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，它通过细胞表面的特殊受体（称为抗体）识别并清除病毒和细菌。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精炼这些蛋白质的三个遗传过程：V(D)J重组、体细胞超突变和类开关重组（CSR）。第一种机制是通过结合相关DNA片段组装抗体基因。重组由RAG1和RAG2酶催化。另一方面，体细胞超突变引入随机点突变，以增加抗体对病原体的结合亲和力。最后，CSR引入了进一步的变化来规定如何消除病原体。体细胞超突变和开关重组都是由B细胞特异性酶：激活诱导胞苷脱氨酶（AID）进行的。在缺乏这些酶的人类和动物中，RAGs和AID在免疫应答中的重要性得到了强调，这些酶对感染非常敏感，并表现出肠道菌群依赖性肠绒毛增生。相反，自身免疫等复杂疾病长期以来一直与RAG和aids依赖性活性有关。此外，RAGs和AID都是混杂的，因为它们也可以靶向非免疫球蛋白基因，包括致癌基因（肿瘤诱导基因）。这种脱靶活性可导致DNA突变和癌基因失调，从而导致恶性转化。由rag和AID（染色体易位）诱导的典型的染色体不规则是人类B细胞淋巴瘤形成的原因。伯基特淋巴瘤和多发性骨髓瘤就是最好的例子。因此，揭示RAG和AID在正常条件下是如何调控的，而在肿瘤发生过程中又是如何解除调控的是关键。本财政年度，我们在几个重要方面进一步加深了对艾滋病生物学的理解：