Characterization of a beta 1----3-N-acetylglucosaminyltransferase associated with synthesis of type 1 and type 2 lacto-series tumor-associated antigens from the human colonic adenocarcinoma cell line SW403

Molecular cloning and characterization of UDP-GlcNAc:lactosylceramide beta 1,3-N-acetylglucosaminyltransferase (beta 3Gn-T5), an essential enzyme for the expression of HNK-1 and Lewis X epitopes on glycolipids

A new member of the UDP-N-acetylglucosamine:beta-galactose beta1,3-N-acetylglucosaminyltransferase (beta3Gn-T) family having the beta3Gn-T motifs was cloned from rat and human cDNA libraries and named beta3Gn-T5 based on its position in a phylogenetic tree. We concluded that beta3Gn-T5 is the most feasible candidate for lactotriaosylceramide (Lc(3)Cer) synthase, an important enzyme which plays a key role in the synthesis of lacto- or neolacto-series carbohydrate chains on glycolipids. beta3Gn-T5 exhibited strong activity to transfer GlcNAc to glycolipid substrates, such as lactosylceramide (LacCer) and neolactotetraosylceramide (nLc(4)Cer; paragloboside), resulting in the synthesis of Lc(3)Cer and neolactopentaosylceramide (nLc(5)Cer), respectively. A marked decrease in LacCer and increase in nLc(4)Cer was detected in Namalwa cells stably expressing beta3Gn-T5. This indicated that beta3Gn-T5 exerted activity to synthesize Lc(3)Cer and decrease LacCer, followed by conversion to nLc(4)Cer via endogenous galactosylation. The following four findings further supported that beta3Gn-T5 is Lc(3)Cer synthase. 1) The beta3Gn-T5 transcript levels in various cells were consistent with the activity levels of Lc(3)Cer synthase in those cells. 2) The beta3Gn-T5 transcript was presented in various tissues and cultured cells. 3) The beta3Gn-T5 expression was up-regulated by stimulation with retinoic acid and down-regulated with 12-O-tetradecanoylphorbol-13-acetate in HL-60 cells. 4) The changes in beta3Gn-T5 transcript levels during the rat brain development were determined. Points 2, 3, and 4 were consistent with the Lc(3)Cer synthase activity reported previously.

Identification and characterization of three novel beta 1,3-N-acetylglucosaminyltransferases structurally related to the beta 1,3-galactosyltransferase family

We have isolated three types of cDNAs encoding novel beta1,3-N-acetylglucosaminyltransferases (designated beta3Gn-T2, -T3, and -T4) from human gastric mucosa and the neuroblastoma cell line SK-N-MC. These enzymes are predicted to be type 2 transmembrane proteins of 397, 372, and 378 amino acids, respectively. They share motifs conserved among members of the beta1,3-galactosyltransferase family and a beta1,3-N-acetylglucosaminyltransferase (designated beta3Gn-T1), but show no structural similarity to another type of beta1,3-N-acetylglucosaminyltransferase (iGnT). Each of the enzymes expressed by insect cells as a secreted protein fused to the FLAG peptide showed beta1,3-N-acetylglucosaminyltransferase activity for type 2 oligosaccharides but not beta1,3-galactosyltransferase activity. These enzymes exhibited different substrate specificity. Transfection of Namalwa KJM-1 cells with beta3Gn-T2, -T3, or -T4 cDNA led to an increase in poly-N-acetyllactosamines recognized by an anti-i-antigen antibody or specific lectins. The expression profiles of these beta3Gn-Ts were different among 35 human tissues. beta3Gn-T2 was ubiquitously expressed, whereas expression of beta3Gn-T3 and -T4 was relatively restricted. beta3Gn-T3 was expressed in colon, jejunum, stomach, esophagus, placenta, and trachea. beta3Gn-T4 was mainly expressed in brain. These results have revealed that several beta1,3-N-acetylglucosaminyltransferases form a family with structural similarity to the beta1,3-galactosyltransferase family. Considering the differences in substrate specificity and distribution, each beta1,3-N-acetylglucosaminyltransferase may play different roles.

Molecular cloning and expression analysis of a mouse UDP-GlcNAc:Gal(beta1-4)Glc(NAc)-R beta1,3-N-acetylglucosaminyltransferase homologous to Drosophila melanogaster Brainiac and the beta1,3-galactosyltransferase family

We have isolated a murine cDNA coding for a beta1,3-N-acetylglucosaminyltransferase enzyme ( beta3GnT). This enzyme is similar in sequence to Drosophila melanogaster Brainiac and to the murine and human beta1,3-galactosyltransferase family of proteins. The mouse beta 3GnT protein is 397 amino acids in length and contains 7 cysteine residues that are conserved in the human orthologue. beta 3GnT is a type II membrane protein localized to the Golgi apparatus. Enzyme assays with recombinant mouse beta 3GnT reveal that it has a preference for acceptors with Gal(beta1-4)Glc(NAc) at the non-reducing termini. Proton NMR analysis of product showed incorporation of GlcNAc in beta1,3 linkage to the terminal Gal of Gal(beta1-4)Glc(beta1-O-benzyl). Northern blot analysis revealed the presence of a single 3.0[emsp4 ]kb transcript in all adult mouse and human organs tested, with highest levels in the kidney, liver, heart and placenta. The beta 3GnT gene is also expressed in a number of tumor cell lines. The human orthologue of beta 3GnT is located on chromosome 2pl5.

Stable expression of a cDNA encoding a human beta 1 --> 3galactosyltransferase responsible for lacto-series type 1 core chain synthesis in non-expressing cells: variation in the nature of cell surface antigens expressed

Transient expression of a human colonic adenocarcinoma Colo 205 cell derived cDNA in cell lines which ordinarily express only neolacto-series glycolipids has resulted in the expression of a beta 1 --> 3galactosyltransferase gene responsible for synthesis of glycolipids based upon the lacto-series type 1 core chain. Calcium phosphate transfected cells were panned on anti-IgM coated plates after initial treatment with a combination of monoclonal antibodies specific for type 1 chain terminal structures (TE-3) and a very broadly specific antibody reactive with multiple type 1 chain derivatives (TE-2). Adherent cells after panning were capable of efficiently transferring Gal in beta 1 --> 3-linkage to the acceptor glycolipid Lc3. Using these reagents, clones of stably transfected human colonic adenocarcinoma HCT-15 cells were produced and isolated. Parental HCT-15 cells do not express type 1 chain based antigens. The nature of the type 1 chain based antigens produced in each of these clones was analyzed by solid phase antibody binding assays. Three types of behavior were observed. Formation of type 1 terminal structures that were either exclusively sialylated or fucosylated, or a mixture of sialylated and fucosylated determinants occurred. In contrast, no difference in type 2 antigen expression between any clone and the parental cells was observed. These data suggest that coordination of subsequent reactions capable of modifying type 1 chain structures is not the same in all clones. The relationship of these results to aspects of cellular regulation of carbohydrate biosynthesis is discussed.

Biosynthesis in vitro of core lacto-series glycosphingolipids by N-acetyl-D-glucosaminyltransferases from human colon carcinoma cells, Colo 205

Two N-acetyl-D-glucosaminyltransferases have been detected in human colon carcinoma Colo 205 cells. These enzymes catalyze the biosynthesis in vitro of the core-glycolipid of Type 1 and Type 2 lacto-series antigens and of the polylactosamine-containing longer chain antigenic structures, respectively. The first enzyme, GlcNAcT-1, which catalyzes the formation of lactotriosylceramide [LcOse3Cer, beta-D-GlcpNAc-(1----3)-LcOse2Cer, the core for all lacto-series Type 1 and Type 2 chains] from lactosylceramide [beta-D-Galp-(1----4)-D-Glcp-Cer, LcOse2Cer] and UDP-GlcNAc shows optimum activity in the presence of nonionic detergent Triton CF-54. The other enzyme, GlcNAcT-2, which catalyzes the biosynthesis in vitro of iLcOse5Cer [beta-D-GlcpNAc-(1----3)-nLcOse4Cer, the core for polylactosamine-containing antigens] from nLcOse4Cer [beta-D-Galp-(1----4)-LcOse3Cer] and UDP-GlcNAc, is optimally active with the zwitterionic detergent, Zwittergent 3-14, when membrane-bound. Both of these activities, however, can be extracted from the membrane by use of a nonionic detergent. Triton X-114, with nearly the same efficiency. These two transferases showed different pH optima, different cation and anion effects, and differential heat-inactivation patterns at 55 degrees. Permethylation studies of the radioactive products isolated from both of the enzyme-catalyzed reactions using respective 3H-substrates and nonradioactive UDP-GlcNAc showed the presence of 2,4,6-tri-O-methylgalactose in the hydrolyzed products. This indicated the presence of a (1----3)-linked beta-D-GlcpNAc group at the nonreducing end in both cases. The linkage of the beta-D-GlcpNAc group to the subterminal D-Gal residue in the two products was confirmed by an almost 90% cleavage of the terminal [3H]GlcNAc group by purified clam and papaya beta-D-hexosaminidases.

Blood group A glycolipid antigen biosynthesis: discrimination between biosynthesized and enzyme preparation derived blood group A antigen by mass spectrometry

A monofucosyl type 1 chain blood group A hexaglycosylceramide was biosynthesized in solution using the type 1 chain blood group H pentaglycosylceramide as precursor, a crude microsomal fraction prepared from the mucosa scraping of a blood group A pig small intestine as enzyme source, and uridine diphosphate-N-acetyl-(1-14C)galactosamine as sugar donor. The radioactive product was enriched using reversed-phase column chromatography and silica gel HPLC. The peak, as detected by a beta-flow scintillation counter, was collected, permethylated, and analyzed by mass spectrometry. Carbohydrate sequence ions were found, indicating the presence of both the biosynthesized and a native, non-14C-containing blood group A hexaglycosylceramide. The blood group A pig small intestinal mucosa used as the enzyme source contain blood group A hexaglycosylceramide as the predominant glycolipid. Therefore, it is concluded that the nonradioactive blood group A hexaglycosylceramide found after the biosynthesis is derived from the enzyme preparation.

Increased CMP-NeuAc:Gal beta 1,4GlcNAc-R alpha 2,6 sialyltransferase activity in human colorectal cancer tissues

The sialyltransferase activities of 10 human colorectal specimens were compared with those of the corresponding adjacent normal mucosa. Using asialofetuin as an acceptor we found, in tumor tissues of 9 out of 10 patients, an increased sialyltransferase activity towards the N-linked chains as determined upon peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase (PNGase) treatment. On the contrary, the activity towards the O-linked chains was not significantly changed. When the specificity of the sialyltransferase acting on N-linked chains was investigated by using N-acetyl-lactosamine (Gal beta 1,4GlcNAc) as an acceptor, we found that the alpha 2,6 sialyltransferase activity expressed by both normal and tumor colorectal tissues was far higher than the alpha 2,3-activity and that alpha 2,6 was the only sialyltransferase activity increased in tumor tissues. Kinetic analysis revealed that normal and tumor alpha 2,6 sialyltransferases have the same apparent Km for the acceptor substrate (469 and 465 microns), but normal enzyme has a higher Km for CMP-NeuAc (303 microns) than the tumor enzyme (50 microns). The higher affinity of tumor enzyme for the nucleotide-sugar might partially explain its increased activity in tumor tissues. In addition, tumor tissues contain a lower amount of sialic acid despite the increase in alpha 2,6 sialyltransferase activity.

Characterization and membrane organization of beta 1----3- and beta 1----4-galactosyltransferases from human colonic adenocarcinoma cell lines Colo 205 and SW403: basis for preferential synthesis of type 1 chain lacto-series carbohydrate structures

Evidence indicates that activation of a beta 1----3N-acetylglucosaminyltransferase is responsible for accumulation of large quantities of lacto-series tumor-associated antigens in human colonic adenocarcinomas. Expression of type 1 and 2 core chain derivatives characterize human colonic adenocarcinomas, whereas normal adult colonic epithelial cells express detectable quantities of only type 1 chain derivatives. The basis for preferential synthesis of type 1 chain lacto-series carbohydrate structures characteristic of normal colonic mucosa and human colonic adenocarcinoma Colo 205 cells has been studied. The beta 1----3- and beta 1----4galactosyltransferase enzymes associated with synthesis of type 1 and 2 core chain structures, respectively, have been separated from a Triton X-100 solubilized membrane fraction of Colo 205 cells by chromatography on an alpha-lactalbumin-Sepharose column and their properties studied. Optimal transfer of beta 1----3-linked galactose to acceptor Lc3 occurred in the presence of 0.1% Triton CF-54 with Triton X-100 providing 75% of maximal activity. The enzyme was active over a broad pH range from 6.5 to 7.5 and had a near absolute requirement for Mn2+. The Km values for donor UDPgalactose and acceptor Lc3 were determined to be 48 and 13 microM, respectively. In contrast, the beta 1----4galactosyltransferase required taurodeoxycholate for maximal activity and the Km for Lc3 was found to be 20-fold higher than that for the beta 1----3-specific enzyme under the same assay conditions. Studies with membrane-bound beta 1----3- and beta 1----4galactosyltransferases as found in Golgi-rich membrane fractions of SW403 and Colo 205 adenocarcinoma cells showed that preferential synthesis of type 1 chain structures occurs under conditions similar to those in vivo for biosynthesis of lacto-series core chains. The results suggest that both the higher affinity of the beta 1----3galactosyltransferase for acceptor Lc3 and the membrane organizational features result in preferential synthesis of type 1 chain structures.

Human cytomegalovirus induces stage-specific embryonic antigen 1 in differentiating human teratocarcinoma cells and fibroblasts

Cell surface expression of stage specific embryonic antigen 1 (SSEA-1), or Lex (III3 FucnLC4), was induced in differentiated human teratocarcinoma cells and in human diploid fibroblasts 3-6 d after infection with human cytomegalovirus (HCMV). In parallel, fucosylated lactoseries glycolipids bearing the SSEA-1/Lex epitope were readily detected in the infected cells but not in the uninfected cells. HCMV infection also results in altered expression of several glycosyltransferases. SSEA-1/Lex induction is probably a consequence of both increased expression of beta 1----3N-acetylglucosaminyltransferase, which catalyzes the rate-limiting step in lactoseries core chain synthesis, and subtle alterations in the relative competition for common precursor structures at key points in the biosynthetic pathway. Since SSEA-1 has been suggested to play a role in some morphogenetic cell-cell interactions during embryonic development, the induction of this antigen at inappropriate times might provide one mechanism whereby intrauterine infection with HCMV can damage the developing fetal nervous system.