title: Evidence of a role for phosphatidylinositol 3-kinase activation in the blocking of apoptosis by polyomavirus middle T antigen.
abstract: A polyomavirus mutant (315YF) blocked in binding phosphatidylinositol 3-kinase (PI 3-kinase) has previously been shown to be partially deficient in transformation and to induce fewer tumors and with a significant delay compared to wild-type virus. The role of polyomavirus middle T antigen-activated PI 3-kinase in apoptosis was investigated as a possible cause of this behavior. When grown in medium containing 1D-3-deoxy-3-fluoro-myo-inositol to block formation of 3'-phosphorylated phosphatidylinositols, F111 rat fibroblasts transformed by wild-type polyomavirus (PyF), but not normal F111 cells, showed a marked loss of viability with evidence of apoptosis. Similarly, treatment with wortmannin, an inhibitor of PI 3-kinase, stimulated apoptosis in PyF cells but not in normal cells. Activation of Akt, a serine/threonine kinase whose activity has been correlated with regulation of apoptosis, was roughly twofold higher in F111 cells transformed by either wild-type virus or mutant 250YS blocked in binding Shc compared to cells transformed by mutant 315YF. In the same cells, levels of apoptosis were inversely correlated with Akt activity. Apoptosis induced by serum withdrawal in Rat-1 cells expressing a temperature-sensitive p53 was shown to be at least partially p53 independent. Expression of either wild-type or 250YS middle T antigen inhibited apoptosis in serum-starved Rat-1 cells at both permissive and restrictive temperatures for p53. Mutant 315YF middle T antigen was partially defective for inhibition of apoptosis in these cells. The results indicate that unlike other DNA tumor viruses which block apoptosis by inactivation of p53, polyomavirus achieves protection from apoptotic death through a middle T antigen-PI 3-kinase-Akt pathway that is at least partially p53 independent.
authors.affiliation: Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: J
authors.initials: J
authors.lastname: Dahl
authors.forename: A
authors.initials: A
authors.lastname: Jurczak
authors.forename: L A
authors.initials: LA
authors.lastname: Cheng
authors.forename: D C
authors.initials: DC
authors.lastname: Baker
authors.forename: T L
authors.initials: TL
authors.lastname: Benjamin
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism*; D017209:Apoptosis; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002461:Cell Line, Transformed; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D006131:Growth Inhibitors / Q000494:pharmacology; D007294:Inositol / Q000031:analogs & derivatives / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D000952:Antigens, Polyomavirus Transforming; D004791:Enzyme Inhibitors; D006131:Growth Inhibitors; D007294:Inositol; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D016159:Tumor Suppressor Protein p53; D000077191:Wortmannin; C080999:3-deoxy-3-fluoroinositol; C494920:Akt1 protein, rat