Cell surface N-acetylneuraminic acid α2,3-galactoside-dependent intercellular adhesion of human colon cancer cells

Sialoglycans on the cell surface of human colon cancer (HCC) cells have been implicated in cellular adhesion and metastasis. To clarify the role of N-acetylneuraminic acid (NeuAc) linked α2,3 to galactose (Gal) on the surface of HCC cells, we studied the intercellular adhesion of HCC cell lines expressing increasing NeuAcα2,3Gal-R. Our model system consisted of the HCC SW48 cell line, which inherently possesses low levels of cell surface α2,3 and α2,6 sialoglycans. To generate SW48 clonal variants with elevated cell surface Neuαcα2,3Gal-R linkages, are transfected the expression vector, pcDNA3, containing either rat liver cDNA encoding Galβ1,3(4)GlcNAc α2,3 sialyltransferase (ST3Gal III) or human placental cDNA encoding Galβ1,3GalNAc/Galβ1,4GlcNAc α2,3 sialyltransferase (ST3Gal TV) into SW48 cells. Selection of neomycin-resistant clones (6001 μg G418/ml) having a higher percentage of cells expressing NeuAcα2,3Gal-R (up to 85% positive Maackia amurenis agglutinin staining compared with 30% for wild type cells) was performed. These ST3Gal III and ST3Gal IV clonal valiants demonstrated increased adherence to IL-1β-activated human umbilical vein endothelial cells (HUVEC) (up to 90% adherent cells compared with 63% for wild type cells). Interestingly, ST3Gal III and ST3Gal IV clonal variants also bound non-activated HUVEC up to 4-fold more effectively than wild type cells. Cell. surface NeuAcα2,3Gal-R expression within the various SW48 clonal variants correlated directly with increased adhesion to HUVEC (r = 0.84). Using HCC HT-29 cells, which express high levels of surface NeuAcα2,3Gal-R, addition of synthetic sialyl, sulfo or GalNAc Lewis X structures were found to specifically inhibit intercellular adhesion. At 1.0 mM, NeuAcα2,3Galβ1,3(Fucα1,4)GlcNAc-OH and Galβ1,4(Fucα1,3)GlcNAcβ1,6(SE6Galβ1,3)GalNAcα1-O-methyl inhibited HT-29 cell adhesion to IL-1β-stimulated HUVEC by 100% and 68%, respectively. GalNAcβ1,4(Fucα1,3)GIcNAcβ1-O-methyl and GalNAcβ1,4(Fucα1,3)GlcNαcβ1,6Manα1,6Manβ1,GM 0-C30H61, however, did not possess inhibitory activity. In conclusion, these studies demonstrated that cell surface NeuAcα2,3Gal-R expression is involved in HCC cellular adhesion to HUVEC. These specific carbohydrate-mediated intercellular adhesive events may play an important role in tumor angiogenesis, metastasis and growth control.