Spliced leader RNA silencing (SLS) - a programmed cell death pathway in Trypanosoma brucei that is induced upon ER stress. 2012

Shulamit Michaeli
The Mina and Everard Goodman Faculty of Life Sciences, and Advanced Materials and Nanotechnology Institute, Bar-Ilan University, Ramat-Gan, 52900, Israel. shulamit.michaeli@biu.ac.il

Trypanosoma brucei is the causative agent of African sleeping sickness. The parasite cycles between its insect (procyclic form) and mammalian hosts (bloodstream form). Trypanosomes lack conventional transcription regulation, and their genes are transcribed in polycistronic units that are processed by trans-splicing and polyadenylation. In trans-splicing, which is essential for processing of each mRNA, an exon, the spliced leader (SL) is added to all mRNAs from a small RNA, the SL RNA. Trypanosomes lack the machinery for the unfolded protein response (UPR), which in other eukaryotes is induced under endoplasmic reticulum (ER) stress. Trypanosomes respond to such stress by changing the stability of mRNAs, which are essential for coping with the stress. However, under severe ER stress that is induced by blocking translocation of proteins to the ER, treatment of cells with chemicals that induce misfolding in the ER, or extreme pH, trypanosomes elicit the spliced leader silencing (SLS) pathway. In SLS, the transcription of the SL RNA gene is extinguished, and tSNAP42, a specific SL RNA transcription factor, fails to bind to its cognate promoter. SLS leads to complete shut-off of trans-splicing. In this review, I discuss the UPR in mammals and compare it to the ER stress response in T. brucei leading to SLS. I summarize the evidence supporting the notion that SLS is a programmed cell death (PCD) pathway that is utilized by the parasites to substitute for the apoptosis observed in higher eukaryotes under prolonged ER stress. I present the hypothesis that SLS evolved to expedite the death process, and rapidly remove from the population unfit parasites that, by elimination via SLS, cause minimal damage to the parasite population.

UI MeSH Term Description Entries
D004721 Endoplasmic Reticulum A system of cisternae in the CYTOPLASM of many cells. In places the endoplasmic reticulum is continuous with the plasma membrane (CELL MEMBRANE) or outer membrane of the nuclear envelope. If the outer surfaces of the endoplasmic reticulum membranes are coated with ribosomes, the endoplasmic reticulum is said to be rough-surfaced (ENDOPLASMIC RETICULUM, ROUGH); otherwise it is said to be smooth-surfaced (ENDOPLASMIC RETICULUM, SMOOTH). (King & Stansfield, A Dictionary of Genetics, 4th ed) Ergastoplasm,Reticulum, Endoplasmic
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D013312 Stress, Physiological The unfavorable effect of environmental factors (stressors) on the physiological functions of an organism. Prolonged unresolved physiological stress can affect HOMEOSTASIS of the organism, and may lead to damaging or pathological conditions. Biotic Stress,Metabolic Stress,Physiological Stress,Abiotic Stress,Abiotic Stress Reaction,Abiotic Stress Response,Biological Stress,Metabolic Stress Response,Physiological Stress Reaction,Physiological Stress Reactivity,Physiological Stress Response,Abiotic Stress Reactions,Abiotic Stress Responses,Abiotic Stresses,Biological Stresses,Biotic Stresses,Metabolic Stress Responses,Metabolic Stresses,Physiological Stress Reactions,Physiological Stress Responses,Physiological Stresses,Reaction, Abiotic Stress,Reactions, Abiotic Stress,Response, Abiotic Stress,Response, Metabolic Stress,Stress Reaction, Physiological,Stress Response, Metabolic,Stress Response, Physiological,Stress, Abiotic,Stress, Biological,Stress, Biotic,Stress, Metabolic
D014346 Trypanosoma brucei brucei A hemoflagellate subspecies of parasitic protozoa that causes nagana in domestic and game animals in Africa. It apparently does not infect humans. It is transmitted by bites of tsetse flies (Glossina). Trypanosoma brucei,Trypanosoma brucei bruceus,Trypanosoma bruceus,brucei brucei, Trypanosoma,brucei, Trypanosoma brucei,bruceus, Trypanosoma,bruceus, Trypanosoma brucei
D017209 Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, i.e., DNA FRAGMENTATION. It is genetically programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Apoptosis, Extrinsic Pathway,Apoptosis, Intrinsic Pathway,Caspase-Dependent Apoptosis,Classic Apoptosis,Classical Apoptosis,Programmed Cell Death,Programmed Cell Death, Type I,Apoptoses, Extrinsic Pathway,Apoptoses, Intrinsic Pathway,Apoptosis, Caspase-Dependent,Apoptosis, Classic,Apoptosis, Classical,Caspase Dependent Apoptosis,Cell Death, Programmed,Classic Apoptoses,Extrinsic Pathway Apoptoses,Extrinsic Pathway Apoptosis,Intrinsic Pathway Apoptoses,Intrinsic Pathway Apoptosis
D020038 RNA, Spliced Leader The small RNAs which provide spliced leader sequences, SL1, SL2, SL3, SL4 and SL5 (short sequences which are joined to the 5' ends of pre-mRNAs by TRANS-SPLICING). They are found primarily in primitive eukaryotes (protozoans and nematodes). SL RNA,Spliced Leader RNA,Spliced Leader Sequences,Trans-Spliced Leader Sequences,SL1 Sequence,SL2 Sequence,SL3 Sequence,SL4 Sequence,SL5 Sequence,Spliced Leader,Leader RNA, Spliced,Leader Sequences, Spliced,Leader Sequences, Trans-Spliced,Leader, Spliced,Sequence, SL1,Sequence, SL2,Sequence, SL3,Sequence, SL4,Sequence, SL5,Sequences, Spliced Leader,Sequences, Trans-Spliced Leader,Trans Spliced Leader Sequences
D034622 RNA Interference A gene silencing phenomenon whereby specific dsRNAs (RNA, DOUBLE-STRANDED) trigger the degradation of homologous mRNA (RNA, MESSENGER). The specific dsRNAs are processed into SMALL INTERFERING RNA (siRNA) which serves as a guide for cleavage of the homologous mRNA in the RNA-INDUCED SILENCING COMPLEX. DNA METHYLATION may also be triggered during this process. Gene Silencing, Post-Transcriptional,Post-Transcriptional Gene Silencing,Co-Suppression,Cosuppression,Posttranscriptional Gene Silencing,RNA Silencing,RNAi,Co Suppression,Gene Silencing, Post Transcriptional,Gene Silencing, Posttranscriptional,Gene Silencings, Posttranscriptional,Interference, RNA,Post Transcriptional Gene Silencing,Post-Transcriptional Gene Silencings,Silencing, Post-Transcriptional Gene

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