Sci. STKE, 12 July 2005
APOPTOSIS NO Deadly Signal
Reminiscent of mild-mannered Clark Kent, the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has an alter ego with potent and deadly effects. When translocated to the nucleus, GAPDH has been associated with transcriptional regulation, and Hara et al. present results implicating it in control of apoptosis. A yeast two-hybrid screen for proteins interacting with GAPDH turned up Siah1, an E3 ubiquitin ligase. In transfected cells, the authors detected interaction of the proteins and increased localization of GAPDH to the nucleus, an effect that required the nuclear localization signal of Siah1. In human embryonic kidney cells undergoing apoptosis in response to staurosporine, the authors detected modification of GAPDH by mass spectrometry and went on to show in vitro that modification of GAPDH by S-nitrosylation (often a consequence of increased generation of nitric oxide within cells) enhanced association with Siah1. These events appear to be important in regulation of apoptosis. In a macrophage cell line undergoing apoptosis in response to lipopolysaccharide, GAPDH became S-nitrosylated and associated with endogenous GAPDH, and the complex moved to the nucleus. All of these effects were blocked by an inhibitor of the nitric oxide-generating enzyme iNOS (inducible nitric oxide synthase). Depletion of GAPDH with small interfering RNA (siRNA) blocked the appearance of phosphorylated histone H2B, a marker associated with apoptosis. In cerebellar granular neurons undergoing apoptosis in response to activation of glutamate receptors, similar effects were observed. Increased binding of Siah1 to GAPDH was blocked in cells from neuronal NOS (nNOS) knockout mice, and depletion of either GAPDH or Siah1 from wild-type cells with siRNA inhibited apoptosis. Exactly how nuclear Siah1 promotes apoptosis remains to be explored, but its action appears to require its RING finger domain, indicating that Siah1-mediated ubiquitination and consequent degradation of nuclear proteins is one likely mechanism. Nitric oxide-mediated modification of metabolic enzymes has been shown to contribute to cell death through energy depletion. Hara et al. propose that this may be a slower process and one associated more closely with necrosis, whereas the faster nuclear actions of GAPDH, which reflect translocation of only a small portion of cytoplasmic enzyme, appear to be independent of effects on glycolysis.
M. R. Hara, N. Agrawal, S. F. Kim, M. B. Cascio, M. Fujimuro, Y. Ozeki, M. Takahashi, J. H. Cheah, S. K. Tankou, L. D. Hester, C. D. Ferris, S. D. Hayward, S. H. Snyder, A. Sawa, S-nitrosylated GAPDH initiates apoptotic cell death by nuclear translocation following Siah1 binding. Nat. Cell Biol. 7, 665-674 (2005). [PubMed]
Citation: NO Deadly Signal. Sci. STKE 2005, tw249 (2005).
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