RESUMEN
Ras proteins are members of a superfamily of related small GTPases. Some members, such as Ras, are oncogenic. However, other members seem to serve as tumor suppressors, such as Rig and Noey2. We now identify and characterize a novel member of the Ras superfamily, RRP22. Like Ras, RRP22 can be posttranslationally modified by farnesyl. Unlike Ras, RRP22 inhibits cell growth and promotes caspase-independent cell death. Examination of human tumor cells shows that RRP22 is frequently down-regulated due to promoter methylation. Moreover, reexpression of RRP22 in an RRP22-negative neural tumor cell line impairs its growth in soft agar. Unusually for a Ras-related protein, RRP22 localizes to the nucleolus in a GTP-dependent manner, suggesting a novel mechanism of action. Thus, we identify a new member of the Ras superfamily that can serve as a potential tumor suppressor.
Asunto(s)
Genes Supresores de Tumor , Proteínas ras/fisiología , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Ciclo Celular/fisiología , Muerte Celular/fisiología , Procesos de Crecimiento Celular/fisiología , Línea Celular Tumoral , Nucléolo Celular/metabolismo , Núcleo Celular/metabolismo , Secuencia Conservada , Metilación de ADN , Regulación hacia Abajo , Glioma/genética , Glioma/metabolismo , Glioma/patología , Humanos , Ratones , Datos de Secuencia Molecular , Células 3T3 NIH , Regiones Promotoras Genéticas , Prenilación de Proteína , Transfección , Proteínas ras/genética , Proteínas ras/metabolismoRESUMEN
Activated Ras proteins interact with a broad range of effector proteins to induce a diverse series of biological consequences. Although typically associated with enhanced growth and transformation, activated Ras may also induce growth antagonistic effects such as senescence or apoptosis. It is now apparent that some of the growth-inhibitory properties of Ras are mediated via the RASSF family of Ras effector/tumor suppressors. To date, four members of this family have been identified (Nore1, RASSF1, RASSF2, and RASSF3). We now identify a fifth member of this group, RASSF4 (AD037). RASSF4 shows approximately 25% identity with RASSF1A and 60% identity with RASSF2. RASSF4 binds directly to activated K-Ras in a GTP-dependent manner via the effector domain, thus exhibiting the basic properties of a Ras effector. Overexpression of RASSF4 induces Ras-dependent apoptosis in 293-T cells and inhibits the growth of human tumor cell lines. Although broadly expressed in normal tissue, RASSF4 is frequently down-regulated by promoter methylation in human tumor cells. Thus, RASSF4 appears to be a new member of the RASSF family of potential Ras effector/tumor suppressors.
Asunto(s)
Proteínas Supresoras de Tumor/genética , Proteínas ras/genética , Proteínas ras/metabolismo , Secuencia de Aminoácidos , Apoptosis/fisiología , Secuencia de Bases , Línea Celular Tumoral , Metilación de ADN , Regulación hacia Abajo , Silenciador del Gen , Guanosina Trifosfato/metabolismo , Humanos , Datos de Secuencia Molecular , Regiones Promotoras Genéticas , Estructura Terciaria de Proteína , Alineación de Secuencia , Transfección , Proteínas Supresoras de Tumor/biosíntesis , Proteínas Supresoras de Tumor/metabolismo , Proteínas Supresoras de Tumor/fisiologíaRESUMEN
The novel tumor suppressor RASSF1A is frequently inactivated during human tumorigenesis by promoter methylation. RASSF1A may serve as a node in the integration of signaling pathways controlling a range of critical cellular functions including cell cycle, genomic instability, and apoptosis. The mechanism of action of RASSF1A remains under investigation. We now identify a novel pathway connecting RASSF1A to Bax via the Bax binding protein MOAP-1. RASSF1A and MOAP-1 interact directly, and this interaction is enhanced by the presence of activated K-Ras. RASSF1A can activate Bax via MOAP-1. Moreover, activated K-Ras, RASSF1A, and MOAP-1 synergize to induce Bax activation and cell death. Analysis of a tumor-derived point mutant of RASSF1A showed that the mutant was defective for the MOAP-1 interaction and for Bax activation. Moreover, inhibition of RASSF1A by shRNA impaired the ability of K-Ras to activate Bax. Thus, we identify a novel pro-apoptotic pathway linking K-Ras, RASSF1A and Bax that is specifically impaired in some human tumors.