A growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation, healing, and cellular differentiation. Usually it is a protein 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, bone morphogenetic proteins stimulate bone cell differentiation, while fibroblast growth factors and vascular endothelial growth factors stimulate blood vessel differentiation (angiogenesis).
Growth factors versus cytokines
Growth factor is sometimes used interchangeably among scientists 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 suspension 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 signaling 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.
While growth factor implies a positive effect on cell division, 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 or proliferation. Some cytokines, such as Fas ligand, are used as "death" signals; they cause target cells to undergo programmed cell death or apoptosis.
The growth factor was first discovered by Rita Levi-Montalcini, which won her a Nobel prize.
Classes of growth factors
Individual growth factor proteins tend to occur as members of larger families of structurally and evolutionarily related proteins. There are many families, some of which are listed below:
- Adrenomedullin (AM)
- Angiopoietin (Ang)
- Autocrine motility factor
- Bone morphogenetic proteins (BMPs)
- Brain-derived neurotrophic factor (BDNF)
- Epidermal growth factor (EGF)
- Erythropoietin (EPO)
- Fibroblast growth factor (FGF)
- Glial cell line-derived neurotrophic factor (GDNF)
- Granulocyte colony-stimulating factor (G-CSF)
- Granulocyte macrophage colony-stimulating factor (GM-CSF)
- Growth differentiation factor-9 (GDF9)
- Healing factor
- Hepatocyte growth factor (HGF)
- Hepatoma-derived growth factor (HDGF)
- Insulin-like growth factor (IGF)
- Keratinocyte growth factor (KGF)
- Migration-stimulating factor (MSF)
- Myostatin (GDF-8)
- Nerve growth factor (NGF) and other neurotrophins
- Platelet-derived growth factor (PDGF)
- Thrombopoietin (TPO)
- Transforming growth factor alpha(TGF-α)
- Transforming growth factor beta(TGF-β)
- Tumor necrosis factor-alpha(TNF-α)
- Vascular endothelial growth factor (VEGF)
- Wnt Signaling Pathway
- placental growth factor (PGF)
- [(Foetal Bovine Somatotrophin)] (FBS)
- IL-1- Cofactor for IL-3 and IL-6. Activates T cells.
- IL-2- 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.
- Renalase- RNLS -Anti-apoptotic survival factor
Growth factors 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:
- neutropenia
- myelodysplastic syndrome (MDS)
- leukemias
- aplastic anaemia
- bone marrow transplantation
- angiogenesis for cardiovascular diseases
See also
- Wound healing#Overview of involved growth factors
- Signal transduction
- Receptor (biochemistry)
- Cytokine
- Angiogenesis
- Human Genome Organisation
- Growth factor receptor
- Mitogen
References
External links
- Growth Factors at the US National Library of Medicine Medical Subject Headings (MeSH)
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