Pregnancy-associated malaria commonly involves the binding of Plasmodium falciparum-infected erythrocytes to placental chondroitin sulfate A (CSA) through the PfEMP1–VAR2CSA protein. VAR2CSA is translationally repressed by an upstream open reading frame. In this study, we report that the P. falciparum translation enhancing factor (PTEF) relieves upstream open reading frame repression and thereby facilitates VAR2CSA translation. VAR2CSA protein levels in var2csa-transcribing parasites are dependent on the expression level of PTEF, and the alleviation of upstream open reading frame repression requires the proteolytic processing of PTEF by PfCalpain. Cleavage generates a C-terminal domain that contains a sterile-alpha-motif-like domain. The C-terminal domain is permissive to cytoplasmic shuttling and interacts with ribosomes to facilitate translational derepression of the var2csa coding sequence. It also enhances translation in a heterologous translation system and thus represents the first non-canonical translation enhancing factor to be found in a protozoan. Our results implicate PTEF in regulating placental CSA binding of infected erythrocytes.
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The authors thank the Scilifelab in Stockholm for RNA-seq and mass spectrometry experiments, K.W. Deitsch for providing luciferase reporter plasmids and for guidance on our experimental design, BEI Resources and MR4 for supplying DSM1, and BILS for providing support for the transcriptomic analysis. This study was supported by the Swedish Research Council (VR/2012-2014/521-2011-3377 to M.W.), the Söderberg Foundation and Swedish Academy of Sciences (to M.W.), the Swedish Strategic Foundation (to M.W.), the EU EviMalar Network of Excellence (to M.W.), a Distinguished Professor Award from Karolinska Institutet (to M.W.) and the Swedish Research Council (VR 2013-8778, 2014-4423 and 2016-06264 to S.S.) and the Knut and Alice Wallenberg Foundation (KAW 2011.0081, RiboCORE to S.S.). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
M.W. is a co-founder and member of the board of directors of Modus Therapeutics AB, a company developing drugs for severe malaria. All other authors declare no financial conflicts of interest.
Supplementary Figures 1-9, Supplementary Table 5, Supplementary References. (PDF 20363 kb)
One spreadsheet summarizing the list of genes deleted on the left arm of chromosome 2 and the right arm of chromosome 9 in 3D7S8.4.2 parasites. (XLSX 39 kb)
Eight spreadsheets providing a detailed description of all differentially expressed genes between NF54CSA and 3D7S8.4.2 at the four time points collected for the RNAseq experiment. (XLSX 168 kb)
Eight spreadsheets providing a list of all proteins detected in mass spectrometry from the blue native gel experiment related to Supplementary Fig. 5. (XLSX 89 kb)
Two spreadsheets describing the sequence similarity of all ribosomal proteins between Plasmodium falciparum and Homo sapiens. (XLSX 41 kb)
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Chan, S., Frasch, A., Mandava, C. et al. Regulation of PfEMP1–VAR2CSA translation by a Plasmodium translation-enhancing factor. Nat Microbiol 2, 17068 (2017). https://doi.org/10.1038/nmicrobiol.2017.68