Affinage

CRB3

Protein crumbs homolog 3 · UniProt Q9BUF7

Length
120 aa
Mass
12.9 kDa
Annotated
2026-06-09
22 papers in source corpus 13 papers cited in narrative 13 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

CRB3 is an apical transmembrane polarity protein that organizes epithelial junctions, the actin cytoskeleton, and ciliogenesis while serving as an upstream activator of tumor-suppressive Hippo signaling (PMID:14718572, PMID:28079891, PMID:37737843). Through its C-terminal ERLI (PDZ-binding) motif it directly binds Par6, with apical delivery of the Par6-aPKC complex facilitated by Morg1 and reinforced by Cdc42, to govern tight junction maturation and 3D cyst morphogenesis (PMID:14718572, PMID:23439680). A distinct FERM-binding domain mediates interaction with Merlin/NF2 to restrain RhoA-driven perijunctional actomyosin contractility and junctional tension, such that CRB3 loss produces hypercontractile, mistensioned junctions rescued by ROCK-II or myosin II inhibition (PMID:41122968); CRB3 also couples to branched-actin and capping regulators Arp3 and Eps8 and anchors phospho-ERM to support apical actin organization and membrane expansion (PMID:27358069, PMID:37840525). CRB3 promotes ciliogenesis by trafficking through Rab11-positive endosomes to the basal body, where it routes GCP6/Rab11 vesicles to CEP290 to enable γTuRC assembly; its loss causes primary cilium defects, ductal hyperplasia and tumorigenesis in vivo and abrogates responsiveness to Hedgehog and Wnt signaling (PMID:37737843). As a Hippo activator, CRB3 recruits Kibra/FRMD6 to engage LATS1/2 and inactivate YAP/TAZ, enforcing contact inhibition; this axis is suppressed transcriptionally by MUC1-C/ZEB1 occupancy of the CRB3 promoter and post-transcriptionally by METTL3-deposited m6A read by YTHDF2 to degrade CRB3 mRNA, and CRB3 downregulation drives EMT, YAP/TAZ–β-catenin activation, and cancer stem cell properties (PMID:28079891, PMID:27658423, PMID:28436991, PMID:35012593). CRB3 overexpression does not engage the presenilin/γ-secretase complex (PMID:17988153).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2004 High

    Established the molecular basis by which CRB3 engages the apical polarity machinery, showing its C-terminal ERLI motif directly binds Par6 and that this interaction tunes tight junction formation.

    Evidence Direct binding assay and ERLI-domain deletion/chimera overexpression with TJ permeability readouts in MDCK cells

    PMID:14718572

    Open questions at the time
    • Did not resolve how the Par6-aPKC complex is targeted apically
    • No structural detail of the ERLI-Par6 interface
  2. 2013 High

    Answered how the Par6-aPKC complex reaches CRB3 at the apical membrane, identifying Morg1 as the targeting factor reinforced by Cdc42.

    Evidence Reciprocal Co-IP, Morg1 depletion with forced apical aPKC rescue, monolayer TJ and 3D cyst assays in MDCK cells

    PMID:23439680

    Open questions at the time
    • Does not establish stoichiometry of the Morg1-Par6-CRB3 assembly
    • Role of Cdc42 nucleotide state not defined
  3. 2016 Medium

    Linked CRB3 to direct actin regulation by showing it binds Arp3 and Eps8 to maintain microfilament architecture underpinning the blood-testis barrier.

    Evidence Co-IP, RNAi knockdown with TJ-permeability assay in Sertoli cells, in vivo knockdown with spermatid phenotypes

    PMID:27358069

    Open questions at the time
    • Single lab; binding partners by Co-IP without reciprocal/structural validation
    • Whether CRB3 directly regulates Arp3/Eps8 activity versus localization unresolved
  4. 2016 Medium

    Extended CRB3 function beyond epithelia, demonstrating it activates Hippo to inhibit YAP and limit myelin elongation in peripheral nerve.

    Evidence In vivo immunofluorescence localization, Dy2j/2j mouse model, YAP nuclear activity and nerve conduction readouts

    PMID:27435623

    Open questions at the time
    • Direct Hippo-component interactions in Schwann cells not mapped
    • Single lab
  5. 2016 Medium

    Identified a transcriptional silencing route for CRB3, with MUC1-C/ZEB1 repressing its promoter to disable Hippo and license YAP/β-catenin–MYC signaling in TNBC.

    Evidence ChIP for promoter occupancy, CRB3 mRNA/protein measurement, LATS1 phosphorylation, YAP localization, YAP/β-catenin Co-IP

    PMID:27658423

    Open questions at the time
    • Direct versus indirect ZEB1 binding not fully dissected
    • Single lab
  6. 2017 Medium

    Defined the Hippo-activating mechanism, showing CRB3 recruits Kibra/FRMD6 to drive LATS1/2 activation, YAP inactivation, and contact inhibition with tumor suppression.

    Evidence Co-IP of CRB3 with Kibra/FRMD6, OE/KD with Hippo pathway readouts, proliferation/apoptosis assays, in vivo tumor suppression in mammary epithelial cells

    PMID:28079891

    Open questions at the time
    • Whether Kibra/FRMD6 recruitment is direct or scaffold-mediated unclear
    • Single lab
  7. 2017 Medium

    Showed that CRB3 loss is sufficient to drive malignant phenotypes, inducing EMT and cancer stem cell properties through TAZ and β-catenin activation.

    Evidence CRB3 knockdown in MCF-10A, TAZ/β-catenin activation assays, sphere formation, epistatic phenocopy by TAZ/β-catenin activation

    PMID:28436991

    Open questions at the time
    • Mechanistic link between CRB3 loss and β-catenin activation not resolved
    • Single lab
  8. 2018 Medium

    Separated CRB3 signaling outputs by domain, showing FERM-binding-domain-dependent, EPB41L4B-mediated proliferation via amphiregulin secretion that is independent of the PDZ-binding domain.

    Evidence FBD vs PDZ-binding domain deletion constructs, AREG secretion and endosome quantification, EPB41L4B knockdown, 3D acini culture

    PMID:30440051

    Open questions at the time
    • How EPB41L4B couples CRB3 to AREG secretion mechanistically unclear
    • Single lab
  9. 2022 Medium

    Revealed post-transcriptional control of CRB3, establishing an m6A-CRB3-Hippo axis in which METTL3/YTHDF2 degrade CRB3 mRNA to suppress Hippo activation.

    Evidence MeRIP-qPCR, RNA stability and luciferase assays, YTHDF2-CRB3 mRNA RIP, METTL3/YTHDF2 KD with CRB3 readouts, CRB3-KD reversal epistasis

    PMID:35012593

    Open questions at the time
    • Mapped m6A sites and their individual contributions not fully defined
    • Single lab
  10. 2023 High

    Uncovered a ciliogenic role, showing CRB3 traffics via Rab11 endosomes to the basal body to route GCP6/Rab11 vesicles to CEP290 for γTuRC assembly, with loss causing cilium defects, hyperplasia, and impaired Hh/Wnt responsiveness.

    Evidence Crb3 global and mammary-conditional knockout mice, Co-IP (CRB3-Rab11, GCP6/Rab11-CEP290), basal body localization, ciliogenesis and Hh/Wnt activation assays

    PMID:37737843

    Open questions at the time
    • Order of CRB3 actions at basal body versus apical membrane not fully resolved
    • How CRB3 selects Rab11 vesicle cargo unknown
  11. 2023 Medium

    Corroborated the ciliary trafficking role in a second system, showing Crb3.L works with Rab11a in Xenopus MCCs to drive basal body migration, apical expansion, and apical actin/pERM organization.

    Evidence Morpholino knockdown of Crb3.L and Rab11a in Xenopus MCCs, colocalization imaging, apical surface and actin meshwork analysis, pERM localization

    PMID:37840525

    Open questions at the time
    • Morpholino-based; off-target controls and rescue depth limited
    • Direct CRB3-pERM interaction not demonstrated
  12. 2025 High

    Defined how CRB3 controls junctional mechanics, showing FBD-mediated binding to Merlin/NF2 restrains RhoA-driven perijunctional actomyosin contractility and enables proper AJC assembly.

    Evidence Conditional Crb3 KO colonoids, Co-IP (CRB3-NF2 via FBD), RhoA activity assay, NF2-KD epistasis, ROCK-II/myosin II inhibitor rescue, vinculin localization

    PMID:41122968

    Open questions at the time
    • How CRB3-NF2 binding inhibits RhoA mechanistically unresolved
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved how CRB3's distinct activities — Par6/junction control, NF2/actomyosin tension, Rab11-dependent ciliogenesis, and Hippo activation — are coordinated spatially and temporally on a single apical protein.
  • No structural model integrating FBD and PDZ-binding outputs
  • Hierarchy between ciliary and junctional CRB3 pools undefined
  • In vivo coordination across tissues not established

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 5 GO:0008092 cytoskeletal protein binding 2
Localization
GO:0005886 plasma membrane 3 GO:0005815 microtubule organizing center 2 GO:0005929 cilium 2 GO:0031410 cytoplasmic vesicle 2
Pathway
R-HSA-162582 Signal Transduction 3 R-HSA-1266738 Developmental Biology 2 R-HSA-1852241 Organelle biogenesis and maintenance 2 R-HSA-8953854 Metabolism of RNA 1
Partners
ARP3EPB41L4BEPS8FRMD6KIBRANF2PARD6RAB11A

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2004 CRB3 directly binds Par6 via its C-terminal ERLI motif (PDZ-binding domain), and overexpression of CRB3 slows development of functional tight junctions in MDCK cells in a manner dependent on this ERLI domain. Direct binding assay, domain deletion/chimera overexpression in MDCK cells, tight junction permeability assays Molecular biology of the cell High 14718572
2013 The WD40 protein Morg1 directly binds Par6 and facilitates apical targeting of the Par6-aPKC complex to CRB3 at the apical membrane; this interaction is reinforced by Cdc42. Depletion of Morg1 disrupts tight junction development and cyst formation, rescued by forced apical targeting of aPKC. Co-IP, epistasis (Morg1 depletion + forced apical aPKC targeting), 3D cyst assay, MDCK cells The Journal of cell biology High 23439680
2016 CRB3 interacts with actin-regulatory proteins Arp3 (branched actin polymerization) and Eps8 (barbed-end capping/bundling) in Sertoli cells. CRB3 knockdown disrupts actin microfilament organization, truncating and branching actin, which destabilizes TJ- and basal ES-protein complexes at the blood-testis barrier, and impairs spermatid/phagosome transport and spermatid polarity in vivo. Co-IP (binding partners Arp3 and Eps8), RNAi knockdown in Sertoli cells with TJ-permeability barrier assay, in vivo CRB3 KD via jetPEI transfection with histological readouts Scientific reports Medium 27358069
2016 CRB3, localized at the tips of the peripheral myelin sheath, activates the Hippo pathway to inhibit YAP transcriptional activity, thereby limiting myelin elongation. Loss of CRB3-mediated Hippo activation results in decreased nuclear YAP and shorter myelin internodes in dystrophic mice. In vivo localization (immunofluorescence), genetic mouse model (Dy2j/2j), YAP nuclear activity assays, functional nerve conduction measurements Nature communications Medium 27435623
2017 CRB3 acts as an upstream activator of the Hippo pathway in mammary epithelial cells by recruiting Kibra and/or FRMD6, leading to activation of LATS1/2 kinases, YAP inactivation, and contact inhibition of proliferation. Co-immunoprecipitation (CRB3 with Kibra/FRMD6), CRB3 overexpression and knockdown with Hippo pathway readouts (LATS phosphorylation, YAP localization), proliferation and apoptosis assays, in vivo tumor suppression Cell death & disease Medium 28079891
2016 MUC1-C associates with ZEB1 on the CRB3 promoter to repress CRB3 transcription in triple-negative breast cancer cells, thereby suppressing CRB3-driven Hippo pathway activation (LATS1/2), leading to YAP dephosphorylation/activation, YAP/β-catenin complex formation, and MYC induction. ChIP (MUC1-C/ZEB1 on CRB3 promoter), CRB3 mRNA/protein measurement upon MUC1-C targeting, LATS1 phosphorylation assay, YAP localization, Co-IP (YAP/β-catenin), MYC expression Molecular cancer research : MCR Medium 27658423
2017 CRB3 downregulation in MCF-10A cells induces EMT, activates TAZ and β-catenin signaling, and confers cancer stem cell properties; TAZ and β-catenin activation was sufficient to recapitulate the CSC phenotype caused by CRB3 loss. CRB3 knockdown in MCF-10A, TAZ/β-catenin activation assays, sphere formation and CSC marker assays, epistasis (TAZ/β-catenin activation phenocopy) Oncogenesis Medium 28436991
2018 CRB3 overexpression drives proliferation in mammary epithelial cells through increased secretion of amphiregulin (AREG), in a manner dependent on the FERM-binding domain (FBD) but not the PDZ-binding domain of CRB3. EPB41L4B was identified as an essential FBD-dependent mediator of CRB3-driven proliferation and associated changes in endocytic trafficking. CRB3 domain deletion constructs (FBD vs PDZ-binding domain), AREG secretion assay, endosome size/number quantification, EPB41L4B knockdown, 3D acini culture assay PloS one Medium 30440051
2022 METTL3-mediated m6A methylation of CRB3 mRNA promotes its degradation via YTHDF2 binding. METTL3 knockdown reduces m6A on CRB3 mRNA, increases CRB3 expression, and activates the Hippo pathway (reducing nuclear YAP); these effects are reversed by CRB3 knockdown, placing CRB3 downstream of METTL3/YTHDF2 in an m6A-CRB3-Hippo axis. m6A epitranscriptomic microarray, MeRIP-qPCR, RNA stability assay, luciferase reporter, RNA immunoprecipitation (YTHDF2-CRB3 mRNA), METTL3/YTHDF2 knockdown with CRB3 mRNA/protein readouts, epistasis (CRB3 KD reversal of Hippo activation) Journal of experimental & clinical cancer research : CR Medium 35012593
2023 CRB3 localizes to the basal body and is trafficked via Rab11-positive endosomes. CRB3 interacts with Rab11 to navigate GCP6/Rab11 vesicles to CEP290, enabling intact γ-tubulin ring complex (γTuRC) assembly for ciliogenesis. CRB3 depletion (Crb3 knockout mice) caused severe primary cilium defects in mammary ductal lumen and renal tubule, and mammary epithelial-specific Crb3 KO promoted ductal hyperplasia and tumorigenesis. CRB3-depleted cells are unresponsive to Hh pathway activation, and CRB3 regulates Wnt signaling. Crb3 knockout and conditional knockout mice (mammary epithelial-specific), Co-IP (CRB3-Rab11, GCP6/Rab11-CEP290), subcellular localization (basal body, Rab11 vesicles), ciliogenesis assays, Hh/Wnt pathway activation assays eLife High 37737843
2023 In Xenopus laevis MCCs, Crb3.L localizes to cytoplasmic vesicles near ascending centrioles/basal bodies, colocalizing partially with Rab11a. Crb3.L depletion causes defective centriole/basal body migration, reduced apical surface, disorganized apical actin meshwork, and defective ciliogenesis; Rab11a depletion phenocopies this. CRB3 anchors phospho-ERM at the growing apical domain to enable actin-dependent apical membrane expansion. Morpholino-mediated knockdown (Crb3.L and Rab11a) in Xenopus MCCs, colocalization imaging (Crb3.L/Rab11a), apical surface quantification, actin meshwork analysis, pERM localization Journal of cell science Medium 37840525
2025 CRB3A interacts with Merlin/NF2 via its FERM-binding domain (FBD). CRB3 deficiency in colonoids leads to increased RhoA activity, hypercontractile perijunctional actomyosin, elevated junctional tension (increased vinculin), and defective AJC assembly; NF2 knockdown phenocopies CRB3 loss. ROCK-II or myosin II inhibition rescues junctional architecture in CRB3-null cells. Conditional Crb3 knockout colonoids, Co-IP (CRB3-NF2 via FBD), RhoA activity assay, ROCK-II/myosin II inhibitor rescue, vinculin localization, NF2 knockdown epistasis JCI insight High 41122968
2007 CRB3 overexpression does not interact with presenilin complex components and does not affect γ/ε-secretase activity (Aβ, AICD, or NICD production) in mammalian cells — negative result. Co-immunoprecipitation, γ-secretase activity assays (Aβ/AICD/NICD measurement), NCT maturation and PS endoproteolysis assays Biochemistry Medium 17988153

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2004 CRB3 binds directly to Par6 and regulates the morphogenesis of the tight junctions in mammalian epithelial cells. Molecular biology of the cell 244 14718572
2022 METTL3 promotes colorectal carcinoma progression by regulating the m6A-CRB3-Hippo axis. Journal of experimental & clinical cancer research : CR 89 35012593
2016 Polarity protein Crumbs homolog-3 (CRB3) regulates ectoplasmic specialization dynamics through its action on F-actin organization in Sertoli cells. Scientific reports 59 27358069
2016 Optimal myelin elongation relies on YAP activation by axonal growth and inhibition by Crb3/Hippo pathway. Nature communications 54 27435623
2013 The WD40 protein Morg1 facilitates Par6-aPKC binding to Crb3 for apical identity in epithelial cells. The Journal of cell biology 43 23439680
2017 CRB3 regulates contact inhibition by activating the Hippo pathway in mammary epithelial cells. Cell death & disease 39 28079891
2016 MUC1-C Represses the Crumbs Complex Polarity Factor CRB3 and Downregulates the Hippo Pathway. Molecular cancer research : MCR 38 27658423
2018 Elevated CRB3 expression suppresses breast cancer stemness by inhibiting β-catenin signalling to restore tamoxifen sensitivity. Journal of cellular and molecular medicine 17 29602199
2017 CRB3 downregulation confers breast cancer stem cell traits through TAZ/β-catenin. Oncogenesis 17 28436991
2015 Epithelial cell polarity determinant CRB3 in cancer development. International journal of biological sciences 17 25552927
2015 The C. elegans Crumbs family contains a CRB3 homolog and is not essential for viability. Biology open 15 25661870
2014 The expression and localization of Crb3 in developmental stages of the mice embryos and in different organs of 1-week-old female mice. Reproduction in domestic animals = Zuchthygiene 10 25131306
2012 Immunocytochemical evidence of the localization of the Crumbs homologue 3 protein (CRB3) in the developing and mature mouse retina. PloS one 10 23226298
2023 Fructose-bisphosphatase1 (FBP1) alleviates experimental osteoarthritis by regulating Protein crumbs homolog 3 (CRB3). Arthritis research & therapy 8 38049890
2007 Overexpression of human CRB1 or related isoforms, CRB2 and CRB3, does not regulate the human presenilin complex in culture cells. Biochemistry 8 17988153
2023 CRB3 navigates Rab11 trafficking vesicles to promote γTuRC assembly during ciliogenesis. eLife 5 37737843
2019 Crumbs protein homolog 3 (CRB3) expression is associated with oestrogen and progesterone receptor positivity in breast cancer. Clinical and experimental pharmacology & physiology 3 31087799
2024 Intestinal mRNA expression analysis of polarity-related genes identified the discriminatory ability of CRB3 as a diagnostic marker for celiac disease. Immunity, inflammation and disease 2 38353316
2018 CRB3 and the FERM protein EPB41L4B regulate proliferation of mammary epithelial cells through the release of amphiregulin. PloS one 2 30440051
2025 Crb3 and NF2: A dynamic duo that controls assembly of the apical junctions and barrier function via Rho/ROCK signaling. bioRxiv : the preprint server for biology 0 39868176
2025 CRB3 and NF2 orchestrate cytoskeletal dynamics to control epithelial barrier assembly. JCI insight 0 41122968
2023 Crb3 is required to organize the apical domain of multiciliated cells. Journal of cell science 0 37840525

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