Bacterial invasion is not required for activation of NF-kappaB in enterocytes

Pathogenic enteric microorganisms induce the NF-kappaB-dependent expression of proinflammatory genes in intestinal epithelial cells. The purpose of the present study was to clarify the contribution of microbial invasion to the degradation of the regulatory protein Ikappa Balpha and the subsequent activation of NF-kappaB in cultured intestinal epithelial cells. Caco-2BBe cells were incubated with Salmonella dublin, Salmonella typhimurium, or a weakly invasive strain of E. coli. S. dublin and S. typhimurium (10(7) organisms/ml) induced equivalent concentration-dependent gel mobility shifts of an NF-kappaB consensus sequence that was preceded by Ikappa Balpha degradation. E. coli (10(7) organisms/ml) did not induce Ikappa Balpha degradation or NF-kappaB translocation. Pretreatment with cytochalasin D blocked invasion of all three strains but had no effect on Ikappa Balpha degradation or NF-kappaB activation. S. dublin and S. typhimurium adhered to Caco-2BBe cells 3- to 10-fold more than E. coli. NF-kappaB activation was prevented by physical separation of S. dublin from Caco-2BBe cells by a 0. 4-micrometers-pore-size filter. Our results imply that bacterial adhesion, rather than invasion or release of a secreted factor, is sufficient to induce IkappaBalpha degradation and NF-kappaB activation in intestinal epithelial cells. Our data suggest that strategies to reduce enteric inflammation should be directed to the reduction of bacterial enterocyte adhesion.