S-palmitoylation and ubiquitination differentially regulate interferon-induced transmembrane protein 3 (IFITM3)-mediated resistance to influenza virus
ABSTRACT The interferon (IFN)-induced transmembrane protein 3 (IFITM3) is a cellular restriction factor that inhibits infection by influenza virus and many other pathogenic viruses. IFITM3 prevents endocytosed virus particles from accessing the host cytoplasm although little is known regarding its regulatory mechanisms. Here we demonstrate that IFITM3 localization to and antiviral remodeling of endolysosomes is differentially regulated by S-palmitoylation and lysine ubiquitination. Although S-palmitoylation enhances IFITM3 membrane affinity and antiviral activity, ubiquitination decreases localization with endolysosomes and decreases antiviral activity. Interestingly, autophagy reportedly induced by IFITM3 expression is also negatively regulated by ubiquitination. However, the canonical ATG5-dependent autophagy pathway is not required for IFITM3 activity, indicating that virus trafficking from endolysosomes to autophagosomes is not a prerequisite for influenza virus restriction. Our characterization of IFITM3 ubiquitination sites also challenges the dual-pass membrane topology predicted for this protein family. We thus evaluated topology by N-linked glycosylation site insertion and protein lipidation mapping in conjunction with cellular fractionation and fluorescence imaging. Based on these studies, we propose that IFITM3 is predominantly an intramembrane protein where both the N and C termini face the cytoplasm. In sum, by characterizing S-palmitoylation and ubiquitination of IFITM3, we have gained a better understanding of the trafficking, activity, and intramembrane topology of this important IFN-induced effector protein.
- SourceAvailable from: Samad Amini-Bavil-Olyaee
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- "The IFITM isoforms are relatively small (130 amino acids) and share a common topology of two conserved transmembrane domains, a short highly conserved cytoplasmic region, and luminal amino-and carboxyl termini (Siegrist et al., 2011; Wee et al., 2012). Recent studies showed that S-palmitoylation and ubiquitination of IFITM3 play crucial roles in its function (Yount et al., 2010, 2012) and that IFITM3 may influence v-ATPase complex activity and facilitates the subcellular localization of clathrin (Wee et al., 2012). Three additional studies showed that the N-terminal 21 amino acid residues of IFITM3 are required for its antiviral activity against VSV and IAV (Everitt et al., 2012; Jia et al., 2012; Weidner et al., 2010). "
ABSTRACT: Vesicle-membrane-protein-associated protein A (VAPA) and oxysterol-binding protein (OSBP) regulate intracellular cholesterol homeostasis, which is required for many virus infections. During entry, viruses or virus-containing vesicles can fuse with endosomal membranes to mediate the cytosolic release of virions, and alterations in endosomal cholesterol can inhibit this invasion step. We show that the antiviral effector protein interferon-inducible transmembrane protein 3 (IFITM3) interacts with VAPA and prevents its association with OSBP, thereby disrupting intracellular cholesterol homeostasis and inhibiting viral entry. By altering VAPA-OSBP function, IFITM3 induces a marked accumulation of cholesterol in multivesicular bodies and late endosomes, which inhibits the fusion of intraluminal virion-containing vesicles with endosomal membranes and thereby blocks virus release into the cytosol. Consequently, ectopic expression or depletion of the VAPA gene profoundly affects IFITM3-mediated inhibition of viral entry. Thus, IFITM3 disrupts intracellular cholesterol homeostasis to block viral entry, further underscoring the importance of cholesterol in virus infection.Cell host & microbe 04/2013; 13(4):452-64. DOI:10.1016/j.chom.2013.03.006 · 12.19 Impact Factor
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ABSTRACT: Interferon inducible transmembrane (IFITM) protein family members IFITM1, 2 and 3 restrict the infection of multiple enveloped viruses. Significant enrichment of a minor IFITM3 allele was recently reported in patients who were hospitalized for seasonal and 2009 H1N1 pandemic flu. This IFITM3 allele lacks the first amino-terminal 21 amino acids and is unable to inhibit influenza A virus. In this study, we find that deleting this 21-amino acid region relocates IFITM3 from the endosomal compartments to cell periphery. This finding likely underlies the lost inhibition of influenza A virus that completes its entry exclusively within endosomes at low pH. Yet, both the wild type IFITM3 and the 21 amino acid-deletion mutant inhibit HIV-1 replication equally well. Given the pH-independent nature of HIV-1 entry, our results suggest that IFITM3 can inhibit viruses that enter cells via different routes and that its N-terminal region is specifically required for controlling pH-dependent viruses.Journal of Virology 10/2012; 86(24). DOI:10.1128/JVI.01828-12 · 4.65 Impact Factor
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ABSTRACT: Over the past few years, several groups have identified new genes that are transcriptionally induced downstream of type I interferon (IFN) signalling and that inhibit infection by individual or multiple families of viruses. Among these IFN-stimulated genes with antiviral activity are two genetically and functionally distinct families - the IFN-induced protein with tetratricopeptide repeats (IFIT) family and the IFN-induced transmembrane protein (IFITM) family. This Review focuses on recent advances in identifying the unique mechanisms of action of IFIT and IFITM proteins, which explain their broad-spectrum activity against the replication, spread and pathogenesis of a range of human viruses.Nature Reviews Immunology 12/2012; 13(1). DOI:10.1038/nri3344 · 33.84 Impact Factor