title: Expression of Nef downregulates CXCR4, the major coreceptor of human immunodeficiency virus, from the surfaces of target cells and thereby enhances resistance to superinfection.
abstract: Lentiviral Nef proteins are key factors for pathogenesis and are known to downregulate functionally important molecules, including CD4 and major histocompatibility complex class I (MHC-I), from the surfaces of infected cells. Recently, we demonstrated that Nef reduces cell surface levels of the human immunodeficiency virus type 1 (HIV-1) entry coreceptor CCR5 (N. Michel, I. Allespach, S. Venzke, O. T. Fackler, and O. T. Keppler, Curr. Biol. 15:714-723, 2005). Here, we report that Nef downregulates the second major HIV-1 coreceptor, CXCR4, from the surfaces of HIV-infected primary CD4 T lymphocytes with efficiencies comparable to those of the natural CXCR4 ligand, stromal cell-derived factor-1 alpha. Analysis of a panel of mutants of HIV-1(SF2) Nef revealed that the viral protein utilized the same signature motifs for downmodulation of CXCR4 and MHC-I, including the proline-rich motif P(73)P(76)P(79)P(82) and the acidic cluster motif E(66)E(67)E(68)E(69.) Expression of wild-type Nef, but not of specific Nef mutants, resulted in a perinuclear accumulation of the coreceptor. Remarkably, the carboxy terminus of CXCR4, which harbors the classical motifs critical for basal and ligand-induced receptor endocytosis, was dispensable for the Nef-mediated reduction of surface exposure. Functionally, the ability of Nef to simultaneously downmodulate CXCR4 and CD4 correlated with maximum-level protection of Nef-expressing target cells from fusion with cells exposing X4 HIV-1 envelopes. Furthermore, the Nef-mediated downregulation of CXCR4 alone on target T lymphocytes was sufficient to diminish cells' susceptibility to X4 HIV-1 virions at the entry step. The downregulation of chemokine coreceptors is a conserved activity of Nef to modulate infected cells, an important functional consequence of which is an enhanced resistance to HIV superinfection.
authors.affiliation: Department of Virology, University of Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Venzke
authors.forename: Nico
authors.initials: N
authors.lastname: Michel
authors.forename: Ina
authors.initials: I
authors.lastname: Allespach
authors.forename: Oliver T
authors.initials: OT
authors.lastname: Fackler
authors.forename: Oliver T
authors.initials: OT
authors.lastname: Keppler
mesh_terms: D020816:Amino Acid Motifs; D019943:Amino Acid Substitution; D015704:CD4 Antigens / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000821:virology*; D002459:Cell Fusion; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry; D002478:Cells, Cultured; D003593:Cytoplasm / Q000737:chemistry; D004252:DNA Mutational Analysis; D015536:Down-Regulation; D005434:Flow Cytometry; D015693:Gene Products, nef / Q000502:physiology*; D006678:HIV; D015497:HIV-1 / Q000502:physiology*; D006680:HLA Antigens / Q000096:biosynthesis; D006801:Humans; D018613:Microscopy, Confocal; D008954:Models, Biological; D016296:Mutagenesis; D009154:Mutation; D019718:Receptors, CXCR4 / Q000378:metabolism*; D014762:Viral Interference / Q000235:genetics*; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D015704:CD4 Antigens; D015693:Gene Products, nef; D006680:HLA Antigens; D019718:Receptors, CXCR4; D054311:nef Gene Products, Human Immunodeficiency Virus