Aurora B Kinase Regulates the Postmitotic Endoreduplication Checkpoint via Phosphorylation of the Retinoblastoma Protein at Serine 780

Abstract

The phenotypic change characteristic of Aurora B inhibition is the induction of polyploidy. Utilizing specific siRNA duplexes and a selective small molecule inhibitor (AZD1152) to inhibit Aurora B activity in tumor cells, we sought to elucidate the mechanism by which Aurora B inhibition results in polyploidy. Cells treated with AZD1152 progressed through mitosis with misaligned chromosomes and exited without cytokinesis and subsequently underwent endoreduplication of DNA despite activation of a p53-dependent pseudo G1 checkpoint. Concomitant with polyploid cell formation, we observed the appearance of Rb hypophosphorylation, an event that occurred independently of cyclindependent kinase inhibition. We went on to discover that Aurora B directly phosphorylates Rb at serine 780 both in vitro and in vivo. This novel interaction plays a critical role in regulating the postmitotic checkpoint to prevent endoreduplication after an aberrant mitosis. Thus, we propose for the first time that Aurora B determines cellular fate after an aberrant mitosis by directly regulating the Rb tumor suppressor protein.

Inhibiting Aurora Kinases Reduces Tumor Growth and Suppresses Tumor Recurrence after Chemotherapy in Patient-Derived Triple-Negative Breast Cancer Xenografts

“…One of the key effector proteins regulated by Aurora B kinase is the RB1 protein (29). However, the RB1 protein expression was not related to the in vivo response of the AS703569 inhibitor in this study, which is in line with previous reports showing that RB1 status alone does not correlate with sensitivity to Aurora kinase inhibitors in vivo (21,30).…”

Determinants for the efficiency of anticancer drugs targeting either Aurora-A or Aurora-B kinases in human colon carcinoma cells

“…Surprisingly, the checkpoint activation causes a G 1 arrest only after MLN8054, which is required to induce apoptosis, but not after ZM447439 treatment, whose efficacy even requires a severe polyploidization. Interestingly, the latter might be related to the most recently discovered phosphorylation of the Rb tumor suppressor protein by Aurora-B, which might contribute to the cell cycle arrest in the postmitotic G 1 phase on unscheduled exit from mitosis (39). In agreement with this, we found that endoreduplication, and thus apoptosis, after Aurora-B inhibition by ZM447439 is not dependent on p53.…”

The induction of polyploidy or apoptosis by the Aurora A kinase inhibitor MK8745 is p53-dependent

“…This p53 dependency for Aurora A inhibition is very distinct from that of Aurora B inhibition, in which all cell types resulted in polyploidy independent of the p53 status. 18 However, in order to rule out any off-target effect on Aurora B, we used Aurora B kinase with histone H3 in an in vitro kinase assay, and no inhibition was observed, with MK8745 further confirming MK8745 as an inhibitor of Aurora A and not Aurora B. p53 (S315), PLK (S137), Aurora A (T288), known substrates of Aurora A 21 also used to further validate target inhibition in the in vitro assay.…”

“…17 However, we have shown previously that AZD 1152HQPA, a specific inhibitor of Aurora B kinase, induces polyploidy independent of p53 status of the cell line. 15,18 Even though many small-molecule inhibitors are undergoing clinical trials, it is still unclear whether polyploidy can be taken as a mechanism of cell death. It is also not certain whether polyploid cells eventually die or become aneuploid.…”

“…We have previously shown that Aurora B inhibition induces polyploidy in a series of cell lines of multiple lineages independent of their p53 status without any cell cycle delay or arrest. 18 Therefore, in this study, we elected to examine the effects of MK8745 on cell cycle as well as on mitosis in HCT 116 isogenic clones (parental, p53…”