Cloning and tissue distribution of the human B3GALT7 gene, a member of the beta1,3-Glycosyltransferase family

Comprehensive prognostic and immune analysis of a glycosylation related risk model in pancreatic cancer

BACKGROUND

Pancreatic cancer (PC) is a malignant tumor with extremely poor prognosis, exhibiting resistance to chemotherapy and immunotherapy. Nowadays, it is ranked as the third leading cause of cancer-related mortality. Glycation is a common epigenetic modification that occurs during the tumor transformation. Many studies have demonstrated a strong correlation between glycation modification and tumor progression. However, the expression status of glycosylation-related genes (GRGs) in PC and their potential roles in PC microenvironment have not been extensively investigated.

METHOD

We systematically integrated RNA sequencing data and clinicopathological parameters of PC patients from TCGA and GTEx databases. A GRGs risk model based on glycosylation related genes was constructed and validated in 60 patients from Pancreatic biobank via RT-PCR. R packages were used to analyze the relationships between GRGs risk scores and overall survival (OS), tumor microenvironment, immune checkpoint, chemotherapy drug sensitivity and tumor mutational load in PC patients. Panoramic analysis was performed on PC tissues. The function of B3GNT8 in PC was detected via in vitro experiments.

RESULTS

In this study, we found close correlations between GRGs risk model and PC patients' overall survival and tumor microenvironment. Multifaceted predictions demonstrated the low-risk cohort exhibits superior OS compared to high-risk counterparts. Meanwhile, the low-risk group was characterized by high immune infiltration and may be more sensitive to immunotherapy or chemotherapy. Panoramic analysis was further confirmed a significant relationship between the GRGs risk score and both the distribution of PC tumor cells as well as CD8 + T cell infiltration. In addition, we also identified a unique glycosylation gene B3GNT8, which could suppress PC progression in vitro and in vivo.

CONCLUSION

We established a GRGs risk model, which could predict prognosis and immune infiltration in PC patients. This risk model may provide a new tool for PC precision treatment.

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.

β3GnT8 Promotes Colorectal Cancer Cells Invasion via CD147/MMP2/Galectin3 Axis

β1,3-N-acetylglucosaminyltransferase (β3GnT8) and β3GnT2 are key enzymes that catalyzes the formation of polylactosamine glycan structures by transferring GlcNAc to tetra-antennary β1-6-branched N-glycan and it also has an important effect on the progression of various types of human cancer. They have been reported to participate in tumor invasion and metastasis by regulating the expression of matrix metalloproteinases (MMPs), CD147, and polylactosamine. However, whether β3GnT8 and β3GnT2 play a role in colorectal cancer and, if so, the underlying mechanisms remain unclear. In our study, we detected the expression of β3GnT8, CD147, MMP2, and galectin3 by immunohistochemistry on 90 paraffin-embedded slices. And β3GnT8, CD147, MMP2, and galectin3 were over-expressed in colorectal cancer tissues. We found that overexpression of β3GnT8 and β3GnT2 promoted invasion of colorectal cancer cells, whereas knockdown of β3GnT8 and β3GnT2 inhibited the invasive activity. Mechanistically, β3GnT8 and β3GnT2 regulated the expression of HG-CD147 and the level of polylactosamines in colorectal cancer cells. Together, these results illustrate that the novel role and the molecular mechanism of β3GnT8 and β3GnT2 in promotion of colorectal cancer invasion. These results suggest that the potential use of β3GnT8 as a tumor target for the therapy of colorectal cancer.

c-Jun-dependent β3GnT8 promotes tumorigenesis and metastasis of hepatocellular carcinoma by inducing CD147 glycosylation and altering N-glycan patterns

β3GnT8, a key polylactosamine synthase, plays a vital role in progression of various types of human cancer. The role of β3GnT8 in hepatocellular carcinoma (HCC) and the underlying mechanisms, however, remain largely unknown. In this study, we found that β3GnT8 and polylactosamine were highly expressed in HCC tissues compared with those in adjacent paracancer tissues. Overexpression of β3GnT8 promoted while knockdown of β3GnT8 inhibited HCC cell invasion and migration in vitro. Importantly, enhanced tumorigenesis was observed in nude mice inoculated with β3GnT8-overexpressing HCC cells, suggesting that β3GnT8 is important for HCC development in vitro and in vivo. Mechanistically, β3GnT8 modulated the N-glycosylation patterns of CD147 and altered the polylactosamine structures in HCC cells by physically interacting with CD147. In addition, our data showed the c-Jun could directly bind to the promoter of β3GnT8 gene and regulate β3GnT8 expression. β3GnT8 regulated HCC cell invasion and migration in a C-Jun-dependent manner. Collectively, our study identified β3GnT8 as a novel regulator for HCC invasion and tumorigenesis. Targeting β3GnT8 may be a potential therapeutic strategy against HCC.

c-Jun-mediated β-1,3-N-acetylglucosaminyltransferase 8 expression: A novel mechanism regulating the invasion and metastasis of colorectal carcinoma cells

β-1,3-N-Acetylglucosaminyltransferase 8 (β3GnT8) is a key enzyme that catalyzes the formation of polylactosamine glycan structures by transferring GlcNAc to tetra-antennary β1-6-branched N-glycans, and it has been reported to participate in tumor invasion and metastasis by regulating the expression of matrix metalloproteinases (MMPs), cluster of differentiation 147 (CD147) and polylactosamine. By contrast, the role of transcription factor c-Jun in cell cycle progression has been well established. c-Jun has an important role in tumor cell invasion and metastasis. However, the precise molecular mechanisms by which c-Jun regulates these processes in colorectal carcinoma cells are not fully elucidated. In the present study, c-Jun had a significant effect on the invasive and migratory abilities of SW480 and LoVo cells. Additionally, overexpression of c-Jun was able to increase the expression of β3GnT8, MMPs, CD147 and polylactosamine. Similarly, knockdown of c-Jun was able to decrease the expression of β3GnT8, MMPs, CD147 and polylactosamine. These results suggest that c-Jun is able to regulate colorectal carcinoma cell invasion and metastasis via β3GnT8. A chromatin immunoprecipitation assay indicated that c-Jun is able to bind directly to the promoter regions of β3GnT8 in SW480 and LoVo cells. This leads to transcriptional activation of β3GnT8, which in turn regulates the expression of tumor invasion and metastasis-associated genes. The results of the present study demonstrate a novel mechanism underlying colorectal carcinoma cell invasion and metastasis, where β3GnT8 is transcriptionally activated via c-Jun binding to its promoter.

Monkeypox Virus Host Factor Screen Using Haploid Cells Identifies Essential Role of GARP Complex in Extracellular Virus Formation

Monkeypox virus (MPXV) is a human pathogen that is a member of the Orthopoxvirus genus, which includes Vaccinia virus and Variola virus (the causative agent of smallpox). Human monkeypox is considered an emerging zoonotic infectious disease. To identify host factors required for MPXV infection, we performed a genome-wide insertional mutagenesis screen in human haploid cells. The screen revealed several candidate genes, including those involved in Golgi trafficking, glycosaminoglycan biosynthesis, and glycosylphosphatidylinositol (GPI)-anchor biosynthesis. We validated the role of a set of vacuolar protein sorting (VPS) genes during infection, VPS51 to VPS54 (VPS51-54), which comprise the Golgi-associated retrograde protein (GARP) complex. The GARP complex is a tethering complex involved in retrograde transport of endosomes to the trans-Golgi apparatus. Our data demonstrate that VPS52 and VPS54 were dispensable for mature virion (MV) production but were required for extracellular virus (EV) formation. For comparison, a known antiviral compound, ST-246, was used in our experiments, demonstrating that EV titers in VPS52 and VPS54 knockout (KO) cells were comparable to levels exhibited by ST-246-treated wild-type cells. Confocal microscopy was used to examine actin tail formation, one of the viral egress mechanisms for cell-to-cell dissemination, and revealed an absence of actin tails in VPS52KO- or VPS54KO-infected cells. Further evaluation of these cells by electron microscopy demonstrated a decrease in levels of wrapped viruses (WVs) compared to those seen with the wild-type control. Collectively, our data demonstrate the role of GARP complex genes in double-membrane wrapping of MVs necessary for EV formation, implicating the host endosomal trafficking pathway in orthopoxvirus infection.IMPORTANCE Human monkeypox is an emerging zoonotic infectious disease caused by Monkeypox virus (MPXV). Of the two MPXV clades, the Congo Basin strain is associated with severe disease, increased mortality, and increased human-to-human transmission relative to the West African strain. Monkeypox is endemic in regions of western and central Africa but was introduced into the United States in 2003 from the importation of infected animals. The threat of MPXV and other orthopoxviruses is increasing due to the absence of routine smallpox vaccination leading to a higher proportion of naive populations. In this study, we have identified and validated candidate genes that are required for MPXV infection, specifically, those associated with the Golgi-associated retrograde protein (GARP) complex. Identifying host targets required for infection that prevents extracellular virus formation such as the GARP complex or the retrograde pathway can provide a potential target for antiviral therapy.

β3GnT8 Promotes Gastric Cancer Invasion by Regulating the Glycosylation of CD147

β1, 3-N-acetylglucosminyltransferase 8(β3GnT8) synthesizes a unique cabohydrate structure known as polylactosamine, and plays a vital role in progression of various human cancer types. However, its involvement in gastric cancer remains unclear. In this study, we analyzed the expression and clinical significance of β3GnT8 by Western blot in 6 paired fresh gastric cancer tissues, noncancerous tissues and immunohistochemistry on 110 paraffin-embedded slices. β3GnT8 was found to be over-expressed in gastric cancer tissues, which correlated with lymph node metastasis and TNM stage. Forced the expression of β3GnT8 promoted migration and invasion of gastric cancer cells, whereas β3GnT8 knockdown led to the opposite results. Further studies showed that the regulated β3GnT8 could convert the heterogeneous N-glycosylated forms of CD147 and change the polylactosamine structures carried on CD147. In addition, our data suggested the annexin A2 (ANXA2) to be an essential interaction partner of β3GnT8 during the process of CD147 glycosylation. Collectively, these results provide a novel molecular mechanism for β3GnT8 in promotion of gastric cancer invasion and metastasis. Targeting β3GnT8 could serve as a new strategy for future gastric cancer therapy.

Transcription factor c-jun regulates β3Gn-T8 expression in gastric cancer cell line SGC-7901

Aberrant glycosylation, a common feature of malignant alteration, is partly due to changes in the expression of glycosyltransferases, including β1,3-N-acetyl-glucosaminyltrans-ferase 8 (β3Gn‑T8), which synthesizes poly-N-acetyllactosamine (poly-LacNAc) chains on β1,6 branched N‑glycans. Although the role of β3Gn‑T8 in tumors has been reported, the regulation of β3Gn‑T8 expression, however, is still poorly understood. In the present study, we used three online bioinformatic software tools to identify multiple c‑jun binding sites in the promoter of the β3Gn‑T8 gene. Using luciferase reporter assay, chromatin immunoprecipitation (ChIP) analysis, RT‑PCR and western blot analysis, we revealed that c‑jun could bind to and activate the β3Gn‑T8 promoter, thus upregulating β3Gn‑T8 expression. This was also confirmed by changes in β3Gn‑T8 activity as demonstrated by flow cytometry, immunofluorescence and lectin blot analysis using LEA lectin. Moreover, expression of glycoprotein HG‑CD147, the substrate of β3Gn‑T8, was also regulated by c‑jun. In addition, c‑jun and β3Gn‑T8 were more highly expressed in the gastric cancer tissues when compared to these levels in the adjacent non‑tumor gastric tissues, and β3Gn‑T8 expression was positively correlated with c‑jun expression. These results suggest that c‑jun plays a significant role in regulating the expression of β3Gn‑T8 in the SGC‑7901 cell line and may be involved in the development of malignancy via the activity of β3Gn‑T8.

Knockdown of β3GnT8 reverses 5-fluorouracil resistance in human colorectal cancer cells via inhibition the biosynthesis of polylactosamine-type N-glycans

Aberrant glycosylation is known to be associated with cancer chemoresistance. β-1,3-N-acetyl-glucosaminyltransferase (β3GnT)8, which synthesizes polylactosamine on β1-6 branched N-glycans, is dramatically upregulated in colorectal cancer (CRC). 5-Fluorouracil (5-FU) resistance remains a major obstacle to the chemotherapy of CRC. However, little is known with regard to the correlation between 5‑FU resistance and the expression of β3GnT8 in CRC. In this study, a 5-FU‑resistant cell line (SW620/5-FU) was generated, and 50% inhibition concentration (IC50) of 5-FU was determined by MTT assay. Flow cytometry and lectin blot analysis were performed to detect the alteration of polylactosamine structures. Quantitative RT-‑PCR and western blot analysis were used to identify and evaluate candidate genes involved in the synthesis of polylactosamine in SW620/5-FU cells. We found polylactosamine chains were significantly increased in SW620/5-FU cells. Inhibition of the biosynthesis of polylactosamine by 3'-azidothymidine (AZT) was able to reduce 5-FU tolerance. Further studies showed that β3GnT8 expression was also upregulated in 5-FU‑resistant cancer cells, and knockdown of β3GnT8 by RNA interference reversed 5-FU resistance through, at least partly, by suppressing the formation of polylactosamine. In conclusion, the alteration of β3GnT8 in CRC cells correlates with tumor sensitivity to the chemotherapeutic drug and has significant implication for the development of new treatment strategies.

β3GnT8 plays an important role in CD147 signal transduction as an upstream modulator of MMP production in tumor cells

Aberrant carbohydration by related glycosyl-transferases plays an important role in the progression of cancer. This study focused on the ablity of β-1,3-N-acetyl-glucosaminyltransferase-8 (β3GnT8) to regulate MMP-2 expression through regulation of the CD147 signal transduction pathway in cancer cells. β3GnT8 catalyzes and then extends a polylactosamine chain specifically on β1-6-branched tetraantennary N-glycans. CD147 is a major carrier of β1-6-branched polylactosamine sugars on tumor cells, and the high glycoform of CD147 (HG-CD147) induces matrix metalloproteinase (MMP) production. In the present study, we analyzed β3GnT8 mRNA expression in 6 cancer cell lines (MCF-7, M231, LN229, U87, SGC-7901 and U251). We found that β3GnT8 expression in the LN229, SGC-7901 and U251 cell lines was higher than that in the other cell lines. Therefore, we established β3GnT8-knockdown cell lines derived from the LN229 and SGC-7901 cell lines to examine the level of polylactosamine and CD147 N-glycosylation. In addition, tunicamycin is widely used as an inhibitor of N-linked glycosylation. Hence, various concentrations of tunicamycin were used to treat the cells in order to study its influence on CD147 N-glycosylation and MMP-2 expression. In conclusion, we found that β3GnT8 regulated the level of N-glycans on CD147 and that N-glycosylation of CD147 has an important effect on MMP-2 expression. Our findings suggest that β3GnT8 affects the signal transduction pathway of MMP-2 by altering the N-glycan structure of CD147.

High expression of β3GnT8 is associated with the metastatic potential of human glioma

Changes in glycosylation due to specific alterations of glycosyltransferase activity have been shown in various tumor cells, including human glioma cells. β1,3-N‑acetylglucosaminyltransferase-8 (β3GnT8) catalyzes the formation of polylactosamine on β1-6 branched N-glycans. Upregulated expression of β3GnT8 was described in some tumors, but its precise role in regulating glioma invasion and metastasis remains unclear. In this study, we report on an investigation of the expression of β3GnT8 in human glioma by immunohistochemical analysis. Out of 42 glioma tissues, 37 (88.1%) showed positive β3GnT8 expression, which was significantly higher than that in normal brain tissues (P<0.001). Additionally, the level of β3GnT8 increased with increased pathological grade of gliomas. Silencing of β3GnT8 in U251 glioma cells attenuated the formation of polylactosamine, and decreased cell proliferation, migration and metastatic ability in vitro and in vivo. By contrast, the overexpression of β3GnT8 in U251 cells exhibited enhanced metastatic potential. A positive correlation between β3GnT8 and matrix metalloproteinase-2 (MMP-2) expression in U251 cells was also observed. The results demonstrated a critical role of β3GnT8 in the metastatic potential of glioma cells, indicating that manipulating β3GnT8 expression may have therapeutic potential for the treatment of malignant glioma.

β3GnT8 regulates the metastatic potential of colorectal carcinoma cells by altering the glycosylation of CD147

Aberrant glycosylation of cell surface glycoproteins is commonly associated with the invasion and metastasis of colorectal carcinomas, which can be attributed to the upregulated expression of glycosyltransferases. Therefore, elucidation of glycosyltransferases and their substrates may improve our understanding of their roles in tumor metastasis. β-1,3-N-acetylglucosaminyltransferase-8 (β3GnT8) is a key enzyme that catalyzes the formation of poly-N-acetyllactosamine (polylactosamine) chains on β1,6-branched N-glycans in vitro, which is also involved in tumor invasion. In the present study, we analyzed the expression of β3GnT8 and its product polylactosamine in four human colorectal carcinoma cell lines (LS-174T, SW620, SW480 and LoVo) with different metastatic potential. We found that the levels of β3GnT8 and polylactosamine chains were gradually increased in the colorectal cancer cell lines in a trend from low to high metastatic potential. Notably, a significantly positive relationship between β3GnT8 expression and HG-CD147 was noted in the colorectal cancer cell lines. To further investigate their relationships, exogenous β3GnT8 was introduced into the LS-174T cells, while expression of β3GnT8 was downregulated in the LoVo cells. The overexpression of β3GnT8 in LS-174T cells increased the level of HG-CD147. Conversely, downregulation of β3GnT8 expression in LoVo cells significantly decreased the expression of HG-CD147. HG-CD147 is a major carrier of β1,6-branched polylactosamine sugars; therefore, the regulation of β3GnT8 significantly altered the β1,6-branched polylactosamine structures on CD147. Hence, we suggest that β3GnT8 plays a key role in the metastasis of colorectal cancer cells by altering the β1,6-branched polylactosamine sugars of CD147.

β3GnT8 regulates laryngeal carcinoma cell proliferation via targeting MMPs/TIMPs and TGF-β1

Previous evidence showed β1, 3-N-acetylglucosaminyltransferase 8 (β3GnT8), which can extend polylactosamine on N-glycans, to be highly expressed in some cancer cell lines and tissues, indicating roles in tumorigenesis. However, so far, the function of β3GnT8 in laryngeal carcinoma has not been characterized. To test any contribution, Hep-2 cells were stably transfected with sense or interference vectors to establish cell lines that overexpressed or were deficient in β3GnT8. Here we showed that cell proliferation was increased in β3GnT8 overexpressed cells but decreased in β3GnT8 knockdown cells using MTT. Furthermore, we demonstrated that change in β3GnT8 expression had significant effects on tumor growth in nude mice.We further provided data suggesting that overexpression of β3GnT8 enhanced the expression of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) at both the mRNA and protein levels, associated with shedding of tissue inhibitors of metalloproteinase TIMP-2. In addition, it caused increased production of transforming growth factor beta 1 (TGF-β1), whereas β3GnT8 gene knockdown caused the reverse effect. The results may indicate a novel mechanism by which effects of β3GnT8 in regulating cellular proliferation are mediated, at least in partvia targeting MMPs/TIMPs and TGF-β1 in laryngeal carcinoma Hep-2 cells. The finding may lay a foundation for further investigations into the β3GnT8 as a potential target for therapy of laryngeal carcinoma.

Localization and characterization of rat transmembrane protein 225 specifically expressed in testis

Testis is the one and only location of spermatogenesis and sexual hormone production. Spermatogenesis is a complicated physiological process regulated by many genes specifically and differentially expressed in the testis. In this study, Transmembrane Protein 225 (TMEM225), which is specifically expressed in rat testis, has been identified. TMEM225 was cloned from the testis cDNA library and was mapped to chromosome 8q22 by browsing the University of California Santa Cruz genomic database. It contains an open reading frame with a length of 696 bp, encoding a protein with four putative transmembrane helices. TMEM225 mRNA expression was evaluated by reverse transcription-polymerase chain reaction and in situ hybridization. In addition, the subcellular location of TMEM225 was evaluated. The results obtained highlighted age related specific expression of TMEM225 in testis, specifically during the adult period after age of 13 months. In situ hybridization analysis indicated that TMEM225 mRNA was mainly expressed in spermatocyte cells and round spermatids. Green fluorescence protein localization analysis showed that rat TMEM225 mainly surrounded the nuclear membrane, with a minority distribution in the cytoplasm, and the distribution of TMEM225 was affected by the deletion of N-terminal transmembrane domain. As the expression phase is not related to the first wave of spermatozoon development, our data presented here suggest that TMEM225 may play an important role in sperm degeneration but not in spermatogenesis.

Regulation of MMP-2 expression and activity by β-1,3-N-acetylglucosaminyltransferase-8 in AGS gastric cancer cells

β-1,3-N-acetylglucosaminyltransferase-8(β3Gn-T8) catalyzes the transfer of GlcNAc to the non-reducing terminus of the Galβ1-4GlcNAc of tetraantennary N-glycan in vitro. It has been reported to be involved in malignant tumors, but a comprehensive understanding of how the glycolsyltransferase correlates with the invasive potential of human gastric cancer is not currently available. Therefore, we investigated the ability and possible mechanism involved with β3Gn-T8 in modulating matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of metalloproteinase-2 (TIMP-2) in AGS gastric cancer cells. Here, we found out that siRNA-mediated suppression of the β3Gn-T8 could directly reduce the MMP-2 expression and activity as observed in RT-PCR, western blot and gelatin zymography analysis. Meanwhile, TIMP-2 expression had been increased. Cell invasion assay using matrigel matrix-coated transwell inserts showed that the invasive property was greatly suppressed in β3Gn-T8 siRNA transfected cells. Furthermore, cells overexpressing β3Gn-T8 gene (when transfected with pEGFP-C1 plasmid) also expressed MMP-2 gene, but TIMP-2 expression had been inhibited. The invasive ability of these cells was also enhanced. Protein-protein interaction analysis using STRING database showed that β3Gn-T8 and MMP-2 may have related signal pathway. In summary, our results reveal a new mechanism by which β3Gn-T8 can regulate MMP-2 and TIMP-2. We suggest that β3Gn-T8 can be used as a novel therapeutic target for human gastric treatment.

Subcellular localization and tumor distribution of human beta3-galactosyltransferase by beta3GalT7 antiserum

A novel member of the human beta3-galactosyltransferase family, the beta3GalT7 gene (AY277592, EC2.4.1.-) was first isolated and cloned by our laboratory. To further study its functions, we constructed a prokaryotic expression system of beta3GalT7 and obtained anti-beta3GalT7 polyclonal antiserum by immunizing rabbit with purified beta3GalT7 protein. Using the antiserum, the expression of beta3GalT7 in various tissues and cell lines was analyzed by Western blot and immunochemical assays. Immunochemistry analysis showed the enzyme was expressed significantly higher in some tumor tissues than in normal tissues, indicating its biofunction in tumorogenesis. By immunofluorescence, the enzyme was observed highly accumulated in cytoplasm around nuclear membrane, implying that beta3GalT7 may play an important role in the assembly of galactose in RER and Golgi.

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.