Impairment of protein trafficking by direct interaction of gliadin peptides with actin

Intestinal celiac disease (CD) is triggered by peptic-tryptic digest of gluten, known as Frazer's Fraction (FF), in genetically predisposed individuals. Here, we investigate the immediate effects of FF on the actin cytoskeleton and the subsequent trafficking of actin-dependent and actin-independent proteins in COS-1 cells. Morphological alterations in the actin filaments were revealed concomitant with a drastic reduction in immunoprecipitated actin from cells incubated with FF. These alterations elicit impaired protein trafficking of intestinal sucrase–isomaltase, a glycoprotein that follows an actin-dependent vesicular transport to the cell surface. However, the actin-independent transport of intestinal lactase phlorizin hydrolase remains unaffected. Moreover, the morphological alteration in actin is induced by direct interaction of this protein with gliadin peptides carrying the QQQPFP epitope revealed by co-immunoprecipitation utilizing a monoclonal anti-gliadin antibody. Finally, stimulation of cells with FF directly influences the binding of actin to Arp2. Altogether, our data demonstrate that FF directly interacts with actin and alters the integrity of the actin cytoskeleton thus leading to an impaired trafficking of intestinal proteins that depend on an intact actin network. This direct interaction could be related to the endocytic segregation of gliadin peptides as well as the delayed endocytic vesicle trafficking and maturation in gliadin-positive intestinal epithelial cells and opens new insights into the pathogenesis of CD.