Chinese Hamster Embryo Cells Research Articles

Carcinogen-mediated induction of SV40 DNA synthesis in SV40 transformed Chinese hamster embryo cells.

Exposure of SV40-transformed Chinese hamster embryo cells (line CO50) to a series of physical and chemical carcinogens (including activation-dependent and activation-independent varieties) resulted in the induction of viral DNA synthesis. The carcinogen mediated amplification of SV40 DNA was demonstrated by a highly sensitive in situ hybridization procedure for the detection of cells synthesizing SV40 DNA. Treatment of CO50 cells with an inhibitor of polycyclic hydrocarbon metabolism (7,8-benzoflavone) prior to the application of benzo[a]pyrene or 7,12-dimethylbenz[a]anthracene prevented the induction of SV40 DNA synthesis, indicating that the induction depends upon the metabolic activation of these compounds. Non-carcinogenic hydrocarbons were inactive under this assay. Two different protocols for determining the inducing potential of a compound are presented. The properties of this test and its possible use as a short-term assay for potential carcinogens is discussed. The possibility that the induction of SV40 DNA synthesis is a reflection of a general gene amplification phenomenon mediated by carcinogens is discussed.

Replication of Chinese hamster embryo cells transformed by temperature-sensitive T-antigen mutants of simian virus 40

Chinese hamster embryo cells transformed by simian virus 40 temperature-sensitive T-antigen mutants replicated when confluent at 40.5 degrees C, regardless of the selection method, selection temperature, or virus strain used.

Effect of lipid soluble antioxidants on cytotoxicity induced by photochemical products of cholesterol.

Lipid soluble antioxidants, butylated hydroxytoluene and vitamin E, were shown to suppress cytotoxicity induced by cholesterol-derived photoproducts in Chinese hamster embryo cells. These cholesterol-derived photoproducts were rather toxic.

Toxic Effects of Cholesterol Derived Photoproducts on Chinese Hamster Embryo Cells

Toxic Effects of Cholesterol Derived Photoproducts on Chinese Hamster Embryo Cells

Photodynamic mutagenicity in mammalian cells

Photoactivation of bound rose bengal in the presence of oxygen causes mutations in chinese hamster embryo cells. Visible light by itself can also cause a slight increase in mutation frequency. Both reactions are amplified by deuterium oxide. Singlet oxygen reactive compounds, β-carotene and 1,3-diphenylisobenzofuran diminish the toxic and mutagenic effects. 12-0-tetradecanoyl-phorbol-13-acetate, a potent tumor promoter, increases the number of mutants induced by the photodynamic action. The enhancement of mutagenesis by deuterium oxide and its reduction by specific singlet oxygen antagonists suggest that this active oxygen species is the direct mutagen.

Karyotype and Tumorigenicity of 1-Methylguanine-Transformed Chinese Hamster Cells2

Chinese hamster embryo cells transformed with the tRNA catabolite 1-methylguanine were characterized by Giemsa-banded karyotyping and by their tumorigenic potency in athymic nude mice. All seven 1-methylguanine-transformed cell lines were hyperdiploid with a modal chromosome number of 23. Three of these lines had an additional marker chromosome derived from the long (q) arm of chromosome no. 4, and they had alterations of chromosome no. 5 as well. Two of these three cell lines were tumorigenic. Nonrandom chromosome changes were observed in the other four 1-methylguanine-transformed cell lines, which included the addition of all or a portion of chromosome no. 6. One of these cell lines was also tumorigenic in nude mice, Specific cytogenetic changes were observed in most 1-methylguanine-transformed populations in contrast to the karyotypic heterogeneity of a benzo[a]pyrene-transformed cell line.

Cytogenetic Studies of a Simian Virus 40 Temperature-Sensitive Mutant-Transformed Chinese Hamster Cell Clone at the Permissive and Nonpermissive Temperature<xref ref-type="fn" rid="FN1">2</xref>

A clone of Chinese hamster embryo cells transformed by tsA58, the temperature-sensitive mutant of simian virus 40, was analyzed for chromosome abnormalities at the permissive temperature (37 degrees C) and nonpermissive temperature (40.5 degrees C). Trypsin-Giemsa-banded metaphases were analyzed 1 week after the temperature shift. The metaphases from cells at both temperatures were pseudodiploid, with numerous chromosome changes primarily affecting chromosomes no. 1 and 2. Other chromosomes (no. 6, 11, and the X) were also frequently involved. A marker chromosome, LM, was present in 35% of the cells at 40.5 degrees C.

Simian virus 40 A gene function: DNA content analysis of Chinese hamster cells transformed by an early temperature-sensitive virus mutant.

Replication of two Chinese hamster embryo cell lines transformed by an early temperature-sensitive mutant of simian virus 40, tsA58, was examined by flow microfluorometry and autoradiography of [3H]thymidine-labeled cells in order to determine whether transformed cell DNA synthesis is initiated by the virus A gene. At the permissive temperature (37 degrees), cells transformed by the mutant were like the wild-type virus transformants in appearance, colony-forming ability, high saturation density, and rapid replication. At the nonpermissive temperature (40.5 degrees), the tsA58 transformed cells resembled normal embryo fibroblasts and seem to return to normal growth patterns. Although both mutant transformed cell lines at 40.5 degrees appeared to cease growth at low saturation density, the cells did not enter a resting state, but continued to replicate. The cultures were maintained at low densities by a balance among cell replication, cell death, and sloughing of dead cells into the supernatant. These results suggest that the simian virus 40 A gene function effected by the tsA58 mutation does not prevent Chinese hamster embryo transformed cells from entering a resting state, although the gene may control other phenotypic characteristics of transformation.

Cell transformation by exogenous methylated purines

Primary Chinese hamster embryo cell cultures generally yield cell lines with a finite lifetime in culture. However, these cells can be converted to continuous lines by exogenous 1-methylguanine and 7-methylguanine, two normal degradation products of tRNA. Continuous lines have also been obtained by treatment with 3-deazaguanine and the carcinogenic hydrocarbon 3,4-benzpyrene, but not with guanine, 3-methylguanine, or the carcinogen l-ethionine. Continuous lines do arise spontaneously at a low frequency, and lines derived after exposure to modified purines have been analyzed and compared to a spontaneously arising continuous line. The spontaneous Chinese hamster cell line has many characteristics of normal finite lines. These control cells exhibit a diploid karyotype, are not tumorigenic in nude mice, and have normal tRNA methyltransferase, methionine adenosyltransferase, and S-adenosylhomocysteine hydrolase activities. However, as compared to finite Chinese hamster cells, these cells are resistant to infection by the tumor virus SV40. The 1-methylguanine and 7-methylguanine transformed lines which have been analyzed in most detail differ greatly with regard to cell morphology. The former appear to be fibroblasts, while the latter are epithelial-like. The 1-methylguanine treated line exhibits a hyperdiploid karyotype with a modal chromosome number of 23. These cells are tumorigenic in nude mice forming well encapsulated, undifferentiated fibrosarcomas. The 7-methylguanine treated line is hypodiploid with a modal chromosome number of 21. This line is not tumorigenic in nude mice. The transformed cell lines derived by treatment with any of the modified purines or the carcinogen 3,4-benzpyrene all demonstrate elevated tRNA methyltransferase activity as well as elevated S-adenosylhomocysteine hydrolase activity. In addition, methionine adenosyltransferase activity is increased in the 3-deazaguanine and benzpyrene derived lines. Elevated levels of methylated degradation products of tRNA may then aid in maintaining the transformed state.

Antioxidant-Mediated Reversal of Ultraviolet Light Cytotoxicity

Several antioxidants were tested for their protective effect in Chinese hamster embryo cell against ultraviolet light (UVL)-irradiation. Ascorbic acid, DL-alpha-tocopherol, butylated hydroxytoluene, and reduced glutathione were all shown to reverse UVL-induced cytotoxicity. At concentrations tested, no protective effect was detected when any of these antioxidants were added prior to UVL irradiation.

Early chromosome changes in diploid Chinese hamster cells after infection with Simian virus 40.

AbstractPrimary and secondary Chinese hamster (ChH) embryo cells infected with SV40 exhibited chromosomal changes within one cell generation (24 h). The initial change seen is an increase in the number of polyploid metaphases (>10%). The majority of the polyploid cells are tetraploid (8×), however, higher ploidy values were also observed (16 ×, 32 × and 64 ×). In approximately 20–30% of the polyploid metaphases there were chromosome changes such as breaks, abnormal chromosomes and loss and addition of chromosomes. The remaining polyploids were normal in regard to chromosome number and chromosome morphology. A primary mouse embryo cell system also responded to SV40 infection with an increase in the number of polyploid cells within 48 h.

Integration of simian virus 40 deoxyribonucleic acid into the deoxyribonucleic acid of primary infected Chinese hamster cells.

Simian virus 40 deoxyribonucleic acid (DNA) became associated in an alkaline-stable form with the DNA of Chinese hamster embryo cells at 15 to 20 hr post-infection, at the time when cell DNA synthesis and T antigen were induced. The integration process was not inhibited by d-arabinosyl cytosine and was only partially inhibited by cycloheximide.

Changes in deoxyribonucleic acid synthesis regulation in Chinese hamster cells infected with simian virus 40.

Infection of primary or secondary cultures of Chinese hamster embryo cells with simian virus 40 at a multiplicity of 20 to 50 induced synthesis of the virus-specific intranuclear T antigen in 80 to 90% of the cells within 48 to 72 hr. In the infected cultures, 30 to 50% more cells were recruited into deoxyribonucleic acid (DNA) synthesis than in the controls, whether or not the cultures were confluent. The newly synthesized DNA was mostly cellular, since little virus was produced (as shown by various techniques: immunofluorescence for viral antigen, virus growth curves, and isolation of viral DNA from infected cultures). Transformed cells could be detected a few weeks after infection and produced tumors when inoculated into irradiated animals. Chromosomal changes were observed soon after infection (24 hr). Initially, there was a marked increase in the proportion of polyploid cells (8 to 14%), most of which were chromosomally normal. In a few weeks, a large majority of the infected population was polyploid (30 to 50%). Thus, the polyploid cells have the ability to proliferate. Evidence is presented to suggest that polyploid cells arise by stimulation of cells in the G(1), G(2), or S phases to undergo two or more successive periods of DNA synthesis without an intervening mitosis. With a subsequent loss or redistribution of chromosomal material, this may lead eventually to a biologically transformed cell; thus, it is suggested that the initial event(s) relevant to transformation occurs at the level of control of cellular DNA synthesis.