1 Division of Respiratory Medicine and.
2 Nottingham Respiratory Research Unit, University of Nottingham, City Hospital, Nottingham, United Kingdom; and.
Am J Respir Cell Mol Biol. 2018 Apr;58(4):449-460. doi: 10.1165/rcmb.2017-0286OC.
Selective repression of the antifibrotic gene CXCL10 contributes to tissue remodeling in idiopathic pulmonary fibrosis (IPF). We have previously reported that histone deacetylation and histone H3 lysine 9 (H3K9) methylation are involved in CXCL10 repression. In this study, we explored the role of H3K27 methylation and the interplay between the two histone lysine methyltransferases enhancer of zest homolog 2 (EZH2) and G9a in CXCL10 repression in IPF. By applying chromatin immunoprecipitation, Re-ChIP, and proximity ligation assays, we demonstrated that, like G9a-mediated H3K9 methylation, EZH2-mediated histone H3 lysine 27 trimethylation (H3K27me3) was significantly enriched at the CXCL10 promoter in fibroblasts from IPF lungs (F-IPF) compared with fibroblasts from nonfibrotic lungs, and we also found that EZH2 and G9a physically interacted with each other. EZH2 knockdown reduced not only EZH2 and H3K27me3 but also G9a and H3K9me3, and G9a knockdown reduced not only G9 and H3K9me3 but also EZH2 and H3K27me3. Depletion and inhibition of EZH2 and G9a also reversed histone deacetylation and restored CXCL10 expression in F-IPF. Furthermore, treatment of fibroblasts from nonfibrotic lungs with the profibrotic cytokine transforming growth factor-β1 increased EZH2, G9a, H3K27me3, H3K9me3, and histone deacetylation at the CXCL10 promoter, similar to that observed in F-IPF, which was correlated with CXCL10 repression and was prevented by EZH2 and G9a knockdown. These findings suggest that a novel and functionally interdependent interplay between EZH2 and G9a regulates histone methylation-mediated epigenetic repression of the antifibrotic CXCL10 gene in IPF. This interdependent interplay may prove to be a target for epigenetic intervention to restore the expression of CXCL10 and other antifibrotic genes in IPF.
选择性抑制抗纤维化基因 CXCL10 有助于特发性肺纤维化 (IPF) 的组织重塑。我们之前报道过组蛋白去乙酰化和组蛋白 H3 赖氨酸 9 (H3K9) 甲基化参与了 CXCL10 的抑制。在这项研究中，我们探讨了组蛋白 H3K27 甲基化的作用以及两种组蛋白赖氨酸甲基转移酶增强子结合锌指蛋白 2 (EZH2) 和 G9a 之间的相互作用在 IPF 中 CXCL10 抑制中的作用。通过应用染色质免疫沉淀、Re-ChIP 和邻近连接测定，我们证明了与 G9a 介导的 H3K9 甲基化一样，EZH2 介导的组蛋白 H3 赖氨酸 27 三甲基化 (H3K27me3) 在来自 IPF 肺的成纤维细胞 (F-IPF) 中明显富集于 CXCL10 启动子，而在非纤维化肺的成纤维细胞中则没有，并且我们还发现 EZH2 和 G9a 相互作用。EZH2 敲低不仅减少了 EZH2 和 H3K27me3，还减少了 G9a 和 H3K9me3，而 G9a 敲低不仅减少了 G9a 和 H3K9me3，还减少了 EZH2 和 H3K27me3。EZH2 和 G9a 的耗竭和抑制也逆转了组蛋白去乙酰化，并恢复了 F-IPF 中的 CXCL10 表达。此外，用促纤维化细胞因子转化生长因子-β1 处理非纤维化肺的成纤维细胞，增加了 CXCL10 启动子处的 EZH2、G9a、H3K27me3、H3K9me3 和组蛋白去乙酰化，与 F-IPF 中观察到的相似，这与 CXCL10 的抑制有关，并且可以通过 EZH2 和 G9a 敲低来预防。这些发现表明，EZH2 和 G9a 之间的一种新的、功能上相互依存的相互作用调节了 IPF 中抗纤维化 CXCL10 基因的组蛋白甲基化介导的表观遗传抑制。这种相互依存的相互作用可能成为一种表观遗传干预的靶点，以恢复 IPF 中 CXCL10 和其他抗纤维化基因的表达。
