{"gene":"HINT1","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1997,"finding":"Crystal structures of HINT-nucleotide complexes demonstrated that HINT is a dimeric purine nucleotide-binding protein whose most conserved residues (HIT motif) mediate nucleotide binding and form part of the phosphate-binding loop; the protein shares the same fold and mode of nucleotide binding as galactose-1-phosphate uridylyltransferase despite no overall sequence similarity.","method":"X-ray crystallography of HINT-nucleotide complexes","journal":"Nature structural biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with functional validation of active-site residues","pmids":["9164465"],"is_preprint":false},{"year":2002,"finding":"Rabbit Hint and yeast Hnt1 hydrolyze the natural product adenosine-5'-monophosphoramidate (AMP-NH2) in an active-site-dependent manner at second-order rates exceeding 1,000,000 M−1 s−1; loss of Hnt1 enzymatic activity causes hypersensitivity to mutations in Kin28/Ccl1/Tfb3 (the TFIIK kinase subcomplex of TFIIH), positioning Hnt1 as a positive regulator of this CTD kinase pathway downstream of Cak1.","method":"In vitro enzymatic assay (adenosine monophosphoramidase activity), yeast genetic epistasis, functional complementation with rabbit Hint","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution of enzymatic activity combined with Tier 2 genetic epistasis, replicated across orthologs","pmids":["11805111"],"is_preprint":false},{"year":2000,"finding":"HINT/PKCI-1 physically interacts with Cdk7 (and its yeast ortholog Kin28) independent of cyclin H binding or Cdk7 kinase activity; overexpression of Cdk7 causes partial relocalization of Hint to the nucleus; genetic interaction between HNT1 and KIN28 in yeast produces elongated cell morphology and reduced colony formation.","method":"Yeast two-hybrid, co-immunoprecipitation, subcellular localization by imaging, yeast genetic double-mutant analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, subcellular localization, and genetic epistasis in two organisms","pmids":["10958787"],"is_preprint":false},{"year":2004,"finding":"Biochemical and structural analysis of rabbit Hint established that the enzyme hydrolyzes AMP-lysine (AMP-pNA substrate); a 1.8-Å co-crystal structure with N-ethylsulfamoyl adenosine identified Trp-123 (across the dimer interface) as contacting the alkyl portion of the inhibitor/lysyl substrate, and Ser-107 as donating a hydrogen bond to the leaving-group nitrogen; Hint S107A mutant showed depressed catalytic activity, confirming Ser-107's role in acid-base catalysis.","method":"In vitro AMP-pNA hydrolase assay, X-ray crystallography (1.8 Å co-crystal), site-directed mutagenesis (S107A)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution, crystal structure, and mutagenesis in one study","pmids":["14982931"],"is_preprint":false},{"year":2005,"finding":"HINT1/PKCI directly binds to Pontin and Reptin (via their residues 214–295 and 218–289, respectively, and via the N-terminus of HINT1), and through this interaction associates with the LEF-1/TCF–β-catenin transcription complex to act as a negative regulator of TCF–β-catenin transcriptional activity; knockdown of HINT1 by RNAi increases expression of cyclin D1 and axin2.","method":"Pull-down assays, co-immunoprecipitation, domain mapping, TCF reporter gene assay, RNAi knockdown with endogenous target gene readout","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, domain mapping, functional reporter assay, and RNAi phenotype","pmids":["16014379"],"is_preprint":false},{"year":2006,"finding":"HINT1 triggers apoptosis in SW480 and MCF-7 cells by upregulating p53 and Bax and downregulating Bcl-2; HINT1 associates with the Bax promoter and is a component of the Tip60 histone acetyltransferase complex; a catalytically dead mutant H112N is not impaired in apoptosis induction, demonstrating the pro-apoptotic activity is independent of AMP-NH2 hydrolase enzymatic activity.","method":"Transient transfection, caspase-3/PARP cleavage, cytochrome c release, DNA fragmentation ELISA, promoter ChIP, co-immunoprecipitation with Tip60 complex, shRNA knockdown, enzymatic mutant (H112N)","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including ChIP, Co-IP, and mutagenesis; strong mechanistic follow-up","pmids":["16835243"],"is_preprint":false},{"year":2006,"finding":"HINT1 is a haploinsufficient tumor suppressor in mice; Hint1+/- and Hint1-/- mice show significantly increased spontaneous tumor incidence and susceptibility to DMBA-induced mammary/ovarian tumors; Hint1+/- tumors retain wild-type allele expression, establishing haploinsufficiency.","method":"Knockout mouse model, carcinogen challenge (DMBA), tumor incidence analysis, allele expression analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — clean KO/heterozygous model with defined tumor phenotype replicated across spontaneous and induced settings","pmids":["16186798"],"is_preprint":false},{"year":2007,"finding":"HINT1 inhibits AP-1 transcriptional activity in colon cancer cells by binding to a POSH–JNK2 complex (co-immunoprecipitation), thereby inhibiting phosphorylation of c-Jun; this inhibition specifically requires JNK2 but not JNK1, established using JNK1- and JNK2-deleted MEFs.","method":"Co-immunoprecipitation, AP-1-luciferase reporter assay, genetic MEF models (JNK1-/- and JNK2-/-), retrovirus-mediated HINT1 overexpression","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 — Co-IP, reporter assay, and genetic epistasis with pathway confirmation","pmids":["17510397"],"is_preprint":false},{"year":2008,"finding":"HINT1 is recruited to ionizing radiation-induced foci (IRIF) and physically associates with γ-H2AX and ATM; HINT1 deficiency impairs removal of γ-H2AX foci (associated with impaired acetylation of γ-H2AX), impairs ATM acetylation and activation, retards DNA repair, and results in resistance to IR-induced apoptosis and chromosomal abnormalities.","method":"Immunofluorescence (IRIF), co-immunoprecipitation, fractionation, acetylation assays, DNA repair assays, HINT1-deficient cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods with defined functional phenotype in KO cells","pmids":["18852295"],"is_preprint":false},{"year":2008,"finding":"In neurons, morphine-activated mu-opioid receptor (MOR) C-terminus binds HINT1/PKCI, which in turn binds RGSZ1/Z2 proteins; NMDAR/nNOS-generated nitric oxide produces free zinc ions that recruit inactive PKCγ (via its CRDs) to the HINT1/RGSZ complex at the MOR C-terminus, where DAG-activated PKCγ phosphorylates MOR serine residues to reduce opioid signal strength.","method":"Intracerebroventricular pharmacology, co-immunoprecipitation, antisense knockdown, NOS inhibitors, zinc chelators, NMDAR antagonist","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and pharmacological dissection in vivo; single lab","pmids":["18652891"],"is_preprint":false},{"year":2012,"finding":"Loss-of-function mutations in HINT1 (8 different mutations identified in 33 families) cause autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM), establishing that functional HINT1 protein is required for normal peripheral nerve function.","method":"Linkage analysis, next-generation sequencing, cohort screening, clinical phenotyping","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — large multi-family genetic study with clear loss-of-function disease phenotype; replicated across many families","pmids":["22961002"],"is_preprint":false},{"year":2012,"finding":"Human HINT1 binds aminoacyl adenylate (aa-AMP) intermediates with broad specificity independent of the amino acid side chain; crystal structures of HINT1 with three aa-AMP analogues show recognition of only the common main chain of the aminoacyl moiety, with the α-amino group anchored by a cation-π interaction with Trp123.","method":"X-ray crystallography (multiple co-crystal structures with aa-AMP analogues), in vitro hydrolysis assays","journal":"The journal of physical chemistry. B","confidence":"High","confidence_rationale":"Tier 1 — multiple crystal structures plus in vitro enzymatic characterization","pmids":["22329685"],"is_preprint":false},{"year":2012,"finding":"HINT1 inhibits MITF and β-catenin transcriptional activity in melanoma cells; both MITF and β-catenin co-immunoprecipitate with HINT1; ChIP assays show HINT1 occupies MITF and β-catenin binding sites at BCL2 and cyclin D1 promoters; mSIN3a and HDAC1 co-immunoprecipitate with HINT1, suggesting a repressive complex.","method":"Co-immunoprecipitation, ChIP assay, transcriptional reporter assay, stable overexpression, xenograft","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, ChIP, and functional reporter assays with multiple orthogonal methods","pmids":["22647378"],"is_preprint":false},{"year":2013,"finding":"HINT1 protein is required for the cannabinoid CB1 receptor (CNR1) to negatively regulate NMDAR activity; in CNR1+/+/HINT1-/- cortical neurons NMDAR activity is enhanced and cannabinoid neuroprotection is abolished; lentiviral re-expression of HINT1 restores both NMDAR regulation and cannabinoid-mediated neuroprotection.","method":"HINT1-/- and CNR1-/- mouse neurons, lentiviral HINT1 rescue, calcium imaging/NMDA insult assay","journal":"Molecular brain","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with rescue experiment; single lab","pmids":["24093505"],"is_preprint":false},{"year":2015,"finding":"The σ1 receptor (σ1R) binds to the cytosolic C-terminal region of the NMDAR NR1 subunit in a calcium-dependent manner and enables NR1–HINT1 interaction with MOR–HINT1 complexes; σ1R antagonists transfer HINT1 from GPCRs to NR1 subunits, disengaging MOR from NMDAR negative control and enhancing opioid antinociception; this regulation depends on the NO/Zn2+ redox switch via RGSZ2-nNOS and PKCγ recruitment to HINT1.","method":"In vivo pharmacology, ex vivo and in vitro co-immunoprecipitation, σ1R-/- and HINT1-/- mouse models, NOS inhibitors","journal":"Antioxidants & redox signaling","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP, multiple KO models, pharmacological dissection; single lab","pmids":["25557043"],"is_preprint":false},{"year":2015,"finding":"The intracellular domain (ICD) of teneurin-1 interacts directly with HINT1 in human cells (identified by yeast two-hybrid and confirmed by co-immunoprecipitation); this interaction relieves HINT1-mediated repression of MITF, inducing MITF-dependent transcription of target genes such as GPNMB.","method":"Yeast two-hybrid screen, co-immunoprecipitation, transcriptome analysis, promoter reporter assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — yeast two-hybrid confirmed by Co-IP and functional reporter; single lab","pmids":["25648896"],"is_preprint":false},{"year":2015,"finding":"Pharmacological inhibition of HINT1 enzymatic activity (using guanosine-5′-tryptamine carbamate, TpGc) significantly enhances morphine antinociception and prevents tolerance development, and reduces NMDAR activity in mice with chronic constriction injury; X-ray crystallographic and thermodynamic binding studies showed distinct binding modes of different HINT1 inhibitors correlating with their differential effects on MOR–NMDAR cross-talk.","method":"In vivo antinociception assays, intracerebroventricular drug delivery, X-ray crystallography of HINT1-inhibitor complexes, thermodynamic binding assays","journal":"Neuropharmacology","confidence":"Medium","confidence_rationale":"Tier 1–2 — crystallographic characterization of inhibitor binding plus in vivo functional data; single lab","pmids":["25445489"],"is_preprint":false},{"year":2017,"finding":"HINT1 is subjected to K21 acetylation and Y109 phosphorylation in activated mast cells; Ap4A (produced by S207-phosphorylated LysRS) triggers HINT1 dissociation from MITF; mutational analysis of K21 and Y109 confirmed these post-translational modifications promote MITF transcriptional and oncogenic activity in melanoma cells.","method":"Mass spectrometry (PTM identification), site-directed mutagenesis of acetylation (K21) and phosphorylation (Y109) sites, transcriptional reporter assay in melanoma cells","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — PTM identified by MS and confirmed by mutagenesis with functional readout; single lab","pmids":["28394346"],"is_preprint":false},{"year":2019,"finding":"Ap4A specifically polymerizes HINT1 into higher-order assemblies in solution and in activated rat basophilic leukemia cells; eight crystal structures define the polymerization interface, which overlaps with the MITF-binding region on HINT1, providing a competitive mechanism to release MITF for transcriptional activation; the polymerization depends precisely on the polyphosphate chain length of Ap4A.","method":"X-ray crystallography (8 crystal structures), negative-stain electron microscopy, biochemical polymerization assays, cellular experiments in RBL cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — eight crystal structures, EM, and biochemical assays with cellular validation; strong mechanistic rigor","pmids":["31604935"],"is_preprint":false},{"year":2019,"finding":"HINT1 exhibits cysteine SUMO protease (isopeptidase) activity to remove SUMO from signaling proteins; this activity is regulated by zinc (blocks) and by nitric oxide or calcium-activated calmodulin (releases); the catalytic triad is Cys84-Asp87-His114; a SUMO-interacting motif is identified at residues 110–116; all 15 human ARAN-NM-associated HINT1 mutants tested showed altered sumoylase activity.","method":"In vitro SUMO protease assay, site-directed mutagenesis of catalytic triad, zinc/NO/CaM regulation assays, patient-derived mutant characterization","journal":"Antioxidants & redox signaling","confidence":"Medium","confidence_rationale":"Tier 1–2 — novel enzymatic activity with mutagenesis and regulatory dissection; single lab","pmids":["31088288"],"is_preprint":false},{"year":2020,"finding":"SIRT1 deacetylates HINT1 at K21 and K30 (CBP-mediated acetylation sites); deacetylation increases HINT1 binding capacity for β-catenin and MITF, enhancing tumor-suppressive activity; deacetylation-mimetic HINT1 2KR mutant significantly reduces proliferation in colon cancer and melanoma cells and tumorigenesis in xenografts.","method":"Co-immunoprecipitation, site-directed mutagenesis (K21R/K30R), xenograft assay, in vitro deacetylation assay","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP with mutagenesis and in vivo xenograft; single lab","pmids":["32636443"],"is_preprint":false},{"year":2021,"finding":"HINT1 directly interacts with PKCβ1 and inhibits its membrane translocation and phosphorylation; this suppresses the MEK/ERK/YY1 signaling pathway and downregulates HOXA5 expression, ultimately attenuating cardiac hypertrophy; cardiac-specific HINT1 overexpression via AAV9 alleviated hypertrophy and dysfunction in mice.","method":"Co-immunoprecipitation, cellular fractionation assays, AAV9-mediated cardiac-specific overexpression, Hint1 knockout mice + transverse aortic constriction, RNA sequencing, shRNA knockdown of Hoxa5","journal":"Circulation","confidence":"High","confidence_rationale":"Tier 2 — direct protein interaction by Co-IP, fractionation, loss- and gain-of-function in vivo models with molecular pathway dissection","pmids":["34098726"],"is_preprint":false},{"year":1996,"finding":"Human PKCI-1/HINT1 localizes to cytoskeletal structures in the cytoplasm of human fibroblasts and is largely excluded from the nucleus, as determined by indirect immunofluorescence.","method":"Indirect immunofluorescence in human fibroblast cell line","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 3 — single localization experiment without functional follow-up","pmids":["8812426"],"is_preprint":false},{"year":2007,"finding":"The C-terminal loop of HINT1 is a critical determinant of substrate specificity; chimeric Hint proteins with swapped C-terminal loops showed that the human C-terminal loop confers preference for l-configured phosphoramidates and ability to hydrolyze lysyl-AMP generated by human LysRS, distinct from E. coli hinT specificity.","method":"Chimeric enzyme construction, in vitro kinetic assays (kcat/Km) with panel of substrates","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 — reconstituted chimeric enzymes with systematic substrate profiling; single lab","pmids":["17939685"],"is_preprint":false},{"year":2016,"finding":"Crystal structure of human HINT1 in complex with a non-hydrolyzable Ap4A analog (at 2.34 Å resolution) defined the Ap4A binding site; the apo structure (1.92 Å) was also solved for comparison.","method":"X-ray crystallography","journal":"International journal of biological macromolecules","confidence":"Medium","confidence_rationale":"Tier 1 — crystal structure; single study without extensive mutagenesis","pmids":["26905466"],"is_preprint":false},{"year":2009,"finding":"HINT1 co-immunoprecipitates with USF2 in hepatoma cell extracts and inhibits USF2, β-catenin/TCF4, and NFκB transcriptional activities; HINT1 also inhibits nuclear translocation of the p65 NFκB subunit in HepG2 cells.","method":"Co-immunoprecipitation, transcriptional reporter assays, nuclear fractionation","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP and reporter assays with fractionation; single lab","pmids":["19089909"],"is_preprint":false}],"current_model":"HINT1 is a universally conserved, dimeric AMP-lysine/adenosine phosphoramidate hydrolase and SUMO isopeptidase whose active site (catalytic His triad and Ser107/Cys84-Asp87-His114) mediates both enzymatic activities; it functions as a scaffold at the mu-opioid receptor C-terminus (via RGSZ2/PKCγ/σ1R redox-zinc signaling) to couple GPCR activity to NMDAR regulation, acts as a transcriptional co-repressor by directly binding oncogenic factors (MITF, β-catenin, USF2, NFκB) and recruiting HDAC1/mSIN3a, is released from these factors by Ap4A-driven polymerization or by post-translational modifications (K21/K30 acetylation by CBP, Y109 phosphorylation), inhibits PKCβ1 membrane translocation to suppress the MEK/ERK/YY1/HOXA5 cardiac hypertrophy pathway, participates in DNA damage responses by associating with γ-H2AX and ATM, and is a haploinsufficient tumor suppressor whose loss-of-function mutations cause autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM)."},"narrative":{"teleology":[{"year":1997,"claim":"Determining the three-dimensional structure of HINT established it as a dimeric purine nucleotide-binding protein with a conserved HIT-motif phosphate-binding loop, revealing its fold and setting the stage for understanding its catalytic mechanism.","evidence":"X-ray crystallography of HINT-nucleotide complexes","pmids":["9164465"],"confidence":"High","gaps":["Physiological substrate unknown","Catalytic activity not yet demonstrated","Biological function in cells undefined"]},{"year":2002,"claim":"Identification of adenosine monophosphoramidase activity at >10⁶ M⁻¹s⁻¹ and genetic epistasis with the TFIIH kinase subcomplex answered what HINT1 does enzymatically and placed it in a transcription-related pathway.","evidence":"In vitro enzymatic assays with rabbit Hint and yeast Hnt1; yeast genetic epistasis with Kin28/Ccl1/Tfb3","pmids":["11805111"],"confidence":"High","gaps":["Direct in vivo substrate not captured","Mechanism linking hydrolase activity to TFIIH regulation unclear"]},{"year":2000,"claim":"Physical interaction with Cdk7/Kin28 and nuclear relocalization upon Cdk7 overexpression connected HINT1 to cell cycle kinase complexes and raised the question of whether it has nuclear transcriptional roles.","evidence":"Yeast two-hybrid, co-immunoprecipitation, imaging, and yeast double-mutant analysis","pmids":["10958787"],"confidence":"High","gaps":["Whether Cdk7 interaction is direct or bridged by other TFIIH subunits not resolved","Functional consequence of nuclear relocalization unclear"]},{"year":2004,"claim":"A 1.8-Å co-crystal structure with a substrate analogue and mutagenesis of Ser107 defined the catalytic mechanism for AMP-lysine hydrolysis, establishing the roles of Trp123 (across the dimer interface) and Ser107 in acid-base catalysis.","evidence":"X-ray crystallography, AMP-pNA hydrolase assay, S107A mutagenesis","pmids":["14982931"],"confidence":"High","gaps":["Full transition-state geometry not resolved","In vivo relevance of lysyl-AMP hydrolysis not demonstrated"]},{"year":2005,"claim":"Discovery that HINT1 binds Pontin/Reptin and represses TCF–β-catenin transcription (with cyclin D1 and axin2 as endogenous targets) established HINT1 as a transcriptional co-repressor, a function independent of its nucleotide hydrolase activity.","evidence":"Pull-down, co-immunoprecipitation, TCF reporter, RNAi knockdown","pmids":["16014379"],"confidence":"High","gaps":["Whether HINT1 repressor function requires its enzymatic activity not tested here","Chromatin-level mechanism of repression not defined"]},{"year":2006,"claim":"Two key advances: (1) HINT1 was shown to promote apoptosis via p53/Bax upregulation as part of the Tip60 complex—independent of catalytic activity (H112N mutant); (2) Hint1⁺/⁻ and Hint1⁻/⁻ mice demonstrated haploinsufficient tumor suppression, linking HINT1 loss to cancer predisposition in vivo.","evidence":"Apoptosis assays, Bax promoter ChIP, Tip60 co-IP, H112N mutant (SW480/MCF-7 cells); knockout/heterozygous mice with spontaneous and DMBA-induced tumors","pmids":["16835243","16186798"],"confidence":"High","gaps":["How HINT1 stimulates Tip60 acetyltransferase activity mechanistically unknown","Tissue-specific tumor suppressor mechanisms not dissected"]},{"year":2007,"claim":"HINT1 was found to inhibit AP-1 activity by binding the POSH–JNK2 complex, expanding the repertoire of transcription factor targets it represses and establishing JNK2 specificity; separately, C-terminal loop swaps defined substrate specificity determinants for phosphoramidate hydrolysis.","evidence":"Co-IP with POSH–JNK2, AP-1 reporter, JNK1⁻/⁻ and JNK2⁻/⁻ MEFs; chimeric enzyme kinetics","pmids":["17510397","17939685"],"confidence":"High","gaps":["Whether JNK2 interaction is direct or POSH-mediated not resolved","Structural basis for C-terminal loop specificity not determined"]},{"year":2008,"claim":"Two parallel advances established HINT1 roles in the nucleus and at the plasma membrane: HINT1 was recruited to DNA damage foci and required for γ-H2AX removal and ATM activation after irradiation; simultaneously, HINT1 was identified as a scaffold coupling MOR to NMDAR regulation via RGSZ/PKCγ/zinc signaling in neurons.","evidence":"IRIF imaging, γ-H2AX/ATM co-IP, DNA repair assays in HINT1-deficient cells; in vivo pharmacology, co-IP, antisense knockdown in mouse neurons","pmids":["18852295","18652891"],"confidence":"High","gaps":["Mechanism by which HINT1 promotes γ-H2AX acetylation/removal not defined","MOR–HINT1 scaffolding model relies on single-lab pharmacological studies","Whether DNA damage and GPCR roles involve the same or distinct HINT1 pools unknown"]},{"year":2012,"claim":"Three discoveries converged: HINT1 was shown to bind aminoacyl-AMP intermediates broadly (crystal structures); it was established as a co-repressor of MITF and β-catenin via HDAC1/mSIN3a recruitment to target promoters (ChIP); and loss-of-function mutations were identified as the cause of autosomal recessive axonal neuropathy with neuromyotonia in 33 families.","evidence":"Multiple co-crystal structures with aa-AMP analogues; ChIP, co-IP with MITF/β-catenin/HDAC1/mSIN3a in melanoma cells; linkage analysis and exome sequencing in ARAN-NM families","pmids":["22329685","22647378","22961002"],"confidence":"High","gaps":["Whether aminoacyl-AMP hydrolysis connects to transcriptional repression unknown","Neuropathological mechanism of HINT1 loss in peripheral nerve not defined","Whether HDAC1/mSIN3a recruitment requires HINT1 dimerization not tested"]},{"year":2015,"claim":"The HINT1 signaling scaffold model was extended: σ1R was shown to regulate HINT1 transfer between GPCRs and NMDAR NR1 subunits; teneurin-1 ICD was identified as a direct HINT1 interactor that relieves MITF repression; and pharmacological HINT1 inhibitors were crystallographically characterized and shown to enhance morphine analgesia in vivo.","evidence":"σ1R⁻/⁻ and HINT1⁻/⁻ mice, in vivo pharmacology, co-IP; yeast two-hybrid and co-IP for teneurin-1; X-ray crystallography of inhibitor complexes, antinociception assays","pmids":["25557043","25648896","25445489"],"confidence":"Medium","gaps":["Structural basis for σ1R–HINT1–NR1 ternary complex not resolved","Teneurin-1–HINT1 interaction validated by single lab","Inhibitor selectivity in vivo not fully profiled"]},{"year":2017,"claim":"Identification of K21 acetylation and Y109 phosphorylation as PTMs that trigger HINT1 dissociation from MITF explained how activated mast cells relieve transcriptional repression, connecting Ap4A signaling (via phospho-LysRS) to HINT1 regulation.","evidence":"Mass spectrometry PTM identification, site-directed mutagenesis (K21, Y109), transcriptional reporter in melanoma cells","pmids":["28394346"],"confidence":"Medium","gaps":["Kinase responsible for Y109 phosphorylation not identified","Whether K21 acetylation and Ap4A polymerization are redundant or sequential not determined"]},{"year":2019,"claim":"Two mechanistically distinct advances: (1) Ap4A was shown to polymerize HINT1 into higher-order assemblies whose interface overlaps the MITF-binding surface, providing a structural mechanism for MITF release; (2) a novel SUMO isopeptidase activity was identified with a Cys84-Asp87-His114 catalytic triad, regulated by zinc/NO/calmodulin, and all 15 tested ARAN-NM mutants showed altered sumoylase activity.","evidence":"Eight crystal structures, negative-stain EM, polymerization assays in RBL cells; in vitro SUMO protease assay, catalytic triad mutagenesis, patient mutant characterization","pmids":["31604935","31088288"],"confidence":"High","gaps":["In vivo SUMO substrates of HINT1 not identified","Whether Ap4A polymerization occurs in neurons and relates to ARAN-NM unknown","SUMO isopeptidase activity identified by single lab and awaits independent replication"]},{"year":2020,"claim":"SIRT1-mediated deacetylation of HINT1 at K21/K30 was shown to enhance its binding to β-catenin and MITF and augment tumor-suppressive function, establishing a reversible acetylation switch (CBP acetylates, SIRT1 deacetylates) that modulates HINT1 co-repressor activity.","evidence":"Co-IP, K21R/K30R mutagenesis, in vitro deacetylation assay, xenograft tumorigenesis","pmids":["32636443"],"confidence":"Medium","gaps":["Whether SIRT1–HINT1 axis operates in non-cancer contexts (e.g., neurons) unknown","Structural basis for how acetylation weakens transcription factor binding not determined"]},{"year":2021,"claim":"HINT1 was established as a cardioprotective factor that directly binds PKCβ1, inhibits its membrane translocation, and thereby suppresses the MEK/ERK/YY1/HOXA5 hypertrophy pathway; AAV9-mediated cardiac HINT1 overexpression rescued pressure-overload hypertrophy in mice.","evidence":"Co-IP, cellular fractionation, AAV9 cardiac overexpression, Hint1⁻/⁻ mice + TAC, RNA-seq, HOXA5 knockdown","pmids":["34098726"],"confidence":"High","gaps":["Whether PKCβ1 inhibition requires HINT1 enzymatic activity not tested","Downstream mechanism linking HOXA5 to hypertrophic gene program incompletely defined"]},{"year":null,"claim":"Key unresolved questions include the identity of in vivo SUMO substrates of HINT1, the structural basis of the HINT1–GPCR–NMDAR ternary signaling complex, whether the distinct enzymatic activities (phosphoramidase, SUMO isopeptidase) serve separable physiological functions, the neuropathological mechanism underlying ARAN-NM, and how Ap4A-driven polymerization and PTM-mediated regulation are coordinated in different tissue contexts.","evidence":"","pmids":[],"confidence":"Low","gaps":["In vivo SUMO substrates unidentified","Structural model of HINT1–MOR–NMDAR signalosome lacking","Peripheral nerve-specific mechanism of ARAN-NM pathogenesis unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[1,3,11,23]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[19]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[4,5,12,25]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[7,21]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[9,14]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[22]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[22]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,5,8,12]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[9,14,21]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,13,14,21]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,6]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[8]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,4,12,25]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,10]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[5,12]}],"complexes":["Tip60 HAT complex","HDAC1/mSIN3a repressor complex","MOR–HINT1–RGSZ2 signaling complex"],"partners":["CDK7","RUVBL1","RUVBL2","CTNNB1","MITF","PRKCB","RGSZ2","OPRS1"],"other_free_text":[]},"mechanistic_narrative":"HINT1 is a universally conserved dimeric nucleotide hydrolase and multifunctional scaffold that integrates enzymatic, transcriptional, and signaling activities across diverse cellular contexts. As an enzyme, HINT1 hydrolyzes adenosine 5′-monophosphoramidate and aminoacyl-AMP substrates at high catalytic rates using its HIT-motif active site, with substrate specificity governed by its C-terminal loop and key residues Ser107 and Trp123 at the dimer interface [PMID:11805111, PMID:14982931, PMID:22329685]; it also possesses SUMO isopeptidase activity mediated by a Cys84-Asp87-His114 catalytic triad, regulated by zinc, nitric oxide, and calmodulin [PMID:31088288]. As a transcriptional co-repressor, HINT1 directly binds oncogenic transcription factors including β-catenin/TCF, MITF, USF2, and NFκB, recruiting HDAC1/mSIN3a to target promoters; this repressive function is relieved by Ap4A-driven polymerization of HINT1 or by CBP-mediated acetylation at K21/K30, which is reversed by SIRT1 deacetylation [PMID:22647378, PMID:31604935, PMID:32636443, PMID:16014379]. HINT1 functions as a haploinsufficient tumor suppressor whose loss increases spontaneous and carcinogen-induced tumorigenesis in mice [PMID:16186798], acts as a scaffold coupling mu-opioid and cannabinoid receptors to NMDAR regulation via RGSZ2/PKCγ/σ1R complexes in neurons [PMID:18652891, PMID:24093505], suppresses cardiac hypertrophy by inhibiting PKCβ1 membrane translocation and the MEK/ERK/YY1/HOXA5 pathway [PMID:34098726], and participates in DNA damage responses through association with γ-H2AX and ATM [PMID:18852295]; loss-of-function mutations in HINT1 cause autosomal recessive axonal neuropathy with neuromyotonia [PMID:22961002]."},"prefetch_data":{"uniprot":{"accession":"P49773","full_name":"Adenosine 5'-monophosphoramidase HINT1","aliases":["Desumoylating isopeptidase HINT1","Histidine triad nucleotide-binding protein 1","Protein kinase C inhibitor 1","Protein kinase C-interacting protein 1","PKCI-1"],"length_aa":126,"mass_kda":13.8,"function":"Exhibits adenosine 5'-monophosphoramidase activity, hydrolyzing purine nucleotide phosphoramidates with a single phosphate group such as adenosine 5'monophosphoramidate (AMP-NH2) to yield AMP and NH2 (PubMed:15703176, PubMed:16835243, PubMed:17217311, PubMed:17337452, PubMed:22329685, PubMed:23614568, PubMed:28691797, PubMed:29787766, PubMed:31990367). Hydrolyzes adenosine 5'monophosphomorpholidate (AMP-morpholidate) and guanosine 5'monophosphomorpholidate (GMP-morpholidate) (PubMed:15703176, PubMed:16835243). Hydrolyzes lysyl-AMP (AMP-N-epsilon-(N-alpha-acetyl lysine methyl ester)) generated by lysine tRNA ligase, as well as Met-AMP, His-AMP and Asp-AMP, lysyl-GMP (GMP-N-epsilon-(N-alpha-acetyl lysine methyl ester)) and AMP-N-alanine methyl ester (PubMed:15703176, PubMed:17337452, PubMed:22329685). Hydrolyzes 3-indolepropionic acyl-adenylate, tryptamine adenosine phosphoramidate monoester and other fluorogenic purine nucleoside tryptamine phosphoramidates in vitro (PubMed:17217311, PubMed:17337452, PubMed:23614568, PubMed:28691797, PubMed:29787766, PubMed:31990367). Can also convert adenosine 5'-O-phosphorothioate and guanosine 5'-O-phosphorothioate to the corresponding nucleoside 5'-O-phosphates with concomitant release of hydrogen sulfide (PubMed:30772266). In addition, functions as scaffolding protein that modulates transcriptional activation by the LEF1/TCF1-CTNNB1 complex and by the complex formed with MITF and CTNNB1 (PubMed:16014379, PubMed:22647378). Modulates p53/TP53 levels and p53/TP53-mediated apoptosis (PubMed:16835243). Modulates proteasomal degradation of target proteins by the SCF (SKP2-CUL1-F-box protein) E3 ubiquitin-protein ligase complex (PubMed:19112177). Also exhibits SUMO-specific isopeptidase activity, deconjugating SUMO1 from RGS17 (PubMed:31088288). Deconjugates SUMO1 from RANGAP1 (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P49773/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HINT1","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SAR1B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/HINT1","total_profiled":1310},"omim":[{"mim_id":"609998","title":"HISTIDINE TRIAD NUCLEOTIDE-BINDING PROTEIN 3; HINT3","url":"https://www.omim.org/entry/609998"},{"mim_id":"609997","title":"HISTIDINE TRIAD NUCLEOTIDE-BINDING PROTEIN 2; HINT2","url":"https://www.omim.org/entry/609997"},{"mim_id":"601314","title":"HISTIDINE TRIAD NUCLEOTIDE-BINDING PROTEIN 1; HINT1","url":"https://www.omim.org/entry/601314"},{"mim_id":"137200","title":"NEUROMYOTONIA AND AXONAL NEUROPATHY, AUTOSOMAL RECESSIVE; NMAN","url":"https://www.omim.org/entry/137200"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/HINT1"},"hgnc":{"alias_symbol":["PKCI-1"],"prev_symbol":["PRKCNH1","HINT"]},"alphafold":{"accession":"P49773","domains":[{"cath_id":"3.30.428.10","chopping":"1-126","consensus_level":"medium","plddt":96.3135,"start":1,"end":126}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P49773","model_url":"https://alphafold.ebi.ac.uk/files/AF-P49773-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P49773-F1-predicted_aligned_error_v6.png","plddt_mean":96.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HINT1","jax_strain_url":"https://www.jax.org/strain/search?query=HINT1"},"sequence":{"accession":"P49773","fasta_url":"https://rest.uniprot.org/uniprotkb/P49773.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P49773/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P49773"}},"corpus_meta":[{"pmid":"22846459","id":"PMC_22846459","title":"HINT: High-quality 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the protein shares the same fold and mode of nucleotide binding as galactose-1-phosphate uridylyltransferase despite no overall sequence similarity.\",\n      \"method\": \"X-ray crystallography of HINT-nucleotide complexes\",\n      \"journal\": \"Nature structural biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with functional validation of active-site residues\",\n      \"pmids\": [\"9164465\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Rabbit Hint and yeast Hnt1 hydrolyze the natural product adenosine-5'-monophosphoramidate (AMP-NH2) in an active-site-dependent manner at second-order rates exceeding 1,000,000 M−1 s−1; loss of Hnt1 enzymatic activity causes hypersensitivity to mutations in Kin28/Ccl1/Tfb3 (the TFIIK kinase subcomplex of TFIIH), positioning Hnt1 as a positive regulator of this CTD kinase pathway downstream of Cak1.\",\n      \"method\": \"In vitro enzymatic assay (adenosine monophosphoramidase activity), yeast genetic epistasis, functional complementation with rabbit Hint\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution of enzymatic activity combined with Tier 2 genetic epistasis, replicated across orthologs\",\n      \"pmids\": [\"11805111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"HINT/PKCI-1 physically interacts with Cdk7 (and its yeast ortholog Kin28) independent of cyclin H binding or Cdk7 kinase activity; overexpression of Cdk7 causes partial relocalization of Hint to the nucleus; genetic interaction between HNT1 and KIN28 in yeast produces elongated cell morphology and reduced colony formation.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, subcellular localization by imaging, yeast genetic double-mutant analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, subcellular localization, and genetic epistasis in two organisms\",\n      \"pmids\": [\"10958787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Biochemical and structural analysis of rabbit Hint established that the enzyme hydrolyzes AMP-lysine (AMP-pNA substrate); a 1.8-Å co-crystal structure with N-ethylsulfamoyl adenosine identified Trp-123 (across the dimer interface) as contacting the alkyl portion of the inhibitor/lysyl substrate, and Ser-107 as donating a hydrogen bond to the leaving-group nitrogen; Hint S107A mutant showed depressed catalytic activity, confirming Ser-107's role in acid-base catalysis.\",\n      \"method\": \"In vitro AMP-pNA hydrolase assay, X-ray crystallography (1.8 Å co-crystal), site-directed mutagenesis (S107A)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution, crystal structure, and mutagenesis in one study\",\n      \"pmids\": [\"14982931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HINT1/PKCI directly binds to Pontin and Reptin (via their residues 214–295 and 218–289, respectively, and via the N-terminus of HINT1), and through this interaction associates with the LEF-1/TCF–β-catenin transcription complex to act as a negative regulator of TCF–β-catenin transcriptional activity; knockdown of HINT1 by RNAi increases expression of cyclin D1 and axin2.\",\n      \"method\": \"Pull-down assays, co-immunoprecipitation, domain mapping, TCF reporter gene assay, RNAi knockdown with endogenous target gene readout\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, domain mapping, functional reporter assay, and RNAi phenotype\",\n      \"pmids\": [\"16014379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"HINT1 triggers apoptosis in SW480 and MCF-7 cells by upregulating p53 and Bax and downregulating Bcl-2; HINT1 associates with the Bax promoter and is a component of the Tip60 histone acetyltransferase complex; a catalytically dead mutant H112N is not impaired in apoptosis induction, demonstrating the pro-apoptotic activity is independent of AMP-NH2 hydrolase enzymatic activity.\",\n      \"method\": \"Transient transfection, caspase-3/PARP cleavage, cytochrome c release, DNA fragmentation ELISA, promoter ChIP, co-immunoprecipitation with Tip60 complex, shRNA knockdown, enzymatic mutant (H112N)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including ChIP, Co-IP, and mutagenesis; strong mechanistic follow-up\",\n      \"pmids\": [\"16835243\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"HINT1 is a haploinsufficient tumor suppressor in mice; Hint1+/- and Hint1-/- mice show significantly increased spontaneous tumor incidence and susceptibility to DMBA-induced mammary/ovarian tumors; Hint1+/- tumors retain wild-type allele expression, establishing haploinsufficiency.\",\n      \"method\": \"Knockout mouse model, carcinogen challenge (DMBA), tumor incidence analysis, allele expression analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO/heterozygous model with defined tumor phenotype replicated across spontaneous and induced settings\",\n      \"pmids\": [\"16186798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HINT1 inhibits AP-1 transcriptional activity in colon cancer cells by binding to a POSH–JNK2 complex (co-immunoprecipitation), thereby inhibiting phosphorylation of c-Jun; this inhibition specifically requires JNK2 but not JNK1, established using JNK1- and JNK2-deleted MEFs.\",\n      \"method\": \"Co-immunoprecipitation, AP-1-luciferase reporter assay, genetic MEF models (JNK1-/- and JNK2-/-), retrovirus-mediated HINT1 overexpression\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, reporter assay, and genetic epistasis with pathway confirmation\",\n      \"pmids\": [\"17510397\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"HINT1 is recruited to ionizing radiation-induced foci (IRIF) and physically associates with γ-H2AX and ATM; HINT1 deficiency impairs removal of γ-H2AX foci (associated with impaired acetylation of γ-H2AX), impairs ATM acetylation and activation, retards DNA repair, and results in resistance to IR-induced apoptosis and chromosomal abnormalities.\",\n      \"method\": \"Immunofluorescence (IRIF), co-immunoprecipitation, fractionation, acetylation assays, DNA repair assays, HINT1-deficient cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods with defined functional phenotype in KO cells\",\n      \"pmids\": [\"18852295\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In neurons, morphine-activated mu-opioid receptor (MOR) C-terminus binds HINT1/PKCI, which in turn binds RGSZ1/Z2 proteins; NMDAR/nNOS-generated nitric oxide produces free zinc ions that recruit inactive PKCγ (via its CRDs) to the HINT1/RGSZ complex at the MOR C-terminus, where DAG-activated PKCγ phosphorylates MOR serine residues to reduce opioid signal strength.\",\n      \"method\": \"Intracerebroventricular pharmacology, co-immunoprecipitation, antisense knockdown, NOS inhibitors, zinc chelators, NMDAR antagonist\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and pharmacological dissection in vivo; single lab\",\n      \"pmids\": [\"18652891\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Loss-of-function mutations in HINT1 (8 different mutations identified in 33 families) cause autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM), establishing that functional HINT1 protein is required for normal peripheral nerve function.\",\n      \"method\": \"Linkage analysis, next-generation sequencing, cohort screening, clinical phenotyping\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large multi-family genetic study with clear loss-of-function disease phenotype; replicated across many families\",\n      \"pmids\": [\"22961002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human HINT1 binds aminoacyl adenylate (aa-AMP) intermediates with broad specificity independent of the amino acid side chain; crystal structures of HINT1 with three aa-AMP analogues show recognition of only the common main chain of the aminoacyl moiety, with the α-amino group anchored by a cation-π interaction with Trp123.\",\n      \"method\": \"X-ray crystallography (multiple co-crystal structures with aa-AMP analogues), in vitro hydrolysis assays\",\n      \"journal\": \"The journal of physical chemistry. B\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple crystal structures plus in vitro enzymatic characterization\",\n      \"pmids\": [\"22329685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"HINT1 inhibits MITF and β-catenin transcriptional activity in melanoma cells; both MITF and β-catenin co-immunoprecipitate with HINT1; ChIP assays show HINT1 occupies MITF and β-catenin binding sites at BCL2 and cyclin D1 promoters; mSIN3a and HDAC1 co-immunoprecipitate with HINT1, suggesting a repressive complex.\",\n      \"method\": \"Co-immunoprecipitation, ChIP assay, transcriptional reporter assay, stable overexpression, xenograft\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, ChIP, and functional reporter assays with multiple orthogonal methods\",\n      \"pmids\": [\"22647378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HINT1 protein is required for the cannabinoid CB1 receptor (CNR1) to negatively regulate NMDAR activity; in CNR1+/+/HINT1-/- cortical neurons NMDAR activity is enhanced and cannabinoid neuroprotection is abolished; lentiviral re-expression of HINT1 restores both NMDAR regulation and cannabinoid-mediated neuroprotection.\",\n      \"method\": \"HINT1-/- and CNR1-/- mouse neurons, lentiviral HINT1 rescue, calcium imaging/NMDA insult assay\",\n      \"journal\": \"Molecular brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with rescue experiment; single lab\",\n      \"pmids\": [\"24093505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The σ1 receptor (σ1R) binds to the cytosolic C-terminal region of the NMDAR NR1 subunit in a calcium-dependent manner and enables NR1–HINT1 interaction with MOR–HINT1 complexes; σ1R antagonists transfer HINT1 from GPCRs to NR1 subunits, disengaging MOR from NMDAR negative control and enhancing opioid antinociception; this regulation depends on the NO/Zn2+ redox switch via RGSZ2-nNOS and PKCγ recruitment to HINT1.\",\n      \"method\": \"In vivo pharmacology, ex vivo and in vitro co-immunoprecipitation, σ1R-/- and HINT1-/- mouse models, NOS inhibitors\",\n      \"journal\": \"Antioxidants & redox signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, multiple KO models, pharmacological dissection; single lab\",\n      \"pmids\": [\"25557043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The intracellular domain (ICD) of teneurin-1 interacts directly with HINT1 in human cells (identified by yeast two-hybrid and confirmed by co-immunoprecipitation); this interaction relieves HINT1-mediated repression of MITF, inducing MITF-dependent transcription of target genes such as GPNMB.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, transcriptome analysis, promoter reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — yeast two-hybrid confirmed by Co-IP and functional reporter; single lab\",\n      \"pmids\": [\"25648896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Pharmacological inhibition of HINT1 enzymatic activity (using guanosine-5′-tryptamine carbamate, TpGc) significantly enhances morphine antinociception and prevents tolerance development, and reduces NMDAR activity in mice with chronic constriction injury; X-ray crystallographic and thermodynamic binding studies showed distinct binding modes of different HINT1 inhibitors correlating with their differential effects on MOR–NMDAR cross-talk.\",\n      \"method\": \"In vivo antinociception assays, intracerebroventricular drug delivery, X-ray crystallography of HINT1-inhibitor complexes, thermodynamic binding assays\",\n      \"journal\": \"Neuropharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — crystallographic characterization of inhibitor binding plus in vivo functional data; single lab\",\n      \"pmids\": [\"25445489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"HINT1 is subjected to K21 acetylation and Y109 phosphorylation in activated mast cells; Ap4A (produced by S207-phosphorylated LysRS) triggers HINT1 dissociation from MITF; mutational analysis of K21 and Y109 confirmed these post-translational modifications promote MITF transcriptional and oncogenic activity in melanoma cells.\",\n      \"method\": \"Mass spectrometry (PTM identification), site-directed mutagenesis of acetylation (K21) and phosphorylation (Y109) sites, transcriptional reporter assay in melanoma cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — PTM identified by MS and confirmed by mutagenesis with functional readout; single lab\",\n      \"pmids\": [\"28394346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ap4A specifically polymerizes HINT1 into higher-order assemblies in solution and in activated rat basophilic leukemia cells; eight crystal structures define the polymerization interface, which overlaps with the MITF-binding region on HINT1, providing a competitive mechanism to release MITF for transcriptional activation; the polymerization depends precisely on the polyphosphate chain length of Ap4A.\",\n      \"method\": \"X-ray crystallography (8 crystal structures), negative-stain electron microscopy, biochemical polymerization assays, cellular experiments in RBL cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — eight crystal structures, EM, and biochemical assays with cellular validation; strong mechanistic rigor\",\n      \"pmids\": [\"31604935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HINT1 exhibits cysteine SUMO protease (isopeptidase) activity to remove SUMO from signaling proteins; this activity is regulated by zinc (blocks) and by nitric oxide or calcium-activated calmodulin (releases); the catalytic triad is Cys84-Asp87-His114; a SUMO-interacting motif is identified at residues 110–116; all 15 human ARAN-NM-associated HINT1 mutants tested showed altered sumoylase activity.\",\n      \"method\": \"In vitro SUMO protease assay, site-directed mutagenesis of catalytic triad, zinc/NO/CaM regulation assays, patient-derived mutant characterization\",\n      \"journal\": \"Antioxidants & redox signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — novel enzymatic activity with mutagenesis and regulatory dissection; single lab\",\n      \"pmids\": [\"31088288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIRT1 deacetylates HINT1 at K21 and K30 (CBP-mediated acetylation sites); deacetylation increases HINT1 binding capacity for β-catenin and MITF, enhancing tumor-suppressive activity; deacetylation-mimetic HINT1 2KR mutant significantly reduces proliferation in colon cancer and melanoma cells and tumorigenesis in xenografts.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis (K21R/K30R), xenograft assay, in vitro deacetylation assay\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP with mutagenesis and in vivo xenograft; single lab\",\n      \"pmids\": [\"32636443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"HINT1 directly interacts with PKCβ1 and inhibits its membrane translocation and phosphorylation; this suppresses the MEK/ERK/YY1 signaling pathway and downregulates HOXA5 expression, ultimately attenuating cardiac hypertrophy; cardiac-specific HINT1 overexpression via AAV9 alleviated hypertrophy and dysfunction in mice.\",\n      \"method\": \"Co-immunoprecipitation, cellular fractionation assays, AAV9-mediated cardiac-specific overexpression, Hint1 knockout mice + transverse aortic constriction, RNA sequencing, shRNA knockdown of Hoxa5\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct protein interaction by Co-IP, fractionation, loss- and gain-of-function in vivo models with molecular pathway dissection\",\n      \"pmids\": [\"34098726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human PKCI-1/HINT1 localizes to cytoskeletal structures in the cytoplasm of human fibroblasts and is largely excluded from the nucleus, as determined by indirect immunofluorescence.\",\n      \"method\": \"Indirect immunofluorescence in human fibroblast cell line\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single localization experiment without functional follow-up\",\n      \"pmids\": [\"8812426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The C-terminal loop of HINT1 is a critical determinant of substrate specificity; chimeric Hint proteins with swapped C-terminal loops showed that the human C-terminal loop confers preference for l-configured phosphoramidates and ability to hydrolyze lysyl-AMP generated by human LysRS, distinct from E. coli hinT specificity.\",\n      \"method\": \"Chimeric enzyme construction, in vitro kinetic assays (kcat/Km) with panel of substrates\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted chimeric enzymes with systematic substrate profiling; single lab\",\n      \"pmids\": [\"17939685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of human HINT1 in complex with a non-hydrolyzable Ap4A analog (at 2.34 Å resolution) defined the Ap4A binding site; the apo structure (1.92 Å) was also solved for comparison.\",\n      \"method\": \"X-ray crystallography\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure; single study without extensive mutagenesis\",\n      \"pmids\": [\"26905466\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"HINT1 co-immunoprecipitates with USF2 in hepatoma cell extracts and inhibits USF2, β-catenin/TCF4, and NFκB transcriptional activities; HINT1 also inhibits nuclear translocation of the p65 NFκB subunit in HepG2 cells.\",\n      \"method\": \"Co-immunoprecipitation, transcriptional reporter assays, nuclear fractionation\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP and reporter assays with fractionation; single lab\",\n      \"pmids\": [\"19089909\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"HINT1 is a universally conserved, dimeric AMP-lysine/adenosine phosphoramidate hydrolase and SUMO isopeptidase whose active site (catalytic His triad and Ser107/Cys84-Asp87-His114) mediates both enzymatic activities; it functions as a scaffold at the mu-opioid receptor C-terminus (via RGSZ2/PKCγ/σ1R redox-zinc signaling) to couple GPCR activity to NMDAR regulation, acts as a transcriptional co-repressor by directly binding oncogenic factors (MITF, β-catenin, USF2, NFκB) and recruiting HDAC1/mSIN3a, is released from these factors by Ap4A-driven polymerization or by post-translational modifications (K21/K30 acetylation by CBP, Y109 phosphorylation), inhibits PKCβ1 membrane translocation to suppress the MEK/ERK/YY1/HOXA5 cardiac hypertrophy pathway, participates in DNA damage responses by associating with γ-H2AX and ATM, and is a haploinsufficient tumor suppressor whose loss-of-function mutations cause autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM).\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"HINT1 is a universally conserved dimeric nucleotide hydrolase and multifunctional scaffold that integrates enzymatic, transcriptional, and signaling activities across diverse cellular contexts. As an enzyme, HINT1 hydrolyzes adenosine 5′-monophosphoramidate and aminoacyl-AMP substrates at high catalytic rates using its HIT-motif active site, with substrate specificity governed by its C-terminal loop and key residues Ser107 and Trp123 at the dimer interface [PMID:11805111, PMID:14982931, PMID:22329685]; it also possesses SUMO isopeptidase activity mediated by a Cys84-Asp87-His114 catalytic triad, regulated by zinc, nitric oxide, and calmodulin [PMID:31088288]. As a transcriptional co-repressor, HINT1 directly binds oncogenic transcription factors including β-catenin/TCF, MITF, USF2, and NFκB, recruiting HDAC1/mSIN3a to target promoters; this repressive function is relieved by Ap4A-driven polymerization of HINT1 or by CBP-mediated acetylation at K21/K30, which is reversed by SIRT1 deacetylation [PMID:22647378, PMID:31604935, PMID:32636443, PMID:16014379]. HINT1 functions as a haploinsufficient tumor suppressor whose loss increases spontaneous and carcinogen-induced tumorigenesis in mice [PMID:16186798], acts as a scaffold coupling mu-opioid and cannabinoid receptors to NMDAR regulation via RGSZ2/PKCγ/σ1R complexes in neurons [PMID:18652891, PMID:24093505], suppresses cardiac hypertrophy by inhibiting PKCβ1 membrane translocation and the MEK/ERK/YY1/HOXA5 pathway [PMID:34098726], and participates in DNA damage responses through association with γ-H2AX and ATM [PMID:18852295]; loss-of-function mutations in HINT1 cause autosomal recessive axonal neuropathy with neuromyotonia [PMID:22961002].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Determining the three-dimensional structure of HINT established it as a dimeric purine nucleotide-binding protein with a conserved HIT-motif phosphate-binding loop, revealing its fold and setting the stage for understanding its catalytic mechanism.\",\n      \"evidence\": \"X-ray crystallography of HINT-nucleotide complexes\",\n      \"pmids\": [\"9164465\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrate unknown\", \"Catalytic activity not yet demonstrated\", \"Biological function in cells undefined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of adenosine monophosphoramidase activity at >10⁶ M⁻¹s⁻¹ and genetic epistasis with the TFIIH kinase subcomplex answered what HINT1 does enzymatically and placed it in a transcription-related pathway.\",\n      \"evidence\": \"In vitro enzymatic assays with rabbit Hint and yeast Hnt1; yeast genetic epistasis with Kin28/Ccl1/Tfb3\",\n      \"pmids\": [\"11805111\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct in vivo substrate not captured\", \"Mechanism linking hydrolase activity to TFIIH regulation unclear\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Physical interaction with Cdk7/Kin28 and nuclear relocalization upon Cdk7 overexpression connected HINT1 to cell cycle kinase complexes and raised the question of whether it has nuclear transcriptional roles.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, imaging, and yeast double-mutant analysis\",\n      \"pmids\": [\"10958787\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Cdk7 interaction is direct or bridged by other TFIIH subunits not resolved\", \"Functional consequence of nuclear relocalization unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"A 1.8-Å co-crystal structure with a substrate analogue and mutagenesis of Ser107 defined the catalytic mechanism for AMP-lysine hydrolysis, establishing the roles of Trp123 (across the dimer interface) and Ser107 in acid-base catalysis.\",\n      \"evidence\": \"X-ray crystallography, AMP-pNA hydrolase assay, S107A mutagenesis\",\n      \"pmids\": [\"14982931\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full transition-state geometry not resolved\", \"In vivo relevance of lysyl-AMP hydrolysis not demonstrated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Discovery that HINT1 binds Pontin/Reptin and represses TCF–β-catenin transcription (with cyclin D1 and axin2 as endogenous targets) established HINT1 as a transcriptional co-repressor, a function independent of its nucleotide hydrolase activity.\",\n      \"evidence\": \"Pull-down, co-immunoprecipitation, TCF reporter, RNAi knockdown\",\n      \"pmids\": [\"16014379\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HINT1 repressor function requires its enzymatic activity not tested here\", \"Chromatin-level mechanism of repression not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Two key advances: (1) HINT1 was shown to promote apoptosis via p53/Bax upregulation as part of the Tip60 complex—independent of catalytic activity (H112N mutant); (2) Hint1⁺/⁻ and Hint1⁻/⁻ mice demonstrated haploinsufficient tumor suppression, linking HINT1 loss to cancer predisposition in vivo.\",\n      \"evidence\": \"Apoptosis assays, Bax promoter ChIP, Tip60 co-IP, H112N mutant (SW480/MCF-7 cells); knockout/heterozygous mice with spontaneous and DMBA-induced tumors\",\n      \"pmids\": [\"16835243\", \"16186798\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How HINT1 stimulates Tip60 acetyltransferase activity mechanistically unknown\", \"Tissue-specific tumor suppressor mechanisms not dissected\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"HINT1 was found to inhibit AP-1 activity by binding the POSH–JNK2 complex, expanding the repertoire of transcription factor targets it represses and establishing JNK2 specificity; separately, C-terminal loop swaps defined substrate specificity determinants for phosphoramidate hydrolysis.\",\n      \"evidence\": \"Co-IP with POSH–JNK2, AP-1 reporter, JNK1⁻/⁻ and JNK2⁻/⁻ MEFs; chimeric enzyme kinetics\",\n      \"pmids\": [\"17510397\", \"17939685\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether JNK2 interaction is direct or POSH-mediated not resolved\", \"Structural basis for C-terminal loop specificity not determined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Two parallel advances established HINT1 roles in the nucleus and at the plasma membrane: HINT1 was recruited to DNA damage foci and required for γ-H2AX removal and ATM activation after irradiation; simultaneously, HINT1 was identified as a scaffold coupling MOR to NMDAR regulation via RGSZ/PKCγ/zinc signaling in neurons.\",\n      \"evidence\": \"IRIF imaging, γ-H2AX/ATM co-IP, DNA repair assays in HINT1-deficient cells; in vivo pharmacology, co-IP, antisense knockdown in mouse neurons\",\n      \"pmids\": [\"18852295\", \"18652891\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which HINT1 promotes γ-H2AX acetylation/removal not defined\", \"MOR–HINT1 scaffolding model relies on single-lab pharmacological studies\", \"Whether DNA damage and GPCR roles involve the same or distinct HINT1 pools unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Three discoveries converged: HINT1 was shown to bind aminoacyl-AMP intermediates broadly (crystal structures); it was established as a co-repressor of MITF and β-catenin via HDAC1/mSIN3a recruitment to target promoters (ChIP); and loss-of-function mutations were identified as the cause of autosomal recessive axonal neuropathy with neuromyotonia in 33 families.\",\n      \"evidence\": \"Multiple co-crystal structures with aa-AMP analogues; ChIP, co-IP with MITF/β-catenin/HDAC1/mSIN3a in melanoma cells; linkage analysis and exome sequencing in ARAN-NM families\",\n      \"pmids\": [\"22329685\", \"22647378\", \"22961002\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether aminoacyl-AMP hydrolysis connects to transcriptional repression unknown\", \"Neuropathological mechanism of HINT1 loss in peripheral nerve not defined\", \"Whether HDAC1/mSIN3a recruitment requires HINT1 dimerization not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The HINT1 signaling scaffold model was extended: σ1R was shown to regulate HINT1 transfer between GPCRs and NMDAR NR1 subunits; teneurin-1 ICD was identified as a direct HINT1 interactor that relieves MITF repression; and pharmacological HINT1 inhibitors were crystallographically characterized and shown to enhance morphine analgesia in vivo.\",\n      \"evidence\": \"σ1R⁻/⁻ and HINT1⁻/⁻ mice, in vivo pharmacology, co-IP; yeast two-hybrid and co-IP for teneurin-1; X-ray crystallography of inhibitor complexes, antinociception assays\",\n      \"pmids\": [\"25557043\", \"25648896\", \"25445489\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis for σ1R–HINT1–NR1 ternary complex not resolved\", \"Teneurin-1–HINT1 interaction validated by single lab\", \"Inhibitor selectivity in vivo not fully profiled\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of K21 acetylation and Y109 phosphorylation as PTMs that trigger HINT1 dissociation from MITF explained how activated mast cells relieve transcriptional repression, connecting Ap4A signaling (via phospho-LysRS) to HINT1 regulation.\",\n      \"evidence\": \"Mass spectrometry PTM identification, site-directed mutagenesis (K21, Y109), transcriptional reporter in melanoma cells\",\n      \"pmids\": [\"28394346\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase responsible for Y109 phosphorylation not identified\", \"Whether K21 acetylation and Ap4A polymerization are redundant or sequential not determined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Two mechanistically distinct advances: (1) Ap4A was shown to polymerize HINT1 into higher-order assemblies whose interface overlaps the MITF-binding surface, providing a structural mechanism for MITF release; (2) a novel SUMO isopeptidase activity was identified with a Cys84-Asp87-His114 catalytic triad, regulated by zinc/NO/calmodulin, and all 15 tested ARAN-NM mutants showed altered sumoylase activity.\",\n      \"evidence\": \"Eight crystal structures, negative-stain EM, polymerization assays in RBL cells; in vitro SUMO protease assay, catalytic triad mutagenesis, patient mutant characterization\",\n      \"pmids\": [\"31604935\", \"31088288\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo SUMO substrates of HINT1 not identified\", \"Whether Ap4A polymerization occurs in neurons and relates to ARAN-NM unknown\", \"SUMO isopeptidase activity identified by single lab and awaits independent replication\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"SIRT1-mediated deacetylation of HINT1 at K21/K30 was shown to enhance its binding to β-catenin and MITF and augment tumor-suppressive function, establishing a reversible acetylation switch (CBP acetylates, SIRT1 deacetylates) that modulates HINT1 co-repressor activity.\",\n      \"evidence\": \"Co-IP, K21R/K30R mutagenesis, in vitro deacetylation assay, xenograft tumorigenesis\",\n      \"pmids\": [\"32636443\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether SIRT1–HINT1 axis operates in non-cancer contexts (e.g., neurons) unknown\", \"Structural basis for how acetylation weakens transcription factor binding not determined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"HINT1 was established as a cardioprotective factor that directly binds PKCβ1, inhibits its membrane translocation, and thereby suppresses the MEK/ERK/YY1/HOXA5 hypertrophy pathway; AAV9-mediated cardiac HINT1 overexpression rescued pressure-overload hypertrophy in mice.\",\n      \"evidence\": \"Co-IP, cellular fractionation, AAV9 cardiac overexpression, Hint1⁻/⁻ mice + TAC, RNA-seq, HOXA5 knockdown\",\n      \"pmids\": [\"34098726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKCβ1 inhibition requires HINT1 enzymatic activity not tested\", \"Downstream mechanism linking HOXA5 to hypertrophic gene program incompletely defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the identity of in vivo SUMO substrates of HINT1, the structural basis of the HINT1–GPCR–NMDAR ternary signaling complex, whether the distinct enzymatic activities (phosphoramidase, SUMO isopeptidase) serve separable physiological functions, the neuropathological mechanism underlying ARAN-NM, and how Ap4A-driven polymerization and PTM-mediated regulation are coordinated in different tissue contexts.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"In vivo SUMO substrates unidentified\", \"Structural model of HINT1–MOR–NMDAR signalosome lacking\", \"Peripheral nerve-specific mechanism of ARAN-NM pathogenesis unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 3, 11, 23]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [4, 5, 12, 25]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [7, 21]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [9, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [22]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 5, 8, 12]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9, 14, 21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 13, 14, 21]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 4, 12, 25]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 10]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [5, 12]}\n    ],\n    \"complexes\": [\n      \"Tip60 HAT complex\",\n      \"HDAC1/mSIN3a repressor complex\",\n      \"MOR–HINT1–RGSZ2 signaling complex\"\n    ],\n    \"partners\": [\n      \"CDK7\",\n      \"RUVBL1\",\n      \"RUVBL2\",\n      \"CTNNB1\",\n      \"MITF\",\n      \"PRKCB\",\n      \"RGSZ2\",\n      \"OPRS1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}