title: Binding of c-Raf1 kinase to a conserved acidic sequence within the carboxyl-terminal region of the HIV-1 Nef protein.
abstract: Nef is a membrane-associated cytoplasmic phosphoprotein that is well conserved among the different human (HIV-1 and HIV-2) and simian immunodeficiency viruses and has important roles in down-regulating the CD4 receptor and modulating T-cell signaling pathways. The ability to modulate T-cell signaling pathways suggests that Nef may physically interact with T-cell signaling proteins. In order to identify Nef binding proteins and map their site(s) of interaction, we targeted a highly conserved acidic sequence at the carboxyl-terminal region of Nef sharing striking similarity with an acidic sequence at the c-Raf1-binding site within the Ras effector region. Here, we used deletion and site-specific mutagenesis to generate mutant Nef proteins fused to bacterial glutathione S-transferase in in vitro precipitation assays and immunoblot analysis to map the specific interaction between the HIV-1LAI Nef and c-Raf1 to a conserved acidic sequence motif containing the core sequence Asp-Asp-X-X-X-Glu (position 174-179). Significantly, we demonstrate that substitution of the nonpolar glycine residue for either or both of the conserved negatively charged aspartic acid residues at positions 174 and 175 in the full-length recombinant Nef protein background completely abrogated binding of c-Raf1 in vitro. In addition, lysates from a permanent CEM T-cell line constitutively expressing the native HIV-1 Nef protein was used to coimmunoprecipitate a stable Nef-c-Raf1 complex, suggesting that molecular interactions between Nef and c-Raf1, an important downstream transducer of cell signaling through the c-Raf1-MAP kinase pathway, occur in vivo. This interaction may account for the Nef-induced perturbations of T-cell signaling and activation pathways in vitro and in vivo.
authors.affiliation: Laboratory of Leukocyte Biology, NCI-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Hodge
authors.forename: K J
authors.initials: KJ
authors.lastname: Dunn
authors.forename: G K
authors.initials: GK
authors.lastname: Pei
authors.forename: M K
authors.initials: MK
authors.lastname: Chakrabarty
authors.forename: G
authors.initials: G
authors.lastname: Heidecker
authors.forename: J A
authors.initials: JA
authors.lastname: Lautenberger
authors.forename: K P
authors.initials: KP
authors.lastname: Samuel
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001665:Binding Sites / Q000235:genetics; D017124:Conserved Sequence; D015693:Gene Products, nef / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010449:Peptide Mapping; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D015693:Gene Products, nef; D054311:nef Gene Products, Human Immunodeficiency Virus; D019908:Proto-Oncogene Proteins c-raf