Chemotaxis promotes neutrophil participation in cellular defense by enabling neutrophil migration to infected tissue and is controlled by persistent cell polarization. One long-standing question of neutrophil polarity has been how the pseudopod and the uropod are coordinated. In our previous report, we suggested that Rho GTPase Cdc42 controls neutrophil polarity through CD11b signaling at the uropod, albeit through an unknown mechanism. Here, we show that Cdc42 controls polarity, unexpectedly, via its effector WASp. Cdc42 controls WASp activation and its distant localization to the uropod. At the uropod, WASp regulates the reorganization of CD11b integrin into detergent resistant membrane domains; in turn, CD11b recruits the microtubule end binding protein EB1 to capture and stabilize microtubules at the uropod. This organization is necessary to maintain neutrophil polarity during migration and is critical for neutrophil emigration into inflamed lungs. These results suggest unrecognized mechanism of neutrophil polarity in which WASp mediates long-distance control of the uropod by Cdc42 to maintain a proper balance between the pseudopod and the uropod.
IntroductionNeutrophils are the most abundant leukocyte and fastest moving cell in the body. Neutrophils play a central role in innate immunity as cellular defense against infecting microorganisms and inflammatory processes and can contribute to hyperinflammatory reactions causing tissue injury. Neutrophils move rapidly toward sites of infection through a multiple-step process that involves tethering, rolling, adhesion, and transmigration to reach the site of infection in the tissue. Moreover, a new step in the neutrophil extravasation cascade, so-called locomotion, has been recently identified where neutrophils crawl onto endothelium toward the nearest endothelial junctions before transmigrating into tissues. [1][2][3] Failure to regulate any of these events of neutrophil extravasation may lead to abnormal innate immune responses, including immunodeficiency or aberrant inflammatory reactions. Therefore, understanding the molecular mechanisms that control neutrophil migration is of significant therapeutic importance.Neutrophils are one of the fastest migrating cells in response to a shallow chemoattractant gradient. Migrating neutrophils are highly polarized cells, which enables them to persistently migrate along the chemotactic gradient. During this process, filamentous actin (F-actin) polymerizes asymmetrically at the cell leading edge, and provides the protrusive forces to propel the cell membrane forward. At the same time, lateral membrane protrusions (so-called secondary/abnormal protrusions) are inhibited by actomyosin contractile complexes forming along the cell sides and the trailing edge, or uropod. [4][5][6] Members of the Rho GTPase family, including Rho, Rac, and Cdc42, are key regulators of chemotaxis. They cycle between an inactive, GDP-bound and active, GTP-bound forms via guanine nucleotide exchange factors (GEFs) and GTPaseactivating proteins (GAP...