title: CD4 down-regulation by HIV-1 and simian immunodeficiency virus (SIV) Nef proteins involves both internalization and intracellular retention mechanisms.
abstract: Among the pleiotropic effects of Nef proteins of HIV and simian immunodeficiency virus (SIV), down-modulation of cell surface expression of CD4 is a prominent phenotype. It has been presumed that Nef proteins accelerate endocytosis of CD4 by linking the receptor to the AP-2 clathrin adaptor. However, the related AP-1 and AP-3 adaptors have also been shown to interact with Nef, hinting at role(s) for these complexes in the intracellular retention of CD4. By using genetic inhibitors of endocytosis and small interfering RNA-induced knockdown of AP-2, we show that accelerated CD4 endocytosis is not a dominant mechanism of HIV-1 (NL4-3 strain) Nef in epithelial cells, T lymphocyte cell lines, or peripheral blood lymphocytes. Furthermore, we show that both the CD4 recycling from the plasma membrane and the nascent CD4 in transit to the plasma membrane are susceptible to intracellular retention in HIV-1 Nef-expressing cells. In contrast, AP-2-mediated enhanced endocytosis constitutes the predominant mechanism for SIV (MAC-239 strain) Nef-induced down-regulation of human CD4 in human cells.
authors.affiliation: Laboratory of Molecular Microbiology, NIAID, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Rose
authors.forename: Katy
authors.initials: K
authors.lastname: Janvier
authors.forename: Soundararajulu
authors.initials: S
authors.lastname: Chandrasekhar
authors.forename: Rafick P
authors.initials: RP
authors.lastname: Sekaly
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
authors.forename: Sundararajan
authors.initials: S
authors.lastname: Venkatesan
mesh_terms: D033963:Adaptor Protein Complex 3; D015704:CD4 Antigens / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D004705:Endocytosis; D004847:Epithelial Cells / Q000821:virology; D005434:Flow Cytometry; D015693:Gene Products, nef / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D019169:Jurkat Cells / Q000821:virology; D008214:Lymphocytes / Q000378:metabolism; D008856:Microscopy, Fluorescence; D010641:Phenotype; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000378:metabolism; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D020798:Two-Hybrid System Techniques; D014616:Vaccinia virus / Q000235:genetics; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism*; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D033963:Adaptor Protein Complex 3; D015704:CD4 Antigens; D002966:Clathrin; D004268:DNA-Binding Proteins; D015693:Gene Products, nef; C429284:NEF protein, SIV; D034741:RNA, Small Interfering; D018808:Transcription Factor AP-1; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D054334:Viral Regulatory and Accessory Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; D049452:Green Fluorescent Proteins; D004247:DNA