EZH1/2 inhibition augments the anti-tumor effects of sorafenib in hepatocellular carcinoma. Homo sapiens

Both EZH2 and its homolog EZH1 function as histone H3 Lysine 27 (H3K27) methyltransferases and repress the transcription of target genes. Dysregulation of H3K27 trimethylation (H3K27me3) plays an important role in the development and progression of cancers such as hepatocellular carcinoma (HCC). This study investigated the relationship between the expression of EZH1/2 and the level of H3K27me3 in HCC cell lines and tissues. Additionally, the role of EZH1/2 in cell growth, tumorigenicity, and resistance to sorafenib were also analyzed. Both the lentiviral knockdown and the pharmacological inhibition of EZH1/2 (UNC1999) diminished the level of H3K27me3 and suppressed cell growth and sphere formation in HCC cells, compared with EZH1 or EZH2 single knockdown. Although a significant association was observed between EZH2 expression and H3K27me3 levels in HCC samples, overexpression of EZH1 appeared to contribute to enhanced H3K27me3 levels in some EZH2lowH3K27me3high cases. Akt suppression following sorafenib treatment resulted in an increase of the H3K27me3 levels through a decrease in EZH2 phosphorylation at serine 21. The combined use of sorafenib and UNC1999, synergistically inhibited cell proliferation in vitro and tumor growth in xenograft models using non-obese diabetic mice with severe combined immunodeficiency. Combination treatment canceled the sorafenib-induced enhancement in H3K27me3 levels, indicating that activation of EZH2 function is one of the mechanisms of sorafenib-resistance in HCC. In conclusion, sorafenib plus EZH1/2 inhibitors may comprise a novel therapeutic approach in HCC.

EZH2及其同源蛋白EZH1均作为组蛋白H3赖氨酸27（histone H3 Lysine 27, H3K27）甲基转移酶发挥功能，可负调控靶基因的转录。H3K27三甲基化（H3K27 trimethylation, H3K27me3）的失调在肝细胞癌（hepatocellular carcinoma, HCC）等多种癌症的发生与进展中发挥关键作用。本研究探讨了HCC细胞系及组织中EZH1/2的表达水平与H3K27me3水平之间的关联，并分析了EZH1/2在细胞增殖、致瘤性以及索拉非尼（sorafenib）耐药性中的作用。与单独敲低EZH1或EZH2相比，慢病毒介导的EZH1/2双敲低以及使用EZH1/2特异性药理学抑制剂UNC1999处理，均能降低HCC细胞中H3K27me3的水平，并抑制细胞增殖与球状体形成。尽管在HCC样本中观察到EZH2的表达与H3K27me3水平存在显著关联，但在部分EZH2低表达且H3K27me3高表达的病例中，EZH1的过表达似乎有助于提升H3K27me3的水平。索拉非尼处理后Akt通路受到抑制，可通过降低EZH2丝氨酸21位点的磷酸化水平，使H3K27me3的水平升高。索拉非尼与UNC1999联合使用，可在体外协同抑制HCC细胞增殖，并在非肥胖糖尿病重症联合免疫缺陷（non-obese diabetic severe combined immunodeficiency, NOD-SCID）小鼠的异种移植模型中协同抑制肿瘤生长。联合治疗抵消了索拉非尼诱导的H3K27me3水平升高，这表明EZH2功能激活是HCC对索拉非尼产生耐药性的机制之一。综上，索拉非尼联合EZH1/2抑制剂有望成为HCC的新型治疗策略。