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，但肿瘤中的放射抗性经常阻止成功的癌症控制;因此，克服放射抗性对于改善放射治疗至关重要。MicroRNA-21（miR-21）是一种在几乎所有类型的人类肿瘤中过表达的致癌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，只有少数报道表明miR-21参与了肿瘤细胞的辐射抗性，其机制尚不清楚。近年来，我们利用miR-21敲入或miR-21敲除小鼠模型、小鼠胚胎成纤维细胞株以及敲除多种人类肿瘤细胞系中的miR-21，发现miR-21参与促进DNA双链断裂（DSB）修复，在辐射抗性中发挥重要作用。基于我们以前的出版物和初步数据，我们将检验miR-21介导的辐射抗性通过其靶点促进DNA DSB修复而发生的假设。由于IR诱导的细胞杀伤主要通过产生DSB发生，并且非同源末端连接（NHEJ）和同源重组修复（HRR）是哺乳动物细胞中修复DNA DSB的两种主要途径，因此重要的是阐明miR-21介导的辐射抗性是否通过刺激NHEJ、HRR或两者而发生。同样重要的是阐明miR-21如何通过其靶点影响DNA修复途径，包括Pten和Cdc 25 A（miR-21的已知靶点）以及GSK 3b（我们小组鉴定的miR- 21的新靶点）。为此目的，设计了两个目标：1）确定miR-21介导的辐射抗性是否通过刺激NHEJ、HRR或两者而发生。2)确定miR-21如何通过其靶点介导辐射抗性。由于miR-21在几乎所有类型的人类肿瘤中过表达，因此该提案的结果不仅有望增强我们对肿瘤细胞放射抗性的认识，而且还为改善肿瘤放射治疗提供了新的靶点和途径。

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.