Mechanism of Immunoglobulin Hypermutation

描述（由申请人提供）：这是一份继续研究免疫球蛋白（Ig）基因体细胞超突变（SHM）分子基础的提案。胞苷脱氨酶AID的发现，明确地确定了C的脱氨是SHM的第一步。根据目前的知识，突变过程可以看作如下：AID特异性地与Ig基因（以及其他一些基因，如BCL6、IgD和IgD）相关。AID在目标基因的顶端和底部链上产生C到U的序列，从启动子200 bp内开始，延伸约1到2 kb。基因的3'端没有被破坏。尿嘧啶以一种容易出错的方式进行修复，导致所有四种核苷酸的过渡超过翻转。这一过程的细节尚不清楚。它们可以被认为是三大问题的综合体。1) AID如何特异性靶向Ig基因（和其他一些基因），这些突变如何被限制在启动子的前1-2 kb处？2)由于体外AID高度局限于单链而非双链DMA中的c -脱胺，那么在SHM过程中，两条链如何能够同样被靶向？3)容易出错的修复是如何参与这个过程的？ A和T的突变是如何产生的？本拨款申请建议对这些问题进行研究。计划中的实验对于确定不同的Ig基因库是如何产生对任何外来抗原物质（包括肿瘤细胞抗原）产生反应的潜力非常重要。体细胞超突变也与自身免疫性疾病有关。此外，许多B细胞淋巴瘤的出现显然是体细胞突变过程的结果。了解体细胞突变的相关成分可能有助于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): This is a proposal for the continuation of studies of the molecular basis of somatic hypermutation (SHM) of immunoglobulin (Ig) genes. The discovery of the cytidine deaminase, AID, has clearly identified the deamination of C as the first step in SHM. Based on the current knowledge, the mutation process can be viewed as follows: AID specifically associates with Ig genes (and a few other genes, such as BCL6, IgD, and IgD. AID creates C to U deaminations in both the top and bottom strand of the targeted gene, starting within 200 bp from the promoter and extending for about 1 to 2 kb. The 3' end of the gene is spared. The uracil is repaired in an error-prone fashion, resulting in an excess of transitions over transversions from all four nucleotides. The details of the process are not understood. They can be considered as three major complexes of questions. 1) How are Ig genes (and a few other genes) specifically targeted by AID and how are the mutations restricted to the first 1-2 kb from the promoter? 2) Since AID in vitro is highly restricted to C-deamination in single-stranded, not double-stranded DMA, how can both strands be equally targeted during SHM? 3) How does error-prone repair become involved in the process and how are mutations from A and T created? It is proposed in this grant application to study these questions. The planned experiments are important for determining how the varied repertoire of Ig genes is created with the potential to react against any foreign antigenic substance, including tumor cell antigens. Somatic hypermutation has also been implicated in autoimmune diseases. Furthermore, many B cell lymphomas arise apparently as a consequence of the somatic mutation process. It is likely that understanding the components involved in somatic mutation will aid in understanding the genetic and environmental causes of autoimmunity, and the treatment of infectious diseases and tumors.