Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor protein tyrosine kinase.As a major adhesion kinase and adaptor molecule in the integrin signaling pathway,PYK2 interacts with and phosphorylates several important proteins,and has been demonstrated to link extracellular signaling events and intracellular kinase cascades.The kinase activity of PYK2 and its protein-protein interactions have been suggested as important mechanisms in the regulation of the signaling pathway that promotes brain tumor invasion and bone resorption.