DNA topoisomerase II alpha interacts with CAD nuclease and is involved in chromatin condensation during apoptotic execution

Apoptotic execution is characterized by dramatic changes in nuclear structu re accompanied by cleavage of nuclear proteins by caspases (reviewed in [1] ), Cell free extracts have proved useful for the identification and functio nal characterization of activities involved in apoptotic execution [2-4] an d for the identification of proteins cleaved by caspases [5], More recent s tudies have suggested that nuclear disassembly is driven largely by factors activated downstream of caspases [6], One such factor, the caspase-activat ed DNase, CAD/CPAN/DFF40 [4,7,8] (CAD) can induce apoptotic chromatin conde nsation in isolated HeLa cell nuclei in the absence of other cytosolic fact ors [6,8], As chromatin condensation occurs even when CAD activity is inhib ited, however, CAD cannot be the sole morphogenetic factor triggered by cas pases [6], Here we show that DNA topoisomerase Ha (Topo II alpha), which is essential for both condensation and segregation of daughter chromosomes in mitosis [9], also functions during apoptotic execution. Simultaneous inhib ition of Topo II alpha and caspases completely abolishes apoptotic chromati n condensation. In addition, we show that CAD binds to Topo II alpha, and t hat their association enhances the decatenation activity of Topo II alpha i n vitro, (C) 2000 Elsevier Science Ltd. All rights reserved.