ROLE OF THE CERAMIDE-SIGNALING PATHWAY IN CYTOKINE RESPONSES TO P-FIMBRIATED ESCHERICHIA-COLI

Escherichia coli express funbriae-associated adhesins through which th ey attach to mucosal cells and activate a cytokine response. The recep tors for E. coli P finbriae are the globoseries of glycosphingolipids; Gal alpha 1-->4Gal beta-containing oligosaccharides bound to ceramide in the outer leaflet of the lipid bilayer. The receptors for type 1 f imbriae are mannosylated glycoproteins rather than glycolipids. This s tudy tested the hypothesis that P-fimbriated E. coli elicit a cytokine response through the release of ceramide in the receptor-bearing cell . We used the A498 human kidney cell line, which expressed functional receptors for P and type 1 fimbriae and secreted higher levels of inte rleukin (IL)-6 when exposed to the fimbriated strains than to isogenic nonf;mbriated controls. P-fimbriated E. coli caused the release of ce ramide and increased the phosphorylation of ceramide to ceramide 1-pho sphate. The IL-6 response to P-fimbriated E. coli was reduced by inhib itors of serine/threonine kinases but not by other protein kinase inhi bitors. In contrast, ceramide levels were not influenced by type 1-fim briated E. coli, and the IL-6 response was insensitive to the serine/t hreonine kinase inhibitors. These results demonstrate that the ceramid e-signaling pathway is activated by P-fimbriated E. coli, and that the receptor specificity of the P fimbriae influences this process. We pr opose that this activation pathway contributes to the cytokine inducti on by P-fimbriated E. coli in epithelial cells.