title: Differential specificity of endocrine FGF19 and FGF21 to FGFR1 and FGFR4 in complex with KLB.
abstract: BACKGROUND
  Recent studies suggest that betaKlotho (KLB) and endocrine FGF19 and FGF21 redirect FGFR signaling to regulation of metabolic homeostasis and suppression of obesity and diabetes. However, the identity of the predominant metabolic tissue in which a major FGFR-KLB resides that critically mediates the differential actions and metabolism effects of FGF19 and FGF21 remain unclear.
  
  
  RESULTS
  We determined the receptor and tissue specificity of FGF21 in comparison to FGF19 by using direct, sensitive and quantitative binding kinetics, and downstream signal transduction and expression of early response gene upon administration of FGF19 and FGF21 in mice. We found that FGF21 binds FGFR1 with much higher affinity than FGFR4 in presence of KLB; while FGF19 binds both FGFR1 and FGFR4 in presence of KLB with comparable affinity. The interaction of FGF21 with FGFR4-KLB is very weak even at high concentration and could be negligible at physiological concentration. Both FGF19 and FGF21 but not FGF1 exhibit binding affinity to KLB. The binding of FGF1 is dependent on where FGFRs are present. Both FGF19 and FGF21 are unable to displace the FGF1 binding, and conversely FGF1 cannot displace FGF19 and FGF21 binding. These results indicate that KLB is an indispensable mediator for the binding of FGF19 and FGF21 to FGFRs that is not required for FGF1. Although FGF19 can predominantly activate the responses of the liver and to a less extent the adipose tissue, FGF21 can do so significantly only in the adipose tissue and adipocytes. Among several metabolic and endocrine tissues, the response of adipose tissue to FGF21 is predominant, and can be blunted by the ablation of KLB or FGFR1.
  
  
  CONCLUSIONS
  Our results indicate that unlike FGF19, FGF21 is unable to bind FGFR4-KLB complex with affinity comparable to FGFR1-KLB, and therefore, at physiological concentration less likely to directly and significantly target the liver where FGFR4-KLB predominantly resides. However, both FGF21 and FGF19 have the potential to activate responses of primarily the adipose tissue where FGFR1-KLB resides.
authors.affiliation: Center for Cancer and Stem Cell Biology, Institute of Biosciences and Technology, Texas A&M Health Science Center, Houston, Texas, United States of America.
authors.forename: Chaofeng
authors.initials: C
authors.lastname: Yang
authors.forename: Chengliu
authors.initials: C
authors.lastname: Jin
authors.forename: Xiaokun
authors.initials: X
authors.lastname: Li
authors.forename: Fen
authors.initials: F
authors.lastname: Wang
authors.forename: Wallace L
authors.initials: WL
authors.lastname: McKeehan
authors.forename: Yongde
authors.initials: Y
authors.lastname: Luo
mesh_terms: D000273:Adipose Tissue; D000818:Animals; D045744:Cell Line, Tumor; D003920:Diabetes Mellitus / Q000235:genetics / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000090265:Klotho Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009765:Obesity / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D051496:Receptor, Fibroblast Growth Factor, Type 1 / Q000235:genetics / Q000378:metabolism*; D051499:Receptor, Fibroblast Growth Factor, Type 4 / Q000235:genetics / Q000378:metabolism*
chemical_list: C117476:FGF19 protein, human; C418622:Klb protein, mouse; D008565:Membrane Proteins; D046912:Multiprotein Complexes; C108526:fibroblast growth factor 15, mouse; C414620:fibroblast growth factor 21; D005346:Fibroblast Growth Factors; C496348:FGFR1 protein, human; C496371:FGFR4 protein, human; C496349:Fgfr1 protein, mouse; C496372:Fgfr4 protein, mouse; D051496:Receptor, Fibroblast Growth Factor, Type 1; D051499:Receptor, Fibroblast Growth Factor, Type 4; D000090265:Klotho Proteins