Elk-1 associates with the mitochondrial permeability transition pore complex in neurons

The nuclear transcription factor E-26-like protein 1 (Elk-1) is thought to impact neuronal differentiation [Sharrocks, A. D. (2001) Nat. Rev. Mol. Cell Biol. 2, 827-837], cell proliferation [Sharrocks, A. D. (2002) Biochem. Soc. Trans. 30,1-9], tumorigenesis [Chai, Y. L., Chipitsyna, G., Cui, J., Liao, B., Liu, S., Aysola, K., Yezdani, M., Reddy, E. S. P. & Rao, V. N. (2001) Oncogene 20, 1357-1367], and apoptosis [Shao, N., Chai, Y., Cui, J., Wang, N., Aysola, K., Reddy, E. S. P. & Rao, V. N. (11998) Oncogene 17, 527-532]. In addition to its nuclear localization, Elk-1 is found throughout the cytoplasm, including localization in neuronal dendrites [Sgambato, V., Vanhoutte, P., Pages, C., Rogard, M., Hipskind, R., Besson, M. J. & Caboche, J. (1998) J. Neurosci. 18, 214-226], raising the possibility that Elk-1 may have alternative extranuclear functions in neurons. Using coimmunoprecipitation and reciprocal coimmunoprecipitation from adult rat brain, we found an association between Elk-1 protein and the mitochondrial permeability transition pore complex (PTP), a structure involved in both apoptotic and necrotic cell death. Electron microscopy in adult rat brain sections confirmed this association with mitochondria. Elk-1 was also identified from purified mitochondrial fractions by using Western blotting, and Elk-1 increased its association with mitochondria following proapoptotic stimuli. Consistent with a role for Elk-1 in neuron viability, overexpression of Elk-1 in primary neurons decreased cell viability, whereas Elk-1 siRNA-mediated knockdown increased cell viability. This decrease in viability induced by Elk-1 overexpression was blocked with application of a PTP inhibitor. These results show an association of the nuclear transcription factor Elk-1 with the mitochondrial PTP and suggest an additional extranuclear function for Elk-1 in neurons.