title: DNA damaging agents and p53 do not cause senescence in quiescent cells, while consecutive re-activation of mTOR is associated with conversion to senescence.
abstract: When the cell cycle is arrested, growth-promoting pathways such as mTOR (Target of Rapamycin) drive cellular senescence, characterized by cellular hyper-activation, hypertrophy and permanent loss of the proliferative potential. While arresting cell cycle, p53 (under certain conditions) can inhibit the mTOR pathway. Senescence occurs when p53 fails to inhibit mTOR. Low concentrations of DNA-damaging drugs induce p53 at levels that do not inhibit mTOR, thus causing senescence. In quiescence caused by serum starvation, mTOR is deactivated. This predicts that induction of p53 will not cause senescence in such quiescent cells. Here we tested this prediction. In proliferating normal cells, etoposide caused senescence (cells could not resume proliferation after removal of etoposide). Serum starvation prevented induction of senescence, but not of p53, by etoposide. When etoposide was removed, such cells resumed proliferation upon addition of serum. Also, doxorubicin did not cause senescent morphology in the absence of serum. Re-addition of serum caused mTOR-dependent senescence in the presence of etoposide or doxorubicin. Also, serum-starvation prevented senescent morphology caused by nutlin-3a in MCF-7 and Mel-10 cells. We conclude that induction of p53 does not activate the senescence program in quiescent cells. In cells with induced p53, re-activation of mTOR by serum stimulation causes senescence, as an equivalent of cellular growth.
authors.affiliation: Department of Cell Stress Biology, Roswell Park Cancer Institute, BLSC, L3-312, Elm and Carlton Streets, Buffalo, NY 14263, USA.
authors.forename: Olga V
authors.initials: OV
authors.lastname: Leontieva
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Blagosklonny
mesh_terms: D002453:Cell Cycle / Q000187:drug effects*; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects*; D048430:Cell Shape / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects*; D004249:DNA Damage; D004317:Doxorubicin / Q000633:toxicity*; D004789:Enzyme Activation; D005047:Etoposide / Q000633:toxicity*; D006801:Humans; D007093:Imidazoles / Q000378:metabolism; D009369:Neoplasms / Q000201:enzymology / Q000473:pathology; D010879:Piperazines / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D044967:Serum / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D007093:Imidazoles; D010879:Piperazines; D047428:Protein Kinase Inhibitors; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C482205:nutlin 3; D005047:Etoposide; D004317:Doxorubicin; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus