Increased Activity of Epithelial Cdc42 Rho GTPase and Tight Junction Permeability in the Cftr Knockout Intestine.

ABSTRACT

Increased intestinal permeability is a manifestation of cystic fibrosis (CF) in people with CF (pwCF) and in CF mouse models. CF transmembrane conductance regulator knockout (Cftr KO) mouse intestine exhibits increased proliferation and Wnt/ß-catenin signaling relative to wild-type mice (WT). Since the Rho GTPase Cdc42 plays a central role in intestinal epithelial proliferation and tight junction remodeling, we hypothesized that Cdc42 may be altered in the Cftr KO crypts. Immunofluorescence showed distinct tight junction localization of Cdc42 in Cftr KO fresh crypts and enteroids, the latter indicating an epithelial-autonomous feature. Quantitative PCR and immunoblots revealed similar expression of Cdc42 in the Cftr KO crypts/enteroids relative to WT, whereas pull-down assays showed increased GTP-bound (active) Cdc42 in proportion to total Cdc42 in Cftr KO enteroids. Cdc42 activity in the Cftr KO and WT enteroids could be reduced by inhibition of the Wnt transducer Disheveled 2. Using a dye permeability assay, Cftr KO enteroids exhibited increased paracellular permeability to 3kD dextran relative to WT. In Cftr KO relative to WT enteroids, leak permeability and Cdc42 tight junction localization were reduced to a greater extent by inhibition of Wnt/ß-catenin signaling with Endo-IWR1. Increased proliferation or inhibition of Cdc42 activity with ML141 had no effect on WT enteroid permeability. In contrast, inhibition of Cdc42 with ML141 increased permeability to both 3kD dextran and tight-junction impermeant 500 kD dextran in Cftr KO enteroids. These data suggest that increased constitutive Cdc42 activity may alter the stability of paracellular permeability in Cftr KO crypt epithelium.