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MUCOSAL BIOLOGY

Serine proteases decrease intestinal epithelial ion permeability by activation of protein kinase C

Inflammation Research Network, Department of Physiology and Pharmacology, University of Calgary, Calgary, Canada

Submitted 11 March 2009 ; accepted in final form 16 May 2009

Epithelial permeability to ions and larger molecules in the gut is essential for fluid balance, and its dysregulation contributes to intestinal pathology. We investigated the effect of digestive serine proteases on epithelial paracellular permeability. Trypsin, chymotrypsin, and elastase elicited sustained increases in transepithelial resistance (R_TE) in polarized monolayers of three intestinal epithelial cell lines. This effect was reflected by decreases in paracellular conductances of Na⁺ and Cl^– and a concomitant decrease in permeability to 3,000 molecular weight dextran. The enzyme activities of the proteases were required, yet activators of known protease-activated receptors (PARs) did not reproduce the effect of these proteases on R_TE. PKC isoform-specific inhibitor significantly reduced the trypsin-induced increase in R_TE whereas PKC activity was increased in cells treated with trypsin and chymotrypsin compared with control cells; this activity was reduced to control levels in the presence of PKC-specific inhibitor. Ca²⁺ chelators and pharmacological inhibitors of cell signaling support the role for PKC in the protease-induced effect. Finally, we showed that treatment with the serine proteases increased occludin immunostaining and zonula occludin-1 coimmunoprecipitation with occludin in the detergent-insoluble fraction of cell lysates, and these increases were ablated by pretreatment with PKC-specific inhibitor. This finding indicates increased insertion of occludin into the cell junctional complex. These data demonstrate a role for serine proteases in the facilitation of epithelial barrier function through a mechanism that is independent of PARs and is mediated by activation of PKC.

epithelium; tight junction; occludin; resistance