FGFR1 Interaction with Co-Receptor Klotho-Beta at the Plasma Membrane

Abstract

FGF21/FGFR1 signalling modulates the survival and glucose sensitivity of fat and liver cells, properties that make this signalling pathway a potential target in the treatment of diabetes. The majority of FGFs interact with heparin proteoglycans in the matrix for presentation to high-affinity receptors such as FGFR1. In contrast, FGF21 exhibits negligible affinity for heparin. To activate FGFR1, FGF21 requires expression of an alternative co-receptor, Klotho-beta (KLB). To study the molecular interaction between FGFR1 and KLB at the cell membrane, we created fluorescent protein-tagged constructs of KLB and FGFR1. By using fluorescence recovery after photobleaching (FRAP), we show that KLB has a lower diffusion coefficient and mobile fraction than FGFR1. Subsequent addition of lactose, an inhibitor of non-specific galactoside binding in the matrix, increased mobility of KLB with no effect on FGFR1. To determine whether the addition of FGF21 induces FGFR1/KLB association, we are presently examining whether FGFR1 mobility slows to KLB levels in the presence of FGF21. We are also measuring homo-Forster Resonance Energy Transfer (homoFRET) on a Total Internal Refection Fluorescence (TIRF) microscope to reconcile these results by examining the oligomeric state of KLB and FGFR1 at the plasma membrane. Overall, these studies will determine whether FGFR1 associates with KLB in the presence of FGF21 revealing important mechanistic information of a novel endocrine factor.