Regulated expression of alpha 2,6-sialyltransferase by the liver-enriched transcription factors HNF-1, DBP, and LAP

ST6Gal1: Oncogenic signaling pathways and targets

The Golgi-sialyltransferase ST6Gal1 (βgalactosidase α2,6 sialyltransferase 1), adds the negatively charged sugar, sialic acid, to the terminal galactose of N-glycosylated proteins. Upregulation of ST6Gal1 is observed in many malignancies, and a large body of research has determined that ST6Gal1-mediated α2,6 sialylation impacts cancer hallmarks. ST6Gal1 affects oncogenic behaviors including sustained proliferation, enhanced self-renewal, epithelial-to-mesenchymal transition, invasion, and chemoresistance. However, there are relatively few ST6GaL1 related signaling pathways that are well-established to mediate these biologies: greater delineation of specific targets and signaling mechanisms that are orchestrated by ST6Gal1 is needed. The aim of this review is to provide a summary of our current understanding of select oncogenic signaling pathways and targets affected by ST6Gal1.

Analysis of the proximal promoter of the human colon-specific B4GALNT2 (Sda synthase) gene: B4GALNT2 is transcriptionally regulated by ETS1

BACKGROUND

The Sda antigen and corresponding biosynthetic enzyme B4GALNT2 are primarily expressed in normal colonic mucosa and are down-regulated to a variable degree in colon cancer tissues. Although their expression profile is well studied, little is known about the underlying regulatory mechanisms.

METHODS

To clarify the molecular basis of Sda expression in the human gastrointestinal tract, we investigated the transcriptional regulation of the human B4GALNT2 gene. The proximal promoter region was delineated using luciferase assays and essential trans-acting factors were identified through transient overexpression and silencing of several transcription factors.

RESULTS

A short cis-regulatory region restricted to the -72 to +12 area upstream of the B4GALNT2 short-type transcript variant contained the essential promoter activity that drives the expression of the human B4GALNT2 regardless of the cell type. We further showed that B4GALNT2 transcriptional activation mostly requires ETS1 and to a lesser extent SP1.

CONCLUSIONS

Results presented herein are expected to provide clues to better understand B4GALNT2 regulatory mechanisms.

A systems-based framework to computationally describe putative transcription factors and signaling pathways regulating glycan biosynthesis

Glycosylation is a common posttranslational modification, and glycan biosynthesis is regulated by a set of glycogenes. The role of transcription factors (TFs) in regulating the glycogenes and related glycosylation pathways is largely unknown. In this work, we performed data mining of TF–glycogene relationships from the Cistrome Cancer database (DB), which integrates chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA-Seq data to constitute regulatory relationships. In total, we observed 22,654 potentially significant TF–glycogene relationships, which include interactions involving 526 unique TFs and 341 glycogenes that span 29 the Cancer Genome Atlas (TCGA) cancer types. Here, TF–glycogene interactions appeared in clusters or so-called communities, suggesting that changes in single TF expression during both health and disease may affect multiple carbohydrate structures. Upon applying the Fisher’s exact test along with glycogene pathway classification, we identified TFs that may specifically regulate the biosynthesis of individual glycan types. Integration with Reactome DB knowledge provided an avenue to relate cell-signaling pathways to TFs and cellular glycosylation state. Whereas analysis results are presented for all 29 cancer types, specific focus is placed on human luminal and basal breast cancer disease progression. Overall, the article presents a computational approach to describe TF–glycogene relationships, the starting point for experimental system-wide validation.

Aberrant sialylation in a patient with a HNF1α variant and liver adenomatosis

Glycosylation is a fundamental post-translational modification of proteins that boosts their structural diversity providing subtle and specialized biological properties and functions. All those genetic diseases due to a defective glycan biosynthesis and attachment to the nascent glycoproteins fall within the wide area of congenital disorders of glycosylation (CDG), mostly causing multisystem involvement. In the present paper, we detailed the unique serum N-glycosylation of a CDG-candidate patient with an unexplained neurological phenotype and liver adenomatosis harboring a recurrent pathogenic HNF1α variant. Serum transferrin isoelectric focusing showed a surprising N-glycosylation pattern consisting on hyposialylation, as well as remarkable hypersialylation. Mass spectrometry-based glycomic analyses of individual serum glycoproteins enabled to unveil hypersialylated complex N-glycans comprising up to two sialic acids per antenna. Further advanced MS analysis showed the additional sialic acid is bonded through an α2-6 linkage to the peripheral N-acetylglucosamine residue.

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Serum N-glycome is altered in a boy with neurological syndrome and HNF1α mutated HCA

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Glycomics reveals unique hypersialylated N-glycans with two NeuAc per antenna

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In-depth MS studies show the additional NeuAc is α2-6 linked to an outer arm GlcNAc

Regulation of ST6GAL1 sialyltransferase expression in cancer cells

The ST6GAL1 sialyltransferase, which adds α2-6 linked sialic acids to N-glycosylated proteins, is overexpressed in a wide range of human malignancies. Recent studies have established the importance of ST6GAL1 in promoting tumor cell behaviors such as invasion, resistance to cell stress and chemoresistance. Furthermore, ST6GAL1 activity has been implicated in imparting cancer stem cell characteristics. However, despite the burgeoning interest in the role of ST6GAL1 in the phenotypic features of tumor cells, insufficient attention has been paid to the molecular mechanisms responsible for ST6GAL1 upregulation during neoplastic transformation. Evidence suggests that these mechanisms are multifactorial, encompassing genetic, epigenetic, transcriptional and posttranslational regulation. The purpose of this review is to summarize current knowledge regarding the molecular events that drive enriched ST6GAL1 expression in cancer cells.

Regulation of human β-galactoside α2,6-sialyltransferase (hST6Gal I) gene expression during differentiation of human osteoblastic MG-63 cells

In this study, we found that gene expression of the human β-galactoside α2,6-sialyltransferase (hST6Gal I) was specifically increased during differentiation of human MG-63 osteoblastic cells by serum starvation (SS). In parallel, a distinct increase in binding to SNA, the α2,6-sialyl-specific lectin, was observed in serum-starved cells, as demonstrated by FACS analysis. 5'-Rapid amplification of cDNA ends analysis demonstrated that the increase of hST6Gal I transcript by SS is mediated by P1 promoter. To elucidate transcriptional regulation of hST6Gal I in SS-induced MG-63 cells, we functionally characterized the P1 promoter region of the hST6Gal I gene. The 5'-deletion analysis of P1 promoter region revealed that the 189 bp upstream region of transcription start site is critical for transcriptional activity of hST6Gal I gene in SS-induced MG-63 cells. This region contains the predicted binding sites for several transcription factors, including AREB6, FOXP1, SIX3, HNF1, YY2, and MOK2. The mutagenesis analysis for these sites and chromatin immunoprecipitation assay demonstrated that the YY2 binding site at -98 to -77 was essential for the SS-induced hST6Gal I gene expression during differentiation of MG-63 cells.

Sialylation of N-glycans: mechanism, cellular compartmentalization and function

Sialylated N-glycans play essential roles in the immune system, pathogen recognition and cancer. This review approaches the sialylation of N-glycans from three perspectives. The first section focuses on the sialyltransferases that add sialic acid to N-glycans. Included in the discussion is a description of these enzymes' glycan acceptors, conserved domain organization and sequences, molecular structure and catalytic mechanism. In addition, we discuss the protein interactions underlying the polysialylation of a select group of adhesion and signaling molecules. In the second section, the biosynthesis of sialic acid, CMP-sialic acid and sialylated N-glycans is discussed, with a special emphasis on the compartmentalization of these processes in the mammalian cell. The sequences and mechanisms maintaining the sialyltransferases and other glycosylation enzymes in the Golgi are also reviewed. In the final section, we have chosen to discuss processes in which sialylated glycans, both N- and O-linked, play a role. The first part of this section focuses on sialic acid-binding proteins including viral hemagglutinins, Siglecs and selectins. In the second half of this section, we comment on the role of sialylated N-glycans in cancer, including the roles of β1-integrin and Fas receptor N-glycan sialylation in cancer cell survival and drug resistance, and the role of these sialylated proteins and polysialic acid in cancer metastasis.

Treatment response in Kawasaki disease is associated with sialylation levels of endogenous but not therapeutic intravenous immunoglobulin G

Objectives

Although intravenous immunoglobulin (IVIG) is highly effective in Kawasaki disease (KD), mechanisms are not understood and 10-20% of patients are treatment-resistant, manifesting a higher rate of coronary artery aneurysms. Murine models suggest that α2-6-linked sialic acid (α2-6Sia) content of IVIG is critical for suppressing inflammation. However, pro-inflammatory states also up-regulate endogenous levels of β-galactoside:α2-6 sialyltransferase-I (ST6Gal-I), the enzyme that catalyzes addition of α2-6Sias to N-glycans. We asked whether IVIG failures correlated with levels of α2-6Sia on infused IVIG or on the patient’s own endogenous IgG.

Methods

We quantified levels of α2-6Sia in infused IVIG and endogenous IgG from 10 IVIG-responsive and 10 resistant KD subjects using multiple approaches. Transcript levels of ST6GAL1, in patient whole blood and B cell lines were evaluated by RT-PCR. Plasma soluble (s)ST6Gal-I levels were measured by ELISA.

Results

There was no consistent difference in median sialylation levels of infused IVIG between groups. However, α2-6Sia levels in endogenous IgG, ST6GAL1 transcript levels, and ST6Gal-I protein in serum from IVIG-resistant KD subjects were lower than in responsive subjects at both pre-treatment and one-year time points (p <0.001, respectively).

Conclusions

Our data indicate sialylation levels of therapeutic IVIG are unrelated to treatment response in KD. Rather, lower sialylation of endogenous IgG and lower blood levels of ST6GALI mRNA and ST6Gal-I enzyme predict therapy resistance. These differences were stable over time, suggesting a genetic basis. Because IVIG-resistance increases risk of coronary artery aneurysms, our findings have important implications for the identification and treatment of such individuals.

Characterization of P1 promoter activity of the beta-galactoside alpha2,6-sialyltransferase I gene (siat 1) in cervical and hepatic cancer cell lines

The level of beta-galactoside alpha2,6-sialyltransferase I (ST6Gal I) mRNA, encoded by the gene siat1, is increased in malignant tissues. Expression is regulated by different promoters - P1, P2 and P3 - generating three mRNA isoforms H, X and YZ. In cervical cancer tissue the mRNA isoform H, which results from P1 promoter activity, is increased. To study the regulation of P1 promoter, different constructs from P1 promoter were evaluated by luciferase assays in cervical and hepatic cell lines. Deletion of a fragment of 1048 bp (-89 to +24 bp) increased 5- and 3-fold the promoter activity in C33A and HepG2 cell lines, respectively. The minimal region with promoter activity was a 37 bp fragment in C33A cells. The activity of this region does not require the presence of an initiator sequence. In HepG2 cells the minimal promoter activity was detected in the 66 bp fragment. Sp1 (-32) mutation increased the promoter activity only in HepG2 cells. HNF1 mutation decreased promoter activity in HepG2 cell line but not in C33A cells. We identified a large region that plays a negative regulation role. The regulation of promoter activity is cell type specific. Our study provides new insights into the complex transcriptional regulation of siat1 gene.

IL-6 and IL-8 increase the expression of glycosyltransferases and sulfotransferases involved in the biosynthesis of sialylated and/or sulfated Lewisx epitopes in the human bronchial mucosa

Bronchial mucins from patients suffering from CF (cystic fibrosis) exhibit glycosylation alterations, especially increased amounts of the sialyl-Lewisx (NeuAcα2-3Galβ1-4[Fucα1-3]GlcNAc-R) and 6-sulfo-sialyl-Lewisx (NeuAcα2-3Galβ1-4[Fucα1-3][SO3H-6]GlcNAc-R) terminal structures. These epitopes are preferential receptors for Pseudomonas aeruginosa, the bacteria responsible for the chronicity of airway infection and involved in the morbidity and early death of CF patients. However, these glycosylation changes cannot be directly linked to defects in CFTR (CF transmembrane conductance regulator) gene expression since cells that secrete airway mucins express no or very low amounts of the protein. Several studies have shown that inflammation may affect glycosylation and sulfation of various glycoproteins, including mucins. In the present study, we show that incubation of macroscopically healthy fragments of human bronchial mucosa with IL-6 (interleukin-6) or IL-8 results in a significant increase in the expression of α1,3/4-fucosyltransferases [FUT11 (fucosyltransferase 11 gene) and FUT3], α2-6- and α2,3-sialyltransferases [ST3GAL6 (α2,3-sialyltransferase 6 gene) and ST6GAL2 (α2,6-sialyltransferase 2 gene)] and GlcNAc-6-O-sulfotransferases [CHST4 (carbohydrate sulfotransferase 4 gene) and CHST6] mRNA. In parallel, the amounts of sialyl-Lewisx and 6-sulfo-sialyl-Lewisx epitopes at the periphery of high-molecular-mass proteins, including MUC4, were also increased. In conclusion, our results indicate that IL-6 and -8 may contribute to the increased levels of sialyl-Lewisx and 6-sulfo-sialyl-Lewisx epitopes on human airway mucins from patients with CF.

Alpha 2,6-sialyltransferase I expression in the placenta of patients with preeclampsia

BACKGROUND

The expression of sialyl-glycoconjugates changes during development, differentiation and oncogenic transformation, tumor invasion and metastasis. Similarly, in the early stage of pregnancy, trophoblast cells have to undergo adhesion, invasion, and proliferation to develop a healthy placenta; the cytobiologic behavior is similar to tumor growth and invasion. Inadequate trophoblast invasion to the spiral artery in the 2nd trimester of pregnancy was believed to be correlated with pregnancy complications, including preeclampsia.

METHODS

Alterations in alpha2,6-sialyltransferase I (ST6Gal I) mRNA in the placental tissues of women with preeclampsia (n=20) and without preeclampsia (n=20 used as a control) were examined by semiquantitative reverse transcription-polymerase chain reaction and real-time quantitative reverse transcription-polymerase chain reaction. The transcription regulators of ST6Gal I including a "constitutive" promoter (Y + Z form), "hepatic" promoter (H form), and lymphoblastic promoter (X form) were investigated. The enzyme activity of ST6Gal I was also examined.

RESULTS

Both mRNA expression and enzyme activity of ST6Gal I did not show a significant difference in the placental tissues of the women of both groups. The transcription regulators of ST6Gal I, including the Y+Z form and the H form, also failed to show any difference. The X form, seldom detected in the study, was excluded from analysis.

CONCLUSION

Our results suggested that ST6Gal I was not involved in the pathogenesis of the preeclampsia.

Preferential reduction of the α-2-6-sialylation from cell surface N-glycans of human diploid fibroblastic cells by in vitro aging

Human diploid fibroblastic cell line, TIG-3, has a finite life span of about 80 population doubling levels (PDL), and is used for in vitro aging studies. Young cells (PDL 23) grew to higher cell densities at a higher growth rate than aged cells (PDL 77). When the electrophoretic mobility of cells was determined, the negative surface charge of the aged cells decreased significantly when compared to that of young cells. Lectin blot analysis of membrane glycoproteins showed that the alpha-2-6-sialylation but not the alpha-2-3-sialylation of N-glycans decreases markedly in the aged cells when compared to the young cells. In support of this observation, the cDNA microarray assay and reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the gene expression of the alpha-2,6-sialyltransferase I (ST6Gal I), which transfers sialic acid to galactose residues of N-glycans, decreases in the aged cells. These results indicate that the concordant decrease of the alpha-2,6-sialylation of N-glycans with the ST6Gal I gene expression is induced in TIG-3 cells by in vitro aging.

Correlation and prognostic significance of beta-galactoside alpha-2,6-sialyltransferase and serum monosialylated alpha-fetoprotein in hepatocellular carcinoma

AIM: To investigate the correlation between tissue ST6Gal I and serum msAFP in HCC patients, and to investigate their prognostic significance.

METHODS: Preoperative sera, paired tumorous and non-tumorous tissues were collected from 19 consecutive patients who had undergone surgical resection of HCC. ST6Gal I activities in the tissues were measured by an in vitro microsomal enzyme activity assay. The percentages of tumor-specific msAFP in the sera were also estimated by an isoelectric focusing-immunoblotting assay.

RESULTS: The tumor ST6Gal I activity was negatively correlated with serum msAFP percentage (r = -0.53, P = 0.019). Both decreased tumor ST6Gal I activity and increased serum msAFP percentage were associated with poor tumor cell differentiation. Univariate analyses showed that both decreased tumor ST6Gal I activity (P = 0.028), increased serum msAFP percentage (P = 0.034) and poor tumor cell differentiation (P = 0.031) were associated with shorter overall survival. Multivariate analysis using the Cox regression model showed that the preoperative serum msAFP percentage (P = 0.022) and tumor cell differentiation status (P = 0.048) were independent prognostic indicators for patient overall survival.

CONCLUSION: Our results indicate that the presence of msAFP in blood circulation is associated with a decreased activity of ST6Gal I activity in HCC. Both tissue ST6Gal I and serum msAFP are potential prognostic markers for patients with operable HCC.

Inhibition of albumin synthesis in chronic diseases: molecular mechanisms

The albumin gene is expressed specifically in the liver after birth, and this expression is regulated predominantly at the transcriptional level. Regulatory proteins occupy specific DNA sequences within the promoter and enhancer of the albumin gene. The interaction between the CCAAT/enhancer binding protein (C/EBP)-beta and the albumin DNA is critical for albumin synthesis. Cachexia-induced hypoalbuminemia is mediated by tumor necrosis factor (TNF)-alpha. In turn, TNF-alpha stimulates oxidative stress, NO synthesis, and phosphorylation of C/EBP-beta within its nuclear localization signal (NLS). Consequently, C/EBP-beta is exported from the nucleus, preventing it to act as a transcriptional factor on the albumin gene. Antioxidants, NOS inhibitors. and dominant negative, nonphosphorylatable C/EBP-beta peptides block phosphorylation of C/EBP-beta within the NLS and its nuclear export as well as rescue the abnormal albumin gene expression, suggesting potential therapeutic interventions.

Transcriptional regulation of human beta-galactoside alpha2,6-sialyltransferase (hST6Gal I) gene in colon adenocarcinoma cell line

Previous studies have shown that hST6Gal I mRNA is overexpressed in colorectal cancer tissues compared with non-malignant or benign tissue. Moreover, Form 1 (hepatic form) mRNA isoform had a marked tendency to accumulate in colon cancer [Int. J. Cancer 88 (2000) 58-65]. These findings suggest that the transcriptional regulation of Form 1 is altered during malignant transformation. We report here transcriptional regulation of the hST6Gal I gene in colon adenocarcinoma cell lines. We characterized P1 promoter region, which regulates Form 1 mRNA expression, using luciferase assays. The result indicates that the nt-156 to -1 region is important for transcriptional activity of hST6Gal I gene in colon adenocarcinoma cell lines. The nt-156 to -1 region contains HNF1 recognition element. Mutation of the HNF1 site reduced luciferase activity by about 80% compared with the wild-type construct, suggesting that HNF1 site is involved in the transcription of Form 1 mRNA in colon cancer cells.

Enhanced expression of alpha 2,6-sialyltransferase ST6Gal I in cervical squamous cell carcinoma

OBJECTIVE

Increased messenger ribonucleic acid (mRNA) expression of beta-galactoside alpha 2,6-sialyltransferase I (ST6Gal I) is important in squamous cell carcinoma (SCC) of the cervix. In many tissues, ST6Gal I is transcriptionally regulated through the use of promoters that originate in the mRNA species that diverge in the 5'-untranslated regions. To clarify the roles of ST6Gal I mRNA species in cervical SCC, we investigated their expression, including a "constitutive" promoter (placental or Y + Z form), "hepatic" promoter (H form), and a specific lymphoblastic promoter (X form), in normal and SCC tissues of the cervix using real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR).

METHODS

Expression of the ST6Gal I species was investigated in normal cervical tissue samples (n = 38) and FIGO IB1 cervical SCC samples (n = 38) by relatively quantitative real-time RT-PCR, using primers designed for amplification of a portion of the coding region common to all mRNA species or ones for amplification of the placental transcript, the hepatic transcript, or lymphoblastic transcript.

RESULTS

ST6Gal I mRNA expression was significantly increased in cancerous tissues compared to that in normal tissues (P = 0.004, Mann-Whitney U test; P < 0.001, paired t test). Expression of the Y + Z form did not appear to be affected by cancer transformation, since it was detected at comparable levels in normal and cancerous tissues (P = 0.986), but H form expression was significantly enhanced in cancerous tissues compared to that in normal tissues (P < 0.001, Mann-Whitney U test and paired t test). Surprisingly, the X form could be detected in some patients with and without cancer, but the detection rate was significantly higher in patients with cancer (86.8% vs 52.6%, respectively; P = 0.021, Fisher's exact test). Although the X transcript was detected at a low level compared to the H and Y + Z transcripts, its expression was also significantly enhanced in patients with cancers compared to those without cancers (P < 0.001, Mann-Whitney U test and paired t test).

CONCLUSIONS

An increased level of hepatic transcripts may be important in cancer transformation because the transcripts contribute to enhance ST6Gal I expression in cancerous tissues.

Transcriptional regulation of human Galbeta1,3GalNAc/Galbeta1, 4GlcNAc alpha2,3-sialyltransferase (hST3Gal IV) gene in testis and ovary cell lines

The mRNA expression of sialyltransferase genes is regulated in a cell-type-specific manner. The mRNAs of human Galbeta1, 3GalNAc/Galbeta1, 4 GlcNAc alpha2,3-sialyltransferase gene (hST3Gal IV) consist of six isoforms, type A1, A2, B1, B2, B3, and BX. These mRNAs are transcribed from different promoters, pA, pB1, pB2, pB3, and pBX, respectively. Type B mRNAs are expressed in several cells, whereas type A mRNAs are specifically expressed in testis, ovary, and placenta, suggesting that pA promoter activity is especially high in these tissues. We show herein germ-cell specific transcriptional regulation of the hST3Gal IV pA promoter. Using a luciferase assay, pA promoter activity is shown to be high in testis and ovary cell lines. We identified the enhancer region of the pA promoter, located at nt -520 to -420. These results suggest that this element plays a critical role in germ-cell specific regulation of the pA promoter. The results of site-directed mutagenesis suggest that AP2 and c-Ets sites in this region are involved in pA promoter activity, which in turn suggests that the hST3Gal IV gene is regulated in a tissue-restricted fashion at the level of transcription.

Variations in gene expression patterns correlated with phenotype of F-11 tumor cells whose expression of GD3-synthase is suppressed

Alteration in ganglioside composition in F-11 cells by suppression of GD3-synthase gene expression resulted in greatly reduced tumor growth and metastasis when the cells were injected into nude mice. To identify genes whose expression is correlated with the decreased level of ganglioside GD3, we analyzed gene expression profiles of the GD3-suppressed F-11 cells and the control F-11 cells using DNA microarrays. We identified a set of GD3-related genes, most of which are involved in tumor growth and development. The genes that define the proliferation-transformation signature are down-regulated, such as creatine kinase-B (CKB), upstream stimulation factor 1 (USF-1), type II cAMP-dependent protein kinase regulatory subunit (RII PKA), and tyrosine hydroxylase (TH). On the other hand, the genes that define the differentiation-reverse transformation signature are up-regulated, including p160 myb-binding protein (P160), brain factor-2, insulin-like growth factor-binding protein (IGFBP), and growth/differentiation factor 11. Transcriptional levels of the genes that showed the most distinct GD3-related expression change were validated by reverse transcription-polymerase chain reaction (RT-PCR). Defining GD3-related genes may lead to identification of clinically relevant therapeutics and to understanding of the mechanism(s) by which ganglioside GD3 affects tumor growth and metastasis.

Isolation of the regulatory regions and genomic organization of the porcine alpha1,3-galactosyltransferase gene

BACKGROUND

Alpha1,3-galactosyltransferase (alpha1,3GT) is an enzyme that produces carbohydrate chains termed alphaGal epitopes found in most mammals, although some species of higher primates, including human, are notable exceptions. The evolutionary origin of the lost alpha1,3GT enzyme activity is not yet known, although it has been suggested that the promoter activity of this gene in the ancestors of higher primates was inactivated.

METHODS

We used 5'-or 3'-RACE, GenomeWalking, reverse transcriptase polymerase chain reaction (RT-PCR) and dual Luciferase reporter assay for identification of the full-length cDNA, which includes the transcription initiation site and the promoter region of porcine alpha1,3GT gene.

RESULTS

The region around exon 1 is guanine and cytosine (GC)-rich (about 70%), comprising a CpG island spanning more than 1.5 kbp. The 5'-flanking region of exon 1 contains multiple transcription factor consensus motifs, including GC-box, SP1, AP2, and GATA-box sites, in the absence of TATA or CAAT-box sequences. The entire gene consists of three 5' noncoding and six coding region exons spanning more than 52 kbp. Detailed analysis of alpha1,3GT transcripts revealed two major alternative splicing patterns in the 5'-untranslated region (5'-UTR) and evidence for minor splicing activity that occurs in a tissue-specific manner. Interspecies comparison of 5'-UTR shows minimal homology between porcine and murine sequences except for exon 2, which suggests that the regulatory regions differ among species.

CONCLUSIONS

These observations have important implications for experiments involving genetic manipulation of the alpha1,3GT gene in transgenic animals in terms of promoter utilization, and particularly in genetically engineering cells for the animal cloning technology by nuclear transfer.

Expression and transcriptional regulation of the human alpha1, 3-fucosyltransferase 4 (FUT4) gene in myeloid and colon adenocarcinoma cell lines

In fucosyltransferase genes, mRNA expression is regulated in a cell-type-specific manner. The expression level of human fucosyltransferase 4 (FUT4) mRNA is high in both colon adenocarcinoma and myeloid cell lines. We will demonstrate here cell-specific expression and transcriptional regulation of the FUT4 gene. FUT4 has two different transcription initiation sites that respectively produce long- and short-form mRNAs. To determine the major FUT4 transcript in colon adenocarcinoma and myeloid cell lines, we analyzed the transcriptional starting sites of the FUT4 gene in myeloid and colon adenocarcinoma cell lines, using 5'-RACE, RT-PCR, and luciferase analysis. The results suggested that the expression level of short-form mRNA is higher than the long-form transcript in the colon adenocarcinoma cell lines and that the expression level of long-form mRNA is higher than the short-form transcript in the myeloid cell lines. Using a luciferase assay, we identified a functional DNA portion within FUT4 genomic DNA that confers a colon adenocarcinoma cell line-specific enhancer, located in nucleotide number (nt) -256 to -44, and a myeloid cell line-specific enhancer, located in nt -686 to -582. The present results suggest that these elements play a critical role in the colon adenocarcinoma and leukemia cell-specific transcriptional regulation of the FUT4 gene.

cDNA cloning, genomic cloning, and tissue-specific regulation of mouse cerebroside sulfotransferase

We have isolated a mouse cDNA clone encoding 3'-phosphoadenylylsulfate-galactosylceramide 3'-sulfotransferase (cerebroside sulfotransferase; CST; EC 2.8.2.11) from a kidney cDNA library, using a human CST cDNA clone [Honke, K., Tsuda, M., Hirahara, Y., Ishii, A., Makita, A. & Wada, Y. (1997) J. Biol. Chem. 272, 4864-4868] as a probe. A recombinant protein of the cloned cDNA showed CST activity. The deduced protein is composed of the same 423 amino acids as human CST and its sequence exhibits 84% identity with that of the human counterpart. Northern-blot analysis and subquantitative reverse transcription-PCR (RT-PCR) analysis showed that the CST gene is preferentially transcribed in stomach, small intestine, brain, kidney, lung, and testis, in that order. To examine differences in transcripts in various tissues, we isolated CST cDNA clones from stomach, small intestine, brain, kidney, and testis by 5'-RACE analysis. We found seven different nucleotide sequences in the 5'-UTR, while the DNA sequences of all the isolated cDNA clones were identical in the coding region. In addition, we isolated CST genomic DNA clones from a mouse genomic library. The clones covered all the 5'-UTR sequences and coding exons including 3'-UTR. RT-PCR analyses of CST mRNAs from various tissues confirmed that CST transcripts are tissue-specifically spliced by alternative use of multiple exons 1. These observations suggest that the tissue-specific expression of the CST gene is explained by alternative usage of multiple 5'-UTR exons flanked with tissue-specific promoters.

Transcription of the beta-galactoside alpha2,6-sialyltransferase gene (SIAT1) in B-lymphocytes: cell type-specific expression correlates with presence of the divergent 5'-untranslated sequence

A single gene, SIAT1, encodes ST6Gal I, the sialyltransferase that mediates transfer of alpha2,6-linked sialic acids to Galbeta1, 4GlcNAc termini of N-linked glycoproteins. In vivo, multiple SIAT1 mRNA forms, differing only in the 5'-untranslated region, are expressed in a tissue-specific manner. This mRNA heterogeneity has been attributed, at least in part, to transcription from a number of physically distinct promoter regions. In mature B-lymphocytes, SIAT1 transcription initiates at P2, a regulatory region known to function only in B-lineage cells. Bacterial chloramphenicol acetyltransferase (CAT) under the control of the P2 region encompassing 415 bp 5'- and 125 bp 3' of the transcriptional initiation site is efficiently expressed in Louckes, a mature B-lymphoblastoid cell line. In contrast, CAT expression in Reh, a T-null/B-null precursor line, and in HepG2, a hepatoma line, are 14-fold and >25-fold less than in Louckes, respectively. The data is consistent with the presence of cis -acting regulatory elements residing both 5' and 3' of the P2 transcriptional initiation site. At least 370 bp of 5'-flanking sequence, coinciding with the inclusion of AP2 and NF-kappaB sites, is necessary for high level expression in Louckes. Exon sequences 3' of the transcription start site are also important for expression. A segment from(+)32 to(+)125 (position(+)1 is transcription start site) is capable of exerting promoter-like activity in Louckes, but not in Reh or HepG2. CAT expression by P2 is negligible in Reh cells. However, enhanced CAT activity is not accompanied by elevated mRNA levels. This observation is consistent with the relief of translational restraints imposed by the(+)32 to(+)125 region. Together, the data demonstrate that efficient and cell-specific transcription regulation in mature B lymphocytes is contained in a 495 bp P2 segment that is comprised of 370 bp of 5'-flanking region and 125 bp of transcribed region of Exon X.

Epithelial-cell-specific transcriptional regulation of human Galbeta1,3GalNAc/Galbeta1,4GlcNAc alpha2,3-sialyltransferase (hST3Gal IV) gene

The mRNA expression of the sialyltransferase genes is regulated in a cell type specific manner. We show here the epithelium cell-specific transcriptional regulation of the human Galbeta1, 3GalNAc/Galbeta1, 4 GlcNAc alpha2,3-sialyltransferase gene (hST3Gal IV). Using a luciferase assay, we identified a functional DNA portion within hST3Gal IV genomic DNA that confers an epithelial cell line specific enhancer, located in nucleotide number (nt) -520 to -420 within the B3 promoter. This element contains two sequences similar to AP2 recognition motifs. Co-transfection with an AP2 expression vector stimulated the enhancer activity of nt -520 to -420 element eight-fold compared with that using parental vector. Site-directed mutagenesis of AP2 sites showed that two AP2 motifs are essential for enhancer activity in HeLa cells. These results suggest that AP2 plays a critical role in the epithelium-cell specific transcriptional regulation of the hST3Gal IV gene.

Isolation and functional analysis of the promoter of the rat CMP-NeuAc:GM3 alpha2,8 sialyltransferase gene 1

A 2.1-kb 5'-flanking fragment of the rat CMP-NeuAc:GM3 alpha2,8 sialyltransferase (GD3-synthase) gene was cloned by the genomic walking procedure. The promoter activity of the fragment was assessed in F-11 cells by transient transfection and the locations for the basal and maximal promoter activities were defined. Primer extension analysis identified a transcription start site approximately 98 bp upstream of the ATG start codon. DNA sequence analysis of the promoter revealed a number of consensus binding sites for known transcription factors such as SP1, AP1, NFkappaB, C/EBP and TFIID, and a repeat GC-GT sequence motif seen for the formation of Z-type DNA. Both TATA and CCAAT boxes were not found in the promoter. Our results from deletion constructs suggested that both positive and negative cis-acting regulatory regions were present in this TATA-less promoter of the rat GD3-synthase gene.

Down-regulation of human sialyltransferase gene expression during in vitro human keratinocyte cell line differentiation

Sialic acids play important roles in biological processes, such as cell-cell communication and cell-matrix interaction. Histochemical analysis using PNA and LFA lectin has shown that the expression of alpha 2,3-sialic acid linked to Gal beta 1,3GalNAc is high in basal cells and decreases following further keratinocyte differentiation. In the present study, we used an in vitro keratinocyte cell line differentiation model to study expression of alpha 2,3-sialic acid linked to Gal beta 1,3 GalNAc. Treatment of the human papillomavirus type 16-immortalized human keratinocyte (PHK16) cell line with high concentrations (1.0 mM) of Ca2+ resulted in PHK16 cell differentiation and redistribution of PNA binding glycoproteins. The synthesis of alpha 2,3-sialic acid linked to Gal beta 1,3GalNAc is mediated by three beta-galactoside alpha 2,3-sialytransferases, which are the gene products of hST30, hST30/N and hST3 Gal II. Ca2+ treatment of PHK16 cells decreased the mRNA expression of hST30/N, whereas the mRNA of hST30 and hST3Gal II was not detected by Northern blot analysis, suggesting that the hST30/N gene is responsible for sialic acid down regulation during keratinocyte differentiation. In order to examine transcriptional regulation of the hST30/N gene, we first determined the transcriptional starting sites of the hST30/N gene in PHK 16 using 5'-RACE analysis. Two kinds of type B isoforms, types B3 and BX, were identified. Type BX is a novel isoform related to the type B form, but which differs upstream of the B3 exon. The results of Northern blot analysis using a type BX-specific probe suggest that the B3 promoter may be regulated by Ca2+. Using a luciferase assay, we identified a functional DNA portion within hST30/N genomic DNA that confers negative transcriptional regulation on the hST30/N B3 promoter during Ca2+ stimulated human keratinocyte differentiation. This element contains some putative transcriptional factor binding sequence motifs such as AP2.

Tissue-specific regulation of mouse core 2 beta-1,6-N-acetylglucosaminyltransferase

Mouse kidney beta-1,6-GlcNAc-transferase (GNT) is the key enzyme for the synthesis of a glycosphingolipid (Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-6(Galbeta1 -3)GalNAcbeta1-3Galalph a1-4Galbeta1-4Glcbeta1-ceramide) that contains the LeX trisaccharide epitope at its nonreducing terminus. The expression of this glycolipid in the kidney is polymorphic; it is expressed in BALB/c but not DBA/2 mice; and a single autosomal gene (Gsl5) is responsible for this polymorphism. We report here the cDNA sequence that encodes the kidney GNT of BALB/c mice, which possess a wild-type Gsl5 gene. The deduced amino acid sequence exhibits 84% identity to that of human core 2 beta-1,6-GlcNAc-transferase, which suggests that kidney GNT is a mouse homologue of human core 2 beta-1, 6-GlcNAc-transferase. The GNT mRNA is expressed abundantly in the kidney, but was not detected in other BALB/c organs or in the kidneys of DBA/2 mice by Northern blot analysis. In addition, we were able to clone and sequence another homologous cDNA from the submandibular gland. The two sequences differ only in their 5'-untranslated region. The submandibular gland type of cDNA was detected in various organs of DBA/2 mice by reverse transcription-polymerase chain reaction, which indicates that the submandibular gland type is ubiquitous and that its expression is not regulated by the Gsl5 gene. Results obtained using the long accurate polymerase chain reaction method indicate that the GNT gene is approximately 45 kilobases long, and the order of the exons from the 5'-end is exon 1 of the kidney type, exon 1 of the ubiquitous type, exon 2, and exon 3. Exons 2 and 3 are present in both transcripts, and the translated region is in exon 3. These data suggest that the expression of GNT is regulated by an alternative splicing mechanism and also probably by tissue-specific enhancers and that Gsl5 regulates the expression of GNT only in the kidney.

Transcriptional regulation of N-acetylglucosaminyltransferase V by the src oncogene

Transformation of baby hamster kidney fibroblasts by the Rous sarcoma virus causes a significant increase in the GlcNAcbeta(1, 6)Man-branched oligosaccharides by elevating the activity and mRNA transcript levels encoding N-acetylglucosaminyltransferase V (GlcNAc-T V). Elevated activity and mRNA levels could be inhibited by blocking cell proliferation with herbimycin A, demonstrating that Src kinase activity can regulate GlcNAc-T V expression. 5' RACE analysis was used to identify a 3-kilobase 5'-untranslated region from GlcNAc-T V mRNA and locate a transcriptional start site in a 25-kilobase pair GlcNAc-T V human genomic clone. A 6-kilobase pair fragment of the 5' region of the gene contained AP-1 and PEA3/Ets binding elements and, when co-transfected with a src expression plasmid into HepG2 cells, conferred src-stimulated transcriptional enhancement upon a luciferase reporter gene. This stimulation by src could be antagonized by co-transfection with a dominant-negative mutant of the Raf kinase, suggesting the involvement of Ets transcription factors in the regulation of GlcNAc-T V gene expression. The src-responsive element was localized by 5' deletion analysis to a 250-base pair region containing two overlapping Ets sites. src stimulation of transcription from this region was inhibited by co-transfection with a dominant-negative mutant of Ets-2, demonstrating that the effects of the src kinase on GlcNAc-T V expression are dependent on Ets.

Specific stimulation of alpha 2-6 sialyltransferase activity by a novel cytosolic factor from rat colon

A factor present in the 100,000 g supernatant from the homogenate of rat colon stimulated the activity of purified Gal beta 1-4GLcNAc alpha 2,6 sialyltransferase [alpha 2-6ST(N)] from rat liver and alpha 2-6ST(N) from either liver microsomes or Golgi membrane. The stimulation of alpha 2-6ST(N) activity by the colon factor using protein acceptors was about four-fold and highly reproducible when the reaction product of the alpha 2-6ST(N) was assayed by either precipitation or affinity chromatography. In contrast, the colon factor did not stimulate the Gal beta 1-4GlcNAc alpha 2,3 sialyltransferase [alpha 2-3ST (N)], from rat jejunum microsomes or purified Gal beta 1-3GalNAc alpha 2,4 sialyltransferase [alpha 2-3ST (O)] from porcine liver, of purified beta 1,4 galactosyltransferase (GT) from bovine milk. In addition to rat colon, the 100,00 g supernatant from the homogenates of rat brain and kidney also stimulated the alpha 2-6ST(N) activity. The stimulation of alpha 2-6ST(N) by the colon factor resulted in a decrease in the Km (by about two-fold) and an increase in Vmax (about 2- to 3-fold) for desialylated alpha 1 acid glycoprotein and CMP-[14C]N-acetylneuraminic acid. The stimulation of alpha 2-6ST(N) activity by the colon factor was temperature dependent, protease sensitive and was inhibited by CTP, but did not need the presence of either metal ions or detergent. The cytosolic factor was partially purified by ion-exchange chromatography with the retention of the activator activity in the peaks containing low molecular weight proteins, but the activity was lost on attempts to further purification. A specific marked stimulation of the alpha 2-6ST(N) activity by cytosolic factors in certain tissues might suggest a physiological role for these factors in the regulation of alpha 2-5ST(N) activity.

Genomic organization and chromosomal assignment of the human beta1, 4-N-acetylgalactosaminyltransferase gene. Identification of multiple transcription units

The beta1,4-N-acetylgalactosaminyltransferase (beta1,4GalNAc-T) (EC) gene is expressed in normal brain tissues and in various malignant transformed cells, such as malignant melanoma, neuroblastoma, and adult T cell leukemia. To analyze the regulatory mechanisms of gene expression, we determined the genomic organization of the beta1, 4GalNAc-T gene. The gene consists of at least 11 exons and spans >8 kilobase pairs. The coding region is located in exons 2-11. To determine the transcription initiation sites, 5'-rapid amplification of cDNA ends analysis and ribonuclease protection assays were performed using RNA obtained from the human melanoma cell line SK-MEL-31. Consequently, we defined three transcription initiation sites and the alternative usage of three exons. Exons 1a and 1b partially overlap; the latter is part (3'-side) of the former and corresponds to the 5'-noncoding region of the cDNA clone previously isolated. The third transcript, exon 1c, corresponds to nucleotides -520 to -412 (position +1 = A of ATG of beta1,4GalNAc-T cDNA), which are considered to be in intron 1 based on the cloned cDNA sequence. Ribonuclease protection assays revealed the corresponding protection bands in samples of the gene-expressing cell lines. 5'-Flanking regions of individual initiation sites showed promoter activity when analyzed by chloramphenicol acetyltransferase assay in SK-MEL-31 cells. The multiple transcription initiation sites and their promoters/enhancers identified here might be differentially involved in the cell type-specific expression of the beta1,4GalNAc-T gene. This gene was assigned to human chromosome 12q13.3 by means of fluorescence in situ hybridization.

The CYP2B1 proximal promoter contains a functional C/EBP regulatory element

Cytochromes P450 2B1 and 2B2 (CYP2B1 and CYP2B2) are well-known phenobarbital-inducible genes in rat liver. Potential transcriptional regulatory elements in the proximal promoter regions of rat CYP2B genes were analyzed by transfection in HepG2 hepatoma cells and by binding of nuclear proteins. Deletion of sequences from -1,400 to -110 had modest effects on promoter activity, but further deletion to -57 decreased the transcriptional activity by more than 90%, suggesting the presence of strong cis-acting elements in this region. Sequences similar to a basal transcription element (BTE) in CYP1A1 and a proposed phenobarbital responsive element (Barbie box) are present from -89 to -67. However, no protection was detected in these regions by DNase I footprinting assay. Instead, a region (FP1) from -64 to -45 was protected by liver nuclear extracts. Mutation of either the BTE or FP1 sequences of CYP2B1, or both, reduced transcriptional activity by 70-80% in HepG2 cells. FP1 was identified as a functional C/EBP site by co-transfection of C/EBP expression vectors and supershift assays with C/EBP antisera. Binding of liver nuclear proteins to sequences within the -110 to +1 region was not detectably altered by pretreatment of rats with phenobarbital.

Molecular cloning and genomic analysis of mouse Galbeta1, 3GalNAc-specific GalNAc alpha2,6-sialyltransferase

cDNA and genomic clones encoding mouse Galbeta1, 3GalNAc-specific GalNAc alpha2,6-sialyltransferase (ST6GalNAc II) were isolated, and the structure organization of the gene was determined. The predicted amino acid sequence is 57.4% identical to the chick ST6GalNAc II sequence but 33.8% identical to the chick ST6GalNA I (GalNAc alpha2, 6-sialyltransferase) sequence. The ST6GalNAc II gene is constitutively expressed in various mouse tissues but highly expressed in lactating mammary gland and adult testis. The gene contains nine exons spanning about 25 kilobases of genomic DNA and encodes a messenger RNA of 1995 nucleotides. Primer extension and S1 nuclease protection analysis of submaxillary gland mRNA showed that the transcription of the ST6GalNAc II gene starts from 68 nucleotides upstream from the translation start site. Characterization of 5'-flanking genomic regions indicated that the Galbeta1,3GalNAc-specific GalNAc alpha2,6-sialyltransferase promoter is embedded in a G+C-rich domain and contains no TATA or CAAT box but has putative binding sites for transcription factors Sp1 and AP-2. Transient transfection experiments involving luciferase reporter genes demonstrated promoter activity in NIH3T3 cells.

Coordinate expression of beta-galactoside alpha 2,6-sialyltransferase mRNA and enzyme activity in suckling rat jejunum cultured in different media: transcriptional induction by dexamethasone

In attempting to elucidate the molecular basis of the expression of alpha 2,6-sialyltransferase (alpha 2,6-ST) in jejunal explants of 7-day-old rats during cultivation, the total jejunal RNA was analysed by hybridization using a cDNA clone encoding rat liver alpha 2,6-ST. Under cultivation in both serum-free and serum-containing media jejunal alpha 2,6-ST mRNA closely paralleled the bound (100,000 g pellet) as well as the soluble (100,000 g supernatant) alpha 2,6-ST activity, the correlation coefficients being 0.976 and 0.816, respectively. Dexamethasone (Dx) treatment enhanced alpha 2,6-ST mRNA and membrane-bound alpha 2,6-ST activity in close correlation. Jejunal alpha 2,6-ST mRNA is sensitive to actinomycin D and is lost with apparently identical kinetics in Dx-stimulated and control explants, suggesting that regulation by Dx may be exerted by altering the rate of mRNA synthesis. Dx-dependent activation resulted in elevation of the 4.3-Kb mRNA and can be inhibited by the antiglucocorticoid onapristone, demonstrating the participation of the glucocorticoid receptor pathway.

A disulfide-bonded dimer of the Golgi beta-galactoside alpha2,6-sialyltransferase is catalytically inactive yet still retains the ability to bind galactose

The alpha2,6-sialyltransferase is a terminal glycosyltransferase localized in the trans Golgi and trans Golgi network. Here we show that 30% of the total rat liver Golgi alpha2,6-sialyltransferase forms a disulfide-bonded 100-kDa species that can be converted to the 50-kDa monomer form of the enzyme upon reduction. Limited proteolysis of both enzyme forms demonstrates that the 100-kDa species is a disulfide-bonded homodimer of the alpha2,6-sialyltransferase. The alpha2,6-sialyltransferase disulfide-bonded dimer is found in bovine liver Golgi membranes and in Golgi membranes prepared and solubilized in the presence of 100 mM iodoacetamide, suggesting that it is not unique to rat liver or formed aberrantly upon membrane lysis. The dimer form of the enzyme possesses no significant catalytic activity and has a much lower affinity for CDP-hexanolamine-agarose compared with the monomer form. In contrast, both the alpha2,6-sialyltransferase monomer and the disulfide-bonded dimer bind strongly to galactose and galactose-terminated substrates. These results suggest that the alpha2,6-sialyltransferase disulfide-bonded dimer lacks catalytic activity due to a weak affinity for its sugar nucleotide donor, CMP-NeuAc, and that this catalytically inactive form of the enzyme may act as a galactose-specific lectin in the Golgi.

Transcriptional regulation of alpha1,3-galactosyltransferase in embryonal carcinoma cells by retinoic acid. Masking of Lewis X antigens by alpha-galactosylation

Treatment of mouse teratocarcinoma F9 cells with all-trans-retinoic acid (RA) causes a 9-fold increase in steady-state levels of mRNA for UDP-Gal:beta-D-Gal alpha1,3-galactosyltransferase (alpha1,3GT) beginning at 36 h. Enzyme activity rises in a similar fashion, which also parallels the induction of laminin and type IV collagen. Nuclear run-on assays indicate that this increase in alpha1,3GT in RA-treated F9 cells, like that of type IV collagen, is transcriptionally regulated. Differentiation also results in increased secretion of soluble alpha1,3GT activity into the growth media. The major alpha-galactosylated glycoprotein present in the media of RA-treated F9 cells, but not of untreated cells, was identified as laminin. Differentiation of F9 cells is accompanied by an increase in alpha-galactosylation of membrane glycoproteins and a decrease in expression of the stage-specific embryonic antigen, SSEA-1 (also known as the Lewis X antigen or LeX), which has the structure Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-R. However, flow cytometric analyses with specific antibodies and lectins, following treatment of cells with alpha-galactosidase, demonstrate that differentiated cells contain LeX antigens that are masked by alpha-galactosylation. Thus, RA induces alpha1,3GT at the transcriptional level, resulting in major alterations in the surface phenotype of the cells and masking of LeX antigens.

Genomic organization and chromosomal mapping of the Gal beta 1,3GalNAc/Gal beta 1,4GlcNAc alpha 2,3-sialyltransferase

In this report we describe the chromosome mapping and genomic organization of the human Gal beta 1,3GalNAc/Gal beta 1,4GlcNAc alpha 2,3-sialyltransferase gene. The gene is localized to human chromosome 11(q23-q24) by in situ hybridization of metaphase chromosomes. It spans more than 25 kilobases of human genomic DNA and is distributed over 14 exons that range in size from 61 to 679 base pairs. Previous characterization of cDNAs encoding the Gal beta 1,3GalNAc/Gal beta 1,4GlcNAc alpha 2,3-sialyltransferase revealed that the gene produces at least three transcripts in human placenta, which code for identical protein sequences except at the 5' ends (Kitagawa, H., and Paulson, J. C. (1994a) J. Biol. Chem. 269, 1394-1401). Repeated screening for clones that contain the 5' end of the cDNA has identified two additional distinct mRNAs that are expressed in human placenta. Comparison of the genomic DNA sequence with that of the five different mRNAs indicates that these transcripts are produced by a combination of alternative splicing and alternative promoter utilization. Northern analysis indicated that one of them is specifically expressed in placenta, testis, and ovary, indicating that its expression is independently regulated from the others.

The expression of CMP-NeuAc: Gal beta 1,4GlcNAc alpha 2,6 sialyltransferase [EC 2.4.99.1] and glycoproteins bearing alpha 2,6-linked sialic acids in human brain tumours

The expression of CMP-NeuAc: Gal beta 1,4GlcNAc alpha 2,6 sialyltransferase (alpha 2,6-ST) [EC 2.4.99.1] and glycoproteins bearing alpha 2,6-linked sialic acids were examined in primary human brain tumours and cell lines. 79% (19/24) of the meningiomas expressed alpha 2,6-ST mRNA, 42% (10/24) of which showed very high expression. alpha 2,6-ST mRNA expression was undetectable in normal brain tissue. In contrast, only 1/13 of the gliomas examined expressed detectable alpha 2,6-ST mRNA. Metastases to the brain did not express measurable amounts of alpha 2,6-ST mRNA. Less expression was found in malignant (i.e. anaplastic) compared to benign (i.e. meningothelial) meningiomas. Two-dimensional SDS-PAGE of glioma and meningioma proteins, followed by Sambucus nigra lectin staining, revealed the presence of a glycoprotein bearing alpha 2,6-linked sialic acids, M(r) = 53 kDa and a pI = 7.0 (MEN-1) that appeared in all seven of the meningiomas examined, but was expressed at barely detectable levels, if at all, in seven out of the seven glioblastomas examined. Thus, decreased alpha 2,6-ST expression may play a role in the aggressive nature of anaplastic meningiomas, but appears to be virtually absent in all tumours of glial origin.

The human UDP-N-acetylglucosamine: alpha-6-D-mannoside-beta-1,2- N-acetylglucosaminyltransferase II gene (MGAT2). Cloning of genomic DNA, localization to chromosome 14q21, expression in insect cells and purification of the recombinant protein

UDP-GlcNAc:alpha-6-D-mannoside [GlcNAc to Man alpha 1-6] beta-1,2-N-acetylglucosaminyltransferase II (GlcNAc-T II, EC 2.4.1.143) is a Golgi enzyme catalyzing an essential step in the conversion of oligomannose to complex N-glycans. A 1.2-kb probe from a rat liver cDNA encoding GlcNAc-T II was used to screen a human genomic DNA library in lambda EMBL3. Southern analysis of restriction endonuclease digests of positive phage clones identified two hybridizing fragments (3.0 and 3.5 kb) which were subcloned into pBlueScript. The inserts of the resulting plasmids (pHG30 and pHG36) are over-lapping clones containing 5.5 kb of genomic DNA. The pHG30 insert (3.0 kb) contains a 1341-bp open reading frame encoding a 447-amino-acid protein, 250 bp of G + C-rich 5'-upstream sequence and 1.4 kb of 3'-downstream sequence. The pHG36 insert (3.5 kb) contains 2.75 kb of 5'-upstream sequence and 750 bp of the 5'-end of the open reading frame. The protein sequence showed the domain structure typical of all previously cloned glycosyltransferases, i.e. a short 9-residue putative cytoplasmic N-terminal domain, a 20-residue hydrophobic non-cleavable putative signal-anchor domain and a 418-residue C-terminal catalytic domain. Northern analysis of human tissues showed a major message at 3 kb and minor signals at 2 and 4.5 kb. There is no sequence similarity to any previously cloned glycosyltransferases including human UDP-GlcNAc:alpha-3-D-mannoside [GlcNAc to Man alpha 1-3] beta-1,2-N-acetylglucosaminyltransferase I (GlcNAc-T I) which has 445 amino acids with a 418-residue C-terminal catalytic domain. The human GlcNAc-T I and II genes (MGAT1 and MGAT2) map to chromosome bands 5q35 and 14q21, respectively, by fluorescence in situ hybridization. The entire coding regions of human GlcNAc-T I and II are each on a single exon. There is 92% identity between the amino acid sequences of the catalytic domains of human and rat GlcNAc-T II. Southern analysis of restriction enzyme digests of human genomic DNA indicates that there is only a single copy of the MGAT2 gene. The full-length coding region of GlcNAc-T II has been expressed in the baculovirus/Sf9 insect cell system, the recombinant enzyme has been purified to near homogeneity with a specific activity of about 20 mumol.min-1.mg-1 and the product synthesized by the recombinant enzyme has been identified by high-resolution 1H-NMR spectroscopy and mass spectrometry.

Branching and elongation with lactosaminoglycan chains of N-linked oligosaccharides result in a shift toward termination with alpha 2-->3-linked rather than with alpha 2-->6-linked sialic acid residues

The activity of bovine colostrum CMP-NeuAc:Gal beta 1-->4GlcNAc beta-R alpha 2-->6-sialyltransferase (alpha 6-NeuAcT) toward oligosaccharides that form part of complex-type, N-linked glycans appears significantly reduced when a bisecting GlcNAc residue or additional branches are present, or when core GlcNAc residues are absent. By contrast human placenta CMP-NeuAc:Gal beta 1-->4GlcNAc beta-R alpha 2-->3-sialyltransferase (alpha 3-NeuAcT) is much less sensitive to structural variations in these acceptors. Furthermore the alpha 3-NeuAcT shows a much higher activity than the alpha 6-NeuAcT with oligosaccharides that form part of linear and branched lactosaminoglycan extensions. These results indicate that, in tissues that express both enzymes, branching and lactosaminoglycan formation of N-linked glycans will cause a shift from termination with alpha 2-->6-linked sialic acid to termination with alpha 2-->3-linked sialic acid residues. These findings provide an enzymatic basis for the sialic acid linkage-type patterns found on the oligosaccharide chains of N-glycoproteins.

Characterization of a promoter region supporting transcription of a novel human beta-galactoside alpha-2,6-sialyltransferase transcript in HepG2 cells

In humans, two transcripts encoding beta-galactoside alpha-2,6-sialytransferase (EC 2.4.99.1.) have previously been described. One of the transcripts is widely expressed, whereas the other is restricted to mature B-cells. In this study we demonstrate the existence of a third transcript in the hepatoma cell-line HepG2. The expression of this transcript is controlled by a promoter region which efficiently supports transcription in HepG2 cells, and which harbours putative binding sites for liver-enriched and acute phase inducible transcription factors.

Expression of GDP-L-Fuc: Gal(beta 1-4)GlcNAc-R (Fuc to GlcNAc) alpha-1,3-fucosyltransferase and its relationship to glycoprotein structure in a human erythroleukemia cell line, HEL

Terminal glycosylation may be a mechanism to control the function of specific biologically active glycoproteins. The biosynthesis of terminal sialyl and fucosyl residues on certain glycoproteins has been linked to the expression of the respective glycosyltransferase. In contrast, a human erythroleukemia cell line, HEL, contained a highly active GDP-L-Fuc: Gal(beta 1-4)GlcNAc-R (Fuc to GlcNAc) alpha-1,3-fucosyltransferase (alpha-1,3-fucosyltransferase) but no detectable alpha-1,3-linked fucosyl residues on the glycoproteins. The alpha-1,3-fucosyltransferase gave apparent Km values for Fuc(alpha 1-2)Gal(beta 1-4)GlcNAc beta-O-benzyl, Gal(beta 1-4)GlcNAc and GDP-fucose of 0.04, 0.68 and 0.12 mM, respectively. The lack of detectable fucosyl residues in alpha-1,3-linkage to GlcNAc on the [3H]fucose-labeled glycoproteins was shown with the use of almond alpha-1,3/4-fucosidase and internal controls to verify that the enzyme was active. Using Western-blot analysis, HEL cell glycoproteins reacted with blood group H type-2 antibody, confirming the presence of Fuc(alpha 1-2)Gal(beta 1-4)GlcNAc as reported by others and the presence of the preferred substrate for the enzyme. It is proposed that controls for terminal glycosylation in addition to glycosyltransferase expression are operative in HEL cells and that they are part of a multi-regulated process controlling terminal modifications of glycoproteins.

Retinoblastoma control element binding proteins are induced during in vivo terminal differentiation of the liver and bind to the DBP promoter

Growth regulation of terminal differentiation was studied by analysis of the promoter of the transcription factor D-site binding protein (DBP) using nuclear extracts from rat liver undergoing regeneration or from normal liver early in development. Four proximal binding sites for nuclear proteins were identified, three of which showed significant quantitative or qualitative changes in associated factors upon growth induction. Two of these sites bound factors common to the retinoblastoma control element and these proteins were induced upon terminal differentiation of the liver. These factors were also rapidly down-regulated upon induction of regenerative growth and consequent dedifferentiation. These results provide a link between the regulation of growth and differentiation in an in vivo model system.