Two missense mutations of H type alpha(1,2)fucosyltransferase gene (FUT1) responsible for para-Bombay phenotype

Mutational Analysis of Bombay Phenotype in Iranian People: Identification of a Novel FUT1 Allele

Bombay phenotype is characterized by lack of ABH antigens on RBCs and in body secretions as a result of mutations in fucosyltransferase 1 (FUT1) and fucosyltransferase 2 (FUT2) genes. The aim of this study was a mutational analysis in Iranians with this phenotype. Serological analyses including ABH and adsorption-elution tests were performed in five unrelated Bombay individuals. ABO genotyping was determined by direct sequencing. The coding regions of FUT1 and FUT2 genes were amplified and sequenced directly or after cloning into suitable vector. A novel missense FUT1 allele was detected (G1051T; G351C). Also four reported FUT1 alleles were revealed. Molecular analysis of FUT2 gene confirmed nonsecretor status in all individuals. This and our previous findings suggest the diversity and population specificity of FUT1 alleles.

Biological functions of fucose in mammals

Fucose is a 6-deoxy hexose in the l-configuration found in a large variety of different organisms. In mammals, fucose is incorporated into N-glycans, O-glycans and glycolipids by 13 fucosyltransferases, all of which utilize the nucleotide-charged form, GDP-fucose, to modify targets. Three of the fucosyltransferases, FUT8, FUT12/POFUT1 and FUT13/POFUT2, are essential for proper development in mice. Fucose modifications have also been implicated in many other biological functions including immunity and cancer. Congenital mutations of a Golgi apparatus localized GDP-fucose transporter causes leukocyte adhesion deficiency type II, which results in severe developmental and immune deficiencies, highlighting the important role fucose plays in these processes. Additionally, changes in levels of fucosylated proteins have proven as useful tools for determining cancer diagnosis and prognosis. Chemically modified fucose analogs can be used to alter many of these fucose dependent processes or as tools to better understand them. In this review, we summarize the known roles of fucose in mammalian physiology and pathophysiology. Additionally, we discuss recent therapeutic advances for cancer and other diseases that are a direct result of our improved understanding of the role that fucose plays in these systems.

Molecular basis of Bombay phenotype in Mashhad, Iran: identification of a novel FUT1 deletion

BACKGROUND AND OBJECTIVES

Bombay phenotype is characterized by the lack of H substance both on red blood cell (RBC) surface and in body secretions. Mutations of fucosyltransferase 1 (FUT1) and fucosyltransferase 2 (FUT2) genes are resulted in this rare phenotype.

MATERIALS AND METHODS

Five unrelated patients were tested by hemagglutination and adsorption/elution techniques for the presence of ABH antigens. The saliva specimens were analysed by hemagglutination inhibition method. The exons 6 and 7 of ABO gene were sequenced to determine ABO genotype. The coding fragments of FUT1 and FUT2 were amplified and sequenced by specific primers.

RESULTS

Serologic investigation confirmed Bombay phenotype in all individuals. FUT1 molecular analysis revealed a novel large deletion. Also two novel homozygous mutations were detected; one was a missense mutation (392T>C, L131P) and the other a three nucleotide deletion (668_670delACT, Y224del). FUT2 sequencing showed one reported null allele (428G>A, W143X) and one homozygous deletion of FUT2.

CONCLUSION

Although FUT2 deletion has been reported, this is the first report of FUT1 deletion. Finding two FUT1 novel alleles in Iranian people is indicative of mutation diversity in this gene.

A novel FUT1 allele was identified in a Chinese individual with para-Bombay phenotype

BACKGROUND

The para-Bombay phenotype is characterised by H-deficient or H partially deficient red blood cells (RBCs) in individuals who secrete ABH antigens in their saliva. Samples from an individual whose RBCs had an apparent para-Bombay phenotype and his family members were investigated and a novel FUT1 allele was identified.

MATERIALS AND METHODS

RBCs' phenotype was characterised by standard serologic technique. Genomic DNA was sequenced with primers that amplified the coding sequence of FUT1 and FUT2, respectively. Routine ABO genotyping analysis was performed. Haplotypes of FUT1 were identified by TOPO cloning sequencing. Recombination expression vectors of FUT1 mutation alleles were constructed and transfected into COS-7 cells. The pα-(1,2)-fucosyltransferase activity of expression protein was determined.

RESULTS

B101/O02 genotype of the proband was correlated with ABH substances in saliva. The proband carried a new FUT1 allele which showed 35C/T, 235G/C and 682A/G heterozygote by directly DNA sequencing. Two haplotypes, 235C and 35T+682G, were identified by TOPO cloning sequencing and COS-7 cells transfected with five recombination vectors including wild-type, 35T, 235C, 682G and 35T+682G alleles were established respectively. The α-(1,2)-fucosyltransferase activities of cell lysates which had transfected with 35T, 235C, 682G and 35T+682G recombination vectors showed 79·45, 16·23, 80·32 and 24·59%, respectively, compared with that of the wild-type FUT1-transfected cell lysates.

CONCLUSION

A novel FUT1 allele 235C was identified, which greatly diminished the activity of α-(1,2)-fucosyltransferase.

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).

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.

Genomic analysis of ABO chimeras and mosaics using hematopoietic colony-derived DNA

BACKGROUND

While there are many case reports dealing with ABO mosaicism and chimerism, there have been few attempts to determine the patient's genotype.

STUDY DESIGN AND METHODS

Peripheral blood and buccal mucosa were obtained from three persons with ABO mosaicism or chimerism. DNA extracted from hematopoietic progenitor cell-derived colonies and from peripheral blood and buccal mucosa were analyzed by polymerase chain reaction-restriction fragment length polymorphism methods. In addition, analyses of short tandem repeat markers were carried out.

RESULTS

Hematopoietic progenitor cell-derived DNA analysis revealed that, in two of the three persons there were 2 apparently distinct progenitor cell lineages whose percentages were close to those in the peripheral blood of the patients, as analyzed by flow cytometry; the exception was Subject 3, who had myelodysplastic syndrome (MDS). Short tandem repeat analysis showed that the former two subjects had two pairs of ABO alleles and the latter subject, with MDS, had loss of heterozygosity in some colony-derived DNA as well as blood DNA.

CONCLUSION

The subjects without MDS had two distinct hematopoietic cell lineages that led to their ABO chimeric status. The subject with MDS was assumed to have an ABO mosaicism caused by the somatic deletion of the ABO gene in the hematopoietic progenitor cells.

Significance of each of three missense mutations, G484A, G667A, and G808A, present in an inactive allele of the human Lewis gene (FUT3) for alpha(1,3/1,4)fucosyltransferase inactivation

Recently, we found three novel missense mutations, G484A (Asp162Asn), G667A (Gly223Arg), and G808A (Val270Met), present in a Lewis-negative allele (le484,667,808) from an African (Xhosa) population. To define the relative contribution of each of the three mutations in the le484,667,808 allele for inactivation of the FUT3-encoded enzyme, we made chimeric FUT3 containing each of the three mutations. A transient expression study indicated that COS7 cells transfected with the FUT3 construct containing the G484A mutation expressed the Lewis antigen and had about 20% enzyme activity as compared with COS7 cells transfected with the wild type FUT3 allele, whereas COS7 cells transfected with the FUT3 construct containing either the G667A mutation or the G808A mutation did not express the Lewis antigen and showed no detectable alpha(1,3/1,4)fucosyltransferase activity. These results suggest that the G667A and/or the G808A missense mutations of FUT3 alleles are responsible for the inactivation of the FUT3-encoded enzyme.

The haptoglobin-gene deletion responsible for anhaptoglobinemia

We have found an allelic deletion of the haptoglobin (Hp) gene from an individual with anhaptoglobinemia. The Hp gene cluster consists of coding regions of the alpha chain and beta chain of the haptoglobin gene (Hp) and of the alpha chain and beta chain of the haptoglobin-related gene (Hpr), in tandem from the 5' side. Southern blot and PCR analyses have indicated that the individual with anhaptoglobinemia was homozygous for the gene deletion and that the gene deletion was included at least from the promoter region of Hp to Hpr alpha but not to Hpr beta (Hpdel). In addition, we found seven individuals with hypohaptoglobinemia in three families, and the genotypes of six of the seven individuals were found to be Hp2/Hpdel. The phenotypes and genotypes in one of these three families showed the father to be hypohaptoglobinemic (Hp2) and Hp2/Hpdel, the mother to be Hp2-1 and Hp1/Hp2, one of the two children to be hypohaptoglobinemic (Hp2) and Hp2/Hpdel, and the other child to be Hp1 and Hp1/Hpdel, showing an anomalous inheritance of Hp phenotypes in the child with Hp1. The Hp2/Hpdel individuals had an extremely low level of Hp (mean+/-SD = 0.049+/-0. 043 mg/ml; n=6), compared with the level (1.64+/-1.07 mg/ml) obtained from 52 healthy volunteers having phenotype Hp2, whereas the serum Hp level of an individual with Hp1/Hpdel was 0.50 mg/ml, which was approximately half the level of Hp in control sera from the Hp1 phenotype (1.26+/-0.33 mg/ml; n=9), showing a gene-dosage effect. The other allele (Hp2) of individuals with Hp2/Hpdel was found to have, in all exons, no mutation, by DNA sequencing. On the basis of the present study, the mechanism of anhaptoglobinemia and the mechanism of anomalous inheritance of Hp phenotypes were well explained. However, the mechanism of hypohaptoglobinemia remains unknown.

Conserved structural features in eukaryotic and prokaryotic fucosyltransferases

Fucosyltransferases are the enzymes transferring fucose from GDP-Fuc to Gal in an alpha1,2-linkage and to GlcNAc in alpha1,3-, alpha1,4-, or alpha1,6-linkages. Since all fucosyltransferases utilize the same nucleotide sugar, their specificity will probably reside in the recognition of the acceptor and in the type of linkage formed. A search of nucleotide and protein databases yielded more than 30 sequences of fucosyltransferases originating from mammals, chicken, nematode, and bacteria. On the basis of protein sequence similarities, these enzymes can be classified into four distinct families: (1) the alpha-2-fucosyltransferases, (2) the alpha-3-fucosyltransferases, (3) the mammalian alpha-6-fucosyltransferases, and (4) the bacterial alpha-6-fucosyltransferases. Nevertheless, using the sensitive hydrophobic cluster analysis (HCA) method, conserved structural features as well as a consensus peptide motif have been clearly identified in the catalytic domains of all alpha-2 and alpha-6-fucosyltranferases, from prokaryotic and eukaryotic origin, that allowed the grouping of these enzymes into one superfamily. In addition, a few amino acids were found strictly conserved in this family, and two of these residues have been reported to be essential for enzyme activity for a human alpha-2-fucosyltransferase. The alpha-3-fucosyltransferases constitute a distinct family as they lack the consensus peptide, but some regions display similarities with the alpha-2 and alpha-6-fucosyltranferases. All these observations strongly suggest that the fucosyltransferases share some common structural and catalytic features.

Distribution of H type 1 and of H type 2 antigens of ABO blood group in different cells of human submandibular gland

We have examined the immunohistochemical distribution of H Type 1 and of H Type 2 substances of the ABO blood group system in human submandibular gland using either of the two anti-H monoclonal antibodies MAb 1E3 and MAb 3A5. MAb 3A5 was specific for H Type 2, and MAb 1E3 reacted with each of H Type 1-H Type 4 artificial antigens. We have developed a competitive inhibition method against H Type 2 and have obtained MAb 1E3, which is fairly specific for H Type 1 under certain conditions. Mucous cells from secretors were strongly stained by 1E3 and weakly by 3A5, whereas those from nonsecretors showed no reaction with 1E3 and 3A5. Serous cells from both secretors and nonsecretors were stained neither by 1E3 nor by 3A5. Striated and interlobular duct cells were strongly stained by 1E3 and by 3A5, regardless of the secretor status. These results indicated that the expressions of the H Type 1 and H Type 2 in different cell types of the submandibular gland were controlled by different genes. In addition, we have determined the acceptor specificity of two alpha(1,2)fucosyltransferases (H and Se enzymes) after transient expressions of the FUT1 and FUT2 in COS7 cells, and found that the H enzyme activity was similar for both Type 1 and Type 2 precursors, and that Se enzyme activity with the Type 1 precursor was higher than that with the Type 2 precursor. Expression of the H Type 1 antigen in mucous cells was found to be dependent on the Se gene, whereas expressions of the H Type 1 and H Type 2 antigens in striated and interlobular duct cells were dependent on the H gene. (J Histochem Cytochem 46:69-76, 1998)

Missense mutation of FUT1 and deletion of FUT2 are responsible for Indian Bombay phenotype of ABO blood group system

The Bombay phenotype fails to express the ABH antigens of ABO blood group system on red blood cells and in secretions because of a lack in activities of the H gene (FUT1)- and Secretor gene (FUT2)-encoded alpha (1,2)fucosyltransferases. In this study, we have examined the FUT1 and the FUT2 from three unrelated Indian individuals with the Bombay phenotype. These three individuals were found to be homozygous for a T725G mutation in the coding region of the FUT1, which inactivated the enzyme activity. In addition, we did not detect any hybridized band corresponding to the FUT2 by Southern blot analysis using the catalytic domain of the FUT2 as a probe, indicating that the three individuals were homozygous for a gene deletion in the FUT2. These results suggest that the T725G mutation of FUT1 and the gene deletion of FUT2 are responsible for the classical Indian Bombay phenotype.

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.