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Endonuclease G is an apoptotic DNase when released from mitochondria

Abstract

Nucleosomal fragmentation of DNA is a hallmark of apoptosis (programmed cell death)1, and results from the activation of nucleases in cells undergoing apoptosis. One such nuclease, DNA fragmentation factor (DFF, a caspase-activated deoxyribonuclease (CAD) and its inhibitor (ICAD)), is capable of inducing DNA fragmentation and chromatin condensation after cleavage by caspase-3 (refs 2,3,4). However, although transgenic mice lacking DFF45 or its caspase cleavage site have significantly reduced DNA fragmentation5,6, these mice still show residual DNA fragmentation and are phenotypically normal5,6,7. Here we report the identification and characterization of another nuclease that is specifically activated by apoptotic stimuli and is able to induce nucleosomal fragmentation of DNA in fibroblast cells from embryonic mice lacking DFF. This nuclease is endonuclease G (endoG), a mitochondrion-specific nuclease that translocates to the nucleus during apoptosis. Once released from mitochondria, endoG cleaves chromatin DNA into nucleosomal fragments independently of caspases. Therefore, endoG represents a caspase-independent apoptotic pathway initiated from the mitochondria.

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Figure 1: Identification of the mitochondrial nuclease.
Figure 2: Purification of the mitochondrial nuclease (arrowed).
Figure 3: EndoG is both necessary and sufficient to cause DNA fragmentation.
Figure 4: Characterization of the release process of endoG.
Figure 5: EndoG is released from mitochondria of apoptotic cells during apoptosis.
Figure 6: DFF-knockout cells can undergo caspase-independent DNA fragmentation.

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Acknowledgements

We thank J. M. Peters, M. Lutter and M. Fang for their assistance in mitochondrion purification and other techniques; Y. Li and R. Harold for technical support; J. Zhang and M. Xu for providing DFF45-knockout MEF cells. We also thank M. Lutter and X. Jiang for recombinant Bcl-xL. X.L. is supported by the Leukemia Society of America; X.W. is supported by grants from NIH and the Welch Foundation.

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Correspondence to Xiaodong Wang.

Supplementary information

Table 1 Mass Fingerprinting of Nuclease and Its Identification as Endonuclease G

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Li, L., Luo, X. & Wang, X. Endonuclease G is an apoptotic DNase when released from mitochondria. Nature 412, 95–99 (2001). https://doi.org/10.1038/35083620

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