EMC2

EMC2 is a soluble cytosolic subunit of the ER membrane protein complex (EMC) that contributes to ER-associated protein biogenesis and membrane protein quality control (PMID:33964204, PMID:26190106). As an unassembled subunit, EMC2 exposes a hydrophobic surface that is shielded by the assembly factor WNK1, which binds at the EMC2-8 interface via a conserved amphipathic helix and directly competes with E3 ubiquitin ligases, so that loss of WNK1 destabilizes both EMC2 and its membrane protein clients (PMID:33964204). EMC2 physically associates with the Hsp90 chaperone machinery, an interaction conserved from yeast where EMC subunits are required for folding of Hsp90 clients (PMID:29808299). Through its scaffolding and protein-stabilization activities EMC2 controls the levels of multiple downstream proteins: it recruits the deubiquitinase USP7 to stabilize ENO1 and activate B-MYB/PDK1/AKT/mTOR signaling (PMID:40303285), cooperates with HSP90 to protect FDFT1 from ER-associated degradation and thereby support cholesterol biosynthesis (PMID:40931051), and promotes ubiquitin-proteasomal degradation of the transferrin receptor TFRC (PMID:39709720). These activities converge on ferroptosis regulation, with EMC2 generally suppressing ferroptosis susceptibility in cancer cells via the FDFT1 and TFRC axes (PMID:39709720, PMID:40931051). EMC2 also functions in the EMC2-SLC25A46-Mic19 axis that maintains ER-mitochondria contact sites (PMID:38168065), and EMC-dependent ER protein biogenesis is exploited by flaviviruses and links West Nile virus replication to ERAD-mediated cell death (PMID:26190106, PMID:31273220).

1. 2007 Low

   Early interactome mapping placed EMC2 (KIAA0103) as a candidate node binding nuclear/spliceosomal partners, before its EMC function was recognized.

   Evidence Yeast two-hybrid screen with in vitro pull-down of RASSF1C and PRP3

   PMID:17335777

   Open questions at the time

   • Pull-down only without reciprocal Co-IP or functional validation
   • Functional relevance of RASSF1C/PRP3 binding never followed up
   • No connection to EMC role established
2. 2015 Medium

   A genome-wide screen positioned EMC2 within the ERAD pathway and showed it is required for West Nile virus-induced cell death without affecting replication, indicating a role linking ER protein degradation to downstream death signaling.

   Evidence Genome-wide CRISPR-Cas9 screen validated across multiple WNV strains and cell lines, with viability and replication readouts

   PMID:26190106

   Open questions at the time

   • Mechanistic placement inferred from pathway co-membership, not biochemistry
   • Direct EMC2 substrate in the death pathway unidentified
3. 2018 Medium

   Yeast work connected EMC2 to chaperone-assisted protein folding by demonstrating physical interaction with Hsp90 and functional requirement of EMC subunits for Hsp90 client maturation.

   Evidence Co-precipitation of bacterially expressed proteins, yeast genetic epistasis with STI1, glucocorticoid receptor folding assay

   PMID:29808299

   Open questions at the time

   • TPR-independence of binding leaves the interaction interface undefined
   • Human relevance not directly tested in this study
4. 2019 Medium

   EMC2 was shown to act in flavivirus infection at or before uncoating and in viral protein biogenesis, refining where in the viral life cycle the EMC contributes.

   Evidence siRNA depletion, novel uncoating assay, ZIKV replicon system, in vivo mosquito depletion

   PMID:31273220

   Open questions at the time

   • Molecular step EMC2 performs during uncoating not resolved
   • Whether host or viral membrane proteins are the relevant clients unknown
5. 2021 High

   The assembly logic of the EMC was resolved by showing WNK1 chaperones the soluble subunit EMC2, shielding its hydrophobic surface from E3 ligases to permit complex assembly.

   Evidence Co-immunoprecipitation, amphipathic-helix mutagenesis, biochemical reconstitution, depletion with EMC client stability readout

   PMID:33964204

   Open questions at the time

   • Structure of the WNK1-EMC2 complex not solved here
   • Identity of competing E3 ligases not pinned down
6. 2023 Low

   EMC2 was first linked to ferroptosis, with overexpression inducing ROS and downregulating GPX4 in liver cancer cells.

   Evidence EMC2 overexpression with ROS, GPX4, and ferroptosis marker readouts

   PMID:37693126

   Open questions at the time

   • Single-lab overexpression study with limited mechanistic detail
   • Pathway connecting EMC2 to ROS/GPX4 unresolved
   • Direction of effect opposite to later studies, not reconciled
7. 2024 Medium

   EMC2 was assigned a direct role in iron handling and ferroptosis by showing it binds TFRC and drives its ubiquitin-proteasomal degradation, with the axis modulating ferroptosis in nasopharyngeal carcinoma.

   Evidence Co-immunoprecipitation, quantitative proteomics, ubiquitination and protease inhibition assays, rescue, xenografts

   PMID:39709720

   Open questions at the time

   • E3 ligase mediating TFRC degradation not identified
   • Whether canonical EMC is involved or EMC2 acts independently unclear
8. 2024 Medium

   EMC2 was placed upstream in the EMC2-SLC25A46-Mic19 axis required to maintain ER-mitochondria contact sites in hepatocytes.

   Evidence Mic19 liver-specific knockout with rescue, interaction studies, EM quantification of contact sites

   PMID:38168065

   Open questions at the time

   • EMC2's direct molecular role within the axis not biochemically resolved
   • Whether contact-site regulation requires the full EMC unknown
9. 2025 Medium

   EMC2 was shown to act as a scaffold recruiting the deubiquitinase USP7 to stabilize ENO1, activating oncogenic B-MYB/PDK1/AKT/mTOR signaling.

   Evidence Co-immunoprecipitation, ubiquitination assays, phospho-Western signaling readouts, in vitro and in vivo tumor growth

   PMID:40303285

   Open questions at the time

   • Whether scaffolding is EMC-dependent unknown
   • Direct USP7 and ENO1 binding surfaces on EMC2 not mapped
10. 2025 Medium

    EMC2 was shown to cooperate with HSP90 to protect FDFT1 from ERAD, sustaining cholesterol synthesis and suppressing ferroptosis, extending its chaperone-linked client-stabilization role to lipid metabolism.

    Evidence Co-immunoprecipitation, knockdown/overexpression with FDFT1 stability, cholesterol and ferroptosis assays in vitro and in vivo

    PMID:40931051

    Open questions at the time

    • Mechanism by which EMC2-HSP90 shields FDFT1 from the ERAD machinery not detailed
    • Generality across cell types beyond TNBC untested
11. 2025 Low

    Time-resolved ER proteomics implicated EMC2 in the UPR-to-apoptosis transition, with its loss delaying apoptosis during prolonged ER stress.

    Evidence Photocatalytic ER proximity labeling (CAT-ER), temporal proteomics during thapsigargin-induced UPR, EMC2 loss-of-function apoptosis kinetics

    PMID:40768357

    Open questions at the time

    • Single finding without dedicated mechanistic follow-up on EMC2
    • How EMC2 influences the apoptotic switch unknown
12. 2025 Medium

    In fission yeast, loss of the EMC2 ortholog impaired mitochondrial respiration and quiescence survival, with rescue by sterol-biosynthesis disruption and membrane fluidization implicating membrane lipid composition in the phenotype.

    Evidence oca3Δ deletion, Seahorse oxygen consumption, epistasis with erg5Δ, pharmacological membrane fluidization

    PMID:40085054

    Open questions at the time

    • Mechanistic link between EMC2 and membrane fluidity not defined
    • Conservation of the respiration phenotype in mammalian cells untested

• How EMC2's canonical EMC scaffolding role mechanistically connects to its EMC-independent client-stabilization activities (USP7-ENO1, HSP90-FDFT1, TFRC) and to ferroptosis remains unresolved.
• No structural model distinguishing EMC-bound from free EMC2 functions
• Whether ferroptosis-related activities require the intact EMC is unknown
• Opposing ferroptosis effects across cancer types not reconciled