The 22 members of the fibroblast growth factor (FGF) family of growth factors mediate their cellular responses by binding to and activating the different isoforms encoded by the four receptor tyrosine kinases (RTKs) designated FGFR1, FGFR2, FGFR3 and FGFR4. These receptors are key regulators of several developmental processes in which cell fate and differentiation to various tissue lineages are determined. Unlike other growth factors, FGFs act in concert with heparin or heparan sulfate proteoglycan (HSPG) to activate FGFRs and to induce the pleiotropic responses that lead to the variety of cellular responses induced by this large family of growth factors. An alternative, FGF-independent, source of FGFR activation originates from the interaction with cell adhesion molecules, typically in the context of interactions on neural cell membranes and is crucial for neuronal survival and development.
Upon ligand binding, receptor dimers are formed and their intrinsic tyrosine kinase is activated causing phosphorylation of multiple tyrosine residues on the receptors. These then serve as docking sites for the recruitment of SH2 (src homology-2) or PTB (phosphotyrosine binding) domains of adaptors, docking proteins or signaling enzymes. Signaling complexes are assembled and recruited to the active receptors resulting in a cascade of phosphorylation events.
This leads to stimulation of intracellular signaling pathways that control cell proliferation, cell differentiation, cell migration, cell survival and cell shape, depending on the cell type or stage of maturation.
View original pathway at:Reactome.
Steinberger D, Vriend G, Mulliken JB, Müller U.; ''The mutations in FGFR2-associated craniosynostoses are clustered in five structural elements of immunoglobulin-like domain III of the receptor.''; PubMedEurope PMCScholia
Anderson J, Burns HD, Enriquez-Harris P, Wilkie AO, Heath JK.; ''Apert syndrome mutations in fibroblast growth factor receptor 2 exhibit increased affinity for FGF ligand.''; PubMedEurope PMCScholia
Tassi E, Al-Attar A, Aigner A, Swift MR, McDonnell K, Karavanov A, Wellstein A.; ''Enhancement of fibroblast growth factor (FGF) activity by an FGF-binding protein.''; PubMedEurope PMCScholia
Turner N, Lambros MB, Horlings HM, Pearson A, Sharpe R, Natrajan R, Geyer FC, van Kouwenhove M, Kreike B, Mackay A, Ashworth A, van de Vijver MJ, Reis-Filho JS.; ''Integrative molecular profiling of triple negative breast cancers identifies amplicon drivers and potential therapeutic targets.''; PubMedEurope PMCScholia
Roberts PJ, Der CJ.; ''Targeting the Raf-MEK-ERK mitogen-activated protein kinase cascade for the treatment of cancer.''; PubMedEurope PMCScholia
Chen J, Lee BH, Williams IR, Kutok JL, Mitsiades CS, Duclos N, Cohen S, Adelsperger J, Okabe R, Coburn A, Moore S, Huntly BJ, Fabbro D, Anderson KC, Griffin JD, Gilliland DG.; ''FGFR3 as a therapeutic target of the small molecule inhibitor PKC412 in hematopoietic malignancies.''; PubMedEurope PMCScholia
Impagnatiello MA, Weitzer S, Gannon G, Compagni A, Cotten M, Christofori G.; ''Mammalian sprouty-1 and -2 are membrane-anchored phosphoprotein inhibitors of growth factor signaling in endothelial cells.''; PubMedEurope PMCScholia
Oldridge M, Wilkie AO, Slaney SF, Poole MD, Pulleyn LJ, Rutland P, Hockley AD, Wake MJ, Goldin JH, Winter RM.; ''Mutations in the third immunoglobulin domain of the fibroblast growth factor receptor-2 gene in Crouzon syndrome.''; PubMedEurope PMCScholia
Cross MJ, Hodgkin MN, Roberts S, Landgren E, Wakelam MJ, Claesson-Welsh L.; ''Tyrosine 766 in the fibroblast growth factor receptor-1 is required for FGF-stimulation of phospholipase C, phospholipase D, phospholipase A(2), phosphoinositide 3-kinase and cytoskeletal reorganisation in porcine aortic endothelial cells.''; PubMedEurope PMCScholia
Cha JY, Maddileti S, Mitin N, Harden TK, Der CJ.; ''Aberrant receptor internalization and enhanced FRS2-dependent signaling contribute to the transforming activity of the fibroblast growth factor receptor 2 IIIb C3 isoform.''; PubMedEurope PMCScholia
Mason JM, Morrison DJ, Bassit B, Dimri M, Band H, Licht JD, Gross I.; ''Tyrosine phosphorylation of Sprouty proteins regulates their ability to inhibit growth factor signaling: a dual feedback loop.''; PubMedEurope PMCScholia
Tavormina PL, Bellus GA, Webster MK, Bamshad MJ, Fraley AE, McIntosh I, Szabo J, Jiang W, Jiang W, Jabs EW, Wilcox WR, Wasmuth JJ, Donoghue DJ, Thompson LM, Francomano CA.; ''A novel skeletal dysplasia with developmental delay and acanthosis nigricans is caused by a Lys650Met mutation in the fibroblast growth factor receptor 3 gene.''; PubMedEurope PMCScholia
Ornitz DM, Marie PJ.; ''FGF signaling pathways in endochondral and intramembranous bone development and human genetic disease.''; PubMedEurope PMCScholia
Lax I, Wong A, Lamothe B, Lee A, Frost A, Hawes J, Schlessinger J.; ''The docking protein FRS2alpha controls a MAP kinase-mediated negative feedback mechanism for signaling by FGF receptors.''; PubMedEurope PMCScholia
Plotnikov A, Zehorai E, Procaccia S, Seger R.; ''The MAPK cascades: signaling components, nuclear roles and mechanisms of nuclear translocation.''; PubMedEurope PMCScholia
Neilson KM, Friesel R.; ''Ligand-independent activation of fibroblast growth factor receptors by point mutations in the extracellular, transmembrane, and kinase domains.''; PubMedEurope PMCScholia
Takeda M, Arao T, Yokote H, Komatsu T, Yanagihara K, Sasaki H, Yamada Y, Tamura T, Fukuoka K, Kimura H, Saijo N, Nishio K.; ''AZD2171 shows potent antitumor activity against gastric cancer over-expressing fibroblast growth factor receptor 2/keratinocyte growth factor receptor.''; PubMedEurope PMCScholia
DaSilva J, Xu L, Kim HJ, Miller WT, Bar-Sagi D.; ''Regulation of sprouty stability by Mnk1-dependent phosphorylation.''; PubMedEurope PMCScholia
Smit L, de Vries-Smits AM, Bos JL, Borst J.; ''B cell antigen receptor stimulation induces formation of a Shc-Grb2 complex containing multiple tyrosine-phosphorylated proteins.''; PubMedEurope PMCScholia
Ong SH, Hadari YR, Gotoh N, Guy GR, Schlessinger J, Lax I.; ''Stimulation of phosphatidylinositol 3-kinase by fibroblast growth factor receptors is mediated by coordinated recruitment of multiple docking proteins.''; PubMedEurope PMCScholia
Rubin C, Litvak V, Medvedovsky H, Zwang Y, Lev S, Yarden Y.; ''Sprouty fine-tunes EGF signaling through interlinked positive and negative feedback loops.''; PubMedEurope PMCScholia
Bai A, Meetze K, Vo NY, Kollipara S, Mazsa EK, Winston WM, Weiler S, Poling LL, Chen T, Ismail NS, Jiang J, Lerner L, Gyuris J, Weng Z.; ''GP369, an FGFR2-IIIb-specific antibody, exhibits potent antitumor activity against human cancers driven by activated FGFR2 signaling.''; PubMedEurope PMCScholia
Kouhara H, Hadari YR, Spivak-Kroizman T, Schilling J, Bar-Sagi D, Lax I, Schlessinger J.; ''A lipid-anchored Grb2-binding protein that links FGF-receptor activation to the Ras/MAPK signaling pathway.''; PubMedEurope PMCScholia
Chardin P, Camonis JH, Gale NW, van Aelst L, Schlessinger J, Wigler MH, Bar-Sagi D.; ''Human Sos1: a guanine nucleotide exchange factor for Ras that binds to GRB2.''; PubMedEurope PMCScholia
Byron SA, Gartside MG, Wellens CL, Mallon MA, Keenan JB, Powell MA, Goodfellow PJ, Pollock PM.; ''Inhibition of activated fibroblast growth factor receptor 2 in endometrial cancer cells induces cell death despite PTEN abrogation.''; PubMedEurope PMCScholia
Schüller AC, Ahmed Z, Levitt JA, Suen KM, Suhling K, Ladbury JE.; ''Indirect recruitment of the signalling adaptor Shc to the fibroblast growth factor receptor 2 (FGFR2).''; PubMedEurope PMCScholia
Byron SA, Gartside MG, Wellens CL, Goodfellow PJ, Birrer MJ, Campbell IG, Pollock PM.; ''FGFR2 mutations are rare across histologic subtypes of ovarian cancer.''; PubMedEurope PMCScholia
Beenken A, Mohammadi M.; ''The FGF family: biology, pathophysiology and therapy.''; PubMedEurope PMCScholia
Brown MD, Sacks DB.; ''Protein scaffolds in MAP kinase signalling.''; PubMedEurope PMCScholia
Wong A, Lamothe B, Lee A, Schlessinger J, Lax I.; ''FRS2 alpha attenuates FGF receptor signaling by Grb2-mediated recruitment of the ubiquitin ligase Cbl.''; PubMedEurope PMCScholia
Roskoski R.; ''RAF protein-serine/threonine kinases: structure and regulation.''; PubMedEurope PMCScholia
Mohammadi M, Dikic I, Sorokin A, Burgess WH, Jaye M, Schlessinger J.; ''Identification of six novel autophosphorylation sites on fibroblast growth factor receptor 1 and elucidation of their importance in receptor activation and signal transduction.''; PubMedEurope PMCScholia
Lorenzi MV, Castagnino P, Chen Q, Chedid M, Miki T.; ''Ligand-independent activation of fibroblast growth factor receptor-2 by carboxyl terminal alterations.''; PubMedEurope PMCScholia
Mohammadi M, Olsen SK, Ibrahimi OA.; ''Structural basis for fibroblast growth factor receptor activation.''; PubMedEurope PMCScholia
Ibrahimi OA, Zhang F, Eliseenkova AV, Itoh N, Linhardt RJ, Mohammadi M.; ''Biochemical analysis of pathogenic ligand-dependent FGFR2 mutations suggests distinct pathophysiological mechanisms for craniofacial and limb abnormalities.''; PubMedEurope PMCScholia
Schlessinger J.; ''Common and distinct elements in cellular signaling via EGF and FGF receptors.''; PubMedEurope PMCScholia
Minegishi Y, Iwanari H, Mochizuki Y, Horii T, Hoshino T, Kodama T, Hamakubo T, Gotoh N.; ''Prominent expression of FRS2beta protein in neural cells and its association with intracellular vesicles.''; PubMedEurope PMCScholia
Hovhannisyan RH, Carstens RP.; ''A novel intronic cis element, ISE/ISS-3, regulates rat fibroblast growth factor receptor 2 splicing through activation of an upstream exon and repression of a downstream exon containing a noncanonical branch point sequence.''; PubMedEurope PMCScholia
Parker BC, Engels M, Annala M, Zhang W.; ''Emergence of FGFR family gene fusions as therapeutic targets in a wide spectrum of solid tumours.''; PubMedEurope PMCScholia
Rousseau F, Saugier P, Le Merrer M, Munnich A, Delezoide AL, Maroteaux P, Bonaventure J, Narcy F, Sanak M.; ''Stop codon FGFR3 mutations in thanatophoric dwarfism type 1.''; PubMedEurope PMCScholia
Ibrahimi OA, Zhang F, Eliseenkova AV, Linhardt RJ, Mohammadi M.; ''Proline to arginine mutations in FGF receptors 1 and 3 result in Pfeiffer and Muenke craniosynostosis syndromes through enhancement of FGF binding affinity.''; PubMedEurope PMCScholia
Hatch NE, Hudson M, Seto ML, Cunningham ML, Bothwell M.; ''Intracellular retention, degradation, and signaling of glycosylation-deficient FGFR2 and craniosynostosis syndrome-associated FGFR2C278F.''; PubMedEurope PMCScholia
Mohammadi M, Dionne CA, Li W, Li N, Spivak T, Honegger AM, Jaye M, Schlessinger J.; ''Point mutation in FGF receptor eliminates phosphatidylinositol hydrolysis without affecting mitogenesis.''; PubMedEurope PMCScholia
Dionne CA, Crumley G, Bellot F, Kaplow JM, Searfoss G, Ruta M, Burgess WH, Jaye M, Schlessinger J.; ''Cloning and expression of two distinct high-affinity receptors cross-reacting with acidic and basic fibroblast growth factors.''; PubMedEurope PMCScholia
Ong SH, Lim YP, Low BC, Guy GR.; ''SHP2 associates directly with tyrosine phosphorylated p90 (SNT) protein in FGF-stimulated cells.''; PubMedEurope PMCScholia
Wang JK, Gao G, Goldfarb M.; ''Fibroblast growth factor receptors have different signaling and mitogenic potentials.''; PubMedEurope PMCScholia
Galvin BD, Hart KC, Meyer AN, Webster MK, Donoghue DJ.; ''Constitutive receptor activation by Crouzon syndrome mutations in fibroblast growth factor receptor (FGFR)2 and FGFR2/Neu chimeras.''; PubMedEurope PMCScholia
Kunii K, Davis L, Gorenstein J, Hatch H, Yashiro M, Di Bacco A, Elbi C, Lutterbach B.; ''FGFR2-amplified gastric cancer cell lines require FGFR2 and Erbb3 signaling for growth and survival.''; PubMedEurope PMCScholia
di Martino E, L'Hôte CG, Kennedy W, Tomlinson DC, Knowles MA.; ''Mutant fibroblast growth factor receptor 3 induces intracellular signaling and cellular transformation in a cell type- and mutation-specific manner.''; PubMedEurope PMCScholia
McKay MM, Morrison DK.; ''Integrating signals from RTKs to ERK/MAPK.''; PubMedEurope PMCScholia
Arai Y, Totoki Y, Hosoda F, Shirota T, Hama N, Nakamura H, Ojima H, Furuta K, Shimada K, Okusaka T, Kosuge T, Shibata T.; ''Fibroblast growth factor receptor 2 tyrosine kinase fusions define a unique molecular subtype of cholangiocarcinoma.''; PubMedEurope PMCScholia
Plotnikov AN, Schlessinger J, Hubbard SR, Mohammadi M.; ''Structural basis for FGF receptor dimerization and activation.''; PubMedEurope PMCScholia
Seo JS, Ju YS, Lee WC, Shin JY, Lee JK, Bleazard T, Lee J, Jung YJ, Kim JO, Shin JY, Yu SB, Kim J, Lee ER, Kang CH, Park IK, Rhee H, Lee SH, Kim JI, Kang JH, Kim YT.; ''The transcriptional landscape and mutational profile of lung adenocarcinoma.''; PubMedEurope PMCScholia
Lim J, Yusoff P, Wong ES, Chandramouli S, Lao DH, Fong CW, Guy GR.; ''The cysteine-rich sprouty translocation domain targets mitogen-activated protein kinase inhibitory proteins to phosphatidylinositol 4,5-bisphosphate in plasma membranes.''; PubMedEurope PMCScholia
Fong CW, Leong HF, Wong ES, Lim J, Yusoff P, Guy GR.; ''Tyrosine phosphorylation of Sprouty2 enhances its interaction with c-Cbl and is crucial for its function.''; PubMedEurope PMCScholia
Tavormina PL, Shiang R, Thompson LM, Zhu YZ, Wilkin DJ, Lachman RS, Wilcox WR, Rimoin DL, Cohn DH, Wasmuth JJ.; ''Thanatophoric dysplasia (types I and II) caused by distinct mutations in fibroblast growth factor receptor 3.''; PubMedEurope PMCScholia
Hart KC, Robertson SC, Donoghue DJ.; ''Identification of tyrosine residues in constitutively activated fibroblast growth factor receptor 3 involved in mitogenesis, Stat activation, and phosphatidylinositol 3-kinase activation.''; PubMedEurope PMCScholia
Hattori Y, Odagiri H, Nakatani H, Miyagawa K, Naito K, Sakamoto H, Katoh O, Yoshida T, Sugimura T, Terada M.; ''K-sam, an amplified gene in stomach cancer, is a member of the heparin-binding growth factor receptor genes.''; PubMedEurope PMCScholia
Cunningham ML, Seto ML, Ratisoontorn C, Heike CL, Hing AV.; ''Syndromic craniosynostosis: from history to hydrogen bonds.''; PubMedEurope PMCScholia
Curto M, Frankel P, Carrero A, Foster DA.; ''Novel recruitment of Shc, Grb2, and Sos by fibroblast growth factor receptor-1 in v-Src-transformed cells.''; PubMedEurope PMCScholia
Li X, Brunton VG, Burgar HR, Wheldon LM, Heath JK.; ''FRS2-dependent SRC activation is required for fibroblast growth factor receptor-induced phosphorylation of Sprouty and suppression of ERK activity.''; PubMedEurope PMCScholia
Kan SH, Elanko N, Johnson D, Cornejo-Roldan L, Cook J, Reich EW, Tomkins S, Verloes A, Twigg SR, Rannan-Eliya S, McDonald-McGinn DM, Zackai EH, Wall SA, Muenke M, Wilkie AO.; ''Genomic screening of fibroblast growth-factor receptor 2 reveals a wide spectrum of mutations in patients with syndromic craniosynostosis.''; PubMedEurope PMCScholia
Del Gatto-Konczak F, Bourgeois CF, Le Guiner C, Kister L, Gesnel MC, Stévenin J, Breathnach R.; ''The RNA-binding protein TIA-1 is a novel mammalian splicing regulator acting through intron sequences adjacent to a 5' splice site.''; PubMedEurope PMCScholia
Robertson SC, Meyer AN, Hart KC, Galvin BD, Webster MK, Donoghue DJ.; ''Activating mutations in the extracellular domain of the fibroblast growth factor receptor 2 function by disruption of the disulfide bond in the third immunoglobulin-like domain.''; PubMedEurope PMCScholia
Carstens RP, Wagner EJ, Garcia-Blanco MA.; ''An intronic splicing silencer causes skipping of the IIIb exon of fibroblast growth factor receptor 2 through involvement of polypyrimidine tract binding protein.''; PubMedEurope PMCScholia
d'Avis PY, Robertson SC, Meyer AN, Bardwell WM, Webster MK, Donoghue DJ.; ''Constitutive activation of fibroblast growth factor receptor 3 by mutations responsible for the lethal skeletal dysplasia thanatophoric dysplasia type I.''; PubMedEurope PMCScholia
Williams EJ, Furness J, Walsh FS, Doherty P.; ''Activation of the FGF receptor underlies neurite outgrowth stimulated by L1, N-CAM, and N-cadherin.''; PubMedEurope PMCScholia
Wilkie AO, Patey SJ, Kan SH, van den Ouweland AM, Hamel BC.; ''FGFs, their receptors, and human limb malformations: clinical and molecular correlations.''; PubMedEurope PMCScholia
Wu Y, Chen Z, Ullrich A.; ''EGFR and FGFR signaling through FRS2 is subject to negative feedback control by ERK1/2.''; PubMedEurope PMCScholia
Dailey L, Ambrosetti D, Mansukhani A, Basilico C.; ''Mechanisms underlying differential responses to FGF signaling.''; PubMedEurope PMCScholia
Zhang X, Ibrahimi OA, Olsen SK, Umemori H, Mohammadi M, Ornitz DM.; ''Receptor specificity of the fibroblast growth factor family. The complete mammalian FGF family.''; PubMedEurope PMCScholia
Lajeunie E, Heuertz S, El Ghouzzi V, Martinovic J, Renier D, Le Merrer M, Bonaventure J.; ''Mutation screening in patients with syndromic craniosynostoses indicates that a limited number of recurrent FGFR2 mutations accounts for severe forms of Pfeiffer syndrome.''; PubMedEurope PMCScholia
Lomri A, Lemonnier J, Hott M, de Parseval N, Lajeunie E, Munnich A, Renier D, Marie PJ.; ''Increased calvaria cell differentiation and bone matrix formation induced by fibroblast growth factor receptor 2 mutations in Apert syndrome.''; PubMedEurope PMCScholia
Brady SC, Coleman ML, Munro J, Feller SM, Morrice NA, Olson MF.; ''Sprouty2 association with B-Raf is regulated by phosphorylation and kinase conformation.''; PubMedEurope PMCScholia
Bellus GA, Spector EB, Speiser PW, Weaver CA, Garber AT, Bryke CR, Israel J, Rosengren SS, Webster MK, Donoghue DJ, Francomano CA.; ''Distinct missense mutations of the FGFR3 lys650 codon modulate receptor kinase activation and the severity of the skeletal dysplasia phenotype.''; PubMedEurope PMCScholia
Gotoh N, Laks S, Nakashima M, Lax I, Schlessinger J.; ''FRS2 family docking proteins with overlapping roles in activation of MAP kinase have distinct spatial-temporal patterns of expression of their transcripts.''; PubMedEurope PMCScholia
Chen H, Ma J, Li W, Eliseenkova AV, Xu C, Neubert TA, Miller WT, Mohammadi M.; ''A molecular brake in the kinase hinge region regulates the activity of receptor tyrosine kinases.''; PubMedEurope PMCScholia
Cantwell-Dorris ER, O'Leary JJ, Sheils OM.; ''BRAFV600E: implications for carcinogenesis and molecular therapy.''; PubMedEurope PMCScholia
Hanafusa H, Torii S, Yasunaga T, Matsumoto K, Nishida E.; ''Shp2, an SH2-containing protein-tyrosine phosphatase, positively regulates receptor tyrosine kinase signaling by dephosphorylating and inactivating the inhibitor Sprouty.''; PubMedEurope PMCScholia
Li Y, Mangasarian K, Mansukhani A, Basilico C.; ''Activation of FGF receptors by mutations in the transmembrane domain.''; PubMedEurope PMCScholia
Onishi-Haraikawa Y, Funaki M, Gotoh N, Shibuya M, Inukai K, Katagiri H, Fukushima Y, Anai M, Ogihara T, Sakoda H, Ono H, Kikuchi M, Oka Y, Asano T.; ''Unique phosphorylation mechanism of Gab1 using PI 3-kinase as an adaptor protein.''; PubMedEurope PMCScholia
Ornitz DM, Xu J, Colvin JS, McEwen DG, MacArthur CA, Coulier F, Gao G, Goldfarb M.; ''Receptor specificity of the fibroblast growth factor family.''; PubMedEurope PMCScholia
Cseh B, Doma E, Baccarini M.; ''"RAF" neighborhood: protein-protein interaction in the Raf/Mek/Erk pathway.''; PubMedEurope PMCScholia
Przylepa KA, Paznekas W, Zhang M, Golabi M, Bias W, Bamshad MJ, Carey JC, Hall BD, Stevenson R, Orlow S, Cohen MM, Jabs EW.; ''Fibroblast growth factor receptor 2 mutations in Beare-Stevenson cutis gyrata syndrome.''; PubMedEurope PMCScholia
Gil A, Sharp PA, Jamison SF, Garcia-Blanco MA.; ''Characterization of cDNAs encoding the polypyrimidine tract-binding protein.''; PubMedEurope PMCScholia
Patterson RL, van Rossum DB, Nikolaidis N, Gill DL, Snyder SH.; ''Phospholipase C-gamma: diverse roles in receptor-mediated calcium signaling.''; PubMedEurope PMCScholia
Wong ES, Lim J, Low BC, Chen Q, Guy GR.; ''Evidence for direct interaction between Sprouty and Cbl.''; PubMedEurope PMCScholia
Hovhannisyan RH, Warzecha CC, Carstens RP.; ''Characterization of sequences and mechanisms through which ISE/ISS-3 regulates FGFR2 splicing.''; PubMedEurope PMCScholia
Wellbrock C, Karasarides M, Marais R.; ''The RAF proteins take centre stage.''; PubMedEurope PMCScholia
Ueda T, Sasaki H, Kuwahara Y, Nezu M, Shibuya T, Sakamoto H, Ishii H, Yanagihara K, Mafune K, Makuuchi M, Terada M.; ''Deletion of the carboxyl-terminal exons of K-sam/FGFR2 by short homology-mediated recombination, generating preferential expression of specific messenger RNAs.''; PubMedEurope PMCScholia
Hovhannisyan RH, Carstens RP.; ''Heterogeneous ribonucleoprotein m is a splicing regulatory protein that can enhance or silence splicing of alternatively spliced exons.''; PubMedEurope PMCScholia
Gartside MG, Chen H, Ibrahimi OA, Byron SA, Curtis AV, Wellens CL, Bengston A, Yudt LM, Eliseenkova AV, Ma J, Curtin JA, Hyder P, Harper UL, Riedesel E, Mann GJ, Trent JM, Bastian BC, Meltzer PS, Mohammadi M, Pollock PM.; ''Loss-of-function fibroblast growth factor receptor-2 mutations in melanoma.''; PubMedEurope PMCScholia
Adar R, Monsonego-Ornan E, David P, Yayon A.; ''Differential activation of cysteine-substitution mutants of fibroblast growth factor receptor 3 is determined by cysteine localization.''; PubMedEurope PMCScholia
Rubin C, Zwang Y, Vaisman N, Ron D, Yarden Y.; ''Phosphorylation of carboxyl-terminal tyrosines modulates the specificity of Sprouty-2 inhibition of different signaling pathways.''; PubMedEurope PMCScholia
Turjanski AG, Vaqué JP, Gutkind JS.; ''MAP kinases and the control of nuclear events.''; PubMedEurope PMCScholia
Tartaglia M, Valeri S, Velardi F, Di Rocco C, Battaglia PA.; ''Trp290Cys mutation in exon IIIa of the fibroblast growth factor receptor 2 (FGFR2) gene is associated with Pfeiffer syndrome.''; PubMedEurope PMCScholia
Muh SJ, Hovhannisyan RH, Carstens RP.; ''A Non-sequence-specific double-stranded RNA structural element regulates splicing of two mutually exclusive exons of fibroblast growth factor receptor 2 (FGFR2).''; PubMedEurope PMCScholia
Carpenter G, Ji Q.; ''Phospholipase C-gamma as a signal-transducing element.''; PubMedEurope PMCScholia
Yigzaw Y, Cartin L, Pierre S, Scholich K, Patel TB.; ''The C terminus of sprouty is important for modulation of cellular migration and proliferation.''; PubMedEurope PMCScholia
Greenman C, Stephens P, Smith R, Dalgliesh GL, Hunter C, Bignell G, Davies H, Teague J, Butler A, Stevens C, Edkins S, O'Meara S, Vastrik I, Schmidt EE, Avis T, Barthorpe S, Bhamra G, Buck G, Choudhury B, Clements J, Cole J, Dicks E, Forbes S, Gray K, Halliday K, Harrison R, Hills K, Hinton J, Jenkinson A, Jones D, Menzies A, Mironenko T, Perry J, Raine K, Richardson D, Shepherd R, Small A, Tofts C, Varian J, Webb T, West S, Widaa S, Yates A, Cahill DP, Louis DN, Goldstraw P, Nicholson AG, Brasseur F, Looijenga L, Weber BL, Chiew YE, DeFazio A, Greaves MF, Green AR, Campbell P, Birney E, Easton DF, Chenevix-Trench G, Tan MH, Khoo SK, Teh BT, Yuen ST, Leung SY, Wooster R, Futreal PA, Stratton MR.; ''Patterns of somatic mutation in human cancer genomes.''; PubMedEurope PMCScholia
Wu YM, Su F, Kalyana-Sundaram S, Khazanov N, Ateeq B, Cao X, Lonigro RJ, Vats P, Wang R, Lin SF, Cheng AJ, Kunju LP, Siddiqui J, Tomlins SA, Wyngaard P, Sadis S, Roychowdhury S, Hussain MH, Feng FY, Zalupski MM, Talpaz M, Pienta KJ, Rhodes DR, Robinson DR, Chinnaiyan AM.; ''Identification of targetable FGFR gene fusions in diverse cancers.''; PubMedEurope PMCScholia
Yusoff P, Lao DH, Ong SH, Wong ES, Lim J, Lo TL, Leong HF, Fong CW, Guy GR.; ''Sprouty2 inhibits the Ras/MAP kinase pathway by inhibiting the activation of Raf.''; PubMedEurope PMCScholia
Gotoh N.; ''Regulation of growth factor signaling by FRS2 family docking/scaffold adaptor proteins.''; PubMedEurope PMCScholia
Jang JH, Shin KH, Park JG.; ''Mutations in fibroblast growth factor receptor 2 and fibroblast growth factor receptor 3 genes associated with human gastric and colorectal cancers.''; PubMedEurope PMCScholia
Dance M, Montagner A, Salles JP, Yart A, Raynal P.; ''The molecular functions of Shp2 in the Ras/Mitogen-activated protein kinase (ERK1/2) pathway.''; PubMedEurope PMCScholia
Wilkie AO, Slaney SF, Oldridge M, Poole MD, Ashworth GJ, Hockley AD, Hayward RD, David DJ, Pulleyn LJ, Rutland P.; ''Apert syndrome results from localized mutations of FGFR2 and is allelic with Crouzon syndrome.''; PubMedEurope PMCScholia
Agazie YM, Movilla N, Ischenko I, Hayman MJ.; ''The phosphotyrosine phosphatase SHP2 is a critical mediator of transformation induced by the oncogenic fibroblast growth factor receptor 3.''; PubMedEurope PMCScholia
Lao DH, Chandramouli S, Yusoff P, Fong CW, Saw TY, Tai LP, Yu CY, Leong HF, Guy GR.; ''A Src homology 3-binding sequence on the C terminus of Sprouty2 is necessary for inhibition of the Ras/ERK pathway downstream of fibroblast growth factor receptor stimulation.''; PubMedEurope PMCScholia
Hart KC, Robertson SC, Kanemitsu MY, Meyer AN, Tynan JA, Donoghue DJ.; ''Transformation and Stat activation by derivatives of FGFR1, FGFR3, and FGFR4.''; PubMedEurope PMCScholia
Wheldon LM, Khodabukus N, Patey SJ, Smith TG, Heath JK, Hajihosseini MK.; ''Identification and characterization of an inhibitory fibroblast growth factor receptor 2 (FGFR2) molecule, up-regulated in an Apert Syndrome mouse model.''; PubMedEurope PMCScholia
Wu DQ, Kan MK, Sato GH, Okamoto T, Sato JD.; ''Characterization and molecular cloning of a putative binding protein for heparin-binding growth factors.''; PubMedEurope PMCScholia
Moffa AB, Tannheimer SL, Ethier SP.; ''Transforming potential of alternatively spliced variants of fibroblast growth factor receptor 2 in human mammary epithelial cells.''; PubMedEurope PMCScholia
Davies H, Bignell GR, Cox C, Stephens P, Edkins S, Clegg S, Teague J, Woffendin H, Garnett MJ, Bottomley W, Davis N, Dicks E, Ewing R, Floyd Y, Gray K, Hall S, Hawes R, Hughes J, Kosmidou V, Menzies A, Mould C, Parker A, Stevens C, Watt S, Hooper S, Wilson R, Jayatilake H, Gusterson BA, Cooper C, Shipley J, Hargrave D, Pritchard-Jones K, Maitland N, Chenevix-Trench G, Riggins GJ, Bigner DD, Palmieri G, Cossu A, Flanagan A, Nicholson A, Ho JW, Leung SY, Yuen ST, Weber BL, Seigler HF, Darrow TL, Paterson H, Marais R, Marshall CJ, Wooster R, Stratton MR, Futreal PA.; ''Mutations of the BRAF gene in human cancer.''; PubMedEurope PMCScholia
Dutt A, Salvesen HB, Chen TH, Ramos AH, Onofrio RC, Hatton C, Nicoletti R, Winckler W, Grewal R, Hanna M, Wyhs N, Ziaugra L, Richter DJ, Trovik J, Engelsen IB, Stefansson IM, Fennell T, Cibulskis K, Zody MC, Akslen LA, Gabriel S, Wong KK, Sellers WR, Meyerson M, Greulich H.; ''Drug-sensitive FGFR2 mutations in endometrial carcinoma.''; PubMedEurope PMCScholia
Del Gatto F, Plet A, Gesnel MC, Fort C, Breathnach R.; ''Multiple interdependent sequence elements control splicing of a fibroblast growth factor receptor 2 alternative exon.''; PubMedEurope PMCScholia
Kanai M, Göke M, Tsunekawa S, Podolsky DK.; ''Signal transduction pathway of human fibroblast growth factor receptor 3. Identification of a novel 66-kDa phosphoprotein.''; PubMedEurope PMCScholia
Stauber DJ, DiGabriele AD, Hendrickson WA.; ''Structural interactions of fibroblast growth factor receptor with its ligands.''; PubMedEurope PMCScholia
Beer HD, Bittner M, Niklaus G, Munding C, Max N, Goppelt A, Werner S.; ''The fibroblast growth factor binding protein is a novel interaction partner of FGF-7, FGF-10 and FGF-22 and regulates FGF activity: implications for epithelial repair.''; PubMedEurope PMCScholia
Klint P, Kanda S, Claesson-Welsh L.; ''Shc and a novel 89-kDa component couple to the Grb2-Sos complex in fibroblast growth factor-2-stimulated cells.''; PubMedEurope PMCScholia
Hall AB, Jura N, DaSilva J, Jang YJ, Gong D, Bar-Sagi D.; ''hSpry2 is targeted to the ubiquitin-dependent proteasome pathway by c-Cbl.''; PubMedEurope PMCScholia
Chellaiah A, Yuan W, Chellaiah M, Ornitz DM.; ''Mapping ligand binding domains in chimeric fibroblast growth factor receptor molecules. Multiple regions determine ligand binding specificity.''; PubMedEurope PMCScholia
Ong SH, Goh KC, Lim YP, Low BC, Klint P, Claesson-Welsh L, Cao X, Tan YH, Guy GR.; ''Suc1-associated neurotrophic factor target (SNT) protein is a major FGF-stimulated tyrosine phosphorylated 90-kDa protein which binds to the SH2 domain of GRB2.''; PubMedEurope PMCScholia
Zhou W, Feng X, Wu Y, Benge J, Zhang Z, Chen Z.; ''FGF-receptor substrate 2 functions as a molecular sensor integrating external regulatory signals into the FGF pathway.''; PubMedEurope PMCScholia
Cha JY, Lambert QT, Reuther GW, Der CJ.; ''Involvement of fibroblast growth factor receptor 2 isoform switching in mammary oncogenesis.''; PubMedEurope PMCScholia
Kyriakis JM, Avruch J.; ''Mammalian MAPK signal transduction pathways activated by stress and inflammation: a 10-year update.''; PubMedEurope PMCScholia
Lao DH, Yusoff P, Chandramouli S, Philp RJ, Fong CW, Jackson RA, Saw TY, Yu CY, Guy GR.; ''Direct binding of PP2A to Sprouty2 and phosphorylation changes are a prerequisite for ERK inhibition downstream of fibroblast growth factor receptor stimulation.''; PubMedEurope PMCScholia
Eswarakumar VP, Lax I, Schlessinger J.; ''Cellular signaling by fibroblast growth factor receptors.''; PubMedEurope PMCScholia
Mohammadi M, Honegger AM, Rotin D, Fischer R, Bellot F, Li W, Dionne CA, Jaye M, Rubinstein M, Schlessinger J.; ''A tyrosine-phosphorylated carboxy-terminal peptide of the fibroblast growth factor receptor (Flg) is a binding site for the SH2 domain of phospholipase C-gamma 1.''; PubMedEurope PMCScholia
Ahmed Z, Schüller AC, Suhling K, Tregidgo C, Ladbury JE.; ''Extracellular point mutations in FGFR2 elicit unexpected changes in intracellular signalling.''; PubMedEurope PMCScholia
Raffioni S, Zhu YZ, Bradshaw RA, Thompson LM.; ''Effect of transmembrane and kinase domain mutations on fibroblast growth factor receptor 3 chimera signaling in PC12 cells. A model for the control of receptor tyrosine kinase activation.''; PubMedEurope PMCScholia
Lim J, Wong ES, Ong SH, Yusoff P, Low BC, Guy GR.; ''Sprouty proteins are targeted to membrane ruffles upon growth factor receptor tyrosine kinase activation. Identification of a novel translocation domain.''; PubMedEurope PMCScholia
Roskoski R.; ''MEK1/2 dual-specificity protein kinases: structure and regulation.''; PubMedEurope PMCScholia
Warzecha CC, Sato TK, Nabet B, Hogenesch JB, Carstens RP.; ''ESRP1 and ESRP2 are epithelial cell-type-specific regulators of FGFR2 splicing.''; PubMedEurope PMCScholia
Mauger DM, Lin C, Garcia-Blanco MA.; ''hnRNP H and hnRNP F complex with Fox2 to silence fibroblast growth factor receptor 2 exon IIIc.''; PubMedEurope PMCScholia
Itoh H, Hattori Y, Sakamoto H, Ishii H, Kishi T, Sasaki H, Yoshida T, Koono M, Sugimura T, Terada M.; ''Preferential alternative splicing in cancer generates a K-sam messenger RNA with higher transforming activity.''; PubMedEurope PMCScholia
Xu H, Lee KW, Goldfarb M.; ''Novel recognition motif on fibroblast growth factor receptor mediates direct association and activation of SNT adapter proteins.''; PubMedEurope PMCScholia
Fukumoto T, Kubota Y, Kitanaka A, Yamaoka G, Ohara-Waki F, Imataki O, Ohnishi H, Ishida T, Tanaka T.; ''Gab1 transduces PI3K-mediated erythropoietin signals to the Erk pathway and regulates erythropoietin-dependent proliferation and survival of erythroid cells.''; PubMedEurope PMCScholia
Hadari YR, Kouhara H, Lax I, Schlessinger J.; ''Binding of Shp2 tyrosine phosphatase to FRS2 is essential for fibroblast growth factor-induced PC12 cell differentiation.''; PubMedEurope PMCScholia
Wesche J, Haglund K, Haugsten EM.; ''Fibroblast growth factors and their receptors in cancer.''; PubMedEurope PMCScholia
Hadari YR, Gotoh N, Kouhara H, Lax I, Schlessinger J.; ''Critical role for the docking-protein FRS2 alpha in FGF receptor-mediated signal transduction pathways.''; PubMedEurope PMCScholia
Cargnello M, Roux PP.; ''Activation and function of the MAPKs and their substrates, the MAPK-activated protein kinases.''; PubMedEurope PMCScholia
Ong SH, Guy GR, Hadari YR, Laks S, Gotoh N, Schlessinger J, Lax I.; ''FRS2 proteins recruit intracellular signaling pathways by binding to diverse targets on fibroblast growth factor and nerve growth factor receptors.''; PubMedEurope PMCScholia
Del Gatto-Konczak F, Olive M, Gesnel MC, Breathnach R.; ''hnRNP A1 recruited to an exon in vivo can function as an exon splicing silencer.''; PubMedEurope PMCScholia
Newman EA, Muh SJ, Hovhannisyan RH, Warzecha CC, Jones RB, McKeehan WL, Carstens RP.; ''Identification of RNA-binding proteins that regulate FGFR2 splicing through the use of sensitive and specific dual color fluorescence minigene assays.''; PubMedEurope PMCScholia
Davies H, Hunter C, Smith R, Stephens P, Greenman C, Bignell G, Teague J, Butler A, Edkins S, Stevens C, Parker A, O'Meara S, Avis T, Barthorpe S, Brackenbury L, Buck G, Clements J, Cole J, Dicks E, Edwards K, Forbes S, Gorton M, Gray K, Halliday K, Harrison R, Hills K, Hinton J, Jones D, Kosmidou V, Laman R, Lugg R, Menzies A, Perry J, Petty R, Raine K, Shepherd R, Small A, Solomon H, Stephens Y, Tofts C, Varian J, Webb A, West S, Widaa S, Yates A, Brasseur F, Cooper CS, Flanagan AM, Green A, Knowles M, Leung SY, Looijenga LH, Malkowicz B, Pierotti MA, Teh BT, Yuen ST, Lakhani SR, Easton DF, Weber BL, Goldstraw P, Nicholson AG, Wooster R, Stratton MR, Futreal PA.; ''Somatic mutations of the protein kinase gene family in human lung cancer.''; PubMedEurope PMCScholia
AZD4547 (Astra Zeneca) is a pan-FGFR inhibitor in Phase I clinical trials for patients with advanced gastric cancer (NCT01457846) and for patient with advanced solid tumors with or without amplified FGFR1 or 2 (NCT00979134) and in Phase I/II trials for breast cancer patients with FGFR1 amplifications (NCT01202591).
A pan-FGFR ATP-competitive inhibitor that is in phase I clinical trials for advanced solid malignancies with amplification or activation of FGFR1 and 2 or activation of FGFR3 (NCT01004224).
E-3810 is a dual VEGFR and FGFR inhibitor that has anti-angiogenic and anti-tumorigenic effects in preclinical studies (Bello, 2011). It is in Phase I clinical trials for patients with solid tumors (NCT01283945).
E7080 is a broad-specificity tyrosine kinase inhibitor that is in Phase I clinical trials for a variety of solid malignancies, including metastatic endometrial cancer (NCT01111461). No specific data regarding its preclinical efficacy against activated FGF receptors is available.
FP-1039 is an FGFR1c:Fc fragment that acts as a broad FGF- ligand trap. Developed by FivePrime therapeutics (http://www.fiveprime.com/index.php?option=com_content&view=article&id=222&Itemid=153), FP-1039 is in Phase I clinical trials in solid malignancies and in Phase II trials in endometrial cancer patients carrying the FGFR2 S252W or P253R alleles.
FP-1039 is an FGFR1c:Fc fragment that acts as a broad FGF- ligand trap. Developed by FivePrime therapeutics (http://www.fiveprime.com/index.php?option=com_content&view=article&id=222&Itemid=153), FP-1039 is in Phase I clinical trials in solid malignancies and in Phase II trials in endometrial cancer patients carrying the FGFR2 S252W or P253R alleles.
PD173074 is potent pan-FGFR reversible inhibitor that interacts with residues in the ATP-binding pocket and inhibits tyrosine kinase activity and autophosphorylation (Mohammadi, 1998; Ezzat, 2005). PD173074 is not suitable for therapeutic use due to issues with toxicity.
Signaling by AKT is one of the key outcomes of receptor tyrosine kinase (RTK) activation. AKT is activated by the cellular second messenger PIP3, a phospholipid that is generated by PI3K. In ustimulated cells, PI3K class IA enzymes reside in the cytosol as inactive heterodimers composed of p85 regulatory subunit and p110 catalytic subunit. In this complex, p85 stabilizes p110 while inhibiting its catalytic activity. Upon binding of extracellular ligands to RTKs, receptors dimerize and undergo autophosphorylation. The regulatory subunit of PI3K, p85, is recruited to phosphorylated cytosolic RTK domains either directly or indirectly, through adaptor proteins, leading to a conformational change in the PI3K IA heterodimer that relieves inhibition of the p110 catalytic subunit. Activated PI3K IA phosphorylates PIP2, converting it to PIP3; this reaction is negatively regulated by PTEN phosphatase. PIP3 recruits AKT to the plasma membrane, allowing TORC2 to phosphorylate a conserved serine residue of AKT. Phosphorylation of this serine induces a conformation change in AKT, exposing a conserved threonine residue that is then phosphorylated by PDPK1 (PDK1). Phosphorylation of both the threonine and the serine residue is required to fully activate AKT. The active AKT then dissociates from PIP3 and phosphorylates a number of cytosolic and nuclear proteins that play important roles in cell survival and metabolism. For a recent review of AKT signaling, please refer to Manning and Cantley, 2007.
The RAS-RAF-MEK-ERK pathway regulates processes such as proliferation, differentiation, survival, senescence and cell motility in response to growth factors, hormones and cytokines, among others. Binding of these stimuli to receptors in the plasma membrane promotes the GEF-mediated activation of RAS at the plasma membrane and initiates the three-tiered kinase cascade of the conventional MAPK cascades. GTP-bound RAS recruits RAF (the MAPK kinase kinase), and promotes its dimerization and activation (reviewed in Cseh et al, 2014; Roskoski, 2010; McKay and Morrison, 2007; Wellbrock et al, 2004). Activated RAF phosphorylates the MAPK kinase proteins MEK1 and MEK2 (also known as MAP2K1 and MAP2K2), which in turn phophorylate the proline-directed kinases ERK1 and 2 (also known as MAPK3 and MAPK1) (reviewed in Roskoski, 2012a, b; Kryiakis and Avruch, 2012). Activated ERK proteins may undergo dimerization and have identified targets in both the nucleus and the cytosol; consistent with this, a proportion of activated ERK protein relocalizes to the nucleus in response to stimuli (reviewed in Roskoski 2012b; Turjanski et al, 2007; Plotnikov et al, 2010; Cargnello et al, 2011). Although initially seen as a linear cascade originating at the plasma membrane and culminating in the nucleus, the RAS/RAF MAPK cascade is now also known to be activated from various intracellular location. Temporal and spatial specificity of the cascade is achieved in part through the interaction of pathway components with numerous scaffolding proteins (reviewed in McKay and Morrison, 2007; Brown and Sacks, 2009). The importance of the RAS/RAF MAPK cascade is highlighted by the fact that components of this pathway are mutated with high frequency in a large number of human cancers. Activating mutations in RAS are found in approximately one third of human cancers, while ~8% of tumors express an activated form of BRAF (Roberts and Der, 2007; Davies et al, 2002; Cantwell-Dorris et al, 2011).
SU5402 is an ATP-competitive FGFR and VEGFR inhibitor that is used as an in vitro reagent. Su5402 is not suitable for therapeutic use due to toxicity issues.
The phospho-tyrosine positions for FRS2-beta were inferred by similarity to the analogous positions in FRS2-alpha. Five out of six tyrosine positions in alpha are present in beta.
This represents WT FGFR2 of either the IIIb or IIIc isoform that is found overexpressed in some cancers. Sites of tyrosine phosphorylation are marked as unknown to circumvent the numbering differences between the isoform variants.
This represents FGFR2 S267C of either the IIIb or IIIC isoform; as such, the positions for tyrosine phosphorylation are marked as unknown to circumvent the difference in numbering between isoforms.
This represents FGFR2 W290C of either the IIIb or IIIC isoform; as such, the positions for tyrosine phosphorylation are marked as unknown to circumvent the difference in numbering between isoforms.
SPRY2 translocates to the plasma membrane upon activation of cells with FGF, and translocation is required for the inhibition of growth factor-stimulated cell migration, proliferation and differentiation. Translocation may be mediated by interactions with PIP2 in the membrane, palmitoylation of the C-terminal region of SPRY2 and/or interactions with caveolin-1.
Sprouty 2 protein is phosphorylated on tyrosine residue 55. The ability of SRC kinase to catalyze this reaction has been demonstrated with purified proteins in vitro (Li et al. 2004) and in cultured cells with studies of the effects of SRC-family pharmacological inhibitors and of dominant-negative mutant SRC proteins (Mason et al. 2004). SRC kinase also phosphorylates numerous tyrosine residues in the C terminal region of SPRY2 including Y227, in response to FGF but not EGF stimulation.
Some evidence suggests that SPRY2 may exert its negative effect by binding to GRB2 and competing with the GRB2:SOS1 interaction that is required for MAPK activation. SPRY2 phosphorylation at Y55 is stimulated in response to both FGF and EGF, and is required for SPRY2 to act as a negative regulator of FGF signaling. Y55 is not thought to be a GRB2 binding site, however. Instead, phosphorylation at Y55 is thought to cause a conformational change in SPRY2 that reveals a cryptic PXXPXPR GRB2-docking site in the C-terminal of SPRY2. SPRY2 has also been shown to be phosphorylated at multiple tyrosine residues in its C-terminal in response to FGF, but not EGF, stimulation. This phosphorylation, in particular at residue 227, is thought to augment the ability of SPRY2 to inhibit FGF signaling through the MAPK cascade, although the mechanism remains to be elucidated.
The N terminal TKB domain of CBL binds to the phospho-tyrosine 55 of SPRY2, targeting SPRY2 for degradation by the 26S proteasome. Y55 is also a binding site for PP2A, which dephosphorylates numerous serine and threonine residues on SPRY2, allowing a conformational change that may promote a SPRY2:GRB2 interaction and limit the extent of MAPK activation following FGF stimulation.
In unstimulated cells, SPRY2 has been shown to be phosphorylated on multiple serine and threonine residues. In these cells, SPRY2 exists in a complex with the regulatory and catalytic subunits (A and C, respectively) of the serine/threonine phosphatase PP2A. After stimulation with FGF, the catalytic activity of PP2A increases and the phosphatase dephophorylates SPRY at serine 112 and serine 115. This is thought to promote changes in tertiary structure that promote GRB2 binding and phosphorylation of Y55 and Y227.
Some evidence suggests that SPRY2 can exert its negative role on FGF signaling at the level of RAF activation. Hypophosphorylated SPRY2 binds to inactive B-RAF, preventing it from activating ERK signaling. MAPK activation results in phosphorylation of SPRY2 on six serine residues (S7, S42, S111, S120, S140 and S167), and inhibits B-RAF binding. Phosphorylation at S111 and S120 directly affects B-RAF binding while the remaining four sites appear to contribute indirectly. Oncogenic forms of B-RAF such as B-RAF V600E, which adopt active kinase conformations, do not associate with SPRY2, regardless of its phosphorylation status. This suggests that two mechanisms affect the SPRY2:B-RAF interaction: SPRY2 phosphorylation and B-RAF conformation.
PPTN11 (also known as SHP2) may exert its positive effects on MAPK activation in response to FGF stimulation by catalyzing the dephosphorylation of tyrosine resides on SPRY2. This dephosphorylation promotes dissociation of the GRB2/SPRY2 complex and as a consequence stimulates GRB2 association with the activated receptor, leading to sustained MAPK signaling.
The Src homology 2 (SH2) domain of the phosphatidylinositol 3-kinase (PIK3) regulatory subunit (PIK3R1, i.e. PI3Kp85) binds to GAB1 in a phosphorylation-independent manner. GAB1 serves as a docking protein which recruits a number of downstream signalling proteins. PIK3R1 can bind to either GAB1 or phosphorylated GAB1.
In this reaction, FGF receptor 2c in the plasma membrane binds an associating extracellular ligand, a requisite step for subsequent activation. The resulting complex consists of dimerized receptor, two ligand molecules, and heparan sulfate. Two isoforms of FGFR2c generated by alternative splicing and differing only by the presence ("long") or absence ("short") of two amino acid residues at positions 428-429 are equally active in ligand binding and dimerization but differ in their abilities to interact with downstream targets.
In this reaction, FGF receptor 2b in the plasma membrane binds an associating extracellular ligand, a requisite step for subsequent activation. The resulting complex consists of dimerized receptor, two ligand molecules, and heparan sulfate. Two isoforms of FGFR2b generated by alternative splicing and differing only by the presence ("long") or absence ("short") of two amino acid residues at positions 428-429 are equally active in ligand binding and dimerization but differ in their abilities to interact with downstream targets.
The intrinsic protein tyrosine kinase activity of the activated FGFR2b receptor leads to multiple phosphorylation events, creating a number of binding sites on its cytoplasmic tail for membrane bound docking proteins to gather intracellular signaling mediators. Two isoforms of FGFR2b generated by alternative splicing and differing only by the presence ("long") or absence ("short") of two amino acid residues at positions 428-429 are equally active in ligand binding and dimerization but differ in their abilities to interact with downstream targets. Based on sequence alignment, FGFR2 contains all 8 of the cytoplasmic tyrosine residues identified in FGFR1.
The intrinsic protein tyrosine kinase activity of the activated FGFR2c receptor leads to multiple phosphorylation events, creating a number of binding sites on its cytoplasmic tail for membrane bound docking proteins to gather intracellular signaling mediators. Two isoforms of FGFR2c generated by alternative splicing and differing only by the presence ("long") or absence ("short") of two amino acid residues at positions 428-429 are equally active in autophosphorylation, but differ in their abilities to interact with downstream targets. Based on sequence alignment, FGFR2 contains all 8 of the cytoplasmic tyrosine residues identified in FGFR1.
Point mutations in FGFR2 that are thought to promote ligand-independent dimerization in the context of autosomal bone development disorders have also been identified in endometrial, ovarian, gastric and lung cancer (Greenman, 2007; Dutt, 2008; Davies, 2005; Byron, 2008; Byron, 2010, Pollock, 2007). Although functional studies on these mutations in FGFR2 in cancer cell lines is limited - only the S267P mutation identified in gastric cancer has been demonstrated biochemically to undergo ligand-independent dimerization (Anderson, 1998) - characterization of paralogous mutations in FGFR3 as well as in other mutations that create unpaired cysteine residues in FGFR2 support the notion that these mutant receptors undergo aberrant intermolecular disulphide bond formation that results in constitutive activation (Galvin, 1996; Neilson and Friesel,1995; Robertson, 1998; d'Avis, 1998)
FGFR2 S267P undergoes ligand-independent dimerization, and appears unable to stably bind FGF2 ligand under the conditions examined (Anderson, 1998). FGFR2b S373C and Y376C are paralogous to the FGFR3 S371C and Y373C mutations that are seen in thanatophoric dysplasia I (Rousseau, 1996; Tavormina, 1995a) and which have been shown to undergo spontaneous dimerization in the absence of ligand (d'Avis, 1998; Adar, 2002). Moreover, other FGFR2 mutations that introduce unpaired cysteine residues have been shown to support formation of intermolecular disulphide bonds (Galvin, 1996; Neilson and Friesel, 1995), supporting the notion that the FGFR2b S373C and Y376C mutants may promote spontaneous receptor dimerization and activation.
Overexpressed FGFR2 in gastric and breast cancer cells has been shown to undergo ligand-independent dimerization (Takeda, 2007; Kunii, 2008; Moffa, 2004; Turner, 2010). Full-length FGFR2 is weakly transforming in NIH 3T3 cells, and is thought to possess a transformation-inhibiting domain in the C-terminus (Itoh, 1994). Interestingly, many cancers with amplifications of FGFR2 show preferrential expression of C-terminally truncated FGFR2 variants, designated C2 and C3, with 788 or 769 residues instead of the wild-type 822 (Hattori, 1990; Itoh, 1994; Ueda, 1999). These variants, which lack a number of carboxy-terminal tyrosine residues, show increased transforming potency compared to the full-length receptor (Cha, 2008; Cha, 2009), and have been shown to be constitutively active and to dimerize spontaneously (Takeda, 2007).
Amplification of full length FGFR2 is only weakly transforming in NIH 3T3 cells, reflecting the presence of a putative transformation-inhibitory region in the c-terminus of the protein (Itoh, 1994, Cha, 2009). C-terminally truncated variants of FGFR2 that are preferrentially expressed in cancer show more potent transformation potential (Cha, 2008; Cha, 2009). These variants lack a number of carboxy-terminal tyrosine residues, including Y770 and Y773. Loss of Y770 contributes to transformation by enhancing FRS2 binding to the C-terminally truncated variant. This suggests that in the context of the full-length protein the presence of Y770 restricts access of FRS2 to the receptor. Loss or mutation of Y773 impairs internalization and degradation of the receptor and promotes sustained signaling (Cha, 2009). Gastric cancer cell lines with FGFR2 amplifications appear to undergo ligand-independent signaling and are sensitive to inhibition with ATP-competitive inhibitors (Takeda, 2007).
FGFR2 amplifications identified in 4% of triple negative breast cancers have also been shown to be constitutively active and to have elevated levels of phosphorylated FRS2 in the absence of ligand. Consistent with this, shRNA knockdown or chemical inhibition restricts proliferation and induces apoptosis in these cells (Kunii, 2008; Turner, 2010)
Amplified FGFR2 has been shown to be a potential target for a number of ATP-competitive inhibitors, some of which are currently in clinical trials for therapeutic use (Takeda, 2007; Turner, 2010; http://clinicaltrials.gov).
Mutations in the highly conserved Pro-Ser dipeptide repeat of FGFR2 have been identified both in Apert syndrome and in endometrial and ovarian cancers (Wilkie, 1995; Dutt, 2008; Pollock, 2007; Byron, 2010). Missense S252W or P253R mutations affect both the 'b' and 'c' isoforms, although mutation in the FGFR2c isoform is believed to be more clinically relevant to the development of Apert syndrome (Lomri, 1998). In the context of endometrial cancer, these mutations are mutually exclusive with KRAS mutations, but are associated at high frequency with PTEN mutations (Byron, 2008). The S252W and P253R mutations allow the receptor to bind to an expanded range of ligands, such that the mesenchymal splice form (FGFR2c) is anomalously activated by the mesenchymal ligands FGF7 and FGF10, establishing an autocrine signaling loop. These mutations also increase the binding affinity for the receptor's normal epithelial ligands 2- to 8-fold (Yu, 2000; Ibrahimi, 2004b). Based on biochemical and crystal studies, the mutations in the IgII-IgIII linker region are predicted to alter the hydrogen bonding network in this region and may change the conformation and thus the ligand-binding properties of the mutant receptors (Stauber, 2000).
Apert sydrome is the most severe of the craniosynostosis syndromes and results almost entirely from two missense mutations in the conserved Ser252 and Pro253 residues in the IgII-IgIII linker of FGFR2 (Wilkie, 1995). These mutations affect both the 'b' and 'c' isoforms, although mutation in the FGFR2c isoform is believed to be more clinically relevant to the development of Apert syndrome (Lomri, 1998). More recently, the same mutations arising somatically have been identified in endometrial and ovarian cancer (Dutt, 2008; Byron, 2008; Pollock, 2007).
The IgII and IgIII domains and the intervening linker of the FGF receptor constitute a binding site for FGFs (Chellaiah, 1999; Stauber, 2000; Plotnikov, 1999). The epithelial isoform FGFR2b binds only to mesenchymally expressed ligands including FGF7 and FGF10 and does not respond to epithelial ligands FGF2, 4, 6, 8 and 9 (Ornitz, 1996). Introduction of the P252W and P252R mutations into FGFR2b allows the aberrant binding and activation by the epithelially expressed ligands FGF 2, 6 and 9, establishing an autocrine signaling loop in epithelial cells. These mutations also increase the binding affinity for the receptor's normal mesenchymal ligands 2- to 8-fold (Yu, 2000; Ibrahimi, 2004b). Based on biochemical and crystal studies, the mutations in the IgII-IgIII linker region are predicted to alter the hydrogen bonding network in this region and may change the conformation and thus the ligand-binding properties of the mutant receptors (Stauber, 2000).
Several missense mutations in the tyrosine kinase domain of FGFR2 have been identified in Crouzon syndrome and similar craniosynostosis disorders (Kan, 2002; Cunningham, 2007). The N549H and K660N mutations are paralogous to FGFR3 N540K and K650N/E mutations identified in hypochondroplasia and thanatophoric dysplasia II (Bellus, 2000). In FGFR3, these mutations have been demonstrated to have weak ligand-independent autophosphorylation and enhanced kinase activity mediated by disruption of a hydrogen-bonding network that holds the receptor in an inactive conformation (Chen, 2007; Bellus, 2000, Raffioni, 1998). Due to the highly conserved nature of these residues across all four FGF receptors, it is generally believed that these germline mutations in FGFR2 are also activating, though this remains to be demonstrated experimentally.
As further support of this notion, activating point mutations in the kinase domain of FGFR2 have also been identified in endometrial, uterine and cervical cancers (Pollock, 2007; Dutt, 2008), and in some cases have been shown to have enhanced kinase activity and to support anchorage-independent growth in NIH 3T3 cells (Dutt, 2008). Knockdown of N549K with short hairpin RNAs or the pan-FGFR inhibitor PD170734 inhibits cell survival in endometrial cancer cells lines, suggesting that FGFR2 activity is required for tumor cell survival (Dutt, 2008; Byron, 2008). Kinase-domain mutants show elevated levels of activity relative to the wild-type even in the absence of receptor phosphorylation, and although their kinase activity is further enhanced upon trans-autophosphorylation, the extent of this is less than that seen in the wild-type, suggesting that the mutant alleles are capable of of supporting ligand-independent activation (Chen, 2007)
After aberrantly dimerizing in response to mesenchymally expressed ligands, FGFR2c S252W and P253R mutants are assumed to undergo transautophosphorylation analagous to the wild-type receptor, although this has not been explicitly demonstrated. Knock-down or chemical inhibition of other FGFR2-activating mutations identified in endometrial cancer cells has been shown to cause cell death (Byron, 2008).
After aberrantly dimerizing in response to epithelially expressed ligands, FGFR2b S252W and P253R mutants are assumed to undergo transautophosphorylation analagous to both the wild-type receptor, although this has not been explicitly demonstrated. Transformation of NIH 3T3 cells with the FGFR2b S252W mutant confers anchorage independent growth and results in increased phosphorylation of FRS2 in a manner that depends on a functional kinase domain (Dutt, 2008). Knock-down or chemical inhibition of other FGFR2-activating mutations identified in endometrial cancer cells has been shown to cause cell death (Byron, 2008).
Several missense mutations in the tyrosine kinase domain of FGFR2 have been identified in Crouzon syndrome and similar craniosynostosis disorders (Kan, 2002; Cunningham, 2007). The N549H and K660N mutations identified in FGFR2 in craniosynostosis disorders are paralogous to FGFR3 N540K and K650N/E mutations identified in hypochondroplasia and thanatophoric dysplasia II (Bellus, 2000). In FGFR3, these mutations have been demonstrated to have weak ligand-independent autophosphorylation and enhanced kinase activity mediated by disruption of a hydrogen-bonding network that holds the receptor in an inactive conformation (Chen, 2007; Bellus, 2000, Raffioni, 1998).
Characterization of FGFR2 proteins containing somatic mutations at these residues support the notion that they have elevated levels of kinase activity. FRS2 is constitutively phosphorylated in the FGFR2 N549K kinase mutant identified in endometrial tumors and knockdown of N549K with short hairpin RNAs or the pan-FGFR inhibitor PD170734 inhibits cell survival in endometrial cancer cells lines, suggesting that FGFR2 activity is required for tumor cell survival. FGFR2 knockdown also results in a significant decrease in the levels of phosphorylated Erk1/2 (Dutt, 2008; Byron, 2008; Pollock, 2007). Crystal structures of FGFR2 kinase mutants N549H and K650N show that the mutations disengage an 'auto-inhibitory brake' on the kinase domain of the receptor. Biochemically, the FGFR2 N549K and K660E mutants show elevated kinase activity relative to the unphosphorylated wild-type protein and have increased activity towards peptide substrates; this activity is stimulated upon receptor phosphorylation, but to a lesser extent than seen with the wild-type receptor (Chen, 2007).
Treatment of FGFR2-amplified gastric and breast cancer cell lines with the antibody GP369 inhibits FGFR2 phosphorylation and downstream signaling and suppresses cell proliferation. Treatment of mice with GP369 inhibits the growth of human cancer xenografts carrying activating FGFR2 mutations. The GP369-binding epitope is contained in the ligand-binding region of the receptor, suggesting that the antibody works by disrupting the ligand-dependent activation of amplified FGFR2 (Bai, 2010).
FP-1039 is a soluble fusion protein consisting of the extracellular region of FGFR1c bound to the Fc region of human IgG1. It is capable of binding to a wide range of FGF ligands and thereby prevents activation of multiple FGF receptors. FP-1039 is in Phase I clinical trials in solid malignancies and in Phase II trials for patients with endometrial cancers harbouring the activating mutations S252W and P253R (reviewed in Wesche, 2011).
FGFR2 is inhibited by a range of in vitro tyrosine kinase inhibitors, including PD170734 and SU5402 (reviewed in Greulich and Pollock, 2010; Wesche, 2011). In addition, there are a number of FGFR2 inhibitors currently in clinical trials that for treatment of solid malignancies (http://ClinicalTrials.gov).
PLC gamma is phosphorylated by activated FGFR, resulting in PLC gamma activation, stimulation of phosphatidyl inositol hydrolysis and generation of two second messengers, diacylglycerol and inositol (1,4,5) P3. Tyrosine phosphorylation of PLCgamma by FGFR4 is weaker than that seen by other isoforms of FGFR.
Dissociation from the activated receptor quickly follows phosphorylation of PLC-gamma. Phosphorylated PLC-gamma catalyzes the hydrolysis of phosphatidylinositol(4, 5)bisphosphate to generate two second messengers, diacylglycerol and inositol (1,4,5) triphosphate.
Recruitment of PLC-gamma by FGF receptors has been best studied in FGFR1c signaling, where it has been shown that autophosphorylation of Tyr766 in the C-terminal tail of FGFR1c creates a specific binding site for the SH2 domain of PLC-gamma. A mutant FGFR1c in which Y766 is replaced by phenylalanine is unable to activate PI hydrolysis and Ca2+ release in response to FGF stimulation. Membrane recruitment of PLC-gamma is also aided by binding of the Pleckstrin homology (PH) domain of this enzyme to PtIns(3,4,5) P3 molecules that are generated in response to PI-3 kinase stimulation. By sequence comparison, Y766 is conserved in all FGFR isoforms, and PLC-gamma signaling is observed, to a greater or lesser extent, downstream of all FGFR receptors upon stimulation with FGFs.
FRS2 (also known as FRS alpha is activated through tyrosine phosphorylation catalyzed by the protein kinase domain of the activated FGFR. FRS2 contains four binding sites for the adaptor protein GRB2 at residues Y196, Y306, Y349 and Y392, and two binding sites for the protein tyrosine phosphatase PPTN11/SHP2 at residues Y436 and Y471. Different FGFR isoforms may generate different phosphorylation patterns on FRS2 leading to alternate downstream signaling.
FRS2 (also known as FRS2alpha) is broadly expressed in adult and fetal tissues. Membrane-bound FRS2 interacts with FGFR as a first step in the phosphorylation of this docking protein. The juxtamembrane binding site for FRS2 does not contain tyrosine, so binding may be independent of receptor activation and/or constitutive. Activation of the FGFR receptor is required for FRS2 phosphorylation and subsequent recruitment of downstream effectors.
Phosphorylated SHC1 links FGFR to Grb2 (Klint et al. 1995) leading to the formation of a signaling complex including Shc, Grb2 and Sos. Transformation of NIH 3T3 cells with v-Src produced a strong constitutive association of FGFR1 with Shc, Grb2 and Sos (Curto et al. 1998) suggesting Src involvement. Recruitment of Grb2-Sos links FGFR to the Ras pathway.
The p46 and p53 isoforms of SHC1 have been shown to be phosphorylated upon FGF stimulation. Three consensus RTK phosphoryation sites are present in SHC1, although phosphorylation of these specific tyrosine residues has not been explicitly demonstrated in response to FGF stimulation. In contrast, the p66 isoform of SHC1 does not appear to undergo FGF-dependent phosphorylation.
FRS2 has 8 canonical MAPK phosphorylation sites which are phosphorylated by activated ERK1/2 after FGF stimulation. Phosphorylation of these 8 threonine residues counteracts the activating effect of tyrosine phosphorylation of FRS2, although the exact mechanism for this negative regulation is not known. Expression of a version of FRS2 in which the 8 threonine residues are mutated to valine results in enhanced tyrosine phosphorylation of FRS2, enhanced GRB2-SOS1 recruitment and a more sustained MAPK response. The 8 threonine residues are not conserved in FRS3; as a result, signaling through FRS3 complexes do not appear to be subject to this downregulation.
FRS3 (also known as FRS2beta) is predominantly expressed in the developing and adult neuroepithelium. As is the case for FRS2 (also known as FRS2alpha), binding of FRS3 to FGFR may be constitutive and/or independent of receptor activation. Elements of the downstream signaling mediated by the two FRS family members appear to be at least partially conserved, as FRS3 is phosphorylated upon FGF stimulation, binds PPTN11/SHP2 and GRB2 and results in ERK activation. Moreover, expression of FRS3 in FRS2-/- MEFs restores ERK activation.
FRS3 (also known as FRS2 beta) is activated through tyrosine phosphorylation catalyzed by the protein kinase domain of the activated FGFR. By sequence comparison, FRS3 has the 2 PPTN11/SHP2-binding sites and has three of the four GRB2-binding sites.
Tyrosine phosphorylation of PPTN11/SHP2 by FGFR kinase is required for activation of the phosphatase activity of PPTN11 and for downstream signaling. Tyrosine phosphorylated PPTN11 plays a major role in the activation of RAS-MAP kinase pathway, although the precise role is not yet clear.
The Src homology 2 (SH2) domain of the phosphatidylinositol 3-kinase (PIK3) regulatory subunit (PIK3R1, i.e. PI3Kp85) binds to GAB1 in a phosphorylation-independent manner. GAB1 serves as a docking protein which recruits a number of downstream signalling proteins. PIK3R1 can bind to either GAB1 or phosphorylated GAB1(Rodrigues et al. 2000, Onishi-Haraikawa et al. 2001). In unstimulated cells, PI3K class IA exists as an inactive heterodimer of a p85 regulatory subunit (encoded by PIK3R1, PIK3R2 or PIK3R3) and a p110 catalytic subunit (encoded by PIK3CA, PIK3CB or PIK3CD). Binding of the iSH2 domain of the p85 regulatory subunit to the ABD and C2 domains of the p110 catalytic subunit both stabilizes p110 and inhibits its catalytic activity. This inhibition is relieved when the SH2 domains of p85 bind phosphorylated tyrosines on activated RTKs or their adaptor proteins. Binding to membrane-associated receptors brings activated PI3K in proximity to its membrane-localized substrate, PIP2 (Mandelker et al. 2009, Burke et al. 2011).
Tyrosine phosphorylated FRS2 recruits GRB2:SOS1 complex by means of the SH3 domain of GRB2, leading to RAS-MAP kinase activation. The FRS2:GRB2-mediated pathway plays a minor role in the activation of RAS-MAP kinase pathway compared to that mediated by FRS2:PPTN11.
The Src homology 2 (SH2) domain of the phosphatidylinositol 3-kinase (PIK3) regulatory subunit (PIK3R1, i.e. PI3Kp85) binds to GAB1 in a phosphorylation-independent manner. GAB1 serves as a docking protein which recruits a number of downstream signalling proteins. PIK3R1 can bind to either GAB1 or phosphorylated GAB1(Rodrigues et al. 2000, Onishi-Haraikawa et al. 2001). In unstimulated cells, PI3K class IA exists as an inactive heterodimer of a p85 regulatory subunit (encoded by PIK3R1, PIK3R2 or PIK3R3) and a p110 catalytic subunit (encoded by PIK3CA, PIK3CB or PIK3CD). Binding of the iSH2 domain of the p85 regulatory subunit to the ABD and C2 domains of the p110 catalytic subunit both stabilizes p110 and inhibits its catalytic activity. This inhibition is relieved when the SH2 domains of p85 bind phosphorylated tyrosines on activated RTKs or their adaptor proteins. Binding to membrane-associated receptors brings activated PI3K in proximity to its membrane-localized substrate, PIP2 (Mandelker et al. 2009, Burke et al. 2011).
Grb2 bound to tyrosine phosphorylated FRS2 forms a ternary complex with Cbl through the binding of the SH3 domains of Grb2 to a proline rich region in Cbl. Grb2-mediated recruitment of Cbl results in ubiquitination of FGFR and FRS2. Cbl is a multidomain protein that posses an intrinsic ubiquitin ligase activity and also functions as a platform for recruitment of a variety of signaling proteins. Multiple mechanisms appear to be required for downregulation of FGFR, as internalization of the receptor is reduced but not abolished if recruitment of CBL to FRS2 is compromised by mutation of GRB2-binding sites.
Once recruited to the activated receptor, PI3K phosphorylates PIP2 to PIP3, leading to activation of AKT signaling. PI3K signaling has been demonstrated in ZMYM2-, FOP- and BCR-FGFR1 fusions (Chen, 2004; Demiroglu, 2001; Guasch, 2001), as well as downstream of a number of other FGFR mutants (see for instance, Byron, 2008; Kunii, 2008; Agazie, 2003; Takeda, 2007).
The ubiquitin ligase CBL exists in a complex with GRB2 and is recruited to tyrosine-phosphorylated FRS2 after FGF stimulation. In addition to promoting the ubiquitination, endocytosis, and degradation of the activated receptor complex, recruitment of the p-CBL:GRB2 complex seems to attenuate FGFR signaling by competing with GRB2:SOS1 for binding to the direct GRB2-binding sites on p-FRS2.
Dissociation from the activated receptor quickly follows phosphorylation of PLC-gamma. Phosphorylated PLC-gamma catalyzes the hydrolysis of phosphatidylinositol(4, 5)bisphosphate to generate two second messengers, diacylglycerol and inositol (1,4,5) triphosphate.
By analogy with the wild-type pathway, PLC-gamma is presumed to be phosphorylated by activated FGFR mutants, resulting in PLC-gamma activation, stimulation of phosphatidyl inositol hydrolysis and generation of two second messengers, diacylglycerol and inositol (1,4,5) P3.
Although it has not been rigourously established, there is some evidence that PLC-gamma signaling may be activated after autophosphorylation of some FGFR mutants, analagous to the wild type receptor (see for instance, Hart, 2000; Chen, 2005; Cha, 2008; di Martino, 2009; Gartside, 2009; Cross, 2000; Hatch, 2006). The extent to which each of the mutants activates this pathway and to which proliferation and tumorigenesis relies on PLC-gamma dependent signaling, remains to be more firmly established.
Fibroblast growth factor binding proteins (FGFBPs) are extracellular proteins that bind to FGFs and extract them from the extracellular matrix, thereby increasing their mitogenic potential (Wu et al, 1991; Tassi et al, 2001; Beer et al, 2005; reviewed in Abuharbeid et al, 2005). FGFBP1 has been shown to bind to FGF1, 2, 7, 10 and 22 by co-immunoprecipitation and/or competition assay (Tassi et al, 2001; Beer et al, 2005). Furthermore, it has been shown that stimulation of FGF7 along with FGFBP1 enhances the proliferation of FGFR2b-expressing cells (Beer et al, 2005). FGFBP expression is upregulated in some cancers and contributes to tumor growth and angiogenesis (reviewed in Abuharbeid et al, 2005).
Repression of FGFR2 exon IIIb splicing in mesenchymal cells depends on intronic splicing silencer (ISS) sequences upstream of exon IIIb as well as an exonic splicing element (ESE) within exon IIIb. These elements are bound by PTB1 and hnRNPA1, respectively, as part of a larger splicing complex, promoting the formation and expression of mature FGFR2c mRNA in mesenchymal cells (Carstens et al, 2000; Gil et al, 1991; Del Gatto et al, 1997; Del Gatto et al, 1999). For more detailed information on splicing and pre-mRNA maturation, please see the mRNA splicing pathway.
Expression of FGFR2 IIIb splice variant is characteristic of epithelial cells. A number of cis-acting elements have been identified in the FGFR2 pre-mRNA that are required for correct expression of the IIIb isoform and repression of the mesenchymal IIIc form (Muh et al, 2002; Hovhannisyan and Carstens, 2005; Hovhannisyan et al, 2006). These include the ISAR and ISE/ISS elements 1-3 in the region between exon 8 and exon 9 of the pre-mRNA. ESRP1 and ESRP2 are RNA-binding mRNA splicing factors that promote epithelial-specific IIIb splicing by binding to the ISE/ISS-3 sequence (Warzecha et al, 2009). A complex of RBFOX2, hnRNPH1 and hnRNPF may cooperate with the ESRP proteins to stimulate IIIb-specific splicing by binding to adjacent exonic GGG motifs (Baraniak et al, 2006; Mauger et al, 2008). This RBFOX2-hnRNP complex appears to compete with the IIIc-promoting trans-acting factor ASF/SF2 for binding to these exonic sites (Mauger et al, 2008). Other factors that appear to contribute to IIIb-specific splicing include hnRNPM, TIA1 and TIAL1, although their precise roles remain to be elucidated (Hovhannisyan and Carstens, 2007; Del Gatto-Konczak et al, 2000; Newman et al, 2006).
In epithelial cells, FGFR2 IIIb-specific alternative splicing is favoured by the binding of ESRP1 and 2, RBFOX2, TIA1 and TIAL1 to the nascent transcript. These proteins, in conjunction with other splicing factors, activate exon IIIb-specific splicing and repress exon IIIc-specific splicing (Warzecha et al, 2009; Baraniak et al, 2006; Mauger et al, 2008; Hovhannisyan and Carstens, 2007; Del Gatto et al, 2000).
In mesenchymal cells, FGFR2 IIIc exon splicing is favoured by the binding of PTB1 to intronic splice silencer (ISS) sequences 1 and 2 that flank the IIIb specific exon, and by the binding of hnRNPA1 to an exonic splicing silencer (ESS) within the IIIb specific exon (Del Gatto-Konczak et al, 1999; Carstens et al, 2000). Binding of these proteins to the nascent mRNA , which occurs in the context of a larger splicing complex, represses IIIb-specific alternative splicing and favours the formation of FGFR2 IIIc-specific mRNA.
A secreted truncated form of FGFR2 known as IIIa TM is produced and stable in a mouse model of Apert Syndrome. FGFR2 IIIa TM is formed from aberrant splicing of FGFR2 exon 7 (IIIa) into exon 10 (containing the transmembrane domain). In WT cells, this transcript is degraded by nonsense-mediated decay, but persists in the disease model by an unknown mechanism. FGFR IIIa TM modulates the binding of FGF1 to FGFR2 in vitro and negatively regulates FGFR2 signaling in vitro and in vivo (Wheldon et al, 2011).
FGFR2 fusions in cholangiocarcinoma and cancers of the breast, lung and thyroid have been shown to promote anchorage independent growth, cellular proliferation and tumorigenesis. In some cases, such as for FGFR2-AHCYL1 and FGFR2-BICC1 fusions in cholangiocarcinoma, these activities have been shown to depend on the FGFR2 kinase domain, suggesting that the fusions undergo autophosphorylation after oligomerization, as is the case for WT FGFR2. FGFR2 fusions, where tested, also show sensitivity to kinase inhibitors such as PD173074 and pazopanib (Arai et al, 2013; Wu et al, 2013; Seo et al, 2012; reviewed in Parker et al, 2014).
FGFR2 fusions have been identified in a number of cancers, including breast, thyroid, lung and cholangiocarcinoma (Wu et al, 2013; Seo et al, 2012; Arai et al, 2013; reviewed in Parker et al, 2014). Many of the 3' fusion partners contain dimerization domains, suggesting the fusion proteins may dimerize contstitutively independent of ligand binding, although this has not been explicitly demonstrated in all cases (Wu et al, 2013; reviewed in Parker et al, 2014).
By BIAcore assay, FGFR2 IIIa TM has been shown to bind FGF1, and in the presence of chip-bound FGFR2b or 2c, to form an FGF1-dependent heterodimer. In COS cells stimulated with FGF2, expression of FGFR IIIa TM abrogates FGF signaling and stabilizes the full length receptors at the cell surface. Consistent with this, in vivo expression of FGFR2 IIIa TM abrogates expression of the FGFR target gene MKP3. These data support the idea that FGFR2 IIIa TM inhibits FGFR signaling by binding and sequestering ligand and/or forming non-functional heterodimers with full-length receptors (Wheldon et al, 2011).
RAS nucleotide is stimulated downstream of activated FGFR2 in a p-PTPN11-dependent manner. The phosphatase activity of PTPN11 is required for activation of the RAS-MAP kinase pathway, although the mechanism for RAS pathway activation is not yet clear (Hadari et al, 1998; reviewed in Mohi et al, 2007; Gotoh et al, 2008).
In humans, the phosphorylated MNK1 kinase phosphorylates the adaptor protein Sprouty2 on Ser112 and Ser121, and also at some other serine and threonine residues. MNK1 appears not to form a complex with Sprouty2. Some of these (including the two main sites mentioned above) conform to the serine-containing consensus sites for phosphorylation by MNK1 kinase (K/R-X-X-S, R-X-S). It appears that serine phosphorylation is required to protect Sprouty2 from degradation.
In the absence of serine phosphorylation, phosphorylation of Tyr55 and subsequent binding to E3 ubiquitin ligase, CBL, is enhanced. Serine phosphorylation of Sprouty2 appears to stabilise the protein by interfering with its potential phosphorylation of Tyr55 (Sprouty2 appears to be a poor substrate for c-Src kinase) in response to growth factor stimulation.
In humans, the phosphorylated adaptor protein Sprouty2 is ubiquitinated by the E3 ubiquitin ligase CBL, marking it for degradation by the 26S proteasome.
Try the New WikiPathways
View approved pathways at the new wikipathways.org.Quality Tags
Ontology Terms
Bibliography
History
External references
DataNodes
overexpressed FGFR2
dimersligand-independent
mutantsmutants with enhanced kinase
activityhomodimer bound to
FGFmutants with enhanced ligand
bindinghomodimer bound to
FGFmutants with enhanced
ligand-bindingligand-independent
mutant dimersligand-independent
mutantswith enhanced
kinase activityenhanced kinase
activityTM:FGF1,2:FGFR2b,
FGFR2cmutant-binding
FGFs:FP-1039with enhanced ligand-binding
bound to FGFsenhanced ligand
bindingwith enhanced ligand-binding
bound to FGFsenhanced ligand
binding(A:C):S112/S115
p-SPRY2The importance of the RAS/RAF MAPK cascade is highlighted by the fact that components of this pathway are mutated with high frequency in a large number of human cancers. Activating mutations in RAS are found in approximately one third of human cancers, while ~8% of tumors express an activated form of BRAF (Roberts and Der, 2007; Davies et al, 2002; Cantwell-Dorris et al, 2011).
inhibitors of
overexpressed FGFR2inhibitors of FGFR2
mutantspre-FGFR2 mRNA:CBC
complexAnnotated Interactions
overexpressed FGFR2
dimersligand-independent
mutantsmutants with enhanced kinase
activityhomodimer bound to
FGFmutants with enhanced ligand
bindinghomodimer bound to
FGFmutants with enhanced
ligand-bindingligand-independent
mutant dimersligand-independent
mutant dimersligand-independent
mutant dimersligand-independent
mutantswith enhanced
kinase activitywith enhanced
kinase activitywith enhanced
kinase activityenhanced kinase
activityTM:FGF1,2:FGFR2b,
FGFR2cmutant-binding
FGFs:FP-1039with enhanced ligand-binding
bound to FGFswith enhanced ligand-binding
bound to FGFswith enhanced ligand-binding
bound to FGFsenhanced ligand
bindingwith enhanced ligand-binding
bound to FGFswith enhanced ligand-binding
bound to FGFswith enhanced ligand-binding
bound to FGFsenhanced ligand
binding(A:C):S112/S115
p-SPRY2(A:C):S112/S115
p-SPRY2SPRY2 has also been shown to be phosphorylated at multiple tyrosine residues in its C-terminal in response to FGF, but not EGF, stimulation. This phosphorylation, in particular at residue 227, is thought to augment the ability of SPRY2 to inhibit FGF signaling through the MAPK cascade, although the mechanism remains to be elucidated.
FGFR2 amplifications identified in 4% of triple negative breast cancers have also been shown to be constitutively active and to have elevated levels of phosphorylated FRS2 in the absence of ligand. Consistent with this, shRNA knockdown or chemical inhibition restricts proliferation and induces apoptosis in these cells (Kunii, 2008; Turner, 2010)
The IgII and IgIII domains and the intervening linker of the FGF receptor constitute a binding site for FGFs (Chellaiah, 1999; Stauber, 2000; Plotnikov, 1999). The epithelial isoform FGFR2b binds only to mesenchymally expressed ligands including FGF7 and FGF10 and does not respond to epithelial ligands FGF2, 4, 6, 8 and 9 (Ornitz, 1996). Introduction of the P252W and P252R mutations into FGFR2b allows the aberrant binding and activation by the epithelially expressed ligands FGF 2, 6 and 9, establishing an autocrine signaling loop in epithelial cells. These mutations also increase the binding affinity for the receptor's normal mesenchymal ligands 2- to 8-fold (Yu, 2000; Ibrahimi, 2004b). Based on biochemical and crystal studies, the mutations in the IgII-IgIII linker region are predicted to alter the hydrogen bonding network in this region and may change the conformation and thus the ligand-binding properties of the mutant receptors (Stauber, 2000).
As further support of this notion, activating point mutations in the kinase domain of FGFR2 have also been identified in endometrial, uterine and cervical cancers (Pollock, 2007; Dutt, 2008), and in some cases have been shown to have enhanced kinase activity and to support anchorage-independent growth in NIH 3T3 cells (Dutt, 2008). Knockdown of N549K with short hairpin RNAs or the pan-FGFR inhibitor PD170734 inhibits cell survival in endometrial cancer cells lines, suggesting that FGFR2 activity is required for tumor cell survival (Dutt, 2008; Byron, 2008). Kinase-domain mutants show elevated levels of activity relative to the wild-type even in the absence of receptor phosphorylation, and although their kinase activity is further enhanced upon trans-autophosphorylation, the extent of this is less than that seen in the wild-type, suggesting that the mutant alleles are capable of of supporting ligand-independent activation (Chen, 2007)
Characterization of FGFR2 proteins containing somatic mutations at these residues support the notion that they have elevated levels of kinase activity. FRS2 is constitutively phosphorylated in the FGFR2 N549K kinase mutant identified in endometrial tumors and knockdown of N549K with short hairpin RNAs or the pan-FGFR inhibitor PD170734 inhibits cell survival in endometrial cancer cells lines, suggesting that FGFR2 activity is required for tumor cell survival. FGFR2 knockdown also results in a significant decrease in the levels of phosphorylated Erk1/2 (Dutt, 2008; Byron, 2008; Pollock, 2007). Crystal structures of FGFR2 kinase mutants N549H and K650N show that the mutations disengage an 'auto-inhibitory brake' on the kinase domain of the receptor. Biochemically, the FGFR2 N549K and K660E mutants show elevated kinase activity relative to the unphosphorylated wild-type protein and have increased activity towards peptide substrates; this activity is stimulated upon receptor phosphorylation, but to a lesser extent than seen with the wild-type receptor (Chen, 2007).
In the absence of serine phosphorylation, phosphorylation of Tyr55 and subsequent binding to E3 ubiquitin ligase, CBL, is enhanced. Serine phosphorylation of Sprouty2 appears to stabilise the protein by interfering with its potential phosphorylation of Tyr55 (Sprouty2 appears to be a poor substrate for c-Src kinase) in response to growth factor stimulation.
inhibitors of
overexpressed FGFR2inhibitors of FGFR2
mutantspre-FGFR2 mRNA:CBC
complexpre-FGFR2 mRNA:CBC
complexpre-FGFR2 mRNA:CBC
complexpre-FGFR2 mRNA:CBC
complexpre-FGFR2 mRNA:CBC
complex