Novel mechanisms controlling the cellular stress response

保护性应激反应（SR）是在所有细胞暴露于生理应激源，如高温，缺血，渗透压休克和许多其他应激源。该反应的特征在于抑制正常细胞转录和翻译以及热休克蛋白（HSP）的合成，热休克蛋白（HSP）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（HSF）的控制，并且在它们介导的应激之后：（i）保护性热休克蛋白的转录;（ii）驱动在人类染色体的未定位的着丝粒周围区域上编码的长非编码RNA Sat III的表达。在应激条件下，不同长度的Sat III转录物被转录并形成特异性转录因子和RNA结合蛋白的支架，这些积累位点被称为核应激体（nSB），并参与介导转录的停止和剪接的控制。已报道非分裂神经元的应激反应是细胞类型特异性的，并且热休克蛋白的表达的动力学和水平根据应激的类型而变化。重要的是，HSF 1功能的改变与衰老、癌症和许多神经退行性疾病有关，并表明HSR的改变可能有助于疾病的病因学。我们已经发现了先前未记录的RBP的支架附着因子B（SAFB）家族在协调神经元和非神经元细胞群体的应激反应中的重要作用。SAFB 1和SAFB 2在人脑中普遍表达，并且在人脑中以非常高的水平存在。我们以前已经表明，他们协调编码和非编码基因的表达，他们参与替代香料。我们有进一步的新发现表明，SAFB 1调节转录/稳定性的Sat III RNA和它的parasitic SAFB 2易位到Sat III/nSB与HSF 1相同的动力学。此外，SAFB 1和SAFB 2都是精氨酸甲基化的结构域，已知介导蛋白质-RNA和蛋白质-蛋白质相互作用。RNA结合蛋白（如SAFB 1/2）参与调节应激反应并在应激体中发现，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SAFB 1和SAFB 2是控制细胞应激反应的关键组分，它们在蛋白复合物中的功能可能受到翻译后精氨酸甲基化的调节。具体来说，我们假设它们是Sat III转录和RBP向nSB的募集所必需的，而nSB反过来又是Sat控制细胞应激反应。具体的研究目标是：1.确定SAFB 1和SAFB 2在调节Sat III转录和nSB形成中的作用。2.定义精氨酸甲基化在控制SAFB 1和SAFB 2功能中的作用。3.确定在压力和非压力条件下发挥作用的新型SAFB 1和SAFB 2相互作用伙伴。4.研究SAFB蛋白在调节人神经元Sat Ⅲ lncRNA转录和nSB形成中的作用，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，新的见解将成为支持神经元和非神经元细胞对环境压力的反应，控制衰老，癌症和支持许多人类神经退行性疾病的过程。

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.