The core 3 structure of the O-glycan, GlcNAc␤1-3GalNAc␣1-Ser͞ Thr, an important precursor in the biosynthesis of mucin-type glycoproteins, is synthesized by ␤1,3-N-acetylglucosaminyltransferase 6 (␤3Gn-T6; core 3 synthase). We generated an anti-␤3Gn-T6 mAb (G8-144 mAb) and performed immunohistochemical analyses. In normal stomach and colon, ␤3Gn-T6 was strongly expressed in the Golgi region of epithelia. In contrast, its expression was markedly down-regulated in gastric and colorectal carcinomas. Tissue specimens from a familial adenomatous polyposis patient showed a clear correlation between the down-regulation of ␤3Gn-T6 expression and the degree of dysplasia͞neoplasia. In vitro, the level of ␤3Gn-T6 transcript was increased according to the differentiation of Caco-2 cells. These results suggested that the expression of ␤3Gn-T6 is closely regulated during differentiation and dedifferentiation. ␤3Gn-T6 would be a useful marker for distinguishing between benign adenomas and premalignant lesions. HT1080 FP-10 cells stably transfected with the ␤3Gn-T6 gene showed a decrease in the core 1 structure, Gal␤1,3GalNAc␣1-Ser͞ Thr, probably due to competition between the core 1 synthase and core 3 synthase. The migration activity of the transfectants was markedly lower than that of mock transfectants in vitro, and lung metastasis after i.v. injection of the transfectants into nude mice was significantly suppressed. These findings indicated that the core structures of O-glycans are profoundly involved in the metastatic capacity of cancer cells.glycosyltransferase ͉ stomach ͉ familial adenomatous polyposis ͉ immunohistochemical analysis

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The sialyl Lewis a antigen is a well known tumor marker, CA19-9, which is frequently elevated in the serum in gastrointestinal and pancreatic cancers. UDPgalactose:N-acetylglucosamine ␤1,3-galactosyltransferase(s) (␤3Gal-Ts) are required for the synthesis of the sialyl Lewis a epitope. In the present study, a novel ␤3Gal-T, named ␤3Gal-T5, was isolated from a Colo205 cDNA library using a degenerate primer strategy based on the amino acid sequences of the four human ␤3Gal-T genes cloned to date. Transfection experiments demonstrated that HCT-15 cells transfected with the ␤3Gal-T5 gene expressed all the type 1 Lewis antigens. In gastrointestinal and pancreatic cancer cell lines, the amounts of ␤3Gal-T5 transcripts were quite well correlated with the amounts of the sialyl Lewis a antigens. The ␤1,3Gal-T activity toward agalacto-lacto-N-neotetraose was also well correlated with the amounts of ␤3Gal-T5 transcripts in a series of cultured cancer cells, and in Namalwa and HCT-15 cells transfected with the ␤3Gal-T5 gene. Thus, the ␤3Gal-T5 gene is the most probable candidate responsible for the synthesis of the type 1 Lewis antigens in gastrointestinal and pancreatic epithelia and tumor cells derived therefrom. In addition, ␤3Gal-T5 is a key enzyme that determines the amounts of the type 1 Lewis antigens including the sialyl Lewis a antigen.