The Regulation of Somatic Hypermutation

描述（由申请人提供）：脊椎动物能够产生大量抗体分子来对抗感染。据估计，人类一生中可以产生的抗体特异性数量超过109种，这一数字大大超过了基因组的编码能力。相反，抗体库的大小是在产生抗体的B淋巴细胞中发生的基因多样化过程的产物。原代B细胞库是在B细胞发育过程中由骨髓中的体细胞（V(D)J）重组产生的。然而，这种储备既不够大，也不够特异性，无法提供高亲和力的抗体来对抗动物可能遇到的各种抗原。因此，抗体多样性的产生在很大程度上取决于V(D)J重组后发生的二次多样化过程。二抗多样化是由免疫球蛋白位点胞苷残基脱胺（产生尿嘧啶）触发的。该过程由胞苷脱氨酶AID催化，该酶被认为结合并脱氨暴露在转录免疫球蛋白基因上的ssDNA，产生U:G错配，通过多种方式解决，产生点突变、基因转换或开关重组。然而，艾滋病诱导的尿嘧啶病变也可以通过作为染色体易位的底物或通过诱变非ig基因（包括致癌基因）导致永久性基因组损伤。因此，严格调控AID对于维持基因组稳定性非常重要。这项建议的长期目标是了解如何调节艾滋病，进而扩展抗体多样化。因此，本提案将侧重于以下主题：a) AID的转录调控（我们提出的实验将确定导致AID转录诱导的程序）；b)在蛋白质水平上对AID的调控（我们使用了一种新的筛选方法来识别与脱氨酶相互作用的整套细胞因子；同时，我们提出了对这些辅助因子之一的详细研究，一种称为RNF126的蛋白质，它似乎满足脱氨酶的靶因子的要求）。体细胞超突变与自身免疫性疾病以及B细胞淋巴瘤的产生有关。因此，本文提出的实验对于更好地理解自身免疫和B细胞淋巴瘤都很重要。公共卫生相关性：这里提出的实验对于确定有益突变如何产生针对外来物质的抗体特异性非常重要。我们提出研究的突变过程与自身免疫性疾病以及B细胞淋巴瘤的产生有关。了解这一过程中涉及的成分将有助于我们更好地了解自身免疫的遗传和环境原因，以及传染病和肿瘤的治疗。

DESCRIPTION (provided by applicant): Vertebrates are able to produce a vast repertoire of antibody molecules to combat infection. The number of antibody specificities that a human can produce during their lifetime is estimated to be in excess of 109, a number that greatly exceeds the coding capacity of the genome. Instead, the size of the antibody repertoire is the product of gene diversification processes that take place in antibody producing B lymphocytes. The primary B cell repertoire is generated by somatic (V(D)J) recombination in the bone marrow during B cell development. However, this repertoire is neither large enough nor specific enough to provide high affinity antibodies against the range of antigens an animal may encounter. Thus the generation of antibody diversity depends in a major way on secondary diversification processes that occur following V(D)J recombination. Secondary antibody diversification is triggered by deamination of cytidine residues (to yield uracil) within the immunoglobulin locus. This process is catalyzed by the cytidine deaminase AID, which is thought to bind and deaminate ssDNA exposed on the transcribed immunoglobulin gene, generating U:G mismatches that are resolved in a variety of ways to generate point mutations, gene conversion or switch recombination. However, AID-induced uracil lesions can also lead to permanent genomic damage by serving as substrates for chromosome translocations or by mutagenizing non-Ig genes, including oncogenes. Therefore, strict regulation of AID is important for maintaining genomic stability. The long term objective of this proposal is to understand how AID, and by extension antibody diversification, is regulated. This proposal will therefore focus on the following topics: a) the transcriptional regulation of AID (where we propose experiments that will determine the program that leads to induction of AID transcription); b) the regulation of AID at the protein level (where we have used a novel screen to identify the entire set of cellular factors that interact with the deaminase; and also, where we propose detailed studies on one of these cofactors, a protein termed RNF126, which appears to satisfy the requirements of a targeting factor for the deaminase). Somatic hypermutation has been implicated in autoimmune diseases as well as in the generation of B cell lymphomas. Thus the experiments proposed here are important for a better understanding of both autoimmunity and B cell lymphomas. PUBLIC HEALTH RELEVANCE: The experiments proposed here are important for determining how beneficial mutation generates antibody specificities against foreign substances. The mutational process which we propose to study has been implicated in autoimmune diseases as well as in the generation of B cell lymphomas. Understanding the components involved in this process will help us gain better knowledge of the genetic and environmental causes of autoimmunity, as well as the treatment of infectious diseases and tumors.