Evidence for two distinct alpha(1,2)-fucosyltransferase genes differentially expressed throughout the rat colon

Helicobacter hepaticus Hh0072 gene encodes a novel alpha1-3-fucosyltransferase belonging to CAZy GT11 family

Lewis x (Le(x)) and sialyl Lewis x (SLe(x))-containing glycans play important roles in numerous physiological and pathological processes. The key enzyme for the final step formation of these Lewis antigens is alpha1-3-fucosyltransferase. Here we report molecular cloning and functional expression of a novel Helicobacter hepaticus alpha1-3-fucosyltransferase (HhFT1) which shows activity towards both non-sialylated and sialylated Type II oligosaccharide acceptor substrates. It is a promising catalyst for enzymatic and chemoenzymatic synthesis of Le(x), sialyl Le(x) and their derivatives. Unlike all other alpha1-3/4-fucosyltransferases characterized so far which belong to Carbohydrate Active Enzyme (CAZy, http://www.cazy.org/) glycosyltransferase family GT10, the HhFT1 shares protein sequence homology with alpha1-2-fucosyltransferases and belongs to CAZy glycosyltransferase family GT11. The HhFT1 is thus the first alpha1-3-fucosyltransferase identified in the GT11 family.

Genes involved in matrix formation in Pseudomonas aeruginosa PA14 biofilms

Pseudomonas aeruginosa forms diverse matrix-enclosed surface-associated multicellular assemblages (biofilms) that aid in its survival in a variety of environments. One such biofilm is the pellicle that forms at the air-liquid interface in standing cultures. We screened for transposon insertion mutants of P. aeruginosa PA14 that were unable to form pellicles. Analysis of these mutants led to the identification of seven adjacent genes, named pel genes, the products of which appear to be involved in the formation of the pellicle's extracellular matrix. In addition to being required for pellicle formation, the pel genes are also required for the formation of solid surface-associated biofilms. Sequence analyses predicted that three pel genes encode transmembrane proteins and that five pel genes have functional homologues involved in carbohydrate processing. Microscopic and macroscopic observations revealed that wild-type P. aeruginosa PA14 produces a cellulase-sensitive extracellular matrix able to bind Congo red; no extracellular matrix was produced by the pel mutants. A comparison of the carbohydrates produced by the wild-type strain and pel mutants suggested that glucose was a principal component of the matrix material. Together, these results suggest that the pel genes are responsible for the production of a glucose-rich matrix material required for the formation of biofilms by P. aeruginosa PA14.

Regulation of the intestinal glycoprotein glycosylation during postnatal development: role of hormonal and nutritional factors

This review focuses on the regulation of the glycoprotein glycosylation process in small intestine and colon during postnatal development. Glycoproteins play a prominent part in intestine as mucins secreted by the goblet cells and as molecules of biological interest largely present in the microvillus membrane of the enterocytes (digestive enzymes, transporters). The age-related changes in the intestinal glycosylation control the quality of glycan chains of glycoproteins. Postnatal maturation is observed at all stages of the glycoprotein glycosylation. But it is essentially characterised in the external glycosylation by a shift from sialylation to fucosylation depending on the transcriptional regulation of the corresponding glycosyltransferases, but also on coordinate changes in the activities of glycosyltransferases and of their regulatory proteins, in nucleotide-sugar bioavailability and in product degradation by oxidases. Many factors have been evoked to trigger these changes, among which are hormonal (glucocorticoids, insulin) and dietary factors. Changes in the structure of the glycoprotein glycans might be important for the transport, the barrier function, the implantation of the immune defences and of the microflora and even probably for the biological activity of some digestive enzymes.

Glucocorticoid-induced maturation of glycoprotein galactosylation and fucosylation processes in the rat small intestine

We determined the role of glucocorticoids in the maturation of glycoprotein galactosylation and fucosylation processes in the rat small intestine during postnatal development. Treatment of suckling rats with hydrocortisone (HC) increased activities of an O-glycan: galactosyltransferase, and of an alpha-1,2-fucosyltransferase, through transcriptional regulation of the FTB gene. The activities of a fucosyltransferase inhibitor and of the enzymes responsible for the synthesis and degradation of GDP-fucose were unaffected by the treatment, whereas a fall in the activity of alpha-L-fucosidase was observed. These changes were accompanied by the precocious appearance of alpha-1,2-fucose residues in complex glycan chains of brush-border membrane glycoproteins that normally appear after weaning, and with a trend to increase in alpha-1,2-fucose residues in mucins. Thus, treatment of suckling rats with hydrocortisone speeds up the maturation of glycoprotein galactosylation and fucosylation processes in the small intestine. The delayed increase in glucocorticoid levels induced by prolonged nursing, or the suppression of glucocorticoids by adrenalectomy (AD) before the normal rise in the hormone, both induced a delay in the increases in activities of the O-glycan: galactosyltransferase and alpha-1,2-fucosyltransferase observed normally after glucocorticoid enhancement. Thus, glucocorticoids might play at least a partial role in the maturation of glycoprotein glycosylation observed at weaning.

Prostate Development and Carcinogenesis

The process involved in the development and carcinogenesis of the prostate gland is complex. During early prostate development, the androgenic hormone from embryonic testicles is required for ductal formation, growth, and branching morphogenesis of the prostate gland. From this early stage, interactions between the epithelium and mesenchyme become firmly established through paracrine influence (i.e., growth factors) from mesenchyme (stroma), in response to testosterone, acting on epithelium to stimulate its proliferation, morphogenetic differentiation, and function. In return, the epithelium also exerts its paracrine effects on mesenchyme by regulating the differentiation and specific organizational pattern of its stromal smooth muscle. In a normal adult prostate, the maintenance of normal glandular structure and function is dependent not only on the constant presence of testosterone, but also on a normal intact and stable stroma. This chapter will concentrate first on factors involved in the normal development of the prostate gland and then on the aberrant changes in the homeostatic balance arising either from within (i.e., mutations) or outside (i.e., changes in hormonal balance) that result in derangements of the prostate gland. Finally, environmental and genetic factors that lead to prostate carcinogenesis including activation of oncogenes and mutations of tumor suppressor genes are also discussed.

Rat encodes the paralogous gene equivalent of the human histo-blood group ABO gene. Association with antigen expression by overexpression of human ABO transferase

We cloned a rat ABO homologue and established human A- and B-transferase transgenic rats. A DNA fragment corresponding to exon 7 of the human ABO gene was amplified from Wistar rat genomic DNA and sequenced. Using the amplified fragments as a probe for Southern blotting, multiple hybridized bands appeared on both EcoRI- and BamHI-digested genomes of seven rat strains, which showed variations in the band numbers among the strains. Four cDNAs were cloned from a Wistar rat, three of which showed A-transferase activity and one of which showed B-transferase activity. These activities were dependent on the equivalent residues at 266 and 268 of human ABO transferase. Wild Wistar rats expressed A-antigen in salivary gland, intestine, and urinary bladder tissue, but B-antigen was not stained in any organs studied, whereas a transcript from the ABO homologue with B-transferase activity was ubiquitous. Human A-transferase and B-transferase were transferred into Wistar rats. A-transgenic rats expressed A-antigen in ectopic tissue of the brain plexus, type II lung epithelium, pancreas, and epidermis. B-antigen in the B-transgenic rat was expressed in the same organs as A-transgenic rats. These results may shed light on the function and evolution of the ABO gene in primates.

Polyamine participation in the maturation of glycoprotein fucosylation, but not sialylation, in rat small intestine

The aim of this study was to determine the role of polyamines in the diet-related maturation of the intestinal glycoprotein glycosylation during postnatal development in the rat. The activity of alpha-2,6-sialyltransferase and the sialylated forms of glycoproteins in the intestinal brush-border membranes were found to decrease considerably after weaning, in parallel with the intestinal level of putrescine. By contrast, the activity of alpha-1,2-fucosyltransferases, the mRNA levels for two alpha-1,2-fucosyltransferase genes, FTA and FTB, and the fucosylated forms of glycoproteins all increased after weaning, in parallel with the levels of spermidine and spermine. These results suggest a possible role of polyamines in the evolution of glycosylation. The treatment of suckling rats with spermidine or spermine reproduced the high intestinal levels of these polyamines corresponding to those normally found after weaning. After these treatments, a rise in the activity of the alpha-1,2-fucosyltransferase was observed, associated with a fall in alpha-L-fucosidase activity. The alpha-1,2-fucosyltransferase FTB gene was found to be regulated at the transcriptional level, but not by its inhibitor, fuctinin. The result of these variations was the precocious appearance of several alpha-1,2-fucoproteins, which are normally found in brush-border membranes after weaning. The treatment of suckling rats with putrescine, which induced only a transitory rise in intestinal putrescine, had a similar but weaker effect on the fucosylation process than spermidine or spermine, and treatment with ornithine was ineffective. alpha-2,6-Sialylation was not affected by any of the treatments. Spermidine and spermine turned out to be more effective than putrescine for intestinal glycoprotein fucosylation, but did not affect their sialylation. Spermidine and spermine, whose intestinal levels where found to increase at weaning time, may have been partly responsible for the natural evolution of the intestinal glycoprotein fucosylation that occurred during this period.

fucosyltransferase1 and H-type complex carbohydrates modulate epithelial cell proliferation during prostatic branching morphogenesis

The prostate undergoes branching morphogenesis dependent on paracrine interactions between the prostatic epithelium and the urogenital mesenchyme. To identify cell-surface molecules that function in this process, monoclonal antibodies raised against epithelial cell-surface antigens were screened for antigen expression in the developing prostate and for their ability to alter development of prostates grown in serum-free organ culture. One antibody defined a unique expression pattern in the developing prostate and inhibited growth and ductal branching of cultured prostates by inhibiting epithelial cell proliferation. Expression cloning showed that this antibody binds fucosyltransferase1, an alpha-(1,2)-fucosyltransferase that synthesizes H-type structures on the complex carbohydrate modifications of some proteins and lipids. The lectin UEA I that binds H-type 2 carbohydrates also inhibited development of cultured prostates. These data demonstrate a previously unrecognized role for fucosyltransferase1 and H-type carbohydrates in controlling the spatial distribution of epithelial cell proliferation during prostatic branching morphogenesis. We also show that fucosyltransferase1 is expressed by epithelial cells derived from benign prostatic hyperplasia or prostate cancer; thus, fucosyltransferase1 may also contribute to pathological prostatic growth. These data further suggest that rare individuals who lack fucosyltransferase1 (Bombay phenotype) should be investigated for altered reproductive function and/or altered susceptibility to benign prostatic hyperplasia and prostate cancer.

Characterization of three members of murine alpha1,2-fucosyltransferases: change in the expression of the Se gene in the intestine of mice after administration of microbes

We cloned three members of a GDP-fucose:beta-galactoside alpha1,2-fucosyltransferase (alpha1,2-fucosyltransferase) family, MFUT-I, -II, and -III, from a cDNA of murine small intestine, and determined their enzymatic properties after transfection of the genes into COS-7 cells, and their expression in murine tissues by Northern blotting. MFUT-I, -II, and -III exhibited sequence homology with the human H (78.4%), Se (79.0%), and Sec1 (74.9%) gene products, respectively. COS-7 cells transfected with MFUT-I and -II exhibited alpha1,2-fucosyltransferase activity and the best acceptor substrate for both gene products was GA1 to yield a fucosyl GA1 structure, but no activity was detected in COS-7 cells with MFUT-III. MFUT-II yielded a 3.5-kb mRNA transcript in several tissues, whereas MFUT-I and -III were predominantly expressed in epididymis and testis, respectively. The administration of microbes into germ-free mice resulted in a rapid increase of the MFUT-II gene (Se gene) for the synthesis of fucosyl GA1 in the intestine.

Comparison of the three rat GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferases FTA, FTB and FTC

The complete coding sequences of three rat alpha1,2fucosyltransferase genes were obtained. Sequence analysis revealed that these genes, called FTA, FTB and FTC, were homologous to human FUT1, FUT2 and Sec1, respectively. A distance analysis between all alpha1,2fucosyltransferase sequences available showed that the two domains of the catalytic region evolved differently with little divergence between the FUT2 and Sec1 N-terminal domains, quite distant from that of FUT1. At variance, FUT1 and FUT2 C-terminal domains were less distant while a high evolutionary rate was noted for Sec1 C-terminal domain. Whereas FTA and FTB encode typical glycosyltransferases, FTC lacks the homologous start codon and encodes a protein devoid of intracellular and transmembrane domains. It is located on rat chromosome 1q34. Transfection experiments revealed that unlike FTA and FTB, FTC does not generate enzyme activity. Analysis by flow cytometry showed that H type 2 epitopes were synthesized in Chinese hamster ovary cells transfected by both FTA and FTB cDNA, but only FTB transfectants possessed H type 3 determinants. In REG rat carcinoma cells, both FTA and FTB allowed synthesis of H type 2 and H type 3 at the cell surface. Western blots showed that, in both cell types, FTA was able to synthesize H type 2 epitopes on a larger set of glycoproteins than FTB. Analysis of the kinetic parameters obtained using small oligosaccharides revealed only a slight preference of FTA for type 2 over other types of acceptor substrates, whereas FTB was barely able to fucosylate this substrate.

Influence of spermine on intestinal maturation of the glycoprotein glycosylation process in neonatal rats

Previous work has shown an inverse evolution of the rat intestinal glycoprotein sialylation that decreases from birth to weaning and of fucosylation that increases markedly after weaning during postnatal development. At weaning time, an increase in the intestinal level of polyamines (and especially that of spermine) was observed, owing partly to the higher level of spermine found in solid food given to rats at this period in comparison with the level found in milk. To study the role of this polyamine as a possible maturation factor of the glycoprotein glycosylation, suckling rats were treated for 4 days with spermine administered orally. This treatment allowed us to mimic the spermine increase that was observed naturally in rat small intestine after weaning because, in intestines of spermine-treated suckling rats, spermine was the only polyamine to be increased and was at a level similar to that of weaned rats. Spermine treatment did not induce appreciable changes in sialyltransferase activity or in sialylation of the brush-border-membrane glycoproteins. On the contrary, this treatment induced a rise in an alpha-1, 2-fucosyltransferase activity that was regulated at the transcriptional level, but not by its inhibitor (fuctinin), and no change in the availability of substrate (GDP-fucose). As a consequence of the increase in alpha-1,2-fucosyltransferase level and of the decrease in alpha-l-fucosidase level after treatment with spermine, several alpha-1,2-fucoproteins, naturally found in brush border membranes after weaning time, appeared precociously in these membranes after the treatment of the immature suckling rats. These results indicate that spermine is a maturation factor for the fucosylation of intestinal brush-border-membrane glycoproteins but not for their sialylation, and that this polyamine might be implicated in the increased fucosylation naturally occurring at weaning time during postnatal development.

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.

Functional analysis of the 5'-flanking region of FTA for expression of rat GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferase

The tissue-specific and species-specific expression of the ABH antigens is well known among vertebrate species and it is regulated by the alpha(1,2)fucosyltransferase that forms the H antigen, a precursor of the A and B antigens. To investigate the mechanisms governing the tissue-specific and species-specific expression of this alpha(1,2)fucosyltransferase, we characterized the gene structure, including the promoter region, of FTA, a rat orthologous homolog of human FUT1 that encodes the H alpha(1, 2)fucosyltransferase and is responsible for the expression of the ABH antigens on human red blood cells. Northern blot and 5'-RACE analyses suggested that at least two forms of FTA mRNA (2.9 and 2.6 kb), which use alternative transcription start sites, are present in the cancer cell lines RCN-9 (rat colon cancer) and PC12 (rat pheochromocytoma), whereas only the 2.6 kb form was detected in normal colon, stomach and pancreas. Transcriptional activity of the 5'-flanking sequence, which contains three putative Sp1-binding sites, but lacks both TATA and CAAT boxes, was examined. Transient transfection experiments of promoter-reporter gene constructs showed high promoter activity in RCN-9, PC12 and human colon cancer (WiDr) cell lines, weak activity in human vascular endothelial (ECV304) cells and no activity in human erythroleukemia (HEL) cells. The results suggest that the 5'-flanking region of FTA contains a tissue-specific promoter. Deletional analysis of the 5'-flanking sequence revealed regions containing cell-type-specific positive acting element(s) and negative regulatory element(s), which are related to the promoter activity.

HIP/PAP gene, encoding a C-type lectin overexpressed in primary liver cancer, is expressed in nervous system as well as in intestine and pancreas of the postimplantation mouse embryo

We originally isolated the HIP/PAP gene in a differential screen of a human hepatocellular carcinoma cDNA library. This gene is expressed at high levels in 25% of primary liver cancers but not in nontumorous liver. HIP/PAP belongs to the family of C-type lectins and acts as an adhesion molecule for hepatocytes. In normal adult human tissues, HIP/PAP expression is found in pancreas (exocrine and endocrine cells) and small intestine (Paneth and neuroendocrine cells). In order to gain insight into the possible role of HIP/PAP in vivo, we have investigated the pattern of HIP/PAP expression in the developing postimplantation mouse embryo by in situ hybridization. Detailed analysis of developing mouse embryos revealed that HIP/PAP gene exhibits a restricted expression pattern during development. Thus, HIP/PAP transcripts are first observed within the nervous system from day 14.5 onwards in trigeminal ganglia, dorsal root ganglia, and spinal cord where it appears to be an early specific marker of a subpopulation of motor neurons. At laster stages, HIP/PAP transcripts were detected in intestine and pancreas at day 16.5 but not in embryonic liver. This highly restricted expression pattern suggests that HIP/PAP might participate in neuronal as well as intestinal and pancreatic cell development.

Increased tumorigenicity of rat colon carcinoma cells after alpha1,2-fucosyltransferase FTA anti-sense cDNA transfection

Accumulation of histo-blood group antigens such as Lewis b, Lewis Y and H increases tumor cell motility and tumorigenesis. Alpha1,2-fucosylation is a key step in the synthesis of these antigens. Two alpha1,2-fucosyltransferases, expressed in colorectal carcinomas, have been characterized (FUT1 and FUT2 in humans, FTA and FTB in rats). To define the relative contribution of each of these enzymes in tumor cell behavior, we have used an anti-sense transfection approach in rat colon carcinoma PROb cells, which synthesize mRNA encoding for both enzymes. We have previously reported that anti-sense transfection of a cDNA fragment of the FTB enzyme decreased H antigenic cell-surface levels and concomitantly decreased tumorigenicity. H antigens, detected by antibodies specific for H type 1, 3 or 4, were detected only on a splice variant of CD44 containing the product of exon v6. We now report the anti-sense transfection of an FTA cDNA fragment into PROb cells, which resulted in decreased enzymatic activity on a type 2 precursor and decreased cell-surface H type 2 antigen exclusively. Compared to controls, FTA anti-sense-transfected cells were significantly more tumorigenic in syngeneic animals but not in immunodeficient SCID mice. The UEA-I lectin, specific for H type 2, revealed that these structures were present on the CD44v6 variant and on an uncharacterized 80-kDa glycoprotein. Our results indicate that FTA and FTB fucosylate distinct glycan chains in the same cell, leading to opposite effects, under control of the immune system.

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.

Cloning and expression of the catalytic domain from rat hepatoma H35 cell GDP-fucose:GM1 alpha 1-->2fucosyltransferase, an enzyme which is activated during early stages of chemical carcinogenesis in rat liver

A ganglioside GM1-specific alpha 1-->2fucosyltransferase is induced during the early stages of chemical carcinogenesis with N-2-acetylaminofluorene (AAF) in rat liver hepatocytes. The induction of this enzyme gives rise to the expression of a fucose-containing ganglioside with the same determinant structure as blood group B on a GM1 ganglioside core. Fucoganglioside synthesis is not found in normal rat liver but is elevated in premalignant liver and is often highly expressed in derived rat hepatoma cell lines. Based upon the consensus sequence from portions of previously cloned human, rabbit, and rat alpha 1-->2fucosyltransferase enzymes, primers were designed which were used in RT-PCR experiments with rat hepatoma H35 cell total RNA to generate cDNAs encoding the extracellular, catalytic domain of the H35 cell alpha 1-->2fucosyltransferase. Sequencing of these PCR fragments showed them to encode a novel enzyme with high homology to other cloned enzymes, particularly secretor alpha 1-->2fucosyltransferases. The derived sequence indicated that the 3' portion of the gene was virtually identical to the alpha 1-->2fucosyltransferase B (FTB) fragment reported earlier in rat PROb colon-adenocarcinoma cells (J-P. Piau et al. Biochem. J. 300, 623-626, 1994). A PCR product corresponding to the H35 cell alpha 1-->2fucosyltransferase was obtained from total RNA isolated from F344 rat liver after 0.03% N-2-acetylaminofluorene administration. No PCR product was obtained from total RNA isolated from normal F344 liver using PCR primers for the H35 cell alpha 1-->2fucosyltransferase. The H35 cell alpha 1-->2fucosyltransferase was expressed in the pPROTA vector and the derived fusion protein demonstrated the ability to transfer fucose to ganglioside GM1 but not to the neolacto-series acceptor nLcOse4Cer.

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.

Evolution of fucosyltransferase genes in vertebrates

Cloning and expression of chimpanzee FUT3, FUT5, and FUT6 genes confirmed the hypothesis that the gene duplications at the origin of the present human cluster of genes occurred between: (i) the great mammalian radiation 80 million years ago and (ii) the separation of man and chimpanzee 10 million years ago. The phylogeny of fucosyltransferase genes was completed by the addition of the FUT8 family of alpha(1,6)fucosyltransferase genes, which are the oldest genes of the fucosyltransferase family. By analysis of data banks, a new FUT8 alternative splice expressed in human retina was identified, which allowed mapping the human FUT8 gene to 14q23. The results suggest that the fucosyltransferase genes have evolved by successive duplications, followed by translocations, and divergent evolution from a single ancestral gene.

Molecular cloning, chromosomal assignment and tissue-specific expression of a murine alpha(1,2)fucosyltransferase expressed in thymic and epididymal epithelial cells

Terminal Fucalpha(1-2)Galbeta epitopes have been proposed to play significant roles in cell-cell interactions in development, cell adhesion, and malignant transformation. To begin to investigate the regulation and function of alpha(1-2)fucosylated epitopes in an animal model, we have isolated and characterized a mouse genomic DNA segment encoding a protein orthologous to the human H blood group locus alpha(1,2)fucosyltransferase (FUT1). This segment maintains an open reading frame encoding 376 amino acids sharing 75% sequence identity with the enzyme encoded by human FUT1, and 55% sequence identity with the enzyme encoded by the human Secretor blood group locus (FUT2). Expression of the open reading frame in COS-7 cells yields an alpha(1,2)fucosyltransferase activity with a Km of 7.6 mM for phenyl-beta-d-galactoside. Southern blotting and interspecific backcross analyses indicate that this murine locus represents a single copy sequence mapping to a novel locus 2.1 centimorgans from the Klk1 locus, in a region of homology between mouse chromosome 7 and the human FUT1 locus on the long arm of chromosome 19. Mouse FUT1 yields a 2.8 kb mRNA transcript identifiable in many organs, including thymus, lung, stomach, pancreas, small intestine, colon, uterus and epidiymis. Hybridization analyses in situ localize expression of FUT1 transcripts to thymic medullary and epididymal epithelial cells, implying that this gene determines the expression of cell surface Fucalpha(1-2)Galbeta epitopes in these tissues.

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.

Molecular cloning and expression of a third type of rabbit GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferase

Recent molecular investigation revealed that two closely related structural genes encode distinct GDP-L-fucose:beta-D-galactoside 2-alpha-L-fucosyltransferases (alpha1,2-fucosyltransferases). Some human cancer cells or tissues may express an aberrant alpha1, 2-fucosyltransferase other than H- and Secretor-type alpha1, 2-fucosyltransferase. However, definite evidence of the existence of a third type of alpha1,2-fucosyltransferase has not been demonstrated. Here we report the molecular cloning of a third type of rabbit alpha1,2-fucosyltransferase (RFT-III) from a rabbit genomic DNA library. The DNA sequence included an open reading frame coding for 347 amino acids, and the deduced amino acid sequence of RFT-III showed 59 and 80% identity with those of the previously reported two types of rabbit alpha1,2-fucosyltransferase, RFT-I and RFT-II, respectively. COS-7 cells transfected with the RFT-III gene exhibited alpha1,2-fucosyltransferase activity toward phenyl-beta-Gal as a substrate. Neuro2a (a murine neuroblastoma cell line) cells transfected with the RFT-III gene expressed fucosyl GM1 (type 3 H) but not Ulex europaeus agglutinin-1 lectin reactive antigens (type 2 H). Kinetic studies revealed that RFT-III exhibits higher affinity to types 1 (Galbeta1, 3GlcNAc) and 3 (Galbeta1, 3GalNAc) than to type 2 (Galbeta1, 4GlcNAc) oligosaccharides, which suggests that RFT-III as well as RFT-II is a Secretor-type alpha1, 2-fucosyltransferase. RFT-III was expressed in the adult gastrointestinal tract. The RFT-I, -II, and -III genes were assigned within 90 kilobases on pulsed field gel electrophoresis analysis. These results constitute direct evidence that, at least in one mammalian species, three active alpha1,2-fucosyltransferases exist.

Molecular genetic analysis of the human Lewis histo-blood group system. II. Secretor gene inactivation by a novel single missense mutation A385T in Japanese nonsecretor individuals

The Lewis histo-blood group system comprises two major antigens, Lewis a and Lewis b. The Lewis b antigen is a product of two fucosyltransferases, the alpha(1,3/1,4)fucosyltransferase (Lewis enzyme; Fuc-TIII) encoded by the Lewis gene and an alpha(1,2)fucosyltransferase which is not required for synthesis of Lewis a antigen. An enzyme responsible for secreting ABH antigens into body secretions (secretor enzyme) is also one of alpha(1,2)fucosyltransferases. A candidate gene encoding secretor enzyme Sec2 gene was recently cloned by Rouquier, S., Lowe, J. B., Kelly, R. J., Fertitta, A. L., Lennon, G. G., and Giorgi, D. ((1995) J. Biol. Chem. 270, 4632-4639) and Kelly, R. J., Rouquier, S., Giorgi, D., Lennon, G. G., and Lowe, J. B. ((1995) J. Biol. Chem. 270, 4640-4649) who demonstrated a G428A nonsense mutation (Trp143 to terminal codon) in Sec2 of nonsecretors. However, the G428A nonsense mutation discovered in the Sec2 gene of nonsecretors in an ethnic group other than Japanese was not found in any of 45 Japanese nonsecretors, whereas one Filipino who had been erroneously registered as a Japanese possessed the G428A mutation heterozygously. In order to explore the Sec2 gene of a Japanese population, we performed a molecular genetic analysis of the Sec2 gene on 226 Japanese individuals, 21 in a family study and 205 in a random sampling study. We discovered two novel mutations in the Sec2 gene, an A385T missense mutation (Ile129 to Phe) that results in inactivation of Sec2-encoded alpha(1,2)fucosyltransferase and a C357T silent mutation which is irrelevant to amino acid substitution, in Japanese nonsecretors. The analysis of Japanese individuals using the polymerase chain reaction-restriction fragment length polymorphism method found three alleles in the Sec2 gene, the first having no mutation, the second having a C357T mutation, and the third having both C357T and A385T mutations, which we designated as Se1, Se2, and sej, respectively. Among 226 Japanese individuals, 40 having a Le(a+b-) phenotype and 5 having a Le(a-b-) nonsecretor phenotype were homozygous for sej/sej, whereas 149 having a Le(a-b+) phenotype and 32 having a Le(a-b-)-secretor phenotype possessed at least one Se1 or Se2. The frequencies of occurrence of Se1, Se2, and sej among 410 alleles examined in a random sample of 205 Japanese individuals were 15, 46, and 39%, respectively, indicating a rather wide distribution of the sej allele in the Japanese population. The results show that the Sec2 gene really encodes the secretor enzyme alpha(1,2)fucosyltransferase and indicate that a ethnic group-specific nonsense or missense point mutation in the Sec2 gene determines nonsecretor status. The phylogenic aspect and biological significance of the Se and Le genes are discussed.

Porcine submaxillary gland GDP-L-fucose: beta-D-galactoside alpha-2-L-fucosyltransferase is likely a counterpart of the human Secretor gene-encoded blood group transferase

Partial amino acid sequence of GDP-L-fucose:beta-D-galactoside alpha-2-L-fucosyltransferase purified from porcine submaxillary glands was determined. Amino acid sequence analysis yielded 100, 93.3, and 84.2%, and 75, 46.6, and 84.2% sequence identity between 12-, 15-, and 19- amino acid tryptic peptides generated from porcine enzyme and amino acid residues 61-72, 111-125, and 308-326 and 89-100, 139-153, and 338-356 of the human Secretor and H type alpha-2-fucosyltransferases, respectively. Higher amino acid sequence homology of the porcine enzyme with the predicted sequence for the human Secretor locus as compared with H gene-encoded blood group beta-D-galactoside alpha-2-L-fucosyltransferase suggests that porcine alpha-2-fucosyltransferase highly corresponds to the human Secretor gene-encoded enzyme.

Molecular cloning and expression of two types of rabbit beta-galactoside alpha 1,2-fucosyltransferase

Two DNA clones encoding rabbit beta-galactoside alpha 1,2-fucosyltransferase (RFT-I and RFT-II) have been isolated from a rabbit genomic DNA library. The DNA sequences revealed open reading frames coding for 373 (RFT-I) and 354 (RFT-II) amino acids, respectively. The deduced amino acid sequences of RFT-I and RFT-II showed 56% identity with each other, and that of RFT-I showed 80% identity with that of human H blood type alpha 1,2-fucosyltransferase. Northern blot analysis of embryo and adult rabbit tissues revealed that the RFT-I gene was expressed in adult brain, and that the RFT-II gene was expressed in salivary and lactating mammary glands. The identities of these enzymes were confirmed by constructing recombinant fucosyltransferases in which the N-terminal part including the cytoplasmic tail and signal anchor domain was replaced with the immunoglobulin signal peptide sequence. RFT-I expressed in COS-7 cells exhibited similar transferase activity to that of human H blood type alpha 1,2-fucosyltransferase. RFT-II expressed in COS-7 cells showed higher affinity for type 1 (Gal beta 1,3GlcNAc) and type 3 (Gal beta 1,3GalNAc) acceptors than type 2 (Gal beta 1,4GlcNAc) ones, which suggested that RFT-II was a putative secretor-type alpha 1,2-fucosyltransferase.