PATHOGENESIS OF SHIGELLA DIARRHEA .17. A MAMMALIAN-CELL MEMBRANE GLYCOLIPID, GB3, IS REQUIRED BUT NOT SUFFICIENT TO CONFER SENSITIVITY TO SHIGA TOXIN

Shiga toxin recognizes a galactose-alpha 1 --> 4-galactose terminal gl ycolipid, globotriaosylceramide (Gb3), in sensitive mammalian cells an d is translocated by endocytosis to the cytoplasm, where it blocks pro tein synthesis. To determine if Gb3 is both required and sufficient fo r toxicity, Gb3 content in cells was altered by blocking key biosynthe tic or degradative path enzymes with specific inhibitors. The resultin g decrease or increase in cellular Gb3 was associated with a decrease or increase in binding of and response to Shiga toxin. Toxin-resistant Gb3-deficient variants of sensitive cells fused with liposomes contai ning Gb3 but not globotetraosylceramide (Gb4) became susceptible, wher eas fusion of Gb3 liposomes to naturally resistant Gb3-deficient CHO c ells increased toxin binding but not cytotoxicity. These data demonstr ate that Gb3 is required, but not sufficient, for the action of Shiga toxin and suggest the existence of a toxin translocation mechanism lin ked to surface glycolipids that is not expressed in CHO cells.