Understanding mechanistic role of SAMHD1 in DNA damage response and therapeutic benefit for malignant glioma

项目总结/摘要 恶性胶质瘤是最常见的成人中枢神经系统恶性肿瘤， 预后恶性胶质瘤的常规治疗是手术切除后进行放射治疗 (RT)以及化疗药物替莫唑胺（TMZ）。尽管试图提高 在使用这种组合疗法的患者的存活率方面，仅取得了适度的成功。因此，迫切需要 需要开发更好的治疗方法来改善患者的预后。TMZ和RT通过诱导癌细胞死亡， DNA损伤;然而，如果DNA修复途径是完整和有效的， 可能会对这些治疗产生抗药性。因此，了解治疗抵抗的根本原因 可能会导致更有效的治疗方法的发展，并最终改善患者的预后。因此，我们认为， 识别新的基因，可以针对减轻恶性胶质瘤的治疗耐药性将有助于 这对正在进行的研究工作很重要。我们确定了不育α基序和HD结构域的新作用 SAMHD 1促进DNA末端切除以促进DNA双链断裂（DSB） 同源重组（homologous recombination，HR）SAMHD 1是一种脱氧核苷三磷酸（dNTP） 三磷酸水解酶，通过消耗dNTPs在非分裂细胞中限制HIV-1感染中具有明确的作用 需要逆转录。我们的初步数据表明，癌细胞中SAMHD 1的缺失会导致 对DNA DSB诱导剂的超敏反应。我们还表明，SAMHD 1被募集到DNA DSB中， DNA损伤的反应。SAMHD 1在DNA损伤后与CtIP相互作用并将CtIP募集到DNA DSB 以促进DNA末端切除和HR，而不依赖于其dNTR活性。SAMHD1是蛋白酶体的靶向蛋白， 通过病毒辅助蛋白Vpx降解。我们有数据显示，各种癌细胞系用 与内源性水平相比，Vpx降低了SAMHD 1的水平，随后增加了SAMHD 1的水平。 对DNA损伤诱导治疗剂的敏感性。值得注意的是，SAMHD 1水平低的恶性胶质瘤患者 水平显示总体存活的概率显著更高。此外，少突胶质细胞瘤，星形细胞瘤 与正常脑相比，成胶质细胞瘤肿瘤样品显示SAMHD 1的显著更高表达 组织.有趣的是，胶质瘤的最具侵袭性的形式GBM表达最高水平的SAMHD 1。采取 总之，我们的初步研究结果表明，SAMHD 1可能是恶性肿瘤的潜在治疗靶点， 胶质瘤治疗因此，我的建议的总体目标是确定机制， SAMHD 1指导DNA DSB修复介导恶性胶质瘤的治疗抗性，并了解我们如何 利用这些知识来改善神经胶质瘤的治疗。

Project Summary/Abstract Malignant Glioma is the most commonly diagnosed adult central nervous system malignancy, and carries a poor prognosis. The conventional treatment for malignant glioma is surgical resection followed by radiation therapy (RT) and the chemotherapeutic drug, temozolomide (TMZ). Despite attempts to improve the probability of survival in patients with this combination of therapies, there has been only modest success. Thus, there is urgent need to develop a better therapy to improve patient outcomes. TMZ and RT cause cancer cell death by inducing DNA damage; however, if DNA repair pathways are intact and effective, there is a high probability that a cell may develop resistance to these treatments. Thus, understanding the underlying cause of treatment resistance could lead to the development of more effective therapies and, ultimately, improve patients' prognosis. Therefore, identifying novel genes that can be targeted to alleviate treatment resistance in malignant glioma will contribute significantly to ongoing research efforts. We identified a novel role for sterile alpha motif and HD domain containing-protein 1 (SAMHD1) in promoting DNA end resection to facilitate DNA double-strand break (DSB) repair by homologous recombination (HR). SAMHD1 is a deoxynucleoside triphosphate (dNTP) triphosphohydrolase with a well-defined role in restricting HIV-1 infection in nondividing cells by depleting dNTPs required for reverse transcription. Our preliminary data indicate that SAMHD1 depletion in cancer cells causes hypersensitivity to DNA DSB-inducing agents. We have also shown that SAMHD1 is recruited to DNA DSBs in response to DNA damage. SAMHD1 interacts with CtIP following DNA damage and recruits CtIP to DNA DSBs to facilitate DNA end resection and HR independent of its dNTPase activity. SAMHD1 is targeted for proteasomal degradation by the viral accessory protein, Vpx. We have data showing that various cancer cell lines treated with Vpx have diminished levels of SAMHD1 compared to endogenous levels, and subsequently, have increased sensitivity to DNA damage inducing therapeutic agents. Strikingly, malignant glioma patients with low SAMHD1 levels show a significantly higher probability of overall survival. Furthermore, oligodendroglioma, astrocytoma and glioblastoma tumor samples show significantly higher expression of SAMHD1 as compared to normal brain tissue. Interestingly, GBM, the most aggressive form of glioma, expresses the highest level of SAMHD1. Taken together, our preliminary findings suggest that SAMHD1 could be a potential therapeutic target for malignant glioma treatment. As such, the overall objective of my proposal is to determine the mechanisms by which SAMHD1 directs DNA DSB repair to mediate treatment resistance in malignant glioma and to see how we can utilize this knowledge to improve glioma treatment.