Regulation of Tie2 Extracellular Complex Formation in Angiogenesis

Pathological angiogenesis is an essential component of tumor growth, development, and metastasis for which few effective therapeutic options exist. Though many cancer therapies target the function of cell surface receptors, mechanisms regulating membrane receptor crosstalk remain unclear. Two important families of receptors in angiogenesis, the Ties and Integrins, respond to the extracellular environment via outside-in and, in the case of Integrins, also inside- out signaling. Recent reports showed that the endothelial specific tyrosine kinase receptor, Tie2, forms complexes with two of the endothelial Integrin heterodimers, α5β1 and αVβ3, providing a convenient mechanism for the integration of extracellular stimuli. Our data confirm the interaction between Integrins and Tie2 and additionally indicate an interaction with the orphan co-receptor Tie1. To elucidate the biological role of these macromolecular complexes, biochemical and biophysical methods including co-immunoprecipitation, FRET microscopy, and cellular based assays were used to follow receptor/Integrin association in response to the Tie2 ligands Angiopoietin-1 and -2 as well as the Integrin ligand fibronectin. Furthermore, structural analysis by small angle x-ray scattering of Tie2-ligand complexes and specific Integrin and Tie complexes are being used to identify the basis for growth factor receptor and Integrin signal transduction