Role of FXR proteins in the cell stress response

mRNA翻译的协调控制是真核细胞稳态的基础，特别是在响应生理和病理应激时。这一程序的改变可能导致受损细胞的生长，这是细胞转化和癌症的标志，或导致细胞过早死亡，如在神经变性和不育症中观察到的。脆性X相关蛋白（FXRPs）是RNA结合蛋白，在mRNA翻译中起关键作用，并具有与细胞应激反应相关的功能。然而，FXRPs调节细胞科普压力所需的mRNA翻译的潜在机制在很大程度上仍然未知。 我们最近的研究确定了FXRPs在细胞对UVC辐射的反应中的新作用，其部分通过促进细胞质RNA颗粒（UVCG）的形成而发生。FXRP诱导的UVCG让人联想到应激颗粒（SG）;已知在应激时隔离未翻译mRNA的RNA灶，其形成促进应激下的细胞存活。作为初步数据，我们发现FXRP衍生的UVCG促进UV诱导的细胞周期停滞，这是修复UV诱导的DNA损伤和存活所需的现象。我们的假设是，FXRPs诱导的UVCG有助于细胞周期停滞后，UVC暴露暂时抑制编码细胞周期功能的mRNA的翻译。因此，本研究计划的目标是确定FXRPs促进UVCG形成的机制，从而导致UVC暴露后细胞周期停滞。为了实现这一目标，我们将解决以下目标：I-证明FXRPs在UVCG形成中的作用; II-研究FXRPs促进UVCG形成的机制; III-证明FXRPs通过UVCG形成在UV C诱导的细胞周期阻滞中的作用。在我们的研究中，我们将使用小鼠胚胎成纤维细胞（MEFs）以及人类HeLa和PC 3细胞系，它们可以有效地形成UVCG。这将确保我们的结果不是细胞类型特异性的。对于果蝇研究，我们将使用S2细胞以及分离的组织。通过结合免疫染色、免疫沉淀、敲除实验、FISH、多核糖体分级分离与RNA-Seq，我们期望建立FXRPs作为调节细胞周期和相关细胞应激抗性的关键参与者，可能通过促进RNA颗粒形成。 在这些研究之后，未来的研究将被设计来确定这种基于RNA颗粒的新机制在与压力相关的人类疾病中的贡献，包括神经变性和不育。

The coordinated control of mRNA translation is fundamental for eukaryotic cell homeostasis, particularly in response to physiological and pathological stress. Alterations of this program can lead to the growth of damaged cells, a hallmark of cell transformation and cancer, or to premature cell death, such as observed in neurodegeneration and infertility. Fragile X-related proteins (FXRPs) are RNA-binding proteins that play a key role in mRNA translation and have a function that is associated with cell stress responses. However, the underlying mechanisms by which FXRPs regulate the mRNA translation that is required for a cell to cope with stress remains largely unknown. Our recent investigations identified a novel role of FXRPs in the cellular response to UVC radiation, which occurs in part by promoting the formation of cytoplasmic RNA granules (UVCGs). FXRP-induced UVCGs are reminiscent of stress granules (SG); RNA foci known to sequester untranslated mRNAs upon stress and formation of which promotes cell survival under stress. As preliminary data, we found that FXRP-derived UVCGs promote UV-induced cell cycle arrest, a phenomenon that is required for the repair of UV-induced DNA damage and survival. Our hypothesis is that UVCGs induced by FXRPs contribute to cell cycle arrest upon UVC exposure by temporarily repressing the translation of mRNAs encoding cell cycle functions. The goal of this research program is therefore to define the mechanisms by which FXRPs promote the formation of UVCGs, leading to cell cycle arrest upon UVC exposure. To achieve this goal, we will address the following objectives: I- to demonstrate the role of FXRPs in UVCG formation; II- to investigate the mechanism(s) by which FXRPs promote UVCG formation; III- to demonstrate the role of FXRPs in UVC-induced cell cycle arrest through UVCG formation. For our studies, we will use mouse embryonic fibroblasts (MEFs) as well as human HeLa and PC3 cell lines, which efficiently form UVCGs. This will ensure that our results are not cell-type specific. For drosophila studies, we will use S2 cells as well as isolated tissues. By combining immunostaining, immunoprecipitation, knockdown experiments, FISH, polysome fractionation combined with RNA-Seq, we expect to establish FXRPs as key players in the regulation of the cell cycle and the associated cellular resistance to stress, potentially by promoting RNA granule formation. Following these studies, future investigations will be designed to determine the contribution of this novel RNA granule-based mechanism in stress-related human disorders, including neurodegeneration and infertility.