Platelet FcRγ inhibits tumor metastasis by preventing the colonization of circulating tumor cells

Fc receptor γ subunit (FcRγ) activation plays a crucial role in cancer carcinogenesis. Here, we aimed to uncover the impact of FcRγ on circulating tumor cells (CTC) colonization and the underlying mechanism. FcRγ deficient (FcRγ^-/-) mice were used to investigate the functional effects of FcRγ in cancer metastasis, and the results demonstrated that FcRγ deficiency significantly promotes metastasis. The tumor metastasis effect, antiplatelet, platelet or neutrophil infusion experiments were conducted with FcRγ deficient (FcRγ^-/-) mice and wild type mice (WT), bearing B16F10 or LCC tumor cells. Blood routine test, flow cytometry, immunofluorescent staining and in vivo image were applied for analysis. Platelet adhesion and neutrophil chemotaxis were analyzed by flow cytometry and ELISA in vitro. Platelet adoptive model was used for mimicing early colonization stage. Our results indicated FcRγ deficiency significantly promoted tumor metastasis accompanied with increased number of platelet and neutrophil in the lung. Further investigation showed that FcRγ^-/- platelet infusion, rather than FcRγ^-/- neutrophils, promoted CTC colonization. While platelet inhibitor Aspirin abrogated the platelet-mediated infiltration of neutrophil in the lung. Mechanistically, platelet FcRγ deficiency facilitated the adhesion of platelets and cancer cells and increased secretion of CXCL5 and CXCL7 which triggered the platelet-induced neutrophil recruitment. In sum, our study indicates that FcRγ is a restrainer in controlling cancer metastasis through regulating the adhesion of platelets and cancer cells and recruiting more neutrophils, which provides a potential target for anti-metastatic therapies. The level of FcRγ expression in platelets could act as a novel biomarker for cancer metastasis.