beta 1,3-galactosyltransferase beta 3Gal-T5 acts on the GlcNA beta 1 -> 3Ga beta 1 -> 4GlcNAc beta 1 -> R sugar chains of carcinoembryonic antigen and other N-linked glycoproteins and is down-regulated in colon adenocarcinomas

We attempted to determine whether beta1,3-galactosyl-transferase beta 3Gal- T5 is involved in the biosynthesis of a specific subset of type 1 chain car bohydrates and expressed in a cancer-associated manner. We transfected Chin ese hamster ovary (CHO) cells expressing Fuc-TIII with beta 3Gal-T cDNAs an d studied the relevant glycoconjugates formed. beta 3Gal-T5 directs synthes is of Lewis type 1 antigens in CHO cells more efficiently than beta 3Gal-T1 , whereas beta 3Gal-T2, -T3, and -T4 are almost unable to direct synthesis. In the clone expressing Fuc-TIII and beta 3Gal-T5 (CHO-FT-T5), sialyl-Lewi s a synthesis is strongly inhibited by swainsonine but not by benzyl-alpha -GalNAc, and sialyl-Lewis x is absent, although it is detected in the clone s expressing Fuc-TIII and beta 3Gal-T1 (CHO-FT-T1) or Fuc-TIII and beta 3Ga l-T2 (CHO-FT-T2). Endo-beta -galactosidase treatment of N-glycans prepared from clone CHO-FT-TB releases (+/-NeuAc alpha2-->3)Gal beta1-->3[Fuc alpha1 -->4]GlcNAc beta1-->3Gal but not GlcNAc beta1-->3Gal or type 2 chain oligos accharides, which are found in CHO-FT-T1 cells. This result indicates that beta 3Gal-T5 expression prevents poly-N-acetyllactosamine and sialyl-Lewis x synthesis on N-glycans, Kinetic studies confirm that beta 3Gal-T5 prefers accepters having the GlcNAc beta1-->3Gal end, including lactotriosylcerami de. Competitive reverse transcriptase mediated-polymerase chain reaction sh ows that the beta 3Gal-T5 transcript is expressed in normal colon mucosa bu t not or poorly in adenocarcinomas, Moreover, recombinant carcinoembryonic antigen purified from a CHO clone expressing Fuc-TIII and beta 3Gal-T5 reac ts with anti-sialyl-Lewis a and carries type 1 chains on oligosaccharides r eleased by endo-beta -galactosidase. We conclude that beta 3Gal-T5 down-reg ulation plays a relevant role in determining the cancer-associated glycosyl ation pattern of N-glycans.