Investigation of the role of the histone modifying enzyme peptidyl arginine deiminase 4 (PAD4) in breast cancer progression

乳腺癌是全世界女性最常见的肿瘤，疾病进展仍然知之甚少。最近的研究表明，除了基因突变，表观遗传改变也有助于肿瘤的发生，不仅在DNA甲基化水平上，而且在组蛋白标记和组蛋白修饰酶水平上也是如此。这项研究计划的目的是阐明表观遗传学改变在乳腺癌中的作用，特别是PAD4的作用，PAD4是一种将组蛋白精氨酸和甲基精氨酸残基转化为瓜氨酸的酶。我的初步数据强烈表明，PAD4抑制了乳腺癌细胞从上皮到间充质的转变，这是一种导致侵袭性致癌癌细胞的转变事件。我提出的研究试图通过进行微阵列和芯片测序分析来确定PAD4的下游基因靶点和潜在的途径，以阐明该酶如何参与维持上皮细胞的表型。此外，我将测试这样一种假设，即PAD4的下调和由此导致的组蛋白瓜氨酸化的减少是浸润性乳腺癌细胞上皮向间质转化计划的一部分，可以被PAD4的过度表达逆转。该项目的预期结果将使人们更好地了解PAD4酶介导的组蛋白修饰在乳腺癌中的作用，并可能有助于开发新的诊断和治疗策略来防止乳腺癌的进展。

Breast cancer is the most common tumor in women worldwide and disease progression still remains poorly understood. Recent studies have shown that in addition to genetic mutations, epigenetic alterations also contribute to tumorigenesis, not only at the levels of DNA methylation but also at the level of histone marks and histone modifying enzymes. The aim of this research proposal is to elucidate the role of epigenetic alteration in breast cancer, in particular the role of PAD4, an enzyme that converts histone arginine and methylarginine residues to citrulline. My preliminary data strongly suggest that PAD4 inhibits epithelial-to-mesenchymal-transition in breast cancer cells, a transition event that gives rise to invasive, tumorigenic cancer cells. My proposed studies seek to determine downstream gene targets and underlying pathways of PAD4 by performing microarray and ChIP-sequencing analyses to elucidate how this enzyme is involved preserving an epithelial cell phenotype. Moreover, I will test the hypothesis that downregulation of PAD4 and the resulting reduction of histone citrullination is part of an epithelial-tomesenchymal- transition program in invasive breast cancer cells and can be reversed by the overexpression of PAD4. The expected results of the proposed project will give rise to a better understanding of the role of histone modifications mediated by enzyme PAD4 in breast cancer and will likely be helpful for the development of novel diagnostic and therapeutic strategies in the prevention of breast cancer progression.