TNFα up-regulates claudin-2 expression in epithelial HT-29/B6 cells via phosphatidylinositol-3-kinase signaling

Abstract

Our aim has been to characterize the molecular mechanisms regulating the expression of the channel-forming tight-junctional protein claudin-2 in response to the pro-inflammatory cytokine tumor necrosis factor-alpha (TNFalpha), which is elevated, for example, in active Crohn's disease. TNFalpha caused an 89% decrease of the paracellular resistance in colonic HT-29/B6 cells, whereas transcellular resistance was unaltered. The claudin-2 protein level was increased by TNFalpha without changes in subcellular tight-junctional protein localization as revealed by confocal laser scanning microscopy. Enhanced gene expression was identified as the source of this increase, since claudin-2-specific mRNA and promoter activity was elevated, whereas mRNA stability remained unaltered. Specific inhibitors and phospho-specific antibodies revealed that the increased gene expression of claudin-2 after TNFalpha treatment was mediated by the phosphatidylinositol-3-kinase pathway. Thus, the up-regulation of claudin-2 by TNFalpha is attributable to the regulation of the expression of the gene, as a result of which epithelial barrier function is disturbed, for example, during chronic intestinal inflammation.

Interleukin-6 (IL-6) Regulates Claudin-2 Expression and Tight Junction Permeability in Intestinal Epithelium

“…Studies have demonstrated that claudin-2 expression is higher in the colons of IBD patients, typically those suffering from Crohn disease and ulcerative colitis (29). TNF␣ and IL-13 are now known to induce claudin-2 expression in cultured intestinal cell monolayers and mouse colon (14,15,33). Our results suggest that IL-6 also plays a role in the elevation of colonic epithelial claudin-2 levels in IBD patients.…”

“…A growing body of evidence suggests that this barrier dysfunction is associated with the release of TNF␣ (11,33), IFN␥ (11,12), IL-1␤ (13), and IL-13 (14,15); however, the precise pathologic mechanism remains unclear. In this study, we have characterized for the first time the role of IL-6 as a cytokine that induces TJ permeability to cations including Na ϩ , via a pathway involving claudin-2 expression.…”

“…Kinugasa et al have shown that the MEK/ERK pathway is required for IL-17-mediated claudin-2 expression in intestinal T84 cells (37). PI3K activity has been shown to be required for TNF␣-and IL-13-induced claudin-2 expression (15,33). The colonic epithelium of active Crohn disease and ulcerative colitis patients also exhibits higher pERK and pAkt activity, suggesting that activated signaling pathways might be associated with the dysregulation of epithelial function in IBD (38).…”

Autophagy Enhances Intestinal Epithelial Tight Junction Barrier Function by Targeting Claudin-2 Protein Degradation

“…Several studies have shown that the inflamed intestinal mucosa in patients with active IBD has increased claudin-2 expression. Moreover, inflammatory cytokines whose levels are increased markedly in IBD patients, including TNF-␣, IL-13, IL-17, and IL-6, cause an increase in claudin-2 expression and a claudin-2-dependent increase in TJ permeability (43)(44)(45)(46)(47). Therefore, the role of claudin-2 in intestinal pathological processes has been attributed, in part, to increases in intestinal TJ permeability.…”

Yersinia enterocolitica induces epithelial barrier dysfunction through regional tight junction changes in colonic HT-29/B6 cell monolayers

“…Modulation of TJ protein expression by different signaling cascades has been described for different cell lines and conditions. [61][62][63] However, so far it is not clear, which signaling cascades alter the expression of ZO-1 and other claudins than claudin-8 in Y. enterocolitica infection. Moreover, the type of interaction remains speculative.…”