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Fibroblast Growth Factor & Receptor

FGF & Receptor Background

What is Fibroblast Growth Factor (FGF)
Fibroblast Growth Factors (FGFs) are a family of growth factors which play an important role in tissue repair and regeneration. They possess high affinity for heparan sulfate proteoglycans (HPSGs) and can interact with heparin-like glycosaminoglycans (HLGAGs) of the extracellular matrix (ECM). Learn More.

History of Fibroblast Growth Factors (FGFs) & Receptors
Fibroblast growth factor (FGF) was initially discovered in pituitary extracts in 1973, and then isolated from the brain and pituitary gland. Due to the fibroblast stimulating activities of those isolated factors, scientists described them as "FGFs". Since FGF1 was isolated at acidic pH, it was firstly named "acidic fibroblast growth factor". While FGF2 was originally isolated at basic pH and named "basic fibroblast growth factor". At present, fibroblast growth factors (FGFs) are known as a large family of growth factors that exist in organisms ranging from nematodes to humans, and some of these factors even cannot simulate fibroblasts. The "FGFs" is used to indicate that these proteins are structurally related. Learn More.

Fibroblast Growth Factor (FGF) Family-Classification of FGFs & Receptors
Based on phylogenetic analysis, the human FGF family can be further divided into seven subfamilies; FGF 1/2, FGF 4/5/6, FGF 3/7/10/22, FGF 8/17/18, FGF 9/16/20, FGF 11/12/13/14, and FGF 19/21/23. According to their mechanisms of action, the FGF family can also be classified into three categories, which are paracrine, endocrine, and intracrine FGFs. Paracrine FGFs refers to members of subfamilies FGF1/2, FGF 4/5/6, FGF 3/7/10/22, FGF 8/17/18, FGF 9/16/20; endocrine FGFs includes the three members of FGF 19/21/23 subfamily; and the four members of subfamily FGF 11/12/13/14 are identified as intracrine FGFs. Learn More.

Mechanisms of Fibroblast Growth Factor (FGF) Action
Paracrine Fibroblast Growth Factors (FGFs) are secreted proteins, and they mainly contain a cleavable N-terminal secreted signal peptide. However, the bipartite secreted signal sequences of FGF 9/16/20 are not cleaved in mature proteins. In addition, there is no N-terminal signal sequence for FGF1 and FGF2; these two FGFs are considered released from damaged cells or by an exocytotic mechanism of which the endoplasmic reticulum-Golgi pathway is not required. Paracrine FGFs bind to the tyrosine kinase FGFR receptors (FGFRs), resulting in functional dimerization, receptor transphosphorylation, and the activation of downstream signaling pathways. These FGFs contain a heparin-binding site, and the heparan sulfate on cell surface is known as a cofactor which helps their binding with receptors. Paracrine FGFs mediate the biological response of neighboring cells from a distance, and their affinities for heparin-like molecules of the extracellular matrix (ECM) regulate the range of their signaling. Learn More.

Fibroblast Growth Factor (FGF) Receptors
Scientists have discovered four Fibroblast Growth Factor (FGF) receptors, FGFR1 through FGFR4, which are highly conserved transmembrane proteins containing receptor tyrosine kinases. FGF receptors all comprise an extracellular ligand-binding domain, a transmembrane domain, and a kinase domain. The extracellular ligand-binding domain contains three immunoglobulin-like domains IgI, IgII, and IgIII which are important in receptor dimerisation. FGFR1–3 can alternatively use part of the IgIII domain, generating different isoforms that are expressed in different tissues and have distinct binding specificities; whereas the FGFR4 has only one possible form of its IgIII domain usage. The truncated protein coded by IgIIIa splice variant is secreted, and may play as an inhibitor for release FGFs. A specific FGF ligand can bind to several FGFRs, though it may have a preference for a particular one. Learn More.

Fibroblast Growth Factor (FGF) Signaling Pathway
When Fibroblast Growth Factors (FGFs) binding with FGFRs in a FGF:FGFR:HPSG ternary complex form, dimerization of FGFRs occurs, which causes the receptors to be phosphorylated at the intracellular tyrosine kinase domain and carboxy-terminal tail. Subsequently, the phosphorylated tyrosine recruits specific molecules, which interact with SH2 (Src homology-2) or PTB (phosphotyrosine binding) domains of adaptors docking proteins or signaling enzymes, forming signaling complexes. Then, a cascade of phosphorylation events occurs at the recruited complexes and induces a number of signaling pathways, such as the RAS/MAP kinase pathway, PI3 kinase/AKT pathway, and PLCγ pathway, resulting in specific cellular responses. Learn More .

Fibroblast Growth Factor (FGF) & Receptor Dysregulation in Cancer
Sometimes, a dysregulation of Fibroblast Growth Factors (FGFs) may occur and causes cancer. The dysregulations usually fall into six categories: (1) a specific FGF ligand is overproduced; (2) the specificity of splice-variant FGFRs to endogenous FGF ligands have changed; (3) FGFRs are mutated, resulting in receptor dimerization or constitutive activation of the kinase; (4) there is a gene translocation in FGFRs that leads to over-expression or activation of the FGFR; (5) germline SNPs exist, which are related with increased risk of cancer; (6) the impairment of the normal attenuation and negative feedback. Considering this, it is no doubt that researchers are pursuing to generate agents to control FGF-ligand/receptor dysregulation. Learn More..

Fibroblast Growth Factor (FGF) Inhibitor
Basic fibroblast growth factor (FGF), also known as bFGF and FGF2, is a member of the fibroblast growth factor family. There are two inhibitors which affect the actions of FGF2: PD 173074 and SU 5402. PD 173074 is an inhibitor of FGFR1. It can potently and selectively antagonize the neurotrophic and neurotropic actions of FGF-2. Nanomolar concentrations of PD 173074 preventes FGF2, but not insulin-like growth factor-1, support of cerebellar granule neuron survival under conditions of serum/K(+) deprivation. As an inhibitor of FGF2, SU 5402 is effective only at a 1,000-fold greater concentration. PD 173074 and SU 5402 show 1,000-fold differential IC(50) values for inhibition of FGF2-stimulated neurite outgrowth in PC12 cells and in granule neurons, and FGF2-induced mitogen-activated protein kinase (p44/42) phosphorylation. The two inhibitors fail to disturb downstream signalling stimuli of FGF2. PD 173074 represents a valuable tool for dissecting the role of FGF2 in normal and pathological nervous system function without compromising the actions of other neurotrophic factors Learn More .

FGF & Receptor References
  1. Ornitz DM, et al. (2001). Fibroblast growth factors. Genome Biol. 2(3): 3005.1-12.
  2. Yun YR, et al. (2010). Fibroblast growth factors: biology, function, and application for tissue regeneration. Tissue Eng. 218142.
  3. Powers CJ, et al. (2000). Fibroblast growth factors, their receptors and signaling. Endocr Relat Cancer. 7(3): 165-97.
  4. Brooks AN, et al. (2012). Molecular pathways: fibroblast growth factor signaling: a new therapeutic opportunity in cancer. Clin Cancer Res. 18(7): 1855-62.

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