Changes in microfilament organization and surface topogrophy upon transformation of chick embryo fibroblasts with Rous sarcoma virus

Altered distributions of the cytoskeletal proteins vinculin and alpha-actinin in cultured fibroblasts transformed by Rous sarcoma virus

It was recently shown by combined immunofluorescence and interference reflection microscopy that a protein named vinculin, along with alpha-actinin, is concentrated at focal adhesion plaques inside cultured normal fibroblasts [Geiger, B. (1979) Cell 18, 193-205]. These plaques are the discrete, isolated sites of strong adhesions formed between the ventral surfaces of the cells and the substrata on which they are grown. We show that after transformation of fibroblasts by Rous sarcoma virus a majority of the cells have many fewer focal adhesion plaques and now exhibit a cluster of small patches that are immunolabelled for both vinculin and alpha-actinin. Such a cluster (rosette) is located near the ventral surface of the cell, usually partly under the nucleus. The significance that these altered distributions of vinculin and alpha-actinin may have for the rounding up and loss of adherence of transformed cells is discussed.

Increased cyclic AMP content directly correlated with morphological transformation of cells infected with a temperature-sensitive mutant of mouse sarcoma virus

Normal rat kidney cells infected with a cold-sensitive mutant of mouse sarcoma virus [NRK(MSV-lb)] morphologically transform when exposed to adenosine 3':5' cyclic monophosphate (cAMP) at the restrictive temperature. The cAMP-induced morphological changes occur rapidly and are reversible. Agents capable of elevating endogenous levels of cAMP [prostaglandin E1 (PGE1) and cholera toxin (CT)] induced morphological transformation of NRK(MSV-lb) cells at the restrictive temperature that was concentration dependent, potentiated by cAMP phosphodiesterase inhibitors, and not prevented by inhibitors of DNA, RNA, and protein synthesis. Prostaglandin E1 stimulated a transient increase in the intracellular level of cAMP with a concomitant morphological transformation and reversion of cells as cAMP levels decline. The maximum increase is reached by 10 min, followed by a decline to near basal level by 80 min. In contrast, incubation of cells with CT resulted in irreversible morphological transformation and increased levels of cAMP first detectable by 1 hr with maximum levels reached by 24 hr. Heated CT (100 degrees C, 20 min) was without effect. Addition of CT to reverted PGE1-treated cells resulted in morphological transformation suggesting the existence of discrete receptors in NRK(MSV-lb) cells.

Cytoplasmic effects of X-irradiation on cultured cells in a non-dividing stage. 4. Studies of sparsely grown, serum-deprived cells

Cultured human glial cells were blocked in interphase (G1) by 24 h of serum starvation and subsequently subjected to 200 Gy, 8 MV X-radiation. Immediately following irradiation the cultures were transferred to serum-containig medium. Time-lapse cinemicrography performed during the next 48 h showed a profoundly disturbed motility with decreased ability for polarization and locomotion of the irradiated cells. Specimens fixed 24 and 48 h after irradiation and investigated by immunofluorescence with tubulin-antibodies and DNase/DNase-antibodies, and by whole cell transmission electron microscopy showed derangements in the distribution of microfilament bundles related to the cytoplasmic ramification of the irradiated cells, but otherwise no detectable alterations in structure or distribution of either microtubules or microfilaments. It is suggested that the alteration in the arrangement of filament bundles is of importance to the impaired locomotion of the irradiated cells.

Changes in surface morphology associated with ageing and carcinogen treatment of Chinese hamster lung cells

The relationship between ageing and transformation has been investigated by a serial study of the changes in cell-surface morphology as normal and carcinogen-treated cells progressed in culture. A progressive increase in the density of cell surface microvilli occurred in association with the adoption of a more rounded profile and concomitant increase in the rate of cell detachment. These changes occurred earlier after carcinogen treatment, which appeared to indicate a carcinogen-induced acceleration of ageing. The alterations have also been described as characteristic of the transformed state. The observations suggest that the expression of in vitro transformation may be the result of continuous selection from a population with genetic instability and variable morphology.

Interferon effects on microfilament organization, cellular fibronectin distribution, and cell motility in human fibroblasts

We have shown previously (Pfeffer et al., 1979, Exp. Cell Res. 121:111-120) that treatment of human fibroblasts, planted at a density of 2x10(3) cells/cm(2), with purified human fibroblasts interferon (640 U/ml) for 3 d at 37 degrees C decreases the overall rate of cell proliferation to 35-40 percent of the control value. In the present experiments we have characterized the phenotype of interferon-inhibited fibroblasts. The mean volume of trypsinized, interferon-treated cells was increased 31 percent abover that of control cells. The interferon-treated population was much more heterogeneous than the control population with respect to volume, and there was a considerable overlap in the volume distributions of the two populations. The cell surface area was, on the average, increased 65 percent after interferon treatment. More than 80 percent of the treated cells had enlarged nuclei, many of which were lobed, and the fraction of binucleated cells was increased fivefold. After interferon treatment, over 40 percent of the cells showed large actin-containing fibers in the form of multiple parallel arrays. Fewer than 5 percent of the control cells contained such large actin fibers. The number of actin fibers of all sizes was tripled in the treated fibroblasts on a per cell basis and, calculated per unit surface area of the cells, the number was increased 82 percent. In contrast, 10-nm filaments and microtubules did not appear to be increased in number per unit surface area of the cells. The increases per cell in the abundance of these structures were directly related to increased cell size. After interferon treatment, fibronection was distributed in arrays of long filaments covering most portions of the cell surface. Interferon treatment markedly decreased the rate of cell locomotion as well as membrane ruffling and saltatory movements of intracellular granules.

Isolation and characterization of a morphologic variant of Chinese hamster (CHO) cells

An epithelioid clone of Chinese hamster (CHO) cells which is spontaneously transformed was exposed to the mutagen N-methyl-N-Nitro-N-Nitrosoguanidine (MNNG), and a fibroblastic variant, clone CHO-F2, was isolated. This clone is partially reverted in several of the in vitro properties characteristic of transformed cells. When compared to wild type CHO, CHO-F2 has a longer doubling time, a lower saturation density and less piling up at high cell density, and a higher serum requirement. CHO-F2 also elaborates less plasminogen activator and has more abundant microtubules and actin cables. On the other hand, both CHO and CHO-F2 grow in agar suspension (although CHO-F2 grows with a lower efficiency), both lack detectable LETS protein, and both are tumorigenic in nude mice. Thus, expression of the individual properties frequently associated with transformation and tumorigenicity can be dissociated. The most critical biochemical change in CHO-F2 appears to be an increase in the intracellular level of cyclic AMP, when compared to CHO, and several growth and morphological properties of CHO-F2 resemble those induced in wild type CHO exposed to exogenous dibutyryl cyclic AMP. The role of cyclic AMP in expression of the transformed phenotype and the significance of individual in vitro parameters of transformation with respect to tumorigenicity are discussed.

Rapid induction of morphological changes in human carcinoma cells A-431 by epidermal growth factors

The morphological effects of epidermal growth factor (EGF) on human carcinoma cells A-431 have been examined by scanning electron microscopy. These flat polygonal cells normally exhibit only small membrane folds, but show extensive ruffling and extension of filopodia within 5 min of exposure to EGF at 37 degrees C. This ruffling activity is transient, subsiding within another 5--15 min, but several other changes in surface morphology follow. Within the first hour of exposure to the hormone, the cell surface becomes exceedingly smooth and the nuclei seem to protrude above the plane of the otherwise thin monolayer, giving the cells a "fried egg" appearance. Cells at the edges of colonies gradually retract from the substrate, leading to reorganization, by 12 h, of the monolayer into multilayered colonies. EGF thus induces both rapid and long-term alterations in the morphology of these epidermoid cells.

The structure and amount of actin in IMR-90 fibroblasts

Double-labelling and peptide isolation have been used to examine the homology between the actin of IMR-90 human embryo fibroblasts and muscle actin. After separation of mixtures of [14C]carboxymethylated muscle actin and [3H]carboxymethylated proteins of IMR-90 cells of electrophoresis on sodium dodecyl sulphate-containing polyacrylamide gels, peptides were generated from the material co-migrating with actin by digestion with chymotrypsin. Peptides homologous with peptides accounting for Cys-217, Cys-256, Cys-284 and Cys-373 of muscle actin are present in this material, but no peptide homologous with a Cys-10-containing peptide was detected. From the amount of actin-derived peptides present, the actin content of IMR-90 fibroblasts was calculated to be 4.2% of the total protein of these cells.

Ultrastructural features of cultured human glia and glioma cells

The fine structure of three lines of human normal glial cells and eight established lines of malignant glioma cells are described. The glial cell lines were ultrastructurally very similar whereas the glioma cell lines differed greatly from one another. In sparse proliferating cultures there were no consistent findings which distinguished the glioma cell lines as a group from the normal glial cells. Only in post-confluent cultures could the consistently irregular cell surfaces and ruffling, both at the cell periphery and centrally on the upper cell surface, with associated pinocytosis, distinguish the glioma from the post-confluent glial cultures, which did not possess these properties. The common attributes of post-confluent glioma cells reflect the cells' continued proliferation. The glioma lines did display individual ultrastructural characteristics which appear to be stable, the glioma lines having retained these during a number of years of continual passage.

The fine structure of growing human glia and glioma cells. Whole cell preparations

Three lines of normal human glia cells and eight established lines of malignant glioma cells have been studied in the electron microscope (E.M.), using preparations of critical-point dried whole cells, sparsely grown on formvar-coated, E. M., gold grids. The malignant cell lines showed a very varied morphology, almost every line having its peculiarities as compared to the essentially identical normal glia lines. The major differences noted concerned the form of the leading lamellae, number of microspikes and the distribution of organelles such as secondary lysosomes and mitochondria. No single consistent finding made it possible to differentiate the glioma cells as a group from the glia cells in sparse cultures. The findings of this study show some of the individual glioma cell lines to have characteristic cell-surface structures. They were found to be identical with the findings in previous SEM studies, suggesting the peculiarities of the individual malignant glioma lines to be stable and retained, despite continual passage.

Reversion of transformed glycolysis to normal by inhibition of protein synthesis in rat kidney cells infected with temperature-sensitive mutant of Rous sarcoma virus

Normal rat kidney cells infected with a temperature-sensitive mutant (LA23) of Rous sarcoma virus exhibit the transformed phenotype when grown at 33 degrees and the normal phenotype at 39 degrees. We have previously shown [Ash, J.F., Vogt, P.K. & Singer, S.J. (1976) Proc. Natl. Acad. Sci. USA 73, 3603-3607] that the addition of protein synthesis inhibitors to LA23-infected cells grown at 33 degrees causes them to revert, over a period of 12 hr, to the normal phenotype with respect to morphological and cytoskeletal characteristics. We now show that reversion of the metabolic characteristics of the transformed phenotype to those of the normal also occurs under these conditions. LA23-infected cells show an increased rate of aerobic glycolysis at 33 degrees compared to that at 39 degrees. They also show a different sensitivity of that rate to dinitrophenol and oligomycin at 33 degrees compared to 39 degrees. Such cells grown at 33 degrees in the presence of cycloheximide or abrin rapidly recover the aerobic glycolysis characteristics of the normal phenotype. These results support the thesis that transformation by the src gene of the Rous sarcoma virus is a pleiotypic and reversible process, such as is involved in a pleiotypic enzymic modification reaction and its reversal.

Nonproducer malignant tumor cells with rescuable sarcoma virus genome isolated from a recurrent Moloney sarcoma

Cells from a secondary tumor developing at the site of a regressed Moloney sarcoma virus-induced tumor could be passaged in adult STU mice by intramuscular and intraperitoneal inoculation. The tumors induced by these cells, as well as by a cell line derived from it, grew progressively and led to death of the animals between 3 and 7 wk after tumor transplantation. No evidence for production of virus from these cells was obtained or for the presence of viral antigens (p30, gp69/71). From both cell variants, sarcoma virus genome could be rescued by infection with helper virus, resulting in the establishment of a cell line producing focus- and XC plaque-forming virus. The rescued producer cells very frequently also produced tumors which finally grew progressively. The nonproducer cells were not immunogenic, as was demonstrated in cross transplantation tests and in studies for cell-mediated cytotoxicity (CMC) and complement-dependent antibody-mediated cytotoxicity (AMC). The producer cells, however, were demonstrated to possess a strong immunogenicity. The nonproducer cells, though nonimmunogenic, revealed a weak immunosensitivity when used for challenge in the transplantation protection assay or as target cell for the demonstration of AMC and CMC, if the immune response was induced by cells producing the sarcoma-helper virus complex, but not by cells producing only helper virus. The nonproducer cells, as well as their rescued producer derivative, showed a stronger reactivity with cytotoxic antibodies than with cytotoxic cells, whereas the helper virus-producing cell line was comparably suitable as target cell for AMC and CMC. The recurrence of a regressed Moloney sarcoma is assumed to be the result of the occurrence of transformed nonproducer cells escaping immune destruction, and not as a consequence of a depleted immune resistance in the host.

Actin content and organization in normal and transformed cells in culture

The amount of actin and total protein per cell in normal rat kidney (NRK) cells in culture is initially high in very low density cultures, but rapidly decreases as the cells come into contact in higher density cultures. In a viral transformant of NRK (442), the level of actin and total protein does not change significantly from low to high density cultures. NRK cells, which are flattened against the substrate, have prominent bundles of actinlike microfilaments in the basal cytoplasm adjacent to the substrate. 442 cells, which adhere poorly and are more spherical in shape, lack well-organized basal microfilament bundles, but may display microfilament bundles in cytoplasmic processes extending from the cell body. The percentage of insoluble actin is less than 20% in both cell lines, and 442 cells consistently contain smaller amounts than NRK cells.