{"gene":"P2RX6","run_date":"2026-04-29T11:37:57","timeline":{"discoveries":[{"year":1996,"finding":"P2X6 receptor subunits were cloned and expressed; they form ATP-gated ion channels with two transmembrane segments and a large extracellular loop, desensitize slowly, do not respond to alpha-beta-methylene-ATP, and are not blocked by suramin or PPADS. P2X6 expresses at lower levels than other P2X subunits, suggesting it does not normally form homomultimeric channels.","method":"cDNA cloning, heterologous expression, electrophysiology","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — original cloning and functional characterization, foundational paper with 768 citations","pmids":["8786426"],"is_preprint":false},{"year":1998,"finding":"P2X4 and P2X6 subunits coassemble into a novel heteromeric ATP receptor with unique pharmacological properties: activated by low-micromolar alpha-beta-methylene ATP (EC50=12 µM) and blocked by suramin and Reactive Blue 2. Heteromeric assembly was demonstrated by specific copurification of epitope-tagged subunits from HEK-293 cells. P2X6 alone does not assemble into surface receptors in Xenopus oocytes.","method":"Xenopus oocyte expression, electrophysiology, co-immunoprecipitation/copurification with epitope tags in HEK-293 cells","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus functional electrophysiology, 204 citations","pmids":["9736638"],"is_preprint":false},{"year":2000,"finding":"Coexpression of rat P2X2 and P2X6 subunits in Xenopus oocytes generates a heteromeric rP2X2/6 receptor with distinct pharmacology from homomeric P2X2: reduced agonist potencies, loss of some agonist activity, biphasic ATP-evoked currents, altered pH modulation, and changed suramin blockade profile.","method":"Xenopus oocyte expression, voltage-clamp electrophysiology","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 — functional reconstitution in heterologous system, 105 citations","pmids":["10864944"],"is_preprint":false},{"year":2005,"finding":"P2X6 receptor subunits do not oligomerize into stable homomers. Chemical cross-linking of P2X6 did not produce higher-order adducts, and AFM imaging showed a mean molecular volume (~145 nm³) consistent with monomers, in contrast to P2X2 which forms trimers (~409 nm³).","method":"Chemical cross-linking, atomic force microscopy (AFM) imaging","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — two orthogonal structural/biochemical methods, 156 citations","pmids":["15657042"],"is_preprint":false},{"year":2004,"finding":"N-linked glycosylation regulates P2X6 receptor function. Functional P2X6 receptors show increased glycosylation (~70 kDa) compared to non-functional receptors (~60 kDa); N-glycosidase F treatment collapses both to ~55 kDa. Functional P2X6 displays a novel phenotype sensitive to alpha-beta-methylene ATP (EC50=0.6 µM), slow desensitization, and resistance to suramin.","method":"Western blot, N-glycosidase F treatment, electrophysiology, RT-PCR","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1–2 — biochemical glycosylation analysis plus functional electrophysiology","pmids":["15044628"],"is_preprint":false},{"year":2006,"finding":"An uncharged 14-amino acid region at the N-terminus of P2X6 inhibits its assembly and ER export. When this region is removed or charged residues are added, P2X6 forms homotrimers, undergoes complex glycosylation, and traffics to the plasma membrane, but remains non-functional. As a heteromer with P2X2 or P2X4, P2X6 exits the ER and is expressed at the cell surface or constitutively internalized depending on partner subunit.","method":"Immunocytochemistry, surface biotinylation, atomic force microscopy, targeted mutagenesis","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis plus multiple orthogonal structural/trafficking methods","pmids":["16452399"],"is_preprint":false},{"year":2002,"finding":"P2X6 receptors co-localize with VE-cadherin at cell-cell junctions in human umbilical vein endothelial cells and are rapidly internalized upon reduction of extracellular Ca2+. Unlike P2X4, P2X6 could not be co-immunoprecipitated with VE-cadherin, indicating distinct association modes at adherens junctions.","method":"Confocal microscopy, electron microscopy, co-immunoprecipitation, Triton X-100 fractionation","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 — localization with functional consequence (internalization), but co-IP was negative for P2X6-VE-cadherin direct interaction","pmids":["12088286"],"is_preprint":false},{"year":2014,"finding":"P2X2, P2X4, and P2X6 subunits can form a heterotrimeric complex containing all three distinct subunits. Sequential co-immunoprecipitation with anti-HA and anti-FLAG beads from tsA 201 cells co-expressing His6-P2X2, HA-P2X4, and FLAG-P2X6 confirmed interaction of all three subunits. AFM imaging with dual antibody decoration confirmed the P2X2/4/6 heterotrimer architecture.","method":"Sequential co-immunoprecipitation, atomic force microscopy imaging with antibody decoration","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1–2 — sequential co-IP plus AFM structural imaging, two orthogonal methods","pmids":["24815693"],"is_preprint":false},{"year":2015,"finding":"P2X6 subunit accumulates in the nucleus of hippocampal neurons in an age-dependent manner. Nuclear localization is facilitated by ER anchorage via the N-terminal domain, and the extracellular domain is required for nuclear entry. Inside the nucleus, P2X6 associates with spectrin α2 (nuclear envelope protein) and interacts with splicing factor 3A1, resulting in reduced mRNA splicing activity.","method":"Immunofluorescence, co-immunoprecipitation, in vivo nuclear fractionation, splicing activity assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2–3 — co-IP plus functional splicing assay, single lab","pmids":["25874565"],"is_preprint":false},{"year":2019,"finding":"ATP-activated P2RX6 promotes renal cell carcinoma migration and invasion by mediating Ca2+ influx, which activates ERK1/2 phosphorylation and upregulates MMP9. METTL14-mediated m6A modification suppresses P2RX6 protein translation, thereby inhibiting this pro-invasive signaling axis.","method":"In vitro migration/invasion assays, Ca2+ influx measurement, Western blot for p-ERK1/2 and MMP9, m6A/METTL14 knockdown and overexpression, in vivo xenograft","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays in vitro and in vivo, but single lab","pmids":["31159832"],"is_preprint":false},{"year":2007,"finding":"P2X6 receptor undergoes alternative splicing during mouse brain development and during in vitro neuronal differentiation. A full-length and an alternatively spliced form were detected; the spliced form predominates during neuronal differentiation of P19 cells, whereas the full-length form predominates during postnatal brain development, suggesting alternative splicing regulates P2X6 function.","method":"RT-PCR, in vitro differentiation model (P19 cells)","journal":"Experimental physiology","confidence":"Low","confidence_rationale":"Tier 3 — RT-PCR detection of splice forms, no direct functional assay of spliced variant","pmids":["17259301"],"is_preprint":false},{"year":1997,"finding":"P2XM (the human P2X6 ortholog, also known as P2RX6) is a p53-inducible gene. Wild-type p53 induces P2XM expression; the gene contains functional p53-binding sites. It is expressed predominantly in skeletal muscle and maps to chromosome 22q11.","method":"p53-tagged genomic cloning, Northern blot, chromosomal mapping","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — direct p53-binding site cloning plus expression validation","pmids":["9242461"],"is_preprint":false},{"year":2005,"finding":"In cardiac fibroblasts, TNFα prevents ATP-induced downregulation of P2X6 mRNA (desensitization), suggesting TNFα interaction with P2X6 abrogates a protective mechanism against Ca2+ overload and cell death. ATP/BzATP via P2X6 induces apoptosis in cardiac fibroblasts and cardiomyocytes, which is exacerbated by TNFα.","method":"Primary cardiac fibroblast culture, apoptosis assays, real-time PCR, P2X6 mRNA quantification after agonist and TNFα treatment","journal":"Journal of molecular and cellular cardiology","confidence":"Low","confidence_rationale":"Tier 3 — mRNA-level mechanism, single lab, no direct protein interaction demonstrated","pmids":["16242142"],"is_preprint":false}],"current_model":"P2RX6 (P2X6) is an ATP-gated cation channel subunit that cannot form functional homomeric receptors due to an inhibitory uncharged N-terminal domain that retains monomeric P2X6 in the ER; it assembles into functional heteromeric channels with P2X2, P2X4, or both (P2X2/4/6 trimers), altering pharmacology including alpha-beta-methylene ATP sensitivity, and its surface trafficking and function are regulated by N-linked glycosylation; additionally, P2X6 undergoes age-dependent nuclear translocation where it interacts with splicing factor 3A1 to reduce mRNA splicing activity, and in cancer contexts mediates ATP-induced Ca2+ influx driving ERK1/2 phosphorylation and MMP9-dependent invasion."},"narrative":{"teleology":[{"year":1996,"claim":"Cloning of P2X6 established it as a member of the P2X ATP-gated ion channel family but revealed unusually low expression, raising the question of whether it forms functional homomeric channels.","evidence":"cDNA cloning and heterologous expression with electrophysiology","pmids":["8786426"],"confidence":"High","gaps":["No evidence for homomeric channel function at physiological expression levels","Subunit stoichiometry unknown","Tissue-specific role not addressed"]},{"year":1997,"claim":"Identification of P2RX6 as a p53-inducible gene with functional p53-binding sites linked it to stress-responsive transcriptional programs, beyond its role as an ion channel subunit.","evidence":"p53-tagged genomic cloning, Northern blot, chromosomal mapping","pmids":["9242461"],"confidence":"Medium","gaps":["Functional consequence of p53-mediated P2X6 induction not tested","No demonstration that p53 regulation affects channel activity or cell fate"]},{"year":1998,"claim":"Demonstration that P2X6 coassembles with P2X4 into heteromeric receptors with novel pharmacology resolved the question of how P2X6 contributes to purinergic signaling despite its inability to form surface homomers.","evidence":"Xenopus oocyte electrophysiology and epitope-tag co-immunoprecipitation in HEK-293 cells","pmids":["9736638"],"confidence":"High","gaps":["Subunit stoichiometry within the heteromer not determined","Native tissue relevance not confirmed"]},{"year":2000,"claim":"Reconstitution of P2X2/6 heteromers showed that P2X6 modifies P2X2 pharmacology including agonist potency, pH sensitivity, and antagonist profile, establishing P2X6 as a modifier subunit rather than an autonomous channel.","evidence":"Voltage-clamp electrophysiology in Xenopus oocytes","pmids":["10864944"],"confidence":"High","gaps":["Relative contribution of each subunit to the pore and gating unknown","No structural data on the heteromeric complex"]},{"year":2004,"claim":"Discovery that N-linked glycosylation controls P2X6 receptor functionality connected post-translational processing to the variable functional outcomes observed across expression systems.","evidence":"Western blot with N-glycosidase F treatment and electrophysiology","pmids":["15044628"],"confidence":"High","gaps":["Specific glycosylation sites responsible not identified","Mechanism linking glycosylation state to channel gating unknown"]},{"year":2005,"claim":"Chemical cross-linking and AFM imaging proved that P2X6 exists as a monomer, unlike P2X2 which forms trimers, providing the biophysical basis for its obligate heteromeric assembly.","evidence":"Chemical cross-linking and atomic force microscopy","pmids":["15657042"],"confidence":"High","gaps":["Structural determinants preventing homomeric assembly beyond the N-terminus not identified"]},{"year":2006,"claim":"Mutagenesis of a 14-residue uncharged N-terminal region revealed the molecular mechanism of P2X6 ER retention: removing this region permits homotrimer formation and surface trafficking, though the homotrimers remain non-functional as channels.","evidence":"Surface biotinylation, immunocytochemistry, AFM, and targeted mutagenesis","pmids":["16452399"],"confidence":"High","gaps":["Why surface-expressed P2X6 homotrimers lack channel function remains unexplained","Whether this N-terminal motif acts via chaperone recognition or intrinsic folding is unclear"]},{"year":2014,"claim":"Sequential co-IP and AFM antibody decoration demonstrated that P2X2, P2X4, and P2X6 form a heterotrimeric complex containing one of each subunit, expanding the combinatorial diversity of purinergic receptors.","evidence":"Sequential co-immunoprecipitation and AFM with antibody decoration in tsA 201 cells","pmids":["24815693"],"confidence":"High","gaps":["Functional properties of the P2X2/4/6 heterotrimer not characterized electrophysiologically","Native tissue occurrence not confirmed"]},{"year":2015,"claim":"Age-dependent nuclear accumulation of P2X6 in hippocampal neurons and its interaction with splicing factor 3A1 revealed an unexpected non-channel function: regulation of mRNA splicing, linking P2X6 to age-related transcriptome changes.","evidence":"Immunofluorescence, nuclear fractionation, co-immunoprecipitation, and splicing activity assays in hippocampal neurons","pmids":["25874565"],"confidence":"Medium","gaps":["Mechanism of nuclear translocation from the ER not fully resolved","Specific mRNA targets whose splicing is affected not identified","Single-lab finding awaits independent confirmation"]},{"year":2019,"claim":"In renal cell carcinoma, ATP-activated P2RX6 drives Ca²⁺ influx leading to ERK1/2 phosphorylation and MMP9-dependent invasion, placing P2X6 in a pro-metastatic signaling axis that is suppressed by METTL14-mediated m⁶A modification of P2RX6 mRNA.","evidence":"In vitro migration/invasion assays, Ca²⁺ imaging, Western blot, METTL14 knockdown/overexpression, in vivo xenograft","pmids":["31159832"],"confidence":"Medium","gaps":["Whether P2X6 acts as a homomer or heteromer in RCC cells not determined","Generalizability to other cancer types unknown","Single-lab finding"]},{"year":null,"claim":"Key unresolved questions include the structural basis for why P2X6 homotrimers are non-functional as channels, the identity of mRNA targets affected by nuclear P2X6–SF3A1 interaction, and whether the P2X2/4/6 heterotrimer exists and functions in native tissues.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of P2X6-containing heteromers","Nuclear P2X6 function not validated in vivo beyond a single lab","Native tissue stoichiometry and subunit composition of P2X6 heteromers undetermined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,1,2,4]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[5]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,5,6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[0,1,2,4]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9]}],"complexes":["P2X2/6 heteromer","P2X4/6 heteromer","P2X2/4/6 heterotrimer"],"partners":["P2RX2","P2RX4","SF3A1","SPTAN1"],"other_free_text":[]},"mechanistic_narrative":"P2RX6 encodes an ATP-gated cation channel subunit that cannot form functional homomeric receptors due to an inhibitory uncharged N-terminal domain that prevents oligomerization and retains monomeric P2X6 in the endoplasmic reticulum [PMID:15657042, PMID:16452399]. P2X6 instead assembles into heteromeric channels with P2X2 and/or P2X4 subunits—including P2X2/6, P2X4/6, and P2X2/4/6 heterotrimers—that traffic to the cell surface and exhibit distinct pharmacological properties such as altered agonist potencies, α,β-methylene-ATP sensitivity, and suramin blockade profiles [PMID:9736638, PMID:10864944, PMID:24815693]. N-linked glycosylation regulates P2X6 surface expression and channel function, and the subunit undergoes age-dependent nuclear translocation in hippocampal neurons where it interacts with splicing factor 3A1 to reduce mRNA splicing activity [PMID:15044628, PMID:25874565]. P2X6 is a p53-inducible gene, and in renal cell carcinoma, ATP-activated P2RX6 mediates Ca²⁺ influx that drives ERK1/2 phosphorylation and MMP9-dependent invasion [PMID:9242461, PMID:31159832]."},"prefetch_data":{"uniprot":{"accession":"O15547","full_name":"P2X purinoceptor 6","aliases":["ATP receptor","P2XM","Purinergic receptor","Purinergic receptor P2X-like 1"],"length_aa":441,"mass_kda":48.8,"function":"May act as a modulatory subunit rather than a functional channel. Unlike other P2XRs members, P2RX6 does not seem to form functional homotrimers (PubMed:22378790). P2RX6 requires the presence of P2RX4 or P2RX2 to shuttle it to the plasma membrane where it may form functional heterotrimeric receptors at the plasma membrane (PubMed:22378790). P2RX6 can be translocated to the nucleus and functions as a nuclear regulator of post-transcriptional modifications in neurons (By similarity)","subcellular_location":"Cell membrane; Endoplasmic reticulum; Nucleus; Nucleus inner membrane","url":"https://www.uniprot.org/uniprotkb/O15547/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/P2RX6","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/P2RX6","total_profiled":1310},"omim":[],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoli","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"skeletal muscle","ntpm":31.7},{"tissue":"tongue","ntpm":11.1}],"url":"https://www.proteinatlas.org/search/P2RX6"},"hgnc":{"alias_symbol":["P2XM","MGC129625","P2X6"],"prev_symbol":["P2RXL1"]},"alphafold":{"accession":"O15547","domains":[{"cath_id":"1.10.287","chopping":"30-61_335-374","consensus_level":"high","plddt":89.9053,"start":30,"end":374},{"cath_id":"2.60.490.10","chopping":"73-121_194-332","consensus_level":"high","plddt":91.7714,"start":73,"end":332}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15547","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15547-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15547-F1-predicted_aligned_error_v6.png","plddt_mean":82.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=P2RX6","jax_strain_url":"https://www.jax.org/strain/search?query=P2RX6"},"sequence":{"accession":"O15547","fasta_url":"https://rest.uniprot.org/uniprotkb/O15547.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15547/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15547"}},"corpus_meta":[{"pmid":"8786426","id":"PMC_8786426","title":"Cloning OF P2X5 and P2X6 receptors and the distribution and properties of an extended family of ATP-gated ion channels.","date":"1996","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/8786426","citation_count":768,"is_preprint":false},{"pmid":"9736638","id":"PMC_9736638","title":"Central P2X4 and P2X6 channel subunits coassemble into a novel heteromeric ATP receptor.","date":"1998","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/9736638","citation_count":204,"is_preprint":false},{"pmid":"15657042","id":"PMC_15657042","title":"Atomic force microscopy imaging demonstrates that P2X2 receptors are trimers but that P2X6 receptor subunits do not oligomerize.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15657042","citation_count":156,"is_preprint":false},{"pmid":"10864944","id":"PMC_10864944","title":"Coexpression of rat P2X2 and P2X6 subunits in Xenopus oocytes.","date":"2000","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/10864944","citation_count":105,"is_preprint":false},{"pmid":"31159832","id":"PMC_31159832","title":"The m6A-suppressed P2RX6 activation promotes renal cancer cells migration and invasion through ATP-induced Ca2+ influx modulating ERK1/2 phosphorylation and MMP9 signaling pathway.","date":"2019","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/31159832","citation_count":99,"is_preprint":false},{"pmid":"9242461","id":"PMC_9242461","title":"Cloning of P2XM, a novel human P2X receptor gene regulated by p53.","date":"1997","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/9242461","citation_count":73,"is_preprint":false},{"pmid":"15044628","id":"PMC_15044628","title":"Functional regulation of P2X6 receptors by N-linked glycosylation: identification of a novel alpha beta-methylene ATP-sensitive phenotype.","date":"2004","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/15044628","citation_count":61,"is_preprint":false},{"pmid":"16452399","id":"PMC_16452399","title":"An uncharged region within the N terminus of the P2X6 receptor inhibits its assembly and exit from the endoplasmic reticulum.","date":"2006","source":"Molecular pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/16452399","citation_count":53,"is_preprint":false},{"pmid":"10633863","id":"PMC_10633863","title":"Expression of two ATP-gated ion channels, P2X5 and P2X6, in developing chick skeletal muscle.","date":"1999","source":"Developmental dynamics : an official publication of the American Association of Anatomists","url":"https://pubmed.ncbi.nlm.nih.gov/10633863","citation_count":47,"is_preprint":false},{"pmid":"12088286","id":"PMC_12088286","title":"P2X4 and P2X6 receptors associate with VE-cadherin in human endothelial cells.","date":"2002","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/12088286","citation_count":46,"is_preprint":false},{"pmid":"16242142","id":"PMC_16242142","title":"P2 receptors in human heart: upregulation of P2X6 in patients undergoing heart transplantation, interaction with TNFalpha and potential role in myocardial cell death.","date":"2005","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/16242142","citation_count":45,"is_preprint":false},{"pmid":"19946698","id":"PMC_19946698","title":"Expression of P2X6 receptors in the enteric nervous system of the rat gastrointestinal tract.","date":"2009","source":"Histochemistry and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/19946698","citation_count":39,"is_preprint":false},{"pmid":"17259301","id":"PMC_17259301","title":"Alternative splicing of P2X6 receptors in developing mouse brain and during in vitro neuronal differentiation.","date":"2007","source":"Experimental physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17259301","citation_count":30,"is_preprint":false},{"pmid":"11591462","id":"PMC_11591462","title":"Immunoreactivity to P2X(6) receptors in the rat hypothalamo-neurohypophysial system: an ultrastructural study with extravidin and colloidal gold-silver labelling.","date":"2001","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/11591462","citation_count":27,"is_preprint":false},{"pmid":"24815693","id":"PMC_24815693","title":"Identification of P2X2/P2X4/P2X6 heterotrimeric receptors using atomic force microscopy (AFM) imaging.","date":"2014","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/24815693","citation_count":19,"is_preprint":false},{"pmid":"10376970","id":"PMC_10376970","title":"Frequent loss of expression or aberrant alternative splicing of P2XM, a p53-inducible gene, in soft-tissue tumours.","date":"1999","source":"British journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/10376970","citation_count":13,"is_preprint":false},{"pmid":"12713031","id":"PMC_12713031","title":"Expression of P2X6, a purinergic receptor subunit, is affected by dietary zinc deficiency in rat hippocampus.","date":"2003","source":"Biological trace element research","url":"https://pubmed.ncbi.nlm.nih.gov/12713031","citation_count":12,"is_preprint":false},{"pmid":"25874565","id":"PMC_25874565","title":"Age-related nuclear translocation of P2X6 subunit modifies splicing activity interacting with splicing factor 3A1.","date":"2015","source":"PloS 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/38392191","citation_count":5,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11131,"output_tokens":3138,"usd":0.040232},"stage2":{"model":"claude-opus-4-6","input_tokens":6548,"output_tokens":2621,"usd":0.147397},"total_usd":0.187629,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"P2X6 receptor subunits were cloned and expressed; they form ATP-gated ion channels with two transmembrane segments and a large extracellular loop, desensitize slowly, do not respond to alpha-beta-methylene-ATP, and are not blocked by suramin or PPADS. P2X6 expresses at lower levels than other P2X subunits, suggesting it does not normally form homomultimeric channels.\",\n      \"method\": \"cDNA cloning, heterologous expression, electrophysiology\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original cloning and functional characterization, foundational paper with 768 citations\",\n      \"pmids\": [\"8786426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"P2X4 and P2X6 subunits coassemble into a novel heteromeric ATP receptor with unique pharmacological properties: activated by low-micromolar alpha-beta-methylene ATP (EC50=12 µM) and blocked by suramin and Reactive Blue 2. Heteromeric assembly was demonstrated by specific copurification of epitope-tagged subunits from HEK-293 cells. P2X6 alone does not assemble into surface receptors in Xenopus oocytes.\",\n      \"method\": \"Xenopus oocyte expression, electrophysiology, co-immunoprecipitation/copurification with epitope tags in HEK-293 cells\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus functional electrophysiology, 204 citations\",\n      \"pmids\": [\"9736638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Coexpression of rat P2X2 and P2X6 subunits in Xenopus oocytes generates a heteromeric rP2X2/6 receptor with distinct pharmacology from homomeric P2X2: reduced agonist potencies, loss of some agonist activity, biphasic ATP-evoked currents, altered pH modulation, and changed suramin blockade profile.\",\n      \"method\": \"Xenopus oocyte expression, voltage-clamp electrophysiology\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — functional reconstitution in heterologous system, 105 citations\",\n      \"pmids\": [\"10864944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"P2X6 receptor subunits do not oligomerize into stable homomers. Chemical cross-linking of P2X6 did not produce higher-order adducts, and AFM imaging showed a mean molecular volume (~145 nm³) consistent with monomers, in contrast to P2X2 which forms trimers (~409 nm³).\",\n      \"method\": \"Chemical cross-linking, atomic force microscopy (AFM) imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — two orthogonal structural/biochemical methods, 156 citations\",\n      \"pmids\": [\"15657042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"N-linked glycosylation regulates P2X6 receptor function. Functional P2X6 receptors show increased glycosylation (~70 kDa) compared to non-functional receptors (~60 kDa); N-glycosidase F treatment collapses both to ~55 kDa. Functional P2X6 displays a novel phenotype sensitive to alpha-beta-methylene ATP (EC50=0.6 µM), slow desensitization, and resistance to suramin.\",\n      \"method\": \"Western blot, N-glycosidase F treatment, electrophysiology, RT-PCR\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — biochemical glycosylation analysis plus functional electrophysiology\",\n      \"pmids\": [\"15044628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"An uncharged 14-amino acid region at the N-terminus of P2X6 inhibits its assembly and ER export. When this region is removed or charged residues are added, P2X6 forms homotrimers, undergoes complex glycosylation, and traffics to the plasma membrane, but remains non-functional. As a heteromer with P2X2 or P2X4, P2X6 exits the ER and is expressed at the cell surface or constitutively internalized depending on partner subunit.\",\n      \"method\": \"Immunocytochemistry, surface biotinylation, atomic force microscopy, targeted mutagenesis\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis plus multiple orthogonal structural/trafficking methods\",\n      \"pmids\": [\"16452399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"P2X6 receptors co-localize with VE-cadherin at cell-cell junctions in human umbilical vein endothelial cells and are rapidly internalized upon reduction of extracellular Ca2+. Unlike P2X4, P2X6 could not be co-immunoprecipitated with VE-cadherin, indicating distinct association modes at adherens junctions.\",\n      \"method\": \"Confocal microscopy, electron microscopy, co-immunoprecipitation, Triton X-100 fractionation\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — localization with functional consequence (internalization), but co-IP was negative for P2X6-VE-cadherin direct interaction\",\n      \"pmids\": [\"12088286\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"P2X2, P2X4, and P2X6 subunits can form a heterotrimeric complex containing all three distinct subunits. Sequential co-immunoprecipitation with anti-HA and anti-FLAG beads from tsA 201 cells co-expressing His6-P2X2, HA-P2X4, and FLAG-P2X6 confirmed interaction of all three subunits. AFM imaging with dual antibody decoration confirmed the P2X2/4/6 heterotrimer architecture.\",\n      \"method\": \"Sequential co-immunoprecipitation, atomic force microscopy imaging with antibody decoration\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — sequential co-IP plus AFM structural imaging, two orthogonal methods\",\n      \"pmids\": [\"24815693\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"P2X6 subunit accumulates in the nucleus of hippocampal neurons in an age-dependent manner. Nuclear localization is facilitated by ER anchorage via the N-terminal domain, and the extracellular domain is required for nuclear entry. Inside the nucleus, P2X6 associates with spectrin α2 (nuclear envelope protein) and interacts with splicing factor 3A1, resulting in reduced mRNA splicing activity.\",\n      \"method\": \"Immunofluorescence, co-immunoprecipitation, in vivo nuclear fractionation, splicing activity assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP plus functional splicing assay, single lab\",\n      \"pmids\": [\"25874565\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ATP-activated P2RX6 promotes renal cell carcinoma migration and invasion by mediating Ca2+ influx, which activates ERK1/2 phosphorylation and upregulates MMP9. METTL14-mediated m6A modification suppresses P2RX6 protein translation, thereby inhibiting this pro-invasive signaling axis.\",\n      \"method\": \"In vitro migration/invasion assays, Ca2+ influx measurement, Western blot for p-ERK1/2 and MMP9, m6A/METTL14 knockdown and overexpression, in vivo xenograft\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays in vitro and in vivo, but single lab\",\n      \"pmids\": [\"31159832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"P2X6 receptor undergoes alternative splicing during mouse brain development and during in vitro neuronal differentiation. A full-length and an alternatively spliced form were detected; the spliced form predominates during neuronal differentiation of P19 cells, whereas the full-length form predominates during postnatal brain development, suggesting alternative splicing regulates P2X6 function.\",\n      \"method\": \"RT-PCR, in vitro differentiation model (P19 cells)\",\n      \"journal\": \"Experimental physiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — RT-PCR detection of splice forms, no direct functional assay of spliced variant\",\n      \"pmids\": [\"17259301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"P2XM (the human P2X6 ortholog, also known as P2RX6) is a p53-inducible gene. Wild-type p53 induces P2XM expression; the gene contains functional p53-binding sites. It is expressed predominantly in skeletal muscle and maps to chromosome 22q11.\",\n      \"method\": \"p53-tagged genomic cloning, Northern blot, chromosomal mapping\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct p53-binding site cloning plus expression validation\",\n      \"pmids\": [\"9242461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In cardiac fibroblasts, TNFα prevents ATP-induced downregulation of P2X6 mRNA (desensitization), suggesting TNFα interaction with P2X6 abrogates a protective mechanism against Ca2+ overload and cell death. ATP/BzATP via P2X6 induces apoptosis in cardiac fibroblasts and cardiomyocytes, which is exacerbated by TNFα.\",\n      \"method\": \"Primary cardiac fibroblast culture, apoptosis assays, real-time PCR, P2X6 mRNA quantification after agonist and TNFα treatment\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — mRNA-level mechanism, single lab, no direct protein interaction demonstrated\",\n      \"pmids\": [\"16242142\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"P2RX6 (P2X6) is an ATP-gated cation channel subunit that cannot form functional homomeric receptors due to an inhibitory uncharged N-terminal domain that retains monomeric P2X6 in the ER; it assembles into functional heteromeric channels with P2X2, P2X4, or both (P2X2/4/6 trimers), altering pharmacology including alpha-beta-methylene ATP sensitivity, and its surface trafficking and function are regulated by N-linked glycosylation; additionally, P2X6 undergoes age-dependent nuclear translocation where it interacts with splicing factor 3A1 to reduce mRNA splicing activity, and in cancer contexts mediates ATP-induced Ca2+ influx driving ERK1/2 phosphorylation and MMP9-dependent invasion.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"P2RX6 encodes an ATP-gated cation channel subunit that cannot form functional homomeric receptors due to an inhibitory uncharged N-terminal domain that prevents oligomerization and retains monomeric P2X6 in the endoplasmic reticulum [PMID:15657042, PMID:16452399]. P2X6 instead assembles into heteromeric channels with P2X2 and/or P2X4 subunits—including P2X2/6, P2X4/6, and P2X2/4/6 heterotrimers—that traffic to the cell surface and exhibit distinct pharmacological properties such as altered agonist potencies, α,β-methylene-ATP sensitivity, and suramin blockade profiles [PMID:9736638, PMID:10864944, PMID:24815693]. N-linked glycosylation regulates P2X6 surface expression and channel function, and the subunit undergoes age-dependent nuclear translocation in hippocampal neurons where it interacts with splicing factor 3A1 to reduce mRNA splicing activity [PMID:15044628, PMID:25874565]. P2X6 is a p53-inducible gene, and in renal cell carcinoma, ATP-activated P2RX6 mediates Ca²⁺ influx that drives ERK1/2 phosphorylation and MMP9-dependent invasion [PMID:9242461, PMID:31159832].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Cloning of P2X6 established it as a member of the P2X ATP-gated ion channel family but revealed unusually low expression, raising the question of whether it forms functional homomeric channels.\",\n      \"evidence\": \"cDNA cloning and heterologous expression with electrophysiology\",\n      \"pmids\": [\"8786426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No evidence for homomeric channel function at physiological expression levels\",\n        \"Subunit stoichiometry unknown\",\n        \"Tissue-specific role not addressed\"\n      ]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Identification of P2RX6 as a p53-inducible gene with functional p53-binding sites linked it to stress-responsive transcriptional programs, beyond its role as an ion channel subunit.\",\n      \"evidence\": \"p53-tagged genomic cloning, Northern blot, chromosomal mapping\",\n      \"pmids\": [\"9242461\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Functional consequence of p53-mediated P2X6 induction not tested\",\n        \"No demonstration that p53 regulation affects channel activity or cell fate\"\n      ]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstration that P2X6 coassembles with P2X4 into heteromeric receptors with novel pharmacology resolved the question of how P2X6 contributes to purinergic signaling despite its inability to form surface homomers.\",\n      \"evidence\": \"Xenopus oocyte electrophysiology and epitope-tag co-immunoprecipitation in HEK-293 cells\",\n      \"pmids\": [\"9736638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Subunit stoichiometry within the heteromer not determined\",\n        \"Native tissue relevance not confirmed\"\n      ]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Reconstitution of P2X2/6 heteromers showed that P2X6 modifies P2X2 pharmacology including agonist potency, pH sensitivity, and antagonist profile, establishing P2X6 as a modifier subunit rather than an autonomous channel.\",\n      \"evidence\": \"Voltage-clamp electrophysiology in Xenopus oocytes\",\n      \"pmids\": [\"10864944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Relative contribution of each subunit to the pore and gating unknown\",\n        \"No structural data on the heteromeric complex\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery that N-linked glycosylation controls P2X6 receptor functionality connected post-translational processing to the variable functional outcomes observed across expression systems.\",\n      \"evidence\": \"Western blot with N-glycosidase F treatment and electrophysiology\",\n      \"pmids\": [\"15044628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific glycosylation sites responsible not identified\",\n        \"Mechanism linking glycosylation state to channel gating unknown\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Chemical cross-linking and AFM imaging proved that P2X6 exists as a monomer, unlike P2X2 which forms trimers, providing the biophysical basis for its obligate heteromeric assembly.\",\n      \"evidence\": \"Chemical cross-linking and atomic force microscopy\",\n      \"pmids\": [\"15657042\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural determinants preventing homomeric assembly beyond the N-terminus not identified\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Mutagenesis of a 14-residue uncharged N-terminal region revealed the molecular mechanism of P2X6 ER retention: removing this region permits homotrimer formation and surface trafficking, though the homotrimers remain non-functional as channels.\",\n      \"evidence\": \"Surface biotinylation, immunocytochemistry, AFM, and targeted mutagenesis\",\n      \"pmids\": [\"16452399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Why surface-expressed P2X6 homotrimers lack channel function remains unexplained\",\n        \"Whether this N-terminal motif acts via chaperone recognition or intrinsic folding is unclear\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Sequential co-IP and AFM antibody decoration demonstrated that P2X2, P2X4, and P2X6 form a heterotrimeric complex containing one of each subunit, expanding the combinatorial diversity of purinergic receptors.\",\n      \"evidence\": \"Sequential co-immunoprecipitation and AFM with antibody decoration in tsA 201 cells\",\n      \"pmids\": [\"24815693\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Functional properties of the P2X2/4/6 heterotrimer not characterized electrophysiologically\",\n        \"Native tissue occurrence not confirmed\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Age-dependent nuclear accumulation of P2X6 in hippocampal neurons and its interaction with splicing factor 3A1 revealed an unexpected non-channel function: regulation of mRNA splicing, linking P2X6 to age-related transcriptome changes.\",\n      \"evidence\": \"Immunofluorescence, nuclear fractionation, co-immunoprecipitation, and splicing activity assays in hippocampal neurons\",\n      \"pmids\": [\"25874565\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism of nuclear translocation from the ER not fully resolved\",\n        \"Specific mRNA targets whose splicing is affected not identified\",\n        \"Single-lab finding awaits independent confirmation\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"In renal cell carcinoma, ATP-activated P2RX6 drives Ca²⁺ influx leading to ERK1/2 phosphorylation and MMP9-dependent invasion, placing P2X6 in a pro-metastatic signaling axis that is suppressed by METTL14-mediated m⁶A modification of P2RX6 mRNA.\",\n      \"evidence\": \"In vitro migration/invasion assays, Ca²⁺ imaging, Western blot, METTL14 knockdown/overexpression, in vivo xenograft\",\n      \"pmids\": [\"31159832\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether P2X6 acts as a homomer or heteromer in RCC cells not determined\",\n        \"Generalizability to other cancer types unknown\",\n        \"Single-lab finding\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for why P2X6 homotrimers are non-functional as channels, the identity of mRNA targets affected by nuclear P2X6–SF3A1 interaction, and whether the P2X2/4/6 heterotrimer exists and functions in native tissues.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of P2X6-containing heteromers\",\n        \"Nuclear P2X6 function not validated in vivo beyond a single lab\",\n        \"Native tissue stoichiometry and subunit composition of P2X6 heteromers undetermined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 1, 2, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 5, 6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [0, 1, 2, 4]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [\n      \"P2X2/6 heteromer\",\n      \"P2X4/6 heteromer\",\n      \"P2X2/4/6 heterotrimer\"\n    ],\n    \"partners\": [\n      \"P2RX2\",\n      \"P2RX4\",\n      \"SF3A1\",\n      \"SPTAN1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}