Spliced‐leader RNA silencing: a novel stress‐induced mechanism in Trypanosoma brucei

Abstract

The signal-recognition particle (SRP) mediates the translocation of membrane and secretory proteins across the endoplasmic reticulum upon interaction with the SRP receptor. In trypanosomes, the main RNA molecule is the spliced-leader (SL) RNA, which donates the SL sequence to all messenger RNA through trans-splicing. Here, we show that RNA interference silencing of the SRP receptor (SRa) in Trypanosoma brucei caused the accumulation of SRP on ribosomes and triggered silencing of SL RNA (SLS). SLS was elicited due to the failure of the SL RNAspecific transcription factor tSNAP42 to bind to its promoter. SL RNA reduction, in turn, eliminated mRNA processing and resulted in a significant reduction of all mRNA tested. SLS was also induced under pH stress and might function as a master regulator in trypanosomes. SLS is reminiscent of, but distinct from, the unfolded protein response and can potentially act as a new target for parasite eradication.

Role of Protein Translocation Pathways across the Endoplasmic Reticulum in Trypanosoma brucei

“…10C). This phe- notype is reminiscent of the one observed previously for SRP54-and SRP receptor subunit ␣-silenced cells (26,28). Remarkably after 3 days, the cells induced the spliced leader silencing pathway (28), and the level of all mRNAs was reduced because of shutoff of SL RNA transcription.…”

“…This phe- notype is reminiscent of the one observed previously for SRP54-and SRP receptor subunit ␣-silenced cells (26,28). Remarkably after 3 days, the cells induced the spliced leader silencing pathway (28), and the level of all mRNAs was reduced because of shutoff of SL RNA transcription. 6 Thus, to investigate the role of SEC63 in protein translocation, we examined the protein translocation defects 2 days after induction before spliced leader silencing was elicited.…”

“…The accumulation of SRP-bound ribosomes on the ER membrane during ␣ subunit of the SRP receptor silencing elicited a signal that led to complete shutoff of spliced leader (SL) RNA transcription. Because in trypanosomes, SL RNA is required for the production of each mRNA by trans-splicing, shutoff of SL RNA transcription stopped mRNA and protein production and led to cell death (28).…”

The silicon trypanosome

“…Individual mRNAs are excised by a transsplicing complex which places identically capped 39 nt leaders at the 5k end of every mRNA (Liang et al 2003); this splicing is co-ordinated with polyadenylation of the RNA located immediately upstream. Indeed, regulation of mRNA biogenesis may well be restricted to the processing steps (Lustig et al 2007 ;Stern et al 2009), while steady-state levels are further influenced by the rate of mRNA degradation (Clayton and Shapira, 2007). In fact, the majority of evidence concerning regulation of gene expression has implicated mRNA decay as the dominant factor (Clayton and Shapira, 2007 ;Haanstra et al 2008 b), and this is the only step for which mechanistic details of the regulation are available.…”

Spliced Leader (SL) RNA: análises de genes e regiões intergênicas com aportes na filogenia, taxonomia e genotipagem de <i>Trypanosoma</i> spp. de todas as classes de vertebrados.

“…Tem sido sugerido que a via SLS é um tipo de morte celular programada (PCD, "programmed cell death"), semelhante a apoptose mediada por caspases nos eucariotos (Lustig et al, 2007;Goldsmith et al, 2010;Michaeli, 2012).…”