Claudins regulate the intestinal barrier in response to immune mediators

Background & Aims: To determine the functional role of immune mediators in the formation of the intestinal barrier, we have examined the regulation of claudin expression by interleukin (IL)-17 in human intestinal epithelial c ells. Methods: Expression of claudins, extracellular signal-related (ERK) m itogen-activated protein kinases (MAPKs), and activated ERK MAPKs was deter mined by immunoblotting, Claudin membrane association was assessed by immun ohistochemistry and claudin messenger RNA expression by Northern blot analy sis. Intestinal epithelial barrier function was characterized through trans epithelial electrical resistance and mannitol tracer flux. Results: IL-17 i nduced the development of a paracellular barrier of T84 cell monolayers. In hibition of ERK activation with the MEK inhibitor PD98059 blocked IL-17 as well as basal development of tight junctions in T84 cells. IL-17 induced fo rmation of tight junctions correlated with up-regulation of claudin-1 and c laudin-2 gene transcription. Inhibition of MEK reduced the activated and ba sal expression of claudin-2 messenger RNA and protein expression. Functiona l MEK was required for the expression and membrane association of claudin-2 but not claudin-1 in T84 cells. Conclusions: MEK activity is required for claudin-mediated formation of tight junctions. IL-17 is able to regulate th e intestinal barrier through the ERK MARK pathway.