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Journal of Virology, March 2006, p. 2815-2822, Vol. 80, No. 6
0022-538X/06/$08.00+0     doi:10.1128/JVI.80.6.2815-2822.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Detection of Cell-Cell Fusion Mediated by Ebola Virus Glycoproteins

Séverine Bär,^1* Ayato Takada,² Yoshihiro Kawaoka,^2,3 and Marc Alizon¹

Department of Cell Biology, Institut Cochin, INSERM U567, CNRS UMR 8104, Université René Descartes, F-75014 Paris, France,¹ Department of Global Epidemiology, Hokkaido University Research Center for Zoonosis Control, Sapporo 060-0818, Japan,² Department of Microbiology and Immunology, University of Tokyo, Shirokanedai, Minato-ku, Tokyo 108-8639, Japan³

Received 7 October 2005/ Accepted 22 December 2005

Ebola viruses (EboV) are enveloped RNA viruses infecting cells by a pH-dependent process mediated by viral glycoproteins (GP) involving endocytosis of virions and their routing into acidic endosomes. As with well-characterized pH-dependent viral entry proteins, in particular influenza virus hemagglutinin, it is thought that EboV GP require activation by low pH in order to mediate fusion of the viral envelope with the membrane of endosomes. However, it has not yet been possible to confirm the direct role of EboV GP in membrane fusion and the requirement for low-pH activation. It was in particular not possible to induce formation of syncytia by exposing cells expressing EboV GP to acidic medium. Here, we have used an assay based on the induction of a ß-galactosidase (lacZ) reporter gene in target cells to detect cytoplasmic exchanges, indicating membrane fusion, with cells expressing EboV GP (Zaire species). Acidic activation of GP-expressing cells was required for efficient fusion with target cells. The direct role of EboV GP in this process is indicated by its inhibition by anti-GP antibodies and by the lack of activity of mutant GP normally expressed at the cell surface but defective for virus entry. Fusion was not observed when target cells underwent acidic treatment, for example, when they were placed in coculture with GP-expressing cells before the activation step. This unexpected feature, possibly related to the nature of the EboV receptor, could explain the impossibility of inducing formation of syncytia among GP-expressing cells.

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* Corresponding author. Mailing address: Deutsches Krebsforschungszentrum-ATV 2.208, ATV F010 and INSERM U375, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany. Phone: 49 6221 424968. Fax: 49 6221 424962. E-mail: s.baer{at}dkfz-heidelberg.de.

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Journal of Virology, March 2006, p. 2815-2822, Vol. 80, No. 6
0022-538X/06/$08.00+0     doi:10.1128/JVI.80.6.2815-2822.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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