RESUMEN
Oncogene-induced senescence (OIS) is a barrier for tumor development. Oncogene-dependent DNA damage and activation of the ARF/p53 pathway play a central role in OIS and, accordingly, ARF and p53 are frequently mutated in human cancer. A number of leukemia/lymphoma-initiating oncogenes, however, inhibit ARF/p53 and only infrequently select for ARF or p53 mutations, suggesting the involvement of other tumor-suppressive pathways. We report that NPM-ALK, the initiating oncogene of anaplastic large cell lymphomas (ALCLs), induces DNA damage and irreversibly arrests the cell cycle of primary fibroblasts and hematopoietic progenitors. This effect is associated with inhibition of p53 and is caused by activation of the p16INK4a/pRb tumor-suppressive pathway. Analysis of NPM-ALK lymphomagenesis in transgenic mice showed p16INK4a-dependent accumulation of senescent cells in premalignant lesions and decreased tumor latency in the absence of p16INK4a. Accordingly, human ALCLs showed no expression of either p16INK4a or pRb. Up-regulation of the histone-demethylase Jmjd3 and de-methylation at the p16INK4a promoter contributed to the effect of NPM-ALK on p16INK4a, which was transcriptionally regulated. These data demonstrate that p16INK4a/pRb may function as an alternative pathway of oncogene-induced senescence, and suggest that the reactivation of p16INK4a expression might be a novel strategy to restore the senescence program in some tumors.
Asunto(s)
Inhibidor p16 de la Quinasa Dependiente de Ciclina/fisiología , Linfoma/genética , Proteínas Tirosina Quinasas/fisiología , Proteína de Retinoblastoma/fisiología , Animales , Células Cultivadas , Senescencia Celular/genética , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Inhibidor p16 de la Quinasa Dependiente de Ciclina/metabolismo , Regulación Neoplásica de la Expresión Génica , Humanos , Linfoma/metabolismo , Ratones , Ratones Noqueados , Neoplasias/genética , Neoplasias/metabolismo , Neoplasias/prevención & control , Proteínas de Fusión Oncogénica/genética , Proteínas de Fusión Oncogénica/metabolismo , Proteínas de Fusión Oncogénica/fisiología , Proteínas Tirosina Quinasas/genética , Proteínas Tirosina Quinasas/metabolismo , Proteína de Retinoblastoma/genética , Proteína de Retinoblastoma/metabolismo , Transducción de Señal/genética , Transducción de Señal/fisiología , Proteínas Supresoras de Tumor/genética , Proteínas Supresoras de Tumor/metabolismo , Proteínas Supresoras de Tumor/fisiologíaRESUMEN
Anaplastic large cell lymphoma (ALCL) is characterized by the presence of the t(2;5)(p23;q35) generating the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion protein, a hyperactive kinase with transforming properties. Among these properties is the ability to regulate activity of the p53 tumor suppressor protein. In many human cancers, p53 is inactivated by mutation or other means, in some cases as a result of up-regulation of the negative regulator MDM2. However, the majority of ALK-expressing ALCL carry wild-type p53 and do not over express MDM2. We demonstrate a novel p53-dependent pathogenetic mechanism in ALK-expressing lymphoma. We confirm previously published reports of NPM-ALK-induced activation of the phosphoinositide (PI) 3-kinase and Jun N-terminal kinase (JNK) stress-activated protein (SAP) kinase proteins, but in this study demonstrate a role for these in the regulation of p53 activity in an intricate signaling system. Specifically, constitutive ALK signaling leads to the functional inactivation and/or degradation of p53 in JNK and MDM2 dependent manners. We also show nuclear exclusion of p53 in a PI 3-kinase-dependent manner. Furthermore, we demonstrate that reactivation of p53 in ALK-expressing cells as a result of pharmacologic inhibition of JNK, PI 3-kinase, and/or MDM2 activities results in the induction of apoptosis suggesting a novel therapeutic modality.
Asunto(s)
Proteínas Quinasas JNK Activadas por Mitógenos/metabolismo , Linfoma/metabolismo , Proteínas Tirosina Quinasas/fisiología , Proteínas Proto-Oncogénicas c-mdm2/metabolismo , Proteína p53 Supresora de Tumor/antagonistas & inhibidores , Apoptosis , Humanos , Linfoma/etiología , Linfoma/patología , Proteína Quinasa 8 Activada por Mitógenos/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Transducción de Señal , Células Tumorales Cultivadas , Proteína p53 Supresora de Tumor/metabolismoRESUMEN
Anaplastic Lymphoma Kinase (ALK) is a receptor tyrosine kinase aberrantly expressed in a variety of tumor types, most notably in Anaplastic Large Cell Lymphoma (ALCL) where a chromosomal translocation generates the oncogenic fusion protein, Nucleophosmin-ALK (NPM-ALK). Whilst much is known regarding the mechanism of transformation by NPM-ALK, the existence of cellular defence pathways to prevent this pathological process has not been investigated. Employing the highly tractable primary murine embryonic fibroblast (MEF) system we show that cellular transformation is not an inevitable consequence of NPM-ALK activity but is combated by p53 and Rb. Activation of p53 and/or Rb by NPM-ALK triggers a potent proliferative block with features reminiscent of senescence. While loss of p53 alone is sufficient to circumvent NPM-ALK-induced senescence and permit cellular transformation, sole loss of Rb permits continued proliferation but not transformation due to p53-imposed restraints. Furthermore, NPM-ALK attenuates p53 activity in an Rb and MDM2 dependent manner but this activity is not sufficient to bypass senescence. These data indicate that senescence may constitute an effective barrier to ALK-induced malignancies that ultimately must be overcome for tumor development.