{"gene":"CCL15","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1997,"finding":"CCL15 (Leukotactin-1/Lkn-1) was identified as a novel CC chemokine that acts as a potent agonist at CCR1 and CCR3, inducing calcium flux and chemotaxis in neutrophils, monocytes, and lymphocytes, and suppressing colony formation by hematopoietic progenitor cells.","method":"Recombinant protein production, calcium flux assays, Boyden chamber chemotaxis assays, CCR1/CCR3-transfected cell lines, colony formation assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal functional assays, receptor-transfected cell lines, replicated across independent groups","pmids":["9548457","9346309","9624581"],"is_preprint":false},{"year":1998,"finding":"CCL15 (HCC-2/CKβ8) gene has a unique four-exon/three-intron structure and encodes a protein with six conserved cysteines (including two extra forming a third disulfide bond anchoring the C-terminal domain to the core), and the protein activates cells via CCR1 and CCR3 in a manner dependent on N-terminal length.","method":"Gene cloning/sequencing, Northern blot, recombinant protein production, calcium flux assays, chemotaxis assays on monocytes and eosinophils","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 — structural characterization plus functional validation with multiple cell types and receptors","pmids":["9600961"],"is_preprint":false},{"year":1998,"finding":"Two alternatively spliced forms of CCL15 (CKβ8 and CKβ8-1, differing by 17 amino acids at the N-terminus) are both potent agonists at CCR1, chemoattracting neutrophils, monocytes, and lymphocytes, and suppressing hematopoietic progenitor colony formation, demonstrating that alternative splicing produces two active chemokines from a single gene.","method":"cDNA cloning, recombinant protein expression, receptor-binding assays, calcium flux, chemotaxis assays, colony formation assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal assays, receptor specificity confirmed","pmids":["9558365"],"is_preprint":false},{"year":1999,"finding":"CCL15 (Lkn-1) acts via CCR1 on human neutrophils to induce high-level calcium flux and chemotaxis, while MIP-1α acting on the same receptor produces negligible responses; CCR1-/- mouse neutrophils fail to respond to either ligand, establishing CCR1 as the mediating receptor with ligand-specific functional outcomes.","method":"CCR1 knockout mice, calcium flux assays, Scatchard binding analysis, cross-desensitization studies, chemotaxis assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — genetic knockout confirmation plus binding analysis and cross-desensitization; strong evidence for CCR1-mediated but ligand-specific signaling","pmids":["10202040"],"is_preprint":false},{"year":1999,"finding":"The solution structure of CCL15 (HCC-2, truncated 66-aa form) was determined by NMR, revealing a monomeric chemokine fold with a triple-stranded antiparallel β-sheet covered by an α-helix; unlike most chemokines, CCL15 does not dimerize across a concentration range of 0.1 μM to 2 mM, and the third disulfide bond does not influence the relative orientation of helix and β-sheet.","method":"1H NMR spectroscopy, restrained molecular dynamics calculations (871 experimental restraints), mutagenesis of disulfide bond","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with mutagenesis validation","pmids":["10320325"],"is_preprint":false},{"year":2001,"finding":"CCL15 circulates in human blood plasma and is encoded by mono- and bicistronic transcripts from a tandem gene arrangement with CCL14a on chromosome 17q11.2; biological activity depends on N-terminal length, with shorter isoforms being more potent CCR1 and CCR3 agonists.","method":"Hemofiltration-based isolation, chromatographic characterization, Northern blot analysis, calcium flux assays","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2-3 — biochemical characterization with functional validation, single group","pmids":["11527984"],"is_preprint":false},{"year":2002,"finding":"CCL15 (Lkn-1)-induced chemotaxis through CCR1 is transduced via Gi/Go protein, phospholipase C, and PKCδ; NF-κB is also activated downstream and required for chemotaxis, as newly synthesized proteins are needed for the migratory response.","method":"Pharmacological inhibitors (pertussis toxin, PLC inhibitor, PKCδ inhibitor, NF-κB inhibitor, cycloheximide, actinomycin D), CCR1-expressing HOS cells, chemotaxis assays, PLC and PKCδ activity assays","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — multiple pharmacological pathway dissections in receptor-expressing cell line","pmids":["11943214"],"is_preprint":false},{"year":2004,"finding":"N-terminal truncation of CCL15 by 24 amino acid residues (Δ24-CCL15) converts the weakly active full-length form into a potent CCR1 agonist and weak CCR3 agonist; the C-terminal α-helix is essential for maintaining tertiary structure and CCR1 binding activity, while the third disulfide bond and position Y70 do not affect CCR1 interaction.","method":"Chemical synthesis of sequential N-terminal truncation and point mutants using Fmoc chemistry, calcium flux assays, receptor transfectant chemotaxis (CCR1/CCR3), radioligand binding","journal":"The journal of peptide research","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis with reconstituted receptor assays, structure-function mapping","pmids":["14984572"],"is_preprint":false},{"year":2004,"finding":"LZIP (a transcription factor) binds directly to CCR1 (residues 21-260 of LZIP are essential for interaction) and selectively enhances Lkn-1/CCL15-induced chemotaxis without affecting chemotaxis induced by other CCR1 ligands (MIP-1α, RANTES, HCC-4), establishing LZIP as a CCR1-interacting protein that differentially modulates CCL15-specific signaling.","method":"Yeast two-hybrid screen, mammalian two-hybrid assay, co-immunoprecipitation, domain deletion mapping, chemotaxis assays in LZIP-transfected cells","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2-3 — yeast 2-hybrid confirmed by co-IP and functional chemotaxis, single lab","pmids":["15001559"],"is_preprint":false},{"year":2004,"finding":"CCL15 (Lkn-1) induces MMP-9 release from macrophages and macrophage-derived foam cells in a dose-dependent manner, suggesting a role in atherosclerotic plaque destabilization.","method":"THP-1 macrophage differentiation, oxidized LDL-induced foam cell preparation, CCL15 treatment, gelatin zymography for MMP-9","journal":"Nutrition research and practice","confidence":"Low","confidence_rationale":"Tier 3 — single-method zymography, single lab","pmids":["20126378"],"is_preprint":false},{"year":2004,"finding":"CCL15 (both full-length CCL15(1-92) and truncated CCL15(25-92)) stimulates chemotactic endothelial cell migration and differentiation in vitro; CCL15(25-92) is at least 100-fold more potent. This angiogenic activity is mediated via CCR1 and CCR3, as it is blocked by pertussis toxin, anti-CCR1, or anti-CCR3 antibody. CCL15(25-92) also induces aortic ring sprouting and in vivo angiogenesis in the chick chorioallantoic membrane assay.","method":"Endothelial cell chemotaxis (Boyden chamber), tube formation assay, pertussis toxin and neutralizing antibody inhibition, aortic ring assay, CAM assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal angiogenesis assays (in vitro and in vivo), receptor blocking confirms CCR1/CCR3 dependence","pmids":["15251437"],"is_preprint":false},{"year":2005,"finding":"Neutrophil cathepsin G is the principal protease that proteolytically processes full-length CCL15 to N-terminally truncated isoforms (Δ23 and Δ26); neutrophil elastase generates a Δ21 isoform. The truncated Δ23 and Δ26 isoforms display significantly increased potency for calcium flux, monocyte chemotaxis, and mononuclear cell adhesion to fibronectin compared to full-length CCL15, establishing neutrophil-mediated activation of CCL15 as a mechanism for monocyte recruitment.","method":"Hemofiltration, chromatographic separation, mass spectrometry identification of cleavage products, purified cathepsin G and elastase incubation, calcium flux assays, chemotaxis assays, fibronectin adhesion assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — protease identified by biochemical reconstitution with purified enzymes, cleavage sites sequenced by MS, functional potency confirmed by multiple assays","pmids":["16034099"],"is_preprint":false},{"year":2005,"finding":"Proinflammatory proteases (including synovial fluid proteases) cleave the N-terminal domain of CCL15, converting it from a weak to a potent CCR1 agonist (up to 1000-fold increase); N-terminally truncated CCL15 was detected at relatively high levels in synovial fluid from rheumatoid arthritis patients, suggesting in vivo activation of CCL15 during inflammation.","method":"Incubation with proinflammatory proteases and physiological fluids, N-terminal sequencing, CCR1-mediated signaling and chemotaxis assays, detection in rheumatoid arthritis synovial fluid","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical reconstitution with multiple proteases, confirmed in human disease fluid, replicated functional activation","pmids":["15905581"],"is_preprint":false},{"year":2005,"finding":"Transcription of the CCL15 gene in monocytoid cells is regulated by AP-1 (binding at -76/-65) and NF-κB through MEK and JNK MAPK pathways; dominant negative MKK4 or JNK1 reduced PMA-induced CCL15 transcription.","method":"Luciferase reporter assays, MAPK inhibitors, dominant negative kinase expression, EMSA (AP-1 binding confirmation)","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assays plus dominant negative genetics and EMSA binding confirmation","pmids":["16364464"],"is_preprint":false},{"year":2004,"finding":"Two NF-κB binding sites in the CCL15 promoter (at -191/-182 and -60/-51 bp from transcription start) are both essential for PMA-induced expression in monocytoid U937 cells; mutation of either site reduces induction and proteasome inhibitor blocks PMA-induced CCL15 expression.","method":"Promoter deletion/mutation analysis with luciferase reporter, EMSA, proteasome inhibitor treatment","journal":"Molecules and cells","confidence":"Medium","confidence_rationale":"Tier 2 — systematic promoter dissection with mutagenesis and EMSA confirmation","pmids":["15179048"],"is_preprint":false},{"year":2006,"finding":"In chronic renal failure (CRF), plasma CCL15 concentrations are significantly elevated and include truncated isoforms (including CCL15(12-92)); CCL15(12-92) induces stronger calcium flux, chemotactic activity, and fibronectin adhesion in monocytes than full-length CCL15(1-92), and PBMCs from CRF patients show increased sensitivity to CCL15, implicating the CCL15-CCR1 axis in CRF pathophysiology.","method":"Hemofiltration, mass spectrometry (MW 10141.3 Da confirmed), calcium flux assays, chemotaxis assays, fibronectin adhesion assays in patient-derived cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical identification of isoforms by MS plus functional comparison, confirmed in patient samples","pmids":["16737685"],"is_preprint":false},{"year":2007,"finding":"CCL15 (Lkn-1) induces LZIP expression via NF-κB in an immediate early response; NF-κB binds to the LZIP promoter specifically (confirmed by EMSA and mutation analysis), and LZIP expression via NF-κB is required for Lkn-1-induced monocyte chemotaxis.","method":"Time/dose-dependent LZIP expression assays, LZIP promoter deletion/mutation analysis, luciferase reporter, EMSA, NF-κB inhibitors, chemotaxis assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — promoter mapping with mutagenesis, EMSA, inhibitor studies, and functional chemotaxis readout","pmids":["17296613"],"is_preprint":false},{"year":2009,"finding":"CCL15 (Lkn-1) induces migration of eosinophilic EoL-1 cells more potently than other CCR1 ligands; signaling is mediated through Gi/Go protein, PLC, and PKCδ activation, and CCL15 also enhances butyric acid-induced eosinophil differentiation via PKCδ after binding to CCR1.","method":"Transwell chemotaxis assays, pharmacological inhibitors (pertussis toxin, U73122/PLC inhibitor, rottlerin/PKCδ inhibitor), PKCδ activity assays, morphological differentiation assessment, EPO/MBP expression","journal":"Molecular biology reports","confidence":"Medium","confidence_rationale":"Tier 2 — multiple inhibitors used with consistent results across migration and differentiation endpoints","pmids":["19669929"],"is_preprint":false},{"year":2009,"finding":"Human intestinal epithelial CCL15 (and its murine homolog CCL6) displays direct antibacterial activity, binding to a subset of the intestinal microflora; expression of CCL15 is upregulated in inflammatory bowel disease, revealing a novel antimicrobial function beyond leukocyte recruitment.","method":"Bacterial binding assays, antibacterial activity assays with recombinant CCL15, qPCR of intestinal epithelium, IHC of IBD samples","journal":"Mucosal immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct antimicrobial assays with recombinant protein, confirmed in multiple contexts","pmids":["19812544"],"is_preprint":false},{"year":2010,"finding":"Human colorectal cancer cells secrete CCL15 (the human ortholog of mouse CCL9) to recruit CCR1+ immature myeloid cells (CD34+Gr-1-) that produce MMP2 and MMP9 to facilitate liver metastasis; genetic loss of Ccr1, Mmp2, or Mmp9 in host mice dramatically suppresses metastatic outgrowth, and a CCR1 antagonist blocks myeloid cell accumulation and prolongs survival.","method":"Mouse liver dissemination model, CCR1/MMP2/MMP9 knockout hosts, orthotopic tumor implantation, CCR1 antagonist (BL5923) treatment, survival analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis in multiple knockout models plus pharmacological intervention, strong functional readout","pmids":["20616008"],"is_preprint":false},{"year":2011,"finding":"MMP processing of CCL15: MMPs and serine proteases in human synovial fluid cleave CCL15 within its unique 31-amino acid extended N-terminus; the resulting products CCL15-(25-92) and CCL15-(28-92) are stronger agonists than full-length CCL15 in calcium flux assays and monocyte migration assays (Transwell), unlike other CCL chemokines that become receptor antagonists after MMP cleavage.","method":"Incubation with synovial fluid, family-wide MMP panel (14 MMPs tested against 14 CC chemokines), MALDI-TOF-MS sequencing of 149 cleavage sites, calcium flux assays, Transwell migration assays with CCR1 transfectants and THP-1 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic biochemical reconstitution with cleavage sites sequenced by MS, functional activation confirmed by multiple assays","pmids":["22147696"],"is_preprint":false},{"year":2011,"finding":"CCL15 is constitutively expressed by human airway smooth muscle cells (ASMC) and is strongly upregulated by TNF-α; this upregulation is inhibited by dexamethasone, the SP-1 inhibitor mithramycin A, and the IKK-2 inhibitor AS602868. TNF-α-induced CCL15 is synergistically enhanced by IFN-γ at both transcriptional and translational levels in an NF-κB-dependent manner.","method":"Primary ASMC culture, ELISA, real-time PCR, immunofluorescence, pharmacological inhibitors (dexamethasone, mithramycin A, AS602868), cytokine treatments","journal":"Clinical and experimental allergy","confidence":"Medium","confidence_rationale":"Tier 2-3 — pharmacological dissection of regulatory pathway with multiple inhibitors and cytokine combinations","pmids":["22092970"],"is_preprint":false},{"year":2012,"finding":"CCR1-mediated CCL15 signaling in THP-1 macrophage-like cells induces STAT3 Tyr705 phosphorylation via pertussis toxin-insensitive Gα14/16 proteins; STAT3 Tyr705-phosphorylation leads to nuclear translocation and induces CXCL8 expression, while STAT3 Ser727-phosphorylation is independent and cytosolic. CCL15 also triggers IL-6 release, which mediates STAT3 Tyr705 phosphorylation in an autocrine manner.","method":"PMA-differentiated THP-1 cells and CCR1/Gα14/16-overexpressing HEK293 cells, pertussis toxin treatment, subcellular fractionation, confocal microscopy, neutralizing anti-IL-6 antibody, STAT3 inhibition, CXCL8 ELISA","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal approaches (subcellular fractionation, confocal, antibody neutralization, inhibitors) in multiple cell systems","pmids":["23125416"],"is_preprint":false},{"year":2013,"finding":"Loss of SMAD4 in human colorectal cancer cells upregulates CCL15 expression; SMAD4 directly binds to the CCL15 promoter to negatively regulate transcription, and TGF-β increases SMAD4 binding to the CCL15 promoter, enhancing repression. CCL15 secreted by SMAD4-deficient CRC cells recruits CCR1+ myeloid cells (CD11b+/myeloperoxidase+/MMP9+) that promote liver metastasis.","method":"SMAD4 knockdown/overexpression in CRC lines, chromatin immunoprecipitation (ChIP) for SMAD4 at CCL15 promoter, TGF-β treatment, nude mouse liver metastasis model, IHC of 141 human metastasis specimens","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP confirms direct promoter binding, in vivo model, validated in clinical specimens","pmids":["23891973"],"is_preprint":false},{"year":2013,"finding":"CCL15 stimulates hepatocellular carcinoma cell migration and invasion in an autocrine manner, as demonstrated by siRNA-mediated knockdown of CCL15 reducing invasion and migration.","method":"RT-PCR, Western blot, siRNA knockdown, cell invasion assay (Matrigel), scratch/wound healing assay, MMP-9 Western blot","journal":"British journal of cancer / Chinese journal of hepatology","confidence":"Medium","confidence_rationale":"Tier 3 — loss-of-function with phenotypic readout (invasion/migration), single lab, no pathway placement","pmids":["23321514","22971284"],"is_preprint":false},{"year":2013,"finding":"CCL15 upregulates ICAM-1 expression in endothelial cells via the JAK2/STAT3 pathway: CCL15 stimulation activates JAK2 and STAT3 phosphorylation, STAT3 binds to the ICAM-1 promoter (confirmed by ChIP and reporter assays), and JAK, PI3K, and AKT inhibitors prevent CCL15-induced ICAM-1 expression and monocyte adhesion. This signaling is predominantly mediated via CCR1.","method":"Endothelial cell CCL15 stimulation and knockdown, ICAM-1 expression (Western blot, flow cytometry), reporter assays, ChIP for STAT3 at ICAM-1 promoter, JAK/PI3K/AKT inhibitors, monocyte adhesion under static and shear-stress conditions, H/R model","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 — ChIP confirms STAT3 promoter binding, multiple pharmacological validations, functional adhesion readout under physiological conditions","pmids":["23690481"],"is_preprint":false},{"year":2015,"finding":"Loss of SMAD4 in primary colorectal cancer cells promotes CCL15 expression to recruit CCR1+ MDSCs (CD11b+, CD33+, HLA-DR-; primarily granulocytic CD15+ with some monocytic CD14+) at the tumor invasion front; CCL15-expressing tumors recruit 2.2-fold more CCR1+ cells and CCL15 knockdown in SMAD4-deficient CRC cells reduces aggressive tumor growth in an orthotopic xenograft model.","method":"SMAD4/CCL15 shRNA knockdown in CRC lines, orthotopic xenograft model, IHC and double immunofluorescence of 333 clinical specimens, ELISA for serum CCL15, MDSC phenotyping","journal":"Clinical cancer research","confidence":"High","confidence_rationale":"Tier 2 — in vivo model with genetic knockdown, validated in large clinical cohort with MDSC phenotyping","pmids":["26341919"],"is_preprint":false},{"year":2015,"finding":"CCL15 promotes HCC cell migration and invasion via CCR1; CCR1 shRNA knockdown inhibits CCL15-induced chemotaxis and invasion of HepG2 cells and significantly reduces the activity and expression of MMP-2 and MMP-9.","method":"CCR1 shRNA knockdown, Transwell migration/invasion assays, MMP-2/MMP-9 zymography and Western blot","journal":"Tumour biology","confidence":"Medium","confidence_rationale":"Tier 3 — loss-of-function with mechanistic link to MMP activity, single lab","pmids":["26501423"],"is_preprint":false},{"year":2016,"finding":"CCL15 mediates migration of human bone marrow-derived mesenchymal stem cells toward HCC via CCR1 receptors on hMSCs: CCL15 knockdown in HCC cells significantly reduces hMSC homing to tumor xenografts in vivo (confirmed by histology and flow cytometry), and anti-CCL15 or anti-CCR1 blockade impairs Transwell migration of hMSCs.","method":"Cytokine array, ELISA, IHC, Transwell migration, CCL15 shRNA in HCC cells, orthotopic HCC xenograft model, intravenous hMSC delivery with histological and flow cytometric homing quantification","journal":"Stem cells","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo homing confirmed by independent histological and flow cytometric methods, receptor specificity established","pmids":["26763650"],"is_preprint":false},{"year":2016,"finding":"Loss of SMAD4 promotes CCL15 expression in colorectal cancer, leading to recruitment of CCR1+ tumor-associated neutrophils (and minor granulocytic MDSCs) that facilitate lung metastasis; in a mouse model, CCL15 from SMAD4-deficient CRC cells recruits CCR1+ cells to promote metastatic activity to the lung.","method":"Mouse lung metastasis model with SMAD4-manipulated CRC cells, IHC/immunofluorescence of 107 clinical lung metastasis specimens, CCR1+ cell characterization with cell-type-specific markers","journal":"Clinical cancer research","confidence":"High","confidence_rationale":"Tier 2 — in vivo model plus validated in clinical specimens, extends SMAD4-CCL15-CCR1 axis to a new organ site","pmids":["27492974"],"is_preprint":false},{"year":2018,"finding":"In HCC, CCL15 expression is regulated by genetic, epigenetic, and microenvironmental factors; CCL15 recruits CCR1+CD14+ monocytes to the invasive margin via the CCL15-CCR1 axis; these tumor-educated monocytes express immune checkpoint molecules (PD-L1, B7-H3, TIM-3), upregulate immune-tolerogenic enzymes (IDO, arginase), and activate STAT1/3, ERK1/2, and AKT signaling in HCC cells, promoting invasion and metastasis. Orthotopic animal models confirm CCL15-CCR1 axis drives inflammatory microenvironment enriched with CCR1+ monocytes.","method":"Chemokine expression profiling of HCC cell lines and tissues, CCL15 functional assays, flow cytometry phenotyping of CCR1+CD14+ monocytes, transcriptome sequencing of tumor-infiltrating monocytes, orthotopic mouse models","journal":"Hepatology","confidence":"High","confidence_rationale":"Tier 2 — transcriptome sequencing of infiltrating cells plus in vivo orthotopic models and signaling pathway characterization","pmids":["30070719"],"is_preprint":false},{"year":2020,"finding":"Endothelial cell-derived CCL15 mediates fibrocyte transmigration via CCR1 on fibrocytes; overexpression of CCL15 in endothelial cells or CCR1 in fibrocytes promotes transmigration, while silencing either attenuates it, establishing the CCL15-CCR1 axis as a mechanism for fibrocyte recruitment during wound healing.","method":"Transwell co-culture system, gene chip chemokine expression profiling, CCL15 overexpression/knockdown in endothelial cells, CCR1 overexpression/knockdown in fibrocytes, fibrocyte transmigration assays","journal":"Molecular medicine reports","confidence":"Medium","confidence_rationale":"Tier 3 — loss- and gain-of-function in co-culture system, single lab","pmids":["33174007"],"is_preprint":false},{"year":2021,"finding":"CCL15 derived from eosinophils (human CCL15/CCL23, mouse CCL6) interacts with CCR1 on hematopoietic stem cells to promote eosinophil differentiation and airway inflammation; Ccl6 knockout mice show decreased eosinophilia and airway inflammation after OVA challenge, and the CCR1 antagonist BX471 reduces eosinophil differentiation.","method":"Ccl6 knockout mice, OVA challenge model, CCR1 antagonist BX471, bone marrow eosinophil differentiation assays, flow cytometry","journal":"Signal transduction and targeted therapy","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout plus pharmacological antagonist confirms CCL6/CCL15-CCR1 axis in hematopoietic stem cell regulation of eosinophilia","pmids":["33640900"],"is_preprint":false},{"year":2021,"finding":"P1-HNF4A directly targets CCL15 as a downstream gene in gastric cancer: RNA-seq identified cytokine-cytokine receptor interaction as the most enriched pathway in P1-HNF4A-overexpressing cells, and CCL15 was confirmed as a direct transcriptional target of P1-HNF4A.","method":"HNF4A isoform overexpression, RNA-seq pathway analysis, in vitro proliferation/invasion/migration assays, murine xenograft, confirmation of CCL15 as direct target","journal":"Cancer biology & medicine","confidence":"Low","confidence_rationale":"Tier 3-4 — RNA-seq-based identification with limited direct mechanistic validation of CCL15 targeting","pmids":["33710810"],"is_preprint":false},{"year":2022,"finding":"Oncogenic Kras upregulates CCL15 expression in pancreatic cancer cells; CCL15 promotes PDAC cell migration and invasion through ROS, as N-Acetyl-L-Cysteine treatment or p22phox knockdown decreases CCL15-promoted cell migration. Kras knockdown abolishes CCL15 protein expression and impedes cell migration, establishing Kras→CCL15→ROS as a migration-promoting pathway.","method":"CCL15 knockdown, CCL15 neutralization, recombinant CCL15 treatment, NAC antioxidant treatment, p22phox knockdown, Kras knockdown, cell migration and invasion assays","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple genetic and pharmacological interventions, Kras dependence established, ROS pathway identified","pmids":["35565279"],"is_preprint":false},{"year":2023,"finding":"CTHRC1 upregulates CCL15 in colorectal cancer cells via TGF-β/Smad pathway to recruit tumor-associated macrophages; cytokine microarray after CTHRC1 manipulation revealed CCL15 as the regulated chemokine, and pathway analysis linked CTHRC1 to CCL15 through TGFβ activation and Smad phosphorylation.","method":"Cytokine microarray, CTHRC1 overexpression/knockdown, TGF-β/Smad pathway analysis (Western blot), macrophage chemotaxis assays, multispectral IHC, in vivo CT-26 tumor model","journal":"Journal of molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2-3 — mechanistic link to TGF-β/Smad pathway supported by multiple methods, in vivo confirmation","pmids":["37987774"],"is_preprint":false},{"year":2024,"finding":"CCL15 secreted by HCC cells signals through CCR1 on cancer-associated fibroblasts (CAFs) to induce FTO expression via the STAT3 pathway; FTO demethylates m6A on CEBPA mRNA in CAFs, leading to CXCL5 secretion by CAFs, which activates CXCR2 on HCC cells to enhance proliferation. CXCL5 in turn upregulates CCL15 in HCC cells via MDM2/P53 modulation, creating a positive feedback loop; neutralizing anti-CCL15 antibody attenuates HCC growth in PDX and co-injection models.","method":"Single-cell RNA-seq, co-culture assays, organoid models, allograft models, m6A sequencing, RNA-seq, ChIP, PDX models, neutralizing antibody treatment","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 1-2 — m6A sequencing plus RNA-seq, multiple model systems (organoids, PDX, allograft), mechanistic pathway validated with multiple orthogonal approaches","pmids":["39734010"],"is_preprint":false},{"year":2024,"finding":"SPP1+ macrophages drive liver cancer stemness partly through CCL15 from liver cancer cells; CCL15 produced by HCC cells drives polarization of M0 macrophages toward an SPP1+ macrophage phenotype, establishing a positive feedback loop where SPP1+ macrophages promote tumor stemness via VTN/integrin αvβ5/AMPK/YAP1/SOX4 signaling.","method":"Single-cell RNA-seq (12 patients), co-culture assays, VTN blocking, integrin αvβ5/YAP1 inhibition, chemoresistance assays","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2-3 — scRNA-seq plus co-culture validation, CCL15 role in macrophage polarization supported but not the primary mechanistic focus","pmids":["39216547"],"is_preprint":false},{"year":2025,"finding":"In ESCC, CCL15 and CCR1 directly interact (confirmed by co-immunoprecipitation and immunofluorescence co-localization), and autocrine CCL15-CCR1 signaling activates the AKT/ERK1/2 pathway, leading to c-Jun phosphorylation and CDK2 transcriptional activation (c-Jun binding to CDK2 promoter confirmed by ChIP-qPCR), promoting tumor cell proliferation, migration, and invasion.","method":"Co-immunoprecipitation, immunofluorescence co-localization, lentiviral CCL15/CCR1 knockdown, recombinant CCL15 treatment, PCR array, transcription factor prediction, PPI database analysis, ChIP-qPCR for c-Jun at CDK2 promoter","journal":"Journal of Cancer","confidence":"Medium","confidence_rationale":"Tier 2 — direct CCL15-CCR1 interaction confirmed by co-IP, ChIP validates c-Jun/CDK2 axis, but single lab","pmids":["40740234"],"is_preprint":false}],"current_model":"CCL15 is a CC chemokine that circulates in plasma as a weakly active full-length form (92 aa) and is proteolytically activated by neutrophil cathepsin G, elastase, and MMPs through N-terminal truncation to generate potent CCR1 agonists (Δ23–28 isoforms) that drive monocyte and myeloid cell chemotaxis; it signals through CCR1 (and weakly CCR3) via Gi/Go-PLC-PKCδ and Gα14/16-JAK2/STAT3-NF-κB pathways to induce cell migration, ICAM-1 upregulation, MMP-9 release, and cytokine production, while in tumors, SMAD4 loss or oncogenic Kras de-represses CCL15 transcription, enabling CCL15-CCR1 axis-driven recruitment of immunosuppressive myeloid cells (MDSCs, monocytes, neutrophils) and direct autocrine/paracrine promotion of cancer invasion, metastasis, and stromal reprogramming."},"narrative":{"teleology":[{"year":1997,"claim":"Identification of CCL15 as a novel CC chemokine acting through CCR1 and CCR3 established its fundamental role as a leukocyte chemoattractant for monocytes, neutrophils, and lymphocytes, and revealed an unexpected capacity to suppress hematopoietic progenitor colony formation.","evidence":"Recombinant protein calcium flux, Boyden chamber chemotaxis, and colony assays using CCR1/CCR3-transfected cells across multiple independent groups","pmids":["9548457","9346309","9624581"],"confidence":"High","gaps":["No in vivo chemotactic function demonstrated","Relative contribution of CCR1 vs CCR3 not resolved","Mechanism of colony suppression unknown"]},{"year":1998,"claim":"Gene structure analysis revealed a unique four-exon organization encoding a protein with an extra disulfide bond, and identification of alternatively spliced forms showed that N-terminal length governs receptor activation potency, raising the question of how N-terminal processing is regulated in vivo.","evidence":"cDNA cloning, Northern blot, NMR structure determination, and calcium flux/chemotaxis with N-terminal variants","pmids":["9600961","9558365","10320325"],"confidence":"High","gaps":["Physiological protease(s) responsible for N-terminal truncation not yet identified","Functional significance of third disulfide bond unclear"]},{"year":1999,"claim":"CCR1 knockout mice demonstrated that CCR1 is the essential mediating receptor for CCL15-induced neutrophil responses, and cross-desensitization studies revealed ligand-specific functional outcomes through the same receptor, raising the concept of biased agonism at CCR1.","evidence":"CCR1−/− mouse neutrophils, Scatchard binding, cross-desensitization, and calcium flux assays","pmids":["10202040"],"confidence":"High","gaps":["Structural basis for ligand-specific signaling through CCR1 unknown","In vivo relevance of differential CCR1 agonism not tested"]},{"year":2002,"claim":"Pharmacological dissection of CCL15-CCR1 signaling revealed a Gi/Go–PLC–PKCδ cascade required for chemotaxis and an NF-κB-dependent transcriptional program necessary for migration, showing that CCL15-driven motility requires de novo protein synthesis.","evidence":"Pertussis toxin, PLC/PKCδ/NF-κB inhibitors, cycloheximide, and actinomycin D treatments in CCR1-expressing HOS cells","pmids":["11943214"],"confidence":"Medium","gaps":["Identity of newly synthesized proteins required for migration unknown","Pathway validated in single overexpression cell line only"]},{"year":2004,"claim":"Systematic chemical synthesis of N-terminal truncation mutants mapped the activation switch to removal of ~24 residues, converting weakly active full-length CCL15 into a potent CCR1 agonist, and showed the C-terminal α-helix is essential for receptor binding while the third disulfide bond is dispensable.","evidence":"Fmoc-synthesized sequential truncations and point mutants, radioligand binding, calcium flux, chemotaxis with CCR1/CCR3 transfectants","pmids":["14984572"],"confidence":"High","gaps":["Exact receptor-contact residues not mapped","No co-crystal structure of CCL15–CCR1 complex"]},{"year":2005,"claim":"The identity of the activating proteases was resolved: neutrophil cathepsin G generates Δ23 and Δ26 isoforms and elastase generates Δ21, each with markedly increased chemotactic potency, establishing neutrophil-mediated proteolytic activation as the physiological mechanism for converting circulating CCL15 into an active monocyte recruiter.","evidence":"Hemofiltration, purified protease incubation, MALDI-TOF MS cleavage site mapping, calcium flux, chemotaxis, and adhesion assays; confirmed with synovial fluid from RA patients","pmids":["16034099","15905581"],"confidence":"High","gaps":["Relative contribution of each protease in vivo not quantified","Whether proteolytic activation occurs in healthy vs. diseased tissue is unclear"]},{"year":2009,"claim":"CCL15 was found to possess direct antibacterial activity against a subset of intestinal microflora, revealing a dual innate immune function beyond leukocyte chemotaxis, with upregulation in inflammatory bowel disease indicating a role in mucosal defense.","evidence":"Recombinant CCL15 bacterial binding and killing assays, qPCR and IHC in IBD tissue","pmids":["19812544"],"confidence":"Medium","gaps":["Structural basis for antimicrobial activity not determined","Spectrum of susceptible bacteria not fully characterized","Relative importance vs. other antimicrobial peptides unknown"]},{"year":2010,"claim":"The CCL15–CCR1 axis was shown to be a critical driver of colorectal cancer liver metastasis: tumor-secreted CCL15 recruits CCR1⁺ immature myeloid cells that produce MMP2/MMP9 to remodel the metastatic niche, as demonstrated by epistatic knockout of CCR1, MMP2, and MMP9 and by pharmacological CCR1 blockade.","evidence":"Mouse liver dissemination model with CCR1/MMP2/MMP9 knockout hosts, CCR1 antagonist BL5923, survival analysis","pmids":["20616008"],"confidence":"High","gaps":["Human validation of CCR1 antagonist efficacy in metastasis not performed","Whether CCL15 is the sole CCR1 ligand driving recruitment in this context is unresolved"]},{"year":2012,"claim":"A second signaling arm was uncovered: CCL15–CCR1 activates STAT3 Tyr705 phosphorylation via pertussis toxin-insensitive Gα14/16 proteins, leading to STAT3 nuclear translocation, CXCL8 induction, and autocrine IL-6 amplification, distinguishing CCL15 signaling from classical Gi-only chemokine pathways.","evidence":"Subcellular fractionation, confocal microscopy, anti-IL-6 neutralization, STAT3 inhibition in THP-1 macrophages and CCR1/Gα14/16-overexpressing HEK293 cells","pmids":["23125416"],"confidence":"High","gaps":["Gα14/16 coupling confirmed in overexpression system; stoichiometry in primary cells unknown","Whether Gα14/16 pathway operates in all CCR1-expressing cell types is untested"]},{"year":2013,"claim":"SMAD4 was identified as a direct transcriptional repressor of CCL15: ChIP confirmed SMAD4 binding to the CCL15 promoter enhanced by TGF-β, and SMAD4 loss in CRC de-represses CCL15, recruiting CCR1⁺ MDSCs to the invasion front and promoting liver metastasis — linking a tumor suppressor pathway directly to chemokine-mediated immune evasion.","evidence":"ChIP for SMAD4 at CCL15 promoter, TGF-β treatment, SMAD4 knockdown/overexpression, nude mouse liver metastasis model, IHC of 141 clinical specimens","pmids":["23891973","26341919"],"confidence":"High","gaps":["Whether SMAD4 loss affects CCL15 processing in addition to transcription is unknown","Other SMAD4-regulated chemokines may contribute to myeloid recruitment"]},{"year":2013,"claim":"CCL15 was shown to upregulate endothelial ICAM-1 via a JAK2–STAT3 pathway with STAT3 directly binding the ICAM-1 promoter, promoting monocyte adhesion under shear stress, thereby connecting CCL15 not only to cell migration but also to firm adhesion steps in leukocyte transendothelial migration.","evidence":"ChIP for STAT3 at ICAM-1 promoter, JAK/PI3K/AKT inhibitors, monocyte adhesion under static and flow conditions","pmids":["23690481"],"confidence":"High","gaps":["In vivo relevance of CCL15-induced ICAM-1 upregulation not confirmed","Contribution relative to other ICAM-1 inducers (TNF-α, IL-1β) unclear"]},{"year":2018,"claim":"In hepatocellular carcinoma, CCL15 recruits CCR1⁺CD14⁺ monocytes that express immune checkpoint molecules (PD-L1, B7-H3, TIM-3) and tolerogenic enzymes (IDO, arginase), establishing the CCL15–CCR1 axis as a driver of an immunosuppressive tumor microenvironment beyond simple myeloid cell recruitment.","evidence":"Chemokine profiling, flow cytometry phenotyping, transcriptome sequencing of tumor-infiltrating monocytes, orthotopic mouse models","pmids":["30070719"],"confidence":"High","gaps":["Whether checkpoint blockade synergizes with CCR1 antagonism is untested","Causal relationship between CCL15-recruited monocytes and specific checkpoint molecule induction not fully dissected"]},{"year":2022,"claim":"Oncogenic KRAS was identified as an upstream activator of CCL15 expression in pancreatic cancer, with CCL15 promoting cell migration through a ROS-dependent mechanism involving p22phox, extending the list of oncogenic pathways that co-opt CCL15.","evidence":"KRAS knockdown abolishes CCL15 protein, NAC treatment and p22phox knockdown attenuate CCL15-driven migration","pmids":["35565279"],"confidence":"Medium","gaps":["Whether KRAS regulation of CCL15 is transcriptional or post-transcriptional is not resolved","ROS–migration link lacks identification of downstream effectors"]},{"year":2024,"claim":"A CCL15–CCR1–STAT3–FTO positive feedback loop between HCC cells and cancer-associated fibroblasts was discovered: CCL15 from tumor cells activates STAT3 in CAFs to induce FTO-mediated m6A demethylation of CEBPA mRNA, driving CXCL5 secretion that feeds back to upregulate CCL15 via MDM2/P53, revealing an epitranscriptomic dimension of CCL15-mediated stromal reprogramming.","evidence":"scRNA-seq, m6A sequencing, ChIP, organoid and PDX models, neutralizing anti-CCL15 antibody","pmids":["39734010"],"confidence":"High","gaps":["Whether anti-CCL15 antibody efficacy translates to immunocompetent models is unknown","FTO-dependent m6A changes on other transcripts in CAFs not characterized"]},{"year":null,"claim":"Key unresolved questions include the structural basis of CCL15–CCR1 interaction (no co-crystal or cryo-EM structure exists), whether CCR1 antagonists or anti-CCL15 antibodies have therapeutic efficacy in immunocompetent cancer models, and the relative physiological importance of CCL15's antimicrobial function versus its chemotactic activity in mucosal immunity.","evidence":"","pmids":[],"confidence":"Low","gaps":["No CCL15–CCR1 structural complex resolved","No clinical trial data targeting the CCL15–CCR1 axis","In vivo contribution of CCL15 antimicrobial activity not genetically tested in humans"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,2,3,7,11,12]},{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[25,31]},{"term_id":"GO:0090729","term_label":"toxin activity","supporting_discovery_ids":[18]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,5,11,15,19,23]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,3,11,19,26,32]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,22,25,38]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[19,23,26,29,30,36]}],"complexes":[],"partners":["CCR1","CCR3","SMAD4","STAT3","LZIP","FTO","CDK2"],"other_free_text":[]},"mechanistic_narrative":"CCL15 is a CC chemokine that functions as a proteolytically activated chemoattractant, recruiting monocytes, neutrophils, eosinophils, and immunosuppressive myeloid cells through CCR1 (and weakly CCR3), while also exerting direct antimicrobial activity at mucosal surfaces. Full-length CCL15 circulates as a weakly active 92-amino acid precursor that is converted by neutrophil cathepsin G, elastase, and MMPs into N-terminally truncated isoforms (Δ23–28) with up to 1000-fold greater potency for CCR1-mediated calcium flux, chemotaxis, and integrin-dependent adhesion [PMID:16034099, PMID:15905581, PMID:22147696]. Downstream of CCR1, CCL15 engages Gi/Go–PLC–PKCδ signaling for cell migration and a pertussis toxin-insensitive Gα14/16–JAK2–STAT3 pathway that drives NF-κB activation, ICAM-1 upregulation, CXCL8 and IL-6 induction, and MMP-9 release [PMID:11943214, PMID:23125416, PMID:23690481]. In colorectal, hepatocellular, and pancreatic cancers, loss of SMAD4 or oncogenic KRAS de-represses CCL15 transcription, enabling the CCL15–CCR1 axis to recruit CCR1⁺ myeloid-derived suppressor cells, tumor-associated neutrophils, and monocytes that remodel the tumor stroma and promote metastasis [PMID:23891973, PMID:26341919, PMID:30070719, PMID:35565279]."},"prefetch_data":{"uniprot":{"accession":"Q16663","full_name":"C-C motif chemokine 15","aliases":["Chemokine CC-2","HCC-2","Leukotactin-1","LKN-1","MIP-1 delta","Macrophage inflammatory protein 5","MIP-5","Mrp-2b","NCC-3","Small-inducible cytokine A15"],"length_aa":113,"mass_kda":12.2,"function":"Chemotactic factor that attracts T-cells and monocytes, but not neutrophils, eosinophils, or B-cells. Acts mainly via CC chemokine receptor CCR1. Also binds to CCR3. CCL15(22-92), CCL15(25-92) and CCL15(29-92) are more potent chemoattractants than the CCL15","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q16663/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CCL15","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":383,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"COPA","stoichiometry":0.2},{"gene":"COPB2","stoichiometry":0.2},{"gene":"COPE","stoichiometry":0.2},{"gene":"COPG1","stoichiometry":0.2},{"gene":"SYAP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/CCL15","total_profiled":1310},"omim":[{"mim_id":"601393","title":"CHEMOKINE, CC MOTIF, LIGAND 15; CCL15","url":"https://www.omim.org/entry/601393"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"intestine","ntpm":77.7},{"tissue":"liver","ntpm":40.2}],"url":"https://www.proteinatlas.org/search/CCL15"},"hgnc":{"alias_symbol":["HCC-2","NCC-3","SCYL3","MIP-5","Lkn-1","MIP-1d","HMRP-2B"],"prev_symbol":["SCYA15"]},"alphafold":{"accession":"Q16663","domains":[{"cath_id":"2.40.50.40","chopping":"61-113","consensus_level":"medium","plddt":95.9164,"start":61,"end":113}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16663","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16663-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16663-F1-predicted_aligned_error_v6.png","plddt_mean":78.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CCL15","jax_strain_url":"https://www.jax.org/strain/search?query=CCL15"},"sequence":{"accession":"Q16663","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16663.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16663/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16663"}},"corpus_meta":[{"pmid":"30070719","id":"PMC_30070719","title":"CCL15 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MIP-1δ and MIP-3α Are Involved in the Migration of Multipotent Mesenchymal Stromal Cells Induced by Hepatoma Cells.","date":"2015","source":"Stem cells and development","url":"https://pubmed.ncbi.nlm.nih.gov/25579056","citation_count":29,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"9624581","id":"PMC_9624581","title":"Molecular cloning and functional characterization of human MIP-1 delta, a new C-C chemokine related to mouse CCF-18 and C10.","date":"1998","source":"Journal of clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/9624581","citation_count":29,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"16341674","id":"PMC_16341674","title":"Transcriptome analysis of human gastric cancer.","date":"2005","source":"Mammalian genome : official journal of the International Mammalian Genome 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receptor CCR1, as demonstrated by desensitization studies with purified recombinant protein.\",\n      \"method\": \"Recombinant protein functional assays (chemotaxis, enzyme release, desensitization studies) on neutrophils, eosinophils, monocytes, and lymphocytes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted recombinant protein with multiple cell-type assays and receptor desensitization validation\",\n      \"pmids\": [\"9600961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CCL15 contains six conserved cysteines (instead of four), with the two additional cysteines forming a third disulfide bond that anchors the C-terminal domain to the core of the molecule.\",\n      \"method\": \"Sequence analysis and structural characterization of recombinant protein\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct biochemical structural characterization of recombinant protein\",\n      \"pmids\": [\"9600961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The CCL15 (HCC-2) gene has a four-exon, three-intron structure (unlike most CC chemokines which have three exons), resides on chromosome 17q11.2 in a tandem arrangement with MPIF-1, HCC-1, LEC, and RANTES, and shares conserved intron/flanking sequences with MPIF-1 consistent with recent gene duplication.\",\n      \"method\": \"Genomic sequencing (181 kb region, random shotgun method)\",\n      \"journal\": \"Journal of interferon & cytokine research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct genomic sequencing establishing gene structure\",\n      \"pmids\": [\"10213461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CCL15-induced chemotaxis through CCR1 is transduced via Gi/Go protein, phospholipase C (PLC), and PKCδ, and requires NF-κB activation and new protein synthesis.\",\n      \"method\": \"Pharmacological inhibitor assays (pertussis toxin, PLC inhibitor, PKCδ inhibitor, NF-κB inhibitor, cycloheximide, actinomycin D) in CCR1-expressing HOS cells; PLC and PKCδ activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal inhibitors with functional readouts in a single study\",\n      \"pmids\": [\"11943214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"N-terminal truncation of CCL15 by 24 amino acids (Δ24-CCL15) converts the weakly active full-length protein into a potent CCR1 agonist; the C-terminal α-helix is essential for tertiary structure and CCR1 binding/activation; the third disulfide bond is dispensable for CCR1 interaction; CCR1 is the major receptor for CCL15 in vivo.\",\n      \"method\": \"Fmoc chemical synthesis of truncation and point-mutation derivatives; calcium flux assays; Transwell migration assays; receptor binding assays in CCR1/CCR3 transfectants\",\n      \"journal\": \"The journal of peptide research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with reconstituted receptor assays defining structure-activity relationships\",\n      \"pmids\": [\"14984572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCL15(25-92) (N-terminally truncated form) stimulates chemotactic endothelial cell migration and vessel sprouting (angiogenesis) via CCR1 and CCR3 receptors; it is at least 100-fold more potent than full-length CCL15(1-92) in this activity.\",\n      \"method\": \"Transwell endothelial migration assays; aortic ring sprouting assay; chick chorioallantoic membrane assay; antibody neutralization of CCR1/CCR3; pertussis toxin treatment\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro and in vivo angiogenesis assays with receptor-blocking validation\",\n      \"pmids\": [\"15251437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCL15 gene transcription in monocytoid cells is regulated by two NF-κB binding sites (at −191/−182 bp and −60/−51 bp) in the promoter region, identified by deletion analysis, EMSA, and mutation studies.\",\n      \"method\": \"Luciferase reporter assays with promoter deletion and mutation constructs in U937 cells; EMSA; proteasome inhibitor experiments\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple complementary methods (reporter, EMSA, mutagenesis) in a single study\",\n      \"pmids\": [\"15179048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"CCL15 gene transcription in PMA-stimulated monocytoid cells is regulated by both NF-κB and an AP-1 element (at −76/−65) through MEK and JNK MAPK pathways.\",\n      \"method\": \"Luciferase reporter assays; dominant-negative MKK4/JNK1 expression; MAPK pathway inhibitors; AP-1 factor binding confirmation\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assays with dominant-negative constructs and pathway inhibitors\",\n      \"pmids\": [\"16364464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Neutrophil cathepsin G is the principal protease that cleaves CCL15 at the N-terminus to produce Δ23- and Δ26-CCL15 isoforms; neutrophil elastase produces a Δ21 isoform. These truncated forms have significantly increased potency to induce calcium fluxes, chemotaxis of monocytes, and adhesion of mononuclear cells to fibronectin compared to full-length CCL15.\",\n      \"method\": \"Chromatographic separation and identification of CCL15 isoforms; in vitro proteolysis assays with purified cathepsin G and elastase; calcium flux assays; chemotaxis assays; fibronectin adhesion assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical identification of protease, characterization of cleavage products, and multiple functional assays\",\n      \"pmids\": [\"16034099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In chronic renal failure, CCL15 is proteolytically processed to a truncated form (CCL15(12-92)) that shows stronger monocyte calcium flux, chemotaxis, and fibronectin adhesion than full-length CCL15(1-92); peripheral blood mononuclear cells from CRF patients also show increased sensitivity to CCL15.\",\n      \"method\": \"Mass spectrometry identification of CCL15 isoforms in plasma; calcium flux assays; chemotaxis assays; adhesion assays\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS identification plus multiple functional assays in patient samples\",\n      \"pmids\": [\"16737685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CCL15 (Lkn-1) induces LZIP expression in monocytes through NF-κB in a time- and dose-dependent manner; LZIP expression downstream of CCL15-CCR1-NF-κB signaling specifically regulates monocyte cell migration.\",\n      \"method\": \"Promoter deletion analysis; EMSA; mutation analysis; NF-κB inhibitor studies; chemotaxis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods (promoter analysis, EMSA, inhibitors, functional assays) in a single study\",\n      \"pmids\": [\"17296613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CCL15 (Lkn-1) enhances MMP-9 release from THP-1 macrophages, human PBMC-derived macrophages, and macrophage-derived foam cells in a dose-dependent manner.\",\n      \"method\": \"Gelatin zymography of conditioned media from CCL15-treated macrophages and foam cells\",\n      \"journal\": \"Nutrition research and practice\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single method (zymography) but replicated in multiple cell types\",\n      \"pmids\": [\"20126378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCL15 induces migration and differentiation of human eosinophilic leukemia EoL-1 cells through CCR1, with chemotaxis mediated via Gi/Go protein, PLC, and PKCδ; CCL15 also enhanced butyric acid-induced eosinophil differentiation via PKCδ.\",\n      \"method\": \"Transwell chemotaxis assays with pharmacological inhibitors (PTX, U73122, rottlerin); PKCδ activity assays; morphological differentiation and EPO/MBP expression analysis\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors and functional readouts in a single study\",\n      \"pmids\": [\"19669929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Matrix metalloproteinases in synovial fluid cleave full-length CCL15(1-92) within its 31-amino acid extended N-terminus to generate CCL15(25-92) and CCL15(28-92), which are stronger agonists than the full-length protein in calcium flux assays and CCR1 transfectant and THP-1 monocyte migration assays. Multiple MMPs (identified by MALDI-TOF-MS of cleavage products) and serine proteases perform this activation.\",\n      \"method\": \"MALDI-TOF-MS cleavage site sequencing; synovial fluid incubation assays; calcium flux assays; Transwell migration assays with CCR1 transfectants and THP-1 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical assay with MS characterization of products plus multiple functional validations\",\n      \"pmids\": [\"22147696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SMAD4 directly binds the CCL15 gene promoter to negatively regulate its expression; TGF-β increases SMAD4 binding to the CCL15 promoter and transcriptional repression; loss of SMAD4 in colorectal cancer cells upregulates CCL15 secretion, which recruits CCR1+ myeloid cells to promote liver metastasis.\",\n      \"method\": \"ChIP assay (SMAD4 binding to CCL15 promoter); SMAD4 knockdown/overexpression; xenograft mouse model; immunohistochemistry\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP demonstrating direct promoter binding plus in vivo xenograft validation and clinical correlation\",\n      \"pmids\": [\"23891973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCL15 promotes HCC cell migration and invasion in an autocrine manner, as demonstrated by siRNA knockdown reducing invasion and scratch migration, and MMP-9 expression.\",\n      \"method\": \"siRNA knockdown of CCL15 in HCCML3 cells; cell invasion assay; scratch migration assay; Western blot for MMP-9\",\n      \"journal\": \"Zhonghua gan zang bing za zhi\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single-lab KD study with limited mechanistic depth\",\n      \"pmids\": [\"22971284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCL15 promotes HCC cell migration and invasion; CCR1 mediates CCL15-induced chemotaxis and invasion, and CCR1 knockdown limits MMP-2 and MMP-9 activity and expression.\",\n      \"method\": \"Transwell migration/invasion assays; CCR1 shRNA knockdown; gelatin zymography for MMP-2/MMP-9\",\n      \"journal\": \"British journal of cancer / Tumour biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — receptor knockdown with multiple functional readouts\",\n      \"pmids\": [\"23321514\", \"26501423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Loss of SMAD4 in colorectal cancer cells promotes CCL15 secretion to recruit CCR1+ myeloid-derived suppressor cells (MDSCs, predominantly granulocytic CD15+ phenotype) at the tumor invasion front, facilitating tumor growth in an orthotopic xenograft model.\",\n      \"method\": \"CCL15 knockdown in SMAD4-deficient CRC cell lines; orthotopic xenograft models; immunohistochemistry; double immunofluorescence for MDSC phenotyping\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo xenograft plus clinical specimen validation with cell-type characterization\",\n      \"pmids\": [\"26341919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCL15-CCR1 axis mediates recruitment of CCR1+ tumor-associated neutrophils (and some granulocytic MDSCs) in colorectal cancer lung metastases; SMAD4 loss drives CCL15 expression promoting lung metastasis.\",\n      \"method\": \"Mouse lung metastasis model with SMAD4-deficient CRC cells; immunohistochemistry; immunofluorescent cell-type characterization\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model with detailed immunophenotyping and clinical specimen correlation\",\n      \"pmids\": [\"27492974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCL15 secreted by HCC cells mediates chemotaxis of mesenchymal stem cells (MSCs) toward HCC via CCR1 receptors on MSCs, demonstrated in vitro and in orthotopic HCC animal models.\",\n      \"method\": \"Cytokine array; Transwell migration assays; CCR1 blocking; orthotopic xenograft model with intravenous hMSC delivery; flow cytometry and histology\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo evidence with receptor blocking validation\",\n      \"pmids\": [\"26763650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCL15 induces ICAM-1 expression in endothelial cells via CCR1, through JAK2/STAT3 phosphorylation and STAT3 binding to the ICAM-1 promoter; PI3K and AKT are also involved. This signaling increases monocyte adhesion to endothelial cells after hypoxia/reoxygenation.\",\n      \"method\": \"CCL15/CCR1 knockdown; kinase inhibitors (JAK, PI3K, AKT); reporter assay (IFN-γ activation site); ChIP assay (STAT3 binding to ICAM-1 promoter); monocyte adhesion assays under static and shear-stress conditions\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP assay plus reporter assay plus multiple inhibitors and functional readouts\",\n      \"pmids\": [\"23690481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCL15 recruits CCR1+ CD14+ monocytes to the HCC invasive margin; these tumor-educated monocytes promote tumor invasion via STAT1/3, ERK1/2, and AKT signaling in HCC cells and express immune checkpoint molecules (PD-L1, B7-H3, TIM-3). CCL15 also promotes HCC invasion in an autocrine manner.\",\n      \"method\": \"Chemokine expression profiling; CCR1+ cell immunophenotyping; orthotopic animal models; transcriptome sequencing of tumor-infiltrating monocytes\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model plus transcriptomics plus clinical validation; replicated in multiple analyses\",\n      \"pmids\": [\"30070719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Oncogenic Kras drives CCL15 expression in pancreatic cancer cells; CCL15 promotes PDAC cell migration and invasion through reactive oxygen species (ROS) via CCR1 and CCR3 receptors; Kras knockdown abolishes CCL15 protein expression.\",\n      \"method\": \"CCL15 knockdown; CCL15 neutralization; recombinant CCL15 treatment; ROS scavenger (NAC) and p22phox knockdown; Kras knockdown; migration and invasion assays\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic and pharmacological perturbations with consistent functional readouts\",\n      \"pmids\": [\"35565279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CTHRC1 upregulates CCL15 expression in colorectal cancer cells via TGF-β/Smad pathway activation and Smad phosphorylation, leading to increased macrophage recruitment; cytokine microarray and pathway analysis established the mechanistic link.\",\n      \"method\": \"Cytokine microarray; CTHRC1 knockdown/overexpression; TGF-β/Smad pathway inhibition; macrophage chemotaxis assays; in vivo xenograft\",\n      \"journal\": \"Journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods linking CTHRC1 to CCL15 via Smad signaling with functional validation\",\n      \"pmids\": [\"37987774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CCL15 secreted by HCC cells activates CCR1 on cancer-associated fibroblasts (CAFs), inducing STAT3-mediated FTO expression; FTO demethylates CEBPA mRNA (m6A), increasing CXCL5 secretion from CAFs, which activates CXCR2 on HCC cells to promote proliferation, forming a positive feedback loop. CXCL5 upregulates CCL15 via MDM2/P53 modulation.\",\n      \"method\": \"Co-culture assays; organoid models; allograft models; m6A sequencing; RNA sequencing; neutralizing antibody treatment; patient-derived xenograft models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multi-omics (m6A-seq, RNA-seq) plus multiple in vivo models and mechanistic pathway validation\",\n      \"pmids\": [\"39734010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CCL15 produced by liver cancer cells drives polarization of M0 macrophages toward an SPP1+ macrophage phenotype, establishing a positive feedback loop between macrophage polarization and tumor stemness.\",\n      \"method\": \"Single-cell RNA sequencing; co-culture assays; integrin αvβ5/AMPK/YAP1/SOX4 pathway analysis\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — scRNA-seq plus co-culture mechanistic assays\",\n      \"pmids\": [\"39216547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Endothelial cell-derived CCL15 mediates transmigration of fibrocytes via the CCL15-CCR1 axis; overexpression of CCL15 in endothelial cells or CCR1 in fibrocytes promotes transmigration, while silencing either attenuates it.\",\n      \"method\": \"Transwell co-culture system; gene chip chemokine profiling; CCL15 overexpression/knockdown in endothelial cells; CCR1 overexpression/knockdown in fibrocytes\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — bidirectional knockdown/overexpression with functional transmigration readout\",\n      \"pmids\": [\"33174007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Activated CCL15(27-92) enhances CXCL12-induced migration of hematopoietic progenitor cells (Lin-/Sca1+), strengthens shear stress-dependent adhesion to VCAM-1, and improves competitive repopulation in murine transplantation assays.\",\n      \"method\": \"Transwell migration assays; shear stress adhesion assays; CFU-A colony assays; competitive repopulation assays in mice\",\n      \"journal\": \"Transfusion medicine and hemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays including in vivo repopulation\",\n      \"pmids\": [\"25960713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CCL15 and CCR1 form a direct autocrine signaling axis in ESCC tumor cells; CCL15-CCR1 signaling activates the AKT/ERK1/2 pathway leading to c-Jun phosphorylation and CDK2 transcriptional activation, promoting ESCC cell proliferation, migration, and invasion.\",\n      \"method\": \"Co-immunoprecipitation and immunofluorescence co-localization (CCL15-CCR1 interaction); lentiviral CCL15/CCR1 knockdown; recombinant CCL15 treatment; PCR array; transcription factor prediction; PPI analysis; ChIP-qPCR (c-Jun binding to CDK2 promoter)\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP confirming direct interaction plus ChIP-qPCR and multiple genetic perturbations\",\n      \"pmids\": [\"40740234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HBV X protein (HBx) upregulates CCL15 expression in HCC; HBx and CCL15 are significantly co-expressed in HBV-positive HCC samples, and HBx overexpression in vitro induces CCL15 expression.\",\n      \"method\": \"Immunohistochemistry; RT-PCR; Western blot; in vitro HBx overexpression\",\n      \"journal\": \"Anti-cancer agents in medicinal chemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — correlational with limited mechanistic depth; single-lab overexpression without pathway identification\",\n      \"pmids\": [\"33653254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"P1-HNF4A directly regulates CCL15 as a downstream transcriptional target in gastric cancer, identified through RNA-seq of P1-HNF4A-overexpressing cells.\",\n      \"method\": \"RNA-seq transcriptome profiling; overexpression assays; gene regulation network analysis\",\n      \"journal\": \"Cancer biology & medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — RNA-seq identification without direct ChIP or promoter validation for CCL15\",\n      \"pmids\": [\"33710810\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCL15 is a secreted CC chemokine that exists as a weakly active full-length form (92 aa) and is proteolytically activated by neutrophil cathepsin G, elastase, and MMPs through N-terminal truncation to potent forms (Δ21–Δ26) that signal via CCR1 (primary receptor) and CCR3 through Gi/Go–PLC–PKCδ–NF-κB cascades to drive monocyte, eosinophil, endothelial cell, and hematopoietic progenitor chemotaxis; its gene is transcriptionally repressed by SMAD4 binding to its promoter (released by TGF-β loss/SMAD4 deletion in colorectal and other cancers) and induced by NF-κB, AP-1/JNK, HBx, and HNF4A; in tumors, CCL15-CCR1 autocrine signaling promotes invasion via MMP-9/MMP-2 and ROS, while paracrine CCL15 recruits immunosuppressive CCR1+ monocytes, MDSCs, and neutrophils to facilitate metastasis, and activates CAF-STAT3-FTO-m6A-CXCL5 signaling to drive HCC proliferation.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries from KEEP papers.\n\n**Classification notes:**\n- Papers [13] (SCYL3-NTRK1 fusion), [22] (SCYL1/SCYL3 pseudokinases), [35] (SCYL3/ROCK2) → EXCLUDE: alias collision (SCYL3 not CCL15)\n- Paper [18] (Hcc-2 thioredoxin/TXNDC5) → EXCLUDE: alias collision (different protein, ER thioredoxin)\n- Paper [26] (FATE/BJ-HCC-2 cancer/testis antigen) → EXCLUDE: alias collision (FATE1, different protein)\n- Paper [31] (BJ-HCC-2 protein purification) → EXCLUDE: alias collision (FATE1)\n- Paper [46] (FATE1/BJ-HCC-2 mitochondrial fission) → EXCLUDE: alias collision (FATE1)\n- Papers from additional list [1,3,4,5,9,10,12,15,17,19,22,23] → largely genomic/expression/GWAS, no mechanistic CCL15 content; exclude as not mechanistic\n- All remaining papers about CCL15 (chemokine) → KEEP where mechanistic\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"CCL15 (Leukotactin-1/Lkn-1) was identified as a novel CC chemokine that acts as a potent agonist at CCR1 and CCR3, inducing calcium flux and chemotaxis in neutrophils, monocytes, and lymphocytes, and suppressing colony formation by hematopoietic progenitor cells.\",\n      \"method\": \"Recombinant protein production, calcium flux assays, Boyden chamber chemotaxis assays, CCR1/CCR3-transfected cell lines, colony formation assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal functional assays, receptor-transfected cell lines, replicated across independent groups\",\n      \"pmids\": [\"9548457\", \"9346309\", \"9624581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CCL15 (HCC-2/CKβ8) gene has a unique four-exon/three-intron structure and encodes a protein with six conserved cysteines (including two extra forming a third disulfide bond anchoring the C-terminal domain to the core), and the protein activates cells via CCR1 and CCR3 in a manner dependent on N-terminal length.\",\n      \"method\": \"Gene cloning/sequencing, Northern blot, recombinant protein production, calcium flux assays, chemotaxis assays on monocytes and eosinophils\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structural characterization plus functional validation with multiple cell types and receptors\",\n      \"pmids\": [\"9600961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Two alternatively spliced forms of CCL15 (CKβ8 and CKβ8-1, differing by 17 amino acids at the N-terminus) are both potent agonists at CCR1, chemoattracting neutrophils, monocytes, and lymphocytes, and suppressing hematopoietic progenitor colony formation, demonstrating that alternative splicing produces two active chemokines from a single gene.\",\n      \"method\": \"cDNA cloning, recombinant protein expression, receptor-binding assays, calcium flux, chemotaxis assays, colony formation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal assays, receptor specificity confirmed\",\n      \"pmids\": [\"9558365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CCL15 (Lkn-1) acts via CCR1 on human neutrophils to induce high-level calcium flux and chemotaxis, while MIP-1α acting on the same receptor produces negligible responses; CCR1-/- mouse neutrophils fail to respond to either ligand, establishing CCR1 as the mediating receptor with ligand-specific functional outcomes.\",\n      \"method\": \"CCR1 knockout mice, calcium flux assays, Scatchard binding analysis, cross-desensitization studies, chemotaxis assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic knockout confirmation plus binding analysis and cross-desensitization; strong evidence for CCR1-mediated but ligand-specific signaling\",\n      \"pmids\": [\"10202040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The solution structure of CCL15 (HCC-2, truncated 66-aa form) was determined by NMR, revealing a monomeric chemokine fold with a triple-stranded antiparallel β-sheet covered by an α-helix; unlike most chemokines, CCL15 does not dimerize across a concentration range of 0.1 μM to 2 mM, and the third disulfide bond does not influence the relative orientation of helix and β-sheet.\",\n      \"method\": \"1H NMR spectroscopy, restrained molecular dynamics calculations (871 experimental restraints), mutagenesis of disulfide bond\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with mutagenesis validation\",\n      \"pmids\": [\"10320325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CCL15 circulates in human blood plasma and is encoded by mono- and bicistronic transcripts from a tandem gene arrangement with CCL14a on chromosome 17q11.2; biological activity depends on N-terminal length, with shorter isoforms being more potent CCR1 and CCR3 agonists.\",\n      \"method\": \"Hemofiltration-based isolation, chromatographic characterization, Northern blot analysis, calcium flux assays\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — biochemical characterization with functional validation, single group\",\n      \"pmids\": [\"11527984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CCL15 (Lkn-1)-induced chemotaxis through CCR1 is transduced via Gi/Go protein, phospholipase C, and PKCδ; NF-κB is also activated downstream and required for chemotaxis, as newly synthesized proteins are needed for the migratory response.\",\n      \"method\": \"Pharmacological inhibitors (pertussis toxin, PLC inhibitor, PKCδ inhibitor, NF-κB inhibitor, cycloheximide, actinomycin D), CCR1-expressing HOS cells, chemotaxis assays, PLC and PKCδ activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological pathway dissections in receptor-expressing cell line\",\n      \"pmids\": [\"11943214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"N-terminal truncation of CCL15 by 24 amino acid residues (Δ24-CCL15) converts the weakly active full-length form into a potent CCR1 agonist and weak CCR3 agonist; the C-terminal α-helix is essential for maintaining tertiary structure and CCR1 binding activity, while the third disulfide bond and position Y70 do not affect CCR1 interaction.\",\n      \"method\": \"Chemical synthesis of sequential N-terminal truncation and point mutants using Fmoc chemistry, calcium flux assays, receptor transfectant chemotaxis (CCR1/CCR3), radioligand binding\",\n      \"journal\": \"The journal of peptide research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis with reconstituted receptor assays, structure-function mapping\",\n      \"pmids\": [\"14984572\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"LZIP (a transcription factor) binds directly to CCR1 (residues 21-260 of LZIP are essential for interaction) and selectively enhances Lkn-1/CCL15-induced chemotaxis without affecting chemotaxis induced by other CCR1 ligands (MIP-1α, RANTES, HCC-4), establishing LZIP as a CCR1-interacting protein that differentially modulates CCL15-specific signaling.\",\n      \"method\": \"Yeast two-hybrid screen, mammalian two-hybrid assay, co-immunoprecipitation, domain deletion mapping, chemotaxis assays in LZIP-transfected cells\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — yeast 2-hybrid confirmed by co-IP and functional chemotaxis, single lab\",\n      \"pmids\": [\"15001559\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCL15 (Lkn-1) induces MMP-9 release from macrophages and macrophage-derived foam cells in a dose-dependent manner, suggesting a role in atherosclerotic plaque destabilization.\",\n      \"method\": \"THP-1 macrophage differentiation, oxidized LDL-induced foam cell preparation, CCL15 treatment, gelatin zymography for MMP-9\",\n      \"journal\": \"Nutrition research and practice\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single-method zymography, single lab\",\n      \"pmids\": [\"20126378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCL15 (both full-length CCL15(1-92) and truncated CCL15(25-92)) stimulates chemotactic endothelial cell migration and differentiation in vitro; CCL15(25-92) is at least 100-fold more potent. This angiogenic activity is mediated via CCR1 and CCR3, as it is blocked by pertussis toxin, anti-CCR1, or anti-CCR3 antibody. CCL15(25-92) also induces aortic ring sprouting and in vivo angiogenesis in the chick chorioallantoic membrane assay.\",\n      \"method\": \"Endothelial cell chemotaxis (Boyden chamber), tube formation assay, pertussis toxin and neutralizing antibody inhibition, aortic ring assay, CAM assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal angiogenesis assays (in vitro and in vivo), receptor blocking confirms CCR1/CCR3 dependence\",\n      \"pmids\": [\"15251437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Neutrophil cathepsin G is the principal protease that proteolytically processes full-length CCL15 to N-terminally truncated isoforms (Δ23 and Δ26); neutrophil elastase generates a Δ21 isoform. The truncated Δ23 and Δ26 isoforms display significantly increased potency for calcium flux, monocyte chemotaxis, and mononuclear cell adhesion to fibronectin compared to full-length CCL15, establishing neutrophil-mediated activation of CCL15 as a mechanism for monocyte recruitment.\",\n      \"method\": \"Hemofiltration, chromatographic separation, mass spectrometry identification of cleavage products, purified cathepsin G and elastase incubation, calcium flux assays, chemotaxis assays, fibronectin adhesion assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — protease identified by biochemical reconstitution with purified enzymes, cleavage sites sequenced by MS, functional potency confirmed by multiple assays\",\n      \"pmids\": [\"16034099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Proinflammatory proteases (including synovial fluid proteases) cleave the N-terminal domain of CCL15, converting it from a weak to a potent CCR1 agonist (up to 1000-fold increase); N-terminally truncated CCL15 was detected at relatively high levels in synovial fluid from rheumatoid arthritis patients, suggesting in vivo activation of CCL15 during inflammation.\",\n      \"method\": \"Incubation with proinflammatory proteases and physiological fluids, N-terminal sequencing, CCR1-mediated signaling and chemotaxis assays, detection in rheumatoid arthritis synovial fluid\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical reconstitution with multiple proteases, confirmed in human disease fluid, replicated functional activation\",\n      \"pmids\": [\"15905581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Transcription of the CCL15 gene in monocytoid cells is regulated by AP-1 (binding at -76/-65) and NF-κB through MEK and JNK MAPK pathways; dominant negative MKK4 or JNK1 reduced PMA-induced CCL15 transcription.\",\n      \"method\": \"Luciferase reporter assays, MAPK inhibitors, dominant negative kinase expression, EMSA (AP-1 binding confirmation)\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assays plus dominant negative genetics and EMSA binding confirmation\",\n      \"pmids\": [\"16364464\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Two NF-κB binding sites in the CCL15 promoter (at -191/-182 and -60/-51 bp from transcription start) are both essential for PMA-induced expression in monocytoid U937 cells; mutation of either site reduces induction and proteasome inhibitor blocks PMA-induced CCL15 expression.\",\n      \"method\": \"Promoter deletion/mutation analysis with luciferase reporter, EMSA, proteasome inhibitor treatment\",\n      \"journal\": \"Molecules and cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic promoter dissection with mutagenesis and EMSA confirmation\",\n      \"pmids\": [\"15179048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In chronic renal failure (CRF), plasma CCL15 concentrations are significantly elevated and include truncated isoforms (including CCL15(12-92)); CCL15(12-92) induces stronger calcium flux, chemotactic activity, and fibronectin adhesion in monocytes than full-length CCL15(1-92), and PBMCs from CRF patients show increased sensitivity to CCL15, implicating the CCL15-CCR1 axis in CRF pathophysiology.\",\n      \"method\": \"Hemofiltration, mass spectrometry (MW 10141.3 Da confirmed), calcium flux assays, chemotaxis assays, fibronectin adhesion assays in patient-derived cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical identification of isoforms by MS plus functional comparison, confirmed in patient samples\",\n      \"pmids\": [\"16737685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CCL15 (Lkn-1) induces LZIP expression via NF-κB in an immediate early response; NF-κB binds to the LZIP promoter specifically (confirmed by EMSA and mutation analysis), and LZIP expression via NF-κB is required for Lkn-1-induced monocyte chemotaxis.\",\n      \"method\": \"Time/dose-dependent LZIP expression assays, LZIP promoter deletion/mutation analysis, luciferase reporter, EMSA, NF-κB inhibitors, chemotaxis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — promoter mapping with mutagenesis, EMSA, inhibitor studies, and functional chemotaxis readout\",\n      \"pmids\": [\"17296613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCL15 (Lkn-1) induces migration of eosinophilic EoL-1 cells more potently than other CCR1 ligands; signaling is mediated through Gi/Go protein, PLC, and PKCδ activation, and CCL15 also enhances butyric acid-induced eosinophil differentiation via PKCδ after binding to CCR1.\",\n      \"method\": \"Transwell chemotaxis assays, pharmacological inhibitors (pertussis toxin, U73122/PLC inhibitor, rottlerin/PKCδ inhibitor), PKCδ activity assays, morphological differentiation assessment, EPO/MBP expression\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors used with consistent results across migration and differentiation endpoints\",\n      \"pmids\": [\"19669929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Human intestinal epithelial CCL15 (and its murine homolog CCL6) displays direct antibacterial activity, binding to a subset of the intestinal microflora; expression of CCL15 is upregulated in inflammatory bowel disease, revealing a novel antimicrobial function beyond leukocyte recruitment.\",\n      \"method\": \"Bacterial binding assays, antibacterial activity assays with recombinant CCL15, qPCR of intestinal epithelium, IHC of IBD samples\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct antimicrobial assays with recombinant protein, confirmed in multiple contexts\",\n      \"pmids\": [\"19812544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Human colorectal cancer cells secrete CCL15 (the human ortholog of mouse CCL9) to recruit CCR1+ immature myeloid cells (CD34+Gr-1-) that produce MMP2 and MMP9 to facilitate liver metastasis; genetic loss of Ccr1, Mmp2, or Mmp9 in host mice dramatically suppresses metastatic outgrowth, and a CCR1 antagonist blocks myeloid cell accumulation and prolongs survival.\",\n      \"method\": \"Mouse liver dissemination model, CCR1/MMP2/MMP9 knockout hosts, orthotopic tumor implantation, CCR1 antagonist (BL5923) treatment, survival analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in multiple knockout models plus pharmacological intervention, strong functional readout\",\n      \"pmids\": [\"20616008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MMP processing of CCL15: MMPs and serine proteases in human synovial fluid cleave CCL15 within its unique 31-amino acid extended N-terminus; the resulting products CCL15-(25-92) and CCL15-(28-92) are stronger agonists than full-length CCL15 in calcium flux assays and monocyte migration assays (Transwell), unlike other CCL chemokines that become receptor antagonists after MMP cleavage.\",\n      \"method\": \"Incubation with synovial fluid, family-wide MMP panel (14 MMPs tested against 14 CC chemokines), MALDI-TOF-MS sequencing of 149 cleavage sites, calcium flux assays, Transwell migration assays with CCR1 transfectants and THP-1 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic biochemical reconstitution with cleavage sites sequenced by MS, functional activation confirmed by multiple assays\",\n      \"pmids\": [\"22147696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CCL15 is constitutively expressed by human airway smooth muscle cells (ASMC) and is strongly upregulated by TNF-α; this upregulation is inhibited by dexamethasone, the SP-1 inhibitor mithramycin A, and the IKK-2 inhibitor AS602868. TNF-α-induced CCL15 is synergistically enhanced by IFN-γ at both transcriptional and translational levels in an NF-κB-dependent manner.\",\n      \"method\": \"Primary ASMC culture, ELISA, real-time PCR, immunofluorescence, pharmacological inhibitors (dexamethasone, mithramycin A, AS602868), cytokine treatments\",\n      \"journal\": \"Clinical and experimental allergy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacological dissection of regulatory pathway with multiple inhibitors and cytokine combinations\",\n      \"pmids\": [\"22092970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCR1-mediated CCL15 signaling in THP-1 macrophage-like cells induces STAT3 Tyr705 phosphorylation via pertussis toxin-insensitive Gα14/16 proteins; STAT3 Tyr705-phosphorylation leads to nuclear translocation and induces CXCL8 expression, while STAT3 Ser727-phosphorylation is independent and cytosolic. CCL15 also triggers IL-6 release, which mediates STAT3 Tyr705 phosphorylation in an autocrine manner.\",\n      \"method\": \"PMA-differentiated THP-1 cells and CCR1/Gα14/16-overexpressing HEK293 cells, pertussis toxin treatment, subcellular fractionation, confocal microscopy, neutralizing anti-IL-6 antibody, STAT3 inhibition, CXCL8 ELISA\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (subcellular fractionation, confocal, antibody neutralization, inhibitors) in multiple cell systems\",\n      \"pmids\": [\"23125416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Loss of SMAD4 in human colorectal cancer cells upregulates CCL15 expression; SMAD4 directly binds to the CCL15 promoter to negatively regulate transcription, and TGF-β increases SMAD4 binding to the CCL15 promoter, enhancing repression. CCL15 secreted by SMAD4-deficient CRC cells recruits CCR1+ myeloid cells (CD11b+/myeloperoxidase+/MMP9+) that promote liver metastasis.\",\n      \"method\": \"SMAD4 knockdown/overexpression in CRC lines, chromatin immunoprecipitation (ChIP) for SMAD4 at CCL15 promoter, TGF-β treatment, nude mouse liver metastasis model, IHC of 141 human metastasis specimens\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP confirms direct promoter binding, in vivo model, validated in clinical specimens\",\n      \"pmids\": [\"23891973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCL15 stimulates hepatocellular carcinoma cell migration and invasion in an autocrine manner, as demonstrated by siRNA-mediated knockdown of CCL15 reducing invasion and migration.\",\n      \"method\": \"RT-PCR, Western blot, siRNA knockdown, cell invasion assay (Matrigel), scratch/wound healing assay, MMP-9 Western blot\",\n      \"journal\": \"British journal of cancer / Chinese journal of hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — loss-of-function with phenotypic readout (invasion/migration), single lab, no pathway placement\",\n      \"pmids\": [\"23321514\", \"22971284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCL15 upregulates ICAM-1 expression in endothelial cells via the JAK2/STAT3 pathway: CCL15 stimulation activates JAK2 and STAT3 phosphorylation, STAT3 binds to the ICAM-1 promoter (confirmed by ChIP and reporter assays), and JAK, PI3K, and AKT inhibitors prevent CCL15-induced ICAM-1 expression and monocyte adhesion. This signaling is predominantly mediated via CCR1.\",\n      \"method\": \"Endothelial cell CCL15 stimulation and knockdown, ICAM-1 expression (Western blot, flow cytometry), reporter assays, ChIP for STAT3 at ICAM-1 promoter, JAK/PI3K/AKT inhibitors, monocyte adhesion under static and shear-stress conditions, H/R model\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — ChIP confirms STAT3 promoter binding, multiple pharmacological validations, functional adhesion readout under physiological conditions\",\n      \"pmids\": [\"23690481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Loss of SMAD4 in primary colorectal cancer cells promotes CCL15 expression to recruit CCR1+ MDSCs (CD11b+, CD33+, HLA-DR-; primarily granulocytic CD15+ with some monocytic CD14+) at the tumor invasion front; CCL15-expressing tumors recruit 2.2-fold more CCR1+ cells and CCL15 knockdown in SMAD4-deficient CRC cells reduces aggressive tumor growth in an orthotopic xenograft model.\",\n      \"method\": \"SMAD4/CCL15 shRNA knockdown in CRC lines, orthotopic xenograft model, IHC and double immunofluorescence of 333 clinical specimens, ELISA for serum CCL15, MDSC phenotyping\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model with genetic knockdown, validated in large clinical cohort with MDSC phenotyping\",\n      \"pmids\": [\"26341919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CCL15 promotes HCC cell migration and invasion via CCR1; CCR1 shRNA knockdown inhibits CCL15-induced chemotaxis and invasion of HepG2 cells and significantly reduces the activity and expression of MMP-2 and MMP-9.\",\n      \"method\": \"CCR1 shRNA knockdown, Transwell migration/invasion assays, MMP-2/MMP-9 zymography and Western blot\",\n      \"journal\": \"Tumour biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — loss-of-function with mechanistic link to MMP activity, single lab\",\n      \"pmids\": [\"26501423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCL15 mediates migration of human bone marrow-derived mesenchymal stem cells toward HCC via CCR1 receptors on hMSCs: CCL15 knockdown in HCC cells significantly reduces hMSC homing to tumor xenografts in vivo (confirmed by histology and flow cytometry), and anti-CCL15 or anti-CCR1 blockade impairs Transwell migration of hMSCs.\",\n      \"method\": \"Cytokine array, ELISA, IHC, Transwell migration, CCL15 shRNA in HCC cells, orthotopic HCC xenograft model, intravenous hMSC delivery with histological and flow cytometric homing quantification\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo homing confirmed by independent histological and flow cytometric methods, receptor specificity established\",\n      \"pmids\": [\"26763650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of SMAD4 promotes CCL15 expression in colorectal cancer, leading to recruitment of CCR1+ tumor-associated neutrophils (and minor granulocytic MDSCs) that facilitate lung metastasis; in a mouse model, CCL15 from SMAD4-deficient CRC cells recruits CCR1+ cells to promote metastatic activity to the lung.\",\n      \"method\": \"Mouse lung metastasis model with SMAD4-manipulated CRC cells, IHC/immunofluorescence of 107 clinical lung metastasis specimens, CCR1+ cell characterization with cell-type-specific markers\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model plus validated in clinical specimens, extends SMAD4-CCL15-CCR1 axis to a new organ site\",\n      \"pmids\": [\"27492974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In HCC, CCL15 expression is regulated by genetic, epigenetic, and microenvironmental factors; CCL15 recruits CCR1+CD14+ monocytes to the invasive margin via the CCL15-CCR1 axis; these tumor-educated monocytes express immune checkpoint molecules (PD-L1, B7-H3, TIM-3), upregulate immune-tolerogenic enzymes (IDO, arginase), and activate STAT1/3, ERK1/2, and AKT signaling in HCC cells, promoting invasion and metastasis. Orthotopic animal models confirm CCL15-CCR1 axis drives inflammatory microenvironment enriched with CCR1+ monocytes.\",\n      \"method\": \"Chemokine expression profiling of HCC cell lines and tissues, CCL15 functional assays, flow cytometry phenotyping of CCR1+CD14+ monocytes, transcriptome sequencing of tumor-infiltrating monocytes, orthotopic mouse models\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transcriptome sequencing of infiltrating cells plus in vivo orthotopic models and signaling pathway characterization\",\n      \"pmids\": [\"30070719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Endothelial cell-derived CCL15 mediates fibrocyte transmigration via CCR1 on fibrocytes; overexpression of CCL15 in endothelial cells or CCR1 in fibrocytes promotes transmigration, while silencing either attenuates it, establishing the CCL15-CCR1 axis as a mechanism for fibrocyte recruitment during wound healing.\",\n      \"method\": \"Transwell co-culture system, gene chip chemokine expression profiling, CCL15 overexpression/knockdown in endothelial cells, CCR1 overexpression/knockdown in fibrocytes, fibrocyte transmigration assays\",\n      \"journal\": \"Molecular medicine reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — loss- and gain-of-function in co-culture system, single lab\",\n      \"pmids\": [\"33174007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCL15 derived from eosinophils (human CCL15/CCL23, mouse CCL6) interacts with CCR1 on hematopoietic stem cells to promote eosinophil differentiation and airway inflammation; Ccl6 knockout mice show decreased eosinophilia and airway inflammation after OVA challenge, and the CCR1 antagonist BX471 reduces eosinophil differentiation.\",\n      \"method\": \"Ccl6 knockout mice, OVA challenge model, CCR1 antagonist BX471, bone marrow eosinophil differentiation assays, flow cytometry\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout plus pharmacological antagonist confirms CCL6/CCL15-CCR1 axis in hematopoietic stem cell regulation of eosinophilia\",\n      \"pmids\": [\"33640900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"P1-HNF4A directly targets CCL15 as a downstream gene in gastric cancer: RNA-seq identified cytokine-cytokine receptor interaction as the most enriched pathway in P1-HNF4A-overexpressing cells, and CCL15 was confirmed as a direct transcriptional target of P1-HNF4A.\",\n      \"method\": \"HNF4A isoform overexpression, RNA-seq pathway analysis, in vitro proliferation/invasion/migration assays, murine xenograft, confirmation of CCL15 as direct target\",\n      \"journal\": \"Cancer biology & medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3-4 — RNA-seq-based identification with limited direct mechanistic validation of CCL15 targeting\",\n      \"pmids\": [\"33710810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Oncogenic Kras upregulates CCL15 expression in pancreatic cancer cells; CCL15 promotes PDAC cell migration and invasion through ROS, as N-Acetyl-L-Cysteine treatment or p22phox knockdown decreases CCL15-promoted cell migration. Kras knockdown abolishes CCL15 protein expression and impedes cell migration, establishing Kras→CCL15→ROS as a migration-promoting pathway.\",\n      \"method\": \"CCL15 knockdown, CCL15 neutralization, recombinant CCL15 treatment, NAC antioxidant treatment, p22phox knockdown, Kras knockdown, cell migration and invasion assays\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple genetic and pharmacological interventions, Kras dependence established, ROS pathway identified\",\n      \"pmids\": [\"35565279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CTHRC1 upregulates CCL15 in colorectal cancer cells via TGF-β/Smad pathway to recruit tumor-associated macrophages; cytokine microarray after CTHRC1 manipulation revealed CCL15 as the regulated chemokine, and pathway analysis linked CTHRC1 to CCL15 through TGFβ activation and Smad phosphorylation.\",\n      \"method\": \"Cytokine microarray, CTHRC1 overexpression/knockdown, TGF-β/Smad pathway analysis (Western blot), macrophage chemotaxis assays, multispectral IHC, in vivo CT-26 tumor model\",\n      \"journal\": \"Journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — mechanistic link to TGF-β/Smad pathway supported by multiple methods, in vivo confirmation\",\n      \"pmids\": [\"37987774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CCL15 secreted by HCC cells signals through CCR1 on cancer-associated fibroblasts (CAFs) to induce FTO expression via the STAT3 pathway; FTO demethylates m6A on CEBPA mRNA in CAFs, leading to CXCL5 secretion by CAFs, which activates CXCR2 on HCC cells to enhance proliferation. CXCL5 in turn upregulates CCL15 in HCC cells via MDM2/P53 modulation, creating a positive feedback loop; neutralizing anti-CCL15 antibody attenuates HCC growth in PDX and co-injection models.\",\n      \"method\": \"Single-cell RNA-seq, co-culture assays, organoid models, allograft models, m6A sequencing, RNA-seq, ChIP, PDX models, neutralizing antibody treatment\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — m6A sequencing plus RNA-seq, multiple model systems (organoids, PDX, allograft), mechanistic pathway validated with multiple orthogonal approaches\",\n      \"pmids\": [\"39734010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPP1+ macrophages drive liver cancer stemness partly through CCL15 from liver cancer cells; CCL15 produced by HCC cells drives polarization of M0 macrophages toward an SPP1+ macrophage phenotype, establishing a positive feedback loop where SPP1+ macrophages promote tumor stemness via VTN/integrin αvβ5/AMPK/YAP1/SOX4 signaling.\",\n      \"method\": \"Single-cell RNA-seq (12 patients), co-culture assays, VTN blocking, integrin αvβ5/YAP1 inhibition, chemoresistance assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — scRNA-seq plus co-culture validation, CCL15 role in macrophage polarization supported but not the primary mechanistic focus\",\n      \"pmids\": [\"39216547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In ESCC, CCL15 and CCR1 directly interact (confirmed by co-immunoprecipitation and immunofluorescence co-localization), and autocrine CCL15-CCR1 signaling activates the AKT/ERK1/2 pathway, leading to c-Jun phosphorylation and CDK2 transcriptional activation (c-Jun binding to CDK2 promoter confirmed by ChIP-qPCR), promoting tumor cell proliferation, migration, and invasion.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, lentiviral CCL15/CCR1 knockdown, recombinant CCL15 treatment, PCR array, transcription factor prediction, PPI database analysis, ChIP-qPCR for c-Jun at CDK2 promoter\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct CCL15-CCR1 interaction confirmed by co-IP, ChIP validates c-Jun/CDK2 axis, but single lab\",\n      \"pmids\": [\"40740234\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCL15 is a CC chemokine that circulates in plasma as a weakly active full-length form (92 aa) and is proteolytically activated by neutrophil cathepsin G, elastase, and MMPs through N-terminal truncation to generate potent CCR1 agonists (Δ23–28 isoforms) that drive monocyte and myeloid cell chemotaxis; it signals through CCR1 (and weakly CCR3) via Gi/Go-PLC-PKCδ and Gα14/16-JAK2/STAT3-NF-κB pathways to induce cell migration, ICAM-1 upregulation, MMP-9 release, and cytokine production, while in tumors, SMAD4 loss or oncogenic Kras de-represses CCL15 transcription, enabling CCL15-CCR1 axis-driven recruitment of immunosuppressive myeloid cells (MDSCs, monocytes, neutrophils) and direct autocrine/paracrine promotion of cancer invasion, metastasis, and stromal reprogramming.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CCL15 is a CC chemokine that functions as a proteolytically activated chemoattractant coupling innate immune cell recruitment to tissue remodeling, angiogenesis, and tumor progression. Full-length CCL15 is weakly active; neutrophil cathepsin G, elastase, and matrix metalloproteinases cleave its extended N-terminus to generate potent truncated isoforms (Δ21–Δ26) that signal through CCR1 (primary receptor) and CCR3 via Gi/Go–PLC–PKCδ–NF-κB cascades to drive chemotaxis of monocytes, eosinophils, endothelial cells, and hematopoietic progenitors [PMID:9600961, PMID:16034099, PMID:22147696, PMID:14984572]. CCL15 transcription is positively regulated by NF-κB, AP-1/JNK, and oncogenic Kras, and negatively regulated by SMAD4 binding to its promoter; loss of SMAD4 in colorectal cancer derepresses CCL15 secretion, recruiting CCR1+ immunosuppressive myeloid cells and neutrophils that facilitate liver and lung metastasis [PMID:23891973, PMID:26341919, PMID:27492974, PMID:15179048]. In hepatocellular carcinoma, paracrine CCL15–CCR1 signaling activates cancer-associated fibroblasts through a STAT3–FTO–m6A–CXCL5 axis that sustains tumor proliferation, while autocrine CCL15–CCR1 signaling promotes invasion via MMP-9/MMP-2 and ROS production [PMID:39734010, PMID:23321514, PMID:35565279, PMID:30070719].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing that CCL15 is a functional chemokine with monocyte and eosinophil chemoattractant activity acting primarily through CCR1 answered the basic question of receptor usage and cell-type specificity for this orphan CC chemokine.\",\n      \"evidence\": \"Recombinant protein chemotaxis and desensitization assays across multiple leukocyte types\",\n      \"pmids\": [\"9600961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of CCR1 selectivity over other CC receptors not defined\", \"In vivo relevance of monocyte vs. eosinophil recruitment not tested\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of a unique six-cysteine/three-disulfide-bond architecture distinguished CCL15 structurally from canonical four-cysteine CC chemokines and raised the question of whether the additional disulfide is functionally required.\",\n      \"evidence\": \"Sequence analysis and structural characterization of recombinant protein\",\n      \"pmids\": [\"9600961\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution 3D structure determined\", \"Functional role of third disulfide bond not yet tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that N-terminal truncation converts weakly active full-length CCL15 into a potent CCR1 agonist (≥100-fold increase) established proteolytic processing as the key activation mechanism, and showed the third disulfide bond is dispensable while the C-terminal α-helix is essential.\",\n      \"evidence\": \"Systematic chemical synthesis of truncation/point mutants with calcium flux, migration, and receptor binding assays in CCR1/CCR3 transfectants and endothelial cells\",\n      \"pmids\": [\"14984572\", \"15251437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the physiological proteases performing N-terminal cleavage was unknown\", \"Crystal structure of truncated active form not determined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identification of neutrophil cathepsin G and elastase as the principal proteases generating potent Δ21–Δ26 CCL15 isoforms provided the missing link between neutrophil activation and CCL15-driven monocyte recruitment.\",\n      \"evidence\": \"In vitro proteolysis with purified cathepsin G/elastase, MS identification of cleavage products, calcium flux and chemotaxis assays\",\n      \"pmids\": [\"16034099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo demonstration of cathepsin G-dependent CCL15 activation not shown\", \"Relative contribution of different proteases in tissue contexts unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Mapping the CCL15–CCR1 signaling cascade to Gi/Go–PLC–PKCδ–NF-κB with a requirement for new protein synthesis defined the intracellular transduction pathway driving chemotaxis.\",\n      \"evidence\": \"Pharmacological inhibitor panel (pertussis toxin, PLC, PKCδ, NF-κB, cycloheximide) in CCR1-transfected HOS cells\",\n      \"pmids\": [\"11943214\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reliance on pharmacological inhibitors in a single transfected cell line\", \"Identity of NF-κB-dependent de novo synthesized proteins required for migration not determined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defining NF-κB and AP-1/JNK as transcriptional regulators of the CCL15 gene promoter established how inflammatory signals control CCL15 expression in monocytoid cells.\",\n      \"evidence\": \"Luciferase reporters with deletion/mutation constructs, EMSA, dominant-negative MKK4/JNK1 in U937 cells\",\n      \"pmids\": [\"15179048\", \"16364464\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Chromatin-level regulation (histone marks, accessibility) not examined\", \"Regulation in non-monocytoid cell types not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showing that MMPs in synovial fluid cleave CCL15 to generate potent truncated agonists extended the proteolytic activation paradigm beyond neutrophil serine proteases to the MMP family and to arthritic tissue contexts.\",\n      \"evidence\": \"MALDI-TOF-MS of synovial fluid cleavage products, calcium flux and migration assays with CCR1 transfectants and THP-1 cells\",\n      \"pmids\": [\"22147696\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific MMP family members responsible not individually confirmed by knockout\", \"In vivo contribution to arthritis pathology not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery that SMAD4 directly binds the CCL15 promoter to repress transcription, and that SMAD4 loss in colorectal cancer derepresses CCL15 to recruit CCR1+ myeloid cells promoting liver metastasis, established the first tumor-suppressor–chemokine axis governing the CCL15-dependent immunosuppressive microenvironment.\",\n      \"evidence\": \"ChIP assay for SMAD4 on CCL15 promoter; SMAD4 knockdown/overexpression; xenograft mouse models; clinical specimen immunohistochemistry\",\n      \"pmids\": [\"23891973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SMAD4 repression is direct or through cofactors not fully resolved\", \"Therapeutic benefit of CCL15/CCR1 blockade in CRC not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstration that CCL15 induces ICAM-1 on endothelial cells via CCR1–JAK2–STAT3 signaling and promotes monocyte adhesion under shear stress revealed a vascular mechanism by which CCL15 facilitates leukocyte extravasation.\",\n      \"evidence\": \"ChIP for STAT3 on ICAM-1 promoter; kinase inhibitors; monocyte adhesion assays under flow\",\n      \"pmids\": [\"23690481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo validation of this endothelial mechanism not performed\", \"Contribution relative to other ICAM-1-inducing chemokines unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extension of the SMAD4–CCL15–CCR1 axis to lung metastasis and identification of recruited cells as tumor-associated neutrophils and granulocytic MDSCs broadened the metastatic organ sites and refined the immunosuppressive cell types mobilized by CCL15.\",\n      \"evidence\": \"Mouse lung metastasis model with SMAD4-deficient CRC cells; immunofluorescent cell-type characterization; clinical specimens\",\n      \"pmids\": [\"27492974\", \"26341919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional proof that recruited neutrophils/MDSCs are necessary for metastasis (depletion experiments) limited\", \"Whether CCL15 acts on other immune cell types at metastatic sites not fully characterized\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showing that CCL15 recruits CCR1+CD14+ monocytes expressing immune checkpoint molecules (PD-L1, B7-H3, TIM-3) to HCC invasive margins linked the CCL15–CCR1 axis to immune evasion and suggested combination immunotherapy potential.\",\n      \"evidence\": \"Orthotopic HCC models; transcriptome sequencing of tumor-infiltrating monocytes; clinical specimen immunophenotyping\",\n      \"pmids\": [\"30070719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CCL15 blockade synergizes with checkpoint inhibitors not tested\", \"Causality between checkpoint molecule upregulation and immune evasion at HCC margins not formally demonstrated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of oncogenic Kras as an upstream driver of CCL15 expression in pancreatic cancer, with CCL15 promoting invasion through ROS via CCR1/CCR3, expanded the oncogene–CCL15 paradigm beyond SMAD4 loss to activating mutations.\",\n      \"evidence\": \"Kras knockdown abolishing CCL15 expression; ROS scavenger and p22phox knockdown; migration/invasion assays\",\n      \"pmids\": [\"35565279\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcription factor intermediary between Kras and CCL15 promoter not identified\", \"In vivo PDAC model validation lacking\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Elucidation of a CCL15–CCR1–STAT3–FTO–m6A–CXCL5 paracrine loop between HCC cells and cancer-associated fibroblasts revealed epitranscriptomic regulation as a downstream effector of CCL15 signaling in the tumor microenvironment.\",\n      \"evidence\": \"Co-culture, organoid, and allograft/PDX models; m6A-seq and RNA-seq; neutralizing antibody treatment\",\n      \"pmids\": [\"39734010\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the FTO–m6A axis operates downstream of CCL15 in non-HCC cancers not tested\", \"Structural basis of CCR1-to-STAT3 signaling in CAFs not resolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Demonstration of a CCL15–CCR1–AKT/ERK–c-Jun–CDK2 transcriptional axis promoting proliferation in ESCC extended the autocrine signaling model to esophageal cancer and identified CDK2 as a downstream transcriptional target.\",\n      \"evidence\": \"Co-IP and co-localization of CCL15–CCR1; ChIP-qPCR of c-Jun on CDK2 promoter; lentiviral knockdown\",\n      \"pmids\": [\"40740234\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-study finding not yet replicated\", \"In vivo tumor growth impact of this axis not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the high-resolution structure of active truncated CCL15 bound to CCR1, the in vivo therapeutic benefit of CCL15/CCR1 blockade in metastatic CRC and HCC, and whether CCL15-recruited myeloid cells are functionally required (via depletion) rather than correlatively associated with metastasis.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal or cryo-EM structure of CCL15–CCR1 complex\", \"No clinical trial data for CCL15/CCR1 antagonism in cancer\", \"Necessity of CCL15-recruited myeloid cells not demonstrated by selective depletion in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 4, 5, 8, 12, 27]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [20, 24, 28]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 8, 9, 13, 14, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 8, 12, 17, 18, 21]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 10, 20, 24, 28]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [14, 17, 18, 21, 24, 25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CCR1\",\n      \"CCR3\",\n      \"SMAD4\",\n      \"MMP9\",\n      \"FTO\",\n      \"CXCL5\",\n      \"CTSG\",\n      \"ELANE\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CCL15 is a CC chemokine that functions as a proteolytically activated chemoattractant, recruiting monocytes, neutrophils, eosinophils, and immunosuppressive myeloid cells through CCR1 (and weakly CCR3), while also exerting direct antimicrobial activity at mucosal surfaces. Full-length CCL15 circulates as a weakly active 92-amino acid precursor that is converted by neutrophil cathepsin G, elastase, and MMPs into N-terminally truncated isoforms (Δ23–28) with up to 1000-fold greater potency for CCR1-mediated calcium flux, chemotaxis, and integrin-dependent adhesion [PMID:16034099, PMID:15905581, PMID:22147696]. Downstream of CCR1, CCL15 engages Gi/Go–PLC–PKCδ signaling for cell migration and a pertussis toxin-insensitive Gα14/16–JAK2–STAT3 pathway that drives NF-κB activation, ICAM-1 upregulation, CXCL8 and IL-6 induction, and MMP-9 release [PMID:11943214, PMID:23125416, PMID:23690481]. In colorectal, hepatocellular, and pancreatic cancers, loss of SMAD4 or oncogenic KRAS de-represses CCL15 transcription, enabling the CCL15–CCR1 axis to recruit CCR1⁺ myeloid-derived suppressor cells, tumor-associated neutrophils, and monocytes that remodel the tumor stroma and promote metastasis [PMID:23891973, PMID:26341919, PMID:30070719, PMID:35565279].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Identification of CCL15 as a novel CC chemokine acting through CCR1 and CCR3 established its fundamental role as a leukocyte chemoattractant for monocytes, neutrophils, and lymphocytes, and revealed an unexpected capacity to suppress hematopoietic progenitor colony formation.\",\n      \"evidence\": \"Recombinant protein calcium flux, Boyden chamber chemotaxis, and colony assays using CCR1/CCR3-transfected cells across multiple independent groups\",\n      \"pmids\": [\"9548457\", \"9346309\", \"9624581\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo chemotactic function demonstrated\", \"Relative contribution of CCR1 vs CCR3 not resolved\", \"Mechanism of colony suppression unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Gene structure analysis revealed a unique four-exon organization encoding a protein with an extra disulfide bond, and identification of alternatively spliced forms showed that N-terminal length governs receptor activation potency, raising the question of how N-terminal processing is regulated in vivo.\",\n      \"evidence\": \"cDNA cloning, Northern blot, NMR structure determination, and calcium flux/chemotaxis with N-terminal variants\",\n      \"pmids\": [\"9600961\", \"9558365\", \"10320325\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological protease(s) responsible for N-terminal truncation not yet identified\", \"Functional significance of third disulfide bond unclear\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"CCR1 knockout mice demonstrated that CCR1 is the essential mediating receptor for CCL15-induced neutrophil responses, and cross-desensitization studies revealed ligand-specific functional outcomes through the same receptor, raising the concept of biased agonism at CCR1.\",\n      \"evidence\": \"CCR1−/− mouse neutrophils, Scatchard binding, cross-desensitization, and calcium flux assays\",\n      \"pmids\": [\"10202040\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for ligand-specific signaling through CCR1 unknown\", \"In vivo relevance of differential CCR1 agonism not tested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Pharmacological dissection of CCL15-CCR1 signaling revealed a Gi/Go–PLC–PKCδ cascade required for chemotaxis and an NF-κB-dependent transcriptional program necessary for migration, showing that CCL15-driven motility requires de novo protein synthesis.\",\n      \"evidence\": \"Pertussis toxin, PLC/PKCδ/NF-κB inhibitors, cycloheximide, and actinomycin D treatments in CCR1-expressing HOS cells\",\n      \"pmids\": [\"11943214\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of newly synthesized proteins required for migration unknown\", \"Pathway validated in single overexpression cell line only\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Systematic chemical synthesis of N-terminal truncation mutants mapped the activation switch to removal of ~24 residues, converting weakly active full-length CCL15 into a potent CCR1 agonist, and showed the C-terminal α-helix is essential for receptor binding while the third disulfide bond is dispensable.\",\n      \"evidence\": \"Fmoc-synthesized sequential truncations and point mutants, radioligand binding, calcium flux, chemotaxis with CCR1/CCR3 transfectants\",\n      \"pmids\": [\"14984572\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact receptor-contact residues not mapped\", \"No co-crystal structure of CCL15–CCR1 complex\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The identity of the activating proteases was resolved: neutrophil cathepsin G generates Δ23 and Δ26 isoforms and elastase generates Δ21, each with markedly increased chemotactic potency, establishing neutrophil-mediated proteolytic activation as the physiological mechanism for converting circulating CCL15 into an active monocyte recruiter.\",\n      \"evidence\": \"Hemofiltration, purified protease incubation, MALDI-TOF MS cleavage site mapping, calcium flux, chemotaxis, and adhesion assays; confirmed with synovial fluid from RA patients\",\n      \"pmids\": [\"16034099\", \"15905581\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of each protease in vivo not quantified\", \"Whether proteolytic activation occurs in healthy vs. diseased tissue is unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"CCL15 was found to possess direct antibacterial activity against a subset of intestinal microflora, revealing a dual innate immune function beyond leukocyte chemotaxis, with upregulation in inflammatory bowel disease indicating a role in mucosal defense.\",\n      \"evidence\": \"Recombinant CCL15 bacterial binding and killing assays, qPCR and IHC in IBD tissue\",\n      \"pmids\": [\"19812544\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis for antimicrobial activity not determined\", \"Spectrum of susceptible bacteria not fully characterized\", \"Relative importance vs. other antimicrobial peptides unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The CCL15–CCR1 axis was shown to be a critical driver of colorectal cancer liver metastasis: tumor-secreted CCL15 recruits CCR1⁺ immature myeloid cells that produce MMP2/MMP9 to remodel the metastatic niche, as demonstrated by epistatic knockout of CCR1, MMP2, and MMP9 and by pharmacological CCR1 blockade.\",\n      \"evidence\": \"Mouse liver dissemination model with CCR1/MMP2/MMP9 knockout hosts, CCR1 antagonist BL5923, survival analysis\",\n      \"pmids\": [\"20616008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human validation of CCR1 antagonist efficacy in metastasis not performed\", \"Whether CCL15 is the sole CCR1 ligand driving recruitment in this context is unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"A second signaling arm was uncovered: CCL15–CCR1 activates STAT3 Tyr705 phosphorylation via pertussis toxin-insensitive Gα14/16 proteins, leading to STAT3 nuclear translocation, CXCL8 induction, and autocrine IL-6 amplification, distinguishing CCL15 signaling from classical Gi-only chemokine pathways.\",\n      \"evidence\": \"Subcellular fractionation, confocal microscopy, anti-IL-6 neutralization, STAT3 inhibition in THP-1 macrophages and CCR1/Gα14/16-overexpressing HEK293 cells\",\n      \"pmids\": [\"23125416\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Gα14/16 coupling confirmed in overexpression system; stoichiometry in primary cells unknown\", \"Whether Gα14/16 pathway operates in all CCR1-expressing cell types is untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"SMAD4 was identified as a direct transcriptional repressor of CCL15: ChIP confirmed SMAD4 binding to the CCL15 promoter enhanced by TGF-β, and SMAD4 loss in CRC de-represses CCL15, recruiting CCR1⁺ MDSCs to the invasion front and promoting liver metastasis — linking a tumor suppressor pathway directly to chemokine-mediated immune evasion.\",\n      \"evidence\": \"ChIP for SMAD4 at CCL15 promoter, TGF-β treatment, SMAD4 knockdown/overexpression, nude mouse liver metastasis model, IHC of 141 clinical specimens\",\n      \"pmids\": [\"23891973\", \"26341919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SMAD4 loss affects CCL15 processing in addition to transcription is unknown\", \"Other SMAD4-regulated chemokines may contribute to myeloid recruitment\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"CCL15 was shown to upregulate endothelial ICAM-1 via a JAK2–STAT3 pathway with STAT3 directly binding the ICAM-1 promoter, promoting monocyte adhesion under shear stress, thereby connecting CCL15 not only to cell migration but also to firm adhesion steps in leukocyte transendothelial migration.\",\n      \"evidence\": \"ChIP for STAT3 at ICAM-1 promoter, JAK/PI3K/AKT inhibitors, monocyte adhesion under static and flow conditions\",\n      \"pmids\": [\"23690481\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of CCL15-induced ICAM-1 upregulation not confirmed\", \"Contribution relative to other ICAM-1 inducers (TNF-α, IL-1β) unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"In hepatocellular carcinoma, CCL15 recruits CCR1⁺CD14⁺ monocytes that express immune checkpoint molecules (PD-L1, B7-H3, TIM-3) and tolerogenic enzymes (IDO, arginase), establishing the CCL15–CCR1 axis as a driver of an immunosuppressive tumor microenvironment beyond simple myeloid cell recruitment.\",\n      \"evidence\": \"Chemokine profiling, flow cytometry phenotyping, transcriptome sequencing of tumor-infiltrating monocytes, orthotopic mouse models\",\n      \"pmids\": [\"30070719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether checkpoint blockade synergizes with CCR1 antagonism is untested\", \"Causal relationship between CCL15-recruited monocytes and specific checkpoint molecule induction not fully dissected\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Oncogenic KRAS was identified as an upstream activator of CCL15 expression in pancreatic cancer, with CCL15 promoting cell migration through a ROS-dependent mechanism involving p22phox, extending the list of oncogenic pathways that co-opt CCL15.\",\n      \"evidence\": \"KRAS knockdown abolishes CCL15 protein, NAC treatment and p22phox knockdown attenuate CCL15-driven migration\",\n      \"pmids\": [\"35565279\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether KRAS regulation of CCL15 is transcriptional or post-transcriptional is not resolved\", \"ROS–migration link lacks identification of downstream effectors\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A CCL15–CCR1–STAT3–FTO positive feedback loop between HCC cells and cancer-associated fibroblasts was discovered: CCL15 from tumor cells activates STAT3 in CAFs to induce FTO-mediated m6A demethylation of CEBPA mRNA, driving CXCL5 secretion that feeds back to upregulate CCL15 via MDM2/P53, revealing an epitranscriptomic dimension of CCL15-mediated stromal reprogramming.\",\n      \"evidence\": \"scRNA-seq, m6A sequencing, ChIP, organoid and PDX models, neutralizing anti-CCL15 antibody\",\n      \"pmids\": [\"39734010\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether anti-CCL15 antibody efficacy translates to immunocompetent models is unknown\", \"FTO-dependent m6A changes on other transcripts in CAFs not characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of CCL15–CCR1 interaction (no co-crystal or cryo-EM structure exists), whether CCR1 antagonists or anti-CCL15 antibodies have therapeutic efficacy in immunocompetent cancer models, and the relative physiological importance of CCL15's antimicrobial function versus its chemotactic activity in mucosal immunity.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No CCL15–CCR1 structural complex resolved\", \"No clinical trial data targeting the CCL15–CCR1 axis\", \"In vivo contribution of CCL15 antimicrobial activity not genetically tested in humans\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 2, 3, 7, 11, 12]},\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [25, 31]},\n      {\"term_id\": \"GO:0090729\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 5, 11, 15, 19, 23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 3, 11, 19, 26, 32]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 22, 25, 38]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [19, 23, 26, 29, 30, 36]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CCR1\",\n      \"CCR3\",\n      \"SMAD4\",\n      \"STAT3\",\n      \"LZIP\",\n      \"FTO\",\n      \"CDK2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}