Affinage

TMEM33

Transmembrane protein 33 · UniProt P57088

Length
247 aa
Mass
28.0 kDa
Annotated
2026-06-10
17 papers in source corpus 11 papers cited in narrative 11 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TMEM33 is a multi-pass endoplasmic reticulum (ER) transmembrane protein that shapes ER and nuclear envelope architecture and serves as a regulatory hub at the ER membrane for calcium signaling, the unfolded protein response, lipid homeostasis, and innate antiviral immunity (PMID:20498018, PMID:25612671, PMID:31048699). Its membrane-shaping function is conserved: the yeast ortholog Pom33 associates with the reticulon Rtn1 and is required for proper nuclear pore complex distribution and density, with nuclear pore targeting achieved through both karyopherin (Kap123) binding and amphipathic α-helices that preferentially bind highly curved membranes (PMID:20498018, PMID:25413348). Human TMEM33 binds multiple reticulons (RTN1A, RTN2B, RTN3C, RTN4C) and the reticulon-homology protein Arl6IP1, localizes to the ER and nuclear envelope, and suppresses reticulon-induced ER tubulation (PMID:25612671). At the ER membrane TMEM33 interacts with the polycystin-2 (PC2) channel and enhances its calcium-conductance, thereby lowering ER calcium content, impairing lysosomal calcium refilling and autophagic flux, and sensitizing cells to ER-stress-induced apoptosis (PMID:31048699); consistent with a calcium-signaling role, TMEM33 is required for VEGF-A-evoked cytosolic calcium oscillations that drive endothelial ERK/Notch signaling and developmental angiogenesis (PMID:30760708). TMEM33 also amplifies the unfolded protein response by binding the ER kinase PERK and elevating PERK/IRE1α downstream effectors (PMID:26268696). In lipid metabolism it acts downstream of the PKM2–NRF1 axis to recruit the E3 ligase RNF5 to ubiquitinate and degrade SCAP, dampening SREBP activation (PMID:34487377), and it negatively regulates virus-triggered interferon induction by promoting K48-linked ubiquitination and degradation of MAVS and acting as a decoy substrate for TBK1 (PMID:33600488).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2010 High

    Established the founding cell-biological role of the TMEM33 family by showing the yeast ortholog Pom33 controls nuclear pore complex distribution and acts within the nuclear envelope architecture network.

    Evidence Yeast genetics (synthetic lethality, deletions), Co-IP and NPC distribution microscopy in budding yeast

    PMID:20498018

    Open questions at the time
    • Did not define the membrane-shaping mechanism
    • Human ortholog function not addressed
    • Direct biochemical activity of Pom33 undefined
  2. 2014 High

    Resolved how the protein is targeted to and acts at curved membranes, identifying amphipathic α-helices that sense high membrane curvature and a karyopherin-binding mechanism for nuclear pore targeting.

    Evidence Co-IP/MS, in vitro binding, circular dichroism and liposome co-flotation, plus structure-function mutagenesis of the fission yeast ortholog Tts1

    PMID:25103238 PMID:25413348

    Open questions at the time
    • Curvature-sensing established in yeast orthologs only
    • Did not connect curvature sensing to mammalian organelle functions
    • Catalytic activity, if any, not defined
  3. 2014 Medium

    Connected human TMEM33 to ER morphology by showing it binds multiple reticulons and counteracts reticulon-driven ER tubulation, linking it to the ER-shaping machinery.

    Evidence Affinity chromatography, Co-IP, immunofluorescence and ER morphology assays in human cells

    PMID:25612671

    Open questions at the time
    • Single-lab finding
    • Mechanism of tubulation suppression not resolved
    • Functional consequence in vivo not tested
  4. 2015 Medium

    Implicated TMEM33 in the unfolded protein response by showing it is ER-stress-inducible, binds PERK, and amplifies PERK/IRE1α downstream signaling and stress-associated apoptosis/autophagy markers.

    Evidence Co-IP, fractionation and immunoblotting of UPR effectors under TMEM33 overexpression in breast cancer cells

    PMID:26268696

    Open questions at the time
    • Largely overexpression-based
    • Direct effect on PERK kinase activity not shown
    • Single-lab
  5. 2019 High

    Defined a calcium-signaling function: TMEM33 enhances the ER channel polycystin-2 to regulate ER/lysosomal calcium and autophagy, and is required for VEGF-A-evoked calcium oscillations driving angiogenesis.

    Evidence ER liposome–planar bilayer electrophysiology, reciprocal Co-IP, mouse KO and zebrafish knockdown with calcium imaging and vascular development assays

    PMID:30760708 PMID:31048699

    Open questions at the time
    • How TMEM33 modulates PC2 gating structurally is unresolved
    • Link between angiogenic calcium signaling and PC2 not directly tied together
  6. 2021 High

    Expanded TMEM33 into lipid homeostasis and innate immunity, defining E3-ligase scaffolding (RNF5→SCAP degradation) and dual antiviral suppression (MAVS degradation and TBK1 decoy).

    Evidence Co-IP, ubiquitination and kinase assays, domain-deletion mutants, mouse PKM2 KO and transcriptional reporters

    PMID:33600488 PMID:34487377

    Open questions at the time
    • Whether these roles operate simultaneously or in distinct cell states is unclear
    • Direct enzymatic role of TMEM33 not established (acts as scaffold/decoy)
  7. 2025 Medium

    Linked TMEM33's curvature/reticulon biology to a secretory ER-phagy route, showing it assembles a RAB22A/TMEM33/RTN4 complex driving RTN4-enriched curved microdomains and vesicle scission.

    Evidence Reciprocal Co-IP, TM2 domain mapping, vesicle biogenesis and extracellular vesicle/autophagy flux assays

    PMID:40301304

    Open questions at the time
    • Single-lab and newly published
    • How RAB22A recruits TMEM33 mechanistically is unresolved
    • Physiological role of the secretory route not established
  8. 2026 Medium

    Introduced a cell-intrinsic immunological role, showing TMEM33 constrains progenitor-exhausted CD8+ T cell maintenance and limits anti-tumor function.

    Evidence Murine constitutive KO, OT-I adoptive transfer, flow cytometry and B16F10-OVA tumor model (preprint)

    PMID:41509280

    Open questions at the time
    • Preprint, not yet peer-reviewed
    • Molecular mechanism in T cells (which TMEM33 pathway) not defined
    • Link to ER/calcium/UPR roles untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown how TMEM33's single membrane-shaping/curvature-sensing activity is mechanistically partitioned across its diverse roles in calcium, UPR, lipid, antiviral, and T-cell biology.
  • No unifying structural model linking curvature sensing to channel/ligase/decoy functions
  • No high-resolution structure of human TMEM33
  • Whether functions are context- or tissue-specific is unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008092 cytoskeletal protein binding 2 GO:0008289 lipid binding 2 GO:0060090 molecular adaptor activity 2 GO:0098772 molecular function regulator activity 2
Localization
GO:0005783 endoplasmic reticulum 5 GO:0005635 nuclear envelope 3
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 2 R-HSA-8953897 Cellular responses to stimuli 2 R-HSA-9612973 Autophagy 2 R-HSA-1430728 Metabolism 1 R-HSA-168256 Immune System 1
Complex memberships
RAB22A/TMEM33/RTN4 complex

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2010 Pom33 (yeast TMEM33 ortholog) is an integral transmembrane protein dynamically associated with nuclear pore complexes (NPCs) in budding yeast. Loss of Pom33 impairs NPC distribution and NPC density in the daughter nucleus, and Pom33 becomes essential for viability in the absence of the Nup84 complex or Ndc1 interaction network. Pom33 associates physically with the reticulon Rtn1. Yeast genetics (synthetic lethality, deletion mutants), co-immunoprecipitation, fluorescence microscopy of NPC distribution The Journal of cell biology High 20498018
2014 Nuclear pore targeting of yeast Pom33 requires two redundant mechanisms: direct interaction of its C-terminal domain (CTD) with the karyopherin Kap123 (identified by Co-IP/MS and confirmed by in vitro binding assay), and membrane association via amphipathic α-helices in the CTD that preferentially bind highly curved lipid membranes (shown by circular dichroism and liposome co-flotation assays). Combined impairment of both lipid-binding and Kap123-binding abolishes NPC targeting. Co-immunoprecipitation/mass spectrometry, in vitro protein-protein binding, circular dichroism, liposome co-flotation, yeast mutant analysis Journal of cell science High 25413348
2014 Fission yeast Tts1 (TMEM33 ortholog) localizes to high-curvature ER domains via an amphipathic helix in its C-terminus and functions in two distinct processes during closed mitosis: (1) promoting spindle pole body (SPB) insertion into the nuclear envelope (NE), dependent on conserved residues at the luminal interface of the third transmembrane region; and (2) modulating NPC distribution during mitotic NE expansion, dependent on the amphipathic helix. Fluorescence microscopy, domain mutagenesis, yeast deletion mutants, live-cell imaging Molecular biology of the cell High 25103238
2014 Human TMEM33 was identified as a reticulon-binding protein by affinity chromatography. TMEM33 binds reticulon 4C, reticulon 1A, reticulon 2B, reticulon 3C, and the reticulon homology domain protein Arl6IP1. TMEM33 localizes to the ER membrane and nuclear envelope, co-localizes with reticulon 4C at ER sheets and partially at ER tubules, and exogenous TMEM33 expression suppresses reticulon 4C-induced ER tubulation. Affinity chromatography, co-immunoprecipitation, immunofluorescence microscopy, ER morphology assay The Kobe journal of medical sciences Medium 25612671
2015 TMEM33 is an ER stress-inducible transmembrane protein that localizes to the ER and physically binds PERK (an ER transmembrane kinase). Exogenous TMEM33 expression increases phosphorylation of eIF2α and IRE1α and elevates their downstream effectors ATF4-CHOP and XBP1-S, as well as apoptotic markers (cleaved caspase-7, cleaved PARP) and autophagosome marker LC3II. Immunoprecipitation, immunofluorescence, subcellular fractionation, immunoblotting, transient transfection Breast cancer research and treatment Medium 26268696
2019 TMEM33 localizes to the ER in zebrafish endothelial cells and is required for cytosolic calcium oscillations in response to VEGF-A. Global or endothelial-specific knockdown of tmem33 impairs ERK phosphorylation, Notch signaling, tip cell filopodia formation, endothelial cell migration, and embryonic vascular development. Zebrafish genetic knockdown (morpholino/CRISPR), live calcium imaging, siRNA knockdown in human ECs, immunofluorescence, in vivo vascular development assays Nature communications High 30760708
2019 TMEM33 interacts with the ion channel polycystin-2 (PC2) at the ER membrane, enhancing PC2 channel opening across the physiological calcium range (demonstrated in ER liposomes fused to planar bilayers). Consequently, TMEM33 reduces intracellular calcium content in a PC2-dependent manner, impairs lysosomal calcium refilling, causes cathepsin translocation, inhibits autophagic flux upon ER stress, and sensitizes cells to apoptosis. TMEM33 invalidation in mice protects against renal ER stress. Co-immunoprecipitation, ER liposome-planar bilayer electrophysiology, mouse TMEM33 knockout, siRNA knockdown, calcium imaging, autophagy and apoptosis assays Nature communications High 31048699
2021 TMEM33 acts as a negative regulator of virus-triggered interferon induction via two mechanisms: (1) it promotes K48-linked ubiquitination and degradation of MAVS; (2) it acts as a decoy substrate for TBK1, reducing phosphorylation of MITA/IRF3. TMEM33 co-localizes with and interacts with RLR cascade components at the ER. The N-terminal TM1 and TM2 domains of TMEM33 are required for IFN suppression. Co-immunoprecipitation, ubiquitination assays, kinase phosphorylation assays, domain deletion mutants, IFN promoter reporter assay, siRNA knockdown, zebrafish cell line overexpression PLoS pathogens High 33600488
2021 TMEM33 functions as a downstream effector of PKM2 in controlling lipid homeostasis. Loss of PKM2 upregulates TMEM33, which recruits the E3 ubiquitin ligase RNF5 to promote proteasomal degradation of SCAP (SREBP-cleavage activating protein), thereby reducing SREBP activation and lipid synthesis. TMEM33 transcription is controlled by NRF1, whose cleavage and activation are regulated by PKM2 levels. Co-immunoprecipitation, ubiquitination assay, protein stability assay, siRNA/shRNA knockdown, mouse PKM2 knockout, transcriptional reporter assays, immunoblotting The EMBO journal High 34487377
2025 TMEM33 physically interacts with RAB22A and binds the TM2 domain of ER-shaping protein RTN4, forming a RAB22A/TMEM33/RTN4 complex. This assembly promotes RTN4 homo-oligomerization, generating RTN4-enriched microdomains of high ER curvature that drive bud scission of RTN4-positive vesicles. These vesicles develop into noncanonical autophagosomes that are secreted as extracellular vesicles via the Rafeesome pathway, constituting a secretory ER-phagy route that bypasses lysosomal degradation. Co-immunoprecipitation, domain mapping (TM2 binding), fluorescence microscopy, vesicle biogenesis assays, extracellular vesicle isolation, autophagy flux assays Cell discovery Medium 40301304
2026 TMEM33 deletion in CD8+ T cells enhances their anti-tumor function. Tmem33 knockout mice show delayed melanoma growth and increased CD8+ T cell infiltration. TMEM33 acts cell-intrinsically in CD8+ T cells to constrain TCF-1+PD-1+ progenitor-exhausted T cell (Tpex) maintenance; its deletion promotes Tpex accumulation, elevated effector function, and reduced exhaustion. Ex vivo deletion also enhanced polyclonal activation of naïve CD8+ T cells. Murine constitutive knockout, adoptive cell transfer (OT-I cells), flow cytometry, ex vivo T cell activation assays, B16F10-OVA tumor model bioRxivpreprint Medium 41509280

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 tmem33 is essential for VEGF-mediated endothelial calcium oscillations and angiogenesis. Nature communications 82 30760708
2010 Pom33, a novel transmembrane nucleoporin required for proper nuclear pore complex distribution. The Journal of cell biology 78 20498018
2021 PKM2-TMEM33 axis regulates lipid homeostasis in cancer cells by controlling SCAP stability. The EMBO journal 50 34487377
2015 TMEM33: a new stress-inducible endoplasmic reticulum transmembrane protein and modulator of the unfolded protein response signaling. Breast cancer research and treatment 34 26268696
2014 Tts1, the fission yeast homologue of the TMEM33 family, functions in NE remodeling during mitosis. Molecular biology of the cell 29 25103238
2014 Nuclear pore targeting of the yeast Pom33 nucleoporin depends on karyopherin and lipid binding. Journal of cell science 28 25413348
2014 Identification and characterization of TMEM33 as a reticulon-binding protein. The Kobe journal of medical sciences 24 25612671
2021 A novel role of Zebrafish TMEM33 in negative regulation of interferon production by two distinct mechanisms. PLoS pathogens 23 33600488
2019 TMEM33 regulates intracellular calcium homeostasis in renal tubular epithelial cells. Nature communications 23 31048699
2024 miR-29a-5p rescues depressive-like behaviors in a CUMS-induced mouse model by facilitating microglia M2-polarization in the prefrontal cortex via TMEM33 suppression. Journal of affective disorders 7 38821373
2021 MiR-103a-3p aggravates renal cell carcinoma by targeting TMEM33. American journal of translational research 7 34956484
2025 The assembly of RAB22A/TMEM33/RTN4 initiates a secretory ER-phagy pathway. Cell discovery 5 40301304
2021 Analysis of the Putative Nucleoporin POM33 in the Filamentous Fungus Sordaria macrospora. Journal of fungi (Basel, Switzerland) 4 34575720
2024 Endoplasmic reticulum localized TMEM33 domain-containing protein is crucial for all life cycle stages of the malaria parasite. Molecular microbiology 3 38238886
2025 TMEM33, an oncogene regulated by miR-214-3p, promotes the progression of lung adenocarcinoma through the Wnt/β-catenin signaling pathway. Oncology research 2 40191724
2026 TMEM33 deletion potentiates anti-tumor CD8+ T cell immunity. bioRxiv : the preprint server for biology 0 41509280
2026 Decellularized extracellular matrix hydrogel-mediated EVs therapy alleviates diabetic erectile dysfunction by targeting the miR-203a-3p/TMEM33 Axis. Journal of nanobiotechnology 0 41981572

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