Expression of human chromosome 19p alpha(1,3)-fucosyltransferase genes in normal tissues. Alternative splicing, polyadenylation, and isoforms

NFκB-mediated activation of the cellular FUT3, 5 and 6 gene cluster by herpes simplex virus type 1

Herpes simplex virus type 1 has the ability to induce expression of a human gene cluster located on chromosome 19 upon infection. This gene cluster contains three fucosyltransferases (encoded by FUT3, FUT5 and FUT6) with the ability to add a fucose to an N-acetylglucosamine residue. Little is known regarding the transcriptional activation of these three genes in human cells. Intriguingly, herpes simplex virus type 1 activates all three genes simultaneously during infection, a situation not observed in uninfected tissue, pointing towards a virus specific mechanism for transcriptional activation. The aim of this study was to define the underlying mechanism for the herpes simplex virus type 1 activation of FUT3, FUT5 and FUT6 transcription. The transcriptional activation of the FUT-gene cluster on chromosome 19 in fibroblasts was specific, not involving adjacent genes. Moreover, inhibition of NFκB signaling through panepoxydone treatment significantly decreased the induction of FUT3, FUT5 and FUT6 transcriptional activation, as did siRNA targeting of p65, in herpes simplex virus type 1 infected fibroblasts. NFκB and p65 signaling appears to play an important role in the regulation of FUT3, FUT5 and FUT6 transcriptional activation by herpes simplex virus type 1 although additional, unidentified, viral factors might account for part of the mechanism as direct interferon mediated stimulation of NFκB was not sufficient to induce the fucosyltransferase encoding gene cluster in uninfected cells.

Characterization of bovine FUT7 furthers understanding of FUT7 evolution in mammals

Background

The Sialyl-Lewis X (Sle^x) is a well-known glycan structure involved in leukocyte homing and recruitment to inflammatory sites. SLe^x is well conserved among species and is mainly synthesized by FucT-VII in vertebrates. The enzyme responsible for its biosynthesis in cattle was not known.

Results

We cloned a cDNA sequence encoding bovine α3-fucosyltransferase VII that shares 83% identity with its human counterpart. Located at the BTA 11 telomeric region, the 1029 bp open reading frame is spread over two different exons, E1 which also contains the unique 5’-untranslated region and E2 which includes the entire 3’-untranslated region. The bfut7 expression pattern is restricted to thymus and spleen. A single transcript leading to the synthesis of a 342 aa protein was identified. The encoded fucosyltransferase, produced as a recombinant enzyme in COS-1 cells, was shown to be specifically responsible for SLe^x synthesis in cattle. In addition, we showed that the gene promoter evolved from fish to mammals towards a complex system related to the immune system. But beyond the fact that the gene regulation seems to be conserved among mammals, we also identified 7 SNPs including 3 missense mutations in the coding region in a small panel of animals.

Conclusions

The FUT7 sequence was highly conserved as well as the specific activity of the encoded protein FucT-VII. In addition, our in silico promoter analysis and the high rate of polymorphism suggested that its function is evolving toward a complex system related to the immune system. Furthermore, comparing bovine to human and mouse sequences, it appeared that a decrease in gene regulation was correlated with an increase in mutation rate and wider tissue expression.

Histo-blood group gene polymorphisms as potential genetic modifiers of infection and cystic fibrosis lung disease severity

BACKGROUND

The pulmonary phenotype in cystic fibrosis (CF) is variable; thus, environmental and genetic factors likely contribute to clinical heterogeneity. We hypothesized that genetically determined ABO histo-blood group antigen (ABH) differences in glycosylation may lead to differences in microbial binding by airway mucus, and thus predispose to early lung infection and more severe lung disease in a subset of patients with CF.

METHODS AND PRINCIPAL FINDINGS

Clinical information and DNA was collected on >800 patients with the DeltaF508/DeltaF508 genotype. Patients in the most severe and mildest quartiles for lung phenotype were enrolled. Blood samples underwent lymphocyte transformation and DNA extraction using standard methods. PCR and sequencing were performed using standard techniques to identify the 9 SNPs required to determine ABO blood type, and to identify the four SNPs that account for 90-95% of Lewis status in Caucasians. Allele identification of the one nonsynonymous SNP in FUT2 that accounts for >95% of the incidence of nonsecretor phenotype in Caucasians was completed using an ABI Taqman assay. The overall prevalence of ABO types, and of FUT2 (secretor) and FUT 3 (Lewis) alleles was consistent with that found in the Caucasian population. There was no difference in distribution of ABH type in the severe versus mild patients, or the age of onset of Pseudomonas aeruginosa infection in the severe or mild groups. Multivariate analyses of other clinical phenotypes, including gender, asthma, and meconium ileus demonstrated no differences between groups based on ABH type.

CONCLUSIONS AND SIGNIFICANCE

Polymorphisms in the genes encoding ABO blood type, secretor or Lewis genotypes were not shown to associate with severity of CF lung disease, or age of onset of P. aeruginosa infection, nor was there any association with other clinical phenotypes in a group of 808 patients homozygous for the DeltaF508 mutation.

Analysis of glycosyltransferase expression in metastatic prostate cancer cells capable of rolling activity on microvascular endothelial (E)-selectin

Prostate cancer (PCa) cell tethering and rolling on microvascular endothelium has been proposed to promote the extravasation of PCa cells. We have shown that these adhesive events are mediated through binding interactions between endothelial (E)-selectin and Lewis carbohydrates on PCa cells. Prior data indicate that E-selectin-mediated rolling of bone-metastatic PCa MDA PCa 2b (MDA) cells is dependent on sialyl Lewis X (sLe(X))-bearing glycoproteins. To explore the molecular basis of sLe(X) synthesis and E-selectin ligand (ESL) activity on PCa cells, we compared and contrasted the expression level of glycosyltransferases, characteristically involved in sLe(X) and ESL synthesis, in ESL(+) MDA cells among other ESL(-) metastatic PCa cell lines. We also created and examined ESL(hi) and ESL(lo) variants of MDA cells to provide a direct comparison of the glycosyltransferase expression level. We found that normal prostate tissue and all metastatic PCa cell lines expressed glycosyltransferases required for sialo-lactosamine synthesis, including N-acetylglucosaminyl-, galactosyl-, and sialyltransferases. However, compared with expression in normal prostate tissue, ESL(+) MDA cells expressed a 31- and 10-fold higher level of alpha1,3 fucosyltransferases (FT) 3 and 6, respectively. Moreover, FT3 and FT6 were expressed at 2- to 354-fold lower levels in ESL(-) PCa cell lines. Consistent with these findings, ESL(hi) MDA cells expressed a 131- and 51-fold higher level of FT3 and FT6, respectively, compared with expression in ESL(lo) MDA cells. We also noted that alpha1,3 FT7 was expressed at a 5-fold greater level in ESL(hi) MDA cells. Furthermore, ESL(lo) MDA cells did not display sLe(X) on glycoproteins capable of bearing sLe(X), notably P-selectin glycoprotein ligand-1. These results implicate the importance of alpha1,3 FT3, FT6, and/or FT7 in sLe(X) and ESL synthesis on metastatic PCa cells.

Virus-induced transcriptional activation of host FUT genes associated with neo-expression of Ley in cytomegalovirus-infected and sialyl-Lex in varicella-zoster virus-infected diploid human cells

Cell surface carbohydrate structures including sialyl-Lewis X (sLe(x)) and Lewis Y (Le(y)) are important ligands in normal and malignant tissues. The aim here was to determine the possible influence on the expression of such antigens by two viruses varicella-zoster virus (VZV) and cytomegalovirus (CMV) involved in persistent infections of humans. We found that infection of human diploid fibroblasts with both viruses resulted in transcriptional activation of several fucosyltransferase (FUT) genes that were either dormant or expressed at low levels in uninfected cells. Both viruses induced FUT3, FUT5, and FUT6, encoding alpha1,3- and/or alpha1,4-specific fucosyltransferases. CMV, but not VZV, induced transcription of FUT1 (encoding an alpha1,2-specific fucosyltransferase), FUT7, and FUT9. The changes in transcription of FUT genes were expectedly associated with expression of Le(y) in CMV-infected cells and sLe(x) in the VZV-infected fibroblasts although no expression of these antigens was observed in uninfected cells. One major explanation for this difference between CMV- and VZV-infected cells was that CMV, but not VZV, induced expression of FUT1, necessary for Le(y) expression. The induced carbohydrate antigens in CMV- and VZV-infected cells could be of significance for virus spread and possible escape from immune responses.

Glycosyltransferases involved in type 1 chain and Lewis antigen biosynthesis exhibit glycan and core chain specificity

Sialyl Lewis A (SLe(a)), Lewis A (Le(a)), and Lewis B (Le(b)) have been studied in many different biological contexts, for example in microbial adhesion and cancer. Their biosynthesis is complex and involves beta1,3-galactosyltransferases (beta3Gal-Ts) and a combined action of alpha2- and/or alpha4-fucosyltransferases (Fuc-Ts). Further, O-glycans with different core structures have been identified, and the ability of beta3Gal-Ts and Fuc-Ts to use these as substrates has not been resolved. Therefore, to examine the in vivo specificity of enzymes involved in SLe(a), Le(a), and Le(b) synthesis, we have transiently transfected CHO-K1 cells with relevant human glycosyltransferases and, on secreted reporter proteins, detected the resulting Lewis antigens on N- and O-linked glycans using western blotting and Le-specific antibodies. beta3Gal-T1, -T2, and -T5 could synthesize type 1 chains on N-linked glycans, but only beta3Gal-T5 worked on O-linked glycans. The latter enzyme could use both core 2 and core 3 precursor structures. Furthermore, the specificity of FUT5 and FUT3 in Le(a) and Le(b) synthesis was different, with FUT5 fucosylating H type 1 only on core 2, but FUT3 fucosylating H type 1 much more efficient on core 3 than on core 2. Finally, FUT1 and FUT2 were both found to direct alpha2-fucosylation on type 1 chains on both N- and O-linked structures. This knowledge enables us to engineer recombinant glycoproteins with glycan- and core chain-specific Lewis antigen substitution. Such tools will be important for investigations on the fine carbohydrate specificity of Le(b)-binding lectins, such as Helicobacter pylori adhesins and DC-SIGN, and may also prove useful as therapeutics.

Promoter analysis of the human alpha1,3/4-fucosyltransferase gene (FUT III)

alpha1,3/4-Fucosyltransferase (FUT3) is involved in the synthesis of sialyl Le(a) tetrasaccharide, a tumor-associated carbohydrate antigen. Fucosyltransferases are thought to be important regulatory enzymes in the synthesis of fucosylated structures. However, there are conflicting data on the role of FUT3 in the synthesis of this carbohydrate structure and more studies on the regulation of FUT III gene expression are needed. Therefore, as first step, the promoter of FUT III gene was cloned and characterized. Sequencing data showed the absence of TATA, CAAT, and GC boxes, but many binding sites for transcription factors, previously described in colon cancer cells, were identified. Analysis of enhancer and silencing elements of deletion mutants revealed the presence of basal promoter elements of the FUT III gene in the region -636 to -674 bp from the translation initiation site, and positive and negative regulatory elements within the -674 bp to -854 bp and -854 to -1220 regions, respectively. 5'-RACE analysis showed the presence of two transcripts with 5'-ends localized within the exon A. The 5'-end of the longer transcript extended -229 nucleotides from the translation start codon and contained a sequence corresponding to an Inr element, localizing the putative transcription initiation site within this sequence. The strong correlation between the promoter activity of the FUT III gene and the high expression of sialyl Le(a) observed in different colon carcinoma cell lines seem to confirm the important regulatory role of FUT3 in the synthesis of sialyl Le(a).

Role of sialyltransferases involved in the biosynthesis of Lewis antigens in human pancreatic tumour cells

The sialylated carbohydrate antigens, sialyl-Lewisx and sialyl-Lewisa, are expressed in pancreatic tumour cells and are related to their metastatic potential. While the action of the fucosyltransferases involved in the synthesis of these antigens has already been investigated, no studies have been carried out on the activity and expression of the alpha 2,3-sialyltransferases in pancreatic tumour cells. We describe the sialyltransferase (ST) activity, mRNA expression, and analysis of the cell carbohydrate structures in four human pancreatic adenocarcinoma cell lines of a wide range of neoplastic differentiation stages and in normal human pancreatic tissues. Total ST activity measured on asialofetuin, employing a CMP fluorescent sialic acid, varied among the pancreatic cell lines and could be correlated to the expression of their cell surface antigens. However, in some of the pancreatic cell lines, no relationship could be established with their ST3Gal III and IV mRNA expression. Human pancreatic tissues also showed ST expression and activity. However, it presented a much higher expression of neutral fucosylated structures than sialylated structures. In conclusion, ST activity levels in pancreatic cells could be correlated to their expression of sialylated epitopes, which indicates their involvement in the formation of the sialyl-Lewis antigens, in addition to fucosyltransferase activities.

LEC12 and LEC29 Gain-of-Function Chinese Hamster Ovary Mutants Reveal Mechanisms for Regulating VIM-2 Antigen Synthesis and E-selectin Binding

LEC12 and LEC29 are two gain-of-function Chinese hamster ovary glycosylation mutants that express the Fut9 gene encoding alpha(1,3)fucosyltransferase IX (alpha(1,3) Fuc-TIX). Both mutants express the Lewis X (Le(X)) determinant Galbeta(1,4)[Fucalpha(1,3)]GlcNAc, and LEC12, but not LEC29 cells, also express the VIM-2 antigen SAalpha(2,3)-Galbeta(1,4)GlcNAcbeta(1,3)Galbeta(1,4)[Fucalpha(1,3)]GlcNAc. Here we show that LEC29 cells transfected with a Fut9 cDNA express VIM-2, and thus LEC29 cells synthesize appropriate acceptors to generate the VIM-2 epitope. Semiquantitative reverse transcription-PCR showed that LEC12 has 10- to 20-fold less Fut9 gene transcripts than LEC29. However, Western analysis revealed that LEC12 has approximately 20 times more Fut9 protein than LEC29. The latter finding was consistent with our previous observation that LEC12 has approximately 40 times more in vitro alpha(1,3)Fuc-T activity than LEC29. The basis for the difference in Fut9 protein levels was found to lie in sequence differences in the 5'-untranslated regions (5'-UTR) of LEC12 and LEC29 Fut9 gene transcripts. Whereas reporter assays with the respective 5'-UTR regions linked to luciferase did not indicate a reduced translation efficiency caused by the LEC29 5'-UTR, transfected full-length LEC29 Fut9 cDNA or in vitro-synthesized full-length LEC29 Fut9 RNA gave less Fut9 protein than similar constructs with a LEC12 5'-UTR. This difference appears to be largely responsible for the reduced alpha(1,3)Fuc-TIX activity and lack of VIM-2 expression of LEC29 cells. This could be of physiological relevance, because LEC29 and parent Chinese hamster ovary cells transiently expressing a Fut9 cDNA were able to bind mouse E-selectin, although they did not express sialyl-Le(X).

Real time PCR for monitoring regulation of host gene expression in herpes simplex virus type 1-infected human diploid cells

Herpes simplex virus type 1 (HSV-1) induces prominent shifts in the rates of transcription of host cellular genes of relevance for the outcome of the viral infection. The quantitative analysis of transcription may be obscured by virus-induced alterations in the levels of RNA encoded by cellular housekeeping genes that are used commonly for normalisation of real time reverse transcription PCR (RT-qPCR). In the present study, we analysed beta-actin, GAPDH and 18S rRNA for their usefulness in normalisation of RT-qPCR analysis of the transcription of the HSV-1 gamma gB-1 gene and FUT5, a cellular gene induced by viral infection. The transcription of these genes was monitored in a TaqMan-based real time RT-PCR system over a 24h interval of virus infection of human embryonic lung fibroblasts. The levels of gB-1 and FUT5 RNA were normalised via difference in the threshold cycle (deltaC(t)) values relative to each and one of the housekeeping genes or calculated in relation to the number of infected cells without any further normalisation. The levels of RNA encoded by beta-actin or GAPDH were found to vary by several orders of magnitude during HSV-1 infection, introducing large errors in the estimation of the gB-1 and FUT5 RNA levels. In contrast, the variation of C(t) values for 18S rRNA was less than one cycle during 24h period of HSV-1 infection. The FUT5 and gB-1 RNA figures obtained by DeltaC(t) normalisation relative 18S rRNA were identical to those calculated in relation to the number of infected cells. These data recommend 18S rRNA for normalisation in HSV-1-infected human cells but discourage the use of beta-actin and GAPDH RNA for this purpose. By applying these procedures, it was shown that the transcription of FUT5 was increased by 50-fold 5-24h after HSV-1 infection and 200-fold by the inhibition of viral DNA replication in HSV-infected cells.

Transposable elements in mammals promote regulatory variation and diversification of genes with specialized functions

Nearly half of mammalian genomes are derived from ancient transposable elements (TEs). We analyzed the prevalence of TEs in untranslated regions of human and mouse mRNAs and found evidence suggesting that TEs affect the expression of many genes through the donation of transcriptional regulatory signals. Furthermore, we found that recently expanded gene classes, such as those involved in immunity or response to external stimuli, have transcripts enriched in TEs, whereas TEs are excluded from mRNAs of highly conserved genes with basic functions in development or metabolism. These results support the view that TEs have played a significant role in the diversification and evolution of mammalian genes.

Alternative promoter identified between a hypermethylated upstream region of repetitive elements and a CpG island in human ABO histo-blood group genes

We have studied the expression of human histo-blood group ABO genes during erythroid differentiation, using an ex vivo culture of AC133(-)CD34(+) cells obtained from peripheral blood. 5'-Rapid amplification of cDNA ends analysis of RNA from those cells revealed a novel transcription start site, which appeared to mark an alternative starting exon (1a) comprising 27 bp at the 5'-end of a CpG island in ABO genes. Results from reverse transcription-PCR specific to exon 1a indicated that the cells of both erythroid and epithelial lineages utilize this exon as the transcription starting exon. Transient transfection experiments showed that the region just upstream from the transcription start site possesses promoter activity in a cell type-specific manner when placed 5' adjacent to the reporter luciferase gene. Results from bisulfite genomic sequencing and reverse transcription-PCR analysis indicated that hypermethylation of the distal promoter region correlated with the absence of transcripts containing exon 1a, whereas hypermethylation in the interspersed repeats 5' adjacent to the distal promoter was commonly observed in all of the cell lines examined. These results suggest that a functional alternative promoter is located between the hypermethylated region of repetitive elements and the CpG island in the ABO genes.

Fucosyltransferases: structure/function studies

Alpha3-fucosyltransferases (alpha3-FucTs) catalyze the final step in the synthesis of a range of important glycoconjugates that function in cell adhesion and lymphocyte recirculation. Six members of this family of enzymes have been cloned from the human genome, and their expression pattern has been shown to be highly regulated. Each enzyme has a unique acceptor substrate binding pattern, and each generates a unique range of fucosylated products. Results from a range of studies have provided information on amino acids in the FucT sequence that contribute to the differential acceptor specificity for the FucTs, and to the binding of the nucleotide sugar donor GDP-fucose. These results, in conjunction with results obtained from the analysis of the disulfide bond pattern, have provided useful clues about the spatial distribution of amino acids that influence or directly contribute to substrate binding. This information is reviewed here, and a molecular fold prediction is presented which has been constructed based on the available information and current modeling methodology.

The polymorphisms of fucosyltransferases

The alpha(1,2)fucosyltransferase Se enzyme regulates the expression of the ABH antigens in secretion. Secretors, who have ABH antigens in their saliva, have at least one functional Se allele in the FUT2 locus, while non-secretors, who fail to express ABH antigens in saliva, are homozygous for the non-functional se allele. Molecular analyses of the FUT2 polymorphism of various populations have indicated the ethnic specificity of null alleles: the null allele se(428) is a common Se enzyme-deficient allele in Africans and Caucasians but does not occur in Asians, whereas the null allele se(357,385) is specific to Asians. The gene frequency of se(428) or se(357,385) is about 0.5 in each respective population. Why the se(428) is absent in Asians is of interest. Also here, we describe the polymorphisms of the fucosyltransferase genes (FUT1, FUT3 and FUT6).

Human alpha (1,3)-fucosyltransferase IV (FUTIV) gene expression is regulated by elk-1 in the U937 cell line

The alpha1,3-fucosyltransferase IV (FucTIV) encoded by its gene (FUTIV) is responsible for synthesis of Le(x) (Galbeta4[Fucalpha3]GlcNAcbeta3Galbeta1,R), which causes compaction in the morula stage of the preimplantation mouse embryo, as well as alpha1,3-fucosylation at multiple internal GlcNAc of unbranched poly-N-acetyllactosamine, termed "myeloglycan," the physiological epitope of E-selectin. Since myeloglycan-type structure is also expressed in various types of human cancer and may mediate E-selectin-dependent metastasis, expression of FUTIV is oncodevelopmentally regulated. The mechanisms controlling FUTIV expression remain to be clarified. In this report, we further characterize FUTIV gene structure and define a non-TATA box-dependent transcriptional start region just upstream from the translational start. FUTIV promoter/reporter fusion constructs defined a "full-length" promoter and highly active fragments in the macrophage-derived U937 and myeloid HL60 cell lines. One highly active fragment contains a consensus binding site for the Ets-1 transcription factor (Withers, D. A., and Hakomori, S. (1997) Glycoconj. J. 14, 764). Gel shift analysis shows specific binding to this site in nuclear extracts from U937 cells. Mutation of the Ets consensus site significantly reduces FUTIV promoter activity in both cell lines. Gel supershift and dominant negative cotransfection experiments identified the Ets family member Elk-1 as one component binding and regulating the FUTIV promoter in U937 cells. The significance of FUTIV regulation by Elk-1 is discussed.

Peritoneal colonization by human pancreatic cancer cells is inhibited by antisense FUT3 sequence

Several alpha(1,3/1,4) fucosyltransferases expressed in human pancreatic cancer cells can participate in the biosynthesis of cell surface sialyl-Lewis a and sialyl-Lewis x antigens that contribute to hematogenous metastatis. Previously, we observed a significant increase of the alpha(1,4) fucosyltransferase activity in tumoral pancreatic cell lines, suggesting that FUT3 could be involved in the sialyl-Lewis antigen expression. Therefore, we invalidated the expression of FUT3 by expressing FUT3 antisense sequence in the human pancreatic tumor BxPC-3 cell line, which expresses the alpha(1,4) fucosyltransferase activity and harbors the cell surface sialyl-Lewis antigens. The decrease of FUT3 transcript after transfection of antisense cDNA of FUT3 in these cells results in a substantial reduction of sialyl-Lewis antigen expression on cell surface. This decreased antigen expression was associated with an inhibition of adhesive properties to E-selectin and a decrease of metastatic power of FUT3 antisense-transfected BxPC-3 cells as tested in nude mice. Our study provides evidence that the expression level of FUT3 may regulate the expression of sialyl-Lewis a and sialyl-Lewis x surface antigens and consequently could play an important role in metastatic properties of human pancreatic cancer cells.

Peritoneal colonization by human pancreatic cancer cells is inhibited by antisense FUT3 sequence

Several alpha(1,3/1,4) fucosyltransferases expressed in human pancreatic cancer cells can participate in the biosynthesis of cell surface sialyl-Lewis a and sialyl-Lewis x antigens that contribute to hematogenous metastatis. Previously, we observed a significant increase of the alpha(1,4) fucosyltransferase activity in tumoral pancreatic cell lines, suggesting that FUT3 could be involved in the sialyl-Lewis antigen expression. Therefore, we invalidated the expression of FUT3 by expressing FUT3 antisense sequence in the human pancreatic tumor BxPC-3 cell line, which expresses the alpha(1,4) fucosyltransferase activity and harbors the cell surface sialyl-Lewis antigens. The decrease of FUT3 transcript after transfection of antisense cDNA of FUT3 in these cells results in a substantial reduction of sialyl-Lewis antigen expression on cell surface. This decreased antigen expression was associated with an inhibition of adhesive properties to E-selectin and a decrease of metastatic power of FUT3 antisense-transfected BxPC-3 cells as tested in nude mice. Our study provides evidence that the expression level of FUT3 may regulate the expression of sialyl-Lewis a and sialyl-Lewis x surface antigens and consequently could play an important role in metastatic properties of human pancreatic cancer cells.

FUT4 and FUT9 genes are expressed early in human embryogenesis

The Le(x) oligosaccharide is expressed in organ buds progressing in mesenchyma, during human embryogenesis. Myeloid-like alpha3-fucosyltransferases are good candidates to synthesize this oligosaccharide. We investigated by Northern analysis all the alpha3-fucosyltransferase gene transcripts and only FUT4 and FUT9 were detected. The enzymes encoded by the FUT4 and FUT9 genes are the first alpha3-fucosyltransferases strongly expressed during the first two months of embryogenesis. The Northern profile of expression of the embryo FUT4 transcripts is similar in size and sequence to the known FUT4 transcripts of 6 kb, 3 kb, and 2.3 kb, but a new FUT9 transcript of 2501 bp, different from the known mouse (2170 bp) and human (3019 bp) transcripts was cloned. FUT3, FUT5, FUT6, and FUT7 were not detected by Northern blot. The FUT3 and FUT6 transcripts start to appear at this stage, but are only detected by reverse transcriptase-PCR analysis. The expression of FUT5 is weaker than FUT3 and FUT6 and the RT-PCR signal is faint and irregular. FUT7 is not detected at all. Using mRNA from 40- to 65-day-old embryos, we have prepared different hexamer and oligo-dT cDNA libraries and cloned, by rapid amplification cDNA ends-PCR, FUT4 and FUT9 alpha3-fucosyltransferase transcripts. The tissue expression of the embryonic FUT9 transcript is closer to that observed for the mouse (brain), than to the known human (stomach) transcripts. The acceptor specificity and the kinetics of the alpha3-fucosyltransferase encoded by this FUT9 transcript are similar to the FUT4 enzyme, except for the utilization of the lac-di-NAc acceptor which is not efficiently transformed by the FUT9 enzyme. Like FUT4, this embryonic FUT9 is N-ethylmaleimide and heat resistant and the corresponding gene was confirmed to be localized in the chromosome band 6q16. Finally, this FUT9 transcript has a single expressed exon as has been observed for most of the other vertebrate alpha2- and alpha3-fucosyltransferases.

Localization of alpha 1,3-fucosyltransferase VI in Weibel-Palade bodies of human endothelial cells

Surface glycosylation of endothelial cells is relevant to various processes including coagulation, inflammation, metastasis, and lymphocyte homing. One of the essential sugars involved in these processes is fucose linked alpha1-->3 to N-acetylglucosamine. A family of alpha1,3-fucosyltransferases (FucTs) called FucT-III, IV, V, VI, VII, and IX is able to catalyze such fucosylations. Reverse transcription-PCR analysis revealed that human umbilical vein endothelial cells express all of the FucTs except FucT-IX. The predominant activity, as inferred by acceptor specificity of enzyme activity in cell lysates, is compatible with the presence of FucT-VI. By using an antibody to recombinant soluble FucT-VI, the enzyme colocalized with beta4-galactosyltransferase-1 to the Golgi apparatus. By using a polyclonal antiserum raised against a 17-aa peptide of the variable (stem) region of the FucT-VI, immunocytochemical staining of FucT-VI was restricted to Weibel-Palade bodies, as determined by colocalization with P-selectin and von Willebrand factor. SDS/PAGE immunoblotting and amino acid sequencing of internal peptides confirmed the identity of the antigen isolated by the peptide-specific antibody as FucT-VI. Storage of a fucosyltransferase in Weibel-Palade bodies suggests a function independent of Golgi-associated glycosylation.

Genetic background of Lewis negative blood group phenotype and its association with atherosclerotic disease in the NHLBI family heart study

OBJECTIVES

To examine the prevalence of four mutations, T59G, T1067A, T202C and C314T, of the human alpha(1,3/1,4) fucosyltransferase 3 (FUT 3) gene amongst persons with Lewis negative and those with Lewis positive blood group phenotype. An additional objective was to explore the hypothesis that these mutations are associated with coronary heart disease and inflammatory reaction.

DESIGN

A population-based cross-sectional study.

SETTING

Analysis of samples and data from the National Heart Lung and Blood Institute Family Heart Study.

SUBJECTS

All Lewis (a-b-) participants (n = 136) and a sample of Lewis positive participants (n = 136) of the Family Heart Study; all were of Caucasian ethnicity.

MAIN OUTCOME MEASURES

The prevalence of examined mutations by Lewis phenotype.

RESULTS

The examined mutations were common and strongly associated with the Lewis (a-b-) phenotype. Accordingly, 90-95% of Lewis (a-b-) individuals amongst Caucasians can be identified by screening for these four mutations. Exploratory analyses suggested that with the exception of T59G, all examined mutations were positively associated with prevalent coronary heart disease, although not statistically significantly, perhaps due to the small number of prevalent coronary heart disease cases. C-reactive protein tended to be higher amongst persons with a TC or CC genotype at position 202 (3.07 +/- 0.41 vs. 2.08 +/- 0.32 mg L-1, P = 0.06).

CONCLUSIONS

Four specific mutations of fucosyltransferase 3 gene are responsible for the vast majority of Lewis (a-b-) phenotypes in Caucasians. These mutations are common in the population at large and may be associated with increased risk of coronary heart disease. Further studies using larger samples are warranted.

Genomic structure and promoter analysis of the human alpha1, 6-fucosyltransferase gene (FUT8)

GDP-L-Fuc:N-acetyl-beta-D-glucosaminide alpha1,6-fucosyltransferase (alpha1,6FucT) catalyzes the transfer of a fucosyl moiety from GDP-fucose to the asparagine-linked GlcNAc residue of complex N-glycans via alpha1,6-linkage. We have cloned the genomic DNA which encodes the human alpha1,6FucT gene ( FUT8 ) and analyzed its structure. It was found that the gene consists of at least nine exons spanning more than a 50 kbp genomic region, and the coding sequence is divided into eight exons. The translation initiation codon was located at exon 2, and thus exon 1 encodes only 5'-untranslated sequences. Transcription initiation site of FUT8 was determined by 5'-rapid amplification of the cDNA end and a primer-extension analysis using the total RNA isolated from SK-OV-3 cells, which have a high level of alpha1,6FucT activity. We then characterized the FUT8 promoter region by a reporter gene assay. The luciferase reporter assay indicated that the 5'-flanking region of exon 1, which covered about 1 kbp, conferred the promoter activity in SK-OV-3 cells. This region contains potential binding sites for some transcription factors, such as bHLH, cMyb, GATA-1, as well as a TATA-box, but not a CCAAT motif. 5'-Untranslated sequences found in ESTs and the cDNA for the FUT8 suggest the presence of an additional exon(s) at the upstream of the first exon identified in this study, and therefore, the transcription of the gene would be regulated by multiple promoters.

Cytomegalovirus induces sialyl Lewis(x) and Lewis(x) on human endothelial cells

BACKGROUND

Cytomegalovirus (CMV) is the primary viral cause of complications in transplant recipients. We sought to understand the mechanisms of its dissemination and induction of vascular disease, which may lead to transplant complications. Sialyl Lewis(x) (sLe(x)) and Lewis(x) (Le(x)) are known for their roles in mediating cell adhesion and as tumor-associated carbohydrate antigens. Herein we explore whether CMV induces surface expression of these important molecules in endothelial cells (EC).

METHODS

Flow cytometry was used to detect surface expression of sLe(x) and Le(x) on CMV-infected human umbilical vein endothelial cells (HUVEC), with or without ultraviolet inactivation of the virus. To elucidate mechanisms of CMV-mediated induction, mRNA coding for predominant HUVEC sialyltransferases (ST) and fucosyltransferases (FT), key enzymes in sLe(x) and Le(x) synthesis, was analyzed by Northern blot. Dual immunohistochemical staining for sLe(x) and Le(x) expression of human colon and placental tissue was performed to investigate in vivo relevance.

RESULTS

sLe(x) expression on CMV-infected HUVEC was strongly up-regulated by 8 days after inoculation. Le(x) expression was detectable earlier and increased steadily over time. In contrast, ultraviolet-inactivated CMV did not induce expression of these molecules. Northern blot assays demonstrated higher levels of important EC glycosyltransferases ST-IV, FT-III, and FT-IV in CMV-infected EC. Finally, high levels of sLe(x) and Le(x) were expressed in CMV-infected EC in vivo.

CONCLUSIONS

Given the known biologic functions of sLe(x) and Le(x), we suggest that CMV induction of these molecules may have widespread consequences ranging from CMV dissemination to induction of CMV-associated vascular disease, including thrombosis.

Fucose in N-glycans: from plant to man

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

alpha1,3Fucosyltransferase VI is expressed in HepG2 cells and codistributed with beta1,4galactosyltransferase I in the golgi apparatus and monensin-induced swollen vesicles

The major alpha1,3fucosyltransferase activity in plasma, liver, and kidney is related to fucosyltransferase VI which is encoded by the FUT6 gene. Here we demonstrate the presence of alpha1, 3fucosyltransferase VI (alpha3-FucT VI) in the human HepG2 hepatoma cell line by specific activity assays, detection of transcripts, and the use of specific antibodies. First, FucT activity in HepG2 cell lysates was shown to prefer sialyl-N-acetyllactosamine as acceptor substrate indicating expression of alpha3-FucT VI. RT-PCR analysis further confirmed the exclusive presence of the alpha3-FucT VI transcripts among the five human alpha3-FucTs cloned to date. alpha3-FucT VI was colocalized with beta1,4galactosyltransferase I (beta4-GalT I) to the Golgi apparatus by dual confocal immunostaining. Pulse/chase analysis of metabolically labeled alpha3-FucT VI showed maturation of alpha3-FucT VI from the early 43 kDa form to the mature, endoglycosidase H-resistant form of 47 kDa which was detected after 2 h of chase. alpha3-FucT VI was released to the medium and accounted for 50% of overall cell-associated and released enzyme activity. Release occurred by proteolytical cleavage which produced a soluble form of 43 kDa. Monensin treatment segregated alpha3-FucT VI from the Golgi apparatus to swollen peripheral vesicles where it was colocalized with beta4-GalT I while alpha2,6(N)sialyltransferase remained associated with the Golgi apparatus. Both constitutive secretion of alpha3-FucT VI and its monensin-induced relocation to vesicles analogous to beta4-GalT I suggest a similar post-Golgi pathway of both alpha3-FucT VI and beta4-GalT I.

A cloned CD15s-negative variant of HL60 cells is deficient in expression of FUT7 and does not adhere to cytokine-stimulated endothelial cells

The initial steps of leukocyte adhesion depend on selectin/ligand interactions. Surface ligands on leukocytes are often modified by addition of the sialyl Lewis x (CD15s) determinant. Biosynthesis of CD15s is dependent upon alpha(2,3)sialyltransferases and alpha(1,3)fucosyltransferases. We report the isolation of an HL60 cell line variant, HL60A2, that no longer expresses CD15s. HL60A2 cells do not adhere to cytokine-stimulated endothelial cells. Enzymatic assays reveal that this cell line has normal alpha(2,3)sialyltransferase activity but is deficient in the alpha(1,3)fucosyltransferase responsible for biosynthesis of CD15s (FUT7). The fucosyltransferase that constructs the non-sialylated antigen, Lewis x (CD15), is expressed at high levels (FUT4). Transcript analyses show that FUT7 and FUT4 are inversely expressed in HL60 and variant cell lines. HL60A2 cells provide a tool to study the regulation of selectin ligands and corresponding human fucosyltransferase genes.

Alpha1,3-fucosyltransferase IX (Fuc-TIX) is very highly conserved between human and mouse; molecular cloning, characterization and tissue distribution of human Fuc-TIX

The amino acid sequence of Fuc-TIX is very highly conserved between mouse and human. The number of non-synonymous nucleotide substitutions of the Fuc-TIX gene between human and mouse was strikingly low, and almost equivalent to that of the alpha-actin gene. This indicates that Fuc-TIX is under a strong selective pressure of preservation during evolution. The human Fuc-TIX (hFuc-TIX) showed a unique characteristics, i.e. hFuc-TIX was not activated by Mn2+ and Co2+, whereas hFuc-TIV and hFuc-TVI were activated by the cations. The hFuc-TIX transcripts were abundantly expressed in brain and stomach, and interestingly were detected in spleen and peripheral blood leukocytes.

Molecular cloning of a novel human PAPS synthetase which is differentially expressed in metastatic and non-metastatic colon carcinoma cells

Subtractive hybridisation was used to select for genes which are differentially expressed between a highly metastatic human colon carcinoma cell line, KM12SM, and the isogenetic non-metastatic cell line, KM12C. This led to the isolation of cDNA clones for a novel human adenosine 5'-phosphosulphate kinase/ATP sulphurylase (PAPS synthetase). Northern hybridisation revealed a single 4.2 kb mRNA species which showed an approximately 20-fold higher level of expression in the non-metastatic cell line than in the metastatic cell line. The overlapping cDNA clones together covered 3,774 bp including the entire coding region of 1,842 bp encoding a protein of 614 amino acids (calculated molecular mass of 69,496 Da). The protein contains consensus sequences for APS kinase and ATP sulphurylase, in its amino- and carboxy-terminal regions, respectively, as well as other sequences that are highly conserved amongst ATP sulphurylases and APS kinases. Interestingly, consensus sequences for GTPase activity were also identified, indicating that enzyme activity may be regulated by an intrinsic GTPase mechanism. Overall the new protein is 78% homologous with a previously described human PAPS synthetase (PAPSS1) indicating that we have identified the second member of a gene family which we have provisionally named PAPSS2. The gene locus for PAPSS2 was identified on chromosome 10 at 10q23.1-q23.2. This locus has synteny with the mouse brachymorphic gene recently identified as a PAPS synthetase (SK2). PAPSS2 appears to be the human homologue of this gene and thus PAPSS2 is likely to be important in human skeletogenesis.

The gain-of-function Chinese hamster ovary mutant LEC11B expresses one of two Chinese hamster FUT6 genes due to the loss of a negative regulatory factor

The LEC11 Chinese hamster ovary (CHO) gain-of-function mutant expresses an alpha(1,3)fucosyltransferase (alpha(1,3)Fuc-T) activity that generates the LeX, sialyl-LeX, and VIM-2 glycan determinants and has been extensively used for studies of E-selectin ligand specificity. In order to identify regulatory mechanisms that control alpha(1,3)Fuc-T expression in mammals, mechanisms of FUT gene expression were investigated in LEC11 cells and two new, independent mutants, LEC11A and LEC11B. Northern and ribonuclease protection analyses, using probes that span the coding region of a cloned CHO FUT gene, detected transcripts in each LEC11 mutant but not in CHO cells or other gain-of-function CHO mutants that express a different alpha(1,3)Fuc-T activity. Coding region sequence analysis and alpha(1,3)Fuc-T acceptor specificity comparisons with recombinant human Fuc-TV and Fuc-TVI showed that the cloned FUT gene is orthologous to the human FUT6 gene. Southern analyses identified two closely related FUT6 genes in the Chinese hamster, whose evolutionary relationships are discussed. The blots showed that rearrangements had occurred in LEC11A and LEC11 genomic DNA, consistent with a cis mechanism of FUT6 gene activation in these mutants. By contrast, somatic cell hybrid analyses revealed that LEC11B cells express FUT6 gene transcripts due to the loss of a trans-acting, negative regulatory factor. Sequencing of reverse transcriptase-polymerase chain reaction products identified unique 5'- and 3'-untranslated region sequences in FUT6 gene transcripts from each LEC11 mutant. Northern and Southern analyses with gene-specific probes showed that LEC11A cells express only the cgFUT6A gene (where cg is Cricetulus griseus), whereas LEC11 and LEC11B cells express only the cgFUT6B gene. In LEC11A x LEC11B hybrid cells, the cgFUT6A gene was predominantly expressed, as predicted if a trans-acting negative regulatory factor functions to suppress cgFUT6B gene expression in CHO cells. This factor is predicted to be a cell type-specific regulator of FUT6 gene expression in mammals.

Synthesis of oligosaccharides by bacterial enzymes

Many human pathogens initiate disease by utilizing their microbial adhesin proteins to attach to glycoconjugates on host cell mucosal surfaces. Soluble oligosaccharides of identical or similar structure to these naturally occurring ligands can both prevent bacterial attachment as well as mediate the release of attached bacteria. Since it has not been possible to isolate large quantities of these compounds, we have developed enzyme-based technologies to synthesize several relevant human oligosaccharides. Using cloned bacterial glycosyltransferases, we can synthesize several hundred grams of these oligosaccharides at a time. The availability of these large quantities will allow these compounds to be tested as anti-adhesive pharmaceutical agents as well as lead to expanded practical applications.

The yeast expression system for recombinant glycosyltransferases

Glycosyltransferases are increasingly being used for in vitro synthesis of oligosaccharides. Since these enzymes are difficult to purify from natural sources, expression systems for soluble forms of the recombinant enzymes have been developed. This review focuses on the current state of development of yeast expression systems. Two yeast species have mainly been used, i.e. Saccharomyces cerevisiae and Pichia pastoris. Safety and ease of fermentation are well recognized for S. cerevisiae as a biotechnological expression system; however, even soluble forms of recombinant glycosyltransferases are not secreted. In some cases, hyperglycosylation may occur. P. pastoris, by contrast, secrete soluble orthoglycosylated forms to the supernatant where they can be recovered in a highly purified form. The review also covers some basic features of yeast fermentation and describes in some detail those glycosyltransferases that have successfully been expressed in yeasts. These include beta1,4galactosyltransferase, alpha2,6sialyltransferase, alpha2,3sialyltransferase, alpha1,3fucosyltransferase III and VI and alpha1,2mannosyltransferase. Current efforts in introducing glycosylation systems of higher eukaryotes into yeasts are briefly addressed.

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.

Hormonal control of H-type alpha(1-2)fucosyltransferase messenger ribonucleic acid in the mouse uterus

The H epitope, an alpha(1-2)fucosylated carbohydrate structure, has been implicated in initial attachment of the murine blastocyst to luminal uterine epithelial cells in vitro. In this study, the expression of the H-type alpha(1-2)fucosyltransferase (FUT1) gene was examined in endometrium of mice. Northern blotting of luminal epithelial RNA identified a single 6.2-kilobase transcript. In situ hybridization studies showed a signal for FUT1 mRNA on Days 1-3 of pregnancy in glands and luminal epithelium. The signal diminished by Day 4 and could not be detected on Day 5 of pregnancy. The in situ signal in endometrial epithelia was highest at estrus and metestrus and was absent at diestrus. Estrogen treatment after ovariectomy gave strong FUT1 mRNA expression in epithelia, but with progesterone, progesterone + estrogen, or vehicle, no message could be detected. A semiquantitative reverse transcription-polymerase chain reaction (PCR) analysis of FUT1 mRNA from luminal epithelium generated large amounts of PCR product on Day 1 of pregnancy; this diminished on Days 2, 3, and 4, and the product was barely detectable on Day 5. A kinetic analysis of FUT1 activity on Day 1 of pregnancy suggested a single enzyme with a Michaelis-Menten constant (Km) of 0.29 mM towards phenyl-beta-D-galactoside and of 1.75 mM towards Galbeta(1-3)GalNAc. These results suggest that expression of the H epitope is regulated at the level of FUT1 transcription and that transcription is stimulated by estrogen in the endometrial epithelium.

In vivo specificity of human alpha1,3/4-fucosyltransferases III-VII in the biosynthesis of LewisX and Sialyl LewisX motifs on complex-type N-glycans. Coexpression studies from bhk-21 cells together with human beta-trace protein

Each of the five human alpha1,3/4-fucosyltransferases (FT3 to FT7) has been stably expressed in BHK-21 cells together with human beta-trace protein (beta-TP) as a secretory reporter glycoprotein. In order to study their in vivo properties for the transfer of peripheral Fuc onto N-linked complex-type glycans, detailed structural analysis was performed on the purified glycoprotein. All fucosyltransferases were found to peripherally fucosylate 19-52% of the diantennary beta-TP N-glycans, and all enzymes were capable of synthesizing the sialyl LewisX (sLex) motif. However, each enzyme produced its own characteristic ratio of sLex/Lex antennae as follows: FT7 (only sLex), FT3 (14:1), FT5 (3:1), FT6 (1.1:1), and FT4 (1:7). Fucose transfer onto beta-TP N-glycans was low in FT3 cells (11% of total antennae), whereas the values for FT7, FT5, FT4, and FT6 cells were 21, 25, 35, and 47%, respectively. FT3, FT4, FT5, and FT7 transfer preponderantly one Fuc per diantennary N-glycan. FT4 preferentially synthesizes di-Lex on asialo diantennary N-glycans and mono-Lex with monosialo chains. In contrast, FT6 forms mostly alpha1,3-difucosylated chains with no, one, or two NeuAc residues. FT3, FT4, and FT6 were proteolytically cleaved and released into the culture medium in significant amounts, whereas FT7 and FT5 were found to be largely resistant toward proteolysis. Studies on engineered soluble variants of FT6 indicate that these forms do not significantly contribute to the in vivo fucose transfer activity of the enzyme when expressed at activity levels comparable to those obtained for the wild-type Golgi form of FT6 in the recombinant host cells.

Expression cloning and characterization of a novel murine alpha1, 3-fucosyltransferase, mFuc-TIX, that synthesizes the Lewis x (CD15) epitope in brain and kidney

The 3-fucosyl-N-acetyllactosamine (Lewis x, CD15, SSEA-1) carbohydrate epitope is widely distributed in many tissues and is developmentally expressed in some rodent and human tissues, i.e. brain and lung, and mouse early embryo. In such tissues, the Lewis x epitope is considered to be involved in cell-cell interactions. We isolated a novel mouse alpha1,3-fucosyltransferase gene, named mFuc-TIX, from an adult mouse brain cDNA library using the expression cloning method. On flow cytometric analysis, Namalwa cells transfected stably with the mFuc-TIX gene showed a marked increase in Lewis x epitopes but not sialyl Lewis x epitopes. As seen experiments involving oligosaccharides as acceptor substrates, mFuc-TIX transfers a fucose to lacto-N-neotetraose but not to either alpha2,3-sialyl lacto-N-neotetraose or lacto-N-tetraose. The substrate specificity of mFuc-TIX was similar to that of mouse myeloid-type alpha1,3-fucosyltransferase (mFuc-TIV). The deduced amino acid sequence of mFuc-TIX, consisting of 359 residues, indicated a type II membrane protein and shows low degrees of homology to the previously cloned alpha1,3-fucosyltransferases, i.e. mFuc-TIV (48.4%), mouse Fuc-TVII (39.1%), and human Fuc-TIII (43.0%), at the amino acid sequence level. A phylogenetic tree of the alpha1, 3-fucosyltransferases constructed by the neighbor-joining method showed that mFuc-TIX is quite distant from the other alpha1, 3-fucosyltransferases. Thus, mFuc-TIX does not belong to any subfamilies of known alpha1,3Fuc-Ts. The mFuc-TIX transcript was mainly detected in brain and kidney with the Northern blotting and competitive reverse transcription-polymerase chain reaction methods, whereas the mFuc-TIV transcript was not detected in brain with these methods. On in situ hybridization, the mFuc-TIX transcript was detected in neuronal cells but not in the glial cells including astrocytes. These results strongly indicated that mFuc-TIX participates in the Lewis x synthesis in neurons of the brain and may be developmentally regulated.

The rat alpha1, 3-fucosyltransferase (rFucT-IV) gene encodes both long and short forms of the enzyme which share the same intracellular location

Fucosyltransferase (FucT) activity has been detected on the surface of mouse germ cells and rat Sertoli cells, and has been postulated to play a role in cell-cell interactions. A recently cloned rat FucT (rFucT-IV) is expressed in the testes, and thus is a candidate for encoding the cell-surface FucT activity. This study maps the 5'-ends of several rFuc-T-IV mRNAs, and these results suggest that initiation of transcription may occur both upstream of the first ATG, as well as between the first two closely spaced, in-frame ATGs. Thus, in certain tissues, notably spleen, significant amounts of both a long and a short form of rFucT-IV would be predicted. This study also determines some basic properties of both the long and short forms of rFucT-IV, and investigates whether the use of alternative ATGs would allow FucT activity to be expressed both on the cell surface and in the Golgi. Plasmids that encode FLAG-epitope-labeled rFucT-IVs that initiate from either of the two ATGs were constructed, and rFucT-IV was expressed either in vitro using cell-free rabbit reticulocyte lysate, or after transfection in tissue culture. The results from these studies demonstrate that rFucT-IV is a glycosylated, transmembrane protein with a short cytoplasmic tail, and that either of the two ATGs in the 5' region of the rFucT-IV gene are capable of acting as functional initiators of translation in vitro, to produce enzymatically active glycoproteins. However, no difference in the intracellular localization between the transferase containing a 48 amino acid or a 15 amino acid cytoplasmic tail was detected by immunocytochemistry, as both show the same pattern of Golgi-like staining in several different cell types, with no indication of surface expression. Thus, the additional amino-terminal 33 amino acids of the long form of rFucT-IV do not appear to influence its intracellular location in the cell types investigated.

Fucosyltransferase activities in human pancreatic tissue: comparative study between cancer tissues and established tumoral cell lines

Human pancreatic cancer is characterized by an alteration in fucose-containing surface blood group antigens such as H antigen, Lewis b, Lewis y, and sialyl-Lewis. These carbohydrate determinants can be synthesized by sequential action of alpha(2,3) sialyltransferases or alpha(1,2) fucosyltransferases (Fuc-T) and alpha(1,3/1,4) fucosyltransferases on (poly)N-acetyllactosamine chains. Therefore, the expression and the function of seven fucosyltransferases were investigated in normal and cancer pancreatic tissues and in four pancreatic carcinoma cell lines. Transcripts of FUT1, FUT2, FUT3, FUT4, FUT5, and FUT7 were detected by RT-PCR in carcinoma cell lines as well as in normal and tumoral tissues. Interestingly, the FUT6 message was only detected in tumoral tissues. Analysis of the acceptor substrate specificity for fucosyltransferases indicated that alpha(1,2) Fuc-T, alpha(1,3) Fuc-T, and alpha(1,4) Fuc-T were expressed in microsome preparations of all tissues as demonstrated by fucose incorporation into phenyl beta-d-galactoside, 2'-fucosyllactose, N-acetyllactosamine, 3'-sialyl-N-acetyllactosamine, and lacto-N-biose. However, these fucosyltransferase activities varied between tissues. A substantial decrease of alpha(1,2) Fuc-T activity was observed in tumoral tissues and cell lines compared to normal tissues. Conversely, the activity of alpha(1,4) Fuc-T, which generates Lewis a and sialyl-Lewis a structures, and that of alpha(1,3) Fuc-T, able to generate a lactodifucotetraose structure, were very important in SOJ-6 and BxPC-3 cell lines. These increases correlated with an enhanced expression of Lewis a, sialyl-Lewis a, and Lewis y on the cell surface. The activity of alpha(1,3) Fuc-T, which participates in the synthesis of the sialyl-Lewis x structure, was not significantly modified in cell lines compared to normal tissues. However, the sialyl-Lewis x antigen was expressed preferentially on the surface of SOJ-6 and BxPC-3 cell lines but was not detected on Panc-1 and MiaPaca-2 cell lines suggesting that several alpha(1,3) Fuc-T might be involved in sialyl-Lewis x synthesis.

Acceptor specificity of the human leukocyte alpha3 fucosyltransferase: role of FucT-VII in the generation of selectin ligands

The alpha3 fucosyltransferase, FucT-VII, is one of the key glycosyltransferases involved in the biosynthesis of the sialyl Lewis X (sLex) antigen on human leukocytes. The sialyl Lewis X antigen (NeuAcalpha(2-3)Galbeta(1-4)[Fucalpha(1-3)]GlcNAc-R) is an essential component of the recruitment of leukocytes to sites of inflammation, mediating the primary interaction between circulating leukocytes and activated endothelium. In order to characterize the enzymatic properties of the leukocyte alpha3 fucosyltransferase FucT-VII, the enzyme has been expressed in Trichoplusia ni insect cells. The enzyme is capable of synthesizing both sLexand sialyl-dimeric-Lexstructures in vitro , from 3'-sialyl-lacNAc and VIM-2 structures, respectively, with only low levels of fucose transfer observed to neutral or 3'-sulfated acceptors. Studies using fucosylated NeuAcalpha(2-3)-(Galbeta(1-4)GlcNAc)3-Me acceptors demonstrate that FucT-VII is able to synthesize both di-fucosylated and tri-fucosylated structures from mono-fucosylated precursors, but preferentially fucosylates the distal GlcNAc within a polylactosamine chain. Furthermore, the rate of fucosylation of the internal GlcNAc residues is reduced once fucose has been added to the distal GlcNAc. These results indicate that FucT-VII is capable of generating complex selectin ligands, in vitro , however the order of fucose addition to the lactosamine chain affects the rate of selectin ligand synthesis.

Protein N-glycosylation: molecular genetics and functional significance

Protein N-glycosylation is a metabolic process that has been highly conserved in evolution. In all eukaryotes, N-glycosylation is obligatory for viability. It functions by modifying appropriate asparagine residues of proteins with oligosaccharide structures, thus influencing their properties and bioactivities. N-glycoprotein biosynthesis involves a multitude of enzymes, glycosyltransferases, and glycosidases, encoded by distinct genes. The majority of these enzymes are transmembrane proteins that function in the endoplasmic reticulum and Golgi apparatus in an ordered and well-orchestrated manner. The complexity of N-glycosylation is augmented by the fact that different asparagine residues within the same polypeptide may be modified with different oligosaccharide structures, and various proteins are distinguished from one another by the characteristics of their carbohydrate moieties. Furthermore, biological consequences of derivatization of proteins with N-glycans range from subtle to significant. In the past, all these features of N-glycosylation have posed a formidable challenge to an elucidation of the physiological role for this modification. Recent advances in molecular genetics, combined with the availability of diverse in vivo experimental systems ranging from yeast to transgenic mice, have expedited the identification, isolation, and characterization of N-glycosylation genes. As a result, rather unexpected information regarding relationships between N-glycosylation and other cellular functions--including secretion, cytoskeletal organization, proliferation, and apoptosis--has emerged. Concurrently, increased understanding of molecular details of N-glycosylation has facilitated the alignment between N-glycosylation deficiencies and human diseases, and has highlighted the possibility of using N-glycan expression on cells as potential determinants of disease and its progression. Recent studies suggest correlations between N-glycosylation capacities of cells and drug sensitivities, as well as susceptibility to infection. Therefore, knowledge of the regulatory features of N-glycosylation may prove useful in the design of novel therapeutics. While facing the demanding task of defining properties, functions, and regulation of the numerous, as yet uncharacterized, N-glycosylation genes, glycobiologists of the 21st century offer exciting possibilities for new approaches to disease diagnosis, prevention, and cure.

Lewis X biosynthesis in Helicobacter pylori. Molecular cloning of an alpha(1,3)-fucosyltransferase gene

The lipopolysaccharide of certain strains of Helicobacter pylori was recently shown to contain the Lewis X (Lex) trisaccharide (Galbeta-1, 4-(Fucalpha(1,3))-GlcNAc). Lex is an oncofetal antigen which appears on human gastric epithelium, and its mimicry by carbohydrate structures on the surface of H. pylori may play an important part in the interaction of this pathogen with its host. Potential roles for bacterial Lex in mucosal adhesion, immune evasion, and autoantibody induction have been proposed (Moran, A. P., Prendergast, M. M., and Appelmelk, B. J. (1996) FEMS Immunol. Med. Microbiol. 16, 105-115). In mammals, the final step of Lex biosynthesis is the alpha(1,3)-fucosylation of GlcNAc in a terminal Galbeta(1-->4)GlcNAc unit, and a corresponding GDP-fucose:N-acetylglucosaminyl alpha(1,3) fucosyltransferase (alpha(1,3)-Fuc-T) activity was recently discovered in H. pylori extracts. We used part of a human alpha(1, 3)-Fuc-T amino acid sequence to search an H. pylori genomic data base for related sequences. Using a probe based upon weakly matching data base sequences, we retrieved clones from a plasmid library of H. pylori DNA. DNA sequence analysis of the library clones revealed a gene which we have named fucT, encoding a protein with localized homology to the human alpha(1,3)-Fuc-Ts. We have demonstrated that fucT encodes an active Fuc-T enzyme by expressing the gene in Escherichia coli. The recombinant enzyme shows a strong preference for type 2 (e.g. LacNAc) over type 1 (e.g. lacto-N-biose) acceptors in vitro. Certain residues in a short segment of the H. pylori protein are completely conserved throughout the alpha(1,3)-Fuc-T family, defining an alpha(1,3)-Fuc-T motif which may be of use in identifying new fucosyltransferase genes.

Distinct substrate specificities of five human alpha-1,3-fucosyltransferases for in vivo synthesis of the sialyl Lewis x and Lewis x epitopes

Five different human alpha-1,3-fucosyltransferase genes, the Fuc-TIII, Fuc-TIV, Fuc-TV, Fuc-TVI and Fuc-TVII genes, have been cloned to date. We transfected HeLa cells and Namalwa cells with each of the five different genes, and established a series of stable cloned transformant cells. Thin-layer chromatography immunostaining analysis revealed that all five enzymes were able to synthesize sialyl Lewis x (sLe(x)) epitopes on glycolipids in HeLa cells, but each enzyme showed a different preference as to the carbohydrate chain length on glycolipids as acceptor substrates. Fuc-TIII and Fuc-TV showed very similar patterns of sLe(x) positive bands, which indicated that the enzymes have similar acceptor substrate specificities. Fuc-TVI exhibited a little different pattern from those of the former two enzymes. Fuc-TIV and Fuc-TVII showed similarity in the positive bands, however, their patterns were quite different from those of the former three enzymes. Four enzymes except for Fuc-TVII were able to synthesize the Lewis x (Le(x)) epitope on glycolipids in HeLa cells. Fuc-TV alone showed a little different pattern of Le(x) positive bands from those of the other three enzymes. Flow cytometric analysis of HeLa cells and Namalwa cells again demonstrated the similar specificities of Fuc-TIII and Fuc-TV. They exhibited similar stronger staining with FH6 (anti-sLe(x)) antibodies than that with the other enzymes. A phylogenetic tree of the five enzymes constructed using the neighbor-joining method showed good agreement with the similarities in the enzyme substrate specificity.

Advances in molecular genetics of alpha-2- and alpha-3/4-fucosyltransferases

Fucosyltransferases are involved in the last steps of the biosynthesis of ABH and Lewis oligosaccharide antigens. Seven human genes (FUT1 to FUT7) and one pseudogene (Sec 1) have been cloned and localized on different chromosomes (9q34.3; 11q21; 19p13.3 and 19q13.3). Their locations and their high degree of primary sequence identity, suggest that they have appeared by successive duplications followed by translocation and divergent evolution. Their expression is tissue specific and they present a switch during human embryo-foetal development similar to that of hemoglobins. Polymorphic genes FUT1-FUT2 and FUT3-FUT5-FUT6 are organized in two clusters and each gene is partially or totally inactivated by different types of point mutations (nonsense, missense and frame shift), complete gene deletion or a fusion gene. The products of the monomorphic genes FUT4 and FUT7 seem implicated in cell-cell interactions during embryo-foetal development and in the leukocyte adhesion phenomena to endothelial cells in the adult. A phylogenetic tree of the 28 available nucleotide coding sequences of fucosyltransferases has allowed us to situate the duplication events with respect to the separation of species from the main evolutionary path (nematods, birds, mammals, primates and humans). Recently, using a computer approach a general structure of fucosyltransferases has been proposed, inspired from the crystalline structure of the beta-glucosyltransferase of bacteriophage T4. This folding contains two domains with an alternate succession alpha and beta chains. In this model the GDP-fucose binding site would be located between the two domains.

Alternative poly(A) site selection in complex transcription units: means to an end?

Many genes have been described and characterized which result in alternative polyadenylation site use at the 3'-end of their mRNAs based on the cellular environment. In this survey and summary article 95 genes are discussed in which alternative polyadenylation is a consequence of tandem arrays of poly(A) signals within a single 3'-untranslated region. An additional 31 genes are described in which polyadenylation at a promoter-proximal site competes with a splicing reaction to influence expression of multiple mRNAs. Some have a composite internal/terminal exon which can be differentially processed. Others contain alternative 3'-terminal exons, the first of which can be skipped in some cells. In some cases the mRNAs formed from these three classes of genes are differentially processed from the primary transcript during the cell cycle or in a tissue-specific or developmentally specific pattern. Immunoglobulin heavy chain genes have composite exons; regulated production of two different Ig mRNAs has been shown to involve B cell stage-specific changes in trans -acting factors involved in formation of the active polyadenylation complex. Changes in the activity of some of these same factors occur during viral infection and take-over of the cellular machinery, suggesting the potential applicability of at least some aspects of the Ig model. The differential expression of a number of genes that undergo alternative poly(A) site choice or polyadenylation/splicing competition could be regulated at the level of amounts and activities of either generic or tissue-specific polyadenylation factors and/or splicing factors.

Effect of L-fucose and D-glucose concentration on L-fucoprotein metabolism in human Hep G2 cells and changes in fucosyltransferase and alpha-L-fucosidase activity in liver of diabetic rats

L-Fucose is a monosaccharide that is present at low concentrations in serum and is a normal constituent of glycoproteins. In some pathological conditions, such as cancer, rheumatoid arthritis, and diabetes, there is an abnormal fucosylation of acute phase serum proteins. Because most serum proteins are produced in the liver, we have examined L-fucose accumulation, metabolism, and secretion of L-fucose-containing proteins in human Hep G2 liver cells. Accumulation of L-fucose by Hep G2 cells approached 3.5 nmol/mg protein after a 48 h incubation. This accumulation appears similar to accumulation in other cells, which we have shown occurs via a specific transport protein. Exogenous L-fucose was incorporated into protein in both O- and N-linked glycosidic linkages. After a 48 h incubation, 61% of the accumulated L-fucose was incorporated into protein and secreted into the medium, whereas 39% of the L-fucose remaining in the cells was incorporated into integral membrane proteins. Utilizing reverse-phase high-performance liquid chromatographic separation of L-[5,6-(3)H]fucose-containing proteins and detection by scintillation counting, we determined that two major fucoproteins and numerous minor fucoproteins were produced and secreted by normal Hep G2 cells. This elution profile was unchanged when glucose-conditioned cells were examined. By size-separating secreted proteins by nondenaturing HPLC we determined that the size of the two major fucoproteins were approximately 60 and approximately 100 kDa. In these studies we also examined the effect of diabetes on hepatic fucosyltransferase and serum alpha-L-fucosidase activity and found that the activity of these enzymes is increased by 40 and 100%, respectively in diabetic rats.

Molecular cloning and expression of a bovine alpha(1,3)-fucosyltransferase gene homologous to a putative ancestor gene of the human FUT3-FUT5-FUT6 cluster

Only one bovine gene, corresponding to the human cluster of genes FUT3-FUT5-FUT6, was found by Southern blot analysis. The cognate bovine alpha(1,3)-fucosyltransferase shares 67.3, 69.0, and 69.3% amino acid sequence identities with human FUC-T3, FUC-T5, and FUC-T6 enzymes, respectively. As revealed by protein sequence alignment, potential sites for asparagine-linked glycosylation and conserved cysteines, the bovine enzyme is an intermediate between FUC-T3, FUC-T5, and FUC-T6 human enzymes. Transfected into COS-7 cells, the bovine gene induced the synthesis of an alpha(1, 3)-fucosyltransferase enzyme with type 2 substrate acceptor pattern specificity and induced expression of fucosylated type 2 epitopes (Lex and sialyl-Lex), but not of type 1 structures (Lea or sialyl-Lea), suggesting that it has an acceptor specificity similar to the human plasma FUC-T6. However, no enzyme activity was detected in bovine plasma. Gene transcripts are detected on tissues such as bovine liver, kidney, lung, and brain. The type 2 sialyl-Lex epitope was found in renal macula densa and biliary ducts, and Lex and Ley epitopes were detected on the brush border of epithelial cells of small and large intestine, suggesting a tissue distribution closer to human FUC-T3, but fucosylated type 1 structures (Lea, Leb, or sialyl-Lea) were not detected at all in any bovine tissue. Analysis of genetic distances on a combined phylogenetic tree of fucosyltransferase genes suggests that the bovine gene is the orthologous homologue of the ancestor of human genes constituting the present FUT3-FUT5-FUT6 cluster.

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.

Cloning of a rat alpha1,3-fucosyltransferase gene: a member of the fucosyltransferase IV family

We report the cloning of a rat alpha1,3-fucosyltransferase gene (rFuc-T), isolated from a rat genomic library by a PCR-cross-hybridization based cloning approach using primers derived from the conserved region of human alpha1,3-Fuc-T sequences. Comparison of the rFuc-T predicted amino acid sequence with those of previously cloned human and murine fucosyltransferases showed highest degree of homology to murine Fuc-TIV (87% identity) and human Fuc-TIV (78% identity), with lower homology (41-49% identity) to Fuc-TIII, V, VI, and VII. COS-1 cells transfected with the rFuc-Tgene expressed a fucosyltransferase activity with type 2 (Gal beta1-->4GlcNAc)-containing oligosaccharides and the glycolipid acceptor neolactotetraosylceramide but only low activity with sialylated substrates; the SSEA-1/Le(x) antigen was detected in transfected cells by immunocytochemistry. Based on these results, we surmise that rFuc-T is a member of the fucosyltransferase IV family. Northern blot analysis with a rFuc-T specific probe indicated a major transcript of 4.2 kb most abundantly expressed in rat spleen; minor transcripts of different sizes were detected in several tissues, including rat brain.

Molecular basis for erythrocyte Le(a+ b+) and salivary ABH partial-secretor phenotypes: expression of a FUT2 secretor allele with an A-->T mutation at nucleotide 385 correlates with reduced alpha(1,2) fucosyltransferase activity

The SewA385T mutation of the FUT2 gene was found to correlate with both the erthrocyte Le(a + b+) and/or salivary ABH partial-secretor phenotypes of Polynesians. Constructs with FUT1 and FUT2 wild type genes, and the FUT2 SewA385T, seG428A and seC571T mutated alleles, were cloned into pcDNAI, and expressed in COS-7 cells. COS-7 cells transfected with the SewA385T allele had weak, but detectable, alpha(1,2)fucosyltransferase activity, with an acceptor substrate pattern similar to the wild type FUT2 gene. Comparative kinetic studies from cell extracts with mutated SewA385T and wild type FUT2 alleles gave similar Km values, but less enzyme activity was present in cells transfected with SewA385T (Vmax 230 pmol h-1 mg-1), as compared to those transfected with FUT2 (Vmax 1030 pmol h-1 mg-1), suggesting that the mutated enzyme is more unstable. These results confirm that the molecular basis for the erythrocyte Le(a + b+), and the associated ABH salivary partial-secretor phenotype, is an amino acid change of Ile129-->Phe in the secretor alpha(1,2)fucosyltransferase.

Identification of a new plasma alpha(1,3)fucosyltransferase (FUT6) allele requires an extended genotyping strategy

Screening the FUT6 gene of 40 Swedish individuals, originally selected for genotyping of FUT3, revealed an unexpected high frequency of mutations. Four were originally typed as homozygous for the enzyme lethal mutation G739A by Taq alpha I restriction pattern, but only one lacked plasma alpha(1,3)fucosyltransferase activity. Cloning and sequencing of FUT6 from 2 of them revealed a new allele, without the G739A mutation, but with two new point mutations C738T and G977A. Segregation of this allele was confirmed in Swedish and Indonesian families. Since G739A and C738T mutations are only one nucleotide apart and induce the same modification of Taq alpha I cleavage, a new screening strategy for FUT6 was adopted. The homozygous inactivating G739A mutation was for the first time identified in Caucasian and Polynesian individuals, both lacking plasma enzyme activity. The mutation C370T was present in 25 of the 40 Swedish individuals and the inactivating mutation C945A was not found at all. These findings stress the dangers of transferring restriction enzyme genotype strategies from one population to another and of inferring phenotypes from genotypes without phenotyping and/or performing confirmatory cloning and sequencing.