The Cell Biology Of Tetherin Antagonism By HIV-1 Vpu

Student thesis: Doctoral ThesisDoctor of Philosophy


The HIV-1 accessory protein Vpu counteracts the restriction factor tetherin, and induces its cell surface downregulation and ubiquitin-dependent endosomal degradation.

We have identified an acidic/dileucine based-sorting determinant, ExxxLV, in the second alpha helix of the Vpu cytoplasmic tail as being required for efficient tetherin antagonism. Mutation of this motif prevents tetherin degradation and downregulation, but not Vpu/tetherin interaction. This effect is similar to Vpu phospho-mutants, which are unable to recruit the SCF-β-TrCP E3 ubiquitin ligase complex. However, ExxxLV mutants are able to bind to β-TrCP and ESCRT-0 component HRS. Tetherin and ExxxLV mutants accumulate at the cell surface and in early endosomes implying that post-binding trafficking of Vpu/tetherin complexes is required to prevent tetherin transit to viral assembly sites on the plasma membrane. Our preliminary data shows that the ExxxLV motif interacts with the trafficking machinery via the clathrin adaptor AP-1 in a manner that is dependent on the tyrosine-based sorting signal in tetherin, although functional redundancy in clathrin trafficking pathways cannot yet rule out other adaptor proteins being involved.

A study performed in our laboratory examined the variation of vpu alleles in HIV-1 infection, and identified several variants in which isoleucine residues in the first alpha helix of the cytoplasmic tail were mutated. We show that these isoleucine mutants were defective for inducing tetherin degradation, despite being capable of interacting with tetherin, thus pheno-copying ExxxLV and phospho-mutants. However, unlike both these mutants, isoleucine mutants fail to interact with HRS, which is required for Vpumediated tetherin degradation and antagonism.

Vpu ExxxLV, isoleucine and phospho-mutants share localisation defects, in which they accumulate at the plasma membrane and in early endosomes. Interestingly, tetherin antagonism, in all of these mutants, can be rescued by C-terminal addition of a clathrinbinding motif. This implies that these mutants might be defective for the same reason: they fail to interact with the clathrin trafficking machinery. Further experiments that will elucidate this hypothesis are underway.

Date of Award2014
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorStuart Neil (Supervisor)

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