Alpha1,4-fucosyltransferase activity: a significant function in the primate lineage has appeared twice independently

Toward α-1,3/4 fucosyltransferases targeted drug discovery: In silico uncovering of promising natural inhibitors of fucosyltransferase 6

Sialyl Lewis X (sLex ) antigen is a fucosylated cell-surface glycan that is normally involved in cell-cell interactions. The enhanced expression of sLex on cell surface glycans, which is attributed to the upregulation of fucosyltransferase 6 (FUT6), has been implicated in facilitating metastasis in human colorectal, lung, prostate, and oral cancers. The role that the upregulated FUT6 plays in the progression of tumor to malignancy, with reduced survival rates, makes it a potential target for anticancer drugs. Unfortunately, the lack of experimental structures for FUT6 has hampered the design and development of its inhibitors. In this study, we used in silico techniques to identify potential FUT6 inhibitors. We first modeled the three-dimensional structure of human FUT6 using AlphaFold. Then, we screened the natural compound libraries from the COCONUT database to sort out potential natural products (NPs) with best affinity toward the FUT6 model. As a result of these simulations, we identified three NPs for which we predicted binding affinities and interaction patterns quite similar to those we calculated for two experimentally tested FUT6 inhibitors, that is, fucose mimetic-1 and a GDP-triazole derived compound. We also performed molecular dynamics (MD) simulations for the FUT6 complexes with identified NPs, to investigate their stability. Analysis of the MD simulations showed that the identified NPs establish stable contacts with FUT6 under dynamics conditions. On these grounds, the three screened compounds appear as promising natural alternatives to experimentally tested FUT6 synthetic inhibitors, with expected comparable binding affinity. This envisages good prospects for future experimental validation toward FUT6 inhibition.

Genetic control of N-glycosylation of human blood plasma proteins

Glycosylation is an important protein modification, which influences the physical and chemical properties as well as biological function of these proteins. Large-scale population studies have shown that the levels of various plasma protein N-glycans are associated with many multifactorial human diseases. Observed associations between protein glycosylation levels and human diseases have led to the conclusion that N-glycans can be considered a potential source of biomarkers and therapeutic targets. Although biochemical pathways of glycosylation are well studied, the understanding of the mechanisms underlying general and tissue-specific regulation of these biochemical reactions in vivo is limited. This complicates both the interpretation of the observed associations between protein glycosylation levels and human diseases, and the development of glycan-based biomarkers and therapeutics. By the beginning of the 2010s, high-throughput methods of N-glycome profiling had become available, allowing research into the genetic control of N-glycosylation using quantitative genetics methods, including genome-wide association studies (GWAS). Application of these methods has made it possible to find previously unknown regulators of N-glycosylation and expanded the understanding of the role of N-glycans in the control of multifactorial diseases and human complex traits. The present review considers the current knowledge of the genetic control of variability in the levels of N-glycosylation of plasma proteins in human populations. It briefly describes the most popular physical-chemical methods of N-glycome profiling and the databases that contain genes involved in the biosynthesis of N-glycans. It also reviews the results of studies of environmental and genetic factors contributing to the variability of N-glycans as well as the mapping results of the genomic loci of N-glycans by GWAS. The results of functional in vitro and in silico studies are described. The review summarizes the current progress in human glycogenomics and suggests possible directions for further research.

Genetically increased circulating FUT3 level leads to reduced risk of Idiopathic Pulmonary Fibrosis: a Mendelian Randomisation Study

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal fibrotic interstitial lung disease. Few circulating biomarkers have been identified to have causal effects on IPF.To identify candidate IPF-influencing circulating proteins, we undertook an efficient screen of circulating proteins by applying a two-sample Mendelian randomisation (MR) approach with existing publicly available data. For instruments we used genetic determinants of circulating proteins which reside cis to the encoded gene (cis-SNPs), identified by two genome-wide association studies (GWASs) in European individuals (3301 and 3200 subjects). We then applied MR methods to test if the levels of these circulating proteins influenced IPF susceptibility in the largest IPF GWAS (2668 cases and 8591 controls). We validated the MR results using colocalization analyses to ensure that both the circulating proteins and IPF shared a common genetic signal.MR analyses of 834 proteins found that a one sd increase in circulating FUT3 and FUT5 was associated with a reduced risk of IPF (OR: 0.81, 95%CI: 0.74-0.88, p=6.3×10^-7, and OR: 0.76, 95%CI: 0.68-0.86, p=1.1×10^-5). Sensitivity analyses including multiple-cis SNPs provided similar estimates both for FUT3 (inverse variance weighted [IVW] OR: 0.84, 95%CI: 0.78-0.91, p=9.8×10^-6, MR-Egger OR: 0.69, 95%CI: 0.50-0.97, p=0.03) and FUT5 (IVW OR: 0.84, 95%CI: 0.77-0.92, p=1.4×10^-4, MR-Egger OR: 0.59, 95%CI: 0.38-0.90, p=0.01) FUT3 and FUT5 signals colocalized with IPF signals, with posterior probabilities of a shared genetic signal of 99.9% and 97.7%. Further transcriptomic investigations supported the protective effects of FUT3 for IPF.An efficient MR scan of 834 circulating proteins provided evidence that genetically increased circulating FUT3 level is associated with reduced risk of IPF.

Complementary Use of Carbohydrate Antigens Lewis a, Lewis b, and Sialyl-Lewis a (CA19.9 Epitope) in Gastrointestinal Cancers: Biological Rationale Towards A Personalized Clinical Application

Carbohydrate antigen 19.9 (CA19.9) is used as a tumor marker for clinical and research purposes assuming that it is abundantly produced by gastrointestinal cancer cells due to a cancer-associated aberrant glycosylation favoring its synthesis. Recent data has instead suggested a different picture, where immunodetection on tissue sections matches biochemical and molecular data. In addition to CA19.9, structurally related carbohydrate antigens Lewis a and Lewis b are, in fact, undetectable in colon cancer, due to the down-regulation of a galactosyltransferase necessary for their synthesis. In the pancreas, no differential expression of CA19.9 or cognate glycosyltransferases occurs in cancer. Ductal cells only express such Lewis antigens in a pattern affected by the relative levels of each glycosyltransferase, which are genetically and epigenetically determined. The elevation of circulating antigens seems to depend on the obstruction of neoplastic ducts and loss of polarity occurring in malignant ductal cells. Circulating Lewis a and Lewis b are indeed promising candidates for monitoring pancreatic cancer patients that are negative for CA19.9, but not for improving the low diagnostic performance of such an antigen. Insufficient biological data are available for gastric and bile duct cancer. Studying each patient in a personalized manner determining all Lewis antigens in the surgical specimens and in the blood, together with the status of the tissue-specific glycosylation machinery, promises fruitful advances in translational research and clinical practice.

ABO phenotype-protected reproduction based on human specific α1,2 L-fucosylation as explained by the Bombay type formation

The metabolic relationship between the formation of the ABO(H) blood group phenotype and human fertility is evident in the case of the (Oh) or Bombay blood type, which Charles Darwin would have interpreted as resulting from reduced male fertility in consanguinities, based on the history of his own family, the Darwin/Wedgwood Dynasty. The classic Bombay type occurs with the extremely rare, human-specific genotype (h/h; se/se), which (due to point mutations) does not encode fucosyltransferases 1(FUT1) and 2 (FUT2). These enzymes are the basis for ABO(H) phenotype formation on the cell surfaces and fucosylation of plasma proteins, involving neonatal immunoglobulin M (IgM). In the normal human blood group O(H), which is not protected by clonal selection with regard to environmental A/B immunization, the plasma contains a mixture of non-immune and adaptive anti-A/B reactive isoagglutinins, which in the O(h) Bombay type show extremely elevated levels, associated with decreased levels of fucosylation-dependent functional plasma proteins, suchs as the van Willebrand factor (vWF) and clotting factor VIII. In fact, while the involvement of adaptive immunoglobulins remains unknown, poor fucosylation may explain the polyreactivity in the Bombay type plasma, which exhibits pronounced complement-binding cross-reactive anti-A/Tn and anti-B IgM levels, with additional anti-H reactivity, acting over a wide range of temperatures, with an amplitude at 37 °C. This aggressive anti-glycan-reactive IgM molecule suggests the induction of ADCC (antibody-dependent) and/or complement-mediated cytotoxicity via overexpressed glycosidic bond sites against the embryogenic stem cell-to-germ cell transformation, which is characterized by fleeting appearances of A-like, developmental trans-species GalNAcα1-O-Ser/Thr-R glycan, also referred to as the Tn (T "nouvelle") antigen.

Mouse intestinal niche cells express a distinct α1,2-fucosylated glycan recognized by a lectin from Burkholderia cenocepacia

In this study, we examined the distribution of fucosylated glycans in mouse intestines using a lectin, BC2LCN (N-terminal domain of the lectin BC2L-C from Burkholderia cenocepacia), as a probe. BC2LCN is specific for glycans with a terminal Fucα1,2Galβ1,3-motif and it is a useful marker for discriminating the undifferentiated status of human induced/embryonic stem cells. Apparent BC2LCN reactivity was detected in the secretory granules of goblet cells in the ileum but not those in the colon. We also found distinctive reactivity in the crypt bottom, which is known as the stem cell zone, of the colon and the ileum. Other lectins for fucosylated glycans, including Ulex europaeus agglutinin-I, Pholiota squarrosa lectin and Aleuria aurantia lectin, did not exhibit similar reactivity in the crypt bottom. Remarkably, BC2LCN-positive epithelial cells could be labeled with a niche cell marker, c-Kit/CD117. Overall, our results indicate that intestinal niche cells express distinct fucosylated glycans recognized by BC2LCN. Increasing evidence suggests that the self-renewal and proliferation of stem cells depend on specific signals derived from niche cells. Our results highlight novel molecular properties of intestinal niche cells in terms of their glycosylation, which may help to understand the regulation of intestinal stem cells. The distinct expression of glycans may reflect the functional roles of niche cells. BC2LCN is a valuable tool for investigating the functional significance of protein glycosylation in stem cell regulation.

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.

Position of human blood group O(H) and phenotype-determining enzymes in growth and infectious disease

The human ABO(H) blood group phenotypes arise from the evolutionarily oldest genetic system found in primate populations. While the blood group antigen A is considered the ancestral primordial structure, under the selective pressure of life‐threatening diseases blood group O(H) came to dominate as the most frequently occurring blood group worldwide. Non‐O(H) phenotypes demonstrate impaired formation of adaptive and innate immunoglobulin specificities due to clonal selection and phenotype formation in plasma proteins. Compared with individuals with blood group O(H), blood group A individuals not only have a significantly higher risk of developing certain types of cancer but also exhibit high susceptibility to malaria tropica or infection by Plasmodium falciparum. The phenotype‐determining blood group A glycotransferase(s), which affect the levels of anti‐A/Tn cross‐reactive immunoglobulins in phenotypic glycosidic accommodation, might also mediate adhesion and entry of the parasite to host cells via trans‐species O‐GalNAc glycosylation of abundantly expressed serine residues that arise throughout the parasite's life cycle, while excluding the possibility of antibody formation against the resulting hybrid Tn antigen. In contrast, human blood group O(H), lacking this enzyme, is indicated to confer a survival advantage regarding the overall risk of developing cancer, and individuals with this blood group rarely develop life‐threatening infections involving evolutionarily selective malaria strains.

Selectin Ligands Sialyl-Lewis a and Sialyl-Lewis x in Gastrointestinal Cancers

The tetrasaccharide structures Siaα2,3Galβ1,3(Fucα1,4)GlcNAc and Siaα2,3Galβ1,4(Fucα1,3)GlcNAc constitute the epitopes of the carbohydrate antigens sialyl-Lewis a (sLe^a) and sialyl-Lewis x (sLe^x), respectively, and are the minimal requirement for selectin binding to their counter-receptors. Interaction of sLe^x expressed on the cell surface of leucocytes with E-selectin on endothelial cells allows their arrest and promotes their extravasation. Similarly, the rolling of cancer cells ectopically expressing the selectin ligands on endothelial cells is potentially a crucial step favoring the metastatic process. In this review, we focus on the biosynthetic steps giving rise to selectin ligand expression in cell lines and native tissues of gastrointestinal origin, trying to understand whether and how they are deregulated in cancer. We also discuss the use of such molecules in the diagnosis of gastrointestinal cancers, particularly in light of recent data questioning the ability of colon cancers to express sLe^a and the possible use of circulating sLe^x in the early detection of pancreatic cancer. Finally, we reviewed the data dealing with the mechanisms that link selectin ligand expression in gastrointestinal cells to cancer malignancy. This promising research field seems to require additional data on native patient tissues to reach more definitive conclusions.

Unexpected distribution of CA19.9 and other type 1 chain Lewis antigens in normal and cancer tissues of colon and pancreas: Importance of the detection method and role of glycosyltransferase regulation

BACKGROUND

CA19.9 antigen has been assumed as an abundant product of cancer cells, due to the reactivity found by immunohistochemical staining of cancer tissues with anti-CA19.9 antibody.

METHODS

Expression and biosynthesis of type 1 chain Lewis antigens in the colon and the pancreas were studied by immunodetection in tissue sections and lysates, quantification of glycosyltransferase transcripts, bisulfite sequencing, and chromatin immunoprecipitation assays.

RESULTS

CA19.9 was poorly detectable in normal colon mucosa and almost undetectable in colon cancer, while it was easily detected in the pancreatic ducts, together with Lewis b antigen, under both normal and cancer conditions. B3GALT5 transcripts were down-regulated in colon cancer, while they remained expressed in pancreatic cancer. Even ST3GAL3 transcript appeared well expressed in the pancreas but poorly in the colon, irrespective of normal or cancer conditions. CpG islands flanking B3GALT5 native promoter presented an extremely low degree of methylation in pancreatic cancer with respect to colon cancer. In a DNA region about 1kb away from the B3GALT5 retroviral promoter, a stretch of CG dinucleotides presented a methylation pattern potentially associated with transcription. Such a DNA region and the transcription factor binding site provided overlapping results by chromatin immunoprecipitation assays, corroborating the hypothesis.

CONCLUSIONS

CA19.9 appears as a physiological product whose synthesis strongly depends on the tissue specific and epigenetically-regulated expression of B3GALT5 and ST3GAL3.

GENERAL SIGNIFICANCE

CA19.9 and other Lewis antigens acquire tumor marker properties in the pancreas due to mechanisms giving rise to reabsorption into vessels and elevation in circulating levels.

In silico analysis of the fucosylation-associated genome of the human blood fluke Schistosoma mansoni: cloning and characterization of the fucosyltransferase multigene family

Fucosylated glycans of the parasitic flatworm Schistosoma mansoni play key roles in its development and immunobiology. In the present study we used a genome-wide homology-based bioinformatics approach to search for genes that contribute to fucosylated glycan expression in S. mansoni, specifically the α2-, α3-, and α6-fucosyltransferases (FucTs), which transfer L-fucose from a GDP-L-fucose donor to an oligosaccharide acceptor. We identified and in silico characterized several novel schistosome FucT homologs, including six α3-FucTs and six α6-FucTs, as well as two protein O-FucTs that catalyze the unrelated transfer of L-fucose to serine and threonine residues of epidermal growth factor- and thrombospondin-type repeats. No α2-FucTs were observed. Primary sequence analyses identified key conserved FucT motifs as well as characteristic transmembrane domains, consistent with their putative roles as fucosyltransferases. Most genes exhibit alternative splicing, with multiple transcript variants generated. A phylogenetic analysis demonstrated that schistosome α3- and α6-FucTs form monophyletic clades within their respective gene families, suggesting multiple gene duplications following the separation of the schistosome lineage from the main evolutionary tree. Quantitative decreases in steady-state transcript levels of some FucTs during early larval development suggest a possible mechanism for differential expression of fucosylated glycans in schistosomes. This study systematically identifies the complete repertoire of FucT homologs in S. mansoni and provides fundamental information regarding their genomic organization, genetic variation, developmental expression, and evolutionary history.

Non-ABO blood group systems phenotyping in non-human primates for blood banking laboratory and xenotransplantation

Some biomedical research procedures, such as organ xenotransplantation, usually require intensive hemotherapy. Knowledge of the whole phenotype of blood donor and graft could be useful in the field of xenotransplantation. Human and simian-type categories of blood groups have been established and they can be tested by standard methods used for human blood grouping. The aim of this work was to study the incidence of non-ABO blood group systems in different species of non-human primates, which are employed in biomedical research. The phenotype of Rh, Lewis, Kidd, Kell, MNSs, Lutheran, P and Duffy antigens was investigated in olive baboon (n = 48), chacma baboon (n = 9), Guinea baboon (n = 14), Rhesus macaque (n = 38) and squirrel monkey (n = 30) by using commercial microtyping cards. Kell, Lutheran, Kidd and Duffy antigens have been detected in all species, Rh in squirrel monkey, MNSs in rhesus macaque and squirrel monkey, and Lewis in baboon and rhesus macaque. There were differences in frequency and haemagglutination scores between species regardless of their gender and age. The main differences were found in squirrel monkey when compared with baboons and macaques. This typing system provides a tool to assess the presence of antigens in animals used for experimental procedures, such as xenotransplantation and xenotransfusion.

Transfection of miRNAs targeting the FUT3 gene inhibits cell proliferation in human gastric cancer cell line KATO-III

AIM: To investigate the effect of inhibition of FUT3 gene expression with miRNAs on the proliferation of gastric cancer cells (KATO-Ⅲ).

METHODS: Vectors carrying two miRNAs targeting the FUT3 gene were constructed and transiently transfected into KATO-III cells using lipidosome-mediated method. RT-PCR was performed to detect the expression of FUT3 mRNA, and immunocytochemistry and flow cytometry analysis were carried out to test expression variation of sLeA antigen. MTT assay and colony-forming assay were used to analyze cell proliferation and to detect the effect of decreased FUT3 expression on cell growth.

RESULTS: Compared to non-transfected cells and cells transfected with empty vector, the relative expression levels of FUT3 mRNA were significantly decreased (0.41 ± 0.01 vs 0.71 ± 0.05, 0.65 ± 0.03, both P < 0.05; 0.36 ± 0.02 vs 0.71 ± 0.05, 0.65 ± 0.03, both P < 0.05); the sLeA antigen expression levels were also significantly reduced (35.51% ± 0.36% vs 52.79% ± 2.62%, 49.75% ± 1.29%, both P < 0.05; 26.05% ± 1.14% vs 52.79% ± 2.62%, 49.75% ± 1.29%, both P < 0.05); cell growth was significantly inhibited (38.10% ± 1.96% vs 5.6% ± 0.63%, 8.9% ± 0.91%, both P < 0.05; 49.04% ± 2.37% vs 5.6% ± 0.63%, 8.9% ± 0.91%, both P < 0.05); and colony-forming ability was significantly reduced (14.10% ± 1.70% vs 29.79% ± 3.05%, 28.92% ± 2.10%, both P < 0.05; 12.50% ± 1.96% vs 29.79% ± 3.05%, 28.92% ± 2.10%, both P < 0.05) in FUT3-miRNA and FUT3-miRNA2 transfeced cells.

CONCLUSION: Transfection of miRNAs targeting the FUT3 gene can effectively inhibit the proliferation of KATO-Ⅲ 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.

Distantly related plant and nematode core α1,3-fucosyltransferases display similar trends in structure-function relationships

Here, we present a comparative structure-function study of a nematode and a plant core α1,3-fucosyltransferase based on deletion and point mutations of the coding regions of Caenorhabditis elegans FUT-1 and Arabidopsis thaliana FucTA (FUT11). In particular, our results reveal a novel "first cluster motif" shared by both core and Lewis-type α1,3-fucosyltransferases of the GT10 family. To evaluate the role of the conserved serine within this motif, this residue was replaced with alanine in FucTA (S218) and FUT-1 (S243). The S218A replacement completely abolished the enzyme activity of FucTA, while the S243A mutant of FUT-1 retained 20% of the "wild-type" activity. Based on the results of homology modeling of FucTA, other residues potentially involved in the donor substrate binding were examined, and mutations of N219 and R226 dramatically affected enzymatic activity. Finally, as both FucTA and FUT-1 were shown to be N-glycosylated, we examined the putative N-glycosylation sites. While alanine replacements at single potential N-glycosylation sites of FucTA resulted in a loss of up to 80% of the activity, a triple glycosylation site mutant still retained 5%, as compared to the control. In summary, our data indicate similar trends in structure-function relationships of distantly related enzymes which perform similar biochemical reactions and form the basis for future work aimed at understanding the structure of α1,3-fucosyltransferases in general.

The biosynthesis of the selectin-ligand sialyl Lewis x in colorectal cancer tissues is regulated by fucosyltransferase VI and can be inhibited by an RNA interference-based approach

Sialyl Lewis x (sLex) is a selectin ligand whose overexpression in epithelial cancers mediates metastasis formation. The molecular basis of sLex biosynthesis in colon cancer tissues is still unclear. The prerequisite for therapeutic approaches aimed at sLex down-regulation in cancer, is the identification of rate-limiting steps in its biosynthesis. We have studied the role of α1,3-fucosyltransferases (Fuc-Ts) potentially involved in sLex biosynthesis in specimens of normal and cancer colon as well as in experimental systems. We found that: (i) in colon cancer, but not in normal mucosa where the antigen was poorly expressed, sLex correlated with a Fuc-T which, like Fuc-TVI, was active on 3'sialyllactosamine at a low concentration (Fuc-T(SLN)); (ii) competitive RT-PCR analysis revealed that the level of Fuc-T mRNA expression in both normal and cancer colon was Fuc-TVI>Fuc-TIII>Fuc-TIV; Fuc-TV and Fuc-TVII expression was negligible; (iii) sLex was expressed only by the gastrointestinal cell lines displaying both Fuc-TVI mRNA and Fuc-T(SLN) activity, but not by those expressing only Fuc-TIII mRNA; (iv) transfection with Fuc-TVI cDNA, but not with Fuc-TIII cDNA, induced sLex expression in gastrointestinal cell lines; (v) Fuc-TVI knock-down with specific siRNA induced down-regulation of Fuc-TVI mRNA and Fuc-T(SLN) activity and a dramatic inhibition of sLex expression. These data indicate that in colon cancer tissues Fuc-TVI is a key regulator of sLex biosynthesis which can be the target of RNA-interference-based gene knock-down approaches.

Activation of host antiviral RNA-sensing factors necessary for herpes simplex virus type 1-activated transcription of host cell fucosyltransferase genes FUT3, FUT5, and FUT6 and subsequent expression of sLe(x) in virus-infected cells

Herpes simplex virus type 1 (HSV-1) induces expression of a selectin receptor, the carbohydrate epitope sialyl Lewis X (sLe(x)), at the surface of infected cells. The molecular background to this phenomenon is that a viral immediate early RNA interacts with as yet unidentified host factors, eventually resulting in transcription of three dormant host fucosyltransferase genes (FUT3, FUT5, and FUT6), whose gene products are rate-limiting for synthesis of sLe(x). The aim of the present study was to define the immediate targets for the viral RNA in this process. We found that the Protein Kinase R (PKR) inhibitors 2-aminopurine (2-AP) and C16 inhibited FUT3, FUT5, and FUT6 expression as well as HSV-1-induced expression of sLe(x), indicating a primary role of PKR as a viral RNA target. The PKR-dependent activation of the FUT genes seemed neither to involve PKR effects on translation nor to involve NF-kappaB- or JNK-dependent activation. IMD-0354, known as an inhibitor of the NF-kappaB-activating factor IKK-2, induced FUT transcription via a novel IKK-2-independent mechanism, irrespective of whether the cells were virus-infected or not. Altogether, the results suggested that PKR is the primary target for HSV-1 early RNA during induction of FUT3, FUT5, and FUT6, and that the subsequent steps in the transcriptional activation of these host genes involve a hitherto unknown IMD-0354, yet IKK-2-independent, pathway.

Evolution of carbohydrate antigens--microbial forces shaping host glycomes?

Many glycans show remarkably discontinuous distribution across evolutionary lineages. These differences play major roles when organisms belonging to different lineages interact as host-pathogen or host-symbiont. Certain lineage-specific glycans have become important signals for multicellular host organisms, which use them as molecular signatures of their pathogens and symbionts through recognition by a toolkit of innate defense molecules. In turn, pathogens have evolved to exploit host lineage-specific glycans and are constantly shaping the glycomes of their hosts. These interactions take place in the face of numerous critical endogenous functions played by glycans within host organisms. Whether due to simple evolutionary divergence or adaptive changes under natural selection resulting from endogenous functional requirements, once different lineages elaborate on differential glycomes these mutual differences provide opportunities for host exploitation and/or pathogen defense between lineages. Such phylogenetic molecular recognition mechanisms will augment and likely contribute to the maintenance of lineage-specific differences in glycan repertoires.

Comparative Analysis of Retroviral and Native Promoters Driving Expression of β1,3-Galactosyltransferase β3Gal-T5 in Human and Mouse Tissues

Beta1,3-galactosyltransferase beta3Gal-T5 is highly expressed in the colons of humans and certain primates due to a retroviral long terminal repeat (LTR) acting as a strong promoter. Because this promoter is inactive in other human tissues or mice, we attempted to understand how adoption of a retrotransposon allowed the gene to acquire tissue-specific expression. We identified three novel 5'-UTRs of beta3Gal-T5 mRNA, types A, B, and C, and found widespread expression of the type A transcript at much lower levels than the LTR transcript, the expression of which is restricted to organs of the gastrointestinal tract. Expression of the type C 5'-UTR transcript was mostly restricted to the ileum, where it was expressed at high levels. We cloned the 5'-flanking regions of both types A and B 5'-UTRs, found deletion constructs functionally active as promoters, and identified CCAAT-binding factor (CBF) and hepatocyte nuclear factor 1 (HNF-1) as the principal nuclear factors controlling the promoters of types A and B 5'-UTR transcripts, respectively. The CCAAT-binding factor binding site and the entire downstream sequence driving the expression of type A transcripts in humans are structurally and functionally conserved in mice, where they constitute a uniquebeta3Gal-T5 promoter that appears to be the ancestral promoter of the gene. The HNF-1 binding motif of the second human promoter is identical to the HNF-1/Cdx binding motif of the LTR promoter but is in the antisense orientation, resulting in much lower binding affinity and promoter strength. These data may explain the successful insertion of the transposon during evolution.

Fucosylation in prokaryotes and eukaryotes

Fucosylated carbohydrate structures are involved in a variety of biological and pathological processes in eukaryotic organisms including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and tumor metastasis. In contrast, fucosylation appears less common in prokaryotic organisms and has been suggested to be involved in molecular mimicry, adhesion, colonization, and modulating the host immune response. Fucosyltransferases (FucTs), present in both eukaryotic and prokaryotic organisms, are the enzymes responsible for the catalysis of fucose transfer from donor guanosine-diphosphate fucose to various acceptor molecules including oligosaccharides, glycoproteins, and glycolipids. To date, several subfamilies of mammalian FucTs have been well characterized; these enzymes are therefore delineated and used as models. Non-mammalian FucTs that possess different domain construction or display distinctive acceptor substrate specificity are highlighted. It is noteworthy that the glycoconjugates from plants and schistosomes contain some unusual fucose linkages, suggesting the presence of novel FucT subfamilies as yet to be characterized. Despite the very low sequence homology, striking functional similarity is exhibited between mammalian and Helicobacter pylori alpha1,3/4 FucTs, implying that these enzymes likely share a conserved mechanistic and structural basis for fucose transfer; such conserved functional features might also exist when comparing other FucT subfamilies from different origins. Fucosyltranferases are promising tools used in synthesis of fucosylated oligosaccharides and glycoconjugates, which show great potential in the treatment of infectious and inflammatory diseases and tumor metastasis.

En bloc duplications, mutation rates, and densities of amino acid changes clarify the evolution of vertebrate alpha-1,3/4-fucosyltransferases

Numerous vertebrates have four alpha-1,3/4-fucosyltransferase genes (FUT9, FUT7, FUT4, and FUT Lewis) belonging to the same family. Until now, studies on the evolution of this family have mainly focused on Lewis genes but how the other alpha-1,3/4-fucosyltransferases have emerged from a common ancestor is not well known. In order to define the respective roles of duplications and mutations, we have compared amino acid sequences representative of bony fish (Takifugu rubripes), amphibians (Xenopus laevis), birds (Gallus gallus), and mammals (Bos taurus). The FUT tree has two fundamental branches, each split into two subfamilies. We found evidence for two duplication events, dated around 710-760 Myr and 590-640 Myr, respectively, compatible with the hypothesis of two rounds of whole genome duplications in chordate genomes, before the emergence of bony vertebrates. Based on the Homo sapiens (human) physical map, we identified blocks of paralogues belonging to regions of FUT9 (6q16), FUT4 (11q21), FUT7 (9q34), and FUT Lewis (19p13) and to a region on HSA1p that is devoid of any FUT. In zebrafish (Danio rerio), an orthologue region of HSA1 harbors an FUT9 specific to bony fish, showing that duplications are not restricted to a single FUT gene but involve blocks of paralogues. In addition, sets of genes within each block clarify the order of duplication events and, as a result, the order of alpha-1,3/4-fucosyltransferase gene emergence. We have also determined the mutation rates and the density of amino acid changes along protein sequences in each alpha-1,3/4-fucosyltransferase subfamily during the main vertebrate transitions. After the emergence of tetrapods, the mutation rate of FUT9 decreased dramatically, suggesting the early acquisition of a crucial fucosyltransferase activity in the first stages of development. The FUT7 mutation rate, which in tetrapod ancestors is about half that in amniote ancestors, may be related to the role of this gene in immune systems. In contrast to other subfamilies, we found a constant mutation rate in FUT Lewis and a rather homogeneous amino acid density change, independently of the vertebrate transition, suggesting that hitherto Lewis epitopes have dispensable functions.

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.

Alteration of gibberellin response in transgenic tobacco plants which express a human Lewis fucosyltransferase

In plants, Lewisa type N-glycans may be involved in cell-to-cell communication and recognition. N-glycoproteins harboring Lewisa glycotopes are mainly found in plasma membranes and cell walls. Some can be also involved in cell wall synthesis or the loosening process, and subsequently in cell elongation. In order to determine the potential role(s) of the alpha4-fucosylation during vegetative development, transgenic tobacco plants overexpressing a human Lewis fucosyltransferase (hFUT3), which transfers a fucose residue in a alpha(1,4)-linkage on complex glycans, have been developed. The heterologous enzyme hFUT3 was strongly expressed and fully functional in transgenic tobacco. Transgenic plants showed a delay in growth linked to a reduction of internode length. Furthermore, transgenic seedling roots were significantly shorter than wild-type roots and the length of their epidermis cells was reduced. Strikingly, root growth was completely and specifically restored following gibberellin treatment. Etiolated hypocotyls of hFUT3 overexpressors were also more sensitive to exogenous gibberellin. Furthermore, paclobutrazol, an inhibitor of gibberellin synthesis, induced a similar effect on control and transgenic dark-grown hypocotyls suggesting that gibberellin biosynthesis was probably not altered in seedlings overexpressing hFUT3. Thus, alpha4-fucosylation could act as a possible modulator of conformation and/or functioning of N-glycoproteins involved in the gibberellin-dependent elongation process.

Suppression of beta 1,3galactosyltransferase beta 3Gal-T5 in cancer cells reduces sialyl-Lewis a and enhances poly N-acetyllactosamines and sialyl-Lewis x on O-glycans

We investigated the role of beta 3 Gal-T5, a member of the beta 1,3galactosyltransferase (beta 1,3Gal-T) family, in cancer-associated glycosylation, focusing on the expression of sialyl-Lewis a (sLea, the epitope of CA19.9 antigen), poly N-acetyllactosamines, and sialyl-Lewis x (sLex) antigen. A clone permanently expressing an antisense fragment of beta 3Gal-T5 was obtained from the human pancreas adenocarcinoma cell line BxPC3 and characterized. Both beta 1,3Gal-T activity and sLea expression are dramatically impaired in the clone. Analysis of the oligosaccharides synthesized in cells metabolically labelled with tritiated galactose shows that a relevant amount of radioactivity is associated to large O-glycans. Endo-beta-galactosidase mostly releases NeuAc alpha 2-3Gal beta 1-3[Fuc alpha 1-4]GlcNAc beta 1-3Gal and NeuAc alpha 2-3Gal beta 1-3GlcNAc beta 1-3Gal from such O-glycans of BxPC3 membranes, but GlcNAc beta 1-3Gal and type 2 chain oligosaccharides, including NeuAc alpha 2-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc beta 1-3Gal, from those of the antisense clone. Furthermore, BxPC3 cells secrete sLea in the culture media but not sLex, while antisense clone secretes mostly sLex, and accumulation of both antigens is prevented by benzyl-alpha-GalNAc. These data indicate that beta 3Gal-T5 suppression turns synthesis of type 1 chain O-glycans to poly N-acetyllactosamine elongation and termination by sLex. In other cell lines and clones, beta 3Gal-T5 transcript, beta 1,3Gal-T activity, and sLea antigen are also correlated, but quantitatively the relative expression ratios are very different from cell type to cell type. We suggest that beta 3Gal-T5 plays a relevant role in gastrointestinal and pancreatic tissues counteracting the glycosylation pattern associated to malignancy, and is necessary for the synthesis and secretion of CA19.9 antigen, whose expression still depends on multiple interacting factors.

Site-specific carbohydrate profiling of human transferrin by nano-flow liquid chromatography/electrospray ionization mass spectrometry

Glycopeptides derived from a lysylendopeptidase digest of commercially available human transferrin were analyzed by nano-flow liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS), which permitted the carbohydrate profiles at Asn432 and Asn630 to be determined. Both are located in a well-known motif for N-glycosylation, Asn-Xaa-Ser/Thr. The contents of the carbohydrates at each site were significantly different from each other, and consisted of a variety of minor types of oligosaccharides in addition to the major one, a biantennary complex-type oligosaccharide. Nano-flow ESI tandem mass spectrometry (MS/MS) of the glycopeptides (Cys421-Lys433 and Ile619-Lys646) containing these two sites yielded predominantly ions originating from the non-reducing termini (oxonium ions) and reducing terminus, resulting from cleavage of the glycosidic bonds of the carbohydrate moieties; this permitted the structural read-out of a small minority of the carbohydrate moieties. In particular, the observation of oxonium ions at m/z 512.2 and 803.2 is useful for probing outer non-reducing terminal fucosylation, which represented carbohydrate structures consisting of Hex, dHex, and HexNAc, and NeuNAc, Hex, dHex, and HexNAc, respectively, from which the Lewis X structure (Galbeta1-4(Fucalpha1-3)GlcNAc) was readily deduced. Moreover, fucosylation at the reducing-terminal GlcNAc (Fucalpha1-6GlcNAc) specifically occurred at Asn630, as demonstrated by treatment of the glycopeptides with alpha1-3/4-L-fucosidase.

Identification of the blood group Lewisadeterminant in the oviducal mucins ofXenopus tropicalis

The amphibian Xenopus tropicalis appears an increasingly appealing model for both genetic and developmental biology studies, compared to the related species Xenopus laevis. Study of the glycosylation pattern of its secreted glycoproteins revealed that this species synthesizes large amounts of Lewis(a) epitope, whereas this motif has previously only been identified in animals within the primate lineage. The use of (1)H-nuclear magnetic resonance spectroscopy enabled us to resolve the sequence of three Lewis(a)-bearing O-linked glycans associated with oviducal secretions, out of which one contained the novel sequence Gal(beta 1-3)GlcNAc(beta 1-6)GalNAc-ol. These structural data suggested the emergence of an alpha 1,4-fucosyltransferase activity in animals outside the primate lineage. On this basis, the screening of a X. tropicalis GenBank database with human Lewis-fucosyltransferase sequences revealed the occurrence of a putative fucosyltransferase gene that presented an unusual acceptor motif.

C-terminal amino acids of Helicobacter pylori alpha1,3/4 fucosyltransferases determine type I and type II transfer

The alpha1,3/4 fucosyltransferase (FucT) enzyme from Helicobacter pylori catalyzes fucose transfer from donor GDP-beta-l-fucose to the GlcNAc group of two series of acceptor substrates in H. pylori lipopolysaccharide: betaGal1,3betaGlcNAc (Type I) or betaGal1,4betaGlcNAc (Type II). Fucose is added either in alpha1,3 linkage of Type II acceptor to produce Lewis X or in alpha1,4 linkage of Type I acceptor to produce Lewis A, respectively. H. pylori FucTs from different strains have distinct Type I or Type II substrate specificities. FucT in H. pylori strain NCTC11639 has an exclusive alpha1,3 activity because it recognizes only Type II substrates, whereas FucT in H. pylori strain UA948 can utilize both Type II and Type I acceptors; thus it has both alpha1,3 and alpha1,4 activity, respectively. To identify elements conferring substrate specificity, 12 chimeric FucTs were constructed by domain swapping between 11639FucT and UA948FucT and characterized for their ability to transfer fucose to Type I and Type II acceptors. Our results indicate that the C-terminal region of H. pylori FucTs controls Type I and Type II acceptor specificity. In particular, the highly divergent C-terminal portion, seven amino acids DNPFIFC at positions 347-353 in 11639FucT, and the corresponding 10 amino acids CNDAHYSALH at positions 345-354 in UA948FucT, controls the Type I and Type II acceptor recognition. This is the opposite of mammalian FucTs where acceptor preference is determined primarily by the N-terminal residues in the hypervariable stem domain.