The role of topoisomerase II in the excision of DNA loop domains during apoptosis.

Disintegration of nuclear DNA into high molecular weight (HMW) and oligonucleosomal DNA fragments represents two major periodicities of DNA fragmentation during apoptosis. These are thought to originate from the excision of DNA loop domains and from the cleavage of nuclear DNA at the internucleosomal positions, respectively. In this report, we demonstrate that different apoptotic insults induced apoptosis in NB-2a neuroblastoma cells that was invariably accompanied by the formation of HMW DNA fragments of about 50-100 kb but proceeded either with or without oligonucleosomal DNA cleavage, depending on the type of apoptotic inducer.