CONSERVATION OF LIGAND SPECIFICITY BETWEEN THE MAMMALIAN AND AMPHIBIAN FIBROBLAST GROWTH-FACTOR RECEPTORS

We have previously cloned and sequenced a newt keratinocyte growth fac tor 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 I-125-fibroblast growth fac tor-1 (FGF-1) and I-125-FGF-7 but not I-125-FGF-2, indistinguishable f rom the human KGFR. Scatchard analysis and cross-linking studies furth er 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 hum an 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-transfec tion of MM14 cells with either a human or newt KGFR expression constru ct conferred a response to FGF-7 as determined by a human alpha-cardia c actin/ luciferase reporter construct. The response to FGF-7 was simi lar to the endogenous FGF response as FGF-7 prevented MM14 myoblasts f rom undergoing terminal differentiation. Thus, both the human and the newt KGFRs transduce signals similar to those transduced via the endog enous mouse FGFR1. Together these data indicate that this newly isolat ed newt KGFR is a functional receptor as it binds two FGF family membe rs with high affinity and mediates signaling in skeletal muscle myobla sts. Because the binding pattern of the newt KGFR is similar to the pa ttern observed for its mammalian counterpart, it emphasizes the strict conservation that this ligand/receptor system has undergone through e volution.