Inhibition of phosphatidylinositol-3-OH kinase/Akt signaling impairs DNA repair in glioblastoma cells following ionizing radiation
Inhibition of phosphatidylinositol-3-OH kinase/Akt signaling impairs DNA repair in glioblastoma cells following ionizing radiation
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DOI：
10.1074/jbc.m703042200
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发表时间：
2007-07-20
影响因子：
4.8
通讯作者：
Maity, Amit
中科院分区：
文献类型：
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作者：
Kao, Gary D.;Jiang, Zibin;Maity, Amit
放射治疗是胶质母细胞瘤治疗的主要手段，但这些肿瘤通常与放射抗性有关。磷脂酰肌醇-3-OH激酶（PI 3 K）/Akt通路的激活与放射抗性相关，该通路由于肿瘤抑制因子磷酸酶和张力蛋白同源物（PTEN）的失活而经常发生在胶质母细胞瘤中。为了直接测试Akt活化和辐射抗性之间的联系，我们利用了PTEN缺陷的U251胶质母细胞瘤细胞，其被工程化以在暴露于多西环素后诱导恢复PTEN。这些细胞显示出高基础水平的Akt激活（即高水平的磷酸化Akt），但PTEN的诱导导致磷酸化Akt大幅减少，并且与放射增敏相关。为了研究PTEN诱导的放射增敏是否归因于DNA损伤的感知受损与修复，我们评估了在针对PTEN诱导的U251细胞中电离辐射后γ-H2 AX的水平。在PTEN诱导的细胞中，α-H2 AX病灶的初始辐射后水平没有降低;然而，这些病灶的分辨率显著延迟。与这些结果相反，诱导磷酸酶死亡的PTEN没有表现出明显的效果。最后，细胞暴露于PI 3 K抑制剂LY 294002并没有减少照射后α-H2 AX病灶的发生，但明显延迟了它们的消退。这些结果共同支持胶质母细胞瘤中Akt激活、DNA损伤修复和放射抗性之间的直接联系。靶向PI 3 K/Akt通路可以调节DNA修复以提高放射治疗的疗效。
Radiation therapy is a mainstay in the treatment of glioblastomas, but these tumors are often associated with radioresistance. Activation of the phosphatidylinositol-3-OH kinase (PI3K)/Akt pathway, which occurs frequently in glioblastomas due to inactivation of the tumor suppressor phosphatase and tensin homologue (PTEN), correlates with radioresistance. To directly test the link between Akt activation and radioresistance, we utilized PTEN-deficient U251 glioblastoma cells engineered to inducibly restore PTEN upon exposure to doxycycline. These cells showed high basal levels of Akt activation (i.e. high levels of phospho-Akt), but induction of PTEN led to substantially decreased phospho-Akt and was associated with radiosensitization. To investigate whether the PTEN-induced radiosensitization was attributable to impaired sensing versus repair of DNA damage, we assessed levels of gamma-H2AX after ionizing radiation in U251 cells induced for PTEN. Initial post-radiation levels of alpha-H2AX foci were not decreased in PTEN-induced cells; however, the resolution of these foci was significantly delayed. In contrast to these results, induction of phosphatase-dead PTEN showed no appreciable effect. Finally, exposure of cells to the PI3K inhibitor LY294002 did not decrease the occurrence of alpha-H2AX foci after irradiation but did markedly delay their resolution. These results together support a direct link between Akt activation, repair of DNA damage, and radioresistance in glioblastoma. Targeting the PI3K/Akt pathway may modulate DNA repair to improve the efficacy of radiation therapy.