The Endoplasmic Reticulum Stress Response Activates Tissue Transglutaminase and Intestinal Inflammation by Reducing Levels of IκBα

Abstract

Background & AimsDefects in resolution of the endoplasmic reticulum (ER) stress response contribute to inflammation and might be involved in pathogenesis of Crohn's disease (CD). We investigated the ability of lipopolysaccharide from Escherichia Coli (EC-LPS) to induce ER stress, and its effects on tissue transglutaminase (TG2), nuclear factor (NF)- κB, and its inhibitor (IκB) κ in cultured intestinal epithelial cells and colonic mucosa samples from patients with CD. MethodsWe investigated effects of EC-LPS on ER stress, calcium release, EC-LPS, and sumoylation and ubiquitination of TG2 in Caco-2 intestinal epithelial cells, cultured intestinal mucosa samples from patients with CD, and mucosal samples from individuals without CD (controls). Mucosa samples were incubated with or without anti-oxidants or the TG2 inhibitor L682777. Levels of TG2 were reduced in Caco-2 cells using small interfering RNAs. Tissues and cells were analyzed by immunoprecipitation, immunoblot, reverse transcriptase-PCR, confocal microscopy, and fluorescence resonance energy transfer microscopy analyses. ResultsEC-LPS induced ER stress in Caco-2 cells, leading to oxidative stress and sumoylation of TG2; this inhibited TG2 ubiquitination and degradation by the proteasome. TG2 induced cross-linking, ubiquitination, and proteasome degradation of IκBα, leading to activation of NF-κB and an inflammatory response in mucosal samples from patients with CD, determined by increased expression of COX-2 and ICAM-1 by lamina propria cells and mucosal expression of inflammatory cytokines such as tumor necrosis factor-α. Knockdown of TG2 in Caco-2 cells, or incubation of CD colon mucosa samples with L682777, increased levels of IkBα following administration of EC-LPS, preventing IκBα crosslinking and degradation. ConclusionInduction of ER stress with EC-LPS activates TG2 in intestinal epithelial cells and tissues from patients with CD. Inhibition of TG2 in colon mucosa from patients with CD reduces activation of NF-kB and the inflammatory response.