Disruption of epithelial barrier integrity via altered GILZ/c-Rel/RACK1 signaling in inflammatory bowel disease (IBD)

Background and aim: Given the role of Receptor for Activated C Kinase 1 (RACK1) in both immune cell activation and in the maintenance of the intestinal epithelial barrier integrity, we investigated whether it was involved in inflammatory bowel disease (IBD). Methods: RACK1 expression was analyzed in intestinal mucosal samples of healthy and IBD patients, in mice with chemically-induced colitis and in diseased in vitro 2D and 3D co-culture models by luciferase assay, RT-qPCR, Western blotting, immunofluorescence and immunohistochemistry. Based on our finding that glucocorticoid-induced leucine zipper (GILZ or tsc22d3) positively correlates with RACK1 expression in IBD patients, GILZ knock-out mice and cell silencing experiments were performed. Results: RACK1 was significantly decreased in IBD, especially in ulcerative colitis. This was associated with a NF-κB/c-Rel-related mechanism, correlating with decreased GILZ protein expression. GILZ depletion confirmed a decrease in RACK1 expression, which favored SRC activation and led to a significant reduction in E-cadherin, resulting in impaired epithelial barrier integrity. Finally, our data highlighted that this novel mechanism could be considered to develop new therapies since dexamethasone, the first line of treatment in IBD, restored RACK1 expression through the glucocorticoid receptor in a c-Rel/GILZ independent manner. Conclusions: We provide the first evidence that an alteration of RACK1/SRC/E-cadherin regulatory mechanism, correlating with decreased GILZ protein expression is involved in epithelial barrier disruption. The clinical relevance is based on the fact that this mechanism involving GILZ/cRel-related RACK1 expression could be considered to improve IBD therapies, particularly in patients with low or no response to glucocorticoid treatment.