Abstract 2991: ATM is activated in mitosis and required for the spindle checkpoint

Abstract

Abstract The ATM kinase, mutation of which leads to the human autosomal recessive disorder Ataxia-Telangiectasia (A-T), plays a critical role in the maintenance of genetic stability. ATM is activated in response to DNA double strand breaks and essential for cell cycle checkpoints. However, ATM function outside the DNA damage response is less clear. Here we report that ATM is activated in mitosis in the absence of DNA damage and is required for the spindle assembly checkpoint. We generated stable cell lines expressing either control shRNA or ATM shRNA and monitored chromosome dynamics and the timing of mitosis by time-lapse video microscopy. The results reveal that ATM-depleted cells proceed into anaphase despite the presence of maloriented and unaligned chromosomes; whereas control cells do not proceed into anaphase until the completion of chromosome alignment on the metaphase plate. We also find ATM-depleted cells exit mitosis much earlier than control cells. In addition, we found ATM-depleted cells do not arrest in mitosis after nocodazole treatment, indicating a spindle assembly checkpoint (SAC) defect. Enzymatic assays indicate that ATM kinase activity is enhanced during mitosis. Further, mitotic ATM activation is mechanistically distinct from that induced by ionizing radiation. Next we demonstrate that mitotic-dependent ATM activation relies on the Aurora-B kinase, a chromosome passenger protein, which is implicated in chromosomal alignment, spindle checkpoint and cytokinesis. Aurora-B phosphorylates ATM at Serine 1403 both in vitro and in vivo. Immunofluorescence experiments show that ATM-Ser1403 phosphorylation has a similar localization pattern to Aurora B during mitosis. More interestingly, we find that ATM Ser1403 phosphorylation is evident in malignant breast cancer tissues and is highly correlated with the mitotic index (p=0.001, Pearson Correlation Test). Cells expressing the mutation of Serine 1403 to Alanine show a defective SAC and accelerated mitotic progression, similar to that of ATM-depleted cells. Collectively, our data demonstrate the functional significance of ATM activation in mitosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2991. doi:10.1158/1538-7445.AM2011-2991