DYNAMICS OF CONTACTS BETWEEN LAMELLAE OF FIBROBLASTS - ESSENTIAL ROLEOF THE ACTIN CYTOSKELETON

We investigated actin cytoskeletal and adhesion molecule dynamics duri ng collisions of leading lamellae of nontransformed and oncogene-trans formed fibroblasts. By using real-time,ideo microscopy, it was found t hat during lamellar collision there peas considerable overlapping of l eading lamellae followed by subsequent retraction, Overlapping of nont ransformed fibroblasts was accompanied by formation of beta-catenin-po sitive contact structures organized into strands oriented parallel to the long axis of the cell that were associated with bundles of actin f ilaments. Maintenance of such cell-tell contact structures critically depended on the contractility of actin cytoskeleton, as inhibition of contractility with serum-free medium or 2,3-butanedione 2-monoxime (BD M) resulted in loss of strand formation. Strand formation was recovere d when cells in serum-free medium were incubated with the microtubule inhibitor nocodazole, which is known to increase contractility. Oncoge ne-transformed fibroblasts reacted to collisions with responses simila r to nontransformed fibroblasts but did not develop well-organized cel l-cell contacts. A model is presented to describe how differences in t he organization of the actin cytoskeleton could account for the struct urally distinct responses to cell-cell contact by polarized fibroblast ic cells versus nonpolarized epithelial cells.