Mechanism for miR-21-modulated radioresistance

描述(申请人提供)：放射治疗是一种常见的癌症治疗方法，但肿瘤中的放射抵抗经常阻碍癌症控制的成功；因此，克服放射抵抗是提高放射治疗水平的关键。MicroRNA-21(miR-21)是一种在几乎所有类型的人类肿瘤中过度表达的癌基因-miR。我们和其他人已经证明了miR-21的过度表达可能导致肿瘤的发生。目前，仅有少数报道表明miR-21参与了肿瘤细胞的辐射抵抗，其机制尚不清楚。最近，通过我们的miR-21基因敲除或敲除小鼠模型，我们发现miR-21在辐射抗性中起着重要的作用，促进DNA双链断裂(DSB)修复。根据我们以前的文献和初步数据，我们将检验miR-21介导的辐射抗性是通过其促进DNA DSB修复的靶点发生的假说。由于IR诱导的细胞杀伤主要是通过产生DSB，而非同源末端连接(NHEJ)和同源重组修复(HRR)是哺乳动物细胞修复DNA DSB的两条主要途径，因此阐明miR-21介导的辐射抵抗是通过刺激NHEJ和HRR还是两者都是重要的。同样重要的是要阐明miR-21如何通过其靶点包括Pten和CDc25A(miR-21的已知靶点)以及GSK3b(本课题组发现的miR-21的新靶点)影响DNA修复途径(S)。为此，我们设计了两个目标：1)确定miR-21介导的辐射抵抗是通过刺激NHEJ、HRR还是两者兼而有之。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都过表达，这一建议的结果不仅有望增强我们对肿瘤细胞辐射抗性的认识，还将为改进肿瘤放射治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.