Kindlin-2 regulates the growth of breast cancer tumors by activating CSF-1-mediated macrophage infiltration

Interplay between tumor cells and host cells in the tumor microenvironment dictates the development of all cancers. In breast cancer, malignant cells educate host macrophages to adopt a pro-tumorigenic phenotype. In this study, we show how the integrin regulatory protein kindlin-2 (FERMT2) promotes metastatic progression of breast cancer through the recruitment and subversion of host macrophages. Kindlin-2 expression was elevated in BC biopsy tissues where its levels correlated with reduced patient survival. Based on these observations, we used CRISPR/Cas9 technology to ablate Kindlin-2 expression in human MDA-MB-231 and murine 4T1 breast cancer cells. Kindlin-2 deficiency inhibited invasive and migratory properties in vitro without affecting proliferation rates. However, in vivo tumor outgrowth was inhibited by >80% in a manner associated with reduced macrophage infiltration and secretion of the macrophage attractant and growth factor CSF-1. The observed loss of CSF-1 appeared to be caused by a more proximal deficiency in TGF-β-dependent signaling in Kindlin-2 deficient cells. Collectively, our results illuminate a Kindlin-2/TGF-β/CSF-1 signaling axis employed by breast cancer cells to capture host macrophage functions that drive tumor progression.

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