Targeting oncogene-driven translation and integrated stress response signaling in Cancer

结直肠癌和肝细胞癌（分别为CRC和HCC）的特点是高内在水平的蛋白质翻译。这构成了旨在干扰蛋白质平衡机制的治疗的预致敏状态。基于我们之前对eIF2B5在结肠癌和CDH1在肝癌中的作用的研究，我们将瞄准CRC和HCC中蛋白质翻译机制的组成部分。这两种途径都确定了真核翻译起始因子2α (eIF2α)磷酸化的调节对CRC和HCC的增殖和存活至关重要。我们现在将更详细地讨论综合应激反应（ISR）网络分子调控的几个方面，以进一步开发这些新的治疗方案。在聚焦shRNA筛选中，我们发现eIF2α鸟嘌呤交换因子（GEF） eIF2B5对于具有致癌WNT信号的结直肠癌细胞存活至关重要。我们可以进一步证明，MYC的诱导导致这些细胞在失去eIF2B5时产生压倒性的蛋白质毒性。此外，在CRC小鼠模型中，当eIF2α-GEF表达降低时，APCmin小鼠存活时间明显延长。由于eIF2B5功能的组成性抑制可能导致救援通路的代偿性激活，我们的目的是在体内研究急性eIF2B5下调对CRC的潜在治疗作用。我们将进一步确定四种eIF2α激酶中哪一种在结直肠癌中占主导地位，以及该激酶的抑制是否可以模拟eIF2B5敲低的作用。通过类器官培养，研究人员将研究WNT通路是否存在对eIF2B5缺失敏感的其他突变，或者致癌MYC水平是否是激活WNT信号的主要下游靶标，并促进了这种脆弱性。这些结果将与目前从多达100个人类CRC类器官培养中建立的生物库的遗传和表型研究相关。在酵母-2杂交筛选中，我们发现了促复合体共激活子CDH1与GADD34相互作用的后期，GADD34是应激下eIF2α去磷酸化的主要调节因子。在哺乳动物细胞中，CDH1促进GADD34的泛素化。在体外和异种移植小鼠模型中，CDH1的缺失导致GADD34周转量减少，蛋白质毒性增加，以及对内质网应激诱导的细胞死亡的超敏反应。我们发现CDH1在nras驱动的肝癌中被诱导，抑制CDH1的诱导可显著延长动物的生存期。在这里，我们的目的是研究致癌NRAS和其他HCC驱动因素对CDH1的调节机制。通过体内筛选，我们将研究ISR的哪些效应物主要参与肝癌的发生。最后，我们的目的是研究在CRC和HCC中eIF2B5和CDH1缺失的作用机制是否存在协同作用。

Colorectal and hepatocellular carcinomas (CRC and HCC, respectively) are characterized by high intrinsic levels of protein translation. This constitutes a pre-sensitized state for therapies which aim at interfering with mechanisms of proteostasis. Based on our previous work focusing on the role of eIF2B5 in colon- and on CDH1 in liver carcinomas, we will target components of the protein translation machinery in CRC and HCC. Both avenues identified the regulation of eukaryotic translation initiation factor 2α (eIF2α) phosphorylation to be essential for the proliferation and survival of CRC and HCC. We will now address several aspects of the molecular regulation of the integrated stress response (ISR) network in greater detail to further the development of these novel treatment options.In a focused shRNA screen we have identified the eIF2α guanine exchange factor (GEF) eIF2B5 as essential for CRC cell survival with oncogenic WNT signaling. We could further show that the induction of MYC leads to overwhelming proteotoxicity in these cells upon loss of eIF2B5. Furthermore, in a CRC mouse model, APCmin mice survived significantly longer when the eIF2α-GEF expression was reduced. As constitutive suppression of eIF2B5 function may result in compensatory activation of rescue pathways, we aim to investigate the potentially therapeutic effects of acute eIF2B5 knockdown in CRC in vivo. We will furthermore determine which of the four eIF2α kinases is dominant in CRC, and whether the inhibition of this kinase can mimick the effects of eIF2B5 knockdown. Using organoid cultures, it will be investigated if there are additional mutations of the WNT pathway which sensitize to loss of eIF2B5, or if oncogenic MYC levels are the major downstream target of activated WNT signaling and facilitate this vulnerability. These results will be correlated to genetic and phenotypic investigations on a biobank that is currently established from up to 100 human CRC organoid cultures. In a yeast-2-hybrid screen, we have identified the anaphase promoting complex co-activator CDH1 to interact with GADD34, the major regulator of eIF2α dephosphorylation under stress. In mammalian cells, CDH1 facilitates the ubiquitylation of GADD34. Loss of CDH1 led to a reduction in GADD34 turnover, increased proteotoxicity, and hypersensitivity towards endoplamatic reticulum stress induced cell death, both in vitro and in a xenograft mouse model. We found that CDH1 is induced in NRAS-driven liver cancer, and that inhibition of CDH1 induction significantly prolonged the survival of the animals. Here we aim to investigate the mechanisms of regulation of CDH1 by oncogenic NRAS and other HCC drivers. Using an in vivo screen, we will investigate which effectors of the ISR are majorily involved in liver carcinogenesis. Finally, we aim to investigate if there is a synergism in the mechanism of action of loss of eIF2B5 and CDH1, both in CRC and HCC.