Abstract
The spindle assembly checkpoint (SAC) is a critical monitoring device in mitosis for the maintenance of genomic stability. Specifically, the SAC complex comprises several factors, including Mad1, Mad2, and Bub1. Ataxia-telangiectasia mutated (ATM) kinase, the crucial regulator in DNA damage response (DDR), also plays a critical role in mitosis by regulating Mad1 dimerization and SAC. Here, we further demonstrated that ATM negatively regulates the phosphorylation of Mad2, another critical component of the SAC, which is also involved in DDR. Mechanistically, we found that phosphorylation of Mad2 is aberrantly increased in ATM-deficient cells. Point-mutation analysis further revealed that Serine 195 mainly mediated Mad2 phosphorylation upon ATM ablation. Functionally, the phosphorylation of Mad2 causes decreased DNA damage repair capacity and is related to the resistance to cancer cell radiotherapy. Altogether, this study unveils the key regulatory role of Mad2 phosphorylation in checkpoint defects and DNA damage repair in ATM-deficient cells.
Highlights
Chromosome complementarity is naturally present in eukaryotic cells
We found that mitotic arrest deficiency (Mad2) phosphorylation was significantly higher in the ATMdeficient HeLa cells expressing S214A than that in other cells, indicating that Mad2 phosphorylation was negatively regulated by Ataxia-telangiectasia mutated (ATM)
We found that Mad2 phosphorylation (S195D) significantly inhibited DNA damage repair via both homologous recombination (HR) and nonhomologous end-joining (Figures 5B,D)
Summary
Chromosome complementarity is naturally present in eukaryotic cells. During cell division, the gain or loss of chromosomes leads to abnormal chromosome numbers, which is termed aneuploidy and has been documented as one of the predispositions of tumorigenesis (Ganem et al, 2007; Storchova and Kuffer, 2008; Torres et al, 2010; Tang et al, 2011). The SAC prevents the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase from recognizing and securing cyclin B, ensuring chromosomes are properly attached to spindle microtubules (Bharadwaj and Yu, 2004; Musacchio and Salmon, 2007; Santaguida and Musacchio, 2009). Mad, Cdc, Mad ( named BubR1 in some species), and Bub form the mitotic checkpoint complex (MCC), which are mainly responsible for inhibiting APC/C, leading to cell cycle arrest (Yu, 2006; Musacchio and Salmon, 2007; Chao et al, 2012). Dysregulation of these proteins, either upregulation or downregulation, results in the breakdown of SAC and eventually genomic instability (Schuyler et al, 2012)
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