Platelet-derived growth factor
Encyclopedia
In molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

, platelet-derived growth factor (PDGF) is one of the numerous growth factor
Growth factor
A growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation and cellular differentiation. Usually it is a protein or a steroid hormone. Growth factors are important for regulating a variety of cellular processes....

s, or protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s that regulate cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

 growth and division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...

. In particular, it plays a significant role in blood vessel formation
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...

 (angiogenesis), the growth of blood vessels from already-existing blood vessel tissue. Uncontrolled angiogenesis is a characteristic of cancer. In chemical terms, platelet-derived growth factor is dimeric
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...

 glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

 composed of two A (-AA) or two B (-BB) chains or a combination of the two (-AB).

PDGF is a potent mitogen
Mitogen
A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein.Mitogenesis is the induction of mitosis, typically via a mitogen....

 for cells of mesenchymal origin, including smooth muscle cells and glial cells. In both mouse and human, the PDGF signalling network consists of four ligands, PDGFA-D, and two receptors, PDGFRalpha and PDGFRbeta. All PDGFs function as secreted, disulphide-linked homodimers, but only PDGFA and B can form functional heterodimers.

Though it is synthesized stored and released by platelets upon activation, it is produced by a plethora of cells including smooth muscle cells, activated macrophages, and endothelial cells

Types/Classification

There are five different isoforms of PDGF that activate cellular response through two different receptors
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

. Known ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

s include A (PDGFA
PDGFA
Platelet-derived growth factor subunit A is a protein that in humans is encoded by the PDGFA gene.-Further reading:...

), B (PDGFB
PDGFB
Platelet-derived growth factor subunit B is a protein that in humans is encoded by the PDGFB gene.-Further reading:...

), C (PDGFC
PDGFC
Platelet-derived growth factor C, also known as PDGF-C, is a 345-amino acid protein that in humans is encoded by the PDGFC gene. Platelet-derived growth factors are important in connective tissue growth, survival and function, and consist of disulphide-linked dimers involving two polypeptide...

), and D (PDGFD
PDGFD
Platelet-derived growth factor D is a protein that in humans is encoded by the PDGFD gene.-Further reading:...

), and an AB heterodimer
Protein dimer
In biochemistry, a dimer is a macromolecular complex formed by two, usually non-covalently bound, macromolecules like proteins or nucleic acids...

 and receptors alpha (PDGFRA
PDGFRA
Alpha-type platelet-derived growth factor receptor is a protein that in humans is encoded by the PDGFRA gene.-Interactions:PDGFRA has been shown to interact with PDGFRB, PLCG1, Sodium-hydrogen antiporter 3 regulator 1, Cbl gene, CRK, Caveolin 1 and PDGFC.-Further reading:...

) and beta (PDGFRB
PDGFRB
Beta-type platelet-derived growth factor receptor is a protein that in humans is encoded by the PDGFRB gene.-Interactions:PDGFRB has been shown to interact with PTPN11, NCK1, Grb2, Caveolin 1, PDGFRA, Sodium-hydrogen antiporter 3 regulator 1, RAS p21 protein activator 1, CRK, SHC1 and...

). PDGF has few other members of the family, for example VEGF sub-family.

Mechanisms

The receptor
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

 for PDGF, PDGFR is classified as a receptor tyrosine kinase
Receptor tyrosine kinase
Receptor tyrosine kinases s are the high-affinity cell surface receptors for many polypeptide growth factors, cytokines, and hormones. Of the 90 unique tyrosine kinase genes identified in the human genome, 58 encode receptor tyrosine kinase proteins....

 (RTK), a type of cell surface receptor. Two types of PDGFRs have been identified: alpha-type and beta-type PDGFRs. The alpha type binds to PDGF-AA, PDGF-BB and PDGF-AB, whereas the beta type PDGFR binds with high affinity to PDGF-BB and PDGF-AB.
PDGF binds to PDGFRs ligand binding pocket located within the second and third immunoglobulin domains. Upon activation by PDGF, these receptors dimerise, and are "switched on" by auto-phosphorylation
Phosphorylation
Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

 of several sites on their cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....

ic domains, which serve to mediate binding of cofactors and subsequently activate signal transduction
Signal transduction
Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...

, for example, through the PI3K
Phosphoinositide 3-kinase
Phosphatidylinositol 3-kinases are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which in turn are involved in cancer. In response to lipopolysaccharide, PI3K phosphorylates p65, inducing...

 pathway. Downstream effects of this include regulation of gene expression
Gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA , transfer RNA or small nuclear RNA genes, the product is a functional RNA...

 and the cell cycle
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

.
The role of PI3K has been investigated by several laboratories. Accumulating data suggests that, while this molecule is, in general, part of growth signaling complex, it plays a more profound role in controlling cell migration.
The different ligand isoforms have variable affinities for the receptor isoforms, and the receptor isoforms may variably form hetero- or homo- dimers. This leads to specificity of downstream signaling. It has been shown that the cis oncogene
Oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, they are often mutated or expressed at high levels.An oncogene is a gene found in the chromosomes of tumor cells whose activation is associated with the initial and continuing conversion of normal cells into cancer...

 is derived from the PDGF B-chain gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

. PDGF-BB is the highest-affinity ligand for the PDGFR-beta; PDGFR-beta is a key marker of hepatic stellate cell activation in the process of fibrogenesis.

Function

PDGFs are mitogenic during early developmental stages, driving the proliferation of undifferentiated mesenchyme
Mesenchyme
Mesenchyme, or mesenchymal connective tissue, is a type of undifferentiated loose connective tissue that is derived mostly from mesoderm, although some are derived from other germ layers; e.g. some mesenchyme is derived from neural crest cells and thus originates from the ectoderm...

 and some progenitor populations. During later maturation stages, PDGF signalling has been implicated in tissue remodelling and cellular differentiation, and in inductive events involved in patterning and morphogenesis. In addition to driving mesenchymal proliferation, PDGFs have been shown to direct the migration, differentiation and function of a variety of specialised mesenchymal and migratory cell types, both during development and in the adult animal. Other growth factors in this family include vascular endothelial growth factors B and C (VEGF-B, VEGF-C) which are active in angiogenesis and endothelial cell growth, and placenta growth factor (PlGF) which is also active in angiogenesis.

PDGF plays a role in embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

nic development, cell proliferation, cell migration, and angiogenesis
Angiogenesis
Angiogenesis is the physiological process involving the growth of new blood vessels from pre-existing vessels. Though there has been some debate over terminology, vasculogenesis is the term used for spontaneous blood-vessel formation, and intussusception is the term for the formation of new blood...

. PDGF has also been linked to several disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

s such as atherosclerosis
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...

, fibrosis
Fibrosis
Fibrosis is the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process. This is as opposed to formation of fibrous tissue as a normal constituent of an organ or tissue...

 and malignant diseases.

In addition, PDGF is a required element in cellular division for fibroblast
Fibroblast
A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing...

, a type of connective tissue cell. In essence, the PDGFs allow a cell to skip the G1 checkpoints
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

 in order to divide.

PDGF is also known to maintain proliferation of oligodendrocyte
Oligodendrocyte
Oligodendrocytes , or oligodendroglia , are a type of brain cell. They are a variety of neuroglia. Their main function is the insulation of axons in the central nervous system of some vertebrates...

 progenitor cells.

History

PDGF was one of the first growth factor
Growth factor
A growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation and cellular differentiation. Usually it is a protein or a steroid hormone. Growth factors are important for regulating a variety of cellular processes....

s characterized, and has led to an understanding of the mechanism of many growth factor signaling pathways.

Clinical significance

Like many other growth factors that have been linked to disease, PDGF and its receptors have provided a market for receptor antagonist
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...

s to treat disease. Such antagonists include (but are not limited to) specific antibodies
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

 that target the molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 of interest, which act only in a neutralizing manner.

The "c-Sis" oncogene
Oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, they are often mutated or expressed at high levels.An oncogene is a gene found in the chromosomes of tumor cells whose activation is associated with the initial and continuing conversion of normal cells into cancer...

 is derived from PDGF.

Age related downregulation of the PDGF receptor on islet beta cells has been demonstrated to prevent islet beta cell proliferation in both animal and human cells and its re-expression triggered beta cell proliferation and corrected glucose regulation via insulin secretion.

Family members

Human genes encoding proteins that belong to the platelet-derived growth factor family include:
  • FIGF
    C-fos induced growth factor
    C-fos induced growth factor is a vascular endothelial growth factor that in humans is encoded by the FIGF gene.-Further reading:...

  • PDGFA
    PDGFA
    Platelet-derived growth factor subunit A is a protein that in humans is encoded by the PDGFA gene.-Further reading:...

    ; PDGFB
    PDGFB
    Platelet-derived growth factor subunit B is a protein that in humans is encoded by the PDGFB gene.-Further reading:...

    ; PDGFC
    PDGFC
    Platelet-derived growth factor C, also known as PDGF-C, is a 345-amino acid protein that in humans is encoded by the PDGFC gene. Platelet-derived growth factors are important in connective tissue growth, survival and function, and consist of disulphide-linked dimers involving two polypeptide...

    ; PDGFD
    PDGFD
    Platelet-derived growth factor D is a protein that in humans is encoded by the PDGFD gene.-Further reading:...

  • PGF
    Placental growth factor
    Placental growth factor is a protein that in humans is encoded by the PGF gene.Placental growth factor is a member of the VEGF sub-family - a key molecule in angiogenesis and vasculogenesis, in particular during embryogenesis. The main source of PGF during pregnancy is the placental trophoblast...

  • VEGF
    Vascular endothelial growth factor
    Vascular endothelial growth factor is a signal protein produced by cells that stimulates vasculogenesis and angiogenesis. It is part of the system that restores the oxygen supply to tissues when blood circulation is inadequate....

    ; VEGF41; VEGFB
    Vascular endothelial growth factor B
    Vascular endothelial growth factor B also known as VEGF-B is a protein that, in humans, is encoded by the VEGF-B gene. VEGF-B is a growth factor that belongs to the vascular endothelial growth factor family, of which VEGF-A is the best-known member....

    ; VEGFC
    Vascular endothelial growth factor C
    Vascular endothelial growth factor C is a VEGF. The human gene encoding it is VEGFC.-Pathological VEGF-C Expression:Lymphedema is caused by an imbalance between lymphatic vessel formation and absorption...

    ;

See also

  • Platelet-activating factor
    Platelet-activating factor
    Platelet-activating factor, also known as a PAF, PAF-acether or AGEPC is a potent phospholipid activator and mediator of many leukocyte functions, including platelet aggregation and degranulation, inflammation, and anaphylaxis...

  • Platelet-derived growth factor receptor
    Platelet-derived growth factor receptor
    Platelet-derived growth factor receptors are cell surface tyrosine kinase receptors for members of the platelet-derived growth factor family. PDGF subunits -A and -B are important factors regulating cell proliferation, cellular differentiation, cell growth, development and many diseases including...

  • atheroma
    Atheroma
    In pathology, an atheroma is an accumulation and swelling in artery walls that is made up of macrophage cells, or debris, that contain lipids , calcium and a variable amount of fibrous connective tissue...

    platelet involvement in smooth muscle proliferation

External links

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