Regulated degradation of the HIV-1 Vpu protein through a betaTrCP-independent pathway limits the release of viral particles.
Viral protein U (Vpu) of HIV-1 has two known functions in replication of the virus: degradation of its cellular receptor CD4 and enhancement of viral particle release. Vpu binds CD4 and simultaneously recruits the betaTrCP subunit of the SCF(betaTrCP) ubiquitin ligase complex through its constitutively phosphorylated DS52GXXS56 motif. In this process, Vpu was found to escape degradation, while inhibiting the degradation of betaTrCP natural targets such as beta-catenin and IkappaBalpha. We further addressed this Vpu inhibitory function with respect to the degradation of Emi1 and Cdc25A, two betaTrCP substrates involved in cell-cycle progression. In the course of these experiments, we underscored the importance of a novel phosphorylation site in Vpu. We show that, especially in cells arrested in early mitosis, Vpu undergoes phosphorylation of the serine 61 residue, which lies adjacent to the betaTrCP-binding motif. This phosphorylation event triggers Vpu degradation by a betaTrCP-independent process. Mutation of Vpu S61 in the HIV-1 provirus extends the half-life of the protein and significantly increases the release of HIV-1 particles from HeLa cells. However, the S61 determinant of regulated Vpu turnover is highly conserved within HIV-1 isolates. Altogether, our results highlight a mechanism where differential phosphorylation of Vpu determines its fate as an adaptor or as a substrate of distinct ubiquitin ligases. Conservation of the Vpu degradation determinant, despite its negative effect on virion release, argues for a role in overall HIV-1 fitness.
Institut Cochin, Université Paris Descartes, CNRS (UMR 8104), Paris, France.
Emilie
E
Estrabaud
Erwann
E
Le Rouzic
Sandra
S
Lopez-Vergès
Marina
M
Morel
Nadia
N
Belaïdouni
Richard
R
Benarous
Catherine
C
Transy
Clarisse
C
Berlioz-Torrent
Florence
F
Margottin-Goguet
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D002522:Chlorocebus aethiops; D044783:F-Box Proteins / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D015497:HIV-1 / Q000235:genetics* / Q000472:pathogenicity; D054298:Human Immunodeficiency Virus Proteins; D006801:Humans; D008969:Molecular Sequence Data; D010766:Phosphorylation; D025801:Ubiquitin / Q000378:metabolism; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism*; D014779:Virus Replication / Q000502:physiology*; D044844:beta-Transducin Repeat-Containing Proteins / Q000235:genetics* / Q000378:metabolism*; D020687:cdc25 Phosphatases / Q000378:metabolism; D000086082:Viroporin Proteins
D018797:Cell Cycle Proteins; D044783:F-Box Proteins; D054298:Human Immunodeficiency Virus Proteins; D025801:Ubiquitin; D054334:Viral Regulatory and Accessory Proteins; D044844:beta-Transducin Repeat-Containing Proteins; D020687:cdc25 Phosphatases; C498960:FBXO5 protein, human; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins; C517004:CDC25A protein, human