Locomotory behavior, contact inhibition and pattern formation of 3T3 and polyoma virus-transformed 3T3 cells in culture

Fibroblast Migration Is Regulated by Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Protein

Myristoylated alanine-rich C-kinase substrate (MARCKS) is a ubiquitously expressed substrate of protein kinase C (PKC) that is involved in reorganization of the actin cytoskeleton. We hypothesized that MARCKS is involved in regulation of fibroblast migration and addressed this hypothesis by utilizing a unique reagent developed in this laboratory, the MANS peptide. The MANS peptide is a myristoylated cell permeable peptide corresponding to the first 24-amino acids of MARCKS that inhibits MARCKS function. Treatment of NIH-3T3 fibroblasts with the MANS peptide attenuated cell migration in scratch wounding assays, while a myristoylated, missense control peptide (RNS) had no effect. Neither MANS nor RNS peptide treatment altered NIH-3T3 cell proliferation within the parameters of the scratch assay. MANS peptide treatment also resulted in inhibited NIH-3T3 chemotaxis towards the chemoattractant platelet-derived growth factor-BB (PDGF-BB), with no effect observed with RNS treatment. Live cell imaging of PDGF-BB induced chemotaxis demonstrated that MANS peptide treatment resulted in weak chemotactic fidelity compared to RNS treated cells. MANS and RNS peptides did not affect PDGF-BB induced phosphorylation of MARCKS or phosphoinositide 3-kinase (PI3K) signaling, as measured by Akt phosphorylation. Further, no difference in cell migration was observed in NIH-3T3 fibroblasts that were transfected with MARCKS siRNAs with or without MANS peptide treatment. Genetic structure-function analysis revealed that MANS peptide-mediated attenuation of NIH-3T3 cell migration does not require the presence of the myristic acid moiety on the amino-terminus. Expression of either MANS or unmyristoylated MANS (UMANS) C-terminal EGFP fusion proteins resulted in similar levels of attenuated cell migration as observed with MANS peptide treatment. These data demonstrate that MARCKS regulates cell migration and suggests that MARCKS-mediated regulation of fibroblast migration involves the MARCKS amino-terminus. Further, this data demonstrates that MANS peptide treatment inhibits MARCKS function during fibroblast migration and that MANS mediated inhibition occurs independent of myristoylation.

Contact inhibition revisited

Contact inhibition of cell movement was originally defined in the 1950s as a way of interpreting studies that were ethological and statistical in nature. Research done in succeeding decades provided a more detailed study of the initial contact and its consequences for the cell. The behavior called contact inhibition is characterized by the cessation of ruffling and forward movement in the lamellipodium of the cell making the contact. A new ruffling membrane then arises elsewhere on the cell perimeter. A comparison between the contact behavior described in the early literature and that of the nerve growth cone, described recently by Steketee and Tosney, suggests that filopodia mediate the sensing function in both cases. Since transformed cells have fewer filopodia than normal cells, the contact behavior may decline in direct response to the degraded function of filopodia. This new "filopodia focal signal transduction" hypothesis of contact inhibition elevates the filopodia sensing function and the cessation of lamellipodial advance to the highest importance as phenomena underlying the altered behavior of cancer cells.

Endothelial cell protrusion and migration in three-dimensional collagen matrices

Many cells display dramatically different morphologies when migrating in 3D matrices vs. on planar substrata. How these differences arise and the implications they have on cell migration are not well understood. To address these issues, we examined the locomotive structure and behavior of bovine aortic endothelial cells (ECs) either inside 3D collagen gels or on 2D surfaces. Using time-lapse imaging, immunofluorescence, and confocal microscopy, we identified key morphological differences between ECs in 3D collagen gels vs. on 2D substrata, and also demonstrated important functional similarities. In 3D matrices, ECs formed cylindrical branching pseudopodia, while on 2D substrata they formed wide flat lamellae. Three distinct cytoplasmic zones were identified in both conditions: (i) a small, F-actin-rich, rapidly moving peripheral zone, (ii) a larger, more stable, intermediate zone characterized by abundant microtubules and small organelles, and (iii) a locomotively inert central zone rich in microtubules, and containing the larger organelles. There were few differences between 2D and 3D cells in the content and behavior of their peripheral and central zones, whereas major differences were seen in the shape and types of movements displayed by the intermediate zone, which appeared critical in distributing cell-matrix adhesions and directing cytoplasmic flow. This morphological and functional delineation of cytoplasmic zones provides a conceptual framework for understanding differences in the behavior of cells in 3D and 2D environments, and indicates that cytoskeletal structure and dynamics in the relatively uncharacterized intermediate zone may be particularly important in cell motility in general.

Distribution of cytoskeletal proteins in neomycin-induced protrusions of human fibroblasts

The organization of actin, tubulin, and vimentin was studied in protruding lamellae of human fibroblasts induced by the aminoglycoside antibiotic neomycin, an inhibitor of the phosphatidylinositol cycle. Neomycin stimulates the simultaneous protrusion of lamellae in all treated cells, and the lamellae remain extended for about 15-20 min, before gradually withdrawing. The pattern and distribution of actin, tubulin, and vimentin during neomycin stimulation were analyzed by fluorescence and electron microscopy. F-actin in the newly formed lamellae is localized in a marginal band at the leading edge. Tubulin is colocalized with F-actin in the marginal band, but the newly formed lamellae are initially devoid of microtubules. Over a period of 10 to 20 min after the addition of neomycin, microtubules grow into the lamellae from the adjacent cytoplasm, while the intensity of tubulin staining of the marginal band decreases. Distribution of vimentin remains unchanged in neomycin-treated cells and vimentin filaments do not enter the new protrusions. Treatment of cells with colchicine and Taxol do not inhibit neomycin-induced protrusion but protrusions are no longer localized at the ends of cell processes and occur all around the cell periphery. We conclude that actin filaments are the major component of the cytoskeleton involved in generating protrusions. Microtubules and, possibly, intermediate filaments control the pattern of protrusions by their interaction with actin filaments.

Cell intercalation during notochord development in Xenopus laevis

Morphometric data from scanning electron micrographs (SEM) of cells in intact embryos and high-resolution time-lapse recordings of cell behavior in cultured explants were used to analyze the cellular events underlying the morphogenesis of the notochord during gastrulation and neurulation of Xenopus laevis. The notochord becomes longer, narrower, and thicker as it changes its shape and arrangement and as more cells are added at the posterior end. The events of notochord development fall into three phases. In the first phase, occurring in the late gastrula, the cells of the notochord become distinct from those of the somitic mesoderm on either side. Boundaries form between the two tissues, as motile activity at the boundary is replaced by stabilizing lamelliform protrusions in the plane of the boundary. In the second phase, spanning the late gastrula and early neurula, cell intercalation causes the notochord to narrow, thicken, and lengthen. Its cells elongate and align mediolaterally as they rearrange. Both protrusive activity and its effectiveness are biased: the anterioposterior (AP) margins of the cells advance and retract but produce much less translocation than the more active left and right ends. The cell surfaces composing the lateral boundaries of the notochord remain inactive. In the last phase, lasting from the mid- to late neurula stage, the increasingly flattened cells spread at all their interior margins, transforming the notochord into a cylindrical structure resembling a stack of pizza slices. The notochord is also lengthened by the addition of cells to its posterior end from the circumblastoporal ring of mesoderm. Our results show that directional cell movements underlie cell intercalation and raise specific questions about the cell polarity, contact behavior, and mechanics underlying these movements. They also demonstrate that the notochord is built by several distinct but carefully coordinated processes, each working within a well-defined geometric and mechanical environment.

Control of neural crest cell dispersion in the trunk of the avian embryo

Many hypotheses have been advanced to explain the orientation and directional migration of neural crest cells. These include positive and negative chemotaxis, haptotaxis, galvanotaxis, and contact inhibition. To test directly the factors that may control the directional dispersion of the neural crest, I have employed a variety of grafting techniques in living embryos. In addition, time-lapse video microscopy has been used to study neural crest cells in tissue culture. Trunk neural crest cells normally disperse from their origin at the dorsal neural tube along two extracellular pathways. One pathway extends laterally between the ectoderm and somites. When either pigmented neural crest cells or neural crest cells isolated from 24-hr cultures are grafted into the space lateral to the somites, they migrate: (1) medially toward the neural tube in the space between the ectoderm and somites and (2) ventrally along intersomitic blood vessels. Once the grafted cells contact the posterior cardinal vein and dorsal aorta they migrate along both blood vessels for several somite lengths in the anterior-posterior axis. Neural crest cells grafted lateral to the somites do not immediately move laterally into the somatic mesoderm of the body wall or the limb. Dispersion of neural crest cells into the mesoderm occurs only after blood vessels and nerves have first invaded, which the grafted cells then follow. The other neural crest pathway extends ventrally alongside the neural tube in the intersomitic space. When neural crest cells were grafted to a ventral position, between the notochord and dorsal aorta, in this intersomitic pathway at the axial level of the last somite, the grafted cells migrate rapidly within 2 hr in two directions: (1) dorsally, in the intersomitic space, until the grafted cells contact the ventrally moving stream of the host neural crest and (2) laterally, along the dorsal aorta and endoderm. All of the above experiments indicate that neither a preestablished chemotactic nor adhesive (haptotactic) gradient exists in the embryo since the grafted neural crest cells will move in the reverse direction along these pathways toward the dorsal neural tube. For the same reason, these experiments also show that dispersal of the neural crest is not directed passively by other environmental controls, since the cells can clearly move counter to their usual pathway and against such putative passive mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

Tension in the culture dish: microfilament organization and migratory behavior of quail neural crest cells

We have investigated one aspect of the migratory behavior of quail neural crest (NC) cells by comparing the organization of microfilament bundles and the ability to distort migratory substrata by NC, somite, and notochord cells in vitro. In contrast to the numerous cytoplasmic stress fibers in somite-derived fibroblasts and notochord cells revealed by rhodamine-phalloidin staining and thin-section electron microscopy, microfilaments in NC cells are restricted to the cell cortex. To test the relative degrees of tension generated by these cell types on the underlying substratum, cells were cultured in collagen gels and on distortable silicone rubber sheets. Explanted somites and notochords produced dramatic radial alignment of 750 micrograms/ml collagen gels, whereas neural crest cells only aligned gels of lower concentrations. Fibroblasts did not migrate individually from explanted somites and notochords into 250 micrograms/ml collagen gels as readily as into higher concentration collagen lattices. In contrast, neural crest cells migrated into matrices of low concentration as well as into higher concentration collagen gels. Neural crest cells and their pigmented derivatives did not distort silicone rubber sheets, whereas somite and notochord-derived fibroblasts wrinkle this substratum after 4 days in culture. Thus, the differences in organization of the actin cytoskeleton reflect the tractional force exerted by these cells on their substratum. We hypothesize that the migratory behavior of NC cells in vivo may be related to their ability to translocate through embryonic extracellular matrices while generating relatively weak adhesions with the substratum, whereas the stronger forces generated by other embryonic cell types upon the delicate extracellular matrix may restrict their migration and may be associated with other morphogenetic events.

A new model for the quantitative analysis of cell movements in vitro: definition of a shape change factor

Changes in shape, in addition to translocations, are an important aspect of cell motility. We propose a simple geometrical model for the quantitative analysis of shape changes undergone by cultured cells. The extent to which images of a given cell do not overlap at the beginning and end of a time interval is used as a measure of motility, and a translation step included to eliminate translocation effects. Initial findings suggest that the method is widely applicable.

Proteoglycans and cell adhesion. Their putative role during tumorigenesis

In this review, evidence that proteoglycans are involved in cell adhesion and related behavior is considered, together with their putative role(s) during tumorigenesis. Proteoglycans are large, carboxylated and/or sulfated structures that interact with specific binding sites on cell surfaces. Their distribution and synthesis in tissues alter with the onset of tumorigenesis so that hyaluronic acid is generally increased and heparan sulfate decreased in the developing tumor and surrounding tissue. However, the precise role of proteoglycans during the tumorigenic process is far from clarified. Data suggest any putative roles will be related to the adhesive properties that these molecules confer to cells. Hyaluronic acid and chondroitin sulfate appear to be weakly adhesive molecules that may promote 'transformed' characteristics when they occur on cells in large amounts. These characteristics include reduced cell spreading, increased cell motility, as well as reduced contact inhibition. Consistent with such properties, neither hyaluronic acid nor chondroitin sulfate are localized in specialized adhesion sites such as focal or close contacts. In contrast, heparan sulfate is associated with increased cell-substratum adhesion and is involved in the spreading of cells onto fibronectin and other substrata. Its presence is generally associated with reduced motility and with a well-spread morphology. Unlike hyaluronate and chondroitin sulfate, heparan sulfate is found in specialized contacts. These adhesive properties of proteoglycans predict an instructive role in tumor development, and recent experiments have defined an involvement of these molecules in metastatic arrest. Additional studies utilizing invasive and metastatic tumor variants including tumor cells that employ different mechanisms to invade are required to clarify the role of proteoglycans in tumor progression.

Inability of mesoderm cells to locomote on the modified free surface of epithelial cell sheets in vitro

Previous work has shown that when chick embryo mesoderm tissue is seeded onto the free, dorsal surface of established sheets of embryonic epithelial endoblast, the former penetrates the latter and spreads on the underlying artificial substratum. In this work, the surface charge on the epithelial sheet has been altered, prior to seeding the mesoderm, to ascertain whether such a change could alter the behavior of the mesoderm with respect to the free surface of the epithelium. Charge alteration was accomplished using the polycations, poly-L-lysine. Surface charge characteristics were examined ultrastructurally using cationized and anionized ferritin. Results showed that although surface charge changes were detectable, there was no difference in the behavior of the mesoderm with respect to the endoblast. Neuraminidase did not detectably affect the epithelial surface charge. These results are consistent with the view that changes in substratum surface charge are not necessarily correlated with changes in adhesiveness.

An inhibitor of animal cell growth increases cell-to-cell adhesion

The interactions of both normal and transformed cells with their environment is mediated to a large extent by the cell surface. Succinylated concanavalin A (succinyl-Con A) is a nontoxic and nonagglutinating derivative of the jack-bean lectin concanavalin A. Succinyl-Con A, presumably through an interaction with the cell surface, reversibly inhibits the growth of normal cells and restores a normal growth phenotype to transformed cells. Whereas at high cell densities migration was inhibited, it turned out that at low cell densities where cells are not in contact with each other, cell movement was not affected by succinyl-Con A. Together with some additional observations, this suggests that this lectin derivative increases cell-to-cell adhesion in culture and thereby may influence cell migration. An increase in cell-to-cell adhesion by this lectin derivative may not be brought about simply by physically linking cells together. It occurs after a lag time, possibly by inducing surface changes. The relationship between cell adhesion in culture, cell movement, and cell growth is discussed.

Correlation between a specific molecular weight form of plasminogen activator and metabolic activity of 3T3 cells

In quiescent cultures of 3T3 cells, plasminogen activator (PA) is found predominantly as a 75,000 dalton species. When quiescent cells are exposed to mitogenic agents such as phorbol myristate acetate, Ca++, or 25% serum, the absolute levels of PA in cell lysates may either increase or decrease. However, a consistent observation is that in the stimulated cultures PA is found predominantly as a 49,000 dalton species. This also is the predominant form of PA in growing and transformed cells. Concomitant with the mitogen-induced stimulation of the 49,000 dalton PA in quiescent cultures is a change in morphology to one that is characteristic of growing and transformed cells. The data suggest that PA is not operative in causing the morphological change that occurs with activation; however, the 49,000 dalton PA in particular is closely related to the pleiotypic response accompanying growth stimulation and transformation.

Biocompatibility of echinoderm skeleton with mammalian cells in vitro: preliminary evidence

The physical and chemical properties of echinoderm skeleton are reviewed. A method is described for preparing cell-free, sterile echinoderm skeletal plates (ossicles) which were used as porous substrates for cell cultures. Ossicles of the starfish Pisaster ochraceus were evaluated as substrates for the culture of three mammalian cell lines. Each line grew vigorously on ossicles, and fibroblasts quickly infiltrated their porous microstructure. Echinoderm skeletal plates provide a simple, convenient alternative to coverslips and porous membranes for SEM or correlated SEM/TEM studies of cell behavior. More importantly, the preliminary evidence for biocompatibility presented suggests that native echinoderm skeleton has potential use as a biomaterial and, because of its microstructure and relative solubility; deserves evaluation as a kind of biodegradable ceramic.

Responses to cell contacts between growth cones, neurites and ganglionic non-neuronal cells

The motility of growth cones of embryonic peripheral neurons is not inhibited by contact with the surfaces of neurites or of non-neuronal cells. Rather, growth cones and microspikes adhere to other cell surfaces and often respond with forward movement and elongation in contact with other cells, as they do on adhesive surfaces in vitro. Furthermore, non-neuronal cells do not display contact inhibition when they contact growth cones or neurites. If anything, surface motility and ruffling is stimulated by contact with a neuronal cell surface and some non-neuronal cells prefer to migrate along neurites rather than on the surface of the culture dish. These observations on the contact behaviour of cells from peripheral nerve ganglia imply that the surfaces of embryonic neurons differ from those of non-neuronal cells in that the neuronal surfaces do no elicit the typical contact inhibition response.

Induction of spreading during fibroblast movement

This paper describes the phenomenon of retraction-induced spreading of embryonic chick heart fibroblasts moving in culture. Measurable criteria of cell spreading (increase in area of the spreading lamella, and total spread area of the cell) are found to change predictably with retraction of a portion of the cell margin. Ruffling activity was found to increase. The leading lamella of a spread fibroblast ordinarily advances slowly, with an average area increase of approximately 21 mu2m/min. A 10- to 30-fold increase in spreading occurs within 8 s after onset of retraction at the trailing edge and then decreases slightly so that by 1 min the increase in spreading is five to tenfold. During this period, there is a linear relationship between area increase at the leading edge and area decrease at the trailing edge. During the next 10--15 min, spreading gradually decreases to normal. Although the relationship between area spreading and area retracting of fibroblasts at different phases of movement is not significantly linear, it is highly correlated (Table II). These results suggest that the rate of fibroblast spreading may be inversely related to the degree of spreading of the cell as a whole.

Cell surface fibronectin and oncogenic transformation

Fibronectin is a large glycoprotein at the cell surface of many different cell types; a related protein is present in plasma. Fibronectin is a dimer of 230,000-dalton subunits and also occurs in larger aggregates; it forms fibrillar networks at the cell surface, between cells and substrata and between adjacent cells, and it is not a typical membrane protein. Cell surface fibronectin is reduced in amount or absent on transformed cells and in many cases its loss correlates with acquisition of tumorigenicity and, in particular, metastatic ability. Exceptions to the correlations with transformation and tumorigenicity exist. Loss of fibronectin and the resulting reduced adhesion appear to be involved in pleiotropic alterations in cell behavior and may be responsible for several aspects of the transformed phenotype in vitro. Fibronectin interacts with other macromolecules (collagen/gelatin, fibrin/fibrinogen, proteoglycans) and is apparently connected to microfilaments inside the cell.

Fibronectins--adhesive glycoproteins of cell surface and blood

A recently characterised class of adhesive, high molecular weight glycoproteins is present on the surfaces of cells, in connective tissue matrices, and in extracellular fluids. These proteins may have important roles in cellular adhesion, malignant transformation, reticuloendothelial system function, and embryonic differentiation.

Cellular alterations dependent upon the polyoma virus Hr-t function: separation of mitogenic from transforming capacities

Hr-t mutants of polyoma virus are restricted in their growth properties (host range) and defective in cell transformation and tumor induction. The present study indicates that these mutants have lost the ability to induce morphological transformation, but have retained a mitogenic function. Thus an early and dramatic difference between wild-type virus and hr-t mutant-infected cultures of rat fibroblasts is the morphological change in individual cells observed by light, fluorescence and scanning electron microscopy. Viruses containing an intact hr-t function (wild-type virus and ts-a mutants) induce a transformed phenotype consisting of stellate cell shape, loss of defined cytoplasmic actin architecture, cellular "underlapping," and increased nuclear and nucleolar sizes. These prominent alterations constitute an abortive transformation, peaking 24-48 hr post-infection, and subsequently resolving in most or all of the cells. In contrast, cells infected with hr-t mutants do not develop the above structural changes, but rather retain their preinfection appearance. Both wild-type virus and hr-t mutants induce cellular DNA synthesis in confluent monolayers of rat cells beginning 12-14 hr post-infection. Flow microfluorometric (FMF) analysis confirms the viral mediated transit of cells from the G1 to the S and G2 phases of the cell cycle, as well as an increase in the proportion of cells with an 8N (octaploid) DNA content. Approximately 50% of the clones isolated from wild-type-infected cultures are polyploid. Stable transformants are found among these polyploid clones, but the majority of the latter resemble the parental cells in their morphology and growth properties. Polyploid clones are derived from hr-t mutant-infected cultures at a much lower frequency, similar to that of mock-infected cultures. Data obtained by sequential labeling of infected cultures with 3 H-thymidine and 5-bromo-deoxyuridine, together with cell number quantitation, indicate that hr-t mutants promote only a single round of cell division, while the wild-type virus and ts-a mutants promote multiple rounds. Loss of the hr-t function in polyoma virus therefore reveals a residual viral mitogenic activity, but prevents the virus from effecting morphological transformation of cells with concomitant loss of defined actin cables, polyploidization and multiple cycles of cell division in confluent cultures.

Effects of LETS glycoprotein on cell motility

Addition of LETS glycoprotein to normal or transformed cells produces increased migration of the cells, as determined by formation of phagokinetic tracks on gold particle-coated coverslips. These tracks arise by a combination of phagocytosis of the gold particles and cellular migration. Increased motility is also evident on plastic in the absence of gold particles. The added LETS protein attaches to the cells in a fibrillar network, and binding is greater to normal than to transformed cells. The effects of LETS protein on migration are consistent with its effects on cell adhesion, morphology and cytoskeleton, and have potential implications for the determination of cellular migration in vivo.