启动子甲基化动态决定急性期蛋白表达模式的机制研究

Acute phase proteins (APPs) are a class of secretory proteins whose blood concentrations undergo large changes in inflammation. Current understanding of the expression regulation of APPs, among which C-reactive protein (CRP) is a representative, is mainly on proximal promoter binding of transcription factors. DNA methylation occurs primarily in CpG motif, and represents a major epigenetic mechanism of gene silencing. Although promoters of most mammalian genes are in CpG islands with little methylation, the promoter of CRP only contains 5 CpG motifs. These CpG motifs either locates in the binding sites of key transcription factors, or harbors the single nucleotide polymorphism (SNP) site that has a marked impact on expression but stays outside the identified regulatory sequences. These imply that CRP expression might be regulated by promoter methylation. Our preliminary results indeed revealed the dependence of CRP expression on the reversible methylation of its promoter. Because the promoters of other APPs also exhibit similarly low CpG densities, this project thus proposes that the expression pattern of APPs is determined by promoter methylation dynamics and will investigate the underlying molecular mechanisms, a comprehensive understanding of which might also lead to new therapy by targeting APP expression.

急性期蛋白是一类在炎症反应中浓度发生剧烈变化的血浆蛋白，在宿主防御和炎症调节中发挥着重要作用。对以C-反应蛋白（C-reactive protein, CRP）为代表的急性期蛋白表达调节的理解，主要集中于转录因子到近端启动子的募集。DNA甲基化是基因表达静默的重要表观遗传学机制，多发生于CpG基序内。虽然大部分哺乳动物基因启动子处于不易甲基化的CpG岛中，但CRP启动子内CpG密度很低。有意思的是，这些CpG或位于关键转录因子结合序列中，或包含显著影响CRP表达的单核苷酸多态性位点，暗示DNA甲基化对CRP表达的重要影响。与此相符，我们的系列预实验亦提示CRP的表达由其启动子的原位甲基化动态可逆调节。由于低CpG密度也是其他急性期蛋白启动子的共同特征，本项目提出“启动子甲基化动态决定急性期蛋白的表达模式”，并将围绕此展开深入研究，阐明其分子机制，为以急性期蛋白表达为标靶的治疗提供新的思路。

本项目深入研究了启动子甲基化对急性期蛋白的表达调节机制，以C-反应蛋白（C-reactive protein）、血清淀粉样蛋白P（serum amyloid P）为实例，明确了其表达与启动子甲基化动态间因果关联，阐明了甲基化修饰酶DNMT3A和TET2在其中的关键作用，揭示了重要转录因子STAT3、NF-κB和C/EBP-β的响应时序及贡献差异，并进而发现可逆甲基化可能是调节启动子内缺乏甲基化基序CpG的基因应激表达的一种普适方式，提出启动子内缺乏CpG的基因可能更易演化出包含CpG的转录因子结合位点以借助甲基化动态实现对表达的快速、可逆调节。此外，本项目还鉴定了参与重要急性期表达调节的新效应分子及功能，探讨了影响其启动子甲基化的遗传多态性与患癌风险之间的关联。