{"gene":"EPB41L4B","run_date":"2026-04-28T17:46:03","timeline":{"discoveries":[{"year":2011,"finding":"Lulu2 (EPB41L4B ortholog) localizes along apical cell-cell boundaries in epithelial cells and directly interacts with p114RhoGEF to activate it, thereby regulating the circumferential actomyosin belt. This interaction is negatively regulated by atypical protein kinase C (aPKC)-mediated phosphorylation of the FERM-adjacent domain of Lulu2.","method":"RNAi knockdown, co-immunoprecipitation, in vitro kinase assay, immunofluorescence localization","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, RNAi phenotype, kinase assay with mutagenesis, replicated in follow-up review","pmids":["22006950"],"is_preprint":false},{"year":2012,"finding":"Lulu2 (EPB41L4B) enhances the catalytic (GEF) activity of p114RhoGEF through a direct interaction, activating the circumferential actomyosin belt and inducing apical constriction in epithelial cells; RNAi-mediated knockdown of Lulu2 severely disorganizes the belt.","method":"RNAi knockdown, in vitro GEF activity assay, co-immunoprecipitation","journal":"Small GTPases","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro GEF assay plus Co-IP plus RNAi phenotype, consistent with independent 2011 paper","pmids":["22790195"],"is_preprint":false},{"year":2015,"finding":"CRB3A recruits both p114RhoGEF and its activator Ehm2 (EPB41L4B) to the cell periphery via the cytoplasmic tail of CRB3A, increasing RhoA activation and reorganizing the cytoskeleton into a circumferential actomyosin belt; downstream ROCK1/2 are essential effectors of this pathway.","method":"Ectopic expression of CRB3A in HeLa cells, RhoA activity assay (G-LISA), co-immunoprecipitation, immunofluorescence, ROCK inhibitor treatment","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, RhoA activity assay, localization, and pharmacological epistasis in a single study","pmids":["26217006"],"is_preprint":false},{"year":2018,"finding":"EPB41L4B is an essential mediator of CRB3-driven proliferation in mammary epithelial cells; CRB3 requires its FERM-binding domain (FBD) to interact with EPB41L4B, and EPB41L4B is required for CRB3-dependent amphiregulin (AREG) secretion and changes in endocytic trafficking (enlarged early and late endosomes).","method":"Ectopic expression, siRNA knockdown, AREG secretion measurement, endosome imaging (confocal), domain-deletion mutants of CRB3","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — KD with defined cellular phenotype and domain-deletion epistasis, single lab","pmids":["30440051"],"is_preprint":false},{"year":2006,"finding":"Ehm2 (EPB41L4B) overexpression decreases adhesion to collagen IV in prostate cancer cells, and its expression is upregulated by the FGFR-4 Arg388 variant.","method":"Transient overexpression, RNAi knockdown, collagen IV adhesion assay, quantitative RT-PCR","journal":"The Prostate","confidence":"Medium","confidence_rationale":"Tier 3 — functional cell assay with both OE and KD, single lab","pmids":["16927306"],"is_preprint":false},{"year":2010,"finding":"Knockdown of Ehm2 (EPB41L4B) in breast cancer cells decreases MMP-9 mRNA, protein, and enzymatic activity, leading to reduced invasion, suggesting Ehm2 promotes invasiveness through regulation of MMP-9 expression.","method":"Ribozyme transgene knockdown, invasion assay, qRT-PCR, gelatin zymography","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 3 — KD with defined molecular and functional phenotype, single lab","pmids":["21047774"],"is_preprint":false},{"year":2013,"finding":"Ehm2 (EPB41L4B) knockdown in keratinocytes reduces cellular adhesion and migration, and decreases N-WASP protein expression, suggesting Ehm2 regulates cytoskeletal dynamics in wound healing through N-WASP.","method":"Anti-Ehm2 transgene knockdown, migration/adhesion assays, Western blot for N-WASP","journal":"Journal of dermatological science","confidence":"Low","confidence_rationale":"Tier 3 — single Co-IP-free Western blot downstream readout, single lab, weak mechanistic link","pmids":["23664528"],"is_preprint":false},{"year":2019,"finding":"The two EPB41L4B splice isoforms differ in subcellular localization: Ehm2/1 is confined to the plasma membrane, while Ehm2/2 is present at both the plasma membrane and cytoplasm. Ehm2/1 overexpression upregulates E-cadherin and suppresses N-cadherin/Snail1 (anti-EMT), while Ehm2/2 overexpression or Ehm2/1 knockdown has the opposite effect.","method":"Immunofluorescence localization, overexpression and siRNA knockdown in A549 cells, Western blot for EMT markers, invasion/migration assays","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 — localization with functional consequence, two isoforms compared, single lab","pmids":["30816447"],"is_preprint":false},{"year":2022,"finding":"Ehm2/1 (EPB41L4B isoform 1) co-localizes with E-cadherin at the plasma membrane of breast cancer cells and stabilizes E-cadherin by inhibiting its ubiquitination, thereby suppressing cell migration and invasion.","method":"Co-localization by immunofluorescence, E-cadherin half-life assay (cycloheximide chase), ubiquitination assay, overexpression and knockdown in MCF-7 cells","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 — co-localization plus ubiquitination assay plus half-life measurement, single lab","pmids":["36422008"],"is_preprint":false}],"current_model":"EPB41L4B (Lulu2/Ehm2) is a FERM-domain scaffold protein that localizes to apical cell-cell junctions and the plasma membrane, where it directly binds and activates p114RhoGEF to stimulate RhoA–ROCK signaling and maintain the circumferential actomyosin belt; this activity is negatively regulated by aPKC phosphorylation of its FERM-adjacent domain, and it is recruited to junctions by the CRB3 complex via its FERM-binding domain, which also mediates CRB3-dependent amphiregulin secretion and endocytic trafficking; additionally, the Ehm2/1 isoform stabilizes E-cadherin at the plasma membrane by inhibiting its ubiquitination."},"narrative":{"teleology":[{"year":2006,"claim":"Initial functional characterization showed EPB41L4B participates in cell-matrix adhesion, as its overexpression reduced collagen IV adhesion in prostate cancer cells, linking the FERM-domain protein to adhesion regulation.","evidence":"Overexpression and RNAi in prostate cancer cells with collagen IV adhesion assay","pmids":["16927306"],"confidence":"Medium","gaps":["No molecular target or binding partner identified","Whether effects are direct or via downstream signaling unknown"]},{"year":2010,"claim":"EPB41L4B knockdown reduced MMP-9 expression and invasion in breast cancer cells, establishing a link between EPB41L4B and extracellular matrix remodeling during tumor invasion.","evidence":"Ribozyme knockdown in breast cancer cells with invasion assays and MMP-9 zymography","pmids":["21047774"],"confidence":"Medium","gaps":["Whether MMP-9 regulation is transcriptional or post-transcriptional not determined","No mechanism connecting FERM domain to MMP-9 expression"]},{"year":2011,"claim":"The central mechanistic question—how does EPB41L4B maintain epithelial architecture—was answered by demonstrating that it directly binds and activates p114RhoGEF at apical junctions, with aPKC phosphorylation of the FERM-adjacent domain serving as a negative regulator.","evidence":"Reciprocal co-immunoprecipitation, RNAi phenotyping, in vitro kinase assay with phospho-mutants, immunofluorescence in epithelial cells","pmids":["22006950"],"confidence":"High","gaps":["Structural basis of FERM-adjacent domain phosphorylation by aPKC unresolved","Whether other kinases also regulate this interaction unknown"]},{"year":2012,"claim":"Quantitative biochemistry confirmed that EPB41L4B directly enhances GEF catalytic activity of p114RhoGEF, establishing it as a bona fide allosteric activator rather than merely a co-localizing scaffold.","evidence":"In vitro GEF activity assay with purified components, RNAi, and co-immunoprecipitation","pmids":["22790195"],"confidence":"High","gaps":["Whether FERM domain alone is sufficient for GEF activation not tested","No structural model of the activation complex"]},{"year":2015,"claim":"The upstream recruitment mechanism was resolved: CRB3A recruits both EPB41L4B and p114RhoGEF to the cell periphery through its cytoplasmic tail, placing the CRB3–EPB41L4B–p114RhoGEF axis as a coherent pathway driving circumferential actomyosin belt formation via ROCK1/2.","evidence":"Ectopic CRB3A expression in HeLa cells, RhoA G-LISA, reciprocal co-immunoprecipitation, ROCK inhibitor epistasis","pmids":["26217006"],"confidence":"High","gaps":["Whether Patj/Pals1 complex members are required for EPB41L4B recruitment not addressed","Relative contribution of CRB3 versus other polarity cues in native epithelia unclear"]},{"year":2018,"claim":"Beyond cytoskeletal regulation, EPB41L4B was shown to be required for CRB3-dependent amphiregulin secretion and regulation of endosome size, expanding its role to vesicular trafficking and growth factor signaling.","evidence":"siRNA knockdown in mammary epithelial cells, amphiregulin ELISA, confocal endosome imaging, CRB3 FERM-binding domain deletion mutants","pmids":["30440051"],"confidence":"Medium","gaps":["Mechanism by which EPB41L4B regulates endosome size not determined","Whether amphiregulin secretion requires RhoA activation or a parallel pathway unknown","Single lab observation"]},{"year":2019,"claim":"Functional divergence of EPB41L4B splice isoforms was established: plasma membrane–restricted Ehm2/1 promotes epithelial identity (E-cadherin up, Snail1 down), while Ehm2/2, which also localizes to the cytoplasm, promotes mesenchymal features.","evidence":"Isoform-specific overexpression and knockdown in A549 cells, immunofluorescence localization, Western blot for EMT markers","pmids":["30816447"],"confidence":"Medium","gaps":["Structural determinants of isoform-specific localization not mapped","Whether opposing EMT effects act through the same p114RhoGEF pathway unknown"]},{"year":2022,"claim":"The mechanism by which Ehm2/1 stabilizes epithelial identity was pinpointed: it co-localizes with and stabilizes E-cadherin at the plasma membrane by inhibiting E-cadherin ubiquitination, directly linking EPB41L4B to post-translational control of adherens junctions.","evidence":"Co-localization immunofluorescence, cycloheximide chase half-life assay, ubiquitination assay in MCF-7 cells","pmids":["36422008"],"confidence":"Medium","gaps":["The E3 ligase whose activity is blocked by Ehm2/1 not identified","Whether E-cadherin stabilization requires FERM domain or a distinct domain unknown","Single lab; no reciprocal validation of direct E-cadherin binding"]},{"year":null,"claim":"Key open questions include the structural basis of EPB41L4B's allosteric activation of p114RhoGEF, the identity of the E3 ubiquitin ligase it antagonizes at E-cadherin, the molecular determinant governing isoform-specific localization, and whether its RhoA-dependent and E-cadherin-stabilizing functions represent parallel or convergent pathways.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure or cryo-EM model of EPB41L4B or its complexes","E3 ligase counterpart for E-cadherin ubiquitination not identified","Isoform-specific domain mapping not performed","In vivo genetic models (knockout mouse) not reported in the timeline"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,7,8]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,3]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[0,2,8]}],"complexes":[],"partners":["ARHGEF18","CRB3","CDH1","PRKCZ"],"other_free_text":[]},"mechanistic_narrative":"EPB41L4B (Lulu2/Ehm2) is a FERM-domain scaffold protein that organizes the apical circumferential actomyosin belt and modulates cell-cell adhesion in epithelial cells. It localizes to apical cell-cell junctions, where it directly binds and activates p114RhoGEF to stimulate RhoA–ROCK signaling; this activation is negatively regulated by aPKC phosphorylation of its FERM-adjacent domain and is recruited to junctions by the CRB3 complex via its FERM-binding domain [PMID:22006950, PMID:22790195, PMID:26217006]. CRB3-dependent amphiregulin secretion and endocytic trafficking require EPB41L4B [PMID:30440051]. The Ehm2/1 splice isoform, which is confined to the plasma membrane, stabilizes E-cadherin by inhibiting its ubiquitination, thereby suppressing epithelial-to-mesenchymal transition and cell invasion [PMID:30816447, PMID:36422008]."},"prefetch_data":{"uniprot":{"accession":"Q9H329","full_name":"Band 4.1-like protein 4B","aliases":["Erythrocyte membrane protein band 4.1-like 4B","FERM-containing protein CG1","Protein EHM2"],"length_aa":900,"mass_kda":99.7,"function":"Up-regulates the activity of the Rho guanine nucleotide exchange factor ARHGEF18 (By similarity). Involved in the regulation of the circumferential actomyosin belt in epithelial cells (PubMed:22006950). Promotes cellular adhesion, migration and motility in vitro and may play a role in wound healing (PubMed:23664528). May have a role in mediating cytoskeletal changes associated with steroid-induced cell differentiation (PubMed:14521927)","subcellular_location":"Cytoplasm; Cell junction, tight junction","url":"https://www.uniprot.org/uniprotkb/Q9H329/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/EPB41L4B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/EPB41L4B","total_profiled":1310},"omim":[{"mim_id":"610340","title":"ERYTHROCYTE MEMBRANE PROTEIN BAND 4.1-LIKE 4B; EPB41L4B","url":"https://www.omim.org/entry/610340"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"liver","ntpm":83.1},{"tissue":"pancreas","ntpm":140.8}],"url":"https://www.proteinatlas.org/search/EPB41L4B"},"hgnc":{"alias_symbol":["EHM2","LULU2"],"prev_symbol":[]},"alphafold":{"accession":"Q9H329","domains":[{"cath_id":"3.10.20.90","chopping":"71-164","consensus_level":"medium","plddt":90.8871,"start":71,"end":164},{"cath_id":"1.20.80.10","chopping":"166-272","consensus_level":"medium","plddt":94.0941,"start":166,"end":272},{"cath_id":"2.30.29.30","chopping":"276-370","consensus_level":"high","plddt":89.0541,"start":276,"end":370}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H329","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H329-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H329-F1-predicted_aligned_error_v6.png","plddt_mean":58.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=EPB41L4B","jax_strain_url":"https://www.jax.org/strain/search?query=EPB41L4B"},"sequence":{"accession":"Q9H329","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H329.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H329/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H329"}},"corpus_meta":[{"pmid":"22006950","id":"PMC_22006950","title":"Lulu2 regulates the circumferential actomyosin tensile system in epithelial cells through p114RhoGEF.","date":"2011","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22006950","citation_count":77,"is_preprint":false},{"pmid":"10783258","id":"PMC_10783258","title":"Molecular cloning of a novel NF2/ERM/4.1 superfamily gene, ehm2, that is expressed in high-metastatic K1735 murine melanoma cells.","date":"2000","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/10783258","citation_count":29,"is_preprint":false},{"pmid":"16927306","id":"PMC_16927306","title":"Increased expression of the metastasis-associated gene Ehm2 in prostate cancer.","date":"2006","source":"The Prostate","url":"https://pubmed.ncbi.nlm.nih.gov/16927306","citation_count":23,"is_preprint":false},{"pmid":"26217016","id":"PMC_26217016","title":"CRB3A Controls the Morphology and Cohesion of Cancer Cells through Ehm2/p114RhoGEF-Dependent Signaling.","date":"2015","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/26217016","citation_count":21,"is_preprint":false},{"pmid":"22790195","id":"PMC_22790195","title":"The circumferential actomyosin belt in epithelial cells is regulated by the Lulu2-p114RhoGEF system.","date":"2012","source":"Small GTPases","url":"https://pubmed.ncbi.nlm.nih.gov/22790195","citation_count":16,"is_preprint":false},{"pmid":"21047774","id":"PMC_21047774","title":"Clinical implications of the influence of Ehm2 on the aggressiveness of breast cancer cells through regulation of matrix metalloproteinase-9 expression.","date":"2010","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/21047774","citation_count":14,"is_preprint":false},{"pmid":"14521927","id":"PMC_14521927","title":"Androgen regulation of the human FERM domain encoding gene EHM2 in a cell model of steroid-induced differentiation.","date":"2003","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/14521927","citation_count":13,"is_preprint":false},{"pmid":"23664528","id":"PMC_23664528","title":"Expressed in high metastatic cells (Ehm2) is a positive regulator of keratinocyte adhesion and motility: The implication for wound healing.","date":"2013","source":"Journal of dermatological science","url":"https://pubmed.ncbi.nlm.nih.gov/23664528","citation_count":10,"is_preprint":false},{"pmid":"30816447","id":"PMC_30816447","title":"Differential expression and functions of Ehm2 transcript variants in lung adenocarcinoma.","date":"2019","source":"International journal of oncology","url":"https://pubmed.ncbi.nlm.nih.gov/30816447","citation_count":8,"is_preprint":false},{"pmid":"36422008","id":"PMC_36422008","title":"Ehm2 transcript variant 1 inhibits breast cancer progression and increases E-cadherin stability.","date":"2022","source":"Carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/36422008","citation_count":3,"is_preprint":false},{"pmid":"30440051","id":"PMC_30440051","title":"CRB3 and the FERM protein EPB41L4B regulate proliferation of mammary epithelial cells through the release of amphiregulin.","date":"2018","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/30440051","citation_count":2,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6911,"output_tokens":2188,"usd":0.026777},"stage2":{"model":"claude-opus-4-6","input_tokens":5482,"output_tokens":2420,"usd":0.131865},"total_usd":0.158642,"stage1_batch_id":"msgbatch_0118RScg3WGaGkaZRtWZbtce","stage2_batch_id":"msgbatch_01Cpfzvtbj42aqp5oYZ5Te2s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2011,\n      \"finding\": \"Lulu2 (EPB41L4B ortholog) localizes along apical cell-cell boundaries in epithelial cells and directly interacts with p114RhoGEF to activate it, thereby regulating the circumferential actomyosin belt. This interaction is negatively regulated by atypical protein kinase C (aPKC)-mediated phosphorylation of the FERM-adjacent domain of Lulu2.\",\n      \"method\": \"RNAi knockdown, co-immunoprecipitation, in vitro kinase assay, immunofluorescence localization\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, RNAi phenotype, kinase assay with mutagenesis, replicated in follow-up review\",\n      \"pmids\": [\"22006950\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Lulu2 (EPB41L4B) enhances the catalytic (GEF) activity of p114RhoGEF through a direct interaction, activating the circumferential actomyosin belt and inducing apical constriction in epithelial cells; RNAi-mediated knockdown of Lulu2 severely disorganizes the belt.\",\n      \"method\": \"RNAi knockdown, in vitro GEF activity assay, co-immunoprecipitation\",\n      \"journal\": \"Small GTPases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro GEF assay plus Co-IP plus RNAi phenotype, consistent with independent 2011 paper\",\n      \"pmids\": [\"22790195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CRB3A recruits both p114RhoGEF and its activator Ehm2 (EPB41L4B) to the cell periphery via the cytoplasmic tail of CRB3A, increasing RhoA activation and reorganizing the cytoskeleton into a circumferential actomyosin belt; downstream ROCK1/2 are essential effectors of this pathway.\",\n      \"method\": \"Ectopic expression of CRB3A in HeLa cells, RhoA activity assay (G-LISA), co-immunoprecipitation, immunofluorescence, ROCK inhibitor treatment\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, RhoA activity assay, localization, and pharmacological epistasis in a single study\",\n      \"pmids\": [\"26217006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"EPB41L4B is an essential mediator of CRB3-driven proliferation in mammary epithelial cells; CRB3 requires its FERM-binding domain (FBD) to interact with EPB41L4B, and EPB41L4B is required for CRB3-dependent amphiregulin (AREG) secretion and changes in endocytic trafficking (enlarged early and late endosomes).\",\n      \"method\": \"Ectopic expression, siRNA knockdown, AREG secretion measurement, endosome imaging (confocal), domain-deletion mutants of CRB3\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD with defined cellular phenotype and domain-deletion epistasis, single lab\",\n      \"pmids\": [\"30440051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Ehm2 (EPB41L4B) overexpression decreases adhesion to collagen IV in prostate cancer cells, and its expression is upregulated by the FGFR-4 Arg388 variant.\",\n      \"method\": \"Transient overexpression, RNAi knockdown, collagen IV adhesion assay, quantitative RT-PCR\",\n      \"journal\": \"The Prostate\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — functional cell assay with both OE and KD, single lab\",\n      \"pmids\": [\"16927306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Knockdown of Ehm2 (EPB41L4B) in breast cancer cells decreases MMP-9 mRNA, protein, and enzymatic activity, leading to reduced invasion, suggesting Ehm2 promotes invasiveness through regulation of MMP-9 expression.\",\n      \"method\": \"Ribozyme transgene knockdown, invasion assay, qRT-PCR, gelatin zymography\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — KD with defined molecular and functional phenotype, single lab\",\n      \"pmids\": [\"21047774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ehm2 (EPB41L4B) knockdown in keratinocytes reduces cellular adhesion and migration, and decreases N-WASP protein expression, suggesting Ehm2 regulates cytoskeletal dynamics in wound healing through N-WASP.\",\n      \"method\": \"Anti-Ehm2 transgene knockdown, migration/adhesion assays, Western blot for N-WASP\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP-free Western blot downstream readout, single lab, weak mechanistic link\",\n      \"pmids\": [\"23664528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The two EPB41L4B splice isoforms differ in subcellular localization: Ehm2/1 is confined to the plasma membrane, while Ehm2/2 is present at both the plasma membrane and cytoplasm. Ehm2/1 overexpression upregulates E-cadherin and suppresses N-cadherin/Snail1 (anti-EMT), while Ehm2/2 overexpression or Ehm2/1 knockdown has the opposite effect.\",\n      \"method\": \"Immunofluorescence localization, overexpression and siRNA knockdown in A549 cells, Western blot for EMT markers, invasion/migration assays\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — localization with functional consequence, two isoforms compared, single lab\",\n      \"pmids\": [\"30816447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Ehm2/1 (EPB41L4B isoform 1) co-localizes with E-cadherin at the plasma membrane of breast cancer cells and stabilizes E-cadherin by inhibiting its ubiquitination, thereby suppressing cell migration and invasion.\",\n      \"method\": \"Co-localization by immunofluorescence, E-cadherin half-life assay (cycloheximide chase), ubiquitination assay, overexpression and knockdown in MCF-7 cells\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-localization plus ubiquitination assay plus half-life measurement, single lab\",\n      \"pmids\": [\"36422008\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"EPB41L4B (Lulu2/Ehm2) is a FERM-domain scaffold protein that localizes to apical cell-cell junctions and the plasma membrane, where it directly binds and activates p114RhoGEF to stimulate RhoA–ROCK signaling and maintain the circumferential actomyosin belt; this activity is negatively regulated by aPKC phosphorylation of its FERM-adjacent domain, and it is recruited to junctions by the CRB3 complex via its FERM-binding domain, which also mediates CRB3-dependent amphiregulin secretion and endocytic trafficking; additionally, the Ehm2/1 isoform stabilizes E-cadherin at the plasma membrane by inhibiting its ubiquitination.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"EPB41L4B (Lulu2/Ehm2) is a FERM-domain scaffold protein that organizes the apical circumferential actomyosin belt and modulates cell-cell adhesion in epithelial cells. It localizes to apical cell-cell junctions, where it directly binds and activates p114RhoGEF to stimulate RhoA–ROCK signaling; this activation is negatively regulated by aPKC phosphorylation of its FERM-adjacent domain and is recruited to junctions by the CRB3 complex via its FERM-binding domain [PMID:22006950, PMID:22790195, PMID:26217006]. CRB3-dependent amphiregulin secretion and endocytic trafficking require EPB41L4B [PMID:30440051]. The Ehm2/1 splice isoform, which is confined to the plasma membrane, stabilizes E-cadherin by inhibiting its ubiquitination, thereby suppressing epithelial-to-mesenchymal transition and cell invasion [PMID:30816447, PMID:36422008].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Initial functional characterization showed EPB41L4B participates in cell-matrix adhesion, as its overexpression reduced collagen IV adhesion in prostate cancer cells, linking the FERM-domain protein to adhesion regulation.\",\n      \"evidence\": \"Overexpression and RNAi in prostate cancer cells with collagen IV adhesion assay\",\n      \"pmids\": [\"16927306\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No molecular target or binding partner identified\",\n        \"Whether effects are direct or via downstream signaling unknown\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"EPB41L4B knockdown reduced MMP-9 expression and invasion in breast cancer cells, establishing a link between EPB41L4B and extracellular matrix remodeling during tumor invasion.\",\n      \"evidence\": \"Ribozyme knockdown in breast cancer cells with invasion assays and MMP-9 zymography\",\n      \"pmids\": [\"21047774\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether MMP-9 regulation is transcriptional or post-transcriptional not determined\",\n        \"No mechanism connecting FERM domain to MMP-9 expression\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The central mechanistic question—how does EPB41L4B maintain epithelial architecture—was answered by demonstrating that it directly binds and activates p114RhoGEF at apical junctions, with aPKC phosphorylation of the FERM-adjacent domain serving as a negative regulator.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, RNAi phenotyping, in vitro kinase assay with phospho-mutants, immunofluorescence in epithelial cells\",\n      \"pmids\": [\"22006950\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of FERM-adjacent domain phosphorylation by aPKC unresolved\",\n        \"Whether other kinases also regulate this interaction unknown\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Quantitative biochemistry confirmed that EPB41L4B directly enhances GEF catalytic activity of p114RhoGEF, establishing it as a bona fide allosteric activator rather than merely a co-localizing scaffold.\",\n      \"evidence\": \"In vitro GEF activity assay with purified components, RNAi, and co-immunoprecipitation\",\n      \"pmids\": [\"22790195\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether FERM domain alone is sufficient for GEF activation not tested\",\n        \"No structural model of the activation complex\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The upstream recruitment mechanism was resolved: CRB3A recruits both EPB41L4B and p114RhoGEF to the cell periphery through its cytoplasmic tail, placing the CRB3–EPB41L4B–p114RhoGEF axis as a coherent pathway driving circumferential actomyosin belt formation via ROCK1/2.\",\n      \"evidence\": \"Ectopic CRB3A expression in HeLa cells, RhoA G-LISA, reciprocal co-immunoprecipitation, ROCK inhibitor epistasis\",\n      \"pmids\": [\"26217006\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether Patj/Pals1 complex members are required for EPB41L4B recruitment not addressed\",\n        \"Relative contribution of CRB3 versus other polarity cues in native epithelia unclear\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Beyond cytoskeletal regulation, EPB41L4B was shown to be required for CRB3-dependent amphiregulin secretion and regulation of endosome size, expanding its role to vesicular trafficking and growth factor signaling.\",\n      \"evidence\": \"siRNA knockdown in mammary epithelial cells, amphiregulin ELISA, confocal endosome imaging, CRB3 FERM-binding domain deletion mutants\",\n      \"pmids\": [\"30440051\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which EPB41L4B regulates endosome size not determined\",\n        \"Whether amphiregulin secretion requires RhoA activation or a parallel pathway unknown\",\n        \"Single lab observation\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Functional divergence of EPB41L4B splice isoforms was established: plasma membrane–restricted Ehm2/1 promotes epithelial identity (E-cadherin up, Snail1 down), while Ehm2/2, which also localizes to the cytoplasm, promotes mesenchymal features.\",\n      \"evidence\": \"Isoform-specific overexpression and knockdown in A549 cells, immunofluorescence localization, Western blot for EMT markers\",\n      \"pmids\": [\"30816447\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural determinants of isoform-specific localization not mapped\",\n        \"Whether opposing EMT effects act through the same p114RhoGEF pathway unknown\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The mechanism by which Ehm2/1 stabilizes epithelial identity was pinpointed: it co-localizes with and stabilizes E-cadherin at the plasma membrane by inhibiting E-cadherin ubiquitination, directly linking EPB41L4B to post-translational control of adherens junctions.\",\n      \"evidence\": \"Co-localization immunofluorescence, cycloheximide chase half-life assay, ubiquitination assay in MCF-7 cells\",\n      \"pmids\": [\"36422008\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The E3 ligase whose activity is blocked by Ehm2/1 not identified\",\n        \"Whether E-cadherin stabilization requires FERM domain or a distinct domain unknown\",\n        \"Single lab; no reciprocal validation of direct E-cadherin binding\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the structural basis of EPB41L4B's allosteric activation of p114RhoGEF, the identity of the E3 ubiquitin ligase it antagonizes at E-cadherin, the molecular determinant governing isoform-specific localization, and whether its RhoA-dependent and E-cadherin-stabilizing functions represent parallel or convergent pathways.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal structure or cryo-EM model of EPB41L4B or its complexes\",\n        \"E3 ligase counterpart for E-cadherin ubiquitination not identified\",\n        \"Isoform-specific domain mapping not performed\",\n        \"In vivo genetic models (knockout mouse) not reported in the timeline\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 7, 8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [0, 2, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"ARHGEF18\",\n      \"CRB3\",\n      \"CDH1\",\n      \"PRKCZ\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}