Department of Molecular Genetics, The Lerner Research Institute, The Cleveland Clinic, Cleveland, Ohio, USA.
Cytometry A. 2010 Jun;77(6):524-33. doi: 10.1002/cyto.a.20885.
Quantitative cytometric studies show that cyclin D1 levels must decline during S phase for proper cell cycle progression, and that cyclin D1 decline follows phosphorylation induced by the checkpoint kinases ataxia telangiectasia mutated (ATM) and ATM and Rad3-related (ATR). ATM is mutated in ataxia telangiectasia (AT), a disease characterized by progressive neurodegeneration. Importantly, neurodegeneration in many cases has been linked to the increased expression of cyclin D1 in neurons leading to inappropriate cell cycle entry. These facts prompted us to test the possibility that ATM normally protects against neural degeneration by suppressing cyclin D1 levels, particularly following genotoxic stress. For this purpose, neural stem cells were induced to differentiate into mature neural cells, including neurons. ATM activity in these cultures was inhibited with a specific chemical inhibitor in the presence or absence of hydrogen peroxide treatment, and the effect on cyclin D1 expression was determined by quantitative, single cell cytometric analyses. As predicted, inhibition of ATM did promote elevation of cyclin D1 in differentiated neurons, particularly under conditions of oxidative stress. The survival of differentiated neurons and of neural stem cells was reduced by such treatments. These data support our suggestion that ATM functions to maintain low levels of cyclin D1 expression in differentiated neurons; and may provide important clues in understanding neural degeneration in general.
定量细胞计量学研究表明，细胞周期蛋白 D1 的水平必须在 S 期下降，才能使细胞周期正常进行，而且细胞周期蛋白 D1 的下降紧随检查点激酶共济失调毛细血管扩张突变（ATM）和 ATM 和 Rad3 相关（ATR）诱导的磷酸化之后。ATM 在共济失调毛细血管扩张症（AT）中发生突变，这种疾病的特征是进行性神经退行性变。重要的是，在许多情况下，神经退行性变与神经元中 cyclin D1 的过度表达有关，导致细胞周期的异常进入。这些事实促使我们检验 ATM 是否通过抑制 cyclin D1 水平，特别是在遗传毒性应激后，来正常保护神经元免受神经退行性变的可能性。为此，我们诱导神经干细胞分化为成熟的神经细胞，包括神经元。在存在或不存在过氧化氢处理的情况下，用特定的化学抑制剂抑制这些培养物中的 ATM 活性，并通过定量、单细胞细胞计量分析来确定对 cyclin D1 表达的影响。正如预测的那样，抑制 ATM 确实会促进分化神经元中 cyclin D1 的升高，特别是在氧化应激条件下。这种处理会降低分化神经元和神经干细胞的存活率。这些数据支持我们的观点，即 ATM 可以维持分化神经元中 cyclin D1 的低表达水平；并可能为理解一般的神经退行性变提供重要线索。
