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Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that has been extensively studied in fibroblasts; however its function in hematopoiesis remains an enigma. FAK is thought to be expressed in myeloid and erythroid progenitors, and its expression is enhanced in response to cytokines such as granu-locyte macrophage colony-stimulating factor. Furthermore, bone marrow cells cultured in granulocyte macrophage colony-stimulating factor show active migration and chemoattractant-induced polarization, which correlates with FAK induction. While loss of FAK in mice results in embryonic lethality, we have deleted FAK in the adult bone marrow. We show an essential role for FAK in regulating hemolytic, myelotoxic, as well as acute inflammatory stress responses in vivo. In vitro, loss of FAK in erythroid and myeloid progenitor's results in impaired cytokine induced growth and survival, as well as defects in the activation and expression of antiapoptotic proteins caspase 3 and Bcl-xL. Additionally, reduced migration and adhesion of myeloid cells on extracellular matrix proteins, as well as impaired activation of Rac GTPase is also observed in the absence of FAK. Our studies reveal an essential role for FAK in integrating growth/survival and adhesion based functions in myeloid and erythroid cells predominantly under conditions of stress.

Abstract 1119 Progenitor B cells are thought to reside in complex bone marrow microenvironments, e.g. niches, where they receive signals for growth and maturation. Here we have conditionally targeted in B cells the non-receptor tyrosine kinase, Focal Adhesion Kinase (FAK), because of its function as an integrator of cell extrinsic signals including CXCL12 and VCAM-1. The number of progenitor (pro-, pre- and immature) B cells is reduced by 30–40% in CD19-Cre Fak fl/fl mice compared to wild type mice, and ex vivo cultured, Fak deleted pro-B cells exhibit impaired IL-7 ± CXCL12 mediated proliferation and survival. A novel quantitative laser scanning cytometry approach was used to demonstrate that Fak deletion also disrupts the non-random gradient distribution in femoral bone marrow of progenitor B cells, which normally are preferentially localized in endosteal regions of the metaphyses and to a lesser degree of the diaphysis. Increased numbers of pro-B cells are detected in the periphery of Fak deleted mice, and mobilization of pro-B cells induced by the inflammatory antigen NP-CGG-alum is increased 3-fold in Fak-deleted versus wild type mice. In addition, intravenously transferred Fak deleted pro-B cells have defective homing specifically to the extra-vascular compartment of the bone marrow. Collectively, these studies illustrate the importance of FAK in regulating progenitor B cell homeostasis and maintenance of their spatial distribution in bone marrow niches. Disclosures: No relevant conflicts of interest to declare.