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。创造基因变异的能力也是有代价的，可能会产生有害的后果。基因组信息的保真度必须在转录和复制过程中得到精心保护，以避免DNA序列意外变化的有害结果。虽然避免突变和DNA损伤是保持基因组完整性的关键，但人类基因组编码多种酶，这些酶被有意地用于诱导基因组DNA中的突变和双链断裂（DSB）。人类免疫系统利用这种DNA编辑酶来对抗我们所接触的大量病原体。例如，活化诱导的脱氨酶（AID）是适应性免疫应答的中心介质，并驱动抗体多样化。APOBEC 3（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突变，作为内在细胞抗病毒防御的一部分。这些病毒DNA的强大突变体的有益作用必须与它们作用于宿主基因组的潜力相平衡。我们认为，人类APOBEC3（hA3）酶威胁宿主基因组的完整性，并可能是人类癌症中DSB和成簇体细胞突变的来源。hA3蛋白编辑细胞DNA的能力暗示它们在驱动基因组不稳定性，并提供了一个令人信服的理由来研究它们的突变体活性是如何调节的。我们的长期目标是了解hA3酶是如何被调节以实现对病毒基因组的有效限制，同时限制细胞DNA中致癌病变的可能性。我们专注于两个hA3成员（hA3A和hA3B），它们都可以定位在细胞核中，并且具有与癌症基因组中的胞嘧啶转换相匹配的突变特征。在强有力的初步数据的支持下，这一提议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引起DSB，（ii）确定hA3蛋白在人类细胞中DSB处产生簇集突变的程度，和（iii）确定什么调节hA3A/hA3B活性。拟议的研究hA3酶作为人类癌症体细胞突变的潜在来源，代表了对这些酶的抗病毒活性的先前研究的创新性偏离。该提案的结果将建立hA3作用于细胞基因组的机制和调节其活性的过程。与人类健康的相关性：我们的研究形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。这些知识有可能导致治疗干预的新策略，以限制驱动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.