DIMINISHED EXPRESSION OF BLOOD GROUP A-ACTIVE GLYCOLIPIDS REDUCED E. COLI HEAT-LABILE TOXIN BINDING TO RECEPTORS OTHER THAN GM1 IN HT29 CELLS.
Diema Claudio D, Galván Estela M, Monferran Clara G.
We have previously resported the presence of Escherichia coli heat-labile toxin (LT-I) receptors alternative to the GM1 ganglioside in HT29 cells. Glycosphingolipids carrying blood group A epitopes represent a major population among these additional receptors. In addition, LT-I could induce cyclic AMP accumulation acting on blood group A-active glycosphingolipids receptors. The aim of the present work was to lower glycosphingolipid expression on the cell surface to determine the effect of this alteraction on toxin binding to cells. Fot this purpose, HT29 cells were cultured in the presence of PPMP (D, L-threo-1phenyl-2-hexadecanoylamino-3-morpholino-1-propanol), a potent inhibitor of ceramide glucosyltransferase. Treatment of cells with 5.0 µM PPMP for 48 h diminished [3H]fucose incorporation into lipid extracts to approximately 20% of control cells. When HT29 cells were grown for 7 days in the continuous presence of 5.0 µM PPMP the expression of blood group A-active glycosphingolipids on the cell surface was strongly reduced as judgded by the loss of fluorescence detected by flow cytometric analysis. We also foundt hat LT-I has approximately 40-60% less binding sites on PPMP ?treated cells than in control cells. These results give further support to the idea that blood group A-active can behave as a type of functional alternative receptors for LT-I in HT29 cells.
