IFITM2

IFITM2 is an interferon-induced transmembrane protein that functions primarily as a broad-spectrum antiviral effector and endosomal trafficking regulator, with additional roles in apoptosis, innate immune signaling, and cell differentiation. Localized predominantly to late endosomes and lysosomes via a YXXφ endocytic motif and phosphoinositide interactions, IFITM2 restricts enveloped viruses—including HCV, SARS-CoV-2, RVFV, HIV-1, and PRV—by blocking viral membrane fusion at the endosomal entry stage, a function dependent on S-palmitoylation (PMID:26354436, PMID:23720721, PMID:33563656, PMID:28630320); paradoxically, endogenous IFITM2 in lung epithelial cells is hijacked by SARS-CoV-2 as a proviral cofactor essential for efficient replication of all variants of concern (PMID:35543509). Beyond antiviral defense, IFITM2 promotes caspase-dependent, p53-independent apoptosis (PMID:19544527), interacts with MDA5 to amplify IFN-β signaling (PMID:37112847), senses neutrophil extracellular trap DNA on CD4+ T cells via ENO1/MPO to drive RAP1B-ERK–mediated Treg differentiation (PMID:40892462), regulates endocytic vesicle formation and AKT/Wnt signaling in neural radial glial cells during cortical development (PMID:40052215), and forms a complex with MYCT1 to govern endolysosomal trafficking and mTORC1 activity in endothelial cells (PMID:41880193).

1. 2003 Medium

   The first interaction partner of IFITM2 was identified—adenovirus precursor terminal protein—suggesting IFITM2 could link viral infection to host apoptosis, though the physiological relevance of this interaction remained uncertain.

   Evidence Yeast two-hybrid screen from HeLa cDNA library with inducible expression and DNA fragmentation assays

   PMID:18159223

   Open questions at the time

   • Yeast two-hybrid interaction not confirmed by reciprocal Co-IP or endogenous validation
   • Relevance to natural adenovirus infection cycle unclear
   • Mechanism linking pTP binding to apoptosis induction unresolved
2. 2009 High

   IFITM2 was established as a pro-apoptotic effector that induces G1 arrest and caspase-dependent cell death independently of p53, revealing a non-antiviral function for the protein.

   Evidence Transient transfection in multiple cell lines with Annexin-V, TUNEL, cell cycle analysis, and caspase inhibitor experiments; siRNA knockdown partially rescued etoposide/UV-induced apoptosis

   PMID:19544527

   Open questions at the time

   • Downstream apoptotic pathway (intrinsic vs. extrinsic) not fully delineated
   • Physiological contexts triggering IFITM2-mediated apoptosis in vivo unknown
   • Relationship between membrane topology and apoptotic function unresolved
3. 2013 High

   The antiviral mechanism of IFITM2 was pinpointed to inhibition of viral membrane fusion at endosomes rather than effects on attachment or endocytosis, establishing IFITM2 as a fusion-stage restriction factor distinct from IFITM1 in its vesicular localization.

   Evidence Overexpression/knockdown with step-by-step entry dissection (attachment, endocytosis, fusion) for RVFV; subcellular localization imaging

   PMID:23720721

   Open questions at the time

   • Biophysical mechanism by which IFITM2 prevents lipid mixing/hemifusion not determined
   • Whether IFITM2 alters membrane rigidity or curvature directly untested
4. 2015 High

   The molecular determinants of IFITM2 anti-HCV activity and localization were defined: S-palmitoylation is essential for antiviral function, while the N-terminal tyrosine-based motif governs late endosome/lysosome targeting but is dispensable for restriction.

   Evidence Site-directed mutagenesis of palmitoylation sites and tyrosine residue, subcellular fractionation and colocalization, HCV entry assays in hepatocytes

   PMID:26354436

   Open questions at the time

   • How palmitoylation mechanistically enables fusion block unclear
   • Identity of palmitoyl acyltransferase(s) modifying IFITM2 not established
5. 2017 High

   A truncated IFITM2 isoform (Δ20) was shown to differentially restrict X4-tropic but not R5-tropic HIV-1, with coreceptor C-terminal identity determining susceptibility, revealing tropism-dependent antiviral specificity.

   Evidence Overexpression/siRNA in macrophages and dendritic cells, chimeric CXCR4/CCR5 swap constructs, HIV-1 entry assays

   PMID:28630320

   Open questions at the time

   • How the CCR5 C-terminus confers resistance to Δ20 IFITM2 restriction mechanistically unknown
   • In vivo relevance of Δ20 isoform expression levels in CD4+ T cells not quantified
6. 2019 Medium

   Post-transcriptional regulation of IFITM2 was uncovered: G3BP1/2 RNA-binding proteins control IFITM2 protein accumulation via 3'-UTR interactions and MEK signaling, establishing a stress granule–linked regulatory axis.

   Evidence G3BP knockdown, MEK inhibition, 3'-UTR reporter assays in MCF7 cells

   PMID:31172368

   Open questions at the time

   • Direct RNA-binding sites on IFITM2 mRNA not mapped
   • Whether G3BP-IFITM2 regulation operates during viral infection untested
   • Single cell line used
7. 2020 Medium

   IFITM2 was shown to restrict pseudorabies virus via a cholesterol-dependent mechanism in endosomes, extending its antiviral breadth to alphaherpesviruses and implicating cholesterol homeostasis in its restriction mechanism.

   Evidence Overexpression/knockdown antiviral assays with cholesterol pathway inhibitors and viral attachment/entry assays

   PMID:32745511

   Open questions at the time

   • Whether IFITM2 directly alters cholesterol distribution or acts indirectly unresolved
   • Single lab, not independently replicated
8. 2021 High

   IFITM2 was identified as the predominant IFITM restricting SARS-CoV-2, but the polybasic furin cleavage site in Spike enables partial evasion by permitting pH-independent entry, revealing a viral countermeasure to IFITM-mediated restriction.

   Evidence siRNA knockdown, pseudovirus and authentic SARS-CoV-2 assays, pharmacological entry-route dissection, IFN treatment with IFITM2 depletion

   PMID:33563656

   Open questions at the time

   • Whether SARS-CoV-2 variants with altered furin site processing differentially evade IFITM2 not systematically tested at time of study
9. 2022 High

   A paradigm shift emerged: endogenous IFITM2 in lung cells acts as a proviral cofactor hijacked by SARS-CoV-2, with depletion reducing viral production by >4 logs across all variants of concern; an N-terminal antibody blocked this proviral role, establishing IFITM2 as a therapeutic target.

   Evidence siRNA knockdown in Calu-3 and iPSC-derived alveolar type II cells, authentic SARS-CoV-2 VOC infection, anti-IFITM2 antibody treatment

   PMID:35543509

   Open questions at the time

   • Molecular mechanism by which IFITM2 facilitates rather than restricts SARS-CoV-2 entry not fully delineated
   • Whether proviral function extends to other coronaviruses unknown
10. 2023 Medium

    IFITM2 was found to interact with MDA5 and amplify IFN-β production, connecting the protein to innate immune signaling beyond its direct antiviral membrane function; the N-terminal domain is required for both antiviral activity and IFN-β activation.

    Evidence Co-immunoprecipitation, MDA5 knockdown epistasis, IFN-β luciferase reporter, N-terminal deletion analysis

    PMID:37112847

    Open questions at the time

    • Single Co-IP without reciprocal validation or endogenous stoichiometry assessment
    • Whether IFITM2-MDA5 interaction occurs in primary immune cells untested
    • Domain on MDA5 mediating interaction not mapped
11. 2024 Medium

    IFITM2 was shown to promote osteogenic differentiation via enhancement of canonical Wnt signaling, broadening its functional repertoire to skeletal biology.

    Evidence siRNA knockdown in C3H10T1/2 cells, osteogenic assays, Wnt luciferase reporter, immunohistochemistry in bone

    PMID:38404731

    Open questions at the time

    • In vivo bone phenotype from IFITM2 loss not shown
    • Mechanism of Wnt pathway activation by IFITM2 not determined
    • Single cell line used
12. 2025 High

    IFITM2 was established as a critical endocytic regulator in radial glial cells during cortical development: the YXXφ motif and K82/K87 phosphoinositide-binding residues drive vesicle formation and polarized PI(3,4)P2 distribution, coupling endocytosis to AKT/GSK3β/Wnt signaling.

    Evidence Conditional IFITM2 knockout, endocytic motif mutagenesis, phosphoinositide binding assays, live imaging, phospho-signaling Western blots in mouse and human models

    PMID:40052215

    Open questions at the time

    • Whether IFITM2 endocytic function in RGCs also modulates viral susceptibility in the developing brain untested
    • Structural basis of phosphoinositide interaction not resolved
13. 2025 Medium

    IFITM2 was discovered to function as a NET-DNA receptor on CD4+ T cells, coupling ENO1/MPO-mediated membrane recruitment to RAP1B-ERK signaling and Treg differentiation during sepsis, establishing a novel immunoregulatory role entirely distinct from antiviral defense.

    Evidence Co-immunoprecipitation, siRNA knockdown, ENO1 inhibition in vivo, Treg differentiation assays, CLP sepsis mouse model

    PMID:40892462

    Open questions at the time

    • Whether IFITM2-mediated Treg induction operates in non-sepsis inflammatory contexts unknown
    • Direct DNA-binding domain on IFITM2 not mapped
    • Single lab, novel mechanism awaiting independent confirmation
14. 2026 Medium

    IFITM2 was found to form a physical complex with MYCT1 in endothelial cells, where loss of MYCT1 causes IFITM2 accumulation in early endosomes leading to mTORC1 hyperactivation and impaired adipose tissue energy storage, linking IFITM2 to endolysosomal trafficking and metabolic regulation.

    Evidence Endothelial-specific MYCT1 knockout mouse, Co-IP of MYCT1–IFITM2 complex, endosome imaging, mTORC1 activity assays

    PMID:41880193

    Open questions at the time

    • Whether IFITM2 directly regulates mTORC1 or acts through altered cargo delivery not resolved
    • Stoichiometry and structural basis of MYCT1-IFITM2 complex unknown
    • Single lab study

• The biophysical mechanism by which IFITM2 blocks viral membrane fusion—whether through direct alteration of membrane curvature, rigidity, cholesterol distribution, or hemifusion intermediate stabilization—remains structurally unresolved; additionally, how the same protein can act as both an antiviral restriction factor and a proviral cofactor for SARS-CoV-2 depending on cellular context is mechanistically unexplained.
• No high-resolution structure of IFITM2 in a membrane environment
• Molecular switch between antiviral and proviral functions not identified
• Integration of antiviral, apoptotic, signaling, and developmental functions into a unified model lacking