Liu Shujun, Liu Zhongfa, Xie Zhiliang, Pang Jiuxia, Yu Jianhua, Lehmann Esther, Huynh Lenguyen, Vukosavljevic Tamara, Takeki Mitsui, Klisovic Rebecca B, Baiocchi Robert A, Blum William, Porcu Pierluigi, Garzon Ramiro, Byrd John C, Perrotti Danilo, Caligiuri Michael A, Chan Kenneth K, Wu Lai-Chu, Marcucci Guido
Division of Hematology-Oncology, The Ohio State University, Columbus, OH 43210, USA.
Blood. 2008 Feb 15;111(4):2364-73. doi: 10.1182/blood-2007-08-110171. Epub 2007 Dec 14.
Bortezomib reversibly inhibits 26S proteasomal degradation, interferes with NF-kappaB, and exhibits antitumor activity in human malignancies. Zinc finger protein Sp1 transactivates DNMT1 gene in mice and is functionally regulated through protein abundance, posttranslational modifications (ie, ubiquitination), or interaction with other transcription factors (ie, NF-kappaB). We hypothesize that inhibition of proteasomal degradation and Sp1/NF-kappaB-mediated transactivation may impair aberrant DNA methyltransferase activity. We show here that, in addition to inducing accumulation of polyubiquitinated proteins and abolishment of NF-kappaB activities, bortezomib decreases Sp1 protein levels, disrupts the physical interaction of Sp1/NF-kappaB, and prevents binding of the Sp1/NF-kappaB complex to the DNMT1 gene promoter. Abrogation of Sp1/NF-kappaB complex by bortezomib causes transcriptional repression of DNMT1 gene and down-regulation of DNMT1 protein, which in turn induces global DNA hypomethylation in vitro and in vivo and re-expression of epigenetically silenced genes in human cancer cells. The involvement of Sp1/NF-kappaB in DNMT1 regulation is further demonstrated by the observation that Sp1 knockdown using mithramycin A or shRNA decreases DNMT1 protein levels, which instead are increased by Sp1 or NF-kappaB overexpression. Our results unveil the Sp1/NF-kappaB pathway as a modulator of DNA methyltransferase activity in human cancer and identify bortezomib as a novel epigenetic-targeting drug.
硼替佐米可逆性抑制26S蛋白酶体降解，干扰核因子κB（NF-κB），并在人类恶性肿瘤中表现出抗肿瘤活性。锌指蛋白Sp1在小鼠中可反式激活DNA甲基转移酶1（DNMT1）基因，并且通过蛋白质丰度、翻译后修饰（即泛素化）或与其他转录因子（即NF-κB）相互作用进行功能调控。我们推测，蛋白酶体降解抑制以及Sp1/NF-κB介导的反式激活可能会损害异常的DNA甲基转移酶活性。我们在此表明，除了诱导多泛素化蛋白积累以及消除NF-κB活性外，硼替佐米还会降低Sp1蛋白水平，破坏Sp1/NF-κB的物理相互作用，并阻止Sp1/NF-κB复合物与DNMT1基因启动子结合。硼替佐米对Sp1/NF-κB复合物的消除导致DNMT1基因的转录抑制以及DNMT1蛋白的下调，这继而在体外和体内诱导整体DNA低甲基化，并使人类癌细胞中表观遗传沉默基因重新表达。使用光神霉素A或短发夹RNA（shRNA）敲低Sp1可降低DNMT1蛋白水平，而Sp1或NF-κB过表达则会使其升高，这一观察结果进一步证明了Sp1/NF-κB参与DNMT1调控。我们的结果揭示了Sp1/NF-κB途径是人类癌症中DNA甲基转移酶活性的调节因子，并确定硼替佐米是一种新型的表观遗传靶向药物。
