RNA-directed targeting of AID in immunity and genomic integrity

 描述(由申请人提供)：DNA双链断裂(DSB)构成了细胞中最具毒性的损伤之一。未修复的DSB可以导致细胞死亡，也可以参与染色体易位，这是包括淋巴瘤在内的许多类型肿瘤的特征。尽管DSB具有毒性，但在类开关重组(CSR)的免疫球蛋白(Ig)基因多样化过程中，DSB被故意引入B细胞基因组的特定区域，称为开关(S)区域，如果没有引入这种DSB会导致免疫缺陷综合征。DNA脱氨酶AID(激活诱导型胞苷脱氨酶)对DSB的产生是必不可少的。虽然S区域(和Ig基因相关可变区基因片段)是主要靶点，但艾滋病有可能在包括癌基因在内的非Ig基因处诱发DSB。这种偏离靶点的DSB是大量成熟B细胞淋巴瘤个体发育背后的主要病变。尽管AID靶向与免疫和癌症都有相关性，但AID特异性的分子机制尚未完全阐明。我们现在已经证明，来自S地区的非编码RNA可以作为分子指南将艾滋病招募到S地区。这一建议验证了这样的假设：Switch转录本不仅将艾滋病病毒招募到S区域以促进CSR，而且还将艾滋病病毒从其他基因组区域隔离开来，以防止B细胞基因多样化过程中的附带损害。在目标1中，我们测试了RNA引导的AID募集是体内CSR的关键这一概念。在目标2中，我们检查了RNA引导的AID募集是否能够保护B细胞基因组免受伴随的AID诱导的DNA损伤。在目标3中，我们设计了用于异位靶向AID的嵌合RNA分子。这些研究将对我们对免疫的基本理解以及这一过程中的简单异常如何导致B细胞淋巴瘤具有深远的影响。

 DESCRIPTION (provided by applicant): DNA double strand breaks (DSBs) constitute one of the most toxic lesions to occur in a cell. Unrepaired DSBs can either lead to cell death or can participate in chromosomal translocations that are hallmarks of many kinds of tumors, including lymphomas. Despite the toxicity associated with DSBs, during the immunoglobulin (Ig) gene diversification process of class switch recombination (CSR), DSBs are deliberately introduced into defined regions, called switch (S) regions, of the B cell genome, and a failure to introduce such DSBs leads to immunodeficiency syndromes. The DNA deaminase AID (activation induced cytidine deaminase) is essential for the generation of DSBs. While S regions (and the Ig gene associated variable region gene segments) are primary targets, AID has the potential to induce DSBs at non-Ig genes, including oncogenes. Such off-target DSBs are the major lesions behind the ontogeny of a large number of mature B cell lymphomas. Despite the relevance of AID targeting to both immunity and cancer, the molecular mechanisms underlying AID specificity are yet to be fully elucidated. We have now shown that noncoding RNA emanating from S regions act as molecular guides to recruit AID to S regions. This proposal tests the hypothesis that switch transcripts not only recruit AID to S regions to facilitate CSR but also sequester AID from other genomic regions to prevent collateral damage during B cell gene diversification. In aim 1, we test the notion that the RNA-guided recruitment of AID is critical fo CSR in vivo. In aim 2, we examine if RNA-guided AID recruitment serves to shelter the B cell genome from collateral AID-induced DNA damage. In aim 3, we design chimeric RNA molecules for ectopic targeting of AID. These studies will have far-reaching implications into our fundamental understanding of both immunity and how simple aberrations in the process could lead to B cell lymphomas.