SKAP2 Promotes Podosome Formation to Facilitate Tumor-Associated Macrophage Infiltration and Metastatic Progression

Tumor-associated macrophages (TAM) play complex and pivotal roles during cancer progression. A subset of metastasis-associated macrophages accumulates within metastatic sites to promote the invasion and growth of tumor cells. Src kinase-associated phosphoprotein 2 (SKAP2), a substrate of Src family kinases, is highly expressed in macrophages from various tumors, but its contribution to the tumor-promoting behavior of TAMs is unknown. Here, we report that SKAP2 regulates podosome formation in macrophages to promote tumor invasion and metastasis. SKAP2 physically interacted with Wiskott-Aldrich syndrome protein (WASP) and localized to podosomes, which were rarely observed in SKAP2-null macrophages. The invasion of peritoneal macrophages derived from SKAP2-null mice was significantly reduced compared with wild-type macrophages, but could be rescued by the restoration of functional SKAP2 containing an intact tyrosine phosphorylation site and the ability to interact with WASP. Furthermore, SKAP2-null mice inoculated with lung cancer cells exhibited markedly decreased lung metastases characterized by reduced macrophage infiltration compared with wild-type mice. Moreover, intravenously injected SKAP2-null macrophages failed to efficiently infiltrate established tumors and promote their growth. Taken together, these findings reveal a novel mechanism by which macrophages assemble the appropriate motile machinery to infiltrate tumors and promote disease progression, and implicate SKAP2 as an attractive candidate for therapeutically targeting TAMs. (C) 2015 AACR.