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 de rived glycoprotein with a strong scattering effect on epithelial cells , A receptor tyrosine kinase encoded by the met proto-oncogene has bee n identified as the cellular receptor for HGF/SF, Following stimulatio n with HGF/SF, cell scattering occurs concurrent with decreased cell-c ell adhesion and disassembly of junctional components, In culture, jun ction formation is cell-cell contact dependent and can be regulated by modulating the Ca2+ concentrations of the growth media, Decreasing th e Ca2+ concentrations below 50 mu M causes rapid disassembly of juncti ons, whereas increasing the Ca2+ concentrations to 1.8 mM induces cell -cell contact and junction assembly, Although associated with decrease d cell-cell adhesion and disassembly of the junctional complex, HGF/SF -induced scattering occurs under high extracellular Ca2+ concentration s, 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 junc tions, 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-s timulating factor 1 (CSF-1), The results have shown that in HGF/SF-sti mulated MDCK cells, adhering junctions were not assembled upon inducti on of cell-cell contact, Immunofluorescence analyses showed that large r amounts of Pg and E-cadherin were Triton X-100 extractable, and more significantly, these proteins were homogeneously distributed along th e membrane and were not concentrated at the areas of cell-cell contact , Similar results were obtained for CSF-MET expressing MDCK cells in r esponse to CSF-1, In contrast, none of the above effects were detected in MDCK cells expressing a mutant CSF-MET chimera containing a phenyl alanine substitution at tyrosine 1356 in met, which fails to scatter i n response to CSF-1, When compared with the unstimulated cells, the in hibition of cell adhesion promoted by HGF/SF correlated with an increa sed stability of the newly synthesized soluble E-cadherin and Pg and a n altered phosphorylation pattern of E-cadherin, as determined by part ial proteolytic peptide mapping.