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Studies on the transformation of mammalian cells by polyoma virus Babiuk, Lorne Allan Ben


Studies were made on the oncogenic properties of a line of polyoma virus-transformed hamster cells. Transplantation of the cells resulted in an increase in oncogenicity. Thus the latent period for the appearance of a tumor was decreased, and as few as five to ten cells were sufficient to produce a tumor in a young hamster. Histological examination revealed marked differences between tumors produced by transplantation of transformed cells and tumors produced by infectious virus. Powassan virus, a group B arbovirus, did not show any oncolytic activity towards tumors induced by polyoma virus-transformed cells. A variety of treatments (ultraviolet irradiation; mitomycin C; heat shocks; and cell fusion) proved unsuccessful in attempts to rescue polyoma virus DNA or infectious virus from polyoma virus transformed cells. In analogous experiments, using simian virus-40-transformed cultures, the rescue process was followed by readily detectable synthesis of SV40 DNA and infectious virus. The ability of heterokaryons (mouse kidney - PyH-1 cells or mouse embryo - 'normal' hamster cells) to support virus multiplication was tested. The presence of hamster nuclei and cytoplasm in heterokaryons, proved inhibitory to polyoma virus multiplication. This inhibitory effect was more pronounced if the hamster cells had been transformed with polyoma virus. Evidence has been presented for the integration of viral DNA into cellular DNA during productive infection of mouse embryo cells as well as in BHK-21 cells, a cell line which does not support virus multiplication but in which a small percentage of the cells can become transformed. Two separate methods were employed to detect viral DNA association with cellular DNA: 1) separation of viral DNA from cellular DNA by precipitation of the latter with salt: 2) separation of cellular DNA (> 100s) from viral DNA in alkaline sucrose gradients. The presence of viral DNA in the cell DNA fraction of alkaline sucrose gradients indicated that viral DNA was associated in an alkaline stable linkage.

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