ABSTRACT
The cellular prion protein was historically characterized owing to its misfolding in prion disease. Although its physiological role remains incompletely understood, PrP(C) has emerged as an evolutionary conserved, multifaceted protein involved in a wide-range of biological processes. PrP(C) is a GPI-anchored protein targeted to the plasma membrane, in raft microdomains, where its interaction with a repertoire of binding partners, which differ depending on cell models, mediates its functions. Among identified PrP(C) partners are cell adhesion molecules. This review will focus on the multiple implications of PrP(C) in cell adhesion processes, mainly the regulation of cell-cell junctions in epithelial and endothelial cells and the consequences on barrier properties. We will show how recent findings argue for a role of PrP(C) in the recruitment of signaling molecules, which in turn control the targeting or the stability of adhesion complexes at the plasma membrane.
ABSTRACT
BACKGROUND & AIMS: Cell adhesion is one function regulated by cellular prion protein (PrP(c)), a ubiquitous, glycosylphosphatidylinositol-anchored glycoprotein. PrP(c) is located in cell-cell junctions and interacts with desmosome proteins in the intestinal epithelium. We investigated its role in intestinal barrier function. METHODS: We analyzed permeability and structure of cell-cell junctions in intestine tissues from PrP(c) knockout (PrP(c-/-)) and wild-type mice. PrP(c) expression was knocked down in cultured human Caco-2/TC7 enterocytes using small hairpin RNAs. We analyzed colon samples from 24 patients with inflammatory bowel disease (IBD). RESULTS: Intestine tissues from PrP(c-/-) mice had greater paracellular permeability than from wild-type mice (105.9 ± 13.4 vs 59.6 ± 10.1 mg/mL fluorescein isothiocyanate-dextran flux; P < .05) and impaired intercellular junctions. PrP(c-/-) mice did not develop spontaneous disease but were more sensitive than wild-type mice to induction of colitis with dextran sulfate (32% mortality vs 4%, respectively; P = .0033). Such barrier defects were observed also in Caco-2/TC7 enterocytes following PrP(c) knockdown; the cells had increased paracellular permeability (1.5-fold over 48 hours; P < .001) and reduced transepithelial electrical resistance (281.1 ± 4.9 vs 370.6 ± 5.7 Ω.cm(2); P < .001). Monolayer shape and cell-cell junctions were altered in cultures of PrP(c) knockdown cells; levels of E-cadherin, desmoplakin, plakoglobin, claudin-4, occludin, zonula occludens 1, and tricellulin were decreased at cell contacts. Cell shape and junctions were restored on PrP(c) re-expression. Levels of PrP(c) were decreased at cell-cell junctions in colonic epithelia from patients with Crohn's disease or ulcerative colitis. CONCLUSIONS: PrP(c) regulates intestinal epithelial cell-cell junctions and barrier function. Its localization is altered in colonic epithelia from patients with IBD, supporting the concept that disrupted barrier function contributes to this disorder.
