Molecular Mechanisms of APOBEC-Induced Mutagenesis in Cancer

项目总结 肿瘤的异质性是目前化疗药物耐药和转移的主要原因 发展，导致病人死亡。在同一患者的同一肿瘤内，肿瘤细胞可能是 微妙甚至显著的不同，使得临床治疗变得更加困难。了解驱动机制 癌症多样性是开发新策略以减弱肿瘤进化和适应的关键一步。 基因组的不稳定性是肿瘤内遗传多样性的一个重要来源，产生了一个细胞群体 取决于从微环境或治疗环境中进行的潜在选择。近年来，下一步- 世代测序技术已经开始识别DNA损伤和错误的基因组签名 DNA修复过程，揭示了导致癌症基因组突变积累的新机制。 到目前为止，在许多癌症类型中发现的30个突变特征中，有一个特别占主导地位： APOBEC的签名。APOBEC3家族的两个成员APOBEC3A(A3A)和APOBEC3B(A3B)， 单链DNA上的靶TPC基序，是APOBEC突变特征的主要来源 在病人的肿瘤样本中检测到。我们的初步观察发现，A3A和 A3B在癌细胞中的表达和突变积累。一方面，A3A很少被发现表达，但 许多肿瘤具有强烈的A3A突变特征。另一方面，A3B在大多数情况下都表达 癌细胞，但只有一小部分具有A3B突变特征。A3A和A3B均大幅增加 肿瘤中的突变，但这些观察使我们提出A3A和A3B的表达不是 像以前认为的那样，评估癌细胞APOBEC状态的可靠方法。我们建议A3A是 在转录水平上受到严格调控，并瞬时表达以产生突变。我们的研究将 解释为什么A3A在癌症中很少表达，但许多癌症都有很强的A3A突变 签名。相反，我们认为A3B在蛋白质水平上受到调控，以保护基因组免受A3B的影响 活动。我们的目标是揭示控制癌细胞中A3A和A3B调控的分子机制。 我们的总体假设是，细胞利用两种不同的机制来调节A3A和A3B并保护 他们的基因组与他们的活动相对抗。此外，我们提出癌症中的特定信号导致 放松对这些保护机制的管制，导致突变激增。我们的具体目标是1) 确定癌细胞中调节A3A表达的信号通路和2)识别蛋白质复合体 控制癌细胞中的A3B活性。我们的长期目标是开发治疗策略，以抑制 由A3A和A3B引起的基因组突变，导致肿瘤异质性、转移和药物 抵抗。

PROJECT SUMMARY Tumor heterogeneity is the main cause of resistance to current chemotherapy drugs as well as metastasis development, leading to patients' death. Within the same tumor from the same patient, tumor cells might be subtly or even dramatically different, making it harder to treat clinically. Understanding mechanisms driving cancer diversity is a critical step toward developing new strategies to attenuate tumor evolution and adaptation. Genomic instability is a prominent source of genetic diversity within tumors, generating a cell population subject to potential selection from a micro-environmental or therapeutic context. In recent years, next- generation sequencing technologies have begun to identify genomic signatures of DNA damage and errors in DNA repair processes, revealing new mechanisms causing an accumulation of mutations in cancer genomes. From the 30 mutational signatures identified across many cancer types to date, one is particularly dominant: the APOBEC signature. APOBEC3A (A3A) and APOBEC3B (A3B), two members of the APOBEC3 family, target TpC motifs on single-stranded DNA and are the major sources of the APOBEC mutational signature detected in patients' tumor samples. Our preliminary observation identified a discrepancy between A3A and A3B expression and mutation accumulation in cancer cells. On one hand, A3A is rarely found expressed, yet many of the tumors have a strong A3A-mutational signature. On the other hand, A3B is expressed in most cancer cells, but only a fraction has an A3B-mutational signature. Both A3A and A3B significantly increase mutations in tumors, but these observations have led us to propose that A3A and A3B expression is not a reliable way to assess the APOBEC status of cancer cells, as previously thought. We propose that A3A is tightly regulated at the transcription level and transiently expressed to generate mutations. Our study will explain why A3A is rarely found expressed in cancer but many cancers have a strong A3A mutational signature. In contrast, we propose that A3B is regulated at the protein level to protect the genome against A3B activity. Our goal is to uncover the molecular mechanisms that govern A3A and A3B regulation in cancer cells. Our overall hypothesis is that cells exploit two separate mechanisms to regulate A3A and A3B and to protect their genome against their activity. In addition, we propose that specific signals in cancer lead to the deregulation of these protective mechanisms, causing a surge of mutations. Our Specific Aims are to 1) define signaling pathways in cancer cells that regulate A3A expression and 2) identify protein complexes controlling A3B activity in cancer cells. Our long-term goal is to develop therapeutic strategies to suppress mutations in the genome caused by A3A and A3B, leading to tumor heterogeneity, metastasis, and drug resistance.