Aurora B is Dispensable for Megakaryocyte Polyploidization, but Contributes to the Endomitotic Process

Polyploidization of megakaryocytes (MKs), the platelet precursors, occurs by endomitosis, a mitotic process that fails at late stages of cytokinesis. Expression and function of Aurora B kinase during endomitosis remain controversial. Here, we report that Aurora B is normally expressed during the human MK endomitotic process. Aurora B localized normally in the midzone or midbody during anaphase and telophase in low ploidy megakaryocytes and in up to 16N rare endomitotic MKs was observed. Aurora B was also functional during cytokinesis as attested by phosphorylation of both its activation site and MgcRacGAP, its main substrate. However, despite its activation, Aurora B did not prevent furrow regression. Inhibition of Aurora B by AZD1152-HQPA decreased cell cycle entry both in 2N to 4N and polyploid MKs and induced apoptosis mainly in 2N to 4N cells. In both MK classes, AZD1152-HQPA induced p53 activation and retinoblastoma hypophosphorylation. Resistance of polyploid MKs to apoptosis correlated to a high BclxL level. Aurora B inhibition did not impair MK polyploidization but profoundly modified the endomitotic process by inducing a mis-segregation of chromosomes and a mitotic failure in anaphase. This indicates that Aurora B is dispensable for MK polyploidization but is necessary to achieve a normal endomitotic process.