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

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.

Kinesin-associated transport is involved in the regulation of cell adhesion.

It has been recently shown that deploymerization of microtubules induces the elongation of focal contacts at the leading edge. On the other hand, cell shape and pseudopodial activity were found to depend on the microtubule-based motor kinesin. In this paper, we examine whether kinesin is involved in controlling the dynamics of adhesive structures at the cell surface. Microinjection of an antiblocking kinesin activity in vitro causes focal contact elongation similar to the effect of microtubule-depolymerizing drugs. Thus, the role of microtubules in cell adhesion lies in the supporting kinesin-based transport to the adhesion sites.

Taxol-treated fibroblasts acquire an epithelioid shape and a circular pattern of actin bundles.

The effects of two microtubule-specific drugs, taxol and colcemid, upon the cell shape and cytoskeleton of several types of cultured fibroblastic cells were compared. While colcemid depolymerized completely the whole microtubular system, taxol induced decentralization of this system, leading to formation of numerous free microtubules filling the central cytoplasm. Morphometric determinations of two cell shape parameters, dispersion and elongation (G. Dunn and A. Brown, J. Cell Sci. (1986) 83, 313-340), have shown that, in all the tested cultures, taxol induced significantly larger decreases of average dispersion than colcemid; in addition, most taxol-treated cells, but not colcemid-treated ones, developed circumferential bundles of actin microfilaments instead of straight bundles. These results show that decentralization of the microtubular system, in contrast to its complete depolymerization, leads to the transformation of a polarized "fibroblast-like" cell morphology to an "epithelioid" morphology characterized by the smooth discoid cell shape and a circular actin pattern. Possible mechanisms of this transformation are briefly discussed.

[The effect of the depolymerization and disintegration of the microtubular system on the cytoskeleton of untransformed and transformed cells]. / Vliianie depolimerizatsii i dezintegratsii sistemy mikrotrubochek na tsitoskelet netransformirovannykh i transformirovannykh kletok.

How important are the changes of microtubule control for the realization of actin cortex changes during neoplastic transformation? To answer this question we studied the actin cytoskeleton and intermediate filaments condition after colcemid destruction or taxol disintegration of microtubule system in non-transformed cells BALB/c 3T3 and in the same cells transformed by Ha-ras gene. We have come to a conclusion that the differences between non-transformed and transformed cells in the actin cytoskeleton organization remain the same after specific inhibitor action on the microtubules; after the microtubules are destroyed the differences between the two cell types appear in the intermediate filament organization; there are reasons to assume that changes in the actin cortex structure may play the central role in morphological transformation expression.

[Disorders of the actin cytoskeleton in transformed epithelial cells]. / Narusheniia aktinovogo tsitoskeleta v transformirovannykh épitelial'nykh kletkakh.

The actin cytoskeleton of 8 transformed epithelial cell lines was studied using electron microscopy of platinum replicas. Seven of these lines belonged to the IAR series of rat liver epithelial cells, being at different stages of neoplastic progression. One cell line (FBT) was derived from the epithelium of bovine fetal trachea. The extent of actin cytoskeleton alteration in cell lines studied has been shown to correlate with other signs of neoplastic transformation. Among various actin-containing cell structures (microfilament bundles, actin meshwork at active edges, cell-cell adherence junctions, and endoplasmic microfilament sheath) the latter was the most sensitive to transformation. The loosening of the sheath and the alteration of its fine structure were observed in all the cell lines. The degree of these changes increased in the following order: FBT; non-tumorigenic IAR lines; IAR lines transformed in vitro; IAR lines obtained from the latter by single or double selection in vivo. The alteration of sheath was the only disturbance of actin cytoskeleton in FBT cells, whereas in other groups of epithelial cell lines some other changes occurred. These involved disruption of actin-containing intercellular junctions, the cell polarization accompanied by progressive shortening of length of the cell active edge containing actin meshwork, and disappearance or reorganization of microfilament bundles.