Delia D, Mizutani S, Panigone S, Tagliabue E, Fontanella E, Asada M, Yamada T, Taya Y, Prudente S, Saviozzi S, Frati L, Pierotti M A, Chessa L
Department of Experimental Oncology, Istituto Nazionale Tumori, Milano, Italy.
Br J Cancer. 2000 Jun;82(12):1938-45. doi: 10.1054/bjoc.2000.1168.
ATM (ataxia-telangiectasia mutated) gene plays a central role in the DNA-damage response pathway. We characterized the ATM protein expression in immortalized cells from AT and AT-variant patients, and heterozygotes and correlated it with two ATM-dependent radiation responses, G1 checkpoint arrest and p53-Ser 15 phosphorylation. On Western blots, the full-length ATM protein was detected in eight of 18 AT cases, albeit at 1-32% of the normal levels, whereas a truncated ATM protein was detected in a single case, despite the prevalence among cases of truncation mutations. Of two ataxia without telangiectasia [A-(T)] cases, one expressed 20% and the other approximately 70% of the normal ATM levels. Noteworthy, among ten asymptomatic heterozygous carriers for AT, normal amounts of ATM protein were found in one and reduced by 40-50% in the remaining cases. The radiation-induced phosphorylation of p53 protein at serine 15, largely mediated by ATM kinase, was defective in AT, A(-T) and in 2/4 heterozygous carriers, while the G1 cell cycle checkpoint was disrupted in all AT and A(-T) cases, and in 3/10 AT heterozygotes. Altogether, our study shows that AT and A(-T) cases bearing truncation mutations of the ATM gene can produce modest amounts of full-length (and only rarely truncated) ATM protein. However, this limited expression of ATM protein provides no benefit regarding the ATM-dependent responses related to G1 arrest and p53-ser15 phosphorylation. Our study additionally shows that the majority of AT heterozygotes express almost halved levels of ATM protein, sufficient in most cases to normally regulate the ATM-dependent DNA damage-response pathway.
共济失调毛细血管扩张症突变（ATM）基因在DNA损伤反应通路中起核心作用。我们对来自共济失调毛细血管扩张症（AT）患者、AT变异型患者、杂合子的永生化细胞中的ATM蛋白表达进行了表征，并将其与两种ATM依赖的辐射反应（G1期检查点停滞和p53丝氨酸15位点磷酸化）相关联。在蛋白质免疫印迹分析中，18例AT患者中有8例检测到全长ATM蛋白，尽管其水平仅为正常水平的1%至32%，而在仅1例患者中检测到截短的ATM蛋白，尽管截短突变在病例中普遍存在。在2例无毛细血管扩张的共济失调[A-（T）]患者中，1例表达水平为正常ATM水平的20%，另1例约为70%。值得注意的是，在10例无症状的AT杂合子携带者中，1例发现ATM蛋白量正常，其余病例中ATM蛋白量减少了40%至50%。p53蛋白丝氨酸15位点的辐射诱导磷酸化主要由ATM激酶介导，在AT、A（-T）患者及4例杂合子携带者中的2例中存在缺陷，而G1期细胞周期检查点在所有AT和A（-T）病例以及10例AT杂合子中的3例中被破坏。总之，我们的研究表明，携带ATM基因截短突变的AT和A（-T）病例可产生适量的全长（且极少截短）ATM蛋白。然而，这种有限的ATM蛋白表达在与G1期停滞和p53丝氨酸15位点磷酸化相关的ATM依赖反应方面并无益处。我们的研究还表明，大多数AT杂合子表达的ATM蛋白水平几乎减半，在大多数情况下足以正常调节ATM依赖的DNA损伤反应通路。
