Department of Molecular Biology at the Institute of Biochemistry and Molecular Biology, Semmelweis University, Budapest, Hungary.
Laboratory of Proteomics Research, Biological Research Centre, Szeged, Hungary.
FEBS Open Bio. 2022 Nov;12(11):2065-2082. doi: 10.1002/2211-5463.13484. Epub 2022 Sep 27.
Endoplasmic reticulum (ER) stress-dependent accumulation of incorrectly folded proteins leads to activation of the unfolded protein response. The role of the unfolded protein response (UPR) is to avoid cell damage and restore the homeostatic state by autophagy; however, excessive ER stress results in apoptosis. Here we investigated the ER stress-dependent feedback loops inside one of the UPR branches by focusing on PERK-induced ATF4 and its two targets, called CHOP and GADD34. Our goal was to qualitatively describe the dynamic behavior of the system by exploring the key regulatory motifs using both molecular and theoretical biological techniques. Using the HEK293T cell line as a model system, we confirmed that the life-or-death decision is strictly regulated. We investigated the dynamic characteristics of the crucial elements of the PERK pathway at both the RNA and protein level upon tolerable and excessive levels of ER stress. Of particular note, inhibition of GADD34 or CHOP resulted in various phenotypes upon high levels of ER stress. Our computer simulations suggest the existence of two new feedback loops inside the UPR. First, GADD34 seems to have a positive effect on ATF4 activity, while CHOP inhibits it. We claim that these newly described feedback loops ensure the fine-tuning of the ATF4-dependent stress response mechanism of the cell.
内质网（ER）应激导致错误折叠蛋白质的积累，从而激活未折叠蛋白反应。未折叠蛋白反应（UPR）的作用是通过自噬来避免细胞损伤并恢复内稳态；然而，过度的 ER 应激会导致细胞凋亡。在这里，我们通过关注 PERK 诱导的 ATF4 及其两个靶标 CHOP 和 GADD34，研究了 UPR 分支之一中 ER 应激依赖性的反馈回路。我们的目标是通过使用分子和理论生物学技术探索关键调节基序，定性描述系统的动态行为。使用 HEK293T 细胞系作为模型系统，我们证实了生死决定受到严格调控。我们研究了在可容忍和过度 ER 应激水平下，PERK 通路的关键元件在 RNA 和蛋白质水平上的动态特征。值得注意的是，在高水平的 ER 应激下，抑制 GADD34 或 CHOP 会导致各种表型。我们的计算机模拟表明，UPR 内存在两个新的反馈回路。首先，GADD34 似乎对 ATF4 活性有正效应，而 CHOP 则抑制它。我们声称，这些新描述的反馈回路确保了细胞中 ATF4 依赖性应激反应机制的精细调节。
