PROJECT 3

项目3 -乳腺癌中DNA脱氨酶的结构生物学 摘要 APOBEC酶家族的标志性活性是在细胞内胞嘧啶脱氨基为尿嘧啶（C至U）。 单链（ss）DNA。这种编辑活动通常在先天免疫反应中起作用， 病毒和转座子限制。然而，我们的实验室和许多其他机构最近的研究强烈表明， APOBEC 3B（A3 B）是基因组突变的主要来源，所述基因组突变驱动多种人类肿瘤的进展。 癌症和耐药性的发展。这一发现-细胞酶主动引入 癌症的突变-与更传统的观点形成鲜明对比，在这种观点中，癌症的突变是由 外源性DNA损伤或DNA复制或修复过程中引入的错误。因为A3 B 虽然不是生命的必需酶，但它是抗癌治疗的一个有前途的靶点。因此，我们的计划 总体假设是，A3 B抑制作为主要治疗方案的辅助治疗，将有助于预防 有害的突变驱动的结果，如耐药性和转移。然而，尽管其强大的 与癌症作为潜在治疗靶点的相关性，还不完全知道A3 B如何结合ssDNA底物， 它如何实现对ssDNA的高选择性而不是RNA，或者它的DNA脱氨酶活性如何在细胞中被调节。 此外，还不知道相关酶如APOBEC 3 H（A3 H）和APOBEC 3F（A3 F）如何与 ssDNA结合残基的不同组成与相似的靶序列接合。在项目3中，我们有 开始通过解决多个A3 B催化域晶体结构来解决这些问题，最近， 实现与A3 B催化结构域的变体以及与A3 B催化结构域的变体结合的ssDNA的共晶结构 相关酶APOBEC 3A（A3 A）。目标1将在此基础上进一步描述全球ssDNA A3 B和A3 H的结合机制。目的2将检查局部二核苷酸靶向机制， 抑制APOBEC家族酶的可能模式。我们的目标是获得更深层次的机械 了解致病性APOBEC介导的ssDNA胞嘧啶脱氨过程，并建立一个 为未来开发APOBEC抑制剂用于癌症治疗奠定了坚实的基础。这些研究将推动 我们的计划旨在实现其长期目标，即抑制乳腺癌中的APOBEC突变，从而 减缓肿瘤发展并改善患者的总体治疗结果。

PROJECT 3 – STRUCTURAL BIOLOGY OF DNA DEAMINASES IN BREAST CANCER ABSTRACT The hallmark activity of the APOBEC family of enzymes is deamination of cytosines to uracils (C-to-U) in single-stranded (ss)DNA. This editing activity normally functions in the innate immune response by contributing to virus and transposon restriction. However, recent studies by our labs and many others strongly indicate that APOBEC3B (A3B) is a major source of genomic mutations that drive the progression of multiple human cancers and the development of drug resistance. This finding – that a cellular enzyme actively introduces mutations in cancer – is in stark contrast to a more conventional view, in which mutations in cancer are caused by DNA damage from exogenous sources or errors introduced during DNA replication or repair. Because A3B is not an essential enzyme for life, it is a promising target for anti-cancer therapies. Thus, our Program's overarching hypothesis is that A3B inhibition, as an adjuvant to primary treatment options, will help to prevent detrimental mutation-driven outcomes such as drug resistance and metastasis. However, despite its strong relevance to cancer as a potential therapeutic target, it is not fully known how A3B engages ssDNA substrates, how it achieves high selectivity for ssDNA over RNA, or how its DNA deaminase activity is regulated in cells. Moreover, it is not known how related enzymes such as APOBEC3H (A3H) and APOBEC3F (A3F) with different compositions of ssDNA-binding residues engage similar target sequences. In Project 3, we have started to address these issues by solving multiple A3B catalytic domain crystal structures and, recently, achieving co-crystal structures of ssDNA bound to a variant of the A3B catalytic domain as well as to the related enzyme APOBEC3A (A3A). Aim 1 will build on this knowledge to further delineate the global ssDNA binding mechanism of A3B and A3H. Aim 2 will examine the local dinucleotide targeting mechanism and possible modes of inhibition of the APOBEC family of enzymes. Our goals are to gain deeper mechanistic understandings of the pathogenic APOBEC-mediated ssDNA cytosine deamination process and to establish a solid foundation for future development of APOBEC inhibitors for cancer therapies. These studies will propel our Program toward achieving its long-term goal of inhibiting APOBEC mutagenesis in breast cancer, thereby slowing tumor evolution and improving overall therapeutic outcomes for patients.