What are the functions of angiogenic growth factors?

Angiogenic growth factors are a class of molecules which have a significant role in the process of blood vessel formation. These growth factors have both vasculogenic and angiogenic properties. Additionally, they are involved in a series of mechanisms during organogenesis. The most common angiogenic growth factors include VEGF, and bFGF. 

Once they come into contact with endothelial cells, they bind to the tyrosine kinase receptors on their membranes. This binding leads to dimerization of the receptors and activation of autophosphorylation of tyrosines on the receptor surface. This then initiates signaling proteins, activators of transcriptions, and signal transducers. Binding of the src-homology 2 regions of these proteins to the phosphotyrosines on receptor tyrosine kinases activates multiple pathways that are significant for triggering the process of the cell cycle. Once VEGF binds to receptors on the surface of normal endothelial cells, signals within these cells become initiated, inducing growth and survival of new blood vessels; this process is known as sprouting angiogenesis.    

Additional growth factors include TNF-a, TGF-b, Ang, HGF. Sources of these growth factors include endothelial cells, fibroblasts, smooth muscle cells, inflammatory cells, platelets, and cancer cells. TNF-a is a cytokine which has pleiotropic effects on various cell types. It is a major regulator of inflammatory responses and is involved in the pathogenesis of various inflammatory and autoimmune diseases. TGF-b functions as a tumor suppression by mediating its antiproliferative effects in several cell types. In early stages of tumorigenesis, TGF-b inhibits cell cycle promotion and the elusion of TGF-B mediation is necessary for the continuation of tumor progression. HGF is produced by stromal and mesenchymal cells and stimulates epithelial cell proliferation and angiogenesis via tyrosine phosphorylation of its receptor (like VEGF and bFGF does).