Modulation of scatter factor/hepatocyte growth factor activity by cell-substratum adhesion

Scatter factor/hepatocyte growth factor (SF/HGF) is a multifunctional growth and motility factor whose activities vary with cell type. Here, the composition of the substratum was found to profoundly alter the scattering activities of SF/HGF, but not its mitogenetic effects, in MDCK cells. Whereas enhancement of DNA synthesis and induction of cell flattening by SF/HGF were independent of substratum composition (i.e. occurred on both fibronectin and vitronectin surfaces), colony dispersion as a result of cell separation fails to occur or is markedly reduced on surfaces where vitronectin is the major adhesive ligand. Prolonged exposure of non-scattering cultures to SF/HGF resulted in cells at colony margins producing long protrusions, which indicate that the motility of these cells is stimulated but 'frustrated' by the lack of breakdown of cell-cell adhesion. Scattering therefore appears to comprise two major components: increased motility and breakdown of cell-cell adhesion. The pathway leading to the breakdown of cell-cell contacts is modulated by downstream signals from extracellular matrix receptors. When cultured on immobilised fibronectin, vitronectin or a surface containing both, colony dissociation correlates with the presence of fibronectin, suggesting that positive signals from fibronectin receptors are required for SF/HGF-induced cell separation. Comparison of the findings in this study with those of a recent report on the modulation of SF/HGF-induced tubulogenesis by ECM (Santos, O. F. P. and Nigam, S. K. (1993) Dev. Biol. 160, 293-302), where vitronectin in type-1 collagen gels alters the pattern of SF/HGF-induced MDCK tubule formation from highly branched to long and unbranched, suggests that cell motility enhancement leads to tubule formation whereas the breakdown of cell-cell adhesion is required for tubule branching.