JAK2介导的磷酸化促进组蛋白甲基转移酶EZH2降解的分子机制研究

The molecular mechanisms of epigenetic regulation included mainly four aspects: DNA methylation, histone modifications, ATP-dependent chromatin remodeling, and non-coding RNA. Histone methylations can alter the structure of the nucleosome and may also serve as a platform for the assembly of multiple protein complexes to regulate gene expression. While H3K4me3 and H3K36me3 are strongly associated with transcriptional activation, H3K9me3, H3K27me3, and H4K20mes are generally considered repressive modifications. Enhancer of Zeste Homolog 2 (EZH2) is the core enzymatic subunit of an epigenetic gene-silencing complex called polycomb repressive complex 2 (PRC2). EZH2 is a SET domain histone methyltransferase that preferentially catalyzes histone 3 lysine 27 (H3K27) methylation, a repressive mark that maintains epigenetic gene silencing. EZH2 is active only when associated with other PRC2 core components EED, SUZ12, and RbAp48. EZH2 influences stem cell renewal by epigenetic repression of genes involved in cell fate decisions. EZH2 has oncogenic activity, and its overexpression has previously been causally linked to differentiation blocks in tumors. Akt phosphorylates EZH2 at serine 21 and suppresses its methyltransferase activity by impeding EZH2 binding to histone H3, which results in a decrease of H3K27me3 and derepression of silenced genes. CDK-mediated phosphorylation is a key mechanism governing EZH2 function and that there is a link between the cell-cycle machinery and epigenetic gene silencing. But, it is unknown wether EZH2 is phosphorylated at tyrosine by stress stimuli. We found that EZH2 could be phosphorylated by JAK2 in thermal stress and IFN-γ and phosphorylated EZH2 was degradated further. In this project, we try to investigate how EZH2 is phosphorylated by JAK2; to demonstrate the mechanism of degradation of phosphorylated EZH2 in the cells; to understand the role of stress and IFN-γ induced degradation of phosphorylated EZH2 in tumorigenesis. The results should shed lights on novel targets in thermo- and immuno- therapeutic strategy against human tumors. Keywords(limited to 5 keywords,seperated by;): EZH2; JAK2; phosphorylation; heat shock; IFN-γ

组蛋白甲基化修饰是表观遗传调控的重要分子机制之一。组蛋白甲基转移酶EZH2与EED、SUZ12等蛋白共同组成PRC2复合物催化组蛋白H3K27的三甲基化修饰，参与肿瘤发生与发展等过程。已知EZH2可以被CDK1和AKT1等磷酸化并且导致其靶基因改变。我们初步发现，热激和干扰素（IFN-γ）通过诱导JAK2活化导致组蛋白甲基转移酶EZH2发生酪氨酸磷酸化修饰并促进EZH2降解。所以。本项目旨在寻找热激和干扰素（IFN-γ）促进EZH2降解的信号通路，初步阐明EZH2特异酪氨酸磷酸化的机制及功能，进而探讨热激和干扰素（IFN-γ）对肿瘤细胞生长的表观遗传调控机制，以期为肿瘤的热疗和免疫治疗提供新的思路和理论依据。

组蛋白甲基化修饰是表观遗传调控的重要分子机制之一。组蛋白甲基转移酶EZH2与EED、SUZ12等蛋白共同组成PRC2复合物催化组蛋白H3K27的三甲基化修饰，参与肿瘤发生与发展等过程。已知EZH2可以被CDK1和AKT1等丝氨酸磷酸化并且导致其靶基因改变。我们研究发现，热激和干扰素（IFN-γ）通过诱导JAK2活化导致组蛋白甲基转移酶EZH2发生酪氨酸磷酸化修饰并促进EZH2降解。磷酸化修饰位点主要发生在Y467。磷酸化介导的EZH2的降解过程依赖泛素蛋白酶体途径。进一步发现Trim35与EZH2在Jak2活化后可以相互结合，并且，证实Trim35可以特异泛素化修饰EZH2，并且导致EZH2降解。Trim35以及其导致的EZH2降解调控Rad51基因表达，并且与乳腺癌细胞生长有关联。本项目研究结果为肿瘤的热疗和免疫治疗提供新的思路和理论依据。