Conservation of ligand specificity between the mammalian and amphibian fibroblast growth factor receptors.

We have previously cloned and sequenced a newt keratinocyte growth factor receptor (KGFR) cDNA which exhibited a unique spatial and temporal expression pattern in the regenerating newt limb. In this report, we further characterize the biochemical and functional properties of this newt KGFR. A stable Chinese hamster ovary transfectant overexpressing the newt KGFR was capable of binding both 125I-fibroblast growth factor-1 (FGF-1) and 125I-FGF-7 but not 125I-FGF-2, indistinguishable from the human KGFR. Scatchard analysis and cross-linking studies further support the conclusion that FGF-1 and FGF-7 are the ligands for the newt KGFR. In addition to their ability to bind to FGFs, both the human and the newt KGFR are also capable of repressing differentiation in mouse MM14 myoblasts. MM14 cells express FGFR1 and are repressed from differentiation by FGF-1, FGF-2, and FGF-4 but not FGF-7. Co-transfection of MM14 cells with either a human or newt KGFR expression construct conferred a response to FGF-7 as determined by a human alpha-cardiac actin/luciferase reporter construct. The response to FGF-7 was similar to the endogenous FGF response as FGF-7 prevented MM14 myoblasts from undergoing terminal differentiation. Thus, both the human and the newt KGFRs transduce signals similar to those transduced via the endogenous mouse FGFR1. Together these data indicate that this newly isolated newt KGFR is a functional receptor as it binds two FGF family members with high affinity and mediates signaling in skeletal muscle myoblasts. Because the binding pattern of the newt KGFR is similar to the pattern observed for its mammalian counterpart, it emphasizes the strict conservation that this ligand/receptor system has undergone through evolution.