The V3 Loop of HIV-1 Env Determines Viral Susceptibility to IFITM3 Impairment of Viral Infectivity

Abstract

Interferon-inducible transmembrane proteins (IFITMs) inhibit a broad spectrum of viruses, including HIV-1. IFITM proteins deter HIV-1 entry when expressed in target cells and also impair HIV-1 infectivity when expressed in virus producer cells. However, little is known about how viruses resist IFITM inhibition. In this study, we have investigated the susceptibilities of different primary isolates of HIV-1 to the inhibition of viral infectivity by IFITMs. Our results demonstrate that the infectivity of different HIV-1 primary isolates, including transmitted founder viruses, is diminished by IFITM3 to various levels, with strain AD8-1 exhibiting strong resistance. Further mutagenesis studies revealed that HIV-1 Env, and the V3 loop sequence in particular, determines the extent of inhibition of viral infectivity by IFITM3. IFITM3-sensitive Env proteins are also more susceptible to neutralization by soluble CD4 or the 17b antibody than are IFITM3-resistant Env proteins. Together, data from our study suggest that the propensity of HIV-1 Env to sample CD4-bound-like conformations modulates viral sensitivity to IFITM3 inhibition.IMPORTANCE Results of our study have revealed the key features of the HIV-1 envelope protein that are associated with viral resistance to the IFITM3 protein. IFITM proteins are important effectors in interferon-mediated antiviral defense. A variety of viruses are inhibited by IFITMs at the virus entry step. Although it is known that envelope proteins of several different viruses resist IFITM inhibition, the detailed mechanisms are not fully understood. Taking advantage of the fact that envelope proteins of different HIV-1 strains exhibit different degrees of resistance to IFITM3 and that these HIV-1 envelope proteins share the same domain structure and similar sequences, we performed mutagenesis studies and determined the key role of the V3 loop in this viral resistance phenotype. We were also able to associate viral resistance to IFITM3 inhibition with the susceptibility of HIV-1 to inhibition by soluble CD4 and the 17b antibody that recognizes CD4-binding-induced epitopes.KEYWORDS IFITM, envelope protein, human immunodeficiency virus T he interferon-inducible transmembrane proteins (IFITMs) inhibit a broad spectrum of viruses, including influenza viruses, West Nile virus, dengue virus, yellow fever virus, Marburg virus, Ebola virus, severe acute respiratory syndrome (SARS) coronavirus, human immunodeficiency virus type 1 (HIV-1), and others (1-5). The importance of IFITM proteins in antiviral defense is further demonstrated by the decreased survival of ifitm3 knockout mice upon infection by influenza A virus (6, 7). Furthermore, an ifitm3 single nucleotide polymorphism, rs12252-C, which leads to the expression of a truncated version of the IFITM3 protein with impaired antiviral activity, is associated with

Interference with the production of infectious viral particles and bimodal inhibition of replication are broadly conserved antiviral properties of IFITMs

“…This heterogeneous behavior allowed us to use genetic elements swapping between IFITM-resistant and –susceptible viruses and to point to the specificities in the mode of virion assembly rather than to the viral glycoprotein as a dominant factor of susceptibility towards IFITMs. However, in agreement with recent studies in the literature [ 23 , 47 , 48 ], we also show that, contrarily to X4-tropic, R5-tropic HIV-1 strains become resistant to IFITM3, likely underlying a novel role for co-receptors in the interplay between HIV and IFITMs. Finally, we have re-examined the effects played by IFITMs during spreading infections and we now reveal that they are mechanistically due to the concurrent action exerted by IFITMs both in target cells protection and in the production of virions of reduced infectivity.…”

Porcine MKRN1 Modulates the Replication and Pathogenesis of Porcine Circovirus Type 2 by Inducing Capsid Protein Ubiquitination and Degradation

“…During viral infection, the virus is recognized by pathogen recognition receptors of infected cells, which trigger signaling cascades to initiate innate intracellular antiviral defenses and to restrict viral replication (29)(30)(31)(32). Three protein degradation systems (the ubiquitin-proteasome system [UPS], lysosomes, and the autophagy system) contribute to the maintenance of protein homeostasis, as well as antiviral defenses against different viral infections (33,34).…”

Functional Mapping of Regions Involved in the Negative Imprinting of Virion Particle Infectivity and in Target Cell Protection by Interferon-Induced Transmembrane Protein 3 against HIV-1

“…Despite the fact that the exact molecular mechanism through which IFITMs act remains unclear, virions produced in the presence of IFITMs exhibit an impaired ability to undergo fusion with cellular membranes, the same step that hinders fusion between the membranes of incoming virions and IFITM-decorated endosomes during target cell infection (15,23,37,40,(43)(44)(45). In the case of HIV-1, partial to complete resistance to this antiviral effect has been shown to be conferred by R5-tropic envelope proteins that use the CCR5 chemokine receptor to access target cells (16,46,47). It appears, therefore, that the antiviral effects that IFITMs have on membrane fusion can be countered through the use of specific envelope glycoproteins or through the engagement of specific coreceptors on target cells.…”