Cell-specific expression of human beta-galactoside alpha 2,6-sialyltransferase transcripts differing in the 5' untranslated region

Role of the ST6GAL1 sialyltransferase in regulating ovarian cancer cell metabolism

The ST6GAL1 sialyltransferase, which adds α2-6-linked sialic acids to N-glycosylated proteins, is upregulated in many malignancies including ovarian cancer. Through its activity in sialylating select surface receptors, ST6GAL1 modulates intracellular signaling to regulate tumor cell phenotype. ST6GAL1 has previously been shown to act as a survival factor that protects cancer cells from cytotoxic stressors such as hypoxia. In the present study, we investigated a role for ST6GAL1 in tumor cell metabolism. ST6GAL1 was overexpressed (OE) in OV4 ovarian cancer cells, which have low endogenous ST6GAL1, or knocked-down (KD) in ID8 ovarian cancer cells, which have high endogenous ST6GAL1. OV4 and ID8 cells with modulated ST6GAL1 expression were grown under normoxic or hypoxic conditions, and metabolism was assessed using Seahorse technology. Results showed that cells with high ST6GAL1 expression maintained a higher rate of oxidative metabolism than control cells following treatment with the hypoxia mimetic, desferrioxamine (DFO). This enrichment was not due to an increase in mitochondrial number. Glycolytic metabolism was also increased in OV4 and ID8 cells with high ST6GAL1 expression, and these cells displayed greater activity of the glycolytic enzymes, hexokinase and phosphofructokinase. Metabolism maps were generated from the combined Seahorse data, which suggested that ST6GAL1 functions to enhance the overall metabolism of tumor cells. Finally, we determined that OV4 and ID8 cells with high ST6GAL1 expression were more invasive under conditions of hypoxia. Collectively, these results highlight the importance of sialylation in regulating the metabolic phenotype of ovarian cancer cells.

Sialyltransferase ST6GAL-1 mediates resistance to chemoradiation in rectal cancer

Locally advanced rectal cancer is typically treated with chemoradiotherapy followed by surgery. Most patients do not display a complete response to chemoradiotherapy, but resistance mechanisms are poorly understood. ST6GAL-1 is a sialyltransferase that adds the negatively charged sugar, sialic acid (Sia), to cell surface proteins in the Golgi, altering their function. We therefore hypothesized that ST6GAL-1 could mediate resistance to chemoradiation in rectal cancer by inhibiting apoptosis. Patient-derived xenograft and organoid models of rectal cancer and rectal cancer cell lines were assessed for ST6GAL-1 protein with and without chemoradiation treatment. ST6GAL-1 mRNA was assessed in untreated human rectal adenocarcinoma by PCR assays. Samples were further assessed by Western blotting, Caspase-Glo apoptosis assays, and colony formation assays. The presence of functional ST6GAL-1 was assessed via flow cytometry using the Sambucus nigra lectin, which specifically binds cell surface α2,6-linked Sia, and via lectin precipitation. In patient-derived xenograft models of rectal cancer, we found that ST6GAL-1 protein was increased after chemoradiation in a subset of samples. Rectal cancer cell lines demonstrated increased ST6GAL-1 protein and cell surface Sia after chemoradiation. ST6GAL-1 was also increased in rectal cancer organoids after treatment. ST6GAL-1 knockdown in rectal cancer cell lines resulted in increased apoptosis and decreased survival after treatment. We concluded that ST6GAL-1 promotes resistance to chemoradiotherapy by inhibiting apoptosis in rectal cancer cell lines. More research will be needed to further elucidate the importance and mechanism of ST6GAL-1-mediated resistance.

Cell surface sialic acid modulates extracellular matrix adhesion and migration in pancreatic adenocarcinoma cells

OBJECTIVES

Tumor cells modulate their extracellular matrix (ECM) adhesion and migration to become more metastatic. Moreover, they show an increase in sialic acid, which could have an effect on their ECM adhesion and migration. This work describes the influence of pancreatic adenocarcinoma cell surface α2,3- and α2,6-sialic acid determinants on the aforementioned processes.

METHODS

We have characterized the cell surface α2,3- and α2,6-sialic acids, and sialyl-Lewis x levels and the integrin levels of 2 pancreatic adenocarcinoma cell lines, Capan-1 and MDAPanc-28, grown at different cell densities, and also of the ST3Gal III overexpressing Capan-1 cells, C31. We have measured their adhesion to several ECM proteins and their migration through collagen with and without blocking their sialic acid determinants.

RESULTS

Adhesion to ECM proteins of Capan-1 and MDAPanc-28 grown at different cell densities, and of C31, depended on their cell surface sialic acid determinants repertoire, correlating the higher α2,6-sialic acid levels with their increased ECM adhesion. Cell migration also depended on their sialic acid determinants expression; and in this case, higher α2,3-sialic acid levels correlated with a more migratory phenotype.

CONCLUSION

This study shows how the intrinsic heterogeneity of cell membrane sialylation regulates the adhesive and migratory potential of pancreatic adenocarcinoma cells.

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.

Conservation of the ST6Gal I gene and its expression in the mammary gland

Milk sialoglycoconjugates can protect the gastrointestinal tract of the suckling neonate by competitively binding to invading pathogens and promoting growth of beneficial flora, and their potential role in postnatal brain development is of particular interest in human infant nutrition. Although the concentration and the distribution of sialoglycoconjugates have been extensively studied in the milk of various species, the investigation of sialyltransferase gene expression in the mammary gland, in the context of lactation, has been limited. The sialyltransferase enzyme ST6Gal I transfers sialic acid from CMP-sialic acid to type 2 (Galβ1,4GlcNAc) free disaccharides or the termini of N- or O-linked oligosaccharides using an α2,6-linkage. Expression of the ST6Gal I gene is primarily regulated at the level of transcription through the use of several cell and development-specific promoters, producing transcripts with divergent 5' untranslated regions (UTR). In the mouse mammary gland, the novel 5'UTR exon (L) appears to be associated with a drastic increase in ST6Gal I gene expression during lactation. We find that rats also possess an exon (L), suggesting conservation of this regulatory mechanism in rodents. In contrast, an exon (L)-containing transcript was not detected in the lactating bovine or human mammary gland. We also observed a trend of increasing ST6Gal I gene expression in the bovine mammary gland, culminating in involution. This is in contrast to species such as mice where the greatest change in ST6Gal I gene expression occurs between pregnancy and lactation, suggesting different roles in rodents vs. other mammals for α2,6-sialylated oligosaccharides present in milk.

Expression of the human CMP-NeuAc:GM3 alpha2,8-sialyltransferase (GD3 synthase) gene through the NF-kappaB activation in human melanoma SK-MEL-2 cells

To elucidate the mechanism underlying the regulation of human GD3 synthase gene expression in human melanoma SK-MEL-2 cells, we identified the promoter region of the human GD3 synthase gene. The 5'-rapid amplification of cDNA end (5'-RACE) using mRNA prepared from SK-MEL-2 cells revealed the presence of multiple transcription start sites of human GD3 synthase gene. Promoter analyses of the 5'-flanking region of the human GD3 synthase gene using luciferase gene reporter system showed the strong promoter activity in SK-MEL-2 cells. Deletion study revealed that the region as the core promoter from -1146 to -646 (A of the translational start ATG as position +1) was indispensable for endogenous expression of human GD3 synthase gene. This region lacks apparent TATA and CAAT boxes but contains putative binding sites for transcription factors c-Ets-1, CREB, AP-1 and NF-kappaB. Electrophoretic mobility shift assays using specific competitors, chromatin immunoprecipitation assay and site-directed mutagenesis demonstrated that only NF-kappaB element in this region is required for the promoter activity in SK-MEL-2 cells. These results indicate that NF-kappaB plays an essential role in the transcriptional activity of human GD3 synthase gene essential for GD3 synthesis in SK-MEL-2 cells.

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.

Characteristics of two CD75-related cell-surface expressed antigens of human lymphocytes

The structure of cell surface carbohydrates expressed on human leukocytes is dependent on the cell's developmental stage, differentiation, and activation. Although modification of oligosaccharide side chains by sialylation is quite common, antigenic determinants on lymphocytes associated with the presence of sialoglycans are still incompletely defined. In the study presented here, monoclonal antibodies (mAbs) were used to characterize two novel but related cell surface carbohydrate antigens. One antigen, denominated as B8, is largely masked by sialyl residues on most lymphocytes, while it is detectable on the majority of B cells. Treatment with sialidase resulted in the exposure of B8 on the surface of blood cells including lymphocytes. Although the second carbohydrate antigen, C1, was sialidase-sensitive, its molecular properties and cellular distribution place it in close vicinity to B8. B8(+) as well as C1(+) lymphocytes were found predominantly in the mantle zone of secondary follicles of tonsillar tissue. These findings raised the possibility that B8 and C1 are closely related to a category of carbohydrate antigens previously classified as CDw76 (recently assigned to CD75s). MAbs directed against B8 or C1 precipitated 34, 37, 43, and 200kDa glycoproteins from tonsillar lymphocytes, indicating that identical cell surface proteins are associated with both antigens. In contrast to B8, however, the expression of C1 was increased on lymphocytes upon activation. Together the results suggest that CD75-related epitopes are distinct molecular entities which may be exposed on glycoproteins and are differently expressed on lymphocytes.

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.

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.

Molecular cloning, gene organization and expression of the human UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4-N-acetylgalactosaminyltransferase responsible for the biosynthesis of the blood group Sda/Cad antigen: evidence for an unusual extended cytoplasmic domain

The nucleotide sequence of the short and long transcripts of beta1,4- N -acetylgalactosaminyltransferase have been submitted to the DDBJ, EMBL, GenBank(R) and GSDB Nucleotide Sequence Databases under accession nos AJ517770 and AJ517771 respectively. The human Sd(a) antigen is formed through the addition of an N -acetylgalactosamine residue via a beta1,4-linkage to a sub-terminal galactose residue substituted with an alpha2,3-linked sialic acid residue. We have taken advantage of the previously cloned mouse cDNA sequence of the UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4- N -acetylgalactosaminyltransferase (Sd(a) beta1,4GalNAc transferase) to screen the human EST and genomic databases and to identify the corresponding human gene. The sequence spans over 35 kb of genomic DNA on chromosome 17 and comprises at least 12 exons. As judged by reverse transcription PCR, the human gene is expressed widely since it is detected in various amounts in almost all cell types studied. Northern blot analysis indicated that five Sd(a) beta1,4GalNAc transferase transcripts of 8.8, 6.1, 4.7, 3.8 and 1.65 kb were highly expressed in colon and to a lesser extent in kidney, stomach, ileum and rectum. The complete coding nucleotide sequence was amplified from Caco-2 cells. Interestingly, the alternative use of two first exons, named E1(S) and E1(L), leads to the production of two transcripts. These nucleotide sequences give rise potentially to two proteins of 506 and 566 amino acid residues, identical in their sequence with the exception of their cytoplasmic tail. The short form is highly similar (74% identity) to the mouse enzyme whereas the long form shows an unusual long cytoplasmic tail of 66 amino acid residues that is as yet not described for any other mammalian glycosyltransferase. Upon transient transfection in Cos-7 cells of the common catalytic domain, a soluble form of the protein was obtained, which catalysed the transfer of GalNAc residues to alpha2,3-sialylated acceptor substrates, to form the GalNAcbeta1-4[Neu5Acalpha2-3]Galbeta1-R trisaccharide common to both Sd(a) and Cad antigens.

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.

Characterization of the promoter region of the human Galbeta1,3(4)GlcNAc alpha2,3-sialyltransferase III (hST3Gal III) gene

Multiple promoters are found in the hST3Gal IV, hST3Gal V and hST3Gal VI genes. These promoters may respond to different physiological signals and stimuli in different cell types. The multiple regulatory pathways of these ubiquitous sialyltransferases may need to be differentially modulated in various cell types. Here, we report transcriptional regulation of the hST3Gal III gene. 5'-RACE analysis determined that the transcription initiation sites map at -181 bp from the translation initiation site in all four cell lines (K-562, HT-29, PC-3 and HepG2) tested. Our results suggest that the hST3Gal III gene does not have multiple mRNAs, as have been identified for the hST3Gal IV, hST3Gal V and hST3Gal VI genes. The 5'-untranslated region was found to be divided into two exons, E1 and E2, indicating that the transcriptional regulation of hST3Gal III depends on the pIII promoter that exists 5'-upstream of exon E1. Luciferase assay results suggest that the nt -303 to -1 region is important for transcriptional activity of the hST3Gal III gene in all four cell lines tested. These results suggest that ubiquitous factors, such as Sp1, may be important for hST3Gal III gene expression.

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.

Genomic structure and promoter analysis of human NeuAc alpha2,3Gal beta1,3GalNAc alpha2,6-sialyltransferase (hST6GalNAc IV) gene

We have cloned the genomic DNA encoding the human NeuAc alpha2,3Gal beta1,3GalNAc alpha2,6-sialyltransferase (hST6GalNAc IV) and analysed its structure. The hST6GalNAc IV gene was found to span about 9 kb and to be composed of six exons. The 5'-RACE (rapid amplification of cDNA ends) results indicated that mRNA isoform of the hST6GalNAc IV was generated by alternative splicing in the 5'-untranslated region. The expression of this gene was highly restricted in human fetal tissues. The potential transcriptional start site was determined by CapSite hunting. Sequence analysis of the 5'-flanking region of this gene lacked canonical TATA and CAAT boxes, but contained several putative binding sites for transcription factors SP1, MZF1, GATA1, LMO2COM, NFAT, HFH8 and USF, etc. Functional analysis of the 5'-flanking region by transient expression method revealed a high transcriptional activity in both HepG2 cells and Molt4 cells in a cell type-dependent manner, but not in SK-N-MC cells. These results suggest cell type-specific regulation of the basal hST6GalNAc IV promoter activity.

Genomic structure, expression, and transcriptional regulation of human Gal beta 1,3 GalNAc alpha 2,3-sialyltransferase gene

In this report, we describe transcriptional regulation of the human Gal beta 1,3 GalNAc alpha 2,3-sialyltransferase II (hST3Gal II) gene. The results of 5'-RACE showed that the forms of two mRNAs differed only in the 5'-untranslated region (Types 1 and 2). According to analysis of the genomic structure, the transcriptional regulation of Type 1 and Type 2 mRNA isoforms depended on the p1 and p2 promoters, respectively. Both the mRNA isoforms were detected in various human tissues except colon, skeletal muscle, and peripheral blood leukocytes by RT-PCR analysis. In colon tissue, the Type 2 mRNA was detected, however, Type 1 mRNA was not detected. To elucidate the molecular basis of hST3Gal II gene expression, we isolated and characterized the function of the genomic region of hST3Gal II containing the p1 and p2 promoters. The activity of p2 promoter is much higher than that of the p1 promoter in the colon adenocarcinoma cell line, COLO205. These results suggest that the hST3Gal II gene is expressed specifically by alternative promoter utilization and is regulated in a tissue-restricted fashion at the level of transcription.

Expression of human protein tyrosine phosphatase epsilon in leucocytes: a potential ERK pathway-regulating phosphatase

The expression of protein tyrosine phosphatase epsilon (PTPepsilon) was studied in human tissues and blood cells. High mRNA expression was observed in peripheral blood leucocytes, particularly in monocytes and granulocytes which revealed at least four distinct transcripts. In lymphocytes, PTPepsilon expression was induced after 12-O-tetradecanoylphorbol-13-acetate (TPA) or antigen-receptor stimulation, indicating that PTPepsilon plays a role in the events taking place after antigen engagement. Previously, PTPepsilon has been shown to be involved in regulating voltage-gated potassium channel activity, insulin-receptor signalling and Janus kinase-signal transducers and activators of transcription (STAT) signalling. Transfection of cells with different PTPepsilon constructs and activator protein-1 reporter gene indicates that the catalytic activity of PTPepsilon is involved in the regulation of the mitogen-activated protein kinase cascade. In particular, the extracellular signal-regulated kinases (ERK1/2) were shown to be inhibited in both phosphorylation status and enzymatic activity after overexpression of PTPepsilon. Thus, PTPepsilon emerges as a phosphatase with a potential to regulate the ERK1/2 pathway either directly or indirectly through its catalytic activity.

Gene structure and transcriptional regulation of human Gal beta1,4(3) GlcNAc alpha2,3-sialyltransferase VI (hST3Gal VI) gene in prostate cancer cell line

We describe transcriptional regulation of the human Gal beta1,4(3) GlcNAc alpha2,3-sialyltransferase VI (hST3Gal VI) gene. The 5'-RACE results indicated that two mRNA forms differ only in the 5'-untranslated region (types 1 and 2). The genomic structure shows that the transcriptional regulation of type 1 and type 2 mRNA depends on the P1 and P2 promoters, respectively. Northern blots of RNA derived from various human tissues showed that the expression level of type 2 mRNA is higher than that of type 1 in the prostate. To elucidate the molecular basis of hST3Gal VI gene expression, we isolated and functionally characterized the genomic region containing the P1 and P2 promoters of hST3Gal VI. The activity of the P2 promoter is much higher than that of the P1 promoter in the prostate adenocarcinoma cell line PC-3. The results suggested that the hST3Gal VI gene is expressed specifically by alternative promoter utilization and is regulated in a tissue-restricted fashion at the level of transcription.

Alpha-2,6-sialylation regulation in CD34+ progenitor cells in the human bone marrow and granulocyte colony-stimulating factor mobilization

The use of peripheral blood (PB) progenitor cells to reconstitute hematopoiesis after high-dose chemotherapy is now common practice in the treatment of malignancies. Growth factors such as granulocyte colony-stimulating factor (G-CSF) induce high proliferation and self-renewal within the stem cell compartment of the bone marrow. This is followed by the release of a very high number of progenitor cells into the peripheral blood, the mechanism of which remains unclear. Previously, we have showed that high cell-surface sialylation reduces matured myeloid attachment to the bone marrow stroma, which is likely to help their release into the peripheral blood. Consequently, we decided to investigate the possibility that sialylation may also contribute to the CD34(+) cell release into the peripheral blood during G-CSF treatment. We found that G-CSF-mobilized PB CD34(+) cells exhibit an increase in the sialyltransferase ST6Gal-I mRNA level. The analysis of the heterogeneity of ST6Gal-I transcripts showed a predominance of the Y form in both bone marrow (BM) and G-CSF PB CD34(+) cells. Higher levels in ST6Gal-I mRNA resulted in a higher expression of alpha-2,6-sialylation on the surface of G-CSF PB CD34(+) cells when compared to noninduced PB CD34(+) cells but not higher to BM CD34(+) cells. Our present results, together with recent observations, suggest that ST6Gal-I and alpha-2,6-sialylation expression in myeloid cells is tightly dependent on the presence of G-CSF in their environment. Up-regulation of ST6Gal-I together with alpha-2,6-sialylation of cell surface glycoproteins is likely to modulate cellular adherence and survival of progenitor cells.

Progress in molecular and genetic studies of IgA nephropathy

Several new findings emerged recently from biochemical, genetic, and molecular studies of patients with IgA nephropathy. It appears that immunoglobulin A1-secreting cells of IgA nephropathy patients produce increased amounts of aberrantly glycosylated IgA1 in which the O-linked glycans in the hinge region are deficient in the content of galactose. The galactose-deficient IgA1 in the circulation is recognized by naturally occurring antibodies with anti-glycan specificity, and immune complexes are formed. These circulating immune complexes escape hepatic degradation and eventually are deposited in the kidney mesangium. Resident mesangial cells bind the IgA-containing immune complexes with the involvement of a novel IgA receptor and become activated. A familial form of IgA nephropathy has been linked to chromosome 6q22-23. Recent progress in molecular analyses of IgA nephropathy thus defines this disease as an autoimmune process with a novel IgA mesangial receptor and certain genetically determined traits.

Genomic structure of human GM3 synthase gene (hST3Gal V) and identification of mRNA isoforms in the 5'-untranslated region

GM3 synthase, which transfers CMP-NeuAc with an alpha2,3-linkage to a galactose residue of lactosylceramide, plays a key role in the biosynthesis of all complex gangliosides. In this study, cDNA and genomic clones encoding human GM3 synthase (hST3Gal V) were isolated, and the structural organization of the gene was determined. The hST3Gal V cDNA was identical in the coding region with cDNA that has been cloned previously from the HL-60 cells but different in the 5'-untranslated region (UTR). The hST3Gal V gene consisted of nine exons, which span approximately 44 kb, with exons ranging in size from 112 to 1242 bp. The coding region was located in exons 4-9, and all exon-intron boundaries except the acceptor site of intron 1 followed the GT-AG rule. The expression of this gene was highly restricted in both human fetal and adult tissues. By comparison of the nucleotide sequences of the genomic DNA with cDNA sequences including 5'-RACE products, we identified four isoforms (types 1-4) of the hST3Gal V mRNA that differ only in the 5'-UTR. Structural analysis of these isoforms suggests that mRNA isoforms of hST3Gal V are produced by a combination of alternative splicing and alternative promoter utilization.

Mouse ST6Gal sialyltransferase gene expression during mammary gland lactation

The sialyltransferase ST6Gal mediates the biosynthetic addition of sialic acid, via an alpha2,6 linkage, to the nonreducing end of terminal lactosamine structures. Transcription of the murine ST6Gal gene, Siat1, is regulated by the selective use of multiple promoters in a tissue- and development-specific manner. Here we report that Siat1 mRNA expression is dramatically elevated in lactating (relative to virgin) mouse mammary gland. The predominant ST6Gal mRNA species expressed in lactating mammary gland is a heretofore undocumented isoform containing a unique 5'-untranslated region originating from the mouse Siat1 genetic region, now defined as Exon L, residing 549-bp 5' of the previously characterized Exon X(2). Thus, the novel ST6Gal mRNA form initiates transcription from the region designated as p4 and incorporates the unique sequence from Exon L in 5'-juxtaposition to commonly shared sequences encoded on Exon I to Exon VI. In contrast, cells derived from virgin mammary tissue expressed only the housekeeping mRNA form derived from p3, with Exon O sequence preceding Exons I-VI. The Exon L-containing, p4 class of mRNA was also not detected in a survey of eight other mouse tissues. Previous reports have indicated a strong correlation between mammary cancers and elevated ST6Gal expression in rats and in human patients. However, we uncovered neither elevated expression of ST6Gal mRNA nor appearance of p4 class in mouse breast carcinomas experimentally induced by transformation with the polyoma-middle T oncogene. A number of established breast carcinoma cell lines were also examined, with ST6Gal mRNA and activity generally low. Moreover, with the exception of the Shionogi cell line, p4 class of ST6Gal mRNA was not expressed in any of the mouse breast carcinoma specimens examined. Taken together, our data indicate that murine ST6Gal induction during lactation is achieved by de novo recruitment of a normally silent promoter. Furthermore, the data provide no support for elevated Siat1 expression on the mRNA level in association with murine mammary gland carcinogenesis. With the single exception of the Shionogi cell line, the p3 class remains the predominant ST6Gal mRNA expressed in all other murine mammary carcinoma cells examined.

The sialyl-alpha2,6-lactosaminyl-structure: biosynthesis and functional role

Sialylation represents one of the most frequently occurring terminations of the oligosaccharide chains of glycoproteins and glycolipids. Sialic acid is commonly found alpha2,3- or alpha2,6-linked to galactose (Gal), alpha2,6-linked to N-acetylgalactosamine (GalNAc) or alpha2,8-linked to another sialic acid. The biosynthesis of the various linkages is mediated by the different members of the sialyltransferase family. The addition of sialic acid in alpha2,6-linkage to the galactose residue of lactosamine (type 2 chains) is catalyzed by beta-galactoside alpha2,6-sialyltransferase (ST6Gal.I). Although expressed by a single gene, this enzyme shows a complex pattern of regulation which allows its tissue- and stage-specific modulation. The cognate oligosaccharide structure, NeuAcalpha2,6Galbeta1,4GlcNAc, is widely distributed among tissues and is involved in biological processes such as the regulation of the immune response and the progression of colon cancer. This review summarizes the current knowledge on the biochemistry of ST6Gal.I and on the functional role of the sialyl-alpha2,6-lactosaminyl structure.

Beta-galactoside alpha2,6 sialyltransferase in human colon cancer: contribution of multiple transcripts to regulation of enzyme activity and reactivity with Sambucus nigra agglutinin

Colon cancer tissues display an increased activity of beta-galactoside alpha2,6 sialyltransferase (ST6Gal.I) and an increased reactivity with the lectin from Sambucus nigra (SNA), specific for alpha2,6-sialyl-linkages. Experimental and clinical studies indicate a contribution of these alterations to tumor progression, but their molecular bases are largely unknown. In many tissues, ST6Gal.I is transcriptionally regulated through the usage of different promoters that originate mRNAs diverging in the 5;-untranslated regions. RT-PCR analysis of 14 carcinoma samples, all expressing an increased ST6Gal.I enzyme activity, and of the corresponding normal mucosa revealed the presence of at least 2 transcripts. One, containing the 5;-untranslated exons, Y+Z, is thought to represent the "housekeeping" expression, and another previously described in hepatic tissues. Both the Y+Z and the hepatic transcripts were detectable in normal and cancer tissues but that latter form had a marked tendency to accumulate in cancer. The extent of alpha2,6-sialylation of glycoconjugates, as determined by SNA-dot blot analysis, was markedly enhanced in all cancer specimens, but the level of reactivity only partially correlated with the level of enzyme expression. Western blot analysis revealed a strikingly heterogeneous pattern of SNA reactivity among cancer tissues. These data indicate that: i) during neoplastic transformation of colonic cells, ST6Gal.I expression may be modulated through a differential promoter usage; ii) the extent of alpha2,6-sialylation of cancer cell membranes is not a direct function of the ST6Gal.I activity, strongly suggesting the existence of other, more complex mechanisms of regulation.

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.

Transcriptional regulation of human beta-galactoside alpha2, 6-sialyltransferase (hST6Gal I) gene during differentiation of the HL-60 cell line

We have previously shown that the expression of beta-galactoside alpha2,6-sialyltransferase (hST6Gal I) mRNA decreases during HL-60 differentiation induced with dimethyl sulfoxide (DMSO) and that transcriptional regulation depends on the P3 promoter that exists 5'-upstream of exon Y (A. Taniguchi et al., FEBS Lett.,441, 191-194, 1998). The regulation of hST6Gal I may be important for the expression of sialyl-Le(x)in HL-60 cells. In the present report, we studied the transcriptional regulation of hST6Gal I gene during DMSO-induced differentiation of HL-60 cells. To elucidate the molecular basis of hST6Gal I gene expression, the genomic region containing the P3 promoter of hST6Gal I was isolated and functionally characterized. Using a luciferase assay, we identified a functional DNA portion that confers an enhancer, located at nucleotide number (nt) -317 to -174 within the P3 promoter of hST6Gal I genomic DNA. This element contains two sequences similar to Sp1 (GC-box) and one sequence similar to Oct-1 recognition motifs (octamer sequence). Site-directed mutagenesis of Sp1 and Oct-1 sites showed that two Sp1 motifs and one Oct-1 motif are essential for transcriptional activity in HL-60 cells. Enhancer activity is suppressed during HL-60 cell differentiation induced with DMSO. These results suggest that GC-box and octamer sequence may play a critical role in the transcriptional regulation of the hST6Gal I gene during HL-60 cell differentiation.

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.

Up-regulation of alpha2,6 sialylation during myeloid maturation: a potential role in myeloid cell release from the bone marrow

The mechanisms by which mature myeloid cells are released from the bone marrow into the peripheral blood are not clearly understood. Glycosylation is likely to play an important role, as has been shown in the homing of lymphocytes to lymph nodes and of neutrophils to inflamed endothelia. Cell surface sialylation is an important component of many cellular adhesive interactions, both as ligand-promoting interactions, as occurs in selectin and sialoadhesin-mediated adhesion, and for reducing cell adhesion as in some cancer cells. We have studied the expression of cell surface alpha2,6-linked sialic acid in the maturation of normal bone marrow myeloid cells, the expression of alpha2,6-sialyltransferase mRNA, and the role of sialylation in the adherence of myeloid cells to bone marrow stroma. Our data show that there is a dramatic increase in cell surface alpha2,6-sialylation during the late stage of maturation. This up-regulation is restricted to specific glycoproteins including CD11b and CD18. It is associated with a relative increase in the level of alpha2,6-sialyltransferase mRNA compared with alpha2,3-sialyltransferase mRNA. The changes in mature bone marrow myeloid cells are associated with reduced cell binding to fibronectin and cultured bone marrow stroma. Our data strongly suggest that alpha2,6-sialylation may be important in the interaction between maturing myeloid cells and bone marrow stroma and may govern the release of cells from the bone marrow into the peripheral blood.

Molecular cloning and functional expression of two members of mouse NeuAcalpha2,3Galbeta1,3GalNAc GalNAcalpha2,6-sialyltransferase family, ST6GalNAc III and IV

Two cDNA clones encoding NeuAcalpha2,3Galbeta1,3GalNAc GalNAcalpha2, 6-sialyltransferase have been isolated from mouse brain cDNA libraries. One of the cDNA clones is a homologue of previously reported rat ST6GalNAc III according to the amino acid sequence identity (94.4%) and the substrate specificity of the expressed recombinant enzyme, while the other cDNA clone includes an open reading frame coding for 302 amino acids. The deduced amino acid sequence is not identical to those of other cloned mouse sialyltransferases, although it shows the highest sequence similarity with mouse ST6GalNAc III (43.0%). The expressed soluble recombinant enzyme exhibited activity toward NeuAcalpha2, 3Galbeta1, 3GalNAc, fetuin, and GM1b, while no significant activity was detected toward Galbeta1,3GalNAc or asialofetuin, or the other glycoprotein substrates tested. The sialidase sensitivity of the 14C-sialylated residue of fetuin, which was sialylated by this enzyme with CMP-[14C]NeuAc, was the same as that of ST6GalNAc III. These results indicate that the expressed enzyme is a new type of GalNAcalpha2,6-sialyltransferase, which requires sialic acid residues linked to Galbeta1,3GalNAc residues for its activity; therefore, we designated it mouse ST6GalNAc IV. Although the substrate specificity of this enzyme is similar to that of ST6GalNAc III, ST6GalNAc IV prefers O-glycans to glycolipids. Glycolipids, however, are better substrates for ST6GalNAc III.

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.

Differential expression of the hepatic transcript of beta-galactoside alpha2,6-sialyltransferase in human colon cancer cell lines

The activity of beta-galactoside alpha2,6-sialyltransferase (ST6Gal.1), the enzyme responsible for the addition of sialic acid in alpha2,6-linkage to N-acetyllactosaminic (Gal beta1,4GlcNAc) units of glycoconjugates, is increased in the vast majority of colon cancer specimens, and a positive correlation with an invasive phenotype has been suggested by several studies. In many tissues, ST6Gal.1 is regulated mainly at the transcriptional level through the use of different cell-specific promoters which generate transcripts differing in their 5'-untranslated regions. With the aim of understanding the molecular bases of the increased ST6Gal.1 expression in colon cancer, we investigated the expression of mRNA species in colon cancer cell lines and the relationship with enzyme activity and extent of alpha2,6-sialylation of cell glycoproteins. All cell lines examined express the form containing the 5'-untranslated exons Y and Z, typical of the "basal" expression of the gene, while others express also the liver transcript. This indicates that colon cancer cell lines can be grouped according to expression of the liver transcript of ST6Gal.1. The cell lines expressing only the Y+Z form display, in general, a lower activity:mRNA ratio, which might indicate reduced translational efficiency. The level of alpha2,6-sialylation of cell glycoproteins, as determined by reactivity with the Sambucus nigra lectin, is closely associated with the level of enzyme activity.

Dorsal root ganglia neuron-specific promoter activity of the rabbit beta-galactoside alpha1,2-fucosyltransferase gene

The rabbit H-blood type alpha1,2-fucosyltransferase (RFT-I), gene and its biosynthetic products, H antigens (Fucalpha1,2Galbeta), are abundantly expressed in a subset of dorsal root ganglia (DRG) neurons. To investigate the regulatory mechanisms for the RFT-I gene expression, we determined the genomic structure and promoter activity of this gene. PCR amplification of the 5' cDNA end analysis revealed two transcriptional start sites, 498 and 82 nucleotides upstream of the translational initiation codon, the latter site yielding a major 3.1-kb transcript specifically expressed in DRG, as revealed by Northern blotting. Promoter analysis of the 5'-flanking region of the RFT-I gene using a luciferase gene reporter system demonstrated strong promoter activity in PC12 cells, which express the rat H-type alpha1,2-fucosyltransferase gene, and Neuro2a mouse neuroblastoma cells. Deletion analysis revealed the 704-base pair minimal promoter region flanking the translational initiation codon, for which two distinct promoter activities were detected and differentially used in PC12 and Neuro2a cells. The minimal promoter region contained a GC-rich domain (GC content 80%), in which a Sp1 binding sequence and a GSG-like nerve growth factor-responsive element were found, but lacked TATA- and CAAT-boxes. Promoter analysis with a primary culture of DRG neurons demonstrated that the minimal promoter region of the RFT-I gene was sufficient for the expression of a reporter gene in DRG neurons. We conclude that the TATA-less GC-rich minimal promoter region of the RFT-I gene controls DRG small neuron-specific expression of the RFT-I gene.

Differentiation elicits negative regulation of human beta-galactoside alpha2,6-sialyltransferase at the mRNA level in the HL-60 cell line

We studied the regulation of the beta-galactoside alpha2,6-sialyltransferase (hST6Gal I) gene during HL-60 cell differentiation induced with dimethyl sulfoxide (DMSO), all transretinoic acid (ATRA), and phorbol myristate acetate (PMA). During HL-60 cell line differentiation, cell surface levels of alpha2,6-sialic acids expression decreased, as measured by flow cytometric analysis using Sambucus nigra agglutinin (SNA). Activities of hST6Gal I and levels of hST6Gal I mRNA dramatically decreased after 1 day of stimulation. Using reverse transcription polymerase chain reaction (PT-PCR), we found the major hST6Gal I mRNA isoform in HL-60 cells contains 5'-untranslated exons Y and Z. These results suggest that the expression of cell surface alpha2,6-sialic acids is controlled at the mRNA level, which is regulated by a promoter located 5'-upstream of exon Y.

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.

Porcine alpha1,3-galactosyltransferase: tissue-specific and regulated expression of splicing isoforms

Expression of the Gal alpha1,3 Gal epitope on membrane glycolipids and glycoproteins is known to vary widely from one tissue to another. In the course of studying the mechanisms underlying this variability, we have isolated from pig cDNA four sequences corresponding to four isoforms of alpha1,3-galactosyltransferase (alpha1,3GT), the Golgi enzyme that links galactose in alpha1,3 on the galactose residue of N-acetyllactosamine. The isoforms differ from each other in the alternative presence of two nucleotide stretches of 36 and 63 base pairs in a segment encoding the stem region of the protein. Stable expression experiments show that all four isoenzymes can confer alpha-galactosyltransferase activity to HeLa cells, and that they are all located within the Golgi compartment, indicating that variations in length in the stem region do not affect enzyme activity or cellular localization. Analysis of RNA from different pig organs and cells shows quantitative differences between tissues in levels of alpha1,3GT, as well as qualitative differences, the four isoforms being unequally represented in different tissues.

Structure and expression of H-type GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferase gene (FUT1). Two transcription start sites and alternative splicing generate several forms of FUT1 mRNA

The expression of the ABO antigens on erythrocyte membranes is regulated by H gene (FUT1)-encoded alpha(1,2)fucosyltransferase activity. We have examined the expression of the FUT1 in several tumor cell lines, including erythroid lineage and normal bone marrow cells, by Northern blot and/or reverse transcription-polymerase chain reaction (RT-PCR) analyses. RT-PCR indicated that bone marrow cells, erythroleukemic cells (HEL), and highly undifferentiated leukemic cells (K562) that have erythroid characteristics expressed the FUT1 mRNA while four leukemic cell lines did not. The FUT1 mRNA was also demonstrated in gastric, colonic, and ovarian (MCAS) cancer cell lines by RT-PCR. Northern blot analysis indicated that a 4. 0-kilobase FUT1 transcript was expressed in some of these tumor cell lines. Rapid amplification of 5' cDNA end (RACE) analysis suggested that the FUT1 transcript had several forms generated by two distinct transcription start sites and alternative splicing. The results of RT-PCR using specific primers for each starting exon suggested that two transcription initiation sites (exon 1A and exon 2A) of the FUT1 were identified in gastric cancer cells and in ovarian cancer cells. Only exon 1A was identified as a transcription start site in another gastric cancer cell line, two colonic cancer cell lines, and in K562 cells, whereas only exon 2A was identified in HEL cells and in bone marrow cells. These two transcription start sites were located 1.8 kilobases apart. Therefore, two distinct promoters appeared to be present in the FUT1. The distinct promoters of the FUT1 and alternative splicing of the FUT1 mRNA may be associated with time- and tissue-specific expression of the FUT1.

Structure and transcriptional regulation of human alpha-mannosidase IIX (alpha-mannosidase II isotype) gene

Golgi alpha-mannosidase II is a key enzyme of N-glycan processing. Its genetic defect is associated with HEMPAS (hereditary erythroblastic multinuclearity with positive acidified serum lysis test). We previously cloned cDNAs of human alpha-mannosidase II (alpha-MII) and its isotype, alpha-mannosidase IIX [alpha-MIIX, Misago, M., Liao, Y. F., Eto, S., Mattei. M. G., Moremen. K. W. & Fukuda, M. N. (1995) Proc. Natl Acad. Sci. USA 92, 11766-11770]. Constitutive expressions of alpha-MII and alpha-MIIX mRNA were shown in various human tissues. To investigate the transcriptional regulation of alpha-MIIX gene, we characterized the cosmid clone of 40-kb that includes the 5'-flanking sequence. This clone contains at least eight exons which encode 396 amino acid residues of a total of 1139 amino acid residues of alpha-MIIX. Primer-extension analysis revealed multiple transcription-initiation sites in the range from -70 to -58 relative to the translation-initiation site. No canonical TATA or CAAT boxes were observed, but a (G + C)-rich region was found in close proximity to the transcription-initiation site. To localize the transcriptional regulatory region of this gene, various regions of the 5' sequences were fused to the luciferase gene, and transient-expression assays were conducted in human melanoma G-361 cells. These studies indicated that sequence from -12 to + 11 relative to the most distal 5'-transcription-initiation site was involved in the promoter function. Within this region, the sequence GGGCGT similar to the consensus sequence of the Sp1 binding site, is present at positions -12 to -7. Enhancer activities were found in the region upstream of this site, notably from -4300 to -252. Thus, the alpha-MIIX promoter located in a CpG island is also regulated by upstream elements, indicating the complexity of alpha-MIIX gene expression.

Linkage-specific action of endogenous sialic acid O-acetyltransferase in Chinese hamster ovary cells

9-O-Acetylation of sialic acids shows cell type-specific and developmentally regulated expression in various systems. In a given cell type, O-acetylation can also be specific to a particular type of glycoconjugate. It is assumed that this regulation is achieved by control of expression of specific 9-O-acetyltransferases. However, it has been difficult to test this hypothesis, as these enzymes have so far proven intractable to purification or molecular cloning. During a cloning attempt, we discovered that while polyoma T antigen-positive Chinese hamster ovary cells (CHO-Tag cells) do not normally express cell-surface 9-O-acetylation, they do so when transiently transfected with a cDNA encoding the lactosamine-specific alpha2-6-sialyltransferase (Galbeta1-4GlcNAc:alpha2-6-sialyltransferase (ST6Gal I); formerly ST6N). This phenomenon is reproducible by stable expression of ST6Gal I in parental CHO cells, but not upon transfection of the competing lactosamine-specific alpha2-3-sialyltransferase (Galbeta1-(3)4GlcNAc:alpha2-3-sialyltransferase; (ST6Gal III) formerly ST3N) into either cell type. Further analyses of stably transfected parental CHO-K1 cells indicated that expression of the ST6Gal I gene causes selective 9-O-acetylation of alpha2-6-linked sialic acid residues on N-linked oligosaccharides. In a similar manner, while the alpha2-3-linked sialic acid residue of the endogenous GM3 ganglioside of CHO cells is not O-acetylated, transfection of an alpha2-8-sialyltransferase (GM3:alpha2-8-sialyltransferase (ST8Sia I); formerly GD3 synthase) caused expression of 9-O-acetylation of the alpha2-8-linked sialic acid residues of newly synthesized GD3. These data indicate either that linkage-specific sialic acid O-acetyltransferase(s) are constitutively expressed in CHO cells or that expression of these enzymes is secondarily induced upon expression of certain sialyltransferases. The former explanation is supported by a low level of background 9-O-acetylation found in parental CHO-K1 cells and by the finding that O-acetylation is not induced when the ST6Gal I or ST8Sia I cDNAs are overexpressed in SV40 T antigen-expressing primate (COS) cells. Taken together, these results indicate that expression of sialic acid 9-O-acetylation can be regulated by the action of specific sialyltransferases that alter the predominant linkage of the terminal sialic acids found on specific classes of glycoconjugates.

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.

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.

Differentiation -dependent expression of human beta-galactoside alpha 2,6-sialyltransferase mRNA in colon carcinoma CaCo-2 cells

We have previously documented a dramatic elevation in the activity of alpha 2,6-sialytransferase towards Gal beta 1,4GlcNAc (EC 2.4.99.1) (alpha 2,6ST) in CaCo-2 cells maintained in culture for several days after confluence to elicit a high degree of enterocytic differentiation phenotype. Northern analysis performed with a probe complementary to a region of human alpha 2,6ST mRNA common to all known transcripts demonstrated that the expression of alpha 2,6ST mRNA in CaCo-2 cells increased with the degree with the degree of differentiation. When probes complementary to 5'-untranslated exons (Y + Z or X) previously identified in transcripts isolated from human placenta and from several human lymphoblastoid cell lines were used, no hybridization signal with mRNA of CaCo-2 cells was found, as reported for the mRNA of hepatoma cell line HepG2 (Wang XC, Vertino A, Eddy RL, Byers MG, Jani-Sait SN, Shows TB, Lau JTY (1993) J Biol Chem 268: 4355-61). These results support the notion that the major alpha 2,6ST transcript of CaCo-2 cells was the hepatoma isoform or a new one, so far unreported. Consistent with the differentiation-dependent increase in alpha 2,6ST-mRNA expression, an elevation of the reactivity with Sambucus nigra agglutinin of differentiated CaCo-2 cell-surface was observed, indicating an enhanced alpha 2,6-sialylation of membrane glycoconjugates.

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.

Organization of the human N-acetylglucosaminyltransferase V gene

UDP-N-acetylglucosamine: alpha-6-D-mannoside beta-1,6-N-acetylglucosaminyltransferase V (GlcNAc transferase V), which catalyzes the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to alpha-6-D-mannoside, is an important enzyme regulating the branch formation in complex-type, N-linked oligosaccharides. It has been reported that the enzymic activity of GlcNAc transferase V increases after viral transformation and the enzymic product is closely related to the metastasis of tumors. We previously reported the purification, cDNA cloning and chromosomal mapping of human GlcNAc transferase V. In this study, we describe the isolation of genomic clones encoding human GlcNAc transferase V and the structure of the gene. The human GlcNAc transferase V gene is divided into 17 exons, and the open reading frame is encoded by exons 2-17, spanning 155 kb. Analysis of the 5'-untranslated regions of mRNAs from various cells showed multiple sequences depending on the cell types. The promoter region of the GlcNAc transferase V gene was characterized by searching for any consensus sequences matching those for transcription-factor binding. The consensus sequences for a TATA box, AP-1, AP-2, and some other transcription factors were found in the 5'-upstream region of exon 1, and consensus sequences for LF-A1, HNF1-HP1, liver-restricted transcription factors and other factors were also found in intron 1. Chloramphenicol acetyltransferase fusion plasmids with either the 5'-upstream region of exon 1 or intron 1 were constructed and transfected into COS-1 cells. Promoter activities of both DNA fragments were detected, indicating that transcription starts within this region. These data suggest that the human GlcNAc transferase V gene employs a multiple promoter system for its transcription, and gene expression may therefore be regulated in tissue-specific and cell-type-specific manners.

Conserved alternative splicing in the 5'-untranslated region of the muscle-specific enolase gene. Primary structure of mRNAs, expression and influence of secondary structure on the translation efficiency

We report here the isolation and characterization of cDNAs covering the 5'-end region of mouse and rat mRNAs that encode the beta or muscle-specific isoform of the glycolytic enzyme enolase. As previously determined for humans, two classes of beta-enolase transcripts with distinct sequences in their 5'-untranslated regions are present in both mouse and rat muscles. A mechanism of alternative splicing, conserved from mouse to man, generates the two forms of mRNA. Secondary-structure predictions indicated that, in all cases, a more stable secondary structure could exist in the 5' end of the message with the longer leader. In vitro transcripts containing defined human or mouse 5'-untranslated sequences were obtained by fusion of the different cDNA clones and tested for their relative translational efficiencies in rabbit reticulocyte lysates. Transcripts containing the human long and short leader sequences showed differences in the translational rate, suggesting a role for the 5'-untranslated region in the regulation of translation. No detectable difference was found between transcripts with the two distinct mouse leader sequences. In addition, both transcripts are bound to polysomes and are equally distributed along differently sized polysomes in C2C12 myogenic cells. The relative expression of the two spliced forms in developing and adult muscle tissues by means of reverse transcription and polymerase chain reaction did not show a stage-specific or a tissue-type-specific pattern. A putative functional role for the 5'-untranslated sequences of beta-enolase transcripts is discussed.