FGF-2/fibroblast growth factor receptor/heparin-like glycosaminoglycan interactions: a compensation model for FGF-2 signaling

Heparin-like glycosaminoglycans (HLGAGs) play a central role in the biologi cal activity and signaling behavior of basic fibroblast growth factor (FGF- P), Recent studies, however, indicate that FGF-2 may be able to signal in t he absence of HLGAG, raising the question of the nature of the role of HLGA G in FGF-2 signaling, In this study, we present a conceptual framework for FGF-2 signaling and derive a simple model from it that describes signaling via both HLGAG-independent and HLGAG-dependent pathways. The model is valid ated with F32 cell proliferation data using wild-type FGF-S, heparin bindin g mutants (K26A, K119A/R120A, K125A), and receptor binding mutants (Y103A, Y111A/W114A). In addition, this model can predict the cellular response of FGF-2 and its mutants as a function of FGF-2 and HLGAG concentration based on experimentally determined thermodynamic parameters. We show that FGF-2-m ediated cellular response is a function of both FGF-2 and HLGAG concentrati ons and that a reduction of one of the components can be compensated for by an increase in the other to achieve the same measure of cellular response, Analysis of the mutant FGF-S molecules show that reduction in heparin bind ing interactions and primary receptor site binding interactions can also be compensated for in the same manner. These results suggest a molecular mech anism that could be used by cells in physiological systems to modulate the FGF-2-mediated cellular response by controlling HLGAG expression.-Padera, R ., Venkataraman, G., Berry, D., Godavarti, R., Sasisekharan, R. FGF-2/fibro blast growth factor receptor/heparin-like glycosaminoglycan interactions: a compensation model for FGF-2 signaling.