{"gene":"CXCL17","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2014,"finding":"GPR35 (proposed as CXCR8) was identified as a receptor for CXCL17. Transfection of GPR35 into Ba/F3 cells rendered them responsive to CXCL17 as measured by calcium-mobilization assays. GPR35 expression is downregulated in lungs of Cxcl17(-/-) mice, which exhibit defects in macrophage recruitment to the lungs.","method":"Calcium mobilization assay in Ba/F3 transfectants; Cxcl17(-/-) mouse model with lung macrophage recruitment readout","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, functional assay in transfected cells; subsequently contradicted by multiple labs","pmids":["25411203"],"is_preprint":false},{"year":2017,"finding":"GPR35 does NOT mediate CXCL17-stimulated migration of THP-1 cells. In AP-TGF-α shedding assay using GPR35-overexpressing HEK293 cells, neither human nor mouse CXCL17 activated GPR35. GPR35 siRNA knockdown and the GPR35 antagonist CID2745687 blocked lodoxamide-induced migration inhibition but did not block CXCL17-stimulated migration of THP-1 cells, indicating CXCL17 signals through a receptor other than GPR35.","method":"AP-TGF-α shedding assay; siRNA knockdown of GPR35 in THP-1 cells; pharmacological antagonism with CID2745687; chemotaxis assay","journal":"British journal of pharmacology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — multiple orthogonal methods (gain-of-function assay, siRNA KD, pharmacological antagonism) in single lab, directly contradicting the GPR35-CXCL17 pairing","pmids":["29068046"],"is_preprint":false},{"year":2018,"finding":"GPR35 failed to signal in response to CXCL17 in assays of β-arrestin recruitment, inositol phosphate production, calcium flux, and receptor endocytosis. In chemotaxis assays, GPR35 did not confer sensitivity to CXCL17. In THP-1 cells, CXCL17-stimulated migration was not blocked by the GPR35 antagonist ML145, indicating CXCL17 acts through an unidentified receptor distinct from GPR35.","method":"β-arrestin recruitment assay; inositol phosphate production assay; calcium flux assay; receptor endocytosis assay; TAXIScan real-time chemotaxis assay; pharmacological antagonism with ML145","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal signaling assays plus chemotaxis; independent lab replicating negative finding for GPR35-CXCL17","pmids":["29875152"],"is_preprint":false},{"year":2012,"finding":"CXCL17 has potent antimicrobial activity against a panel of pathogenic and opportunistic bacteria, and its mechanism of antimicrobial action involves peptide-mediated bacterial membrane disruption.","method":"In vitro antimicrobial assay against pathogenic bacteria panel; bacterial membrane disruption assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Weak — direct in vitro antimicrobial assay with mechanistic readout (membrane disruption), single lab","pmids":["22611239"],"is_preprint":false},{"year":2012,"finding":"CXCL17 undergoes endoproteolysis during protein maturation in gastric mucosa. Mature CXCL17 acts as a chemoattractant for monocytes and macrophages, signaling through ERK1/2 and p38 but not JNK pathways. CXCL17 also induces production of proangiogenic factor VEGF-A from treated monocytes, and exhibits anti-inflammatory effects on LPS-activated macrophages.","method":"Western blotting for endoproteolysis; in vitro chemotaxis assay; signaling pathway inhibition (ERK1/2, p38, JNK); VEGF-A production assay; LPS-activated macrophage anti-inflammatory assay","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple in vitro assays with pathway inhibitor controls in single lab","pmids":["23115081"],"is_preprint":false},{"year":2012,"finding":"CXCL17 expressed by tumor cells recruits CD11b+Gr1(high)F4/80(-) myeloid-derived cells (approximately 90%, neutrophil-like morphology) as determined by chemotactic assays in vitro, and promotes tumor angiogenesis (CD31+ vessels) in vivo in immunodeficient mice.","method":"In vitro chemotaxis assay; in vivo xenograft tumor model with CXCL17-expressing NIH3T3 cells; flow cytometry; immunohistochemistry for CD31","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro chemotaxis combined with in vivo tumor model, single lab","pmids":["22952881"],"is_preprint":false},{"year":2019,"finding":"CXCL17 secreted by breast cancer cells increases accumulation of CD11b+Gr-1+ MDSCs in the lungs. These MDSCs express PDGF-BB, which mediates angiogenesis in the lung metastatic niche and facilitates cancer extravasation, colonization, and lung metastasis.","method":"In vitro chemotaxis assay; in vivo spontaneous metastasis mouse model; MDSC depletion; PDGF receptor inhibitor treatment; in vitro and in vivo models","journal":"Breast cancer research : BCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo models with depletion and inhibitor rescue experiments, single lab","pmids":["30755260"],"is_preprint":false},{"year":2010,"finding":"CXCL17 induces infiltration and accumulation of immature myeloid dendritic cells in the tumor epithelial layer, and this recruitment is followed by a cellular immune reaction in intraepithelial precursor lesions of pancreatic cancer (IPMN). The function was confirmed in syngeneic mouse models.","method":"Gene expression profiling; immunohistochemical analysis; syngeneic mouse model with functional readout (dendritic cell recruitment, immune response)","journal":"Gastroenterology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mouse model functional validation combined with clinical sample analysis, single lab","pmids":["20955708"],"is_preprint":false},{"year":2018,"finding":"CXCL17 is a direct target of miR-221-3p. CXCL17 inhibits expression of CCL24, CCL26, and periostin via the p38 MAPK pathway in bronchial epithelial cells. In a mouse model, overexpression of miR-221-3p suppressed CXCL17 expression and exacerbated airway eosinophilic inflammation.","method":"miR-221-3p target validation; siRNA/inhibitor experiments in BEAS-2B cells; p38 MAPK pathway inhibition assay; house dust mite mouse model with airway-specific miR-221-3p overexpression","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro pathway studies with signaling inhibitors plus in vivo mouse model, single lab","pmids":["29644894"],"is_preprint":false},{"year":2017,"finding":"CXCL17 recruits CD11b+Gr-1+ MDSCs (but not Tregs) by direct chemotaxis in vitro. MDSCs then recruit Tregs through CCL5 and CCL4. Blockade of CCL5 or CCL4 abolished the anti-inflammatory effects of CXCL17 in an imiquimod-induced psoriasis-like skin inflammation model.","method":"In vitro chemotaxis assay for MDSCs and Tregs; in vivo injection of recombinant CXCL17; anti-CCL5/anti-CCL4 antibody blockade; flow cytometry; immunofluorescence","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro chemotaxis plus in vivo model with antibody rescue, single lab","pmids":["28389593"],"is_preprint":false},{"year":2018,"finding":"CXCL17-/- mice showed reduced numbers of CXCR8+CD8+ TEM and TRM cells in the vaginal mucosa after intravaginal HSV-1 infection, associated with more virus replication and more latency in dorsal root ganglia. This indicates the CXCL17/CXCR8 pathway promotes mobilization of protective CD8+ TEM and TRM cells to mucosal tissues.","method":"Cxcl17(-/-) mouse model; intravaginal HSV-1 infection; flow cytometry for CD8+ T cell subsets; viral burden measurement; ganglia latency assay","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple cellular and virological readouts, single lab","pmids":["29549178"],"is_preprint":false},{"year":2019,"finding":"Cxcl17(-/-) mice have higher numbers of CD4+ and CD8+ T cells in spleen and lymph nodes, produce higher levels of proinflammatory cytokines upon activation, and develop exacerbated disease in an EAE model of T cell-dependent autoimmunity, with markedly reduced survival compared to wild-type littermates.","method":"Cxcl17(-/-) mouse model; T cell population analysis by flow cytometry; cytokine profiling; experimental autoimmune encephalomyelitis (EAE) model; survival analysis","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple immune and disease phenotype readouts, single lab","pmids":["30860634"],"is_preprint":false},{"year":2018,"finding":"CXCL17 promotes cell metastasis and inhibits autophagy in hepatocellular carcinoma via the LKB1-AMPK pathway. Knockdown of CXCL17 activated AMPK and LKB1, enhanced nuclear translocation of LKB1, and stimulated autophagy markers (LC-3B, p62). Overexpression of CXCL17 suppressed these effects.","method":"CXCL17 siRNA knockdown and overexpression in HCC cells; Western blotting for AMPK, LKB1, LC-3B, p62; nuclear fractionation; invasion/migration assays","journal":"Gene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, correlative signaling assays without direct mechanistic validation (no reconstitution or mutagenesis)","pmids":["30597237"],"is_preprint":false},{"year":2024,"finding":"CXCL17 is an allosteric inhibitor of CXCR4. Using BRET-based assays, CXCL17 inhibited CXCR4-mediated signaling and ligand binding only in intact cells. This effect was mimicked by known glycosaminoglycan (GAG) binders (surfen, protamine sulfate), and disruption of putative GAG binding domains in CXCL17 prevented CXCR4 inhibition, indicating that CXCL17 requires GAG-containing accessory proteins to inhibit CXCR4. CXCL17 also interacted with neuropilin-1, a VEGFR2 co-receptor.","method":"BRET-based signaling and ligand binding assays; GAG domain mutagenesis in CXCL17; pharmacological mimicry with surfen and protamine sulfate; neuropilin-1 interaction assay","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro BRET-based functional assays with mutagenesis of GAG binding domains and pharmacological controls, multiple orthogonal methods in single rigorous study","pmids":["38502733"],"is_preprint":false},{"year":2023,"finding":"CXCL17 binds efficaciously to glycosaminoglycans (GAGs) via key C-terminal motifs, as quantified by solid-phase assays and bio-layer interferometry. CXCL17 failed to adopt a classical chemokine fold by modeling. Recombinant CXCL17 dimerizes as a function of concentration. CXCL17 inhibited CXCR1-mediated chemotaxis of transfectants to CXCL8 in a dose-dependent manner but was inactive via CXCR1 directly.","method":"Solid-phase GAG binding assays; bio-layer interferometry; in silico structural modeling; chemotaxis assays with CXCR1 transfectants; recombinant protein production in mammalian and prokaryotic systems","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — multiple orthogonal binding and functional assays, single lab","pmids":["37942327"],"is_preprint":false},{"year":2025,"finding":"GPR25 was identified as a receptor for CXCL17 via AlphaFold 3 prediction and experimental validation. Recombinant CXCL17 activated human GPR25 in transfected HEK293T cells (EC50 ~100 nM) in a NanoBiT β-arrestin recruitment assay, but had no effect on 17 other GPCRs tested. Deletion of three conserved C-terminal residues from CXCL17 abolished activation. Alanine substitution of W95 or R178 in GPR25's predicted orthosteric binding pocket abolished response to CXCL17. Wild-type CXCL17 with wild-type GPR25 induced TGF-α shedding and chemotactic cell movement.","method":"AlphaFold 3 modeling; NanoBiT β-arrestin recruitment assay; C-terminal truncation mutagenesis of CXCL17; alanine mutagenesis of GPR25 binding pocket residues; TGF-α shedding assay; chemotaxis assay","journal":"The FEBS journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in transfected cells with mutagenesis of both ligand and receptor validated by multiple functional assays, rigorous controls including panel of 17 other GPCRs","pmids":["40279398"],"is_preprint":false},{"year":2026,"finding":"GPR25 mediates CXCL17-induced chemotaxis via a two-step mechanism: the GPR25 N-terminus orients CXCL17 for activation via its C-terminus. GPR25 residues W95, R178, and R264 are essential for chemotactic responsiveness. An N-terminally truncated CXCL17 (64-119) retains chemotactic activity via GPR25 but with reduced potency. A chimeric FPR1:GPR25 construct responded to CXCL17 with reduced potency, implicating the GPR25 N-terminus in recognition.","method":"Site-directed mutagenesis of GPR25; chimeric FPR1:GPR25 receptor constructs; N-terminal truncation of CXCL17; chemotaxis assay with L1.2 transfectants; computational modeling of CXCL17:GPR25 complex","journal":"Basic & clinical pharmacology & toxicology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of both ligand and receptor with multiple functional readouts, validates and extends the GPR25 deorphanization finding from an independent lab","pmids":["42207165"],"is_preprint":false},{"year":2025,"finding":"Human CXCL17 activates MRGPRX2, MRGPRX1, and MAS1 at micromolar concentrations in NanoBiT β-arrestin recruitment assays in transfected HEK293T cells, and induces chemotactic movement via these receptors. Removal of C-terminal residues from CXCL17 does not abolish MRGPR activation (in contrast to GPR25), indicating CXCL17 activates MRGPRs through a mechanism distinct from GPR25 activation.","method":"NanoBiT β-arrestin recruitment assay in HEK293T transfectants; C-terminal truncation mutagenesis of CXCL17; chemotaxis assay; panel of 10 human MRGPRs tested","journal":"Archives of biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, functional assays in transfected cells, no in vivo validation, awaiting independent replication","pmids":["41167449"],"is_preprint":false},{"year":2024,"finding":"Endothelial cell expression of CXCL17 is transcriptionally regulated by the YAP/TEAD1 complex activated by hypoxia-reoxygenation. CXCL17 recruits MDSCs (through binding to GPR35) during liver ischemia-reperfusion injury, and these MDSCs attenuate injury by inhibiting M1 macrophage polarization via upregulation of STAT3 signaling.","method":"Bulk RNA-sequencing; scRNA-seq; αGr-1 antibody depletion; adoptive transfer of MDSCs; in vivo mouse IRI model; hepatic endothelial cell hypoxia-reoxygenation stimulation; ChIP/transcription factor analysis implied","journal":"Hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo model with MDSC depletion and adoptive transfer rescue, combined with mechanistic transcriptional analysis, single lab","pmids":["38407233"],"is_preprint":false},{"year":2020,"finding":"CXCL17 reduces type I collagen expression in skin fibroblasts by inducing MMP1 and miR-29 expression, indicating post-transcriptional regulation of collagen via these effectors. Local injection of CXCL17 attenuated bleomycin-induced skin fibrosis in mice.","method":"Western blotting; RT-PCR for collagen, MMP1, miR-29; bleomycin mouse model with CXCL17 injection; ELISA for serum CXCL17","journal":"Journal of dermatological science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro mechanistic data combined with in vivo mouse model, single lab","pmids":["33055012"],"is_preprint":false},{"year":2021,"finding":"In intestinal epithelial cells (Caco-2), mycotoxins trigger ROS-dependent CXCL17 production via p38 and JNK pathways. CXCL17 then mediates immunoprotective responses (reduced inflammation and apoptosis) through the PI3K/AKT/mTOR pathway.","method":"Caco-2 cell model; ROS measurement; signaling pathway inhibitors (p38, JNK, PI3K/AKT/mTOR); apoptosis and inflammation assays","journal":"Biochemical pharmacology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, in vitro only, signaling pathway assignment based on inhibitor studies without genetic validation","pmids":["33932472"],"is_preprint":false},{"year":2019,"finding":"CXCL17 increases migration of THP-1 mononuclear macrophages by activating the Src/FAK signaling pathway, as demonstrated by Western blotting. M2 macrophages polarized in conditioned media promoted proliferation of lung adenocarcinoma cells.","method":"Transwell invasion assay; Western blotting for Src and FAK phosphorylation; conditioned medium from M1/M2 macrophages; CCK-8 proliferation assay","journal":"Cellular oncology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, correlative Western blot analysis without genetic validation of Src/FAK pathway","pmids":["31832986"],"is_preprint":false},{"year":2023,"finding":"Recombinant CXCL17 treatment alleviates hyperoxia-induced lung injury in neonatal mice by activating the AKT pathway, reducing apoptosis, oxidative stress, and inflammation, as validated in both a mouse model and primary murine alveolar epithelial type II cells.","method":"Hyperoxia mouse model; recombinant CXCL17 treatment; Western blotting for AKT pathway; TUNEL staining for apoptosis; ELISA for inflammatory factors; DHE staining for ROS","journal":"Molecular biotechnology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway assignment based on correlation with AKT activation without genetic validation","pmids":["37710083"],"is_preprint":false},{"year":2025,"finding":"CXCL17 promotes cardiac fibroblast proliferation by activating AKT signaling and upregulating bFGF in a positive feedback loop. Both CXCL17 and bFGF activate AKT signaling synergistically. In vivo, CXCL17 increased cardiac fibrosis in an isoprenaline-induced mouse model, reversible by a CXCL17-blocking antibody.","method":"In vitro fibroblast proliferation assay; Western blotting for AKT signaling; bFGF measurement; isoprenaline mouse model; CXCL17-blocking antibody treatment","journal":"Cardiovascular journal of Africa","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, pathway assignment by correlation, in vivo blocking antibody validation is supportive but limited","pmids":["40778660"],"is_preprint":false}],"current_model":"CXCL17 is a mucosal chemoattractant that recruits monocytes, macrophages, myeloid-derived suppressor cells, and dendritic cells; its primary receptor is GPR25 (activated via a two-step mechanism requiring the CXCL17 C-terminus for insertion into the GPR25 orthosteric binding pocket), while it also inhibits CXCR4 signaling allosterically through a glycosaminoglycan-dependent mechanism, and possesses direct antimicrobial activity via bacterial membrane disruption; proposed binding to GPR35/CXCR8 has been refuted by multiple independent laboratories using orthogonal assays."},"narrative":{"mechanistic_narrative":"CXCL17 is a mucosal chemoattractant chemokine that recruits monocytes, macrophages, myeloid-derived suppressor cells (MDSCs), and dendritic cells to epithelial and tumor microenvironments and shapes local immune tone [PMID:23115081, PMID:20955708, PMID:28389593]. It is synthesized as a precursor that undergoes endoproteolytic maturation in gastric mucosa, and mature CXCL17 drives monocyte/macrophage chemotaxis through ERK1/2 and p38 signaling while inducing the proangiogenic factor VEGF-A and exerting anti-inflammatory effects on LPS-activated macrophages [PMID:23115081]. Its principal signaling receptor is the orphan GPCR GPR25, which CXCL17 activates with ~100 nM potency to drive β-arrestin recruitment, TGF-α shedding, and chemotaxis through a two-step mechanism in which the GPR25 N-terminus orients the ligand so its essential C-terminal residues insert into the orthosteric pocket formed by GPR25 residues W95, R178, and R264 [PMID:40279398, PMID:42207165]. Beyond its own receptor, CXCL17 acts as a glycosaminoglycan-dependent allosteric inhibitor of CXCR4 signaling and binds GAGs through C-terminal motifs, consistent with a non-classical chemokine fold [PMID:38502733, PMID:37942327]. CXCL17 also possesses direct antimicrobial activity, killing bacteria by membrane disruption [PMID:22611239]. The originally proposed receptor GPR35 (\"CXCR8\") does not transduce CXCL17 signaling: multiple independent laboratories found no activation across β-arrestin, inositol phosphate, calcium flux, endocytosis, TGF-α shedding, and chemotaxis assays, and GPR35 antagonists fail to block CXCL17-stimulated migration [PMID:29068046, PMID:29875152]. In vivo, CXCL17 recruits MDSCs that promote tumor angiogenesis and metastasis via PDGF-BB while also restraining autoimmune and inflammatory pathology [PMID:22952881, PMID:30755260, PMID:30860634].","teleology":[{"year":2012,"claim":"Established that CXCL17 is not merely an immune signaling molecule but a direct effector with antimicrobial activity, defining a host-defense role at mucosal surfaces.","evidence":"In vitro antimicrobial assays against a bacterial panel with bacterial membrane disruption readout","pmids":["22611239"],"confidence":"Medium","gaps":["Membrane-disruption mechanism not resolved at structural/residue level","No in vivo demonstration of antimicrobial protection"]},{"year":2012,"claim":"Defined CXCL17 as a maturation-processed chemoattractant for monocytes/macrophages acting through MAPK signaling, with angiogenic and anti-inflammatory consequences.","evidence":"Western blot for endoproteolysis, chemotaxis with ERK1/2/p38/JNK inhibitors, VEGF-A induction, and LPS-macrophage assays","pmids":["23115081"],"confidence":"Medium","gaps":["Receptor mediating these effects not identified at the time","Protease responsible for endoproteolysis unknown"]},{"year":2014,"claim":"First proposed a receptor for CXCL17, naming GPR35 (CXCR8), to explain its chemoattractant activity and link it to lung macrophage recruitment.","evidence":"Calcium mobilization in GPR35-transfected Ba/F3 cells plus Cxcl17(-/-) mouse lung phenotype","pmids":["25411203"],"confidence":"Medium","gaps":["Single calcium readout in one cell background","Subsequently contradicted by independent labs"]},{"year":2018,"claim":"Refuted the GPR35-CXCL17 pairing through multiple orthogonal signaling and chemotaxis assays, re-opening the question of the true CXCL17 receptor.","evidence":"AP-TGF-α shedding, β-arrestin, inositol phosphate, calcium, endocytosis, siRNA knockdown, and GPR35 antagonists (CID2745687, ML145) in THP-1 cells","pmids":["29068046","29875152"],"confidence":"High","gaps":["Did not identify the actual receptor","Left mechanism of CXCL17 chemotaxis unexplained"]},{"year":2024,"claim":"Revealed a distinct mechanism by which CXCL17 modulates other chemokine axes, acting as a GAG-dependent allosteric inhibitor of CXCR4 rather than a direct agonist.","evidence":"BRET signaling/ligand-binding assays in intact cells, GAG-domain mutagenesis, GAG-binder mimicry (surfen, protamine), and neuropilin-1 interaction","pmids":["38502733"],"confidence":"High","gaps":["Identity of the GAG-containing accessory protein not defined","Physiological relevance of CXCR4 inhibition not tested in vivo"]},{"year":2023,"claim":"Characterized CXCL17's biochemical behavior as a non-classical chemokine, showing GAG binding via C-terminal motifs and indirect modulation of CXCR1 signaling.","evidence":"Solid-phase GAG assays, bio-layer interferometry, structural modeling, and CXCR1 transfectant chemotaxis","pmids":["37942327"],"confidence":"Medium","gaps":["No experimental structure to confirm non-canonical fold","Functional role of concentration-dependent dimerization unclear"]},{"year":2025,"claim":"Deorphanized GPR25 as a bona fide CXCL17 receptor and mapped the activation determinants, resolving the long-standing receptor question.","evidence":"AlphaFold 3 modeling, NanoBiT β-arrestin recruitment (EC50 ~100 nM) across 17 GPCRs, CXCL17 C-terminal truncation, and GPR25 W95/R178 alanine mutagenesis with TGF-α shedding/chemotaxis","pmids":["40279398"],"confidence":"High","gaps":["Downstream G-protein coupling not fully dissected","No in vivo GPR25-CXCL17 genetic confirmation"]},{"year":2026,"claim":"Defined a two-step ligand-recognition mechanism in which the GPR25 N-terminus orients CXCL17 for C-terminus-driven activation, extending the deorphanization from an independent lab.","evidence":"GPR25 mutagenesis (W95/R178/R264), FPR1:GPR25 chimeras, CXCL17 N-terminal truncation, and L1.2 transfectant chemotaxis with computational modeling","pmids":["42207165"],"confidence":"High","gaps":["High-resolution complex structure still lacking","Contribution of each step to signaling efficacy not quantified"]},{"year":2025,"claim":"Identified additional candidate receptors (MRGPRX2, MRGPRX1, MAS1) engaged through a C-terminus-independent mechanism distinct from GPR25, suggesting receptor multiplicity.","evidence":"NanoBiT β-arrestin assays and chemotaxis in HEK293T transfectants across 10 MRGPRs with CXCL17 C-terminal truncation","pmids":["41167449"],"confidence":"Medium","gaps":["Micromolar potency raises physiological-relevance questions","No in vivo validation; awaits independent replication"]},{"year":null,"claim":"It remains unresolved how CXCL17's multiple receptors (GPR25, MRGPRs), GAG-dependent allosteric activity, and direct antimicrobial function are integrated at native mucosal sites in vivo.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of CXCL17 in complex with any receptor","Relative in vivo contributions of GPR25 vs MRGPR signaling unknown","GAG accessory protein required for CXCR4 inhibition unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[4,15,16]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13]},{"term_id":"GO:0090729","term_label":"toxin activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[15,16,13]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,9,11]}],"complexes":[],"partners":["GPR25","CXCR4","NRP1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6UXB2","full_name":"C-X-C motif chemokine 17","aliases":["Dendritic cell and monocyte chemokine-like protein","DMC","VEGF coregulated chemokine 1"],"length_aa":119,"mass_kda":13.8,"function":"Chemokine that acts as a chemoattractant for monocytes, macrophages and dendritic cells, and which is involved in immune regulation and lymphocyte trafficking (PubMed:16455961, PubMed:23115081, PubMed:39293486, PubMed:40279398). Activates the C-X-C chemokine receptor GPR25 (PubMed:39293486, PubMed:40279398). Plays a key role in lymphocyte homing by activating the receptor GPR25 on lymphocytes, mediating lymphocyte recruitment into the respiratory, upper gastrointestinal, biliary and genito-urinary tracts (PubMed:39293486, PubMed:40279398). Plays a role in angiogenesis and possibly in the development of tumors (PubMed:16989774, PubMed:23115081). Acts as an anti-inflammatory in the stomach (PubMed:23115081). May play a role in the innate defense against infections (PubMed:17307946) Seems to exhibit much higher chemoattractant potency on monocytes and macrophages than 6-Cys CXCL17","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q6UXB2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CXCL17","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CXCL17","total_profiled":1310},"omim":[{"mim_id":"611387","title":"CXC CHEMOKINE LIGAND 17; CXCL17","url":"https://www.omim.org/entry/611387"},{"mim_id":"602646","title":"G PROTEIN-COUPLED RECEPTOR 35; GPR35","url":"https://www.omim.org/entry/602646"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"esophagus","ntpm":125.8},{"tissue":"lung","ntpm":140.3},{"tissue":"salivary gland","ntpm":146.4},{"tissue":"stomach 1","ntpm":338.0}],"url":"https://www.proteinatlas.org/search/CXCL17"},"hgnc":{"alias_symbol":["Dcip1","UNQ473","DMC","VCC1"],"prev_symbol":[]},"alphafold":{"accession":"Q6UXB2","domains":[{"cath_id":"-","chopping":"52-59_100-119","consensus_level":"medium","plddt":66.7639,"start":52,"end":119}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UXB2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UXB2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UXB2-F1-predicted_aligned_error_v6.png","plddt_mean":59.66},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CXCL17","jax_strain_url":"https://www.jax.org/strain/search?query=CXCL17"},"sequence":{"accession":"Q6UXB2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UXB2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UXB2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UXB2"}},"corpus_meta":[{"pmid":"20955708","id":"PMC_20955708","title":"CXCL17 and ICAM2 are associated with a potential anti-tumor immune response in early intraepithelial stages of human pancreatic carcinogenesis.","date":"2010","source":"Gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/20955708","citation_count":146,"is_preprint":false},{"pmid":"25411203","id":"PMC_25411203","title":"Cutting edge: GPR35/CXCR8 is the receptor of the mucosal chemokine CXCL17.","date":"2014","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/25411203","citation_count":125,"is_preprint":false},{"pmid":"30755260","id":"PMC_30755260","title":"CXCL17-derived CD11b+Gr-1+ myeloid-derived suppressor cells contribute to lung metastasis of breast cancer through platelet-derived growth factor-BB.","date":"2019","source":"Breast cancer research : BCR","url":"https://pubmed.ncbi.nlm.nih.gov/30755260","citation_count":84,"is_preprint":false},{"pmid":"22611239","id":"PMC_22611239","title":"CXCL17 is a mucosal chemokine elevated in idiopathic pulmonary fibrosis that exhibits broad antimicrobial activity.","date":"2012","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/22611239","citation_count":80,"is_preprint":false},{"pmid":"22952881","id":"PMC_22952881","title":"CXCL17 expression by tumor cells recruits CD11b+Gr1 high F4/80- cells and promotes tumor progression.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22952881","citation_count":78,"is_preprint":false},{"pmid":"23115081","id":"PMC_23115081","title":"CXCL17, an orphan chemokine, acts as a novel angiogenic and anti-inflammatory factor.","date":"2012","source":"American journal of physiology. 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Transfection of GPR35 into Ba/F3 cells rendered them responsive to CXCL17 as measured by calcium-mobilization assays. GPR35 expression is downregulated in lungs of Cxcl17(-/-) mice, which exhibit defects in macrophage recruitment to the lungs.\",\n      \"method\": \"Calcium mobilization assay in Ba/F3 transfectants; Cxcl17(-/-) mouse model with lung macrophage recruitment readout\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, functional assay in transfected cells; subsequently contradicted by multiple labs\",\n      \"pmids\": [\"25411203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GPR35 does NOT mediate CXCL17-stimulated migration of THP-1 cells. In AP-TGF-α shedding assay using GPR35-overexpressing HEK293 cells, neither human nor mouse CXCL17 activated GPR35. GPR35 siRNA knockdown and the GPR35 antagonist CID2745687 blocked lodoxamide-induced migration inhibition but did not block CXCL17-stimulated migration of THP-1 cells, indicating CXCL17 signals through a receptor other than GPR35.\",\n      \"method\": \"AP-TGF-α shedding assay; siRNA knockdown of GPR35 in THP-1 cells; pharmacological antagonism with CID2745687; chemotaxis assay\",\n      \"journal\": \"British journal of pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — multiple orthogonal methods (gain-of-function assay, siRNA KD, pharmacological antagonism) in single lab, directly contradicting the GPR35-CXCL17 pairing\",\n      \"pmids\": [\"29068046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"GPR35 failed to signal in response to CXCL17 in assays of β-arrestin recruitment, inositol phosphate production, calcium flux, and receptor endocytosis. In chemotaxis assays, GPR35 did not confer sensitivity to CXCL17. In THP-1 cells, CXCL17-stimulated migration was not blocked by the GPR35 antagonist ML145, indicating CXCL17 acts through an unidentified receptor distinct from GPR35.\",\n      \"method\": \"β-arrestin recruitment assay; inositol phosphate production assay; calcium flux assay; receptor endocytosis assay; TAXIScan real-time chemotaxis assay; pharmacological antagonism with ML145\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal signaling assays plus chemotaxis; independent lab replicating negative finding for GPR35-CXCL17\",\n      \"pmids\": [\"29875152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CXCL17 has potent antimicrobial activity against a panel of pathogenic and opportunistic bacteria, and its mechanism of antimicrobial action involves peptide-mediated bacterial membrane disruption.\",\n      \"method\": \"In vitro antimicrobial assay against pathogenic bacteria panel; bacterial membrane disruption assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Weak — direct in vitro antimicrobial assay with mechanistic readout (membrane disruption), single lab\",\n      \"pmids\": [\"22611239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CXCL17 undergoes endoproteolysis during protein maturation in gastric mucosa. Mature CXCL17 acts as a chemoattractant for monocytes and macrophages, signaling through ERK1/2 and p38 but not JNK pathways. CXCL17 also induces production of proangiogenic factor VEGF-A from treated monocytes, and exhibits anti-inflammatory effects on LPS-activated macrophages.\",\n      \"method\": \"Western blotting for endoproteolysis; in vitro chemotaxis assay; signaling pathway inhibition (ERK1/2, p38, JNK); VEGF-A production assay; LPS-activated macrophage anti-inflammatory assay\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple in vitro assays with pathway inhibitor controls in single lab\",\n      \"pmids\": [\"23115081\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CXCL17 expressed by tumor cells recruits CD11b+Gr1(high)F4/80(-) myeloid-derived cells (approximately 90%, neutrophil-like morphology) as determined by chemotactic assays in vitro, and promotes tumor angiogenesis (CD31+ vessels) in vivo in immunodeficient mice.\",\n      \"method\": \"In vitro chemotaxis assay; in vivo xenograft tumor model with CXCL17-expressing NIH3T3 cells; flow cytometry; immunohistochemistry for CD31\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro chemotaxis combined with in vivo tumor model, single lab\",\n      \"pmids\": [\"22952881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CXCL17 secreted by breast cancer cells increases accumulation of CD11b+Gr-1+ MDSCs in the lungs. These MDSCs express PDGF-BB, which mediates angiogenesis in the lung metastatic niche and facilitates cancer extravasation, colonization, and lung metastasis.\",\n      \"method\": \"In vitro chemotaxis assay; in vivo spontaneous metastasis mouse model; MDSC depletion; PDGF receptor inhibitor treatment; in vitro and in vivo models\",\n      \"journal\": \"Breast cancer research : BCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo models with depletion and inhibitor rescue experiments, single lab\",\n      \"pmids\": [\"30755260\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CXCL17 induces infiltration and accumulation of immature myeloid dendritic cells in the tumor epithelial layer, and this recruitment is followed by a cellular immune reaction in intraepithelial precursor lesions of pancreatic cancer (IPMN). The function was confirmed in syngeneic mouse models.\",\n      \"method\": \"Gene expression profiling; immunohistochemical analysis; syngeneic mouse model with functional readout (dendritic cell recruitment, immune response)\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mouse model functional validation combined with clinical sample analysis, single lab\",\n      \"pmids\": [\"20955708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CXCL17 is a direct target of miR-221-3p. CXCL17 inhibits expression of CCL24, CCL26, and periostin via the p38 MAPK pathway in bronchial epithelial cells. In a mouse model, overexpression of miR-221-3p suppressed CXCL17 expression and exacerbated airway eosinophilic inflammation.\",\n      \"method\": \"miR-221-3p target validation; siRNA/inhibitor experiments in BEAS-2B cells; p38 MAPK pathway inhibition assay; house dust mite mouse model with airway-specific miR-221-3p overexpression\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro pathway studies with signaling inhibitors plus in vivo mouse model, single lab\",\n      \"pmids\": [\"29644894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CXCL17 recruits CD11b+Gr-1+ MDSCs (but not Tregs) by direct chemotaxis in vitro. MDSCs then recruit Tregs through CCL5 and CCL4. Blockade of CCL5 or CCL4 abolished the anti-inflammatory effects of CXCL17 in an imiquimod-induced psoriasis-like skin inflammation model.\",\n      \"method\": \"In vitro chemotaxis assay for MDSCs and Tregs; in vivo injection of recombinant CXCL17; anti-CCL5/anti-CCL4 antibody blockade; flow cytometry; immunofluorescence\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro chemotaxis plus in vivo model with antibody rescue, single lab\",\n      \"pmids\": [\"28389593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CXCL17-/- mice showed reduced numbers of CXCR8+CD8+ TEM and TRM cells in the vaginal mucosa after intravaginal HSV-1 infection, associated with more virus replication and more latency in dorsal root ganglia. This indicates the CXCL17/CXCR8 pathway promotes mobilization of protective CD8+ TEM and TRM cells to mucosal tissues.\",\n      \"method\": \"Cxcl17(-/-) mouse model; intravaginal HSV-1 infection; flow cytometry for CD8+ T cell subsets; viral burden measurement; ganglia latency assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple cellular and virological readouts, single lab\",\n      \"pmids\": [\"29549178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cxcl17(-/-) mice have higher numbers of CD4+ and CD8+ T cells in spleen and lymph nodes, produce higher levels of proinflammatory cytokines upon activation, and develop exacerbated disease in an EAE model of T cell-dependent autoimmunity, with markedly reduced survival compared to wild-type littermates.\",\n      \"method\": \"Cxcl17(-/-) mouse model; T cell population analysis by flow cytometry; cytokine profiling; experimental autoimmune encephalomyelitis (EAE) model; survival analysis\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple immune and disease phenotype readouts, single lab\",\n      \"pmids\": [\"30860634\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CXCL17 promotes cell metastasis and inhibits autophagy in hepatocellular carcinoma via the LKB1-AMPK pathway. Knockdown of CXCL17 activated AMPK and LKB1, enhanced nuclear translocation of LKB1, and stimulated autophagy markers (LC-3B, p62). Overexpression of CXCL17 suppressed these effects.\",\n      \"method\": \"CXCL17 siRNA knockdown and overexpression in HCC cells; Western blotting for AMPK, LKB1, LC-3B, p62; nuclear fractionation; invasion/migration assays\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, correlative signaling assays without direct mechanistic validation (no reconstitution or mutagenesis)\",\n      \"pmids\": [\"30597237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CXCL17 is an allosteric inhibitor of CXCR4. Using BRET-based assays, CXCL17 inhibited CXCR4-mediated signaling and ligand binding only in intact cells. This effect was mimicked by known glycosaminoglycan (GAG) binders (surfen, protamine sulfate), and disruption of putative GAG binding domains in CXCL17 prevented CXCR4 inhibition, indicating that CXCL17 requires GAG-containing accessory proteins to inhibit CXCR4. CXCL17 also interacted with neuropilin-1, a VEGFR2 co-receptor.\",\n      \"method\": \"BRET-based signaling and ligand binding assays; GAG domain mutagenesis in CXCL17; pharmacological mimicry with surfen and protamine sulfate; neuropilin-1 interaction assay\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro BRET-based functional assays with mutagenesis of GAG binding domains and pharmacological controls, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"38502733\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CXCL17 binds efficaciously to glycosaminoglycans (GAGs) via key C-terminal motifs, as quantified by solid-phase assays and bio-layer interferometry. CXCL17 failed to adopt a classical chemokine fold by modeling. Recombinant CXCL17 dimerizes as a function of concentration. CXCL17 inhibited CXCR1-mediated chemotaxis of transfectants to CXCL8 in a dose-dependent manner but was inactive via CXCR1 directly.\",\n      \"method\": \"Solid-phase GAG binding assays; bio-layer interferometry; in silico structural modeling; chemotaxis assays with CXCR1 transfectants; recombinant protein production in mammalian and prokaryotic systems\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — multiple orthogonal binding and functional assays, single lab\",\n      \"pmids\": [\"37942327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR25 was identified as a receptor for CXCL17 via AlphaFold 3 prediction and experimental validation. Recombinant CXCL17 activated human GPR25 in transfected HEK293T cells (EC50 ~100 nM) in a NanoBiT β-arrestin recruitment assay, but had no effect on 17 other GPCRs tested. Deletion of three conserved C-terminal residues from CXCL17 abolished activation. Alanine substitution of W95 or R178 in GPR25's predicted orthosteric binding pocket abolished response to CXCL17. Wild-type CXCL17 with wild-type GPR25 induced TGF-α shedding and chemotactic cell movement.\",\n      \"method\": \"AlphaFold 3 modeling; NanoBiT β-arrestin recruitment assay; C-terminal truncation mutagenesis of CXCL17; alanine mutagenesis of GPR25 binding pocket residues; TGF-α shedding assay; chemotaxis assay\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in transfected cells with mutagenesis of both ligand and receptor validated by multiple functional assays, rigorous controls including panel of 17 other GPCRs\",\n      \"pmids\": [\"40279398\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GPR25 mediates CXCL17-induced chemotaxis via a two-step mechanism: the GPR25 N-terminus orients CXCL17 for activation via its C-terminus. GPR25 residues W95, R178, and R264 are essential for chemotactic responsiveness. An N-terminally truncated CXCL17 (64-119) retains chemotactic activity via GPR25 but with reduced potency. A chimeric FPR1:GPR25 construct responded to CXCL17 with reduced potency, implicating the GPR25 N-terminus in recognition.\",\n      \"method\": \"Site-directed mutagenesis of GPR25; chimeric FPR1:GPR25 receptor constructs; N-terminal truncation of CXCL17; chemotaxis assay with L1.2 transfectants; computational modeling of CXCL17:GPR25 complex\",\n      \"journal\": \"Basic & clinical pharmacology & toxicology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of both ligand and receptor with multiple functional readouts, validates and extends the GPR25 deorphanization finding from an independent lab\",\n      \"pmids\": [\"42207165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Human CXCL17 activates MRGPRX2, MRGPRX1, and MAS1 at micromolar concentrations in NanoBiT β-arrestin recruitment assays in transfected HEK293T cells, and induces chemotactic movement via these receptors. Removal of C-terminal residues from CXCL17 does not abolish MRGPR activation (in contrast to GPR25), indicating CXCL17 activates MRGPRs through a mechanism distinct from GPR25 activation.\",\n      \"method\": \"NanoBiT β-arrestin recruitment assay in HEK293T transfectants; C-terminal truncation mutagenesis of CXCL17; chemotaxis assay; panel of 10 human MRGPRs tested\",\n      \"journal\": \"Archives of biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, functional assays in transfected cells, no in vivo validation, awaiting independent replication\",\n      \"pmids\": [\"41167449\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Endothelial cell expression of CXCL17 is transcriptionally regulated by the YAP/TEAD1 complex activated by hypoxia-reoxygenation. CXCL17 recruits MDSCs (through binding to GPR35) during liver ischemia-reperfusion injury, and these MDSCs attenuate injury by inhibiting M1 macrophage polarization via upregulation of STAT3 signaling.\",\n      \"method\": \"Bulk RNA-sequencing; scRNA-seq; αGr-1 antibody depletion; adoptive transfer of MDSCs; in vivo mouse IRI model; hepatic endothelial cell hypoxia-reoxygenation stimulation; ChIP/transcription factor analysis implied\",\n      \"journal\": \"Hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo model with MDSC depletion and adoptive transfer rescue, combined with mechanistic transcriptional analysis, single lab\",\n      \"pmids\": [\"38407233\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CXCL17 reduces type I collagen expression in skin fibroblasts by inducing MMP1 and miR-29 expression, indicating post-transcriptional regulation of collagen via these effectors. Local injection of CXCL17 attenuated bleomycin-induced skin fibrosis in mice.\",\n      \"method\": \"Western blotting; RT-PCR for collagen, MMP1, miR-29; bleomycin mouse model with CXCL17 injection; ELISA for serum CXCL17\",\n      \"journal\": \"Journal of dermatological science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro mechanistic data combined with in vivo mouse model, single lab\",\n      \"pmids\": [\"33055012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In intestinal epithelial cells (Caco-2), mycotoxins trigger ROS-dependent CXCL17 production via p38 and JNK pathways. CXCL17 then mediates immunoprotective responses (reduced inflammation and apoptosis) through the PI3K/AKT/mTOR pathway.\",\n      \"method\": \"Caco-2 cell model; ROS measurement; signaling pathway inhibitors (p38, JNK, PI3K/AKT/mTOR); apoptosis and inflammation assays\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, in vitro only, signaling pathway assignment based on inhibitor studies without genetic validation\",\n      \"pmids\": [\"33932472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"CXCL17 increases migration of THP-1 mononuclear macrophages by activating the Src/FAK signaling pathway, as demonstrated by Western blotting. M2 macrophages polarized in conditioned media promoted proliferation of lung adenocarcinoma cells.\",\n      \"method\": \"Transwell invasion assay; Western blotting for Src and FAK phosphorylation; conditioned medium from M1/M2 macrophages; CCK-8 proliferation assay\",\n      \"journal\": \"Cellular oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, correlative Western blot analysis without genetic validation of Src/FAK pathway\",\n      \"pmids\": [\"31832986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Recombinant CXCL17 treatment alleviates hyperoxia-induced lung injury in neonatal mice by activating the AKT pathway, reducing apoptosis, oxidative stress, and inflammation, as validated in both a mouse model and primary murine alveolar epithelial type II cells.\",\n      \"method\": \"Hyperoxia mouse model; recombinant CXCL17 treatment; Western blotting for AKT pathway; TUNEL staining for apoptosis; ELISA for inflammatory factors; DHE staining for ROS\",\n      \"journal\": \"Molecular biotechnology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway assignment based on correlation with AKT activation without genetic validation\",\n      \"pmids\": [\"37710083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CXCL17 promotes cardiac fibroblast proliferation by activating AKT signaling and upregulating bFGF in a positive feedback loop. Both CXCL17 and bFGF activate AKT signaling synergistically. In vivo, CXCL17 increased cardiac fibrosis in an isoprenaline-induced mouse model, reversible by a CXCL17-blocking antibody.\",\n      \"method\": \"In vitro fibroblast proliferation assay; Western blotting for AKT signaling; bFGF measurement; isoprenaline mouse model; CXCL17-blocking antibody treatment\",\n      \"journal\": \"Cardiovascular journal of Africa\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, pathway assignment by correlation, in vivo blocking antibody validation is supportive but limited\",\n      \"pmids\": [\"40778660\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CXCL17 is a mucosal chemoattractant that recruits monocytes, macrophages, myeloid-derived suppressor cells, and dendritic cells; its primary receptor is GPR25 (activated via a two-step mechanism requiring the CXCL17 C-terminus for insertion into the GPR25 orthosteric binding pocket), while it also inhibits CXCR4 signaling allosterically through a glycosaminoglycan-dependent mechanism, and possesses direct antimicrobial activity via bacterial membrane disruption; proposed binding to GPR35/CXCR8 has been refuted by multiple independent laboratories using orthogonal assays.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CXCL17 is a mucosal chemoattractant chemokine that recruits monocytes, macrophages, myeloid-derived suppressor cells (MDSCs), and dendritic cells to epithelial and tumor microenvironments and shapes local immune tone [#4, #7, #9]. It is synthesized as a precursor that undergoes endoproteolytic maturation in gastric mucosa, and mature CXCL17 drives monocyte/macrophage chemotaxis through ERK1/2 and p38 signaling while inducing the proangiogenic factor VEGF-A and exerting anti-inflammatory effects on LPS-activated macrophages [#4]. Its principal signaling receptor is the orphan GPCR GPR25, which CXCL17 activates with ~100 nM potency to drive \\u03b2-arrestin recruitment, TGF-\\u03b1 shedding, and chemotaxis through a two-step mechanism in which the GPR25 N-terminus orients the ligand so its essential C-terminal residues insert into the orthosteric pocket formed by GPR25 residues W95, R178, and R264 [#15, #16]. Beyond its own receptor, CXCL17 acts as a glycosaminoglycan-dependent allosteric inhibitor of CXCR4 signaling and binds GAGs through C-terminal motifs, consistent with a non-classical chemokine fold [#13, #14]. CXCL17 also possesses direct antimicrobial activity, killing bacteria by membrane disruption [#3]. The originally proposed receptor GPR35 (\\\"CXCR8\\\") does not transduce CXCL17 signaling: multiple independent laboratories found no activation across \\u03b2-arrestin, inositol phosphate, calcium flux, endocytosis, TGF-\\u03b1 shedding, and chemotaxis assays, and GPR35 antagonists fail to block CXCL17-stimulated migration [#1, #2]. In vivo, CXCL17 recruits MDSCs that promote tumor angiogenesis and metastasis via PDGF-BB while also restraining autoimmune and inflammatory pathology [#5, #6, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established that CXCL17 is not merely an immune signaling molecule but a direct effector with antimicrobial activity, defining a host-defense role at mucosal surfaces.\",\n      \"evidence\": \"In vitro antimicrobial assays against a bacterial panel with bacterial membrane disruption readout\",\n      \"pmids\": [\"22611239\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Membrane-disruption mechanism not resolved at structural/residue level\", \"No in vivo demonstration of antimicrobial protection\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined CXCL17 as a maturation-processed chemoattractant for monocytes/macrophages acting through MAPK signaling, with angiogenic and anti-inflammatory consequences.\",\n      \"evidence\": \"Western blot for endoproteolysis, chemotaxis with ERK1/2/p38/JNK inhibitors, VEGF-A induction, and LPS-macrophage assays\",\n      \"pmids\": [\"23115081\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor mediating these effects not identified at the time\", \"Protease responsible for endoproteolysis unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"First proposed a receptor for CXCL17, naming GPR35 (CXCR8), to explain its chemoattractant activity and link it to lung macrophage recruitment.\",\n      \"evidence\": \"Calcium mobilization in GPR35-transfected Ba/F3 cells plus Cxcl17(-/-) mouse lung phenotype\",\n      \"pmids\": [\"25411203\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single calcium readout in one cell background\", \"Subsequently contradicted by independent labs\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Refuted the GPR35-CXCL17 pairing through multiple orthogonal signaling and chemotaxis assays, re-opening the question of the true CXCL17 receptor.\",\n      \"evidence\": \"AP-TGF-\\u03b1 shedding, \\u03b2-arrestin, inositol phosphate, calcium, endocytosis, siRNA knockdown, and GPR35 antagonists (CID2745687, ML145) in THP-1 cells\",\n      \"pmids\": [\"29068046\", \"29875152\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the actual receptor\", \"Left mechanism of CXCL17 chemotaxis unexplained\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed a distinct mechanism by which CXCL17 modulates other chemokine axes, acting as a GAG-dependent allosteric inhibitor of CXCR4 rather than a direct agonist.\",\n      \"evidence\": \"BRET signaling/ligand-binding assays in intact cells, GAG-domain mutagenesis, GAG-binder mimicry (surfen, protamine), and neuropilin-1 interaction\",\n      \"pmids\": [\"38502733\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the GAG-containing accessory protein not defined\", \"Physiological relevance of CXCR4 inhibition not tested in vivo\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Characterized CXCL17's biochemical behavior as a non-classical chemokine, showing GAG binding via C-terminal motifs and indirect modulation of CXCR1 signaling.\",\n      \"evidence\": \"Solid-phase GAG assays, bio-layer interferometry, structural modeling, and CXCR1 transfectant chemotaxis\",\n      \"pmids\": [\"37942327\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No experimental structure to confirm non-canonical fold\", \"Functional role of concentration-dependent dimerization unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Deorphanized GPR25 as a bona fide CXCL17 receptor and mapped the activation determinants, resolving the long-standing receptor question.\",\n      \"evidence\": \"AlphaFold 3 modeling, NanoBiT \\u03b2-arrestin recruitment (EC50 ~100 nM) across 17 GPCRs, CXCL17 C-terminal truncation, and GPR25 W95/R178 alanine mutagenesis with TGF-\\u03b1 shedding/chemotaxis\",\n      \"pmids\": [\"40279398\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream G-protein coupling not fully dissected\", \"No in vivo GPR25-CXCL17 genetic confirmation\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined a two-step ligand-recognition mechanism in which the GPR25 N-terminus orients CXCL17 for C-terminus-driven activation, extending the deorphanization from an independent lab.\",\n      \"evidence\": \"GPR25 mutagenesis (W95/R178/R264), FPR1:GPR25 chimeras, CXCL17 N-terminal truncation, and L1.2 transfectant chemotaxis with computational modeling\",\n      \"pmids\": [\"42207165\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution complex structure still lacking\", \"Contribution of each step to signaling efficacy not quantified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified additional candidate receptors (MRGPRX2, MRGPRX1, MAS1) engaged through a C-terminus-independent mechanism distinct from GPR25, suggesting receptor multiplicity.\",\n      \"evidence\": \"NanoBiT \\u03b2-arrestin assays and chemotaxis in HEK293T transfectants across 10 MRGPRs with CXCL17 C-terminal truncation\",\n      \"pmids\": [\"41167449\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Micromolar potency raises physiological-relevance questions\", \"No in vivo validation; awaits independent replication\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how CXCL17's multiple receptors (GPR25, MRGPRs), GAG-dependent allosteric activity, and direct antimicrobial function are integrated at native mucosal sites in vivo.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of CXCL17 in complex with any receptor\", \"Relative in vivo contributions of GPR25 vs MRGPR signaling unknown\", \"GAG accessory protein required for CXCR4 inhibition unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [4, 15, 16]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0090729\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [15, 16, 13]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 9, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GPR25\", \"CXCR4\", \"NRP1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}