A naturally occurring secreted form of fibroblast growth factor (FGF) receptor 1 binds basic FGF in preference over acidic FGF.

Alternatively spliced variants of fibroblast growth factor receptor 1 mRNA are predicted to encode secreted forms and membrane-bound forms of receptors. The predicted amino acid sequences of these receptor variants differ in a portion of the extracellular region. In this study, we characterized the function of one of these splice variants which was predicted by its cDNA to be a secreted FGF receptor. We expressed this secreted form of the human FGFR1 (sFGFR1) in Chinese hamster ovary cells. The sFGFR1 protein oligomerized upon ligand binding. Surprisingly, the sFGFR1 preferentially bound basic FGF over acidic FGF. In cross-linking experiments, the sFGFR1 showed higher binding affinity for basic FGF (Kd approximately 30 nM) than for acidic FGF (Kd greater than 300 nM). These results suggest that this secreted form of FGF receptor has an unusual ligand binding specificity that may be important for its biological role in vivo.