Mechanism and regulation of DNA end processing in V(D)J recombination and repair

描述（由申请人提供）：B淋巴细胞和T淋巴细胞是适应性免疫系统的原代细胞，通过抗原特异性受体提供抵御无数外来分子的主要防线。抗原受体基因之间的巨大多样性是通过V(D)J重组产生的，在这个过程中，单个的V、D和J基因片段被重新排列。V(D)J重组缺陷导致人类患者的联合免疫缺陷，也可导致淋巴细胞恶性肿瘤。在V(D)J重组过程中起关键作用的一个因子是非同源末端连接（NHEJ） DNA修复因子Artemis。Artemis最初是在一种人类放射敏感的严重联合免疫缺陷综合征中被发现的失活基因。在患者中也发现了半形性Artemis等位基因，并与不同严重程度的联合免疫缺陷有关。Artemis作为一种DNA核酸酶，在V(D)J重组过程中处理断裂端以及结扎前的一般双链断裂修复，发挥着至关重要的作用。其内在的外核和内核溶解活性是通过与dna依赖性蛋白激酶催化亚基NHEJ因子的相互作用来调节的。然而，Artemis活性在体内调控的确切机制尚不清楚。本研究的主要目的是为了更好地了解V(D)J重排和一般DNA修复过程中DNA末端加工的机制和调控。提出了三个具体目标。目的1是明确参与激活和调节青蒿素核内溶活性的分子机制。目的2是利用小鼠作为模型系统，阐明由半胚性阿尔忒弥斯病等位基因P70引起的肿瘤发生的分子机制。这种过早翻译终止突变导致人类患者部分免疫缺陷和易患淋巴细胞恶性肿瘤。此外，还将研究Artemis、ATM和Mre11之间的遗传相互作用。Aim 3将利用先前开发的Artemis-P70小鼠模型，该模型提供了一个有价值的体内系统来定义允许无义突变解读的治疗方法的影响。这类新兴药物对突变细胞和小鼠的DNA修复、基因组不稳定性、V(D)J重组和淋巴细胞发育表型的影响将被确定。总之，这些研究将为V(D)J编码端连接和一般DSB修复过程中发生的分子事件提供重要见解，阐明异常V(D)J端加工对淋巴细胞发育和肿瘤易感性的影响，并有可能为无义突变引起的原发性免疫缺陷找到新的治疗方法。

DESCRIPTION (provided by applicant): B and T lymphocytes, the primary cells of the adaptive immune system, provide a major line of defense against a myriad of foreign molecules by virtue of antigen-specific receptors. The vast diversity amongst the antigen receptors genes is generated through V(D)J recombination, a process in which individual V, D, and J gene segments are rearranged. Defects in V(D)J recombination lead to combined immunodeficiencies in human patients and can also result in lymphoid malignancies. One factor that plays a critical role during V(D)J recombination is the non-homologous end joining (NHEJ) DNA repair factor, Artemis. Artemis was initially discovered as the gene inactivated in a human radiosensitive severe combined immunodeficiency syndrome. Hypomorphic Artemis alleles have also been identified in patients and are associated with combined immunodeficiencies of varying severity. Artemis plays a vital role as a DNA nuclease that processes broken ends during V(D)J recombination as well as general double strand break repair prior to ligation. Its intrinsic exo- and endonucleolytic activities are modulated by interaction with the DNA-dependent protein kinase catalytic subunit NHEJ factor. However, the precise mechanisms by which Artemis activities are regulated in vivo are not well understood. The major goals of this proposal are to gain a better understanding of the mechanisms and regulation of DNA end processing during V(D)J rearrangements and general DNA repair. Three specific aims are proposed. Aim 1 is to define the molecular mechanisms involved in activating and regulating Artemis endonucleolytic activities. Aim 2 is to elucidate the molecular mechanisms underlying tumorigenesis caused by a hypomorphic, Artemis disease allele, P70, using the mouse as a model system. This premature translation termination mutation leads to partial immunodeficiency and predisposition to lymphoid malignancy in human patients. In addition, the genetic interactions between Artemis, ATM and Mre11 will be examined. Aim 3 will capitalize on the previously developed Artemis-P70 mouse model, which provides a valuable in vivo system to define the impact of therapeutics that allow read-through of nonsense mutations. The impact of this emerging class of drugs on the DNA repair, genome instability, V(D)J recombination, and lymphocyte development phenotypes in mutant cells and mice will be determined. Together, these studies will provide important insights into the molecular events that occur during V(D)J coding end joining and general DSB repair, elucidate the impact of aberrant V(D)J end processing on lymphocyte development and tumor predisposition, and potentially identify novel therapeutics for primary immunodeficiencies caused by nonsense mutations. PUBLIC HEALTH RELEVANCE: This proposal will examine the molecular mechanisms and regulation of DNA end processing during V(D)J recombination and the consequences of aberrant end processing on immune system development and lymphoid malignancies. In addition, the impact of premature termination codon read-through therapeutics on treating immunodeficiency, DNA repair and genome instability phenotypes using a unique mouse model will be examined. Together, these studies will not only provide important insights into the basic mechanisms of V(D)J recombination, but also lead to a better understanding of the in vivo consequences of specific human disease alleles as well as potentially identify novel therapeutics for inherited primary immunodeficiencies.