Topoisomerase IIα maintains genomic stability through decatenation G(2) checkpoint signaling

Topoisomerase IIα (topoIIα) 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 due to insufficient decatenation of daughter chromatids. Here we examine the effects of both topoIIα and topoIIβ 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 topoIIα by siRNA was associated with severely reduced decatenatory activity, delayed progression from G(2) into mitosis, and insensitivity to G2 arrest induced by the topoII catalytic inhibitor ICRF-193. Furthermore, interphase nuclei of topoIIα-depleted cells displayed increased frequencies of losses and gains of the tumor suppressor genetic locus p16(INK4A). This study demonstrates that the topoIIα 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.