Growth factor

From Freepedia

Growth factor is a protein that acts as a signalling molecule between cells (like cytokines and hormones) that attaches to specific receptors on the surface of a target cell and promote differentiation and maturation of these cells.

The term growth factor is sometimes used interchangeably among scientitsts with the term cytokine. Historically, cytokines were associated with hematopoietic (blood forming) cells and immune system cells (e.g., lymphocytes and tissue cells from spleen, thymus, and lymph nodes). For the circulatory system and bone marrow in which cells can occur in a liquid suspsension and not bound up in solid tissue, it makes sense for them to communicate by soluble, circulating protein molecules. However, as different lines of research converged, it became clear that some of the same signalling proteins the hematopoietic and immune systems used were also being used by all sorts of other cells and tissues, during development and in the mature organism.

Growth factor signifies a positive effect on cell growth and cellular differentiation, but cytokine is a neutral term in regards to what it is being signalled. In this sense some cytokines can be growth factors such as G-CSF and GM-CSF as listed below. However some cytokines are actually used as "death" signals such as the FAS ligand which causes target lymphocytes to commit a form of suicide known as programmed cell death or apoptosis.

The names of individual growth factors often have little to do with their most important functions and exist due to the historical cirumstances under which they arose. For example, fibroblast growth factor (FGF) was found in a cow brain extract by Gospadarowicz and colleagues and tested in a bioassay which caused fibroblasts to proliferate. They then further fractionated the extract using acidic and basic pH and isolated two slightly different forms that were named "acidic fibroblast growth factor" (aFGF) and "basic fibroblast growth factor" (bFGF). These proteins shared a very high degree of identical amino acid sequeneces but they were unique. Currently (as of 2005) there are 23 members of the FGF family that are structurally related signalling molecules (named FGF-1, FGF-2, FGF-3, and so on), which in turn bind to a family of receptor molecules consisting of 4 members (FGFR-1, FGFR-2, FGFR-3, and FGFR-4). This information still does not say what FGF does. It turns out that not long after aFGF and bFGF were isolated, other scientists isolated a pair of heparin-binding growth factors which they named HBGF-1 and HBGF-2, and yet another group of scientists isolated a pair of growth factors that caused proliferation of cells in a bioassay containing blood vessel endothelium cells which they called ECGF-1 and ECGF-2. It turns out that these were the same sets of proteins, all isolated and named independently, but the FGF name which was first was the one that stuck. However, one of the most imporant functions of bFGF (also known as FGF-2) is that is promotes the endothelial cell proliferation, the physical organization of endothelial cells into tiny tubes, and thus promotes the formation of new blood vessels. This is a process known as angiogenesis and bFGF is a more potent angiongenic factor than VEGF (vascular endothelial growth factor) or PDGF (platelet-derived growth factor). Apart from stimulating blood vessel formation, bFGF is an important player in wound healing by stimulating the proliferation of fiboblasts that give rise to the granuation tissue that fills up a wound space/cavity early in the wound healing process.

Individual growth factor proteins tend to occur as members of larger families of structurally and evolutionarily related proteins. The above example discusses FGFs, but there are dozens and dozens of growth factor families such as TGF-beta (transforming growth factor), BMP (bone morphogenic protein), neurotrophins (NGF, BDNF, and NT3) and so on....

Several well known growth factors are :

For the last two decades growth factors have been increasingly used in treatment of hematologic and oncologic diseases like:

See also:

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