Inhibition of junction assembly in cultured epithelial cells by hepatocyte growth factor/scatter factor is concomitant with increased stability and altered phosphorylation of the soluble junctional molecules.

Hepatocyte growth factor/scatter factor (HGF/SF) is a mesenchymally derived glycoprotein with a strong scattering effect on epithelial cells. A receptor tyrosine kinase encoded by the met proto-oncogene has been identified as the cellular receptor for HGF/SF. Following stimulation with HGF/SF, cell scattering occurs concurrent with decreased cell-cell adhesion and disassembly of junctional components. In culture, junction formation is cell-cell contact dependent and can be regulated by modulating the Ca2+ concentrations of the growth media. Decreasing the Ca2+ concentrations below 50 microM causes rapid disassembly of junctions, whereas increasing the Ca2+ concentrations to 1.8 mM induces cell-cell contact and junction assembly. Although associated with decreased cell-cell adhesion and disassembly of the junctional complex, HGF/SF-induced scattering occurs under high extracellular Ca2+ concentrations. To gain insight into the mechanisms of HGF/SF-induced scattering of epithelial cells, we have studied the effect(s) of HGF/SF on junction assembly by examining the solubility, stability, phosphorylation, and subcellular localization of the major components of the adhering junctions, plakoglobin (Pg) and E-cadherin, in Madin-Darby canine kidney (MDCK) epithelial cells and in a MDCK cell line expressing an exogenous chimeric met receptor (CSF-MET) that scatters in response to colony-stimulating factor 1 (CSF-1). The results have shown that in HGF/SF-stimulated MDCK cells, adhering junctions were not assembled upon induction of cell-cell contact. Immunofluorescence analyses showed that larger amounts of Pg and E-cadherin were Triton X-100 extractable, and more significantly, these proteins were homogeneously distributed along the membrane and were not concentrated at the areas of cell-cell contact. Similar results were obtained for CSF-MET expressing MDCK cells in response to CSF-1. In contrast, none of the above effects were detected in MDCK cells expressing a mutant CSF-MET chimera containing a phenylalanine substitution at tyrosine 1356 in met, which fails to scatter in response to CSF-1. When compared with the unstimulated cells, the inhibition of cell adhesion promoted by HGF/SF correlated with an increased stability of the newly synthesized soluble E-cadherin and Pg and an altered phosphorylation pattern of E-cadherin, as determined by partial proteolytic peptide mapping.