RESUMO
Reactive oxygen species (ROS) steady-state levels are required for entry into the S phase of the cell cycle in normal cells, as well as in tumour cells. However, the contribution of mitochondrial ROS to normal cell proliferation has not been well investigated thus far. A previous report showed that Romo1 was responsible for the high ROS levels in tumour cells. Here, we show that endogenous ROS generated by Romo1 are indispensable for cell cycle transition from G1 to S phase in normal WI-38 human lung fibroblasts. The ROS level in these cells was down-regulated by Romo1 knockdown, resulting in cell cycle arrest in the G1 phase. This arrest was associated with an increase in the level of p27(Kip1). These results demonstrate that mitochondrial ROS generated by Romo1 expression is required for normal cell proliferation and it is suggested that Romo1 plays an important role in redox signalling during normal cell proliferation.
Assuntos
Ciclo Celular/fisiologia , Inibidor de Quinase Dependente de Ciclina p27/fisiologia , Fibroblastos/metabolismo , Regulação da Expressão Gênica/fisiologia , Proteínas de Membrana/fisiologia , Mitocôndrias/metabolismo , Proteínas Mitocondriais/fisiologia , Espécies Reativas de Oxigênio/metabolismo , Divisão Celular , Linhagem Celular , Inibidor de Quinase Dependente de Ciclina p27/biossíntese , Inibidor de Quinase Dependente de Ciclina p27/genética , Técnicas de Silenciamento de Genes , Humanos , Proteínas de Membrana/antagonistas & inibidores , Proteínas de Membrana/genética , Proteínas Mitocondriais/antagonistas & inibidores , Proteínas Mitocondriais/genética , RNA Interferente Pequeno/farmacologiaRESUMO
Low levels of endogenous reactive oxygen species (ROS) originating from NADPH oxidase have been implicated in various signaling pathways induced by growth factors and mediated by cytokines. However, the main source of ROS is known to be the mitochondria, and increased levels of ROS from the mitochondria have been observed in many cancer cells. Thus far, the mechanism of ROS production in cancer cell proliferation in the mitochondria is not well-understood. We recently identified a novel protein, ROS modulator 1 (Romo1), and reported that increased expression of Romo1-triggered ROS production in the mitochondria. The experiments conducted in the present study showed that Romo1-derived ROS were indispensable for the proliferation of both normal and cancer cells. Furthermore, whilst cell growth was inhibited by blocking the ERK pathway in cells transfected with siRNA directed against Romo1, the cell growth was recovered by addition of exogenous hydrogen peroxide. The results of this study suggest that Romo1-induced ROS may play an important role in redox signaling in cancer cells.
Assuntos
Proliferação de Células , Proteínas de Membrana/metabolismo , Proteínas Mitocondriais/metabolismo , Neoplasias/metabolismo , Neoplasias/patologia , Espécies Reativas de Oxigênio/metabolismo , Linhagem Celular Tumoral , Células HeLa , HumanosRESUMO
The constitutive activation of JNK has been implicated in Ras-induced cellular transformation and activated JNK is down-regulated by the tumor suppressor protein, RASSF1A. In this study, we examined whether RASSF1A blocked oncogenic Ras-induced JNK activation. Exogenous expression of H-RasG12V induced JNK phosphorylation and RASSF1A co-transfected with H-RasG12V efficiently suppressed Ras-triggered JNK activation in various cancer cell lines. RASSF1A expression revived the H-RasG12V-induced p27Kip1 down-regulation. JNK siRNA treatment also promoted recovery from the H-RasG12V-induced p27Kip1 down-regulation. These results demonstrate that RASSF1A inhibited H-RasG12V-induced JNK activation and JNK-mediated p27Kip1 down-regulation. From these results, we propose that RASSF1A exerts a tumor-suppressing effect by blocking oncogenic Ras-induced JNK activation.