beta-galactoside alpha2,6-sialyltransferase and the sialyl alpha 2,6-galactosyl-linkage in tissues and cell lines

Beta-Galactoside alpha2,6 sialyltransferase (ST6Gal.I) is the principal sialyltransferase responsible for the biosynthesis of the sialyl alpha2,6-galactosyl linkage. This enzyme and its cognate glycosidic structure are overexpressed in several malignancies and are related to cancer progression. The expression of the enzyme is regulated mainly through the expression of three principal mRNA species differing in the 5' untranslated exons. The form known as YZ is considered associated with the basal expression of the gene, while forms H and X are specific of the liver and of B-lymphocytes, respectively. Using a panel of human cancer cell lines we have studied the expression of ST6Gal.I activity by two different methods, the expression of alpha2,6-sialylated sugar chains by the lectin from Sambucus nigra (SNA) and the expression of the different mRNA species by RT-PCR using oligonucleotide primers complementary to the isoform-specific regions. We report that very high levels of ST6Gal.I activity result in high levels of SNA reactivity and are associated with the expression of the H transcript in colon and liver cell lines and of the X transcript in B cells.