毛细血管扩张性共济失调突变蛋白在细胞凋亡过程中被Caspase┐3降解

新近的研究揭示：ｃａｓｐａｓｅ蛋白酶在细胞凋亡中起着死亡执行者的重要功能．一些蛋白相继被证明在细胞凋亡中可被ｃａｓｐａｓｅ特异切割，其中参与ＤＮＡ损伤修复过程的聚ＡＤＰ核糖聚合酶（ＰＡＲＰ）以及ＤＮＡ依赖的蛋白激酶（ＤＮＡ－ＰＫ），在细胞凋亡过程中被ｃａｓｐａｓｅ选择性切割具有特殊的功能意义．为探索与ＤＮＡ－ＰＫ催化亚基有较高同源性，含有ｃａｓｐａｓｅ切割位点，且功能上目前也被认为是感受ＤＮＡ损伤和参与信号传导途径的ＡＴＭ（Ａｔａｘｉａｔｅｌａｎｇ－ｉｅｃｔａｓｉａｍｕｔａｔｅｄ）蛋白，是否在凋亡过程中也可被切割而降解？应用体外转录与翻译系统获得ＡＴＭ蛋白的ＰＩ３Ｋ结构域，同时通过建立无细胞反应体系获得含ｃａｓｐａｓｅ活性的细胞抽提液，将两者在体外共同保温．结果发现：ＡＴＭ蛋白与ｃａｓｐａｓｅ－３能免疫共沉淀，ＡＴＭ蛋白的ＰＩ３Ｋ结构域可被ｃａｓｐａｓｅ－３特异切割，并观察到辐射诱发细胞调亡中ＡＴＭ蛋白的降解．从而进一步证实了ＤＮＡ损伤修复的抑制，促进细胞凋亡的发生．

Caspase 3 mediated Cleavage of Ataxia Telangiectasia Mutated Protein in Induction of Apoptosis

Apoptosis is a distinct form of programmed cell death,and plays a key role in normal development as well as in the pathogenesis of many diseases.Different stimuli,including DNA damaging agent such as ionizing radiation,can induce apoptosis.Specific cysteine proteases of caspase family initiate the execution phase of apoptosis,and a growing list of proteins has been shown to be degraded by caspase during apoptosis.Poly(ADP ribose) polymerase (PARP) and DNA dependent protein kinase (DNA PK),both involved in DNA damage sensing and repair,are inactivated by caspase cleavage.It is suggested that some DNA repair proteins may be selectively targeted for destruction during apoptosis.Like PARP and DNA PK,ATM (for ataxia telangiectasia mutated),which is deficient in patients suffering from the recessive disorder ataxia telangiectasia,is believed to contribute to DNA repair,and also has the conserved sequence for caspase cleavingsa.Is it ,too,a target of caspase in apoptotic cells?To challenge this question,an in vitro translation of PI3K domain of ATM which contained the caspase cleaving sequence was performed,and the translated product was proved to be cleaved by caspase 3 in vitro using the cell free system.Moreover,ATM was observed to be cleaved during radiation induced apoptosis.These results further demonstrate that repair mechanisms need to be inactived for apoptosis to proceed efficiently.