title: CD4 phosphorylation partially reverses Nef down-regulation of CD4.
abstract: HIV Nef down-regulates CD4 from the cell surface in the absence of CD4 phosphorylation, whereas PMA down-regulates CD4 through a phosphorylation-dependent pathway. In this study we show that the down-regulation of CD4 in human Jurkat T cells expressing Nef was nearly complete (approximately 95%), whereas that induced by PMA was partial (approximately 40%). Unexpectedly, treating T cells expressing Nef with PMA restored the surface CD4 up to 35% of the steady state level. Both mutating the phosphorylation sites in the CD4 cytoplasmic tail (Ser408 and Ser415) and the use of a protein kinase C inhibitor, bisindolylmaleimide1, abolished the restoration of surface CD4, suggesting that the restoration required CD4 phosphorylation. CD4 and Nef could be cross-linked by a chemical cross-linker, 3,3-dithiobis[sulfosuccinimidyl-propionate], in control T cell membranes, but not in PMA-treated T cell membrane, suggesting that CD4 and Nef interacted with each other in T cells, and the phosphorylation disrupted the CD4-Nef interaction. We propose that this dissociation switches CD4 internalization from the Nef-mediated, nearly complete down-regulation to a phosphorylation-dependent, partial down-regulation, resulting in a net gain of CD4 on the T cell surface.
authors.affiliation: Skirball Institute of Biomedical Research, New York University School of Medicine, New York, NY 10016, USA. jiny@saturn.med.nyu.edu
authors.forename: Yong-Jiu
authors.initials: YJ
authors.lastname: Jin
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Zhang
authors.forename: J Gildade
authors.initials: JG
authors.lastname: Boursiquot
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Burakoff
mesh_terms: D015704:CD4 Antigens / Q000096:biosynthesis / Q000378:metabolism*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D002999:Clone Cells; D003432:Cross-Linking Reagents / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics / Q000276:immunology*; D004357:Drug Synergism; D015693:Gene Products, nef / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D006678:HIV / Q000276:immunology*; D006801:Humans; D019169:Jurkat Cells; D010766:Phosphorylation; D012694:Serine / Q000235:genetics / Q000378:metabolism; D013194:Staining and Labeling; D016176:T-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism / Q000821:virology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D015704:CD4 Antigens; D003432:Cross-Linking Reagents; D015693:Gene Products, nef; D054311:nef Gene Products, Human Immunodeficiency Virus; D012694:Serine; D013755:Tetradecanoylphorbol Acetate