J Proteome Res. 2020 Apr 3;19(4):1533-1547. doi: 10.1021/acs.jproteome.9b00773. Epub 2020 Mar 24.
Acquisition of drug resistance remains a chief impediment to successful cancer therapy, and we previously described a transient drug-tolerant cancer cell population (DTPs) whose survival is in part dependent on the activities of the histone methyltransferases G9a/EHMT2 and EZH2, the latter being the catalytic component of the polycomb repressive complex 2 (PRC2). Here, we apply multiple proteomic techniques to better understand the role of these histone methyltransferases (HMTs) in the establishment of the DTP state. Proteome-wide comparisons of lysine methylation patterns reveal that DTPs display an increase in methylation on K116 of PRC member Jarid2, an event that helps stabilize and recruit PRC2 to chromatin. We also find that EZH2, in addition to methylating histone H3K27, also can methylate G9a at K185, and that methylated G9a better recruits repressive complexes to chromatin. These complexes are similar to complexes recruited by histone H3 methylated at K9. Finally, a detailed histone post-translational modification (PTM) analysis shows that EZH2, either directly or through its ability to methylate G9a, alters H3K9 methylation in the context of H3 serine 10 phosphorylation, primarily in a cancer cell subpopulation that serves as DTP precursors. We also show that combinations of histone PTMs recruit a different set of complexes to chromatin, shedding light on the temporal mechanisms that contribute to drug tolerance.
耐药性的获得仍然是癌症治疗成功的主要障碍，我们之前描述了一个短暂的耐药性癌细胞群体（DTPs），其存活部分依赖于组蛋白甲基转移酶 G9a/EHMT2 和 EZH2 的活性，后者是多梳抑制复合物 2（PRC2）的催化成分。在这里，我们应用多种蛋白质组学技术来更好地理解这些组蛋白甲基转移酶（HMTs）在 DTP 状态建立中的作用。赖氨酸甲基化模式的全蛋白质组比较表明，DTPs 显示出 PRC 成员 Jarid2 的 K116 上甲基化增加的现象，这有助于稳定并将 PRC2 募集到染色质上。我们还发现，EZH2 除了甲基化组蛋白 H3K27 外，还可以甲基化 G9a 的 K185，并且甲基化的 G9a 更好地将抑制复合物募集到染色质上。这些复合物与组蛋白 H3 甲基化 K9 募集的复合物相似。最后，详细的组蛋白翻译后修饰（PTM）分析表明，EZH2 可以直接或通过其甲基化 G9a 的能力，改变 H3K9 甲基化在 H3 丝氨酸 10 磷酸化的背景下，主要在作为 DTP 前体的癌细胞亚群中。我们还表明，组蛋白 PTM 的组合将不同的复合物募集到染色质上，揭示了导致药物耐受性的时间机制。
