Deciphering the mechanism behind Fibroblast Growth Factor (FGF) induced biphasic signal-response profiles

Abstract

BackgroundThe Fibroblast Growth Factor (FGF) pathway is driving various aspects of cellular responses in both normal and malignant cells. One interesting characteristic of this pathway is the biphasic nature of the cellular response to some FGF ligands like FGF2. Specifically, it has been shown that phenotypic behaviors controlled by FGF signaling, like migration and growth, reach maximal levels in response to intermediate concentrations, while high levels of FGF2 elicit weak responses. The mechanisms leading to the observed biphasic response remains unexplained.ResultsA combination of experiments and computational modeling was used to understand the mechanism behind the observed biphasic signaling responses. FGF signaling involves a tertiary surface interaction that we captured with a computational model based on Ordinary Differential Equations (ODEs). It accounts for FGF2 binding to FGF receptors (FGFRs) and heparan sulfate glycosaminoglycans (HSGAGs), followed by receptor-phosphorylation, activation of the FRS2 adapter protein and the Ras-Raf signaling cascade. Quantitative protein assays were used to measure the dynamics of phosphorylated ERK (pERK) in response to a wide range of FGF2 ligand concentrations on a fine-grained time scale for the squamous cell lung cancer cell line H1703. We developed a novel approach combining Particle Swarm Optimization (PSO) and feature-based constraints in the objective function to calibrate the computational model to the experimental data. The model is validated using a series of extracellular and intracellular perturbation experiments. We demonstrate that in silico model predictions are in accordance with the observed in vitro results.ConclusionsUsing a combined approach of computational modeling and experiments we found that competition between binding of the ligand FGF2 to HSGAG and FGF receptor leads to the biphasic response. At low to intermediate concentrations of FGF2 there are sufficient free FGF receptors available for the FGF2-HSGAG complex to enable the formation of the trimeric signaling unit. At high ligand concentrations the ligand binding sites of the receptor become saturated and the trimeric signaling unit cannot be formed. This insight into the pathway is an important consideration for the pharmacological inhibition of this pathway.

Dose-dependent functions of fibroblast growth factor 9 regulate the fate of murine XY primordial germ cells†

“…A high concentration of FGF maintained a prolonged ERK1/2 activity, whereas a lower concentration of FGF shortened the activation period of ERK1/2 signaling, inducing cell differentiation or proliferation, respectively [47]. It is not fully understood how these dose-dependent mechanisms function, but it is suggested that competition between binding of the FGF ligand to heparan sulfate glycosaminoglycans and FGF receptors leads to different responses in cells [48]. Nevertheless, it is clear that different FGF concentrations can differentially regulate intracellular signaling and, thus, cellular responses to this growth factor, and that this has important implications for understanding how quantitative and temporal changes in FGF concentrations can influence cell proliferation, migration, survival, and differentiation during embryo development, including the regulation of XY PGC proliferation and/or differentiation.…”

The impact of tumor receptor heterogeneity on the response to anti-angiogenic cancer treatment

“…To date, several multiscale modeling studies have linked PK/PD models with the downstream signaling and cell-surface reactions. 63,64 We can implement a similar approach, combining our model with downstream signaling models [65][66][67] to enable broader application of our model. In addition, anti-angiogenic therapy is usually used in combination with chemotherapy in the clinic.…”

Systems biology of the microvasculature

“…FGFR signaling is complicated by the existence of multiple FGF ligands and the requirement for cell surface heparin sulfate proteoglycans (HSPGs) to stabilize FGF ligand-receptor complexes. A variety of computational models have been developed to study FGF ligand-receptor binding and regulation by HSPGs in vitro 72–75 , showing that HSPGs able to form active FGF2-HSPG-FGFR signaling complexes are required for effective downstream signaling 76 . FGF binding to EC receptors and to the vascular basement membrane under physiological flow conditions has also been simulated, both in vivo 77, 78 and in the context of a bioreactor 79, 80 .…”