title: Simian and human immunodeficiency virus Nef proteins use different surfaces to downregulate class I major histocompatibility complex antigen expression.
abstract: 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.
authors.affiliation: Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA.
authors.forename: T
authors.initials: T
authors.lastname: Swigut
authors.forename: A J
authors.initials: AJ
authors.lastname: Iafrate
authors.forename: J
authors.initials: J
authors.lastname: Muench
authors.forename: F
authors.initials: F
authors.lastname: Kirchhoff
authors.forename: J
authors.initials: J
authors.lastname: Skowronski
mesh_terms: D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017252:CD3 Complex / Q000378:metabolism; D015704:CD4 Antigens / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D004705:Endocytosis; D015693:Gene Products, nef / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000235:genetics / Q000502:physiology; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008253:Macaca mulatta; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D015302:Simian Immunodeficiency Virus / Q000235:genetics / Q000502:physiology; D013601:T-Lymphocytes / Q000378:metabolism / Q000821:virology; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D017252:CD3 Complex; D015704:CD4 Antigens; D015693:Gene Products, nef; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; D014443:Tyrosine