Shi Yijiang, Frost Patrick J, Hoang Bao Q, Benavides Angelica, Sharma Sanjai, Gera Joseph F, Lichtenstein Alan K
Department of Medicine, Greater Los Angeles VA Healthcare System and University of California at Los Angeles Medical School, Los Angeles, California, USA.
Cancer Res. 2008 Dec 15;68(24):10215-22. doi: 10.1158/0008-5472.CAN-08-1066.
Prior work indicates that c-myc translation is up-regulated in multiple myeloma cells. To test a role for interleukin (IL)-6 in myc translation, we studied the IL-6-responsive ANBL-6 and IL-6-autocrine U266 cell lines as well as primary patient samples. IL-6 increased c-myc translation, which was resistant to rapamycin, indicating a mechanism independent of mammalian target of rapamycin (mTOR) and cap-dependent translation. In contrast, the cytokine enhanced cap-independent translation via a stimulatory effect on the myc internal ribosome entry site (IRES). As known IRES-trans-activating factors (ITAF) were unaffected by IL-6, we used a yeast-three-hybrid screen to identify novel ITAFs and identified hnRNP A1 (A1) as a mediator of the IL-6 effect. A1 specifically interacted with the myc IRES in filter binding assays as well as EMSAs. Treatment of myeloma cells with IL-6 induced serine phosphorylation of A1 and increased its binding to the myc IRES in vivo in myeloma cells. Primary patient samples also showed binding between A1 and the IRES. RNA interference to knock down hnRNP A1 prevented an IL-6 increase in myc protein expression, myc IRES activity, and cell growth. These data point to hnRNP A1 as a critical regulator of c-myc translation and a potential therapeutic target in multiple myeloma.
先前的研究表明，c-myc的翻译在多发性骨髓瘤细胞中上调。为了测试白细胞介素（IL）-6在myc翻译中的作用，我们研究了IL-6反应性ANBL-6和IL-6自分泌U266细胞系以及原发性患者样本。IL-6增加了c-myc的翻译，且对雷帕霉素耐药，这表明其机制独立于哺乳动物雷帕霉素靶蛋白（mTOR）和帽依赖性翻译。相反，细胞因子通过对myc内部核糖体进入位点（IRES）的刺激作用增强了帽依赖性翻译。由于已知的IRES反式激活因子（ITAF）不受IL-6影响，我们使用酵母三杂交筛选来鉴定新的ITAF，并确定异质性核糖核蛋白A1（A1）是IL-6效应的介质。在滤膜结合试验以及电泳迁移率变动分析中，A1与myc IRES特异性相互作用。用IL-6处理骨髓瘤细胞可诱导A1的丝氨酸磷酸化，并增加其在骨髓瘤细胞体内与myc IRES的结合。原发性患者样本也显示A1与IRES之间存在结合。通过RNA干扰敲低异质性核糖核蛋白A1可阻止IL-6增加myc蛋白表达、myc IRES活性和细胞生长。这些数据表明异质性核糖核蛋白A1是c-myc翻译的关键调节因子，也是多发性骨髓瘤潜在的治疗靶点。
