title: Reinitiation of host DNA synthesis in senescent human diploid cells by infection with Simian virus 40.
abstract: Human diploid fibroblasts, TIG-1, cease to proliferate at about 60-62 population doubling level. In their senescent state used in this study, the percentage of nuclei labeled by [3H]thymidine for 48 h was around 1-2% in fresh medium containing 5-40% fetal bovine serum. The percentage of labelled nuclei increased up to 10-fold after infection with SV40. This increase reflects stimulation of cell DNA synthesis because: 1. The increase also occurred when ts A900 was used for infection at the non-permissive temperature, under these conditions viral DNA synthesis is inhibited; 2, the increase paralleled the stimulation of [3H]thymidine incorporation into DNA in a Hirt-precipitate fraction from SV40-infected cells. UV-irradiated SV40 had reduced ability to induce DNA synthesis. A viable deletion mutant of SV40, d1940, had almost the same activity to induce cell DNA synthesis as did wild-type SV40. Equilibrium density gradient centrifugation analysis of DNA labelled with 5-bromodeoxyuridine (BrdU) supported semiconservative replication rather than repair synthesis. We conclude that a considerable fraction of human diploid cells in a senescent population initiate host DNA replication by infection with SV40, although these cells cannot be stimulated with fetal bovine serum.
mesh_terms: D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D002460:Cell Line; D002470:Cell Survival; D004247:DNA / Q000096:biosynthesis*; D004260:DNA Repair; D003849:Deoxyguanosine / Q000378:metabolism; D005347:Fibroblasts; D006801:Humans; D013539:Simian virus 40 / Q000276:immunology / Q000502:physiology*
chemical_list: D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D004247:DNA; D003849:Deoxyguanosine