TNF- -induced increase in intestinal epithelial tight junction permeability requires NF- B activation

Ma, Thomas Y., Gary K. Iwamoto, Neil T. Hoa, Vimesh Akotia, Ali Pedram, Michel A. Boivin, and Hamid M. Said. TNFinduced increase in intestinal epithelial tight junction permeability requires NFB activation. Am J Physiol Gastrointest Liver Physiol 286: G367–G376, 2004; 10.1152/ajpgi.00173.2003.—Crohn’s disease (CD) patients have an abnormal increase in intestinal epithelial permeability. The defect in intestinal tight junction (TJ) barrier has been proposed as an important etiologic factor of CD. TNFincreases intestinal TJ permeability. Because TNFlevels are markedly increased in CD, TNFincrease in intestinal TJ permeability could be a contributing factor of intestinal permeability defect in CD. Our purpose was to determine some of the intracellular mechanisms involved in TNFmodulation of intestinal epithelial TJ permeability by using an in vitro intestinal epithelial system consisting of filtergrown Caco-2 monolayers. TNFproduced a concentrationand time-dependent increase in Caco-2 TJ permeability. TNF-induced increase in Caco-2 TJ permeability correlated with Caco-2 NFB activation. Inhibition of TNF-induced NFB activation by selected NFB inhibitors, curcumin and triptolide, prevented the increase in Caco-2 TJ permeability, indicating that NFB activation was required for the TNF-induced increase in Caco-2 TJ permeability. This increase in Caco-2 TJ permeability was accompanied by downregulation of zonula occludens (ZO)-1 proteins and alteration in junctional localization of ZO-1 proteins. TNFmodulation of ZO-1 protein expression and junctional localization were also prevented by NFB inhibitors. TNFdid not induce apoptosis in Caco-2 cells, suggesting that apoptosis was not the mechanism involved in TNF-induced increase in Caco-2 TJ permeability. These results demonstrate for the first time that TNF-induced increase in Caco-2 TJ permeability was mediated by NFB activation. The increase in permeability was associated with NFB-dependent downregulation of ZO-1 protein expression and alteration in junctional localization.