title: Persistent ER stress induces the spliced leader RNA silencing pathway (SLS), leading to programmed cell death in Trypanosoma brucei.
abstract: 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 Ca(2+), 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.
authors.affiliation: The Mina & Everard Goodman Faculty of Life Sciences, and Advanced Materials and Nanotechnology Institute, Bar-Ilan University, Ramat-Gan, Israel.
authors.forename: Hanoch
authors.initials: H
authors.lastname: Goldshmidt
authors.forename: Devorah
authors.initials: D
authors.lastname: Matas
authors.forename: Anat
authors.initials: A
authors.lastname: Kabi
authors.forename: Shai
authors.initials: S
authors.lastname: Carmi
authors.forename: Ronen
authors.initials: R
authors.lastname: Hope
authors.forename: Shulamit
authors.initials: S
authors.lastname: Michaeli
mesh_terms: D017209:Apoptosis / Q000235:genetics*; D015152:Blotting, Northern; D015153:Blotting, Western; D053938:DNA Fragmentation; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000473:pathology*; D056890:Eukaryota; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation / Q000235:genetics*; D020868:Gene Silencing / Q000502:physiology*; D020287:In Situ Nick-End Labeling; D053078:Membrane Potential, Mitochondrial; D046529:Microscopy, Electron, Transmission; D016253:Microscopy, Immunoelectron; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D020038:RNA, Spliced Leader / Q000235:genetics*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013312:Stress, Physiological; D014346:Trypanosoma brucei brucei / Q000502:physiology*; D056811:Unfolded Protein Response / Q000502:physiology
chemical_list: D012333:RNA, Messenger; D020038:RNA, Spliced Leader; D017382:Reactive Oxygen Species