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

Pathogenic enteric microorganisms induce the NF-kappa B-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 I kappa B alpha and the subsequent activation of NF-kappa B 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-kappa B consensus sequence that was preceded by I kappa B alpha degradation. E. coli (10(7) organisms/ml) did not induce I kappa B alpha degradation or NF-kappa B translocation. Pretreatment with cytochalasin D blocked invasion of all three strains but had no effect on I kappa B alpha degradation or NF-kappa B activation. S. dublin and S, typhimurium adhered to Caco-2BBe cells 3- to 10-fold more than E. coli. NF-kappa B activation was prevented by physical separation of S. dublin from Caco-2BBe cells by a 0.4-mu m-pore-size filter. Our results imply that bacterial adhesion, rather than invasion or release of a secreted factor, is sufficient to induce I kappa B alpha degradation and NF-kappa B activation in intestinal epithelial cells. Our data suggest that strategies to reduce enteric inflammation should be directed to the reduction of bacterial enterocyte adhesion.