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Regulation of PfEMP1–VAR2CSA translation by a Plasmodium translation-enhancing factor

Nature Microbiology volume 2, Article number: 17068 (2017) Cite this article

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Abstract

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.

The PfEMP1 family of proteins is encoded by the var gene loci, which are present in ∼60 variant copies per genome1. The var genes are highly polymorphic across parasite strains2 and generally exhibit mutually exclusive expression, with each parasite actively transcribing only one var gene at any one time3,4. However, the mechanisms that regulate exclusive allelic regulation in the transcription and translation of var genes remain elusive. One particular PfEMP1 variant, VAR2CSA, has been studied in great detail given that it plays an important role in the development of pregnancy-associated malaria (PAM). VAR2CSA mediates the binding of infected erythrocytes (IEs) to the glycosaminoglycan chondroitin sulfate A (CSA) expressed at the surface of syncytiotrophoblasts in the placental lining5,6. The encoding var2csa gene exhibits a 5′ upstream regulatory element that is unique within the var gene family7. It also contains a conserved upstream open reading frame (uORF) spanning 360 nucleotides that represses the translation of the coding region of var2csa (ref. 8).

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Figure 1: ptef expression is associated with the CSA-binding capacity of IEs.
Figure 2: Proteolytic processing separates antagonistic targeting motifs in the PTEF protein.
Figure 3: PTEF localizes to multiple cellular compartments.
Figure 4: CTD fragment of PTEF interacts with the ribosomes.
Figure 5: PTEF is required for efficient VAR2CSA translation.
Figure 6: tGFP synthesis in RTTF in the presence of PTEF domains.

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Acknowledgements

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.

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Authors and Affiliations

  1. Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institutet, Box 280, Nobels väg 16, 171 77 Stockholm, Sweden

    Sherwin Chan, Alejandra Frasch, Jun-Hong Ch'ng, Maria del Pilar Quintana, Nicolas Joannin & Mats Wahlgren

  2. Department of Cell and Molecular Biology, Uppsala University, Box-596, 751 24 Uppsala, Sweden

    Chandra Sekhar Mandava & Suparna Sanyal

  3. Department of Microbiology, National University of Singapore 117545, Singapore

    Jun-Hong Ch'ng

  4. Escuela de Medicina y Ciencias de la Salud, Facultad de Ciencias Naturales y Matemáticas, Universidad del Rosario, Calle 12C No. 6-25, Bogotá, Colombia

    Maria del Pilar Quintana

  5. Department of Oncology-Pathology, Cancer Proteomics, Karolinska Institutet, 17176 Stockholm, Sweden

    Mattias Vesterlund

  6. University of Montpellier, Faculty of Medicine, Laboratory of Parasitology-Mycology, Montpellier F34090, France

    Mehdi Ghorbal & Jose-Juan Lopez-Rubio

  7. CNRS – 5290, IRD 224 – University of Montpellier (UMR ‘MiVEGEC’), Montpellier, France

    Mehdi Ghorbal & Jose-Juan Lopez-Rubio

  8. Department of Genetics and Genomic Sciences, Institute of Genomics and Multiscale Biology, Icahn School of Medicine at Mount Sinai, New York, 10029, New York, USA

    Oscar Franzén

  9. Institute for Research in Biomedicine, Università della Svizzera italiana, 6500, Bellinzona, Switzerland

    Sonia Barbieri & Antonio Lanzavecchia

  10. Institute of Microbiology, ETH Zurich, 8093, Zurich, Switzerland

    Antonio Lanzavecchia

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Contributions

S.C. and M.W. conceived the study. S.C., A.F., J.H.C. and M.P.Q. performed all experiments. C.S.M. and S.S. performed the RTTF assay. M.V. performed the MS experiment. J.J.L.R. and M.G. assisted in CRISPR design. S.B. and A.L. generated the recombinant PAM1.4. N.J. and O.F. performed computational analysis. S.C., A.F., C.S.M., S.S. and M.W. interpreted data and wrote the manuscript.

Corresponding author

Correspondence to Mats Wahlgren.

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Competing interests

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 information

Supplementary Information

Supplementary Figures 1-9, Supplementary Table 5, Supplementary References. (PDF 20363 kb)

Supplementary Table 1

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)

Supplementary Table 2

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)

Supplementary Table 3

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)

Supplementary Table 4

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

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