ATM (Ataxia Telangiectasia Mutated) signaling through cyclin D1

描述（由申请人提供）：共济失调毛细血管扩张症（AT）是由共济失调毛细血管扩张突变基因（ATM）突变引起的常染色体隐性遗传病。ATM是一种蛋白激酶，它被DAN双链断裂激活，进而激活DNA修复和细胞周期检查点机制，以维持基因组的稳定性。ATM这些功能的丧失解释了AT的许多症状，如易患癌症、辐射敏感性和免疫缺陷。然而，尚不清楚ATM丢失如何引发神经退行性变，从而导致AT中的共济失调（运动功能障碍）。我们最近发现，ATM诱导Thr286残基上cyclin D1的不稳定磷酸化，并抑制cyclin D1的表达。我们还发现细胞周期蛋白D1的抑制在DNA损伤后诱导G1检查点中起着关键作用。我们将研究ATM和细胞周期蛋白D1在DNA损伤引起的神经元细胞死亡中的作用。神经元的代谢需求被认为会产生高水平的活性氧，从而损害DNA。ATM感知到这种损伤，激活细胞周期检查点和DNA修复机制来应对这种内源性基因毒性应激。我们假设，当ATM缺陷神经元暴露于基因毒性应激时，cyclin D1的表达会继续，因为它的Thr286残基没有磷酸化。cyclin D1的高表达会覆盖G1检查点，并促进增殖神经细胞中DNA病变的积累（目的1）。在有丝分裂后的神经元中，cyclin D1的高表达会引发异常的细胞周期进程和细胞死亡（Aim 2）。在Aim 3中，我们将研究在增殖过程中积累的DNA损伤是否会使有丝分裂后神经元对DNA损伤治疗敏感。使用来自ATM-/-和+/+小鼠的原代神经细胞以及人类神经干细胞，我们研究了ATM依赖性cyclin D1抑制是否能保护神经元免受氧化应激。基因毒性应激的生物学后果将在使用特定抑制剂、shRNA或中和抗体注射操纵ATM和cyclin D1的活性或表达后确定。这些实验经过精心设计，以阐明通过其控制cyclin D1表达的能力，ATM在基因毒性应激下的神经细胞中起关键作用的新概念的有效性。

DESCRIPTION (provided by applicant): Ataxia telangiectasia (AT) is an autosomal recessive disease caused by mutation in ataxia telangiectasia mutated (ATM) gene. ATM, a protein kinase, is activated by DAN double strand break and in turn it activates DNA repair and cell cycle checkpoint mechanisms to maintain genomic stability. The loss of these functions of ATM explains many symptoms of AT such as predisposition to cancer, radiation sensitivity, and immunodeficiency. However, it is not clear how ATM loss triggers neurodegeneration, which causes ataxia (motor dysfunction) in AT. We recently found that ATM induces destabilizing phosphorylation of cyclin D1 on the Thr286 residue, and suppresses cyclin D1 expression. We have also found that the suppression of cyclin D1 plays a critical role in inducing a G1 checkpoint following DNA damage. We will examine the roles of ATM and cyclin D1 in neuronal cell death induced by DNA damage. Metabolic demand in neurons is considered to generate high levels of reactive oxygen species which damage DNA. ATM senses such damage and would activate cell cycle checkpoint and DNA repair mechanism to cope with such endogenous genotoxic stress. We hypothesized that when ATM deficient neurons are exposed to genotoxic stress, cyclin D1 expression continues because its Thr286 residue is not phosphorylated. The high expression of cyclin D1 would override the G1 checkpoint and contribute to accumulation of DNA lesions in proliferating neural cells (Aim 1). In postmitotic neurons, high cyclin D1 expression would trigger aberrant cell cycle progression and cell death (Aim 2). In Aim 3, we will examine, if DNA lesions accumulated during proliferation would sensitize postmitotic neuron to DNA damaging treatment. Using primary neural cells from ATM-/- and +/+ mice, and human neural stem cells, we examine if ATM dependent cyclin D1 suppression protects neurons from oxidative stress. Biological consequence of genotoxic stress will be determined following manipulating the activity or expression of ATM and cyclin D1 using a specific inhibitor, shRNA or neutralizing antibody injection. The experiments are carefully designing to elucidate the validity of the novel concept that through its ability to control cyclin D1 expression, ATM plays a critical role in neuronal cells under genotoxic stress. PUBLIC HEALTH RELEVANCE: We have found that under DNA damaging condition, ATM (ataxia telangiectasia mutated) controls cell cycle progression at least in part by its ability to target cyclin D1. Appling this new concept of ATM-cyclin D1 dependent cell cycle regulation to the biology of the neurons, this proposal will address molecular mechanism of degeneration of neurons in ataxia telangiectasia (AT). The finding obtained from these studies may advance our fundamental understanding on pathogenesis of AT, as well as other related neurodegenerative diseases, such as brain stroke, Parkinson disease, and Alzheimer's disease.