Ligand bias underlies differential signaling of multiple FGFs via FGFR1

Abstract

FGFR1 signals differently in response to the FGF ligands FGF4, FGF8 and FGF9, but the mechanism behind the differential ligand recognition is poorly understood. Here, we use biophysical tools to quantify multiple aspects of FGFR1 signaling in response to the three FGFs: potency, efficacy, ligand-induced oligomerization and downregulation, and conformation of the active FGFR1 dimers. We show that FGF4, FGF8, and FGF9 are biased ligands, and that bias can explain differences in FGF8 and FGF9-mediated cellular responses. Our data suggest that ligand bias arises due to structural differences in the ligand-bound FGFR1 dimers, which impact the interactions of the FGFR1 transmembrane helices, leading to differential recruitment and activation of the downstream signaling adaptor FRS2. This study expands the mechanistic understanding of FGF signaling during development and brings the poorly understood concept of receptor tyrosine kinase ligand bias into the spotlight.

Quantitation of FGFR3 signaling via GRB2 recruitment on micropatterned surfaces

“…Fibroblast growth factor receptors (FGFRs) are a subclass of RTKs and comprise 4 members (Farrell and Breeze 2018) that are evolutionary highly conserved across multi-cellular species (Rebscher et al 2009; Lemmon and Schlessinger 2010). FGFRs are activated by binding of their ligand fgf, which typically involves receptor dimerization (Ornitz and Itoh 2015), although formation of larger clusters has been observed for FGFR1 in a ligand-specific manner suggesting that the FGFR oligomerization state mediates cellular responses to different ligands (Karl et al 2022). Activation of the receptor leads to multiple trans-autophosphorylation events of several tyrosine residues in the tyrosine kinase domain (residues Y577, Y579, Y647, Y648 and Y760 in FGFR3) (Ornitz and Itoh 2015).…”

Measurement of FGFR3 signaling at the cell membrane via total internal reflection fluorescence microscopy to compare the activation of FGFR3 mutants

“…Fibroblast growth factor receptors (FGFRs) are a subclass of RTKs and comprise four members ( 2 ) that are evolutionary highly conserved across multicellular species ( 1 , 3 ). FGFRs are activated by binding of their ligand fgf, which typically involves receptor dimerization ( 4 ), although formation of larger clusters has been observed for FGFR1 in a ligand-specific manner, suggesting that the FGFR oligomerization state mediates cellular responses to different ligands ( 5 ). Activation of the receptor leads to multiple transautophosphorylation events of several tyrosine residues in the tyrosine kinase domain (residues Y577, Y579, Y647, Y648, and Y760 in FGFR3) ( 4 ).…”