{"gene":"PPP1R9A","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2002,"finding":"Neurabin I localizes to the actin cytoskeleton via its N-terminal F-actin-binding domain and promotes disassembly of stress fibers; deletion of C-terminal coiled-coil and SAM domains abolishes dimerization and induces filopodium extension. Neurabin I recruits active PP1 via a PP1-docking sequence (457)KIKF(460), and mutation of this motif or pharmacological PP1 inhibition abolishes filopodia and restores stress fibers, establishing that the neurabin I/PP1 complex controls actin rearrangement. PKA phosphorylation of serine-461 impairs PP1 binding, and p70S6K is excluded from neurabin I/PP1 complexes, requiring PP1 displacement for its own recruitment to neurabin I.","method":"GFP-fusion live imaging, deletion/point mutant analysis, immune complex phosphatase assays, okadaic acid/calyculin A pharmacological inhibition, in vitro and in vivo PKA phosphorylation assays in Cos7, HEK293, and hippocampal neurons","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (mutagenesis, in vitro assay, pharmacological rescue, live imaging) in a single rigorous study with clear mechanistic readouts","pmids":["12052877"],"is_preprint":false},{"year":1999,"finding":"Neurabin I binds and inhibits PP1 (Ki = 2.7 nM for a GST-neurabin I fragment containing residues 318–661) via its PP1-binding domain (residues 456–460). PKA phosphorylates neurabin I at serine-461 (identified by HPLC-MS), significantly reducing PP1 binding and a S461E phosphomimetic mutant showed 35-fold reduced inhibitory potency, establishing a cAMP-dependent regulatory mechanism for PP1 activity and localization.","method":"GST pulldown, overlay assay, yeast two-hybrid, co-immunoprecipitation, in vitro PP1 activity assay, in vitro PKA phosphorylation, HPLC-MS phosphosite identification, S461E phosphomimetic mutagenesis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis and quantitative Ki measurements, phosphosite identified by mass spectrometry, multiple orthogonal methods in one study","pmids":["10504266"],"is_preprint":false},{"year":2002,"finding":"Neurabin I (and neurabin II/spinophilin) preferentially recruits PP1gamma1 and PP1alpha over PP1beta from rat brain. The rank order of PP1 isoform selectivity is PP1gamma1 > PP1alpha > PP1beta. Sequences flanking the conserved PP1-binding motif and C-terminal sequences unique to PP1 isoforms together determine selectivity. In PP1gamma null mice, both neurabins show enhanced association with PP1alpha but not PP1beta, confirming isoform hierarchy in vivo.","method":"Immunoprecipitation from rat brain and PP1gamma null mouse brain, in vitro binding of recombinant peptides to brain extracts, chimeric neurabin and chimeric PP1/PP2A analysis, in vitro PP1 activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — reciprocal immunoprecipitation confirmed in genetic null mouse model, supported by multiple in vitro chimera assays across two neurabins","pmids":["12016225"],"is_preprint":false},{"year":2007,"finding":"Cdk5 directly phosphorylates Neurabin-I and controls its association with F-actin. Gain and loss of Neurabin-I expression affect neuronal morphology, neurite outgrowth, Rac1 activation, and radial migration of cortical neurons. Mutation of the Cdk5 phosphorylation site reduces the morphological and migratory phenotypic consequences of Neurabin-I overexpression both in vitro and in vivo, demonstrating that Cdk5-mediated phosphorylation regulates Neurabin-I function in the actin cytoskeleton during corticogenesis.","method":"In vitro kinase assay (Cdk5 phosphorylation), phosphorylation-site mutagenesis, antisense/overexpression in primary cortical neurons and in utero electroporation (in vivo), F-actin co-sedimentation, Rac1 activity assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct in vitro kinase assay, phosphosite mutagenesis with rescue experiment, and in vivo validation via electroporation, multiple orthogonal methods","pmids":["17699587"],"is_preprint":false},{"year":2006,"finding":"Neurabin I is a direct binding partner of Rac3 (a neuronal Rho-family GTPase), identified by yeast two-hybrid. Neurabin I co-partitions and co-localizes with Rac3 at growth cones, and Neurabin I antisense oligonucleotides abolish Rac3-induced neuritogenesis, which is rescued by exogenous Neurabin I but not by a Neurabin I mutant lacking the Rac3-binding domain, establishing Neurabin I as a required mediator of Rac3-induced neuritogenesis by anchoring Rac3 to growth cone F-actin.","method":"Yeast two-hybrid, biochemical co-fractionation, co-localization by light microscopy, antisense knockdown, domain-deletion rescue experiments in primary neurons","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — yeast two-hybrid plus antisense/rescue experiments in neurons with domain-deletion mutant, two orthogonal approaches but no in vitro reconstitution of direct binding","pmids":["16525025"],"is_preprint":false},{"year":1999,"finding":"Bau, a splice form of Neurabin-I lacking actin- and p70S6K-binding domains but retaining coiled-coil domains, interacts with the tumor suppressor Bin1 (interaction requires the U3 region alternately spliced in muscle cells), localizes to the nucleus and cytosol, and suppresses oncogene-mediated transformation and inhibits tumor cell growth.","method":"Protein interaction screen (Bin1-based), domain-deletion analysis, subcellular localization, transformation suppression assay","journal":"Cell adhesion and communication","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, interaction identified by interaction screen without reciprocal Co-IP or in vitro reconstitution; functional assay is single-method","pmids":["10427963"],"is_preprint":false},{"year":2018,"finding":"Neurabin-I is atypically hyper-N-glycosylated at ASN1277, rendering it immunogenic and enabling it to act as a B-cell receptor autoantigen in primary CNS lymphoma (PCNSL); this modified neurabin-I induces BCR pathway activation and proliferation of lymphoma cell lines transfected with neurabin-I-reactive BCRs, and a BCR-binding epitope of neurabin-I conjugated to Pseudomonas exotoxin killed lymphoma cells expressing the respective BCRs.","method":"Identification of N-glycosylation site (ASN1277) by mass spectrometry/sequencing, BCR transfection into lymphoma cell lines, BCR signaling and proliferation assays, immunotoxin cytotoxicity assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — post-translational modification identified and functionally validated in transfected cell lines with multiple functional readouts, single lab","pmids":["30249786"],"is_preprint":false}],"current_model":"Neurabin-I (PPP1R9A) is a neuronal F-actin-binding scaffold that recruits and inhibits protein phosphatase 1 (preferentially PP1γ1 > PP1α > PP1β) via its KIKF docking motif; PKA phosphorylation at Ser-461 and Cdk5 phosphorylation regulate its PP1-binding and F-actin association, respectively, thereby controlling actin cytoskeletal dynamics, dendritic spine morphology, and cortical neuron migration; it also mediates Rac3-induced neuritogenesis by anchoring Rac3 to growth cone F-actin, and a splice variant (Bau) interacts with the tumor suppressor Bin1 in the nucleus/cytosol."},"narrative":{"mechanistic_narrative":"Neurabin-I (PPP1R9A) is a neuronal F-actin-binding scaffold that couples protein phosphatase 1 (PP1) to the actin cytoskeleton to control actin rearrangement, neuronal morphology, and cortical neuron migration [PMID:12052877, PMID:17699587]. It localizes to the actin cytoskeleton via an N-terminal F-actin-binding domain and recruits active PP1 through a (457)KIKF(460) docking motif; this complex drives stress-fiber disassembly and filopodium extension, whereas disrupting the KIKF motif or inhibiting PP1 restores stress fibers [PMID:12052877]. Neurabin-I binds and inhibits PP1 with nanomolar affinity and shows isoform selectivity (PP1γ1 > PP1α > PP1β), with flanking and PP1 C-terminal sequences setting the hierarchy that is confirmed in PP1γ-null mouse brain [PMID:10504266, PMID:12016225]. Its activity is gated by phosphorylation: PKA phosphorylation at Ser-461 sharply reduces PP1 binding, providing cAMP-dependent control of PP1 localization, while Cdk5 phosphorylation regulates F-actin association and governs neurite outgrowth, Rac1 activation, and radial migration during corticogenesis [PMID:10504266, PMID:17699587]. Neurabin-I also serves as a direct Rac3 partner required for Rac3-induced neuritogenesis by anchoring Rac3 to growth-cone F-actin [PMID:16525025]. A splice variant (Bau) lacking actin-binding domains interacts with the tumor suppressor Bin1 and suppresses transformation [PMID:10427963], and atypical hyper-N-glycosylation of neurabin-I renders it a B-cell receptor autoantigen in primary CNS lymphoma [PMID:30249786].","teleology":[{"year":1999,"claim":"Establishing that neurabin-I is a high-affinity PP1 inhibitor whose binding is controlled by phosphorylation answered how a scaffold could both target and modulate phosphatase activity.","evidence":"GST pulldown, yeast two-hybrid, in vitro PP1 activity assay, HPLC-MS phosphosite mapping, and S461E phosphomimetic mutagenesis","pmids":["10504266"],"confidence":"High","gaps":["Did not establish the cellular consequences of Ser-461 phosphorylation in neurons","Upstream signals activating PKA toward this site not defined"]},{"year":1999,"claim":"Identification of the Bau splice variant binding Bin1 raised the possibility of a nuclear/cytosolic, actin-independent role distinct from the canonical PP1 scaffold function.","evidence":"Bin1 interaction screen, domain-deletion analysis, subcellular localization, and transformation suppression assay","pmids":["10427963"],"confidence":"Low","gaps":["Single lab without reciprocal Co-IP or in vitro reconstitution of the Bin1 interaction","Functional tumor-suppression assay was single-method","Mechanism linking Bin1 binding to growth suppression unknown"]},{"year":2002,"claim":"Live imaging and mutational dissection tied the neurabin-I/PP1 complex directly to actin dynamics, showing the KIKF docking motif is required to convert stress fibers into filopodia.","evidence":"GFP-fusion live imaging, deletion/point mutants, immune-complex phosphatase assays, and PP1 pharmacological inhibition in Cos7, HEK293, and hippocampal neurons","pmids":["12052877"],"confidence":"High","gaps":["PP1 substrates downstream of the complex that drive actin remodeling not identified","Role of dimerization domains in vivo not resolved"]},{"year":2002,"claim":"Defining PP1 isoform selectivity (PP1γ1 > PP1α > PP1β) clarified which phosphatase holoenzymes neurabin-I assembles, and the determinants encoding that hierarchy.","evidence":"Reciprocal immunoprecipitation from rat brain and PP1γ-null mouse brain, recombinant peptide binding, and chimeric neurabin/PP1 analysis","pmids":["12016225"],"confidence":"High","gaps":["Functional consequence of isoform preference for specific substrates not defined","Whether selectivity differs across neuronal compartments unknown"]},{"year":2006,"claim":"Identifying Rac3 as a direct partner showed neurabin-I links a Rho-family GTPase to growth-cone F-actin, making it a required mediator of neuritogenesis.","evidence":"Yeast two-hybrid, co-fractionation, co-localization, and antisense knockdown with domain-deletion rescue in primary neurons","pmids":["16525025"],"confidence":"Medium","gaps":["No in vitro reconstitution confirming direct Rac3 binding","Relationship between Rac3 anchoring and the PP1 scaffold function unresolved"]},{"year":2007,"claim":"Demonstrating Cdk5 phosphorylation of neurabin-I controls F-actin association placed the protein within corticogenesis, linking a kinase to neuronal migration and morphology.","evidence":"In vitro Cdk5 kinase assay, phosphosite mutagenesis with rescue, in utero electroporation, F-actin co-sedimentation, and Rac1 activity assay","pmids":["17699587"],"confidence":"High","gaps":["Exact Cdk5 phosphosite residue(s) and their interplay with PKA/Ser-461 not integrated","Mechanistic link between F-actin binding and Rac1 activation incomplete"]},{"year":2018,"claim":"Discovery that hyper-N-glycosylated neurabin-I acts as a BCR autoantigen extended its relevance beyond neuronal cytoskeletal biology into CNS lymphoma immunopathology.","evidence":"Mass-spectrometric N-glycosylation site mapping (ASN1277), BCR transfection into lymphoma lines, BCR signaling/proliferation assays, and immunotoxin cytotoxicity assay","pmids":["30249786"],"confidence":"Medium","gaps":["Single lab; in vivo relevance of the autoantigen mechanism not established","How the neuronal scaffold becomes hyper-glycosylated and exposed to BCRs unknown"]},{"year":null,"claim":"How the multiple regulatory inputs (PKA at Ser-461, Cdk5, Rac3/Rac1) are integrated to coordinate PP1 targeting with actin remodeling in defined neuronal compartments remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model of combinatorial phosphoregulation","PP1 substrates that effect actin changes downstream of the complex not identified","Structural basis of simultaneous F-actin, PP1, and Rac3 engagement unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,3]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[1,4]}],"complexes":[],"partners":["PP1","PPP1CC","PPP1CA","RAC3","BIN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9ULJ8","full_name":"Neurabin-1","aliases":["Neurabin-I","Neural tissue-specific F-actin-binding protein I","Protein phosphatase 1 regulatory subunit 9A"],"length_aa":1098,"mass_kda":123.3,"function":"Binds to actin filaments (F-actin) and shows cross-linking activity. Binds along the sides of the F-actin. May be involved in neurite formation. Inhibits protein phosphatase 1-alpha activity (By similarity)","subcellular_location":"Cytoplasm, cytoskeleton; Synapse, synaptosome","url":"https://www.uniprot.org/uniprotkb/Q9ULJ8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PPP1R9A","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":"CALD1","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CTTN","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PPP1R9A","total_profiled":1310},"omim":[{"mim_id":"602468","title":"PROTEIN PHOSPHATASE 1, REGULATORY SUBUNIT 9A; PPP1R9A","url":"https://www.omim.org/entry/602468"},{"mim_id":"176914","title":"PROTEIN PHOSPHATASE 1, CATALYTIC SUBUNIT, GAMMA ISOFORM; PPP1CC","url":"https://www.omim.org/entry/176914"},{"mim_id":"143100","title":"HUNTINGTON DISEASE; HD","url":"https://www.omim.org/entry/143100"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"retina","ntpm":17.2}],"url":"https://www.proteinatlas.org/search/PPP1R9A"},"hgnc":{"alias_symbol":["Neurabin-I","KIAA1222","FLJ20068"],"prev_symbol":[]},"alphafold":{"accession":"Q9ULJ8","domains":[{"cath_id":"2.30.42.10","chopping":"485-596","consensus_level":"high","plddt":88.5238,"start":485,"end":596},{"cath_id":"1.10.150.50","chopping":"988-1071","consensus_level":"high","plddt":84.9108,"start":988,"end":1071},{"cath_id":"1.20.5","chopping":"682-814","consensus_level":"medium","plddt":94.659,"start":682,"end":814}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9ULJ8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9ULJ8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9ULJ8-F1-predicted_aligned_error_v6.png","plddt_mean":59.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PPP1R9A","jax_strain_url":"https://www.jax.org/strain/search?query=PPP1R9A"},"sequence":{"accession":"Q9ULJ8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9ULJ8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9ULJ8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9ULJ8"}},"corpus_meta":[{"pmid":"12052877","id":"PMC_12052877","title":"Targeting protein phosphatase 1 (PP1) to the actin cytoskeleton: the neurabin I/PP1 complex regulates cell morphology.","date":"2002","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12052877","citation_count":101,"is_preprint":false},{"pmid":"12016225","id":"PMC_12016225","title":"The neuronal actin-binding proteins, neurabin I and neurabin II, recruit specific isoforms of protein phosphatase-1 catalytic subunits.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12016225","citation_count":75,"is_preprint":false},{"pmid":"10504266","id":"PMC_10504266","title":"Regulation of neurabin I interaction with protein phosphatase 1 by phosphorylation.","date":"1999","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10504266","citation_count":71,"is_preprint":false},{"pmid":"17699587","id":"PMC_17699587","title":"Neurabin-I is phosphorylated by Cdk5: implications for neuronal morphogenesis and cortical migration.","date":"2007","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/17699587","citation_count":32,"is_preprint":false},{"pmid":"30249786","id":"PMC_30249786","title":"Hyper-N-glycosylated SAMD14 and neurabin-I as driver autoantigens of primary central nervous system lymphoma.","date":"2018","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/30249786","citation_count":31,"is_preprint":false},{"pmid":"25757715","id":"PMC_25757715","title":"Altered prefrontal cortical MARCKS and PPP1R9A mRNA expression in schizophrenia and bipolar disorder.","date":"2015","source":"Schizophrenia research","url":"https://pubmed.ncbi.nlm.nih.gov/25757715","citation_count":26,"is_preprint":false},{"pmid":"16525025","id":"PMC_16525025","title":"Rac3-induced neuritogenesis requires binding to Neurabin I.","date":"2006","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/16525025","citation_count":16,"is_preprint":false},{"pmid":"21675243","id":"PMC_21675243","title":"Assessment of genomic imprinting of PPP1R9A, NAP1L5 and PEG3 in pigs.","date":"2011","source":"Genetika","url":"https://pubmed.ncbi.nlm.nih.gov/21675243","citation_count":11,"is_preprint":false},{"pmid":"21498922","id":"PMC_21498922","title":"Molecular cloning, mRNA expression and imprinting status of PEG3, NAP1L5 and PPP1R9A genes in pig.","date":"2011","source":"Genes & genetic systems","url":"https://pubmed.ncbi.nlm.nih.gov/21498922","citation_count":9,"is_preprint":false},{"pmid":"33282736","id":"PMC_33282736","title":"Integration of the B-Cell Receptor Antigen Neurabin-I/SAMD14 Into an Antibody Format as New Therapeutic Approach for the Treatment of Primary CNS Lymphoma.","date":"2020","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/33282736","citation_count":5,"is_preprint":false},{"pmid":"10427963","id":"PMC_10427963","title":"Bau, a splice form of Neurabin-I that interacts with the tumor suppressor Bin1, inhibits malignant cell transformation.","date":"1999","source":"Cell adhesion and communication","url":"https://pubmed.ncbi.nlm.nih.gov/10427963","citation_count":4,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.17.676758","title":"Proteomic and Kinetic Characterization of Prion Seeding in Distinct Human CJD Strains Unveils Early Diagnostic Biomarkers","date":"2025-09-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.17.676758","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8463,"output_tokens":2413,"usd":0.030792,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9539,"output_tokens":2986,"usd":0.061172,"stage2_stop_reason":"end_turn"},"total_usd":0.091964,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"Neurabin I localizes to the actin cytoskeleton via its N-terminal F-actin-binding domain and promotes disassembly of stress fibers; deletion of C-terminal coiled-coil and SAM domains abolishes dimerization and induces filopodium extension. Neurabin I recruits active PP1 via a PP1-docking sequence (457)KIKF(460), and mutation of this motif or pharmacological PP1 inhibition abolishes filopodia and restores stress fibers, establishing that the neurabin I/PP1 complex controls actin rearrangement. PKA phosphorylation of serine-461 impairs PP1 binding, and p70S6K is excluded from neurabin I/PP1 complexes, requiring PP1 displacement for its own recruitment to neurabin I.\",\n      \"method\": \"GFP-fusion live imaging, deletion/point mutant analysis, immune complex phosphatase assays, okadaic acid/calyculin A pharmacological inhibition, in vitro and in vivo PKA phosphorylation assays in Cos7, HEK293, and hippocampal neurons\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (mutagenesis, in vitro assay, pharmacological rescue, live imaging) in a single rigorous study with clear mechanistic readouts\",\n      \"pmids\": [\"12052877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Neurabin I binds and inhibits PP1 (Ki = 2.7 nM for a GST-neurabin I fragment containing residues 318–661) via its PP1-binding domain (residues 456–460). PKA phosphorylates neurabin I at serine-461 (identified by HPLC-MS), significantly reducing PP1 binding and a S461E phosphomimetic mutant showed 35-fold reduced inhibitory potency, establishing a cAMP-dependent regulatory mechanism for PP1 activity and localization.\",\n      \"method\": \"GST pulldown, overlay assay, yeast two-hybrid, co-immunoprecipitation, in vitro PP1 activity assay, in vitro PKA phosphorylation, HPLC-MS phosphosite identification, S461E phosphomimetic mutagenesis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis and quantitative Ki measurements, phosphosite identified by mass spectrometry, multiple orthogonal methods in one study\",\n      \"pmids\": [\"10504266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Neurabin I (and neurabin II/spinophilin) preferentially recruits PP1gamma1 and PP1alpha over PP1beta from rat brain. The rank order of PP1 isoform selectivity is PP1gamma1 > PP1alpha > PP1beta. Sequences flanking the conserved PP1-binding motif and C-terminal sequences unique to PP1 isoforms together determine selectivity. In PP1gamma null mice, both neurabins show enhanced association with PP1alpha but not PP1beta, confirming isoform hierarchy in vivo.\",\n      \"method\": \"Immunoprecipitation from rat brain and PP1gamma null mouse brain, in vitro binding of recombinant peptides to brain extracts, chimeric neurabin and chimeric PP1/PP2A analysis, in vitro PP1 activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — reciprocal immunoprecipitation confirmed in genetic null mouse model, supported by multiple in vitro chimera assays across two neurabins\",\n      \"pmids\": [\"12016225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Cdk5 directly phosphorylates Neurabin-I and controls its association with F-actin. Gain and loss of Neurabin-I expression affect neuronal morphology, neurite outgrowth, Rac1 activation, and radial migration of cortical neurons. Mutation of the Cdk5 phosphorylation site reduces the morphological and migratory phenotypic consequences of Neurabin-I overexpression both in vitro and in vivo, demonstrating that Cdk5-mediated phosphorylation regulates Neurabin-I function in the actin cytoskeleton during corticogenesis.\",\n      \"method\": \"In vitro kinase assay (Cdk5 phosphorylation), phosphorylation-site mutagenesis, antisense/overexpression in primary cortical neurons and in utero electroporation (in vivo), F-actin co-sedimentation, Rac1 activity assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct in vitro kinase assay, phosphosite mutagenesis with rescue experiment, and in vivo validation via electroporation, multiple orthogonal methods\",\n      \"pmids\": [\"17699587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Neurabin I is a direct binding partner of Rac3 (a neuronal Rho-family GTPase), identified by yeast two-hybrid. Neurabin I co-partitions and co-localizes with Rac3 at growth cones, and Neurabin I antisense oligonucleotides abolish Rac3-induced neuritogenesis, which is rescued by exogenous Neurabin I but not by a Neurabin I mutant lacking the Rac3-binding domain, establishing Neurabin I as a required mediator of Rac3-induced neuritogenesis by anchoring Rac3 to growth cone F-actin.\",\n      \"method\": \"Yeast two-hybrid, biochemical co-fractionation, co-localization by light microscopy, antisense knockdown, domain-deletion rescue experiments in primary neurons\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — yeast two-hybrid plus antisense/rescue experiments in neurons with domain-deletion mutant, two orthogonal approaches but no in vitro reconstitution of direct binding\",\n      \"pmids\": [\"16525025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Bau, a splice form of Neurabin-I lacking actin- and p70S6K-binding domains but retaining coiled-coil domains, interacts with the tumor suppressor Bin1 (interaction requires the U3 region alternately spliced in muscle cells), localizes to the nucleus and cytosol, and suppresses oncogene-mediated transformation and inhibits tumor cell growth.\",\n      \"method\": \"Protein interaction screen (Bin1-based), domain-deletion analysis, subcellular localization, transformation suppression assay\",\n      \"journal\": \"Cell adhesion and communication\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, interaction identified by interaction screen without reciprocal Co-IP or in vitro reconstitution; functional assay is single-method\",\n      \"pmids\": [\"10427963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Neurabin-I is atypically hyper-N-glycosylated at ASN1277, rendering it immunogenic and enabling it to act as a B-cell receptor autoantigen in primary CNS lymphoma (PCNSL); this modified neurabin-I induces BCR pathway activation and proliferation of lymphoma cell lines transfected with neurabin-I-reactive BCRs, and a BCR-binding epitope of neurabin-I conjugated to Pseudomonas exotoxin killed lymphoma cells expressing the respective BCRs.\",\n      \"method\": \"Identification of N-glycosylation site (ASN1277) by mass spectrometry/sequencing, BCR transfection into lymphoma cell lines, BCR signaling and proliferation assays, immunotoxin cytotoxicity assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — post-translational modification identified and functionally validated in transfected cell lines with multiple functional readouts, single lab\",\n      \"pmids\": [\"30249786\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Neurabin-I (PPP1R9A) is a neuronal F-actin-binding scaffold that recruits and inhibits protein phosphatase 1 (preferentially PP1γ1 > PP1α > PP1β) via its KIKF docking motif; PKA phosphorylation at Ser-461 and Cdk5 phosphorylation regulate its PP1-binding and F-actin association, respectively, thereby controlling actin cytoskeletal dynamics, dendritic spine morphology, and cortical neuron migration; it also mediates Rac3-induced neuritogenesis by anchoring Rac3 to growth cone F-actin, and a splice variant (Bau) interacts with the tumor suppressor Bin1 in the nucleus/cytosol.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Neurabin-I (PPP1R9A) is a neuronal F-actin-binding scaffold that couples protein phosphatase 1 (PP1) to the actin cytoskeleton to control actin rearrangement, neuronal morphology, and cortical neuron migration [#0, #3]. It localizes to the actin cytoskeleton via an N-terminal F-actin-binding domain and recruits active PP1 through a (457)KIKF(460) docking motif; this complex drives stress-fiber disassembly and filopodium extension, whereas disrupting the KIKF motif or inhibiting PP1 restores stress fibers [#0]. Neurabin-I binds and inhibits PP1 with nanomolar affinity and shows isoform selectivity (PP1\\u03b31 > PP1\\u03b1 > PP1\\u03b2), with flanking and PP1 C-terminal sequences setting the hierarchy that is confirmed in PP1\\u03b3-null mouse brain [#1, #2]. Its activity is gated by phosphorylation: PKA phosphorylation at Ser-461 sharply reduces PP1 binding, providing cAMP-dependent control of PP1 localization, while Cdk5 phosphorylation regulates F-actin association and governs neurite outgrowth, Rac1 activation, and radial migration during corticogenesis [#1, #3]. Neurabin-I also serves as a direct Rac3 partner required for Rac3-induced neuritogenesis by anchoring Rac3 to growth-cone F-actin [#4]. A splice variant (Bau) lacking actin-binding domains interacts with the tumor suppressor Bin1 and suppresses transformation [#5], and atypical hyper-N-glycosylation of neurabin-I renders it a B-cell receptor autoantigen in primary CNS lymphoma [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing that neurabin-I is a high-affinity PP1 inhibitor whose binding is controlled by phosphorylation answered how a scaffold could both target and modulate phosphatase activity.\",\n      \"evidence\": \"GST pulldown, yeast two-hybrid, in vitro PP1 activity assay, HPLC-MS phosphosite mapping, and S461E phosphomimetic mutagenesis\",\n      \"pmids\": [\"10504266\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish the cellular consequences of Ser-461 phosphorylation in neurons\", \"Upstream signals activating PKA toward this site not defined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of the Bau splice variant binding Bin1 raised the possibility of a nuclear/cytosolic, actin-independent role distinct from the canonical PP1 scaffold function.\",\n      \"evidence\": \"Bin1 interaction screen, domain-deletion analysis, subcellular localization, and transformation suppression assay\",\n      \"pmids\": [\"10427963\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single lab without reciprocal Co-IP or in vitro reconstitution of the Bin1 interaction\", \"Functional tumor-suppression assay was single-method\", \"Mechanism linking Bin1 binding to growth suppression unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Live imaging and mutational dissection tied the neurabin-I/PP1 complex directly to actin dynamics, showing the KIKF docking motif is required to convert stress fibers into filopodia.\",\n      \"evidence\": \"GFP-fusion live imaging, deletion/point mutants, immune-complex phosphatase assays, and PP1 pharmacological inhibition in Cos7, HEK293, and hippocampal neurons\",\n      \"pmids\": [\"12052877\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PP1 substrates downstream of the complex that drive actin remodeling not identified\", \"Role of dimerization domains in vivo not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defining PP1 isoform selectivity (PP1\\u03b31 > PP1\\u03b1 > PP1\\u03b2) clarified which phosphatase holoenzymes neurabin-I assembles, and the determinants encoding that hierarchy.\",\n      \"evidence\": \"Reciprocal immunoprecipitation from rat brain and PP1\\u03b3-null mouse brain, recombinant peptide binding, and chimeric neurabin/PP1 analysis\",\n      \"pmids\": [\"12016225\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of isoform preference for specific substrates not defined\", \"Whether selectivity differs across neuronal compartments unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying Rac3 as a direct partner showed neurabin-I links a Rho-family GTPase to growth-cone F-actin, making it a required mediator of neuritogenesis.\",\n      \"evidence\": \"Yeast two-hybrid, co-fractionation, co-localization, and antisense knockdown with domain-deletion rescue in primary neurons\",\n      \"pmids\": [\"16525025\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution confirming direct Rac3 binding\", \"Relationship between Rac3 anchoring and the PP1 scaffold function unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating Cdk5 phosphorylation of neurabin-I controls F-actin association placed the protein within corticogenesis, linking a kinase to neuronal migration and morphology.\",\n      \"evidence\": \"In vitro Cdk5 kinase assay, phosphosite mutagenesis with rescue, in utero electroporation, F-actin co-sedimentation, and Rac1 activity assay\",\n      \"pmids\": [\"17699587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact Cdk5 phosphosite residue(s) and their interplay with PKA/Ser-461 not integrated\", \"Mechanistic link between F-actin binding and Rac1 activation incomplete\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that hyper-N-glycosylated neurabin-I acts as a BCR autoantigen extended its relevance beyond neuronal cytoskeletal biology into CNS lymphoma immunopathology.\",\n      \"evidence\": \"Mass-spectrometric N-glycosylation site mapping (ASN1277), BCR transfection into lymphoma lines, BCR signaling/proliferation assays, and immunotoxin cytotoxicity assay\",\n      \"pmids\": [\"30249786\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; in vivo relevance of the autoantigen mechanism not established\", \"How the neuronal scaffold becomes hyper-glycosylated and exposed to BCRs unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple regulatory inputs (PKA at Ser-461, Cdk5, Rac3/Rac1) are integrated to coordinate PP1 targeting with actin remodeling in defined neuronal compartments remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of combinatorial phosphoregulation\", \"PP1 substrates that effect actin changes downstream of the complex not identified\", \"Structural basis of simultaneous F-actin, PP1, and Rac3 engagement unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 3]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PP1\", \"PPP1CC\", \"PPP1CA\", \"RAC3\", \"BIN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}