Neutrophils migrate towards developing tumors where they promote angiogenesis, setting the stage for metastasis. Investigating neutrophil migration should lead to novel drug targets to prevent neutrophil accumulation in tumors. Neutrophils and other cells rely on activation of the heterotrimeric G-protein Gai to regulate directional cell migration, but few links from Gai to chemotactic effectors are known. Through affinity chromatography using primary neutrophil lysate, we identify Homer3 as a novel Gai2-binding protein. RNAi-mediated knockdown of Homer3 in neutrophil-like HL-60 cells impairs chemotaxis and the establishment of polarity of the actin cytoskeleton. Most previously-characterized proteins that are required for cell polarity are needed for actin assembly or activation of core chemotactic effectors such as the Rac GTPase. In contrast, Homer3 knockdown cells show a normal magnitude and kinetics of chemoattractant-induced activation of PI3K and Rac effectors. Chemoattractant-stimulated Homer3 knockdown cells also exhibit a normal initial magnitude of actin polymerization, but they fail to polarize actin assembly and are defective in the initiation of cell polarity and motility. Our data suggest that Homer3 acts as a scaffold that spatially organizes actin assembly to support neutrophil polarity and motility downstream of GPCR activation.
Citation Format: Julie Wu, Anne Pipathsouk, A Keizer-Gunnink, Wynand Alkema, Fabrizia Fusetti, Shanshan Liu, Steve Atschuler, Lani Wu, Arjan Kortholt, Orion Weiner. Homer3 regulates the establishment of neutrophil polarity. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr B48.
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