Epigenetic Regulation Of Sex-dependent Liver Cancer

描述(申请人提供)：肝细胞癌(肝细胞癌)在男性中的发病率是女性的三倍多。肝癌也不成比例地影响雄性啮齿动物，为研究性别依赖性肝癌的发生机制提供了一个有价值的模型。我们和其他人已经证明，促炎细胞因子，而不是性激素，是男性肿瘤促进的主要驱动力。然而，这个过程并不是细胞因子所特有的。阻断肿瘤坏死因子-a、干扰素-g或白介素6均可减少雄性小鼠实验性肝癌的发生。因此，癌症倾向似乎是男性化肝脏的一种先天特征。性别依赖的肝细胞编程，而不是上游免疫，可能解释性别二型性肿瘤的发生。我们已经报道，雄性小鼠的肝细胞癌与性别特异的全基因组转录签名的丢失有关，这一过程被称为肝脏性别破坏。这种泛染色体的改变意味着在肝细胞转化中染色质的破坏。此外，我们和其他人已经表明，男性肝细胞癌的易感性是成熟的印记，因为随着年龄的增长，去势的好处越来越少。肝脏的阳刚化是由脑下垂体的搏动性生长激素引起的。肝细胞通过Stat5b转导这一信号，Stat5b转位到细胞核，启动男性转录程序。肝脏男性化涉及数千个基因的同步改变，这表明参与了根水平的染色质修饰物。然而，虽然核小体松弛可能促进所需的Stat5b访问g相关序列(GAS)和其他DNA基序，但一个意想不到的结果可能是密切相关的促炎转录因子不成比例地结合。因此，我们假设，阳性的Stat5b依赖的表观遗传重塑引起染色质对促肿瘤促炎细胞因子的超敏反应。不幸的是，由于缺乏合适的连续细胞系，性别特异性肝细胞功能的分子研究一直受到阻碍。我们已经开发了一种性二型连续肝细胞培养系统，并在此建议使用它来探索将染色质状态定义为阳性或阴性的表观遗传学机制。接下来，我们将测试男性表观遗传学特征是否通过促进转录因子(STAT1、STAT3、NF-kB)对同源DNA序列的访问而增加对促炎细胞因子的敏感性。细胞研究将与野生型C57BL/6和Stat5b-/-小鼠的雄性和雌性肝脏的全面体内表观遗传学图谱相补充。前炎性化学损伤模型(DEN)将被用来评估转录因子结合和急性时相反应，重点是性二型基因。最后，我们将确定Stat5b缺乏是否足以保护雄性小鼠免受DEN引发的肝癌的影响，这表明了炎症相关肝癌的易感性存在共同的下游机制。这些研究首次定义了肝脏性别分化的表观遗传学修饰物，并询问了一种基于染色质对炎症敏感性的性别特异性肿瘤促进的新机制。 公共卫生相关性：肝细胞癌是美国上升最快的癌症，表现出明显的性别差异。这些研究探索了基于DNA和相关蛋白质修饰的肝脏性别分化的细胞基础，并展示了炎症可能如何选择性地增加男性患癌症的风险。

DESCRIPTION (provided by applicant): Hepatocellular carcinoma HCC) arises in men more than three times as often as women. Liver cancer also disproportionately affects male rodents, providing a valuable model to study mechanisms of sex-dependent hepatocarcinogenesis. We and others have shown that proinflammatory cytokines, not sex hormones, are the primary drivers of male tumor promotion. However, the process is not cytokine-specific. Interruption of either TNF-a, IFN-g or IL-6 reduces experimental liver cancer in male mice. Therefore, cancer predilection appears to be an innate characteristic of the masculinized liver. Sex-dependent hepatocyte programming, not upstream immunity, may explain gender-dimorphic tumor incidence. We have reported that HCC in male mice is associated with loss of a sex-specific genome-wide transcriptional signature, a process termed liver-gender disruption. Such pan-chromosomal alterations implicate chromatin disruption in hepatocellular transformation. Moreover, we and others have shown that male HCC susceptibility is maturationally imprinted, as there is a decreasing benefit of castration with advancing age. Liver masculinization is enacted by pulsatile growth hormone from the pituitary. Hepatocytes transduce this signal through Stat5b, which translocates to the nucleus and initiates the male transcription program. Liver masculinization involves the synchronous alteration of thousands of genes, suggesting involvement of root-level chromatin modifiers. Nevertheless, while nucleosomal relaxation may facilitate required Stat5b access to g-associated sequences (GAS) and other DNA motifs, an unintended consequence might be disproportionate binding of closely related proinflammatory transcription factors. Because of this, we hypothesize that masculine Stat5b-dependent epigenetic remodeling invokes chromatin hypersensitivity to tumor-promoting proinflammatory cytokines. Unfortunately, molecular studies of gender-specific hepatocyte function have been hampered by the lack of a suitable continuous cell line. We have developed a sexually dimorphic continuous hepatocyte culture system, and propose here to use it to probe epigenetic mechanisms that define a chromatin state as masculine or feminine. Next, we will test whether the masculine epigenetic profile increases sensitivity to proinflammatory cytokines by facilitating access of transcription factors (Stat1, Stat3, NF-kB) to cognate DNA sequences. Cell studies will be complemented with comprehensive in vivo epigenetic profiling of male and female liver in wild- type C57BL/6 and Stat5b-/- mice. A proinflammatory chemical injury model (DEN) will be used to assess transcription factor binding and acute-phase responses, with an emphasis on sexually dimorphic genes. Finally, we will determine whether Stat5b deficiency is sufficient to protect male mice from DEN-initiated HCC, suggesting a common downstream mechanism for susceptibility to inflammation-associated liver cancer. These studies are the first to define epigenetic modifiers of liver sexual differentiation, and to interrogate a novel mechanism of gender-specific tumor promotion predicated on chromatin sensitivity to inflammation. PUBLIC HEALTH RELEVANCE: Hepatocellular carcinoma, the fastest rising cancer in the United States, exhibits marked gender disparity. These studies explore a cellular basis for liver sexual differentiation based on DNA and associated protein modifications, and show how inflammation may selectively increase cancer risk in men.