Growth factors, which generally considered as a subset of cytokines, refer to the diffusible signaling proteins that stimulate cell growth, differentiation, survival, inflammation, and tissue repair. They can be secreted by neighboring cells, distant tissues and glands, or even tumor cells themselves. Normal cells show a requirement for several growth factors to maintain proliferation and viability. Growth advantage is often found for the cells which secrete a growth factor.
Growth factor can exert their stimulation though endocrine, paracrine or autocrine mechanisms. Due to their short half-lives and slow diffusion in intercellular spaces, growth factors usually act locally. Typically, the signal transduction of growth factors is initiated by binding to their receptors on the surface of target cells. The specific instruction conveyed by a growth factor to a particular subpopulation of cells depends on the type of receptors, number of target cell, and the intracellular signal transduction subsequent to factor binding. Moreover, external factors such as the binding ability of a growth factor to extracellular matrices (ECM), ECM degradation, and concentration of the growth factor may have an effect on the ultimate response of a target cell to a specific growth factor.
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