Role of Base Excision Repair in Limiting Hepatocellular Carcinomas

摘要 长期饮食暴露于真菌毒素、黄曲霉毒素B1(AFB1)和乙肝病毒(乙肝)的组合 感染与早发性肝细胞癌(HC)的风险显著增加相关 数以百万计的人生活在东亚、中南美洲和撒哈拉以南非洲。即使在饮食上 暴露于黄曲霉毒素是导致癌症发展的第二大全球环境风险因素， 关于癌症发生的分子机制，仍有一些重要的问题。深入探讨 对这些机制的了解对于识别影响个体的遗传风险因素至关重要。 易感性的人谁是乙肝病毒感染者和黄曲霉毒素B-1接触。在这方面，由于AFB1的致癌作用是 在高频G-T转换的驱动下，启动和完成修复的DNA修复通路 黄曲霉毒素B_1诱导的DNA加合物和乙肝病毒诱导的炎症所致的碱基损伤 生物学意义。这些途径定义了靶组织中的突变负荷，并最终限制了 细胞进展为癌症。尽管核苷酸切除修复(NER)途径已被证明 修复AFB1 DNA加合物，这里提供的小鼠数据证明了DNA碱基切除的敲除 由DNA糖基酶NEIL1启动的修复(BER)途径明显比NER更重要 相对于去除高度诱变的AFB1-Fapy-DG加合物。因此，我们的数据表明 NEIL1基因的缺陷可能会导致人类感染肝癌。为了最大限度地提高与人类的相关性 健康，所有已知的NEIL1变种将被描述为来自世界上黄曲霉毒素摄取的地区 和乙肝病毒感染的流行。所有变种的生物化学特性都将与 WT NEIL1，并在细胞和转基因小鼠中表达，以了解催化- NEIL1的折衷变体改变了对黄曲霉毒素暴露的易感性。这些目标将考验 假设NEIL1的致癌和其他催化受损变体的表达可以 有效阻断修复，促进诱变和致癌增加。特征描述 NEIL1的表型显性致癌变异将提供设计的分子基础 高危人群和早发性肝细胞癌队列中的人类流行病学研究。此外，此应用程序 建议建立慢性炎症的分子机制，即由 乙肝表面抗原和DNA修复缺陷协同驱动黄曲霉毒素B_1诱导 诱变和致癌。总体而言，这些研究与以下方面有直接的人类健康相关性 通过识别遗传风险因素和生物化学来理解全球环境健康问题 以前没有被认为与黄曲霉毒素B_1诱导的致癌相关的通路。

Summary The combination of chronic dietary exposure to the fungal toxin, aflatoxin B1 (AFB1), and hepatitis B viral (HBV) infection is associated with a significant increased risk for early onset hepatocellular carcinomas (HCCs) in millions of people living in East Asia, Central and South America, and sub-Saharan Africa. Even though dietary exposures to aflatoxins constitute the second largest global environmental risk factor for cancer development, there are still significant questions concerning the molecular mechanisms driving carcinogenesis. In-depth knowledge of these mechanisms is critical for the identification of genetic risk factors that affect individual susceptibility for people who are HBV infected and AFB1 exposed. In this regard, since AFB1 carcinogenesis is driven by high frequency G to T transversions, the DNA repair pathways that initiate and complete repair of persistent AFB1-induced DNA adducts and base damage from HBV-induced inflammation have strong biological significance. These pathways define the mutagenic burden in the target tissues and ultimately limit cellular progression to cancer. Although the nucleotide excision repair (NER) pathway has been shown to repair AFB1 DNA adducts, murine data presented herein demonstrate that knockout of the DNA base excision repair (BER) pathway, initiated by the DNA glycosylase NEIL1, is significantly more important than NER relative to the removal of the highly mutagenic AFB1-Fapy-dG adducts. Thus, our data suggest that deficiencies in NEIL1 could contribute to the initiation of HCCs in humans. To maximize relevance to human health, all known variants of NEIL1 will be characterized from regions of the world where aflatoxin ingestion and HBV infection are prevalent. All variants will be characterized for their biochemical properties relative to WT NEIL1 and expressed in cells and transgenic mice to understand the potential for catalytically- compromised variants of NEIL1 to alter susceptibility to aflatoxin exposures. These aims will test the hypothesis that expression of the oncogenic and other catalytically-compromised variants of NEIL1 can efficiently block repair and promote increased mutagenesis and carcinogenesis. Characterization of phenotypically dominant oncogenic variants of NEIL1 will provide the molecular basis from which to design human epidemiological studies in at-risk populations and early onset HCC cohorts. Further, this application proposes to establish the molecular mechanisms by which the combination of chronic inflammation driven by the hepatitis B surface antigen and deficiencies in DNA repair could synergistically drive AFB1-induced mutagenesis and carcinogenesis. Overall, these studies have direct human health relevance pertaining to understanding a global environmental health problem by identifying genetic risk factors and biochemical pathways previously not recognized as germane to AFB1-induced carcinogenesis.