RESUMO
ING1b can stimulate cell cycle arrest, repair, senescence, and apoptosis. The actions of ING1b are attributed to its activation of the tumor suppressor p53. Here we investigate the more subtle effects of ING1b on the cell cycle and DNA damage responses in the absence of p53. To this end, we have generated isogenic cell lines that expressed ING1b and p53 either individually or in combination under the control of inducible promoters. A five- to 10-fold induction of ING1b over the endogenous protein in a p53-null H1299 background slightly impairs proliferation by increasing the doubling time by approximately 10%. Significantly, ectopic expression of ING1b enhanced the G(2)/M DNA damage checkpoint induced by adriamycin. We demonstrated that the DNA damage-induced cell death mediated by the cooperation between ING1b and p53 was more prominent than by the individual proteins alone. In adriamycin-treated cells, p53 was stabilized and induced the expression of p21(CIP1/WAF1), but the expression of ING1b was not affected. The exact targets of ING1b in the p53-null background are not known, but we demonstrated that the transcriptional activities of other members of the p53 family, p63alpha and p73alpha, could be activated by ING1b. These data indicate that ING1 has a subtle antiproliferative effect even in the absence of p53, and ING1b enhances the DNA damage responses through p53-dependent and -independent mechanisms.
Assuntos
Divisão Celular/fisiologia , Proteínas de Membrana , Proteínas/metabolismo , Proteína Supressora de Tumor p53/fisiologia , Proteínas de Ciclo Celular , Morte Celular/efeitos dos fármacos , Morte Celular/fisiologia , Sobrevivência Celular/efeitos dos fármacos , Sobrevivência Celular/fisiologia , Inibidor de Quinase Dependente de Ciclina p21 , Ciclinas/metabolismo , Dano ao DNA/efeitos dos fármacos , Dano ao DNA/fisiologia , Proteínas de Ligação a DNA/metabolismo , Doxorrubicina/metabolismo , Doxorrubicina/farmacologia , Citometria de Fluxo , Genes Supressores de Tumor/fisiologia , Humanos , Proteína 1 Inibidora do Crescimento , Peptídeos e Proteínas de Sinalização Intracelular , Proteínas Nucleares/metabolismo , Compostos Organoplatínicos/farmacologia , Fosfoproteínas/metabolismo , Proteínas/genética , Proteínas Recombinantes/efeitos dos fármacos , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Transativadores/metabolismo , Fatores de Transcrição , Ativação Transcricional/fisiologia , Tubulina (Proteína)/metabolismo , Células Tumorais Cultivadas , Proteína Tumoral p73 , Proteínas Supressoras de TumorRESUMO
ING1b is a candidate tumor suppressor that can stimulate the transcriptional activity of p53 and inhibit cell proliferation. The molecular basis of how ING1b activates p53 function remains unclear. Here we show that ING1b could stimulate the activity of p53 by increasing the level and stability of the p53 protein. The stabilization and activation of p53 by ING1b could be reversed by MDM2 in a dose-dependent manner. Conversely, ING1b could reverse the inhibition and degradation of p53 caused by MDM2 in a dose-dependent manner. Furthermore, ING1b and MDM2 bound to p53 in a mutually exclusive manner. In agreement with these observations, we found that similarly to MDM2, ING1b binds to the NH(2)-terminal region of p53. These data suggest a model in which ING1b disrupts the interaction between p53 and MDM2, leading to the stabilization of p53 and growth inhibition.
