Mechanism for miR-21-modulated radioresistance

描述（由申请人提供）：放射治疗是一种常见的癌症治疗方法，但肿瘤的放射耐药性经常阻碍成功的癌症控制；因此，克服放射耐药是改善放射治疗的关键。MicroRNA-21 （miR-21）是一种在几乎所有类型的人类肿瘤中过表达的onco-miR。我们和其他人已经证明过表达miR-21可能导致肿瘤发生。目前仅有少数报道显示miR-21参与肿瘤细胞的放射耐药，其机制尚不清楚。最近，通过我们的miR-21敲入或miR-21敲除小鼠模型，来自小鼠品系的胚胎成纤维细胞和敲除几种人类肿瘤细胞系中的miR-21，我们发现miR-21在辐射抗性中起重要作用，参与促进DNA双链断裂（DSB）修复。基于我们之前的出版物和初步数据，我们将验证mir -21介导的辐射耐药是通过其靶点促进DNA DSB修复而发生的。由于ir诱导的细胞杀伤主要通过产生DSB发生，而非同源末端连接（non-homologous end joining， NHEJ）和同源重组修复（homologous recombination repair， HRR）是哺乳动物细胞修复DNA DSB的两种主要途径，因此阐明mir -21介导的辐射耐药是通过刺激NHEJ、HRR还是两者同时发生是很重要的。阐明miR-21如何通过其靶点包括Pten和Cdc25A （miR-21的已知靶点）以及GSK3b（我们小组发现的miR-21的新靶点）影响DNA修复途径也很重要。为此，设计了两个目标：1)确定miR-21介导的辐射耐药是否通过刺激NHEJ、HRR或两者同时发生。2)确定miR-21如何通过其靶标介导辐射抗性。由于miR-21在几乎所有类型的人类肿瘤中都过表达，因此本研究的结果不仅可以增强我们对肿瘤细胞放射抵抗的认识，还可以为改善肿瘤放疗提供新的靶点和途径。

DESCRIPTION (provided by applicant): Radiotherapy is a common cancer therapeutic approach but radioresistance in tumors frequently prevents successful cancer control; therefore, overcoming radioresistance is essential for improving radiotherapy. MicroRNA-21 (miR-21) is an onco-miR that over- expresses in almost all types of human tumors. We and others have demonstrated that over- expression of miR-21 could result in tumorigenesis. Currently, there are only a few reports showed that miR-21 contributes to radioresistance of tumor cells, and the mechanism remains unclear. Recently, by using our miR-21 knock-in or miR-21 knockout mouse models, the embryo fibroblast cells derived from the mouse strains and knocking down miR-21 in several human tumor cell lines, we found that miR-21 plays an important role in radioresistance that is involved in promoting DNA double strand break (DSB) repair. Based on our previous publications and preliminary data, we will test the hypothesis that miR-21-mediated radioresistance occurs through its targets to promote DNA DSB repair. Since IR-induced cell killing occurs mainly by generating DSBs, and non-homologous end joining (NHEJ) and homologous recombination repair (HRR) are the two major pathways in mammalian cells to repair DNA DSB, it is important to elucidate if miR-21-mediated radioresistance occurs through stimulating NHEJ, HRR or both. It is also important to elucidate how miR-21 affects the DNA repair pathway(s) via its targets including Pten and Cdc25A (known targets of miR-21), as well as GSK3b (a novel target of miR- 21 identified by our group). For this purpose, two aims are designed: 1) Determine if miR-21- mediated radioresistance occurs through stimulating NHEJ, HRR or both. 2) Determine how miR-21 mediates radioresistance through its targets. Since miR-21 over-expressed in almost all types of human tumors, the results from this proposal are expected to not only enhance our knowledge of tumor cell radioresistance, but also provide novel targets and pathways for improving tumor radiotherapy.