A Genetic Screen Identifies a Critical Role for the WDR81-WDR91 Complex in the Trafficking and Degradation of Tetherin.

Radu Rapiteanu,Luther J Davis,Paul J Lehner,J Paul Luzio,Richard T Timms,James C Williamson

doi:10.1111/tra.12409

Abstract

Tetherin (BST2/CD317) is a viral restriction factor that anchors enveloped viruses to host cells and limits viral spread. The HIV‐1 Vpu accessory protein counteracts tetherin by decreasing its cell surface expression and targeting it for ubiquitin‐dependent endolysosomal degradation. Although the Vpu‐mediated downregulation of tetherin has been extensively studied, the molecular details are not completely elucidated. We therefore used a forward genetic screen in human haploid KBM7 cells to identify novel genes required for tetherin trafficking. Our screen identified WDR81 as a novel gene required for tetherin trafficking and degradation in both the presence and absence of Vpu. WDR81 is a BEACH‐domain containing protein that is also required for the degradation of EGF‐stimulated epidermal growth factor receptor (EGFR) and functions in a complex with the WDR91 protein. In the absence of WDR81 the endolysosomal compartment appears swollen, with enlarged early and late endosomes and reduced delivery of endocytosed dextran to cathepsin‐active lysosomes. Our data suggest a role for the WDR81‐WDR91 complex in the fusion of endolysosomal compartments and the absence of WDR81 leads to impaired receptor trafficking and degradation.

Highlights

As obligate intracellular parasites, viruses have evolved multiple strategies to manipulate host cellular pathways, to enable their replication and evade immune detection
A haploid genetic screen identifies a requirement for WDR81 in the Vpu-mediated downregulation of tetherin To identify novel host factors required for the HIV1-Vpu-mediated downregulation and degradation of tetherin and CD4, we performed a forward genetic screen in human near-haploid KBM7 cells
Our forward genetic screen identified a requirement for WDR81 in the human immunodeficiency virus (HIV)-Vpu-mediated degradation of tetherin

Summary

Introduction

Viruses have evolved multiple strategies to manipulate host cellular pathways, to enable their replication and evade immune detection. Tetherin inhibits the release of a wide spectrum of enveloped viruses, including human immunodeficiency virus (HIV) and Ebola, from infected cells [1,2,3,4,5,6,7,8,9,10,11,12,13] Tetherin achieves this by targeting the lipid bilayer of the viral envelope, a molecular component that cannot be mutated or eliminated. Tetherin is an interferon inducible, transmembrane protein with an unusual topology, that is key to its antiviral function It encodes an extended extra-cellular alpha helix with both extremities embedded in cellular membranes using different anchors: an N-terminal transmembrane domain and a C-terminal glycosylphosphatidyl-inositol (GPI) anchor [14,15,16,17]. Tetherin downregulation from the PM relies on clathrin-mediated endocytosis [40,43], Rab GTPase [44] and the endosomal sorting complex required for transport (ESCRT) proteins HRS [45], TSG101 [45] and UBAP1 [46]

Methods

Results

Conclusion