Histone lysine methylation is thought to play a role in the pathogenesis of rheumatoid arthritis (RA). We previously reported aberrant expression of the gene encoding mixed-lineage leukemia 1 (MLL1), which catalyzes methylation of histone H3 lysine 4 (H3K4), in RA synovial fibroblasts (SFs). The aim of this study was to elucidate the involvement of MLL1 in the activated phenotype of RASFs. SFs were isolated from synovial tissues obtained from patients with RA or osteoarthritis (OA) during total knee joint replacement. MLL1 mRNA and protein levels were determined after stimulation with tumor necrosis factor α (TNFα). We also examined changes in trimethylation of H3K4 (H3K4me3) levels in the promoters of RA-associated genes (matrix-degrading enzymes, cytokines, and chemokines) and the mRNA levels upon small interfering RNA-mediated depletion of MLL1 in RASFs. We then determined the levels of H3K4me3 and mRNAs following treatment with the WD repeat domain 5 (WDR5)/MLL1 inhibitor MM-102. H3K4me3 levels in the gene promoters were also compared between RASFs and OASFs. After TNFα stimulation, MLL1 mRNA and protein levels were higher in RASFs than OASFs. Silencing of MLL1 significantly reduced H3K4me3 levels in the promoters of several cytokine (interleukin-6 [IL-6], IL-15) and chemokine (C–C motif chemokine ligand 2 [CCL2], CCL5, C-X-C motif chemokine ligand 9 [CXCL9], CXCL10, CXCL11, and C-X3-C motif chemokine ligand 1 [CX3CL1]) genes in RASFs. Correspondingly, the mRNA levels of these genes were significantly decreased. MM-102 significantly reduced the promoter H3K4me3 and mRNA levels of the CCL5, CXCL9, CXCL10, and CXCL11 genes in RASFs. In addition, H3K4me3 levels in the promoters of the IL-6, IL-15, CCL2, CCL5, CXCL9, CXCL10, CXCL11, and CX3CL1 genes were significantly higher in RASFs than OASFs. Our findings suggest that MLL1 regulates the expression of particular cytokines and chemokines in RASFs and is associated with the pathogenesis of RA. These results could lead to new therapies for RA.

组蛋白赖氨酸甲基化被认为在类风湿性关节炎 (RA) 的发病机制中发挥作用。我们之前报道了编码混合谱系白血病 1 (MLL1) 的基因在 RA 滑膜成纤维细胞 (SF) 中的异常表达，该基因催化组蛋白 H3 赖氨酸 4 (H3K4) 的甲基化。本研究的目的是阐明 MLL1 在 RASF 激活表型中的作用。 SFs 是从 RA 或骨关节炎 (OA) 患者全膝关节置换术期间获得的滑膜组织中分离出来的。用肿瘤坏死因子 α (TNFα) 刺激后测定 MLL1 mRNA 和蛋白质水平。我们还检测了 RA 相关基因（基质降解酶、细胞因子和趋化因子）启动子中 H3K4 (H3K4me3) 水平的三甲基化变化以及 RASF 中小干扰 RNA 介导的 MLL1 缺失后 mRNA 水平的变化。然后，我们测定了 WD 重复结构域 5 (WDR5)/MLL1 抑制剂 MM-102 处理后 H3K4me3 和 mRNA 的水平。还比较了 RASF 和 OASF 之间基因启动子中的 H3K4me3 水平。 TNFα刺激后，RASF中的MLL1 mRNA和蛋白水平高于OASF。 MLL1 的沉默显着降低了几种细胞因子（白细胞介素 6 [IL-6]、IL-15）和趋化因子（C–C 基序趋化因子配体 2 [CCL2]、CCL5、CXC 基序趋化因子配体 9 [CXCL9] 启动子中 H3K4me3 的水平。 ]、CXCL10、CXCL11 和 C-X3-C 基序趋化因子配体 1 [CX3CL1]) RASF 中的基因。相应地，这些基因的mRNA水平显着降低。 MM-102 显着降低 RASF 中 CCL5、CXCL9、CXCL10 和 CXCL11 基因的启动子 H3K4me3 和 mRNA 水平。此外，RASF 中 IL-6、IL-15、CCL2、CCL5、CXCL9、CXCL10、CXCL11 和 CX3CL1 基因启动子中的 H3K4me3 水平显着高于 OASF。我们的研究结果表明，MLL1 调节 RASF 中特定细胞因子和趋化因子的表达，并与 RA 的发病机制相关。这些结果可能会导致 RA 的新疗法。