Abstract
Inhibitor of apoptosis (IAP) proteins have a crucial role in apoptosis, through negative regulation of caspases in species from fruitflies to mammals. In Caenorhabditis elegans, however, no IAP homolog or caspase inhibitor has been identified, calling into question how the cell-killing caspase CED-3 can be negatively regulated. Here we show that inactivation of the C. elegans csp-3 gene, which encodes a protein similar to the small subunit of the CED-3 caspase, causes cells that normally live to undergo apoptosis in a CED-3–dependent manner. Biochemical analysis reveals that CSP-3 associates with the large subunit of the CED-3 zymogen and inhibits zymogen autoactivation. However, CSP-3 does not block CED-3 activation induced by CED-4, nor does it inhibit the activity of the activated CED-3 protease. Therefore CSP-3 uses a previously unreported mechanism to protect cells from apoptosis.
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Acknowledgements
We thank members of the Xue laboratory and N. Yan for comments and discussions, A. Seluzicki for the initial observation, M. Driscoll (Rutgers University) for the bzIs8 strain, J. Hutton (University of Colorado Health Science Center) for the inIs179 strain and T. Blumenthal (University of Colorado) for anti–CstF-64 antibody. This work was supported by US National Institutes of Health R01 grants (GM059083 and GM079097 to D.X. and GM072633 to Yigong S.), a Burroughs Welcome Fund Career Award to D.X. and a grant from Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan to S.M. X.G. is supported by University of Colorado Matching Grant to the SCR Training Grant (T32 GM08759).
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X.G. performed most of the experiments. X.G. and D.X. designed and interpreted all experiments. Yigong S. performed the structural modeling of the CSP-3–CED-3 complex. S.Y. and S.M. isolated csp-3 deletion alleles. Yong S. and A.N. contributed to some of the experiments. X.G. and D.X. wrote the paper and others commented on the manuscript.
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Geng, X., Shi, Y., Nakagawa, A. et al. Inhibition of CED-3 zymogen activation and apoptosis in Caenorhabditis elegans by caspase homolog CSP-3. Nat Struct Mol Biol 15, 1094–1101 (2008). https://doi.org/10.1038/nsmb.1488
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DOI: https://doi.org/10.1038/nsmb.1488
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