Mechanism of Immunoglobulin Hypermutation

描述(由申请人提供)：这是一项继续研究免疫球蛋白(Ig)基因体细胞超突变(SHM)的分子基础的建议。胞苷脱氨酶AID的发现清楚地将C的脱氨反应确定为SHM的第一步。根据目前的知识，突变过程可以被认为是：AID特异性地与Ig基因(以及一些其他基因，如BCL6、IGD和IGD)相关联。AID在目标基因的顶链和底链上都会产生C到U的脱氨基，从启动子开始，延伸到大约1到2kb。基因的3‘端幸免于难。尿嘧啶以一种容易出错的方式修复，导致所有四个核苷酸的转换超过颠换。这一过程的细节尚不清楚。它们可以被认为是三个主要的问题复合体。1)免疫球蛋白基因(和其他一些基因)是如何被AID特异性靶向的，突变是如何被限制在启动子的第一个1-2kb的？2)由于AID在体外高度限制在单链而不是双链DMA中的C-脱氨基，那么在SHM过程中两条链如何被同等地靶向？3)容易出错的修复如何参与这一过程，A和T的突变是如何产生的？在这项拨款申请中，建议对这些问题进行研究。计划中的实验对于确定免疫球蛋白基因的不同谱系是如何创建的，并具有对抗任何外来抗原物质的潜力，包括肿瘤细胞抗原，是很重要的。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。了解体细胞突变所涉及的成分可能有助于理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.