Keratinocyte growth factor (KGF) is a member of the fibroblast growth factor (FGF) family. FGFs are also know as heparin-binding growth factors because they bind to heparin and their ability to bind and activate their receptors is modulated by heparin. Suggestive of a paracrine effector, KGF is produced by cells of mesenchymal origin but is active primarily, if not exclusively on epithelial cells. KGF is onvolved in a variety of physiological and pathological processes including proliferation, differentiation, wound healing, cytoprotection, and inflammatory bowel disease. To explore the role of heparin in KGF signaling, nine peptides spanning defined motifs in the predicted structure of KGF were synthesized, and their heparin and receptor binding properties were analyzed. Peptides corresponding to the amino and carboxy termini bound heparin, and one peptide bound heparin with nearly the same affinity as KGF. Competitive binding studies showed that this peptide along with two other overlapping peptides effectively competed with KGF for binding to the KGF receptor. Two of these three peptides was also selectively recognized by a neutralizing monoclonal antibody against KGF only in the presence of heparin. Together these data suggest that within the resolution of the methods used, the sites for heparin and receptor binding both reside in the amino and carboxy termini of KGF, which are spatially juxtaposed in the predicted three dimensional structure of this molecule. Hepatocyte growth factor (HGF) is a secreted, heparin-binding polypeptide that stimulates the proliferation, migration, and differentiation of a wide array of cellular targets including hepatocytes, various epithelial cells, melanocytes, endothelial and hematopoietic cells. Multiple mRNA species transcribed from a single HGF gene encode at least three distinct proteins: the full-length HGF molecule and two truncated HGF isoforms known as NK1 and NK2, which consist of the N-terminal domain (N) linked in tandem with the first one (K1) or two (K1+K2) kringle domains, respectively. Both truncated isoforms bind directly to the HGF receptor (c-Met), and both retain some degree of scatter activity. We have thoroughly characterized the biological and biophysical properties of NK1, NK2, as well as there components N and K1 expressed separately. NK1 retains almost all of the mitogenic potency of full-length HGF. N domain retains the heparin binding properties of full- length HGF, mediates heparin-stimulated ligand oligomerization, but has little mitogenic activity. In contrast, the K1 domain does not bind heparin, but at concentrations of 30 nM or more stimulates DNA synthesis and MAP kinase activity in HGF- responsive cells. These results suggest that structurally distinct domains of HGF are the primary mediators of heparin binding and receptor activation. The 3-dimensional solution structure of N is now being investigated by NMR spectroscopy. Our long term goals include solving the structure of NK1 using NMR, as a first step toward high resolution mapping of the HGF receptor binding site, and defining the structural basis by which heparin proteoglycan promotes ligand-receptor interaction and receptor activation.
