Clag9 is not essential for PfEMP1 surface expression in non-cytoadherent Plasmodium falciparum parasites with a chromosome 9 deletion.
BACKGROUND
The expression of the clonally variant virulence factor PfEMP1 mediates the sequestration of Plasmodium falciparum infected erythrocytes in the host vasculature and contributes to chronic infection. Non-cytoadherent parasites with a chromosome 9 deletion lack clag9, a gene linked to cytoadhesion in previous studies. Here we present new clag9 data that challenge this view and show that surface the non-cytoadherence phenotype is linked to the expression of a non-functional PfEMP1.


RESULTS
Loss of adhesion in P. falciparum D10, a parasite line with a large chromosome 9 deletion, was investigated. Surface iodination analysis of non-cytoadherent D10 parasites and COS-7 surface expression of the CD36-binding PfEMP1 CIDR1α domain were performed and showed that these parasites express an unusual trypsin-resistant, non-functional PfEMP1 at the erythrocyte surface. However, the CIDR1α domain of this var gene expressed in COS-7 cells showed strong binding to CD36. Atomic Force Microscopy showed a slightly modified D10 knob morphology compared to adherent parasites. Trafficking of PfEMP1 and KAHRP remained functional in D10. We link the non-cytoadherence phenotype to a chromosome 9 breakage and healing event resulting in the loss of 25 subtelomeric genes including clag9. In contrast to previous studies, knockout of the clag9 gene from 3D7 did not interfere with parasite adhesion to CD36.


CONCLUSIONS
Our data show the surface expression of non-functional PfEMP1 in D10 strongly indicating that genes other than clag9 deleted from chromosome 9 are involved in this virulence process possibly via post-translational modifications.
Institut Pasteur, Biology of Parasite-Host Interactions Unit, Department of Parasitology and Mycology, Paris, France.
Adéla
A
Nacer
Emeric
E
Roux
Sébastien
S
Pomel
Christine
C
Scheidig-Benatar
Hiroshi
H
Sakamoto
Frank
F
Lafont
Artur
A
Scherf
Denise
D
Mattei
D000818:Animals; D018955:CD36 Antigens / Q000378:metabolism; D019556:COS Cells; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D002872:Chromosome Deletion; D004912:Erythrocytes / Q000166:cytology / Q000469:parasitology; D005786:Gene Expression Regulation; D055786:Gene Knockout Techniques; D006801:Humans; D010963:Plasmodium falciparum / Q000166:cytology / Q000235:genetics* / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism
D018955:CD36 Antigens; D015815:Cell Adhesion Molecules; D015800:Protozoan Proteins; C407823:clag9 protein, Plasmodium falciparum; C085731:erythrocyte membrane protein 1, Plasmodium falciparum; D014357:Trypsin