The actin regulatory protein HS1 interacts with Arp2/3 and mediates efficient neutrophil chemotaxis.

HS1 is an actin regulatory protein and cortactin homolog that is expressed in hematopoietic cells. Antigen receptor stimulation induces HS1 phosphorylation, and HS1 is essential for T cell activation. HS1 is also expressed in neutrophils; however, the function of HS1 in neutrophils is not known. Here we show that HS1 localizes to the neutrophil leading edge, and is phosphorylated in response to the chemoattractant formyl-Met-Leu-Phe (fMLP) in adherent cells. Using live imaging in microchannels, we show that depletion of endogenous HS1 in the neutrophil-like PLB-985 cell line impairs chemotaxis. We also find that HS1 is necessary for chemoattractant-induced activation of Rac GTPase signaling and Vav1 phosphorylation, suggesting that HS1-mediated Rac activation is necessary for efficient neutrophil chemotaxis. We identify specific phosphorylation sites that mediate HS1-dependent neutrophil motility. Expression of HS1 Y378F, Y397F is sufficient to rescue migration of HS1-deficient neutrophils, however, a triple phospho-mutant Y222F, Y378F, Y397F did not rescue migration of HS1-deficient neutrophils. Moreover, HS1 phosphorylation on Y222, Y378, and Y397 regulates its interaction with Arp2/3. Collectively, our findings identify a novel role for HS1 and its phosphorylation during neutrophil directed migration.