A caspase-activated DNase that degrades DNA during apoptosis, and its inhibitor ICAD

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  • A Corrigendum to this article was published on 28 May 1998


The homeostasis of animals is regulated not only by the growth and differentiation of cells, but also by cell death through a process known as apoptosis. Apoptosis is mediated by members of the caspase family of proteases, and eventually causes the degradation of chromosomal DNA. A caspase-activated deoxyribonuclease (CAD) and its inhibitor (ICAD) have now been identified in the cytoplasmic fraction of mouse lymphoma cells. CAD is a protein of 343 amino acids which carries a nuclear-localization signal; ICAD exists in a long and a short form. Recombinant ICAD specifically inhibits CAD-induced degradation of nuclear DNA and its DNase activity. When CAD is expressed with ICAD in COS cells or in a cell-free system, CAD is produced as a complex with ICAD: treatment with caspase 3 releases the DNase activity which causes DNA fragmentation in nuclei. ICAD therefore seems to function as a chaperone for CAD during its synthesis, remaining complexed with CAD to inhibit its DNase activity; caspases activated by apoptotic stimuli then cleave ICAD, allowing CAD to enter the nucleus and degrade chromosomal DNA.

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Figure 1: CAD and ICAD activity in extracts from mouse WR19L cells.
Figure 2: Identification of ICAD.
Figure 3: Comparison of amino-acid sequences of mouse ICAD-S and ICAD-L and of mouse ICAD-L and human DFF-45.
Figure 4: Specific inhibition of CAD activity by recombinant ICAD.
Figure 5: Identification and amino-acid sequence of CAD.
Figure 6: Expression of mouse CAD in COS cells.
Figure 7: Expression of mouse CAD in a cell-free system, and binding of CAD with ICAD.
Figure 8: A model for the function of CAD and ICAD in apoptosis.


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We thank R. V. Talanian for the caspase 3 expression system, M. A. Blanar for pGEX-2T[128/129], and S. Kumagai for secretarial assistance. This work was supported in part by Grants-in-Aid from the Ministry of Education, Science, Sports and Culture in Japan.

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Correspondence to Shigekazu Nagata.

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