RAG and AID biology

RAG 和 AID 生物学

• 批准号: 8559296
• 负责人: rafael c casellas
• 金额: $ 310.25万
• 依托单位: NATIONAL INSTITUTE OF ARTHRITIS AND MUSCULOSKELETAL AND SKIN DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8559296
• 关键词: Affect; Affinity; African; African Burkitt' s lymphoma; Animals; Antibodies; Antibody Affinity; Architecture; Autoimmunity; Automobile Driving; B-Cell Lymphomas; B-Lymphocytes; Bacteria; Binding; Bioinformatics; Biology; Burkitt Lymphoma; Cell surface; Cells; Child; Chromosomal Rearrangement; Chromosomal translocation; Clinical; Complex; DNA; DNA Damage; DNA Double Strand Break; DNA Sequence Rearrangement; Development; Disease; Enzyme Activation; Enzymes; Event; Exhibits; Fc Receptor; Frequencies; Gene Mutation; Gene Targeting; Genes; Genetic Processes; Genetic Recombination; Genomics; Goals; Human; Hyperplasia; Immune response; Immune system; Immunoglobulin Class Switching; Immunoglobulin Somatic Hypermutation; Immunoglobulin Switch Recombination; Immunoglobulins; Individual; Infection; Laboratories; Lead; Lymphocyte; MYC gene; Malaria; Malignant - descriptor; Measures; Molecular; Molecular Biology; Multiple Myeloma; Mus; Nature; Nuclear; Oncogene Deregulation; Oncogenes; Peripheral; Plasmacytoma; Point Mutation; Problem Solving; Process; Proteins; Publishing; Random Allocation; Reaction; Recurrence; Regulatory Element; Rest; Role; Site; Specificity; Techniques; Transgenic Organisms; United States National Academy of Sciences; V(D)J Recombination; Variant; Virus; activation-induced cytidine deaminase; c-myc Genes; interest; intestinal villi; pathogen; receptor; replication factor A; tool; tumor; tumorigenesis

B lymphocytes are cells of the immune system that recognize and get rid of viruses and bacteria though special receptors on their cell surface called antibodies. The affinity and specificity of these receptors for pathogens depends to a great extent on three genetic processes that assemble and refine these proteins: V(D)J recombination, somatic hypermutation, and class switch recombination (CSR). The first mechanism assembles the antibody gene by combining related DNA segments. The recombination is catalyzed by the RAG1 and RAG2 enzymes. Somatic hypermutation on the other hand introduces random point mutations to increase the binding affinity of the antibody for the pathogen in question. Lastly, CSR introduces further changes to dictate how pathogens are eliminated. Both somatic hypermutation and switch recombination are carried out by a B cell specific enzyme: Activation-Induced Cytidine Deaminase (AID). The importance of RAGs and AID in the immune response is highlighted in humans and animals deficient for these enzymes, which are highly susceptible to infection and exhibit gut flora-dependent hyperplasia of intestinal villi. Conversely, complex diseases such as autoimmunity have long been associated with RAG and AID-dependent activity. Moreover, both RAGs and AID are promiscuous, in that they can also target non-immunoglobulin genes, including oncogenes (tumor-inducing genes). This off-targeting activity can lead to DNA mutations and oncogene deregulation, resulting in malignant transformation. A typical chromosomal irregularity induced by RAGs and AID (chromosomal translocations) are responsible for the formation of B cell lymphomas in humans. Burkitt lymphomas and multiple myeloma are prime examples. Thus, unraveling how RAG and AID activities are regulated under normal conditions and deregulated during tumorigenesis is key. This fiscal year we have furthered our understanding of AID biology in several important ways: i) Human Burkitt lymphomas (BL) are divided into two main clinical variants: the endemic form, affecting African children infected with malaria; and the sporadic form, distributed across the rest of the world. However, while sporadic translocations decapitate the Myc oncogene regulatory elements that control its expression, most endemic events occur hundreds of kilobases away from Myc. The origin of these rearrangements and how they deregulate oncogenes at such distances has been unclear. To solve this problem we have recapitulated endemic BL-like translocations in mouse plasmacytomas. In the study published in the Proceedings of the National Academy of Sciences we show that long-range deregulation of Myc is directly proportional to the physical interaction of immunoglobulin regulatory domains with translocated sites. Our studies thus uncover the extent of remodeling by these regulators and provide a rationale to the transformation of B cells in endemic Burkitt lymphomas. ii) The origin of lymphocyte chromosomal translocations has been ascribed to selection of random rearrangements, targeted DNA damage (RAG and AID activity), or frequent nuclear interactions between translocation partners. However, the individual contributions of these processes have not been measured directly or at a large scale. We therefore examined the role of global nuclear architecture and frequency of DNA damage in the genesis of chromosomal translocations by measuring these parameters simultaneously in cultured B lymphocytes. In the absence of recurrent DNA damage, translocation between Igh or c-myc and all other genes is directly related to their contact frequency. In contrast, translocations associated with recurrent site-directed DNA damage are proportional to the rate of DNA double strand break formation, as measured by accumulation of replication protein A (RPA) at the site of damage. Our findings published in Nature demonstrate that translocations are not simply random events but that nuclear organization determines which gene pairs translocate and that DNA break formation governs the rate of recurrent chromosomal rearrangements.

B淋巴细胞是免疫系统的细胞，通过其细胞表面上的特殊受体称为抗体，并清除了病毒和细菌。这些受体对病原体的亲和力和特异性在很大程度上取决于组装和完善这些蛋白质的三个遗传过程：v（d）J重组，体细胞超成熟和类开关重组（CSR）。第一种机制通过组合相关的DNA片段来组装抗体基因。重组是由RAG1和RAG2酶催化的。另一方面，体细胞超突变引入随机点突变，以增加有关病原体的抗体的结合亲和力。最后，CSR引入了进一步的更改，以决定如何消除病原体。 B细胞特异性酶：激活诱导的胞苷脱氨酶（AID）进行了体细胞超突变和开关重组。缺乏这些酶的人类和动物强调了破布和帮助对免疫反应的重要性，这些酶非常容易感染并表现出肠道绒毛的肠道依赖性增生。相反，诸如自身免疫之类的复杂疾病长期以来一直与抹布和依赖辅助活性有关。此外，抹布和辅助都是混杂的，因为它们还可以靶向非免疫球蛋白基因，包括肿瘤基因（肿瘤诱导基因）。这种不靶向活性会导致DNA突变和癌基因放松管制，从而导致恶性转化。 RAG和AID（染色体易位）引起的典型染色体不规则性是负责人类B细胞淋巴瘤的形成。伯基特淋巴瘤和多发性骨髓瘤是主要的例子。因此，在正常条件下阐明抹布和援助活动的调节是关键的。这个财政年度，我们通过几种重要方式进一步了解了援助生物学： i）人类伯基特淋巴瘤（BL）分为两个主要的临床变异：流行形式，影响感染疟疾的非洲儿童；零星形式分布在世界其他地区。但是，尽管零星的易位斩首了控制其表达的Myc Oncogene调节元件，但大多数地方性事件都发生在远离MYC的数百千座。这些重排的起源及其在这种距离上如何放松肿瘤基因尚不清楚。为了解决这个问题，我们在小鼠浆细胞瘤中概括了类似BL样的易位。在美国国家科学院论文集发表的研究中，我们表明，MYC的长期放松管制与免疫球蛋白调节域与转运地点的物理相互作用成正比。因此，我们的研究揭示了这些调节剂重塑的程度，并为中流伯基特淋巴瘤中B细胞的转化提供了理由。 ii）淋巴细胞染色体易位的起源已归因于选择随机重排，靶向DNA损伤（抹布和AID活动）或转运伙伴之间频繁的核相互作用。但是，这些过程的个人贡献尚未直接或大规模测量。因此，我们通过在培养的B淋巴细胞中同时测量这些参数来研究全球核结构和DNA损伤在染色体易位的起源中的作用。在没有复发性DNA损伤的情况下，IGH或C-MYC和所有其他基因之间的易位与它们的接触频率直接相关。相比之下，与复发位置指导的DNA损伤相关的易位与DNA双链断裂形成的速率成正比，这是通过在损伤部位的复制蛋白A（RPA）的积累来衡量的。我们在自然界中发表的发现表明，易位不仅是随机事件，而且核组织确定了哪种基因对转移器，而DNA断裂形成控制了复发性染色体重排的速率。