{"gene":"ERBB2","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":2000,"finding":"ErbB2 acts as a ligand-less signaling subunit that heterodimerizes with ErbB1, ErbB3, and ErbB4; ErbB2-containing heterodimers decrease the rate of ligand dissociation, internalize slowly, avoid lysosomal degradation by returning to the cell surface, and strongly recruit MAPK and PI3K survival/mitogenic pathways. ErbB2 overexpression upregulates active cyclin-D/CDK complexes and p21waf1, linking it to cell cycle dysregulation and chemoresistance.","method":"Review synthesizing biochemical and cell-biological experiments (receptor internalization assays, signaling pathway activation studies, cell cycle analyses)","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods across many labs, extensively replicated findings on heterodimerization, trafficking, and downstream signaling","pmids":["11156523"],"is_preprint":false},{"year":2002,"finding":"Conditional cardiomyocyte-specific deletion of ErbB2 in mice causes severe dilated cardiomyopathy with cardiac dysfunction, demonstrating that ErbB2 signaling in the heart (where it is enriched in T-tubules) is essential for adult cardiac function.","method":"Cre-loxP conditional knockout in ventricular cardiomyocytes; cardiac phenotyping including chamber dilation, wall thinning, and contractility measurements","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean conditional KO with specific cellular phenotype; replicated in a second independent study (PMID:14749494)","pmids":["12072561","14749494"],"is_preprint":false},{"year":2001,"finding":"ERBB2/HER2 interacts with PDZ-domain proteins ERBIN and PICK1 through its C-terminal PDZ-binding sequence. ERBIN localizes ErbB2 to the basolateral epithelium, while PICK1 is involved in receptor clustering. ERBIN and PICK1 bind ErbB2 through distinct mechanisms that are regulated in cells.","method":"Co-immunoprecipitation, pulldown assays, domain-mapping experiments, subcellular localization studies","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal binding assays with domain mapping, single lab with multiple orthogonal methods","pmids":["11278603"],"is_preprint":false},{"year":2004,"finding":"ErbB2/Neu/HER2 is a calmodulin (CaM)-binding protein; it binds CaM in a Ca2+-dependent manner. CaM antagonist W7 down-regulates ErbB2 phosphorylation and inhibits downstream ERK1/2 and Akt/PKB phosphorylation, demonstrating that CaM regulates ErbB2 activity and signaling in vivo.","method":"CaM-agarose pulldown, Ca2+-dependent affinity chromatography, biotinylated CaM overlay assay on immunoprecipitated ErbB2, pharmacological inhibition with W7 in live cells, Western blotting for phospho-ERK and phospho-Akt","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal biochemical methods (pulldown, overlay, chromatography, pharmacological inhibition), single lab","pmids":["15080792"],"is_preprint":false},{"year":2007,"finding":"Protein tyrosine phosphatase PTPN13 negatively regulates Her2/ErbB2 by dephosphorylating the Her2 signaling domain. Growth factor-induced phosphorylation of PTPN13 is required for Her2 dephosphorylation (negative feedback). Tumor-derived PTPN13 mutations reduce its phosphatase activity, elevating Her2 oncogenic potential and cancer cell invasiveness.","method":"siRNA phosphatase library screen, PTPN13 knockdown with phosphorylation readout, PTPN13 phosphatase activity assays with tumor-derived mutants, invasion assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA screen with functional follow-up and activity assays, single lab with multiple methods","pmids":["17982484"],"is_preprint":false},{"year":2008,"finding":"Caspases cleave the cytoplasmic tail of HER-2 at Asp1016/Asp1019 to release a ~47-kDa product, which is further cleaved at Asp1125 into a 22-kDa (proteasome-degraded) and predicted 25-kDa fragment. Both 47- and 25-kDa cleavage products translocate to mitochondria, release cytochrome c via a Bcl-xL-suppressible mechanism, and induce caspase-dependent apoptosis through a functional BH3-like domain, acting analogously to Bad.","method":"In vitro caspase cleavage assays, site-directed mutagenesis of caspase cleavage sites, mitochondrial fractionation/translocation assays, cytochrome c release assay, co-immunoprecipitation with Bcl-xL, apoptosis readouts","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution with mutagenesis, multiple orthogonal functional assays, single lab","pmids":["18420586"],"is_preprint":false},{"year":2014,"finding":"Overexpressed HER2/ErbB2 constitutively activates heat-shock factor 1 (HSF1) via the PI3K-AKT-mTOR axis, which in turn sustains HSP90 chaperone activity. This stabilizes HSP90 clients including MIF, AKT, mutant p53, and HSF1 itself. Pharmacological or siRNA-mediated HER2 inhibition blocks pSer326-HSF1, destabilizes these clients, and suppresses tumor proliferation in vitro and in vivo.","method":"HER2 inhibition by lapatinib, CP724.714, or siRNA knockdown; Western blotting for phospho-HSF1 (Ser326); HSP90 client stability assays; in vivo mouse ErbB2 tumor model; heat-shock stress experiments; pathway rescue with PI3K inhibitors","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pharmacological and genetic perturbations with consistent mechanistic readouts, in vitro and in vivo, single lab","pmids":["24384723"],"is_preprint":false},{"year":2012,"finding":"The atypical histone macroH2A1.2 (but not macroH2A1.1) interacts with nuclear HER-2 in cancer cells via its evolutionarily conserved macro domain (specifically requiring the -EIS- trinucleotide insert). This interaction promotes HER-2 expression and tumorigenicity; inhibition of HER-2 kinase activity diminishes macroH2A1 expression. Chromatin immunoprecipitation shows macroH2A1.2 enrichment at the HER-2 promoter.","method":"Co-immunoprecipitation, ChIP, domain-mapping mutagenesis, siRNA knockdown, overexpression studies, tumorigenicity assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, ChIP, mutagenesis, functional assays), single lab","pmids":["22589551"],"is_preprint":false},{"year":2016,"finding":"Septins form complexes with ErbB2 at the plasma membrane (identified by co-immunoprecipitation/MS), protecting ErbB2 from ubiquitylation, endocytosis and lysosomal degradation. Knockdown of septin-2 or pharmacological disruption of septin oligomerization (forchlorfenuron) increases ErbB2 ubiquitylation, triggers its endocytosis and lysosomal degradation via cathepsin B, and reduces surface ErbB2 levels. This mechanism is distinct from and additive with Hsp90-mediated ErbB2 stabilization.","method":"Co-immunoprecipitation followed by mass spectrometry, septin-2 siRNA knockdown, forchlorfenuron treatment, ubiquitylation assays, lysosomal inhibitor experiments, surface ErbB2 quantification","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — MS-confirmed interaction, multiple genetic and pharmacological perturbations, mechanistic follow-up with pathway inhibitors, single lab with multiple orthogonal methods","pmids":["27048593"],"is_preprint":false},{"year":2018,"finding":"Recurrent HER2 transmembrane domain (TMD) and juxtamembrane domain (JMD) mutations (G660D, R678Q, E693K, Q709L) are activating. Structural modeling and saturation mutagenesis show that TMD/JMD mutations improve the active dimer interface or stabilize an activating conformation. G660D employs asymmetric kinase dimerization for activation and signaling. Anti-HER2 antibodies and small-molecule kinase inhibitors block the activity of these mutants.","method":"Saturation mutagenesis screen, structural modeling of TMD/JMD dimer interfaces, kinase activity assays, inhibitor treatment of mutant-expressing cells, clinical case validation","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — saturation mutagenesis plus structural modeling plus functional kinase assays; clinically validated","pmids":["30449325"],"is_preprint":false},{"year":2020,"finding":"HER2 ubiquitination and internalization (endocytosis), rather than simple overexpression, are the key mechanisms underlying intracellular delivery and efficacy of anti-HER2 antibody-drug conjugates (T-DM1 and T-DXd) in lung cancer. Co-treatment with irreversible pan-HER inhibitors enhances HER2 ubiquitination and consequent ADC internalization and efficacy.","method":"Ubiquitination assays, internalization/endocytosis assays, cell viability assays in cell lines and patient-derived xenograft models, clinical trial (T-DM1 in ERBB2-amplified/mutant lung cancers)","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical mechanism (ubiquitination, endocytosis) validated in multiple preclinical models and translated to a clinical trial","pmids":["32213539"],"is_preprint":false},{"year":2006,"finding":"In ADPKD epithelia, apical localization of EGFR complexes is associated with heterodimerization of EGFR (HER-1) with HER-2, while basolateral localization in normal adult epithelia is associated with EGFR homodimers. Specific inhibition of HER-2 (by AG825 or ErbB2 siRNA) reverses the migration defect of ADPKD epithelial cells and inhibits cyst development in PKD1 heterozygous mice, with p38MAPK acting downstream of HER-2 stimulation.","method":"Co-immunoprecipitation (heterodimerization), specific HER-2 inhibitor AG825, ErbB2 siRNA knockdown, cell migration bioassay, p38MAPK inhibition, in vivo PKD1 mouse model","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological perturbations with specific functional readout, in vitro and in vivo, single lab","pmids":["16797938"],"is_preprint":false},{"year":2010,"finding":"In prolactinoma cells, constitutively active HER2/ErbB2 potently induces prolactin (PRL) mRNA and secretion (~250-fold and ~100-fold respectively) and increases cell proliferation. Lapatinib (dual EGFR/HER2 TKI) blocks receptor signaling and suppresses PRL expression more effectively than gefitinib (EGFR-only), demonstrating a HER2-specific mechanism.","method":"Stable transfection of constitutively active HER2 into GH3 cells, mRNA and secretion measurements, lapatinib vs. gefitinib treatment, soft agar colony formation, oral lapatinib in rat prolactinoma models, cultured human prolactinoma cells","journal":"Molecular endocrinology (Baltimore, Md.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — constitutively active construct plus pharmacological inhibition with receptor-specific comparison, in vitro and in vivo, single lab","pmids":["21106881"],"is_preprint":false},{"year":2010,"finding":"In endometrial cancer cells, HER-2 activates the PI3K/AKT pathway (HER-2/PI3K-AKT axis): siRNA-based knockdown of HER-2 significantly reduces phospho-AKT. This axis confers resistance to paclitaxel; HER-2 knockdown increases paclitaxel sensitivity, and this sensitization is cancelled by dominant-negative AKT, confirming AKT as the mediating node.","method":"siRNA knockdown of HER-2, Western blotting for p-AKT, dominant-negative AKT rescue experiment, paclitaxel cytotoxicity assays","journal":"British journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with mechanistic rescue experiment (dominant-negative AKT), single lab with orthogonal genetic approaches","pmids":["20664599"],"is_preprint":false},{"year":1992,"finding":"EGF (and TGF-α) treatment of ovarian and mammary carcinoma cells significantly reduces HER-2 protein expression at the cell surface and total cellular level. In OVCAR-3 cells, EGF reduces HER-2 mRNA levels, but this effect is not observed in HER-2-overexpressing lines, suggesting that mRNA down-regulation is not the sole mechanism.","method":"ELISA for total HER-2 protein, living-cell RIA for surface HER-2, mRNA analysis, dose-response experiments with EGF and TGF-α","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct quantitative measurement of HER-2 protein and mRNA after defined ligand treatment, multiple cell lines, single lab","pmids":["1355758"],"is_preprint":false},{"year":2019,"finding":"In HER2-mutant (L755S, V842I) MSI colorectal cancer cell lines, irreversible pan-HER inhibitors are superior to reversible inhibitors or individual antibodies, functionally validating these ERBB2 mutations as activating and demonstrating differential dependency on the kinase active conformation.","method":"Functional treatment of ERBB2-mutated CRC cell lines with reversible/irreversible HER inhibitors, EGFR antibodies, trastuzumab, and siRNA-mediated ERBB2 knockdown; viability assays","journal":"Gut","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional cell-line experiments with genetic and pharmacological perturbations comparing inhibitor classes, single lab","pmids":["26001389"],"is_preprint":false}],"current_model":"ERBB2/HER2 is a ligand-less receptor tyrosine kinase that signals as an obligate heterodimerization partner (with ErbB1, ErbB3, and ErbB4), activating MAPK, PI3K-AKT-mTOR, and HSF1-HSP90 axes; its activity is restrained by PTPN13-mediated dephosphorylation and septin-dependent protection from ubiquitylation/lysosomal degradation; upon apoptotic stimulation, caspase cleavage of the cytoplasmic tail releases Bad-like pro-apoptotic fragments; calmodulin binds ErbB2 in a Ca²⁺-dependent manner to regulate its phosphorylation; activating mutations in the transmembrane and juxtamembrane domains stabilize the active dimer interface; and HER2 ubiquitination and endocytosis—regulated by irreversible pan-HER inhibitors—determines the intracellular delivery efficacy of antibody-drug conjugates."},"narrative":{"mechanistic_narrative":"ERBB2/HER2 is a ligand-less receptor tyrosine kinase that functions as the preferred heterodimerization partner for ErbB1, ErbB3, and ErbB4, generating signaling-competent complexes that slow ligand dissociation, evade lysosomal degradation by recycling to the cell surface, and strongly engage MAPK and PI3K survival/mitogenic pathways, driving cyclin-D/CDK activity and chemoresistance [PMID:11156523]. Downstream, HER2 activates the PI3K/AKT axis to confer drug resistance [PMID:20664599] and constitutively drives HSF1 (Ser326) phosphorylation via PI3K-AKT-mTOR to sustain HSP90 chaperone activity and stabilize oncogenic clients [PMID:24384723]. Its activity is held in check by negative regulators: the phosphatase PTPN13 dephosphorylates the HER2 signaling domain in a growth-factor-induced feedback loop, and tumor-derived PTPN13 mutations elevate HER2 oncogenic and invasive potential [PMID:17982484], while calmodulin binds HER2 in a Ca2+-dependent manner to modulate its phosphorylation and downstream ERK/AKT signaling [PMID:15080792]. Receptor stability and trafficking are governed by septin complexes at the plasma membrane, which shield HER2 from ubiquitylation, endocytosis, and cathepsin-B-dependent lysosomal degradation [PMID:27048593], and HER2 ubiquitination/internalization governs the delivery and efficacy of anti-HER2 antibody-drug conjugates [PMID:32213539]. Recurrent transmembrane and juxtamembrane mutations (e.g., G660D) are activating by stabilizing the active dimer interface and promoting asymmetric kinase dimerization, and remain sensitive to anti-HER2 antibodies and kinase inhibitors [PMID:30449325]. Upon apoptotic stimulation, caspases cleave the HER2 cytoplasmic tail to release fragments bearing a functional BH3-like domain that translocate to mitochondria and trigger Bcl-xL-suppressible cytochrome c release and caspase-dependent apoptosis, acting analogously to Bad [PMID:18420586]. HER2 signaling is also physiologically essential in adult cardiomyocytes, where its deletion causes dilated cardiomyopathy [PMID:12072561, PMID:14749494].","teleology":[{"year":1992,"claim":"Established that HER2 protein levels are dynamically down-regulated by EGFR ligands, an early indication that receptor abundance is actively controlled rather than fixed.","evidence":"ELISA and surface RIA quantification of HER2 protein and mRNA after EGF/TGF-alpha treatment in ovarian and mammary carcinoma cells","pmids":["1355758"],"confidence":"Medium","gaps":["Mechanism of protein down-regulation not resolved (mRNA effect insufficient)","No link to ubiquitylation or trafficking machinery established at this stage"]},{"year":2000,"claim":"Defined HER2's core mechanism as a ligand-less heterodimerization partner that biases trafficking toward recycling and amplifies MAPK/PI3K survival signaling, explaining its oncogenic potency.","evidence":"Review synthesizing receptor internalization assays, signaling activation studies, and cell cycle analyses","pmids":["11156523"],"confidence":"High","gaps":["Does not identify the regulators controlling dimer choice","Mechanistic basis of recycling vs degradation not molecularly resolved"]},{"year":2001,"claim":"Identified PDZ-domain partners that spatially organize HER2, linking its C-terminal tail to basolateral localization and receptor clustering.","evidence":"Co-IP, pulldown, and domain-mapping with ERBIN and PICK1; subcellular localization studies","pmids":["11278603"],"confidence":"Medium","gaps":["Functional consequence of clustering for signaling output not quantified","Single-lab interaction data"]},{"year":2002,"claim":"Demonstrated a physiological, non-oncogenic requirement for HER2 in adult cardiomyocytes, establishing the basis for cardiac vulnerability to HER2-directed therapy.","evidence":"Cardiomyocyte-specific Cre-loxP conditional knockout with cardiac phenotyping; replicated independently","pmids":["12072561","14749494"],"confidence":"High","gaps":["Ligand/dimer partner driving cardiac HER2 signaling not defined here","Downstream effectors in cardiomyocytes not mapped"]},{"year":2004,"claim":"Showed HER2 is a Ca2+-dependent calmodulin-binding protein whose phosphorylation and ERK/AKT output depend on CaM, adding a calcium-sensing layer to receptor regulation.","evidence":"CaM-agarose pulldown, overlay assay, Ca2+-dependent chromatography, and W7 pharmacological inhibition in cells","pmids":["15080792"],"confidence":"Medium","gaps":["CaM-binding site on HER2 not mapped","W7 effects not exclusive to CaM-HER2 axis","Single lab"]},{"year":2007,"claim":"Identified PTPN13 as a negative-feedback phosphatase for HER2 and linked its loss-of-function mutations to enhanced HER2 oncogenicity, establishing dephosphorylation as a tumor-suppressive brake.","evidence":"siRNA phosphatase library screen, PTPN13 knockdown, activity assays with tumor-derived mutants, invasion assays","pmids":["17982484"],"confidence":"Medium","gaps":["Direct phosphosite specificity on HER2 not enumerated","Single lab"]},{"year":2008,"claim":"Revealed a pro-apoptotic dimension of HER2: caspase cleavage of its cytoplasmic tail liberates BH3-like fragments that engage the mitochondrial apoptotic pathway, recasting the receptor as a Bad-like effector under apoptotic stress.","evidence":"In vitro caspase cleavage, mutagenesis of cleavage sites, mitochondrial translocation and cytochrome c release assays, Bcl-xL co-IP","pmids":["18420586"],"confidence":"High","gaps":["Physiological contexts triggering this cleavage in vivo unclear","Relative contribution vs canonical apoptotic regulators not quantified"]},{"year":2010,"claim":"Established the HER2/PI3K-AKT axis as a node for paclitaxel resistance and tissue-specific oncogenic outputs (prolactin induction in prolactinoma), connecting HER2 to therapy resistance and endocrine tumor biology.","evidence":"siRNA knockdown with dominant-negative AKT rescue in endometrial cancer; constitutively active HER2 with lapatinib vs gefitinib in prolactinoma models","pmids":["20664599","21106881"],"confidence":"Medium","gaps":["Effector specificity downstream of AKT not fully resolved","Tissue-specific transcriptional mechanisms not mapped"]},{"year":2012,"claim":"Uncovered a nuclear HER2 function via macroH2A1.2 interaction at the HER2 promoter, defining a feed-forward loop sustaining HER2 expression and tumorigenicity.","evidence":"Co-IP, ChIP, macro-domain mutagenesis, knockdown and overexpression, tumorigenicity assays","pmids":["22589551"],"confidence":"Medium","gaps":["How HER2 reaches the nucleus not defined","Single lab"]},{"year":2014,"claim":"Connected HER2 overexpression to constitutive HSF1 activation and HSP90 client stabilization, explaining how HER2 maintains a proteostatic environment supporting oncogenic clients.","evidence":"Lapatinib/CP724.714/siRNA HER2 inhibition, phospho-HSF1(Ser326) blotting, client stability assays, in vivo ErbB2 tumor model, PI3K rescue","pmids":["24384723"],"confidence":"Medium","gaps":["Direct kinase phosphorylating Ser326-HSF1 downstream of HER2 not identified","Single lab"]},{"year":2016,"claim":"Identified septin complexes as plasma-membrane protectors of HER2, resolving a long-standing question of how surface HER2 evades ubiquitylation and lysosomal degradation independently of HSP90.","evidence":"Co-IP/MS, septin-2 siRNA, forchlorfenuron disruption, ubiquitylation and lysosomal inhibitor assays, surface HER2 quantification","pmids":["27048593"],"confidence":"High","gaps":["E3 ligase mediating HER2 ubiquitylation upon septin loss not identified","Septin-HER2 contact interface not structurally defined"]},{"year":2018,"claim":"Mechanistically explained activating transmembrane/juxtamembrane mutations as stabilizers of the active dimer interface and asymmetric kinase dimerization, defining a druggable mutational class.","evidence":"Saturation mutagenesis, structural modeling of TMD/JMD interfaces, kinase activity assays, inhibitor treatment, clinical validation","pmids":["30449325"],"confidence":"High","gaps":["Quantitative signaling differences among individual mutants not fully resolved","Resistance trajectories under inhibitor pressure not addressed here"]},{"year":2019,"claim":"Validated HER2 kinase-domain mutations as activating in MSI colorectal cancer and showed differential dependence on the active conformation, refining inhibitor-class selection.","evidence":"Functional treatment of ERBB2-mutant CRC lines with reversible/irreversible inhibitors, antibodies, and siRNA; viability assays","pmids":["26001389"],"confidence":"Medium","gaps":["Structural basis of conformational dependency for these specific mutants not solved","Single lab"]},{"year":2020,"claim":"Demonstrated that HER2 ubiquitination and endocytosis—not mere overexpression—govern antibody-drug conjugate delivery, and that pan-HER inhibitors enhance ADC efficacy by promoting internalization, translating receptor trafficking biology into therapy.","evidence":"Ubiquitination and internalization assays, viability assays in cell lines and PDX, clinical trial of T-DM1 in ERBB2-altered lung cancer","pmids":["32213539"],"confidence":"High","gaps":["E3 ligase coupling inhibitor treatment to ubiquitylation not pinpointed","Predictive biomarkers of internalization capacity not defined"]},{"year":null,"claim":"The integration of opposing trafficking forces (septin protection vs ubiquitin-driven endocytosis) and the molecular identity of the E3 ligase(s) controlling HER2 degradation remain unresolved, despite their therapeutic centrality to ADC efficacy.","evidence":"","pmids":[],"confidence":"Medium","gaps":["HER2 E3 ubiquitin ligase not identified in the corpus","Mechanism coupling kinase inhibition to receptor ubiquitylation unknown","How nuclear, mitochondrial, and surface pools of HER2 are partitioned is unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,9]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,8]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[7]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,13]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[9,10]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[8,10]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[6]}],"complexes":[],"partners":["EGFR","ERBB3","ERBB4","PTPN13","CALM1","ERBIN","PICK1","MACROH2A1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P04626","full_name":"Receptor tyrosine-protein kinase erbB-2","aliases":["Metastatic lymph node gene 19 protein","MLN 19","Proto-oncogene Neu","Proto-oncogene c-ErbB-2","Tyrosine kinase-type cell surface receptor HER2","p185erbB2"],"length_aa":1255,"mass_kda":137.9,"function":"Protein tyrosine kinase that is part of several cell surface receptor complexes, but that apparently needs a coreceptor for ligand binding. Essential component of a neuregulin-receptor complex, although neuregulins do not interact with it alone. GP30 is a potential ligand for this receptor. Regulates outgrowth and stabilization of peripheral microtubules (MTs). Upon ERBB2 activation, the MEMO1-RHOA-DIAPH1 signaling pathway elicits the phosphorylation and thus the inhibition of GSK3B at cell membrane. This prevents the phosphorylation of APC and CLASP2, allowing its association with the cell membrane. In turn, membrane-bound APC allows the localization of MACF1 to the cell membrane, which is required for microtubule capture and stabilization In the nucleus is involved in transcriptional regulation. Associates with the 5'-TCAAATTC-3' sequence in the PTGS2/COX-2 promoter and activates its transcription. Implicated in transcriptional activation of CDKN1A; the function involves STAT3 and SRC. Involved in the transcription of rRNA genes by RNA Pol I and enhances protein synthesis and cell growth","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P04626/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ERBB2","classification":"Not Classified","n_dependent_lines":243,"n_total_lines":1208,"dependency_fraction":0.201158940397351},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ERBB2","total_profiled":1310},"omim":[{"mim_id":"621339","title":"HISTIDINE-RICH CARBOXYL TERMINUS PROTEIN 1; HRCT1","url":"https://www.omim.org/entry/621339"},{"mim_id":"619465","title":"VISCERAL NEUROPATHY, FAMILIAL, 2, AUTOSOMAL RECESSIVE; VSCN2","url":"https://www.omim.org/entry/619465"},{"mim_id":"619448","title":"STEROID RECEPTOR-ASSOCIATED AND -REGULATED PROTEIN; SRARP","url":"https://www.omim.org/entry/619448"},{"mim_id":"618789","title":"CDV3 HOMOLOG; CDV3","url":"https://www.omim.org/entry/618789"},{"mim_id":"618717","title":"EPITHELIAL MITOGEN; EPGN","url":"https://www.omim.org/entry/618717"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Plasma membrane","reliability":"Enhanced"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ERBB2"},"hgnc":{"alias_symbol":["NEU","HER-2","CD340","HER2","c-ERB2","c-ERB-2","MLN-19","p185(erbB2)"],"prev_symbol":["NGL"]},"alphafold":{"accession":"P04626","domains":[{"cath_id":"3.80.20.20","chopping":"20-123_133-215","consensus_level":"medium","plddt":91.0849,"start":20,"end":215},{"cath_id":"2.10.220.10","chopping":"271-332","consensus_level":"medium","plddt":85.6931,"start":271,"end":332},{"cath_id":"3.80.20.20","chopping":"348-510","consensus_level":"high","plddt":93.6482,"start":348,"end":510},{"cath_id":"2.10.220.10","chopping":"543-628","consensus_level":"medium","plddt":86.8565,"start":543,"end":628},{"cath_id":"3.30.200.20","chopping":"711-802_1002-1022","consensus_level":"medium","plddt":74.6674,"start":711,"end":1022},{"cath_id":"1.10.510.10","chopping":"804-866_884-994","consensus_level":"medium","plddt":89.8014,"start":804,"end":994}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P04626","model_url":"https://alphafold.ebi.ac.uk/files/AF-P04626-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P04626-F1-predicted_aligned_error_v6.png","plddt_mean":74.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ERBB2","jax_strain_url":"https://www.jax.org/strain/search?query=ERBB2"},"sequence":{"accession":"P04626","fasta_url":"https://rest.uniprot.org/uniprotkb/P04626.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P04626/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P04626"}},"corpus_meta":[{"pmid":"11156523","id":"PMC_11156523","title":"Molecular 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B","url":"https://pubmed.ncbi.nlm.nih.gov/24903996","citation_count":16,"is_preprint":false},{"pmid":"31805897","id":"PMC_31805897","title":"HER2 gene (ERBB2) amplification is a rare event in non-liver-fluke associated cholangiocarcinogenesis.","date":"2019","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31805897","citation_count":16,"is_preprint":false},{"pmid":"31488078","id":"PMC_31488078","title":"Combined targeting of HER-2 and HER-3 represents a promising therapeutic strategy in colorectal cancer.","date":"2019","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31488078","citation_count":16,"is_preprint":false},{"pmid":"31838585","id":"PMC_31838585","title":"HER2 gene (ERBB2) amplification is a low-frequency driver with potential predictive value in gallbladder carcinoma.","date":"2019","source":"Virchows Archiv : an international journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/31838585","citation_count":16,"is_preprint":false},{"pmid":"1355758","id":"PMC_1355758","title":"Epidermal growth factor reduces HER-2 protein level in human ovarian carcinoma cells.","date":"1992","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/1355758","citation_count":16,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":52874,"output_tokens":4663,"usd":0.114283,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12747,"output_tokens":4847,"usd":0.092455,"stage2_stop_reason":"end_turn"},"total_usd":0.206738,"stage1_batch_id":"msgbatch_01AsR7g8dGTEiEw9U83bJeWn","stage2_batch_id":"msgbatch_01YV5ZyxtFNUZEjxRcpd9jzb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"ErbB2 acts as a ligand-less signaling subunit that heterodimerizes with ErbB1, ErbB3, and ErbB4; ErbB2-containing heterodimers decrease the rate of ligand dissociation, internalize slowly, avoid lysosomal degradation by returning to the cell surface, and strongly recruit MAPK and PI3K survival/mitogenic pathways. ErbB2 overexpression upregulates active cyclin-D/CDK complexes and p21waf1, linking it to cell cycle dysregulation and chemoresistance.\",\n      \"method\": \"Review synthesizing biochemical and cell-biological experiments (receptor internalization assays, signaling pathway activation studies, cell cycle analyses)\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods across many labs, extensively replicated findings on heterodimerization, trafficking, and downstream signaling\",\n      \"pmids\": [\"11156523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Conditional cardiomyocyte-specific deletion of ErbB2 in mice causes severe dilated cardiomyopathy with cardiac dysfunction, demonstrating that ErbB2 signaling in the heart (where it is enriched in T-tubules) is essential for adult cardiac function.\",\n      \"method\": \"Cre-loxP conditional knockout in ventricular cardiomyocytes; cardiac phenotyping including chamber dilation, wall thinning, and contractility measurements\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean conditional KO with specific cellular phenotype; replicated in a second independent study (PMID:14749494)\",\n      \"pmids\": [\"12072561\", \"14749494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ERBB2/HER2 interacts with PDZ-domain proteins ERBIN and PICK1 through its C-terminal PDZ-binding sequence. ERBIN localizes ErbB2 to the basolateral epithelium, while PICK1 is involved in receptor clustering. ERBIN and PICK1 bind ErbB2 through distinct mechanisms that are regulated in cells.\",\n      \"method\": \"Co-immunoprecipitation, pulldown assays, domain-mapping experiments, subcellular localization studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal binding assays with domain mapping, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"11278603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"ErbB2/Neu/HER2 is a calmodulin (CaM)-binding protein; it binds CaM in a Ca2+-dependent manner. CaM antagonist W7 down-regulates ErbB2 phosphorylation and inhibits downstream ERK1/2 and Akt/PKB phosphorylation, demonstrating that CaM regulates ErbB2 activity and signaling in vivo.\",\n      \"method\": \"CaM-agarose pulldown, Ca2+-dependent affinity chromatography, biotinylated CaM overlay assay on immunoprecipitated ErbB2, pharmacological inhibition with W7 in live cells, Western blotting for phospho-ERK and phospho-Akt\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal biochemical methods (pulldown, overlay, chromatography, pharmacological inhibition), single lab\",\n      \"pmids\": [\"15080792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Protein tyrosine phosphatase PTPN13 negatively regulates Her2/ErbB2 by dephosphorylating the Her2 signaling domain. Growth factor-induced phosphorylation of PTPN13 is required for Her2 dephosphorylation (negative feedback). Tumor-derived PTPN13 mutations reduce its phosphatase activity, elevating Her2 oncogenic potential and cancer cell invasiveness.\",\n      \"method\": \"siRNA phosphatase library screen, PTPN13 knockdown with phosphorylation readout, PTPN13 phosphatase activity assays with tumor-derived mutants, invasion assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA screen with functional follow-up and activity assays, single lab with multiple methods\",\n      \"pmids\": [\"17982484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Caspases cleave the cytoplasmic tail of HER-2 at Asp1016/Asp1019 to release a ~47-kDa product, which is further cleaved at Asp1125 into a 22-kDa (proteasome-degraded) and predicted 25-kDa fragment. Both 47- and 25-kDa cleavage products translocate to mitochondria, release cytochrome c via a Bcl-xL-suppressible mechanism, and induce caspase-dependent apoptosis through a functional BH3-like domain, acting analogously to Bad.\",\n      \"method\": \"In vitro caspase cleavage assays, site-directed mutagenesis of caspase cleavage sites, mitochondrial fractionation/translocation assays, cytochrome c release assay, co-immunoprecipitation with Bcl-xL, apoptosis readouts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution with mutagenesis, multiple orthogonal functional assays, single lab\",\n      \"pmids\": [\"18420586\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Overexpressed HER2/ErbB2 constitutively activates heat-shock factor 1 (HSF1) via the PI3K-AKT-mTOR axis, which in turn sustains HSP90 chaperone activity. This stabilizes HSP90 clients including MIF, AKT, mutant p53, and HSF1 itself. Pharmacological or siRNA-mediated HER2 inhibition blocks pSer326-HSF1, destabilizes these clients, and suppresses tumor proliferation in vitro and in vivo.\",\n      \"method\": \"HER2 inhibition by lapatinib, CP724.714, or siRNA knockdown; Western blotting for phospho-HSF1 (Ser326); HSP90 client stability assays; in vivo mouse ErbB2 tumor model; heat-shock stress experiments; pathway rescue with PI3K inhibitors\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pharmacological and genetic perturbations with consistent mechanistic readouts, in vitro and in vivo, single lab\",\n      \"pmids\": [\"24384723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The atypical histone macroH2A1.2 (but not macroH2A1.1) interacts with nuclear HER-2 in cancer cells via its evolutionarily conserved macro domain (specifically requiring the -EIS- trinucleotide insert). This interaction promotes HER-2 expression and tumorigenicity; inhibition of HER-2 kinase activity diminishes macroH2A1 expression. Chromatin immunoprecipitation shows macroH2A1.2 enrichment at the HER-2 promoter.\",\n      \"method\": \"Co-immunoprecipitation, ChIP, domain-mapping mutagenesis, siRNA knockdown, overexpression studies, tumorigenicity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, ChIP, mutagenesis, functional assays), single lab\",\n      \"pmids\": [\"22589551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Septins form complexes with ErbB2 at the plasma membrane (identified by co-immunoprecipitation/MS), protecting ErbB2 from ubiquitylation, endocytosis and lysosomal degradation. Knockdown of septin-2 or pharmacological disruption of septin oligomerization (forchlorfenuron) increases ErbB2 ubiquitylation, triggers its endocytosis and lysosomal degradation via cathepsin B, and reduces surface ErbB2 levels. This mechanism is distinct from and additive with Hsp90-mediated ErbB2 stabilization.\",\n      \"method\": \"Co-immunoprecipitation followed by mass spectrometry, septin-2 siRNA knockdown, forchlorfenuron treatment, ubiquitylation assays, lysosomal inhibitor experiments, surface ErbB2 quantification\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — MS-confirmed interaction, multiple genetic and pharmacological perturbations, mechanistic follow-up with pathway inhibitors, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27048593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Recurrent HER2 transmembrane domain (TMD) and juxtamembrane domain (JMD) mutations (G660D, R678Q, E693K, Q709L) are activating. Structural modeling and saturation mutagenesis show that TMD/JMD mutations improve the active dimer interface or stabilize an activating conformation. G660D employs asymmetric kinase dimerization for activation and signaling. Anti-HER2 antibodies and small-molecule kinase inhibitors block the activity of these mutants.\",\n      \"method\": \"Saturation mutagenesis screen, structural modeling of TMD/JMD dimer interfaces, kinase activity assays, inhibitor treatment of mutant-expressing cells, clinical case validation\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — saturation mutagenesis plus structural modeling plus functional kinase assays; clinically validated\",\n      \"pmids\": [\"30449325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HER2 ubiquitination and internalization (endocytosis), rather than simple overexpression, are the key mechanisms underlying intracellular delivery and efficacy of anti-HER2 antibody-drug conjugates (T-DM1 and T-DXd) in lung cancer. Co-treatment with irreversible pan-HER inhibitors enhances HER2 ubiquitination and consequent ADC internalization and efficacy.\",\n      \"method\": \"Ubiquitination assays, internalization/endocytosis assays, cell viability assays in cell lines and patient-derived xenograft models, clinical trial (T-DM1 in ERBB2-amplified/mutant lung cancers)\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical mechanism (ubiquitination, endocytosis) validated in multiple preclinical models and translated to a clinical trial\",\n      \"pmids\": [\"32213539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In ADPKD epithelia, apical localization of EGFR complexes is associated with heterodimerization of EGFR (HER-1) with HER-2, while basolateral localization in normal adult epithelia is associated with EGFR homodimers. Specific inhibition of HER-2 (by AG825 or ErbB2 siRNA) reverses the migration defect of ADPKD epithelial cells and inhibits cyst development in PKD1 heterozygous mice, with p38MAPK acting downstream of HER-2 stimulation.\",\n      \"method\": \"Co-immunoprecipitation (heterodimerization), specific HER-2 inhibitor AG825, ErbB2 siRNA knockdown, cell migration bioassay, p38MAPK inhibition, in vivo PKD1 mouse model\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological perturbations with specific functional readout, in vitro and in vivo, single lab\",\n      \"pmids\": [\"16797938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In prolactinoma cells, constitutively active HER2/ErbB2 potently induces prolactin (PRL) mRNA and secretion (~250-fold and ~100-fold respectively) and increases cell proliferation. Lapatinib (dual EGFR/HER2 TKI) blocks receptor signaling and suppresses PRL expression more effectively than gefitinib (EGFR-only), demonstrating a HER2-specific mechanism.\",\n      \"method\": \"Stable transfection of constitutively active HER2 into GH3 cells, mRNA and secretion measurements, lapatinib vs. gefitinib treatment, soft agar colony formation, oral lapatinib in rat prolactinoma models, cultured human prolactinoma cells\",\n      \"journal\": \"Molecular endocrinology (Baltimore, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — constitutively active construct plus pharmacological inhibition with receptor-specific comparison, in vitro and in vivo, single lab\",\n      \"pmids\": [\"21106881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In endometrial cancer cells, HER-2 activates the PI3K/AKT pathway (HER-2/PI3K-AKT axis): siRNA-based knockdown of HER-2 significantly reduces phospho-AKT. This axis confers resistance to paclitaxel; HER-2 knockdown increases paclitaxel sensitivity, and this sensitization is cancelled by dominant-negative AKT, confirming AKT as the mediating node.\",\n      \"method\": \"siRNA knockdown of HER-2, Western blotting for p-AKT, dominant-negative AKT rescue experiment, paclitaxel cytotoxicity assays\",\n      \"journal\": \"British journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with mechanistic rescue experiment (dominant-negative AKT), single lab with orthogonal genetic approaches\",\n      \"pmids\": [\"20664599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"EGF (and TGF-α) treatment of ovarian and mammary carcinoma cells significantly reduces HER-2 protein expression at the cell surface and total cellular level. In OVCAR-3 cells, EGF reduces HER-2 mRNA levels, but this effect is not observed in HER-2-overexpressing lines, suggesting that mRNA down-regulation is not the sole mechanism.\",\n      \"method\": \"ELISA for total HER-2 protein, living-cell RIA for surface HER-2, mRNA analysis, dose-response experiments with EGF and TGF-α\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct quantitative measurement of HER-2 protein and mRNA after defined ligand treatment, multiple cell lines, single lab\",\n      \"pmids\": [\"1355758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In HER2-mutant (L755S, V842I) MSI colorectal cancer cell lines, irreversible pan-HER inhibitors are superior to reversible inhibitors or individual antibodies, functionally validating these ERBB2 mutations as activating and demonstrating differential dependency on the kinase active conformation.\",\n      \"method\": \"Functional treatment of ERBB2-mutated CRC cell lines with reversible/irreversible HER inhibitors, EGFR antibodies, trastuzumab, and siRNA-mediated ERBB2 knockdown; viability assays\",\n      \"journal\": \"Gut\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional cell-line experiments with genetic and pharmacological perturbations comparing inhibitor classes, single lab\",\n      \"pmids\": [\"26001389\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ERBB2/HER2 is a ligand-less receptor tyrosine kinase that signals as an obligate heterodimerization partner (with ErbB1, ErbB3, and ErbB4), activating MAPK, PI3K-AKT-mTOR, and HSF1-HSP90 axes; its activity is restrained by PTPN13-mediated dephosphorylation and septin-dependent protection from ubiquitylation/lysosomal degradation; upon apoptotic stimulation, caspase cleavage of the cytoplasmic tail releases Bad-like pro-apoptotic fragments; calmodulin binds ErbB2 in a Ca²⁺-dependent manner to regulate its phosphorylation; activating mutations in the transmembrane and juxtamembrane domains stabilize the active dimer interface; and HER2 ubiquitination and endocytosis—regulated by irreversible pan-HER inhibitors—determines the intracellular delivery efficacy of antibody-drug conjugates.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ERBB2/HER2 is a ligand-less receptor tyrosine kinase that functions as the preferred heterodimerization partner for ErbB1, ErbB3, and ErbB4, generating signaling-competent complexes that slow ligand dissociation, evade lysosomal degradation by recycling to the cell surface, and strongly engage MAPK and PI3K survival/mitogenic pathways, driving cyclin-D/CDK activity and chemoresistance [#0]. Downstream, HER2 activates the PI3K/AKT axis to confer drug resistance [#13] and constitutively drives HSF1 (Ser326) phosphorylation via PI3K-AKT-mTOR to sustain HSP90 chaperone activity and stabilize oncogenic clients [#6]. Its activity is held in check by negative regulators: the phosphatase PTPN13 dephosphorylates the HER2 signaling domain in a growth-factor-induced feedback loop, and tumor-derived PTPN13 mutations elevate HER2 oncogenic and invasive potential [#4], while calmodulin binds HER2 in a Ca2+-dependent manner to modulate its phosphorylation and downstream ERK/AKT signaling [#3]. Receptor stability and trafficking are governed by septin complexes at the plasma membrane, which shield HER2 from ubiquitylation, endocytosis, and cathepsin-B-dependent lysosomal degradation [#8], and HER2 ubiquitination/internalization governs the delivery and efficacy of anti-HER2 antibody-drug conjugates [#10]. Recurrent transmembrane and juxtamembrane mutations (e.g., G660D) are activating by stabilizing the active dimer interface and promoting asymmetric kinase dimerization, and remain sensitive to anti-HER2 antibodies and kinase inhibitors [#9]. Upon apoptotic stimulation, caspases cleave the HER2 cytoplasmic tail to release fragments bearing a functional BH3-like domain that translocate to mitochondria and trigger Bcl-xL-suppressible cytochrome c release and caspase-dependent apoptosis, acting analogously to Bad [#5]. HER2 signaling is also physiologically essential in adult cardiomyocytes, where its deletion causes dilated cardiomyopathy [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Established that HER2 protein levels are dynamically down-regulated by EGFR ligands, an early indication that receptor abundance is actively controlled rather than fixed.\",\n      \"evidence\": \"ELISA and surface RIA quantification of HER2 protein and mRNA after EGF/TGF-alpha treatment in ovarian and mammary carcinoma cells\",\n      \"pmids\": [\"1355758\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of protein down-regulation not resolved (mRNA effect insufficient)\", \"No link to ubiquitylation or trafficking machinery established at this stage\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined HER2's core mechanism as a ligand-less heterodimerization partner that biases trafficking toward recycling and amplifies MAPK/PI3K survival signaling, explaining its oncogenic potency.\",\n      \"evidence\": \"Review synthesizing receptor internalization assays, signaling activation studies, and cell cycle analyses\",\n      \"pmids\": [\"11156523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not identify the regulators controlling dimer choice\", \"Mechanistic basis of recycling vs degradation not molecularly resolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified PDZ-domain partners that spatially organize HER2, linking its C-terminal tail to basolateral localization and receptor clustering.\",\n      \"evidence\": \"Co-IP, pulldown, and domain-mapping with ERBIN and PICK1; subcellular localization studies\",\n      \"pmids\": [\"11278603\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of clustering for signaling output not quantified\", \"Single-lab interaction data\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrated a physiological, non-oncogenic requirement for HER2 in adult cardiomyocytes, establishing the basis for cardiac vulnerability to HER2-directed therapy.\",\n      \"evidence\": \"Cardiomyocyte-specific Cre-loxP conditional knockout with cardiac phenotyping; replicated independently\",\n      \"pmids\": [\"12072561\", \"14749494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ligand/dimer partner driving cardiac HER2 signaling not defined here\", \"Downstream effectors in cardiomyocytes not mapped\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed HER2 is a Ca2+-dependent calmodulin-binding protein whose phosphorylation and ERK/AKT output depend on CaM, adding a calcium-sensing layer to receptor regulation.\",\n      \"evidence\": \"CaM-agarose pulldown, overlay assay, Ca2+-dependent chromatography, and W7 pharmacological inhibition in cells\",\n      \"pmids\": [\"15080792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CaM-binding site on HER2 not mapped\", \"W7 effects not exclusive to CaM-HER2 axis\", \"Single lab\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified PTPN13 as a negative-feedback phosphatase for HER2 and linked its loss-of-function mutations to enhanced HER2 oncogenicity, establishing dephosphorylation as a tumor-suppressive brake.\",\n      \"evidence\": \"siRNA phosphatase library screen, PTPN13 knockdown, activity assays with tumor-derived mutants, invasion assays\",\n      \"pmids\": [\"17982484\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct phosphosite specificity on HER2 not enumerated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed a pro-apoptotic dimension of HER2: caspase cleavage of its cytoplasmic tail liberates BH3-like fragments that engage the mitochondrial apoptotic pathway, recasting the receptor as a Bad-like effector under apoptotic stress.\",\n      \"evidence\": \"In vitro caspase cleavage, mutagenesis of cleavage sites, mitochondrial translocation and cytochrome c release assays, Bcl-xL co-IP\",\n      \"pmids\": [\"18420586\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological contexts triggering this cleavage in vivo unclear\", \"Relative contribution vs canonical apoptotic regulators not quantified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Established the HER2/PI3K-AKT axis as a node for paclitaxel resistance and tissue-specific oncogenic outputs (prolactin induction in prolactinoma), connecting HER2 to therapy resistance and endocrine tumor biology.\",\n      \"evidence\": \"siRNA knockdown with dominant-negative AKT rescue in endometrial cancer; constitutively active HER2 with lapatinib vs gefitinib in prolactinoma models\",\n      \"pmids\": [\"20664599\", \"21106881\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effector specificity downstream of AKT not fully resolved\", \"Tissue-specific transcriptional mechanisms not mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Uncovered a nuclear HER2 function via macroH2A1.2 interaction at the HER2 promoter, defining a feed-forward loop sustaining HER2 expression and tumorigenicity.\",\n      \"evidence\": \"Co-IP, ChIP, macro-domain mutagenesis, knockdown and overexpression, tumorigenicity assays\",\n      \"pmids\": [\"22589551\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How HER2 reaches the nucleus not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected HER2 overexpression to constitutive HSF1 activation and HSP90 client stabilization, explaining how HER2 maintains a proteostatic environment supporting oncogenic clients.\",\n      \"evidence\": \"Lapatinib/CP724.714/siRNA HER2 inhibition, phospho-HSF1(Ser326) blotting, client stability assays, in vivo ErbB2 tumor model, PI3K rescue\",\n      \"pmids\": [\"24384723\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct kinase phosphorylating Ser326-HSF1 downstream of HER2 not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified septin complexes as plasma-membrane protectors of HER2, resolving a long-standing question of how surface HER2 evades ubiquitylation and lysosomal degradation independently of HSP90.\",\n      \"evidence\": \"Co-IP/MS, septin-2 siRNA, forchlorfenuron disruption, ubiquitylation and lysosomal inhibitor assays, surface HER2 quantification\",\n      \"pmids\": [\"27048593\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase mediating HER2 ubiquitylation upon septin loss not identified\", \"Septin-HER2 contact interface not structurally defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Mechanistically explained activating transmembrane/juxtamembrane mutations as stabilizers of the active dimer interface and asymmetric kinase dimerization, defining a druggable mutational class.\",\n      \"evidence\": \"Saturation mutagenesis, structural modeling of TMD/JMD interfaces, kinase activity assays, inhibitor treatment, clinical validation\",\n      \"pmids\": [\"30449325\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative signaling differences among individual mutants not fully resolved\", \"Resistance trajectories under inhibitor pressure not addressed here\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Validated HER2 kinase-domain mutations as activating in MSI colorectal cancer and showed differential dependence on the active conformation, refining inhibitor-class selection.\",\n      \"evidence\": \"Functional treatment of ERBB2-mutant CRC lines with reversible/irreversible inhibitors, antibodies, and siRNA; viability assays\",\n      \"pmids\": [\"26001389\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of conformational dependency for these specific mutants not solved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated that HER2 ubiquitination and endocytosis—not mere overexpression—govern antibody-drug conjugate delivery, and that pan-HER inhibitors enhance ADC efficacy by promoting internalization, translating receptor trafficking biology into therapy.\",\n      \"evidence\": \"Ubiquitination and internalization assays, viability assays in cell lines and PDX, clinical trial of T-DM1 in ERBB2-altered lung cancer\",\n      \"pmids\": [\"32213539\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase coupling inhibitor treatment to ubiquitylation not pinpointed\", \"Predictive biomarkers of internalization capacity not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The integration of opposing trafficking forces (septin protection vs ubiquitin-driven endocytosis) and the molecular identity of the E3 ligase(s) controlling HER2 degradation remain unresolved, despite their therapeutic centrality to ADC efficacy.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"HER2 E3 ubiquitin ligase not identified in the corpus\", \"Mechanism coupling kinase inhibition to receptor ubiquitylation unknown\", \"How nuclear, mitochondrial, and surface pools of HER2 are partitioned is unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"GO:0004672\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 13]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [9, 10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [8, 10]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"EGFR\", \"ERBB3\", \"ERBB4\", \"PTPN13\", \"CALM1\", \"ERBIN\", \"PICK1\", \"MACROH2A1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":7,"faith_pct":85.71428571428571}}