Regulation of APOBEC3 cytidine deaminase-induced mutation during cancerdevelopment

摘要 APOBEC特征突变（TCA和TCT三核苷酸中的C至T和C至G取代） 序列）包含人类癌症中第二丰富的突变标签。此特征码 由胞苷脱氨酶的APOBEC家族的几个成员的异常活性引起，这些成员通常 在许多细胞过程中起作用，包括限制病毒。最近，我们发现APOBEC3A (A3A)在APOBEC突变的乳腺癌细胞系中表达升高，导致细胞凋亡增加。 胞苷脱氨酶活性和乳腺癌突变。本提案的目的是， 新鉴定的APOBEC突变特征的组分，确定A3A mRNA表达是如何被激活的。 在癌症中上调，确定蛋白酶体对A3A蛋白丰度的控制，并表征DNA修复 限制A3A诱变的途径。目标1将确定A3A的原因和后果， APOBEC3B诱导的插入/缺失突变。目标2将描述导致异常的机制， 通过识别转录因子和信号通路上调乳腺癌中的A3A 负责增加A3A表达。此外，我们将研究导致 A3A的蛋白酶体依赖性降解，并评估有缺陷的后 A3A丰度的翻译控制。Aim3将表征同源的抗突变作用， 重组蛋白BRCA1和BRCA2在模板转换介导的A3A依赖性脱碱基旁路中的作用 复制分叉处的站点。我们将确定BRCA 1或BRCA 2缺陷是否会增加APOBEC诱导的 在人类细胞系中的突变，并在遗传上定义参与该途径的其他蛋白质。成功 这些目标的完成将增强我们对A3A调节及其在癌症病因学中的作用的理解。 此外，这些努力将确定限制APOBEC诱导的诱变的方法，这可以提供 通过限制导致耐药性的持续肿瘤演变来实现治疗益处。

Abstract APOBEC signature mutations (C to T and C to G substitutions in TCA and TCT trinucleotide sequences) comprise the second most abundant mutation signature in human cancers. This signature is caused by aberrant activity of several members of the APOBEC family of cytidine deaminases, which normally function in many cellular processes including the restriction of viruses. Recently, we found that APOBEC3A (A3A) expression is elevated in APOBEC-mutated breast cancer cell lines, resulting in increased cellular cytidine deaminase activity and breast cancer mutagenesis. The objectives of this proposal are to characterize newly identified components of the APOBEC mutation signature, determine how A3A mRNA expression is upregulated in cancer, define proteasomal controls on A3A protein abundance, and characterize DNA repair pathways that limit A3A mutagenesis. Aim1 will determine the causes and consequences of A3A- and APOBEC3B-induced insertion/deletion mutations. Aim 2 will characterize the mechanisms leading to aberrant up-regulation of A3A in breast cancers by identifying the transcription factors and signaling pathways responsible for increasing A3A expression. Additionally, we will investigate the mechanism(s) leading to proteasome-dependent degradation of A3A and assess the mutagenic consequences of defective post- translational control of A3A abundance. Aim3 will characterize anti-mutagenic roles of the homologous recombination proteins BRCA1 and BRCA2 in template switch-mediated bypass of A3A-dependent abasic sites at replication forks. We will determine whether BRCA1 or BRCA2-deficiency elevates APOBEC-induced mutation in human cell lines and genetically define additional proteins involved in the pathway. Successful completion of these aims will enhance our understanding of A3A regulation and its role in cancer etiology. Additionally, these efforts will identify means to limit APOBEC-induced mutagenesis, which could provide therapeutic benefit by limiting continued tumor evolution that leads to drug resistance.