HIV-1 Envelope Glycoproteins Proteolytic Cleavage Protects Infected Cells from ADCC Mediated by Plasma from Infected Individuals.

Jérémie Prévost,Dani Vézina,Amos B Smith,Beatrice H Hahn,Halima Medjahed,Hung-Ching Chen,Andrés Finzi

doi:10.3390/v13112236

Abstract

The HIV-1 envelope glycoprotein (Env) is synthesized in the endoplasmic reticulum as a trimeric gp160 precursor, which requires proteolytic cleavage by a cellular furin protease to mediate virus-cell fusion. Env is conformationally flexible but controls its transition from the unbound “closed” conformation (State 1) to downstream CD4-bound conformations (States 2/3), which are required for fusion. In particular, HIV-1 has evolved several mechanisms that reduce the premature “opening” of Env which exposes highly conserved epitopes recognized by non-neutralizing antibodies (nnAbs) capable of mediating antibody-dependent cellular cytotoxicity (ADCC). Env cleavage decreases its conformational transitions favoring the adoption of the “closed” conformation. Here we altered the gp160 furin cleavage site to impair Env cleavage and to examine its impact on ADCC responses mediated by plasma from HIV-1-infected individuals. We found that infected primary CD4+ T cells expressing uncleaved, but not wildtype, Env are efficiently recognized by nnAbs and become highly susceptible to ADCC responses mediated by plasma from HIV-1-infected individuals. Thus, HIV-1 limits the exposure of uncleaved Env at the surface of HIV-1-infected cells at least in part to escape ADCC responses.

Highlights

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) is a class I viral membrane fusion protein which mediates viral entry using the CD4 cellular receptor
We used protein radioactive labelling of 293T cells transfected with the different infectious molecular clones (IMCs) constructs followed by Env immunoprecipitation to confirm the effect of the mutations on Env cleavage (Figure 1B–E)
Env glycoproteins expressed from the wild-type (WT) construct were efficiently cleaved while their cleavage-deficient (Cl−) counterpart yielded little to no detectable gp120 in the 293T whole-cell lysates (Figure 1B,D)

Summary

Introduction

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) is a class I viral membrane fusion protein which mediates viral entry using the CD4 cellular receptor. Proprotein convertases present in the TGN, including furin and furin-like proteases, catalyze the cleavage of the immature gp160 polyprotein [12,13,14,15] into two functional non-covalently linked subunits: the exterior gp120 subunit, which is responsible for viral attachment and the transmembrane gp subunit, which mediates membrane fusion. HIV-1 Env possesses a highly conserved furin cleavage site at the gp120-gp junction (508REKR511) which is adjacent to the hydrophobic fusion peptide at the gp N-terminus, with furin cleavage being essential for viral infectivity [6,8,17,18]. A putative secondary furin cleavage site (500KAKR503), located a few residues upstream of the primary cleavage site, has been described but its function remains unclear [17,19]

Methods

Results

Conclusion