title: Interaction of HIV-1 Nef protein with the host protein Alix promotes lysosomal targeting of CD4 receptor.
abstract: Nef is an accessory protein of human immunodeficiency viruses that promotes viral replication and progression to AIDS through interference with various host trafficking and signaling pathways. A key function of Nef is the down-regulation of the coreceptor CD4 from the surface of the host cells. Nef-induced CD4 down-regulation involves at least two independent steps as follows: acceleration of CD4 endocytosis by a clathrin/AP-2-dependent pathway and targeting of internalized CD4 to multivesicular bodies (MVBs) for eventual degradation in lysosomes. In a previous work, we found that CD4 targeting to the MVB pathway was independent of CD4 ubiquitination. Here, we report that this targeting depends on a direct interaction of Nef with Alix/AIP1, a protein associated with the endosomal sorting complexes required for transport (ESCRT) machinery that assists with cargo recruitment and intraluminal vesicle formation in MVBs. We show that Nef interacts with both the Bro1 and V domains of Alix. Depletion of Alix or overexpression of the Alix V domain impairs lysosomal degradation of CD4 induced by Nef. In contrast, the V domain overexpression does not prevent cell surface removal of CD4 by Nef or protein targeting to the canonical ubiquitination-dependent MVB pathway. We also show that the Nef-Alix interaction occurs in late endosomes that are enriched in internalized CD4. Together, our results indicate that Alix functions as an adaptor for the ESCRT-dependent, ubiquitin-independent targeting of CD4 to the MVB pathway induced by Nef.
authors.affiliation: From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil.
authors.forename: Nathaly A
authors.initials: NA
authors.lastname: Amorim
authors.affiliation: From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil.
authors.forename: Eulália M L
authors.initials: EM
authors.lastname: da Silva
authors.affiliation: From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil.
authors.forename: Rodrigo O
authors.initials: RO
authors.lastname: de Castro
authors.affiliation: From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil.
authors.forename: Mara E
authors.initials: ME
authors.lastname: da Silva-Januário
authors.affiliation: the Department of Virology, Institute of Microbiology Paulo de Góes, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21941-590, Brazil, and.
authors.forename: Luiza M
authors.initials: LM
authors.lastname: Mendonça
authors.affiliation: the Cell Biology and Metabolism Program, Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
authors.affiliation: the Department of Virology, Institute of Microbiology Paulo de Góes, Federal University of Rio de Janeiro, Rio de Janeiro, RJ 21941-590, Brazil, and.
authors.forename: Luciana J
authors.initials: LJ
authors.lastname: da Costa
authors.affiliation: From the Department of Cell and Molecular Biology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP 14049-900, Brazil, lldasilva@fmrp.usp.br.
authors.forename: Luis L P
authors.initials: LL
authors.lastname: daSilva
mesh_terms: D015704:CD4 Antigens / Q000235:genetics / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism*; D011992:Endosomes / Q000235:genetics / Q000378:metabolism; D015658:HIV Infections / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008247:Lysosomes / Q000201:enzymology* / Q000235:genetics; D011485:Protein Binding; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism*
chemical_list: D015704:CD4 Antigens; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D056827:Endosomal Sorting Complexes Required for Transport; C117020:PDCD6IP protein, human; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1
keywords: Alix; Endosome; Human Immunodeficiency Virus (HIV); Intracellular Trafficking; Lysosome; Multivesicular Body (MVB); Nef; Protein Sorting