Modulation of Aflatoxin B1-induced hepatocarcinogenesis by RB loss

描述(申请人提供)：肝癌是全球癌症死亡的第三大原因。该病发生的主要危险因素是环境性质的。这些危险因素包括强烈调节肿瘤易感性的因素，如慢性乙肝病毒感染或暴露于DNA破坏肝癌致癌物黄曲霉毒素B1(AFB1)。肿瘤的发展在很大程度上是由颠覆关键细胞通路的遗传损伤推动的。视网膜母细胞瘤肿瘤抑制因子(Rb)通路在大多数肝肿瘤中发生突变。虽然Rb在大多数肝脏肿瘤中是突变的，但Rb丢失如何在肝脏中特异性地促进肿瘤的发生尚不清楚。此外，RB缺乏与暴露于导致肝癌的环境因素(如黄曲霉毒素FB1)之间的相互作用及其对肿瘤形成的影响尚不清楚。这是一个关键的考虑因素，因为众所周知，Rb是对DNA损伤做出适当的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，诱导更多的突变，并导致基因组不稳定，这是癌细胞的一个特征。关键的是，Rb在动物DNA损伤检查点中的作用以及检查点的取消如何有助于肿瘤的发生还没有研究。我们已经培育出具有肝细胞特异性Rb缺陷的小鼠。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缺失易于在基因毒性损伤后诱发肝脏肿瘤。因此，我们假设在暴露于环境相关的遗传毒性致癌物，如黄曲霉毒素1后，Rb的丢失增强了肝脏中肿瘤的形成。我们建议描绘RB如何改变小鼠肝脏对AFB1的反应，并探索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)，这可能是推动肿瘤形成的重要因素。其次，我们将具体阐明Rb缺失在黄曲霉毒素B_1诱导的小鼠肝肿瘤发生中的作用。这些研究将确定体内Rb功能的关键方面，并描绘Rb丢失的特定后果，这些后果与遗传毒性损伤后肿瘤的形成密切相关。

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.