Novel mechanisms controlling the cellular stress response

所有细胞在暴露于生理应激源，如高温、缺血、渗透休克和许多其他应激源后，都会产生保护性应激反应。这种反应的特点是抑制正常的细胞转录和翻译以及热休克蛋白(HSPs)的合成，热休克蛋白主要通过防止蛋白质的异常折叠和聚集以及介导抗凋亡作用来保护细胞免受损伤。哺乳动物中的SR受热休克转录因子(HSFs)的控制，在一种胁迫下，它们介导：(I)保护性热休克蛋白的转录；(Ii)驱动编码在人类染色体非定位着丝粒周围区域的长非编码RNASat III的表达。在胁迫条件下，不同长度的Sat III转录物被转录并形成特定转录因子和RNA结合蛋白的支架，这些聚集的位置被称为核应激体(NSB)，参与介导转录的停止和剪接的控制。据报道，未分裂神经元的应激反应是细胞类型特异性的，热休克蛋白的表达动力学和水平因应激类型而异。重要的是，HSF1功能改变与衰老、癌症和许多神经退行性疾病有关，并表明HSR改变可能有助于疾病病因学。我们已经发现支架附着因子B(SAFB)家族的RBPs在协调神经性和非神经性细胞群体的应激反应中发挥着以前未见文献报道的重要作用。SAFB1和SAFB2在人脑中广泛表达，并且水平很高。我们之前已经证明，它们协调编码和非编码基因的表达，并参与替代调味品。我们有更新的发现表明，SAFB1调节Sat III RNA的转录/稳定性，其类似物SAFB2以与HSF1相同的动力学方式移位到Sat III/NSB。此外，SAFB1和SAFB2在已知的调节蛋白质-RNA和蛋白质-蛋白质相互作用的区域中都是精氨酸甲基化的。在应激体中发现的参与调节应激反应的RNA结合蛋白(如SAFB1/2)也被证明与衰老过程和人类神经退行性疾病的病因学有关。我们认为SAFB1和SAFB2是调节细胞对应激反应的关键成分，它们在蛋白质复合体中的功能可能受到翻译后精氨酸甲基化的调节。具体地说，我们假设它们是Sat III转录所必需的，并将RBP招募到NSB，进而控制细胞应激反应。具体的研究目标是：1.明确SAFB1和SAFB2在调节sat III转录和NSB形成中的作用。2.确定精氨酸甲基化在调控SAFB1和SAFB2功能中的作用。3.确定在应激和非应激条件下发挥作用的新的SAFB1和SAFB2相互作用伙伴。4.研究SAFB蛋白在调节神经细胞Sat III转录和NSB形成中的作用。本研究的结果将阐明SAFB(和其他RNA结合蛋白)调节Sat III转录和NSB形成从而调节细胞应激反应的机制。因此，将对支持神经元和非神经细胞对环境应激的反应、控制衰老、癌症和支持许多人类神经退行性疾病的过程有新的见解。

A protective stress response (SR) is generated in all cells following exposure to physiological stressors such as elevated temperatures, ischaemia, osmotic shock and many other stressors. The response is characterized by the suppression of normal cellular transcription and translation and the synthesis of heat shock proteins (HSPs) that protect cells from damage largely by preventing the abnormal folding and aggregation of proteins and by mediating anti-apoptotic effects. The SR in mammals is under the control of heat shock transcription factors (HSFs) and following a stress they mediate: (i) the transcription of protective heat shock protein; (ii) drive the expression of the long non-coding RNAs Sat III encoded on non-mapped peri-centromeric regions of human chromosomes. Under stress conditions Sat III transcripts of varying length are transcribed and form scaffolds for specific transcription factors and RNA binding proteins and these sites of accumulation are termed nuclear stress bodies (nSBs) and are involved in mediating the cessation of transcription and control of splicing. The stress response of non-dividing neurones has been reported to be cell-type specific and the kinetics and level of expression of HSPs vary according to the type of stress. Importantly, altered HSF1 function is associated with ageing, cancer and many neurodegenerative diseases and suggests an altered HSR may contribute to disease aetiology. We have found previously undocumented important roles for the scaffold attachment factor B (SAFB) family of RBPs in coordinating the stress response in neuronal and non-neuronal populations of cells. SAFB1 and SAFB2 are ubiquitously expressed and found at very highly levels in the human brain. We have previously shown they coordinate the expression of coding and non-coding genes and that they are involved in alternative spicing. We have further novel findings showing that SAFB1 regulates the transcription/ stability of Sat III RNA and its paralogue SAFB2 translocated to Sat III/nSBs with the same kinetics as HSF1. In addition, both SAFB1 and SAFB2 are arginine methylated in domains known to mediate both protein-RNA and protein-protein interactions. RNA binding proteins (such as SAFB1/2) involved in regulating the stress response and found in stress bodies have also been shown to implicated in the ageing process and in the aetiology of human neurodegenerative disease.We propose that SAFB1 and SAFB2 are key components governing the cellular response to stress, and that their functions in protein complexes may be regulated by post-translational arginine methylation. Specifically, we hypothesise they are required for Sat III transcription and the recruitment of RBPs to nSBs which in turn Sat govern the cellular stress response. The specific research objectives are: 1. Identify the roles SAFB1 and SAFB2 play in regulating Sat III transcription and nSB formation. 2. Define the role arginine methylation plays in governing the functions of SAFB1 and SAFB2. 3. Identify novel SAFB1 and SAFB2 interaction partners that function under stress and non-stress conditions. 4. Characterise the role SAFB proteins play in regulating Sat III lncRNA transcription and the formation of nSBs in human neurones.The outcome of this study will be to elucidate the mechanisms by which SAFB (and other RNA binding proteins) regulate Sat III transcription and nSB formation and thereby the cellular stress response. Hence novel insights will made into the processes that underpin the neuronal and non-neuronal cell response to environmental stress, govern ageing, cancer and underpin a number of human neurodegenerative disease conditions.