The Ig Domain Protein CD9P-1 Down-regulates CD81 Ability to Support Plasmodium yoelii Infection

Birke Bartosch,Olivier Silvie,Stéphanie Charrin,Laurence Cocquerel,Jean-François Franetich,Samir Yalaoui,Dominique Mazier,Eric Rubinstein,Claude Boucheix

doi:10.1074/jbc.m109.057927

Abstract

Invasion of hepatocytes by Plasmodium sporozoites is a prerequisite for establishment of a malaria natural infection. The molecular mechanisms underlying sporozoite invasion are largely unknown. We have previously reported that CD81 is required on hepatocytes for infection by Plasmodium falciparum and Plasmodium yoelii sporozoites. CD81 belongs to the tetraspanin superfamily of transmembrane proteins. By interacting with each other and with other transmembrane proteins, tetraspanins may play a role in the lateral organization of membrane proteins. In this study, we investigated the role of the two major molecular partners of CD81 in hepatocytic cells, CD9P-1/EWI-F and EWI-2, two transmembrane proteins belonging to a novel subfamily of immunoglobulin proteins. We show that CD9P-1 silencing increases the host cell susceptibility to P. yoelii sporozoite infection, whereas EWI-2 knock-down has no effect. Conversely, overexpression of CD9P-1 but not EWI-2 partially inhibits infection. Using CD81 and CD9P-1 chimeric molecules, we demonstrate the role of transmembrane regions in CD81-CD9P-1 interactions. Importantly, a CD9P-1 chimera that no longer associates with CD81 does not affect infection. Based on these data, we conclude that CD9P-1 acts as a negative regulator of P. yoelii infection by interacting with CD81 and regulating its function.

Highlights

Malaria remains the most important parasitic human disease, responsible for nearly one million deaths each year [1]
CD9P-1/FPRP and EWI-2/PGRL Are the Major Partners of CD81 in Human and Mouse Hepatocytic Cells—We have previously shown that the two major surface proteins co-immunoprecipitated with CD81 in primary human hepatocytes correspond to the two main partners of CD81, CD9P-1 and EWI-2, two members of a novel subfamily of immunoglobulin proteins [20]
The high molecular mass protein comigrates with the major protein immunoprecipitated by a new mAb 8G1 specific for mouse CD9P-1, and the 65 kDa protein co-migrates with the major protein immunoprecipitated by an antibody specific for EWI-2

Summary

Introduction

Malaria remains the most important parasitic human disease, responsible for nearly one million deaths each year [1]. We have examined whether the two major CD81 partners, CD9P-1 and EWI-2, play a role in the infection of hepatocytic cells by Plasmodium sporozoites. In Hepa1-6 cells, like in human hepatocytes, CD81 co-immunoprecipitated two major proteins with molecular masses consistent with that of CD9P-1 (125 kDa) and EWI-2 (65 kDa) (Fig. 1).

Results

Conclusion