SIV Nef Proteins Recruit the AP-2 Complex to Antagonize Tetherin and Facilitate Virion Release

Fengwen Zhang,Paul D Bieniasz,Theodora Hatziioannou,Matthew W Mcnatt,Melinda Ng,Wilmina N Landford,Ronald C Desrosiers

doi:10.1371/journal.ppat.1002039

Fengwen Zhang, Paul D Bieniasz + Show 5 more

Open Access

https://doi.org/10.1371/journal.ppat.1002039

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Abstract

Lentiviral Nef proteins have multiple functions and are important for viral pathogenesis. Recently, Nef proteins from many simian immunodefiency viruses were shown to antagonize a cellular antiviral protein, named Tetherin, that blocks release of viral particles from the cell surface. However, the mechanism by which Nef antagonizes Tetherin is unknown. Here, using related Nef proteins that differ in their ability to antagonize Tetherin, we identify three amino-acids in the C-terminal domain of Nef that are critical specifically for its ability to antagonize Tetherin. Additionally, divergent Nef proteins bind to the AP-2 clathrin adaptor complex, and we show that residues important for this interaction are required for Tetherin antagonism, downregulation of Tetherin from the cell surface and removal of Tetherin from sites of particle assembly. Accordingly, depletion of AP-2 using RNA interference impairs the ability of Nef to antagonize Tetherin, demonstrating that AP-2 recruitment is required for Nef proteins to counteract this antiviral protein.

Highlights

Human and simian immunodeficiency viruses encode several small, so called ‘accessory’, proteins that do not appear to be required for viral replication in most in vitro replication systems
We show that three amino acids in the Nef C-terminal flexible loop are important for Tetherin antagonism
We show that the interaction between Nef and AP-2 adaptor complexes is important for Tetherin downregulation from the cell surface, removal from sites of particle assembly and antagonism

Summary

Introduction

Human and simian immunodeficiency viruses encode several small, so called ‘accessory’, proteins that do not appear to be required for viral replication in most in vitro replication systems. Tetherin (BST-2/CD317/HM1.24) is a cell surface membrane protein with an unusual topology, consisting of a short N-terminal cytoplasmic tail (CT), a transmembrane domain (TM), an extracellular coiled-coil and a glycophosphatidyl inositol anchor at the C-terminus [5,6,7,8]. This topology, rather than primary sequence appears key for Tetherin’s ability to retain nascent mature viral particles at the cell membrane [9]. Tetherin appears to work by inserting either of its membrane anchors into the lipid envelope of nascent virions. The spectrum of activity of Tetherin proteins against enveloped viruses is broad and includes retroviruses, filoviruses, arenaviruses, rhabdoviruses and herpes viruses [12,13,14,15,16,17]

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