Goodarzi Aaron A, Jonnalagadda Jyoti C, Douglas Pauline, Young David, Ye Ruiqiong, Moorhead Greg B G, Lees-Miller Susan P, Khanna Kum Kum
Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.
EMBO J. 2004 Nov 10;23(22):4451-61. doi: 10.1038/sj.emboj.7600455. Epub 2004 Oct 28.
Ionizing radiation induces autophosphorylation of the ataxia-telangiectasia mutated (ATM) protein kinase on serine 1981; however, the precise mechanisms that regulate ATM activation are not fully understood. Here, we show that the protein phosphatase inhibitor okadaic acid (OA) induces autophosphorylation of ATM on serine 1981 in unirradiated cells at concentrations that inhibit protein phosphatase 2A-like activity in vitro. OA did not induce gamma-H2AX foci, suggesting that it induces ATM autophosphorylation by inactivation of a protein phosphatase rather than by inducing DNA double-strand breaks. In support of this, we show that ATM interacts with the scaffolding (A) subunit of protein phosphatase 2A (PP2A), that the scaffolding and catalytic (C) subunits of PP2A interact with ATM in undamaged cells and that immunoprecipitates of ATM from undamaged cells contain PP2A-like protein phosphatase activity. Moreover, we show that IR induces phosphorylation-dependent dissociation of PP2A from ATM and loss of the associated protein phosphatase activity. We propose that PP2A plays an important role in the regulation of ATM autophosphorylation and activity in vivo.
电离辐射可诱导共济失调毛细血管扩张症突变（ATM）蛋白激酶在丝氨酸1981位点发生自磷酸化；然而，调节ATM激活的精确机制尚未完全阐明。在此，我们表明蛋白磷酸酶抑制剂冈田酸（OA）在未受辐射的细胞中，以在体外抑制蛋白磷酸酶2A样活性的浓度诱导ATM在丝氨酸1981位点发生自磷酸化。OA未诱导γ-H2AX焦点形成，这表明它通过使一种蛋白磷酸酶失活而非诱导DNA双链断裂来诱导ATM自磷酸化。为此，我们证明ATM与蛋白磷酸酶2A（PP2A）的支架（A）亚基相互作用，PP2A的支架和催化（C）亚基在未受损细胞中与ATM相互作用，并且从未受损细胞中免疫沉淀得到的ATM含有PP2A样蛋白磷酸酶活性。此外，我们证明电离辐射（IR）诱导PP2A从ATM上发生磷酸化依赖性解离以及相关蛋白磷酸酶活性丧失。我们提出PP2A在体内调节ATM自磷酸化和活性中起重要作用。
