltransferase), the only enzyme responsible for core fucosylation in humans, was significantly upregulated by high phosphate. Exposed to high phosphate media and blocking core fucosylation in VSMCs by knocking down Fut8 using a siRNA markedly reduced calcium and phosphorus deposition and Cbfα1 expression (osteoblast-specific transcription factor), and increased α-Sma expression (smooth muscle cell marker). Fut8 siRNA significantly inhibited TGF-β/Smad2/3 signaling activation in VSMCs cultured in high phosphate media. In conclusion, this study provides evidence to suggest core fucosylation plays a major role in the process of VC and appropriate blockade of core fucosylation may represent a potential therapeutic strategy for treating VC in end-stage renal disease.

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

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

Integrated Proteomic and Glycoproteomic Analyses of Prostate Cancer Cells Reveal Glycoprotein Alteration in Protein Abundance and Glycosylation

Prostate cancer is the most common cancer among men in the U.S. and worldwide, and androgen-deprivation therapy remains the principal treatment for patients. Although a majority of patients initially respond to androgen-deprivation therapy, most will eventually develop castration resistance. An increased understanding of the mechanisms that underline the pathogenesis of castration resistance is therefore needed to develop novel therapeutics. LNCaP and PC3 prostate cancer cell lines are models for androgen-dependence and androgen-independence, respectively. Herein, we report the comparative analysis of these two prostate cancer cell lines using integrated global proteomics and glycoproteomics. Global proteome profiling of the cell lines using isobaric tags for relative and absolute quantitation (iTRAQ) labeling and two- dimensional (2D) liquid chromatography-tandem MS (LC-MS/MS) led to the quantification of 8063 proteins. To analyze the glycoproteins, glycosite-containing peptides were isolated from the same iTRAQ-labeled peptides from the cell lines using solid phase extraction followed by LC-MS/MS analysis. Among the 1810 unique N-linked glycosite-containing peptides from 653 identified N-glycoproteins, 176 glycoproteins were observed to be different between the two cell lines. A majority of the altered glycoproteins were also observed with changes in their global protein expression levels. However, alterations in 21 differentially expressed glycoproteins showed no change at the protein abundance level, indicating that the glycosylation site occupancy was different between the two cell lines. To determine the glycosylation heterogeneity at specific glycosylation sites, we further identified and quantified 1145 N-linked glycopeptides with attached glycans in the same iTRAQ-labeled samples. These intact glycopeptides contained 67 glycan compositions and showed increased fucosylation in PC3 cells in several of the examined glycosylation sites. The increase in fucosylation could be caused by the detected changes in enzymes belonging to the glycan biosynthesis pathways of protein fucosylation observed in our proteomic analysis. The altered protein fucosylation forms have great potential in aiding our understanding of castration resistance and may lead to the development of novel therapeutic approaches and specific detection strategies for prostate cancer.

Rapid analysis of cell surface N-glycosylation from living cells using mass spectrometry

Cell surfaces are covered with a dense carbohydrate layer referred to as the glycocalyx. Because different cell types express different glycan signatures, it is of paramount importance to have robust methods to analyze the glycome of living cells. To achieve this, a common procedure involves cell lysis and extraction of membrane (glyco)proteins and yields a major proportion of high-mannose N-glycans that most likely stem from intracellular proteins derived from the ER. Using HEK 293 cells as a model system, we developed a reproducible, sensitive, and fast method to profile surface N-glycosylation from living cells. We directly released glycopeptides from cell surfaces through tryptic digestion of freshly harvested and vital cells, thereby improving the detection and quantification of complex-type N-glycans by increasing their relative amount from 14 to 85%. It was also possible to detect 25 additional structures in HEK 293, 48 in AGE1.HN, 42 in CHO-K1, and 51 in Hep G2 cells. The additional signals provided deeper insight into cell-type-specific N-glycan features such as antennarity, fucosylation, and sialylation. Thus, this protocol, which can potentially be applied to any cells, will be useful in the fields of glycobiotechnology and biomarker discovery.

Strategy integrating stepped fragmentation and glycan diagnostic ion-based spectrum refinement for the identification of core fucosylated glycoproteome using mass spectrometry

Core fucosylation (CF) is a special glycosylation pattern of proteins that has a strong relationship with cancer. The Food and Drug Administration (FDA) has approved the core fucosylated α-fetoprotein as a biomarker for the early diagnosis of hepatocellular carcinoma (HCC). The technology for identifying core fucosylated proteins has significant practical value. The major method for core fucosylated glycoprotein/glycopeptide analysis is neutral loss-based MS(3) scanning under collision-induced dissociation (CID) by ion trap mass spectrometry. However, due to the limited speed and low resolution of the MS(3) scan mode, it is difficult to achieve high-throughput, with only dozens of core fucosylated proteins identified in a single run. In this work, we developed a novel strategy for the identification of CF glycopeptides at a large scale, integrating the stepped fragmentation function, one novel feature of quadrupole-orbitrap mass spectrometry, with "glycan diagnostic ion"-based spectrum optimization. By using stepped fragmentation, we were able to obtain both highly accurate glycan and peptide information of a simplified CF glycopeptide in one spectrum. Moreover, the spectrum could be recorded with the same high speed as the conventional MS(2) scan. By using the "glycan diagnostic ion"-based spectrum refinement method, the efficiency of the CF glycopeptide discovery was significantly improved. We demonstrated the feasibility and reproducibility of our method by analyzing CF glycoproteomes of mouse liver tissue and HeLa cell samples spiked with standard CF glycoprotein. In total, 1364 and 856 CF glycopeptides belonging to 702 and 449 CF glycoproteins were identified, respectively, within a 78-min gradient analysis, which was approximately a 7-fold increase in the identification efficiency of CF glycopeptides compared to the currently used method. In this work, we took core fucosylated glycopeptides as a practical example to demonstrate the great potential of our novel method for use in glycoproteome analysis, and we also anticipate using the flexible novel method in other research fields.

Donor assists acceptor binding and catalysis of human α1,6-fucosyltransferase

α1,6-Core-fucosyltransferase (FUT8) is a vital enzyme in mammalian physiological and pathophysiological processes such as tumorigenesis and progress of, among others, non-small cell lung cancer and colon carcinoma. It was also shown that therapeutic antibodies have a dramatically higher efficacy if the α1,6-fucosyl residue is absent. However, specific and potent inhibitors for FUT8 and related enzymes are lacking. Hence, it is crucial to elucidate the structural basis of acceptor binding and the catalytic mechanism. We present here the first structural model of FUT8 in complex with its acceptor and donor molecules. An unusually large acceptor, i.e., a hexasaccharide from the core of N-glycans, is required as minimal structure. Acceptor substrate binding of FUT8 is being dissected experimentally by STD NMR and SPR and theoretically by molecular dynamics simulations. The acceptor binding site forms an unusually large and shallow binding site. Binding of the acceptor to the enzyme is much faster and stronger if the donor is present. This is due to strong hydrogen bonding between O6 of the proximal N-acetylglucosamine and an oxygen atom of the β-phosphate of GDP-fucose. Therefore, we propose an ordered Bi Bi mechanism for FUT8 where the donor molecule binds first. No specific amino acid is present that could act as base during catalysis. Our results indicate a donor-assisted mechanism, where an oxygen of the β-phosphate deprotonates the acceptor. Knowledge of the mechanism of FUT8 is now being used for rational design of targeted inhibitors to address metastasis and prognosis of carcinomas.

Expression of alpha 1,6-fucosyltransferase 8 in hepatitis B virus-related hepatocellular carcinoma influences tumour progression

BACKGROUND

Alpha 1,6-fucosyltransferase 8 expression was demonstrated to be enhanced during hepatocarcinogenesis.

AIMS

Our study aimed to find out the clinical significance and biological function of alpha 1,6-fucosyltransferase 8 in hepatitis B virus-related hepatocellular carcinoma.

METHODS

Alpha 1,6-fucosyltransferase 8 expression levels were determined in 52 pairs of tissues to compare its expression between tumour tissues [with/without portal vein tumour thrombus] and adjacent noncancerous liver tissues. Relationship between alpha 1,6-fucosyltransferase 8 expression and clinical indicators was also investigated. An alpha 1,6-fucosyltransferase 8-knockdown (by RNAi) cell line MHCC97-H/siFUT8 was established to reveal functional impact of alpha 1,6-fucosyltransferase 8 on cell growth, migration and invasion in hepatocellular carcinoma, respectively using Cell Counting Kit-8, wound healing migration assay, transwell assay and gelatin zymography.

RESULTS

We observed a higher alpha 1,6-fucosyltransferase 8 expression level in tumour tissues than adjacent noncancerous liver tissues. In portal vein tumour thrombus group, alpha 1,6-fucosyltransferase 8 protein expressed more in portal vein tumour thrombus tissues than that in adjacent noncancerous liver tissues. The expression level in tumour tissues was highly correlated with tumour size and presence of satellite nodules (P<0.05). Furthermore, alpha 1,6-fucosyltransferase 8-knockdown suppressed the tumour proliferation, migration and invasion of MHCC97-H cells.

CONCLUSION

These findings suggest that alpha 1,6-fucosyltransferase 8 expression might be a good indicator of poor prognosis in hepatocellular carcinoma. High alpha 1,6-fucosyltransferase 8 expression may play an important role in hepatitis B virus-related hepatocellular carcinoma progression.

Donor substrate binding and enzymatic mechanism of human core α1,6-fucosyltransferase (FUT8)

BACKGROUND

Fucosylation is essential for various biological processes including tumorigenesis, inflammation, cell-cell recognition and host-pathogen interactions. Biosynthesis of fucosylated glycans is accomplished by fucosyltransferases. The enzymatic product of core α1,6-fucosyltransferase (FUT8) plays a major role in a plethora of pathological conditions, e.g. in prognosis of hepatocellular carcinoma and in colon cancer. Detailed knowledge of the binding mode of its substrates is required for the design of molecules that can modulate the activity of the enzyme.

METHODS

We provide a detailed description of binding interactions of human FUT8 with its natural donor substrate GDP-fucose and related compounds. GDP-Fuc was placed in FUT8 by structural analogy to the structure of protein-O-fucosyltransferase (cePOFUT) co-crystallized with GDP-Fuc. The epitope of the donor substrate bound to FUT8 was determined by STD NMR. The in silico model is further supported by experimental data from SPR binding assays. The complex was optimized by molecular dynamics simulations.

RESULTS

Guanine is specifically recognized by His363 and Asp453. Furthermore, the pyrophosphate is tightly bound via numerous hydrogen bonds and contributes affinity to a major part. Arg365 was found to bind both the β-phosphate and the fucose moiety at the same time.

CONCLUSIONS

Discovery of a novel structural analogy between cePOFUT and FUT8 allows the placement of the donor substrate GDP-Fuc. The positioning was confirmed by various experimental and computational techniques.

GENERAL SIGNIFICANCE

The model illustrates details of the molecular basis of substrate recognition for a human fucosyltransferase for the first time and, thus, provides a basis for structure-based design of inhibitors.

Increased levels of tetra-antennary N-linked glycan but not core fucosylation are associated with hepatocellular carcinoma tissue

BACKGROUND

Alterations in glycosylation have long been associated with the development of cancer. In the case of primary hepatocellular carcinoma (HCC), one alteration that has often been associated is increased amounts of fucose attached to the N-glycans of serum proteins secreted by the liver.

METHODS

In an effort to determine the origin of this increased fucosylation, we have conducted N-linked glycan analysis of HCC tissue, the surrounding nontumor tissue, and compared this to tissue from a nondiseased adult liver.

RESULTS

Surprisingly, no difference in the level of fucosylation was observed from the three donor groups, suggesting that the increased levels of fucosylation observed in serum of those with HCC is not the result of increased synthesis of fucosylated proteins in the cancer tissue. On the other hand, increased levels of a tetra-antennary glycan were observed in the HCC tissue as compared with the surrounding tissue or to the nondiseased livers.

CONCLUSIONS

This represents, to our knowledge, one of the first reports associating increased levels of branching with the development of HCC.

IMPACT

The identification of increased levels of tetra-antennary glycan on liver tumor tissue, as opposed to adjacent or nondiseased tissue may lead to improved detection of HCC.

Fragmentation and site-specific quantification of core fucosylated glycoprotein by multiple reaction monitoring-mass spectrometry

Glycosylation modifications of proteins have been attracting increasing attention due to their roles in the physiological and pathological processes of the cell. Core fucosylation (CF), one special type of glycan structure in glycoproteins, has been linked with tumorigenesis. The study of protein glycosylation has been hindered by the technical challenges caused by the microheterogeneity of glycan modifications. In commonly used methods, sugar chains on the peptide were released using endoglycosidase, and the glycan and peptides were analyzed separately with mass spectrometry. Although mass spectrometric analysis can be performed easily in this way, an increase in false positives when assigning glycosites was inevitable. Our earlier research demonstrated a strategy combining Endo F3-catalyzed partial deglycosylation with MS(3) (MS/MS/MS) scanning triggered by the neutral loss of a fucose to precisely identify CF proteins on a large scale. In this research, fragmentations of partially deglycosylated glycopeptides were studied using a triple quadrupole mass spectrometer, and a quantification method that coupled our published identification strategy with multiple reaction monitoring-mass spectrometry (MRM-MS) analysis was developed to obtain site-specific quantification information of core fucosylated peptides. To illustrate the feasibility of the quantification method, the CF peptides of target proteins in clinical serum were quantified and compared as a preliminary demonstration.

Aberrant glycosylation associated with enzymes as cancer biomarkers

BACKGROUND

One of the new roles for enzymes in personalized medicine builds on a rational approach to cancer biomarker discovery using enzyme-associated aberrant glycosylation. A hallmark of cancer, aberrant glycosylation is associated with differential expressions of enzymes such as glycosyltransferase and glycosidases. The aberrant expressions of the enzymes in turn cause cancer cells to produce glycoproteins with specific cancer-associated aberrations in glycan structures.

CONTENT

In this review we provide examples of cancer biomarker discovery using aberrant glycosylation in three areas. First, changes in glycosylation machinery such as glycosyltransferases/glycosidases could be used as cancer biomarkers. Second, most of the clinically useful cancer biomarkers are glycoproteins. Discovery of specific cancer-associated aberrations in glycan structures of these existing biomarkers could improve their cancer specificity, such as the discovery of AFP-L3, fucosylated glycoforms of AFP. Third, cancer-associated aberrations in glycan structures provide a compelling rationale for discovering new biomarkers using glycomic and glycoproteomic technologies.

SUMMARY

As a hallmark of cancer, aberrant glycosylation allows for the rational design of biomarker discovery efforts. But more important, we need to translate these biomarkers from discovery to clinical diagnostics using good strategies, such as the lessons learned from translating the biomarkers discovered using proteomic technologies to OVA 1, the first FDA-cleared In Vitro Diagnostic Multivariate Index Assay (IVDMIA). These lessons, providing important guidance in current efforts in biomarker discovery and translation, are applicable to the discovery of aberrant glycosylation associated with enzymes as cancer biomarkers as well.

Glycomic analyses of glycoproteins in bile and serum during rat hepatocarcinogenesis

Fucosylated alpha-fetoprotein (AFP) is a specific tumor marker for hepatocellular carcinomas (HCC). However, the mechanisms underlying the increase in fucosylated AFP in serum of patients with HCC are largely unknown. Recently, we reported that fucosylation is a possible signal for the secretion of glycoproteins into bile in the liver. This finding might lead to the selective secretion of fucosylated AFP into bile and the selective secretion might be disrupted in hepatocarcinogenesis. In this study, therefore, we analyzed the oligosaccharide structures of glycoproteins in bile and serum of LEC rats, which are a rat model of spontaneous hepatocarcinogenesis. Lectin microarraying showed enhanced binding of 13 lectins to bile, compared with in serum from normal LEC rats, and the binding of these lectins to serum of LEC rats bearing HCC was higher than in normal rats. Structural analyses involving HPLC and mass spectrometry showed that the fucosylation levels of serum glycoproteins were not increased in CH rats but were in HCC rats, although the fucosylation levels of biliary glycoproteins were increased in both CH and HCC rats. These results suggested that the sorting machinery through fucosylation might be disrupted in the liver with HCC.

Fucosylation and gastrointestinal cancer

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

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

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

Glycoproteomic profiling of serum peptides in canine lymphoma and transitional cell carcinoma

Differential expression of fucosylated glycoproteins has been correlated with malignancy and metastatic potential in various types of neoplasia. Utilizing glycoproteomics techniques, changes in fucosylated serum peptides associated with naturally occurring canine lymphoma and transitional cell carcinoma (TCC) have been evaluated. In both types of neoplasia, the majority of the fucosylated peptides that changed increased with the cancer. In one lymphoma case that was examined over the course of the disease, the same fucosylated peptides that increased during pre-chemotherapy decreased during post-chemotherapy, and then subsequently increased upon recurrence of the lymphoma. When comparing all the fucosylated peptides that increased in both types of cancer, there were only two peptides in common allowing discrimination between lymphoma and TCC based on their peptide profiles. These results emphasize the prospect of glycopeptide profiling in proteomics for use in discovering a panel of non-invasive, diagnostic or prognostic biomarkers of cancer.

A high expression of GDP-fucose transporter in hepatocellular carcinoma is a key factor for increases in fucosylation

Changes in the levels of fucosylation regulate the biological phenotype of cancer cells and a specific fucosylation, such as fucosylated alpha-fetoprotein (AFP-L3) has been clinically used as a tumor marker for hepatocellular carcinoma (HCC). However, detailed molecular mechanisms that explain the increased fucosylation in HCC remain unknown despite 10 years of study by these researchers. Fucosylation is regulated by complicated mechanisms that involve several factors: fucosyltransferases, GDP-fucose transporter (GDP-Fuc Tr), and synthetic enzymes of GDP-fucose, such as GDP-mannose 4, 6-dehydratase (GMD), GDP-4-keto-6-deoxy-mannose-3, 5-epimerase-4-reductase (FX), and GDP-fucose pyrophosphorylase. In this study, the expression of fucosylation-related genes in HCC tissues was studied and it was found that GDP-Fuc Tr is a key factor for increases in fucosylation. A real-time reverse transcription polymerase chain reaction (RT-PCR) analysis showed significant increases in GDP-Fuc Tr and FX expression in HCC, and levels of the GMD protein were upregulated by posttranslational modification in HCC tissues. In vitro cell experiments showed that the level of GDP-Fuc Tr was the most significantly correlated with the level of cellular fucosylation and the overexpression of GDP-Fuc Tr dramatically increased fucosylation in Hep3B cells. The importance of GDP-Fuc Tr in the increase of fucosylation was also confirmed with immunohistochemical analyses. These findings suggest that the upregulation of GDP-Fuc Tr plays a pivotal role in increased fucosylation in HCC and represents an attractive target for new treatments and diagnosis for HCC.

The alpha-L-fucosidase from Sulfolobus solfataricus

Glycoside hydrolases form hyperthermophilic archaea are interesting model systems for the study of catalysis at high temperatures and, at the moment, their detailed enzymological characterization is the only approach to define their role in vivo. Family 29 of glycoside hydrolases classification groups alpha-L-fucosidases involved in a variety of biological events in Bacteria and Eukarya. In Archaea the first alpha-L-fucosidase was identified in Sulfolobus solfataricus as interrupted gene expressed by programmed -1 frameshifting. In this review, we describe the identification of the catalytic residues of the archaeal enzyme, by means of the chemical rescue strategy. The intrinsic stability of the hyperthermophilic enzyme allowed the use of this method, which resulted of general applicability for beta and alpha glycoside hydrolases. In addition, the presence in the active site of the archaeal enzyme of a triad of catalytic residues is a rather uncommon feature among the glycoside hydrolases and suggested that in family 29 slightly different catalytic machineries coexist.

Fucosylation in prokaryotes and eukaryotes

Fucosylated carbohydrate structures are involved in a variety of biological and pathological processes in eukaryotic organisms including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and tumor metastasis. In contrast, fucosylation appears less common in prokaryotic organisms and has been suggested to be involved in molecular mimicry, adhesion, colonization, and modulating the host immune response. Fucosyltransferases (FucTs), present in both eukaryotic and prokaryotic organisms, are the enzymes responsible for the catalysis of fucose transfer from donor guanosine-diphosphate fucose to various acceptor molecules including oligosaccharides, glycoproteins, and glycolipids. To date, several subfamilies of mammalian FucTs have been well characterized; these enzymes are therefore delineated and used as models. Non-mammalian FucTs that possess different domain construction or display distinctive acceptor substrate specificity are highlighted. It is noteworthy that the glycoconjugates from plants and schistosomes contain some unusual fucose linkages, suggesting the presence of novel FucT subfamilies as yet to be characterized. Despite the very low sequence homology, striking functional similarity is exhibited between mammalian and Helicobacter pylori alpha1,3/4 FucTs, implying that these enzymes likely share a conserved mechanistic and structural basis for fucose transfer; such conserved functional features might also exist when comparing other FucT subfamilies from different origins. Fucosyltranferases are promising tools used in synthesis of fucosylated oligosaccharides and glycoconjugates, which show great potential in the treatment of infectious and inflammatory diseases and tumor metastasis.

The effect of dissolved oxygen on the production and the glycosylation profile of recombinant human erythropoietin produced from CHO cells

Human recombinant erythropoietin (rHuEPO) was produced from Chinese hamster ovary (CHO) cells transfected with the human EPO gene. The cells were grown in batch cultures in controlled bioreactors in which the set-points for dissolved oxygen varied between 3% and 200%. The cell-specific growth rate and final cell yield was significantly lower under hyperoxic conditions (200% DO). However, there was no significant difference in growth rates at other oxygen levels compared to control cultures run under a normoxic condition (50% DO). The specific productivity of EPO was significantly lower at a DO set-point of 3% and 200% but maintained a consistently high value between 10% to 100% DO. The EPO produced under all conditions as analyzed by two-dimensional electrophoresis showed a molecular weight range of 33 to 37 kDa and a low isoelectric point range of 3.5 to 5.0. This corresponds to a highly glycosylated and sialylated protein with a profile showing at least seven distinct isoforms. The glycan pattern of isolated samples of EPO was analyzed by weak anion exchange (WAX) HPLC and by normal-phase HPLC incorporating sequential digestion with exoglycosidase arrays. Assigned structures were confirmed by mass spectrometry (MALDI-MS). The most prominent glycan structures were core fucosylated tetranntenary with variable sialylation. However, significant biantennary, triantennary, and non-fucosylated glycans were also identified. Detailed analysis of these glycan structures produced under variable dissolved oxygen levels did not show consistently significant variations except for the ratio of fucosylated to non-fucosylated isoforms. Maximum core fucosylation (80%) was observed at 50% and 100% DO, whereas higher or lower DO levels resulted in reduced fucosylation. This observation of lower fucosylation at high or low DO levels is consistent with previous data reported for glycoprotein production in insect cells.

Optimisation of the cellular metabolism of glycosylation for recombinant proteins produced by Mammalian cell systems

Many biopharmaceuticals are now produced as secreted glycoproteins from mammalian cell culture. The glycosylation profile of these proteins is essential to ensure structural stability and biological and clinical activity. However, the ability to control the glycosylation is limited by our understanding of the parameters that affect the heterogeneity of added glycan structures. It is clear that the glycosylation process is affected by a number of factors including the 3-dimensional structure of the protein, the enzyme repertoire of the host cell, the transit time in the Golgi and the availability of intracellular sugar-nucleotide donors. From a process development perspective there are many culture parameters that can be controlled to enable a consistent glycosylation profile to emerge from each batch culture. A further, but more difficult goal is to control the culture conditions to enable the enrichment of specific glycoforms identified with desirable biological activities. The purpose of this paper is to discuss the cellular metabolism associated with protein glycosylation and review the attempts to manipulate, control or engineer this metabolism to allow the expression of human glycosylation profiles in producer lines such as genetically engineered Chinese hamster ovary (CHO) cells.

Reactive oxygen species modify oligosaccharides of glycoproteins in vivo: a study of a spontaneous acute hepatitis model rat (LEC rat)

The Long-Evans Cinnamon (LEC) rat, an animal model of Wilson's disease, spontaneously develops hepatitis as the result of abnormal copper accumulation in liver. The findings of this study show that copper, hydrogen peroxide, and lipid peroxides accumulate to drastically high levels in LEC rat serum in acute hepatitis but not chronic hepatitis. The effect of these reactive oxygen species (ROS) on oligosaccharides of glycoproteins in the LEC rat serum was examined. Lectin blot and lectin ELISA analyses showed that sialic acid and galactose residues of serum glycoproteins including transferrin were decreased in acute hepatitis. Further analyses of oligosaccharide structures of transferrin demonstrated that di-sialylated and asialo-agalacto biantennary sugar chains, but not tri-sialylated sugar chain, exist on transferrin in the acute hepatitis rats. In addition, treatment of non-hepatitis rat serum with copper ions and hydrogen peroxide decreased tri-sialylated sugar chain of the normal transferrin and increased di-sialylated and asialo-agalacto biantennary sugar chains. This is the first evidence to show that ROS result in the cleavage of oligosaccharides of glycoproteins in vivo, and indicate this cleavage of oligosaccharides may contribute the development of acute hepatitis.

Reaction mechanism and substrate specificity for nucleotide sugar of mammalian alpha1,6-fucosyltransferase--a large-scale preparation and characterization of recombinant human FUT8

FUT8, mammalian alpha1,6-fucosyltransferase, catalyzes the transfer of a fucose residue from the donor substrate, guanosine 5'-diphosphate (GDP)-beta-L-fucose, to the reducing terminal GlcNAc of the core structure of asparagine-linked oligosaccharide via an alpha1,6-linkage. FUT8 is a typical type II membrane protein, which is localized in the Golgi apparatus. We have previously shown that two neighboring arginine residues that are conserved among alpha1,2-, alpha1,6-, and protein O-fucosyltransferases play an important role in donor substrate binding. However, details of the catalytic and reaction mechanisms and the ternary structure of FUT8 are not understood except for the substrate specificity of the acceptor. To develop a better understanding of FUT8, we established a large-scale production system for recombinant human FUT8, in which the enzyme is produced in soluble form by baculovirus-infected insect cells. Kinetic analyses and inhibition studies using derivatives of GDP-beta-L-fucose revealed that FUT8 catalyzes the reaction which depends on a rapid equilibrium random mechanism and strongly recognizes the base portion and diphosphoryl group of GDP-beta-L-fucose. These results may also be applicable to other fucosyltransferases and glycosyltransferases.

Core fucosylation of N-linked glycans in leukocyte adhesion deficiency/congenital disorder of glycosylation IIc fibroblasts

Leukocyte adhesion deficiency/congenital disorder of glycosylation IIc (LAD II/CDG IIc) is a genetic disease characterized by a decreased expression of fucose in glycoconjugates, resulting in leukocyte adhesion deficiency and severe morphological and neurological abnormalities. The biochemical defect is a reduced transport of guanosine diphosphate-L-fucose (GDP-L-fucose) from cytosol into the Golgi compartment, which reduces its availability as substrate for fucosyltransferases. The aim of this study was to determine the effects of a limited supply of GDP-L-fucose inside the Golgi on core fucosylation (alpha1,6-fucose linked to core N-acetylglucosamine [GlcNAc]) of N-linked glycans in LAD II fibroblasts. The results showed that, although [3H]fucose incorporation was generally reduced in LAD II cells, core fucosylation was affected to a greater extent compared with other types of fucosylation of N-linked oligosaccharides. In particular, core fucosylation was found to be nearly absent in biantennary negatively charged oligosaccharides, whereas other types of structures, in particular triantennary neutral species, were less affected by the reduction. Expression and activity of alpha1,6-fucosyltransferase (FUT8) in control and LAD II fibroblasts were comparable, thus excluding the possibility of a decreased activity of the transferase. The data obtained confirm that the concentration of GDP-L-fucose inside the Golgi can differentially affect the various types of fucosylation in vivo and also indicate that core fucosylation is not dependent only on the availability of GDP-L-fucose, but it is significantly influenced by the type of oligosaccharide structure. The relevant reduction in core fucosylation observed in some species of oligosaccharides could also provide clues for the identification of glycans involved in the severe developmental abnormalities observed in LAD II.

Establishment ofFUT8 knockout Chinese hamster ovary cells: An ideal host cell line for producing completely defucosylated antibodies with enhanced antibody-dependent cellular cytotoxicity

To generate industrially applicable new host cell lines for antibody production with optimizing antibody-dependent cellular cytotoxicity (ADCC) we disrupted both FUT8 alleles in a Chinese hamster ovary (CHO)/DG44 cell line by sequential homologous recombination. FUT8 encodes an alpha-1,6-fucosyltransferase that catalyzes the transfer of fucose from GDP-fucose to N-acetylglucosamine (GlcNAc) in an alpha-1,6 linkage. FUT8(-/-) cell lines have morphology and growth kinetics similar to those of the parent, and produce completely defucosylated recombinant antibodies. FUT8(-/-)-produced chimeric anti-CD20 IgG1 shows the same level of antigen-binding activity and complement-dependent cytotoxicity (CDC) as the FUT8(+/+)-produced, comparable antibody, Rituxan. In contrast, FUT8(-/-)-produced anti-CD20 IgG1 strongly binds to human Fcgamma-receptor IIIa (FcgammaRIIIa) and dramatically enhances ADCC to approximately 100-fold that of Rituxan. Our results demonstrate that FUT8(-/-) cells are ideal host cell lines to stably produce completely defucosylated high-ADCC antibodies with fixed quality and efficacy for therapeutic use.

Identification of an archaeal alpha-L-fucosidase encoded by an interrupted gene. Production of a functional enzyme by mutations mimicking programmed -1 frameshifting

The analysis of the complete genome of the thermoacidophilic Archaeon Sulfolobus solfataricus revealed two open reading frames (ORF), named SSO11867 and SSO3060, interrupted by a -1 frameshift and encoding for the N- and the C-terminal fragments, respectively, of an alpha-l-fucosidase. We report here that these ORFs are actively transcribed in vivo, and we confirm the presence of the -1 frameshift between them at the cDNA level, explaining why we could not find alpha-fucosidase activity in S. solfataricus extracts. Detailed analysis of the region of overlap between the two ORFs revealed the presence of the consensus sequence for a programmed -1 frameshifting. Two specific mutations, mimicking this regulative frameshifting event, allow the expression, in Escherichia coli, of a fully active thermophilic and thermostable alpha-l-fucosidase (EC ) with micromolar substrate specificity and showing transfucosylating activity. The analysis of the fucosylated products of this enzyme allows, for the first time, assigning a retaining reaction mechanism to family 29 of glycosyl hydrolases. The presence of an alpha-fucosidase putatively regulated by programmed -1 frameshifting is intriguing both with respect to the regulation of gene expression and, in post-genomic era, for the definition of gene function in Archaea.

Neutrophils promote the release of alpha-6-fucosyltransferase from blood platelets through the action of cathepsin G and elastase

Human blood platelets release alpha-6-fucosyltransferase during coagulation of blood or after stimulation with thrombin or other agonists that cause platelet activation (Antoniewicz et al., FEBS Lett. 244 (1989) 388-390). However, in the absence of neutrophils the thrombin-stimulated platelets release only a small fraction of alpha-6-fucosyltransferase activity (Kościelak et al., Acta Biochim. Polon. 42 (1995) 35-40). We show that the effect of neutrophils is reproduced by cathepsin G or (less efficiently) by elastase, the two enzymes that are released by neutrophils during coagulation of blood. We have also localized alpha-6-fucosyltransferase to membrane and alpha-granule fractions of platelets that had been disrupted by nitrogen cavitation. It is concluded that thrombin-activated neutrophils release cathepsin G and elastase that promote degranulation of platelets and hence the secretion of alpha-6-fucosyltransferase.

alpha1,6fucosyltransferase is highly and specifically expressed in human ovarian serous adenocarcinomas

An elevated level of alpha1,6fucosylation in N-glycans represents one of the cancer-related alterations of oligosaccharides and is associated with the metastatic potential of hepatoma cells. However, expression of alpha1,6fucosyltransferase (alpha1,6FucT), which is involved in this aberrant glycosylation, has not been intensively explored in other malignant tumors. We report on a study of the expression of alpha1,6FucT in various types of epithelial ovarian carcinoma tissue, as well as normal ovary, benign and borderline ovarian tumors. The activity assay showed that alpha1,6FucT is highly and specifically elevated in serous adenocarcinomas but not in normal and other ovarian tumor tissues. This elevation was due to enhancement of mRNA expression, as evidenced by Northern blot analysis. Furthermore, we have shown immunohistochemically that alpha1,6FucT expression is localized predominantly in cancer cells. Lectin blot analysis using Lens culinaris agglutinin, which preferentially recognizes alpha1,6fucose residue, suggested that several glycoproteins were likely targets for modification by alpha1, 6fucosylation in serous adenocarcinoma tissues. These findings suggest that the elevated expression of alpha1,6FucT and the resulting modification of N-glycans are distinctive features of this type of ovarian cancer and may be related to the progression of this malignancy.

Ancestral exonic organization of FUT8, the gene encoding the alpha6-fucosyltransferase, reveals successive peptide domains which suggest a particular three-dimensional core structure for the alpha6-fucosyltransferase family

Based on PCR strategies and expression studies, we define the genomic organization of the FUT8b gene. This gene encodes the only known mammalian enzyme transferring fucose in an alpha1-->6 linkage on the asparagine-branched GlcNAc residue of the chitobiose unit of complex N:-glycans. The intron/exon organization of the bovine coding sequence determines five successive functional domains. The first exon encodes a domain homologous to cytoskeleton proteins, the second presents a proline-rich region including a motif XPXPPYXP similar to the peptide ligand of the SH3-domain proteins, the third encodes a gyrase-like domain (an enzyme which can bind nucleotides), and the fourth encodes a peptide sequence homologous to the catalytic domain of proteins transferring sugars. Finally, the last exon encodes a domain homologous to the SH3 conserved motif of the SH2-SH3 protein family. This organization suggests that intramolecular interactions might give a tulip-shaped scaffolding, including the catalytic pocket of the enzyme in the Golgi lumen. Deduced from the published sequence of chromosome 14 (AL109847), the human gene organization of FUT8 seems to be similar to that of bovine FUT8b, although the exon partition is more pronounced (bovine exons 1 and 2 correspond to human exons 1-6). The mosaicism and phylogenetic positions of the alpha6-fucosyltransferase genes are compared with those of other fucosyltransferase genes.

Glycoproteins and their relationship to human disease

Glycoproteins are proteins that carry N- and O-glycosidically-linked carbohydrate chains of complex structures and functions. N-glycan chains are assembled in the endoplasmic reticulum and the Golgi by a controlled sequence of glycosyltransferase and glycosidase processing reactions involving dolichol intermediates. The assembly of O-glycans occurs in the Golgi and does not involve dolichol. For most reactions, families of glycosyltransferases exist; the expression of the individual enzymes within a family is often subject to complex regulation. The biosynthesis of N- and O-glycan is controlled at the level of gene expression, mRNA, enzyme protein activity and localization, and through substrate and cofactor concentrations at the site of synthesis. This complex regulation results in many hundreds of structures, the range of which varies in different species, cell types, tissue types, states of development and differentiation. In diseased cells, the relative proportions of these structures are often characteristically different from normal, and may be useful for the assessment of the stage of the disease and for diagnosis. Knowledge of disease-specific glycoprotein structures and their functions may be used therapeutically, in immunotherapy, in blocking cell adhesion or interfering with other binding or biological processes. Recently, some of the mechanisms underlying glycoprotein alterations in disease have been elucidated. This opens the possibility of an active interference in the disease process. The functions of glycans in diseased cells will become more clear with the tools of molecular biology and transgenic animal models.

Occurence of GDP-L-fucose: beta-N-acetylglucosamine (Fuc to asn-linked GlcNAc) alpha 1,6-fucosyltransferases in porcine, sheep, bovine, rabbit and chicken tissues

Transgenic animals are a promising source of pharmaceutically-relevant proteins or as a source of organs for xenotransplantation. Beside other posttranslational modifications, glycosylation has been shown to be a critical parameter for the correct function of several glycoproteins. To analyse the contribution of alpha 1,6-fucosylation to N-glycan variability, we partly purified alpha 1,6-fucosyltransferase (alpha 1,6-Fuc-T) activities from various tissues (brain, lung, heart, liver) of agriculturally-relevant animals (porcine, sheep, bovine, rabbit, chicken) and compared some of their biochemical properties. All tissues displayed alpha1,6-Fuc-T activity, although at different levels. No differences were observed in their stability against chemicals, temperature or time, whereas the activities were distinguishable by their pH-optima and their cation preferences. Similarities were found for tissues between species. Lung and heart enzymes showed a narrow pH-optimum around pH 6.0 and an enhanced activity in the presence of divalent cations. alpha 1,6-Fuc-T activities in brain and liver were characterised by a broad pH-optimum from 5.5 to 8.0. Some activities of these tissues were decreased by the addition of EDTA, while others did not show any influence of EDTA or divalent cations. From the significant differences of the alpha 1,6-Fuc-T activities in the tissues, it is possible to hypothesise the presence of more than one single alpha 1, 6-Fuc-T in mammalian tissues.

The alpha1-6-fucosyltransferase gene and its biological significance

GDP-L-Fuc:N-acetyl-beta-D-glucosaminide alpha1-6-fucosyltransferase (alpha1-6FucT) catalyzes the transfer of fucose from GDP-Fuc to N-linked type complex glycoproteins. This enzyme was purified from a human fibroblast cell line, porcine brain, a human gastric cancer cell line and human blood platelets. cDNA cloning of porcine and human alpha1-6FucT was performed from a porcine brain and gastric cancer cell cDNA libraries, respectively. Their homology is 92.2% at the nucleotide level and 95.7% at the amino acid level. No putative N-glycosylation sites were found in the predicted amino acid sequence. No homology to other fucosyltransferases such as alpha1-2FucT, alpha1-3FucT and alpha1-4FucT was found except for a region consisting of nine amino acids. The alpha1-6FucT gene is located at chromosome 14q24.3, which is also a different location from other fucosyltransferases reported to date. The alpha1-6FucT gene is the oldest gene family in the phylogenic trees among the nine cloned fucosyltransferase genes. alpha1-6FucT is widely expressed in various rat tissues and the expression of alpha1-6FucT in the liver is enhanced during hepatocarcinogenesis of LEC rats which develop hereditary hepatitis and hepatomas. In cases of human liver diseases, alpha1-6FucT is expressed in both hepatoma tissues and their surrounding tissues with chronic liver disease, but not in the case of normal liver. Serum alpha1-6-fucosylated alpha-fetoprotein (AFP) has been employed for an early diagnosis of patients with hepatoma. The mechanisms by which alpha1-6 fucosylation of AFP occurs in the hepatoma is not due to the up-regulation of alpha1-6FucT alone. Interestingly, when the alpha1-6FucT gene is transfected into Hep3B, a human hepatoma cell line, tumor formation in the liver of nude mice after splenic injection is dramatically suppressed. In this review, we focus on alpha1-6FucT and summarize its properties, gene expression and biological significance.

Fucose in N-glycans: from plant to man

Fucosylated oligosaccharides occur throughout nature and many of them play a variety of roles in biology, especially in a number of recognition processes. As reviewed here, much of the recent emphasis in the study of the oligosaccharides in mammals has been on their potential medical importance, particularly in inflammation and cancer. Indeed, changes in fucosylation patterns due to different levels of expression of various fucosyltransferases can be used for diagnoses of some diseases and monitoring the success of therapies. In contrast, there are generally at present only limited data on fucosylation in non-mammalian organisms. Here, the state of current knowledge on the fucosylation abilities of plants, insects, snails, lower eukaryotes and prokaryotes will be summarised.

Gene expression of alpha1-6 fucosyltransferase in human hepatoma tissues: a possible implication for increased fucosylation of alpha-fetoprotein

The 1-6 fucosylated -fetoprotein (AFP) present in serum of patients with hepatocellular carcinoma (HCC) has been employed for the differential clinical diagnosis of HCC from chronic liver diseases. The molecular mechanism by which this alteration occurs, however, remains largely unknown. To address this issue, we purified GDP-L-Fuc:N-acetyl-beta-D-glucosaminide 1-6 fucosyltransferase (1-6 FucT), an enzyme involved in the 1-6 fucosylation of N-glycans from porcine brain, as well as from a human gastric cancer cell line, and cloned their genes. In this study, levels of 1-6 FucT mRNA expression and the activity of this enzyme for 12 human HCC tissues were examined and compared with that in surrounding tissues and normal livers. The mean +/- SD for 1-6 FucT activity was 78 +/- 41 pmol/h/mg in normal control liver, 202 +/- 127 pmol/h/mg in adjacent uninvolved liver tissues (chronic hepatitis: 181 +/- 106 pmol/h/mg; liver cirrhosis: 233 +/- 164 pmol/h/mg), and 195 +/- 72 pmol/h/mg in HCC tissues. The mRNA expression of 1-6 FucT was also enhanced in proportion to enzymatic activity except for a few cases, suggesting that 1-6 FucT expression is increased in chronic liver diseases, especially liver cirrhosis. Transfection of 1-6 FucT gene into cultured rat hepatocytes markedly increased 1-6 FucT activity and led to an increase in lens culinaris agglutinin (LCA) binding proteins in both cell lysates and condition media. When the 1-6 FucT gene was transfected into a human HCC cell line, Hep3B, which originally showed low levels of 1-6 FucT expression, 1-6-fucosylated AFP was dramatically increased in the condition media. Collectively, these results suggest that the enhancement of 1-6 FucT expression increased the fucosylation of several proteins, including AFP, and that the level of 1-6-fucosylated AFP in patients with HCC was in part caused by up-regulation of the 1-6 FucT gene expression.