Background：

Non-receptor protein-tyrosine kinase that regulates reorganization of the actin cytoskeleton， cell polarization， cell migration， adhesion， spreading and bone remodeling. Plays a role in the regulation of the humoral immune response， and is required for normal levels of marginal B-cells in the spleen and normal migration of splenic B-cells. Required for normal macrophage polarization and migration towards sites of inflammation. Regulates cytoskeleton rearrangement and cell spreading in T-cells， and contributes to the regulation of T-cell responses. Promotes osteoclastic bone resorption; this requires both PTK2B/PYK2 and SRC. May inhibit differentiation and activity of osteoprogenitor cells. Functions in signaling downstream of integrin and collagen receptors， immune receptors， G-protein coupled receptors (GPCR)， cytokine， chemokine and growth factor receptors， and mediates responses to cellular stress. Forms multisubunit signaling complexes with SRC and SRC family members upon activation;