EZH2介导H3K27三甲基化调控TIMP2启动子区DNA甲基化促进上皮性卵巢癌侵袭转移的机制研究

The enhancer of zeste homolog 2 (EZH2), which acts as a histone methyltransferase for lysine 27 of histone H3 and can also control DNA methylation, contributes to epigenetic silencing of target chromatin and plays a pivotal role in the progression of several solid tumor. Our early studies and foreign researchers all showed that high levels of EZH2 expression are associated with progression and metastasis of ovarian cancer, but the underlying mechanism is still not fully understood. Our recently studies indicate that DNA hypermethylation of the TIMP2 gene promoters and low expression level of TIMP2 are detected in ovarian cancer tissues; EZH2 knockdown markedly reduces the DNA methylation of the TIMP2 gene promoters and increases the expression of TIMP2, thereby decreasing the invasive activity of ovarian cancer cells. TIMP2 is critical for invasion and metastasis of cancer cells, but the upstream mechanism is unclear. We assume that EZH2 mediate TIMP2 transcriptional silencing by methylating lysine 27 in histone H3 (3meH3K27) and subsequent recruiting DNA methyltransferases (DNMTs) to TIMP2 gene promoters that catalyze de novo DNA methylation, and contributes to invasion and metastasis of epithelial ovarian cancer. In this study, we will investigate the role of EZH2 in catalyzing H3K27 trimethylation and subsequent DNA methylation of the TIMP2 gene promoters to promote the invasion and metastasis of epithelial ovarian cancer cells. Our results will provide for the first time evidence that EZH2 plays an active role in regulating TIMP2 expression by catalyzing H3K27 trimethylation and subsequent DNA methylation of the TIMP2 gene promoters and thereby promoting invasion and metastasis of epithelial ovarian cancer. Our results wiil indicate that EZH2 is a potential therapeutic target for treatment of epithelial ovarian cancer.

EZH2通过将组蛋白H3上第27位赖氨酸残基甲基化而改变染色质构象，抑制相关基因转录，促进肿瘤进展。我们和他人研究均证实， EZH2与卵巢癌侵袭转移密切相关，但作用机制不清。我们前期研究发现，卵巢癌组织中TIMP2启动子区DNA甲基化，TIMP2表达水平低于正常组织；降低EZH2的表达，TIMP2启动子区DNA甲基化水平降低，TIMP2表达水平升高。研究表明TIMP2是肿瘤侵袭进展中重要的调节因子，但是上游调节机制不清。我们设想卵巢癌中高表达的EZH2介导H3K27三甲基化，募集DNMT使得TIMP2启动子区DNA高甲基化，进而导致TIMP2的低表达，促进了卵巢癌的侵袭转移。我们将首次在组织、细胞和动物水平研究EZH2介导H3K27三甲基化调控TIMP2启动子DNA甲基化，促进卵巢癌侵袭转移的机制；本项目将为我们在TIMP2上游选择EZH2为治疗靶点抑制卵巢癌侵袭进展提供理论基础和新思路。

EZH2能够通过将组蛋白H3上第27位赖氨酸残基甲基化而改变染色质构象，抑制相关基因转录；也能通过直接募集DNA甲基化转移酶到基因启动子区域，改变基因甲基化水平调控基因的表达，从而促进肿瘤进展。本课题重点研究EZH2在卵巢癌侵袭转移中的下游靶基因以及EZH2调控其下游基因(Tissue Inhibitors Of Metalloproteinase 2)TIMP2的具体机制，从而有助于阐明卵巢癌侵袭转移的表观遗传学调控机制。我们的研究发现，卵巢癌组织中EZH2与TIMP2表达水平呈负相关，EZH2与TIMP2联合检测对于预测患者生存期很有意义。在卵巢癌细胞株中，EZH2能够调控TIMP2的表达，改变EZH2的表达水平可以影响癌细胞的侵袭迁移能力，此种改变可以被TIMP2逆转。EZH2调控TIMP2的表达是通过直接与TIMP2启动子P2启动子区相结合，改变启动子区DNA甲基化水平而实现。本研究首次提出EZH2能够通过与TIMP2启动子相结合，改变其甲基化水平从而调控TIMP2的表达，促进卵巢癌的侵袭转移，为EZH2作为卵巢癌转移的表观遗传学靶点提供理论依据。