Shahrabani-Gargir Limor, Pandita Tej K, Werner Haim
Department of Clinical Biochemistry, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
Endocrinology. 2004 Dec;145(12):5679-87. doi: 10.1210/en.2004-0613. Epub 2004 Sep 2.
The IGF-I receptor (IGF-IR) has a central role in cell cycle progression as well as in the establishment of the transformed phenotype. Increased expression of the IGF-IR gene, in addition, is correlated with acquisition of radioresistance for cell killing. The ataxia-telangiectasia mutated (ATM) gene product has a pivotal role in coordinating the cellular response to DNA damage. The present study was aimed at testing the hypothesis that the ability of ATM to coordinate the DNA damage response that will lead to cell survival or, alternatively, to apoptosis depends, to a significant extent, on its capacity to control IGF-IR gene expression. The potential involvement of ATM in regulation of IGF-IR expression and function was investigated in isogenic cells with and without ATM function [AT22IJE-T/pEBS7 (ATM -/-) and ATM-corrected AT22IJE-T/YZ5 (ATM +/+) cells and 293 human embryonic kidney cells transfected with small interfering RNAs targeted to ATM]. In addition, the effect of ATM on IGF-IR expression was assessed in nonisogenic cells with ATM function (HFF + human telomerase reverse transcriptase) and without ATM function (GM5823 + human telomerase reverse transcriptase). Results obtained showed that IGF-IR gene expression and IGF-IR promoter activity were largely reduced in ATM -/- cells. Addition of the radiomimetic agent neocarzinostatin for 4 h, however, induced a significant increase in IGF-IR levels in cells without ATM function. In addition, IGF-I-induced IGF-IR and insulin receptor substrate-1 phosphorylation were greatly impaired in ATM-deficient cells. Furthermore, we identified zinc-finger transcription factors Sp1 and WT1 as potential mediators of the effect of ATM on IGF-IR gene expression. The present data suggests that the IGF-IR gene is a novel downstream target in an ATM-mediated DNA damage response pathway. Deregulated expression of the IGF-IR gene after ionizing radiation may be linked to genomic instability and enhanced transforming capacity.
胰岛素样生长因子-I受体（IGF-IR）在细胞周期进程以及转化表型的形成中发挥着核心作用。此外，IGF-IR基因表达的增加与细胞杀伤的放射抗性获得相关。共济失调毛细血管扩张症突变（ATM）基因产物在协调细胞对DNA损伤的反应中起关键作用。本研究旨在检验这一假设，即ATM协调导致细胞存活或凋亡的DNA损伤反应的能力在很大程度上取决于其控制IGF-IR基因表达的能力。在具有和不具有ATM功能的同基因细胞[AT22IJE-T/pEBS7（ATM -/-）和ATM校正的AT22IJE-T/YZ5（ATM +/+）细胞以及用靶向ATM的小干扰RNA转染的293人胚肾细胞]中研究了ATM在IGF-IR表达和功能调节中的潜在作用。此外，在具有ATM功能（HFF +人端粒酶逆转录酶）和不具有ATM功能（GM5823 +人端粒酶逆转录酶）的非同基因细胞中评估了ATM对IGF-IR表达的影响。获得的结果表明，在ATM -/-细胞中IGF-IR基因表达和IGF-IR启动子活性大大降低。然而，添加放射模拟剂新制癌菌素4小时可诱导无ATM功能的细胞中IGF-IR水平显著增加。此外，IGF-I诱导的IGF-IR和胰岛素受体底物-1磷酸化在ATM缺陷细胞中大大受损。此外，我们确定锌指转录因子Sp1和WT1是ATM对IGF-IR基因表达影响的潜在介质。目前的数据表明，IGF-IR基因是ATM介导的DNA损伤反应途径中的一个新的下游靶点。电离辐射后IGF-IR基因的失调表达可能与基因组不稳定和增强的转化能力有关。
