title: HIV-1 Nef-induced down-regulation of MHC class I requires AP-1 and clathrin but not PACS-1 and is impeded by AP-2.
abstract: Major histocompatibility complex class I is down-regulated from the surface of human immunodeficiency virus (HIV)-1-infected cells by Nef, a virally encoded protein that is thought to reroute MHC-I to the trans-Golgi network (TGN) in a phosphofurin acidic cluster sorting protein (PACS) 1, adaptor protein (AP)-1, and clathrin-dependent manner. More recently, an alternative model has been proposed, in which Nef uses AP-1 to direct MHC-I to endosomes and lysosomes. Here, we show that knocking down either AP-1 or clathrin with small interfering RNA inhibits the down-regulation of HLA-A2 (an MHC-I isotype) by Nef in HeLa cells. However, knocking down PACS-1 has no effect, not only on Nef-induced down-regulation of HLA-A2 but also on the localization of other proteins containing acidic cluster motifs. Surprisingly, knocking down AP-2 actually enhances Nef activity. Immuno-electron microscopy labeling of Nef-expressing cells indicates that HLA-A2 is rerouted not to the TGN, but to endosomes. In AP-2-depleted cells, more of the HLA-A2 localizes to the inner vesicles of multivesicular bodies. We propose that depleting AP-2 potentiates Nef activity by altering the membrane composition and dynamics of endosomes and causing increased delivery of HLA-A2 to a prelysosomal compartment.
authors.affiliation: University of Cambridge, Cambridge Institute for Medical Research, Cambridge CB2 0XY, United Kingdom.
authors.forename: Nienke B
authors.initials: NB
authors.lastname: Lubben
authors.forename: Daniela A
authors.initials: DA
authors.lastname: Sahlender
authors.forename: Alison M
authors.initials: AM
authors.lastname: Motley
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Lehner
authors.forename: Philippe
authors.initials: P
authors.lastname: Benaroch
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Robinson
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000378:metabolism*; D033962:Adaptor Protein Complex 2 / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D015153:Blotting, Western; D002966:Clathrin / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics*; D015693:Gene Products, nef / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism*; D015789:HLA-A2 Antigen / Q000235:genetics* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D033961:Adaptor Protein Complex 1; D033962:Adaptor Protein Complex 2; D048868:Adaptor Proteins, Signal Transducing; D002966:Clathrin; D015693:Gene Products, nef; D015789:HLA-A2 Antigen; C491914:PACS1 protein, human; C499638:PACS2 protein, human; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus