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Journal of Virology, March 2001, p. 2993-3000, Vol. 75, No. 6
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.6.2993-3000.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Human Immunodeficiency Virus Type 1 Nef Functions at the Level of Virus Entry by Enhancing Cytoplasmic Delivery of Virions

Evelyne Schaeffer,1,2 Romas Geleziunas,1 and Warner C. Greene1,3,*

Gladstone Institute of Virology and Immunology1 and Departments of Medicine and of Microbiology and Immunology,3 University of California, San Francisco, California, and Unité 338 INSERM, 67084 Strasbourg Cedex, France2

Received 11 October 2000/Accepted 7 December 2000

The Nef protein of the type 1 human immunodeficiency virus (HIV-1) plays a key although poorly understood role in accelerating the progression of clinical disease in vivo. Nef exerts several biological effects in vitro, including enhancement of virion infectivity, downregulation of CD4 and major histocompatibility complex class I receptor expression, and modulation of various intracellular signaling pathways. The positive effect of Nef on virion infectivity requires its expression in the producer cell, although its effect is manifested in the subsequent target cell of infection. Prior studies suggest that Nef does not alter viral entry into target cells; nevertheless, it enhances proviral DNA synthesis, arguing for an action of Nef at the level of viral uncoating or reverse transcription. However, these early studies discounting an effect of Nef on virion entry may be confounded by the recent finding that HIV enters cells by both fusion and endocytosis. Using epifluorescence microscopy to monitor green fluorescent protein-Vpr-labeled HIV virion entry into HeLa cells, we find that endocytosis forms a very active pathway for virus uptake. Virions entering via the endocytic pathway do not support productive infection of the host cell, presumably reflecting their inability to escape from the endosomes. Conversely, our studies now demonstrate that HIV Nef significantly enhances CD4- and chemokine receptor-dependent entry of HIV virions into the cytoplasmic compartment of target cells. Mutations in Nef either impairing its ability to downregulate CD4 or disrupting its polyproline helix compromise virion entry into the cytoplasm. We conclude that Nef acts at least in part as a regulator of cytosolic viral entry and that this action contributes to its positive effects on viral infectivity.

* Corresponding author. Mailing address: Gladstone Institute of Virology and Immunology, P.O. Box 419100, San Francisco, CA 94141-9100. Phone: (415) 695-3800. Fax: (415) 826-1817. E-mail: wgreene{at}gladstone.ucsf.edu.

Journal of Virology, March 2001, p. 2993-3000, Vol. 75, No. 6
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.6.2993-3000.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.