Class A G protein-coupled receptor of the lymphocyte plasma membrane, and the receptor for the chemoattractant cytokine CXCL17. GPR25 was cloned in 1997 and remained an orphan for nearly three decades before three independent laboratories, using in vivo homing assays, beta-arrestin recruitment and TGF-alpha shedding in transfected cells, and chemotaxis of transfected pre-B cells, converged on CXCL17 as its agonist; site-directed mutagenesis in two of those studies identified the same orthosteric pocket residues, Trp95 and Arg178, as essential, and activation depends on the conserved C-terminal fragment of CXCL17. Because CXCL17 is produced by the epithelia of the airways, oral cavity, stomach, and biliary and genitourinary tracts - the non-intestinal mucosae - the GPR25-CXCL17 axis provides the tissue-selective chemoattractant pathway for those barrier surfaces, complementing the separately known homing systems for intestine and skin. GPR25 is induced on innate lymphocytes before they leave the bone marrow and is imprinted in secondary lymphoid tissue on activated B and T cells; it marks tissue-resident memory B and T cells and regulatory T cells in non-intestinal mucosae and lung, and is also expressed on T cells in cerebrospinal fluid. Adoptive transfer shows that GPR25 drives homing into mucosal barrier tissues but not into intestine, peripheral lymph nodes or spleen. Independently of chemotaxis, GPR25 is induced by TGF-beta signalling and is required for efficient formation of lung and liver tissue-resident memory CD8 T cells. CXCL17 itself is promiscuous - it also activates MRGPRX1, MRGPRX2 and MAS1 at micromolar concentrations, through a mechanism that does not require its C-terminal fragment - and whether CXCL17 should be classified as a chemokine at all is debated; neither question undermines GPR25 as one of its receptors.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004930 G protein-coupled receptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic assertion of generic G protein-coupled receptor activity, from a node spanning a broad set of chemokine and peptide receptor descendants. Reason: Correct family-level statement, and consistent with the now-established ligand-specific function. The more informative term for this gene is the C-X-C chemokine receptor activity it carries with IDA support from two papers, but the parent is not wrong and the phylogenetic assertion is sound. |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic assertion that GPR25 is active in the plasma membrane. Reason: Core location. GPR25 is a cell-surface receptor on lymphocytes; the chemotaxis and beta-arrestin assays all read out surface receptor engagement. |
| GO:0007186 G protein-coupled receptor signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic assertion that GPR25 signals through the G protein-coupled receptor pathway. Reason: Core biological process. CXCL17 binding triggers G protein signalling and modulates the RhoA pathway to control cytoskeletal dynamics and integrin function during lymphocyte recruitment. Supporting Evidence: PMID:39293486 Here we leveraged diverse omics datasets to identify GPR25 as a lymphocyte receptor for CXCL17 |
| GO:0004930 G protein-coupled receptor activity | IEA GO_REF:0000120 | ACCEPT | Summary: Generic receptor activity from combined automated methods. Reason: Correct, and subsumed by the ligand-specific C-X-C chemokine receptor activity annotation that this gene now carries with IDA support. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Plasma membrane localisation from the UniProt subcellular-location vocabulary. Reason: Core location. |
| GO:0007186 G protein-coupled receptor signaling pathway | IEA GO_REF:0000002 | ACCEPT | Summary: GPCR signalling assignment from the InterPro class A signature. Reason: Core biological process, now directly supported by experimental work. |
| GO:0016020 membrane | IEA GO_REF:0000002 | ACCEPT | Summary: Generic membrane localisation from the InterPro GPCR signatures. Reason: Correct, though the plasma membrane annotations carried by this gene are more informative. |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | REMOVE | Summary: Binary interactions recovered in a proteome-scale human interactome map. Reason: No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. The partners recovered here are largely unrelated membrane and ER proteins typical of high-throughput binary screens for multi-pass membrane baits, and none of them figures in the established CXCL17-GPR25 biology. Removal does not imply the reported interaction is false. |
| GO:0005515 protein binding | IPI PMID:31515488 Extensive disruption of protein interactions by genetic vari... | REMOVE | Summary: Binary interaction from a systematic study of variant effects on protein interactions. Reason: No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. Removal does not imply the reported interaction is false. |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | REMOVE | Summary: A large set of binary interactions from the human reference interactome map. Reason: Bare protein binding carries no functional information. This single reference contributes more than twenty separate GOA rows for GPR25, all of them uninformative about what the receptor does. No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. Removal does not imply the reported interaction is false. |
| GO:0005515 protein binding | IPI PMID:39083597 Multiplexed mapping of the interactome of GPCRs with recepto... | REMOVE | Summary: Interaction with a receptor activity-modifying protein from a multiplexed GPCR-RAMP interactome screen. Reason: Bare protein binding carries no functional information. A RAMP interaction could in principle be functionally informative for a GPCR, but the screen does not establish a consequence for GPR25 trafficking or pharmacology, so the annotation as it stands says nothing about function. No more informative molecular function is supportable from this evidence, so the row is removed rather than rewritten. Removal does not imply the reported interaction is false. |
| GO:0005886 plasma membrane | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | ACCEPT | Summary: GPR25 acts at the plasma membrane of transfected HEK293T cells, where CXCL17 triggers beta-arrestin recruitment, TGF-alpha shedding and chemotactic movement. Reason: Core location. Supporting Evidence: PMID:40279398 Only the pairing of wild-type CXCL17 with wild-type GPR25 could cause shedding of transforming growth factor Ξ± and induce chemotactic movement of transfected HEK293T cells. |
| GO:0016494 C-X-C chemokine receptor activity | IDA PMID:39293486 A lymphocyte chemoaffinity axis for lung, non-intestinal muc... | ACCEPT | Summary: GPR25 identified as the lymphocyte receptor for CXCL17, with chemotaxis in vitro and CXCL17-dependent homing to non-intestinal mucosal tissues in vivo. Reason: Core molecular function, and the strongest deorphanization in this review batch. Three independent laboratories using three different assay platforms agree: OcΓ³n et al. (Nature 2024, in vivo adoptive-transfer homing in wild-type and Cxcl17-null recipients), Hu et al. (FEBS J 2025, beta-arrestin recruitment and TGF-alpha shedding in HEK293T cells with an EC50 near 100 nM and no activity at seventeen other GPCRs), and Yang, Giblin and Pease (Basic Clin Pharmacol Toxicol 2026, chemotaxis of L1.2 pre-B transfectants to nanomolar CXCL17). The last two independently converged on the same orthosteric residues, Trp95 and Arg178, as essential. A fourth laboratory provides in vivo genetics for GPR25 function in tissue-resident memory CD8 T cells (PMID:41270189). The residual controversy in the literature concerns the ligand, not the receptor: CXCL17 also activates MRGPRX1, MRGPRX2 and MAS1, but only at micromolar concentrations and through a determinant that does not require the C-terminal fragment on which GPR25 activation depends, so CXCL17 promiscuity does not weaken the GPR25 assignment. A separate proposal to reclassify CXCL17 as a chemoattractant distinct from the chemokine family is a question about the ligand's nomenclature and does not affect this term, whose scope covers C-X-C-named chemokine ligands. Supporting Evidence: PMID:39293486 Here we leveraged diverse omics datasets to identify GPR25 as a lymphocyte receptor for CXCL17 PMID:42207165 In conclusion, we verify GPR25 as a bona fide CXCL17 receptor and suggest a two-step model of GPR25 activation |
| GO:0016494 C-X-C chemokine receptor activity | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | ACCEPT | Summary: CXCL17 activates human GPR25 with an EC50 near 100 nM and no effect on seventeen other receptors tested; alanine substitution of the predicted pocket residues Trp95 or Arg178 abolishes the response. Reason: Core molecular function, independently replicated. The structure-guided mutagenesis here was reproduced by a separate laboratory in a different cell background, which also recovered Trp95 and Arg178 (plus Arg264) as required for the chemotactic response. The residual controversy concerns CXCL17's promiscuity rather than GPR25's identity as one of its receptors: the MRGPR responses need micromolar ligand and survive C-terminal truncation, whereas GPR25 activation is abolished by removing three C-terminal residues. Supporting Evidence: PMID:40279398 we identified the rarely studied orphan G protein-coupled receptor 25 (GPR25) as a receptor of CXCL17 PMID:40279398 Alanine replacement of W95 or R178 of human GPR25, two conserved residues in the predicted orthosteric ligand binding pocket, almost abolished its response to CXCL17. PMID:41167449 However, removal of C-terminal residues from CXCL17 did not affect its activation of these three MRGPRs, even though this region is essential for GPR25 activation. |
| GO:0030595 leukocyte chemotaxis | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | ACCEPT | Summary: CXCL17 induces chemotactic movement of GPR25-expressing cells. Reason: Correct, and the direct functional output of the receptor. The lymphocyte-specific child term carried by this gene is more informative, but the parent is not wrong. Supporting Evidence: PMID:40279398 Only the pairing of wild-type CXCL17 with wild-type GPR25 could cause shedding of transforming growth factor Ξ± and induce chemotactic movement of transfected HEK293T cells. |
| GO:0048247 lymphocyte chemotaxis | IDA PMID:39293486 A lymphocyte chemoaffinity axis for lung, non-intestinal muc... | ACCEPT | Summary: GPR25 mediates lymphocyte chemotaxis to CXCL17, and lymphocyte recruitment to barrier epithelia in vivo. Reason: Core biological process and the physiological purpose of the receptor. Replicated independently with L1.2 pre-B transfectants migrating to nanomolar CXCL17. Supporting Evidence: PMID:39293486 GPR25 characterizes B and T tissue resident memory cells and regulatory T lymphocytes in non-intestinal mucosal tissues and lungs in humans and mediates lymphocyte homing to barrier epithelia of the airways, oral cavity, stomach, and biliary and genitourinary tracts in mouse models. PMID:42207165 GPR25 was expressed in the murine pre-B cell line L1.2 and mediated robust migration of transfectants to nanomolar concentrations of recombinant CXCL17 (24-119). |
| GO:0070098 chemokine-mediated signaling pathway | IDA PMID:39293486 A lymphocyte chemoaffinity axis for lung, non-intestinal muc... | ACCEPT | Summary: CXCL17 signalling through GPR25 activates the RhoA pathway and regulates cytoskeletal dynamics and integrins during lymphocyte recruitment. Reason: Core biological process, the direct downstream consequence of the ligand-receptor pairing. Supporting Evidence: PMID:39293486 Here we leveraged diverse omics datasets to identify GPR25 as a lymphocyte receptor for CXCL17 |
| GO:0097021 lymphocyte migration into lymphoid organs | IDA PMID:39293486 A lymphocyte chemoaffinity axis for lung, non-intestinal muc... | MODIFY | Summary: Curator assignment of lymphocyte migration into lymphoid organs from the in vivo homing experiments. Reason: The biology is right but the term is scoped to the wrong destination. GO:0097021 is defined as movement of a lymphocyte within the lymphatic system into lymphoid organs such as lymph nodes, spleen or Peyer's patches. The full text of this paper reports the opposite result for those destinations - GPR25-transduced T cells homed to trachea, stomach, tongue, gallbladder and uterine mucosae but not to intestines, peripheral lymph nodes or spleen. GPR25 is imprinted in secondary lymphoid tissue but directs migration out to peripheral mucosal barriers. The general lymphocyte migration term states what was shown without asserting lymphoid-organ entry; a mucosal-homing child term would be better still and is raised in the suggested questions. Proposed replacements: lymphocyte migration Supporting Evidence: PMID:39293486 In WT recipients, GPR25 enhanced homing to trachea, stomach, tongue, gallbladder and uterine mucosae, but not to the intestines or control peripheral lymph nodes (PLNs) or spleen |
| GO:0004930 G protein-coupled receptor activity | IDA PMID:39293486 A lymphocyte chemoaffinity axis for lung, non-intestinal muc... | ACCEPT | Summary: Direct demonstration that GPR25 functions as a G protein-coupled receptor for CXCL17. Reason: Correct, and subsumed by the ligand-specific C-X-C chemokine receptor activity annotation made from the same paper. Supporting Evidence: PMID:39293486 Here we leveraged diverse omics datasets to identify GPR25 as a lymphocyte receptor for CXCL17 |
| GO:0004930 G protein-coupled receptor activity | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | ACCEPT | Summary: GPR25 recruits beta-arrestin and drives TGF-alpha shedding in response to CXCL17, the hallmark behaviour of an agonist-activated GPCR. Reason: Correct, and subsumed by the ligand-specific C-X-C chemokine receptor activity annotation made from the same paper. Supporting Evidence: PMID:40279398 we identified the rarely studied orphan G protein-coupled receptor 25 (GPR25) as a receptor of CXCL17 |
| GO:0048247 lymphocyte chemotaxis | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | ACCEPT | Summary: CXCL17-induced, GPR25-dependent chemotactic movement. Reason: Core biological process. Supporting Evidence: PMID:40279398 Only the pairing of wild-type CXCL17 with wild-type GPR25 could cause shedding of transforming growth factor Ξ± and induce chemotactic movement of transfected HEK293T cells. |
| GO:0070098 chemokine-mediated signaling pathway | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | ACCEPT | Summary: CXCL17 engagement of GPR25 initiates receptor signalling, read out as beta-arrestin recruitment and TGF-alpha shedding. Reason: Core biological process. Supporting Evidence: PMID:40279398 we identified the rarely studied orphan G protein-coupled receptor 25 (GPR25) as a receptor of CXCL17 |
| GO:0097021 lymphocyte migration into lymphoid organs | IDA PMID:40279398 Identification of orphan GPR25 as a receptor for the chemoki... | MODIFY | Summary: Curator assignment of lymphocyte migration into lymphoid organs from the chemotaxis experiments in this paper. Reason: Same term-scoping problem as the companion annotation from PMID:39293486. This study assayed chemotactic movement of transfected HEK293T cells, not migration into lymph nodes, spleen or Peyer's patches, and the in vivo work in the companion paper specifically excluded those destinations for GPR25. The general lymphocyte migration term is the accurate statement. Proposed replacements: lymphocyte migration Supporting Evidence: PMID:39293486 In WT recipients, GPR25 enhanced homing to trachea, stomach, tongue, gallbladder and uterine mucosae, but not to the intestines or control peripheral lymph nodes (PLNs) or spleen |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-379044 | ACCEPT | Summary: Reactome placement of GPR25 at the plasma membrane in a peptide ligand-binding receptor pathway. Reason: Core location, consistent with all experimental evidence. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-744886 | ACCEPT | Summary: Reactome placement of GPR25 at the plasma membrane. Reason: Core location. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-744887 | ACCEPT | Summary: Reactome placement of GPR25 at the plasma membrane. Reason: Core location. |
| GO:0004930 G protein-coupled receptor activity | TAS PMID:9020062 Discovery of a novel human G protein-coupled receptor gene (... | ACCEPT | Summary: Author statement in the original cloning paper that GPR25 encodes a member of the G protein-coupled receptor family. Reason: Correct, though inferred from sequence in 1997 rather than measured; it is now supported by direct evidence and subsumed by the ligand-specific term. Supporting Evidence: PMID:9020062 isolation of a gene, GPR25, encoding an additional member of the G protein-coupled receptor family (GPCR) |
| GO:0005886 plasma membrane | TAS PMID:9020062 Discovery of a novel human G protein-coupled receptor gene (... | ACCEPT | Summary: Plasma membrane location asserted in the original cloning paper on the basis of the seven-transmembrane prediction. Reason: Correct location, subsequently confirmed experimentally. |
| GO:0007186 G protein-coupled receptor signaling pathway | TAS PMID:9020062 Discovery of a novel human G protein-coupled receptor gene (... | ACCEPT | Summary: G protein-coupled receptor signalling asserted from family membership in the cloning paper. Reason: Correct, and now experimentally supported. |
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Download this section (compressed HTML)Q: Does CXCL17 signal through MRGPRX1, MRGPRX2 and MAS1 at physiologically attainable concentrations, or are those micromolar responses an in vitro property of a cationic peptide? The answer decides how much of CXCL17 biology is GPR25 biology, without bearing on whether GPR25 is a CXCL17 receptor.
Suggested experts: Zhan-Yun Guo, James E Pease
Q: Is the TGF-beta-induced role of GPR25 in lung and liver tissue-resident memory CD8 T cell formation downstream of CXCL17, or a ligand-independent output? Gpr25-deficient cells entered tissues normally and failed at a later step, which is not obviously a chemotaxis phenotype.
Suggested experts: Pandurangan Vijayanand, Hayley Feng
Q: Should GO acquire a child term for lymphocyte homing to mucosal barrier epithelia? GPR25 is currently annotated with lymphocyte migration into lymphoid organs, which the primary data explicitly exclude, and the accurate alternative is the uninformative general migration term.
Q: Does GPR25 have additional endogenous agonists, and is CXCL17 its only ligand? The receptor was assayed against a panel of one ligand family; no counter-screen of orphan ligands has been reported.
Suggested experts: Eugene C Butcher, Borja OcΓ³n
Experiment: Transfer wild-type, Gpr25-null and Gpr25 W95A/R178A-reconstituted CD8 T cells into wild-type and Cxcl17-null recipients, infect, and score tissue entry and subsequent TRM differentiation including TCF1 acquisition, separating the entry step from the residency step.
Hypothesis: The tissue-resident memory phenotype of GPR25 loss requires CXCL17 binding.
Type: Adoptive transfer with receptor pocket mutants in ligand-null hosts
Experiment: Quantify CXCL17 protein in airway, gastric and biliary mucosal lavage and tissue by targeted mass spectrometry, and compare with the measured EC50 values at GPR25 and at the three MRGPRs determined side by side in one laboratory with one ligand preparation.
Hypothesis: CXCL17 does not reach concentrations at mucosal surfaces sufficient to activate MRGPRX1, MRGPRX2 or MAS1.
Type: Quantitative ligand measurement plus matched pharmacology
Experiment: Determine a cryo-EM structure of the CXCL17-GPR25-G protein complex and test the predicted N-terminal orientation contacts and the Trp95, Arg178 and Arg264 pocket contacts by mutagenesis in both chemotaxis and beta-arrestin assays.
Hypothesis: GPR25 has a structurally defined CXCL17 binding mode consistent with the two-step model.
Type: Structural biology with structure-guided mutagenesis
Experiment: Screen GPR25 against a broad orphan-ligand and chemoattractant library in a beta-arrestin recruitment assay, with the W95A pocket mutant as a counter-screen to distinguish orthosteric from allosteric or assay-artefact hits.
Hypothesis: GPR25 responds to ligands other than CXCL17.
Type: Deorphanization counter-screen
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