Hepatocyte growth factor scatter factor has distinct classes of binding site in heparan sulfate from mammary cells

Hepatocyte growth factor/scatter factor (HGF/SF) is a heparan sulfate (HS)-binding growth factor and morphogen for mammary epithelial cells that is produced by mammary stromal fibroblasts. HS chains, purified as peptidoglycans from a panel of cell lines representative of the ductal epithelial cell (Huma 123), the myoepithelial cell (Huma 109), the stromal fibroblast (Rama 27), and malignant mammary epithelial cells (MCF-7 and ZR-75), were used in a biosensor-based assay to identify the classes of HGF/SF-binding sites in the polysaccharide chains. At least three distinct binding sites were identified. One site exhibits fast association and fast dissociation kinetics [k(ass) (1.4-7.7) x 10(6) M-1 s(-1); k(diss) 0.0032-0.0096 s(-1)] and is present on the HS from benign Huma 123 epithelial cells, Huma 109 myoepithelial-like cells, and ZR-75 malignant cells. The second binding site, found on HS from the malignant MCF-7 cells, has slower HGF/SF-binding kinetics (k(ass) 0.20 x 10(6) M-1 s(-1); k(diss) 0.00055 g(-1)). The third binding site possesses fast association and slow dissociation kinetics (k(ass); 1.1 x 10(6) M-1 s(-1);k(diss) 0.00020 s(-1)) and was found on the HS isolated from the culture medium of the Huma 123 benign epithelial cells. The first and second binding sites have a similar K-d, 1-3 nM, while the third binding site has a considerably higher affinity for HGF/SF (K-d 200 pM). The three binding sites seem to be mutually exclusive, since each sample of HS possessed just one of the sites.