Epigenetic Regulation Of Sex-dependent Liver Cancer

描述（由申请人提供）：肝细胞癌（HCC）在男性中的发病率是女性的三倍以上。肝癌对雄性啮齿动物的影响也不成比例，这为研究性别依赖性肝癌发生机制提供了一个有价值的模型。我们和其他人已经表明，促炎细胞因子，而不是性激素，是男性肿瘤促进的主要驱动因素。然而，这个过程不是细胞因子特异性的。阻断TNF-a、IFN-g或IL-6均可减少雄性小鼠的实验性肝癌。因此，癌症偏好似乎是男性化肝脏的先天特征。性别依赖的肝细胞编程，而不是上游免疫，可能解释性别二型肿瘤的发病率。我们已经报道，雄性小鼠的HCC与性别特异性全基因组转录特征的缺失有关，这一过程被称为肝性别破坏。这种泛染色体改变涉及肝细胞转化中的染色质破坏。此外，我们和其他人已经表明，男性HCC易感性是成熟的，因为阉割的好处随着年龄的增长而减少。肝脏的雄性化是由脑垂体的搏动生长激素引起的。肝细胞通过Stat5b转导该信号，Stat5b易位到细胞核并启动雄性转录程序。肝脏男性化涉及数千个基因的同步改变，表明涉及根水平的染色质修饰因子。然而，尽管核小体松弛可能促进所需的Stat5b进入g相关序列（GAS）和其他DNA基序，但意想不到的后果可能是密切相关的促炎转录因子的不成比例结合。因此，我们假设男性依赖stat5b的表观遗传重塑会引起染色质对促肿瘤的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两性二态的连续肝细胞培养系统，并建议在这里使用它来探索定义染色质状态为男性或女性的表观遗传机制。接下来，我们将测试男性表观遗传谱是否通过促进转录因子（Stat1, Stat3, NF-kB）进入同源DNA序列来增加对促炎细胞因子的敏感性。细胞研究将辅以野生型C57BL/6和Stat5b-/-小鼠的雄性和雌性肝脏的全面体内表观遗传分析。促炎化学损伤模型（DEN）将用于评估转录因子结合和急性期反应，重点是两性二态基因。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HCC，从而提示炎症相关肝癌易感性的共同下游机制。这些研究首次定义了肝脏性别分化的表观遗传修饰因子，并探讨了基于染色质对炎症敏感性的性别特异性肿瘤促进新机制。

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.