{"gene":"GPR34","run_date":"2026-06-10T01:55:21","timeline":{"discoveries":[{"year":2012,"finding":"GPR34 is a functional receptor for lysophosphatidylserine (LysoPS), specifically recognizing LysoPS with a fatty acid at the sn-2 position. In HEK293 cells expressing GPR34 with a Gαq/Gαi1 chimera, LysoPS elevated intracellular Ca2+ levels, stimulated AP-TGFα release, and induced CHO-K1 cell migration. Replacement of the serine head group abolished reactivity, and 2-acyl-LysoPS (generated by PS-PLA1) was more potent than 1-acyl-LysoPS, confirming sn-2 positional selectivity.","method":"Intracellular Ca2+ assay, AP-TGFα release assay, cell migration assay, synthetic LysoPS analogues, catalytically inactive mutant PS-PLA1 controls","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal functional assays with mutagenesis controls and chemical probes in a single rigorous study","pmids":["22343749"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structure of human GPR34 bound to LysoPS (18:1) and Gi protein revealed that the negatively charged serine head group of LysoPS occupies a polar cavity formed by TM3, TM6, and TM7, while the hydrophobic acyl tail resides in a lateral open hydrophobic groove formed by TM3-5. A selective antagonist YL-365 binds competitively in a portion of the orthosteric pocket and induces allosteric changes in the receptor.","method":"Cryo-EM structure determination of active (agonist-bound) and inactive (antagonist-bound) GPR34 complexes; virtual screening; fusion protein design for inactive-state structure","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures of both active and inactive states with functional validation of antagonist, replicated in part by independent structure paper (PMID:38326347)","pmids":["37733739"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structures of human GPR34-Gi complex bound to S3E-LysoPS or the aromatic surrogate M1 showed a laterally open ligand-binding pocket allowing membrane-lateral entry of lipidic agonists. The serine amine and carboxylate groups are recognized by a charged residue cluster, and the acyl chain fits into an L-shaped hydrophobic pocket in the TM4-5 gap. Molecular dynamics simulations supported that 2-acyl LysoPS is the physiological ligand due to its regioselectivity.","method":"Cryo-EM structure determination, molecular dynamics simulations, structure-activity validation with synthetic analogues","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — independent cryo-EM structural study with MD simulations and functional assays, replicating and extending the binding mode defined in PMID:37733739","pmids":["38326347"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structures of human GPR34 and GPR174 in complex with LysoPS and Gi protein elucidated the lipid-binding modes and structural features of these receptors in the active state, providing insights into ligand recognition and signaling of LysoPS receptors.","method":"Cryo-EM structure determination, structural comparison, functional studies","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — independent cryo-EM structural study with functional validation, orthogonal to PMID:37733739 and PMID:38326347","pmids":["38048360"],"is_preprint":false},{"year":2010,"finding":"GPR34-deficient mice showed significantly lower numbers of granulocytes and macrophages in spleens after immunization, increased paw swelling in delayed-type hypersensitivity, higher pathogen burden after Cryptococcus neoformans infection, and altered basal/stimulated TNF-α, GM-CSF, and IFN-γ levels, establishing a functional role for GPR34 in cellular immune responses.","method":"GPR34 knockout mouse model, immunization challenge, delayed-type hypersensitivity test, pulmonary infection model, cytokine measurement","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular and immune phenotypes across multiple challenge models in a single study","pmids":["21097509"],"is_preprint":false},{"year":2014,"finding":"GPR34-deficient microglia showed morphological changes in retinal and cortical microglia and reduced phagocytosis activity in both retina and acutely isolated cortical slices. RNA sequencing revealed differentially expressed transcripts involved in cell motility and phagocytosis, but no differences in microglial motility after lesion were detected.","method":"GPR34 knockout mouse, RNA sequencing of microglia, phagocytosis assays in retina and cortical slices, in vivo lesion models","journal":"Glia","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO with multiple orthogonal phenotypic readouts (morphology, transcriptomics, functional phagocytosis assays) across two tissue types","pmids":["25142016"],"is_preprint":false},{"year":2021,"finding":"GPR34 on ILC3s acts as a damage-sensing receptor for LysoPS released by apoptotic neutrophils. ILC3-specific deletion of Gpr34 suppressed IL-22 production and tissue repair during colon and skin injury. Downstream signaling via PI3K-AKT or ERK was required for ILC3 activation and IL-22 production.","method":"ILC3-specific Gpr34 conditional knockout, co-culture of neutrophils and ILC3s, metabolomic analysis, PI3K-AKT/ERK inhibition, intestinal epithelial injury model","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific KO with multiple in vivo and in vitro readouts, pathway inhibition experiments, metabolomic identification of ligand","pmids":["34107271"],"is_preprint":false},{"year":2019,"finding":"GPR34 expressed by spinal dorsal horn microglia promotes neuropathic pain after nerve injury. GPR34-deficient mice showed attenuated nerve injury-induced pro-inflammatory cytokine expression and reduced pain behavior. LysoPS levels were elevated in the dorsal horn after injury, and intrathecal administration of a GPR34 antagonist reduced neuropathic pain, placing GPR34 upstream of pro-inflammatory microglial activation.","method":"GPR34 knockout mice, von Frey hair test, qRT-PCR for cytokines, in situ hybridization, LC-MS/MS quantification of LysoPS, intrathecal antagonist administration","journal":"Journal of neuroinflammation","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO plus pharmacological blockade with multiple orthogonal readouts (behavior, cytokines, ligand measurement)","pmids":["30975169"],"is_preprint":false},{"year":2024,"finding":"LysoPS in the tumor microenvironment inhibits ILC1 antitumor activity via GPR34. Genetic deletion of LysoPS synthase Abhd16a in tumors or Gpr34 in ILC1s, or pharmacological antagonism of GPR34, enhanced ILC1 antitumor activity, identifying GPR34 as a metabolic immune checkpoint on ILC1s.","method":"Gpr34 conditional KO in ILC1s, Abhd16a knockout in tumor cells, GPR34 antagonist treatment, in vivo tumor models","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific KO plus ligand-synthesis KO plus pharmacological blockade with consistent functional readouts","pmids":["39358444"],"is_preprint":false},{"year":2024,"finding":"LysoPS-GPR34 signaling mediates microglia-driven neuroinflammation in demyelination. Myelin debris-induced microglial activation and proinflammatory cytokine production depended on LysoPS and GPR34, signaling through PI3K-AKT and ERK. In vivo, reducing LysoPS in myelin or genetic/pharmacological GPR34 inhibition reduced neuroinflammation and pathologies in multiple sclerosis and stroke mouse models.","method":"GPR34 knockout and pharmacological inhibition, PI3K-AKT/ERK pathway analysis, mouse models of MS and stroke, in vitro microglial stimulation","journal":"Cellular & molecular immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — KO plus pharmacological blockade plus pathway inhibition in multiple in vivo and in vitro models","pmids":["39030423"],"is_preprint":false},{"year":2012,"finding":"The t(X;14)(p11;q32) translocation in MALT lymphoma deregulates GPR34 expression by placing it under IGH control. Overexpression of GPR34 in lymphoma and HeLa cells resulted in phosphorylation of ERK, PKC, and CREB; induced CRE, AP1, and NF-κB-mediated gene transcription; and increased cell proliferation.","method":"Translocation cloning, GPR34 overexpression in lymphoma and HeLa cells, phosphorylation assays, reporter gene assays (CRE, AP1, NF-κB), cell proliferation assays","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — overexpression with multiple signaling readouts in a single lab study","pmids":["22966169"],"is_preprint":false},{"year":2022,"finding":"The GPR34 C-terminal truncation mutant Q340X, which lacks the phosphorylation motif for β-arrestin-mediated desensitization, showed significantly delayed internalization after LysoPS stimulation, increased resistance to apoptosis, greater transforming potential, and significantly activated CRE, NF-κB, and AP1 reporter activities compared to wild-type GPR34.","method":"Isogenic Flp-InTRex293 stable cell lines, internalization assays, apoptosis assays, reporter gene assays (CRE, NF-κB, AP1), soft agar transformation assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic cell line system with multiple functional assays in a single lab study","pmids":["34086889"],"is_preprint":false},{"year":2016,"finding":"In dendritic cells, NF-κB and MAPK signaling pathways regulate GPR34 expression. DCs lacking GPR34 showed higher caspase-3/7 activity and increased apoptosis levels, establishing GPR34 as a pro-survival factor in DCs.","method":"GPR34 knockout mouse, whole-transcriptome RNA sequencing of DCs, pathway inhibition experiments (NF-κB, MAPK), caspase-3/7 activity assay, apoptosis measurement","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with transcriptomics and functional pathway experiments in a single lab study","pmids":["26851221"],"is_preprint":false},{"year":2016,"finding":"A tri-basic motif in the first intracellular loop of GPR34 acts as the key topogenic signal dictating the orientation of transmembrane domain-1 (TM1). Charge disruption of this motif perturbed topogenesis, caused loss of a conformation-sensitive epitope, altered post-translational processing, and arrested trafficking in the Golgi. A cleavable N-terminal signal sequence as surrogate topogenic determinant rescued TM1 orientation, conformational epitope, and cell surface trafficking.","method":"FLAG-tag and conformation-sensitive native epitope monitoring, mutant panel expression, signal sequence insertion rescue, N-tail truncation and site-directed mutagenesis, Golgi trafficking analysis","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic mutagenesis panel with multiple readouts in a single lab study","pmids":["27086875"],"is_preprint":false},{"year":2014,"finding":"LysoPS stimulates chemotactic migration of colorectal cancer cells through GPR34 and the PI3K/Akt pathway. GPR34 was the predominantly expressed LysoPS receptor on colorectal cancer cell lines. GPR34 knockdown by siRNA or treatment with the PI3K inhibitor wortmannin suppressed LysoPS-induced migration.","method":"RT-PCR for receptor expression, siRNA knockdown of GPR34, chemotaxis assay, PI3K inhibitor (wortmannin) treatment","journal":"Anticancer research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — siRNA KD with pharmacological pathway inhibition, functional readout, single lab","pmids":["25275042"],"is_preprint":false},{"year":2025,"finding":"GPR34 is stabilized by the deubiquitinase USP8. USP8 was identified as a deubiquitinase for GPR34; effects of GPR34 deletion on ferroptosis and tumor progression in anaplastic thyroid carcinoma were reversed by USP8 overexpression. Pharmacological inhibition of USP8 with DUB-IN-3 restrained ATC growth.","method":"Co-immunoprecipitation/protein interaction studies to identify USP8 as a DUB, GPR34 deletion in vitro/in vivo, USP8 overexpression rescue, DUB-IN-3 inhibitor treatment, ferroptosis assays","journal":"Mediators of inflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — identification of DUB-substrate relationship with functional rescue, single lab study","pmids":["40862294"],"is_preprint":false},{"year":2024,"finding":"LysoPS released from injured retinal ganglion cells activates the GPR34-PI3K-AKT-NINJ1 signaling axis in microglia, upregulating inflammatory cytokines (IL-6, IL-8, VEGFA, FGF2) and promoting microglial extracellular trap formation and retinal neovascularization. Inhibition of this axis suppressed these effects in vitro and in vivo.","method":"In vitro microglial stimulation with LysoPS, GPR34 inhibition (genetic and pharmacological), PI3K-AKT pathway analysis, NINJ1 expression measurement, in vivo retinal neovascularization model","journal":"Journal of neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo experiments with pathway dissection in a single lab study","pmids":["39468551"],"is_preprint":false},{"year":2025,"finding":"GPR34 promotes GPR34+ macrophage efferocytosis and CXCL16 secretion in pancreatic cancer. GPR34+ macrophages responded to LysoPS, and their efferocytosis promoted MHC-I degradation via the lysosomal pathway, leading to CD8+ T cell exhaustion. Gpr34ΔLyz2 mouse models confirmed this in vivo.","method":"Single-cell RNA sequencing, Gpr34 conditional KO (Lyz2-Cre), in vitro co-culture, efferocytosis assays, MHC-I degradation analysis, CXCL16 measurement","journal":"Signal transduction and targeted therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple mechanistic readouts in a single study","pmids":["42045172"],"is_preprint":false},{"year":2025,"finding":"GPR34 deficiency in cDC1 (but not cDC2 or macrophages) led to reduced apoptotic cell uptake and impaired cross-presentation to CD8 T cells. PLA1A (but not ABHD16A) deficiency reduced the OT-I T cell response to apoptotic cell-associated antigen, identifying PLA1A-generated lysoPS as the GPR34 ligand mediating cDC1 efferocytosis.","method":"GPR34 knockout mice, adoptive transfer of apoptotic cell-OVA, OT-I T cell proliferation assay, PLA1A and ABHD16A knockout comparison, cell-type-specific phenotyping","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with specific cellular phenotype and ligand-source identification in a single study","pmids":["41212150"],"is_preprint":false},{"year":2024,"finding":"GPR34 knock-in (gain-of-function) promotes peritoneal cavity accumulation of plasma cells and memory B cells through lysoPS-dependent migration. KI cells showed robust migration to lysoPS ex vivo. Maintenance of KI cells in the peritoneal cavity was dependent on stromal PLA1A, the lysoPS-generating enzyme expressed in omental fibroblasts.","method":"GPR34 knock-in mouse, adoptive transfer experiments, bone marrow chimeras, ex vivo migration assay, PLA1A conditional KO","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KI plus stromal KO with functional migration assay and in vivo localization, single lab","pmids":["39412501"],"is_preprint":false},{"year":2025,"finding":"Selective agonism of GPR34 with compound M1 enhanced microglial uptake of Aβ fibrils (but not monomeric or oligomeric Aβ) through reduction of intracellular cAMP levels. This effect required functional TREM2 signaling. Gpr34 knockdown confirmed GPR34 as the molecular target of M1.","method":"Flow cytometry-based Aβ uptake assay, cAMP measurement, Gpr34 knockdown, intrahippocampal M1 injection in hAPP knock-in mice, TREM2 signaling requirement testing","journal":"Alzheimer's research & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo assays with KD confirmation and pathway dependency established in a single study","pmids":["41261421"],"is_preprint":false},{"year":2018,"finding":"The majority of GPR34 mutations in MALT lymphoma are nonsense and frameshift changes clustered in the C-terminal cytoplasmic tail, generating truncated proteins that lack the phosphorylation motif for β-arrestin-mediated receptor desensitization and internalization, suggesting constitutive or enhanced signaling.","method":"Whole exome sequencing of MALT lymphoma cases, mutational mapping to functional protein domains","journal":"Haematologica","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — sequencing-based inference about mechanism without direct functional validation of specific mutations in this paper","pmids":["29674500"],"is_preprint":false},{"year":2023,"finding":"GPR34 knockdown in BV-2 microglia exposed to Aβ1-42 decreased TNF-α, IL-1β, IL-6, and iNOS levels and suppressed ERK/NF-κB signaling activation. GPR34 overexpression-induced ERK/NF-κB activation and cytokine upregulation were abolished by the ERK inhibitor FR180204, placing GPR34 upstream of ERK/NF-κB in microglial neuroinflammation.","method":"siRNA knockdown and overexpression in BV-2 cells, ERK inhibitor (FR180204), western blot and immunofluorescence for signaling components, APP/PS1 mouse model with GPR34 knockdown","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD, OE, and pathway inhibitor rescue with in vitro and in vivo corroboration in a single study","pmids":["37557947"],"is_preprint":false},{"year":2005,"finding":"GPR34 contains an intronless coding region but has an evolutionarily conserved 5' noncoding intron-exon structure. An alternatively used cryptic intron shortens the N-terminus by 47 amino acids. Multiple conserved in-frame AUGs serve as translational start points, with combinatory mutagenesis confirming preference for the second in-frame AUG in human GPR34.","method":"Genomic sequencing across vertebrate species, reporter constructs, combinatory mutagenesis, expression analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis of translational start sites with reporter validation in a single study","pmids":["16338117"],"is_preprint":false},{"year":2012,"finding":"LysoPS has no or very weak agonistic activity at most vertebrate GPR34 orthologues except some fish subtypes. Using chimeric receptors, single positions in the second extracellular loop and transmembrane helix 5 of carp GPR34 subtype 2a were identified as critical for lysoPS responsiveness; transferring these positions to human GPR34 enabled lysoPS activation. Aminoethyl-carbamoyl ATP was identified as an antagonist of carp GPR34.","method":"Chimeric receptor construction, site-directed mutagenesis, functional assays across vertebrate orthologues, phylogenetic analysis","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mutagenesis with functional rescue in a single study; note this paper's conclusion partially contradicts other studies confirming lysoPS activity at human GPR34","pmids":["22348703"],"is_preprint":false},{"year":2025,"finding":"In Gpr34 knockout mice at postnatal day 18, elevated numbers of neurons, oligodendrocytes, and microglia showed markers of cell death (cleaved-caspase 3, phospho-RIP3, annexin V), with reduced microglial localization to areas of high cell death. KO microglia showed increased intracellular accumulation of myelin basic protein and SNAP25, suggesting altered handling of apoptotic debris. Transcriptomic analysis revealed persistent immune pathway alterations, and 3-month KO mice displayed sustained hypolocomotion.","method":"Gpr34 KO mouse, immunohistochemistry for cell death markers, microglial localization analysis, ex vivo phagocytosis assay, transcriptomic analysis, locomotion behavioral testing","journal":"Journal of neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with multiple histological and functional readouts in a single study","pmids":["41964003"],"is_preprint":false},{"year":2025,"finding":"GPR34 KO iPSC-derived microglia showed reduced Ca2+ and phosphorylated ERK signaling in response to LysoPS and myelin stimulation, and were selectively impaired in phagocytosis of myelin but not Aβ or E. coli. GPR34 KO accelerated conversion of homeostatic microglia to DAM states in healthy and amyloid mouse models. GPR34 agonism promoted interaction with and activation of ERK.","method":"GPR34 KO iPSC-derived microglia, Ca2+ imaging, pERK measurement, selective phagocytosis assays, RNA-sequencing, amyloid mouse models","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays in human iPSC-derived microglia and mouse models; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.03.28.646038"],"is_preprint":true}],"current_model":"GPR34 is a Gi/o-coupled GPCR (P2Y family) that functions as a receptor for lysophosphatidylserine (LysoPS), particularly the 2-acyl form generated by phosphatidylserine-specific phospholipase A1 (PLA1A/PS-PLA1); structural studies show LysoPS enters a laterally open orthosteric pocket where its serine head group is recognized by a charged residue cluster in TM3/6/7 and its acyl tail fits an L-shaped hydrophobic groove in TM4-5, leading to Gi-mediated signaling through PI3K-AKT and ERK pathways; GPR34 is highly enriched in microglia, macrophages, dendritic cells, and innate lymphoid cells, where it regulates phagocytosis of apoptotic cells and myelin debris, maintains microglial homeostatic state, controls pro-inflammatory cytokine production, promotes DC survival, and mediates tissue repair and neuropathic pain; C-terminal truncation mutations found in MALT lymphoma impair receptor desensitization and internalization, conferring enhanced signaling through NF-κB, AP1, and CRE pathways and increased cell proliferation, while GPR34 can be stabilized post-translationally by the deubiquitinase USP8."},"narrative":{"mechanistic_narrative":"GPR34 is a Gi-coupled G-protein-coupled receptor that functions as a sensor for lysophosphatidylserine (LysoPS), enabling innate immune and microglial cells to detect dying cells and tissue damage [PMID:22343749, PMID:34107271]. It selectively recognizes the 2-acyl form of LysoPS generated by PS-specific phospholipase A1: replacement of the serine head group abolishes activity and 2-acyl-LysoPS is more potent than the 1-acyl species [PMID:22343749]. Cryo-EM structures of the active GPR34-Gi complex show that the charged serine head group is read out by a polar residue cluster in TM3/TM6/TM7 while the acyl tail enters an L-shaped hydrophobic groove through a laterally open pocket that permits membrane-lateral ligand entry, and a competitive antagonist (YL-365) occupies part of this orthosteric site [PMID:37733739, PMID:38326347, PMID:38048360]. Ligand engagement drives Gi signaling through PI3K-AKT and ERK, and through ERK/NF-κB, to control downstream effector programs [PMID:34107271, PMID:39030423, PMID:37557947]. GPR34 is enriched in microglia and other myeloid and innate lymphoid cells, where it promotes phagocytosis of apoptotic cells and myelin debris, maintains microglial homeostasis, and tunes pro-inflammatory cytokine output [PMID:25142016, PMID:39030423, PMID:bio_10.1101_2025.03.28.646038]. Through this damage-sensing role it acts across contexts: it drives microglia-dependent neuropathic pain and demyelinating neuroinflammation, supports ILC3-mediated tissue repair via IL-22, and serves as a metabolic immune checkpoint that restrains ILC1 and CD8 T cell antitumor responses [PMID:34107271, PMID:30975169, PMID:39358444, PMID:39030423, PMID:42045172]. In MALT lymphoma, a t(X;14) translocation deregulates GPR34 under IGH control and C-terminal truncation mutations remove the β-arrestin phosphorylation motif, delaying receptor internalization and enhancing constitutive signaling through CRE, AP1, and NF-κB to increase proliferation and transformation [PMID:22966169, PMID:34086889].","teleology":[{"year":2012,"claim":"Established the endogenous ligand and signaling output of an orphan receptor by showing GPR34 responds to LysoPS with strict sn-2 acyl positional selectivity.","evidence":"Ca2+, AP-TGFα release and migration assays in HEK293/CHO with synthetic LysoPS analogues and catalytically inactive PS-PLA1 controls","pmids":["22343749"],"confidence":"High","gaps":["Does not resolve the in vivo cellular source of 2-acyl-LysoPS","G-protein coupling specificity tested using a Gαq/Gαi1 chimera rather than native Gi"]},{"year":2012,"claim":"Probed why LysoPS responsiveness varies across orthologues, mapping ECL2 and TM5 residues that gate lipid activation.","evidence":"Chimeric receptor and site-directed mutagenesis across vertebrate orthologues with functional assays and an ATP-derived antagonist","pmids":["22348703"],"confidence":"Medium","gaps":["Conclusion of weak human GPR34 LysoPS activity partially conflicts with other studies","Physiological relevance of fish-specific responsiveness unclear"]},{"year":2010,"claim":"First demonstrated a physiological function for GPR34, linking it to cellular immune responses and host defense.","evidence":"GPR34 knockout mice subjected to immunization, delayed-type hypersensitivity, and Cryptococcus infection with cytokine measurement","pmids":["21097509"],"confidence":"High","gaps":["Did not identify the ligand source or signaling pathway in vivo","Cell-type responsible for phenotypes not dissected"]},{"year":2014,"claim":"Connected GPR34 to microglial phagocytosis, identifying its homeostatic role in clearing debris in the CNS.","evidence":"GPR34 KO mouse microglia analyzed by RNA-seq, morphology, and phagocytosis assays in retina and cortical slices","pmids":["25142016"],"confidence":"High","gaps":["No microglial motility defect detected","Ligand driving phagocytosis not defined in this study"]},{"year":2021,"claim":"Defined GPR34 as a damage-sensing receptor on ILC3s detecting LysoPS from apoptotic neutrophils to drive tissue repair, and pinned the downstream pathway.","evidence":"ILC3-specific conditional KO, neutrophil-ILC3 co-culture, metabolomics, and PI3K-AKT/ERK inhibition in injury models","pmids":["34107271"],"confidence":"High","gaps":["LysoPS-generating enzyme in this context not specified","Receptor desensitization dynamics in ILC3s not addressed"]},{"year":2019,"claim":"Placed GPR34 upstream of pro-inflammatory microglial activation in neuropathic pain, validated pharmacologically.","evidence":"GPR34 KO mice, von Frey behavior, cytokine qRT-PCR, LC-MS/MS LysoPS quantification, and intrathecal antagonist","pmids":["30975169"],"confidence":"High","gaps":["Source of injury-induced LysoPS in dorsal horn not identified","Direct receptor-cytokine signaling steps not delineated"]},{"year":2023,"claim":"Resolved the structural basis of lipid recognition and Gi coupling, explaining sn-2 selectivity and membrane-lateral ligand entry.","evidence":"Cryo-EM of active and inactive GPR34-Gi complexes with agonist and antagonist, MD simulations, and structure-activity validation (three independent structural studies)","pmids":["37733739","38326347","38048360"],"confidence":"High","gaps":["Conformational transitions during activation not captured kinetically","Structural basis of β-arrestin/desensitization not addressed"]},{"year":2016,"claim":"Identified GPR34 as a pro-survival factor in dendritic cells and mapped a topogenic determinant required for correct folding and surface trafficking.","evidence":"GPR34 KO DC transcriptomics and caspase assays; mutagenesis of a tri-basic ICL1 motif with conformational-epitope and Golgi trafficking readouts","pmids":["26851221","27086875"],"confidence":"Medium","gaps":["Link between trafficking signal and DC survival function not established","Pro-survival downstream effectors not identified"]},{"year":2012,"claim":"Established GPR34 deregulation as oncogenic in MALT lymphoma, with truncations removing the desensitization motif to enhance signaling.","evidence":"Translocation cloning and overexpression with phosphorylation and CRE/AP1/NF-κB reporters; isogenic Q340X truncation cell lines with internalization, apoptosis, and soft-agar transformation assays; exome sequencing of mutation clustering","pmids":["22966169","34086889","29674500"],"confidence":"Medium","gaps":["Whether truncated receptors signal constitutively or only with enhanced ligand response not fully resolved","Exome mapping (idx 21) lacks direct functional validation of individual mutations"]},{"year":2024,"claim":"Defined GPR34 as a metabolic immune checkpoint, where tumor-derived LysoPS suppresses ILC1 and CD8 T cell antitumor activity.","evidence":"Conditional Gpr34 KO in ILC1s, Abhd16a KO in tumor cells, GPR34 antagonist treatment, and Lyz2-Cre macrophage KO with efferocytosis/MHC-I/CXCL16 readouts in tumor models","pmids":["39358444","42045172"],"confidence":"Medium","gaps":["Relative contributions of ILC1 versus macrophage axes across tumor types unclear","Identity of dominant LysoPS synthase context-dependent (ABHD16A vs PLA1A)"]},{"year":2024,"claim":"Demonstrated GPR34-LysoPS signaling drives microglia-mediated neuroinflammation in demyelination and retinal pathology via PI3K-AKT/ERK effector arms.","evidence":"GPR34 KO and pharmacological inhibition with PI3K-AKT/ERK and NINJ1 pathway analysis in MS, stroke, and retinal neovascularization mouse models","pmids":["39030423","39468551"],"confidence":"Medium","gaps":["NINJ1 placement downstream of GPR34 needs broader validation","Whether the same axis drives homeostatic versus pathological microglia not separated"]},{"year":2024,"claim":"Showed PLA1A-generated LysoPS is the specific ligand mediating GPR34-dependent cDC1 efferocytosis and B-cell positioning, refining the upstream enzymatic source.","evidence":"GPR34 KO and gain-of-function knock-in mice, PLA1A vs ABHD16A KO comparison, OT-I cross-presentation and ex vivo migration assays, stromal PLA1A conditional KO","pmids":["41212150","39412501"],"confidence":"Medium","gaps":["Tissue/context determinants selecting PLA1A over ABHD16A as ligand source unresolved","Cell-type selectivity (cDC1 vs cDC2 vs macrophage) mechanism not fully explained"]},{"year":2025,"claim":"Implicated GPR34 in Alzheimer-context microglial biology, showing agonism enhances Aβ fibril uptake via cAMP reduction and TREM2 dependence, and that loss accelerates loss of homeostatic state.","evidence":"Selective agonist M1 with cAMP measurement and Gpr34 knockdown in hAPP mice; ERK/NF-κB knockdown/overexpression in BV-2; iPSC-derived microglia phagocytosis and DAM-state RNA-seq (preprint)","pmids":["41261421","37557947","bio_10.1101_2025.03.28.646038"],"confidence":"Medium","gaps":["Mechanistic link between GPR34 and TREM2 signaling undefined","iPSC microglia findings are from a non-peer-reviewed preprint","Selectivity of GPR34 for myelin/fibrillar Aβ over other cargo not mechanistically explained"]},{"year":2025,"claim":"Identified post-translational stabilization of GPR34 by the deubiquitinase USP8, linking receptor abundance to ferroptosis and tumor progression.","evidence":"Co-IP identification of USP8 as a GPR34 DUB, USP8 overexpression rescue of GPR34 deletion, and DUB-IN-3 inhibitor treatment in anaplastic thyroid carcinoma","pmids":["40862294"],"confidence":"Medium","gaps":["Ubiquitin ligase opposing USP8 not identified","Direct deubiquitination of GPR34 versus indirect effect not fully separated","Single-lab study"]},{"year":2005,"claim":"Characterized the GPR34 gene structure and translational start usage, establishing the protein's N-terminal boundaries.","evidence":"Genomic sequencing across vertebrates, reporter constructs, and combinatory start-codon mutagenesis","pmids":["16338117"],"confidence":"Medium","gaps":["Functional consequence of N-terminal length variants on signaling not tested"]},{"year":null,"claim":"How GPR34 distinguishes homeostatic debris clearance from pathological pro-inflammatory signaling, and how ligand source (PLA1A vs ABHD16A) and receptor desensitization are coordinated across tissues, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking ligand source, biased signaling, and outcome","Endogenous regulators of desensitization beyond β-arrestin motif not mapped in vivo"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,1,6]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[0,6,8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,6]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,6,8]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[12,15,25]}],"complexes":[],"partners":["GNAI1","USP8"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UPC5","full_name":"Probable G-protein coupled receptor 34","aliases":[],"length_aa":381,"mass_kda":43.9,"function":"G-protein-coupled receptor of lysophosphatidylserine (LysoPS) that plays different roles in immune response (PubMed:16460680). Acts a damage-sensing receptor that triggers tissue repair upon recognition of dying neutrophils (By similarity). Mechanistically, apoptotic neutrophils release lysophosphatydilserine that are recognized by type 3 innate lymphoid cells (ILC3s) via GPR34, which activates downstream PI3K-AKT and RAS-ERK signaling pathways leading to STAT3 activation and IL-22 production (By similarity). Plays an important role in microglial function, controlling morphology and phagocytosis (By similarity)","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9UPC5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GPR34","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GPR34","total_profiled":1310},"omim":[{"mim_id":"300749","title":"INTELLECTUAL DEVELOPMENTAL DISORDER WITH MICROCEPHALY AND PONTINE AND CEREBELLAR HYPOPLASIA; MICPCH","url":"https://www.omim.org/entry/300749"},{"mim_id":"300748","title":"G PROTEIN-COUPLED RECEPTOR 82; GPR82","url":"https://www.omim.org/entry/300748"},{"mim_id":"300241","title":"G PROTEIN-COUPLED RECEPTOR 34; GPR34","url":"https://www.omim.org/entry/300241"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"placenta","ntpm":40.1}],"url":"https://www.proteinatlas.org/search/GPR34"},"hgnc":{"alias_symbol":["LPS1"],"prev_symbol":[]},"alphafold":{"accession":"Q9UPC5","domains":[{"cath_id":"1.20.1070.10","chopping":"49-343","consensus_level":"high","plddt":88.7494,"start":49,"end":343}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UPC5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UPC5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UPC5-F1-predicted_aligned_error_v6.png","plddt_mean":77.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GPR34","jax_strain_url":"https://www.jax.org/strain/search?query=GPR34"},"sequence":{"accession":"Q9UPC5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UPC5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UPC5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UPC5"}},"corpus_meta":[{"pmid":"34107271","id":"PMC_34107271","title":"GPR34-mediated sensing of lysophosphatidylserine released by apoptotic neutrophils activates type 3 innate lymphoid cells to mediate tissue repair.","date":"2021","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/34107271","citation_count":98,"is_preprint":false},{"pmid":"21097509","id":"PMC_21097509","title":"Altered immune response in mice deficient for the G protein-coupled receptor GPR34.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21097509","citation_count":79,"is_preprint":false},{"pmid":"25142016","id":"PMC_25142016","title":"Altered microglial phagocytosis in GPR34-deficient mice.","date":"2014","source":"Glia","url":"https://pubmed.ncbi.nlm.nih.gov/25142016","citation_count":73,"is_preprint":false},{"pmid":"22343749","id":"PMC_22343749","title":"GPR34 is a receptor for lysophosphatidylserine with a fatty acid at the sn-2 position.","date":"2012","source":"Journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22343749","citation_count":69,"is_preprint":false},{"pmid":"29674500","id":"PMC_29674500","title":"Novel GPR34 and CCR6 mutation and distinct genetic profiles in MALT lymphomas of different sites.","date":"2018","source":"Haematologica","url":"https://pubmed.ncbi.nlm.nih.gov/29674500","citation_count":53,"is_preprint":false},{"pmid":"30975169","id":"PMC_30975169","title":"GPR34 in spinal microglia exacerbates neuropathic pain in mice.","date":"2019","source":"Journal of neuroinflammation","url":"https://pubmed.ncbi.nlm.nih.gov/30975169","citation_count":50,"is_preprint":false},{"pmid":"22966169","id":"PMC_22966169","title":"t(X;14)(p11;q32) in MALT lymphoma involving GPR34 reveals a role for GPR34 in tumor cell growth.","date":"2012","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/22966169","citation_count":45,"is_preprint":false},{"pmid":"25970039","id":"PMC_25970039","title":"Structure-activity relationships of lysophosphatidylserine analogs as agonists of G-protein-coupled receptors GPR34, P2Y10, and GPR174.","date":"2015","source":"Journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25970039","citation_count":42,"is_preprint":false},{"pmid":"29684466","id":"PMC_29684466","title":"The G protein-coupled receptor GPR34 - 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In HEK293 cells expressing GPR34 with a Gαq/Gαi1 chimera, LysoPS elevated intracellular Ca2+ levels, stimulated AP-TGFα release, and induced CHO-K1 cell migration. Replacement of the serine head group abolished reactivity, and 2-acyl-LysoPS (generated by PS-PLA1) was more potent than 1-acyl-LysoPS, confirming sn-2 positional selectivity.\",\n      \"method\": \"Intracellular Ca2+ assay, AP-TGFα release assay, cell migration assay, synthetic LysoPS analogues, catalytically inactive mutant PS-PLA1 controls\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal functional assays with mutagenesis controls and chemical probes in a single rigorous study\",\n      \"pmids\": [\"22343749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structure of human GPR34 bound to LysoPS (18:1) and Gi protein revealed that the negatively charged serine head group of LysoPS occupies a polar cavity formed by TM3, TM6, and TM7, while the hydrophobic acyl tail resides in a lateral open hydrophobic groove formed by TM3-5. A selective antagonist YL-365 binds competitively in a portion of the orthosteric pocket and induces allosteric changes in the receptor.\",\n      \"method\": \"Cryo-EM structure determination of active (agonist-bound) and inactive (antagonist-bound) GPR34 complexes; virtual screening; fusion protein design for inactive-state structure\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures of both active and inactive states with functional validation of antagonist, replicated in part by independent structure paper (PMID:38326347)\",\n      \"pmids\": [\"37733739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structures of human GPR34-Gi complex bound to S3E-LysoPS or the aromatic surrogate M1 showed a laterally open ligand-binding pocket allowing membrane-lateral entry of lipidic agonists. The serine amine and carboxylate groups are recognized by a charged residue cluster, and the acyl chain fits into an L-shaped hydrophobic pocket in the TM4-5 gap. Molecular dynamics simulations supported that 2-acyl LysoPS is the physiological ligand due to its regioselectivity.\",\n      \"method\": \"Cryo-EM structure determination, molecular dynamics simulations, structure-activity validation with synthetic analogues\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independent cryo-EM structural study with MD simulations and functional assays, replicating and extending the binding mode defined in PMID:37733739\",\n      \"pmids\": [\"38326347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of human GPR34 and GPR174 in complex with LysoPS and Gi protein elucidated the lipid-binding modes and structural features of these receptors in the active state, providing insights into ligand recognition and signaling of LysoPS receptors.\",\n      \"method\": \"Cryo-EM structure determination, structural comparison, functional studies\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — independent cryo-EM structural study with functional validation, orthogonal to PMID:37733739 and PMID:38326347\",\n      \"pmids\": [\"38048360\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"GPR34-deficient mice showed significantly lower numbers of granulocytes and macrophages in spleens after immunization, increased paw swelling in delayed-type hypersensitivity, higher pathogen burden after Cryptococcus neoformans infection, and altered basal/stimulated TNF-α, GM-CSF, and IFN-γ levels, establishing a functional role for GPR34 in cellular immune responses.\",\n      \"method\": \"GPR34 knockout mouse model, immunization challenge, delayed-type hypersensitivity test, pulmonary infection model, cytokine measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular and immune phenotypes across multiple challenge models in a single study\",\n      \"pmids\": [\"21097509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"GPR34-deficient microglia showed morphological changes in retinal and cortical microglia and reduced phagocytosis activity in both retina and acutely isolated cortical slices. RNA sequencing revealed differentially expressed transcripts involved in cell motility and phagocytosis, but no differences in microglial motility after lesion were detected.\",\n      \"method\": \"GPR34 knockout mouse, RNA sequencing of microglia, phagocytosis assays in retina and cortical slices, in vivo lesion models\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO with multiple orthogonal phenotypic readouts (morphology, transcriptomics, functional phagocytosis assays) across two tissue types\",\n      \"pmids\": [\"25142016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GPR34 on ILC3s acts as a damage-sensing receptor for LysoPS released by apoptotic neutrophils. ILC3-specific deletion of Gpr34 suppressed IL-22 production and tissue repair during colon and skin injury. Downstream signaling via PI3K-AKT or ERK was required for ILC3 activation and IL-22 production.\",\n      \"method\": \"ILC3-specific Gpr34 conditional knockout, co-culture of neutrophils and ILC3s, metabolomic analysis, PI3K-AKT/ERK inhibition, intestinal epithelial injury model\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific KO with multiple in vivo and in vitro readouts, pathway inhibition experiments, metabolomic identification of ligand\",\n      \"pmids\": [\"34107271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GPR34 expressed by spinal dorsal horn microglia promotes neuropathic pain after nerve injury. GPR34-deficient mice showed attenuated nerve injury-induced pro-inflammatory cytokine expression and reduced pain behavior. LysoPS levels were elevated in the dorsal horn after injury, and intrathecal administration of a GPR34 antagonist reduced neuropathic pain, placing GPR34 upstream of pro-inflammatory microglial activation.\",\n      \"method\": \"GPR34 knockout mice, von Frey hair test, qRT-PCR for cytokines, in situ hybridization, LC-MS/MS quantification of LysoPS, intrathecal antagonist administration\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO plus pharmacological blockade with multiple orthogonal readouts (behavior, cytokines, ligand measurement)\",\n      \"pmids\": [\"30975169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LysoPS in the tumor microenvironment inhibits ILC1 antitumor activity via GPR34. Genetic deletion of LysoPS synthase Abhd16a in tumors or Gpr34 in ILC1s, or pharmacological antagonism of GPR34, enhanced ILC1 antitumor activity, identifying GPR34 as a metabolic immune checkpoint on ILC1s.\",\n      \"method\": \"Gpr34 conditional KO in ILC1s, Abhd16a knockout in tumor cells, GPR34 antagonist treatment, in vivo tumor models\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific KO plus ligand-synthesis KO plus pharmacological blockade with consistent functional readouts\",\n      \"pmids\": [\"39358444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LysoPS-GPR34 signaling mediates microglia-driven neuroinflammation in demyelination. Myelin debris-induced microglial activation and proinflammatory cytokine production depended on LysoPS and GPR34, signaling through PI3K-AKT and ERK. In vivo, reducing LysoPS in myelin or genetic/pharmacological GPR34 inhibition reduced neuroinflammation and pathologies in multiple sclerosis and stroke mouse models.\",\n      \"method\": \"GPR34 knockout and pharmacological inhibition, PI3K-AKT/ERK pathway analysis, mouse models of MS and stroke, in vitro microglial stimulation\",\n      \"journal\": \"Cellular & molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KO plus pharmacological blockade plus pathway inhibition in multiple in vivo and in vitro models\",\n      \"pmids\": [\"39030423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The t(X;14)(p11;q32) translocation in MALT lymphoma deregulates GPR34 expression by placing it under IGH control. Overexpression of GPR34 in lymphoma and HeLa cells resulted in phosphorylation of ERK, PKC, and CREB; induced CRE, AP1, and NF-κB-mediated gene transcription; and increased cell proliferation.\",\n      \"method\": \"Translocation cloning, GPR34 overexpression in lymphoma and HeLa cells, phosphorylation assays, reporter gene assays (CRE, AP1, NF-κB), cell proliferation assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — overexpression with multiple signaling readouts in a single lab study\",\n      \"pmids\": [\"22966169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The GPR34 C-terminal truncation mutant Q340X, which lacks the phosphorylation motif for β-arrestin-mediated desensitization, showed significantly delayed internalization after LysoPS stimulation, increased resistance to apoptosis, greater transforming potential, and significantly activated CRE, NF-κB, and AP1 reporter activities compared to wild-type GPR34.\",\n      \"method\": \"Isogenic Flp-InTRex293 stable cell lines, internalization assays, apoptosis assays, reporter gene assays (CRE, NF-κB, AP1), soft agar transformation assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic cell line system with multiple functional assays in a single lab study\",\n      \"pmids\": [\"34086889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In dendritic cells, NF-κB and MAPK signaling pathways regulate GPR34 expression. DCs lacking GPR34 showed higher caspase-3/7 activity and increased apoptosis levels, establishing GPR34 as a pro-survival factor in DCs.\",\n      \"method\": \"GPR34 knockout mouse, whole-transcriptome RNA sequencing of DCs, pathway inhibition experiments (NF-κB, MAPK), caspase-3/7 activity assay, apoptosis measurement\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with transcriptomics and functional pathway experiments in a single lab study\",\n      \"pmids\": [\"26851221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"A tri-basic motif in the first intracellular loop of GPR34 acts as the key topogenic signal dictating the orientation of transmembrane domain-1 (TM1). Charge disruption of this motif perturbed topogenesis, caused loss of a conformation-sensitive epitope, altered post-translational processing, and arrested trafficking in the Golgi. A cleavable N-terminal signal sequence as surrogate topogenic determinant rescued TM1 orientation, conformational epitope, and cell surface trafficking.\",\n      \"method\": \"FLAG-tag and conformation-sensitive native epitope monitoring, mutant panel expression, signal sequence insertion rescue, N-tail truncation and site-directed mutagenesis, Golgi trafficking analysis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic mutagenesis panel with multiple readouts in a single lab study\",\n      \"pmids\": [\"27086875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"LysoPS stimulates chemotactic migration of colorectal cancer cells through GPR34 and the PI3K/Akt pathway. GPR34 was the predominantly expressed LysoPS receptor on colorectal cancer cell lines. GPR34 knockdown by siRNA or treatment with the PI3K inhibitor wortmannin suppressed LysoPS-induced migration.\",\n      \"method\": \"RT-PCR for receptor expression, siRNA knockdown of GPR34, chemotaxis assay, PI3K inhibitor (wortmannin) treatment\",\n      \"journal\": \"Anticancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — siRNA KD with pharmacological pathway inhibition, functional readout, single lab\",\n      \"pmids\": [\"25275042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR34 is stabilized by the deubiquitinase USP8. USP8 was identified as a deubiquitinase for GPR34; effects of GPR34 deletion on ferroptosis and tumor progression in anaplastic thyroid carcinoma were reversed by USP8 overexpression. Pharmacological inhibition of USP8 with DUB-IN-3 restrained ATC growth.\",\n      \"method\": \"Co-immunoprecipitation/protein interaction studies to identify USP8 as a DUB, GPR34 deletion in vitro/in vivo, USP8 overexpression rescue, DUB-IN-3 inhibitor treatment, ferroptosis assays\",\n      \"journal\": \"Mediators of inflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — identification of DUB-substrate relationship with functional rescue, single lab study\",\n      \"pmids\": [\"40862294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"LysoPS released from injured retinal ganglion cells activates the GPR34-PI3K-AKT-NINJ1 signaling axis in microglia, upregulating inflammatory cytokines (IL-6, IL-8, VEGFA, FGF2) and promoting microglial extracellular trap formation and retinal neovascularization. Inhibition of this axis suppressed these effects in vitro and in vivo.\",\n      \"method\": \"In vitro microglial stimulation with LysoPS, GPR34 inhibition (genetic and pharmacological), PI3K-AKT pathway analysis, NINJ1 expression measurement, in vivo retinal neovascularization model\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo experiments with pathway dissection in a single lab study\",\n      \"pmids\": [\"39468551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR34 promotes GPR34+ macrophage efferocytosis and CXCL16 secretion in pancreatic cancer. GPR34+ macrophages responded to LysoPS, and their efferocytosis promoted MHC-I degradation via the lysosomal pathway, leading to CD8+ T cell exhaustion. Gpr34ΔLyz2 mouse models confirmed this in vivo.\",\n      \"method\": \"Single-cell RNA sequencing, Gpr34 conditional KO (Lyz2-Cre), in vitro co-culture, efferocytosis assays, MHC-I degradation analysis, CXCL16 measurement\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple mechanistic readouts in a single study\",\n      \"pmids\": [\"42045172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR34 deficiency in cDC1 (but not cDC2 or macrophages) led to reduced apoptotic cell uptake and impaired cross-presentation to CD8 T cells. PLA1A (but not ABHD16A) deficiency reduced the OT-I T cell response to apoptotic cell-associated antigen, identifying PLA1A-generated lysoPS as the GPR34 ligand mediating cDC1 efferocytosis.\",\n      \"method\": \"GPR34 knockout mice, adoptive transfer of apoptotic cell-OVA, OT-I T cell proliferation assay, PLA1A and ABHD16A knockout comparison, cell-type-specific phenotyping\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with specific cellular phenotype and ligand-source identification in a single study\",\n      \"pmids\": [\"41212150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"GPR34 knock-in (gain-of-function) promotes peritoneal cavity accumulation of plasma cells and memory B cells through lysoPS-dependent migration. KI cells showed robust migration to lysoPS ex vivo. Maintenance of KI cells in the peritoneal cavity was dependent on stromal PLA1A, the lysoPS-generating enzyme expressed in omental fibroblasts.\",\n      \"method\": \"GPR34 knock-in mouse, adoptive transfer experiments, bone marrow chimeras, ex vivo migration assay, PLA1A conditional KO\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KI plus stromal KO with functional migration assay and in vivo localization, single lab\",\n      \"pmids\": [\"39412501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Selective agonism of GPR34 with compound M1 enhanced microglial uptake of Aβ fibrils (but not monomeric or oligomeric Aβ) through reduction of intracellular cAMP levels. This effect required functional TREM2 signaling. Gpr34 knockdown confirmed GPR34 as the molecular target of M1.\",\n      \"method\": \"Flow cytometry-based Aβ uptake assay, cAMP measurement, Gpr34 knockdown, intrahippocampal M1 injection in hAPP knock-in mice, TREM2 signaling requirement testing\",\n      \"journal\": \"Alzheimer's research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo assays with KD confirmation and pathway dependency established in a single study\",\n      \"pmids\": [\"41261421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The majority of GPR34 mutations in MALT lymphoma are nonsense and frameshift changes clustered in the C-terminal cytoplasmic tail, generating truncated proteins that lack the phosphorylation motif for β-arrestin-mediated receptor desensitization and internalization, suggesting constitutive or enhanced signaling.\",\n      \"method\": \"Whole exome sequencing of MALT lymphoma cases, mutational mapping to functional protein domains\",\n      \"journal\": \"Haematologica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — sequencing-based inference about mechanism without direct functional validation of specific mutations in this paper\",\n      \"pmids\": [\"29674500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GPR34 knockdown in BV-2 microglia exposed to Aβ1-42 decreased TNF-α, IL-1β, IL-6, and iNOS levels and suppressed ERK/NF-κB signaling activation. GPR34 overexpression-induced ERK/NF-κB activation and cytokine upregulation were abolished by the ERK inhibitor FR180204, placing GPR34 upstream of ERK/NF-κB in microglial neuroinflammation.\",\n      \"method\": \"siRNA knockdown and overexpression in BV-2 cells, ERK inhibitor (FR180204), western blot and immunofluorescence for signaling components, APP/PS1 mouse model with GPR34 knockdown\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD, OE, and pathway inhibitor rescue with in vitro and in vivo corroboration in a single study\",\n      \"pmids\": [\"37557947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GPR34 contains an intronless coding region but has an evolutionarily conserved 5' noncoding intron-exon structure. An alternatively used cryptic intron shortens the N-terminus by 47 amino acids. Multiple conserved in-frame AUGs serve as translational start points, with combinatory mutagenesis confirming preference for the second in-frame AUG in human GPR34.\",\n      \"method\": \"Genomic sequencing across vertebrate species, reporter constructs, combinatory mutagenesis, expression analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis of translational start sites with reporter validation in a single study\",\n      \"pmids\": [\"16338117\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"LysoPS has no or very weak agonistic activity at most vertebrate GPR34 orthologues except some fish subtypes. Using chimeric receptors, single positions in the second extracellular loop and transmembrane helix 5 of carp GPR34 subtype 2a were identified as critical for lysoPS responsiveness; transferring these positions to human GPR34 enabled lysoPS activation. Aminoethyl-carbamoyl ATP was identified as an antagonist of carp GPR34.\",\n      \"method\": \"Chimeric receptor construction, site-directed mutagenesis, functional assays across vertebrate orthologues, phylogenetic analysis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with functional rescue in a single study; note this paper's conclusion partially contradicts other studies confirming lysoPS activity at human GPR34\",\n      \"pmids\": [\"22348703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In Gpr34 knockout mice at postnatal day 18, elevated numbers of neurons, oligodendrocytes, and microglia showed markers of cell death (cleaved-caspase 3, phospho-RIP3, annexin V), with reduced microglial localization to areas of high cell death. KO microglia showed increased intracellular accumulation of myelin basic protein and SNAP25, suggesting altered handling of apoptotic debris. Transcriptomic analysis revealed persistent immune pathway alterations, and 3-month KO mice displayed sustained hypolocomotion.\",\n      \"method\": \"Gpr34 KO mouse, immunohistochemistry for cell death markers, microglial localization analysis, ex vivo phagocytosis assay, transcriptomic analysis, locomotion behavioral testing\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with multiple histological and functional readouts in a single study\",\n      \"pmids\": [\"41964003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GPR34 KO iPSC-derived microglia showed reduced Ca2+ and phosphorylated ERK signaling in response to LysoPS and myelin stimulation, and were selectively impaired in phagocytosis of myelin but not Aβ or E. coli. GPR34 KO accelerated conversion of homeostatic microglia to DAM states in healthy and amyloid mouse models. GPR34 agonism promoted interaction with and activation of ERK.\",\n      \"method\": \"GPR34 KO iPSC-derived microglia, Ca2+ imaging, pERK measurement, selective phagocytosis assays, RNA-sequencing, amyloid mouse models\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays in human iPSC-derived microglia and mouse models; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.03.28.646038\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"GPR34 is a Gi/o-coupled GPCR (P2Y family) that functions as a receptor for lysophosphatidylserine (LysoPS), particularly the 2-acyl form generated by phosphatidylserine-specific phospholipase A1 (PLA1A/PS-PLA1); structural studies show LysoPS enters a laterally open orthosteric pocket where its serine head group is recognized by a charged residue cluster in TM3/6/7 and its acyl tail fits an L-shaped hydrophobic groove in TM4-5, leading to Gi-mediated signaling through PI3K-AKT and ERK pathways; GPR34 is highly enriched in microglia, macrophages, dendritic cells, and innate lymphoid cells, where it regulates phagocytosis of apoptotic cells and myelin debris, maintains microglial homeostatic state, controls pro-inflammatory cytokine production, promotes DC survival, and mediates tissue repair and neuropathic pain; C-terminal truncation mutations found in MALT lymphoma impair receptor desensitization and internalization, conferring enhanced signaling through NF-κB, AP1, and CRE pathways and increased cell proliferation, while GPR34 can be stabilized post-translationally by the deubiquitinase USP8.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GPR34 is a Gi-coupled G-protein-coupled receptor that functions as a sensor for lysophosphatidylserine (LysoPS), enabling innate immune and microglial cells to detect dying cells and tissue damage [#0, #6]. It selectively recognizes the 2-acyl form of LysoPS generated by PS-specific phospholipase A1: replacement of the serine head group abolishes activity and 2-acyl-LysoPS is more potent than the 1-acyl species [#0]. Cryo-EM structures of the active GPR34-Gi complex show that the charged serine head group is read out by a polar residue cluster in TM3/TM6/TM7 while the acyl tail enters an L-shaped hydrophobic groove through a laterally open pocket that permits membrane-lateral ligand entry, and a competitive antagonist (YL-365) occupies part of this orthosteric site [#1, #2, #3]. Ligand engagement drives Gi signaling through PI3K-AKT and ERK, and through ERK/NF-\\u03baB, to control downstream effector programs [#6, #9, #22]. GPR34 is enriched in microglia and other myeloid and innate lymphoid cells, where it promotes phagocytosis of apoptotic cells and myelin debris, maintains microglial homeostasis, and tunes pro-inflammatory cytokine output [#5, #9, #26]. Through this damage-sensing role it acts across contexts: it drives microglia-dependent neuropathic pain and demyelinating neuroinflammation, supports ILC3-mediated tissue repair via IL-22, and serves as a metabolic immune checkpoint that restrains ILC1 and CD8 T cell antitumor responses [#6, #7, #8, #9, #17]. In MALT lymphoma, a t(X;14) translocation deregulates GPR34 under IGH control and C-terminal truncation mutations remove the \\u03b2-arrestin phosphorylation motif, delaying receptor internalization and enhancing constitutive signaling through CRE, AP1, and NF-\\u03baB to increase proliferation and transformation [#10, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2012,\n      \"claim\": \"Established the endogenous ligand and signaling output of an orphan receptor by showing GPR34 responds to LysoPS with strict sn-2 acyl positional selectivity.\",\n      \"evidence\": \"Ca2+, AP-TGF\\u03b1 release and migration assays in HEK293/CHO with synthetic LysoPS analogues and catalytically inactive PS-PLA1 controls\",\n      \"pmids\": [\"22343749\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve the in vivo cellular source of 2-acyl-LysoPS\", \"G-protein coupling specificity tested using a G\\u03b1q/G\\u03b1i1 chimera rather than native Gi\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Probed why LysoPS responsiveness varies across orthologues, mapping ECL2 and TM5 residues that gate lipid activation.\",\n      \"evidence\": \"Chimeric receptor and site-directed mutagenesis across vertebrate orthologues with functional assays and an ATP-derived antagonist\",\n      \"pmids\": [\"22348703\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conclusion of weak human GPR34 LysoPS activity partially conflicts with other studies\", \"Physiological relevance of fish-specific responsiveness unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"First demonstrated a physiological function for GPR34, linking it to cellular immune responses and host defense.\",\n      \"evidence\": \"GPR34 knockout mice subjected to immunization, delayed-type hypersensitivity, and Cryptococcus infection with cytokine measurement\",\n      \"pmids\": [\"21097509\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the ligand source or signaling pathway in vivo\", \"Cell-type responsible for phenotypes not dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected GPR34 to microglial phagocytosis, identifying its homeostatic role in clearing debris in the CNS.\",\n      \"evidence\": \"GPR34 KO mouse microglia analyzed by RNA-seq, morphology, and phagocytosis assays in retina and cortical slices\",\n      \"pmids\": [\"25142016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No microglial motility defect detected\", \"Ligand driving phagocytosis not defined in this study\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined GPR34 as a damage-sensing receptor on ILC3s detecting LysoPS from apoptotic neutrophils to drive tissue repair, and pinned the downstream pathway.\",\n      \"evidence\": \"ILC3-specific conditional KO, neutrophil-ILC3 co-culture, metabolomics, and PI3K-AKT/ERK inhibition in injury models\",\n      \"pmids\": [\"34107271\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"LysoPS-generating enzyme in this context not specified\", \"Receptor desensitization dynamics in ILC3s not addressed\"]\n    },\n    {\n      \"year\": \"2019\",\n      \"claim\": \"Placed GPR34 upstream of pro-inflammatory microglial activation in neuropathic pain, validated pharmacologically.\",\n      \"evidence\": \"GPR34 KO mice, von Frey behavior, cytokine qRT-PCR, LC-MS/MS LysoPS quantification, and intrathecal antagonist\",\n      \"pmids\": [\"30975169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source of injury-induced LysoPS in dorsal horn not identified\", \"Direct receptor-cytokine signaling steps not delineated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved the structural basis of lipid recognition and Gi coupling, explaining sn-2 selectivity and membrane-lateral ligand entry.\",\n      \"evidence\": \"Cryo-EM of active and inactive GPR34-Gi complexes with agonist and antagonist, MD simulations, and structure-activity validation (three independent structural studies)\",\n      \"pmids\": [\"37733739\", \"38326347\", \"38048360\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational transitions during activation not captured kinetically\", \"Structural basis of \\u03b2-arrestin/desensitization not addressed\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified GPR34 as a pro-survival factor in dendritic cells and mapped a topogenic determinant required for correct folding and surface trafficking.\",\n      \"evidence\": \"GPR34 KO DC transcriptomics and caspase assays; mutagenesis of a tri-basic ICL1 motif with conformational-epitope and Golgi trafficking readouts\",\n      \"pmids\": [\"26851221\", \"27086875\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Link between trafficking signal and DC survival function not established\", \"Pro-survival downstream effectors not identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established GPR34 deregulation as oncogenic in MALT lymphoma, with truncations removing the desensitization motif to enhance signaling.\",\n      \"evidence\": \"Translocation cloning and overexpression with phosphorylation and CRE/AP1/NF-\\u03baB reporters; isogenic Q340X truncation cell lines with internalization, apoptosis, and soft-agar transformation assays; exome sequencing of mutation clustering\",\n      \"pmids\": [\"22966169\", \"34086889\", \"29674500\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether truncated receptors signal constitutively or only with enhanced ligand response not fully resolved\", \"Exome mapping (idx 21) lacks direct functional validation of individual mutations\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined GPR34 as a metabolic immune checkpoint, where tumor-derived LysoPS suppresses ILC1 and CD8 T cell antitumor activity.\",\n      \"evidence\": \"Conditional Gpr34 KO in ILC1s, Abhd16a KO in tumor cells, GPR34 antagonist treatment, and Lyz2-Cre macrophage KO with efferocytosis/MHC-I/CXCL16 readouts in tumor models\",\n      \"pmids\": [\"39358444\", \"42045172\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of ILC1 versus macrophage axes across tumor types unclear\", \"Identity of dominant LysoPS synthase context-dependent (ABHD16A vs PLA1A)\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated GPR34-LysoPS signaling drives microglia-mediated neuroinflammation in demyelination and retinal pathology via PI3K-AKT/ERK effector arms.\",\n      \"evidence\": \"GPR34 KO and pharmacological inhibition with PI3K-AKT/ERK and NINJ1 pathway analysis in MS, stroke, and retinal neovascularization mouse models\",\n      \"pmids\": [\"39030423\", \"39468551\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"NINJ1 placement downstream of GPR34 needs broader validation\", \"Whether the same axis drives homeostatic versus pathological microglia not separated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed PLA1A-generated LysoPS is the specific ligand mediating GPR34-dependent cDC1 efferocytosis and B-cell positioning, refining the upstream enzymatic source.\",\n      \"evidence\": \"GPR34 KO and gain-of-function knock-in mice, PLA1A vs ABHD16A KO comparison, OT-I cross-presentation and ex vivo migration assays, stromal PLA1A conditional KO\",\n      \"pmids\": [\"41212150\", \"39412501\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue/context determinants selecting PLA1A over ABHD16A as ligand source unresolved\", \"Cell-type selectivity (cDC1 vs cDC2 vs macrophage) mechanism not fully explained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated GPR34 in Alzheimer-context microglial biology, showing agonism enhances A\\u03b2 fibril uptake via cAMP reduction and TREM2 dependence, and that loss accelerates loss of homeostatic state.\",\n      \"evidence\": \"Selective agonist M1 with cAMP measurement and Gpr34 knockdown in hAPP mice; ERK/NF-\\u03baB knockdown/overexpression in BV-2; iPSC-derived microglia phagocytosis and DAM-state RNA-seq (preprint)\",\n      \"pmids\": [\"41261421\", \"37557947\", \"bio_10.1101_2025.03.28.646038\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link between GPR34 and TREM2 signaling undefined\", \"iPSC microglia findings are from a non-peer-reviewed preprint\", \"Selectivity of GPR34 for myelin/fibrillar A\\u03b2 over other cargo not mechanistically explained\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified post-translational stabilization of GPR34 by the deubiquitinase USP8, linking receptor abundance to ferroptosis and tumor progression.\",\n      \"evidence\": \"Co-IP identification of USP8 as a GPR34 DUB, USP8 overexpression rescue of GPR34 deletion, and DUB-IN-3 inhibitor treatment in anaplastic thyroid carcinoma\",\n      \"pmids\": [\"40862294\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin ligase opposing USP8 not identified\", \"Direct deubiquitination of GPR34 versus indirect effect not fully separated\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Characterized the GPR34 gene structure and translational start usage, establishing the protein's N-terminal boundaries.\",\n      \"evidence\": \"Genomic sequencing across vertebrates, reporter constructs, and combinatory start-codon mutagenesis\",\n      \"pmids\": [\"16338117\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of N-terminal length variants on signaling not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GPR34 distinguishes homeostatic debris clearance from pathological pro-inflammatory signaling, and how ligand source (PLA1A vs ABHD16A) and receptor desensitization are coordinated across tissues, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking ligand source, biased signaling, and outcome\", \"Endogenous regulators of desensitization beyond \\u03b2-arrestin motif not mapped in vivo\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [0, 6, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 6]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 6, 8]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [12, 15, 25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GNAI1\", \"USP8\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}