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.

The type 1 carbohydrate chain, Gal␤1-3GlcNAc, is synthesized by UDP-galactose:␤-N-acetylglucosamine ␤1,3-galactosyltransferase (␤3Gal-T). Among six ␤3Gal-Ts cloned to date, ␤3Gal-T5 is an essential enzyme for the synthesis of type 1 chain in epithelium of digestive tracts or pancreatic tissue. It forms the type 1 structure on glycoproteins produced from such tissues. In the present study, we found that the transcriptional regulation of the ␤3Gal-T5 gene is controlled by homeoproteins, i.e. members of caudal-related homeobox protein (Cdx) and hepatocyte nuclear factor (HNF) families. We found an important region (؊151 to ؊121 from the transcription initiation site), named the ␤3Gal-T5 control element (GCE), for the promoter activity. GCE contained the consensus sequences for members of the Cdx and HNF families. Mutations introduced into this sequence abolished the transcriptional activity. Four factors, Cdx1, Cdx2, HNF1␣, and HNF1␤, could bind to GCE and transcriptionally activate the ␤3Gal-T5 gene. Transcriptional regulation of the ␤3Gal-T5 gene was consistent with that of members of the Cdx and HNF1 families in two in vivo systems. 1) During in vitro differentiation of Caco-2 cells, transcriptional up-regulation of ␤3Gal-T5 was observed in correlation with the increase in transcripts for Cdx2 and HNF1␣. 2) Both transcript and protein levels of ␤3Gal-T5 were determined to be significantly reduced in colon cancer. This down-regulation was correlated with the decrease of Cdx1 and HNF1␤ expression in cancer tissue. This is the first finding that a glycosyltransferase gene is transcriptionally regulated under the control of homeoproteins in a tissue-specific manner. ␤3Gal-T5, controlled by the intestinal homeoproteins, may play an important role in the specific function of intestinal cells by modifying the carbohydrate structure of glycoproteins.

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