S-palmitoylation and ubiquitination differentially regulate interferon-induced transmembrane protein 3 (IFITM3)-mediated resistance to influenza virus

Laboratory of Chemical Biology and Microbial Pathogenesis, The Rockefeller University, New York, New York 10065, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 04/2012; 287(23):19631-41. DOI: 10.1074/jbc.M112.362095
Source: PubMed

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.

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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). "
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