A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. Usually it is a secreted

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

or a steroid hormone. Growth factors are important for regulating a variety of cellular processes. Growth factors typically act as signaling molecules between cells. Examples are cytokines and hormones that bind to specific receptors on the surface of their target cells. They often promote cell differentiation and maturation, which varies between growth factors. For example, epidermal growth factor (EGF) enhances osteogenic differentiation ( osteogenesis or bone formation), while fibroblast growth factors and

vascular endothelial growth factor Vascular endothelial growth factor (VEGF, ), originally known as vascular permeability factor (VPF), is a signal protein produced by many cells that stimulates the formation of blood vessels. To be specific, VEGF is a sub-family of growth factors ...

s stimulate blood vessel differentiation ( angiogenesis).

Comparison to cytokines

''Growth factor'' is sometimes used interchangeably among scientists with the term '' cytokine.'' Historically, cytokines were associated with hematopoietic (blood and lymph 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 suspension and not bound up in solid tissue, it makes sense for them to communicate by soluble, circulating protein

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s. However, as different lines of research converged, it became clear that some of the same signaling proteins which the hematopoietic and immune systems use were also being used by all sorts of other cells and tissues, during development and in the mature organism. While ''growth factor'' implies a positive effect on cell proliferation, ''cytokine'' is a neutral term with respect to whether a molecule affects proliferation. While some cytokines can be growth factors, such as G-CSF and GM-CSF, others have an inhibitory effect on

cell growth Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a de ...

or cell proliferation. Some cytokines, such as Fas ligand, are used as "death" signals; they cause target cells to undergo programmed cell death or '' apoptosis''. The nerve growth factor (NGF) was first discovered by Rita Levi-Montalcini, which won her a Nobel Prize in Physiology or Medicine.

List of classes

Individual growth factor proteins tend to occur as members of larger families of structurally and

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

IL-2 The Ilyushin Il-2 (Russian language, Russian: Илью́шин Ил-2) is a Ground attack aircraft, ground-attack plane that was produced by the Soviet Union in large numbers during the World War II, Second World War. The word ''shturmovík'' (C ...

– T-cell growth factor. Stimulates IL-1 synthesis. Activates B-cells and NK cells. ** IL-3 – Stimulates production of all non-lymphoid cells. ** IL-4 – Growth factor for activated B cells, resting T cells, and mast cells. ** IL-5 – Induces differentiation of activated B cells and eosinophils. ** IL-6 – Stimulates Ig synthesis. Growth factor for plasma cells. ** IL-7 – Growth factor for pre-B cells. * Keratinocyte growth factor (KGF) * Migration-stimulating factor (MSF) * Macrophage-stimulating protein (MSP), also known as hepatocyte growth factor-like protein (HGFLP) * Myostatin (GDF-8) * Neuregulins ** Neuregulin 1 (NRG1) ** Neuregulin 2 (NRG2) ** Neuregulin 3 (NRG3) ** Neuregulin 4 (NRG4) * Neurotrophins ** Brain-derived neurotrophic factor (BDNF) ** Nerve growth factor (NGF) ** Neurotrophin-3 (NT-3) ** Neurotrophin-4 (NT-4) * Placental growth factor (PGF) * Platelet-derived growth factor (PDGF) * Renalase (RNLS) – Anti-apoptotic survival factor * T-cell growth factor (TCGF) * Thrombopoietin (TPO) * Transforming growth factors ** Transforming growth factor alpha (TGF-α) ** Transforming growth factor beta (TGF-β) * Tumor necrosis factor-alpha (TNF-α) *

Vascular endothelial growth factor Vascular endothelial growth factor (VEGF, ), originally known as vascular permeability factor (VPF), is a signal protein produced by many cells that stimulates the formation of blood vessels. To be specific, VEGF is a sub-family of growth factors ...

(VEGF)

In platelets

The alpha granules in blood platelets contain growth factors PDGF, IGF-1, EGF, and TGF-β which begin healing of wounds by attracting and activating macrophages, fibroblasts, and endothelial cells.

Uses in medicine

For the last two decades, growth factors have been increasingly used in the treatment of hematologic and oncologic diseases and cardiovascular diseases such as: * skin wound healing and regeneration of other tissues such as bone (PDGF-BB) * neutropenia * myelodysplastic syndrome (MDS) * leukemias * aplastic anaemia * bone marrow transplantation * angiogenesis for cardiovascular diseases

References

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