Analysis of malignancy in human cells: malignant and transformed phenotypes are under separate genetic control

Human cell hybrids derived from malignant HeLa and normal fibroblast parental cells expressed many of the transformed properties of the HeLa parent but their tumor-producing capability was suppressed. Hybrids derived from HeLa/HeLa fusions retained both their transformed and malignant phenotypes. Thus, an apparent separation of the control of the transformed versus malignant phenotype is indicated. Furthermore, several transformed properties--including lack of density-dependent inhibition of growth, lectin agglutination, lowered requirement for serum growth factors, and anchorage independence--are expressed coordinately in the nontumorigenic hybrids. This finding suggests that none of these properties by themselves, or in concert, endows a cell with tumorigenic potential.

Neoplastic transformation of human diploid fibroblast cells by chemical carcinogens

Cultured fibroblast cells derived from a skin biopsy sample taken from normal human adult were exposed to a potent carcinogen, 4-nitroquinoline 1-oxide. Alterations of cell growth pattern such as higher density and piling up of cells were noticed in some fractions of cultures that were successively subcultured after nitroquinoline oxide treatment. Morphologically altered cells retained this growth pattern and became established lines of transformed cells without showing the limited life-span characteristic of normal cells in culture. The transformed cells showed a higher saturation density and the ability to grow in soft agar, properties that are usually correlated with neoplastic transformation of cells in culture. Selection of preexisting transformed human cells as a mechanism of this observed transformation seemed unlikely because clones of these normal cells could also be used to assess the transforming effect of nitroquinoline oxide. Preliminary results suggest that numerous cell divisions were required for the development of the transformation after nitroquinoline oxide treatment of these human cells. When the transformed cell lines were injected subcutaneously into nude (athymic) mice, solid tumors were produced at the site of inoculation. Treatment with N-methyl-N'-nitro-N-nitrosoguanidine also induced cell transformation, in a manner similar to treatment with nitroquinoline oxide. However, transformation was not induced with (i) 4-aminoquinoline 1-oxide (a noncarcinogenic derivative of 4-nitroquinoline 1-oxide), (ii) 3-methylcholanthrene (a carcinogen that cannot be metabolically activated by the target cells employed), or (iii) the solvent dimethyl sulfoxide.

Stable transformation of mouse, rabbit and monkey cells and abortive transformation of human cells by BK virus, a human papovavirus

Semi-permissive mouse, rabbit and monkey cells were stably transformed by BK virus (BKV). The specificity of transformation was demonstrated by the presence of BKV tumour (T) antigen in nuclei of transformed cells and by virus rescue with Sendai virus-mediated fusion or transfection. Two out of seven BKV-transformed cell lines were oncogenic. Permissive human cells were only abortively transformed by BKV, since morphologically modified cells persisted in culture for a few passages and eventually died.

Binding of dextran sulfate by virus-transformed cells, with reference to altered growth behavior by its treatment

Binding of 3H-labeled dextran sulfate on transformed and untransformed cells was studied in relation to the altered growth of transformed cells by this treatment. 3T3 and SV3T3 cells, and the isolated cells (SV3T3-R5) insensitive to dextran sulfate treatment were used. The rate of binding of 3H-dextran sulfate on SV3T3 cells was dose-dependent when examined by the liquid scintillation method. It was revealed in autoradiographic analysis that there was no difference in the binding capacity of 3H-dextran sulfate among 3T3, SV3T3, and SV3T3-R5 cells. The rate of binding proceeded linearly during the first 10 hr and then tended to decline. Thin sections (0.3 approximately 0.5 micron) of SV3T3 cells were autoradiographed to examine the site of localization of 3H-dextran sulfate. Depending on the incubation time with the cells, 3H-dextran sulfate was located first on the cell surface and then in the cytoplasm when incubated further. Finally, silver grains were detected even in the nucleus of SV3T3 cells. This process of localization was similar in 3T3 cells. Binding of 3H-dextran sulfate on SV3T3 cells was independent of the presence of calf serum in the medium.

Cell contact-induced inhibition of division in Dictyostelium

The developmental stage at which Dictyostelium discoideum strain v12/M2 cells was inhibited in resuming cell division was monitored by a Coulter counter. Neither vegetative nor pre-aggregating v12/M2 amoebae used as inocula in liquid growth cultures exhibited a delay in recommencing cell division. Inocula prepared from aggregates were delayed for 3 h before the onset of division. Although cyclic AMP had no effect upon vegetative or preaggregating stages the aggregating amoebae were inhibited for 9 h before resuming division. Following the onset of division by both controls and cyclic AMP-treated cells the normal growth rate of vegetative amoebae (3.2 h/generation) was attained. Aggregateless mutant vegetative amoebae and those of comparable ages to vas/M2 aggregates were not inhibited in the rate of cell division by cyclic AMP. Cyclic AMP sustains the delay in cell division only among amoebae derived from aggregates. Cyclic AMP induces structural components in the plasma membranes which may be necessary in cell adhesion and interactions. Consequently interactions between the membranes of apposing cells may transmit stimuli intracellularly to inhibit cell division.

Recent advances in the study of membrane bound saccharides

The review discusses with the biosynthesis, the changes upon cell density or transformation, the external exposure and the physiological functions of the saccharide moieties of membrane bound sphingoglycolipids and glycoproteins. The structure of biological membranes and some cellular recognition functions tentatively ascribed to membrane bound glycosyl transferases are also reviewed.

Factors involved in the modulation of cell proliferation in vivo and in vitro: the role of fibroblast and epidermal growth factors in the proliferative response of mammalian cells

The control of proliferation of mesoderm-derived cells by EGF and FGF has been examined taking, as an example, the vascular endothelium. The mechanisms by which cell proliferation can be brought to a stop in vivo and in vitro have been reviewed.

Role of contact inhibition in the regulation of receptor-mediated uptake of low density lipoprotein in cultured vascular endothelial cells

Bovine vascular endothelial cells during logarithmic growth bind, internalize, and degrade low density lipoprotein (LDL) via a receptor-mediated pathway. However, contact-inhibited (confluent) monolayers bind but do not internalize LDL. This is in contrast to aortic smooth muscle cells or endothelial cells that have lost the property of contact inhibition. These cells internalize and degrade LDL at both high and low cell densities. The LDL receptors of smooth muscle and sparse endothelial cells down-regulate in response to LDL. In contrast, normal endothelial cells at confluency show little response. When contact inhibition in endothelial monolayers was locally released by wounding, and LDL was present, only cells released from contact inhibition accumulated LDL cholesterol. In smooth muscle cells under the same conditions, the entire culture interiorized lipid. It thus appears that in endothelial cells, unlike smooth muscle cells, contact inhibition is the major factor regulating cellular uptake of LDL cholesteryl ester. Reversal of contact inhibition by wounding provides a mechanism by which the endothelium could be the primary initiator of the atherosclerotic plaque.

Surface ATPase activity at cell-cell contacts in hepatic parenchymal cells and in cAMP-treated hepatoma cells in monolayer culture

Histochemical investigation shows that ATPase activity is located intensively on the surface of cell contacts in hepatoma cells grown in confluent monolayer culture. Dibutyryl cyclic AMP and theophylline-treated hepatoma cells which exhibit contact-inhibited growth show the absence of localization of intense ATPase activity at cell-cell contacts. However, after removal of these additives the activity fully recovers to the intense level of control cells, when the release of cells from contact inhibition of growth occurs. Cultured hepatic parenchymal cells in monolayer have little or no ATPase activity at their surface immediately after contacts are established, and again after growth to a confluent state. In a different type of hepatoma cell which is less malignant and forms a small tissue mass or island, cell surface ATPase activity at cell-cell contacts in an island is very weak or scarcely detected even when cells are not treated with dibutyryl cyclic AMP and theophylline.

Restoration of in vitro growth control to malignant cells

A glycoprotein (molecular weight, ca. 160,000) from culture medium of contact-inhibited hamster melanocytes restores contact inhibition of growth to malignant melanocytes of man, mouse, and hamsters, and also effectively inhibits growth in vitro of a broad spectrum of malignant and normal cell types of ectodermal, mesodermal and endodermal origins, including human colon carcinomas. The melanocyte contact inhibitory factor (MCIF) produces G1 growth arrest in malignant melanocytes; inhibition of all cell types is reversible, does related, and nontoxic at concentrations below 200 microgram/ml, but selectively lethal to malignant cells at higher concentrations. An electrophoretically identical protein is present in culture media of contact-inhibited melanocytes, fibroblasts, and epidermal cells, but absent from those of colon carcinomas, HeLa cells and malignant melanomas. Nevertheless, an MCIF-like band is present in whole cell homogenates of human colon carcinomas and hamster melanomas. MCIF may permit normal surface interactions required for feedback inhibition of growth.

A proposal that malignancies represent genetic changes in cell surface RNA

A great number of experimental studies have now been performed with malignant cells. The mass of data generated presents a confusing and often apparently contradictory picture of the fundamental molecular biological defect which most scientists sense must be the cause of transformation of a normal cell into a malignant one. This paper proposes the hypothesis that RNA on the exterior of the cell membrane organizes the various functional molecular aggregates such as transport complexes (permeases), lectin receptor sites, transmembrane microfilament attachment sites, hormone receptor complexes, and the elusive contact inhibition components. Furthermore it is proposed that a defect in the production of or competition for the assembly of exterior-organizer RNA (exoRNA) complexes is the primary molecular defect inherent in all malignancies. The defect could be caused by deletion of a chromosome region producing or controlling exoRNA, mutation of the genes involved in exoRNA production or by insertion of viral genetic material into the genome thereby producing an incomplete viral RNA (vRNA) which competes for exoRNA binding sites in cell surface complexes. Such changes would be genetically transmitted and could represent a range of genetic change between chromosomal deletion and point mutation. Several experiments are suggested to directly test the hypothesis.

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

The social behavior of 3T3 cells and their polynoma virus-transformed derivative (Py3T3 cells) was examined by time-lapse cinemicrography in order to determine what factors are responsible for the marked differences in the patterns formed by the two cell lines in culture. Contrary to expectations, both cell types have been found to exhibit contact inhibition of cell locomotion. Therefore, the tendency of 3T3 cells to form monolayers and of Py3T3 cells to form crisscrossed multilayers cannot be explained on the basis of the presence versus the absence of contact inhibition. Morevover, with the exception of cell division control, the social behavior of the two cell types is qualitively similar. Both exhibit cell underlapping and, after contact between lamelliopodia, both show inhibition of locomotory activity and adhesion formation. Neither cell type was observed to migrate over the surface of another cell. The two cell types do show quantitative differences in the frequency of underlapping, the frequency with which contact results in inhibition of locomotion, and the proportion of the cell margin that adheres to the substratum. The increased frequency pf Py3T3 underlapping is correlated with the reduced frequency of substratum adhesions, which in turn favors underlapping. On the basis of these observations, it is concluded that the differences in culture patterns are the result of differences in the shapes of the individual cells, such that underlapping, and hence crisscrossing, is favored in Py3T3 cell interactions and discouraged in 3T3 cells.

Intracellular protein degradation in growing, in density-inhibited, and in serum-restricted fibroblast cultures

Exponentially growing Balb/3T3 mouse fibroblasts contain protein populations with slow and fast turnover. These two stability classes were labelled selectively with 3H-leucine. The intracellular degradation of the proteins was then followed as the release into the medium of radioactive leucine. The degradation rate of both stability classes of protein is increased by about 55% in cultures whose growth is inhibited by high cell density. Serum-deprivation, which also halts cell growth, accelerates protein breakdown to a smaller extent, the increases for relatively stable and unstable proteins being 30% and 13%, respectively. The density-dependent increase in protein breakdown is also found in BHK21 cells but not in chick fibroblasts. Protein degradation in Balb/3T3 cells transformed by simian virus 40 is affected by serum-deprivation but not by cell density. The proteins which are relatively stable during growth were shown to become less stable in density-inhibited or serum-deprived cultures, and vice versa. Cycloheximide inhibits degradation to a variable extent. Dibutyryl adenosine-3',5'-cyclic monophosphate has no effect on the protein degradation under the conditions investigated here.

Specific changes in the collagen phenotype of BALB 3T3 cells as a result of transformation by sarcoma viruses or a chemical carcinogen

Radioactive proline-labeled procollagen, accumulated during a 3-hr incubation of normal and transformed BALB 3T3 cultures, was treated with pepsin and the resulting collagen components were analyzed by carboxymethyl-cellulose chromatography and sodium dodecyl sulfate/polyacrylamide gel electrophoresis in the presence or absence of reducing agent. Collagen in the medium of three subclones of BALB 3T3 A-31 that exhibited contact-inhibition of growth at confluence, as well as in the medium of one that did not, consisted of alpha(1) and alpha(2) subunits in the ratio of 3:1, suggesting that 3T3 cells synthesize type I collagen, [alpha(1)(I)](2)alpha(2), and another type, which we have designated X, composed of alpha(1) chains, which may or may not be identical to alpha(1)(I). Culture medium from 3T3 transformed by Kirsten or Moloney sarcoma virus contained type I collagen and another type differing from I and X and designated as type Y. The latter appeared to be similar to type III collagen [alpha(1)(III)](3), since it contained intrahelical disulfide bonds. Analysis of intracellular collagen also demonstrated the presence of type III in Ki-3T3 and its absence from 3T3 cells. Collagen components from the medium of a simian virus 40 transformant were identical to those of the contact-inhibited clones, while the collagen from a 4-nitroquinoline-1-oxide-induced transformant was composed mainly of two components differing from alpha(1)(I), alpha(2), or alpha(1)(III). These results suggest that the type of collagen accumulated in transformed cell cultures may be specifically related to the transforming agent.