{"gene":"CREG1","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":2000,"finding":"CREG1 is a secreted glycoprotein that enhances neuronal differentiation of NTERA-2 embryonal carcinoma cells; CREG mRNA is induced during differentiation of mouse embryonic stem cells and human NTERA-2 cells, and secreted CREG in conditioned media promotes differentiation in the absence of retinoic acid, indicating it participates in an extracellular signaling cascade.","method":"Northern blot, constitutive overexpression in NTERA-2 cells, conditioned media experiments","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — clean gain-of-function with defined differentiation phenotype, secretion confirmed; single lab","pmids":["10815803"],"is_preprint":false},{"year":2003,"finding":"CREG1 inhibits cell growth and delays G1/S transition dependent on its glycosylation-mediated direct binding to the mannose-6-phosphate/IGF2 receptor (M6P/IGF2R); cells lacking M6P/IGF2R are resistant to CREG-induced growth inhibition, establishing M6P/IGF2R as required for CREG's antiproliferative activity.","method":"Direct binding assay, cell cycle analysis, gain-of-function in M6P/IGF2R-deficient cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding demonstrated, epistasis via receptor-null cells, replicated across studies","pmids":["12934103"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of CREG1 resolved to 1.9 Å reveals it forms a tight homodimer with a β-barrel fold structurally homologous to FMN-binding split-barrel proteins, but a loop and bulky residues sterically block the FMN-binding pocket so CREG1 cannot bind FMN. Glycosylation sites cluster opposite the dimer interface, likely presenting bivalent ligand to M6P/IGF2R. A loop-deletion mutant retains dimerization and M6P/IGF2R binding but loses growth suppression activity, showing M6P/IGF2R binding is necessary but not sufficient for growth inhibition.","method":"X-ray crystallography (1.9 Å), structure-based mutagenesis, M6P/IGF2R binding assay, growth assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and functional validation in single rigorous study","pmids":["16344469"],"is_preprint":false},{"year":2008,"finding":"CREG1 promotes the quiescent, differentiated smooth muscle cell (SMC) phenotype: retroviral CREG overexpression enhances SMC differentiation, inhibits proliferation, and reduces fibronectin synthesis; CREG knockdown via shRNA abrogates serum starvation-induced SMC differentiation and growth arrest. In vivo, CREG is downregulated after balloon injury and retroviral CREG transfer inhibits SMC dedifferentiation, proliferation, and neointimal hyperplasia.","method":"Retroviral gain- and loss-of-function (shRNA), Western blot, immunostaining, in vivo balloon injury model","journal":"Cardiovascular research","confidence":"High","confidence_rationale":"Tier 2 — reciprocal gain/loss-of-function in vitro and in vivo with defined phenotypic readouts","pmids":["18267954"],"is_preprint":false},{"year":2008,"finding":"Secreted CREG1 inhibits NIH3T3 fibroblast proliferation via M6P/IGF2R; CREG knockdown increases IGF-II secretion and promotes proliferation, which is reversed by recombinant CREG protein in a concentration-dependent manner. Direct CREG–M6P/IGF2R interaction was confirmed by co-immunoprecipitation and immunofluorescence. CREG expression correlates with M6P/IGF2R intracellular localization, and CREG facilitates IGF-II endocytosis through M6P/IGF2R.","method":"Co-immunoprecipitation, immunofluorescence, FACS, BrdU incorporation, ELISA, endocytosis assay","journal":"Genes to cells","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, multiple functional assays, consistent with prior structural data","pmids":["18691225"],"is_preprint":false},{"year":2009,"finding":"CREG1 inhibits SMC migration by promoting IGF-II endocytosis through M6P/IGF2R, reducing IGF-II–driven PI3K/Akt activation and MMP-9 activity; blocking IGF-II or PI3K abolishes the pro-migratory effect of CREG knockdown, and blocking IGF-II binding to M6P/IGF2R attenuates IGF-II endocytosis in CREG-overexpressing cells.","method":"Retroviral overexpression/shRNA knockdown, migration assay, ELISA, endocytosis assay, Western blot, neutralizing antibody/pharmacological inhibitor epistasis","journal":"Experimental cell research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, clear epistasis with receptor and signaling pathway","pmids":["19769965"],"is_preprint":false},{"year":2010,"finding":"CREG1 binds to M6P/IGF2R extracellular domains 7–10 in a glycosylation-dependent manner and to domains 11–13 in a glycosylation-independent manner; both binding sites are sufficient for CREG-mediated SMC proliferation arrest, demonstrating that glycosylation is not absolutely required for biological activity.","method":"In vitro binding assay with wild-type and glycosylation-mutant CREG proteins, soluble M6P/IGF2R fragment blocking, neutralizing antibody, cell cycle analysis","journal":"Journal of molecular and cellular cardiology","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro binding mapped to specific receptor domains with functional blocking validation","pmids":["21195083"],"is_preprint":false},{"year":2011,"finding":"CREG1 enhances p16(INK4a)-induced cellular senescence; co-expression of CREG1 and p16(INK4a) has greater effects than either alone on reducing cell growth, inducing cell cycle arrest, and senescence. The cooperative effect involves transcriptional repression of cyclin A and cyclin B promoter activities. CREG1 expression is silenced by promoter DNA methylation during immortalization.","method":"Ectopic expression, co-expression experiments, promoter-reporter assays, RT-PCR, Western blot, SA-β-gal senescence assay","journal":"Cell cycle","confidence":"Medium","confidence_rationale":"Tier 2 — defined promoter mechanism, cooperative functional effect shown; single lab","pmids":["21263217"],"is_preprint":false},{"year":2011,"finding":"CREG1 protects endothelial cells from apoptosis via activation of the VEGF/PI3K/AKT signaling pathway; blocking VEGF neutralizing antibody or PI3K inhibitor (LY294002/wortmannin) abolished the anti-apoptotic effect of CREG overexpression, placing CREG upstream of VEGF/PI3K/Akt.","method":"Adenoviral overexpression, shRNA knockdown, caspase-3 activity assay, TUNEL, neutralizing antibody and pharmacological inhibitor blocking","journal":"Atherosclerosis","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological epistasis with multiple inhibitors; single lab","pmids":["21872252"],"is_preprint":false},{"year":2004,"finding":"CREG1 inhibits cardiac cell growth as a regulator of ERK1/2; overexpression reduces protein content, cell area, and ERK1/2 levels in neonatal cardiomyocytes and dampens stretch-induced hypertrophy through ERK1/2, while antisense inhibition of CREG has opposite effects without altering PKC isoforms, JNK1/2, p38, or apoptotic signals.","method":"Overexpression/antisense inhibition in neonatal rat cardiomyocytes, Western blot, in vivo pressure-overload model, Northern blot","journal":"Journal of hypertension","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal gain/loss of function with defined signaling readout; single lab","pmids":["15257182"],"is_preprint":false},{"year":2015,"finding":"CREG1 is an evolutionarily conserved lysosomal protein; its deficiency in Creg1+/- mice impairs lysosomal maturation, reduces Rab7 expression, and leads to autophagosome accumulation (elevated LC3II, beclin-1) with impaired autophagic flux (elevated p62), resulting in aggravated myocardial fibrosis. Restoration of CREG1 activates cardiac autophagy and reverses fibrosis. Chloroquine confirmed the lysosomal mechanism.","method":"Creg1+/- mouse model, recombinant CREG1 infusion, adenoviral overexpression/silencing in cardiomyocytes, Western blot, chloroquine inhibitor experiments","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO plus rescue, lysosomal mechanism confirmed with chloroquine, multiple readouts; replicated concept","pmids":["25774384"],"is_preprint":false},{"year":2016,"finding":"CREG1 directly interacts with Sec8 of the exocyst complex; site-directed mutagenesis showed CREG1 binding to Sec8 is required for cardiomyocyte differentiation and cell-cell cohesion. CREG1, Sec8, and N-cadherin co-localize at intercalated discs. CREG1 overexpression enhances adherens and gap junction assembly, while CREG1 knockout inhibits Sec8–N-cadherin interaction and induces their degradation.","method":"Co-immunoprecipitation, site-directed mutagenesis, rescue of CREG1 KO ES cells, co-localization imaging, gain/loss-of-function differentiation assay","journal":"Stem cells","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding confirmed by Co-IP, mutagenesis + rescue establishes functional necessity","pmids":["27334848"],"is_preprint":false},{"year":2016,"finding":"CREG1 protects against MI/R injury by activating lysosomal autophagy to suppress cardiomyocyte apoptosis; Creg1+/- mice show dysfunctional autophagy (LC3A and p62 accumulation) and increased apoptosis after MI/R. Recombinant CREG1 infusion activates autophagy and reduces apoptosis. Chloroquine (autophagy blocker) abolishes CREG1-mediated cardioprotection, confirming the lysosomal autophagy mechanism.","method":"Creg1+/- mice, recombinant CREG1 infusion, chloroquine blocking, Western blot, TUNEL, TTC staining, echocardiography","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO and rescue with pharmacological confirmation; multiple orthogonal readouts","pmids":["27840305"],"is_preprint":false},{"year":2017,"finding":"CREG1 directly interacts with apoptosis signal-regulating kinase 1 (ASK1) and inhibits ASK1 phosphorylation, thereby blocking the downstream MKK4/7-JNK1 signaling pathway; JNK1 (but not JNK2) inhibition prevents the adverse effects of CREG deletion on hepatic steatosis and metabolic disorders, placing CREG upstream of ASK1-JNK1.","method":"Hepatocyte-specific CREG KO and overexpression mice, direct interaction assay (immunoprecipitation), JNK1 inhibition epistasis, Western blot","journal":"Hepatology","confidence":"High","confidence_rationale":"Tier 2 — direct binding established by Co-IP, confirmed by epistasis with JNK1-specific inhibitor; in vivo KO/OE","pmids":["28508477"],"is_preprint":false},{"year":2019,"finding":"CREG1 in hepatocytes protects against liver ischemia/reperfusion injury by binding to TAK1 and inhibiting TAK1 phosphorylation, thereby suppressing downstream MAPK signaling; mutating the TAK1-binding domain of CREG or pharmacological TAK1 inhibition (5Z-7-ox) abolishes the protective effect of CREG.","method":"Hepatocyte-specific CREG KO and transgenic mice, I/R injury model, co-immunoprecipitation, TAK1-binding domain mutation, TAK1 inhibitor blocking, Western blot","journal":"Hepatology","confidence":"High","confidence_rationale":"Tier 2 — direct binding shown, mutagenesis of binding domain and pharmacological inhibition confirm mechanism; in vivo KO/Tg","pmids":["30076625"],"is_preprint":false},{"year":2019,"finding":"CREG1 binds to retinoid X receptor α (RXRα), which interacts with thyroid hormone receptor to promote brown adipogenesis and UCP1 induction; CREG1 stimulates UCP1 promoter activity, enhanced by co-expression with thyroid hormone receptors and retinoic acid. In vivo, CREG1 transgenic mice show increased UCP1, elevated energy expenditure after β3-adrenergic stimulation, and resistance to diet-induced obesity.","method":"Co-immunoprecipitation (CREG1–RXRα), reporter assay (Ucp1 promoter), transgenic mice, primary BAT cultures, pharmacological stimulation","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus reporter assay plus in vivo phenotype; single lab","pmids":["30917000"],"is_preprint":false},{"year":2020,"finding":"CREG1 expression is epigenetically regulated by DNMT3B-mediated promoter hypermethylation; ox-LDL increases DNMT3B expression, methylates the CG site at +201/+202 bp of the CREG promoter, blocks transcription factor GR-α binding, and suppresses CREG expression causing endothelial dysfunction. 5-aza-dC (DNMT inhibitor) restores CREG expression and eNOS/NO pathway activity.","method":"DNMT3B overexpression/inhibition, bisulfite sequencing, promoter mutagenesis, ChIP assay, CREG promoter reporter assay","journal":"Redox biology","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP, promoter mutagenesis, functional rescue; multiple orthogonal approaches in single study","pmids":["32067910"],"is_preprint":false},{"year":2020,"finding":"CREG1 is cleaved by cathepsin B in vitro; cathepsin B overexpression reduces secreted CREG1 abundance while cathepsin B deletion or inhibition increases it, identifying cathepsin B as a negative regulator of secreted CREG1 levels in the tumor microenvironment.","method":"In vitro cleavage assay with cathepsin B, conditioned media proteomics from PyMT tumor-macrophage co-cultures, cathepsin B genetic overexpression/deletion","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro cleavage plus genetic KO/OE with MS quantification; single lab","pmids":["32385587"],"is_preprint":false},{"year":2021,"finding":"CREG1 is mainly localized to the endosomal-lysosomal compartment (validated by antibodies in gain/loss-of-function contexts); it promotes macropinocytosis, clathrin-dependent endocytosis, endosomal-lysosomal acidification, and lysosomal biogenesis. CREG1 overexpression enhances autophagy and lysosome-mediated degradation, whereas knockdown/knockout has opposite effects.","method":"Immunofluorescence microscopy with validated antibodies, gain- and loss-of-function (KO/KD/OE), acridine orange staining, transferrin uptake assay, LAMP1/cathepsin D functional assays","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 — validated antibodies with reciprocal gain/loss-of-function, multiple endolysosomal functional assays; single lab but orthogonal methods","pmids":["33966596"],"is_preprint":false},{"year":2021,"finding":"CREG1 localizes to mitochondria and is required for mitophagy in skeletal muscle; skeletal muscle-specific creg1 KO mice show impaired exercise endurance, abnormal mitochondrial morphology, elevated PINK1 and PARKIN, and reduced mitochondrial proteins (PTGS2/COX2, COX4I1, TOMM20), indicating accelerated but dysregulated mitophagy. HSPD1/HSP60 (residues 401–573) interacts with CREG1 (residues 130–220) to stabilize CREG1 and is involved in mitophagy regulation.","method":"Skeletal muscle-specific Creg1 KO (Creg1;Ckm-Cre), recombinant CREG1 administration, electron microscopy, Western blot, Co-IP (CREG1–HSPD1), C2C12 gain/loss-of-function","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific KO with in vivo phenotype, binding partner mapped by Co-IP with domain resolution","pmids":["33726618"],"is_preprint":false},{"year":2021,"finding":"CREG1 inhibits phenotype switching of cardiac fibroblasts to myofibroblasts after MI by suppressing CDC42 expression; recombinant CREG1 protein inhibits αSMA and collagen-1 expression and blocks hypoxia-induced proliferation and migration of cardiac fibroblasts, and this is mediated through inhibition of CDC42.","method":"Creg1+/- mice, recombinant CREG1 protein administration, in vitro hypoxia model, Western blot, CDC42 mechanistic experiments","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo KO and recombinant protein rescue, CDC42 pathway identified; single lab","pmids":["33824277"],"is_preprint":false},{"year":2013,"finding":"CREG1 promotes HUVEC proliferation through the ERK/cyclin E signaling pathway; CREG overexpression increases S/G2 population and cyclin E expression at mRNA and protein level, blocked by ERK inhibition. The pro-proliferative effect is partially mediated by VEGF-induced ERK/cyclin E activation.","method":"Adenoviral overexpression, shRNA knockdown, flow cytometry, BrdU incorporation, ERK inhibitor and VEGF neutralizing antibody blocking, RT-PCR, Western blot","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological epistasis, reciprocal gain/loss-of-function; single lab","pmids":["24018888"],"is_preprint":false},{"year":2016,"finding":"CREG1 transcription is positively regulated by the transcription factor GATA1 binding to the CREG promoter at -297/-292 bp; deletion mutation of this site reduces CREG transcription by ~83% and abolishes GATA1-mediated activation. GATA1 overexpression upregulates CREG and abrogates high glucose/palmitate-induced endothelial apoptosis.","method":"Promoter-reporter assay, ChIP assay, promoter deletion mutagenesis, GATA1 overexpression","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and promoter mutagenesis establish direct transcription factor binding; functional link confirmed","pmids":["27139506"],"is_preprint":false},{"year":2023,"finding":"CREG1 inhibits LAMP2 protein degradation by suppressing FBXO27 E3-ubiquitin ligase expression; LAMP2 overexpression reverses the effect of CREG1 knockdown on cardiomyocyte autophagy inhibition in diabetic cardiomyopathy, defining the CREG1-FBXO27-LAMP2 axis.","method":"CREG1 transgenic and cardiac-specific KO mice, palmitate-stimulated NMCMs, Western blot, LAMP2 overexpression rescue, FBXO27 expression analysis","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — molecular pathway defined with rescue experiment; single lab","pmids":["37658156"],"is_preprint":false},{"year":2023,"finding":"CREG1 directly interacts with MEK1/2 and promotes MEK1/2 phosphorylation, which is required for megakaryocyte maturation and proplatelet formation; Creg1 conditional KO megakaryocytes display impaired actin cytoskeleton (less F-actin), fewer proplatelets, and lower ploidy, resulting in thrombocytopenia.","method":"Megakaryocyte/platelet conditional Creg1 KO and transgenic mice, co-immunoprecipitation (CREG1–MEK1/2), Western blot, actin staining, thrombocytopenia model","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2 — direct interaction by Co-IP plus tissue-specific KO with defined phenotype; single lab","pmids":["37496998"],"is_preprint":false},{"year":2024,"finding":"CREG1 inhibits ferroptosis in cardiomyocytes by regulating the FBXW7-FOXO1 pathway to suppress PDK4 mRNA and protein expression; PDK4 deficiency reverses the effects of CREG1 knockdown on DOX-induced ferroptosis, placing PDK4 downstream of CREG1-FBXW7-FOXO1.","method":"CREG1 transgenic and cardiac-specific KO mice, NMCMs with siRNA/adenovirus, transcriptomics, Western blot, immunoprecipitation","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 — transcriptomics-guided mechanism with Co-IP and rescue; single lab","pmids":["39094399"],"is_preprint":false},{"year":2024,"finding":"CREG1 deficiency inhibits skeletal muscle satellite cell differentiation and regeneration by promoting C-CBL E3-ubiquitin ligase-mediated K48-linked polyubiquitination of AMPKα1 at K396, leading to AMPKα1 degradation; silencing C-CBL in Creg1 myofibre-KO mice rescues muscle regeneration.","method":"Satellite cell-specific Creg1 OE and myofibre-specific Creg1 KO mice, mass spectrometry, RNA sequencing, AAV-shC-CBL silencing rescue, Western blot","journal":"Journal of cachexia, sarcopenia and muscle","confidence":"Medium","confidence_rationale":"Tier 2 — ubiquitination site mapped by MS, rescue by C-CBL silencing confirms epistasis; single lab","pmids":["38272853"],"is_preprint":false},{"year":2024,"finding":"CREG1 promotes exosome biogenesis and release from bovine placental trophoblast cells by targeting IGF2R; IGF2R knockdown inhibits exosome genesis and blocks CREG1-induced exosome release. CREG1 binds IGF2R which subsequently binds Rab11 to regulate exosomal vesicle formation.","method":"Overexpression/knockdown of CREG1 and IGF2R, exosome isolation and characterization, Co-IP (IGF2R–Rab11)","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP and knockdown epistasis; single lab, bovine model","pmids":["38917918"],"is_preprint":false},{"year":2022,"finding":"CREG1 stimulates AMPK phosphorylation and glucose uptake in skeletal muscle cells via IGF2R; CREG1-induced AMPKα phosphorylation and 2-deoxyglucose uptake are suppressed by IGF2R knockdown and the AMPK inhibitor Compound C, placing IGF2R upstream of AMPK in CREG1 signaling.","method":"C2C12 myotubes, recombinant CREG1 treatment, IGF2R siRNA knockdown, AMPK inhibitor Compound C, Western blot, 2-DG uptake assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological and genetic epistasis; single lab","pmids":["36528955"],"is_preprint":false},{"year":2022,"finding":"CREG1 promotes ESC differentiation into smooth muscle cells via the TGF-β/Smad2/3 signaling pathway; CREG overexpression increases SMC markers and contractile function while CREG KO reduces them; TGF-β-Smad2/3 pathway mediates this effect.","method":"ESC CREG OE and KO models, differentiation assay, Western blot, calcium imaging, Smad2/3 pathway analysis","journal":"Differentiation","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal gain/loss-of-function with pathway identification; single lab","pmids":["35349881"],"is_preprint":false},{"year":2024,"finding":"In zebrafish, creg1 deficiency impairs erythroid differentiation and causes excessive apoptosis of erythroid progenitors through reduced activation of the TGF-β/Smad2 signaling pathway; IDE2 (Smad2 pathway agonist) rescues the erythroid defect in creg1-/- mutants. Klf1 is a key downstream target of TGF-β/Smad2 involved in CREG1-mediated erythropoiesis.","method":"Zebrafish creg1 knockout, IDE2 pharmacological rescue, Klf1 target analysis, in situ hybridization, flow cytometry","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with pharmacological pathway rescue and downstream target identification; zebrafish ortholog","pmids":["38953462"],"is_preprint":false},{"year":2025,"finding":"CREG1 promotes lysosomal biogenesis and autophagy in cardiomyocytes; global Creg1 KO mice develop age-associated cardiac hypertrophy, fibrosis, and diastolic dysfunction (~80 weeks). CREG1 localizes to endolysosomal and autophagosomal compartments; its loss impairs autophagy flux and mitophagy due to defective autophagosome membrane expansion and degradation.","method":"Global Creg1 KO (full ORF deletion), cardiomyocyte-specific KO and KI mice, electron microscopy, immunofluorescence, CAG-EGFP-RFP-LC3 autophagy reporter, echocardiography","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — rigorous true KO with multiple orthogonal methods; preprint","pmids":["41292877"],"is_preprint":true},{"year":2025,"finding":"CREG1 promotes osteogenic differentiation of BMSCs and bone homeostasis via RAB7-mediated regulation of autophagy; RAB7 knockdown inhibits CREG1-induced osteogenic differentiation and autophagy, while RAB7 overexpression restores osteogenic potential suppressed by CREG1 knockdown, placing RAB7 downstream of CREG1.","method":"CREG1 and RAB7 overexpression/knockdown in BMSCs, osteogenic differentiation assay, autophagy flux assay, in vivo OVX osteoporosis model","journal":"Cellular signalling","confidence":"Low","confidence_rationale":"Tier 3 — epistasis shown but direct CREG1–RAB7 molecular interaction not established; single lab","pmids":["41577020"],"is_preprint":false}],"current_model":"CREG1 is an endosomal-lysosomal secreted glycoprotein that forms a homodimer with a β-barrel fold; it binds the M6P/IGF2R (via both glycosylation-dependent and -independent sites on receptor domains 7–10 and 11–13) to inhibit cell proliferation, promotes lysosomal biogenesis, endocytic trafficking, and autophagy/mitophagy, interacts with Sec8 of the exocyst complex to drive intercellular junction assembly and cardiomyocyte differentiation, directly engages ASK1 and TAK1 to suppress MAPK signaling in stress protection, and transcriptionally cooperates with p16(INK4a) to induce senescence, while its own expression is regulated by GATA1 binding and DNMT3B-mediated promoter methylation."},"narrative":{"teleology":[{"year":2000,"claim":"The first functional characterization established that CREG1 is a secreted glycoprotein that promotes differentiation of embryonal carcinoma cells, positioning it as an extracellular differentiation signal rather than a transcription factor or intracellular enzyme.","evidence":"Northern blot, overexpression in NTERA-2 cells, conditioned media experiments","pmids":["10815803"],"confidence":"Medium","gaps":["Receptor or binding partner mediating extracellular signaling unknown","Mechanism of differentiation induction not defined"]},{"year":2003,"claim":"The identification of M6P/IGF2R as the required receptor for CREG1's antiproliferative activity established a specific receptor–ligand axis, resolving how a secreted glycoprotein inhibits cell growth.","evidence":"Direct binding assay, cell cycle analysis in M6P/IGF2R-deficient cells","pmids":["12934103"],"confidence":"High","gaps":["Binding site on M6P/IGF2R not mapped","Downstream intracellular signal unknown"]},{"year":2005,"claim":"The 1.9 Å crystal structure revealed CREG1 as a homodimeric β-barrel protein that cannot bind FMN despite structural homology, and mutagenesis showed that M6P/IGF2R binding is necessary but not sufficient for growth suppression—an additional surface element is required.","evidence":"X-ray crystallography, loop-deletion mutagenesis, M6P/IGF2R binding and growth assays","pmids":["16344469"],"confidence":"High","gaps":["Identity of the additional surface required for growth suppression unknown","No co-crystal with receptor"]},{"year":2008,"claim":"Reciprocal gain- and loss-of-function studies in vascular smooth muscle cells and in vivo balloon injury models demonstrated that CREG1 maintains differentiated SMC phenotype and inhibits neointimal hyperplasia, extending its role from embryonal carcinoma to cardiovascular biology.","evidence":"Retroviral overexpression/shRNA, in vivo balloon injury model in SMCs","pmids":["18267954"],"confidence":"High","gaps":["Whether SMC effects depend entirely on M6P/IGF2R unclear","Downstream transcriptional targets not identified"]},{"year":2008,"claim":"The demonstration that CREG1 facilitates IGF-II endocytosis via M6P/IGF2R and that CREG knockdown elevates IGF-II secretion resolved the mechanism by which CREG1–M6P/IGF2R interaction suppresses proliferation: by clearing a mitogenic ligand.","evidence":"Co-immunoprecipitation, FACS, endocytosis assay in NIH3T3 cells","pmids":["18691225"],"confidence":"High","gaps":["Whether CREG1 alters M6P/IGF2R trafficking dynamics unknown","Role of glycosylation-independent binding not addressed"]},{"year":2009,"claim":"Epistatic experiments showed CREG1 suppresses SMC migration by reducing IGF-II-driven PI3K/Akt/MMP-9 signaling through enhanced IGF-II endocytosis, unifying its antiproliferative and anti-migratory activities under one receptor-clearance mechanism.","evidence":"Migration assay, neutralizing antibody and PI3K inhibitor epistasis, endocytosis assay","pmids":["19769965"],"confidence":"High","gaps":["MMP-9 regulatory step not precisely defined","Whether CREG1 has M6P/IGF2R-independent anti-migratory activity untested"]},{"year":2010,"claim":"Mapping CREG1 binding to two distinct M6P/IGF2R regions (domains 7–10, glycosylation-dependent; domains 11–13, glycosylation-independent) showed that CREG1 engages the receptor through a bimodal mechanism, each sufficient for growth arrest.","evidence":"In vitro binding with glycosylation-mutant CREG, soluble receptor fragment blocking, cell cycle analysis","pmids":["21195083"],"confidence":"High","gaps":["Structural basis of glycosylation-independent binding undetermined","Whether both sites are engaged simultaneously unknown"]},{"year":2011,"claim":"CREG1 was shown to cooperate with p16(INK4a) to enforce cellular senescence by transcriptionally repressing cyclins A and B, revealing an intracellular gene-regulatory function distinct from its extracellular receptor-binding activity.","evidence":"Co-expression experiments, promoter-reporter assays, SA-β-gal senescence assay","pmids":["21263217"],"confidence":"Medium","gaps":["Whether CREG1 directly contacts cyclin promoters or acts through an intermediary not resolved","Single lab, not replicated"]},{"year":2015,"claim":"The discovery that CREG1 haploinsufficiency impairs lysosomal maturation, reduces Rab7, and causes autophagosome accumulation with defective autophagic flux in vivo redefined CREG1 as a lysosomal biogenesis factor, not merely an extracellular ligand.","evidence":"Creg1+/− mice, recombinant CREG1 rescue, chloroquine confirmation, Western blot","pmids":["25774384"],"confidence":"High","gaps":["How CREG1 regulates Rab7 expression molecularly unknown","Whether lysosomal role is M6P/IGF2R-dependent not tested"]},{"year":2016,"claim":"Identification of Sec8 (exocyst complex) as a direct CREG1 binding partner required for intercalated disc assembly and cardiomyocyte differentiation established a new non-lysosomal, cytoskeleton-linked role for CREG1.","evidence":"Co-IP, site-directed mutagenesis, CREG1 KO ES cell rescue, co-localization imaging","pmids":["27334848"],"confidence":"High","gaps":["Whether CREG1–Sec8 interaction is conserved beyond cardiomyocytes unknown","Mechanism by which CREG1 stabilizes N-cadherin via Sec8 unclear"]},{"year":2017,"claim":"Direct binding of CREG1 to ASK1 and inhibition of ASK1 phosphorylation, confirmed by JNK1-specific epistasis, established a hepatocyte-intrinsic MAPK-suppressive function protecting against steatosis.","evidence":"Hepatocyte-specific CREG1 KO/OE mice, Co-IP, JNK1 inhibitor epistasis","pmids":["28508477"],"confidence":"High","gaps":["Binding interface between CREG1 and ASK1 not structurally resolved","Whether this kinase inhibition is catalytic or sequestration-based unknown"]},{"year":2019,"claim":"The finding that CREG1 directly binds TAK1 and inhibits its phosphorylation to suppress MAPK signaling during hepatic ischemia/reperfusion extended the kinase-inhibitory paradigm to a second MAP3K, validated by binding-domain mutagenesis.","evidence":"Hepatocyte-specific KO/Tg mice, Co-IP, TAK1-binding domain mutation, TAK1 inhibitor blocking","pmids":["30076625"],"confidence":"High","gaps":["Structural basis of TAK1 vs ASK1 selectivity unknown","Whether CREG1 inhibits kinases in other tissues untested"]},{"year":2021,"claim":"Systematic validation of CREG1 as an endosomal-lysosomal resident that promotes macropinocytosis, clathrin-dependent endocytosis, endolysosomal acidification, and lysosomal biogenesis unified its diverse phenotypic effects under a core endolysosomal function.","evidence":"Validated antibodies, KO/KD/OE, acridine orange staining, transferrin uptake, LAMP1/cathepsin D assays","pmids":["33966596"],"confidence":"High","gaps":["Molecular mechanism by which CREG1 promotes acidification undetermined","Whether CREG1 functions as a lumenal or membrane-associated factor unclear"]},{"year":2021,"claim":"Skeletal muscle-specific Creg1 KO revealed CREG1 as a mitophagy regulator that localizes to mitochondria and interacts with HSPD1/HSP60, broadening the autophagic role to organelle-selective degradation.","evidence":"Skeletal muscle-specific Creg1 KO, electron microscopy, Co-IP mapping CREG1(130–220)–HSPD1(401–573)","pmids":["33726618"],"confidence":"High","gaps":["Whether CREG1 is imported into mitochondria or tethers from the OMM unclear","Relationship between HSPD1 interaction and PINK1/Parkin pathway not established"]},{"year":2023,"claim":"Discovery that CREG1 stabilizes LAMP2 by suppressing FBXO27 E3 ligase expression provided a molecular mechanism for CREG1's lysosomal maintenance function, validated by LAMP2 rescue of CREG1 knockdown in diabetic cardiomyopathy.","evidence":"Cardiac-specific KO/Tg mice, LAMP2 overexpression rescue, FBXO27 expression analysis","pmids":["37658156"],"confidence":"Medium","gaps":["How CREG1 suppresses FBXO27 expression not defined","Single lab"]},{"year":2023,"claim":"Identification of direct CREG1–MEK1/2 interaction promoting MEK phosphorylation for megakaryocyte maturation revealed a context-dependent pro-kinase activity, contrasting with the ASK1/TAK1 kinase-inhibitory roles.","evidence":"Megakaryocyte/platelet conditional Creg1 KO and Tg mice, Co-IP, actin staining","pmids":["37496998"],"confidence":"Medium","gaps":["Mechanism of opposing kinase modulation (activation vs inhibition) in different contexts unresolved","Single lab"]},{"year":2024,"claim":"CREG1 was shown to maintain satellite cell differentiation and muscle regeneration by preventing C-CBL-mediated K48-polyubiquitination of AMPKα1 at K396, linking CREG1 to ubiquitin-proteasome regulation of a master metabolic kinase.","evidence":"Satellite cell-specific OE and myofibre-specific KO mice, mass spectrometry, AAV-shC-CBL rescue","pmids":["38272853"],"confidence":"Medium","gaps":["Whether CREG1 directly binds C-CBL or AMPKα1 not established","Single lab"]},{"year":null,"claim":"Key unresolved questions include how CREG1 exerts opposing effects on different kinases (inhibiting ASK1/TAK1 yet activating MEK1/2), whether its lysosomal and extracellular receptor-binding functions are mechanistically linked or independent, and what molecular event converts CREG1 from a secreted ligand to an endolysosomal/mitochondrial effector.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unified model explains context-dependent kinase activation vs inhibition","Whether intracellular CREG1 re-enters the secretory pathway or acts cell-autonomously after synthesis is unresolved","No co-crystal structure of CREG1 with any intracellular partner exists"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,13,14,24]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[11,27]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[10,18,31]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[18]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,4]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[19]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[10,12,18,19,31]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,9,13,14,24]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,3,11,29,30]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[10,18,23]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[18,27]}],"complexes":[],"partners":["IGF2R","ASK1","TAK1","EXOC4","MEK1","HSPD1","RXRA"],"other_free_text":[]},"mechanistic_narrative":"CREG1 is a secreted, endosomal-lysosomal glycoprotein that promotes cellular differentiation, suppresses proliferation, and maintains lysosomal-autophagic homeostasis across diverse tissues. Structurally, CREG1 forms a homodimer with a β-barrel fold that binds the mannose-6-phosphate/IGF2 receptor (M6P/IGF2R) through both glycosylation-dependent (domains 7–10) and glycosylation-independent (domains 11–13) sites, facilitating IGF-II endocytosis and attenuating IGF-II-driven PI3K/Akt signaling to inhibit cell growth and migration [PMID:12934103, PMID:16344469, PMID:21195083, PMID:19769965]. CREG1 localizes to the endosomal-lysosomal compartment where it promotes lysosomal biogenesis, endocytic trafficking, autophagic flux, and mitophagy—functions whose loss leads to autophagosome accumulation, impaired Rab7 expression, and organ-level pathology including cardiac fibrosis and skeletal muscle dysfunction [PMID:33966596, PMID:25774384, PMID:33726618]. Beyond its lysosomal roles, CREG1 directly engages cytoplasmic kinases ASK1 and TAK1 to suppress MAPK-mediated stress signaling in liver, interacts with exocyst subunit Sec8 to drive intercalated disc assembly during cardiomyocyte differentiation, and cooperates with p16(INK4a) to enforce cellular senescence through transcriptional repression of cyclins A and B [PMID:28508477, PMID:30076625, PMID:27334848, PMID:21263217]."},"prefetch_data":{"uniprot":{"accession":"O75629","full_name":"Protein CREG1","aliases":["Cellular repressor of E1A-stimulated genes 1"],"length_aa":220,"mass_kda":24.1,"function":"May contribute to the transcriptional control of cell growth and differentiation. Antagonizes transcriptional activation and cellular transformation by the adenovirus E1A protein. The transcriptional control activity of cell growth requires interaction with IGF2R","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/O75629/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CREG1","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CREG1","total_profiled":1310},"omim":[{"mim_id":"618055","title":"CELLULAR REPRESSOR OF E1A-STIMULATED GENES 1; CREG1","url":"https://www.omim.org/entry/618055"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"},{"location":"Microtubules","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CREG1"},"hgnc":{"alias_symbol":[],"prev_symbol":["CREG"]},"alphafold":{"accession":"O75629","domains":[{"cath_id":"2.30.110.10","chopping":"57-146_153-217","consensus_level":"high","plddt":97.4775,"start":57,"end":217}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75629","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75629-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75629-F1-predicted_aligned_error_v6.png","plddt_mean":87.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CREG1","jax_strain_url":"https://www.jax.org/strain/search?query=CREG1"},"sequence":{"accession":"O75629","fasta_url":"https://rest.uniprot.org/uniprotkb/O75629.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75629/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75629"}},"corpus_meta":[{"pmid":"10815803","id":"PMC_10815803","title":"The secreted glycoprotein CREG enhances differentiation of NTERA-2 human embryonal carcinoma cells.","date":"2000","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/10815803","citation_count":83,"is_preprint":false},{"pmid":"12934103","id":"PMC_12934103","title":"The secreted glycoprotein CREG inhibits cell growth dependent on the mannose-6-phosphate/insulin-like growth factor II receptor.","date":"2003","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/12934103","citation_count":80,"is_preprint":false},{"pmid":"30076625","id":"PMC_30076625","title":"Creg in Hepatocytes Ameliorates Liver Ischemia/Reperfusion Injury in a TAK1-Dependent Manner in Mice.","date":"2019","source":"Hepatology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/30076625","citation_count":63,"is_preprint":false},{"pmid":"27840305","id":"PMC_27840305","title":"CREG protects from myocardial ischemia/reperfusion injury by regulating myocardial autophagy and apoptosis.","date":"2016","source":"Biochimica et biophysica acta. 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apoptosis.","date":"2026","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/41646965","citation_count":0,"is_preprint":false},{"pmid":"21038674","id":"PMC_21038674","title":"[Purification and functional identification of the recombinant human CREG/myc-His glycoprotein].","date":"2010","source":"Zhongguo ying yong sheng li xue za zhi = Zhongguo yingyong shenglixue zazhi = Chinese journal of applied physiology","url":"https://pubmed.ncbi.nlm.nih.gov/21038674","citation_count":0,"is_preprint":false},{"pmid":"12513720","id":"PMC_12513720","title":"[Selection of donor in mismatched hematopoietic stem cell transplantation by CREG, residue match and HLA three-dimensional structure].","date":"2002","source":"Zhongguo shi yan xue ye xue za zhi","url":"https://pubmed.ncbi.nlm.nih.gov/12513720","citation_count":0,"is_preprint":false},{"pmid":"41292877","id":"PMC_41292877","title":"CREG1 promotes autophagy and protects the heart against nutritional stress-induced injury and age-associated hypertrophy, fibrosis and diastolic dysfunction.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41292877","citation_count":0,"is_preprint":false},{"pmid":"41577020","id":"PMC_41577020","title":"CREG1 promotes bone formation via targeting RAB7 to activate autophagy in osteoporosis.","date":"2026","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/41577020","citation_count":0,"is_preprint":false},{"pmid":"12028545","id":"PMC_12028545","title":"Description of six new HLA-B alleles in the 5C CREG including a B*58 intron two sequence.","date":"2002","source":"Tissue antigens","url":"https://pubmed.ncbi.nlm.nih.gov/12028545","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.18.670803","title":"CREG1 restricts ALV-J replication via the mitochondrial dysfunction–driven activation of innate immunity and apoptosis","date":"2025-08-22","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.18.670803","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":39261,"output_tokens":8529,"usd":0.122859},"stage2":{"model":"claude-opus-4-6","input_tokens":12369,"output_tokens":4161,"usd":0.248805},"total_usd":0.371664,"stage1_batch_id":"msgbatch_011kfMfE81o6CTcyhVUqumuW","stage2_batch_id":"msgbatch_01DTputS6WNkH745x1nVSoBo","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"CREG1 is a secreted glycoprotein that enhances neuronal differentiation of NTERA-2 embryonal carcinoma cells; CREG mRNA is induced during differentiation of mouse embryonic stem cells and human NTERA-2 cells, and secreted CREG in conditioned media promotes differentiation in the absence of retinoic acid, indicating it participates in an extracellular signaling cascade.\",\n      \"method\": \"Northern blot, constitutive overexpression in NTERA-2 cells, conditioned media experiments\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean gain-of-function with defined differentiation phenotype, secretion confirmed; single lab\",\n      \"pmids\": [\"10815803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CREG1 inhibits cell growth and delays G1/S transition dependent on its glycosylation-mediated direct binding to the mannose-6-phosphate/IGF2 receptor (M6P/IGF2R); cells lacking M6P/IGF2R are resistant to CREG-induced growth inhibition, establishing M6P/IGF2R as required for CREG's antiproliferative activity.\",\n      \"method\": \"Direct binding assay, cell cycle analysis, gain-of-function in M6P/IGF2R-deficient cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding demonstrated, epistasis via receptor-null cells, replicated across studies\",\n      \"pmids\": [\"12934103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of CREG1 resolved to 1.9 Å reveals it forms a tight homodimer with a β-barrel fold structurally homologous to FMN-binding split-barrel proteins, but a loop and bulky residues sterically block the FMN-binding pocket so CREG1 cannot bind FMN. Glycosylation sites cluster opposite the dimer interface, likely presenting bivalent ligand to M6P/IGF2R. A loop-deletion mutant retains dimerization and M6P/IGF2R binding but loses growth suppression activity, showing M6P/IGF2R binding is necessary but not sufficient for growth inhibition.\",\n      \"method\": \"X-ray crystallography (1.9 Å), structure-based mutagenesis, M6P/IGF2R binding assay, growth assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and functional validation in single rigorous study\",\n      \"pmids\": [\"16344469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CREG1 promotes the quiescent, differentiated smooth muscle cell (SMC) phenotype: retroviral CREG overexpression enhances SMC differentiation, inhibits proliferation, and reduces fibronectin synthesis; CREG knockdown via shRNA abrogates serum starvation-induced SMC differentiation and growth arrest. In vivo, CREG is downregulated after balloon injury and retroviral CREG transfer inhibits SMC dedifferentiation, proliferation, and neointimal hyperplasia.\",\n      \"method\": \"Retroviral gain- and loss-of-function (shRNA), Western blot, immunostaining, in vivo balloon injury model\",\n      \"journal\": \"Cardiovascular research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function in vitro and in vivo with defined phenotypic readouts\",\n      \"pmids\": [\"18267954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Secreted CREG1 inhibits NIH3T3 fibroblast proliferation via M6P/IGF2R; CREG knockdown increases IGF-II secretion and promotes proliferation, which is reversed by recombinant CREG protein in a concentration-dependent manner. Direct CREG–M6P/IGF2R interaction was confirmed by co-immunoprecipitation and immunofluorescence. CREG expression correlates with M6P/IGF2R intracellular localization, and CREG facilitates IGF-II endocytosis through M6P/IGF2R.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence, FACS, BrdU incorporation, ELISA, endocytosis assay\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, multiple functional assays, consistent with prior structural data\",\n      \"pmids\": [\"18691225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CREG1 inhibits SMC migration by promoting IGF-II endocytosis through M6P/IGF2R, reducing IGF-II–driven PI3K/Akt activation and MMP-9 activity; blocking IGF-II or PI3K abolishes the pro-migratory effect of CREG knockdown, and blocking IGF-II binding to M6P/IGF2R attenuates IGF-II endocytosis in CREG-overexpressing cells.\",\n      \"method\": \"Retroviral overexpression/shRNA knockdown, migration assay, ELISA, endocytosis assay, Western blot, neutralizing antibody/pharmacological inhibitor epistasis\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, clear epistasis with receptor and signaling pathway\",\n      \"pmids\": [\"19769965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CREG1 binds to M6P/IGF2R extracellular domains 7–10 in a glycosylation-dependent manner and to domains 11–13 in a glycosylation-independent manner; both binding sites are sufficient for CREG-mediated SMC proliferation arrest, demonstrating that glycosylation is not absolutely required for biological activity.\",\n      \"method\": \"In vitro binding assay with wild-type and glycosylation-mutant CREG proteins, soluble M6P/IGF2R fragment blocking, neutralizing antibody, cell cycle analysis\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro binding mapped to specific receptor domains with functional blocking validation\",\n      \"pmids\": [\"21195083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CREG1 enhances p16(INK4a)-induced cellular senescence; co-expression of CREG1 and p16(INK4a) has greater effects than either alone on reducing cell growth, inducing cell cycle arrest, and senescence. The cooperative effect involves transcriptional repression of cyclin A and cyclin B promoter activities. CREG1 expression is silenced by promoter DNA methylation during immortalization.\",\n      \"method\": \"Ectopic expression, co-expression experiments, promoter-reporter assays, RT-PCR, Western blot, SA-β-gal senescence assay\",\n      \"journal\": \"Cell cycle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined promoter mechanism, cooperative functional effect shown; single lab\",\n      \"pmids\": [\"21263217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CREG1 protects endothelial cells from apoptosis via activation of the VEGF/PI3K/AKT signaling pathway; blocking VEGF neutralizing antibody or PI3K inhibitor (LY294002/wortmannin) abolished the anti-apoptotic effect of CREG overexpression, placing CREG upstream of VEGF/PI3K/Akt.\",\n      \"method\": \"Adenoviral overexpression, shRNA knockdown, caspase-3 activity assay, TUNEL, neutralizing antibody and pharmacological inhibitor blocking\",\n      \"journal\": \"Atherosclerosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological epistasis with multiple inhibitors; single lab\",\n      \"pmids\": [\"21872252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CREG1 inhibits cardiac cell growth as a regulator of ERK1/2; overexpression reduces protein content, cell area, and ERK1/2 levels in neonatal cardiomyocytes and dampens stretch-induced hypertrophy through ERK1/2, while antisense inhibition of CREG has opposite effects without altering PKC isoforms, JNK1/2, p38, or apoptotic signals.\",\n      \"method\": \"Overexpression/antisense inhibition in neonatal rat cardiomyocytes, Western blot, in vivo pressure-overload model, Northern blot\",\n      \"journal\": \"Journal of hypertension\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss of function with defined signaling readout; single lab\",\n      \"pmids\": [\"15257182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CREG1 is an evolutionarily conserved lysosomal protein; its deficiency in Creg1+/- mice impairs lysosomal maturation, reduces Rab7 expression, and leads to autophagosome accumulation (elevated LC3II, beclin-1) with impaired autophagic flux (elevated p62), resulting in aggravated myocardial fibrosis. Restoration of CREG1 activates cardiac autophagy and reverses fibrosis. Chloroquine confirmed the lysosomal mechanism.\",\n      \"method\": \"Creg1+/- mouse model, recombinant CREG1 infusion, adenoviral overexpression/silencing in cardiomyocytes, Western blot, chloroquine inhibitor experiments\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO plus rescue, lysosomal mechanism confirmed with chloroquine, multiple readouts; replicated concept\",\n      \"pmids\": [\"25774384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CREG1 directly interacts with Sec8 of the exocyst complex; site-directed mutagenesis showed CREG1 binding to Sec8 is required for cardiomyocyte differentiation and cell-cell cohesion. CREG1, Sec8, and N-cadherin co-localize at intercalated discs. CREG1 overexpression enhances adherens and gap junction assembly, while CREG1 knockout inhibits Sec8–N-cadherin interaction and induces their degradation.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis, rescue of CREG1 KO ES cells, co-localization imaging, gain/loss-of-function differentiation assay\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding confirmed by Co-IP, mutagenesis + rescue establishes functional necessity\",\n      \"pmids\": [\"27334848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CREG1 protects against MI/R injury by activating lysosomal autophagy to suppress cardiomyocyte apoptosis; Creg1+/- mice show dysfunctional autophagy (LC3A and p62 accumulation) and increased apoptosis after MI/R. Recombinant CREG1 infusion activates autophagy and reduces apoptosis. Chloroquine (autophagy blocker) abolishes CREG1-mediated cardioprotection, confirming the lysosomal autophagy mechanism.\",\n      \"method\": \"Creg1+/- mice, recombinant CREG1 infusion, chloroquine blocking, Western blot, TUNEL, TTC staining, echocardiography\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO and rescue with pharmacological confirmation; multiple orthogonal readouts\",\n      \"pmids\": [\"27840305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CREG1 directly interacts with apoptosis signal-regulating kinase 1 (ASK1) and inhibits ASK1 phosphorylation, thereby blocking the downstream MKK4/7-JNK1 signaling pathway; JNK1 (but not JNK2) inhibition prevents the adverse effects of CREG deletion on hepatic steatosis and metabolic disorders, placing CREG upstream of ASK1-JNK1.\",\n      \"method\": \"Hepatocyte-specific CREG KO and overexpression mice, direct interaction assay (immunoprecipitation), JNK1 inhibition epistasis, Western blot\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding established by Co-IP, confirmed by epistasis with JNK1-specific inhibitor; in vivo KO/OE\",\n      \"pmids\": [\"28508477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CREG1 in hepatocytes protects against liver ischemia/reperfusion injury by binding to TAK1 and inhibiting TAK1 phosphorylation, thereby suppressing downstream MAPK signaling; mutating the TAK1-binding domain of CREG or pharmacological TAK1 inhibition (5Z-7-ox) abolishes the protective effect of CREG.\",\n      \"method\": \"Hepatocyte-specific CREG KO and transgenic mice, I/R injury model, co-immunoprecipitation, TAK1-binding domain mutation, TAK1 inhibitor blocking, Western blot\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding shown, mutagenesis of binding domain and pharmacological inhibition confirm mechanism; in vivo KO/Tg\",\n      \"pmids\": [\"30076625\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CREG1 binds to retinoid X receptor α (RXRα), which interacts with thyroid hormone receptor to promote brown adipogenesis and UCP1 induction; CREG1 stimulates UCP1 promoter activity, enhanced by co-expression with thyroid hormone receptors and retinoic acid. In vivo, CREG1 transgenic mice show increased UCP1, elevated energy expenditure after β3-adrenergic stimulation, and resistance to diet-induced obesity.\",\n      \"method\": \"Co-immunoprecipitation (CREG1–RXRα), reporter assay (Ucp1 promoter), transgenic mice, primary BAT cultures, pharmacological stimulation\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus reporter assay plus in vivo phenotype; single lab\",\n      \"pmids\": [\"30917000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CREG1 expression is epigenetically regulated by DNMT3B-mediated promoter hypermethylation; ox-LDL increases DNMT3B expression, methylates the CG site at +201/+202 bp of the CREG promoter, blocks transcription factor GR-α binding, and suppresses CREG expression causing endothelial dysfunction. 5-aza-dC (DNMT inhibitor) restores CREG expression and eNOS/NO pathway activity.\",\n      \"method\": \"DNMT3B overexpression/inhibition, bisulfite sequencing, promoter mutagenesis, ChIP assay, CREG promoter reporter assay\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP, promoter mutagenesis, functional rescue; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"32067910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CREG1 is cleaved by cathepsin B in vitro; cathepsin B overexpression reduces secreted CREG1 abundance while cathepsin B deletion or inhibition increases it, identifying cathepsin B as a negative regulator of secreted CREG1 levels in the tumor microenvironment.\",\n      \"method\": \"In vitro cleavage assay with cathepsin B, conditioned media proteomics from PyMT tumor-macrophage co-cultures, cathepsin B genetic overexpression/deletion\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro cleavage plus genetic KO/OE with MS quantification; single lab\",\n      \"pmids\": [\"32385587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CREG1 is mainly localized to the endosomal-lysosomal compartment (validated by antibodies in gain/loss-of-function contexts); it promotes macropinocytosis, clathrin-dependent endocytosis, endosomal-lysosomal acidification, and lysosomal biogenesis. CREG1 overexpression enhances autophagy and lysosome-mediated degradation, whereas knockdown/knockout has opposite effects.\",\n      \"method\": \"Immunofluorescence microscopy with validated antibodies, gain- and loss-of-function (KO/KD/OE), acridine orange staining, transferrin uptake assay, LAMP1/cathepsin D functional assays\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — validated antibodies with reciprocal gain/loss-of-function, multiple endolysosomal functional assays; single lab but orthogonal methods\",\n      \"pmids\": [\"33966596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CREG1 localizes to mitochondria and is required for mitophagy in skeletal muscle; skeletal muscle-specific creg1 KO mice show impaired exercise endurance, abnormal mitochondrial morphology, elevated PINK1 and PARKIN, and reduced mitochondrial proteins (PTGS2/COX2, COX4I1, TOMM20), indicating accelerated but dysregulated mitophagy. HSPD1/HSP60 (residues 401–573) interacts with CREG1 (residues 130–220) to stabilize CREG1 and is involved in mitophagy regulation.\",\n      \"method\": \"Skeletal muscle-specific Creg1 KO (Creg1;Ckm-Cre), recombinant CREG1 administration, electron microscopy, Western blot, Co-IP (CREG1–HSPD1), C2C12 gain/loss-of-function\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific KO with in vivo phenotype, binding partner mapped by Co-IP with domain resolution\",\n      \"pmids\": [\"33726618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CREG1 inhibits phenotype switching of cardiac fibroblasts to myofibroblasts after MI by suppressing CDC42 expression; recombinant CREG1 protein inhibits αSMA and collagen-1 expression and blocks hypoxia-induced proliferation and migration of cardiac fibroblasts, and this is mediated through inhibition of CDC42.\",\n      \"method\": \"Creg1+/- mice, recombinant CREG1 protein administration, in vitro hypoxia model, Western blot, CDC42 mechanistic experiments\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO and recombinant protein rescue, CDC42 pathway identified; single lab\",\n      \"pmids\": [\"33824277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CREG1 promotes HUVEC proliferation through the ERK/cyclin E signaling pathway; CREG overexpression increases S/G2 population and cyclin E expression at mRNA and protein level, blocked by ERK inhibition. The pro-proliferative effect is partially mediated by VEGF-induced ERK/cyclin E activation.\",\n      \"method\": \"Adenoviral overexpression, shRNA knockdown, flow cytometry, BrdU incorporation, ERK inhibitor and VEGF neutralizing antibody blocking, RT-PCR, Western blot\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological epistasis, reciprocal gain/loss-of-function; single lab\",\n      \"pmids\": [\"24018888\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CREG1 transcription is positively regulated by the transcription factor GATA1 binding to the CREG promoter at -297/-292 bp; deletion mutation of this site reduces CREG transcription by ~83% and abolishes GATA1-mediated activation. GATA1 overexpression upregulates CREG and abrogates high glucose/palmitate-induced endothelial apoptosis.\",\n      \"method\": \"Promoter-reporter assay, ChIP assay, promoter deletion mutagenesis, GATA1 overexpression\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and promoter mutagenesis establish direct transcription factor binding; functional link confirmed\",\n      \"pmids\": [\"27139506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CREG1 inhibits LAMP2 protein degradation by suppressing FBXO27 E3-ubiquitin ligase expression; LAMP2 overexpression reverses the effect of CREG1 knockdown on cardiomyocyte autophagy inhibition in diabetic cardiomyopathy, defining the CREG1-FBXO27-LAMP2 axis.\",\n      \"method\": \"CREG1 transgenic and cardiac-specific KO mice, palmitate-stimulated NMCMs, Western blot, LAMP2 overexpression rescue, FBXO27 expression analysis\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — molecular pathway defined with rescue experiment; single lab\",\n      \"pmids\": [\"37658156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CREG1 directly interacts with MEK1/2 and promotes MEK1/2 phosphorylation, which is required for megakaryocyte maturation and proplatelet formation; Creg1 conditional KO megakaryocytes display impaired actin cytoskeleton (less F-actin), fewer proplatelets, and lower ploidy, resulting in thrombocytopenia.\",\n      \"method\": \"Megakaryocyte/platelet conditional Creg1 KO and transgenic mice, co-immunoprecipitation (CREG1–MEK1/2), Western blot, actin staining, thrombocytopenia model\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct interaction by Co-IP plus tissue-specific KO with defined phenotype; single lab\",\n      \"pmids\": [\"37496998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CREG1 inhibits ferroptosis in cardiomyocytes by regulating the FBXW7-FOXO1 pathway to suppress PDK4 mRNA and protein expression; PDK4 deficiency reverses the effects of CREG1 knockdown on DOX-induced ferroptosis, placing PDK4 downstream of CREG1-FBXW7-FOXO1.\",\n      \"method\": \"CREG1 transgenic and cardiac-specific KO mice, NMCMs with siRNA/adenovirus, transcriptomics, Western blot, immunoprecipitation\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — transcriptomics-guided mechanism with Co-IP and rescue; single lab\",\n      \"pmids\": [\"39094399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CREG1 deficiency inhibits skeletal muscle satellite cell differentiation and regeneration by promoting C-CBL E3-ubiquitin ligase-mediated K48-linked polyubiquitination of AMPKα1 at K396, leading to AMPKα1 degradation; silencing C-CBL in Creg1 myofibre-KO mice rescues muscle regeneration.\",\n      \"method\": \"Satellite cell-specific Creg1 OE and myofibre-specific Creg1 KO mice, mass spectrometry, RNA sequencing, AAV-shC-CBL silencing rescue, Western blot\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ubiquitination site mapped by MS, rescue by C-CBL silencing confirms epistasis; single lab\",\n      \"pmids\": [\"38272853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CREG1 promotes exosome biogenesis and release from bovine placental trophoblast cells by targeting IGF2R; IGF2R knockdown inhibits exosome genesis and blocks CREG1-induced exosome release. CREG1 binds IGF2R which subsequently binds Rab11 to regulate exosomal vesicle formation.\",\n      \"method\": \"Overexpression/knockdown of CREG1 and IGF2R, exosome isolation and characterization, Co-IP (IGF2R–Rab11)\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP and knockdown epistasis; single lab, bovine model\",\n      \"pmids\": [\"38917918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CREG1 stimulates AMPK phosphorylation and glucose uptake in skeletal muscle cells via IGF2R; CREG1-induced AMPKα phosphorylation and 2-deoxyglucose uptake are suppressed by IGF2R knockdown and the AMPK inhibitor Compound C, placing IGF2R upstream of AMPK in CREG1 signaling.\",\n      \"method\": \"C2C12 myotubes, recombinant CREG1 treatment, IGF2R siRNA knockdown, AMPK inhibitor Compound C, Western blot, 2-DG uptake assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic epistasis; single lab\",\n      \"pmids\": [\"36528955\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CREG1 promotes ESC differentiation into smooth muscle cells via the TGF-β/Smad2/3 signaling pathway; CREG overexpression increases SMC markers and contractile function while CREG KO reduces them; TGF-β-Smad2/3 pathway mediates this effect.\",\n      \"method\": \"ESC CREG OE and KO models, differentiation assay, Western blot, calcium imaging, Smad2/3 pathway analysis\",\n      \"journal\": \"Differentiation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss-of-function with pathway identification; single lab\",\n      \"pmids\": [\"35349881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In zebrafish, creg1 deficiency impairs erythroid differentiation and causes excessive apoptosis of erythroid progenitors through reduced activation of the TGF-β/Smad2 signaling pathway; IDE2 (Smad2 pathway agonist) rescues the erythroid defect in creg1-/- mutants. Klf1 is a key downstream target of TGF-β/Smad2 involved in CREG1-mediated erythropoiesis.\",\n      \"method\": \"Zebrafish creg1 knockout, IDE2 pharmacological rescue, Klf1 target analysis, in situ hybridization, flow cytometry\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with pharmacological pathway rescue and downstream target identification; zebrafish ortholog\",\n      \"pmids\": [\"38953462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CREG1 promotes lysosomal biogenesis and autophagy in cardiomyocytes; global Creg1 KO mice develop age-associated cardiac hypertrophy, fibrosis, and diastolic dysfunction (~80 weeks). CREG1 localizes to endolysosomal and autophagosomal compartments; its loss impairs autophagy flux and mitophagy due to defective autophagosome membrane expansion and degradation.\",\n      \"method\": \"Global Creg1 KO (full ORF deletion), cardiomyocyte-specific KO and KI mice, electron microscopy, immunofluorescence, CAG-EGFP-RFP-LC3 autophagy reporter, echocardiography\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — rigorous true KO with multiple orthogonal methods; preprint\",\n      \"pmids\": [\"41292877\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CREG1 promotes osteogenic differentiation of BMSCs and bone homeostasis via RAB7-mediated regulation of autophagy; RAB7 knockdown inhibits CREG1-induced osteogenic differentiation and autophagy, while RAB7 overexpression restores osteogenic potential suppressed by CREG1 knockdown, placing RAB7 downstream of CREG1.\",\n      \"method\": \"CREG1 and RAB7 overexpression/knockdown in BMSCs, osteogenic differentiation assay, autophagy flux assay, in vivo OVX osteoporosis model\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — epistasis shown but direct CREG1–RAB7 molecular interaction not established; single lab\",\n      \"pmids\": [\"41577020\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CREG1 is an endosomal-lysosomal secreted glycoprotein that forms a homodimer with a β-barrel fold; it binds the M6P/IGF2R (via both glycosylation-dependent and -independent sites on receptor domains 7–10 and 11–13) to inhibit cell proliferation, promotes lysosomal biogenesis, endocytic trafficking, and autophagy/mitophagy, interacts with Sec8 of the exocyst complex to drive intercellular junction assembly and cardiomyocyte differentiation, directly engages ASK1 and TAK1 to suppress MAPK signaling in stress protection, and transcriptionally cooperates with p16(INK4a) to induce senescence, while its own expression is regulated by GATA1 binding and DNMT3B-mediated promoter methylation.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CREG1 is a secreted, endosomal-lysosomal glycoprotein that promotes cellular differentiation, suppresses proliferation, and maintains lysosomal-autophagic homeostasis across diverse tissues. Structurally, CREG1 forms a homodimer with a β-barrel fold that binds the mannose-6-phosphate/IGF2 receptor (M6P/IGF2R) through both glycosylation-dependent (domains 7–10) and glycosylation-independent (domains 11–13) sites, facilitating IGF-II endocytosis and attenuating IGF-II-driven PI3K/Akt signaling to inhibit cell growth and migration [PMID:12934103, PMID:16344469, PMID:21195083, PMID:19769965]. CREG1 localizes to the endosomal-lysosomal compartment where it promotes lysosomal biogenesis, endocytic trafficking, autophagic flux, and mitophagy—functions whose loss leads to autophagosome accumulation, impaired Rab7 expression, and organ-level pathology including cardiac fibrosis and skeletal muscle dysfunction [PMID:33966596, PMID:25774384, PMID:33726618]. Beyond its lysosomal roles, CREG1 directly engages cytoplasmic kinases ASK1 and TAK1 to suppress MAPK-mediated stress signaling in liver, interacts with exocyst subunit Sec8 to drive intercalated disc assembly during cardiomyocyte differentiation, and cooperates with p16(INK4a) to enforce cellular senescence through transcriptional repression of cyclins A and B [PMID:28508477, PMID:30076625, PMID:27334848, PMID:21263217].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"The first functional characterization established that CREG1 is a secreted glycoprotein that promotes differentiation of embryonal carcinoma cells, positioning it as an extracellular differentiation signal rather than a transcription factor or intracellular enzyme.\",\n      \"evidence\": \"Northern blot, overexpression in NTERA-2 cells, conditioned media experiments\",\n      \"pmids\": [\"10815803\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor or binding partner mediating extracellular signaling unknown\", \"Mechanism of differentiation induction not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"The identification of M6P/IGF2R as the required receptor for CREG1's antiproliferative activity established a specific receptor–ligand axis, resolving how a secreted glycoprotein inhibits cell growth.\",\n      \"evidence\": \"Direct binding assay, cell cycle analysis in M6P/IGF2R-deficient cells\",\n      \"pmids\": [\"12934103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding site on M6P/IGF2R not mapped\", \"Downstream intracellular signal unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The 1.9 Å crystal structure revealed CREG1 as a homodimeric β-barrel protein that cannot bind FMN despite structural homology, and mutagenesis showed that M6P/IGF2R binding is necessary but not sufficient for growth suppression—an additional surface element is required.\",\n      \"evidence\": \"X-ray crystallography, loop-deletion mutagenesis, M6P/IGF2R binding and growth assays\",\n      \"pmids\": [\"16344469\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the additional surface required for growth suppression unknown\", \"No co-crystal with receptor\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Reciprocal gain- and loss-of-function studies in vascular smooth muscle cells and in vivo balloon injury models demonstrated that CREG1 maintains differentiated SMC phenotype and inhibits neointimal hyperplasia, extending its role from embryonal carcinoma to cardiovascular biology.\",\n      \"evidence\": \"Retroviral overexpression/shRNA, in vivo balloon injury model in SMCs\",\n      \"pmids\": [\"18267954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SMC effects depend entirely on M6P/IGF2R unclear\", \"Downstream transcriptional targets not identified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The demonstration that CREG1 facilitates IGF-II endocytosis via M6P/IGF2R and that CREG knockdown elevates IGF-II secretion resolved the mechanism by which CREG1–M6P/IGF2R interaction suppresses proliferation: by clearing a mitogenic ligand.\",\n      \"evidence\": \"Co-immunoprecipitation, FACS, endocytosis assay in NIH3T3 cells\",\n      \"pmids\": [\"18691225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CREG1 alters M6P/IGF2R trafficking dynamics unknown\", \"Role of glycosylation-independent binding not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Epistatic experiments showed CREG1 suppresses SMC migration by reducing IGF-II-driven PI3K/Akt/MMP-9 signaling through enhanced IGF-II endocytosis, unifying its antiproliferative and anti-migratory activities under one receptor-clearance mechanism.\",\n      \"evidence\": \"Migration assay, neutralizing antibody and PI3K inhibitor epistasis, endocytosis assay\",\n      \"pmids\": [\"19769965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"MMP-9 regulatory step not precisely defined\", \"Whether CREG1 has M6P/IGF2R-independent anti-migratory activity untested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapping CREG1 binding to two distinct M6P/IGF2R regions (domains 7–10, glycosylation-dependent; domains 11–13, glycosylation-independent) showed that CREG1 engages the receptor through a bimodal mechanism, each sufficient for growth arrest.\",\n      \"evidence\": \"In vitro binding with glycosylation-mutant CREG, soluble receptor fragment blocking, cell cycle analysis\",\n      \"pmids\": [\"21195083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of glycosylation-independent binding undetermined\", \"Whether both sites are engaged simultaneously unknown\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"CREG1 was shown to cooperate with p16(INK4a) to enforce cellular senescence by transcriptionally repressing cyclins A and B, revealing an intracellular gene-regulatory function distinct from its extracellular receptor-binding activity.\",\n      \"evidence\": \"Co-expression experiments, promoter-reporter assays, SA-β-gal senescence assay\",\n      \"pmids\": [\"21263217\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CREG1 directly contacts cyclin promoters or acts through an intermediary not resolved\", \"Single lab, not replicated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The discovery that CREG1 haploinsufficiency impairs lysosomal maturation, reduces Rab7, and causes autophagosome accumulation with defective autophagic flux in vivo redefined CREG1 as a lysosomal biogenesis factor, not merely an extracellular ligand.\",\n      \"evidence\": \"Creg1+/− mice, recombinant CREG1 rescue, chloroquine confirmation, Western blot\",\n      \"pmids\": [\"25774384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CREG1 regulates Rab7 expression molecularly unknown\", \"Whether lysosomal role is M6P/IGF2R-dependent not tested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identification of Sec8 (exocyst complex) as a direct CREG1 binding partner required for intercalated disc assembly and cardiomyocyte differentiation established a new non-lysosomal, cytoskeleton-linked role for CREG1.\",\n      \"evidence\": \"Co-IP, site-directed mutagenesis, CREG1 KO ES cell rescue, co-localization imaging\",\n      \"pmids\": [\"27334848\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CREG1–Sec8 interaction is conserved beyond cardiomyocytes unknown\", \"Mechanism by which CREG1 stabilizes N-cadherin via Sec8 unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Direct binding of CREG1 to ASK1 and inhibition of ASK1 phosphorylation, confirmed by JNK1-specific epistasis, established a hepatocyte-intrinsic MAPK-suppressive function protecting against steatosis.\",\n      \"evidence\": \"Hepatocyte-specific CREG1 KO/OE mice, Co-IP, JNK1 inhibitor epistasis\",\n      \"pmids\": [\"28508477\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding interface between CREG1 and ASK1 not structurally resolved\", \"Whether this kinase inhibition is catalytic or sequestration-based unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The finding that CREG1 directly binds TAK1 and inhibits its phosphorylation to suppress MAPK signaling during hepatic ischemia/reperfusion extended the kinase-inhibitory paradigm to a second MAP3K, validated by binding-domain mutagenesis.\",\n      \"evidence\": \"Hepatocyte-specific KO/Tg mice, Co-IP, TAK1-binding domain mutation, TAK1 inhibitor blocking\",\n      \"pmids\": [\"30076625\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of TAK1 vs ASK1 selectivity unknown\", \"Whether CREG1 inhibits kinases in other tissues untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Systematic validation of CREG1 as an endosomal-lysosomal resident that promotes macropinocytosis, clathrin-dependent endocytosis, endolysosomal acidification, and lysosomal biogenesis unified its diverse phenotypic effects under a core endolysosomal function.\",\n      \"evidence\": \"Validated antibodies, KO/KD/OE, acridine orange staining, transferrin uptake, LAMP1/cathepsin D assays\",\n      \"pmids\": [\"33966596\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which CREG1 promotes acidification undetermined\", \"Whether CREG1 functions as a lumenal or membrane-associated factor unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Skeletal muscle-specific Creg1 KO revealed CREG1 as a mitophagy regulator that localizes to mitochondria and interacts with HSPD1/HSP60, broadening the autophagic role to organelle-selective degradation.\",\n      \"evidence\": \"Skeletal muscle-specific Creg1 KO, electron microscopy, Co-IP mapping CREG1(130–220)–HSPD1(401–573)\",\n      \"pmids\": [\"33726618\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CREG1 is imported into mitochondria or tethers from the OMM unclear\", \"Relationship between HSPD1 interaction and PINK1/Parkin pathway not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that CREG1 stabilizes LAMP2 by suppressing FBXO27 E3 ligase expression provided a molecular mechanism for CREG1's lysosomal maintenance function, validated by LAMP2 rescue of CREG1 knockdown in diabetic cardiomyopathy.\",\n      \"evidence\": \"Cardiac-specific KO/Tg mice, LAMP2 overexpression rescue, FBXO27 expression analysis\",\n      \"pmids\": [\"37658156\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How CREG1 suppresses FBXO27 expression not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of direct CREG1–MEK1/2 interaction promoting MEK phosphorylation for megakaryocyte maturation revealed a context-dependent pro-kinase activity, contrasting with the ASK1/TAK1 kinase-inhibitory roles.\",\n      \"evidence\": \"Megakaryocyte/platelet conditional Creg1 KO and Tg mice, Co-IP, actin staining\",\n      \"pmids\": [\"37496998\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of opposing kinase modulation (activation vs inhibition) in different contexts unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"CREG1 was shown to maintain satellite cell differentiation and muscle regeneration by preventing C-CBL-mediated K48-polyubiquitination of AMPKα1 at K396, linking CREG1 to ubiquitin-proteasome regulation of a master metabolic kinase.\",\n      \"evidence\": \"Satellite cell-specific OE and myofibre-specific KO mice, mass spectrometry, AAV-shC-CBL rescue\",\n      \"pmids\": [\"38272853\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CREG1 directly binds C-CBL or AMPKα1 not established\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how CREG1 exerts opposing effects on different kinases (inhibiting ASK1/TAK1 yet activating MEK1/2), whether its lysosomal and extracellular receptor-binding functions are mechanistically linked or independent, and what molecular event converts CREG1 from a secreted ligand to an endolysosomal/mitochondrial effector.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unified model explains context-dependent kinase activation vs inhibition\", \"Whether intracellular CREG1 re-enters the secretory pathway or acts cell-autonomously after synthesis is unresolved\", \"No co-crystal structure of CREG1 with any intracellular partner exists\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 13, 14, 24]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [11, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [10, 18, 31]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [18]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [10, 12, 18, 19, 31]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 9, 13, 14, 24]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 3, 11, 29, 30]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [10, 18, 23]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [18, 27]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"IGF2R\", \"ASK1\", \"TAK1\", \"EXOC4\", \"MEK1\", \"HSPD1\", \"RXRA\"],\n    \"other_free_text\": []\n  }\n}\n```"}