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DNA Damage and Cellular Stress Responses

Mitochondrial c-Jun NH₂-Terminal Kinase Prevents the Accumulation of Reactive Oxygen Species and Reduces Necrotic Damage in Neural Tumor Cells that Lack Trophic Support

Departments of ¹ Developmental Neurobiology and ² Neuroanatomy and Cellular Biology, Cajal Institute, Consejo Superior de Investigaciones Cientificas, Madrid, Spain

Requests for reprints: José M. Frade, Cajal Institute, Consejo Superior de Investigaciones Cientificas, Avda Doctor Arce 37, E-28002 Madrid, Spain. Phone: 34-91-5854740; Fax: 34-91-5854754. E-mail: frade{at}cajal.csic.es

In response to different stress signals, the c-Jun NH₂-terminal kinase (JNK) can trigger cell death. However, JNK also facilitates the survival and cell cycle progression of tumor cells by mechanisms that are poorly defined. Here, we show that schwannoma RN22 cells can survive and proliferate under serum-free conditions although serum withdrawal rapidly induces mitochondrial fission and swelling. Although the morphologic changes observed in the mitochondria did not trigger cytochrome c release, they were accompanied by an increase in the mitochondrial membrane potential (_M) and of immunoreactivity for active JNK in these organelles. Pharmacologic inhibition of JNK provoked a further increase of the _M, an increase in reactive oxygen species (ROS) production, and a sustained decrease in cell viability due to necrosis. This increase in necrosis was prevented by the presence of ROS scavengers. Immunoreactivity for active JNK was also observed in the mitochondria of neuroblastoma 1E-115 and neuroblastoma 2a neuroblastoma cell lines on serum withdrawal, whereas active JNK was barely detected in serum-deprived fibroblasts. Accordingly, the reduction in neural tumor cell viability induced by JNK inhibition was largely attenuated in serum-deprived fibroblasts. These data indicate that local activation of JNK in the mitochondria can protect against necrotic cell death associated with ROS production, facilitating the growth of neural tumor cells subjected to serum deprivation. (Mol Cancer Res 2007;5(1):47–60)