1
|
Gullingsrud J, Milman N, Saveria T, Chesnokov O, Williamson K, Srivastava A, Gamain B, Duffy PE, Oleinikov AV. High-throughput screening platform identifies small molecules that prevent sequestration of Plasmodium falciparum-infected erythrocytes. J Infect Dis 2014; 211:1134-43. [PMID: 25355939 DOI: 10.1093/infdis/jiu589] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND We developed a 2-step approach to screen molecules that prevent and/or reverse Plasmodium falciparum-infected erythrocyte (IE) binding to host receptors. IE adhesion and sequestration in vasculature causes severe malaria, and therefore antiadhesion therapy might be useful as adjunctive treatment. IE adhesion is mediated by the polymorphic family (approximately 60 members) of P. falciparum EMP1 (PfEMP1) multidomain proteins. METHODS We constructed sets of PfEMP1 domains that bind ICAM-1, CSA, or CD36, receptors that commonly support IE binding. Combinations of domain-coated beads were assayed by Bio-Plex technology as a high-throughput molecular platform to screen antiadhesion molecules (antibodies and small molecules). Molecules identified as so-called hits in the screen (first step) then could be assayed individually for inhibition of binding of live IE to receptors (second step). RESULTS In proof-of-principle studies, the antiadhesion activity of several antibodies was concordant in Bio-Plex and live IE assays. Using this 2-step approach, we identified several molecules in a small molecule library of 10 000 compounds that could inhibit and reverse binding of IEs to ICAM-1 and CSA receptors. CONCLUSION This 2-step screening approach should be efficient for identification of antiadhesion drug candidates for falciparum malaria.
Collapse
Affiliation(s)
| | - Neta Milman
- Seattle Biomedical Research Institute, Seattle, Washington
| | - Tracy Saveria
- Seattle Biomedical Research Institute, Seattle, Washington
| | - Olga Chesnokov
- Charles E. Schmidt College of Medicine, Department of Biomedical Science, Florida Atlantic University, Boca Raton
| | | | - Anand Srivastava
- Inserm UMR 1134 Université Paris Diderot, Sorbonne Paris Cité, UMR S1134 Institut National de la Transfusion Sanguine, Paris, France
| | - Benoit Gamain
- Inserm UMR 1134 Université Paris Diderot, Sorbonne Paris Cité, UMR S1134 Institut National de la Transfusion Sanguine, Paris, France
| | - Patrick E Duffy
- Laboratory of Malaria Immunology and Vaccinology, National Institutes of Health, Bethesda, Maryland
| | - Andrew V Oleinikov
- Seattle Biomedical Research Institute, Seattle, Washington Charles E. Schmidt College of Medicine, Department of Biomedical Science, Florida Atlantic University, Boca Raton
| |
Collapse
|
2
|
Comparison of the absolute and relative efficiencies of electroporation-based transfection protocols for Plasmodium falciparum. Malar J 2012; 11:210. [PMID: 22720754 PMCID: PMC3407700 DOI: 10.1186/1475-2875-11-210] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Accepted: 06/21/2012] [Indexed: 11/18/2022] Open
Abstract
Background Several electroporation protocols exist to transfect exogenous DNA into Plasmodium falciparum. To date, however, only a subjective analysis of their relative efficiencies has been reported. Methods A time-course of luciferase reporter expression is used to provide an objective quantitative analysis of the absolute efficiency of three electroporation techniques; direct electroporation of ring stage infected erythrocytes, preloading of erythrocytes and a novel “double-tap” protocol that combines both approaches. Results Preloading of erythrocytes shows a mean efficiency of 9.59x10-6, some 5–180 fold more efficient than matched experiments utilizing the “double-tap” and direct electroporation of ring stage infected erythrocytes alone, respectively. Conclusion Evidence presented here provides the first quantitative assessment of both the absolute and relative efficiencies of a key molecular tool used to study the biology and pathogenesis of this important human pathogen.
Collapse
|
3
|
var gene transcription and PfEMP1 expression in the rosetting and cytoadhesive Plasmodium falciparum clone FCR3S1.2. Malar J 2011; 10:17. [PMID: 21266056 PMCID: PMC3036667 DOI: 10.1186/1475-2875-10-17] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Accepted: 01/25/2011] [Indexed: 11/10/2022] Open
Abstract
Background The pathogenicity of Plasmodium falciparum is in part due to the ability of the parasitized red blood cell (pRBC) to adhere to intra-vascular host cell receptors and serum-proteins. Binding of the pRBC is mediated by Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), a large multi-variant molecule encoded by a family of ≈60 var genes. Methods The study of var gene transcription in the parasite clone FCR3S1.2 was performed by semi-quantitative PCR and quantitative PCR (qPCR). The expression of the major PfEMP1 in FCR3S1.2 pRBC was analysed with polyclonal sera in rosette disruption assays and immunofluorecence. Results Transcripts from var1 (FCR3S1.2var1; IT4var21) and other var genes were detected by semi-quantitative PCR but results from qPCR showed that one var gene transcript dominated over the others (FCR3S1.2var2; IT4var60). Antibodies raised in rats to the recombinant NTS-DBL1α of var2 produced in E. coli completely and dose-dependently disrupted rosettes (≈95% at a dilution of 1/5). The sera reacted with the Maurer's clefts in trophozoite stages (IFA) and to the infected erythrocyte surface (FACS) indicating that FCR3S1.2var2 encodes the dominant PfEMP1 expressed in this parasite. Conclusion The major transcript in the rosetting model parasite FCR3S1.2 is FCR3S1.2var2 (IT4var60). The results suggest that this gene encodes the PfEMP1-species responsible for the rosetting phenotype of this parasite. The activity of previously raised antibodies to the NTS-DBL1α of FCR3S1.2var1 is likely due to cross-reactivity with NTS-DBL1α of the var2 encoded PfEMP1.
Collapse
|
4
|
Hughes KR, Biagini GA, Craig AG. Continued cytoadherence of Plasmodium falciparum infected red blood cells after antimalarial treatment. Mol Biochem Parasitol 2009; 169:71-8. [PMID: 19800372 PMCID: PMC2814047 DOI: 10.1016/j.molbiopara.2009.09.007] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 09/21/2009] [Accepted: 09/23/2009] [Indexed: 11/02/2022]
Abstract
Development of severe disease in Plasmodium falciparum malaria infection is thought to be, at least in part, due to the sequestration of trophozoite-stage infected red blood cells in the microvasculature. The process of cytoadherence is mediated by binding of the parasite protein PfEMP-1 on the surface of infected red blood cells to endothelial cell receptors. Although antimalarial treatments rapidly kill parasites, significant mortality is still seen in severe malaria, particularly within 24h of hospital admission. We find that cytoadherence of infected red blood cells continues for several hours after killing of the parasite by antimalarials; after 24h treatment using a range of antimalarials binding is approximately one-third the level of untreated parasite cultures. This is consistent with the maintained presence of PfEMP-1 on the surface of drug-treated infected red blood cells. A specific advantage of artesunate over other treatments tested is seen on addition of this drug to younger ring stage parasites, which do not mature to the cytoadherent trophozoite-stage. These findings show that cytoadherence, a potential pathogenic property of P. falciparum infected red blood cells, continues long after the parasite has been killed. These data support the development of adjunctive therapies to reverse the pathophysiological consequences of cytoadherence.
Collapse
Affiliation(s)
- Katie R Hughes
- Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, L3 5QA, UK.
| | | | | |
Collapse
|
5
|
Buckee CO, Bull PC, Gupta S. Inferring malaria parasite population structure from serological networks. Proc Biol Sci 2009; 276:477-85. [PMID: 18826933 PMCID: PMC2581777 DOI: 10.1098/rspb.2008.1122] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The malaria parasite Plasmodium falciparum is characterized by high levels of genetic diversity at antigenic loci involved in virulence and immune evasion. Knowledge of the population structure and dynamics of these genes is important for designing control programmes and understanding the acquisition of immunity to malaria; however, high rates of homologous and non-homologous recombination as well as complex patterns of expression within hosts have hindered attempts to elucidate these structures experimentally. Here, we analyse serological data from Kenya using a novel network technique to deconstruct the relationships between patients' immune responses to different parasite isolates. We show that particular population structures and expression patterns produce distinctive signatures within serological networks of parasite recognition, which can be used to discriminate between competing hypotheses regarding the organization of these genes. Our analysis suggests that different levels of immune selection occur within different groups of the same multigene family leading to mixed population structures.
Collapse
Affiliation(s)
- Caroline O Buckee
- Department of Zoology, University of Oxford, Tinbergen Building, South Parks Road, Oxford OX1 3PS, UK.
| | | | | |
Collapse
|
6
|
Abstract
The persistence of the human malaria parasite Plasmodium falciparum during blood stage proliferation in its host depends on the successive expression of variant molecules at the surface of infected erythrocytes. This variation is mediated by the differential control of a family of surface molecules termed PfEMP1 encoded by approximately 60 var genes. Each individual parasite expresses a single var gene at a time, maintaining all other members of the family in a transcriptionally silent state. PfEMP1/var enables parasitized erythrocytes to adhere within the microvasculature, resulting in severe disease. This review highlights key regulatory mechanisms thought to be critical for monoallelic expression of var genes. Antigenic variation is orchestrated by epigenetic factors including monoallelic var transcription at separate spatial domains at the nuclear periphery, differential histone marks on otherwise identical var genes, and var silencing mediated by telomeric heterochromatin. In addition, controversies surrounding var genetic elements in antigenic variation are discussed.
Collapse
Affiliation(s)
- Artur Scherf
- Biology of Host-Parasite Interactions Unit, CNRS URA2581, Institut Pasteur 75724 Paris, France.
| | | | | |
Collapse
|
7
|
Kyes SA, Kraemer SM, Smith JD. Antigenic variation in Plasmodium falciparum: gene organization and regulation of the var multigene family. EUKARYOTIC CELL 2007; 6:1511-20. [PMID: 17644655 PMCID: PMC2043368 DOI: 10.1128/ec.00173-07] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Sue A Kyes
- Molecular Parasitology Group, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom
| | | | | |
Collapse
|
8
|
Kyes S, Christodoulou Z, Pinches R, Kriek N, Horrocks P, Newbold C. Plasmodium falciparum var
gene expression is developmentally controlled at the level of RNA polymerase II‐mediated transcription initiation. Mol Microbiol 2007; 63:1237-47. [PMID: 17257309 DOI: 10.1111/j.1365-2958.2007.05587.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Plasmodium falciparum var gene family codes for a major virulence factor in this most lethal of human malaria parasites. A single var protein variant type is expressed on each infected red blood cell, with antigenic variation allowing progeny parasites to escape host immune detection. The control of mutually exclusive var gene expression in the parasite relies on in situ epigenetic changes. Whether control of expression occurs at transcription initiation or post transcription, however, remains to be established. Recent evidence supports existence of a unique var transcription site at the nuclear periphery containing the dominantly expressed var gene, although silent var genes can colocalize to the same region. We demonstrate here that exclusive var gene expression is controlled at the level of transcription initiation during ring stages and that var genes are transcribed by RNA polymerase II. This represents another example where P. falciparum differs from the paradigm for antigenic variation, Trypanosoma brucei.
Collapse
Affiliation(s)
- Sue Kyes
- Weatherall Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, Headington, Oxford, UK.
| | | | | | | | | | | |
Collapse
|
9
|
Viebig NK, Gamain B, Scheidig C, Lépolard C, Przyborski J, Lanzer M, Gysin J, Scherf A. A single member of the Plasmodium falciparum var multigene family determines cytoadhesion to the placental receptor chondroitin sulphate A. EMBO Rep 2006; 6:775-81. [PMID: 16025132 PMCID: PMC1369142 DOI: 10.1038/sj.embor.7400466] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2005] [Revised: 05/13/2005] [Accepted: 05/31/2005] [Indexed: 11/08/2022] Open
Abstract
In high-transmission regions, protective clinical immunity to Plasmodium falciparum develops during the early years of life, limiting serious complications of malaria in young children. Pregnant women are an exception and are especially susceptible to severe P. falciparum infections resulting from the massive adhesion of parasitized erythrocytes to chondroitin sulphate A (CSA) present on placental syncytiotrophoblasts. Epidemiological studies strongly support the feasibility of an intervention strategy to protect pregnant women from disease. However, different parasite molecules have been associated with adhesion to CSA. In this work, we show that disruption of the var2csa gene of P. falciparum results in the inability of parasites to recover the CSA-binding phenotype. This gene is a member of the var multigene family and was previously shown to be composed of domains that mediate binding to CSA. Our results show the central role of var2CSA in CSA adhesion and support var2CSA as a leading vaccine candidate aimed at protecting pregnant women and their fetuses.
Collapse
MESH Headings
- Animals
- Antibodies, Protozoan
- Antigenic Variation
- Blotting, Northern
- Blotting, Southern
- CD36 Antigens/biosynthesis
- CD36 Antigens/metabolism
- Cell Adhesion
- Chondroitin Sulfates/chemistry
- Cloning, Molecular
- Crossing Over, Genetic
- Exons
- Female
- Genome
- Genome, Protozoan
- Humans
- Malaria, Falciparum/prevention & control
- Malaria, Falciparum/transmission
- Models, Biological
- Models, Genetic
- Multigene Family
- Mutation
- Phenotype
- Placenta/metabolism
- Plasmids/metabolism
- Plasmodium falciparum/genetics
- Plasmodium falciparum/metabolism
- Pregnancy
- Pregnancy Complications, Parasitic/prevention & control
- Protein Binding
- Protozoan Proteins/genetics
- RNA/metabolism
- Time Factors
- Trophoblasts/metabolism
Collapse
Affiliation(s)
- Nicola K Viebig
- Unité de Biologie des Interactions Hôte-Parasite, CNRS URA 2581, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Benoit Gamain
- Unité de Biologie des Interactions Hôte-Parasite, CNRS URA 2581, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Christine Scheidig
- Unité de Biologie des Interactions Hôte-Parasite, CNRS URA 2581, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France
| | - Catherine Lépolard
- Unité de Parasitologie Expérimentale URA IPP/UNIV-MED EA 3282, IFR 48, Université de la Méditerranée (Aix-Marseille II), 27 Boulevard Jean Moulin, 13385, Marseille Cedex 5, France
| | - Jude Przyborski
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Michael Lanzer
- Hygiene Institut, Abteilung Parasitologie, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
| | - Jürg Gysin
- Unité de Parasitologie Expérimentale URA IPP/UNIV-MED EA 3282, IFR 48, Université de la Méditerranée (Aix-Marseille II), 27 Boulevard Jean Moulin, 13385, Marseille Cedex 5, France
| | - Artur Scherf
- Unité de Biologie des Interactions Hôte-Parasite, CNRS URA 2581, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France
- Tel: +33 1 45 68 86 16; Fax: +33 1 45 68 83 48; E-mail:
| |
Collapse
|
10
|
Horrocks P, Pinches RA, Chakravorty SJ, Papakrivos J, Christodoulou Z, Kyes SA, Urban BC, Ferguson DJP, Newbold CI. PfEMP1 expression is reduced on the surface of knobless Plasmodium falciparum infected erythrocytes. J Cell Sci 2005; 118:2507-18. [PMID: 15923663 DOI: 10.1242/jcs.02381] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a key virulence factor for this species of human malarial parasite. PfEMP1 is expressed on the surface of infected erythrocytes (IEs) and directly mediates adhesion to a variety of host cells. A number of other parasite-encoded proteins are similarly exported to the IE plasma membrane and play an indirect role in this adhesion process through the modification of the erythrocyte cytoskeleton and the formation of electron dense knobs into which PfEMP1 is anchored. Analysis of the specific contribution of knob-associated proteins to adhesion is difficult due to rapid PfEMP1 switching during in vitro culture. Furthermore, these studies typically assume that the level and distribution of PfEMP1 exposed in knobby (K(+)) and knobless (K(-)) IEs is unaltered, an assumption not yet supported with data. We describe here the preparation and characterisation of a panel of isogenic K(+) and K(-) parasite clones that express one of two defined PfEMP1 variants. Analysis of the cytoadhesive properties of these clones shows that both static and flow adhesion is reduced in all the K(-) clones and, further, that this correlates with an approximately 50% reduction in PfEMP1 displayed on the IE surface. However, despite this reduction, the gross distribution of PfEMP1 in K(-) IEs appears unaltered. These data impact on our current interpretation of the role of knobs in adhesion and the mechanism of trafficking PfEMP1 to the IE surface.
Collapse
Affiliation(s)
- Paul Horrocks
- Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, OX3 9DS, UK.
| | | | | | | | | | | | | | | | | |
Collapse
|
11
|
Carret CK, Horrocks P, Konfortov B, Winzeler E, Qureshi M, Newbold C, Ivens A. Microarray-based comparative genomic analyses of the human malaria parasite Plasmodium falciparum using Affymetrix arrays. Mol Biochem Parasitol 2005; 144:177-86. [PMID: 16174539 DOI: 10.1016/j.molbiopara.2005.08.010] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2005] [Revised: 08/16/2005] [Accepted: 08/16/2005] [Indexed: 12/13/2022]
Abstract
Microarray-based comparative genomic hybridization (CGH) provides a powerful tool for whole genome analyses and the rapid detection of genomic variation that underlies virulence and disease. In the field of Plasmodium research, many of the parasite genomes that one might wish to study in a high throughput manner are not laboratory clones, but clinical isolates. One of the key limitations to the use of clinical samples in CGH, however, is the miniscule amounts of genomic DNA available. Here we describe the successful application of multiple displacement amplification (MDA), a non-PCR-based amplification method that exhibits clear advantages over all other currently available methods. Using MDA, CGH was performed on a panel of NF54 and IT/FCR3 clones, identifying previously published deletions on chromosomes 2 and 9 as well as polymorphism in genes associated with disease pathology.
Collapse
Affiliation(s)
- Céline Karine Carret
- Pathogen Microarrays Group, The Wellcome Trust Sanger Institute, Genome Campus, Hinxton, Cambridge CB10 1SA, UK.
| | | | | | | | | | | | | |
Collapse
|
12
|
Springer AL, Smith LM, Mackay DQ, Nelson SO, Smith JD. Functional interdependence of the DBLbeta domain and c2 region for binding of the Plasmodium falciparum variant antigen to ICAM-1. Mol Biochem Parasitol 2005; 137:55-64. [PMID: 15279951 DOI: 10.1016/j.molbiopara.2004.03.019] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2003] [Revised: 12/12/2003] [Accepted: 03/28/2004] [Indexed: 11/18/2022]
Abstract
Cytoadherence of Plasmodium falciparum-infected erythrocytes is associated with severe malaria and is primarily mediated through binding of the variant surface antigen P. falciparum erythrocyte membrane protein 1 (PfEMP1) to specific host ligands. Infected erythrocyte binding to Intercellular Adhesion Molecule 1 (ICAM-1) has been implicated as having a role in cerebral malaria, a major cause of death from P. falciparum infection. We have examined ICAM-1-binding PfEMP1 proteins in the cytoadhesive P. falciparum strain IT4/25/5 in order to extend our understanding of binding. For A4tres, the ICAM-1 binding region was previously shown to reside within contiguous DBL2beta and c2 domains. We determined the gene sequence encoding IT-ICAM var, and showed that ICAM-1 binding in this protein also maps to DBL2betac2 domains that have 48% amino acid identity to A4tres. By truncation and chimera analysis, most of the DBL2beta and the first half of the c2 region were required for A4tres binding to ICAM-1, suggesting this tandem should be considered a structural-functional combination for ICAM-1 binding. Of interest, a chimera formed between two different ICAM-1 binding domains did not bind ICAM-1, suggesting a functional interdependence between DBL2beta and c2 from the same protein. As gene recombination and gene conversion are important mechanisms for generating diversity in the PfEMP1 protein family, this finding implies an extra level of constraint on the functional evolution of binding traits. Knowledge about the PfEMP1::ICAM-1 interaction may allow the development of interventions to prevent binding and disease.
Collapse
Affiliation(s)
- Amy L Springer
- Seattle Biomedical Research Institute, 307 Westlake Avenue N, Suite 500, WA 98109-5219, USA
| | | | | | | | | |
Collapse
|
13
|
Corredor V, Meyer EVS, Lapp S, Corredor-Medina C, Huber CS, Evans AG, Barnwell JW, Galinski MR. A SICAvar switching event in Plasmodium knowlesi is associated with the DNA rearrangement of conserved 3′ non-coding sequences. Mol Biochem Parasitol 2004; 138:37-49. [PMID: 15500914 DOI: 10.1016/j.molbiopara.2004.05.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2003] [Revised: 04/23/2004] [Accepted: 05/09/2004] [Indexed: 10/26/2022]
Abstract
Plasmodium knowlesi variant antigens are expressed at the surface of infected erythrocytes and are encoded by the Schizont Infected Cell Agglutination variant antigen (SICAvar) multigene family. The 3' region of the SICAvar gene locus encoding the 205 kDa variant antigen expressed in the Pk1(B+)1+ parasites was found to be altered compared to the Pk1(A+) parental clone. Here we report that this alteration is the result of a DNA rearrangement and that the original and altered 205 SICAvar alleles appear to encode bona fide variant antigens. Importantly, 205A and 205B SICAvar RNA sequences are detectable in similar apparent quantities as determined by quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) amplification experiments. However, expression of the 205 kDa SICA protein at the surface of the infected erythrocyte is not characteristic of the Pk1(A+) parasites and the 205 SICAvar transcript has not been detected in Pk1(A+) parasites by northern blot analysis. Furthermore, we report that many distinct SICAvar transcripts were detected in P. knowlesi Pk1(B+)1+ cDNA library hybridization screens. Of special interest, in light of these data, distinctive differences at the 3' end of the 205A and 205B alleles are observed, which may be of functional importance. An analysis of the 3' untranslated region (UTR) of SICAvar genes in more than 100 sequences revealed a surprising common sequence pattern characterized by blocks of imperfect, GT-rich, heptad repeated motifs (Block I), followed by A and T rich homopolymers (Block II) and in a large number of genes, GC-rich segments (Block III). We show that this region undergoes extensive recombination and that the preferential stability of the 205 SICAvar transcript in Pk1(B+)1+ parasites may be associated with the presence of its specific Block III sequences. We speculate that the conserved yet polymorphic SICAvar 3'UTR sequences, and comparable regions in P. falciparum var genes, function in the stage-specific and developmentally regulated post-transcriptional gene silencing (PTGS) of variant antigen transcripts.
Collapse
Affiliation(s)
- Vladimir Corredor
- Emory Vaccine Center, Yerkes National Primate Research Center, Emory University, 954 Gatewood Road, Atlanta, GA 30329, USA
| | | | | | | | | | | | | | | |
Collapse
|
14
|
Horrocks P, Pinches R, Christodoulou Z, Kyes SA, Newbold CI. Variable var transition rates underlie antigenic variation in malaria. Proc Natl Acad Sci U S A 2004; 101:11129-34. [PMID: 15256597 PMCID: PMC503751 DOI: 10.1073/pnas.0402347101] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2004] [Indexed: 11/18/2022] Open
Abstract
Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is expressed on the surface of infected erythrocytes where it plays a central role in both infected erythrocytes cytoadhesion and immune evasion. Switches in clonal expression of PfEMP1 result in antigenic variation that facilitates long-term chronic infection of the host. The var gene family encodes PfEMP1 variants, with transcriptional switching between different var variants providing the molecular basis for antigenic variation. Despite the importance of var transcriptional switching in the evasion of the immune response, little is known about the way in which this process is regulated. Here we report the measurement of transition on and off rates for a series of var gene variants. We find (i) that on and off rates for a given variant are dissimilar, (ii) that these rates vary dramatically among different variants, and (iii) that in isogenic clones expressing the same var gene, both on and off rates are constant and appear to be an intrinsic property of that particular gene. These data would suggest that the information that determines the probability of the activation or silencing of var genes is present in their surrounding DNA. Furthermore, some transitions appear to be disallowed depending on the recent variant antigen expression history of the parasite clone. These findings have important implications for both the underlying molecular mechanisms of antigenic variation and the processes that promote chronicity of infection in vivo.
Collapse
Affiliation(s)
- Paul Horrocks
- Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
| | | | | | | | | |
Collapse
|
15
|
Horrocks P, Kyes S, Pinches R, Christodoulou Z, Newbold C. Transcription of a subtelomerically located var gene variant in Plasmodium falciparum appears to require the truncation of an adjacent var gene. Mol Biochem Parasitol 2004; 134:193-9. [PMID: 15003839 DOI: 10.1016/j.molbiopara.2003.11.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2003] [Revised: 11/20/2003] [Accepted: 11/26/2003] [Indexed: 11/21/2022]
Abstract
The Plasmodium falciparum R29 clone preferentially transcribes the R29var gene variant on rosette selection, unlike other isogenic clones from the same parasite lineage. Characterisation of the R29var gene locus revealed that this gene lies internal to, and is in a tail-to-tail orientation with, a second var gene variant (A4var) at one end of chromosome 13. In the R29 clone, a spontaneous deletion event between these two var variants deletes all of the A4var gene and the subtelomeric repetitive sequence arrays. We have previously shown that a simple disruption of the A4var gene is not sufficient to preferentially activate the R29var gene in rosette-selected parasites. We therefore hypothesised that the truncation of the chromosome end may be a key factor in predisposing the R29var variant to transcription under rosette selection conditions. Here, we have generated a panel of isogenic parasite clones with both intact and truncated A4var-R29var loci, and show that R29var transcription is only detected in rosette-selected clones with a truncated locus. Furthermore, we present provisional data describing the relative frequency with which this spontaneous deletion event occurs. These data have implications in our understanding of how spontaneous deletion events within subtelomeric var loci may affect transcription of these var gene variants.
Collapse
Affiliation(s)
- Paul Horrocks
- Molecular Parasitology Group, Nuffield Department of Medicine, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK.
| | | | | | | | | |
Collapse
|
16
|
Kraemer SM, Smith JD. Evidence for the importance of genetic structuring to the structural and functional specialization of the Plasmodium falciparum var gene family. Mol Microbiol 2004; 50:1527-38. [PMID: 14651636 DOI: 10.1046/j.1365-2958.2003.03814.x] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The var gene family encodes Plasmodium falciparum erythrocyte membrane 1 (PfEMP1) proteins that act as virulence factors responsible for both antigenic variation and cytoadherence of infected erythrocytes. These proteins orchestrate infected erythrocyte sequestration from blood circulation and contribute to adhesion-based complications of P. falciparum malaria infections. For this study, we analysed the genetic organization and strain structure of var genes and present evidence for three separately evolving groups that have, in part, functionally diverged and differ between subtelomeric and central chromosomal locations. Our analyses suggest that a recombination hierarchy limits reassortment between groups and may explain why some var genes are unusually conserved between parasite strains. This recombination hierarchy, coupled with binding and immune selection, shapes the variant antigen repertoire and has structural, functional and evolutionary consequences for the PfEMP1 protein family that are directly relevant to malaria pathogenesis.
Collapse
Affiliation(s)
- Susan M Kraemer
- Seattle Biomedical Research Institute, 4 Nickerson Street, Seattle, WA 98109, USA
| | | |
Collapse
|
17
|
Andrews KT, Pirrit LA, Przyborski JM, Sanchez CP, Sterkers Y, Ricken S, Wickert H, Lépolard C, Avril M, Scherf A, Gysin J, Lanzer M. Recovery of adhesion to chondroitin-4-sulphate in Plasmodium falciparum varCSA disruption mutants by antigenically similar PfEMP1 variants. Mol Microbiol 2003; 49:655-69. [PMID: 12864850 DOI: 10.1046/j.1365-2958.2003.03595.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Protection against maternal malaria has been associated with the acquisition of a specific antibody response that prevents adhesion of Plasmodium falciparum-infected erythrocytes to the glycosaminoglycan chondroitin-4-sulphate (CSA), which is present in the placental intervillous space. These antibodies are directed against variant forms of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) that mediate binding to CSA. We have generated insertional disruption mutants of the gene encoding the CSA-binding phenotype in the P. falciparum clone FCR3 (varCSA) to test the hypothesis that strategies targeting the parasite's determinant for this adhesive phenotype may prevent sequestration of infected erythrocytes in the placenta and hence the development of maternal malaria. The varCSA-disruption mutants were initially unable to adhere to CSA; however, they could recover the phenotype after repeated selection over CSA. We show that recovery of CSA binding is varCSA independent and mediated by the activation of a novel var variant. Importantly, the corresponding PfEMP1 protein reacts with a monoclonal antibody recognizing the DBL3 gamma domain of the varCSA gene product, indicating that the DBL3 gamma CSA-binding domains are conserved between these PfEMP1-binding variants. Our data support strategies exploring these conserved epitopes as vaccine candidates against maternal malaria.
Collapse
|
18
|
Duffy MF, Reeder JC, Brown GV. Regulation of antigenic variation in Plasmodium falciparum: censoring freedom of expression? Trends Parasitol 2003; 19:121-4. [PMID: 12643994 DOI: 10.1016/s1471-4922(03)00003-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Plasmodium falciparum employs a strategy of clonal antigenic variation to evade the host immune response during the intraerythrocytic stage of its life cycle. The major variant parasite molecule is the P. falciparum erythrocyte membrane protein (PfEMP)1, which is encoded by the var multigene family. The parasite switches between different PfEMP1 molecules through regulation of var transcription. Recent studies have shed considerable light on this process, but much remains unknown. However, striking parallels between transcriptional control of var and genes in other organisms provide direction for future studies.
Collapse
Affiliation(s)
- Michael F Duffy
- Department of Medicine, The University of Melbourne, Royal Melbourne Hospital, Royal Parade, Melbourne, Victoria 3050, Australia.
| | | | | |
Collapse
|
19
|
Horrocks P, Pinches R, Kriek N, Newbold C. Stage-specific promoter activity from stably maintained episomes in Plasmodium falciparum. Int J Parasitol 2002; 32:1203-6. [PMID: 12204219 DOI: 10.1016/s0020-7519(02)00123-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Genomic DNA is organised at its simplest level within phased arrays of nucleosomes, a structure key to the correct transcriptional regulation of the encoded genes. Here we studied chromatin formation on DNA transfected into Plasmodium falciparum either as an episomal plasmid or following integration by homologous recombination. We show that stably maintained and replicated plasmid assembles phased arrays of nucleosomes and that a reporter gene is transcribed in an appropriate temporal manner. These data provide a key observation for the future investigation of promoter structure and function with transfected DNA in Plasmodium spp.
Collapse
Affiliation(s)
- Paul Horrocks
- Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, OX3 9DS, Oxford, UK.
| | | | | | | |
Collapse
|