RESUMEN
During development of the mammalian brain, many neural precursor cells (NPCs) undergo apoptosis. The regulation of such cell death, however, is poorly understood. We now show that the survival of mouse embryonic NPCs in vitro was increased by culture at a high cell density and that this effect was attributable to activation of Notch signaling. Expression of an active form of Notch1 thus markedly promoted NPC survival. Hes proteins, key effectors of Notch signaling in inhibition of neurogenesis, were not sufficient for the survival-promoting effect of Notch1. This effect of Notch1 required a region of the protein containing the RAM domain and was accompanied by up-regulation of the anti-apoptotic proteins Bcl-2 and Mcl-1. Moreover, knockdown of these proteins by RNA interference resulted in blockade of the Notch1-induced survival. These results reveal a new function of Notch, the promotion of NPC survival.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Proteínas de la Membrana/metabolismo , Neuronas/metabolismo , Células Madre/metabolismo , Animales , Anticuerpos Monoclonales/metabolismo , Supervivencia Celular , Células Cultivadas , Colorantes Fluorescentes , Eliminación de Gen , Proteínas Fluorescentes Verdes , Immunoblotting , Inmunohistoquímica , Luciferasas/metabolismo , Proteínas de la Membrana/química , Proteínas de la Membrana/genética , Ratones , Ratones Noqueados , Microscopía Fluorescente , Células 3T3 NIH , Estructura Terciaria de Proteína , Compuestos de Quinolinio , Interferencia de ARN , Receptores Notch , Retroviridae/genética , Succinimidas , Regulación hacia ArribaRESUMEN
p53 plays a key role in DNA damage-induced apoptosis. Recent studies have reported that the phosphatidylinositol 3-OH-kinase-Akt pathway inhibits p53-mediated transcription and apoptosis, although the underlying mechanisms have yet to be determined. Mdm2, a ubiquitin ligase for p53, plays a central role in regulation of the stability of p53 and serves as a good substrate for Akt. In this study, we find that expression of Akt reduces the protein levels of p53, at least in part by enhancing the degradation of p53. Both Akt expression and serum treatment induced phosphorylation of Mdm2 at Ser186. Akt-mediated phosphorylation of Mdm2 at Ser186 had little effect on the subcellular localization of Mdm2. However, both Akt expression and serum treatment increased Mdm2 ubiquitination of p53. The serum-induced increase in p53 ubiquitination was blocked by LY294002, a phosphatidylinositol 3-OH-kinase inhibitor. Moreover, when Ser186 was replaced by Ala, Mdm2 became resistant to Akt enhancement of p53 ubiquitination and degradation. Collectively, these results suggest that Akt enhances the ubiquitination-promoting function of Mdm2 by phosphorylation of Ser186, which results in reduction of p53 protein. This study may shed light on the mechanisms by which Akt promotes survival, proliferation, and tumorigenesis.