Staufen2 (STAU2) is an RNA binding protein involved in the posttranscriptional regulation of gene expression. In neurons, STAU2 is required to maintain the balance between differentiation and proliferation of neural stem cells through asymmetric cell division. However, the importance of controlling STAU2 expression for cell cycle progression is not clear in non-neuronal dividing cells. We recently showed that STAU2 transcription is inhibited in response to DNA-damage due to E2F1 displacement from the STAU2 gene promoter. We now study the regulation of STAU2 steady-state levels in unstressed cells and its consequence for cell proliferation. CRISPR/Cas9-mediated and RNAi-dependent STAU2 depletion in the non-transformed hTERT-RPE1 cells both facilitate cell proliferation suggesting that STAU2 expression influences pathway(s) linked to cell cycle controls. Such effects are not observed in the CRISPR STAU2-KO cancer HCT116 cells nor in the STAU2-RNAi-depleted HeLa cells. Interestingly, a physiological decrease in the steady-state level of STAU2 is controlled by caspases. This effect of peptidases is counterbalanced by the activity of the CHK1 pathway suggesting that STAU2 partial degradation/stabilization fines tune cell cycle progression in unstressed cells. A large-scale proteomic analysis using STAU2/biotinylase fusion protein identifies known STAU2 interactors involved in RNA translation, localization, splicing, or decay confirming the role of STAU2 in the posttranscriptional regulation of gene expression. In addition, several proteins found in the nucleolus, including proteins of the ribosome biogenesis pathway and of the DNA damage response, are found in close proximity to STAU2. Strikingly, many of these proteins are linked to the kinase CHK1 pathway, reinforcing the link between STAU2 functions and the CHK1 pathway. Indeed, inhibition of the CHK1 pathway for 4 h dissociates STAU2 from proteins involved in translation and RNA metabolism. These results indicate that STAU2 is involved in pathway(s) that control(s) cell proliferation, likely via mechanisms of posttranscriptional regulation, ribonucleoprotein complex assembly, genome integrity and/or checkpoint controls. The mechanism by which STAU2 regulates cell growth likely involves caspases and the kinase CHK1 pathway.

中文翻译：

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STAU2 蛋白水平受半胱天冬酶和 CHK1 通路控制，并调节非转化 hTERT-RPE1 细胞的细胞周期进程

Staufen2 (STAU2) 是一种 RNA 结合蛋白，参与基因表达的转录后调控。在神经元中，STAU2 需要通过不对称细胞分裂来维持神经干细胞分化和增殖之间的平衡。然而，在非神经元分裂细胞中，控制 STAU2 表达对细胞周期进程的重要性尚不清楚。我们最近发现 STAU2 转录因 E2F1 从 STAU2 基因启动子的置换而受到 DNA 损伤的抑制。我们现在研究未受应激细胞中 STAU2 稳态水平的调节及其对细胞增殖的影响。未转化的 hTERT-RPE1 细胞中 CRISPR/Cas9 介导和 RNAi 依赖性 STAU2 耗竭均促进细胞增殖，表明 STAU2 表达影响与细胞周期控制相关的通路。在 CRISPR STAU2-KO 癌症 HCT116 细胞和 STAU2-RNAi 耗尽的 HeLa 细胞中均未观察到这种效应。有趣的是，STAU2 稳态水平的生理下降是由半胱天冬酶控制的。肽酶的这种作用被 CHK1 通路的活性抵消，表明 STAU2 部分降解/稳定微调未受压细胞中的细胞周期进程。使用 STAU2/生物素化酶融合蛋白的大规模蛋白质组学分析确定了参与 RNA 翻译、定位、剪接、或衰变证实了 STAU2 在基因表达的转录后调控中的作用。此外，在核仁中发现的几种蛋白质，包括核糖体生物发生途径的蛋白质和 DNA 损伤反应的蛋白质，都与 STAU2 非常接近。引人注目的是，其中许多蛋白质与激酶 CHK1 通路相关，加强了 STAU2 功能与 CHK1 通路之间的联系。事实上，抑制 CHK1 通路 4 小时会使 STAU2 与参与翻译和 RNA 代谢的蛋白质分离。这些结果表明，STAU2 参与控制细胞增殖的途径，可能通过转录后调节、核糖核蛋白复合物组装、基因组完整性和/或检查点控制机制。