Affinage

HEG1

Protein HEG homolog 1 · UniProt Q9ULI3

Length
1381 aa
Mass
147.5 kDa
Annotated
2026-06-10
36 papers in source corpus 15 papers cited in narrative 15 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

HEG1 is a large sialylated, mucin-like transmembrane protein whose cytoplasmic tail functions as a membrane anchor for the CCM signaling machinery at endothelial cell-cell junctions, where it governs flow-responsive vascular homeostasis (PMID:23814056, PMID:38099436). Its tail binds a hydrophobic pocket at the F1-F3 interface of the KRIT1 FERM domain, a site distinct from and non-overlapping with the adjacent Rap1 GTPase binding surface, allowing assembly of a KRIT1-Rap1-HEG1 ternary complex (PMID:23814056); this interaction can be displaced orthosterically by a small molecule that occupies the same pocket (PMID:33977234), and KRIT1 further engages the CCM2 paralog Ccm2l within the Heg-CCM pathway during cardiovascular development (PMID:23328253). Through this complex HEG1 stabilizes KRIT1 protein and dampens the mechanosensitive transcription factors KLF2/KLF4, acting via the MEKK3-MEK5-ERK5-MEF2 pathway, with HEG1 itself being transcriptionally and post-translationally induced by stable laminar flow (PMID:29364115, PMID:38099436); loss of endothelial HEG1 derepresses KLF2/4 and exacerbates atherosclerosis (PMID:38099436). At forming vessel junctions HEG1 drives oscillatory actomyosin contractility required for junction straightening and continuous lumen formation, a defect rescuable by optogenetic RhoA activation (PMID:39249713). HEG1 additionally controls nitric oxide bioavailability through a flow-dependent interaction with eNOS and by promoting CUL3-mediated proteasomal degradation of PHACTR1, sustaining SP1-driven eNOS transcription; its endothelial loss causes hypertension and atherosclerosis (PMID:40667131, PMID:40986512). In the liver, endothelial HEG1 sustains Wnt2/Wnt9b/Rspo3 ligand production to maintain hepatocyte canonical Wnt signaling, metabolic zonation, and protection from steatosis (PMID:35202885, PMID:42119921). Distinct from its vascular roles, HEG1 is exploited in mesothelioma and gastric cancer, where it supports tumor cell viability and proliferation (PMID:28361969, PMID:32284171) and stabilizes AKT1 by reducing its ubiquitination, a function itself regulated by the deubiquitinase USP48 (PMID:41013721).

Mechanistic history

Synthesis pass · year-by-year structured walk · 14 steps
  1. 2013 High

    Established the structural basis for how HEG1 couples to CCM signaling, showing its tail and Rap1 bind KRIT1 simultaneously rather than competitively.

    Evidence Crystal structure of the KRIT1-Rap1-HEG1 ternary complex with SPR affinity measurement and KRIT1(K570I) mutagenesis

    PMID:23814056

    Open questions at the time
    • Does not address how the complex is regulated in cells
    • No demonstration of the functional consequence of complex assembly in vivo
  2. 2013 Medium

    Placed the CCM2 paralog Ccm2l within the Heg-CCM interaction network and mapped the KRIT1 regions binding each partner, expanding the molecular roster of the pathway.

    Evidence Zebrafish morpholino epistasis and biochemical deletion/pulldown mapping

    PMID:23328253

    Open questions at the time
    • Morpholino-based, single lab
    • Direct HEG1-Ccm2l functional relationship not resolved
  3. 2017 Medium

    Identified HEG1 as a sialylated mucin-like protein supporting tumor cell viability, opening a cancer-relevant role distinct from its vascular function.

    Evidence siRNA silencing and viability assays in mesothelioma cell lines with monoclonal antibody characterization

    PMID:28361969

    Open questions at the time
    • Molecular mechanism of viability support not defined in this study
    • Single tumor type
  4. 2018 High

    Demonstrated that HEG1 stabilizes KRIT1 protein and that the pair dampens flow-responsive klf2a, linking HEG1 to mechanosensitive gene control and cardiac valve formation.

    Evidence Zebrafish loss-of-function with klf2a/notch1b reporters, Western blot, and flow manipulation

    PMID:29364115

    Open questions at the time
    • Downstream signaling pathway from KRIT1 to klf2a not dissected here
    • Mammalian validation absent in this study
  5. 2018 High

    Defined the O-glycosylated SKM9-2 epitope and its disialylated core-1 glycan structure, characterizing the post-translational decoration of HEG1.

    Evidence Truncation/alanine-scanning mutagenesis, mass spectrometry, lectin binding, and neuraminidase treatment

    PMID:30250045

    Open questions at the time
    • Functional role of the glycosylation not established
    • Limited to the antibody epitope region
  6. 2020 Medium

    Connected HEG1 to a miR-23b-dependent anti-apoptotic, anti-autophagic axis sustaining mesothelioma proliferation.

    Evidence siRNA and miRNA-inhibitor transfection with proliferation, apoptosis, and LC3-II assays

    PMID:32284171

    Open questions at the time
    • Mechanistic link between HEG1 and miR-23b unresolved
    • Single lab, cell-line only
  7. 2022 High

    Revealed a non-junctional paracrine role: liver endothelial HEG1 drives Wnt ligand production controlling hepatocyte Wnt signaling and metabolic zonation.

    Evidence Global and liver endothelial-specific knockout mice with RNA-seq, histology, and 3D vascular imaging

    PMID:35202885

    Open questions at the time
    • How HEG1 controls Wnt ligand expression mechanistically is unclear
    • Junctional/CCM contribution to this role not separated
  8. 2023 High

    Established HEG1 as a flow-induced atheroprotective regulator acting through KRIT1 and the MEKK3-MEK5-ERK5-MEF2 pathway to restrain KLF2/4.

    Evidence Flow-chamber siRNA experiments in human aortic endothelial cells plus endothelial-specific knockout mice and carotid ligation

    PMID:38099436

    Open questions at the time
    • Mechanism of HEG1 release into media not defined
    • Connection between HEG1 polarization and pathway activation incomplete
  9. 2024 High

    Showed HEG1 drives junctional actomyosin contractility needed for lumen formation, linking the complex to mechanical junction remodeling.

    Evidence Live imaging of Heg1/Myosin reporters in zebrafish CRISPR mutants with optogenetic RhoA rescue

    PMID:39249713

    Open questions at the time
    • Molecular link from HEG1-KRIT1 to RhoA/actomyosin not defined
    • Mammalian confirmation absent
  10. 2025 Medium

    Implicated HEG1 in NO bioavailability via a direct flow-dependent eNOS interaction, connecting it to blood pressure control.

    Evidence Endothelial-specific knockout mice, HEG1-eNOS co-IP, blood pressure monitoring, ACE inhibition (preprint)

    PMID:40667131

    Open questions at the time
    • Single co-IP without reciprocal/structural validation
    • Preprint not yet peer-reviewed
    • Mechanism by which HEG1 modulates eNOS activity unresolved
  11. 2025 Medium

    Identified a cancer mechanism whereby HEG1 stabilizes AKT1 by reducing its ubiquitination, with USP48 acting as the deubiquitinase stabilizing HEG1.

    Evidence Co-IP, K48-ubiquitination assays, knockdown/overexpression in gastric cancer cells, and xenografts

    PMID:41013721

    Open questions at the time
    • No structural or reconstitution data
    • Whether HEG1 acts directly on AKT1 ubiquitination is unclear
    • Single lab
  12. 2025 Medium

    Characterized a malignancy-specific keratan sulfate O-glycan modification of the HEG1 core protein in mesothelioma.

    Evidence Immunohistochemistry with endoglycosidase treatments, HPLC disaccharide analysis, and recombinant HEG1·IgG glycoform Western blots

    PMID:40525709

    Open questions at the time
    • Functional consequence of KS modification not established
    • Single lab biochemical study
  13. 2026 Medium

    Showed HEG1 promotes CUL3-mediated PHACTR1 degradation to sustain SP1-driven eNOS transcription, providing a transcriptional route to NO control and hypertension protection.

    Evidence Endothelial-specific knockout mice, proteomics/transcriptomics, ubiquitination assays, and PHACTR1 pharmacological inhibition

    PMID:40986512

    Open questions at the time
    • Direct HEG1 role in the CUL3-PHACTR1 ubiquitination machinery not structurally defined
    • Relationship to the direct eNOS interaction pathway not integrated
  14. 2026 High

    Extended the liver paracrine axis, showing endothelial HEG1 protects against steatosis via BMP signaling and Wnt2/Wnt9b/Rspo3-dependent hepatocyte fatty-acid oxidation, with RSPO3 restoration sufficient for rescue.

    Evidence Two endothelial knockout models across three liver disease models with transcriptomics, lipidomics, RSPO3 knock-in rescue, and BMP activator treatment

    PMID:42119921

    Open questions at the time
    • Upstream control of BMP signaling by HEG1 unresolved
    • Connection to CCM/junctional functions not delineated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How HEG1's molecular activities are partitioned between its junctional CCM-anchoring role, its paracrine Wnt-ligand-supporting role, and its tumor-intrinsic AKT-stabilizing role within a single protein remains unresolved.
  • No unifying mechanism linking the vascular, hepatic, and oncogenic functions
  • Role and regulation of the extensive O-glycosylation in signaling is undefined
  • No mammalian structural data on HEG1 tail function beyond the KRIT1 interface

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 2 GO:0060090 molecular adaptor activity 2
Localization
GO:0005886 plasma membrane 3
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-1266738 Developmental Biology 2 R-HSA-392499 Metabolism of proteins 2
Complex memberships
KRIT1-Rap1-HEG1 ternary complex

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2013 The KRIT1 FERM domain binds both Rap1 GTPase and the HEG1 cytoplasmic tail simultaneously; crystal structure of the KRIT1-Rap1-HEG1 ternary complex revealed that HEG1 binds in a hydrophobic pocket at the KRIT1 F1-F3 interface with no overlap with the Rap1-binding site (Kd ~1.2 µM), and Rap1 binds on the F1-F2 surface. A KRIT1(K570I) mutant with 8-fold reduced Rap1 affinity confirmed the specific ionic interaction between the F2 lobe and Rap1. Crystal structure of ternary complex, surface plasmon resonance / binding affinity measurements, mutagenesis (KRIT1 K570I) The Journal of biological chemistry High 23814056
2021 A small-molecule inhibitor (HKi2) competes orthosterically with the HEG1 cytoplasmic tail for the KRIT1 FERM domain binding pocket; crystal structure of HKi2-KRIT1 FERM confirmed it occupies the same pocket as HEG1. Acute inhibition of the HEG1-KRIT1 interaction in human endothelial cells increased KLF4 and KLF2 mRNA and protein levels and triggered PI3K-dependent Akt phosphorylation. Crystal structure of inhibitor-KRIT1 complex, in vitro colocalization displacement assay, siRNA knockdown, pharmacological inhibition in endothelial cells, genome-wide RNA-seq, zebrafish in vivo reporter FASEB bioAdvances High 33977234
2018 Zebrafish Heg1 stabilizes Krit1 protein levels; Heg1 expression is positively regulated by blood flow; both Heg1 and Krit1 dampen expression of the mechanosensitive gene klf2a, and loss of Krit1 causes increased klf2a and notch1b expression throughout the endocardium, preventing cardiac valve leaflet formation. Zebrafish genetic loss-of-function (mutants/morpholinos), in vivo reporter assays for klf2a and notch1b, Western blot for Krit1 protein levels, blood-flow manipulation experiments eLife High 29364115
2013 Ccm2l (a novel CCM2 paralog) binds CCM1/KRIT1 directly, and CCM2 overexpression can partially rescue ccm2l morphant cardiovascular defects. Deletion and mutational analyses mapped the regions of CCM1 that mediate its binding to Ccm2l, CCM2, and HEG1, placing ccm2l as a component of the Heg-CCM pathway in cardiovascular development. Morpholino knockdown in zebrafish, genetic epistasis (morpholino co-injection), biochemical binding/deletion analysis (pulldown/Co-IP) Developmental biology Medium 23328253
2017 HEG1 is a sialylated mucin-like membrane protein (~400 kDa); gene silencing of HEG1 significantly suppressed the survival and proliferation of mesothelioma cells, indicating HEG1 supports mesothelioma cell viability. siRNA gene silencing in mesothelioma cell lines, cell viability/proliferation assays, monoclonal antibody characterization (SKM9-2) Scientific reports Medium 28361969
2018 The SKM9-2 epitope on HEG1 was identified as the O-glycosylated region 893-SKSPSLVSLPT-903; the SKxPSxVS sequence is essential for antibody recognition. Mass spectrometry and lectin analysis showed the epitope contains two disialylated core 1 O-linked glycan-modified serine residues (Ser893 and Ser900), while Ser897 is not glycosylated. Truncated HEG1 binding assays, alanine scanning mutagenesis, mass spectrometry, lectin binding analysis, neuraminidase treatment Scientific reports High 30250045
2023 Stable flow induces HEG1 mRNA and protein expression in endothelial cells, promotes HEG1 translocation to the downstream side of cells and release into the media. HEG1 knockdown prevents stable flow-induced KLF2/4 expression by regulating KRIT1 and the MEKK3-MEK5-ERK5-MEF2 pathway. Endothelial-specific HEG1 knockout mice develop exacerbated atherosclerotic plaques. siRNA knockdown in human aortic endothelial cells under defined flow conditions, endothelial-specific inducible knockout mice (HEG1iECKO), partial carotid ligation model, Western blot, qPCR, immunostaining Circulation High 38099436
2025 HEG1 regulates NO bioavailability via a flow-dependent direct interaction with eNOS (NOS3) in endothelial cells. Endothelial-specific Heg1 knockout mice develop spontaneous hypertension and severe atherosclerosis, both of which are prevented by ACE inhibition. Endothelial-specific Heg1 knockout mice, co-immunoprecipitation (HEG1-eNOS interaction), blood pressure monitoring, ACE inhibitor treatment bioRxivpreprint Medium 40667131
2026 Endothelial HEG1 facilitates CUL3-mediated proteasomal degradation of PHACTR1. HEG1 deletion leads to increased PHACTR1 levels, its nuclear translocation, and suppression of SP1-mediated eNOS transcription and NO production, resulting in impaired vasodilation and hypertension. Endothelial-specific Heg1 deletion mice, proteomics, transcriptomics, ubiquitination assays, pharmacological PHACTR1 inhibition (CCG-1423), vascular function analysis European heart journal Medium 40986512
2022 Liver endothelial Heg deficiency reduces expression of Wnt ligands/agonists (Wnt2, Wnt9b, Rspo3) in endothelial cells, limiting Axin2-mediated canonical Wnt signaling and cytochrome P450 expression in hepatocytes, thereby altering liver metabolic zonation. Global (Heg-/-) and liver endothelial-specific (Lyve1-Cre;Hegfl/fl) conditional knockout mice, RNA-seq, histology, biochemical assays, 3D vascular network visualization Cellular and molecular gastroenterology and hepatology High 35202885
2026 Endothelial Heg1 deletion exacerbates hepatic steatosis under metabolic stress by downregulating BMP signaling, reducing Wnt2, Wnt9b, and Rspo3 expression in endothelial cells, which attenuates hepatocyte Wnt signaling, decreases PPARα and fatty acid oxidation enzyme expression. Restoration of RSPO3 in endothelial cells reversed the steatotic phenotype. Two endothelial-specific Heg1 knockout models, three liver disease models (HFD, MCD diet, alcohol), transcriptomics, lipidomics, RSPO3 conditional knock-in rescue, BMP activator treatment Cellular and molecular gastroenterology and hepatology High 42119921
2024 Zebrafish Heg1 is dynamically localized at endothelial cell-cell junctions during anastomosis and is required for oscillatory actomyosin contractility along junctions. In heg1 and krit1 mutants, cell-cell interfaces become entangled due to lack of junctional actomyosin contractility, preventing continuous lumen formation; optogenetic RhoA activation restores junction straightening in mutants. Live imaging with Heg1 and Myosin reporters in zebrafish, CRISPR/Cas9 mutants, optogenetic RhoA activation, confocal microscopy Angiogenesis High 39249713
2025 HEG1 stabilizes AKT1 by reducing its ubiquitination in gastric cancer cells, leading to sustained AKT signaling. The deubiquitinase USP48 directly interacts with HEG1 and stabilizes it by removing K48-linked polyubiquitin chains, preventing its proteasomal degradation. Immunoprecipitation, ubiquitination assays (K48-linked polyubiquitin chain analysis), siRNA/overexpression in gastric cancer cells, in vivo tumor xenograft, RNA-seq European journal of medical research Medium 41013721
2025 HEG1 protein is decorated with low-sulfated keratan sulfate (KS) O-glycans in malignant pleural mesothelioma; the KS modification is carried on the HEG1 core protein as demonstrated by western blot of HEG1·IgG recombinant fusion proteins secreted from KS-expressing cells, and sensitivity to endo-β-galactosidase and keratanase II but not PNGase F confirmed O-linked glycan attachment. Immunohistochemistry with endoglycosidase treatments, reversed-phase ion-pair HPLC disaccharide analysis, western blot of recombinant HEG1·IgG glycoforms Pathology international Medium 40525709
2020 HEG1 suppression in malignant mesothelioma cell lines reduces cell proliferation and induces apoptosis; microRNA-23b (miR-23b) acts downstream of HEG1 to support cell proliferation by suppressing apoptosis and autophagy (LC3-II induction). Combined inhibition of miR-23b and HEG1 showed additive antiproliferative effects. siRNA knockdown, miRNA inhibitor transfection in mesothelioma cell lines, MTS assay, Annexin V apoptosis assay, western blot (LC3-II) Biochemical and biophysical research communications Medium 32284171

Source papers

Stage 0 corpus · 36 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2007 HEG-DB: a database of predicted highly expressed genes in prokaryotic complete genomes under translational selection. Nucleic acids research 66 17933767
2017 HEG1 is a novel mucin-like membrane protein that serves as a diagnostic and therapeutic target for malignant mesothelioma. Scientific reports 54 28361969
2018 Heg1 and Ccm1/2 proteins control endocardial mechanosensitivity during zebrafish valvulogenesis. eLife 50 29364115
2015 Hericium erinaceus polysaccharide-protein HEG-5 inhibits SGC-7901 cell growth via cell cycle arrest and apoptosis. International journal of biological macromolecules 49 25703932
2023 HEG1 Protects Against Atherosclerosis by Regulating Stable Flow-Induced KLF2/4 Expression in Endothelial Cells. Circulation 43 38099436
2020 Generation and Application of the Zebrafish heg1 Mutant as a Cardiovascular Disease Model. Biomolecules 38 33198188
2020 HEG1, BAP1, and MTAP are useful in cytologic diagnosis of malignant mesothelioma with effusion. Diagnostic cytopathology 35 32441895
2013 The structure of the ternary complex of Krev interaction trapped 1 (KRIT1) bound to both the Rap1 GTPase and the heart of glass (HEG1) cytoplasmic tail. The Journal of biological chemistry 32 23814056
2013 The design and in vivo evaluation of engineered I-OnuI-based enzymes for HEG gene drive. PloS one 32 24040217
2020 HEG1 Is a Highly Specific and Sensitive Marker of Epithelioid Malignant Mesothelioma. The American journal of surgical pathology 30 32205484
2013 ccm2-like is required for cardiovascular development as a novel component of the Heg-CCM pathway. Developmental biology 29 23328253
2005 Site-specific reverse splicing of a HEG-containing group I intron in ribosomal RNA. Nucleic acids research 25 15817568
2021 LncRNA SNHG12 promotes proliferation and epithelial mesenchymal transition in hepatocellular carcinoma through targeting HEG1 via miR-516a-5p. Cellular signalling 18 33774129
2022 Hypothesis: HEG1 and claudin-4 staining will allow a diagnosis of epithelioid and biphasic mesothelioma versus non-small-cell lung carcinoma with only two stains in most cases. Histopathology 17 36008876
2008 A RNA transcript (Heg) in mononuclear cells is negatively correlated with CD14 mRNA and TSH receptor autoantibodies. Clinical and experimental immunology 17 18778364
2021 Inhibition of the HEG1-KRIT1 interaction increases KLF4 and KLF2 expression in endothelial cells. FASEB bioAdvances 16 33977234
2022 Liver Endothelial Heg Regulates Vascular/Biliary Network Patterning and Metabolic Zonation Via Wnt Signaling. Cellular and molecular gastroenterology and hepatology 14 35202885
2018 Identification of mesothelioma-specific sialylated epitope recognized with monoclonal antibody SKM9-2 in a mucin-like membrane protein HEG1. Scientific reports 14 30250045
2021 Membranous HEG1 expression is a useful marker in the differential diagnosis of epithelioid and biphasic malignant mesothelioma versus carcinomas. Pathology international 11 34240508
2006 In vivo expression of a group I intron HEG from the antisense strand of Didymium ribosomal DNA. RNA biology 10 17361110
2011 Decrease in TSH Receptor Autoantibodies during Antithyroid Treatment: Relationship with a Long Noncoding Heg RNA and Cdk1 mRNA in Mononuclear Cells. ISRN endocrinology 9 22363873
2010 Sexual mating of Botrytis cinerea illustrates PRP8 intein HEG activity. Fungal genetics and biology : FG & B 9 20093192
2019 A novel function for HEG1 in promoting metastasis in hepatocellular carcinoma. Clinical science (London, England : 1979) 8 31654571
2024 Novel chimeric antigen receptor-expressing T cells targeting the malignant mesothelioma-specific antigen sialylated HEG1. International journal of cancer 6 38212893
2022 Circ_0005397 enhances hepatocellular carcinoma progression through miR-1283/HEG1. Annals of hepatology 6 35500803
2020 HEG1-responsive microRNA-23b regulates cell proliferation in malignant mesothelioma cells. Biochemical and biophysical research communications 6 32284171
2026 Shear stress-induced endothelial HEG1 signalling regulates vascular tone and blood pressure. European heart journal 5 40986512
2024 Oscillatory contractile forces refine endothelial cell-cell interactions for continuous lumen formation governed by Heg1/Ccm1. Angiogenesis 3 39249713
2025 Flow-sensitive HEG1 controls eNOS activity to prevent endothelial dysfunction, hypertension, and atherosclerosis. bioRxiv : the preprint server for biology 1 40667131
2026 The specificity of HEG1 as mesothelioma marker depends on the differential diagnosis. Virchows Archiv : an international journal of pathology 0 41656400
2026 Liver Endothelial Heg1 Signal Limits Hepatic Steatosis via Wnt-Mediated Fatty Acid Oxidation in Hepatocytes. Cellular and molecular gastroenterology and hepatology 0 42119921
2025 Role of HEG1 and Claudin-4 Immunohistochemistry in the Differential Diagnosis of Lung Adenocarcinoma from Malignant Mesothelioma in Pleural Effusion Cytology. Turk patoloji dergisi 0 40091315
2025 Expression of Heart Development Protein With EGF-Like Domains 1 (HEG1) Decorated With Low-Sulfated Keratan Sulfate in Human Malignant Pleural Mesothelioma. Pathology international 0 40525709
2025 HEG1 promotes gastric cancer progression by stabilizing AKT1 and is functionally regulated by the deubiquitinase USP48. European journal of medical research 0 41013721
2024 [Research progress on HEG1 in cardiovascular generation and tumor development]. Zhonghua yu fang yi xue za zhi [Chinese journal of preventive medicine] 0 38228561
2024 Aberrant expression of MRAS and HEG1 as the biomarkers for osimertinib resistance in LUAD. Discover oncology 0 39560891

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