Microfilament-organizing centers in areas of cell contact: cytoskeletal interactions during cell attachment and locomotion.

Abstract

In this article we discuss three aspects of cell contact formation : (a) the molecular architecture of the cytomatrix in cell-to-substrate focal contacts, (b) the dynamic properties of membrane-and microfilament-associated proteins in the contact areas, and (c) the involvement of microtubules in the coordinated and directed formation of new substrate contacts during cell locomotion . We show that different microfilament-associated proteins exhibit distinct patterns of association with focal contacts : some proteins are specifically associated with focal contacts (vinculin and talin) ; a-actinin is enriched in the contact areas but also is present along the stress fibers and in the lamellipodium; actin and filamin are detected throughout the contact areas but in apparently reduced amounts compared with the associated stress fibers ; and tropomyosin, myosin, and spectrin are either absent from the endofacial surfaces of contact areas or are present in only very small amounts. Fluorescence photobleaching recovery analyses performed with living cells microinjected with fluorescently labeled actin, vinculin, and a-actinin indicate that each of these proteins maintains a dynamic equilibrium between a soluble cytoplasmic pool and a membrane-bound fraction . Correlation of the distribution of vinculin and tubulin in motile fibroblasts to local movements of the leading edge of the same cells indicates that free-end microtubules extend into actively ruffling areas along the lamellipodium and that new vinculin-containing contacts are preferentially formed in these protruding regions .Cells move by cycles ofanterior membrane protrusion, establishment ofcontact with the underlying substrate, and retraction of the posterior trailing edge (for reviews, see references 1 and 2). The spatial and temporal coordination ofthese three major phases of the locomotory cycle is an essential element of directional cell motility.Apparently, cells sense and identify external stimuli that affect their motility. These include chemotactic stimuli, contacts with neighboring cells, and changes in the texture or adhesivity of the substrate . In addition, a central mechanism probably exists that integrates these stimuli and coordinates the dynamic molecular events that occur in different domains of the cell. The most active region is the leading lamellipodium. This area is very rich in actin filaments in the form of dense webs and small bundles (3-7). Besides actin, the leading lamella contains a-actinin (8-10) and, often, filamin . The THE JOURNAL OF CELL BIOLOGY " VOLUME 99 No . 1 Pt . 2 JULY 1984 83s-91s 0 The Rockefeller University Press -0021-9525/84/07/083s/09 $1 .00 focal contacts with the substrate that are formed under the leading lamella are particularly rich in the cytoskeletal protein vinculin and eventually, as they mature, become associated with the termini of stress fibers (9,(11)(12)(13)(14)(15)(16) . In fact, we suggest that focal contacts and the associated vinculin serve as organizing centers for the assembly of actin-c...

The actin filament severing protein actophorin promotes the formation of rigid bundles of actin filaments crosslinked with alpha-actinin.

“…In the fibroblast, a progression of cytoskeletal arrangements is seen from the newly polymerized actin network at the leading edge (Wang, 1985), to the production of "arcs" (Heath, 1983) composed of small bundles of filaments which are continually swept towards the nucleus where an arrangement oflarger perinuclear actin bundles known as the cellular geodome is found . As actophorin-like proteins (Mabuchi, 1983;Bamburg et al, 1980) and gelsolin (another actin filament severing protein), have been isolated from a number of vertebrate sources, it is possible that severing activity in concert with crosslinking proteins also found in protruding lamella (Geiger et al, 1984) form an increasingly anisotropic gel by a mechanism similar to that postulated here.…”

Pathogenesis of Degenerative Joint Disease in the Human Temporomandibular Joint

“…Many of the cellular functions that are affected by the stress response to hydrostatic pressure depend on the integrity of the cytoskeleton, and include: (i) decreased protein synthesis (Cerveza et al, 1981;Ornelles et al, 1986;Hesketh, 1991), (ii) changes in cell shape (Luna and Hitt, 1992), (iii) changes in adhesion (Geiger et al, 1984;Turner and Burridge, 1991;Luna and Hitt, 1992), (iv) altered enzyme activity (Masters, 1984(Masters, , 1992Knull and Walsh, 1992), and (v) decreased mRNA translation and stability (Hesketh, 1991;Larson et al, 1991). Thus, the up-regulation of heat shock protein synthesis and the down-regulation of the synthesis of other macromolecules in response to excessive hydrostatic pressure loads could at least partially account for the decreased synthesis of proteins, glycosaminoglycans, and proteoglycans reported in articular cartilage in degenerative joint disease (Hall, 1991).…”

Developmental Stage Dependent Expression of the Endothelial Stress Fibers and Organization of Fibronectin Fibrils in the Aorta of Chick Embryos

“…6). Since the distribution pattern of such stress fiber terminus observed with electron microscopy and with immunofluorescence microscopy using antivinculin IgG were remarkably similar to those of the adhesion plaque of cultured cells (Geiger et al, 1984;Burridge, 1986), these dense area or spots are the supposable adhesion plaques in the aortic endothelia (Fig. 5a, b).…”

“…3a). Vinculin is a protein found in the adhesion plaque of tissue cultured cells including vascular endothelial cells (Geiger et al, 1984;Burridge, 1986). By double staining with anti-vinculin IgG and fluorescein-phalloidin, discrete positive fluorescent spots with anti-vinculin IgG staining were demonstrated to be located at the ends of, as well as along, stress fibers ( Fig.…”

“…The stress fiber is a cable like structure consisting mainly of actin microfilaments and is supposed to enhance the cell adhesion to substrate (Byer et al , 1984;Geiger et al ., 1984;Burridge, 1986;Gotlieb et al , 1991). Vascular endothelial cell is the typical cell which expressed prominent stress fibers both in vitro and frequently in tissues.…”