[Expression of virus-specific functions in 3-methylcholanthrene-induced leukemia in rats].

It was isolated and identified MR-Le virus from Wistar rats with myelogenous leukemia. The comparison of isolated in vivo and in vitro MR-Le virus with endogenous oncovirus RaLV in protein profile as well as results of molecular hybridization pointed out that RaLV did not participate in the induction of MR leukemia. The question about the role of MR-Le virus in the etiology of MR leukemia is opened now.

Expression of retrovirus-related functions in the methylcholanthrene-induced rat myelogenous leukemia.

The rat MR-leukemia (MR-Le) induced in Wistar rats by methylcholanthrene and whole-body irradiation, has been shown to be transmitted by means of cell-free filtrates of spleen and liver extracts. These earlier results lead us to determine the expression of retroviral functions by MR-Le myeloblasts in vivo and in vitro. DNA polymerase activity associated with particulate material purified from plasma of rats carrying MR-Le and from MR-Le tissue culture fluid, increased with the number of MR-Le myeloblasts.

Allogenic modification of rat sarcoma cells in vitro by staphylococcal exotoxin.

The effect of toxin preparations from Clostridium welchii and Staphylococcus aureus on the growth of some experimental animal tumor cell lines was investigated. While clostridium toxin exerted considerable cytotoxicity, it did not influence either in vivo or in vitro growth of recovered cells. However, staphylotoxin treated sarcoma cells, while showing normal in vitro growth and metabolism, exhibited decreased growth rates when transplanted into susceptible hosts.

Organization of proviral DNA and protein composition of hormonally stimulated C57Bl/10 strain-associated mouse mammary tumor virus.

Two continuous lines, BL-MaTU/A1 and BL-MaTU/s6, were established from C57Bl/10 mammary adenocarcinomas induced by DMBA-prolactin-estradiol treatment. Under in vivo stimulation with dexamethasone, insulin, prolactin, and prostaglandin A1, the cells produce detectable amounts of B-type particles with biochemical properties similar to the GR-MuMTV. Analysis of restriction endonuclease-generated fragments of cellular DNA revealed identical patterns in the integration sites and internal recognition sites of MuMTV proviral equivalents in the tumor cells and normal organs of C57Bl/10 strain mice.

Conditions for hormone-stimulated expression of endogenous C57Bl strain-associated mammary tumor virus genome.

Full MMTV-Y gene expression can occur in dexamethasone-insulin-prolactin-stimulated cell cultured derived from C57Bl/10 mammary adenocarcinomas induced by syncarcinogenic action of chemical carcinogens (dimethylbenzanthracene), and mammotropic hormones (estrogen and prolactin). The rate of the hormone-stimulated virus production, as determined by biochemical, immunological and electron microscopical methods, was comparable to the level of spontaneous MMTV production by cells of established mouse mammary cancer cultures (CCL-51 and Mm5mt/cl). On the contrary, no virus production has been detected in hormone-stimulated cultures derived from C57Bl/10 mammary tumors induced by chemical carcinogen alone (urethan).

Growth characteristics and tumorigenicity of long-term cultures of the rat RBA myelogenous leukemia.

A continuous cell line, RBA-BC, has been derived from the buffy coat of heparinized blood of a Sprague--Dawley rat with developed RBA myeloblastosis. Separations of myeloblasts from the RBA-BC cell line was accomplished by velocity sedimentation in Verografin density gradients. The cells were monitored during long-term culture by generation time analysis.

Viruses harboured in blasts of the rat myelogenous leukemia (RBA-Le), induced by chicken sarcoma virus.

It was shown that the rat myelogenous leukemia RBA-Le harbours three kinds of viruses. 1. Rat leukemogenic virus, which can be recovered from leukemic cells, medium of cultured leukemic cells and the plasma of leukemic rats.

Transformation of rat liver cells with chicken sarcoma virus B77 and murine sarcoma virus.

Rat liver cells in vitro were transformed with chicken sarcoma virus B77, giving RL(B77) cells, and with murine sarcoma virus (Harvey), giving RL(MSV) cells. Rat liver cells transformed spontaneously in vitro were designated RL cells. In addition, the RL(MSV) cell line was adapted for growth in culture fluid containing 25 mug of 5-bromodeoxyuridine per ml.