The human APOBEC3A deaminase - genomic instability and regulation

描述（由申请人提供）：突变产生生命所必需的遗传多样性。创造遗传变异的能力也是有代价的，有可能造成有害后果。在转录和复制过程中必须小心翼翼地保留基因组信息的保真度，以避免 DNA 序列意外改变带来的有害后果。尽管避免突变和 DNA 损伤是维持基因组完整性的关键，但人类基因组编码多种酶，这些酶被有意用于诱导基因组 DNA 中的突变和双链断裂 (DSB)。人类免疫系统利用此类 DNA 编辑酶来对抗我们所接触的大量病原体。例如，激活诱导脱氨酶 (AID) 是适应性免疫反应的中心介质，并驱动抗体多样化。 APOBEC3（载脂蛋白 B mRNA 编辑酶催化多肽 3）亚家族的相关胞嘧啶脱氨酶使病毒基因组发生突变，作为内在细胞抗病毒防御的一部分。这些强大的病毒 DNA 突变体的有益作用必须与其作用于宿主基因组的潜力相平衡。我们提出人类 APOBEC3 (hA3) 酶威胁宿主基因组完整性，并且可能是人类癌症中 DSB 和集群体细胞突变的来源。 hA3 蛋白编辑细胞 DNA 的能力表明它们与基因组不稳定有关，并为研究其突变活性如何受到调节提供了令人信服的理由。我们的长期目标是了解如何调节 hA3 酶以实现对病毒基因组的有效限制，同时限制细胞 DNA 致癌损伤的可能性。我们重点关注两个 hA3 成员（hA3A 和 hA3B），它们都可以定位于细胞核，并且具有与癌症基因组中胞嘧啶转变相匹配的突变特征。在强有力的初步数据的支持下，该提案将确定细胞基因组如何容易受到 hA3A/hA3B 活性的破坏性影响。我们的具体目标是：(i) 确定 hA3 酶如何使基因组脱氨基并导致 DSB，(ii) 确定 hA3 蛋白在人类细胞中 DSB 处产生簇突变的程度，以及 (iii) 确定调节 hA3A/hA3B 活性的因素。拟议的研究将 hA3 酶作为人类癌症体细胞突变的潜在来源，代表了与之前专注于这些酶的抗病毒活性的研究的创新背离。该提案的结果将建立 hA3 对细胞基因组的作用机制以及调节其活性的过程。与人类健康的相关性：我们的研究构成了一系列研究的基础，这些研究有望揭示 hA3 突变酶的失调如何导致人类癌症。这些知识有可能带来新的治疗干预策略，以限制导致癌症进展的体细胞突变。

DESCRIPTION (provided by applicant): Mutations generate the genetic diversity that is essential for life. The ability to create genetic variation also comes at a price, with the potentil for detrimental consequences. The fidelity of genomic information must be meticulously preserved during transcription and replication, to avoid deleterious outcomes of unintended changes to DNA sequences. Although avoidance of mutation and DNA damage is key to maintaining genomic integrity, the human genome encodes multiple enzymes that are employed intentionally to induce mutations and double-strand breaks (DSBs) in genomic DNA. The human immune system employs such DNA editing enzymes to combat the large array of pathogens to which we are exposed. For example, the activation-induced deaminase (AID) is a central mediator of the adaptive immune response, and drives antibody diversification. The related cytosine deaminases of the APOBEC3 (apolipoprotein B mRNA editing enzyme catalytic polypeptide 3) subfamily mutate virus genomes as part of the intrinsic cellular antiviral defense. The beneficial effects of these powerful mutators of viral DNA must be balanced with their potential to act on the host genome. We propose that human APOBEC3 (hA3) enzymes threaten host genome integrity, and could be the source of DSBs and clustered somatic mutations in human cancers. The ability of hA3 proteins to edit cellular DNA implicates them in driving genomic instability and provides a compelling reason to investigate how their mutator activity is regulated. Our long-term goal is to understand how hA3 enzymes are regulated to achieve efficient restriction of virus genomes, while limiting the potential for oncogenic lesions n cellular DNA. We focus on two hA3 members (hA3A and hA3B) that can both be localized in the nucleus and have a mutational signature that matches that seen with cytosine transitions in cancer genomes. Supported by strong preliminary data, this proposal will determine how the cellular genome is susceptible to damaging effects of hA3A/hA3B activity. Our Specific Aims will be: (i) To determine how hA3 enzymes deaminate the genome and cause DSBs, (ii) To determine the extent to which hA3 proteins generate clustered mutations at DSBs in human cells, and (iii) To determine what regulates hA3A/hA3B activity. The proposed research into hA3 enzymes as potential sources for somatic mutations in human cancers, represents an innovative departure from previous studies focused on antiviral activities of these enzymes. The results of this proposal will establish mechanisms for hA3 action on the cellular genome and processes that regulate their activity. RELEVANCE TO HUMAN HEALTH: Our studies form the foundation in a continuum of research that is expected to reveal how misregulation of hA3 mutator enzymes contributes to human cancers. Such knowledge has the potential to lead to novel strategies for therapeutic interventions to limit somatic mutations that drive cancer progression.