Topoisomerase IIα maintains genomic stability through decatenation G2 checkpoint signaling

Topoisomerase II alpha (topoII alpha) is an essential mammalian enzyme that topologically modifies DNA and is required for chromosome segregation during mitosis. Previous research suggests that inhibition of topoII decatenatory activity triggers a G(2) checkpoint response, which delays mitotic entry because of insufficient decatenation of daughter chromatids. Here we examine the effects of both topoII alpha and topoII beta on decatenatory activity in cell extracts, DNA damage and decatenation G(2) checkpoint function, and the frequencies of p16(INK4A) allele loss and gain. In diploid human fibroblast lines, depletion of topoII alpha by small-interfering RNA was associated with severely reduced decatenatory activity, delayed progression from G(2) into mitosis and insensitivity to G(2) arrest induced by the topoII catalytic inhibitor ICRF-193. Furthermore, interphase nuclei of topoII alpha-depleted cells showed increased frequencies of losses and gains of the tumor suppressor genetic locus p16(INK4A). This study shows that the topoII alpha protein is required for decatenation G(2) checkpoint function, and inactivation of decatenation and the decatenation G(2) checkpoint leads to abnormal chromosome segregation and genomic instability. Oncogene (2010) 29, 4787-4799; doi:10.1038/onc.2010.232; published online 21 June 2010