Agonist-induced formation of FGFR1 homodimers and signaling differ among members of the FGF family

Abstract

a b s t r a c tFibroblast growth factor receptor 1 (FGFR1) is known to be activated by homodimerization in the presence of both the FGF agonist ligand and heparan sulfate glycosaminoglycan. FGFR1 homodimers in turn trigger a variety of downstream signaling cascades via autophosphorylation of tyrosine residues in the cytoplasmic domain of FGFR1. By means of Bioluminescence Energy Resonance Transfer (BRET) as a sign of FGFR1 homodimerization, we evaluated in HEK293T cells the effects of all known FGF agonist ligands on homodimer formation. A significant correlation between BRET 2 signaling and ERK1/2 phosphorylation was observed, leading to a further characterization of the binding and signaling properties of the FGF subfamilies. FGF agonist ligand-FGFR1 binding interactions appear as the main mechanism for the control of FGFR1 homodimerization and MAPK signaling which demonstrated a high correlation. The bioinformatic analysis demonstrates the interface of the two pro-triplets SSS (Ser-Ser-Ser) and YGS (Tyr-Gly-Ser) located in the extracellular and intracellular domain of the FGFR1. These pro-triplets are postulated participate in the FGFR1 homodimerization interface interaction. The findings also reveal that FGF agonist ligands within the same subfamily of the FGF gene family produced similar increases in FGFR1 homodimer formation and MAPK signaling. Thus, the evolutionary relationship within this gene family appears to have a distinct functional relevance.

On the Origin of the Triplet Puzzle of Homologies in Receptor Heteromers: Immunoglobulin Triplets in Different Types of Receptors

“…In fact, indications exist for their location in this interface (BorrotoEscuela et al 2011a, b;Romero-Fernandez et al 2011; see also Figs. S1, S2 of the Electronic Supplementary Material) which according to the analysis of the present work can involve GPCR-GPCR, GPCR-RTK, and RTK-RTK heteromers as well as GluR1-cytokine receptor heteromers.…”

“…The most important role may have the triplet homology SSS (Ser-Ser-Ser) which is not only located at the antigenbinding site of both heavy and light variable chains of IgG and IgM but also is common in GPCRs and found also in RTKs and in the cytokine receptor, interferon-γ receptor IFGR1. Furthermore, the SSS triplet homology may exist in the receptor interface of the 5HT1A-FGFR1 heteromer and of the FGFR1 homomer (Borroto-Escuela et al 2011a, b;Romero-Fernandez et al 2011). The SSS triplet appears to be observed first in frogs to continue into vertebrates including humans as shown in GABAB1 (Fig.…”

“…For example, the triplet of amino acid residues SSS (Ser-Ser-Ser) appears as a homology in four receptor heteromers-GABAB1-mGluR1, GABAB1-CXCR4, KOP-CCR5, and IL4R-IL13R-but does not appear as a homology in any of known non-heteromers (GABAB2-A2A, A2A-D1, A1-D2, NTS1-D1, TSHR-D2, KOP-MOP, and CD4-D2; see Tarakanov and Fuxe 2010). According to the recent biochemical studies (Borroto-Escuela et al 2011a, b;Romero-Fernandez et al 2011), such triplets exist in the interacting domains forming the receptor interface and may be crucial for the formation of heteromers. This bioinformatic analysis has been continued in this work indicating for the first time that several triplet homologies of GABAB1 receptor as well as other G-protein-coupled receptor (GPCR) heteromers and GPCR-receptor tyrosine kinase (RTK) heteromers may use triplets from the variable chains of immunoglobulins (Ig), known to be involved in the recognition of a special epitope of an antigen.…”

On the origin of the triplet puzzle of homologies in receptor heteromers: toll-like receptor triplets in different types of receptors

“…These observations strengthen the hypothesis that these triplet homologies participate in recognizing the other receptor protomer of the heteromer via postulated 'guideand-clasp' interactions in the receptor interface Fuxe 2010, 2011). In fact, indications exist for their location in this interface(Borroto-Escuela et al 2011a, b;Romero-Fernandez et al 2011) which according to the analysis of the present work can involve GPCR-GPCR heteromers.…”

“…For example, the triplet of amino acid residues LLE (Leu-Leu-Glu) appears as a homology in five receptor heteromers: TLR1-TLR2, TLR2-TLR6, GABAB1-GA-BAB2, GABAB1-mGluR1, and GABAB1-CXCR4, but does not appear as a homology in any of known non-heteromers (GABAB2-A2A, A2A-D1, A1-D2, NTSR1-D1, TSHR-D2, KOP-MOP, and CD4-D2; see Tarakanov and Fuxe 2010). According to recent biochemical studies (Borroto-Escuela et al 2011a, b;Romero-Fernandez et al 2011), such triplets exist in the interacting domains forming the receptor interface and may be crucial for the formation of heteromers. This bioinformatic analysis has been continued in this work indicating for the first time that several triplet homologies of the GABAB1 receptor subunit of the GABAB receptor as well as protomers of G-protein coupled receptor (GPCR) heteromers and GPCR-RTK (receptor tyrosine kinase) heteromers may use triplets from TLRs.…”