Turning Inhibition of Translation Initiation into Cancer Therapy

 描述(申请人提供)：这个项目的总体目标是扩大我们对翻译启动抑制与白介素24(IL-24)引发的细胞和肿瘤抑制之间的联系的细胞和分子机制的理解。IL-24作为一种以基因为基础的治疗实体瘤的临床试验表明，IL-24是有效和安全的。这一建议与当前的观点是一致的，即现代抗癌治疗必须是靶向性的，在对正常细胞影响最小的情况下抑制肿瘤的生长，并且可以通过靶向癌症发生、维持和/或进展的基本机制来获得有效的低毒抗癌药物。研究表明，IL-24可导致细胞内钙离子部分耗竭，激活内质网应激，进而抑制真核细胞起始因子2α(eIF2)的磷酸化。EIF2的磷酸化和三元复合体的可用性不仅控制着最初认为的总体翻译速度，而且控制着特定基因簇的表达。大多数致癌蛋白的严格翻译控制解释了不受限制的翻译起始和恶性转化之间的联系，这一联系在两个实验模型和许多过度表达翻译起始因子的人类癌症中都得到了很好的证实。磷酸化的eIF2与鸟核苷酸交换因子eIF2B高亲和力结合，从而抑制eIF2*GDP向eIF2*GTP的循环，耗尽启动新一轮翻译所需的三元复合体。已经证实，部分耗尽内质网钙离子储存库会激活eIF2激酶，使eIF2磷酸化，从而限制翻译启动的速度。此外，我还证明了IL-24诱导结合免疫球蛋白(Bip)和C/-EBP同源蛋白(CHOP)的表达，这是三元复合体丰度的两个下游标志。这一应用的工作假设是，IL-24发挥抗癌活性，因为它有助于恢复对翻译启动的生理限制。我已经证明，Sigma 1受体(Sigma 1 R)与IL-24相互作用，这种IL-24：Sig1R是IL-24诱导的内质网应激、钙动员、eIF2的磷酸化和癌细胞凋亡的关键上游信号。在本申请中，我们建议继续努力确定IL-24作为翻译起始抑制物对癌细胞的特异性作用。具体地说，我们将1)使用卡梅隆钙指示蛋白来直接评估IL-24处理后内质网储存库的钙含量(特异性目标1)，2)确定三元复合体的耗尽是否介导了IL-24的抗癌作用，(特异性目标2)，以及3)确定Sig1R在IL-24介导的翻译起始抑制中的作用(特异性目标3)。对于这些建议的研究，我们 将与哈佛医学院的何塞·A·哈尔佩林博士合作，他是癌症治疗中针对翻译启动的专家。

 DESCRIPTION (provided by applicant): The overall goal of this project is to expand our understanding of the cellular and molecular mechanisms that link translation initiation inhibition to apoptosis and tumor suppression triggered by Interleukin-24 (IL-24). Clinical testing of IL-24 as a gene-based therapeutic for the treatment of solid tumors demonstrated that IL-24 is efficacious and is safe. This proposal is consistent with the current view that modern anti-cancer therapy must be target-specific, inhibit the growth of cancer with minimal effect on normal cells, and that effective anti- cancer agents of low toxicity can be achieved by targeting the fundamental mechanisms responsible for the genesis, maintenance, and/or progression of cancer. I have shown that IL-24 causes partial depletion of intracellular Ca++ and activation of endoplasmic reticulum (ER) stress, which in turn induces inhibitory phosphorylation of eukaryotic initiation factor 2 alpha (eIF2). Phosphorylation of eIF2 and the availability of he ternary complex control not only the overall rate of translation, as initially thought, but also th expression of specific gene clusters. The tight translational control of most oncogenic proteins explains the link between unrestricted translation initiation and malignant transformation that has been well established in both experimental models and in numerous human cancers that overexpress translation initiation factors. Phosphorylated eIF2 binds with high affinity to the guanine nucleotide exchange factor eIF2B and thereby inhibits recycling of eIF2*GDP into eIF2*GTP, depleting the ternary complex necessary to initiate a new round of translation. It is well established that partial depletion of ER Ca++ stores activates the eIF2 kinases that phosphorylate eIF2 and thereby limits the rate of translation initiation. Furthermore, I have demonstrated that IL-24 induces expression of Binding immunoglobulin protein (BiP) and C/-EBP homologous protein (CHOP), two down-stream markers of ternary complex abundance. The working hypothesis of this application is that IL-24 exerts anticancer activities because it helps restore physiological restraints on translation initiation. I have demonstrated that Sigma 1 Receptor (Sig1R) interacts with IL-24 and that this IL-24:Sig1R is a critical upstream signal for IL-24-induced ER-stress, calcium mobilization, phosphorylation of eIF2 and apoptosis on cancer cells. In this application we propose to continue our efforts to characterize the cancer cell- specific actions of IL-24 as an inhibitor of translation initiation. Specifically, we will 1)use cameleon calcium indicator proteins to assess directly the calcium content of the ER-stores after IL-24 treatment (Specific Aim 1), 2) determine whether depletion of the ternary complex mediates the anticancer effect of IL-24, (Specific Aim 2), and 3) determine the role of Sig1R on IL-24-mediated inhibition of translation initiation (Specific Aim 3). For these proposed studies we will collaborate with Dr. Jose A. Halperin, from Harvard Medical School, and expert on targeting translation initiation for cancer therapy.