X-irradiation enhancement of transformation by benzo(a)pyrene in hamster embryo cells

The addition of benzo(a)pyrene to cells obtained from Syrian hamster embryo cultures that had been plated to produce discrete colonies resulted in transformation. Altered colonies were not seen in controls. Prior irradiation of hamster embryo cells increased the transformation by benzo(a)pyrene, both per cell and per total colony. Maximum enhancement occurred when benzo(a)pyrene was added 48 hr after irradiation. Enhancement was greatest after 250-500 R, and decreased with higher doses of radiation. The addition of benzo(a)pyrene 72 hr after irradiation resulted in very little enhancement. Although transformation increased with benzo(a)pyrene concentration, enhancement was independent of concentration within the range used. No colony with transformed morphology was recognized among the colonies of normal cells that survived irradiation.

Transformation of rat and hamster embryo cells by extracts of city smog

Extracts of particulate matter from condensates of city air were tested for their ability to transform rat or hamster cell cultures. Uninfected rat embryo cultures were not transformed, but cultures chronically infected with Rauscher leukemia virus were transformed by benzpyrene or by extracts of city smog. The smog extracts were 600 times more active than pure benzpyrene as transforming agents. Hamster embryo cultures infected with hamster leukemia virus were equally as sensitive as leukemia-infected rat cultures to the transforming effects of smog; uninfected hamster cultures were also transformed, although tenfold higher doses of smog extract were required.

Calcium as a regulator of the proliferation of normal, but not of transformed, chicken fibroblasts in a plasma-containing medium

In a culture medium of low calcium concentration containing 5% heat-inactivated chicken plasma, normal chicken fibroblasts divide very slowly, while their counterparts transformed with Schmidt-Ruppin Rous sarcoma virus divide much more rapidly. In the same low-calcium medium, the use of heat-inactivated serum, rather than heat-inactivated plasma, results in rapid division of both normal and transformed cells. The use of heat-inactivated plasma rather than serum, and the use of a low-calcium medium, combine to permit the demonstration of a marked difference between the proliferative behaviors of normal and neoplastic cells and suggest a basis for the autonomy of the latter.

Reversal of malignant transformation by tumor DNA

Walker-256 carcinosarcoma cells grown in tissue culture medium containing inhibitory DNA prepared from the tumor are shown to have an unaltered growth in vitro, but a diminished capacity to produce malignant tumors on injection into the rat. Coincident with this change in virulence is the induction of tRNA methylase inhibitors in these malignant cells. Within days after the DNA is removed from the growth medium, the tRNA methylase inhibitors disappear and the oncogenicity reappears.

Ovarian influence on pulmonary carcinogenesis by hydrazine sulfate in BALB/c/Cb/Se mice

Daily administration of hydrazine sulfate, 1.13 mg/mouse for 150 doses, to BALB/c/Cb/Se female mice in various hormonal states varied the incidence and the average number of pulmonary tumors per tumor-bearing mouse as follows: in intact virgins, 90.0% and 3; in breeders, 100% and 14; in gonadectomized mice, 60.0% and 5. Histologically, in intact virgins, 3.3% were carcinomas and 96.6% were adenomas; in breeders, 47.2% were carcinomas and 52.7% were adenomas; in gonadectomized mice, 4% were carcinomas and 96% were adenomas. Many pulmonary carcinomas induced in breeders infiltrated the thoracic wall and the mediastinal organs and metastasized to the adrenal glands and myocardium. The greater biologic and morphologic malignancy of the induced tumors observed in breeders, as compared to those in intact virgin and gonadectomized mice, was associated with an increased ovarian hormone production.

Evidence for a DNA replicative genome for RNA-containing tumor viruses

The requirement for DNA synthesis in the reproduction of RNA tumor viruses was examined using 5-bromodeoxyuridine (BrdU). Addition of BrdU for the first 12 hr after exposure of cells to Rous sarcoma virus resulted in a large decrease in infectious progeny. However, incorporation of [(3)H]uridine into the viral RNA of virions was unaffected. Also, the numbers of virions visualized by electron microscopy were similar in BrdU-treated and untreated samples. Viral group-specific antigen was synthesized after BrdU treatment, and BrdU had little effect on transformation of cells by Rous sarcoma virus. The results support the hypothesis that the replicative genome of RNA-containing tumor viruses contains DNA.

Regulation of acetylcholinesterase in neuroblastoma cells

The specific activity of mouse neuroblastoma acetylcholinesterase (EC 3.1.1.7) increased 25-fold when the rate of cell division was restricted. The results show that acetylcholinesterase activity is regulated in neuroblastoma cells and that the regulatory mechanism is inversely related to the rate of cell division. Under the same conditions the specific activity of catechol-O-methyl transferase (EC 2.1.1.6) did not change significantly.

Tumorigenesis in mouse skin: inhibition by synthetic inhibitors of proteases

Three synthetic inhibitors of proteases (tosyl lysine chloromethyl ketone, tosyl phenylalanine chloromethyl ketone, and tosyl arginine methyl ester) inhibit the tumorigenesis initiated in mouse skin by 7,12-dimethylbenz(a)anthracene and promoted by croton oil or its active principle, phorbol ester. These protease inhibitors, when applied directly to mouse skin, inhibit some of the irritant effects of the tumor promoter and are not toxic.

Mechanism of oncogenic transformation by Rous sarcoma virus. I. Intracellular inactivation of cell-transforming ability of Rous sarcoma virus by 5-bromodeoxyuridine and light

Chick embryo fibroblasts brought into stationary phase of growth by maintenance in serum-free Eagle's MEM medium were infected with the Bryan strain of Rous sarcoma virus (B-RSV) and incubated for 18 hr in the presence of 5-bromo-deoxyuridine (BUdR). The cells were then allowed to resume growth and deoxyribonucleic acid (DNA) synthesis by addition of an enriched F12 medium containing serum and RSV antibody to prevent spread of viral infection. After 48 hr, the cultures were exposed for various periods to visible light, overlaid with solid culture medium, and observed for the appearance of foci of transformed cells. In cultures treated with BUdR at the time of infection, exposure to light resulted in a suppression of focus formation of from 50 to 90% in various experiments. Treatment with BUdR for 18 hr before infection or on the day after infection, followed by exposure to light, had no effect on focus formation. In cultures in which almost all cells were infected, treatment with BUdR followed by exposure to light did not result in cell death. This suggests that suppression of transformation is not due to selective killing of infected cells by this treatment but rather to the intracellular inactivation of the transforming ability of Rous sarcoma proviral DNA.