Mapping of two different alpha-1,2-fucosyltransferase genes to rat chromosome 1q22-q31

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.

Three bovine alpha2-fucosyltransferase genes encode enzymes that preferentially transfer fucose on Galbeta1-3GalNAc acceptor substrates

To investigate the synthesis of alpha2-fucosylated epitopes in the bovine species, we have characterized cDNAs from various tissues. We found three distinct alpha2-fucosyltransferase genes, named bovine fut1, fut2, and sec1 which are homologous to human FUT1, FUT2, and Sec1 genes, respectively. Their open reading frames (ORF) encode polypeptides of 360 (bovine H), 344 (bovine Se), and 368 (bovine Sec1) amino acids, respectively. These enzymes transfer fucose in alpha1,2 linkage to ganglioside GM(1)and galacto- N -biose, but not to the phenyl-beta-D-galactoside, type 1 or type 2 acceptors, suggesting that their substrate specificity is different and more restricted than the other cloned mammalian alpha2-fucosyltransferases. Southern blot analyses detected four related alpha2-fucosyltransferase sequences in the bovine genome while only three have been described in other species. The supernumerary entity seems to be related to the alpha2-fucosyltransferase activity which can also use type 1 and phenyl-beta-D-galactoside substrate acceptors. It was exclusively found in bovine intestinal tract. Our results show that, at least in one mammalian species, four alpha2-fucosyltransferases are present, three adding a fucose on alpha1,2 linkage on type 3/4 acceptor (Galbeta1-3GalNAc) and another able to transfer also fucose on phenyl-beta-D-galactoside and type 1 (Galbeta1-3GlcNAc) acceptors. The phylogenetic tree of the enzymes homologous to those encoded by the bovine fut1, fut2, and sec1 genes revealed two main families, one containing all the H-like proteins and the second containing all the Se-like and Sec1-like proteins. The Sec1-like family had a higher evolutionary rate than the Se-like family.

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.