Human
gliomas express very high levels of cell-surface alpha2,3-linked terminal
sialic acids on
glycoproteins bearing N-linked
oligosaccharides, most notably on
alpha3beta1 integrin, which is the predominant
integrin found in these
tumors. Alpha2,6-linked terminal
sialic acids, however, are not expressed. Two stable transfectants were made using a tumorigenic human
glioma cell line, U-373 MG. Galbeta1,4GlcNAc alpha2,6-sialyltransferase (
ST6Gal I) transfectants were made to replace the endogenous alpha2,3-linked
sialic acids with alpha2,6-linked
sialic acids. And Galbeta1,3(4)GlcNAc alpha2,3-sialyltransferase (
ST3Gal III) transfectants were made to increase further the expression of cell-surface, N-
glycan, alpha2,3-linked
sialic acids. Although
ST3Gal III transfection resulted in increased invasivity when compared with parental U-373 MG and vector-transfected control cells in vitro,
ST6Gal I transfection abolished invasion in vitro and induced alterations in both cell morphology, cell-spreading, and adhesion-mediated
protein tyrosine phosphorylation. Furthermore, the
ST6Gal I transfectants produced no intracranial
tumors in severe combined immunodeficient mice, whereas parental U-373 MG cells, the vector-transfected control cells, and
ST3Gal III-transfected U-373 MG cells did. These results suggest that both the linkage and expression levels of the terminal
sialic acids of
alpha3beta1 integrin N-
glycans play an important role in
glioma cell-extracellular matrix interactions. Thus, manipulating
ST6Gal I gene expression may have therapeutic potential for the treatment of
malignant gliomas.