What are Growth Factors and How Do They Work?
First discovered by Rita Levi-Montalcini, growth factors are compact polypeptides, that bind to transmembrane receptors harboring kinase activity, to stimulate specific combinations of intracellular signaling pathways. The intracellular signaling pathways that are activated by growth factors are mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K), phospholipase C-γ, and transcription factors like the signal transducers and activators of transcription (STATs) or SMAD proteins. This activation of growth factor receptors creates a short, time-limited signal, which causes different parts of cellular proliferation and differentiation such as mitosis, clonal expansion, gene regulation, and cell apoptosis. Unlike hormones which have a wider systemic influence, growth factors usually transmit signals between cells to modulate their activity. They act as chemical messengers, communicating with different cells to stimulate growth. Depending on their function, growth factors can produce endocrine, paracrine, autocrine, or juxtracrine responses in cells.