Characterization of the receptor for keratinocyte growth factor: Evidence for multiple fibroblast growth factor receptors

Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor (FGF) family. KGF exhibits potent mitogenic activity for a variety of epithelial cell types but is distinct from other known FGFs in that it is not mitogenic for fibroblasts or endothelial cells. We report saturable specific binding of ¹²⁵I-KGF to surface receptors on intact Balb/MK mouse epidermal keratinocytes. ¹²⁵I-KGF binding was competed efficiently by acidic FGF (aFGF) but with 20-fold lower efficiency by basic FGF (bFGF). The pattern of ¹²⁵I-acidic FGF binding and competition on Balb/MK keratinocytes and NIH/3T3 fibroblasts suggests that these cell types possess related but distinct FGF receptors. Scatchard analysis of ¹²⁵I-KGF binding suggested major and minor high affinity receptor components (K_D = 400 and 25 pM, respectively) as well as a third high capacity/low affinity heparin-like component. Covalent affinity cross-linking of ¹²⁵I-KGF to its receptor on Balb/MK cells revealed two species of 115 and 140 kDa. KGF also stimulated the rapid tyrosine phosphorylation of a 90-kDa protein in Balb/MK cells but not in NIH/3T3 fibroblasts. Together these results indicate that Balb/MK keratinocytes possess high affinity KGF receptors to which the FGFs may also bind. However, these receptors are distinct from the receptor(s) for aFGF and bFGF on NIH/3T3 fibroblasts, which fail to interact with KGF.