Modulation of Aflatoxin B1-induced hepatocarcinogenesis by RB loss

描述（由申请人提供）：肝癌是全球癌症死亡的第三大原因。该病发展的主要危险因素是环境因素。这些危险因素包括强烈调节肿瘤易感性的药物，如慢性乙型肝炎病毒感染或暴露于破坏DNA的肝癌原黄曲霉毒素B1 （AFB1）。肿瘤的发展在很大程度上是由破坏关键细胞通路的遗传病变驱动的。在这种途径中，视网膜母细胞瘤肿瘤抑制因子（RB）途径在大多数肝脏肿瘤中发生突变。虽然RB在大多数肝脏肿瘤中发生突变，但RB丢失如何特异性地促进肝脏肿瘤发生尚不清楚。此外，rb缺乏与暴露于导致肝癌的环境因子（如AFB1）之间的相互作用以及这如何影响肿瘤形成尚不清楚。这是一个关键的考虑因素，因为已经确定RB是对DNA损伤的适当细胞周期检查点反应所必需的。在没有RB的情况下，细胞在DNA损伤的情况下继续增殖，诱导额外的突变并导致基因组不稳定，这是癌细胞的一个标志。关键的是，RB在动物DNA损伤检查点中的作用以及检查点取消如何促进肿瘤发生尚未得到研究。我们已经产生了肝细胞特异性rb缺乏症小鼠。我们发现RB缺乏会导致肝细胞倍性异常（总DNA含量），这表明这些细胞在遗传上是不稳定的。我们还发现，RB丢失易诱发基因毒性损伤后的肝脏肿瘤。因此，我们假设RB丢失会在暴露于环境相关的基因毒性致癌物（如AFB1）后增强肝脏肿瘤的形成。我们建议描述RB如何改变小鼠肝脏对AFB1的反应，并探讨这如何促进肿瘤的形成。首先，我们将确定RB丢失如何影响肝脏对AFB1暴露的急性检查点反应，并确定这种异常反应的特征（例如基因组不稳定的发展），这可能是驱动肿瘤形成的重要因素。其次，我们将具体阐明rb缺失对afb1诱导的小鼠肝脏肿瘤发展的影响。这些研究将确定RB在体内功能的关键方面，并描述RB丢失与基因毒性损伤后肿瘤形成相关的具体后果。

DESCRIPTION (provided by applicant): Liver cancer is the third leading cause of cancer deaths throughout the world. The major risk factors for development of this disease are environmental in nature. These risk factors include agents that strongly modulate tumor susceptibility such as chronic infection with hepatitis B virus or exposure to the DNA damaging hepatocarcinogen aflatoxin B1 (AFB1). Tumor development is largely driven by genetic lesions that subvert critical cellular pathways. 1 such pathway, the retinoblastoma tumor suppressor (RB) pathway is mutated in the majority of liver tumors. Although RB is mutated in most liver tumors, how RB loss specifically contributes to tumorigenesis in the liver is unknown. Furthermore, the interplay between RB-deficiency and exposure to the environmental agents that cause liver cancer, e.g. AFB1, and how this impacts tumor formation is unclear. This is a critical consideration because it is well established that RB is required for the appropriate cell cycle checkpoint response to DNA damage. In the absence of RB, cells continue to proliferate in the presence of DNA damage, inducing additional mutations and leading to genome instability, a hallmark of cancer cells. Critically, the role of RB in DNA damage checkpoints in animals and how checkpoint abrogation contributes to tumorigenesis has not been studied. We have generated mice that have hepatocyte-specific RB-deficiency. We have found that RB deficiency causes abnormal hepatocyte ploidy (total DNA content), suggesting that these cells are inherently genetically unstable. We have also found that RB loss predisposes to the induction of liver tumors following genotoxic damage. Thus, we hypothesize that RB loss enhances tumor formation in the liver following exposure to environmentally-relevant genotoxic carcinogens, such as AFB1. We propose to delineate how RB modifies the response to AFB1 in the mouse liver and probe how this contributes to tumor formation. First, we will determine how RB loss influences the acute checkpoint response of the liver to AFB1 exposure and identify features of this aberrant response (e.g. development of genome instability) that may be important for driving tumor formation. Second, we will specifically elucidate the effects of RB-loss on AFB1-induced liver tumor development in the mouse. These studies will identify critical facets of RB function in vivo and delineate specific consequences of RB loss that are germane to tumor formation following genotoxic insult.