Fibroblast growth factor receptor 2

Fibroblast growth factor receptor 2 (FGFR2) also known as CD332 (is_associated_with::cluster of differentiation 332) is a is_associated_with::protein that in humans is encoded by the FGFR2 is_associated_with::gene residing on is_associated_with::chromosome 10. FGFR2 is a receptor for is_associated_with::fibroblast growth factor.

The protein encoded by this gene is a member of the is_associated_with::fibroblast growth factor receptor family, where amino acid sequence is highly conserved between members and throughout evolution. FGFR family members differ from one another in their ligand affinities and tissue distribution. A full-length representative protein consists of an extracellular region, composed of three is_associated_with::immunoglobulin domains, a single hydrophobic membrane-spanning segment and a cytoplasmic is_associated_with::tyrosine kinase domain. The extracellular portion of the protein interacts with fibroblast growth factors, setting in motion a cascade of downstream signals, ultimately influencing is_associated_with::mitogenesis and differentiation. This particular family member is a high-affinity receptor for acidic, basic and/or is_associated_with::keratinocyte growth factor, depending on the isoform.

Isoforms
FGFR2 has two naturally occurring isoforms FGFR2IIIb and FGFR2IIIc, created by splicing of the third immunoglobulin-like domain. FGFR2IIIb is predominantly found in is_associated_with::ectoderm derived tissues and endothelial organ lining, i.e. skin and internal organs. FGFR2IIIc is found in is_associated_with::mesenchyme, which includes is_associated_with::craniofacial bone and for this reason the mutations of this gene and isoform are associated with is_associated_with::craniosynostosis.

Interactions
Fibroblast growth factor receptor 2 has been shown to interact with is_associated_with::FGF1.

The spliced isoforms, however differ in binding:


 * FGFR2IIIb binds to FGF-1, -3, -7, -10, -22
 * FGFR2IIIc binds to FGF-1, -2, -4, -6, -8, -9, -17 and -18

These differences in binding are not surprising, since FGF ligand is known to bind to the second and third is_associated_with::immunoglobulin domain of the receptor.

Clinical significance
Mutations (changes) are associated with numerous medical conditions that include abnormal bone development (e.g. craniosynostosis syndromes) and cancer.

Craniosynostosis syndromes

 * is_associated_with::Apert syndrome, the best-known type of is_associated_with::acrocephalosyndactyly. This condition is characterized by abnormalities of the skull and face, such as a is_associated_with::cleft palate, and the hands and feet.
 * is_associated_with::Antley-Bixler syndrome (characterized by trapezoidal, craniofacial and skeletal is_associated_with::synostosis, plus is_associated_with::camptodactyly). Inherited as a recessive trait.
 * is_associated_with::Pfeiffer syndrome (another type of acrocephalosyndactyly). Inherited as a dominant trait, includes broad thumbs and large toes.
 * Crouzon syndrome (a craniofacial disorder with no clinically significant hand or foot problems).. is_associated_with::Cleft palate can be a feature of this syndrome. Inherited as a dominant trait.


 * is_associated_with::Jackson-Weiss syndrome

Cancer

 * is_associated_with::Breast cancer, a mutation or is_associated_with::single nucleotide polymorphism (SNP) in is_associated_with::intron 2 of the FGFR2 is_associated_with::gene is associated with a higher breast cancer risk; however the risk is only mildly increased from about 10% lifetime breast cancer risk in the average woman in the industrialized world, to 12-14% risk in carriers of the SNP.

Function and mutations
FGFR2 has important roles in embryonic development and tissue repair, especially bone and blood vessels. Like the other members of the is_associated_with::Fibroblast growth factor receptor family, these receptors signal by binding to their ligand and dimerisation (pairing of receptors), which causes the tyrosine kinase domains to initiate a cascade of intracellular signals. On a molecular level these signals mediate cell division, growth and differentiation.

As mentioned, FGFR2 mutations are associated with is_associated_with::craniosynostosis syndromes, which are skull malformations caused by premature fusion of cranial sutures and other disease features according to the mutation itself. Analysis of chromosomal anomalies in patients led to the identification and confirmation of FGFR2 as a cleft lip and/or palate locus. On a molecular level, mutations that affect FGFR2IIIc are associated with marked changes in is_associated_with::osteoblast proliferation and differentiation. Alteration in FGFR2 signalling is thought to underlie the craniosynostosis syndromes. To date, there are two mechanisms of altered FGFR2 signalling. The first is associated with constitutive activation of FGFR, where the FGFR2 receptor is always signalling, regardless of the amount of FGF ligand. This mechanism is found in patients with Crouzon and Pfeiffer syndrome. The second, which is associated with Apert syndrome is a loss of specificity of the FGFR2 isoform, resulting in the receptor binding to FGFs that it does not normally bind.