Affinage

EPB41L4B

Band 4.1-like protein 4B · UniProt Q9H329

Length
900 aa
Mass
99.7 kDa
Annotated
2026-06-09
11 papers in source corpus 9 papers cited in narrative 11 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

EPB41L4B (Lulu2/Ehm2/EHM2) is a FERM-domain protein that organizes apical junctional actomyosin in epithelial cells by directly binding and activating the RhoGEF p114RhoGEF at apical cell-cell boundaries, driving RhoA activation and assembly of the circumferential actomyosin belt (PMID:22006950). This activating interaction is gated by atypical protein kinase C, which phosphorylates the FERM-adjacent domain of EPB41L4B to disrupt p114RhoGEF binding (PMID:22006950). The pathway is positioned downstream of the apical polarity determinant CRB3A, which recruits both EPB41L4B and p114RhoGEF to the cell periphery through its cytoplasmic tail to amplify RhoA signaling via ROCK1/2 (PMID:26217016); engagement specifically through the CRB3 FERM-binding domain also makes EPB41L4B an essential mediator of CRB3-dependent endocytic trafficking, amphiregulin secretion, and mammary epithelial proliferation (PMID:30440051). A plasma-membrane-confined splice isoform, Ehm2/1, additionally stabilizes E-cadherin at the cell surface by inhibiting its ubiquitination (PMID:36422008). EPB41L4B expression is induced by androgen in androgen-receptor-expressing cells (PMID:14521927).

Mechanistic history

Synthesis pass · year-by-year structured walk · 5 steps
  1. 2003 Low

    Established EPB41L4B/EHM2 as a hormone-responsive FERM-domain gene, defining its molecular class and identifying multiple isoforms before any functional role was known.

    Evidence expression profiling, RT-PCR and Western blot with DHT vs dexamethasone treatment in AR-expressing cells

    PMID:14521927

    Open questions at the time
    • No protein-level function demonstrated
    • Mechanism linking androgen receptor to EHM2 transcription not defined
    • Distinct roles of the two isoforms unresolved
  2. 2011 High

    Defined the core molecular function: how EPB41L4B controls cortical actomyosin, by showing it directly activates p114RhoGEF at apical junctions, and revealed aPKC phosphorylation as the negative switch on this interaction.

    Evidence RNAi with circumferential belt phenotype, co-IP/interaction assays, immunofluorescence, and phosphorylation/domain-mutagenesis assays in epithelial cells

    PMID:22006950

    Open questions at the time
    • Structural basis of the FERM-p114RhoGEF interaction not resolved
    • How the aPKC phospho-switch is spatially controlled at junctions unclear
  3. 2015 High

    Placed EPB41L4B within an apical polarity hierarchy by showing CRB3A recruits it and p114RhoGEF to the periphery to drive RhoA-ROCK signaling, connecting a polarity receptor to actomyosin output.

    Evidence ectopic CRB3A expression in HeLa cells, RhoA activation assays, CRB3A cytoplasmic-tail domain mutagenesis (epistasis), immunofluorescence

    PMID:26217016

    Open questions at the time
    • Direct CRB3A-EPB41L4B binding interface not mapped here
    • Integration with the aPKC phospho-switch not addressed
  4. 2018 Medium

    Extended EPB41L4B function beyond actomyosin to membrane trafficking, showing it acts through the CRB3 FERM-binding domain to control endocytosis, amphiregulin secretion, and proliferation.

    Evidence CRB3 domain-deletion mutants, EPB41L4B knockdown/knockout, endosome quantification, AREG secretion and 3D acini assays in mammary epithelial cells

    PMID:30440051

    Open questions at the time
    • Molecular mechanism linking EPB41L4B to endosomal trafficking not defined
    • Relationship between trafficking role and p114RhoGEF/RhoA activity unclear
  5. 2022 Medium

    Identified an isoform-specific mechanism for adhesion control, showing membrane-localized Ehm2/1 stabilizes E-cadherin by blocking its ubiquitination.

    Evidence colocalization, E-cadherin half-life/stability and ubiquitination assays, isoform overexpression/knockdown in MCF-7 cells

    PMID:36422008

    Open questions at the time
    • The ubiquitin ligase whose activity is inhibited is not identified
    • Whether stabilization is direct or via junctional actomyosin remodeling is unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the junctional actomyosin-activating function, the CRB3-dependent trafficking function, and the isoform-specific E-cadherin stabilization mechanistically integrate within a single regulatory program remains unresolved.
  • No structural model of EPB41L4B domain interactions
  • No unifying mechanism connecting actomyosin, trafficking and adhesion roles
  • Cancer-context phenotypes rest largely on single-lab correlative knockdown studies

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 2 GO:0008092 cytoskeletal protein binding 1
Localization
GO:0005886 plasma membrane 3
Pathway
R-HSA-162582 Signal Transduction 2 R-HSA-5653656 Vesicle-mediated transport 1
Partners
ARHGEF18CDH1CRB3PATJ

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2011 Lulu2 (EPB41L4B) localizes along apical cell-cell boundaries in epithelial cells and is required for organization of the circumferential actomyosin belt; it directly interacts with and activates p114RhoGEF at apical cell-cell junctions to regulate actomyosin contractility. RNAi knockdown with phenotypic readout, co-immunoprecipitation/interaction assays, localization by immunofluorescence The Journal of cell biology High 22006950
2011 The interaction between Lulu2 and p114RhoGEF is negatively regulated by phosphorylation of the FERM-adjacent domain of Lulu2 by atypical protein kinase C (aPKC). Phosphorylation assay, domain mutagenesis, interaction/activity assays The Journal of cell biology Medium 22006950
2011 Patj (an apical cell polarity regulator) recruits p114RhoGEF to apical cell-cell boundaries via PDZ domain-mediated interaction, placing Patj upstream of the Lulu2-p114RhoGEF actomyosin regulatory system. Co-immunoprecipitation, PDZ domain interaction assays, localization experiments The Journal of cell biology Medium 22006950
2015 CRB3A recruits Ehm2 (EPB41L4B) and p114RhoGEF to the cell periphery via functional motifs in its cytoplasmic tail, and Ehm2 acts as an activator of p114RhoGEF downstream of CRB3A to increase RhoA activation and reorganize the cytoskeleton into a circumferential actomyosin belt; ROCK1/2 are critical effectors downstream of this pathway. Ectopic expression of CRB3A in HeLa cells, RhoA activation assays, epistasis by domain mutation of CRB3A cytoplasmic tail, immunofluorescence localization Molecular and cellular biology High 26217016
2018 EPB41L4B is an essential mediator of CRB3-driven mammary epithelial cell proliferation and CRB3-dependent changes in endocytic trafficking; this function requires the FERM-binding domain (FBD) of CRB3 but not its PDZ-binding domain, indicating EPB41L4B acts downstream of the CRB3 FBD to regulate endosomal trafficking and amphiregulin (AREG) secretion. Ectopic CRB3 expression, EPB41L4B knockdown/knockout, CRB3 domain-deletion mutants, endosome size/number quantification, AREG secretion measurement, 3D acini culture PloS one Medium 30440051
2006 Ehm2 overexpression in prostate cancer cells decreases adhesion to collagen IV, as shown by transient overexpression and RNAi knockdown experiments. Transient overexpression, RNA interference, collagen IV adhesion assay The Prostate Low 16927306
2010 Knockdown of Ehm2 in breast cancer cells decreases matrix metalloproteinase-9 (MMP-9) mRNA, protein, and enzymatic activity, leading to reduced invasion, and also induces apoptosis. Hammerhead ribozyme transgene knockdown, RT-PCR, Western blot, MMP-9 activity assay, invasion assay, flow cytometry Molecular cancer research : MCR Low 21047774
2013 Ehm2 knockdown in keratinocytes (HaCaT cells) reduces cellular adhesion and migration/motility, and is associated with reduced NWasp protein expression, placing NWasp downstream of Ehm2 in cytoskeletal regulation. Anti-Ehm2 transgene knockdown, migration/adhesion assays, Western blot for NWasp Journal of dermatological science Low 23664528
2019 The two Ehm2 splice isoforms differ in subcellular localization: Ehm2/1 is confined to the plasma membrane, while Ehm2/2 localizes to both plasma membrane and cytoplasm. Ehm2/1 overexpression inhibits growth/invasion/migration and upregulates E-cadherin while downregulating N-cadherin and Snail1, whereas Ehm2/2 overexpression increases invasiveness and has opposite effects on EMT markers. Immunofluorescence for localization, overexpression and knockdown of isoforms in A549 cells, in vitro invasion/migration/viability assays, Western blot for EMT markers International journal of oncology Low 30816447
2022 Ehm2/1 (isoform 1) co-localizes with E-cadherin at the plasma membrane of breast cancer cells, increases E-cadherin protein stability and half-life, and inhibits E-cadherin ubiquitination; downregulation of Ehm2/1 promotes E-cadherin ubiquitination. Co-localization by immunofluorescence, E-cadherin half-life/stability assays, ubiquitination assay, overexpression and knockdown in MCF-7 cells, migration/invasion assays Carcinogenesis Medium 36422008
2003 Androgen (DHT) specifically induces EHM2 expression in androgen receptor-expressing cells but not dexamethasone, establishing EHM2 as an androgen-regulated gene encoding a FERM-domain protein. The gene produces at least two isoforms: a 3.8 kb transcript (504 aa) and a brain-specific 5.8 kb transcript (913 aa). Expression profiling, quantitative RT-PCR, Western blotting, hormone treatment (DHT vs. dexamethasone), genomic and phylogenetic analysis Biochemical and biophysical research communications Low 14521927

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 Lulu2 regulates the circumferential actomyosin tensile system in epithelial cells through p114RhoGEF. The Journal of cell biology 77 22006950
2000 Molecular cloning of a novel NF2/ERM/4.1 superfamily gene, ehm2, that is expressed in high-metastatic K1735 murine melanoma cells. Genomics 29 10783258
2006 Increased expression of the metastasis-associated gene Ehm2 in prostate cancer. The Prostate 23 16927306
2015 CRB3A Controls the Morphology and Cohesion of Cancer Cells through Ehm2/p114RhoGEF-Dependent Signaling. Molecular and cellular biology 21 26217016
2012 The circumferential actomyosin belt in epithelial cells is regulated by the Lulu2-p114RhoGEF system. Small GTPases 16 22790195
2010 Clinical implications of the influence of Ehm2 on the aggressiveness of breast cancer cells through regulation of matrix metalloproteinase-9 expression. Molecular cancer research : MCR 14 21047774
2003 Androgen regulation of the human FERM domain encoding gene EHM2 in a cell model of steroid-induced differentiation. Biochemical and biophysical research communications 13 14521927
2013 Expressed in high metastatic cells (Ehm2) is a positive regulator of keratinocyte adhesion and motility: The implication for wound healing. Journal of dermatological science 10 23664528
2019 Differential expression and functions of Ehm2 transcript variants in lung adenocarcinoma. International journal of oncology 8 30816447
2022 Ehm2 transcript variant 1 inhibits breast cancer progression and increases E-cadherin stability. Carcinogenesis 3 36422008
2018 CRB3 and the FERM protein EPB41L4B regulate proliferation of mammary epithelial cells through the release of amphiregulin. PloS one 2 30440051

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