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6 Transformation by Polyoma Virus and SV40


Cell division is controlled in multicellular organisms. Tumours grow because cancer cells continue to multiply in conditions which regulate the multiplication of normal cells. Polyoma virus and SV40 can effect this change in the growth control of a cell and these viruses cause tumours when they are injected into susceptible animals. Transformation of cells growing in vitro by these viruses is believed to be an analogous process to the induction of tumours in animals because cells transformed in vitro by polyoma virus and SV40 acquire a set of properties (see Table 6.1), some of which, including increased malignancy, are characteristic of tumour cells. It is well to remember, however, that the tumours which polyoma virus and SV40 induce when they are injected in large amounts into susceptible rodents do not usually metastasize; neither does the histology of such induced tumours closely resemble the histology of spontaneous malignant tumours. This is also true of the tumours which develop when cells transformed in vitro by these viruses are injected into host animals. In other words, transformation of cultivated fibroblasts by these viruses provides a model system in which we can study in a quantitative way at least some of the events that lead to the seemingly spontaneous development of malignant tumours in animals and man.

Cell lines are maintained in culture by the periodic replacement of the medium and serum. Populations of untransformed cells divide while they remain sparse, but as the cell density and the number of cell to cell contacts...

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