G9a-Mediated Methylation of ERα Links the PHF20/MOF Histone Acetyltransferase Complex to Hormonal Gene Expression. Homo sapiens

The euchromatin histone methyltransferase 2 (EHMT2, aka G9a) methylates histone H3K9 to repress gene expression, but it also acts as a coactivator for some nuclear receptors. The molecular mechanisms underlying this activation remain elusive. Here we show that G9a functions as a bona fide coactivator of the endogenous estrogen receptor α (ERα) in breast cancer cells in a histone methylation-independent manner. G9a dimethylates ERα protein at lysine 235 both in vitro and in cells. Dimethylation of ERαK235 (ERαK235me2) is recognized by the Tudor domain of PHF20, which in turn recruits the MOF histone acetyltransferase (HAT) complex to ERα target gene promoters to deposit histone H4K16 acetylation promoting active transcription. Together, our in vitro and in vivo data establish the molecular mechanism by which G9a functions as an ERα coactivator. Along with the PHF20/MOF complex, G9a links the crosstalk between ERα methylation and histone acetylation governing the epigenetic regulation of hormonal gene expression. Overall design: G9a KD RNA-seq and PHF20 KD RNA-seq with and without E2 treatment

常染色质组蛋白甲基转移酶2（euchromatin histone methyltransferase 2，EHMT2，又名G9a）可通过甲基化组蛋白H3K9抑制基因表达，同时亦可作为部分核受体的共激活因子。目前，介导该激活过程的分子机制仍未明确。本研究发现，G9a可在乳腺癌细胞中以不依赖组蛋白甲基化的方式，作为内源性雌激素受体α（estrogen receptor α，ERα）的真正共激活因子。G9a可在体外及细胞内对ERα蛋白的赖氨酸235位点进行二甲基化修饰。ERαK235的二甲基化修饰（ERαK235me2）可被PHF20的Tudor结构域识别，进而招募MOF组蛋白乙酰转移酶（histone acetyltransferase，HAT）复合物结合至ERα靶基因的启动子区域，催化组蛋白H4K16发生乙酰化修饰以促进转录激活。综上，本研究的体外与体内实验数据阐明了G9a作为ERα共激活因子的分子机制。G9a与PHF20/MOF复合物协同，搭建起ERα甲基化与组蛋白乙酰化之间的交叉调控网络，进而介导激素应答基因的表观遗传调控。实验整体设计：设置G9a敲低、PHF20敲低的RNA测序样本，分别施加雌二醇（E2）处理与空白对照。