J. Virol., 02 1996, 820-829, Vol 70, No. 2
Copyright © 1996, American Society for Microbiology

The envelope glycoprotein of human immunodeficiency virus type 2 enhances viral particle release: a Vpu-like factor?

S Bour, U Schubert, K Peden and K Strebel
Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892, USA.

The Vpu protein is a human immunodeficiency virus type 1 (HIV-1)- specific accessory protein that is required for the efficient release of viral particles from infected cells. Even though HIV-2 does not encode Vpu, we found that this virus is nevertheless capable of efficiently releasing virus particles. In fact, the rate of virus release from HeLa cells transfected with a full-length molecular clone of HIV-2, ROD10, was comparable to that observed for the vpu+ HIV-1 NL4- 3 isolate and was not further enhanced by expression of Vpu in trans. However, consistent with previous observations showing that HIV-2 particle release is Vpu responsive in the context of HIV-1/HIV-2 chimeric constructs; exchanging the gag-pol region of NL4-3 with the corresponding region from pROD10 rendered the resulting chimeric virus Vpu responsive. Our finding that the responsiveness of HIV-2 particle release to Vpu is context dependent suggested the presence of a Vpu- like factor(s) encoded by HIV-2. Using chimeric proviruses encoding HIV- 2 gag and pol in the context of the HIV-1 provirus that were coexpressed with subgenomic HIV-2 constructs, we found that the HIV-2 envelope glycoprotein had the ability to enhance HIV-2 particle release with an efficiency comparable to that of the HIV-1 Vpu protein. Conversely, inactivation of the HIV-2 env gene in the original ROD10 clone resulted in a decrease in the rate of viral particle release to a level that was comparable to that of Vpu-deficient HIV-1 isolates. Providing the wild-type envelope in trans rescued the particle release defect of the ROD10 envelope mutant. Thus, unlike HIV-1, which encodes two separate proteins to regulate virus release or to mediate viral entry, the HIV-2 Env protein has evolved to perform both functions.

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