Laboratory of Gene Expression, Fondazione A. Cesalpino, Rome, Italy.
Oncogene. 2011 Jun 9;30(23):2670-8. doi: 10.1038/onc.2010.635. Epub 2011 Mar 14.
The DNp73 proteins act as trans-repressors of p53 and p73-dependent transcription and exert both anti-apoptotic activity and pro-proliferative activity. DNp73s are frequently up-regulated in a variety of human cancers, including human hepatocellular carcinomas (HCCs). Increased levels of DNp73 proteins confer to HCC cells resistance to apoptosis and, irrespective to p53 status, a chemoresistant phenotype. Here, we show that interferon (IFN)α down-regulates DNp73 expression in primary human hepatocytes (PHHs) and HCC cell lines. IFNα has been used as pro-apoptotic agent in the treatment of malignancies and there is increasing evidence of IFNα effectiveness in HCC treatment and prevention of recurrence. The precise mechanisms by which class I IFNs exert their anti-proliferative and anti-tumor activity remain unclear. IFNα binding to its receptor activates multiple intracellular signaling cascades regulating the transcription of numerous direct target genes through the recruitment of a complex comprising of STAT1, STAT2 and IFN regulatory factor (IRF)9 to their promoters. We found that, in response to IFNα, the P2p73 promoter undergoes substantial chromatin remodeling. Histone deacetylases (HDACs) replace histone acetyl transferases. STAT2 is recruited onto the endogenous P2p73 promoter together with the polycomb group protein Ezh2, leading to increased H3K27 methylation and transcriptional repression. The reduction of DNp73 levels by IFNα is paralleled by an increased susceptibility to IFNα-triggered apoptosis of Huh7 hepatoma cells. Our results show, for the first time, that IFN-stimulated gene factor 3 recruitment may serve both in activating and repressing gene expression and identify the down-regulation of DNp73 as an additional mechanism to counteract the chemoresistance of liver cancer cells.
DNp73 蛋白作为 p53 和 p73 依赖性转录的反式阻遏物发挥作用，并具有抗凋亡活性和促增殖活性。DNp73 在多种人类癌症中频繁上调，包括人类肝细胞癌（HCC）。DNp73 蛋白水平的升高赋予 HCC 细胞对凋亡的抗性，并且与 p53 状态无关，具有化学抗性表型。在这里，我们表明干扰素（IFN）α在原代人肝细胞（PHH）和 HCC 细胞系中下调 DNp73 的表达。IFNα 已被用作治疗恶性肿瘤的促凋亡剂，越来越多的证据表明 IFNα 在 HCC 治疗和预防复发方面有效。I 类干扰素发挥其抗增殖和抗肿瘤活性的确切机制尚不清楚。IFNα 与其受体结合激活多种细胞内信号级联反应，通过募集包含 STAT1、STAT2 和干扰素调节因子（IRF）9 的复合物到其启动子，调节众多直接靶基因的转录。我们发现，响应 IFNα，P2p73 启动子经历了大量染色质重塑。组蛋白去乙酰化酶（HDACs）取代组蛋白乙酰转移酶。STAT2 与多梳蛋白组蛋白 Ezh2 一起募集到内源性 P2p73 启动子，导致 H3K27 甲基化增加和转录抑制。IFNα 下调 DNp73 水平伴随着 Huh7 肝癌细胞对 IFNα 触发的凋亡的敏感性增加。我们的研究结果首次表明，IFN 刺激基因因子 3 的募集既可以激活又可以抑制基因表达，并确定 DNp73 的下调是抵消肝癌细胞化学抗性的另一种机制。
