IRE1a: a Conditional Tumor Suppressor

项目概要/摘要 细胞对内质网内未折叠蛋白质增加的适应性反应， 未折叠蛋白反应（UPR）是一种基本的和保守的细胞存活机制。癌 发育通常与一系列细胞毒性条件有关，如缺氧、营养缺乏和pH 变化这些条件触发一组细胞应激反应途径，包括ER应激反应。 内质网（ER）应激反应的许多方面是适应性的，并保护肿瘤细胞免受 细胞死亡表明在肿瘤生长中起关键作用。对ER应激反应的作用知之甚少 在癌症和肿瘤进展的早期阶段的途径。Ras原癌基因的激活突变是 是人类癌症中最常见的。小鼠和人角质形成细胞和原代肺上皮细胞 对致癌Ras表达的反应是增殖，随后是过早衰老。逃离 衰老反应与恶性进展直接相关。IRE 1 α是一种ER跨膜蛋白， 具有丝氨酸/苏氨酸激酶和核糖核酸内切酶结构域。响应ER应激，IRE 1 α剪接 XBP 1转录物产生一个有效的转录因子，诱导对解决至关重要的基因的表达 ER应激，并在一些研究中是重要的基因表达调控恶性表型。的 IRE 1 α核酸酶也靶向其他mRNA，在一个称为RIDD的过程中降解（受调节的IRE 1 α- 依赖性衰变），其可以在UPR中起作用以降低编码被加工蛋白质的mRNA的水平。 通过内质网，但也介导细胞死亡的持续内质网应激。IRE 1 α和剪接的Xbp 1都是 在癌症中升高，IRE 1 α激酶和RNA酶结构域中的特定体细胞突变已经被证实是 在癌症中发现，但这些功能的后果是未知的。这项建议的主要目的是 了解IRE 1 α表达和RNase输出如何调节细胞对致癌基因的反应， Ras并促进或抑制Ras驱动的癌症。根据初步和提交的数据， 假设IRE 1 α是一种条件性肿瘤抑制因子，其在癌症中作用依赖于 Xbp 1剪接和RIDD之间的平衡。我们认为ER应激水平和Ras信号强度 调节IRE 1 α输出的平衡，驱动RNase朝向Xbp 1剪接和增殖或RIDD， 衰老此外，我们提出了一个新的范式ER应力依赖性和独立的RIDD的目标。ID1 mRNA是一个主要的ER应激非依赖性、Ras依赖性RIDD靶点，其被IRE 1 α RNase降解， 是癌基因诱导衰老的关键。我们将使用KRas诱导的NSCLC小鼠模型， 表皮鳞状细胞癌，以测试Ire 1 α或Xbp 1消融、IRE 1 α过表达和特异性 IRE 1 α人类癌症突变对癌症发展的影响这些研究将提供新的和有影响力的 关于IRE 1 α通路在上皮细胞癌变中的作用的信息，并确定IRE 1 α 代表抗癌治疗的重要靶点。

PROJECT SUMMARY/ABSTRACT The adaptive response of cells to increased unfolded proteins within the endoplasmic reticulum, or the unfolded protein response (UPR), is a fundamental and conserved cellular survival mechanism. Cancer development is often associated with a range of cytotoxic conditions like hypoxia, nutrient deprivation, and pH changes. These conditions trigger a set of cellular stress response pathways including the ER-stress response. Many aspects of the endoplasmic reticulum (ER)-stress response are adaptive and protect tumor cells from cell death suggesting a crucial role in tumor growth. Much less is known about the role of ER-stress response pathways in early stages of cancer and tumor progression. Activating mutations in Ras proto-oncogenes are among the most common in human cancer. Mouse and human keratinocytes and primary lung epithelial cells respond to expression of oncogenic Ras with proliferation followed by premature senescence. Escape from the senescence response is directly linked to malignant progression. IRE1α is an ER transmembrane protein that has both serine/threonine kinase and endoribonuclease domains. In response to ER-stress IRE1α splices the XBP1 transcript to generate a potent transcription factor that induces expression of genes critical for resolution of ER stress, and in some studies is important in expression of genes regulating the malignant phenotype. The IRE1α nuclease also targets other mRNAs for degradation in a process called RIDD (regulated IRE1α- dependent decay), which can function in the UPR to reduce levels of mRNA’s that encode proteins processed through the ER but also mediates cell death to unremitting ER stress. Both IRE1α and spliced Xbp1 are elevated in cancer, and specific somatic mutations within the IRE1α kinase and RNase domains have been identified in cancers but the function consequences of these are unknown. The major goal of this proposal is to understand how IRE1α expression and RNase outputs modulate cellular responses to oncogenic Ras and promote or suppress Ras-driven cancer. Based on preliminary and submitted data we hypothesize that IRE1α is a conditional tumor suppressor whose actions in cancer depend on the balance between Xbp1 splicing and RIDD. We propose that both ER stress levels and Ras signal strength regulate the balance of IRE1α outputs driving the RNase towards Xbp1 splicing and proliferation or RIDD and senescence. Further we propose a new paradigm of ER stress dependent and independent RIDD targets. Id1 mRNA is a major ER stress independent, Ras dependent RIDD target whose degradation by the IRE1α RNase is essential for oncogene induced senescence. We will use mouse models of KRas-induced NSCLC and epidermal squamous cancer to test the effect of Ire1α or Xbp1 ablation, IRE1α overexpression and specific IRE1α human cancer mutations on cancer development. Together these studies will provide new and impactful information on the role of the IRE1α pathway in epithelial cell carcinogenesis and determine if IRE1α represents a significant target for anticancer therapeutics.