HIV envelope tail truncation confers resistance to SERINC5 restriction

Tafhima Haider,Xenia Snetkov,Clare Jolly

doi:10.1073/pnas.2101450118

Tafhima Haider, Xenia Snetkov + Show 1 more

Open Access

https://doi.org/10.1073/pnas.2101450118

Copy DOI

Abstract

SERINC5 is a potent lentiviral restriction factor that gets incorporated into nascent virions and inhibits viral fusion and infectivity. The envelope glycoprotein (Env) is a key determinant for SERINC restriction, but many aspects of this relationship remain incompletely understood, and the mechanism of SERINC5 restriction remains unresolved. Here, we have used mutants of HIV-1 and HIV-2 to show that truncation of the Env cytoplasmic tail (ΔCT) confers complete resistance of both viruses to SERINC5 and SERINC3 restriction. Critically, fusion of HIV-1 ΔCT virus was not inhibited by SERINC5 incorporation into virions, providing a mechanism to explain how EnvCT truncation allows escape from restriction. Neutralization and inhibitor assays showed ΔCT viruses have an altered Env conformation and fusion kinetics, suggesting that EnvCT truncation dysregulates the processivity of entry, in turn allowing Env to escape targeting by SERINC5. Furthermore, HIV-1 and HIV-2 ΔCT viruses were also resistant to IFITMs, another entry-targeting family of restriction factors. Notably, while the EnvCT is essential for Env incorporation into HIV-1 virions and spreading infection in T cells, HIV-2 does not require the EnvCT. Here, we reveal a mechanism by which human lentiviruses can evade two potent Env-targeting restriction factors but show key differences in the capacity of HIV-1 and HIV-2 to exploit this. Taken together, this study provides insights into the interplay between HIV and entry-targeting restriction factors, revealing viral plasticity toward mechanisms of escape and a key role for the long lentiviral EnvCT in regulating these processes.

Highlights

The evolutionary arms race between human immunodeficiency virus type-1 (HIV-1) and host has allowed for efficient viral replication and transmission
Using replication-competent viral mutants, we show that Env cytoplasmic tail (EnvCT) truncation (ΔCT virus) renders both HIV-1 and HIV-2 resistant to SERINC5 and SERINC3 inhibition of infection, despite SERINC being incorporated into viral particles
To determine the consequence of EnvCT deletion for SERINC5 restriction, we used an established cotransfection assay to interrogate SERINC5 restriction [3, 4, 8, 10]. 293T cells were cotransfected with replication-competent HIV-1 or HIV-2 molecular clones encoding either a full-length (WT) or truncated (ΔCT) EnvCT alongside increasing doses of plasmid encoding SERINC5, allowing overexpression of SERINC5 in producer cells

Summary

Introduction

The evolutionary arms race between human immunodeficiency virus type-1 (HIV-1) and host has allowed for efficient viral replication and transmission. Viruses including pandemic HIV-1 and related lentiviruses have evolved to evade or directly antagonize host restriction factors, often by encoding viral accessory proteins The lentiviral accessory protein Nef antagonizes SERINC5, excluding it from incorporation into viral particles [3, 4, 8] by removing SERINC5 from the plasma membrane via AP2–dependent endocytosis [9]. The HIV-1 Env cytoplasmic tail (EnvCT) is crucial for Env trafficking to sites of virus assembly at the plasma membrane and for incorporation into virions, most importantly during viral replication in CD4+ T cells that are the main targets for HIV-1 in vivo [13,14,15]. Our data suggest a mechanism by which human lentiviruses can evade restriction that is mediated by the EnvCT but reveal key differences in the likely fitness cost imposed by this on pandemic HIV-1 and nonpandemic HIV-2

Methods

Results

Conclusion