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Five human cell lines producing oncornaviruses type D were studied by the method of molecular hybridization of viral and cellular nucleic acids. Repeated sequences of viral genome equivalents were found in nuclear DNA and numerous copies of viral genome were found in the cytoplasm. The viruses produced by the cell lines were found to be identical or closely related as regards nucleotide sequences of their genomes.

Here we report studies on non-viral proteins specific for transformation precipitated by immune sera. These sera were from rats injected by PR-RSV transformed rat XC cells and from rabbits immunized by subcutaneous injections of cytoplasmic membranes from rat cells transformed by Fujinami avian sarcoma virus. Immune complexes were analyzed in one- or two-dimensional gel electrophoresis and by autoradiography. Only by using antisera obtained from rats bearing XC-cells induced tumors, two proteins were identified with an apparent molecular weight (Mr) of 105 000 (p105) and 98 000 (p98) and an isoelectric point of 6.4 and 6.2, respectively, in extracts of mammalian cells transformed by avian sarcoma viruses (ASV). These proteins were common to all ASV-transformed cell lines. In kinase reaction, the protein p98 can be phosphorylated. Similar proteins were neither detected in normal nor in chemically transformed cells. None of the proteins were precipitated with control serum from rat, rabbit, and goat.

The method of molecular hybridization of nucleic acids of oncornavirus type D produced by HEp2 cells with cellular nucleic acids was applied. No sequences homologous to the viral nucleic acids were found in normal human embryo cells as well as in bovine, porcine, murine, and chicken cells. No such sequences were found in tissues of malignant lymphomas. Sequences homologous to the viral nucleic acids were found in some cancer cells, predominantly in hormone-associated tumors of females.

The results of studies of a co-carcinogenic effect of two human infectious viruses in tissue culture are reported here. Viable vaccinia virus actively replicating in the cells of primary BALB/c tissue culture and in a number of continuous murine cell lines has been shown to induce in them expression of major structural p30 protein of murine retroviruses. Vaccinia virus has been also shown to cause biochemical transformation of murine cells. Evidence for the capacity of herpes simplex virus type 2 to induce malignant transformation of BALB/3T3 murine cell line has been obtained and confirmed by transplantation to mice. Transformed cell clones did not contain complete infectious herpes simplex virus but were resistant to superinfection with this virus. N-tropic endogenous murine retrovirus of C type with buoyant density in the saccharose density gradient of 1.18 g/cm3 and a reverse transcriptase activity was expressed in the transformed cells. In the virion structure six proteins typical of these viruses with the prevalence of p30 have been demonstrated. Competitive radioimmunoassay revealed a very high level of virus production: p30 level reached 7500 ng p30 R-MuLV per mg of viral protein. Specificity of this results was shown in control experiments.

Comparative study has shown that by the gel diffusion assay both anti-HEp-2 virus serum and anti-breast cancer milk ultrasediment serum precipitated an identical antigen in human milk specimens, which was not identical with the group specific antigen of the HEp-2 virus. At the same time tha anti-breast cancer milk serum did not precipitate the HEp-2 virus. However, molecular hybridization experiments revealed nucleotide sequences homologous to nucleic acids of oncornavirus of D-type in milk obtained from breast carcinoma patients as well as in milk of healthy donors.