Abstract
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.
| Original language | English |
|---|---|
| Article number | 107 |
| Journal | Parasites and Vectors |
| Volume | 5 |
| Issue number | 1 |
| DOIs | |
| State | Published - 31 May 2012 |
Bibliographical note
Funding Information:The author is a member of the COST Action BM0802 “Life and death of protozoan parasites” and appreciates support from the Action. The research on SLS is supported by a grant from the Israel Science Foundation. I wish to thank Itai Dov Tkacz for the help in preparing the Figures. I thank all my students: Yaniv Lustig, Hanoch Goldshmidt, Ronen Hope, Devorah Matas, Shai Carmi, Anat Kabi and Efrat Ben-Mayor, Asher Pivko together with whom I discovered SLS, and who are working to understand the mechanism, machinery and the biological role of this exciting and novel pathway. I thank Prof. Michael Duszenko for our many insightful discussions that led me to propose the biological role of SLS.
Funding
The author is a member of the COST Action BM0802 “Life and death of protozoan parasites” and appreciates support from the Action. The research on SLS is supported by a grant from the Israel Science Foundation. I wish to thank Itai Dov Tkacz for the help in preparing the Figures. I thank all my students: Yaniv Lustig, Hanoch Goldshmidt, Ronen Hope, Devorah Matas, Shai Carmi, Anat Kabi and Efrat Ben-Mayor, Asher Pivko together with whom I discovered SLS, and who are working to understand the mechanism, machinery and the biological role of this exciting and novel pathway. I thank Prof. Michael Duszenko for our many insightful discussions that led me to propose the biological role of SLS.
| Funders | Funder number |
|---|---|
| Israel Science Foundation |
Keywords
- ER quality control
- Programmed cell death
- Spliced leader silencing
- Translocation to the ER
- Unfolded protein response
