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Journal of Virology, June 2000, p. 5691-5701, Vol. 74, No. 12
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Simian and Human Immunodeficiency Virus Nef Proteins Use Different Surfaces To Downregulate Class I Major Histocompatibility Complex Antigen Expression

Tomek Swigut,1 A. John Iafrate,1 Jan Muench,2 Frank Kirchhoff,2 and Jacek Skowronski1,*

Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724,1 and Institute for Clinical and Molecular Virology, University of Erlangen-Nuernberg, 91054 Erlangen, Germany2

Received 24 November 1999/Accepted 10 March 2000

Simian immunodeficiency virus (SIV) and human immunodeficiency virus type 1 (HIV-1) Nef proteins are related regulatory proteins that share several functions, including the ability to downregulate class I major histocompatibility complex (MHC) and CD4 expression on the cell surface and to alter T-cell-receptor-initiated signal transduction in T cells. We compared the mechanisms used by SIV mac239 Nef and HIV-1 Nef to downregulate class I MHC and found that the ability of SIV Nef to downregulate class I MHC requires a unique C-terminal region of the SIV mac239 Nef molecule which is not found in HIV-1 Nef. Interestingly, mutation of the PxxP motif in SIV Nef, unlike in HIV-1 Nef, does not affect class I MHC downregulation. We also found that downregulation of class I MHC by SIV Nef requires a conserved tyrosine in the cytoplasmic domain of the class I MHC heavy chain and involves accelerated endocytosis of class I complexes, as previously found with HIV-1 Nef. Thus, while SIV and HIV-1 Nef proteins use a similar mechanism to downregulate class I MHC expression, they have evolved different surfaces for molecular interactions with cell factors that regulate class I MHC traffic. Mutations in the C-terminal domain of SIV mac239 Nef selectively disrupt class I MHC downregulation, having no detectable effect on other functions of Nef, such as the downregulation of CD4 and CD3 surface expression, the stimulation of SIV virion infectivity, and the induction of SIV replication from T cells infected in the absence of stimulation. The resulting mutants will be useful reagents for studying the importance of class I MHC downregulation for SIV replication and AIDS pathogenesis in infected rhesus macaques.

* Corresponding author. Mailing address: Cold Spring Harbor Laboratory, P.O. Box 100, 1 Bungtown Rd., Cold Spring Harbor, NY 11724. Phone: (516) 367-8407. Fax: (516) 367-8454. E-mail: skowrons{at}cshl.org.

Journal of Virology, June 2000, p. 5691-5701, Vol. 74, No. 12
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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