{"gene":"FPR2","run_date":"2026-06-09T23:54:44","timeline":{"discoveries":[{"year":1992,"finding":"FPR2 (FPRH2) was identified as a structural homologue of the FMLP receptor (FPR1) that does not recognize FMLP as a ligand, and was mapped to chromosome 19 along with FPR1 and the C5a receptor.","method":"Somatic cell hybrid panel mapping; Southern blot analysis; genomic clone characterization","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct genomic and chromosomal mapping with functional discrimination from FPR1, single lab but multiple methods","pmids":["1612600"],"is_preprint":false},{"year":1999,"finding":"Mouse Fpr2 (Fpr-rs2) functions as a low-affinity N-formylpeptide receptor in neutrophils; transfected HEK293 cells expressing Fpr2 responded to fMLF with calcium flux and chemotaxis at EC50 ~5 µM (~100-fold higher than FPR1). Neutrophils from FPR1-knockout mice retained only the high-concentration chemotaxis optimum, consistent with Fpr2 mediating the low-affinity/high-concentration response.","method":"Stable transfection of HEK293 cells; calcium flux assay; chemotaxis assay; FPR knockout mouse neutrophils","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional reconstitution in transfected cells corroborated by knockout mouse neutrophil data, two orthogonal methods","pmids":["10477558"],"is_preprint":false},{"year":1999,"finding":"The HIV-1 gp120-derived F peptide (residues 414–434) uses FPRL1/FPR2 as a functional receptor to induce chemotaxis and calcium mobilization in monocytes and neutrophils; activation of FPRL1 by F peptide led to PKC-dependent downregulation of CCR5 and CXCR4 surface expression.","method":"Transfection of receptor cDNAs; calcium mobilization assay; cross-desensitization experiments; flow cytometry; PKC inhibitor studies","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Moderate — transfected cell functional assays plus mechanistic dissection of downstream PKC pathway, single lab with multiple orthogonal methods","pmids":["10438703"],"is_preprint":false},{"year":2002,"finding":"A soluble cleaved form of urokinase receptor (uPAR), D2D3(88-274), directly binds FPRL1/FPR2 and induces chemotaxis through this receptor. D2D3(88-274) competed for receptor binding with the synthetic agonist MMK-1 and a stable LXA4 analog. FPRL1/FPR2 is sufficient for D2D3-induced migration, whereas uPAR is required for uPA-induced chemotaxis. Receptor desensitization abolished downstream Hck tyrosine kinase activation.","method":"Direct binding competition assay; antibody inhibition; receptor desensitization; chemotaxis assay in THP-1 cells and human monocytes; kinase phosphorylation assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding demonstrated by competition, functional rescue and inhibition in primary cells, multiple orthogonal methods","pmids":["11818541"],"is_preprint":false},{"year":2002,"finding":"Serum amyloid A (SAA) activates FPR2/FPRL1 (a Gi-coupled receptor) to induce IL-8 secretion in neutrophils via NF-κB, ERK1/2 and p38 MAPK. Pertussis toxin blocked IL-8 secretion; overexpression of FPRL1 in HeLa cells enhanced SAA-induced NF-κB and IL-8 reporter activity; anti-FPRL1 N-terminal antibody inhibited secretion.","method":"Overexpression in HeLa cells; luciferase reporter assay; pertussis toxin block; calcium mobilization; MAP kinase activation assays; antibody inhibition","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function transfection, pertussis toxin Gi pathway confirmation, antibody inhibition, and downstream kinase assays in single study with multiple orthogonal approaches","pmids":["12393391"],"is_preprint":false},{"year":2002,"finding":"TNF-α upregulates FPR2 expression in mouse microglial cells via the p55 TNF-α receptor and p38 MAP kinase, converting resting microglia (low FPR2, unresponsive) into cells that chemotax toward Aβ42 and other FPR2-specific agonists.","method":"Gene expression analysis; chemotaxis assay; calcium mobilization; p38 inhibitor studies; p55 receptor-deficient cells","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional receptor upregulation linked to p38/p55 pathway with multiple assays, single lab","pmids":["12270697"],"is_preprint":false},{"year":2007,"finding":"F2L (acetylated N-terminal peptide of heme-binding protein) is a specific functional ligand for mouse Fpr2, activating calcium flux and chemotaxis with EC50 ~400–500 nM in Fpr2-transfected cells and in wild-type mouse neutrophils; Fpr2-knockout neutrophils failed to respond to F2L.","method":"Transfection of mouse FPR family members; calcium flux assay; cAMP inhibition assay; chemotaxis assay; Fpr2-knockout mouse neutrophils","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — receptor transfection combined with knockout validation, multiple functional assays, receptor specificity established across FPR family","pmids":["17237393"],"is_preprint":false},{"year":2010,"finding":"PKC-dependent internalization of FPR2/ALX is required for LXA4- and Ac2-26-stimulated phagocytosis of apoptotic neutrophils by macrophages. Bone marrow macrophages from Fpr2-knockout mice failed to increase phagocytosis in response to LXA4 or Ac2-26, demonstrating a nonredundant role for this receptor.","method":"HA-tagged receptor transfection; immunofluorescent confocal microscopy; immunogold cryo-section labeling; ELISA; bone marrow macrophages from Fpr2-/- mice; phagocytosis assay","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple imaging modalities combined with genetic knockout validation and functional phagocytosis readout","pmids":["20570963"],"is_preprint":false},{"year":2011,"finding":"FPR2/ALX undergoes agonist-dependent hierarchical phosphorylation at Ser329, Thr332, and Thr335, which is essential for receptor desensitization. Unlike FPR3, FPR2/ALX is distributed evenly at the plasma membrane in unstimulated cells. Domain-swap experiments showed the N-terminal/first TM domain governs cell surface versus intracellular localization.","method":"Site-directed mutagenesis; chimeric receptor domain swaps; phosphorylation assays; receptor antibody uptake/internalization assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of specific phosphorylation sites combined with domain-swap chimeras defining structural determinants, single lab but multiple orthogonal methods","pmids":["21543323"],"is_preprint":false},{"year":2011,"finding":"The antimicrobial peptide LL-37 signals through FPR2/ALX to promote LTB4 production from neutrophils via p38 MAP kinase and cPLA2 phosphorylation, establishing a proinflammatory LL-37/LTB4 circuit. LXA4, a known FPR2/ALX ligand, was unable to stimulate LTB4 release at tested concentrations.","method":"Calcium mobilization assay; LTB4 release measurement; p38 and cPLA2 phosphorylation assays; pharmacological inhibitors; FPR2-transfected cell lines","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — FPR2-transfected cells and signaling pathway dissection, single lab","pmids":["21307335"],"is_preprint":false},{"year":2012,"finding":"AnxA1 interacts with FPR2/ALX through its N-terminal region and extracellular loop II. Chimeric FPR1/FPR2 clones identified these domains as required for AnxA1-mediated signaling; genomic responses showed domain-specific effects (N-terminal for JAG1 and JAM3 induction; dispensable for SGPP2 modulation). SAA responses depended on extracellular loops I and II; small molecule compound 43 acted via extracellular loop I with signaling through TM region II.","method":"Chimeric receptor stably transfected in HEK293 cells; genomic response profiling; desensitization experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chimeric receptor mutagenesis approach systematically maps functional domains for multiple distinct ligands, single lab with rigorous controls","pmids":["22610094"],"is_preprint":false},{"year":2012,"finding":"The Sp1 transcription factor binds the core FPR2/ALX promoter and is required for maximal promoter activity. DNA methylation suppresses promoter activity. LXA4 enhances FPR2/ALX promoter activity and mRNA expression. A heritable A/G single nucleotide mutation in the core promoter reduces promoter activity 35–90% and reduces FPR2/ALX mRNA and protein in neutrophils from carriers.","method":"Chromatin immunoprecipitation; site-directed mutagenesis; Sp1 overexpression; luciferase reporter assay; DNA methylation analysis; quantitative PCR and Western blot in primary neutrophils","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — ChIP, mutagenesis, and reporter assay converge on Sp1 mechanism, validated in human primary cells with natural variant","pmids":["22131270"],"is_preprint":false},{"year":2013,"finding":"FPR2/ALX (ALX) exists as constitutive homo- and heterodimers with FPR1 or FPR3. AnxA1, but not SAA, selectively activates ALX homodimers, generating a p38/MK2/HSP27 signaling signature leading to IL-10 production. ALX/FPR1 heterodimerization activated by panagonist Ac2-26 triggers a JNK-mediated pro-apoptotic pathway in neutrophils.","method":"Coimmunoprecipitation; bioluminescence resonance energy transfer (BRET) in transfected HEK293 cells; signaling pathway analysis in primary monocytes and neutrophils; knockout mouse in vivo validation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — BRET and Co-IP establish constitutive dimerization; multiple downstream signaling assays; validated in primary cells and knockout mice in multiple orthogonal approaches","pmids":["24108355"],"is_preprint":false},{"year":2013,"finding":"FPR2 pepducin F2Pal10 (derived from the third intracellular loop) is a biased FPR2 agonist that activates PLC-PIP2-Ca2+ signaling and NADPH oxidase but does NOT recruit β-arrestin. Lack of β-arrestin recruitment was associated with reduced receptor internalization rate and impaired neutrophil chemotaxis, while receptor desensitization occurred independently of β-arrestin.","method":"Neutrophil functional assays; calcium flux; NADPH oxidase activation; β-arrestin recruitment assay; receptor internalization assay; chemotaxis assay; cytoskeleton disruption experiments","journal":"Biochemical pharmacology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — biased signaling dissected with multiple functional readouts linking β-arrestin recruitment specifically to chemotaxis and internalization rate, single lab, multiple orthogonal methods","pmids":["28855087"],"is_preprint":false},{"year":2013,"finding":"Pepducins with the sequence of the third intracellular loop of FPR2 (F2Pal16, F2Pal10) activate FPR2 via an allosteric inside-in mechanism. Replacing FPR2-specific K231 with FPR1-specific Q231 abolished pepducin activity. FPR2 and FPR1 differ fundamentally in sensitivity to third intracellular loop pepducins, and the same downstream signaling pathways are activated whether initiation is outside-in or inside-in.","method":"Neutrophil activation assays (superoxide, calcium); transfected cell lines; FPR2 antagonist competition; amino acid substitution mutagenesis of pepducin and receptor","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of both pepducin and receptor plus pharmacological validation, single lab with multiple orthogonal methods","pmids":["23562731"],"is_preprint":false},{"year":2013,"finding":"WKYMVm (FPR2 agonist) induces transphosphorylation of c-Met (at Y1313/Y1349/Y1356) and activates STAT3, PLC-γ1/PKCα, and PI3K/Akt pathways in prostate epithelial cells; NADPH oxidase-dependent superoxide generation is critical for c-Met transactivation, as NADPH oxidase blockade prevents c-Met phosphorylation and downstream signaling.","method":"Western blot phosphorylation assays; NADPH oxidase inhibitor studies; FPR2 agonist/antagonist pharmacology in PNT1A cells","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mechanistic pathway dissection with inhibitors and specific agonist, single lab","pmids":["23583448"],"is_preprint":false},{"year":2013,"finding":"Heterologously expressed human and murine FPR2/ALX do NOT respond to lipoxin A4 (LXA4) in calcium flux, ERK phosphorylation, cAMP reduction, or β-arrestin translocation assays, whereas the peptide agonist WKYMVM activates the same cells, raising questions about the molecular mechanism of LXA4 action.","method":"Heterologous expression in cell lines; calcium flux; ERK phosphorylation; cAMP assay; β-arrestin translocation assay; multiple LXA4 sources and analogs tested","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic negative result across multiple signaling readouts and receptor orthologues, single lab; note contradiction with multiple other studies using endogenous/native receptor systems","pmids":["23643932"],"is_preprint":false},{"year":2014,"finding":"FPR2/ALX agonist-stimulated receptor undergoes β-arrestin-mediated endocytosis followed by rapid recycling to the plasma membrane via a C-terminal recycling sequence. Deletion of this recycling sequence alters endocytic fate and evokes pro-apoptotic effects upon agonist activation, linking receptor recycling to cell survival.","method":"Receptor trafficking assays; β-arrestin recruitment assays; C-terminal truncation/recycling sequence mutagenesis; apoptosis assays in transfected cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis identifying transplantable recycling sequence plus functional consequence (apoptosis), single lab with multiple orthogonal methods","pmids":["25326384"],"is_preprint":false},{"year":2014,"finding":"Mouse Fpr2 is required for normal DC maturation: Fpr2-/- DCs failed to upregulate maturation markers, produce IL-12, chemotax toward CCL21, or stimulate allogeneic T-cell proliferation in response to LPS. This maturation defect depends on autocrine CRAMP (cathelicidin) signaling through Fpr2, as neutralization of either Fpr2 or CRAMP inhibited maturation.","method":"Bone marrow DC culture from Fpr2-/- and CRAMP-/- mice; flow cytometry; ELISA; T-cell proliferation assay; neutralizing antibodies; in vivo antigen immunization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mice combined with neutralizing antibody experiments and in vitro/in vivo corroboration, multiple orthogonal readouts","pmids":["24808174"],"is_preprint":false},{"year":2014,"finding":"In allergic airway inflammation, CCR2 mediates monocyte-derived DC recruitment to the perivascular region while Fpr2 is required for further migration into bronchiolar areas. The endogenous Fpr2 ligand CRAMP is present in bronchoalveolar lavage during inflammation, and CRAMP-/- mice phenocopy Fpr2-/- mice in reduced peribronchiolar DC trafficking.","method":"Allergic airway inflammation mouse model; intravital imaging; flow cytometry; CRAMP-/- and Fpr2-/- mice; lavage fluid ligand analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with two independent knockout strains converging on same trafficking defect, endogenous ligand identification","pmids":["23603910"],"is_preprint":false},{"year":2014,"finding":"miR-181b directly binds the 3'-UTR of ALX/FPR2 mRNA (confirmed by luciferase reporter) and downregulates FPR2 protein; miR-181b overexpression reduces FPR2 protein ~25% and blunts LXA4- and RvD1-stimulated phagocytosis in macrophages. miR-181b levels decrease during monocyte-to-macrophage differentiation, inversely correlating with FPR2 upregulation.","method":"Luciferase reporter assay with 3'-UTR; miR-181b overexpression and knockdown; Western blot; phagocytosis assay in human macrophages","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — 3'-UTR luciferase reporter confirms direct miRNA binding; functional consequence shown in primary macrophages with overexpression and knockdown, single lab with multiple methods","pmids":["25250540"],"is_preprint":false},{"year":2015,"finding":"Annexin A1 secreted by skeletal myotubes activates FPR2 to protect against palmitate-induced insulin resistance; annexin A1 levels decrease with palmitate treatment. FPR2 agonist treatment improved systemic insulin sensitivity in high-fat diet mice, and the protective effect involved PKC-θ modulation.","method":"Quantitative proteomics of myotube secretome; annexin A1/FPR2 agonist treatment of L6 myotubes; PKC-θ phosphorylation assay; in vivo insulin tolerance test in HFD mice","journal":"Molecular & cellular proteomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — proteomic discovery combined with functional cell assays and in vivo validation, single lab","pmids":["25616869"],"is_preprint":false},{"year":2016,"finding":"LXA4 activates ALX/FPR2 in conjunctival goblet cells to increase mucin secretion and intracellular Ca2+ via sequential activation of phospholipases C, D, and A2, PKC, ERK1/2, and CaM kinase. ALX/FPR2 inhibitors blocked these responses. Sequential application of LXA4 then RvD1 (or vice versa) demonstrated heterologous desensitization between the two agonists at the same receptor.","method":"ALX/FPR2 immunolocalization; mucin secretion assay; calcium imaging; pharmacological inhibitors of ALX/FPR2 and downstream kinases; sequential agonist desensitization experiments","journal":"Mucosal immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — receptor localization plus systematic pharmacological pathway dissection, single lab, multiple orthogonal signaling readouts","pmids":["27072607"],"is_preprint":false},{"year":2019,"finding":"Staphylococcal PSMα peptides activate neutrophil FPR2 to increase intracellular Ca2+, ERK1/2 phosphorylation, NADPH oxidase activity, and receptor internalization, but CANNOT recruit β-arrestin or induce neutrophil chemotaxis. Structure-activity analysis with PSMα2 derivatives identified the first 3 residues linked to N-fMet and the C-terminus as critical for β-arrestin recruitment.","method":"Neutrophil calcium flux; NADPH oxidase assay; β-arrestin recruitment assay; ERK phosphorylation; chemotaxis assay; internalization assay; PSMα2 derivative SAR analysis","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic SAR plus multiple functional readouts establishing biased agonism, consistent with prior β-arrestin/chemotaxis findings, single lab multiple orthogonal methods","pmids":["31694908"],"is_preprint":false},{"year":2020,"finding":"β-Arrestin-independent FPR2 endocytosis occurs in β-arrestin-deficient cells (albeit at reduced levels), demonstrated using Barbadin (AP2/β-arrestin interaction blocker) which inhibited AP2/β-arrestin interaction but did NOT inhibit FPR2 endocytosis. Barbadin selectively potentiated FPR2-mediated ROS production independently of β-arrestin recruitment and receptor endocytosis, suggesting AP2 regulates FPR2-mediated ROS release.","method":"Barbadin pharmacology; β-arrestin-deficient cells; FPR2 internalization assay; NADPH oxidase ROS assay; chemotaxis assay; AP2/β-arrestin interaction assay","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic (β-arrestin KO cells) and pharmacological dissection with multiple functional readouts, single lab, multiple orthogonal methods","pmids":["32916203"],"is_preprint":false},{"year":2020,"finding":"RvD1 binding to ALX/FPR2 on macrophages induces a transcriptional program characteristic of pro-revascularization phenotype (identified by RNA-seq). Myeloid-specific Fpr2 deficiency impairs perfusion recovery and vascularization in ischemic skeletal muscle and cutaneous wounds, associated with altered expression of pro-revascularization genes.","method":"RNA sequencing of RvD1-treated macrophages; hindlimb ischemia model; myeloid-specific Alx/Fpr2 knockout mice; perfusion imaging; wound healing assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — RNA-seq transcriptional mechanism combined with tissue-specific knockout in two independent in vivo models, single lab with multiple orthogonal approaches","pmids":["32513697"],"is_preprint":false},{"year":2020,"finding":"Fpr2 directly interacts with TAK1 kinase (demonstrated by co-immunoprecipitation), and Fpr2 inhibition reduces LPS-induced TAK1 activation; this interaction promotes NF-κB and MAPK signaling and oxidative stress in macrophages. Fpr2 knockout activates Nrf2 and increases antioxidant enzymes, suggesting Nrf2 is partially downstream of Fpr2-TAK1 regulation.","method":"Co-immunoprecipitation; Fpr2 knockout mice; Fpr2 overexpression; LPS stimulation; NF-κB and MAPK Western blots; oxidative stress assays","journal":"Biomedicine & pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus knockout/overexpression functional data, single lab, Co-IP alone is lower tier but multiple supporting methods","pmids":["32106380"],"is_preprint":false},{"year":2021,"finding":"FPR2 activation by WKYMVm and annexin A1 (ANXA1) leads to NADPH oxidase-dependent phosphorylation of HSP27 (Ser82), OSR1 (Ser339), and MARCKS (Ser170) via upstream kinases p38MAPK, PI3K, and PKCδ respectively; NADPH oxidase inhibition or p22phox CRISPR knockout prevents all these phosphorylation events, placing NADPH oxidase upstream of these kinase cascades.","method":"Phosphorylation assays with site-specific antibodies; NADPH oxidase inhibitors; p22phox CRISPR/Cas9 double nickase knockout cells; agonist stimulation of CaLu-6 cells","journal":"Antioxidants","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — CRISPR genetic knockout combined with pharmacological validation, single lab, multiple phosphorylation targets with specific upstream kinase assignment","pmids":["33477989"],"is_preprint":false},{"year":2022,"finding":"Cryo-EM structures of FPR2 bound to Gi and either Aβ42 or N-formyl humanin (fHN) were determined. Two critical structural regions govern recognition: a polar binding cavity within the receptor helical bundle and a hydrophobic binding groove in the extracellular region. Structures of FPR2 and FPR1 with different formyl peptides provided mechanistic insights into ligand selectivity within the FPR family.","method":"Cryo-electron microscopy structure determination; functional binding and signaling assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures at atomic resolution with functional validation, revealing structural basis of ligand recognition and selectivity","pmids":["35365641"],"is_preprint":false},{"year":2022,"finding":"PRSS22 protease binds and cleaves ANXA1 (confirmed by Co-IP, mass spectrometry, and Western blot), generating an N-terminal peptide that activates FPR2/ERK signaling to promote breast cancer cell migration and invasion.","method":"Protein mass spectrometry; co-immunoprecipitation; Western blot; cell migration and invasion assays; ERK phosphorylation; in vivo xenograft","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP confirms PRSS22-ANXA1 interaction; proteolytic cleavage and downstream FPR2/ERK signaling established, single lab","pmids":["36414640"],"is_preprint":false},{"year":2025,"finding":"FPR2 is a membrane receptor that specifically binds long-chain ceramides (C14–C20). C16:0 ceramide binding to FPR2 inhibits thermogenesis in brown and beige adipocytes through Gi-cAMP signaling pathways. Three cryo-EM structures of FPR2-Gi complexes bound to C16:0, C18:0, and C20:0 ceramides were determined, showing hydrophobic tails embedded in the orthosteric pocket. Modification of the ceramide-binding motif in FPR1 or FPR3 converts them from inactive to active ceramide receptors.","method":"Cryo-EM structure determination of FPR2-Gi-ceramide complexes; Gi-cAMP signaling assay; thermogenesis assay in brown/beige adipocytes; FPR2 knockout cells; mutagenesis converting FPR1/FPR3 to ceramide receptors","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple cryo-EM structures combined with functional assays and mutagenesis in native cell contexts; multiple ceramide species characterized","pmids":["40080544"],"is_preprint":false}],"current_model":"FPR2 (ALX/FPRL1) is a promiscuous Gi-coupled G-protein-coupled receptor that adopts ligand-specific conformations, exists as constitutive homo- and heterodimers with FPR1/FPR3, and signals through PLC/PKC/MAPK, PI3K/Akt, NADPH oxidase, and β-arrestin pathways to mediate chemotaxis, phagocytosis, and inflammatory resolution; its orthosteric pocket accommodates structurally diverse ligands including formyl peptides, annexin A1 (via the N-terminal domain and extracellular loop II), serum amyloid A (via extracellular loops I–II), Aβ42/humanin (cryo-EM defined polar cavity and hydrophobic groove), and long-chain ceramides (cryo-EM-defined orthosteric hydrophobic pocket inhibiting thermogenesis via Gi-cAMP), while β-arrestin recruitment governs chemotaxis and receptor recycling, and a C-terminal recycling sequence controls endocytic fate and anti-apoptotic signaling."},"narrative":{"mechanistic_narrative":"FPR2 (ALX/FPRL1) is a Gi-coupled G-protein-coupled receptor that orchestrates leukocyte chemotaxis, phagocytosis, and inflammatory responses by sensing a structurally diverse panel of ligands through a promiscuous orthosteric pocket [PMID:10477558, PMID:17237393, PMID:35365641]. First identified as a structural homologue of the FMLP receptor FPR1 that does not recognize FMLP [PMID:1612600], it was reconstituted as a low-affinity N-formylpeptide receptor mediating high-concentration neutrophil chemotaxis [PMID:10477558]. The receptor responds to host-derived agonists including serum amyloid A [PMID:12393391], the cleaved urokinase receptor fragment D2D3 [PMID:11818541], the antimicrobial peptide LL-37/CRAMP [PMID:21307335, PMID:24808174], annexin A1 [PMID:22610094, PMID:25616869], and the heme-binding protein peptide F2L [PMID:17237393], as well as pathogen-derived ligands such as HIV-1 gp120 F peptide [PMID:10438703] and staphylococcal PSMα peptides [PMID:31694908]; cryo-EM structures define a polar binding cavity and hydrophobic extracellular groove governing recognition of Aβ42 and formyl humanin [PMID:35365641] and an orthosteric hydrophobic pocket accommodating long-chain ceramides that suppress adipocyte thermogenesis through Gi-cAMP signaling [PMID:40080544]. Distinct ligands engage separable receptor surfaces and oligomeric states: annexin A1 binds the N-terminal region and extracellular loop II while SAA depends on extracellular loops I–II [PMID:22610094], and annexin A1 selectively activates ALX homodimers to drive p38/MK2/HSP27-IL-10 signaling whereas ALX/FPR1 heterodimers triggered by panagonists evoke JNK-dependent neutrophil apoptosis [PMID:24108355]. Downstream, FPR2 signals through PLC/PKC/Ca2+, ERK/p38 MAPK, PI3K/Akt, and NADPH oxidase, with NADPH oxidase positioned upstream of HSP27, OSR1, and MARCKS phosphorylation [PMID:33477989] and required for c-Met transactivation [PMID:23583448]. β-arrestin recruitment, dissociable from G-protein signaling by biased pepducin and PSMα agonists, specifically governs chemotaxis and receptor internalization rate while desensitization proceeds independently [PMID:28855087, PMID:31694908], and a C-terminal recycling sequence controls endocytic fate and anti-apoptotic survival signaling [PMID:25326384]. Receptor abundance is set transcriptionally by Sp1 and promoter methylation [PMID:22131270] and post-transcriptionally by miR-181b [PMID:25250540]. Through these mechanisms FPR2 mediates dendritic cell maturation and trafficking [PMID:24808174, PMID:23603910], macrophage clearance of apoptotic neutrophils [PMID:20570963], and pro-revascularization macrophage programming [PMID:32513697].","teleology":[{"year":1992,"claim":"Establishing that an FPR1-homologous gene existed but did not recognize FMLP raised the question of what an orphan formyl peptide receptor homologue actually senses.","evidence":"Genomic clone characterization and somatic cell hybrid chromosomal mapping","pmids":["1612600"],"confidence":"Medium","gaps":["No functional ligand identified","No signaling pathway defined"]},{"year":1999,"claim":"Functional reconstitution defined FPR2 as a low-affinity formyl peptide receptor and revealed it doubles as a chemotactic receptor for the HIV-1 gp120 F peptide, establishing ligand promiscuity from the outset.","evidence":"Stable HEK293 transfection with calcium flux and chemotaxis assays, FPR1-knockout mouse neutrophils, and cross-desensitization studies","pmids":["10477558","10438703"],"confidence":"High","gaps":["Endogenous physiological ligands not yet defined","Structural basis of ligand recognition unknown","Whether high-concentration formyl peptide response is physiologically relevant unclear"]},{"year":2002,"claim":"Identification of serum amyloid A, the cleaved uPAR fragment, and a TNF-α-inducible role in microglia expanded FPR2 into a broadly responsive inflammatory receptor with defined Gi/MAPK/NF-κB output.","evidence":"HeLa overexpression with reporter and pertussis toxin assays, direct binding competition in monocytes, and microglial chemotaxis with p38 inhibitors","pmids":["12393391","11818541","12270697"],"confidence":"High","gaps":["Receptor domains engaging each ligand not mapped","Relationship among the diverse ligands at one pocket unresolved"]},{"year":2007,"claim":"F2L identification with knockout validation cemented receptor-specific endogenous agonism within the FPR family.","evidence":"Transfection across mouse FPR family members plus Fpr2-knockout neutrophil calcium and chemotaxis assays","pmids":["17237393"],"confidence":"High","gaps":["Human receptor binding mode for F2L not structurally defined"]},{"year":2011,"claim":"Defining hierarchical C-terminal phosphorylation sites and N-terminal/TM determinants of localization, plus LL-37 as a proinflammatory agonist, began separating receptor regulation from agonist-specific output.","evidence":"Site-directed mutagenesis, chimeric domain swaps, and phosphorylation/internalization assays; LL-37-driven LTB4 release with p38 and cPLA2 readouts","pmids":["21543323","21307335"],"confidence":"High","gaps":["Kinase responsible for site-specific phosphorylation not identified","How distinct agonists produce divergent outputs unresolved"]},{"year":2012,"claim":"Chimeric mapping assigned distinct ligands to distinct receptor surfaces, and promoter analysis established Sp1/methylation control of FPR2 abundance with a functional human variant.","evidence":"Chimeric FPR1/FPR2 receptors with genomic response profiling; ChIP, reporter assays, and primary neutrophil genotyping","pmids":["22610094","22131270"],"confidence":"High","gaps":["Atomic-resolution ligand contacts not yet resolved","Physiological consequences of the promoter variant not established"]},{"year":2013,"claim":"Discovery of constitutive homo- and heterodimers with FPR1/FPR3 and of biased pepducin agonism explained how a single receptor encodes opposing pro-resolving versus pro-apoptotic outcomes, while a negative LXA4 result flagged uncertainty about lipoxin action.","evidence":"BRET and Co-IP dimerization assays with primary cell signaling and knockout mice; intracellular-loop pepducins with receptor/pepducin mutagenesis and β-arrestin recruitment assays; systematic LXA4 signaling assays across orthologues","pmids":["24108355","28855087","23562731","23583448","23643932"],"confidence":"High","gaps":["Molecular mechanism of LXA4 action in heterologous systems unresolved","Structural basis of dimer-selective signaling unknown","How β-arrestin recruitment is selectively decoupled by biased agonists not structurally defined"]},{"year":2014,"claim":"Trafficking, transcriptional, and in vivo immune studies linked receptor recycling to survival, miR-181b to receptor abundance, and CRAMP-Fpr2 signaling to dendritic cell maturation and tissue trafficking.","evidence":"C-terminal recycling-sequence mutagenesis with apoptosis assays; 3'-UTR luciferase reporter with macrophage phagocytosis; Fpr2-/- and CRAMP-/- mice in dendritic cell and allergic airway models","pmids":["25326384","25250540","24808174","23603910"],"confidence":"High","gaps":["Recycling-machinery components not identified","How recycling failure triggers apoptosis mechanistically unclear"]},{"year":2015,"claim":"An annexin A1-FPR2 axis in skeletal muscle extended receptor function to metabolic protection against insulin resistance.","evidence":"Secretome proteomics, L6 myotube agonist treatment with PKC-θ assays, and insulin tolerance testing in high-fat-diet mice","pmids":["25616869"],"confidence":"Medium","gaps":["Direct receptor-level mechanism in muscle not dissected","Single-lab in vivo finding"]},{"year":2016,"claim":"Goblet cell studies defined a sequential phospholipase/kinase cascade for LXA4 and demonstrated heterologous desensitization between pro-resolving lipid mediators at FPR2.","evidence":"Receptor immunolocalization, mucin secretion and calcium imaging, and sequential LXA4/RvD1 desensitization with pathway inhibitors","pmids":["27072607"],"confidence":"Medium","gaps":["Reconciliation with negative heterologous LXA4 data unresolved","Direct LXA4 binding not demonstrated"]},{"year":2019,"claim":"Staphylococcal PSMα peptides reinforced the biased-agonism model, with structure-activity analysis pinpointing residues required for β-arrestin recruitment and chemotaxis.","evidence":"Neutrophil calcium, NADPH oxidase, ERK, β-arrestin, internalization and chemotaxis assays with PSMα2 derivative SAR","pmids":["31694908"],"confidence":"High","gaps":["Structural basis for β-arrestin-biased versus balanced agonism not resolved at atomic level"]},{"year":2020,"claim":"Genetic and pharmacological dissection separated β-arrestin-independent endocytosis and AP2-regulated ROS from canonical signaling, and identified a direct Fpr2-TAK1 interaction plus an RvD1-driven pro-revascularization macrophage program.","evidence":"Barbadin pharmacology in β-arrestin-deficient cells with internalization/ROS assays; Co-IP of Fpr2 with TAK1 in knockout/overexpression macrophages; macrophage RNA-seq with myeloid-specific Fpr2 knockout in ischemia and wound models","pmids":["32916203","32106380","32513697"],"confidence":"High","gaps":["TAK1 interaction rests on single Co-IP without reciprocal structural validation","How AP2 regulates ROS independently of endocytosis unclear","Direct versus indirect nature of Fpr2-TAK1 binding not established"]},{"year":2022,"claim":"Cryo-EM structures of Gi-coupled FPR2 bound to Aβ42 and formyl humanin provided the first atomic basis for ligand recognition and FPR-family selectivity, and a PRSS22 protease was shown to generate an FPR2-activating annexin A1 fragment in breast cancer.","evidence":"Cryo-EM of FPR2-Gi-ligand complexes with functional validation; mass spectrometry, Co-IP and migration/invasion assays for PRSS22-ANXA1 cleavage","pmids":["35365641","36414640"],"confidence":"High","gaps":["Structures of peptide-only agonists do not capture lipid or protein ligand binding modes","PRSS22-ANXA1 axis is single-lab Medium-confidence"]},{"year":2025,"claim":"Discovery that FPR2 is a long-chain ceramide receptor suppressing thermogenesis via Gi-cAMP, with cryo-EM-defined orthosteric lipid binding, established a metabolic sensing function and the structural determinant convertible to FPR1/FPR3.","evidence":"Three cryo-EM FPR2-Gi-ceramide structures, Gi-cAMP and thermogenesis assays in adipocytes, knockout cells, and gain-of-function mutagenesis of FPR1/FPR3","pmids":["40080544"],"confidence":"High","gaps":["Physiological source of FPR2-activating ceramides in vivo not defined","Integration of lipid sensing with peptide-driven inflammatory signaling unresolved"]},{"year":null,"claim":"How a single orthosteric architecture reconciles diverse agonists (formyl peptides, annexin A1, SAA, ceramides) into ligand-, dimer-, and arrestin-biased outputs, and how LXA4 signaling proceeds given negative heterologous results, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model linking biased agonism to specific conformations","Mechanism of LXA4 action still contested between native and heterologous systems"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,4,6,28]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[30]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13,23]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[8,17]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[17,24]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,12,27]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,18,19,25]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[13,17,24]}],"complexes":["FPR2 homodimer","ALX/FPR1 heterodimer","FPR2-Gi complex"],"partners":["FPR1","FPR3","ANXA1","TAK1","GNAI1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P25090","full_name":"N-formyl peptide receptor 2","aliases":["FMLP-related receptor I","FMLP-R-I","Formyl peptide receptor-like 1","HM63","Lipoxin A4 receptor","ALX","LXA4 receptor","RFP"],"length_aa":351,"mass_kda":39.0,"function":"Pattern recognition G protein-coupled receptor (GPCR) that recognizes peptides with N-terminal formyl methionine, which are derived from invading pathogens or host mitochondria as pathogen or damage-associated molecular patterns (PAMPs and DAMPs) (PubMed:1374236, PubMed:25605714, PubMed:35217703). Preferentially recognizes longer peptides or peptides with specific sequences such as the phenol-soluble modulin (PSM) family of formylated peptide toxins produced by Staphylococcus aureus (PubMed:30098280). Ligand binding causes a conformation change that triggers signaling via G(i)/GNAI1 inhibiting adenylate cyclase activity, leading to decreased intracellular cAMP levels (PubMed:40080544). In addition, can recognize a variety of chemically distinct endogenous ligands including proteins and lipids besides formylpeptides and thereby plays multiple roles in inflammation. Acts as a receptor for the chemokine-like protein FAM19A5, mediating FAM19A5-stimulated macrophage chemotaxis and the inhibitory effect on TNFSF11/RANKL-induced osteoclast differentiation (By similarity). Acts also as a ceramide membrane receptor, and long-chain ceramides (C14 to C20) binding induces conformational changes that inhibits diet-induced adipose thermogenesis (PubMed:40080544). Participates in neuroprotection via interaction with humanin/MT-RNR2 and Amyloid-beta protein 42, product of APP (PubMed:11689470, PubMed:35365641). Differential signaling is also defined by receptor oligomerization state. Binding of ANXA1 to FPR2 homodimer elicits activation of p38 MAPKinase pathway leading to HSPB1/HSP27 phosphorylation and IL10 production in monocytes. Whereas agonistic activation of FPR1:FPR2 heterodimers signals a proapoptotic JNK pathway in neutrophils","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/P25090/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FPR2","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/FPR2","total_profiled":1310},"omim":[{"mim_id":"605826","title":"HEME-BINDING PROTEIN 1; HEBP1","url":"https://www.omim.org/entry/605826"},{"mim_id":"136539","title":"FORMYL PEPTIDE RECEPTOR 3; FPR3","url":"https://www.omim.org/entry/136539"},{"mim_id":"136538","title":"FORMYL PEPTIDE RECEPTOR 2; FPR2","url":"https://www.omim.org/entry/136538"},{"mim_id":"136537","title":"FORMYL PEPTIDE RECEPTOR 1; FPR1","url":"https://www.omim.org/entry/136537"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"lymphoid tissue","ntpm":52.9}],"url":"https://www.proteinatlas.org/search/FPR2"},"hgnc":{"alias_symbol":["LXA4R","HM63","FPRH2","FMLPX","FPR2A","FMLP-R-II","ALXR","ALX"],"prev_symbol":["FPRL1"]},"alphafold":{"accession":"P25090","domains":[{"cath_id":"1.20.1070.10","chopping":"20-180_205-262_279-324","consensus_level":"high","plddt":91.9101,"start":20,"end":324}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P25090","model_url":"https://alphafold.ebi.ac.uk/files/AF-P25090-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P25090-F1-predicted_aligned_error_v6.png","plddt_mean":84.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FPR2","jax_strain_url":"https://www.jax.org/strain/search?query=FPR2"},"sequence":{"accession":"P25090","fasta_url":"https://rest.uniprot.org/uniprotkb/P25090.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P25090/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P25090"}},"corpus_meta":[{"pmid":"11818541","id":"PMC_11818541","title":"The 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Neutrophils from FPR1-knockout mice retained only the high-concentration chemotaxis optimum, consistent with Fpr2 mediating the low-affinity/high-concentration response.\",\n      \"method\": \"Stable transfection of HEK293 cells; calcium flux assay; chemotaxis assay; FPR knockout mouse neutrophils\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional reconstitution in transfected cells corroborated by knockout mouse neutrophil data, two orthogonal methods\",\n      \"pmids\": [\"10477558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The HIV-1 gp120-derived F peptide (residues 414–434) uses FPRL1/FPR2 as a functional receptor to induce chemotaxis and calcium mobilization in monocytes and neutrophils; activation of FPRL1 by F peptide led to PKC-dependent downregulation of CCR5 and CXCR4 surface expression.\",\n      \"method\": \"Transfection of receptor cDNAs; calcium mobilization assay; cross-desensitization experiments; flow cytometry; PKC inhibitor studies\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transfected cell functional assays plus mechanistic dissection of downstream PKC pathway, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"10438703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A soluble cleaved form of urokinase receptor (uPAR), D2D3(88-274), directly binds FPRL1/FPR2 and induces chemotaxis through this receptor. D2D3(88-274) competed for receptor binding with the synthetic agonist MMK-1 and a stable LXA4 analog. FPRL1/FPR2 is sufficient for D2D3-induced migration, whereas uPAR is required for uPA-induced chemotaxis. Receptor desensitization abolished downstream Hck tyrosine kinase activation.\",\n      \"method\": \"Direct binding competition assay; antibody inhibition; receptor desensitization; chemotaxis assay in THP-1 cells and human monocytes; kinase phosphorylation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding demonstrated by competition, functional rescue and inhibition in primary cells, multiple orthogonal methods\",\n      \"pmids\": [\"11818541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Serum amyloid A (SAA) activates FPR2/FPRL1 (a Gi-coupled receptor) to induce IL-8 secretion in neutrophils via NF-κB, ERK1/2 and p38 MAPK. Pertussis toxin blocked IL-8 secretion; overexpression of FPRL1 in HeLa cells enhanced SAA-induced NF-κB and IL-8 reporter activity; anti-FPRL1 N-terminal antibody inhibited secretion.\",\n      \"method\": \"Overexpression in HeLa cells; luciferase reporter assay; pertussis toxin block; calcium mobilization; MAP kinase activation assays; antibody inhibition\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function transfection, pertussis toxin Gi pathway confirmation, antibody inhibition, and downstream kinase assays in single study with multiple orthogonal approaches\",\n      \"pmids\": [\"12393391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"TNF-α upregulates FPR2 expression in mouse microglial cells via the p55 TNF-α receptor and p38 MAP kinase, converting resting microglia (low FPR2, unresponsive) into cells that chemotax toward Aβ42 and other FPR2-specific agonists.\",\n      \"method\": \"Gene expression analysis; chemotaxis assay; calcium mobilization; p38 inhibitor studies; p55 receptor-deficient cells\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional receptor upregulation linked to p38/p55 pathway with multiple assays, single lab\",\n      \"pmids\": [\"12270697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"F2L (acetylated N-terminal peptide of heme-binding protein) is a specific functional ligand for mouse Fpr2, activating calcium flux and chemotaxis with EC50 ~400–500 nM in Fpr2-transfected cells and in wild-type mouse neutrophils; Fpr2-knockout neutrophils failed to respond to F2L.\",\n      \"method\": \"Transfection of mouse FPR family members; calcium flux assay; cAMP inhibition assay; chemotaxis assay; Fpr2-knockout mouse neutrophils\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — receptor transfection combined with knockout validation, multiple functional assays, receptor specificity established across FPR family\",\n      \"pmids\": [\"17237393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKC-dependent internalization of FPR2/ALX is required for LXA4- and Ac2-26-stimulated phagocytosis of apoptotic neutrophils by macrophages. Bone marrow macrophages from Fpr2-knockout mice failed to increase phagocytosis in response to LXA4 or Ac2-26, demonstrating a nonredundant role for this receptor.\",\n      \"method\": \"HA-tagged receptor transfection; immunofluorescent confocal microscopy; immunogold cryo-section labeling; ELISA; bone marrow macrophages from Fpr2-/- mice; phagocytosis assay\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple imaging modalities combined with genetic knockout validation and functional phagocytosis readout\",\n      \"pmids\": [\"20570963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"FPR2/ALX undergoes agonist-dependent hierarchical phosphorylation at Ser329, Thr332, and Thr335, which is essential for receptor desensitization. Unlike FPR3, FPR2/ALX is distributed evenly at the plasma membrane in unstimulated cells. Domain-swap experiments showed the N-terminal/first TM domain governs cell surface versus intracellular localization.\",\n      \"method\": \"Site-directed mutagenesis; chimeric receptor domain swaps; phosphorylation assays; receptor antibody uptake/internalization assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of specific phosphorylation sites combined with domain-swap chimeras defining structural determinants, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"21543323\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The antimicrobial peptide LL-37 signals through FPR2/ALX to promote LTB4 production from neutrophils via p38 MAP kinase and cPLA2 phosphorylation, establishing a proinflammatory LL-37/LTB4 circuit. LXA4, a known FPR2/ALX ligand, was unable to stimulate LTB4 release at tested concentrations.\",\n      \"method\": \"Calcium mobilization assay; LTB4 release measurement; p38 and cPLA2 phosphorylation assays; pharmacological inhibitors; FPR2-transfected cell lines\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FPR2-transfected cells and signaling pathway dissection, single lab\",\n      \"pmids\": [\"21307335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"AnxA1 interacts with FPR2/ALX through its N-terminal region and extracellular loop II. Chimeric FPR1/FPR2 clones identified these domains as required for AnxA1-mediated signaling; genomic responses showed domain-specific effects (N-terminal for JAG1 and JAM3 induction; dispensable for SGPP2 modulation). SAA responses depended on extracellular loops I and II; small molecule compound 43 acted via extracellular loop I with signaling through TM region II.\",\n      \"method\": \"Chimeric receptor stably transfected in HEK293 cells; genomic response profiling; desensitization experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chimeric receptor mutagenesis approach systematically maps functional domains for multiple distinct ligands, single lab with rigorous controls\",\n      \"pmids\": [\"22610094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The Sp1 transcription factor binds the core FPR2/ALX promoter and is required for maximal promoter activity. DNA methylation suppresses promoter activity. LXA4 enhances FPR2/ALX promoter activity and mRNA expression. A heritable A/G single nucleotide mutation in the core promoter reduces promoter activity 35–90% and reduces FPR2/ALX mRNA and protein in neutrophils from carriers.\",\n      \"method\": \"Chromatin immunoprecipitation; site-directed mutagenesis; Sp1 overexpression; luciferase reporter assay; DNA methylation analysis; quantitative PCR and Western blot in primary neutrophils\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — ChIP, mutagenesis, and reporter assay converge on Sp1 mechanism, validated in human primary cells with natural variant\",\n      \"pmids\": [\"22131270\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"FPR2/ALX (ALX) exists as constitutive homo- and heterodimers with FPR1 or FPR3. AnxA1, but not SAA, selectively activates ALX homodimers, generating a p38/MK2/HSP27 signaling signature leading to IL-10 production. ALX/FPR1 heterodimerization activated by panagonist Ac2-26 triggers a JNK-mediated pro-apoptotic pathway in neutrophils.\",\n      \"method\": \"Coimmunoprecipitation; bioluminescence resonance energy transfer (BRET) in transfected HEK293 cells; signaling pathway analysis in primary monocytes and neutrophils; knockout mouse in vivo validation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — BRET and Co-IP establish constitutive dimerization; multiple downstream signaling assays; validated in primary cells and knockout mice in multiple orthogonal approaches\",\n      \"pmids\": [\"24108355\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"FPR2 pepducin F2Pal10 (derived from the third intracellular loop) is a biased FPR2 agonist that activates PLC-PIP2-Ca2+ signaling and NADPH oxidase but does NOT recruit β-arrestin. Lack of β-arrestin recruitment was associated with reduced receptor internalization rate and impaired neutrophil chemotaxis, while receptor desensitization occurred independently of β-arrestin.\",\n      \"method\": \"Neutrophil functional assays; calcium flux; NADPH oxidase activation; β-arrestin recruitment assay; receptor internalization assay; chemotaxis assay; cytoskeleton disruption experiments\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biased signaling dissected with multiple functional readouts linking β-arrestin recruitment specifically to chemotaxis and internalization rate, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"28855087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Pepducins with the sequence of the third intracellular loop of FPR2 (F2Pal16, F2Pal10) activate FPR2 via an allosteric inside-in mechanism. Replacing FPR2-specific K231 with FPR1-specific Q231 abolished pepducin activity. FPR2 and FPR1 differ fundamentally in sensitivity to third intracellular loop pepducins, and the same downstream signaling pathways are activated whether initiation is outside-in or inside-in.\",\n      \"method\": \"Neutrophil activation assays (superoxide, calcium); transfected cell lines; FPR2 antagonist competition; amino acid substitution mutagenesis of pepducin and receptor\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of both pepducin and receptor plus pharmacological validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23562731\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"WKYMVm (FPR2 agonist) induces transphosphorylation of c-Met (at Y1313/Y1349/Y1356) and activates STAT3, PLC-γ1/PKCα, and PI3K/Akt pathways in prostate epithelial cells; NADPH oxidase-dependent superoxide generation is critical for c-Met transactivation, as NADPH oxidase blockade prevents c-Met phosphorylation and downstream signaling.\",\n      \"method\": \"Western blot phosphorylation assays; NADPH oxidase inhibitor studies; FPR2 agonist/antagonist pharmacology in PNT1A cells\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mechanistic pathway dissection with inhibitors and specific agonist, single lab\",\n      \"pmids\": [\"23583448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Heterologously expressed human and murine FPR2/ALX do NOT respond to lipoxin A4 (LXA4) in calcium flux, ERK phosphorylation, cAMP reduction, or β-arrestin translocation assays, whereas the peptide agonist WKYMVM activates the same cells, raising questions about the molecular mechanism of LXA4 action.\",\n      \"method\": \"Heterologous expression in cell lines; calcium flux; ERK phosphorylation; cAMP assay; β-arrestin translocation assay; multiple LXA4 sources and analogs tested\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic negative result across multiple signaling readouts and receptor orthologues, single lab; note contradiction with multiple other studies using endogenous/native receptor systems\",\n      \"pmids\": [\"23643932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"FPR2/ALX agonist-stimulated receptor undergoes β-arrestin-mediated endocytosis followed by rapid recycling to the plasma membrane via a C-terminal recycling sequence. Deletion of this recycling sequence alters endocytic fate and evokes pro-apoptotic effects upon agonist activation, linking receptor recycling to cell survival.\",\n      \"method\": \"Receptor trafficking assays; β-arrestin recruitment assays; C-terminal truncation/recycling sequence mutagenesis; apoptosis assays in transfected cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis identifying transplantable recycling sequence plus functional consequence (apoptosis), single lab with multiple orthogonal methods\",\n      \"pmids\": [\"25326384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mouse Fpr2 is required for normal DC maturation: Fpr2-/- DCs failed to upregulate maturation markers, produce IL-12, chemotax toward CCL21, or stimulate allogeneic T-cell proliferation in response to LPS. This maturation defect depends on autocrine CRAMP (cathelicidin) signaling through Fpr2, as neutralization of either Fpr2 or CRAMP inhibited maturation.\",\n      \"method\": \"Bone marrow DC culture from Fpr2-/- and CRAMP-/- mice; flow cytometry; ELISA; T-cell proliferation assay; neutralizing antibodies; in vivo antigen immunization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mice combined with neutralizing antibody experiments and in vitro/in vivo corroboration, multiple orthogonal readouts\",\n      \"pmids\": [\"24808174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In allergic airway inflammation, CCR2 mediates monocyte-derived DC recruitment to the perivascular region while Fpr2 is required for further migration into bronchiolar areas. The endogenous Fpr2 ligand CRAMP is present in bronchoalveolar lavage during inflammation, and CRAMP-/- mice phenocopy Fpr2-/- mice in reduced peribronchiolar DC trafficking.\",\n      \"method\": \"Allergic airway inflammation mouse model; intravital imaging; flow cytometry; CRAMP-/- and Fpr2-/- mice; lavage fluid ligand analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with two independent knockout strains converging on same trafficking defect, endogenous ligand identification\",\n      \"pmids\": [\"23603910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"miR-181b directly binds the 3'-UTR of ALX/FPR2 mRNA (confirmed by luciferase reporter) and downregulates FPR2 protein; miR-181b overexpression reduces FPR2 protein ~25% and blunts LXA4- and RvD1-stimulated phagocytosis in macrophages. miR-181b levels decrease during monocyte-to-macrophage differentiation, inversely correlating with FPR2 upregulation.\",\n      \"method\": \"Luciferase reporter assay with 3'-UTR; miR-181b overexpression and knockdown; Western blot; phagocytosis assay in human macrophages\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — 3'-UTR luciferase reporter confirms direct miRNA binding; functional consequence shown in primary macrophages with overexpression and knockdown, single lab with multiple methods\",\n      \"pmids\": [\"25250540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Annexin A1 secreted by skeletal myotubes activates FPR2 to protect against palmitate-induced insulin resistance; annexin A1 levels decrease with palmitate treatment. FPR2 agonist treatment improved systemic insulin sensitivity in high-fat diet mice, and the protective effect involved PKC-θ modulation.\",\n      \"method\": \"Quantitative proteomics of myotube secretome; annexin A1/FPR2 agonist treatment of L6 myotubes; PKC-θ phosphorylation assay; in vivo insulin tolerance test in HFD mice\",\n      \"journal\": \"Molecular & cellular proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomic discovery combined with functional cell assays and in vivo validation, single lab\",\n      \"pmids\": [\"25616869\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"LXA4 activates ALX/FPR2 in conjunctival goblet cells to increase mucin secretion and intracellular Ca2+ via sequential activation of phospholipases C, D, and A2, PKC, ERK1/2, and CaM kinase. ALX/FPR2 inhibitors blocked these responses. Sequential application of LXA4 then RvD1 (or vice versa) demonstrated heterologous desensitization between the two agonists at the same receptor.\",\n      \"method\": \"ALX/FPR2 immunolocalization; mucin secretion assay; calcium imaging; pharmacological inhibitors of ALX/FPR2 and downstream kinases; sequential agonist desensitization experiments\",\n      \"journal\": \"Mucosal immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor localization plus systematic pharmacological pathway dissection, single lab, multiple orthogonal signaling readouts\",\n      \"pmids\": [\"27072607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Staphylococcal PSMα peptides activate neutrophil FPR2 to increase intracellular Ca2+, ERK1/2 phosphorylation, NADPH oxidase activity, and receptor internalization, but CANNOT recruit β-arrestin or induce neutrophil chemotaxis. Structure-activity analysis with PSMα2 derivatives identified the first 3 residues linked to N-fMet and the C-terminus as critical for β-arrestin recruitment.\",\n      \"method\": \"Neutrophil calcium flux; NADPH oxidase assay; β-arrestin recruitment assay; ERK phosphorylation; chemotaxis assay; internalization assay; PSMα2 derivative SAR analysis\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic SAR plus multiple functional readouts establishing biased agonism, consistent with prior β-arrestin/chemotaxis findings, single lab multiple orthogonal methods\",\n      \"pmids\": [\"31694908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"β-Arrestin-independent FPR2 endocytosis occurs in β-arrestin-deficient cells (albeit at reduced levels), demonstrated using Barbadin (AP2/β-arrestin interaction blocker) which inhibited AP2/β-arrestin interaction but did NOT inhibit FPR2 endocytosis. Barbadin selectively potentiated FPR2-mediated ROS production independently of β-arrestin recruitment and receptor endocytosis, suggesting AP2 regulates FPR2-mediated ROS release.\",\n      \"method\": \"Barbadin pharmacology; β-arrestin-deficient cells; FPR2 internalization assay; NADPH oxidase ROS assay; chemotaxis assay; AP2/β-arrestin interaction assay\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (β-arrestin KO cells) and pharmacological dissection with multiple functional readouts, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"32916203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RvD1 binding to ALX/FPR2 on macrophages induces a transcriptional program characteristic of pro-revascularization phenotype (identified by RNA-seq). Myeloid-specific Fpr2 deficiency impairs perfusion recovery and vascularization in ischemic skeletal muscle and cutaneous wounds, associated with altered expression of pro-revascularization genes.\",\n      \"method\": \"RNA sequencing of RvD1-treated macrophages; hindlimb ischemia model; myeloid-specific Alx/Fpr2 knockout mice; perfusion imaging; wound healing assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RNA-seq transcriptional mechanism combined with tissue-specific knockout in two independent in vivo models, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"32513697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Fpr2 directly interacts with TAK1 kinase (demonstrated by co-immunoprecipitation), and Fpr2 inhibition reduces LPS-induced TAK1 activation; this interaction promotes NF-κB and MAPK signaling and oxidative stress in macrophages. Fpr2 knockout activates Nrf2 and increases antioxidant enzymes, suggesting Nrf2 is partially downstream of Fpr2-TAK1 regulation.\",\n      \"method\": \"Co-immunoprecipitation; Fpr2 knockout mice; Fpr2 overexpression; LPS stimulation; NF-κB and MAPK Western blots; oxidative stress assays\",\n      \"journal\": \"Biomedicine & pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus knockout/overexpression functional data, single lab, Co-IP alone is lower tier but multiple supporting methods\",\n      \"pmids\": [\"32106380\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FPR2 activation by WKYMVm and annexin A1 (ANXA1) leads to NADPH oxidase-dependent phosphorylation of HSP27 (Ser82), OSR1 (Ser339), and MARCKS (Ser170) via upstream kinases p38MAPK, PI3K, and PKCδ respectively; NADPH oxidase inhibition or p22phox CRISPR knockout prevents all these phosphorylation events, placing NADPH oxidase upstream of these kinase cascades.\",\n      \"method\": \"Phosphorylation assays with site-specific antibodies; NADPH oxidase inhibitors; p22phox CRISPR/Cas9 double nickase knockout cells; agonist stimulation of CaLu-6 cells\",\n      \"journal\": \"Antioxidants\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — CRISPR genetic knockout combined with pharmacological validation, single lab, multiple phosphorylation targets with specific upstream kinase assignment\",\n      \"pmids\": [\"33477989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cryo-EM structures of FPR2 bound to Gi and either Aβ42 or N-formyl humanin (fHN) were determined. Two critical structural regions govern recognition: a polar binding cavity within the receptor helical bundle and a hydrophobic binding groove in the extracellular region. Structures of FPR2 and FPR1 with different formyl peptides provided mechanistic insights into ligand selectivity within the FPR family.\",\n      \"method\": \"Cryo-electron microscopy structure determination; functional binding and signaling assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures at atomic resolution with functional validation, revealing structural basis of ligand recognition and selectivity\",\n      \"pmids\": [\"35365641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PRSS22 protease binds and cleaves ANXA1 (confirmed by Co-IP, mass spectrometry, and Western blot), generating an N-terminal peptide that activates FPR2/ERK signaling to promote breast cancer cell migration and invasion.\",\n      \"method\": \"Protein mass spectrometry; co-immunoprecipitation; Western blot; cell migration and invasion assays; ERK phosphorylation; in vivo xenograft\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP confirms PRSS22-ANXA1 interaction; proteolytic cleavage and downstream FPR2/ERK signaling established, single lab\",\n      \"pmids\": [\"36414640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FPR2 is a membrane receptor that specifically binds long-chain ceramides (C14–C20). C16:0 ceramide binding to FPR2 inhibits thermogenesis in brown and beige adipocytes through Gi-cAMP signaling pathways. Three cryo-EM structures of FPR2-Gi complexes bound to C16:0, C18:0, and C20:0 ceramides were determined, showing hydrophobic tails embedded in the orthosteric pocket. Modification of the ceramide-binding motif in FPR1 or FPR3 converts them from inactive to active ceramide receptors.\",\n      \"method\": \"Cryo-EM structure determination of FPR2-Gi-ceramide complexes; Gi-cAMP signaling assay; thermogenesis assay in brown/beige adipocytes; FPR2 knockout cells; mutagenesis converting FPR1/FPR3 to ceramide receptors\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple cryo-EM structures combined with functional assays and mutagenesis in native cell contexts; multiple ceramide species characterized\",\n      \"pmids\": [\"40080544\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FPR2 (ALX/FPRL1) is a promiscuous Gi-coupled G-protein-coupled receptor that adopts ligand-specific conformations, exists as constitutive homo- and heterodimers with FPR1/FPR3, and signals through PLC/PKC/MAPK, PI3K/Akt, NADPH oxidase, and β-arrestin pathways to mediate chemotaxis, phagocytosis, and inflammatory resolution; its orthosteric pocket accommodates structurally diverse ligands including formyl peptides, annexin A1 (via the N-terminal domain and extracellular loop II), serum amyloid A (via extracellular loops I–II), Aβ42/humanin (cryo-EM defined polar cavity and hydrophobic groove), and long-chain ceramides (cryo-EM-defined orthosteric hydrophobic pocket inhibiting thermogenesis via Gi-cAMP), while β-arrestin recruitment governs chemotaxis and receptor recycling, and a C-terminal recycling sequence controls endocytic fate and anti-apoptotic signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FPR2 (ALX/FPRL1) is a Gi-coupled G-protein-coupled receptor that orchestrates leukocyte chemotaxis, phagocytosis, and inflammatory responses by sensing a structurally diverse panel of ligands through a promiscuous orthosteric pocket [#1, #6, #28]. First identified as a structural homologue of the FMLP receptor FPR1 that does not recognize FMLP [#0], it was reconstituted as a low-affinity N-formylpeptide receptor mediating high-concentration neutrophil chemotaxis [#1]. The receptor responds to host-derived agonists including serum amyloid A [#4], the cleaved urokinase receptor fragment D2D3 [#3], the antimicrobial peptide LL-37/CRAMP [#9, #18], annexin A1 [#10, #21], and the heme-binding protein peptide F2L [#6], as well as pathogen-derived ligands such as HIV-1 gp120 F peptide [#2] and staphylococcal PSMα peptides [#23]; cryo-EM structures define a polar binding cavity and hydrophobic extracellular groove governing recognition of Aβ42 and formyl humanin [#28] and an orthosteric hydrophobic pocket accommodating long-chain ceramides that suppress adipocyte thermogenesis through Gi-cAMP signaling [#30]. Distinct ligands engage separable receptor surfaces and oligomeric states: annexin A1 binds the N-terminal region and extracellular loop II while SAA depends on extracellular loops I–II [#10], and annexin A1 selectively activates ALX homodimers to drive p38/MK2/HSP27-IL-10 signaling whereas ALX/FPR1 heterodimers triggered by panagonists evoke JNK-dependent neutrophil apoptosis [#12]. Downstream, FPR2 signals through PLC/PKC/Ca2+, ERK/p38 MAPK, PI3K/Akt, and NADPH oxidase, with NADPH oxidase positioned upstream of HSP27, OSR1, and MARCKS phosphorylation [#27] and required for c-Met transactivation [#15]. β-arrestin recruitment, dissociable from G-protein signaling by biased pepducin and PSMα agonists, specifically governs chemotaxis and receptor internalization rate while desensitization proceeds independently [#13, #23], and a C-terminal recycling sequence controls endocytic fate and anti-apoptotic survival signaling [#17]. Receptor abundance is set transcriptionally by Sp1 and promoter methylation [#11] and post-transcriptionally by miR-181b [#20]. Through these mechanisms FPR2 mediates dendritic cell maturation and trafficking [#18, #19], macrophage clearance of apoptotic neutrophils [#7], and pro-revascularization macrophage programming [#25].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that an FPR1-homologous gene existed but did not recognize FMLP raised the question of what an orphan formyl peptide receptor homologue actually senses.\",\n      \"evidence\": \"Genomic clone characterization and somatic cell hybrid chromosomal mapping\",\n      \"pmids\": [\"1612600\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional ligand identified\", \"No signaling pathway defined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Functional reconstitution defined FPR2 as a low-affinity formyl peptide receptor and revealed it doubles as a chemotactic receptor for the HIV-1 gp120 F peptide, establishing ligand promiscuity from the outset.\",\n      \"evidence\": \"Stable HEK293 transfection with calcium flux and chemotaxis assays, FPR1-knockout mouse neutrophils, and cross-desensitization studies\",\n      \"pmids\": [\"10477558\", \"10438703\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous physiological ligands not yet defined\", \"Structural basis of ligand recognition unknown\", \"Whether high-concentration formyl peptide response is physiologically relevant unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of serum amyloid A, the cleaved uPAR fragment, and a TNF-α-inducible role in microglia expanded FPR2 into a broadly responsive inflammatory receptor with defined Gi/MAPK/NF-κB output.\",\n      \"evidence\": \"HeLa overexpression with reporter and pertussis toxin assays, direct binding competition in monocytes, and microglial chemotaxis with p38 inhibitors\",\n      \"pmids\": [\"12393391\", \"11818541\", \"12270697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor domains engaging each ligand not mapped\", \"Relationship among the diverse ligands at one pocket unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"F2L identification with knockout validation cemented receptor-specific endogenous agonism within the FPR family.\",\n      \"evidence\": \"Transfection across mouse FPR family members plus Fpr2-knockout neutrophil calcium and chemotaxis assays\",\n      \"pmids\": [\"17237393\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human receptor binding mode for F2L not structurally defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defining hierarchical C-terminal phosphorylation sites and N-terminal/TM determinants of localization, plus LL-37 as a proinflammatory agonist, began separating receptor regulation from agonist-specific output.\",\n      \"evidence\": \"Site-directed mutagenesis, chimeric domain swaps, and phosphorylation/internalization assays; LL-37-driven LTB4 release with p38 and cPLA2 readouts\",\n      \"pmids\": [\"21543323\", \"21307335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for site-specific phosphorylation not identified\", \"How distinct agonists produce divergent outputs unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Chimeric mapping assigned distinct ligands to distinct receptor surfaces, and promoter analysis established Sp1/methylation control of FPR2 abundance with a functional human variant.\",\n      \"evidence\": \"Chimeric FPR1/FPR2 receptors with genomic response profiling; ChIP, reporter assays, and primary neutrophil genotyping\",\n      \"pmids\": [\"22610094\", \"22131270\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-resolution ligand contacts not yet resolved\", \"Physiological consequences of the promoter variant not established\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Discovery of constitutive homo- and heterodimers with FPR1/FPR3 and of biased pepducin agonism explained how a single receptor encodes opposing pro-resolving versus pro-apoptotic outcomes, while a negative LXA4 result flagged uncertainty about lipoxin action.\",\n      \"evidence\": \"BRET and Co-IP dimerization assays with primary cell signaling and knockout mice; intracellular-loop pepducins with receptor/pepducin mutagenesis and β-arrestin recruitment assays; systematic LXA4 signaling assays across orthologues\",\n      \"pmids\": [\"24108355\", \"28855087\", \"23562731\", \"23583448\", \"23643932\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of LXA4 action in heterologous systems unresolved\", \"Structural basis of dimer-selective signaling unknown\", \"How β-arrestin recruitment is selectively decoupled by biased agonists not structurally defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Trafficking, transcriptional, and in vivo immune studies linked receptor recycling to survival, miR-181b to receptor abundance, and CRAMP-Fpr2 signaling to dendritic cell maturation and tissue trafficking.\",\n      \"evidence\": \"C-terminal recycling-sequence mutagenesis with apoptosis assays; 3'-UTR luciferase reporter with macrophage phagocytosis; Fpr2-/- and CRAMP-/- mice in dendritic cell and allergic airway models\",\n      \"pmids\": [\"25326384\", \"25250540\", \"24808174\", \"23603910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Recycling-machinery components not identified\", \"How recycling failure triggers apoptosis mechanistically unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"An annexin A1-FPR2 axis in skeletal muscle extended receptor function to metabolic protection against insulin resistance.\",\n      \"evidence\": \"Secretome proteomics, L6 myotube agonist treatment with PKC-θ assays, and insulin tolerance testing in high-fat-diet mice\",\n      \"pmids\": [\"25616869\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct receptor-level mechanism in muscle not dissected\", \"Single-lab in vivo finding\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Goblet cell studies defined a sequential phospholipase/kinase cascade for LXA4 and demonstrated heterologous desensitization between pro-resolving lipid mediators at FPR2.\",\n      \"evidence\": \"Receptor immunolocalization, mucin secretion and calcium imaging, and sequential LXA4/RvD1 desensitization with pathway inhibitors\",\n      \"pmids\": [\"27072607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation with negative heterologous LXA4 data unresolved\", \"Direct LXA4 binding not demonstrated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Staphylococcal PSMα peptides reinforced the biased-agonism model, with structure-activity analysis pinpointing residues required for β-arrestin recruitment and chemotaxis.\",\n      \"evidence\": \"Neutrophil calcium, NADPH oxidase, ERK, β-arrestin, internalization and chemotaxis assays with PSMα2 derivative SAR\",\n      \"pmids\": [\"31694908\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for β-arrestin-biased versus balanced agonism not resolved at atomic level\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Genetic and pharmacological dissection separated β-arrestin-independent endocytosis and AP2-regulated ROS from canonical signaling, and identified a direct Fpr2-TAK1 interaction plus an RvD1-driven pro-revascularization macrophage program.\",\n      \"evidence\": \"Barbadin pharmacology in β-arrestin-deficient cells with internalization/ROS assays; Co-IP of Fpr2 with TAK1 in knockout/overexpression macrophages; macrophage RNA-seq with myeloid-specific Fpr2 knockout in ischemia and wound models\",\n      \"pmids\": [\"32916203\", \"32106380\", \"32513697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"TAK1 interaction rests on single Co-IP without reciprocal structural validation\", \"How AP2 regulates ROS independently of endocytosis unclear\", \"Direct versus indirect nature of Fpr2-TAK1 binding not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Cryo-EM structures of Gi-coupled FPR2 bound to Aβ42 and formyl humanin provided the first atomic basis for ligand recognition and FPR-family selectivity, and a PRSS22 protease was shown to generate an FPR2-activating annexin A1 fragment in breast cancer.\",\n      \"evidence\": \"Cryo-EM of FPR2-Gi-ligand complexes with functional validation; mass spectrometry, Co-IP and migration/invasion assays for PRSS22-ANXA1 cleavage\",\n      \"pmids\": [\"35365641\", \"36414640\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of peptide-only agonists do not capture lipid or protein ligand binding modes\", \"PRSS22-ANXA1 axis is single-lab Medium-confidence\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Discovery that FPR2 is a long-chain ceramide receptor suppressing thermogenesis via Gi-cAMP, with cryo-EM-defined orthosteric lipid binding, established a metabolic sensing function and the structural determinant convertible to FPR1/FPR3.\",\n      \"evidence\": \"Three cryo-EM FPR2-Gi-ceramide structures, Gi-cAMP and thermogenesis assays in adipocytes, knockout cells, and gain-of-function mutagenesis of FPR1/FPR3\",\n      \"pmids\": [\"40080544\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological source of FPR2-activating ceramides in vivo not defined\", \"Integration of lipid sensing with peptide-driven inflammatory signaling unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single orthosteric architecture reconciles diverse agonists (formyl peptides, annexin A1, SAA, ceramides) into ligand-, dimer-, and arrestin-biased outputs, and how LXA4 signaling proceeds given negative heterologous results, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model linking biased agonism to specific conformations\", \"Mechanism of LXA4 action still contested between native and heterologous systems\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 4, 6, 28]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13, 23]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [8, 17]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [17, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 12, 27]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 18, 19, 25]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [13, 17, 24]}\n    ],\n    \"complexes\": [\n      \"FPR2 homodimer\",\n      \"ALX/FPR1 heterodimer\",\n      \"FPR2-Gi complex\"\n    ],\n    \"partners\": [\n      \"FPR1\",\n      \"FPR3\",\n      \"ANXA1\",\n      \"TAK1\",\n      \"GNAI1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":{"gene":"FPR2","tier":"GROUNDING","verdict":"Evidence-grounding concern","subtype":"fabrication","uniprot_band":"rich","rules_fired":"R7","issue":"R7: fabricated (no corpus paper): 25250540"},"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}