Scatter factor induces segregation of multinuclear cells into several discrete motile domains

Abstract

The effects of scatter factor, HGF/SF, on multinuclear MDCK epitheliocytes were examined. Multinuclear cells were obtained by blocking cytokinesis by low concentration of cytochalasin D; these large cells had discoid shape and did not move much on the substrate. Incubation of these cells with HGF/SF induced their profound reorganization: their cytoplasm was reversibly segregated into several individually moving motile flattened domains, termed lamelloplasts and connected with one another by cylindrical domains termed cables. One or several nuclei were present in many lamelloplasts, but some lamelloplasts were anuclear. Nuclei were absent from the cables. Lamelloplasts continuously formed actin-rich ruffles at their edges; their cytoplasm contained small actin bundles and numerous focal adhesions. In contrast, cable, had no ruffles or focal adhesions. Dense networks of vimentin and keratin intermediate filaments were present in lamelloplasts; bundles of filaments of both types were seen in the cables. Segregation was accompanied by redistribution of centrosomes from perinuclear zone into lamelloplasts. As a result each lamelloplast in segregated cell acquired individual complex of centrosome and radiating microtubules. The cables contained numerous parallel microtubules but never had centrosomes. This reorganization of microtubular system was essential for segregation as alterations of shape and actin cytoskeleton were prevented by microtubule specific drugs: colcemid and Taxol (paclitaxel). It is suggested that mechanism of segregation is based on activation of two types of opposite actin reorganization: formation of actin networks in lamelloplasts and their dismantlement in the cables. Spatial distribution of the domains in which these opposite types of reorganizations occur may be regulated by microtubular system. It is also suggested that mechanisms of HGF/SF-induced segregation may be closely related to the mechanisms of important physiological reorganizations of cells, such as polarization of pseudopodial activities in motile cells and cytokinesis.