Zhang Bao-Le, Guo Ting-Wen, Gao Le-Le, Ji Guang-Quan, Gu Xiao-He, Shao Yu-Qi, Yao Rui-Qin, Gao Dian-Shuai
Department of Neurobiology and Anatomy, Xuzhou Key Laboratory of Neurobiology, Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou 221004, Jiangsu, China.
Oncotarget. 2017 Jul 11;8(28):45105-45116. doi: 10.18632/oncotarget.15126.
The specific mechanisms for epigenetic regulation of gene transcription remain to be elucidated. We previously demonstrated that hyperacetylation of histone H3K9 in promoter II of glioma cells promotes high transcription of the glial cell line-derived neurotrophic factor (GDNF) gene. This hyperacetylation significantly enhanced Egr-1 binding and increased the recruitment of RNA polymerase II (RNA POL II) to that region (P < 0.05). Egr-1 expression was abnormally increased in C6 glioma cells. Further overexpression of Egr-1 significantly increased Egr-1 binding to GDNF promoter II, while increasing RNA POL II recruitment, thus increasing GDNF transcription (P < 0.01). When the acetylation of H3K9 in the Egr-1 binding site was significantly reduced by the histone acetyltransferase (HAT) inhibitor curcumin, binding of Egr-1 to GDNF promoter II, RNA POL II recruitment, and GDNF mRNA expression were significantly downregulated (P < 0.01). Moreover, curcumin attenuated the effects of Egr-1 overexpression on Egr-1 binding, RNA POL II recruitment, and GDNF transcription (P < 0.01). Egr-1 and RNA POL II co-existed in the nucleus of C6 glioma cells, with overlapping regions, but they were not bound to each other. In conclusion, highly expressed Egr-1 may be involved in the recruitment of RNA POL II in GDNF promoter II in a non-binding manner, and thereby involved in regulating GDNF transcription in high-grade glioma cells. This regulation is dependent on histone hyperacetylation in GDNF promoter II.
基因转录表观遗传调控的具体机制仍有待阐明。我们之前证明，胶质瘤细胞启动子II中组蛋白H3K9的高乙酰化促进了胶质细胞源性神经营养因子（GDNF）基因的高转录。这种高乙酰化显著增强了Egr-1的结合，并增加了RNA聚合酶II（RNA POL II）向该区域的募集（P<0.05）。Egr-1在C6胶质瘤细胞中表达异常增加。进一步过表达Egr-1显著增加了Egr-1与GDNF启动子II的结合，同时增加了RNA POL II的募集，从而增加了GDNF的转录（P<0.01）。当组蛋白乙酰转移酶（HAT）抑制剂姜黄素显著降低Egr-1结合位点处H3K9的乙酰化时，Egr-1与GDNF启动子II的结合、RNA POL II的募集以及GDNF mRNA的表达均显著下调（P<0.01）。此外，姜黄素减弱了Egr-1过表达对Egr-1结合、RNA POL II募集和GDNF转录的影响（P<0.01）。Egr-1和RNA POL II共存于C6胶质瘤细胞的细胞核中，存在重叠区域，但它们彼此不结合。总之，高表达的Egr-1可能以非结合方式参与GDNF启动子II中RNA POL II的募集，从而参与调节高级别胶质瘤细胞中GDNF的转录。这种调节依赖于GDNF启动子II中的组蛋白高乙酰化。
