[Random distribution of the level of growth factors in malignant and revertant clones from murine and human tumors]. / Sluchainoe raspredelenie urovnia ékspressii rostovykh faktorov u zlokachestvennykh i revertantnykh klonov myshinykh i chelovecheskikh opukholei.

It is well known that artificial increase in expression of growth factors and their receptors can lead to tumorigenic transformation of cells. Additionally, multiple data on the increased expression of growth factors in many human and animal tumorigenic cells have been published. Nevertheless description of the functional role of endogenous growth factors in maintenance of tumorigenic phenotype remains obscure. Previously, we described a new model for studying neoplastic transformation and dormant metastasis. This model consists of cognate tumorigenic and nontumorigenic cell clones, the latter being obtained as a result of spontaneous reversion of tumorigenic ones. All revertant clones demonstrate the three well known features of normal cells: monolayer growth on a plastic, incapability to grow in soft agar with regular culture media with 10% FCS, and incapability to form tumors in syngeneic animals. Using RT-PCR, we measured expression ratios of main growth factors, commonly believed to be associated with malignization, in tumorigenic and revertant clones of our model. For some of these clones, we also measured an activity of growth factors in conditioned media. The data obtained argue that the levels of growth factor expression, measured by both the methods, are distributed between tumorigenic and revertant clones in a sporadic manner and do not correlate with cell tumorigenicity. Thus, our experimental observations enable us to consider the variability of growth factor expression as insignificant events in the reversion of tumorigenic cells to a nontumorigenic phenotype.

[Spontaneous reversion of tumor cells as a source of dormant metastases]. / Spontannaia reversiia opukholevykh kletok kak istochnik molchashchikh metastazov.

In the present paper we have shown that JB6 and PDV murine skin carcinoma cells, as well as previously described sarcoma B6-4 cells, can revert to a nontumor phenotype. Revertant carcinoma clones could not grow in soft agar conditions and like sarcoma revertants acquired dependence on peptide growth factors, and exhibited a reduced expression of c-jun. Spontaneous revertants were shown to be instable. They could revert back to a transformed phenotype in 1-5 months of in vitro passaging. Being inoculated in syngeneic animals, these transformed cells show a recurrence in 2-5 months, similar to that of a dormant metastasis. Thus, dormant revertant cells are believed to be included in many tumors of different origin. So, spontaneous reversions of tumor cells may play an important role in the dormant metastatic process. The cause of these frequent spontaneous transient reversions and revertant instability appears to be of epigenetic nature. Causes and mechanisms of cell transformations and reversions remain to be clarified.

[Regulation of the expression of the c-fos gene in cells, reverting from being transformed to the pseudonormal phenotype]. / Reguliatsiia ékspressii gena c-fos v kletkakh, revertiruiushchikh ot transformirovannogo k psevdonormal'nomu fenotipu.

Regulation of c-fos expression in mice sarcoma cell lines CBA and C3H was investigated. Each of the cell lines was represented by a pair of clones: the tumorigenic and the one, which was produced from it by cloning. It was found, that c-fos expression in cells of the pseudonormal phenotype was similar to that in the normal fibroblasts. Experiments with cells reverted to pseudonormal phenotype transfected transiently or permanently with an indicator plasmid fos-cat have shown, that a 600 bp sequence of the c-fos promotor including the TATA site, provides the expression level of the chloramphenicol acetyltransferase, correlating with the level of the c-fos mRNA expression. In the tumorigenic cells, permanent high activity of the cat gene expression was observed which was comparable to that in the normal fibroblasts stimulated by the embrionic serum or TPA. Activity of the transcription factors interacting with regulatory elements SRE, DSE, TRE did not correlate with the c-fos expression level in all the cells.

[The spontaneous aneuploidy of the embryonic fibroblasts in C3H/He and CBA/Ca mouse strains occurring during their neoplastic evolution]. / Spontannaia aneuploidiia émbrional'nykh fibroblastov myshei linii C3H/He i CBA/Ca, voznikaiushchaia v protsesse ikh neoplasticheskoi évoliutsii.

Karyological analysis of 6 cell lines with distinct tumorigenic properties of mouse strains C3H/He and CBA/Ca has been carried out using differential chromosome staining. All the cell lines are characterized by a decreased number of copies of normal chromosome 7, the increased number of normal copies of chromosome 10 being specific of the cell lines with intermediate tumorigenicity. Cell lines with maximum tumorigenicity differed from all other lines by the increased number of copies of chromosome 5 and by the decreased number of copies of chromosome 6. A wide independent variability was observed in the number of chromosomes and of several types of abnormal chromosomes throughout the neoplastic evolution of cells, to begin from the early immortal passages. But the proportion of normal chromosomes per cell in the studied lines revealed relatively stable values. The potential phenotypical heterogenicity of the lines with maximum tumorigenicity, expressed in their clonal progeny, was associated with the instability in the number of chromosome 15 copies in cells of these lines. It is concluded that multiple genetic events are required in the spontaneous neoplastic evolution of fibroblasts, and only specific traits of the karyotypic instability, associated with the variability of the number of copies of specific chromosomes, may constitute the genetic basis for the above process.

[The rate of macrophage inclusion in the elimination of tumor cells when administered to syngeneic animals]. / Skorost' vkliucheniia makrofagov v éliminatsiiu opukholevykh kletok pri ikh vvedenii singennym zhivotnym.

A degree of destruction of tumour cells after their inoculation to a syngenic recipient correlates positively with sensitivity to the lytic effect of macrophages. A clear-cut participation of macrophages in elimination of tumours cells can be detected 8 h after their inoculation.

[The karyotypic variability of mouse embryonic fibroblasts of 2 genotypes during spontaneous neoplastic transformation]. / Kariotipicheskaia izmenchivost' émbrional'nykh fibroblastov myshei dvukh genotipov v protsesse spontannoi neoplasticheskoi transformatsii.

Karyological analysis of 6 lines with distinct tumorigenic properties of mouse strains C3H/He and C57BL/6 has been carried out using a differential staining of chromosomes. The number of normal copies of chromosomes varied in all the investigated cell lines. The more and the less stable chromosomes different from line to line. All the cell lines were characterized by decreased numbers of copies of normal chromosome 7; a decreased number of normal copies of chromosome 2 and 16 was detected in the course of the cell spontaneous neoplastic evolution. The decreased number of normal copies of chromosomes 8, 12 and X, and the increased number of normal copies of chromosome 10 were specific of the cell lines with intermediate tumorigenicity. The maximum tumorigenic cell lines differed from all other lines by increased numbers of copies of chromosomes 4 and 5, and by a decrease in copy number of chromosome 6. The data obtained are discussed in terms of the search of the regularity of karyotypic changes in the course of the cell neoplastic evolution.

[Changes in the growth characteristics of mouse and rat fibroblasts during tumor progression]. / Izmenenie rostovykh kharakteristik fibroblastov myshei i krys v protsesse opukholevoi progressii.

Changes in growth characteristics (the growth in a mat of normal cells, contact inhibition of division, growth-substrate dependence, dependence on the serum growth factors) and tumourigenicity were compared in 6 cells lines of mice and rats during their in vitro and in vivo long passages. All these factors progressed independently of a tumourigenicity increase, i.e. they obeyed the Fould principle. The trait responsible for the cell capacity to proliferate on a layer of normal cells proved to be the most correct one relative to tumourigenicity prediction.

[Heterogeneity of mouse sarcoma cells based on tumorigenicity determined by the different degree of contact inhibition of cell division]. / Geterogennost' kletok myshinoi sarkomy po opukholerodnosti, obuslovlennaia raznoi stepen'iu kontaktnogo tormozheniia deleniia kletok.

The mouse CBA sarcoma characterized by great cellular heterogeneity was obtained from spontaneously in vitro transformed embryonic fibroblasts. The clones of the given sarcoma distinct in this property were studied. It was shown that the only feature limiting the growth of clones characterized by weak tumorigenicity was contact inhibition of cellular growth. This property is easily estimated by the in vitro methods.

[Heterogeneity of murine sarcoma cells for transplantability due to their different susceptibilities to the lytic action of macrophages]. / Geterogennost' kletok myshinoi sarkomy po privivaemosti, obuslovlennaia ikh raznoi chuvstvitel'nost'iu k liziruiuemu deistviiu makrofagov.

Sarcoma was induced in C57BL/6 mice with 20-methylcholanthrene. The sarcoma cells were found to be heterogeneous in their transplantability. The study of 9 clones distinct in this property has shown that heterogeneous transplantability was due to different susceptibility to lytic action of macrophages.

[Markers of malignant transformation in mouse cell lines]. / Issledovanie markerov zlokachestvennoi transformatsii v liniiakh kletok myshei.

The expression of three phenotypic markers of transformation in vitro, i.e. serum dependence, contact inhibition and anchorage dependence of growth has been investigated using the lines of mouse cells obtained from spontaneously in vitro transformed embryonal fibroblasts (three stages of a continuous passage in vitro being considered) and from induced tumours. The results obtained indicate that in the cell lines arising spontaneously in the continuous passage in vitro the origin of the transformation features can be observed. Anchorage independence demonstrates not high (r = 0.69) but much better correlation with tumourigenicity than other studied markers.

[The "immunologic portrait" and tumorigenicity of neoplastic cells induced in mice by 3-methylcholanthrene]. / "Immunologicheskii portret" i opukholerodnost' kletok novoobrazovanii, indutsirovannykh u myshei 3-metilkholantrenom.

Immunogenicity of 11 3-methylcholanthrene-induced tumours has been tested in vitro, which was a necessary step in constructing a complex characteristic of cell resistance to the host immune reactions. Such a complex estimate is shown to be useful for predicting the extreme tumourigenicity variants in vivo.

[Immunological and morphological properties of in vitro transformed fibroblasts. III. Recognition by macrophages and activated lymphocytes of mouse and rat cells of various degrees of tumorigenicity]. / Immunologicheskie i morfologicheskie svoistva fibroblastov, transformirovannykh in vitro. III. Raspoznavanie makrofagami i aktivirovannymi limfotsitami myshinykh i krysinykh kletok raznoi stepeni opukholerodnosti.

Data are provided on the development of tumorigenicity in cells of 6 independently produced lines of mouse and rat embryonic fibroblasts during their prolonged passage in vitro. The data on the development of lysis of these cells by macrophages and activated lymphocytes during the same passage indicate that enhanced cell lysis of cells by natural effectors and, hence, cell recognition by them may be regarded as an obligatory manifestation of cell malignization.

[Immunological and morphological properties of fibroblasts transformed in vitro. II. The change in the susceptibility of FC3H3 cells to lymphocytes--natural killers and macrophages during their selection for malignancy]. / Immunologicheskie i morfologicheskie svoistva fibroblastov, transformirovannykh in vitro. II. Izmenenie chuvsvitel'nosti kletok FC3H3 k limfotsitam--estestvennym killeram i makrofagam v protsesse ikh selektsii na zlokachestvennost'.

The previous report contained the information on obtaining in vitro continuous cell lines of embryonic fibroblasts of mice of 4 genotypes, including C3H. In this paper, data on the degree of lysis of some derivatives of FC3H3 cells by natural killers and macrophages are given. It was shown that normal cells were not lysed by these effectors unlike cells which overcame Hayflick's limit and got minimum malignancy in vitro. However, it was established that the in vivo selection of cells for high tumorigenicity resulted in the formation of tumor cells resistant to lymphocytes--natural killers and macrophages.

[Immunological and morphological properties of fibroblasts transformed in vitro. I. The isolation of continuous mouse cell lines, their malignancy, H-2 antigens and complement sensitivity]. / Immunologicheskie i morfologicheskie svoistva fibroblastov, transformirovannykh in vitro. I. Poluchenie dlitel'no perevivaemykh myshinykh kletochnykh linii, ikh zlokachestvennost', H-2-antigeny, chuvstvitel'nost' k komplementu.

7 continuous cell lines with different degrees of malignancy were obtained from cultures of embryo fibroblasts of 4 strains of mice. Three of them were selected in vivo for enhanced malignancy. A study of regularities of changes in immunologic and some cytologic characteristics of these cells in the processes of transformation and malignization has been started. The data are presented that in these processes the density of H-2 antigens in embryo fibroblasts many vary significantly in both directions. These alterations are stochastic and do not depend on transformation or malignization of cells. It is also shown that the sensitivity of the cells under study to the complement lytic action may significantly vary, and does not always correlate with the density of antigens which are the targets of the complement lytic action.

[Mechanism of lysis by natural killers of target cells infected with Mycoplasma]. / K mekhanizmu lizisa estestvennymi killerami kletok-mishenei, zarazhennykh mikoplazmoi.

NK lymphocytes destroyed target cells contaminated with Mycoplasma to a greater extent as compared with normal cells. The mechanism of that phenomenon is based on the production into the environment by effector lymphocytes cocultivated with contaminated cells of high quantity of mycoplasma that has a non-specific cytolytic effect.