Regulation of Integrin Trafficking, Cell Adhesion, and Cell Migration by WASH and the Arp2/3 Complex

WASH is a nucleation-promoting factor for the Arp2/3 complex that is implicated in multiple endocytic trafficking pathways including receptor recycling, cargo degradation, and retromer-mediated receptor retrieval. We sought to examine whether WASH plays an important role in trafficking of specialized cargo molecules such as integrins, for which trafficking is highly regulated during cell migration. We observed that subdomains of early/sorting endosomes associated with dynamic WASH and filamentous actin, and alpha 5-integrins trafficked through this population of endosomes. Depletion of WASH caused accumulation of alpha 5-integrins in intracellular compartments, reduction of alpha 5integrin localization at focal adhesions, and reduction in focal adhesion number. Transport of alpha 5-integrins from internal endocytic structures to focal adhesions was disrupted upon WASH depletion or Arp2/3 complex inhibition. Furthermore, WASH-depleted cells displayed greatly reduced affinity for specific extracellular matrix proteins including fibronectin and impaired cell spreading ability. Interestingly, the reduced adhesion capacity of WASH-depleted cells resulted in their migrating more rapidly than control cells in wound healing assays. Our results define a requirement for WASH, Arp2/3 complex, and actin in specialized trafficking of integrins. These findings highlight a role for actin dynamics in influencing cell adhesion and migration via endocytic trafficking of integrins, in addition to the well-established role of actin in plasma membrane dynamics and contractility. (C) 2012 Wiley Periodicals, Inc