Affinage

CRB3

Protein crumbs homolog 3 · UniProt Q9BUF7

Length
120 aa
Mass
12.9 kDa
Annotated
2026-04-28
22 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CRB3 is an apical transmembrane polarity determinant that organizes epithelial architecture, tight junctions, and primary cilia through distinct cytoplasmic domain interactions and upstream regulation of the Hippo pathway. Its C-terminal PDZ-binding motif (ERLI) recruits Par6-aPKC to the apical membrane to govern tight junction morphogenesis, facilitated by the adaptor Morg1 and Cdc42 (PMID:14718572, PMID:23439680), while its FERM-binding domain engages Merlin/NF2 and EPB41L4B to control perijunctional actomyosin contractility, endocytic trafficking, and junctional complex assembly (PMID:41122968, PMID:30440051). CRB3 recruits Kibra/FRMD6 to activate LATS and suppress YAP/TAZ, enforcing contact inhibition and restraining proliferation; loss of CRB3 activates TAZ/β-catenin signaling, promotes epithelial–mesenchymal transition, and confers stem-cell properties (PMID:28079891, PMID:28436991). CRB3 also localizes to the basal body, where it navigates Rab11-positive vesicles carrying GCP6 to CEP290 for γ-tubulin ring complex assembly, and its depletion causes severe ciliogenesis defects, loss of Hedgehog responsiveness, and disrupted centriole migration in vivo (PMID:37737843, PMID:37840525).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2004 High

    Establishing CRB3 as a polarity protein that directly recruits the Par6-aPKC complex to regulate tight junction formation answered how Crumbs-family proteins connect to the conserved Par complex in mammalian epithelia.

    Evidence Direct binding assay and ERLI-motif mutagenesis in MDCK cells with tight junction permeability readout

    PMID:14718572

    Open questions at the time
    • Upstream signals initiating CRB3 apical delivery were unknown
    • Whether CRB3-Par6 interaction is sufficient or requires co-factors was unresolved
  2. 2013 High

    Identification of Morg1 as a bridging adaptor between CRB3 and Par6-aPKC, reinforced by Cdc42, resolved how CRB3 efficiently recruits the polarity complex to the apical membrane.

    Evidence Co-IP, pulldown, siRNA in MDCK cells, 3D cyst assay with epistasis rescue by forced apical aPKC targeting

    PMID:23439680

    Open questions at the time
    • Whether Morg1 is required in all epithelial subtypes was untested
    • Structural basis of the tripartite CRB3-Morg1-Par6 complex unknown
  3. 2016 Medium

    Three parallel studies revealed CRB3 functions beyond tight junctions: regulating actin organization at the blood–testis barrier, activating the Hippo pathway to limit YAP-driven myelin elongation, and being transcriptionally repressed by MUC1-C/ZEB1 to modulate Hippo-YAP-MYC signaling in cancer.

    Evidence Co-IP of CRB3 with Arp3/Eps8 and Sertoli cell RNAi (actin); in vivo Dy2j/2j mouse model with YAP nuclear rescue (myelin); ChIP of MUC1-C/ZEB1 on CRB3 promoter with phospho-LATS and luciferase reporter (cancer)

    PMID:27358069 PMID:27435623 PMID:27658423

    Open questions at the time
    • Direct interaction between CRB3 and Hippo core kinases was not demonstrated
    • Whether CRB3-actin and CRB3-Hippo branches operate independently or converge was unclear
    • Myelin phenotype studied in a single disease model
  4. 2017 Medium

    Demonstrating that CRB3 recruits Kibra and FRMD6 to activate LATS and suppress YAP/TAZ established CRB3 as an upstream scaffold for the Hippo pathway that enforces contact inhibition and opposes EMT-driven stemness.

    Evidence Co-IP of CRB3 with Kibra/FRMD6, overexpression/knockdown in mammary epithelial cells with proliferation, apoptosis, junction, and tumor growth assays; CRB3 KD inducing TAZ/β-catenin and mammosphere formation in MCF10A cells

    PMID:28079891 PMID:28436991

    Open questions at the time
    • Whether CRB3-Kibra interaction is direct or scaffolded was unresolved
    • Relative contributions of TAZ versus β-catenin downstream of CRB3 loss not dissected
  5. 2018 Medium

    Domain dissection showed that the FERM-binding domain—not the PDZ-binding domain—drives CRB3-dependent proliferation through EPB41L4B-mediated endocytic trafficking and amphiregulin secretion, revealing a second functional axis of the CRB3 cytoplasmic tail.

    Evidence CRB3 FBD versus PDZ deletion mutants in 3D acinar culture with AREG secretion, EPB41L4B siRNA knockdown, and endosome quantification

    PMID:30440051

    Open questions at the time
    • How EPB41L4B couples CRB3-FBD to endosomal machinery was not defined
    • Whether AREG secretion is the sole proliferative effector downstream of the FBD was untested
  6. 2022 Medium

    Showing that METTL3-mediated m6A methylation of CRB3 mRNA triggers YTHDF2-dependent degradation revealed an epitranscriptomic layer controlling CRB3 protein levels and, consequently, Hippo pathway activity.

    Evidence MeRIP-qPCR, RIP of YTHDF2 on CRB3 mRNA, RNA stability assay, epistasis knockdown of CRB3 reversing METTL3-depletion effects on YAP

    PMID:35012593

    Open questions at the time
    • Specific m6A sites on CRB3 mRNA were not mapped at nucleotide resolution
    • Whether this regulatory axis operates in normal epithelia or only in cancer cells was unclear
  7. 2023 High

    Discovery that CRB3 localizes to the basal body and navigates Rab11-positive vesicles carrying GCP6 to CEP290 for γTuRC assembly established CRB3 as a direct regulator of ciliogenesis, linking it to Hedgehog and Wnt signaling.

    Evidence Co-IP of CRB3-Rab11 and GCP6-Rab11-CEP290, Crb3 knockout mice with ciliary defects in mammary and renal epithelia, γTuRC assembly assay, Hh/Wnt signaling readouts

    PMID:37737843

    Open questions at the time
    • Whether CRB3 directly contacts GCP6 or acts solely through Rab11 was not resolved
    • Structural basis of CRB3 recognition by Rab11 unknown
  8. 2023 Medium

    Parallel work in Xenopus multiciliated cells confirmed CRB3 colocalizes with Rab11a on vesicles near ascending basal bodies and anchors phospho-ERM to enable actin-dependent apical membrane expansion, generalizing the CRB3-Rab11 ciliogenesis mechanism across vertebrates.

    Evidence Morpholino knockdown of Crb3.L and Rab11a in Xenopus MCCs with live imaging, pERM colocalization, and Rab11a phenocopy

    PMID:37840525

    Open questions at the time
    • Rescue experiments with human CRB3 in Xenopus MCCs were not performed
    • Whether ERM anchoring is a direct CRB3 interaction or indirect via scaffold proteins was not established
  9. 2025 High

    Identifying Merlin/NF2 as a direct FERM-binding domain partner of CRB3 that restrains RhoA-ROCK-myosin II contractility at junctions unified the polarity and actomyosin branches and explained how CRB3 loss causes junctional collapse via hypercontractility.

    Evidence Conditional Crb3 knockout colonoids, Co-IP of CRB3A-NF2 via FBD, NF2 siRNA phenocopy, ROCK-II/myosin II inhibitor rescue of junctional architecture

    PMID:41122968

    Open questions at the time
    • Whether NF2 links CRB3-FBD to the Hippo kinase cascade directly or through separate effectors was not resolved
    • Contribution of EPB41L4B versus NF2 at the FBD under different cellular contexts not compared

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the PDZ-binding (Par6-aPKC) and FERM-binding (NF2/EPB41L4B) arms of CRB3 are coordinately regulated in space and time, and whether the junctional and ciliary pools of CRB3 share trafficking machinery, remain open mechanistic questions.
  • No structural model of the CRB3 cytoplasmic tail in complex with its partners
  • Relative stoichiometry and competition between NF2, EPB41L4B, Kibra, and FRMD6 at the FBD is undefined
  • Whether CRB3 isoforms (CRB3A vs CRB3B) partition between junctional and ciliary functions has not been rigorously tested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 5
Localization
GO:0005886 plasma membrane 4 GO:0005815 microtubule organizing center 2 GO:0005929 cilium 2 GO:0031410 cytoplasmic vesicle 2
Pathway
R-HSA-162582 Signal Transduction 5 R-HSA-1500931 Cell-Cell communication 3 R-HSA-1852241 Organelle biogenesis and maintenance 2
Partners
EPB41L4BFRMD6KIBRAMORG1NF2PARD6BPRKCZRAB11A
Complex memberships
CRB3-Par6-aPKC apical polarity complexCRB3-Rab11-GCP6 ciliogenesis trafficking complex

Evidence

Reading pass · 12 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 this interaction regulates tight junction morphogenesis in epithelial cells. Expression of CRB3 or a chimera containing its transmembrane and cytoplasmic domains slowed development of functional tight junctions in MDCK cells, dependent on the ERLI motif. Direct binding assay, chimeric protein expression, loss-of-function in MDCK cells with TJ permeability readout Molecular biology of the cell High 14718572
2013 The WD40 protein Morg1 directly binds Par6 and interacts with CRB3 to facilitate apical targeting of the Par6-aPKC complex. Cdc42 reinforces Par6-aPKC binding to CRB3. Morg1 depletion disrupts tight junction development and cyst formation, rescued by forced apical targeting of aPKC. Co-IP, pulldown, siRNA knockdown in MDCK cells, 3D cyst assay, epistasis rescue by aPKC apical targeting The Journal of cell biology High 23439680
2016 CRB3 in Sertoli cells interacts with the actin branching protein Arp3 and barbed-end capping/bundling protein Eps8. CRB3 knockdown reorganizes actin microfilaments (truncation and excessive branching), destabilizing F-actin-based adhesion complexes at the blood-testis barrier and disrupting spermatid transport and polarity. Co-IP (Arp3, Eps8), RNAi knockdown in Sertoli cells with TJ-permeability barrier assay, in vivo RNAi via jetPEI with spermatid transport readout Scientific reports Medium 27358069
2016 CRB3, localized at the tips of the peripheral myelin sheath, activates the Hippo pathway to limit YAP transcriptional activity, thereby restraining myelin elongation. YAP promotes myelin gene transcription and excessive myelin growth when CRB3-Hippo signaling is reduced. Loss-of-function in vivo (Dy2j/2j mice with reduced internode lengths), YAP nuclear localization rescue, Hippo pathway activity assay Nature communications Medium 27435623
2016 MUC1-C associates with ZEB1 on the CRB3 promoter to repress CRB3 transcription, thereby suppressing the CRB3-driven Hippo pathway (LATS1/2 phosphorylation), activating YAP, and promoting YAP/β-catenin-mediated MYC induction. ChIP (MUC1-C/ZEB1 on CRB3 promoter), siRNA knockdown, phospho-LATS1 assay, co-IP (MUC1-C/YAP), luciferase reporter Molecular cancer research : MCR Medium 27658423
2017 CRB3 acts as an upstream activator of the Hippo pathway in mammary epithelial cells by recruiting Kibra and/or FRMD6, leading to LATS activation, YAP inactivation, and contact inhibition. CRB3 overexpression decreases proliferation, promotes apoptosis, and enhances tight and adherens junction formation. Co-IP (CRB3 with Kibra, FRMD6), CRB3 overexpression/knockdown with proliferation, apoptosis, and junction assays; in vivo tumor growth assay Cell death & disease Medium 28079891
2017 CRB3 downregulation in breast epithelial MCF10A cells induces epithelial-mesenchymal transition and activates TAZ and β-catenin, conferring cancer stem cell properties. TAZ and β-catenin activation downstream of CRB3 loss is sufficient to drive the stem cell phenotype. CRB3 knockdown, TAZ/β-catenin expression and activity assays, mammosphere formation, gain-of-function rescue experiments Oncogenesis Medium 28436991
2018 CRB3 promotes proliferation via its FERM-binding domain (FBD), not its PDZ-binding domain, by inducing secretion of amphiregulin (AREG) through increased endocytic trafficking. The FERM-domain protein EPB41L4B is an essential mediator of CRB3-driven proliferation and endosomal changes. CRB3 domain mutants (FBD vs. PDZ deletion), 3D acinar culture, AREG secretion assay, siRNA knockdown of EPB41L4B, endosome quantification PloS one Medium 30440051
2022 METTL3 promotes m6A methylation on CRB3 mRNA, leading to YTHDF2-dependent mRNA degradation and reduced CRB3 protein. YTHDF2 directly binds CRB3 mRNA (verified by RIP assay). Increased CRB3 activates the Hippo pathway and reduces nuclear YAP; CRB3 knockdown reverses the Hippo activation caused by METTL3 depletion. m6A epitranscriptomic microarray, MeRIP-qPCR, RNA stability assay, luciferase reporter, RIP (YTHDF2-CRB3 mRNA), siRNA knockdown epistasis Journal of experimental & clinical cancer research : CR Medium 35012593
2023 CRB3 localizes to the basal body and interacts with Rab11 to navigate GCP6/Rab11 trafficking vesicles to CEP290, enabling intact γ-tubulin ring complex (γTuRC) assembly. CRB3 depletion causes defective ciliogenesis, loss of Hh pathway responsiveness, and altered Wnt signaling. Crb3 knockout mice show severe primary cilium defects in mammary ductal lumen and renal tubule. Co-IP (CRB3-Rab11, GCP6-Rab11-CEP290), Crb3 knockout mice (mammary- and whole-body), immunofluorescence for basal body localization, Hh/Wnt signaling assays, γTuRC assembly assay eLife High 37737843
2023 In Xenopus MCCs, Crb3.L localizes to cytoplasmic vesicles near ascending centrioles/basal bodies, partially colocalizing with Rab11a. Crb3.L depletion causes abnormal centriole/basal body migration, reduced apical surface, disorganized actin meshwork, and defective ciliogenesis. Rab11a depletion phenocopies Crb3.L loss, suggesting Crb3.L controls centriole migration via Rab11a-dependent apical trafficking. Crb3.L anchors phospho-activated ERM at the growing apical domain to enable actin-dependent apical membrane expansion. Morpholino knockdown of Crb3.L and Rab11a in Xenopus MCCs, live imaging/colocalization, pERM co-localization, actin organization assay Journal of cell science Medium 37840525
2025 CRB3A interacts with the actin cytoskeletal linker Merlin (NF2) via its FERM-binding domain (FBD). CRB3 loss leads to increased RhoA activity, hypercontractile perijunctional actomyosin, and impaired apical junctional complex (AJC) assembly. NF2 knockdown phenocopies CRB3 loss. ROCK-II or myosin II inhibition restores junctional architecture in CRB3-null cells. Conditional Crb3 knockout colonoids (Crb3ERΔIEC), Co-IP (CRB3A-NF2 via FBD), RhoA activity assay, NF2 siRNA phenocopy, ROCK-II/myosin II inhibitor rescue, barrier function assay, vinculin tension readout JCI insight High 41122968

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 243 14718572
2022 METTL3 promotes colorectal carcinoma progression by regulating the m6A-CRB3-Hippo axis. Journal of experimental & clinical cancer research : CR 87 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 53 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 38 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
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 Fructose-bisphosphatase1 (FBP1) alleviates experimental osteoarthritis by regulating Protein crumbs homolog 3 (CRB3). Arthritis research & therapy 7 38049890
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