{"gene":"HTR2A","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1990,"finding":"HTR2A (HTR2) encodes a G-protein-coupled receptor expressed primarily in the cerebral cortex that upon stimulation activates hydrolysis of inositol phospholipids, and the gene was chromosomally mapped to human chromosome 13 (near ESD and RB1) and mouse chromosome 14.","method":"Somatic cell hybrid analysis, linkage studies with RFLP","journal":"Somatic cell and molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct chromosomal mapping combined with functional annotation of inositol phospholipid hydrolysis, replicated across species","pmids":["1980030"],"is_preprint":false},{"year":1995,"finding":"Agonist-induced desensitization of 5-HT2A receptor-mediated phosphoinositide hydrolysis can occur without down-regulation of receptor number or surface expression; the intermediate phase (2–6 h) of desensitization is mediated by PKC alpha and/or epsilon isoforms, whereas the late phase (24 h) is independent of these PKC isoforms. A binding-incompetent mutant (F340L) showed that ligand binding is required for desensitization.","method":"Stable cell-line expressing cloned 5-HT2A receptor; radioligand binding, inositol phosphate assay, immunohistochemistry, Western blot with isoform-selective antibodies, phorbol ester-mediated PKC down-regulation, site-directed mutagenesis","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in defined cell line, mutagenesis, multiple orthogonal biochemical methods in a single study","pmids":["8531139"],"is_preprint":false},{"year":1998,"finding":"5-HT2A and 5-HT2C receptors couple to both phospholipase C (PLC-mediated IP accumulation) and phospholipase A2 (PLA2-mediated arachidonic acid release), and agonists show differential (biased) relative efficacies for these two pathways at the 5-HT2A receptor — all agonists tested had greater relative efficacy for PLA2-AA than for PLC-IP, supporting agonist-directed trafficking of receptor stimulus.","method":"Second-messenger assays (inositol phosphate accumulation and arachidonic acid release) in cell lines expressing cloned receptors","journal":"Annals of the New York Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal second-messenger assays in a single lab establishing biased signaling","pmids":["9928246"],"is_preprint":false},{"year":1998,"finding":"5-HT2A receptor activation in arterial smooth muscle activates the MAPK/ERK pathway (MEK and ERK1/2 phosphorylation) in a receptor- and tyrosine kinase-dependent manner, partially independent of L-type calcium channel activation and PLC signaling.","method":"Isolated rat arteries (contractile assay with tyrosine kinase and MEK inhibitors); Western blot for phospho-MEK and phospho-ERK in cultured aortic smooth muscle cells","journal":"Annals of the New York Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological inhibition plus Western blot in two complementary preparations from a single lab","pmids":["9928253"],"is_preprint":false},{"year":1998,"finding":"5-HT2A receptor activation by 5-HT agonists (but not 5-HT3 agonists) induces peripheral thermal hyperalgesia in rats; 5-HT2 receptor mRNA was detected in dorsal root ganglia neurons, indicating peripheral expression mediating nociception.","method":"Intradermal injection of receptor-subtype-selective agonists/antagonists in rats with paw-withdrawal latency assay; in situ hybridization for 5-HT2 receptor mRNA in DRG","journal":"Pain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological specificity confirmed with selective antagonist ketanserin blocking 5-HT effect, complemented by mRNA localization","pmids":["9718253"],"is_preprint":false},{"year":1998,"finding":"5-HT2A receptor-stimulated phosphoinositide hydrolysis does not fully account for the discriminative (hallucinogenic) stimulus effects of psychedelics; non-hallucinogenic compounds (lisuride, quipazine, 6-F-DET) also activated PLC via 5-HT2A, and the rank order of PI hydrolysis efficacy did not correlate with hallucinogen drug-discrimination substitution.","method":"PC12 cells stably expressing rat 5-HT2A receptor; [3H]inositol phosphate accumulation assay; comparison with published drug-discrimination data","journal":"Pharmacology, biochemistry, and behavior","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single-lab, single in vitro assay, but finding is clearly negative/dissociative; informative for signaling mechanism","pmids":["11900766"],"is_preprint":false},{"year":2002,"finding":"5-HT2A receptor activation increases de novo BDNF mRNA synthesis in C6 glioma cells via a calcium-dependent and protein-kinase-dependent pathway; the effect is blocked by ketanserin (5-HT2A antagonist), actinomycin D (transcription inhibitor), EGTA (calcium chelator), staurosporine (PKC/PKA inhibitor), thapsigargin (Ca2+ ATPase inhibitor), and KN-62 (CaM kinase inhibitor), but not by cycloheximide.","method":"RT-PCR and Northern blot of BDNF mRNA in C6 glioma cells; pharmacological dissection with receptor antagonists, kinase inhibitors, and ion channel modulators","journal":"Neuromolecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal RNA detection methods plus multiple pathway inhibitors in a single lab","pmids":["12095161"],"is_preprint":false},{"year":2004,"finding":"5-HT2A and 5-HT2C receptor C-termini each contain a class I PDZ ligand (SXV motif) and interact with distinct sets of PDZ proteins in vitro: 5-HT2A robustly binds CIPP but not Veli-3/CASK/Mint1 complex or SAP102, whereas 5-HT2C binds those complexes; residues at the -1 position and upstream of the PDZ ligand are major determinants of PDZ selectivity. These interactions also occur in living cells in intracellular compartments.","method":"Affinity chromatography using immobilized synthetic peptides + mass spectrometry; immunofluorescence; electron microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — proteomic pulldown with mass spectrometry identification, validated by cell imaging; multiple orthogonal methods in one rigorous study","pmids":["14988405"],"is_preprint":false},{"year":2004,"finding":"Activation of 5-HT2A receptors in the hypothalamic paraventricular nucleus (PVN) induces heterologous desensitization of co-localized 5-HT1A receptors in oxytocin and CRF neurons, reducing oxytocin and ACTH responses to a 5-HT1A agonist; 5-HT2A and 5-HT1A receptors co-localize within individual neuroendocrine cells in the PVN.","method":"In vivo pharmacology (microinjection of MDL100907 into PVN); neuroendocrine readout (oxytocin and ACTH plasma levels); double-label immunocytochemistry","journal":"The Journal of pharmacology and experimental therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo pharmacological rescue experiment combined with anatomical co-localization, single lab","pmids":["15064330"],"is_preprint":false},{"year":2004,"finding":"The naturally occurring His452Tyr SNP in the 5-HT2A receptor C-terminus reduces agonist-stimulated signaling through both Gq (phospholipase C) and G13 (phospholipase D) pathways, impairs agonist-induced high-affinity binding and GTPγS turnover, and alters receptor desensitization kinetics.","method":"Stable NIH3T3 cells expressing wild-type or 452Tyr variant; inositol phosphate and phospholipase D assays; [35S]GTPγS binding; agonist competition binding","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-directed mutagenesis plus multiple orthogonal functional assays (PLC, PLD, G-protein coupling) in a defined cell system","pmids":["15496511"],"is_preprint":false},{"year":2008,"finding":"5-HT2A receptor trafficking, targeting, and signaling are regulated by scaffolding proteins (PSD-95, arrestin, caveolin) and by p90 ribosomal S6 kinase (RSK), which phosphorylates the receptor and attenuates its signaling.","method":"Co-immunoprecipitation, receptor trafficking assays, kinase interaction studies (as reviewed from primary experimental work)","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and trafficking assays reviewed from primary studies; single lab, multiple interaction partners identified","pmids":["18640136"],"is_preprint":false},{"year":2010,"finding":"5-HT2A and 5-HT2C receptors show constitutive activity in vitro; inverse agonists decrease basal signaling below baseline, and protean ligands can act as agonists for one response while acting as inverse agonists for another pathway coupled to the same receptor, demonstrating response-dependent constitutive activity. Evidence also suggests this constitutive activity is physiologically relevant in vivo.","method":"Cell-based second-messenger assays (inositol phosphate, arachidonic acid); in vivo behavioral pharmacology","journal":"Trends in pharmacological sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro assays plus in vivo behavioral evidence reviewed across studies, but predominantly from one group","pmids":["16269190"],"is_preprint":false},{"year":2011,"finding":"5-HT2A receptor and dopamine D2 receptor form a physical heterocomplex (co-immunoprecipitation in HEK293 cells); D2R activation increases hallucinogenic agonist affinity for 5-HT2AR and decreases 5-HT2AR-induced inositol phosphate production; in vivo, 5-HT2AR expression is necessary for the full locomotor effects of D2R antagonist.","method":"Radioligand binding assays; inositol phosphate second-messenger assay; co-immunoprecipitation in HEK293 cells; in vivo locomotor activity in 5-HT2AR knockout mice","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal functional and physical interaction evidence with multiple methods, single lab","pmids":["21645528"],"is_preprint":false},{"year":2012,"finding":"5-HT2A receptor endocytosis and recycling are functionally selective: serotonin (5-HT), dopamine (DA), DOI, and clozapine each trigger receptor endocytosis, but ketanserin does not. PKC-mediated receptor phosphorylation is required for 5-HT- and DOI-induced but not DA- or clozapine-induced internalization. Recycling back to the cell surface requires protein phosphatase 2A (PP2A)-mediated dephosphorylation for those ligands that required PKC for endocytosis.","method":"Cell-based receptor trafficking assays; PKC inhibition; phosphorylation assays; PP2A inhibition; quantitative receptor internalization/recycling measurements","journal":"Molecular pharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple ligands tested with orthogonal kinase/phosphatase intervention experiments establishing mechanistic pathway, single lab but rigorous","pmids":["23034456"],"is_preprint":false},{"year":2012,"finding":"5-HT2A receptor forms heterocomplexes with mGlu2 receptor (confirmed by quantitative SNAP/CLIP-tag HTRF), but co-expression of both receptors in HEK-293 cells does not alter signaling mediated by either receptor individually (no change in Gq, Gi, or cAMP pathways), indicating that physical heterocomplex formation does not necessarily translate into functional second-messenger crosstalk.","method":"Quantitative SNAP/CLIP-tag HTRF assay for heterocomplex formation; Gq/Gi/cAMP second-messenger assays in HEK-293 cells; radioligand competition binding in prefrontal cortex membranes","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative HTRF for complex formation plus multiple signaling assays; single lab but orthogonal methods","pmids":["22300836"],"is_preprint":false},{"year":2013,"finding":"Systemic activation of 5-HT2A receptors with (R)-DOI produces potent blockade of TNF-α-induced expression of pro-inflammatory adhesion molecules (ICAM-1, VCAM-1), cytokines (IL-6, IL-1β), and chemokines (MCP-1, CX3CL1) in the aorta and intestine in vivo, and reduces circulating IL-6; this anti-inflammatory effect is abolished by selective 5-HT2A receptor antagonists.","method":"Systemic drug administration in rats; gene expression analysis (qPCR) and protein immunostaining in tissues; receptor-selective antagonist rescue experiments","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo pharmacology with receptor-selective antagonist confirmation, multiple inflammatory markers measured at gene and protein levels","pmids":["24098382"],"is_preprint":false},{"year":2013,"finding":"5-HT2A receptor antagonists (ketanserin, sarpogrelate) inhibit hepatic stellate cell (HSC) activation: they reduce viability, inhibit wound healing, induce apoptosis, and suppress α-SMA, procollagen type I, TGF-β, and Smad2/3 expression in LX-2 cells; in vivo, sarpogrelate reduces lobular inflammation and α-SMA, TGF-β, Smad2/3 expression in thioacetamide-induced cirrhosis.","method":"In vitro: cell viability, apoptosis, wound-healing, and gene expression assays in LX-2 cells; in vivo: rat cirrhosis model with histology and protein expression","journal":"Liver international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo experiments; multiple readouts; single lab","pmids":["23362947"],"is_preprint":false},{"year":2015,"finding":"5-HT2A receptor activation is necessary for CO2-induced arousal from sleep: selective 5-HT2A antagonists dose-dependently blocked CO2-induced arousal in wild-type mice; 5-HT2A (but not 5-HT2C) receptor agonists restored CO2-induced arousal in mice genetically lacking 5-HT neurons (Lmx1bf/f/p), demonstrating a permissive role downstream of serotonergic neuron activity.","method":"In vivo pharmacology with subtype-selective antagonists and agonists; CO2 and hypoxia arousal assays; genetic model (Lmx1bf/f/p mice lacking 5-HT neurons); dose-response analysis","journal":"Journal of neurophysiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological and genetic approaches converge on same conclusion; multiple receptor subtypes systematically ruled out","pmids":["25925320"],"is_preprint":false},{"year":2015,"finding":"Htr2a cortical expression responds rapidly (within 6 h) to acute environmental stress (sleep deprivation) with a twofold increase in Htr2a mRNA; this induction requires the immediate early gene Egr3, as it is absent in Egr3-/- mice.","method":"Sleep deprivation stress in wild-type and Egr3-/- mice; quantitative RT-PCR of cortical Htr2a mRNA","journal":"ACS chemical neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout ablation establishes transcriptional dependency on Egr3; single lab, single stress paradigm","pmids":["25857407"],"is_preprint":false},{"year":2018,"finding":"Chronic THC exposure during adolescence induces pro-hallucinogenic signaling of the 5-HT2A receptor: supersensitive coupling toward inhibitory Gαi1, Gαi3, Gαo, and Gαz proteins without changes in canonical Gαq/11 pathway; this shift in signaling bias is blocked by the Akt/mTOR inhibitor rapamycin, which also prevents THC-induced prepulse inhibition disruption.","method":"Chronic THC administration in mice; G-protein coupling assays ([35S]GTPγS); behavioral PPI assay; rapamycin co-treatment; protein expression analysis","journal":"Neuropsychopharmacology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — G-protein coupling assays with multiple Gα subtypes plus pathway inhibitor experiment linking Akt/mTOR to 5-HT2AR signaling bias; multiple orthogonal methods","pmids":["29748632"],"is_preprint":false},{"year":2019,"finding":"Sustained 5-HT2A receptor activation (20 min exposure to serotonin or DOI) in layer V pyramidal neurons of the mouse prefrontal cortex produces long-lasting depression (LTD) of AMPA receptor-mediated excitatory postsynaptic currents; this LTD is absent in 5-HT2AR knockout mice, rescued by viral 5-HT2AR re-expression in pyramidal neurons, occludes electrically induced LTD, and involves phosphorylation of GluA2 at Ser880 and AMPA receptor internalization.","method":"Whole-cell patch-clamp electrophysiology in PFC slices; 5-HT2AR knockout mice; viral rescue; GluA2 phosphorylation (Western blot); AMPA receptor internalization assay","journal":"Cerebral cortex","confidence":"High","confidence_rationale":"Tier 1 / Strong — electrophysiological LTD measurement with genetic knockout and viral rescue, plus biochemical mechanistic validation; multiple orthogonal methods in a single study","pmids":["29917056"],"is_preprint":false},{"year":2020,"finding":"HTR2A promotes cardiac hypertrophy by activating the PI3K-PDK1-AKT-mTOR signaling cascade; HTR2A knockdown suppressed ISO-induced cardiomyocyte hypertrophy (reduced cell size, β-Mhc, Anp, Bnp expression), while overexpression promoted it; inhibition of PI3K, PDK1, or AKT-mTOR blocked HTR2A-driven hypertrophy.","method":"shRNA knockdown and adenoviral overexpression in neonatal rat cardiomyocytes; ISO-induced hypertrophy model; phospho-AKT/mTOR Western blot; pharmacological inhibitors (perifosine, rapamycin, PI3K inhibitor, PDK1 inhibitor)","journal":"Cell stress & chaperones","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with pathway inhibitors, single lab, in vitro cardiomyocyte model","pmids":["32519137"],"is_preprint":false},{"year":1999,"finding":"In adult rat skeletal muscle, the 5-HT2A receptor localizes exclusively to plasma membranes (not transverse tubules), as determined by subcellular fractionation and immunoblot; this localization is the same in red and white muscle, indicating expression is independent of metabolic or contractile fiber type. The absence from TT makes 5-HT2AR an unlikely participant in excitation-contraction coupling.","method":"Subcellular fractionation of adult rat skeletal muscle; immunoblot of membrane fractions","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct subcellular fractionation with functional inference; single lab, single method","pmids":["10198219"],"is_preprint":false},{"year":2009,"finding":"Glucocorticoid receptor (GR) activation increases 5-HT2A receptor levels: GR under-expressing mice show decreased hippocampal 5-HT2A protein and frontal cortex binding; GR over-expressing mice show increased 5-HT2A levels; corticosterone treatment of organotypic hippocampal cultures increases 5-HT2A receptor levels, and this is blocked by either the GR antagonist mifepristone or the mineralocorticoid receptor antagonist spironolactone.","method":"Western blot and radioligand binding ([3H]-MDL100907) in transgenic GR mice; organotypic hippocampal cultures with corticosterone and receptor antagonists","journal":"Experimental neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic mouse and in vitro culture with pharmacological intervention; two orthogonal methods; single lab","pmids":["19379741"],"is_preprint":false},{"year":2010,"finding":"Layer V pyramidal cells of anterior cortex constitute the largest 5-HT2A-receptor-expressing neuronal population in the cerebral cortex; parvalbumin-expressing fast-spiking GABAergic interneurons in middle layers also express 5-HT2A receptors and are depolarized and excited by serotonin through 5-HT2A receptor activation.","method":"BAC transgenic EGFP reporter mice; 5-HT2A knockout mice for antibody validation; immunohistochemistry; whole-cell electrophysiology","journal":"Frontiers in neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — genetic reporter + KO validation + electrophysiology; multiple orthogonal methods establishing both cellular identity and functional consequence","pmids":["20802802"],"is_preprint":false},{"year":2013,"finding":"5-HT2A receptor activation (DOI) decreases the firing rate of dorsal raphe 5-HT neurons in wild-type but not 5-HT2AR-/- mice; this inhibitory effect is mediated specifically through 5-HT2AR (not 5-HT2CR) and requires intact noradrenergic neurons (abolished by DSP4 noradrenergic neurotoxin); 5-HT2AR blockade (MDL100907) combined with escitalopram increases cortical norepinephrine outflow and produces antidepressant-like behavior.","method":"In vivo electrophysiology (dorsal raphe firing); microdialysis (cortical 5-HT and NE); 5-HT2AR knockout and 5-HT2CR knockout mice; DSP4 noradrenergic lesion; forced swim test","journal":"Experimental brain research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic models plus pharmacological dissection plus in vivo electrophysiology and microdialysis converging on mechanism","pmids":["23411676"],"is_preprint":false}],"current_model":"HTR2A encodes a Gq/11-coupled GPCR that, upon serotonin binding, activates phospholipase C (inositol phosphate/Ca²⁺ signaling) and phospholipase A2 (arachidonic acid release), and exhibits biased/functional-selective coupling to inhibitory Gαi/o proteins with certain hallucinogenic ligands or after chronic THC exposure via Akt/mTOR-dependent mechanisms; receptor desensitization involves PKC phosphorylation (intermediate phase) and β-arrestin/clathrin-mediated internalization followed by PP2A-dependent recycling; the receptor's C-terminal PDZ ligand scaffolds it to CIPP and other PDZ proteins that modulate its targeting and signaling; 5-HT2AR physically interacts with dopamine D2R and mGlu2 receptors and functionally cross-talks with 5-HT1A receptors; in cortical pyramidal neurons, sustained 5-HT2AR activation drives AMPA receptor internalization (GluA2-Ser880 phosphorylation) and LTD of glutamatergic synaptic transmission; the receptor also activates MAPK/ERK in vascular smooth muscle, drives PI3K-PDK1-AKT-mTOR signaling in cardiomyocytes to promote hypertrophy, mediates peripheral thermal hyperalgesia, blocks TNF-α-driven inflammation, and its cortical expression is acutely up-regulated by stress via an Egr3-dependent transcriptional mechanism."},"narrative":{"mechanistic_narrative":"HTR2A encodes a Gq/11-coupled, cortex-enriched G-protein-coupled receptor that transduces serotonin signals into phosphoinositide hydrolysis and downstream calcium- and protein-kinase-dependent responses [PMID:1980030, PMID:12095161]. Beyond canonical Gq-PLC coupling, the receptor displays pronounced functional selectivity: agonists drive differential efficacy toward PLA2-mediated arachidonic acid release versus PLC-mediated inositol phosphate accumulation [PMID:9928246], couple to G13/phospholipase D [PMID:15496511], and after chronic adolescent THC exposure acquire supersensitive coupling to inhibitory Gαi/o/z proteins through an Akt/mTOR-dependent mechanism [PMID:29748632]. Receptor desensitization and trafficking are tightly regulated: agonist-induced desensitization proceeds without loss of surface receptor and is mediated in its intermediate phase by PKCα/ε [PMID:8531139], while ligand-selective endocytosis requires PKC phosphorylation and subsequent recycling depends on PP2A-mediated dephosphorylation [PMID:23034456]. The receptor's C-terminal class I PDZ ligand confers selective binding to CIPP and other scaffolding proteins that govern its targeting [PMID:14988405], and the receptor physically heterocomplexes with dopamine D2 and metabotropic glutamate mGlu2 receptors, with consequences for ligand affinity and signaling that depend on the partner [PMID:21645528, PMID:22300836]. In the cerebral cortex, 5-HT2AR is expressed most abundantly in layer V pyramidal neurons and in fast-spiking parvalbumin interneurons [PMID:20802802], where sustained activation drives GluA2-Ser880 phosphorylation, AMPA receptor internalization, and long-lasting depression of glutamatergic transmission [PMID:29917056]; cortical Htr2a expression is itself acutely up-regulated by stress through an Egr3-dependent transcriptional program [PMID:25857407] and by glucocorticoid receptor signaling [PMID:19379741]. Peripherally, the receptor activates MAPK/ERK in vascular smooth muscle [PMID:9928253], drives PI3K-PDK1-AKT-mTOR-dependent cardiomyocyte hypertrophy [PMID:32519137], mediates thermal hyperalgesia [PMID:9718253], blocks TNF-α-driven inflammation [PMID:24098382], and is required for CO2-induced arousal from sleep [PMID:25925320].","teleology":[{"year":1990,"claim":"Establishing the receptor's identity and primary effector answered whether HTR2A was a functional serotonin GPCR and where it acts, anchoring all later mechanistic work.","evidence":"Somatic cell hybrid chromosomal mapping with functional inositol phospholipid hydrolysis annotation","pmids":["1980030"],"confidence":"High","gaps":["Did not resolve G-protein identity or downstream branching","No cell-type resolution of cortical expression"]},{"year":1995,"claim":"Dissecting desensitization mechanism showed that signal attenuation can occur independently of receptor down-regulation, separating regulatory phases and implicating specific PKC isoforms.","evidence":"Stable cell line with radioligand binding, IP assays, isoform-selective antibodies, and F340L binding-incompetent mutant","pmids":["8531139"],"confidence":"High","gaps":["Late-phase (24 h) desensitization mechanism left undefined","Did not address β-arrestin involvement"]},{"year":1998,"claim":"Demonstrating differential agonist efficacy for PLA2 versus PLC, ERK activation in smooth muscle, peripheral nociceptive expression, and dissociation of PLC from hallucinogenic behavior established that the receptor signals through multiple branched pathways with agonist-directed trafficking.","evidence":"Second-messenger assays in receptor-expressing cell lines, arterial contractile and Western blot assays, in vivo paw-withdrawal with in situ hybridization, and PC12 PI hydrolysis versus drug-discrimination comparison","pmids":["9928246","9928253","9718253","11900766"],"confidence":"Medium","gaps":["Molecular basis of biased efficacy not resolved","Behavioral readout of hallucinogenesis remained mechanistically uncoupled from measured signaling"]},{"year":2002,"claim":"Linking receptor activation to de novo BDNF transcription identified a calcium- and kinase-dependent transcriptional output of 5-HT2AR signaling.","evidence":"RT-PCR/Northern blot of BDNF mRNA in C6 glioma with antagonist and kinase/calcium inhibitor dissection","pmids":["12095161"],"confidence":"Medium","gaps":["Transcription factors mediating BDNF induction not identified","Performed in glioma cells, not neurons"]},{"year":2004,"claim":"Identifying a selective PDZ-ligand interaction with CIPP, heterologous desensitization of co-localized 5-HT1A receptors, and a hypofunctional His452Tyr variant defined the receptor's scaffolding and cross-talk machinery and a natural functional polymorphism.","evidence":"Peptide affinity chromatography with mass spectrometry and imaging; in vivo PVN microinjection with neuroendocrine readout and double-label immunocytochemistry; mutagenesis with PLC/PLD/GTPγS assays","pmids":["14988405","15064330","15496511"],"confidence":"High","gaps":["Functional consequence of CIPP scaffolding on signaling not directly tested","Mechanism of 5-HT1A heterologous desensitization unresolved"]},{"year":2010,"claim":"Cataloging scaffolding/regulatory partners and constitutive activity refined how the receptor is targeted and how basal signaling is tuned, including RSK-mediated negative feedback.","evidence":"Co-IP and trafficking assays reviewed from primary work; cell-based and in vivo constitutive-activity pharmacology","pmids":["18640136","16269190"],"confidence":"Medium","gaps":["Review-level evidence not from a single rigorous study","Physiological relevance of constitutive activity not fully established"]},{"year":2010,"claim":"Mapping cortical 5-HT2AR to layer V pyramidal neurons and parvalbumin interneurons answered which cells the receptor acts in and showed direct depolarizing excitation of interneurons.","evidence":"BAC transgenic EGFP reporter with KO antibody validation, immunohistochemistry, and whole-cell electrophysiology","pmids":["20802802"],"confidence":"High","gaps":["Circuit-level integration of pyramidal versus interneuron effects unresolved"]},{"year":2011,"claim":"Demonstrating physical D2R and (later) mGlu2R heterocomplexes clarified that receptor-receptor interactions reciprocally modulate ligand affinity and signaling, but that complex formation does not always produce second-messenger crosstalk.","evidence":"Co-IP, radioligand binding, IP assays, and 5-HT2AR-KO locomotor pharmacology (D2R); quantitative SNAP/CLIP HTRF and Gq/Gi/cAMP assays (mGlu2)","pmids":["21645528","22300836"],"confidence":"Medium","gaps":["Stoichiometry and in vivo prevalence of heterocomplexes unknown","Discrepant functional outcomes between partners unexplained"]},{"year":2012,"claim":"Resolving ligand-selective endocytosis and PP2A-dependent recycling established that trafficking is functionally selective, with distinct kinase/phosphatase requirements per ligand.","evidence":"Cell-based trafficking assays with PKC inhibition, phosphorylation measurement, and PP2A inhibition across multiple ligands","pmids":["23034456"],"confidence":"High","gaps":["Identity of receptor phosphosites not mapped","DA/clozapine-induced internalization mechanism (PKC-independent) undefined"]},{"year":2013,"claim":"In vivo work established the receptor's role in dorsal raphe firing control, systemic anti-inflammatory action, and hepatic stellate cell activation, broadening its mechanistic reach beyond cortical signaling.","evidence":"In vivo electrophysiology/microdialysis with KO mice and noradrenergic lesion; systemic (R)-DOI with antagonist rescue and inflammatory marker profiling; LX-2 cell and rat cirrhosis antagonist studies","pmids":["23411676","24098382","23362947"],"confidence":"High","gaps":["Downstream signaling for anti-inflammatory effect not delineated","Cell-type and pathway specificity in liver fibrosis incompletely defined"]},{"year":2015,"claim":"Defining stress- and serotonin-dependent regulation showed that Htr2a expression is acutely induced via Egr3 and that the receptor is permissively required for CO2-induced arousal.","evidence":"Sleep-deprivation qRT-PCR in Egr3-/- mice; subtype-selective pharmacology and Lmx1b serotonin-neuron-null arousal assays","pmids":["25857407","25925320"],"confidence":"Medium","gaps":["Direct Egr3 binding to Htr2a regulatory region not shown","Neural circuit mediating arousal effect unresolved"]},{"year":2018,"claim":"Showing that chronic THC shifts the receptor toward Gαi/o coupling via Akt/mTOR established a mechanism for drug-induced pro-hallucinogenic signaling bias.","evidence":"Chronic THC in mice with [35S]GTPγS coupling assays across Gα subtypes, PPI behavior, and rapamycin co-treatment","pmids":["29748632"],"confidence":"High","gaps":["Molecular link between Akt/mTOR and altered G-protein coupling unmapped","Durability and reversibility of the bias shift unknown"]},{"year":2019,"claim":"Establishing that sustained 5-HT2AR activation drives AMPA receptor internalization and LTD in cortical pyramidal neurons defined a synaptic plasticity mechanism with genetic causality.","evidence":"Patch-clamp in PFC slices with 5-HT2AR-KO, viral rescue, GluA2-Ser880 Western blot, and AMPA internalization assay","pmids":["29917056"],"confidence":"High","gaps":["Signaling chain from receptor to GluA2 phosphorylation not fully traced","Behavioral correlate of cortical LTD not established here"]},{"year":2020,"claim":"Demonstrating PI3K-PDK1-AKT-mTOR-dependent cardiac hypertrophy linked the receptor to a peripheral growth-signaling cascade through gain- and loss-of-function.","evidence":"shRNA knockdown and adenoviral overexpression in neonatal rat cardiomyocytes with ISO hypertrophy, phospho-AKT/mTOR Western blot, and pathway inhibitors","pmids":["32519137"],"confidence":"Medium","gaps":["Proximal coupling of receptor to PI3K not defined","In vivo cardiac relevance from intact-animal genetics not shown"]},{"year":null,"claim":"How agonist-specific conformations are decoded into distinct effector branches (PLC vs PLA2 vs Gi/o vs PDZ-scaffolded outputs) and how this signaling diversity maps onto the receptor's many physiological roles remains the central open question.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural basis for biased signaling in the timeline","Receptor phosphosite code linking PKC/RSK to trafficking unmapped","Integration of cortical and peripheral functions under one mechanism unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,9,19]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[8,12]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[22,24]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,19]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[20,24]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[15]}],"complexes":[],"partners":["DRD2","GRM2","HTR1A","CIPP","DLG4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P28223","full_name":"5-hydroxytryptamine receptor 2A","aliases":["Serotonin receptor 2A"],"length_aa":471,"mass_kda":52.6,"function":"G-protein coupled receptor for 5-hydroxytryptamine (serotonin) (PubMed:1330647, PubMed:18703043, PubMed:19057895, PubMed:21645528, PubMed:22300836, PubMed:35084960, PubMed:38552625). Also functions as a receptor for various drugs and psychoactive substances, including mescaline, psilocybin, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and lysergic acid diethylamide (LSD) (PubMed:28129538, PubMed:35084960). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of downstream effectors (PubMed:28129538, PubMed:35084960). HTR2A is coupled to G(q)/G(11) G alpha proteins and activates phospholipase C-beta, releasing diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3) second messengers that modulate the activity of phosphatidylinositol 3-kinase and promote the release of Ca(2+) ions from intracellular stores, respectively (PubMed:18703043, PubMed:28129538, PubMed:35084960). Beta-arrestin family members inhibit signaling via G proteins and mediate activation of alternative signaling pathways (PubMed:28129538, PubMed:35084960). Affects neural activity, perception, cognition and mood (PubMed:18297054). Plays a role in the regulation of behavior, including responses to anxiogenic situations and psychoactive substances. Plays a role in intestinal smooth muscle contraction, and may play a role in arterial vasoconstriction (By similarity) (Microbial infection) Acts as a receptor for human JC polyomavirus/JCPyV","subcellular_location":"Cell membrane; Cell projection, dendrite; Cell projection, axon; Cytoplasmic vesicle; Membrane, caveola; Presynapse","url":"https://www.uniprot.org/uniprotkb/P28223/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HTR2A","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HTR2A","total_profiled":1310},"omim":[{"mim_id":"616417","title":"ADHESION G PROTEIN-COUPLED RECEPTOR L3; ADGRL3","url":"https://www.omim.org/entry/616417"},{"mim_id":"613884","title":"CHROMOSOME 13q14 DELETION SYNDROME","url":"https://www.omim.org/entry/613884"},{"mim_id":"610509","title":"RIC3 ACETYLCHOLINE RECEPTOR CHAPERONE; RIC3","url":"https://www.omim.org/entry/610509"},{"mim_id":"608516","title":"MAJOR DEPRESSIVE DISORDER; MDD","url":"https://www.omim.org/entry/608516"},{"mim_id":"604099","title":"GLUTAMATE RECEPTOR, METABOTROPIC, 2; GRM2","url":"https://www.omim.org/entry/604099"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"blood vessel","ntpm":5.4},{"tissue":"brain","ntpm":18.2}],"url":"https://www.proteinatlas.org/search/HTR2A"},"hgnc":{"alias_symbol":["5-HT2A"],"prev_symbol":["HTR2"]},"alphafold":{"accession":"P28223","domains":[{"cath_id":"1.20.1070.10","chopping":"67-278_307-401","consensus_level":"medium","plddt":90.7267,"start":67,"end":401}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P28223","model_url":"https://alphafold.ebi.ac.uk/files/AF-P28223-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P28223-F1-predicted_aligned_error_v6.png","plddt_mean":73.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HTR2A","jax_strain_url":"https://www.jax.org/strain/search?query=HTR2A"},"sequence":{"accession":"P28223","fasta_url":"https://rest.uniprot.org/uniprotkb/P28223.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P28223/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P28223"}},"corpus_meta":[{"pmid":"15309042","id":"PMC_15309042","title":"The 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A binding-incompetent mutant (F340L) showed that ligand binding is required for desensitization.\",\n      \"method\": \"Stable cell-line expressing cloned 5-HT2A receptor; radioligand binding, inositol phosphate assay, immunohistochemistry, Western blot with isoform-selective antibodies, phorbol ester-mediated PKC down-regulation, site-directed mutagenesis\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in defined cell line, mutagenesis, multiple orthogonal biochemical methods in a single study\",\n      \"pmids\": [\"8531139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"5-HT2A and 5-HT2C receptors couple to both phospholipase C (PLC-mediated IP accumulation) and phospholipase A2 (PLA2-mediated arachidonic acid release), and agonists show differential (biased) relative efficacies for these two pathways at the 5-HT2A receptor — all agonists tested had greater relative efficacy for PLA2-AA than for PLC-IP, supporting agonist-directed trafficking of receptor stimulus.\",\n      \"method\": \"Second-messenger assays (inositol phosphate accumulation and arachidonic acid release) in cell lines expressing cloned receptors\",\n      \"journal\": \"Annals of the New York Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal second-messenger assays in a single lab establishing biased signaling\",\n      \"pmids\": [\"9928246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"5-HT2A receptor activation in arterial smooth muscle activates the MAPK/ERK pathway (MEK and ERK1/2 phosphorylation) in a receptor- and tyrosine kinase-dependent manner, partially independent of L-type calcium channel activation and PLC signaling.\",\n      \"method\": \"Isolated rat arteries (contractile assay with tyrosine kinase and MEK inhibitors); Western blot for phospho-MEK and phospho-ERK in cultured aortic smooth muscle cells\",\n      \"journal\": \"Annals of the New York Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological inhibition plus Western blot in two complementary preparations from a single lab\",\n      \"pmids\": [\"9928253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"5-HT2A receptor activation by 5-HT agonists (but not 5-HT3 agonists) induces peripheral thermal hyperalgesia in rats; 5-HT2 receptor mRNA was detected in dorsal root ganglia neurons, indicating peripheral expression mediating nociception.\",\n      \"method\": \"Intradermal injection of receptor-subtype-selective agonists/antagonists in rats with paw-withdrawal latency assay; in situ hybridization for 5-HT2 receptor mRNA in DRG\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological specificity confirmed with selective antagonist ketanserin blocking 5-HT effect, complemented by mRNA localization\",\n      \"pmids\": [\"9718253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"5-HT2A receptor-stimulated phosphoinositide hydrolysis does not fully account for the discriminative (hallucinogenic) stimulus effects of psychedelics; non-hallucinogenic compounds (lisuride, quipazine, 6-F-DET) also activated PLC via 5-HT2A, and the rank order of PI hydrolysis efficacy did not correlate with hallucinogen drug-discrimination substitution.\",\n      \"method\": \"PC12 cells stably expressing rat 5-HT2A receptor; [3H]inositol phosphate accumulation assay; comparison with published drug-discrimination data\",\n      \"journal\": \"Pharmacology, biochemistry, and behavior\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single-lab, single in vitro assay, but finding is clearly negative/dissociative; informative for signaling mechanism\",\n      \"pmids\": [\"11900766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"5-HT2A receptor activation increases de novo BDNF mRNA synthesis in C6 glioma cells via a calcium-dependent and protein-kinase-dependent pathway; the effect is blocked by ketanserin (5-HT2A antagonist), actinomycin D (transcription inhibitor), EGTA (calcium chelator), staurosporine (PKC/PKA inhibitor), thapsigargin (Ca2+ ATPase inhibitor), and KN-62 (CaM kinase inhibitor), but not by cycloheximide.\",\n      \"method\": \"RT-PCR and Northern blot of BDNF mRNA in C6 glioma cells; pharmacological dissection with receptor antagonists, kinase inhibitors, and ion channel modulators\",\n      \"journal\": \"Neuromolecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal RNA detection methods plus multiple pathway inhibitors in a single lab\",\n      \"pmids\": [\"12095161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"5-HT2A and 5-HT2C receptor C-termini each contain a class I PDZ ligand (SXV motif) and interact with distinct sets of PDZ proteins in vitro: 5-HT2A robustly binds CIPP but not Veli-3/CASK/Mint1 complex or SAP102, whereas 5-HT2C binds those complexes; residues at the -1 position and upstream of the PDZ ligand are major determinants of PDZ selectivity. These interactions also occur in living cells in intracellular compartments.\",\n      \"method\": \"Affinity chromatography using immobilized synthetic peptides + mass spectrometry; immunofluorescence; electron microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — proteomic pulldown with mass spectrometry identification, validated by cell imaging; multiple orthogonal methods in one rigorous study\",\n      \"pmids\": [\"14988405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Activation of 5-HT2A receptors in the hypothalamic paraventricular nucleus (PVN) induces heterologous desensitization of co-localized 5-HT1A receptors in oxytocin and CRF neurons, reducing oxytocin and ACTH responses to a 5-HT1A agonist; 5-HT2A and 5-HT1A receptors co-localize within individual neuroendocrine cells in the PVN.\",\n      \"method\": \"In vivo pharmacology (microinjection of MDL100907 into PVN); neuroendocrine readout (oxytocin and ACTH plasma levels); double-label immunocytochemistry\",\n      \"journal\": \"The Journal of pharmacology and experimental therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo pharmacological rescue experiment combined with anatomical co-localization, single lab\",\n      \"pmids\": [\"15064330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The naturally occurring His452Tyr SNP in the 5-HT2A receptor C-terminus reduces agonist-stimulated signaling through both Gq (phospholipase C) and G13 (phospholipase D) pathways, impairs agonist-induced high-affinity binding and GTPγS turnover, and alters receptor desensitization kinetics.\",\n      \"method\": \"Stable NIH3T3 cells expressing wild-type or 452Tyr variant; inositol phosphate and phospholipase D assays; [35S]GTPγS binding; agonist competition binding\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-directed mutagenesis plus multiple orthogonal functional assays (PLC, PLD, G-protein coupling) in a defined cell system\",\n      \"pmids\": [\"15496511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"5-HT2A receptor trafficking, targeting, and signaling are regulated by scaffolding proteins (PSD-95, arrestin, caveolin) and by p90 ribosomal S6 kinase (RSK), which phosphorylates the receptor and attenuates its signaling.\",\n      \"method\": \"Co-immunoprecipitation, receptor trafficking assays, kinase interaction studies (as reviewed from primary experimental work)\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and trafficking assays reviewed from primary studies; single lab, multiple interaction partners identified\",\n      \"pmids\": [\"18640136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"5-HT2A and 5-HT2C receptors show constitutive activity in vitro; inverse agonists decrease basal signaling below baseline, and protean ligands can act as agonists for one response while acting as inverse agonists for another pathway coupled to the same receptor, demonstrating response-dependent constitutive activity. Evidence also suggests this constitutive activity is physiologically relevant in vivo.\",\n      \"method\": \"Cell-based second-messenger assays (inositol phosphate, arachidonic acid); in vivo behavioral pharmacology\",\n      \"journal\": \"Trends in pharmacological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro assays plus in vivo behavioral evidence reviewed across studies, but predominantly from one group\",\n      \"pmids\": [\"16269190\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"5-HT2A receptor and dopamine D2 receptor form a physical heterocomplex (co-immunoprecipitation in HEK293 cells); D2R activation increases hallucinogenic agonist affinity for 5-HT2AR and decreases 5-HT2AR-induced inositol phosphate production; in vivo, 5-HT2AR expression is necessary for the full locomotor effects of D2R antagonist.\",\n      \"method\": \"Radioligand binding assays; inositol phosphate second-messenger assay; co-immunoprecipitation in HEK293 cells; in vivo locomotor activity in 5-HT2AR knockout mice\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal functional and physical interaction evidence with multiple methods, single lab\",\n      \"pmids\": [\"21645528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"5-HT2A receptor endocytosis and recycling are functionally selective: serotonin (5-HT), dopamine (DA), DOI, and clozapine each trigger receptor endocytosis, but ketanserin does not. PKC-mediated receptor phosphorylation is required for 5-HT- and DOI-induced but not DA- or clozapine-induced internalization. Recycling back to the cell surface requires protein phosphatase 2A (PP2A)-mediated dephosphorylation for those ligands that required PKC for endocytosis.\",\n      \"method\": \"Cell-based receptor trafficking assays; PKC inhibition; phosphorylation assays; PP2A inhibition; quantitative receptor internalization/recycling measurements\",\n      \"journal\": \"Molecular pharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple ligands tested with orthogonal kinase/phosphatase intervention experiments establishing mechanistic pathway, single lab but rigorous\",\n      \"pmids\": [\"23034456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"5-HT2A receptor forms heterocomplexes with mGlu2 receptor (confirmed by quantitative SNAP/CLIP-tag HTRF), but co-expression of both receptors in HEK-293 cells does not alter signaling mediated by either receptor individually (no change in Gq, Gi, or cAMP pathways), indicating that physical heterocomplex formation does not necessarily translate into functional second-messenger crosstalk.\",\n      \"method\": \"Quantitative SNAP/CLIP-tag HTRF assay for heterocomplex formation; Gq/Gi/cAMP second-messenger assays in HEK-293 cells; radioligand competition binding in prefrontal cortex membranes\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative HTRF for complex formation plus multiple signaling assays; single lab but orthogonal methods\",\n      \"pmids\": [\"22300836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Systemic activation of 5-HT2A receptors with (R)-DOI produces potent blockade of TNF-α-induced expression of pro-inflammatory adhesion molecules (ICAM-1, VCAM-1), cytokines (IL-6, IL-1β), and chemokines (MCP-1, CX3CL1) in the aorta and intestine in vivo, and reduces circulating IL-6; this anti-inflammatory effect is abolished by selective 5-HT2A receptor antagonists.\",\n      \"method\": \"Systemic drug administration in rats; gene expression analysis (qPCR) and protein immunostaining in tissues; receptor-selective antagonist rescue experiments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo pharmacology with receptor-selective antagonist confirmation, multiple inflammatory markers measured at gene and protein levels\",\n      \"pmids\": [\"24098382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"5-HT2A receptor antagonists (ketanserin, sarpogrelate) inhibit hepatic stellate cell (HSC) activation: they reduce viability, inhibit wound healing, induce apoptosis, and suppress α-SMA, procollagen type I, TGF-β, and Smad2/3 expression in LX-2 cells; in vivo, sarpogrelate reduces lobular inflammation and α-SMA, TGF-β, Smad2/3 expression in thioacetamide-induced cirrhosis.\",\n      \"method\": \"In vitro: cell viability, apoptosis, wound-healing, and gene expression assays in LX-2 cells; in vivo: rat cirrhosis model with histology and protein expression\",\n      \"journal\": \"Liver international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo experiments; multiple readouts; single lab\",\n      \"pmids\": [\"23362947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"5-HT2A receptor activation is necessary for CO2-induced arousal from sleep: selective 5-HT2A antagonists dose-dependently blocked CO2-induced arousal in wild-type mice; 5-HT2A (but not 5-HT2C) receptor agonists restored CO2-induced arousal in mice genetically lacking 5-HT neurons (Lmx1bf/f/p), demonstrating a permissive role downstream of serotonergic neuron activity.\",\n      \"method\": \"In vivo pharmacology with subtype-selective antagonists and agonists; CO2 and hypoxia arousal assays; genetic model (Lmx1bf/f/p mice lacking 5-HT neurons); dose-response analysis\",\n      \"journal\": \"Journal of neurophysiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological and genetic approaches converge on same conclusion; multiple receptor subtypes systematically ruled out\",\n      \"pmids\": [\"25925320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Htr2a cortical expression responds rapidly (within 6 h) to acute environmental stress (sleep deprivation) with a twofold increase in Htr2a mRNA; this induction requires the immediate early gene Egr3, as it is absent in Egr3-/- mice.\",\n      \"method\": \"Sleep deprivation stress in wild-type and Egr3-/- mice; quantitative RT-PCR of cortical Htr2a mRNA\",\n      \"journal\": \"ACS chemical neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout ablation establishes transcriptional dependency on Egr3; single lab, single stress paradigm\",\n      \"pmids\": [\"25857407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Chronic THC exposure during adolescence induces pro-hallucinogenic signaling of the 5-HT2A receptor: supersensitive coupling toward inhibitory Gαi1, Gαi3, Gαo, and Gαz proteins without changes in canonical Gαq/11 pathway; this shift in signaling bias is blocked by the Akt/mTOR inhibitor rapamycin, which also prevents THC-induced prepulse inhibition disruption.\",\n      \"method\": \"Chronic THC administration in mice; G-protein coupling assays ([35S]GTPγS); behavioral PPI assay; rapamycin co-treatment; protein expression analysis\",\n      \"journal\": \"Neuropsychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — G-protein coupling assays with multiple Gα subtypes plus pathway inhibitor experiment linking Akt/mTOR to 5-HT2AR signaling bias; multiple orthogonal methods\",\n      \"pmids\": [\"29748632\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Sustained 5-HT2A receptor activation (20 min exposure to serotonin or DOI) in layer V pyramidal neurons of the mouse prefrontal cortex produces long-lasting depression (LTD) of AMPA receptor-mediated excitatory postsynaptic currents; this LTD is absent in 5-HT2AR knockout mice, rescued by viral 5-HT2AR re-expression in pyramidal neurons, occludes electrically induced LTD, and involves phosphorylation of GluA2 at Ser880 and AMPA receptor internalization.\",\n      \"method\": \"Whole-cell patch-clamp electrophysiology in PFC slices; 5-HT2AR knockout mice; viral rescue; GluA2 phosphorylation (Western blot); AMPA receptor internalization assay\",\n      \"journal\": \"Cerebral cortex\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — electrophysiological LTD measurement with genetic knockout and viral rescue, plus biochemical mechanistic validation; multiple orthogonal methods in a single study\",\n      \"pmids\": [\"29917056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HTR2A promotes cardiac hypertrophy by activating the PI3K-PDK1-AKT-mTOR signaling cascade; HTR2A knockdown suppressed ISO-induced cardiomyocyte hypertrophy (reduced cell size, β-Mhc, Anp, Bnp expression), while overexpression promoted it; inhibition of PI3K, PDK1, or AKT-mTOR blocked HTR2A-driven hypertrophy.\",\n      \"method\": \"shRNA knockdown and adenoviral overexpression in neonatal rat cardiomyocytes; ISO-induced hypertrophy model; phospho-AKT/mTOR Western blot; pharmacological inhibitors (perifosine, rapamycin, PI3K inhibitor, PDK1 inhibitor)\",\n      \"journal\": \"Cell stress & chaperones\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with pathway inhibitors, single lab, in vitro cardiomyocyte model\",\n      \"pmids\": [\"32519137\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"In adult rat skeletal muscle, the 5-HT2A receptor localizes exclusively to plasma membranes (not transverse tubules), as determined by subcellular fractionation and immunoblot; this localization is the same in red and white muscle, indicating expression is independent of metabolic or contractile fiber type. The absence from TT makes 5-HT2AR an unlikely participant in excitation-contraction coupling.\",\n      \"method\": \"Subcellular fractionation of adult rat skeletal muscle; immunoblot of membrane fractions\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct subcellular fractionation with functional inference; single lab, single method\",\n      \"pmids\": [\"10198219\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Glucocorticoid receptor (GR) activation increases 5-HT2A receptor levels: GR under-expressing mice show decreased hippocampal 5-HT2A protein and frontal cortex binding; GR over-expressing mice show increased 5-HT2A levels; corticosterone treatment of organotypic hippocampal cultures increases 5-HT2A receptor levels, and this is blocked by either the GR antagonist mifepristone or the mineralocorticoid receptor antagonist spironolactone.\",\n      \"method\": \"Western blot and radioligand binding ([3H]-MDL100907) in transgenic GR mice; organotypic hippocampal cultures with corticosterone and receptor antagonists\",\n      \"journal\": \"Experimental neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic mouse and in vitro culture with pharmacological intervention; two orthogonal methods; single lab\",\n      \"pmids\": [\"19379741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Layer V pyramidal cells of anterior cortex constitute the largest 5-HT2A-receptor-expressing neuronal population in the cerebral cortex; parvalbumin-expressing fast-spiking GABAergic interneurons in middle layers also express 5-HT2A receptors and are depolarized and excited by serotonin through 5-HT2A receptor activation.\",\n      \"method\": \"BAC transgenic EGFP reporter mice; 5-HT2A knockout mice for antibody validation; immunohistochemistry; whole-cell electrophysiology\",\n      \"journal\": \"Frontiers in neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — genetic reporter + KO validation + electrophysiology; multiple orthogonal methods establishing both cellular identity and functional consequence\",\n      \"pmids\": [\"20802802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"5-HT2A receptor activation (DOI) decreases the firing rate of dorsal raphe 5-HT neurons in wild-type but not 5-HT2AR-/- mice; this inhibitory effect is mediated specifically through 5-HT2AR (not 5-HT2CR) and requires intact noradrenergic neurons (abolished by DSP4 noradrenergic neurotoxin); 5-HT2AR blockade (MDL100907) combined with escitalopram increases cortical norepinephrine outflow and produces antidepressant-like behavior.\",\n      \"method\": \"In vivo electrophysiology (dorsal raphe firing); microdialysis (cortical 5-HT and NE); 5-HT2AR knockout and 5-HT2CR knockout mice; DSP4 noradrenergic lesion; forced swim test\",\n      \"journal\": \"Experimental brain research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic models plus pharmacological dissection plus in vivo electrophysiology and microdialysis converging on mechanism\",\n      \"pmids\": [\"23411676\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HTR2A encodes a Gq/11-coupled GPCR that, upon serotonin binding, activates phospholipase C (inositol phosphate/Ca²⁺ signaling) and phospholipase A2 (arachidonic acid release), and exhibits biased/functional-selective coupling to inhibitory Gαi/o proteins with certain hallucinogenic ligands or after chronic THC exposure via Akt/mTOR-dependent mechanisms; receptor desensitization involves PKC phosphorylation (intermediate phase) and β-arrestin/clathrin-mediated internalization followed by PP2A-dependent recycling; the receptor's C-terminal PDZ ligand scaffolds it to CIPP and other PDZ proteins that modulate its targeting and signaling; 5-HT2AR physically interacts with dopamine D2R and mGlu2 receptors and functionally cross-talks with 5-HT1A receptors; in cortical pyramidal neurons, sustained 5-HT2AR activation drives AMPA receptor internalization (GluA2-Ser880 phosphorylation) and LTD of glutamatergic synaptic transmission; the receptor also activates MAPK/ERK in vascular smooth muscle, drives PI3K-PDK1-AKT-mTOR signaling in cardiomyocytes to promote hypertrophy, mediates peripheral thermal hyperalgesia, blocks TNF-α-driven inflammation, and its cortical expression is acutely up-regulated by stress via an Egr3-dependent transcriptional mechanism.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HTR2A encodes a Gq/11-coupled, cortex-enriched G-protein-coupled receptor that transduces serotonin signals into phosphoinositide hydrolysis and downstream calcium- and protein-kinase-dependent responses [#0, #6]. Beyond canonical Gq-PLC coupling, the receptor displays pronounced functional selectivity: agonists drive differential efficacy toward PLA2-mediated arachidonic acid release versus PLC-mediated inositol phosphate accumulation [#2], couple to G13/phospholipase D [#9], and after chronic adolescent THC exposure acquire supersensitive coupling to inhibitory Gαi/o/z proteins through an Akt/mTOR-dependent mechanism [#19]. Receptor desensitization and trafficking are tightly regulated: agonist-induced desensitization proceeds without loss of surface receptor and is mediated in its intermediate phase by PKCα/ε [#1], while ligand-selective endocytosis requires PKC phosphorylation and subsequent recycling depends on PP2A-mediated dephosphorylation [#13]. The receptor's C-terminal class I PDZ ligand confers selective binding to CIPP and other scaffolding proteins that govern its targeting [#7], and the receptor physically heterocomplexes with dopamine D2 and metabotropic glutamate mGlu2 receptors, with consequences for ligand affinity and signaling that depend on the partner [#12, #14]. In the cerebral cortex, 5-HT2AR is expressed most abundantly in layer V pyramidal neurons and in fast-spiking parvalbumin interneurons [#24], where sustained activation drives GluA2-Ser880 phosphorylation, AMPA receptor internalization, and long-lasting depression of glutamatergic transmission [#20]; cortical Htr2a expression is itself acutely up-regulated by stress through an Egr3-dependent transcriptional program [#18] and by glucocorticoid receptor signaling [#23]. Peripherally, the receptor activates MAPK/ERK in vascular smooth muscle [#3], drives PI3K-PDK1-AKT-mTOR-dependent cardiomyocyte hypertrophy [#21], mediates thermal hyperalgesia [#4], blocks TNF-α-driven inflammation [#15], and is required for CO2-induced arousal from sleep [#17].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Establishing the receptor's identity and primary effector answered whether HTR2A was a functional serotonin GPCR and where it acts, anchoring all later mechanistic work.\",\n      \"evidence\": \"Somatic cell hybrid chromosomal mapping with functional inositol phospholipid hydrolysis annotation\",\n      \"pmids\": [\"1980030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve G-protein identity or downstream branching\", \"No cell-type resolution of cortical expression\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Dissecting desensitization mechanism showed that signal attenuation can occur independently of receptor down-regulation, separating regulatory phases and implicating specific PKC isoforms.\",\n      \"evidence\": \"Stable cell line with radioligand binding, IP assays, isoform-selective antibodies, and F340L binding-incompetent mutant\",\n      \"pmids\": [\"8531139\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Late-phase (24 h) desensitization mechanism left undefined\", \"Did not address β-arrestin involvement\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Demonstrating differential agonist efficacy for PLA2 versus PLC, ERK activation in smooth muscle, peripheral nociceptive expression, and dissociation of PLC from hallucinogenic behavior established that the receptor signals through multiple branched pathways with agonist-directed trafficking.\",\n      \"evidence\": \"Second-messenger assays in receptor-expressing cell lines, arterial contractile and Western blot assays, in vivo paw-withdrawal with in situ hybridization, and PC12 PI hydrolysis versus drug-discrimination comparison\",\n      \"pmids\": [\"9928246\", \"9928253\", \"9718253\", \"11900766\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of biased efficacy not resolved\", \"Behavioral readout of hallucinogenesis remained mechanistically uncoupled from measured signaling\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Linking receptor activation to de novo BDNF transcription identified a calcium- and kinase-dependent transcriptional output of 5-HT2AR signaling.\",\n      \"evidence\": \"RT-PCR/Northern blot of BDNF mRNA in C6 glioma with antagonist and kinase/calcium inhibitor dissection\",\n      \"pmids\": [\"12095161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcription factors mediating BDNF induction not identified\", \"Performed in glioma cells, not neurons\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identifying a selective PDZ-ligand interaction with CIPP, heterologous desensitization of co-localized 5-HT1A receptors, and a hypofunctional His452Tyr variant defined the receptor's scaffolding and cross-talk machinery and a natural functional polymorphism.\",\n      \"evidence\": \"Peptide affinity chromatography with mass spectrometry and imaging; in vivo PVN microinjection with neuroendocrine readout and double-label immunocytochemistry; mutagenesis with PLC/PLD/GTPγS assays\",\n      \"pmids\": [\"14988405\", \"15064330\", \"15496511\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of CIPP scaffolding on signaling not directly tested\", \"Mechanism of 5-HT1A heterologous desensitization unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Cataloging scaffolding/regulatory partners and constitutive activity refined how the receptor is targeted and how basal signaling is tuned, including RSK-mediated negative feedback.\",\n      \"evidence\": \"Co-IP and trafficking assays reviewed from primary work; cell-based and in vivo constitutive-activity pharmacology\",\n      \"pmids\": [\"18640136\", \"16269190\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Review-level evidence not from a single rigorous study\", \"Physiological relevance of constitutive activity not fully established\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Mapping cortical 5-HT2AR to layer V pyramidal neurons and parvalbumin interneurons answered which cells the receptor acts in and showed direct depolarizing excitation of interneurons.\",\n      \"evidence\": \"BAC transgenic EGFP reporter with KO antibody validation, immunohistochemistry, and whole-cell electrophysiology\",\n      \"pmids\": [\"20802802\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Circuit-level integration of pyramidal versus interneuron effects unresolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrating physical D2R and (later) mGlu2R heterocomplexes clarified that receptor-receptor interactions reciprocally modulate ligand affinity and signaling, but that complex formation does not always produce second-messenger crosstalk.\",\n      \"evidence\": \"Co-IP, radioligand binding, IP assays, and 5-HT2AR-KO locomotor pharmacology (D2R); quantitative SNAP/CLIP HTRF and Gq/Gi/cAMP assays (mGlu2)\",\n      \"pmids\": [\"21645528\", \"22300836\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and in vivo prevalence of heterocomplexes unknown\", \"Discrepant functional outcomes between partners unexplained\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolving ligand-selective endocytosis and PP2A-dependent recycling established that trafficking is functionally selective, with distinct kinase/phosphatase requirements per ligand.\",\n      \"evidence\": \"Cell-based trafficking assays with PKC inhibition, phosphorylation measurement, and PP2A inhibition across multiple ligands\",\n      \"pmids\": [\"23034456\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of receptor phosphosites not mapped\", \"DA/clozapine-induced internalization mechanism (PKC-independent) undefined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"In vivo work established the receptor's role in dorsal raphe firing control, systemic anti-inflammatory action, and hepatic stellate cell activation, broadening its mechanistic reach beyond cortical signaling.\",\n      \"evidence\": \"In vivo electrophysiology/microdialysis with KO mice and noradrenergic lesion; systemic (R)-DOI with antagonist rescue and inflammatory marker profiling; LX-2 cell and rat cirrhosis antagonist studies\",\n      \"pmids\": [\"23411676\", \"24098382\", \"23362947\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling for anti-inflammatory effect not delineated\", \"Cell-type and pathway specificity in liver fibrosis incompletely defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defining stress- and serotonin-dependent regulation showed that Htr2a expression is acutely induced via Egr3 and that the receptor is permissively required for CO2-induced arousal.\",\n      \"evidence\": \"Sleep-deprivation qRT-PCR in Egr3-/- mice; subtype-selective pharmacology and Lmx1b serotonin-neuron-null arousal assays\",\n      \"pmids\": [\"25857407\", \"25925320\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct Egr3 binding to Htr2a regulatory region not shown\", \"Neural circuit mediating arousal effect unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showing that chronic THC shifts the receptor toward Gαi/o coupling via Akt/mTOR established a mechanism for drug-induced pro-hallucinogenic signaling bias.\",\n      \"evidence\": \"Chronic THC in mice with [35S]GTPγS coupling assays across Gα subtypes, PPI behavior, and rapamycin co-treatment\",\n      \"pmids\": [\"29748632\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between Akt/mTOR and altered G-protein coupling unmapped\", \"Durability and reversibility of the bias shift unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Establishing that sustained 5-HT2AR activation drives AMPA receptor internalization and LTD in cortical pyramidal neurons defined a synaptic plasticity mechanism with genetic causality.\",\n      \"evidence\": \"Patch-clamp in PFC slices with 5-HT2AR-KO, viral rescue, GluA2-Ser880 Western blot, and AMPA internalization assay\",\n      \"pmids\": [\"29917056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling chain from receptor to GluA2 phosphorylation not fully traced\", \"Behavioral correlate of cortical LTD not established here\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrating PI3K-PDK1-AKT-mTOR-dependent cardiac hypertrophy linked the receptor to a peripheral growth-signaling cascade through gain- and loss-of-function.\",\n      \"evidence\": \"shRNA knockdown and adenoviral overexpression in neonatal rat cardiomyocytes with ISO hypertrophy, phospho-AKT/mTOR Western blot, and pathway inhibitors\",\n      \"pmids\": [\"32519137\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Proximal coupling of receptor to PI3K not defined\", \"In vivo cardiac relevance from intact-animal genetics not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How agonist-specific conformations are decoded into distinct effector branches (PLC vs PLA2 vs Gi/o vs PDZ-scaffolded outputs) and how this signaling diversity maps onto the receptor's many physiological roles remains the central open question.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural basis for biased signaling in the timeline\", \"Receptor phosphosite code linking PKC/RSK to trafficking unmapped\", \"Integration of cortical and peripheral functions under one mechanism unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 9, 19]},\n      {\"term_id\": \"GO:0004930\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [8, 12]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [22, 24]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 19]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [20, 24]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DRD2\", \"GRM2\", \"HTR1A\", \"CIPP\", \"DLG4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}