Transfer of terminal alpha 2,6-linked
sialic acids to N-
glycans is catalyzed by
beta-galactoside alpha 2,6-sialyltransferase (
ST6Gal I). Expression of
ST6Gal I and its products is reportedly increased in
colon cancers. To investigate directly the functional effects of
ST6Gal I expression, human
colon cancer (HT29) cells were transfected with specific
antisense DNA.
ST6Gal I mRNA and
protein were virtually undetectable in six strains of transfected HT29 cells. ST6Gal activity was reduced to 14% of control (P<0.005) in transfected cells. Expression of terminal alpha 2,6- and alpha 2,3-linked
sialic acids, and unmasked
N-acetyllactosamine oligosaccharides, respectively, was assessed using flow cytometry and fluoresceinated Sambucus nigra, Maackia amurensis and Erythrina cristagalli
lectins. Results indicated a major reduction in expression of alpha 2,6-linked
sialic acids and counterbalancing increase in unmasked N-acetyllactosamines in
antisense DNA-transfected cells, without altered expression of alpha 2,3-linked
sialic acids or
ganglioside profiles. The ability of transfected cells to form colonies in soft
agar and to invade extracellular matrix material (
Matrigel), respectively, in vitro was reduced by approx. 98% (P<0.0001) and more than 3-fold (P<0.005) compared to parental HT29 cells. These results indicate that N-
glycans bearing terminal alpha 2,6-linked
sialic acids may enhance the invasive potential of
colon cancer cells.