RESUMEN
Transient induction of p53 can cause reversible quiescence and irreversible senescence. Using nutlin-3a (a small molecule that activates p53 without causing DNA damage), we have previously identified cell lines in which nutlin-3a caused quiescence. Importantly, nutlin-3a caused quiescence by actively suppressing the senescence program (while still causing cell cycle arrest). Noteworthy, in these cells nutlin-3a inhibited the mTOR (mammalian Target of Rapamycin) pathway, which is known to be involved in the senescence program. Here we showed that shRNA-mediated knockdown of TSC2, a negative regulator of mTOR, partially converted quiescence into senescence in these nutlin-arrested cells. In accord, in melanoma cell lines and mouse embryo fibroblasts, which easily undergo senescence in response to p53 activation, nutlin-3a failed to inhibit mTOR. In these senescence-prone cells, the mTOR inhibitor rapamycin converted nutlin-3a-induced senescence into quiescence. We conclude that status of the mTOR pathway can determine, at least in part, the choice between senescence and quiescence in p53-arrested cells.
Asunto(s)
Senescencia Celular/fisiología , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Transducción de Señal/fisiología , Proteína p53 Supresora de Tumor/metabolismo , Animales , Senescencia Celular/efectos de los fármacos , Técnicas de Silenciamiento del Gen , Humanos , Imidazoles/farmacología , Immunoblotting , Ratones , Piperazinas/farmacología , Transducción de Señal/efectos de los fármacos , Serina-Treonina Quinasas TORRESUMEN
Cellular senescence is currently viewed as a response to DNA damage. In this report, we showed that non-damaging agents such as sodium butyrate-induced p21 and ectopic expression of either p21 or p16 cause cellular senescence without detectable DNA breaks. Nevertheless, senescent cells displayed components of DNA damage response (DDR) such as gammaH2AX foci and uniform nuclear staining for p-ATM. Importantly, there was no accumulation of 53BP1 in gammaH2AX foci of senescent cells. Consistently, comet assay failed to detect DNA damage. Rapamycin, an inhibitor of mTO R, which was shown to suppress cellular senescence, decreased gammaH2AX foci formation. Thus, cellular senescence leads to activation of atypical DDR without detectable DNA damage. Pseudo-DDR may be a marker of general over-activation of senescent cells.
Asunto(s)
Senescencia Celular/genética , Daño del ADN/genética , Animales , Biomarcadores/análisis , Biomarcadores/metabolismo , Línea Celular Tumoral , Núcleo Celular/genética , Núcleo Celular/metabolismo , Núcleo Celular/ultraestructura , Células Cultivadas , Inhibidor p16 de la Quinasa Dependiente de Ciclina , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/efectos de los fármacos , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/genética , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , ADN/genética , ADN/metabolismo , Histonas/genética , Histonas/metabolismo , Histonas/ultraestructura , Humanos , Péptidos y Proteínas de Señalización Intracelular/antagonistas & inhibidores , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Ratones , Proteínas de Neoplasias/efectos de los fármacos , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Proteínas Serina-Treonina Quinasas/antagonistas & inhibidores , Proteínas Serina-Treonina Quinasas/metabolismo , Ratas , Transducción de Señal/genética , Sirolimus/farmacología , Estrés Fisiológico/genética , Serina-Treonina Quinasas TORRESUMEN
When the cell cycle is arrested but cellular growth is not, then cells senesce, permanently losing proliferative potential. Here we demonstrated that the duration of cell cycle arrest determines a progressive loss of proliferative capacity. In human and rodent cell lines, rapamycin (an inhibitor of mTOR) dramatically decelerated loss of proliferative potential caused by ectopic p21, p16 and sodium butyrate-induced p21. Thus, when the cell cycle was arrested by these factors in the presence of rapamycin, cells retained the capacity to resume proliferation, once p21, p16 or sodium butyrate were removed. While rapamycin prevented the permanent loss of proliferative potential in arrested cells, it did not force the arrested cells into proliferation. During cell cycle arrest, rapamycin transformed the irreversible arrest into a reversible condition. Our data demonstrate that senescence can be pharmacologically suppressed.