Focal adhesion kinase (FAK) deficiency in mononuclear phagocytes alters murine breast tumor progression.

While it has long been recognized that mononuclear phagocytes play a significant role in determining breast tumor progression, the molecular factors that contribute to these events are not fully understood. In this report, we sought to determine whether focal adhesion kinase (FAK) expression in this cell population influences primary breast tumor initiation and growth. Using the MMTV-polyoma middle T (PyVmT) murine model of spontaneous breast cancer, we found that FAK expression in mononuclear phagocytes accelerates tumor initiation/progression during the early stages of PyVmT tumor growth but subsequently restricts tumor growth once the tumors have transitioned to malignancy. Mononuclear phagocytes accumulated at the site of developing tumors in a FAK-independent manner. However, once in the tumor, our data suggest that FAK expression is upregulated in the tumor-associated myeloid cells, and its activity in this population of cells may influence the immune landscape of the tumor by supporting the recruitment and/or survival of NK cells. Together, these data support a model in which FAK expression in the mononuclear phagocyte compartment positively regulates the early steps of tumor progression but subsequently functions to restrict tumor growth as the tumors transition to invasive carcinoma.