Immunoglobulin Somatic Mutation

免疫球蛋白体细胞突变

• 批准号: 6558275
• 负责人: URSULA B STORB
• 金额: $ 26.18万
• 依托单位: UNIVERSITY OF CHICAGO
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-12-01 至 2007-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6558275
• 关键词: B lymphocyte; DNA damage; aminohydrolases; binding sites; cell cycle; clinical research; gene mutation; gene targeting; genetic regulatory element; genetically modified animals; human subject; immunoglobulin genes; laboratory mouse; messenger RNA; nucleosomes; transcription factor

DESCRIPTION (provided by applicant): The process of somatic hypermutation (SHM) of immunoglobulin (Ig) genes takes place in B lymphocytes after specific interaction with antigen and T lymphocytes. SHM has several steps and requirements. In our working model, the cell needs to produce a postulated mutator factor (MuF) which has to be targeted to Ig genes by transcription. The MuF may act as an endonuclease that creates a nick or double-strand break in the gene. The nick/break is believed to be repaired in an error-prone fashion, creating mutations. Mismatch repair may remove some of the mutations or fix them by "correcting" the wildtype nucleotide on the complementary DNA strand. Cell replication propagates the mutations to one or both daughter cells. The following investigations are proposed: 1) What is the role of a specific E-box site in SHM? Such a transactivator site was found to enhance SHM without enhancing transcription. 2) How does the position of nucleosomes affect the SHM process? SHM occurs in clusters that suggest involvement of nucleosomes in the targeting of mutations. Mono-nucleosomal DNA from a mutable mouse transgene will be tested for phasing of nucleosomes over the SHM target relative to mutations. 3) Can a double-strand DNA break induce SHM? The possibility will be tested that introduction of a double strand break into a SHM target gene induces mutations without the need for the initiating events of SHM. 4) When during the cell cycle does SHM occur? It is still unknown if DNA replication of the genome is involved directly in SHM, and/or if recombination is required. Single cells will be isolated at various cell cycle stages and screened for molecular intermediates consistent with an ongoing mutation process. 5) Which mRNAs are modified by the cytidine deaminase, AID, in mutating B lymphocytes? The cytosine deaminase, AID, is required for SHM. The potential target mRNAs will be identified. The planned experiments are important for learning how the varied repertoire of Ig genes is created with the potential to react against any foreign antigenic determinant, 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. Surprisingly, the BCL6 proto-oncogene is highly mutated in human memory B cells. This is likely to be involved in tumorigenesis. Thus, a better understanding of the somatic mutation process may aid in the understanding and perhaps prevention, diagnosis and treatment of human B lymphomas related to BCL6 expression.

描述（由申请人提供）：免疫球蛋白（Ig）基因的体细胞超突变（SHM）的过程发生在与抗原和T淋巴细胞的特异性相互作用后发生在B淋巴细胞中。 SHM有几个步骤和要求。在我们的工作模型中，细胞需要产生一个假定的突变因子（MUF），该因子必须通过转录靶向Ig基因。 MUF可以充当核酸内切酶，在基因中产生刻度或双链断裂。据信，刻痕/断裂是以错误的方式修复的，从而产生突变。不匹配修复可能会去除某些突变或通过“纠正”互补DNA链上的野生型核苷酸来修复它们。细胞复制将突变传播到一个或两个子细胞。提出了以下调查：1）在SHM中，特定的电子框站点的作用是什么？发现这种反式激活部位可增强SHM而不增强转录。 2）核小体的位置如何影响SHM过程？ SHM发生在簇中，表明核小体参与突变的靶向。将测试来自可突变小鼠转基因的单核体DNA，以相对于突变而在SHM靶标上的核小体进行测试。 3）双链DNA断裂可以诱导SHM吗？将测试的可能性是，将双链断裂成SHM靶基因会引起突变，而无需SHM的启动事件。 4）何时在细胞周期中发生SHM？基因组的DNA复制是否直接涉及SHM，并且/或是否需要重组。单个细胞将在各种细胞周期阶段分离，并筛选与持续突变过程一致的分子中间体。 5）胞苷脱氨酶有助于突变B淋巴细胞，将哪些mRNA辅助修饰？ SHM需要胞嘧啶脱氨酶AID。将确定潜在的目标mRNA。计划的实验对于学习如何创建Ig基因的各种曲目，其可能与任何外国抗原决定因素（包括肿瘤细胞抗原）反应。躯体超突变也与自身免疫性疾病有关。此外，许多B细胞淋巴瘤显然是由于体细胞突变过程而产生的。了解躯体突变所涉及的成分可能有助于理解自身免疫性的遗传和环境原因，以及治疗传染病和肿瘤的治疗。令人惊讶的是，Bcl6原癌基因在人记忆B细胞中高度突变。这可能与肿瘤发生有关。因此，对躯体突变过程的更好理解可能有助于了解与Bcl6表达相关的人类B淋巴瘤的理解，诊断和治疗。