Apical integrins as a switchable target to regulate the epithelial barrier

Abstract

Tight junctions regulate epithelial barrier function and have been shown to be influenced by multiple classes of proteins. Apical integrins have been identified as potential regulators of epithelial barrier function; however, only indirect approaches have been used to measure integrin regulation of the epithelial barrier. Here, we used polymeric nanowires conjugated with anti-integrin β1 antibodies to specifically target apically localized integrins in either their closed or open conformation. Barrier regulation by apical integrins was found to be conformation specific. Nanowires targeting integrins in the closed conformation increased epithelial permeability and caused zonula occludens-1 (ZO-1, also known as TJP1) to change from a linear to a ruffled morphology. Claudin-2 and claudin-4 colocalized with ZO-1 and were also ruffled; however, claudin-1 and claudin-7 remained linear. Ruffling was dependent on myosin light chain kinases (MLCKs) and Rho kinases (ROCKs). Conversely, targeting integrins in the open conformation decreased epithelial permeability and made junctions more linearized. Anti-integrin β1 nanowires differentially affected actin and talin (analyzed using pan-talin antibodies), depending on whether they contained activating or inhibitory antibodies. Thus, apical integrins can act as a conformation-sensitive switch that regulates epithelial barrier function.