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Growth Factors

Growth factors is a term used to describe a broad range of structurally diverse molecular families and individual proteins best known for their ability to enhance cell proliferation, differentiation, and growth. They have an array of putative functions during development including regulating tissue morphogenesis, angiogenesis, cell differentiation, and neurite outgrowth. They also play important roles in the maintenance of tissue homeostasis and wound healing in the adult. However, when unregulated, many growth factors and their receptors can promote tumor formation due to their highly potent activity. Because of these properties, growth factors are required in many cell culture protocols. They are used to maintain, grow, and differentiate many different cell types.

The terms growth factor and cytokine are often used interchangeably. Growth factor, as the name implies, generally refers to molecules that impart a positive effect on cell growth and differentiation, while cytokine is a more generic term referring to a molecule that acts as a messenger between cells. The relaying message can have either positive or negative effects on cell division. The discovery of growth factors is credited to Rita Levi-Montalcini for her research on nerve growth factor (NGF). She was awarded the Nobel Prize in the physiology or medicine category in 1986.

Growth factors initiate a signaling cascade that begins when a growth factor binds to a transmembrane receptor typically leading to dimerization. Often, the receptor contains cytoplasmic tyrosine kinase domains that when dimerized, cause multiple phosphorylation events on specific tyrosine residues. These phosphotyrosine residues recruit multiple signaling proteins that set off a cascade of events ultimately leading to the activation or inhibition of target gene transcription in the nucleus.