Genomic instability mediated via differential DNA repair mechanisms in B cells

描述(申请人提供)：许多类型的B细胞淋巴瘤的一个特点是染色体易位，这是一种基因组重排，涉及免疫球蛋白(Ig)基因和原癌基因之一。复发性c-myc易位是一个典型的例子，通常以IgH或IGL为易位伙伴。C-myc重排见于几种侵袭性B细胞淋巴瘤，包括Burkitt淋巴瘤(90%)、弥漫性大B细胞淋巴瘤(DLBCL，7-14%)、浆母细胞淋巴瘤(~50%)等。C-myc重排在这些疾病中的存在具有重要的诊断和预后意义。例如，在接受化疗(如R-CHOP)的DLBCL患者中，c-myc重排与预后不良相关。因此，阐明c-myc基因重排的机制具有重要意义。这种机制的研究不仅有助于我们对DNA修复的基本了解，而且还将指导翻译应用，如诊断侵袭性B细胞淋巴瘤或开发更好的治疗策略。在这个应用中，我们建议阐明不同的B细胞亚群中不同的DNA修复机制是如何影响c-myc基因组不稳定性水平的。以往对IgH-c-myc易位的研究使人们对易位机制有了更深入的了解，例如，激活诱导脱氨酶(AID)在Ig和c-myc基因座上产生DNA双链断裂(DSB)中的作用。然而，这些先前的研究没有考虑B细胞的激活状态或微环境对DNA修复途径结果的影响。AID通过在Ig基因座诱导点突变或DSB，是抗体多样性的核心角色。如何防止AID引发的损伤引起全基因组损伤尚不完全清楚。先前的研究提出了一种差异DNA修复机制，以保护某些非Ig基因座，如c-myc免受AID攻击。然而，调控这种保护机制的决定因素在很大程度上仍不清楚。我们的初步研究揭示了靶序列、DNA修复机制和B细胞的激活或分化状态之间的复杂相互作用，这似乎协调了c-myc基因座上基因组的稳定性。我们建议使用我们新颖而独特的小鼠模型和新技术来阐明不同B细胞亚群中c-myc基因座上DSB发生的调控机制。

DESCRIPTION (provided by applicant): A hallmark of many types of B cell lymphoma is chromosomal translocation, one type of genomic rearrangement, involving one of the immunoglobulin (Ig) loci and a proto-oncogene. Recurrent c-myc translocation is a classical example, often with Igh or Igl as translocation partners. c-myc rearrangements are observed in several aggressive B cell lymphomas including Burkitt lymphoma (BL, >90%), diffuse large B-cell lymphoma (DLBCL, 7-14%), plasmablastic lymphoma (~50%) and others. The presence of c-myc rearrangements in these diseases has critical diagnostic and prognostic implications. For example, c-myc rearrangements are associated with a poor prognosis in DLBCL patients treated with chemotherapy (e.g. R- CHOP). Thus, it is highly significant to elucidate the mechanisms of genomic rearrangements of c-myc. Such mechanistic studies will not only contribute significantly to our basic understanding of DNA repair but also guide the translational applications such as diagnosing aggressive B cell lymphomas or developing better therapeutic strategies. In this application, we propose to elucidate how differential DNA repair mechanisms operate in distinct B cell subpopulations to influence the level of c-myc genomic instability. Previous studies of Igh-c-myc translocation have resulted in a much deeper understanding of translocation mechanism, e.g. the role of activation-induced deaminase (AID) in generating DNA double stranded breaks (DSBs) at both Ig and c-myc loci. However, these previous studies have not considered the influence of activation status or microenvironment of B cells on the outcome of DNA repair pathways. AID is a central player of antibody diversity via inducing point mutations or DSBs at Ig loci. How AID-initiated lesions are prevented from inducing genome-wide damage is not completely understood. Prior studies proposed a differential DNA repair mechanism that protects certain non-Ig loci such as c-myc from AID attack. However, determinants that regulate such protective mechanisms remain largely unknown. Our preliminary studies reveal a complex interplay between target sequence, DNA repair mechanism, and activation or differentiation status of B cells, which appears to coordinately regulate genome stability at c-myc locus. We propose to employ our novel and unique mouse model and new techniques to elucidate the mechanisms regulating the occurrence of DSBs at c-myc locus in different subpopulations of B cells.