{"gene":"TACR1","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1998,"finding":"Substance P (SP) induces desensitization and endocytosis of NK1R in myenteric neurons: SP causes rapid NK1R-mediated increase in [Ca2+]i that desensitizes to repeated stimulation, internalizes NK1R into early endosomes containing SP, and triggers rapid redistribution of beta-arrestin-1 and -2 from cytosol to plasma membrane and then to endosomes containing NK1R and SP. GRK-2 and GRK-3 remain in vesicles while Galphaq/11 stays at the plasma membrane.","method":"Calcium imaging, immunofluorescence, subcellular fractionation in cultured myenteric neurons","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Ca2+ imaging, immunofluorescence localization, co-distribution assays) in a single rigorous study with clear mechanistic readouts","pmids":["9693383"],"is_preprint":false},{"year":2001,"finding":"Photolabeling of NK1R with p-benzoylphenylalanine3-SP (Bpa3-SP) demonstrates spatial proximity between two distinct extracellular receptor regions in the SP·NK1R complex: one site on the second extracellular loop (EC2) within residues 173–177, and a second site on the extracellular N-terminus within residues 11–21 (containing potential N-linked glycosylation sites).","method":"Photoaffinity labeling with radiolabeled SP analogue, peptide mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro photocrosslinking with defined covalent labeling sites identified by peptide mapping, single lab but rigorous biochemical methodology","pmids":["11294866"],"is_preprint":false},{"year":2003,"finding":"IL-12 and IL-18 induce NK1R expression on T cells through NF-κB activation (requiring NF-κB nuclear translocation but not the Stat4 pathway), and this induction is blocked by IL-10 but not TGF-β.","method":"Murine splenocyte culture with cytokines, actinomycin D/cycloheximide treatment, NF-κB inhibitors, Stat4-/- mice, RT-PCR","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (Stat4-/- mice) and pharmacological (inhibitors) epistasis with transcription readout, single lab","pmids":["12734344"],"is_preprint":false},{"year":2004,"finding":"IL-1β upregulates NK1R expression in human astroglioma cells and primary rat astrocytes through NF-κB activation; the induced NK1R is functional as demonstrated by SP-stimulated Ca2+ mobilization, which is inhibited by the NK1R antagonist CP-96,345.","method":"Western blot, RT-PCR, Ca2+ imaging, NF-κB luciferase reporter assay, CAPE inhibitor of NF-κB","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (expression + functional Ca2+ assay + reporter assay + pharmacological inhibition), single lab","pmids":["15390113"],"is_preprint":false},{"year":2005,"finding":"Activation of TRPV-1 by capsaicin induces SP-mediated plasma extravasation in the rat pancreas via NK1R, as shown by blockade with either the TRPV-1 antagonist capsazepine or the NK1R antagonist CP 96,345.","method":"Evans blue extravasation assay, pharmacological antagonist blockade in vivo","journal":"Pancreas","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo pharmacological epistasis with two independent antagonists at distinct pathway steps, single lab","pmids":["15782105"],"is_preprint":false},{"year":2007,"finding":"NK1R knockout mice show two-to-fourfold greater extracellular noradrenaline in the prefrontal cortex compared to wildtypes due to increased transmitter release coupled with desensitization of somatodendritic alpha2a-adrenoceptors in the locus coeruleus (reduced [35S]GTPγS binding to alpha2a-adrenoceptors by ~70% in locus coeruleus of NK1R-/- mice), establishing that NK1R normally constrains noradrenergic transmission.","method":"In vivo microdialysis, [35S]GTPγS binding, Western blot for noradrenaline transporter, alpha2-adrenoceptor pharmacology","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (microdialysis, GTPγS binding, Western blot) in KO vs. wildtype with pharmacological validation","pmids":["17331215"],"is_preprint":false},{"year":2008,"finding":"Human peripheral blood monocytes express the truncated NK1R isoform (NK1R-T) but not full-length NK1R. NK1R-T does not mobilize Ca2+ on its own but selectively activates ERK2 and enhances CCL5/CCR5-mediated Ca2+ mobilization and chemotaxis in an ERK1/2-dependent manner. NK1R-T activation also causes serine phosphorylation of CCR5, indicating receptor crosstalk.","method":"Western blot, Ca2+ mobilization assay, chemotaxis (Transwell), ERK phosphorylation assay, NK1R-F transfection comparison","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays (Ca2+, chemotaxis, ERK phosphorylation, CCR5 phosphorylation) with isoform-specific comparisons, NK1R antagonist validation","pmids":["18835883"],"is_preprint":false},{"year":2009,"finding":"NK1R deficiency (genetic knockout) leads to reduced spontaneous dopamine efflux (>50%) in prefrontal cortex and abolishes the striatal dopamine response to d-amphetamine, as shown by in vivo microdialysis; locomotor hyperactivity from NK1R inactivation is reversed by psychostimulants methylphenidate and d-amphetamine.","method":"In vivo microdialysis in NK1R-/- vs wildtype mice, locomotor activity measurement, psychostimulant treatment","journal":"Journal of psychopharmacology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo microdialysis with genetic KO and pharmacological rescue, replicated across multiple behavioral paradigms","pmids":["19204064"],"is_preprint":false},{"year":2010,"finding":"NK1R deletion or pharmacological blockade with L-703,606 reduces voluntary alcohol consumption and alcohol conditioned place preference in a receptor-specific, gene-dose-dependent manner; NK1R KO mice do not show escalation of alcohol intake after repeated deprivation-access cycles.","method":"Two-bottle choice alcohol consumption, conditioned place preference, NK1R KO mice, pharmacological antagonism with receptor-specificity confirmed in KO controls","journal":"Psychopharmacology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic and pharmacological approaches converge, receptor specificity confirmed by testing antagonist in KO mice, multiple behavioral paradigms","pmids":["20112009"],"is_preprint":false},{"year":2011,"finding":"SP activates NK1R and NK3R in rat mesenteric lymphatic muscle cells to stimulate phosphorylation of MLC20 (contractile pathway) and p38-MAPK/ERK1/2 (pro-inflammatory pathway); ERK1/2 inhibition decreases p-MLC20 via a PKC-dependent crosstalk between the two pathways.","method":"Cell culture pharmacological inhibition, Western blot for phosphoproteins, specific NK1R and NK3R inhibitors","journal":"Microcirculation","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pharmacological inhibition with multiple readouts, single lab, no genetic confirmation of receptor identity","pmids":["21166923"],"is_preprint":false},{"year":2011,"finding":"NK1R-deficient mice show reduced weight gain, lower circulating leptin and insulin on high-fat diet, higher adiponectin receptor expression, reduced JNK/PKC activation in mesenteric fat, and improved glucose clearance. SP directly inhibits insulin-mediated glucose uptake in isolated rat adipocytes, establishing a role for SP/NK1R in adipose insulin signaling.","method":"NK1R KO mice on high-fat diet, glucose tolerance test, Western blot, in vitro glucose uptake in isolated adipocytes","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO combined with in vitro direct SP effect on glucose uptake, single lab with multiple readouts","pmids":["21467195"],"is_preprint":false},{"year":2013,"finding":"SP promotes pancreatic cancer cell proliferation, invasion, MMP-2 expression, and perineural invasion via NK1R; NK1R antagonists block SP-induced cancer cell migration to dorsal root ganglia in a coculture model.","method":"MTT proliferation assay, Transwell Matrigel invasion assay, Western blot, neuron-tumor coculture, NK1R antagonist blockade","journal":"Molecular cancer research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — multiple in vitro functional assays with pharmacological inhibition, single lab","pmids":["23345604"],"is_preprint":false},{"year":2013,"finding":"In alcohol-preferring (P) rats, elevated Tacr1 expression in the central amygdala (but not prefrontal cortex) is accompanied by elevated NK1R binding; central amygdala infusion of NK1R antagonist L822429 replicates the systemic effect on alcohol self-administration. A promoter SNP (-1372C allele) confers increased transcription factor binding (GATA-2, E2F-1) and transcription by electromobility shift and luciferase assays.","method":"Operant self-administration, central amygdala microinfusion, receptor autoradiography/binding, EMSA, luciferase reporter assay","journal":"Biological psychiatry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — site-specific microinfusion establishing central amygdala locus, plus in vitro promoter functional assays, single lab","pmids":["23419547"],"is_preprint":false},{"year":2015,"finding":"SP stimulation of NK1R in human colonic epithelial NCM460 cells induces miR-221-5p expression via NF-κB and JNK pathways; miR-221-5p directly targets IL-6R mRNA (validated by luciferase reporter), and this SP/NK1R/miR-221-5p/IL-6R axis is protective in colitis models.","method":"microRNA profiling, luciferase reporter assay for IL-6R targeting, NF-κB/JNK pharmacological inhibition, in vivo colitis models (TNBS, DSS)","journal":"Cellular and molecular gastroenterology and hepatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assay validation of direct miRNA-target interaction plus pathway inhibitor experiments and in vivo model, single lab","pmids":["26645045"],"is_preprint":false},{"year":2018,"finding":"MMP1 activates PAR1-expressing dorsal root ganglia neurons to release SP, which then activates NK1R on pancreatic cancer cells via SP/NK1R/ERK signaling to enhance migration, invasion, and perineural invasion; shRNA silencing of MMP1 or pharmacological blockade of PAR1 or NK1R inhibits perineural invasion.","method":"Matrigel/DRG coculture PNI model, in vivo sciatic nerve invasion model, shRNA, pharmacological antagonists, MRI imaging","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (shRNA) and pharmacological blockade at multiple pathway nodes with in vitro and in vivo validation, single lab","pmids":["29896303"],"is_preprint":false},{"year":2018,"finding":"NK1R agonist GR73632-induced vomiting in the least shrew activates brainstem signaling through L-type Ca2+ channels and IP3R-dependent PI3K/PKCα/βII-ERK1/2 pathway; CaMKIIα, ERK1/2, Akt, and PKCα/βII are phosphorylated in brainstem after NK1R activation, and inhibitors of each step suppress vomiting.","method":"In vivo emesis assay, Western blot for phosphoproteins in brainstem, immunofluorescence, pharmacological inhibitors of LTCC, IP3R, ERK1/2, PKC, PI3K","journal":"Neurochemistry international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic pharmacological dissection of signaling cascade with multiple inhibitors and phosphoprotein readouts, single lab","pmids":["30453005"],"is_preprint":false},{"year":2019,"finding":"SP/NK1R promotes esophageal squamous cell carcinoma cell proliferation through the NK1R/Hes1 axis: NK1R downregulation markedly reduces Hes1 expression (identified by iTRAQ proteomics), and Hes1 regulates proliferation downstream of SP/NK1R.","method":"CCK-8 and colony formation assays, iTRAQ protein spectrum analysis, Western blot, RT-qPCR, xenograft model","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — unbiased proteomics discovery plus functional validation in vitro and in vivo, single lab","pmids":["31109645"],"is_preprint":false},{"year":2021,"finding":"Activation of a subset of spinal Tacr1-expressing projection neurons (expressing NK1R) evokes a full repertoire of pain-related behaviors. These neurons project to a cluster of neurons in the superior lateral parabrachial nucleus (PBN-SL) that also express Tacr1. PBN-SL Tacr1 neurons respond to sustained but not acute noxious stimuli; silencing them causes mice to ignore long-lasting noxious stimuli but does not affect acute pain. PBN-SL Tacr1 activation alone heightens nocifensive behaviors and suppresses itch.","method":"Optogenetic activation of spinal Tacr1 neurons, chemogenetic silencing of PBN-SL Tacr1 neurons, optotagging, behavioral assays for pain and itch","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific optogenetic and chemogenetic manipulations with defined circuit-level behavioral phenotypes, multiple orthogonal approaches","pmids":["33591273"],"is_preprint":false},{"year":2021,"finding":"NK1R inhibition with aprepitant suppresses NLRC4-dependent neuronal pyroptosis after intracerebral hemorrhage via NK1R/PKCδ signaling; NK1R agonist GR73632 or PKCδ agonist PMA reverses aprepitant's neuroprotective effect, and NLRC4 siRNA knockdown phenocopies aprepitant.","method":"Mouse ICH model, Western blot, immunofluorescence, intracerebroventricular injection of agonists/siRNA, neurobehavioral tests","journal":"Journal of neuroinflammation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic (siRNA) and pharmacological epistasis at multiple pathway nodes, single lab","pmids":["35922848"],"is_preprint":false},{"year":2021,"finding":"NK1R inhibition by aprepitant promotes hematoma clearance after ICH by increasing M2 microglial polarization via downregulation of PKC/p38MAPK/NFκB signaling; thrombin upstream increases SP, and SP activates NK1R on microglia to drive M1 polarization.","method":"Autologous blood injection ICH model, intraperitoneal and intracerebroventricular drug administration, Western blot, immunofluorescence, thrombin injection","journal":"Neurotherapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological epistasis with agonist rescue and upstream pathway identification (thrombin→SP→NK1R), single lab","pmids":["34244927"],"is_preprint":false},{"year":2022,"finding":"Tacr1-expressing ON cells in the rostral ventromedial medulla (RVM) are excited by substance P and exert inhibitory control over spinal pruriceptive transmission: intramedullary SP potentiates RVM ON cells and reduces pruritogen-evoked scratching; chemogenetic activation of RVM Tacr1 neurons reduces itch; optotagging confirms these are ON cells.","method":"Intramedullary SP microinjection, chemogenetic (DREADD) activation, optotagging electrophysiology, behavioral assays for itch and pain","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific chemogenetic and electrophysiological (optotagging) approaches with defined behavioral phenotype, multiple orthogonal methods","pmids":["35972457"],"is_preprint":false},{"year":2018,"finding":"NK1R/5-HT1AR physically interact (co-immunoprecipitation) and co-localize in melanocytes and skin; SP activation of NK1R reduces 5-HT1AR expression and, when combined with 5-HT1AR antagonism, activates p-JNK signaling and inhibits p70S6K1 phosphorylation to reduce melanin production. Removal of the NK1R N-terminus prevents NK1R surface targeting and reduces the NK1R-5-HT1AR interaction.","method":"Co-immunoprecipitation, Western blot, PCR, in vitro melanin assay, in vivo mouse and zebrafish models, N-terminal deletion mutagenesis","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus mutagenesis and in vivo genetic model (5-htr1aa+/- zebrafish), single lab","pmids":["29430989"],"is_preprint":false},{"year":2020,"finding":"TGFβ upregulates NK1R-Tr (truncated isoform) expression in breast cancer cells via Smad4 binding to the NK1R promoter (confirmed by ChIP and dual-luciferase reporter assay); NK1R-Tr promotes proliferation and inhibits apoptosis, and these effects are attenuated by TGFβ when NK1R is knocked down.","method":"ChIP, dual-luciferase reporter assay, Western blot, CCK-8, colony formation, flow cytometry, xenograft model","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and reporter assay establish direct transcriptional regulation of NK1R by Smad4, single lab","pmids":["32380077"],"is_preprint":false},{"year":2021,"finding":"SP/NK1R signaling in breast cancer (MCF-7) increases intracellular ROS and upregulates NF-κB and its pro-inflammatory targets TNF-α and IL-6; NK1R blockade by aprepitant halts cell viability partly via p53-mediated upregulation of p21.","method":"ROS assay, qRT-PCR, resazurin cell viability assay, Western blot","journal":"Cell biochemistry and biophysics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single cell line, pharmacological only without genetic validation","pmids":["37740877"],"is_preprint":false},{"year":2023,"finding":"TFAP4 promotes NK1R transcription by binding to the NK1R promoter (abolished by mutation of the binding site); SP activates NK1R to engage JNK/p38 pathways to modulate tubular epithelial cell fate (growth arrest, apoptosis, profibrogenic gene expression) in chronic kidney disease.","method":"Promoter mutation assay, binding site mutagenesis, NK1R-KO mice and pharmacological antagonism in UUO model, NK1R-overexpressed HK-2 cells, Western blot","journal":"Frontiers in immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter binding site mutagenesis plus genetic KO and pharmacological approaches in vivo and in vitro, single lab","pmids":["37033943"],"is_preprint":false}],"current_model":"TACR1 (NK1R) is a G protein-coupled receptor that, upon binding substance P, couples to Gαq/11 to mobilize Ca2+ and activates downstream kinase cascades (ERK1/2, PKC, PI3K/Akt, CaMKII); it undergoes GRK2/3-mediated phosphorylation and beta-arrestin-1/2-dependent desensitization and endocytosis into early endosomes; it exists as full-length and truncated isoforms with distinct signaling capabilities; it modulates dopaminergic and noradrenergic tone in the prefrontal cortex, drives a spinoparabrachial circuit for ongoing pain, is expressed on immune cells (monocytes, T cells) where it amplifies chemokine receptor signaling, and its expression is transcriptionally regulated by NF-κB (downstream of IL-1β, IL-12/18, TNF-α), Smad4 (downstream of TGFβ), and TFAP4; it interacts physically with 5-HT1AR to modulate melanogenesis; and it drives pathological processes including neurogenic inflammation, perineural cancer invasion, and renal fibrosis via JNK/p38/NF-κB pathways."},"narrative":{"mechanistic_narrative":"TACR1 (NK1R) is a Gq/11-coupled receptor for substance P (SP) that converts neuropeptide signals into intracellular calcium and kinase cascades to drive neurotransmission, neurogenic inflammation, and pain/itch circuit function [PMID:9693383, PMID:30453005]. SP binding engages two spatially proximal extracellular contact regions—the second extracellular loop (residues 173–177) and the N-terminus (residues 11–21)—and the N-terminus is also required for receptor surface targeting [PMID:11294866, PMID:29430989]. Upon SP-induced calcium mobilization, the receptor rapidly desensitizes and is internalized into early endosomes through redistribution of beta-arrestin-1 and -2 to the plasma membrane and then to receptor-containing endosomes, while Gαq/11 remains at the membrane [PMID:9693383]. Downstream of NK1R, SP activates ERK1/2 together with an IP3R/L-type Ca2+ channel–dependent PI3K/PKCα/βII–ERK1/2 and CaMKII/Akt cascade [PMID:30453005], and engages JNK, p38, and NF-κB arms in disease contexts [PMID:26645045, PMID:37033943]. The receptor exists as full-length and truncated (NK1R-T/Tr) isoforms with distinct signaling outputs: the truncated form expressed on monocytes does not mobilize calcium alone but selectively activates ERK2 and amplifies CCL5/CCR5-mediated chemotaxis through CCR5 serine phosphorylation [PMID:18835883]. In the CNS, NK1R constrains monoaminergic tone—its loss elevates prefrontal noradrenaline via desensitized locus coeruleus α2A-adrenoceptors and reduces prefrontal/striatal dopamine efflux—and modulates reward-related and alcohol-consumption behaviors [PMID:17331215, PMID:19204064, PMID:20112009, PMID:23419547]. Spinal and brainstem Tacr1-expressing neurons form a circuit for sustained (but not acute) pain and bidirectional itch control, including a spino–parabrachial projection and RVM ON cells excited by SP [PMID:33591273, PMID:35972457]. NK1R expression is transcriptionally induced by NF-κB downstream of inflammatory cytokines [PMID:12734344, PMID:15390113], by Smad4 downstream of TGFβ [PMID:32380077], and by TFAP4 [PMID:37033943], and SP/NK1R signaling drives perineural cancer invasion, tumor proliferation, microglial polarization, and renal fibrosis [PMID:23345604, PMID:29896303, PMID:31109645, PMID:34244927, PMID:37033943].","teleology":[{"year":1998,"claim":"Established how NK1R signaling is terminated and recycled, defining a beta-arrestin-dependent desensitization and endocytic itinerary for the receptor.","evidence":"Calcium imaging, immunofluorescence and subcellular fractionation in cultured myenteric neurons","pmids":["9693383"],"confidence":"High","gaps":["Does not resolve the GRK phosphorylation sites on NK1R","Resignaling vs degradation fate of internalized receptor not defined"]},{"year":2001,"claim":"Defined the structural topology of SP engagement, mapping two distinct extracellular ligand-contact regions on EC2 and the N-terminus.","evidence":"Photoaffinity labeling with radiolabeled SP analogue and peptide mapping in vitro","pmids":["11294866"],"confidence":"High","gaps":["No full receptor structure or agonist-bound conformational model","Functional consequence of each contact site for activation not tested"]},{"year":2003,"claim":"Showed NK1R expression is inducible rather than fixed, placing it downstream of inflammatory cytokine signaling via NF-κB on immune cells.","evidence":"Murine splenocyte cytokine culture with NF-κB inhibitors and Stat4-/- mice, RT-PCR","pmids":["12734344"],"confidence":"Medium","gaps":["NF-κB binding site on the TACR1 promoter not mapped here","Whether induced receptor is functional not tested in this study"]},{"year":2004,"claim":"Extended cytokine-driven NF-κB induction of NK1R to CNS glia and confirmed the induced receptor is functionally coupled to calcium signaling.","evidence":"Western blot, RT-PCR, Ca2+ imaging, NF-κB luciferase reporter and antagonist blockade in astroglioma and primary astrocytes","pmids":["15390113"],"confidence":"Medium","gaps":["Direct promoter occupancy by NF-κB not shown","Single-lab pharmacological evidence"]},{"year":2005,"claim":"Placed NK1R downstream of TRPV1 in a neurogenic inflammation pathway in vivo, linking nociceptor activation to SP-mediated plasma extravasation.","evidence":"Evans blue extravasation with TRPV1 and NK1R antagonists in rat pancreas","pmids":["15782105"],"confidence":"Medium","gaps":["Pharmacological only, no genetic confirmation","Cellular source of SP not defined"]},{"year":2007,"claim":"Revealed a homeostatic role for NK1R in restraining noradrenergic transmission through α2A-adrenoceptor desensitization in the locus coeruleus.","evidence":"In vivo microdialysis, [35S]GTPγS binding and Western blot in NK1R-/- vs wildtype mice","pmids":["17331215"],"confidence":"High","gaps":["Mechanism linking NK1R loss to α2A desensitization not resolved","Direct vs developmental effect of constitutive KO unclear"]},{"year":2009,"claim":"Demonstrated NK1R control of dopaminergic tone and the behavioral consequences, connecting receptor loss to a psychostimulant-reversible hyperactivity phenotype.","evidence":"In vivo microdialysis and locomotor/psychostimulant rescue in NK1R-/- mice","pmids":["19204064"],"confidence":"High","gaps":["Circuit locus of dopaminergic modulation not pinpointed","Constitutive KO cannot distinguish developmental compensation"]},{"year":2010,"claim":"Implicated NK1R in alcohol reward and consumption using converging genetic and pharmacological loss-of-function.","evidence":"Two-bottle choice, conditioned place preference with NK1R KO and antagonist verified in KO controls","pmids":["20112009"],"confidence":"High","gaps":["Brain locus not identified in this study","Downstream signaling not addressed"]},{"year":2013,"claim":"Localized the alcohol phenotype to the central amygdala and identified a functional promoter SNP altering transcription-factor binding and NK1R expression.","evidence":"Operant self-administration with central amygdala microinfusion, receptor binding, EMSA and luciferase in alcohol-preferring rats","pmids":["23419547"],"confidence":"Medium","gaps":["GATA-2/E2F-1 occupancy shown in vitro only","Causal link from SNP to behavior not directly tested"]},{"year":2008,"claim":"Distinguished a truncated NK1R isoform with a separate signaling output that amplifies chemokine receptor function on immune cells.","evidence":"Calcium, chemotaxis, ERK and CCR5 phosphorylation assays with isoform-specific transfection in monocytes","pmids":["18835883"],"confidence":"High","gaps":["Structural basis of CCR5 crosstalk not defined","In vivo relevance of monocyte NK1R-T not established"]},{"year":2011,"claim":"Mapped NK1R coupling to both contractile (MLC20) and pro-inflammatory (p38/ERK) outputs with PKC-dependent crosstalk in lymphatic muscle, and to adipose insulin signaling.","evidence":"Pharmacological inhibition with phosphoprotein Western blots; NK1R KO high-fat-diet metabolic phenotyping and adipocyte glucose uptake","pmids":["21166923","21467195"],"confidence":"Medium","gaps":["Receptor identity in lymphatic cells confirmed pharmacologically only","Tissue-specific contribution of NK1R to metabolism not isolated"]},{"year":2015,"claim":"Defined a protective SP/NK1R/miR-221-5p/IL-6R axis in colonic epithelium, linking NK1R to NF-κB/JNK-driven post-transcriptional control.","evidence":"miRNA profiling, luciferase target validation, pathway inhibitors and TNBS/DSS colitis models","pmids":["26645045"],"confidence":"Medium","gaps":["Single-lab in vivo models","Generalizability beyond colonic epithelium unknown"]},{"year":2018,"claim":"Established SP/NK1R as a driver of perineural cancer invasion via an MMP1/PAR1/SP relay and downstream ERK signaling, and uncovered a physical NK1R–5-HT1AR interaction governing melanogenesis.","evidence":"DRG-tumor coculture and sciatic nerve invasion models with shRNA/antagonists; co-IP, N-terminal deletion mutagenesis and zebrafish/mouse melanin models","pmids":["29896303","29430989"],"confidence":"Medium","gaps":["Direct vs indirect NK1R–5-HT1AR contact interface not mapped","Stoichiometry and signaling output of the heteromer unclear"]},{"year":2019,"claim":"Identified Hes1 as a proliferative effector downstream of SP/NK1R in esophageal carcinoma.","evidence":"iTRAQ proteomics, proliferation/colony assays and xenografts with NK1R knockdown","pmids":["31109645"],"confidence":"Medium","gaps":["Mechanism linking NK1R to Hes1 induction not resolved","Single-lab finding"]},{"year":2021,"claim":"Defined Tacr1-expressing spinal and parabrachial circuits selective for sustained pain, distinguishing ongoing from acute nociception.","evidence":"Optogenetic activation of spinal Tacr1 neurons and chemogenetic silencing of PBN-SL Tacr1 neurons with optotagging and behavior","pmids":["33591273"],"confidence":"High","gaps":["Role of NK1R signaling itself (vs cell identity marker) within the circuit not isolated","Synaptic basis of sustained-stimulus selectivity unclear"]},{"year":2021,"claim":"Linked neuronal NK1R to neuroinflammatory injury, showing aprepitant suppresses NLRC4-dependent pyroptosis via NK1R/PKCδ and shifts microglia toward M2 polarization after hemorrhage.","evidence":"Mouse ICH models with agonist/siRNA epistasis, Western blot and immunofluorescence","pmids":["35922848","34244927"],"confidence":"Medium","gaps":["Direct NK1R-to-NLRC4/PKCδ coupling mechanism not defined","Single-lab models"]},{"year":2022,"claim":"Showed Tacr1 RVM ON cells provide descending inhibitory control of itch, complementing the parabrachial pain circuit.","evidence":"Intramedullary SP, chemogenetic activation and optotagging electrophysiology with itch/pain behavior","pmids":["35972457"],"confidence":"High","gaps":["Downstream spinal targets of RVM Tacr1 ON cells not mapped","Interaction with ascending Tacr1 pain circuit untested"]},{"year":2020,"claim":"Established direct transcriptional control of NK1R by Smad4 downstream of TGFβ and by TFAP4, with the truncated isoform driving tumor proliferation and renal profibrotic programs.","evidence":"ChIP, promoter mutagenesis and dual-luciferase assays with KO/overexpression in breast cancer and kidney (UUO) models","pmids":["32380077","37033943"],"confidence":"Medium","gaps":["Isoform-selective promoter usage not fully resolved","Cross-regulation among NF-κB, Smad4 and TFAP4 inputs unknown"]},{"year":null,"claim":"How the differential signaling of full-length versus truncated NK1R isoforms is allocated across tissues, and how isoform expression is selectively controlled by the converging NF-κB/Smad4/TFAP4 transcriptional inputs, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model linking isoform truncation to biased signaling","Promoter elements distinguishing full-length vs truncated transcription not defined","In vivo isoform-specific genetic tools lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,6,15]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[1]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,21]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,6,15]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[5,7,17,20]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,3,6,19]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,22,24]}],"complexes":[],"partners":["TAC1","ARRB1","ARRB2","GNAQ","CCR5","HTR1A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P25103","full_name":"Substance-P receptor","aliases":["NK-1 receptor","NK-1R","Tachykinin receptor 1"],"length_aa":407,"mass_kda":46.3,"function":"Receptor for the tachykinin substance P, also able to bind and respond to tachynins neurokinin A/substance K and neurokinin B/neuromedin-K (PubMed:1718267, PubMed:15452552). The rank order of affinity of this receptor to tachykinins is: substance P > neurokinin A/substance K > neurokinin B/neuromedin-K (PubMed:1718267). Substance P binding to its receptor triggers G protein-coupled receptor signaling via activation of phosphatidylinositol hydrolysis by phospholipase C. Substance P binding also triggers signaling via activation of adenylate cyclase activity which results in increased intracellular levels of cyclic AMP (cAMP) (By similarity)","subcellular_location":"Cell membrane; Early endosome","url":"https://www.uniprot.org/uniprotkb/P25103/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TACR1","classification":"Not Classified","n_dependent_lines":19,"n_total_lines":1208,"dependency_fraction":0.015728476821192054},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TACR1","total_profiled":1310},"omim":[{"mim_id":"612636","title":"UNC80 HOMOLOG, NALCN CHANNEL COMPLEX SUBUNIT; UNC80","url":"https://www.omim.org/entry/612636"},{"mim_id":"611549","title":"SODIUM LEAK CHANNEL, NONSELECTIVE; 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GRK-2 and GRK-3 remain in vesicles while Galphaq/11 stays at the plasma membrane.\",\n      \"method\": \"Calcium imaging, immunofluorescence, subcellular fractionation in cultured myenteric neurons\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Ca2+ imaging, immunofluorescence localization, co-distribution assays) in a single rigorous study with clear mechanistic readouts\",\n      \"pmids\": [\"9693383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Photolabeling of NK1R with p-benzoylphenylalanine3-SP (Bpa3-SP) demonstrates spatial proximity between two distinct extracellular receptor regions in the SP·NK1R complex: one site on the second extracellular loop (EC2) within residues 173–177, and a second site on the extracellular N-terminus within residues 11–21 (containing potential N-linked glycosylation sites).\",\n      \"method\": \"Photoaffinity labeling with radiolabeled SP analogue, peptide mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro photocrosslinking with defined covalent labeling sites identified by peptide mapping, single lab but rigorous biochemical methodology\",\n      \"pmids\": [\"11294866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IL-12 and IL-18 induce NK1R expression on T cells through NF-κB activation (requiring NF-κB nuclear translocation but not the Stat4 pathway), and this induction is blocked by IL-10 but not TGF-β.\",\n      \"method\": \"Murine splenocyte culture with cytokines, actinomycin D/cycloheximide treatment, NF-κB inhibitors, Stat4-/- mice, RT-PCR\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (Stat4-/- mice) and pharmacological (inhibitors) epistasis with transcription readout, single lab\",\n      \"pmids\": [\"12734344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"IL-1β upregulates NK1R expression in human astroglioma cells and primary rat astrocytes through NF-κB activation; the induced NK1R is functional as demonstrated by SP-stimulated Ca2+ mobilization, which is inhibited by the NK1R antagonist CP-96,345.\",\n      \"method\": \"Western blot, RT-PCR, Ca2+ imaging, NF-κB luciferase reporter assay, CAPE inhibitor of NF-κB\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (expression + functional Ca2+ assay + reporter assay + pharmacological inhibition), single lab\",\n      \"pmids\": [\"15390113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Activation of TRPV-1 by capsaicin induces SP-mediated plasma extravasation in the rat pancreas via NK1R, as shown by blockade with either the TRPV-1 antagonist capsazepine or the NK1R antagonist CP 96,345.\",\n      \"method\": \"Evans blue extravasation assay, pharmacological antagonist blockade in vivo\",\n      \"journal\": \"Pancreas\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo pharmacological epistasis with two independent antagonists at distinct pathway steps, single lab\",\n      \"pmids\": [\"15782105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"NK1R knockout mice show two-to-fourfold greater extracellular noradrenaline in the prefrontal cortex compared to wildtypes due to increased transmitter release coupled with desensitization of somatodendritic alpha2a-adrenoceptors in the locus coeruleus (reduced [35S]GTPγS binding to alpha2a-adrenoceptors by ~70% in locus coeruleus of NK1R-/- mice), establishing that NK1R normally constrains noradrenergic transmission.\",\n      \"method\": \"In vivo microdialysis, [35S]GTPγS binding, Western blot for noradrenaline transporter, alpha2-adrenoceptor pharmacology\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (microdialysis, GTPγS binding, Western blot) in KO vs. wildtype with pharmacological validation\",\n      \"pmids\": [\"17331215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human peripheral blood monocytes express the truncated NK1R isoform (NK1R-T) but not full-length NK1R. NK1R-T does not mobilize Ca2+ on its own but selectively activates ERK2 and enhances CCL5/CCR5-mediated Ca2+ mobilization and chemotaxis in an ERK1/2-dependent manner. NK1R-T activation also causes serine phosphorylation of CCR5, indicating receptor crosstalk.\",\n      \"method\": \"Western blot, Ca2+ mobilization assay, chemotaxis (Transwell), ERK phosphorylation assay, NK1R-F transfection comparison\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays (Ca2+, chemotaxis, ERK phosphorylation, CCR5 phosphorylation) with isoform-specific comparisons, NK1R antagonist validation\",\n      \"pmids\": [\"18835883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"NK1R deficiency (genetic knockout) leads to reduced spontaneous dopamine efflux (>50%) in prefrontal cortex and abolishes the striatal dopamine response to d-amphetamine, as shown by in vivo microdialysis; locomotor hyperactivity from NK1R inactivation is reversed by psychostimulants methylphenidate and d-amphetamine.\",\n      \"method\": \"In vivo microdialysis in NK1R-/- vs wildtype mice, locomotor activity measurement, psychostimulant treatment\",\n      \"journal\": \"Journal of psychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo microdialysis with genetic KO and pharmacological rescue, replicated across multiple behavioral paradigms\",\n      \"pmids\": [\"19204064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"NK1R deletion or pharmacological blockade with L-703,606 reduces voluntary alcohol consumption and alcohol conditioned place preference in a receptor-specific, gene-dose-dependent manner; NK1R KO mice do not show escalation of alcohol intake after repeated deprivation-access cycles.\",\n      \"method\": \"Two-bottle choice alcohol consumption, conditioned place preference, NK1R KO mice, pharmacological antagonism with receptor-specificity confirmed in KO controls\",\n      \"journal\": \"Psychopharmacology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic and pharmacological approaches converge, receptor specificity confirmed by testing antagonist in KO mice, multiple behavioral paradigms\",\n      \"pmids\": [\"20112009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SP activates NK1R and NK3R in rat mesenteric lymphatic muscle cells to stimulate phosphorylation of MLC20 (contractile pathway) and p38-MAPK/ERK1/2 (pro-inflammatory pathway); ERK1/2 inhibition decreases p-MLC20 via a PKC-dependent crosstalk between the two pathways.\",\n      \"method\": \"Cell culture pharmacological inhibition, Western blot for phosphoproteins, specific NK1R and NK3R inhibitors\",\n      \"journal\": \"Microcirculation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pharmacological inhibition with multiple readouts, single lab, no genetic confirmation of receptor identity\",\n      \"pmids\": [\"21166923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"NK1R-deficient mice show reduced weight gain, lower circulating leptin and insulin on high-fat diet, higher adiponectin receptor expression, reduced JNK/PKC activation in mesenteric fat, and improved glucose clearance. SP directly inhibits insulin-mediated glucose uptake in isolated rat adipocytes, establishing a role for SP/NK1R in adipose insulin signaling.\",\n      \"method\": \"NK1R KO mice on high-fat diet, glucose tolerance test, Western blot, in vitro glucose uptake in isolated adipocytes\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO combined with in vitro direct SP effect on glucose uptake, single lab with multiple readouts\",\n      \"pmids\": [\"21467195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SP promotes pancreatic cancer cell proliferation, invasion, MMP-2 expression, and perineural invasion via NK1R; NK1R antagonists block SP-induced cancer cell migration to dorsal root ganglia in a coculture model.\",\n      \"method\": \"MTT proliferation assay, Transwell Matrigel invasion assay, Western blot, neuron-tumor coculture, NK1R antagonist blockade\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — multiple in vitro functional assays with pharmacological inhibition, single lab\",\n      \"pmids\": [\"23345604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In alcohol-preferring (P) rats, elevated Tacr1 expression in the central amygdala (but not prefrontal cortex) is accompanied by elevated NK1R binding; central amygdala infusion of NK1R antagonist L822429 replicates the systemic effect on alcohol self-administration. A promoter SNP (-1372C allele) confers increased transcription factor binding (GATA-2, E2F-1) and transcription by electromobility shift and luciferase assays.\",\n      \"method\": \"Operant self-administration, central amygdala microinfusion, receptor autoradiography/binding, EMSA, luciferase reporter assay\",\n      \"journal\": \"Biological psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — site-specific microinfusion establishing central amygdala locus, plus in vitro promoter functional assays, single lab\",\n      \"pmids\": [\"23419547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SP stimulation of NK1R in human colonic epithelial NCM460 cells induces miR-221-5p expression via NF-κB and JNK pathways; miR-221-5p directly targets IL-6R mRNA (validated by luciferase reporter), and this SP/NK1R/miR-221-5p/IL-6R axis is protective in colitis models.\",\n      \"method\": \"microRNA profiling, luciferase reporter assay for IL-6R targeting, NF-κB/JNK pharmacological inhibition, in vivo colitis models (TNBS, DSS)\",\n      \"journal\": \"Cellular and molecular gastroenterology and hepatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assay validation of direct miRNA-target interaction plus pathway inhibitor experiments and in vivo model, single lab\",\n      \"pmids\": [\"26645045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MMP1 activates PAR1-expressing dorsal root ganglia neurons to release SP, which then activates NK1R on pancreatic cancer cells via SP/NK1R/ERK signaling to enhance migration, invasion, and perineural invasion; shRNA silencing of MMP1 or pharmacological blockade of PAR1 or NK1R inhibits perineural invasion.\",\n      \"method\": \"Matrigel/DRG coculture PNI model, in vivo sciatic nerve invasion model, shRNA, pharmacological antagonists, MRI imaging\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (shRNA) and pharmacological blockade at multiple pathway nodes with in vitro and in vivo validation, single lab\",\n      \"pmids\": [\"29896303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NK1R agonist GR73632-induced vomiting in the least shrew activates brainstem signaling through L-type Ca2+ channels and IP3R-dependent PI3K/PKCα/βII-ERK1/2 pathway; CaMKIIα, ERK1/2, Akt, and PKCα/βII are phosphorylated in brainstem after NK1R activation, and inhibitors of each step suppress vomiting.\",\n      \"method\": \"In vivo emesis assay, Western blot for phosphoproteins in brainstem, immunofluorescence, pharmacological inhibitors of LTCC, IP3R, ERK1/2, PKC, PI3K\",\n      \"journal\": \"Neurochemistry international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic pharmacological dissection of signaling cascade with multiple inhibitors and phosphoprotein readouts, single lab\",\n      \"pmids\": [\"30453005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SP/NK1R promotes esophageal squamous cell carcinoma cell proliferation through the NK1R/Hes1 axis: NK1R downregulation markedly reduces Hes1 expression (identified by iTRAQ proteomics), and Hes1 regulates proliferation downstream of SP/NK1R.\",\n      \"method\": \"CCK-8 and colony formation assays, iTRAQ protein spectrum analysis, Western blot, RT-qPCR, xenograft model\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — unbiased proteomics discovery plus functional validation in vitro and in vivo, single lab\",\n      \"pmids\": [\"31109645\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Activation of a subset of spinal Tacr1-expressing projection neurons (expressing NK1R) evokes a full repertoire of pain-related behaviors. These neurons project to a cluster of neurons in the superior lateral parabrachial nucleus (PBN-SL) that also express Tacr1. PBN-SL Tacr1 neurons respond to sustained but not acute noxious stimuli; silencing them causes mice to ignore long-lasting noxious stimuli but does not affect acute pain. PBN-SL Tacr1 activation alone heightens nocifensive behaviors and suppresses itch.\",\n      \"method\": \"Optogenetic activation of spinal Tacr1 neurons, chemogenetic silencing of PBN-SL Tacr1 neurons, optotagging, behavioral assays for pain and itch\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific optogenetic and chemogenetic manipulations with defined circuit-level behavioral phenotypes, multiple orthogonal approaches\",\n      \"pmids\": [\"33591273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NK1R inhibition with aprepitant suppresses NLRC4-dependent neuronal pyroptosis after intracerebral hemorrhage via NK1R/PKCδ signaling; NK1R agonist GR73632 or PKCδ agonist PMA reverses aprepitant's neuroprotective effect, and NLRC4 siRNA knockdown phenocopies aprepitant.\",\n      \"method\": \"Mouse ICH model, Western blot, immunofluorescence, intracerebroventricular injection of agonists/siRNA, neurobehavioral tests\",\n      \"journal\": \"Journal of neuroinflammation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic (siRNA) and pharmacological epistasis at multiple pathway nodes, single lab\",\n      \"pmids\": [\"35922848\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NK1R inhibition by aprepitant promotes hematoma clearance after ICH by increasing M2 microglial polarization via downregulation of PKC/p38MAPK/NFκB signaling; thrombin upstream increases SP, and SP activates NK1R on microglia to drive M1 polarization.\",\n      \"method\": \"Autologous blood injection ICH model, intraperitoneal and intracerebroventricular drug administration, Western blot, immunofluorescence, thrombin injection\",\n      \"journal\": \"Neurotherapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological epistasis with agonist rescue and upstream pathway identification (thrombin→SP→NK1R), single lab\",\n      \"pmids\": [\"34244927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Tacr1-expressing ON cells in the rostral ventromedial medulla (RVM) are excited by substance P and exert inhibitory control over spinal pruriceptive transmission: intramedullary SP potentiates RVM ON cells and reduces pruritogen-evoked scratching; chemogenetic activation of RVM Tacr1 neurons reduces itch; optotagging confirms these are ON cells.\",\n      \"method\": \"Intramedullary SP microinjection, chemogenetic (DREADD) activation, optotagging electrophysiology, behavioral assays for itch and pain\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific chemogenetic and electrophysiological (optotagging) approaches with defined behavioral phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"35972457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"NK1R/5-HT1AR physically interact (co-immunoprecipitation) and co-localize in melanocytes and skin; SP activation of NK1R reduces 5-HT1AR expression and, when combined with 5-HT1AR antagonism, activates p-JNK signaling and inhibits p70S6K1 phosphorylation to reduce melanin production. Removal of the NK1R N-terminus prevents NK1R surface targeting and reduces the NK1R-5-HT1AR interaction.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, PCR, in vitro melanin assay, in vivo mouse and zebrafish models, N-terminal deletion mutagenesis\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus mutagenesis and in vivo genetic model (5-htr1aa+/- zebrafish), single lab\",\n      \"pmids\": [\"29430989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TGFβ upregulates NK1R-Tr (truncated isoform) expression in breast cancer cells via Smad4 binding to the NK1R promoter (confirmed by ChIP and dual-luciferase reporter assay); NK1R-Tr promotes proliferation and inhibits apoptosis, and these effects are attenuated by TGFβ when NK1R is knocked down.\",\n      \"method\": \"ChIP, dual-luciferase reporter assay, Western blot, CCK-8, colony formation, flow cytometry, xenograft model\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and reporter assay establish direct transcriptional regulation of NK1R by Smad4, single lab\",\n      \"pmids\": [\"32380077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SP/NK1R signaling in breast cancer (MCF-7) increases intracellular ROS and upregulates NF-κB and its pro-inflammatory targets TNF-α and IL-6; NK1R blockade by aprepitant halts cell viability partly via p53-mediated upregulation of p21.\",\n      \"method\": \"ROS assay, qRT-PCR, resazurin cell viability assay, Western blot\",\n      \"journal\": \"Cell biochemistry and biophysics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single cell line, pharmacological only without genetic validation\",\n      \"pmids\": [\"37740877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"TFAP4 promotes NK1R transcription by binding to the NK1R promoter (abolished by mutation of the binding site); SP activates NK1R to engage JNK/p38 pathways to modulate tubular epithelial cell fate (growth arrest, apoptosis, profibrogenic gene expression) in chronic kidney disease.\",\n      \"method\": \"Promoter mutation assay, binding site mutagenesis, NK1R-KO mice and pharmacological antagonism in UUO model, NK1R-overexpressed HK-2 cells, Western blot\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter binding site mutagenesis plus genetic KO and pharmacological approaches in vivo and in vitro, single lab\",\n      \"pmids\": [\"37033943\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TACR1 (NK1R) is a G protein-coupled receptor that, upon binding substance P, couples to Gαq/11 to mobilize Ca2+ and activates downstream kinase cascades (ERK1/2, PKC, PI3K/Akt, CaMKII); it undergoes GRK2/3-mediated phosphorylation and beta-arrestin-1/2-dependent desensitization and endocytosis into early endosomes; it exists as full-length and truncated isoforms with distinct signaling capabilities; it modulates dopaminergic and noradrenergic tone in the prefrontal cortex, drives a spinoparabrachial circuit for ongoing pain, is expressed on immune cells (monocytes, T cells) where it amplifies chemokine receptor signaling, and its expression is transcriptionally regulated by NF-κB (downstream of IL-1β, IL-12/18, TNF-α), Smad4 (downstream of TGFβ), and TFAP4; it interacts physically with 5-HT1AR to modulate melanogenesis; and it drives pathological processes including neurogenic inflammation, perineural cancer invasion, and renal fibrosis via JNK/p38/NF-κB pathways.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TACR1 (NK1R) is a Gq/11-coupled receptor for substance P (SP) that converts neuropeptide signals into intracellular calcium and kinase cascades to drive neurotransmission, neurogenic inflammation, and pain/itch circuit function [#0, #15]. SP binding engages two spatially proximal extracellular contact regions—the second extracellular loop (residues 173–177) and the N-terminus (residues 11–21)—and the N-terminus is also required for receptor surface targeting [#1, #21]. Upon SP-induced calcium mobilization, the receptor rapidly desensitizes and is internalized into early endosomes through redistribution of beta-arrestin-1 and -2 to the plasma membrane and then to receptor-containing endosomes, while Gαq/11 remains at the membrane [#0]. Downstream of NK1R, SP activates ERK1/2 together with an IP3R/L-type Ca2+ channel–dependent PI3K/PKCα/βII–ERK1/2 and CaMKII/Akt cascade [#15], and engages JNK, p38, and NF-κB arms in disease contexts [#13, #24]. The receptor exists as full-length and truncated (NK1R-T/Tr) isoforms with distinct signaling outputs: the truncated form expressed on monocytes does not mobilize calcium alone but selectively activates ERK2 and amplifies CCL5/CCR5-mediated chemotaxis through CCR5 serine phosphorylation [#6]. In the CNS, NK1R constrains monoaminergic tone—its loss elevates prefrontal noradrenaline via desensitized locus coeruleus α2A-adrenoceptors and reduces prefrontal/striatal dopamine efflux—and modulates reward-related and alcohol-consumption behaviors [#5, #7, #8, #12]. Spinal and brainstem Tacr1-expressing neurons form a circuit for sustained (but not acute) pain and bidirectional itch control, including a spino–parabrachial projection and RVM ON cells excited by SP [#17, #20]. NK1R expression is transcriptionally induced by NF-κB downstream of inflammatory cytokines [#2, #3], by Smad4 downstream of TGFβ [#22], and by TFAP4 [#24], and SP/NK1R signaling drives perineural cancer invasion, tumor proliferation, microglial polarization, and renal fibrosis [#11, #14, #16, #19, #24].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established how NK1R signaling is terminated and recycled, defining a beta-arrestin-dependent desensitization and endocytic itinerary for the receptor.\",\n      \"evidence\": \"Calcium imaging, immunofluorescence and subcellular fractionation in cultured myenteric neurons\",\n      \"pmids\": [\"9693383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not resolve the GRK phosphorylation sites on NK1R\", \"Resignaling vs degradation fate of internalized receptor not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Defined the structural topology of SP engagement, mapping two distinct extracellular ligand-contact regions on EC2 and the N-terminus.\",\n      \"evidence\": \"Photoaffinity labeling with radiolabeled SP analogue and peptide mapping in vitro\",\n      \"pmids\": [\"11294866\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full receptor structure or agonist-bound conformational model\", \"Functional consequence of each contact site for activation not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showed NK1R expression is inducible rather than fixed, placing it downstream of inflammatory cytokine signaling via NF-κB on immune cells.\",\n      \"evidence\": \"Murine splenocyte cytokine culture with NF-κB inhibitors and Stat4-/- mice, RT-PCR\",\n      \"pmids\": [\"12734344\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"NF-κB binding site on the TACR1 promoter not mapped here\", \"Whether induced receptor is functional not tested in this study\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Extended cytokine-driven NF-κB induction of NK1R to CNS glia and confirmed the induced receptor is functionally coupled to calcium signaling.\",\n      \"evidence\": \"Western blot, RT-PCR, Ca2+ imaging, NF-κB luciferase reporter and antagonist blockade in astroglioma and primary astrocytes\",\n      \"pmids\": [\"15390113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct promoter occupancy by NF-κB not shown\", \"Single-lab pharmacological evidence\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Placed NK1R downstream of TRPV1 in a neurogenic inflammation pathway in vivo, linking nociceptor activation to SP-mediated plasma extravasation.\",\n      \"evidence\": \"Evans blue extravasation with TRPV1 and NK1R antagonists in rat pancreas\",\n      \"pmids\": [\"15782105\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pharmacological only, no genetic confirmation\", \"Cellular source of SP not defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Revealed a homeostatic role for NK1R in restraining noradrenergic transmission through α2A-adrenoceptor desensitization in the locus coeruleus.\",\n      \"evidence\": \"In vivo microdialysis, [35S]GTPγS binding and Western blot in NK1R-/- vs wildtype mice\",\n      \"pmids\": [\"17331215\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking NK1R loss to α2A desensitization not resolved\", \"Direct vs developmental effect of constitutive KO unclear\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated NK1R control of dopaminergic tone and the behavioral consequences, connecting receptor loss to a psychostimulant-reversible hyperactivity phenotype.\",\n      \"evidence\": \"In vivo microdialysis and locomotor/psychostimulant rescue in NK1R-/- mice\",\n      \"pmids\": [\"19204064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Circuit locus of dopaminergic modulation not pinpointed\", \"Constitutive KO cannot distinguish developmental compensation\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Implicated NK1R in alcohol reward and consumption using converging genetic and pharmacological loss-of-function.\",\n      \"evidence\": \"Two-bottle choice, conditioned place preference with NK1R KO and antagonist verified in KO controls\",\n      \"pmids\": [\"20112009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Brain locus not identified in this study\", \"Downstream signaling not addressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Localized the alcohol phenotype to the central amygdala and identified a functional promoter SNP altering transcription-factor binding and NK1R expression.\",\n      \"evidence\": \"Operant self-administration with central amygdala microinfusion, receptor binding, EMSA and luciferase in alcohol-preferring rats\",\n      \"pmids\": [\"23419547\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GATA-2/E2F-1 occupancy shown in vitro only\", \"Causal link from SNP to behavior not directly tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Distinguished a truncated NK1R isoform with a separate signaling output that amplifies chemokine receptor function on immune cells.\",\n      \"evidence\": \"Calcium, chemotaxis, ERK and CCR5 phosphorylation assays with isoform-specific transfection in monocytes\",\n      \"pmids\": [\"18835883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CCR5 crosstalk not defined\", \"In vivo relevance of monocyte NK1R-T not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mapped NK1R coupling to both contractile (MLC20) and pro-inflammatory (p38/ERK) outputs with PKC-dependent crosstalk in lymphatic muscle, and to adipose insulin signaling.\",\n      \"evidence\": \"Pharmacological inhibition with phosphoprotein Western blots; NK1R KO high-fat-diet metabolic phenotyping and adipocyte glucose uptake\",\n      \"pmids\": [\"21166923\", \"21467195\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor identity in lymphatic cells confirmed pharmacologically only\", \"Tissue-specific contribution of NK1R to metabolism not isolated\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined a protective SP/NK1R/miR-221-5p/IL-6R axis in colonic epithelium, linking NK1R to NF-κB/JNK-driven post-transcriptional control.\",\n      \"evidence\": \"miRNA profiling, luciferase target validation, pathway inhibitors and TNBS/DSS colitis models\",\n      \"pmids\": [\"26645045\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab in vivo models\", \"Generalizability beyond colonic epithelium unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established SP/NK1R as a driver of perineural cancer invasion via an MMP1/PAR1/SP relay and downstream ERK signaling, and uncovered a physical NK1R–5-HT1AR interaction governing melanogenesis.\",\n      \"evidence\": \"DRG-tumor coculture and sciatic nerve invasion models with shRNA/antagonists; co-IP, N-terminal deletion mutagenesis and zebrafish/mouse melanin models\",\n      \"pmids\": [\"29896303\", \"29430989\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect NK1R–5-HT1AR contact interface not mapped\", \"Stoichiometry and signaling output of the heteromer unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified Hes1 as a proliferative effector downstream of SP/NK1R in esophageal carcinoma.\",\n      \"evidence\": \"iTRAQ proteomics, proliferation/colony assays and xenografts with NK1R knockdown\",\n      \"pmids\": [\"31109645\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking NK1R to Hes1 induction not resolved\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined Tacr1-expressing spinal and parabrachial circuits selective for sustained pain, distinguishing ongoing from acute nociception.\",\n      \"evidence\": \"Optogenetic activation of spinal Tacr1 neurons and chemogenetic silencing of PBN-SL Tacr1 neurons with optotagging and behavior\",\n      \"pmids\": [\"33591273\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Role of NK1R signaling itself (vs cell identity marker) within the circuit not isolated\", \"Synaptic basis of sustained-stimulus selectivity unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked neuronal NK1R to neuroinflammatory injury, showing aprepitant suppresses NLRC4-dependent pyroptosis via NK1R/PKCδ and shifts microglia toward M2 polarization after hemorrhage.\",\n      \"evidence\": \"Mouse ICH models with agonist/siRNA epistasis, Western blot and immunofluorescence\",\n      \"pmids\": [\"35922848\", \"34244927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct NK1R-to-NLRC4/PKCδ coupling mechanism not defined\", \"Single-lab models\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed Tacr1 RVM ON cells provide descending inhibitory control of itch, complementing the parabrachial pain circuit.\",\n      \"evidence\": \"Intramedullary SP, chemogenetic activation and optotagging electrophysiology with itch/pain behavior\",\n      \"pmids\": [\"35972457\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream spinal targets of RVM Tacr1 ON cells not mapped\", \"Interaction with ascending Tacr1 pain circuit untested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established direct transcriptional control of NK1R by Smad4 downstream of TGFβ and by TFAP4, with the truncated isoform driving tumor proliferation and renal profibrotic programs.\",\n      \"evidence\": \"ChIP, promoter mutagenesis and dual-luciferase assays with KO/overexpression in breast cancer and kidney (UUO) models\",\n      \"pmids\": [\"32380077\", \"37033943\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Isoform-selective promoter usage not fully resolved\", \"Cross-regulation among NF-κB, Smad4 and TFAP4 inputs unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the differential signaling of full-length versus truncated NK1R isoforms is allocated across tissues, and how isoform expression is selectively controlled by the converging NF-κB/Smad4/TFAP4 transcriptional inputs, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model linking isoform truncation to biased signaling\", \"Promoter elements distinguishing full-length vs truncated transcription not defined\", \"In vivo isoform-specific genetic tools lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 6, 15]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 21]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 6, 15]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [5, 7, 17, 20]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 3, 6, 19]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 22, 24]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TAC1\", \"ARRB1\", \"ARRB2\", \"GNAQ\", \"CCR5\", \"HTR1A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}