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

Apoptotic execution is characterized by dramatic changes in nuclear structure accompanied by cleavage of nuclear proteins by caspases (reviewed in [1]), Cell free extracts have proved useful for the identification and functional characterization of activities involved in apoptotic execution [2-4] and for the identification of proteins cleaved by caspases [5], More recent studies have suggested that nuclear disassembly is driven largely by factors activated downstream of caspases [6], One such factor, the caspase-activated DNase, CAD/CPAN/DFF40 [4,7,8] (CAD) can induce apoptotic chromatin condensation in isolated HeLa cell nuclei in the absence of other cytosolic factors [6,8], As chromatin condensation occurs even when CAD activity is inhibited, however, CAD cannot be the sole morphogenetic factor triggered by caspases [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 inhibition of Topo II alpha and caspases completely abolishes apoptotic chromatin condensation. In addition, we show that CAD binds to Topo II alpha, and that their association enhances the decatenation activity of Topo II alpha in vitro, (C) 2000 Elsevier Science Ltd. All rights reserved.