Expression of the large T protein of polyoma virus promotes the establishment in culture of "normal" rodent fibroblast cell lines.

Transfer into mouse and rat embryo fibroblasts in primary culture of cloned polyoma virus genes encoding only the large T protein led to the establishment of flat colonies in sparse subcultures at a frequency equal to that of transformation by wild-type virus. Cell lines could be derived from such colonies and maintained in culture for large numbers of generations without entering crisis. They exhibited a normal phenotype, by the criteria of growth on plastic to a low saturation density and of anchorage dependency. However, they required a lower serum concentration for growth than spontaneously established 3T3 cells. Similar results were obtained after transfer of recombinant DNA molecules encoding only the amino-terminal 40% of the large T protein, suggesting that this "immortalization" function corresponds to the activity of an amino-terminal domain of the protein. Immunoprecipitation analysis of T antigens in cell lines established after transfer of the full-size and of the truncated large T genes demonstrated the expression of the full-size large T protein and of a Mr 40,000 antigen expressed from the amino-terminal part of the gene, respectively. After transfer of a "large T only" plasmid that carries a tsa mutation, cell lines were established at 33 degrees C with the same efficiency as with the wild-type large T gene, but their growth was arrested after a shift to 40 degrees C, with a progressive loss in cell viability. This result indicates a continuous requirement for a large T function in the maintenance of "immortality."