Persistent ER stress induces the spliced leader RNA silencing pathway (SLS), leading to programmed cell death in Trypanosoma brucei.
Persistent ER stress induces the spliced leader RNA silencing pathway (SLS), leading to programmed cell death in Trypanosoma brucei.
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持续的ER应力诱导剪接的Leader RNA沉默途径（SLS），导致Brucei锥虫的程序性细胞死亡。
DOI：
10.1371/journal.ppat.1000731
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发表时间：
2010-01-22
期刊：
影响因子：
6.7
通讯作者：
Michaeli S
中科院分区：
文献类型：
--
作者：
Goldshmidt H;Matas D;Kabi A;Carmi S;Hope R;Michaeli S
锥虫是在昆虫宿主（原环形式）和哺乳动物宿主（血流形式）之间循环的寄生虫。这些寄生虫缺乏常规的转录调控，包括诱导未折叠蛋白反应（UPR）的因子。然而，它们具有应激反应机制，剪接前导RNA沉默（SLS）途径。SLS通过干扰转录因子tSNAP 42与其同源启动子的结合来关闭剪接的前导RNA（SL RNA）转录，从而消除所有mRNA的反式剪接。诱导内质网（ER）的压力，在原环锥虫eliminate的变化，转录组中发现的其他真核生物中的常规UPR诱导相似。ER应激下的上调机制依赖于mRNA的差异稳定化。转录组的变化伴随着ER伴侣BiP的ER扩张和升高。延长的ER应激诱导SLS途径。RNAi沉默SEC63（一种参与蛋白质跨ER膜易位的因子）或SEC61（易位通道）也诱导SLS。这些基因的沉默或长期的ER应激导致程序性细胞死亡（PCD），这通过暴露磷脂酰丝氨酸、DNA梯状化、活性氧（ROS）产生增加、细胞质Ca2+增加和线粒体膜电位降低以及透射电子显微镜（TEM）观察到的典型形态学变化来证明。ER应激反应也以血流形式诱导，如果应激持续，则导致SLS。我们建议，长期的ER应力诱导SLS，这是一个独特的死亡途径，取代传统的半胱天冬酶介导的PCD中观察到的高等真核生物。锥虫是非洲昏睡病、利什曼病和恰加斯病等主要寄生虫病的病原体，这些疾病影响着数百万人，主要是发展中国家的人。这些生物很早就从真核生物中分化出来，并具有独特的分子机制，如反式剪接和RNA编辑。锥虫缺乏控制蛋白质编码基因转录的聚合酶II启动子。真核生物通过一种独特的转录程序对内质网（ER）中蛋白质的解折叠做出反应，称为解折叠蛋白反应（UPR）。在这项研究中，我们证明，尽管缺乏转录调控，前环锥虫改变其转录组作为响应ER应力的差异mRNA稳定。长时间的内质网应激诱导一个独特的过程，剪接前导RNA沉默（SLS），关闭反式剪接和所有mRNA的产生。SLS是由长期的ER应激和在寄生虫的两个生命阶段中参与ER易位的因子的敲低诱导的。SLS诱导程序性细胞死亡（PCD），其通过后生动物中的细胞凋亡的标志（DNA片段化、膜翻转和超微结构变化）而明显。我们建议SLS作为一个独特的死亡途径，取代传统的半胱天冬酶介导的PCD中观察到的高等真核生物。
Trypanosomes are parasites that cycle between the insect host (procyclic form) and mammalian host (bloodstream form). These parasites lack conventional transcription regulation, including factors that induce the unfolded protein response (UPR). However, they possess a stress response mechanism, the spliced leader RNA silencing (SLS) pathway. SLS elicits shut-off of spliced leader RNA (SL RNA) transcription by perturbing the binding of the transcription factor tSNAP42 to its cognate promoter, thus eliminating trans-splicing of all mRNAs. Induction of endoplasmic reticulum (ER) stress in procyclic trypanosomes elicits changes in the transcriptome similar to those induced by conventional UPR found in other eukaryotes. The mechanism of up-regulation under ER stress is dependent on differential stabilization of mRNAs. The transcriptome changes are accompanied by ER dilation and elevation in the ER chaperone, BiP. Prolonged ER stress induces SLS pathway. RNAi silencing of SEC63, a factor that participates in protein translocation across the ER membrane, or SEC61, the translocation channel, also induces SLS. Silencing of these genes or prolonged ER stress led to programmed cell death (PCD), evident by exposure of phosphatidyl serine, DNA laddering, increase in reactive oxygen species (ROS) production, increase in cytoplasmic Ca2+, and decrease in mitochondrial membrane potential, as well as typical morphological changes observed by transmission electron microscopy (TEM). ER stress response is also induced in the bloodstream form and if the stress persists it leads to SLS. We propose that prolonged ER stress induces SLS, which serves as a unique death pathway, replacing the conventional caspase-mediated PCD observed in higher eukaryotes. Trypanosomes are the causative agent of major parasitic diseases such as African sleeping sickness, leishmaniasis and Chagas' disease that affect millions of people mostly in developing countries. These organisms diverged very early from the eukaryotic linage and possess unique molecular mechanisms such as trans-splicing and RNA editing. Trypanosomes lack polymerase II promoters that govern the transcription of protein coding genes. Eukaryotes respond to unfolding of proteins in the endoplasmic reticulum (ER) by a distinct transcriptional programming known as the unfolded protein response (UPR). In this study, we demonstrate that despite the lack of transcriptional regulation, procyclic trypanosomes change their transcriptome as a response to ER stress by differential mRNA stabilization. Prolonged ER stress induces a unique process, the spliced leader RNA silencing (SLS), that shuts off the trans-splicing and the production of all mRNAs. SLS is induced both by prolonged ER stress and by knock-down of factors involved in ER translocation in both life stages of the parasite. SLS induces programmed cell death (PCD) evident by the hallmark of apoptosis in metazoa (DNA fragmentation, membrane flipping and ultrastructural changes). We propose that SLS serves as a unique death pathway replacing the conventional caspase-mediated PCD observed in higher eukaryotes.
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