title: HIV-1 Nef enhances both membrane expression and virion incorporation of Env products. A model for the Nef-dependent increase of HIV-1 infectivity.
abstract: The expression of human immunodeficiency virus Nef increases the viral infectivity through mechanisms still not fully elucidated. Here we report that wild-type (wt) human immunodeficiency virus, type 1 (HIV-1), particles were neutralized by higher concentrations of either anti-Env glycoprotein (gp) 41 antibodies or recombinant soluble human CD4 compared with Deltanef HIV-1. This appeared to be the result of a Nef-induced increase of virion incorporation of both gp41 (transmembrane (TM)) and surface gp120 Env products likely originating from enhanced steady-state levels of cell membrane-associated Env products. This, in turn, seemed to be the consequence of a reduced retention of the Env precursor. Most interesting, we found that both the Nef-directed increase of Env membrane expression and the Nef-induced enhancement of HIV-1 infectivity relied on the presence of the intracytoplasmic domain of TM, supporting the hypothesis of a functional correlation between these effects. Mutagenesis studies allowed us to establish that the two leucine residues at the TM C terminus, which are part of a sorting motif involved in the control of Env membrane expression, and the 181-210-residue Nef C-terminal region were critically involved in the Nef/Env functional interaction. In conclusion, we propose that Nef increases the infectivity of HIV-1 at least in part by enhancing the amounts of Env products incorporated into virus particles.
authors.affiliation: Laboratory of Virology, Istituto Superiore di Sanità, Rome, 00161 Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Schiavoni
authors.forename: Susanna
authors.initials: S
authors.lastname: Trapp
authors.forename: Anna Claudia
authors.initials: AC
authors.lastname: Santarcangelo
authors.forename: Valentina
authors.initials: V
authors.lastname: Piacentini
authors.forename: Katherina
authors.initials: K
authors.lastname: Pugliese
authors.forename: Andreas
authors.initials: A
authors.lastname: Baur
authors.forename: Maurizio
authors.initials: M
authors.lastname: Federico
mesh_terms: D015967:Gene Expression Regulation, Viral; D015693:Gene Products, nef / Q000235:genetics / Q000378:metabolism*; D015700:HIV Envelope Protein gp41 / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D014774:Virulence / Q000235:genetics; D014779:Virus Replication; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D015693:Gene Products, nef; D015700:HIV Envelope Protein gp41; D054311:nef Gene Products, Human Immunodeficiency Virus