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IFITM proteins incorporated into HIV-1 virions impair viral fusion and spread.

ABSTRACT: The interferon-induced transmembrane (IFITM) proteins protect cells from diverse virus infections by inhibiting virus-cell fusion. IFITM proteins also inhibit HIV-1 replication through mechanisms only partially understood. We show that when expressed in uninfected lymphocytes, IFITM proteins exert protective effects during cell-free virus infection, but this restriction can be overcome upon HIV-1 cell-to-cell spread. However, when present in virus-producing lymphocytes, IFITM proteins colocalize with viral Env and Gag proteins and incorporate into nascent HIV-1 virions to limit entry into new target cells. IFITM in viral membranes is associated with impaired virion fusion, offering additional and more potent defense against virus spread. Thus, IFITM proteins act additively in both productively infected cells and uninfected target cells to inhibit HIV-1 spread, potentially conferring these proteins with greater breadth and potency against enveloped viruses.

SUBMITTER: Compton AA

PROVIDER: S-EPMC7104936 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

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IFITM proteins incorporated into HIV-1 virions impair viral fusion and spread.

Compton Alex A AA Bruel Timothée T Porrot Françoise F Mallet Adeline A Sachse Martin M Euvrard Marine M Liang Chen C Casartelli Nicoletta N Schwartz Olivier O

Cell host & microbe 20141126 6

The interferon-induced transmembrane (IFITM) proteins protect cells from diverse virus infections by inhibiting virus-cell fusion. IFITM proteins also inhibit HIV-1 replication through mechanisms only partially understood. We show that when expressed in uninfected lymphocytes, IFITM proteins exert protective effects during cell-free virus infection, but this restriction can be overcome upon HIV-1 cell-to-cell spread. However, when present in virus-producing lymphocytes, IFITM proteins colocalize ...[more]

PMID: 25464829

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Project description:The interferon-inducible transmembrane (IFITM) protein family represents a new class of cellular restriction factors that block early stages of viral replication; the underlying mechanism is currently not known. Here we provide evidence that IFITM proteins restrict membrane fusion induced by representatives of all three classes of viral membrane fusion proteins. IFITM1 profoundly suppressed syncytia formation and cell-cell fusion induced by almost all viral fusion proteins examined; IFITM2 and IFITM3 also strongly inhibited their fusion, with efficiency somewhat dependent on cell types. Furthermore, treatment of cells with IFN also markedly inhibited viral membrane fusion and entry. By using the Jaagsiekte sheep retrovirus envelope and influenza A virus hemagglutinin as models for study, we showed that IFITM-mediated restriction on membrane fusion is not at the steps of receptor- and/or low pH-mediated triggering; instead, the creation of hemifusion was essentially blocked by IFITMs. Chlorpromazine (CPZ), a chemical known to promote the transition from hemifusion to full fusion, was unable to rescue the IFITM-mediated restriction on fusion. In contrast, oleic acid (OA), a lipid analog that generates negative spontaneous curvature and thereby promotes hemifusion, virtually overcame the restriction. To explore the possible effect of IFITM proteins on membrane molecular order and fluidity, we performed fluorescence labeling with Laurdan, in conjunction with two-photon laser scanning and fluorescence-lifetime imaging microscopy (FLIM). We observed that the generalized polarizations (GPs) and fluorescence lifetimes of cell membranes expressing IFITM proteins were greatly enhanced, indicating higher molecularly ordered and less fluidized membranes. Collectively, our data demonstrated that IFITM proteins suppress viral membrane fusion before the creation of hemifusion, and suggested that they may do so by reducing membrane fluidity and conferring a positive spontaneous curvature in the outer leaflets of cell membranes. Our study provides novel insight into the understanding of how IFITM protein family restricts viral membrane fusion and infection.

Project description:Interferon-induced transmembrane proteins (IFITMs) are a family of interferon-inducible proteins that inhibit a broad range of viruses by interfering with viral-to-cellular membrane fusion. The antiviral activity of IFITMs is highly regulated by several posttranslational modifications and by a number of protein domains that modulate steady-state protein levels, trafficking, and antiviral effectiveness. Taking advantage of the natural diversity existing among IFITMs of different animal species, we have compared 21 IFITMs for their ability to inhibit HIV-1 at two steps, during virus entry into cells (target cell protection) and during the production of novel virion particles (negative imprinting of virion particles' infectivity). We found a high functional heterogeneity among IFITM homologs with respect to both antiviral modalities, with IFITM members that exhibit enhanced viral inhibition, while others have no ability to block HIV-1. These differences could not be ascribed to known regulatory domains and could only be partially explained through differential protein stability, implying the existence of additional mechanisms. Through the use of chimeras between active and inactive IFITMs, we demonstrate that the cross talk between distinct domains of IFITMs is an important contributor of their antiviral potency. Finally, we identified murine IFITMs as natural variants competent for target cell protection, but not for negative imprinting of virion particles' infectivity, suggesting that the two properties may, at least in principle, be uncoupled. Overall, our results shed new light on the complex relationship between IFITMs and viral infection and point to the cross talk between IFITM domains as a novel layer of regulation of their activity. IMPORTANCE IFITMs are broad viral inhibitors capable of interfering with both early and late phases of the replicative cycle of many different viruses. By comparing 21 IFITM proteins issued from different animal species for their ability to inhibit HIV-1, we have identified several that exhibit either enhanced or impaired antiviral behavior. This functional diversity is not driven by differences in known domains and can only be partly explained through differential protein stability. Chimeras between active and inactive IFITMs point to the cross talk between individual IFITM domains as important for optimal antiviral activity. Finally, we show that murine IFITMs are not capable of decreasing the infectivity of newly produced HIV-1 virion particles, although they retain target cell protection abilities, suggesting that these properties may be, in principle, disconnected. Overall, our results shed new light on the complex layers of regulation of IFITM proteins and enrich our current understanding of these broad antiviral factors.

Project description:HIV-1 incorporates a large array of host proteins into virions. Determining the host protein composition in HIV virions has technical difficulties, including copurification of microvesicles. We developed an alternative purification technique using cholesterol that differentially modulates the density of virions and microvesicles (density modification, DM) allowing for high-yield virion purification that is essential for tandem mass spectrometric and quantitative proteomic (iTRAQ) analysis. DM purified virions were analyzed using iTRAQ and validated against Optiprep (60% iodixanol) purified virions. We were able to characterize host protein incorporation in DM-purified HIV particles derived from CD4+ T-cell lines; we compared this data set to a reprocessed data set of monocyte-derived macrophages (MDM) derived HIV-1 using the same bioinformatics pipeline. Seventy-nine clustered proteins were shared between the MDM derived and T-cell derived data set. These clusters included an extensive collection of actin isoforms, HLA proteins, chaperones, and a handful of other proteins, many of which have previously been documented to interact with viral proteins. Other proteins of note were ERM proteins, the dynamin domain containing protein EH4, a phosphodiesterase, and cyclophilin A. As these proteins are incorporated in virions produced in both cell types, we hypothesize that these proteins may have direct interactions with viral proteins or may be important in the viral life cycle. Additionally, identified common set proteins are predicted to interact with >1000 related human proteins. Many of these secondary interacting proteins are reported to be incorporated into virions, including ERM proteins and adhesion molecules. Thus, only a few direct interactions between host and viral proteins may dictate the host protein composition in virions. Ultimately, interaction and expression differences in host proteins between cell types may drive virion phenotypic diversity, despite conserved viral protein-host protein interactions between cell types.

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IFITM proteins incorporated into HIV-1 virions impair viral fusion and spread.

Publications

IFITM proteins incorporated into HIV-1 virions impair viral fusion and spread.

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