What is the mechanism of action of growth factor?

Growth factors are powerful regulators of cellular function, including proliferation, differentiation, migration, and survival/apoptosis. 

Growth factor stimulation of cells is a sophisticated and multistep mechanism that transmits extracellular stimuli into the target cell through various signaling cascades. When binding to their cognate receptors on the cell surface, growth factors facilitate cellular anabolic metabolism by inducing the uptake and utilization of nutrients such as glucose, glutamine, and amino acids through the upregulation of nutrient transporters onto the cell surface. Growth factors activate various signaling pathways, among which the PI3K-AKT pathway appears to play a dominant role. Binding of growth factors such as PDGF, bFGF, or VEGF to receptors of the transmembrane tyrosine kinase type induces a dimerization process. This results in the activation of the tyrosine kinase domains of the receptors. After this occurs, specific signal transduction cascades become activated and they can reach the nucleus, or they may directly affect the function of cellular proteins such as enzymes or cytoskeletal proteins. The regulation of gene transcription may also cause indirect effects of growth factors because the expression of growth factors and receptors can be regulated by other growth factors. The majority of growth factors promote proliferation, migration, and inhibit apoptosis, as they are positive regulators of the cell cycle. Growth factor stimulation ultimately results in the production and activation of early nuclear proteins which in turn promote transcription of the genes for cyclins, CDKs, and other cell cycle regulators.