Antagonism of tetherin restriction of HIV-1 release by vpu involves binding and sequestration of the restriction factor in a perinuclear compartment

The vpu accessory protein promotes hiv-1 release by counteracting tetherin/bst-2,an interferon-regulated restriction factor,which retains virions at the cell-surface. recent reports proposed b-trcp-dependent proteasomal and/or endo-lysosomal degradation of tetherin as potential mechanisms by which vpu could down-regulate tetherin cell-surface expression and antagonize this restriction. in all of these studies,tetherin degradation did not,however,entirely account for vpu anti-tetherin activity. here,we show that vpu can promote hiv-1 release without detectably affecting tetherin steady-state levels or turnover,suggesting that tetherin degradation may not be necessary and/or sufficient for vpu anti-tetherin activity. even though vpu did not enhance tetherin internalization from the plasma membrane (pm),it did significantly slow-down the overall transport of the protein towards the cell-surface. accordingly,vpu expression caused a specific removal of cell-surface tetherin and a re-localization of the residual pool of tetherin in a perinuclear compartment that co-stained with the tgn marker tgn46 and vpu itself. this re-localization of tetherin was also observed with a vpu mutant unable to recruit b-trcp,suggesting that this activity is taking place independently from b-trcp-mediated trafficking and/or degradation processes. we also show that vpu co-immunoprecipitates with tetherin and that this interaction involves the transmembrane domains of the two proteins. importantly,this association was found to be critical for reducing cell-surface tetherin expression,re-localizing the restriction factor in the tgn and promoting hiv-1 release. overall,our results suggest that association of vpu to tetherin affects the outward trafficking and/or recycling of the restriction factor from the tgn and as a result promotes its sequestration away fromthe pm where productive hiv-1 assembly takes place. this mechanismof antagonismthat results in tgn trapping is likely to be augmented by b-trcp-dependent degradation,underlining the need for complementary and perhaps synergistic strategies to effectively counteract the powerful restrictive effects of human tetherin. © 2010 dubé et al.