Chromatin Landscaping of TGF-P/SMAD Signaling Targets

转化生长因子-β/SMAD信号网络在抑制正常上皮细胞生长中起重要作用。在肿瘤过程中，转化生长因子-β/SMAD信号的遗传和表观遗传缺失可导致转化细胞的生长和侵袭。在卵巢癌中，最近有报道称，尽管上游调控因子，如TbetaRII，在基因上保持完整和功能，但转化生长因子-β/SMAD信号转导可以对转化生长因子-β的激活剂无反应。因此，似乎其他异常事件，可能影响到共同激活剂 或这一生长抑制途径的共抑制物，引发转化生长因子-β/SMAD下游靶点的表观遗传扰动。到目前为止，这些尚未探索的干扰有可能逐渐改变目标基因启动子内和周围的染色质结构，并且可能是体细胞遗传的。我们推测，表观遗传去调控的转化生长因子-β/SMAD信号通路可能会改变转化生长因子-β/SMAD靶基因的转录谱，从而启动和促进卵巢表面上皮细胞的肿瘤生长。为了验证我们的假设，我们将全面调查和比较卵巢癌和正常卵巢上皮中转化生长因子-β/SMAD靶基因启动子的区域染色质图谱(激活或抑制状态)。相对于这种表观遗传现象，SMAD介导的转录调控还依赖于其他机制，如组织特异性因子、启动子序列以及与其他DMA结合转录因子的协同作用。我们将使用计算工具来确定假定的转化生长因子-β/SMAD靶序列，并确定它们与卵巢上皮细胞局部染色质结构的功能关系。一种新的基于微阵列的ChlP芯片分析将被开发来实验地确定这些预测的启动子的染色质重塑(即组蛋白修饰)是否在卵巢癌中发生。统计方法将是 建议对SMAD复合体和改变的染色质结构之间的相互作用进行建模，并定义卵巢癌细胞中独特的表观遗传特征。具体地说，我们将1)开发KbTSMAD(转化生长因子-β/SMAD信号通路知识库)，这是转化生长因子-β/SMAD信号通路及其直接靶基因启动子的信息源；2)确定卵巢癌细胞这些下游基因座染色质重塑的轮廓；3)发展统计学方法来模拟转化生长因子-β/SMAD复合体与改变的染色质结构之间的协同作用，并确定独特的表观遗传学 卵巢癌细胞中的信号。

The TGF-beta/SMAD signaling network plays an important role in growth inhibition of normal epithelia. In neoplastic processes, genetic and epigenetic losses of TGF-beta/SMAD signaling can result in outgrowth and invasion of transformed cells. In ovarian cancer, it has recently been reported that TGF-beta/SMAD signaling can become non-responsive to activators of TGF-beta, despite the fact that upstream regulators, such as TbetaRII, remain genetically intact and functional. Thus, it appears that other aberrant events, perhaps affecting co-activators or co-repressors of this growth inhibitory pathway, trigger epigenetic perturbations in TGF-beta/SMAD downstream targets. These as of yet un-explored perturbations have the potential to gradually alter chromatin structure in and around promoters of target genes and may be somatically heritable. We hypothesize that epigenetic deregulation TGF-beta/SMAD signaling may alter transcriptional profiles of TGF-beta/SMAD target genes, resulting in the initiation and promotion of neoplastic outgrowth of the ovarian surface epithelium. To test our hypothesis, we will comprehensively survey and compare regional chromatin profiles (active or repressed state) of TGF-beta/SMAD target promoters in ovarian cancer versus normal epithelia. Relative to this epigenetic phenomenon, SMAD-mediated transcription regulation also depends on other mechanisms, such as tissue-specific factors, promoter sequences, and cooperative interaction with other DMA-binding transcription factors. We will use computational tools to identify putative TGF-beta/SMAD target sequences and determine their functional relationship with local chromatin structure in ovarian epithelia. A novel microarray-based ChlP-on-chip assay will be developed to experimentally determine whether chromatin remodeling (i.e., histone modifications) of these predicted promoters occurs in ovarian cancer. Statistical approaches will be proposed to model the interaction between SMAD complexes and altered chromatin structure and to define unique epigenetic signatures in ovarian cancer cells. Specifically, we will 1) develop KbTSMAD (Knowledge base of TGF-beta/SMAD signaling pathway), an information resource of the TGF-beta/SMAD signaling pathway and its direct target gene promoters; 2) determine profiles of chromatin remodeling in these downstream loci in ovarian cancer cells; and 3) develop statistical approaches for modeling the synergistic interaction between TGF-beta/SMAD complex and altered chromatin structure and for defining unique epigenetic signatures in ovarian cancer cells.