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p27BBP/eIF6 is an evolutionarily conserved regulator of ribosomal function. It is necessary for 60S biogenesis and impedes improper joining of 40S and 60S subunits, regulated by protein kinase C or Efl1p. No data on p27BBP/eIF6 during early development of Metazoa are available. We studied the distribution, post-translational changes and association with the cytoskeleton of p27BBP/ eIF6 during Xenopus oogenesis and early development. Results indicate that p27BBP/eIF6 is present throughout oogenesis, partly associated with 60S subunits, partly free and with little cytoskeleton bound. During prophase I, p27BBP/eIF6 is detected as a single band of 27-kDa. Upon maturation induced by progesterone or protein kinase C, a serine-phosphorylated 29 kDa isoform appears and is kept throughout development to the neurula stage. Confocal microscopy showed that the distribution of p27BBP/eIF6 and its association with the cytoskeleton varies according to oogenesis stages. Briefly, in stage 6 oocytes, p27BBP/eIF6 has a limited dot-like distribution, and does not co-localize with cytokeratin, whereas upon maturation it spreads throughout the cytoplasm. After fertilization, a large fraction coalesces around cytomembranes and a cytochalasin B-sensitive co-localization with cytokeratin occurs. RNAse removes p27BBP/eIF6 from the cytokeratin fibres. Developmental data suggest a role of p27BBP/eIF6 in controlling ribosomal availability or regulating cross-talk between ribosomes and the cytoskeleton.

Keratinocyte adhesion to basal lamina and lateral interactions among basal epidermal cells are mediated, besides other molecules, by integrin receptors that are sorted to defined membrane domains. The hemidesmosome-associated integrin alpha 6 beta 4 is sharply localized to the basal surface of basal cells while alpha 2 beta 1 and alpha 3 beta 1 are enriched laterally. This integrin sorting pattern is perfectly reproducible in vitro by cultured keratinocytes and takes place progressively in primary or secondary culture in the presence of 1.8 mM Ca2+. The polarized topography of integrins is gradually lost with higher passage numbers and between passage 5 and passage 7 there is a complete pericellular redistribution of the above integrins. Along with the decreased basal adhesive value of alpha 6 beta 4 there is a marked increase in the number of focal contacts in high-passage keratinocyte colonies. A similar loss of polarized topography of integrins occurs under low-Ca2+ culture conditions. Increasing the number of culture passages beyond the fifth induces the appearance of the fibronectin receptor alpha 5 beta 1 on the surface of keratinocytes, particularly at intercellular junctions and in some focal contacts. The receptor alpha 5 beta 1 is not detectably exposed by low-passage cells. We propose that forcing keratinocytes into more frequent cell cycles by continuous passaging may perturb the polarized topography of integrins and the adhesion mechanisms of keratinocytes. Then, low-passage keratinocytes are, in our opinion, the most reliable in vitro models for studying the physiology of epidermal cells.

The action of transforming growth factor-beta (TGF-beta) on the morphology, cytoskeleton and extracellular matrix was investigated in FRTL-5 thyroid epithelial cells. After treatment with TGF-beta, FRTL-5 cells became flat and developed straight and thick bundles of actin microfilaments. This effect of TGF-beta was observed even in the presence of thyrotropin, which has a strong microfilament disrupting action. TGF-beta also influenced some aspects of the extracellular matrix organization. Immunofluorescence staining of FRTL-5 cells revealed both the appearance of a fibrillar array of fibronectin in association with the basal plasma membrane and a change in the morphology of basally located laminin patches. TGF-beta induced the formation of adhesion structures at the ventral portion of the cell membrane. Vinculin was focally concentrated at the end of stress fibers in areas corresponding to focal adhesions as revealed by interference reflection microscopy (IRM). The ability to modulate cytoskeleton organization and extracellular matrix protein distribution might mediate some of the reported TGF-beta effects on the expression of specific functional properties in thyroid cells.

The MCF-7 and CG-5 breast carcinoma cell lines were grown under different concentrations of estrogen and with or without the addition of tamoxifen to the media. Similar results were obtained with either cell lines. Cells cultured in estrogen-supplemented medium showed a marked change of the cell shape with the appearance of long projections sprouting from the cell body, adhesion areas being localized at the tips of these projections. A redistribution of bundles of prekeratin and actin fibres could be visualized by appropriate immuno-cytochemical procedures. Vimentin intermediate filaments and microtubules did not appear significantly modified by hormone conditioning. Tamoxifen treatment resulted in structural and cytoskeletal changes similar to those observed in estrogen stimulated cells. These data indicate that the shape and the cytoskeletal architecture of breast cancer cells can be conditioned by hormone treatment.

Metastatic clones growing in 0.6% 'hard' agar were selected from the non-metastatic Rous sarcoma virus (RSV)-transformed tumorigenic B77-3T3 mouse fibroblast line. The incidence of spontaneous lung metastases varied among clones around 100%, while it was lower than 5% in the parental tumor line. The organization of microfilaments, microtubules and intermediate filaments as well as the pattern of extracellular fibronectin matrix were analyzed by immunofluorescence in two representative clones (B77-AA6 and B77-AA12) and was compared with the structural features displayed by a highly metastasizing RSV-induced mouse sarcoma line (SR-BALB). In the metastatic clones studied microtubules and intermediate filaments were similarly organized in a pattern not significantly different from that of the non-metastatic parental cell line. The major finding was a marked concentration of actin-containing structures in the periphery of cells and notably at the level of surface protrusions, suggesting a high surface motility. In the same lines the production of fibronectin and its distribution in the cell layer and culture medium were analyzed. Metabolic labelling and immunofluorescence experiments indicated that the nonmetastasizing cells (B77-3T3) retain higher amounts of fibronectin in the cell layer and organize this molecule in extracellular fibers, while the metastatic clones (B77-AA6 and B77-AA12) as well as the metastatic line (SR-BALB) are unable to retain and organize fibronectin at their surface. This paper shows that the progression of tumorigenic cell lines toward a metastatic phenotype involves a redistribution of cytoskeletal actin and a loss of organized fibronectin matrix.

Rous sarcoma virus-transformed baby hamster kidney fibroblasts (RSV/B4-BHK) adhere to a fibronectin-coated substratum by means of dot-like adhesion sites called podosomes in view of their shape and function as cellular feet (Tarone et al.: Exp Cell Res 159:141, 1985). Podosomes concentrate tyrosine-phosphorylated proteins, including pp60v-src, and appear in many cells transformed by oncogenes coding for tyrosine kinases. In this paper we used orthovanadate, an inhibitor of phosphotyrosine phosphatases, in order to increase the cellular concentration of phosphotyrosine and to study whether this treatment induced the cytoskeleton remodeling leading to the formation of podosomes. Indeed, orthovanadate (10-100 microM) induced in a time- and dose-dependent manner the redistribution of F-actin and the formation of podosomes in BHK cells. Cytoskeleton remodeling occurred along with a marked increase of tyrosine phosphorylated proteins. The vanadate effect on the cytoskeletal phenotype was enhanced by the simultaneous treatment of cells with a phorbol ester. Under the latter conditions almost all BHK cells showed podosomes. The vanadate effect was reversible insofar as podosomes and tyrosine-phosphorylated proteins disappeared. Then, vanadate treatment of normal cells induced the cascade of events leading to the cytoskeletal changes typical of transformation and suggested that the transformed cytoskeletal phenotype may be primarily induced by the tyrosine phosphorylation of unknown target(s) operated by endogenous kinases.

The cytoskeleton and the adhesion complex of chick embryo chondrocytes maintained in vitro have been studied by fluorescence and interference reflection microscopy during the process of cell spreading. The pattern of actin-containing microfilaments and the distribution of vinculin speckles on adhesion plaques have been found to change as a function of the culture time. Newly plated chondrocytes adhere to the substratum mostly around a peripheral ring-like region and show a complex tridimensional array of microfilaments. When chondrocytes flatten, they develop stress fibres and show a diffuse system of vinculin-containing adhesion plaques scattered over the entire ventral side of the cells. Upon infection with Rous sarcoma virus (RSV) chondrocytes display one or more actin-containing ruffles located on the dorsal side similar to the 'actin flowers' earlier described in other cell types. These structures have been found to accumulate vinculin too. In chondrocytes infected with two td-ts mutants of RSV, 'actin flowers' have been found to persist at the restrictive temperature. At this temperature, however, in the majority of cells, stress fibres and adhesion plaques reappear.

Specific antibodies against actin and tubulin have been used to follow the distribution and organization of actin and tubulin containing structures in N-18 neuroblastoma cells induced to sprout axons. Immunofluorescence microscopy shows that during the time of axonal sprouting microtubules converge into growing processes forming dense bundles in which individual microtubules cannot be resolved. In the growth cone where individual fluorescent fibers can again be distinguished microtubules seem to be excluded from the very margin. Actin is predominantly located at the cell periphery both in cell bodies and in cell processes. It appears to be present in areas of high surface motility and is especially abundant at the tip of the growth cone.

Cell shape is involved in a variety of cellular activities including proliferation, adhesion, migration, and transformation. Agents known to promote differentiation, such as retinoic acid, butyrate, and dibutyryl cyclic AMP, induce marked alterations in cell shape which are often accompanied by changes in cell functions. In this paper we study the effects of the differentiating polar solvent dimethyl sulfoxide (DMSO) on cytoskeleton, adhesion, and growth properties of cultured mouse B16 melanoma cells. DMSO induced a progressive reorganization of the cytoskeleton which was fully developed in 4 days of continuous exposure to the agent. DMSO-treated cells developed thick and regularly oriented microfilament bundles of the stress fiber type ending at vinculin-rich areas of focal contact between the ventral membrane and the substratum (interference reflection microscopy-dark adhesion plaques). Such a rearrangement of the cytoskeleton resulted in increased adhesion to the substratum and inhibition of cell growth in comparison to control untreated cells. Cells which became highly flattened and tightly adherent after exposure to DMSO for 4 days progressively reverted their phenotype to that of control untreated cells within 3 days of DMSO withdrawal. Namely, they lost stress fibers and adhesion plaques, became rounded and less adherent, and increased their growth rate. These results indicate that DMSO can change the transformed appearance of B16 mouse melanoma cells to a phenotype which is typical of a variety of nontransformed cells in culture.

By immunofluorescence and interference reflection microscopy (IRM) we found that F-actin and a group of cytoskeletal proteins involved in microfilament-membrane interaction, including vinculin, alpha-actinin, fimbrin and talin, are specifically organized in discrete dot-like structures corresponding to cell-substratum contact sites in both monocytes and monocyte-derived cells such as macrophages and osteoclasts. These proteins have a precise topological distribution; vinculin and talin form a doughnut-like ring, while actin, fimbrin and alpha-actinin are organized in dots matching the rings. An identical dot-like organization of F-actin and associated cytoskeletal proteins was also detected in malignant fibroblasts transformed by Rous Sarcoma virus (RSV) but not in the corresponding untransformed cells in culture. It is concluded that RSV transformation induces fibroblasts to express a cytoskeletal organization and a pattern of adhesion that are normally found in cells of monocytic origin. We propose that the occurrence of this cytoskeletal organization in RSV-transformed fibroblasts and in monocyte-derived cells may reflect a common ability to migrate across anatomical boundaries.

The ultrastructure of F-actin-containing punctate adhesion structures (podosomes) and of their rosette-like clusters has been studied by transmission electron microscopy in Rous sarcoma virus transformed chick embryo chondrocytes. Peculiar "glove finger" invaginations were found to take origin from the ventral membrane at sites of close contact; they were directed toward the center of the cell perpendicularly from the substratum. These new structures may be the sites where the local release of proteases takes place at the side of cell-to-substratum adhesion in podosome-bearing cells. The cytoplasmic face of glove finger invaginations and of the plasma membrane at cell-to-cell contact is lined by thick accumulations of microfilamentous material.

Cells of clone NB41A3 of the C-1300 mouse neuroblastoma were grown to a critical density at which many of the cells flatten, assume a variety of shapes and sizes and some sprout processes resembling neurites. We have studied the distribution of actin and tubulin in these cells using fluorescence microscopy and antibodies against actin or tubulin under these conditions. Actin-containing structures are variably arranged and predominantly associated with motile areas of the cell periphery including the growth cone. Microtubules appear to run radially from the perinuclear area towards the cell periphery. When neurites are present, microtubules converge into them and run to the growth cone but rarely contact its edge.

The distribution of cytoskeletal structures has been studied by electron and immunofluorescence microscopy in human embryonic epithelial cells (EUE cells) exposed to a hypertonic medium containing 0.274 M NaCl. A first noticeable effect involved an increase of cell size. Microtubules, microfilaments and intermediate filaments were also considerably changed under these experimental conditions. The most marked effect was on intermediate filaments of the keratin type which formed very thick bundles around the nucleus and gave rise to an intracellular cagework which is likely i) to increase mechanical resistance and ii) to avoid cell collapse in conditions of hyperosmolarity. A remarkable increase in complexity of the microfilamentous network was also found: stress fibers became thicker and more densely arranged and vinculin-containing streaks at focal cell-substratum contacts increased in number and size; this indicated improved cellular adhesion. The phenotypic adaptation of EUE cells to conditions of hyperosmolarity is slowly reversible under defined experimental conditions.

Human umbilical vein endothelial cells (ECs) have been shown to attach to a substratum of fibrinogen (fg). Later, ECs undergo spreading, organization of thick microfilament bundles of the stress fiber type, and formation of focal contacts (adhesion plaques) that correspond to accumulation of vinculin at the cytoplasmic aspect of the ventral membrane. The rate of attachment to fg and the type of spreading is virtually identical to that obtained on substrata coated with fibronectin (FN). Antibodies to fg, but not to FN, prevent EC adhesion to fg; conversely, antibodies to FN, but not to fg, prevent adhesion of ECs to a FN-coated substratum. The removal of residual FN contamination from fg preparations by means of DEAE-cellulose chromatography does not result in any difference in EC adhesion on fg. Moreover, pretreatment of cells with inhibitors of synthesis and release of proteins does not impair their adhesion capacity on an fg-coated substratum. In contrast, human arterial smooth muscle cells do not adhere and spread on fg substrata but do so on FN. The synthetic peptides (Gly-Arg-Gly-Asp[GRGD] and Gly-Arg-Gly-Asp-Ser-Pro[GRGDSP]) containing the tripeptide Arg-Gly-Asp (RGD), originally found to be responsible for the cell binding activity of FN, have been found to inhibit EC spreading and the redistribution of their cytoskeleton, including the formation of stress fibers and the localization of vinculin either on fg or on FN. Conversely, the synthetic peptide Arg-Gly-Gly (RGG) was completely uneffective in inhibiting the adhesion and the sequence of events leading to spreading and cytoskeletal organization. These results indicate that ECs, but not smooth muscle cells, specifically adhere and spread on an fg substratum and this occurs by recognition mechanisms similar to those reported for FN.

The cytoskeleton, the shape, and the adhesion complexes of MCF-7 breast carcinoma cells have been studied by fluorescence, phase contrast, and interference reflection microscopy. Cells have been grown in media containing different concentrations of estrogen and with or without the addition of the antiestrogen tamoxifen. The pattern of actin microfilaments and keratin intermediate filaments (tonofilaments) and the distribution of adhesion areas change as a function of the estrogen concentration. When cells are cultured in estrogen-deprived medium, they appear roundish and flattened and adhere firmly to the substratum, with multiple vinculin-positive adhesion plaques at their ventral surface. Upon stimulation with estrogen, these cells display pseudopodial cytoplasmic protrusions and ruffling membranes; in interference reflection microscopy the adhesion areas are mostly localized in these projections. A rearrangement of microfilaments and of tonofilaments in the cell projections and the formation of a dense network of keratin fibers takes place. Tamoxifen affects cellular shape and cytoskeletal arrangement in a way similar to that induced by estrogen. An effect of estrogen-receptor stimulation on the adhesion structures and on the rearrangement of intermediate and actin filaments (and accordingly of the shape and internal structure of breast cancer cells) can be suggested. Such an effect might be direct or mediated through unknown mechanisms; it seems, however, to be independent of the well known estrogenic effect on cell proliferation.

A specific antibody against nerve growth factor (NGF) and indirect immunofluorescence microscopy have been used to follow the in vitro binding of NGF to cells made permeable to large molecules. All cells tested, both target (sensory neurons and PCI2 cells) and nontarget (3T3, BKH 2I, C6 glioma cells), revealed a decoration of cytoskeletal structures which on the basis of their form, reactivity with antibodies, and sensitivity to specific drugs may be identified as microtubules (MTs) and microfilaments (MFs). The decoration of either structure depends on the fixation and permeabilization conditions: MFs, in the form of stress fibers, are stained by NGF when the plasma membrane is permeabilized with methanol/acetone; MTs become intensely stained when the plasma membrane is solubilized with a nonionic detergent in the presence of a MT-stabilizing medium. The two procedures do not affect the staining of these structures with specific antibodies. Binding of 125I-labeled NGF to PCI2 cells was not competitively inhibited by a 100-fold excess of several positively charged proteins but it was markedly decreased in the presence of DNase I. 125I-Labeled NGF interacted with MTs and F-actin (fixed with paraformaldehyde) in a range of concentrations similar to that used for their cellular localization with NGF-anti-NGF. Our studies show that the specificity and affinity of NGF binding to MTs and MFs is in the range of that of antibodies against tubulin and actin. The possible relevance of these findings to the mechanism of action of NGF in target cells is discussed.

The organization of actin-containing microfilaments and vimentin-containing intermediate filaments has been investigated in B chronic lymphocytic leukemia (B-CLL), hairy cell leukemia (HCL), and normal B cells cultured in vitro under basal conditions and after induction with 12-O-tetradecanoyl-phorbol-13-acetate (TPA). In uninduced B-CLL cells, F-actin was predominantly associated with dot-shaped structures scattered over the ventral membrane representing spotty close contact adhesion sites analogous to "podosomes" described in other cell types. On TPA induction, podosomes became clustered in sharply defined areas sitting in the cell center beneath the nucleus. In some cells, long actin-containing protrusions appeared. In HCL cells, F-actin was associated with thin microvilli responsible for the "hairy" appearance; occasional cells showed scattered podosomes. On TPA induction, HCL cells sprouted long dendritic processes rich in submembraneous F-actin, which made intertwined networks. Therefore, in both B-CLL and HCL cells, adhesion structures were present and the capacity for adhesion in vitro was marked, which might explain some peculiar clinical features of the diseases. Adhesion structures and adhesive properties never appeared in normal B cells. These data further support the notion that B-CLL and HCL, although clinically different, may share common biological features and suggest that in these disorders, cytoskeleton modifications may represent a hallmark of transformation.