A novel beta1,3-N-acetylglucosaminyltransferase involved in invasion of cancer cells as assayed in vitro

B3GNT7 regulates mucin O-glycosylation to alleviate colonic inflammation

BACKGROUND

B3GNT7, a glycosyltransferase of significant importance that is highly expressed in intestinal epithelial cells, plays a pivotal role in intestinal physiological processes. This study elucidates novel insights into the potential role and underlying mechanisms of B3GNT7 in ulcerative colitis (UC).

METHODS

An experimental colitis model was induced using DSS in mice to investigate B3GNT7 expression in the colon via transcriptomics and immunohistochemistry. Bioinformatics analysis was employed to delineate the biological functions of B3GNT7. Additionally, the correlation between the transcription levels of B3GNT7 in colonic tissues from patients with UC, sourced from the IBDMDB database, and the severity of colonic inflammation was analyzed to elucidate potential mechanisms.

RESULTS

The DSS-induced colitis model was successfully established, and transcriptomic analysis identified a marked downregulation of B3GNT7 expression in the colonic tissues compared to the controls. Functional enrichment analysis indicated B3GNT7's predominant role in mucin O-glycosylation. Protein interaction analysis revealed that B3GNT7 predominantly interacts with members of the mucin MUC family, including MUC2, MUC3, and MUC6. In patients with UC, B3GNT7 transcription levels were significantly reduced, particularly in those with moderate to severe disease activity. The expression level of B3GNT7 exhibited a negative correlation with the endoscopic severity of UC. Gene set enrichment analysis (GSEA) further demonstrated significant enrichment of B3GNT7 in the mucin O-glycosylation synthesis pathway.

CONCLUSION

The downregulation of B3GNT7 expression in the colonic tissues of UC patients may contribute to the compromised mucin barrier function and the exacerbation of colitis.

Beta3Gn-T7 Is a Keratan Sulfate β1,3 N-Acetylglucosaminyltransferase in the Adult Brain

Keratan sulfate (KS) glycan is covalently attached to a core protein of proteoglycans. KS is abundant in neuropils and presents densely in close proximity to the perineuronal region of the perineuronal net-positive neurons in the adult brain under physiological conditions. We previously showed that the synthesis of KS positive for the R-10G antibody in the adult brain is mediated by GlcNAc-6-sulfotransferase 3 (GlcNAc6ST3; encoded by Chst5). Deficiency in both GlcNAc6ST3 and GlcNAc6ST1, encoded by Chst2, completely abolished KS. Protein-tyrosine phosphatase receptor type z1 (Ptprz1)/phosphacan was identified as a KS scaffold. KS requires the extension of GlcNAc by β1,3 N-acetylglucosaminyltransferase (Beta3Gn-T). Members of the Beta3Gn-T family involved in the synthesis of adult brain KS have not been identified. In this study, we show by a method of gene targeting that Beta3Gn-T7, encoded by B3gnt7, is a major Beta3Gn-T for the synthesis of KS in neuropils and the perineuronal region in the adult brain. Intriguingly, the B3gnt7 gene is selectively expressed in oligodendrocyte precursor cells (OPCs) and oligodendrocytes similar to that of GlcNAc6ST3. These results indicate that Beta3Gn-T7 in oligodendrocyte lineage cells may play a role in the formation of neuropils and perineuronal nets in the adult brain through the synthesis of R-10G-positive KS-modified proteoglycan.

Interleukin-22 regulates B3GNT7 expression to induce fucosylation of glycoproteins in intestinal epithelial cells

Interleukin (IL)-22 is a cytokine that plays a critical role in intestinal epithelial homeostasis. Its downstream functions are mediated through interaction with the heterodimeric IL-22 receptor and subsequent activation of signal transducer and activator of transcription 3 (STAT3). IL-22 signaling can induce transcription of genes necessary for intestinal epithelial cell proliferation, tissue regeneration, tight junction fortification, and antimicrobial production. Recent studies have also implicated IL-22 signaling in the regulation of intestinal epithelial fucosylation in mice. However, whether IL-22 regulates intestinal fucosylation in human intestinal epithelial cells and the molecular mechanisms that govern this process are unknown. Here, in experiments performed in human cell lines and human-derived enteroids, we show that IL-22 signaling regulates expression of the B3GNT7 transcript, which encodes a β1-3-N-acetylglucosaminyltransferase that can participate in the synthesis of poly-N-acetyllactosamine (polyLacNAc) chains. Additionally, we find that IL-22 signaling regulates levels of the α1-3-fucosylated Lewis X (Lex) blood group antigen, and that this glycan epitope is primarily displayed on O-glycosylated intestinal epithelial glycoproteins. Moreover, we show that increased expression of B3GNT7 alone is sufficient to promote increased display of Lex-decorated carbohydrate glycan structures primarily on O-glycosylated intestinal epithelial glycoproteins. Together, these data identify B3GNT7 as an intermediary in IL-22-dependent induction of fucosylation of glycoproteins and uncover a novel role for B3GNT7 in intestinal glycosylation.

Construction and investigation of β3GNT2-associated regulatory network in esophageal carcinoma

Background

Glycosyltransferases play a crucial role in various cancers. β1, 3-N-acetylglucosaminyltransferase 2, a polylactosamine synthase, is an important member of the glycosyltransferase family. However, the biological function and regulatory mechanism of β3GNT2 in esophageal carcinoma (ESCA) is still poorly understood.

Methods

The Cancer Genome Atlas and Genotype-Tissue Expression databases were used for gene expression and prognosis analysis. Quantitative real-time PCR, Western blot, and immunohistochemistry were performed to detect the expression of β3GNT2 in ESCA cell lines and tissues. In vitro assays and xenograft tumor models were utilized to evaluate the impact of β3GNT2 on ESCA progression. The downstream effectors and upstream regulators of β3GNT2 were predicted by online software and verified by functional experiments.

Results

We found that β3GNT2 was highly expressed in ESCA tissues and positively correlated with poor prognosis in ESCA patients. β3GNT2 expression was closely associated with the tumor size, TNM stage, and overall survival of ESCA patients. Functionally, β3GNT2 promoted ESCA cell growth, migration, and invasion in vitro, as well as tumorigenesis in vivo. Mechanistically, β3GNT2 knockdown decreased the expression of the polylactosamine on EGFR. Knockdown of β3GNT2 also inhibited the JAK/STAT signaling pathway. Meanwhile, the JAK/STAT inhibitor could partly reverse the biological effects caused by β3GNT2 overexpression. Moreover, β3GNT2 expression was positively regulated by CREB1 and negatively regulated by miR-133b. Both CREB1 and miR-133b was involved in the β3GNT2-mediated ESCA progression.

Conclusions

Our study, for the first time, reveals the importance of β3GNT2 in ESCA progression and offers a potential therapeutic target for ESCA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s11658-022-00306-y.

A Continuous Battle for Host-Derived Glycans Between a Mucus Specialist and a Glycan Generalist in vitro and in vivo

The human gastrointestinal tract is colonized by a diverse microbial community, which plays a crucial role in human health. In the gut, a protective mucus layer that consists of glycan structures separates the bacteria from the host epithelial cells. These host-derived glycans are utilized by bacteria that have adapted to this specific compound in the gastrointestinal tract. Our study investigated the close interaction between two distinct gut microbiota members known to use mucus glycans, the generalist Bacteroides thetaiotaomicron and the specialist Akkermansia muciniphila in vitro and in vivo. The in vitro study, in which mucin was the only nutrient source, indicated that B. thetaiotaomicron significantly upregulated genes coding for Glycoside Hydrolases (GHs) and mucin degradation activity when cultured in the presence of A. muciniphila. Furthermore, B. thetaiotaomicron significantly upregulated the expression of a gene encoding for membrane attack complex/perforin (MACPF) domain in co-culture. The transcriptome analysis also indicated that A. muciniphila was less affected by the environmental changes and was able to sustain its abundance in the presence of B. thetaiotaomicron while increasing the expression of LPS core biosynthesis activity encoding genes (O-antigen ligase, Lipid A and Glycosyl transferases) as well as ABC transporters. Using germ-free mice colonized with B. thetaiotaomicron and/or A. muciniphila, we observed a more general glycan degrading profile in B. thetaiotaomicron while the expression profile of A. muciniphila was not significantly affected when colonizing together, indicating that two different nutritional niches were established in mice gut. Thus, our results indicate that a mucin degrading generalist adapts to its changing environment, depending on available carbohydrates while a mucin degrading specialist adapts by coping with competing microorganism through upregulation of defense related genes.

Comparison of human poly-N-acetyl-lactosamine synthase structure with GT-A fold glycosyltransferases supports a modular assembly of catalytic subsites

Poly-N-acetyl-lactosamine (poly-LacNAc) structures are composed of repeating [-Galβ(1,4)-GlcNAcβ(1,3)-]n glycan extensions. They are found on both N- and O-glycoproteins and glycolipids and play an important role in development, immune function, and human disease. The majority of mammalian poly-LacNAc is synthesized by the alternating iterative action of β1,3-N-acetylglucosaminyltransferase 2 (B3GNT2) and β1,4-galactosyltransferases. B3GNT2 is in the largest mammalian glycosyltransferase family, GT31, but little is known about the structure, substrate recognition, or catalysis by family members. Here we report the structures of human B3GNT2 in complex with UDP:Mg2+ and in complex with both UDP:Mg2+ and a glycan acceptor, lacto-N-neotetraose. The B3GNT2 structure conserves the GT-A fold and the DxD motif that coordinates a Mg2+ ion for binding the UDP-GlcNAc sugar donor. The acceptor complex shows interactions with only the terminal Galβ(1,4)-GlcNAcβ(1,3)- disaccharide unit, which likely explains the specificity for both N- and O-glycan acceptors. Modeling of the UDP-GlcNAc donor supports a direct displacement inverting catalytic mechanism. Comparative structural analysis indicates that nucleotide sugar donors for GT-A fold glycosyltransferases bind in similar positions and conformations without conserving interacting residues, even for enzymes that use the same donor substrate. In contrast, the B3GNT2 acceptor binding site is consistent with prior models suggesting that the evolution of acceptor specificity involves loops inserted into the stable GT-A fold. These observations support the hypothesis that GT-A fold glycosyltransferases employ coevolving donor, acceptor, and catalytic subsite modules as templates to achieve the complex diversity of glycan linkages in biological systems.

A phylogenetic view and functional annotation of the animal β1,3-glycosyltransferases of the GT31 CAZy family

The formation of β1,3-linkages on animal glycoconjugates is catalyzed by a subset of β1,3-glycosyltransferases grouped in the Carbohydrate-Active enZYmes family glycosyltransferase-31 (GT31). This family represents an extremely diverse set of β1,3-N-acetylglucosaminyltransferases [B3GNTs and Fringe β1,3-N-acetylglucosaminyltransferases], β1,3-N-acetylgalactosaminyltransferases (B3GALNTs), β1,3-galactosyltransferases [B3GALTs and core 1 β1,3-galactosyltransferases (C1GALTs)], β1,3-glucosyltransferase (B3GLCT) and β1,3-glucuronyl acid transferases (B3GLCATs or CHs). The mammalian enzymes were particularly well studied and shown to use a large variety of sugar donors and acceptor substrates leading to the formation of β1,3-linkages in various glycosylation pathways. In contrast, there are only a few studies related to other metazoan and lower vertebrates GT31 enzymes and the evolutionary relationships of these divergent sequences remain obscure. In this study, we used bioinformatics approaches to identify more than 920 of putative GT31 sequences in Metazoa, Fungi and Choanoflagellata revealing their deep ancestry. Sequence-based analysis shed light on conserved motifs and structural features that are signatures of all the GT31. We leverage pieces of evidence from gene structure, phylogenetic and sequence-based analyses to identify two major subgroups of GT31 named Fringe-related and B3GALT-related and demonstrate the existence of 10 orthologue groups in the Urmetazoa, the hypothetical last common ancestor of all animals. Finally, synteny and paralogy analysis unveiled the existence of 30 subfamilies in vertebrates, among which 5 are new and were named C1GALT2, C1GALT3, B3GALT8, B3GNT10 and B3GNT11. Altogether, these various approaches enabled us to propose the first comprehensive analysis of the metazoan GT31 disentangling their evolutionary relationships.

Role of keratan sulfate expression in human pancreatic cancer malignancy

Keratan sulfate (KS) is a sulfated linear polymer of N-acetyllactosamine. Proteoglycans carrying keratan sulfate epitopes were majorly observed in cornea, cartilage and brain; and mainly involved in embryonic development, cornea transparency, and wound healing process. Recently, expression of KS in cancer has been shown to be highly associated with advanced tumor grade and poor prognosis. Therefore, we aimed to identify the expression of KS epitope in human pancreatic cancer primary and metastatic tumor lesions. Immunohistochemical analysis of KS expression was performed on primary pancreatic tumors and metastatic tissues. We observed an increased expression of KS epitope on primary tumor tissues compared to uninvolved normal and tumor stroma; and is associated with worse overall survival. Moreover, lung metastatic tumors show a higher-level expression of KS compared to primary tumors. Interestingly, KS biosynthesis specific glycosyltransferases expression was differentially regulated in metastatic pancreatic tumors. Taken together, these results indicate that aberrant expression of KS is predictive of pancreatic cancer progression and metastasis and may serve as a novel prognostic biomarker for pancreatic cancer.

The expression of keratan sulfate reveals a unique subset of microglia in the mouse hippocampus after pilocarpine-induced status epileptics

Induction of keratan sulfate in microglia has been found in several animal models of neurological disorders. However, the significance of keratan sulfate-expressing microglia is not fully understood. To address this issue, we analyzed the characteristics of microglia labeled by the 5D4 epitope, a marker of high-sulfated keratan sulfate, in the mouse hippocampus during the latent period after pilocarpine-induced status epilepticus (SE). Only 5D4-negative (5D4^- ) microglia were found in the CA1 region of vehicle-treated controls and pilocarpine-treated mice at 1 day after SE onset. A few 5D4⁺ microglia appeared in the strata oriens and radiatum at 5 days post-SE, and they were distributed into the stratum pyramidale at 14 days post-SE. The expressions of genes related to both anti- and pro-inflammatory cytokines were higher in 5D4⁺ cells than in 5D4^- cells at 5 but not 14 days post-SE. The expressions of genes related to phagocytosis were higher in 5D4⁺ cells than in 5D4^- cells throughout the latent period. The phagocytic activity of microglia, as measured by engulfment of the zymosan bioparticles, was higher in 5D4⁺ cells than in 5D4^- cells. The contact ratios between excitatory synaptic boutons and microglia were also higher in 5D4⁺ cells than in 5D4^- cells at 5 and 14 days post-SE. The excitatory/inhibitory ratios of synaptic boutons within the microglial domain were lower in 5D4⁺ cells than in 5D4^- cells at 14 days post-SE. Our findings indicate that 5D4⁺ microglia may play some role in epileptogenesis via pruning of excitatory synapses during the latent period after SE.

Identification of novel biomarkers associated with poor patient outcomes in invasive breast carcinoma

Breast carcinoma (BC) corresponds to 23 % of all cancers in women, with 1.38 million new cases and 460,000 deaths worldwide annually. Despite the significant advances in the identification of molecular markers and different modalities of treatment for primary BC, the ability to predict its metastatic behavior is still limited. The purpose of this study was to identify novel molecular markers associated with distinct clinical outcomes in a Brazilian cohort of BC patients. We generated global gene expression profiles using tumor samples from 24 patients with invasive ductal BC who were followed for at least 5 years, including a group of 15 patients with favorable outcomes and another with nine patients who developed metastasis. We identified a set of 58 differentially expressed genes (p ≤ 0.01) between the two groups. The prognostic value of this metastasis signature was corroborated by its ability to stratify independent BC patient datasets according to disease-free survival and overall survival. The upregulation of B3GNT7, PPM1D, TNKS2, PHB, and GTSE1 in patients with poor outcomes was confirmed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) in an independent sample of patients with BC (47 with good outcomes and eight that presented metastasis). The expression of BCL2-associated agonist of cell death (BAD) protein was determined in 1276 BC tissue samples by immunohistochemistry and was consistent with the reduced BAD mRNA expression levels in metastatic cases, as observed in the oligoarray data. These findings point to novel prognostic markers that can distinguish breast carcinomas with metastatic potential from those with favorable outcomes.

Differential expression patterns of N-acetylglucosaminyl transferases and polylactosamines in uterine lesions

Polylactosamine (polyLacNAc) is a fundamental structure in glycoconjugates and it is expressed in specific cells/tissues associated with the development and carcinogenesis. β1,3-N-acetylglucosaminyl transferases ((β3GnTs) play an important role in polyLacNAc synthesis, however the roles of these glycosyltransferases and their products in cancer progression are still unclear. In this sense, this work aimed to evaluate differential expression pattern of the N-acetylglucosaminyl transferases and polylactosamines in invasive and premalignant lesions of the uterus cervix. The expression of β3GnT2 and β3GnT3 were evaluated in normal (n=10) and uterine cervix lesions (n=120), both malignant [squamous carcinoma (SC)] and premalignant [cervical intraepithelial neoplasia (CIN), grades 1, 2 and 3] using immunohistochemistry. Besides, lectin histochemistry with Phytolacca americana lectin (PWM) and Wheat germ agglutinin (WGA) was also carried out to observe the presence of polyLacNAc chains and N-acetylglucosamine (GlcNAc), respectively. The β3GnT3 was expressed in almost all samples (99%) and β3GnT2 was higher expressed in disease samples mainly in CIN 3, when compared with normal (P=0.002), CIN 1 (P=0.009) and CIN 2 (P=0.03). The expression of polyLacNAc was higher is SC samples, when compared with normal (P=0.03), CIN 1 (P=0.02) and CIN 3 (P=0.004), and was observed only nuclear expression in nearly 50% of the SC samples, showing a statistically significant when compared with normal (P=0.01), CIN 1 (P=0.002), CIN 2 (P=0.007) and CIN 3 (P=0.04). Deferring from transferases and polyLacNAc chains, GlcNAc (WGA ligand) reveals a gradual staining pattern decrease with the increase of the lesion degree, being more expressed in CIN 1 lesions when compared with normal (P<0.0001), CIN 2 (P<0.0001), SC (P<0.0001) and CIN 3 (P=0.0003). Our data reveal that β3GnT2 and polyLacNAc may be involved in the progression of the pre-malignant lesions of the human uterine cervix. In addition, polyLacNAc expression only in the nucleus can be associated a poor prognostic in uterine lesions.

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

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

B3GNT3 expression suppresses cell migration and invasion and predicts favorable outcomes in neuroblastoma

Aberrant expression of the simple mucin-type carbohydrate antigens such as T, Tn, sialyl-T and sialyl-Tn is associated with poor prognosis in several cancers. β1,3-N-acetylglucosaminyltransferase-3 (B3GNT3), a member of the β3GlcNAcT family, is responsible for forming extended core 1 (T antigen) oligosaccharides. The role of B3GNT3, which is expressed in various tissues including human fetal brain, in regulating neuroblastoma (NB) formation and cell behaviors remains unclear. Here, we showed that increased B3GNT3 expression evaluated using immunohistochemistry in NB tumor tissues correlated well with the histological grade of differentiation as well as a favorable Shimada's subset of pathology. Univariate and multivariate analyses revealed that positive B3GNT3 expression in tumor tissues predicted a favorable prognosis in NB patients independent of other prognostic markers. B3GNT3 overexpression suppresses T antigen formation and malignant phenotypes including migration and invasion of SK-N-SH cells, whereas B3GNT3 knockdown enhances these phenotypes of SK-N-SH cells. Moreover, B3GNT3 expression decreased phosphorylation of focal adhesion kinase (FAK), Src, paxillin, Akt and ERK1/2. We conclude that B3GNT3 predicts a favorable cancer behavior of NB and suppresses malignant phenotypes by modulating mucin-type O-glycosylation and signaling in NB cells.

S100A7 promotes the migration and invasion of osteosarcoma cells via the receptor for advanced glycation end products

Osteosarcoma is the most common malignant tumor of bone in childhood and adolescence. Despite intensive research for new therapies, the outcome in patients with metastasis remains extremely poor. S100 proteins are involved in the proliferation, cell cycle progression and metastasis of numerous malignant tumors, including osteosarcoma. In the present study, we identified S100A7 as a candidate to promote the migration of osteosarcoma cells. S100A7 promoted the migration and invasion of osteosarcoma cells as assayed in vitro. An in vitro pull-down assay revealed the binding of the recombinant S100A7 protein with its putative receptor, the receptor for advanced glycation end products (RAGE). The downregulation of RAGE by a specific siRNA markedly suppressed the migration and invasion of osteosarcoma cells. Furthermore, the matrix metalloproteinase activity of osteosarcoma cells was enhanced by S100A7 and suppressed by the downregulation of RAGE. These results indicate that S100A7 promotes the migration and invasion of osteosarcoma cells through RAGE. The S100A7-RAGE axis may thus be a new target for preventing the invasion and/or metastasis of osteosarcoma.

Transcription of HERV-E and HERV-E-related sequences in malignant and non-malignant human haematopoietic cells

Infection of a human T-cell leukaemia cell line (HSB-2) with HHV-6 led to the induction of exosome-like-particles attached to newly formed HHV-6 enveloped particles and to amplification of a 1642 bp molecule consisting of a partial human endogenous retrovirus (HERV)-E polymerase gene and repetitive sequences. We initiated an analysis of transcriptional patterns of predicted genes from HERV-E sequences in normal and malignant haematopoietic cells. Transcription patterns of regions corresponding to gag, pol and env genes at different chromosomal loci varied among cell types tested. Several specific transcripts were only observed in malignant haematopoietic cells and transcriptional activity varied among different malignant cell types. A transcript of 7.1 kb spanning the complete gag, pol and env gene region, originating from chromosome 8p23, was identified in normal peripheral blood cells and cells of the chronic myeloid leukaemia cell line K562. Our study describes new active HERV-E sequences and new loci throughout the human genome.

Enzymes responsible for synthesis of corneal keratan sulfate glycosaminoglycans

Keratan sulfate glycosaminoglycans are among the most abundant carbohydrate components of the cornea and are suggested to play an important role in maintaining corneal extracellular matrix structure. Keratan sulfate carbohydrate chains consist of repeating N-acetyllactosamine disaccharides with sulfation on the 6-O positions of N-acetylglucosamine and galactose. Despite its importance for corneal function, the biosynthetic pathway of the carbohydrate chain and particularly the elongation steps are poorly understood. Here we analyzed enzymatic activity of two glycosyltransferases, beta1,3-N-acetylglucosaminyltansferase-7 (beta3GnT7) and beta1,4-galactosyltransferase-4 (beta4GalT4), in the production of keratan sulfate carbohydrate in vitro. These glycosyltransferases produced only short, elongated carbohydrates when they were reacted with substrate in the absence of a carbohydrate sulfotransferase; however, they produced extended GlcNAc-sulfated poly-N-acetyllactosamine structures with more than four repeats of the GlcNAc-sulfated N-acetyllactosamine unit in the presence of corneal N-acetylglucosamine 6-O sulfotransferase (CGn6ST). Moreover, we detected production of highly sulfated keratan sulfate by a two-step reaction in vitro with a mixture of beta3GnT7/beta4GalT4/CGn6ST followed by keratan sulfate galactose 6-O sulfotransferase treatment. We also observed that production of highly sulfated keratan sulfate in cultured human corneal epithelial cells was dramatically reduced when expression of beta3GnT7 or beta4GalT4 was suppressed by small interfering RNAs, indicating that these glycosyltransferases are responsible for elongation of the keratan sulfate carbohydrate backbone.

Comprehensive Enzymatic Characterization of Glycosyltransferases with a β3GT or β4GT Motif

Bioinformatics is a very powerful tool in the field of glycoproteomics, as well as genomics and proteomics. The bioinformatics technique accelerates the comprehensive identification and in silico cloning of human glycogenes containing glycosyltransferases, glycolytic enzymes, sugar-nucleotide synthetases, sugar-nucleotide transporters, and so forth. Glycosyltransferase genes play central roles in carbohydrate chain biosynthesis and have been analyzed for their biological functions. At present, over 180 human glycosyltransferases were identified, cloned, and expressed in various expression systems to detect the activity for carbohydrate synthesis. The recombinant proteins for glycosyltransferase were successfully identified for their enzyme activities and substrate specificities. Their substrate specificities were determined using various donor substrates and acceptors. This section reviews the functions, substrate specificities, and enzymatic reactions of glycosyltransferases such as beta1,3-glycosyltransferase family and beta1,4-glycosyltransferase family.

Characterization of a novel galactose beta1,3-N-acetylglucosaminyltransferase (beta3Gn-T8): the complex formation of beta3Gn-T2 and beta3Gn-T8 enhances enzymatic activity

We characterized a novel member of the beta1,3-N-acetylglucosaminyltransferase (beta3Gn-T) gene family, beta3Gn-T8. A recombinant soluble form of beta3Gn-T8 was expressed in Pichia pastoris (P. pastoris), and its substrate specificity was compared with that of beta3Gn-T2. The two enzymes had similar substrate specificities and recognized tetraantennary N-glycans and 2,6-branched triantennary glycans in preference to 2,4-branched triantennary glycans, biantennary glycans, and lacto-N-neotetraose (LNnT), indicating their specificity for 2,6-branched structures such as [Galbeta1-->4GlcNAcbeta1-->2(Galbeta1-->4GlcNAcbeta1-->6)Manalpha1--> 6Man]. Interestingly, when soluble recombinant beta3Gn-T2 and beta3Gn-T8 were mixed, the Vmax/Km value of the mixture was 9.3- and 160-fold higher than those of individual beta3Gn-T2 and -T8, respectively. Sephacryl S-300 gel filtration of the enzymes revealed that apparent molecular weights of each beta3Gn-T2, beta3Gn-T8, and the mixture were 90-160, 45-65, and 110-210 kDa, respectively, suggesting that beta3Gn-T2 and -T8 can form a complex with enhanced enzymatic activity. This is the first report demonstrating that in vitro mixed glycosyltransferases show enhanced enzymatic activity through the formation of a heterocomplex. These results suggested that beta3Gn-T8 and beta3Gn-T2 are cooperatively involved in the elongation of specific branch structures of multiantennary N-glycans.

Characterization of a cDNA encoding a protein with limited similarity to beta1, 3-N-acetylglucosaminyltransferase

Glycosyltransferases constitute a large group of enzymes that are involved in a wide range of functions in all living organisms. By large-scale sequencing analysis of a human fetal brain cDNA library, we isolated a novel human putative glycosyltransferase gene named beta3GnTL1. Its cDNA is 1372 base pair in length, encoding a predicted protein with 361 amino acid residues. The human beta3GnTL1 is located to chromosome 17q25.3 by comparison of its cDNA with human gemome database. RT-PCR result shows the beta3GnTL1 is expressed at various levels in most of tissues examined.

The effects of N-glycosylation sites and the N-terminal region on the biological function of β1,3-N-acetylglucosaminyltransferase 2 and its secretion

Human beta1,3-N-acetylglucosaminyltransferase 2 (beta3GnT2) is thought to be an enzyme that extends the polylactosamine acceptor chains, but its function and structure analysis are unknown. To obtain insight into the structure of beta3GnT2, the effects of N-glycosylation on its biological function were evaluated using the addition of inhibitors, site-directed mutagenesis of potential N-glycosylation sites, and deletion of its N-terminal region using a fusion protein with GFP(uv) in a baculovirus expression system. Four of five potential N-glycosylation sites were found to be occupied, and their biological function and secretion were inhibited with the treatment of N-glycosylation inhibitor, tunicamycin. The N-glycosylation at Asn219 was necessary for the beta3GnT activity; moreover, N-glycosylation at Asn127 and Asn219 was critical for efficient protein secretion. When Ser221 was replaced with Thr, fusion protein was expressed as a single band, indicating that the double band of the expressed fusion protein was due to the heterogeneity of the glycosylation at Asn219. The truncated protein consisting of amino acids 82-397 (GFP(uv)-beta3GnT2Delta83), which lacked both one N-glycosylation site at Asn79 and the stem region of glycosyltransferase, was expressed as only a small form and showed no beta3GnT activity. These results suggest that the N-glycosylation site at Asn219, which is conserved throughout the beta1,3-glycosyltransferase family, is indispensable not only with regard to its biological function, but also to its secretion. The N-terminal region, which belongs to a stem region of glycosyltransferase, might also be important to the active protein structure.

Improvement of GFPuv-beta 3GnT2 fusion protein production by suppressing protease in baculovirus expression system

The effects of protease inhibitors on the production of recombinant protein were investigated using a recombinant baculovirus containing GFPuv-human beta 1,3-N-acetylglucosaminyltransferase 2 (beta 3GnT2) connected to the prepromelittin signal sequence. The addition of leupeptin as a cysteine protease inhibitor at 2.5 microg/ml improved intra- and extracellular beta 3GnT activities 5- and 3-fold, respectively, compared to those without addition, which was due to a suppression of protease activity. With the leupeptin addition only four degraded molecular bands lower than 32 kDa appeared, but 9 degraded molecular bands between 29 kDa and 41 kDa existed without addition. In contrast, pepstatin A as a carboxyl protease inhibitor had no influence on the improvement of beta 3GnT production, judging from SDS-PAGE. Moreover, when 50 microM carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132), known as a proteasome inhibitor, was used in combination with the leupeptin, a ladder of low molecular mass bands of fusion protein was diminished. The intracellular beta 3GnT activity increased 9-fold, to as high as that without addition of two kinds of protease, but the extracellular activity was not different from that with the addition of only leupeptin. These findings indicate that the decrease in cell viability causes the decrease in the secretion rate of intracellular fusion protein, resulting the accumulation of the full-length of fusion protein.

Analysis of gene expression profiles of hepatocellular carcinomas with regard to 18F-fluorodeoxyglucose uptake pattern on positron emission tomography

PURPOSE

18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET) scan has been found to reflect tumour aggressiveness and prognosis in various types of cancer. In this study, the gene expression profiles of hepatocellular carcinomas (HCCs) were evaluated to determine whether HCCs with high 18F-FDG uptake have more aggressive biological potential than those with low uptake.

METHODS

Surgical specimens were obtained from ten patients with HCC (six males and four females, age range 38-68 years). The tumour samples were divided into two groups based on the 18F-FDG PET scan findings: high 18F-FDG uptake (n=4) and low 18F-FDG uptake (n=6).

RESULTS

The pathological tumour grade was closely correlated with the 18F-FDG uptake pattern: HCCs with high 18F-FDG uptake were pathologically Edmondson-Steiner grade III, while those with low uptake were either grade II or grade II with a focal area of grade III. The total RNA was extracted from the frozen tissues of all HCCs (n=10) and adjacent non-cancerous tissue (n=7). The gene expression profiles were evaluated using an oligoDNA microarray. The HCCs with high 18F-FDG uptake showed increased expression of 11 genes--including vascular cell adhesion molecule-1, vinexin beta and core 1 UDP-galactose:N-acetylgalactosamine-alpha-R-beta 1,3-galactosyltransferase and the natural killer cell inhibitory receptor--compared to those with low uptake (p<0.005). Nine genes, including regulator of mitotic spindle assembly 1, grb2-related adaptor protein and beta-1,3-n-acetylglucosaminyltransferase, were repressed.

CONCLUSION

Gene expression is closely related to cell survival, cell-to-cell adhesion or cell spreading; therefore, HCCs with high 18F-FDG uptake appear to have more aggressive biological properties than those with low uptake.

Comparative analysis of GFPUV-β1,3-N-acetylglucosaminyltransferase 2 production in two insect-cell-based expression systems

Active beta1,3-N-acetylglucosaminyltransferase 2 (beta3GnT2) was produced in the baculovirus expression system (BES) and in stably transformed insect Tn-5B1-4 cells. beta3GnT2 was expressed as a secreted fusion protein with GFP(UV) with three different types of signal sequence to enhance the secretion of the fusion protein. In the stably transformed cells, the maximal beta3GnT2 activity differed between isolates, but their secretion efficiencies were similar. The difference between the maximal beta3GnT activities of the isolates studied was considered to be due to the presence of a copy number of the fusion gene, as determined on the basis of the results of Southern blot analysis. The beta3GnT activities of the culture supernatant in BES (Tn-5B1-4 cells) without or with the addition of the protease inhibitor, leupeptin, were 0.68 and 2.01 mU/ml, respectively. The stably transformed Tn-5B1-4 cells (Tn-pXme11) exhibited a beta3GnT activity of 6.83 mU/ml, which was 3.4-fold higher than that observed for BES with the leupeptin addition. The purity of fusion protein purified from the culture supernatant of the Tn-pXme11 was higher than 95% on SDS-PAGE, in contrast with that purified from the culture supernatant of the baculovirus-infected cells which contained low-molecular-weight fragments of the fusion protein. The stably transformed cell line is more suitable than BES for the efficient production of the secretory protein, beta3GnT2.

β1,3-N-Acetylglucosaminyltransferase-7 (β3Gn-T7) acts efficiently on keratan sulfate-related glycans

beta1,3-N-Acetylglucosaminyltransferase-7 (beta3Gn-T7) has been identified as an anti-migration factor for a lung cancer cell line but its enzymatic activity has not yet been characterized. Here we show that beta3Gn-T7 efficiently acts on keratan sulfate-related glycans including Galbeta1-->4(SO(3)(-)-->6)GlcNAcbeta1-->3Galbeta1-->4(SO(3)(-)-->6)GlcNAc (L2L2), while lacto-N-tetraose and lacto-N-neo-tetraose were poor substrates. Moreover, we found that among the other five beta3Gn-Ts and i antigen-producing beta3Gn-T (iGn-T), beta3Gn-T2 and iGn-T act well on L2L2, although these specific activities were lower than those for a tetraantennary N-glycan. These results indicate that beta3Gn-T7 is the one that most efficiently elongates L2L2 and may be involved in the biosynthesis of keratan sulfate.

Extended core 1 and core 2 branched O-glycans differentially modulate sialyl Lewis X-type L-selectin ligand activity

It has been established that sialyl Lewis x in core 2 branched O-glycans serves as an E- and P-selectin ligand. Recently, it was discovered that 6-sulfosialyl Lewis x in extended core 1 O-glycans, NeuNAcalpha2-->3Galbeta1-->4(Fucalpha1-->3(sulfo-->6))GlcNAcbeta1--> 3Galbeta1-->3GalNAcalpha1-->Ser/Thr, functions as an L-selectin ligand in high endothelial venules. Extended core 1 O-glycans can be synthesized when a core 1 extension enzyme is present. In this study, we first show that beta1,3-N-acetylglucosaminyltransferase-3 (beta3GlcNAcT-3) is almost exclusively responsible for core 1 extension among seven different beta3GlcNAcTs and thus acts on core 1 O-glycans attached to PSGL-1. We found that transcripts encoding beta3GlcNAcT-3 were expressed in human neutrophils and lymphocytes but that their levels were lower than those of transcripts encoding core 2 beta1,6-N-acetylglucosaminyltransferase I (Core2GlcNAcT-I). Neutrophils also expressed transcripts encoding fucosyltransferase VII (FucT-VII) and Core2GlcNAcT-I, whereas lymphocytes expressed only small amounts of transcripts encoding FucT-VII. To determine the roles of sialyl Lewis x in extended core 1 O-glycans, Chinese hamster ovary (CHO) cells were stably transfected to express PSGL-1, FucT-VII, and either beta3GlcNAcT-3 or Core2GlcNAcT-I. Glycan structural analyses disclosed that PSGL-1 expressed in these transfected cells carried comparable amounts of sialyl Lewis x in extended core 1 and core 2 branched O-glycans. In a rolling assay, CHO cells expressing sialyl Lewis x in extended core 1 O-glycans supported a significant degree of shear-dependent tethering and rolling of neutrophils and lymphocytes, although less than CHO cells expressing sialyl Lewis x in core 2 branched O-glycans. These results indicate that sialyl Lewis x in extended core 1 O-glycans can function as an L-selectin ligand and is potentially involved in neutrophil adhesion on neutrophils bound to activated endothelial cells.

Glycodynamics of Mucin Biosynthesis in Gastrointestinal Tumor Cells

Glycoproteins found in the secretions and on the surfaces of cancer cells include mucins and mucin-like glycoproteins. These molecules have been shown to carry antigens that are characteristically expressed on cancer cells, including Tn and T antigens and Lewis epitopes. The structures of O-glycans are often abnormal in gastrointestinal tumors, or else are present in abnormal amounts, and these structures greatly contribute to the phenotype and biology of cancer cells. It has been shown that glycans of cancer cells have functional importance in cell adhesion, invasion and metastasis. The possible mechanisms leading to these cancer-specific changes in carbohydrate structures (termed glycodynamics) involve altered mRNA expression and catalytic activities of glycosyltransferases and sulfotransferases found in tissues and cells of gastrointestinal tumors. In a number of cases it has been possible to correlate enzyme changes with oligosaccharide structures. Different mechanisms have been suggested leading to the synthesis of cancer-specific Lewis, T and Tn antigens, but the regulation of cancer mucin antigens generally appears to be very complex and is poorly understood. The expression levels of specific mucin antigens and enzymes in gastro-intestinal tumors have diagnostic as well as prognostic value. These antigens also have potential for cancer immunotherapy. However, we first need to unravel the complexity of the control of glycosylation in cancer cells. Most importantly, studies of the functional implications of the glycodynamics in cancer cells, as related to cell adhesion and impact on the immune system will provide promising directions for future research.