{"gene":"GRIPAP1","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2000,"finding":"GRASP-1 (GRIPAP1) is a neuronal RasGEF that physically associates with the AMPA receptor/GRIP complex in vivo, and overexpression of GRASP-1 in cultured neurons specifically reduces the synaptic targeting of AMPA receptors. Subcellular distribution of both AMPA receptors and GRASP-1 is rapidly regulated by NMDA receptor activation.","method":"Co-immunoprecipitation, overexpression in cultured neurons, subcellular fractionation, immunostaining","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP and neuronal overexpression with defined receptor trafficking phenotype, foundational paper with 127 citations","pmids":["10896157"],"is_preprint":false},{"year":2002,"finding":"GRASP-1 is a substrate of caspase-3; cleavage separates the N-terminal RasGEF catalytic domain from the C-terminal GRIP-interacting region, potentially disrupting regulation of RasGEF activity by GRIP. Cleavage occurs in specific brain regions during postnatal development and ischemia.","method":"Cleavage site-specific antibody (CGP), Western blotting, in vivo ischemia model","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo demonstration with site-specific antibody, single lab","pmids":["12207967"],"is_preprint":false},{"year":2007,"finding":"GRASP-1 acts as a scaffold protein for the JNK signaling pathway by binding both JNK and the upstream activator MEKK-1, thereby potently activating JNK but not ERK signaling. Mutations preventing caspase-3 cleavage of GRASP-1 dramatically inhibit its JNK pathway-activating activity, linking caspase-3 activation to JNK signaling.","method":"Co-immunoprecipitation, overexpression/mutagenesis, JNK/ERK activity assays","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — binding partners identified by Co-IP and functional pathway activity measured with mutagenesis, single lab","pmids":["17761173"],"is_preprint":false},{"year":2010,"finding":"GRASP-1 is a neuron-specific effector of Rab4 that coordinates recycling endosome maturation in dendrites. GRASP-1 segregates Rab4 from EEA1/Neep21/Rab5-positive early endosomal membranes and coordinates coupling to Rab11-labeled recycling endosomes by interacting with the endosomal SNARE syntaxin 13. GRASP-1 is necessary for AMPA receptor recycling, maintenance of spine morphology, and synaptic plasticity.","method":"Co-immunoprecipitation, live imaging, electron microscopy, shRNA knockdown, immunofluorescence co-localization, spine morphology and LTP assays","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, imaging, EM, KD with defined cellular phenotypes), 89 citations, strong mechanistic resolution","pmids":["20098723"],"is_preprint":false},{"year":2012,"finding":"In the spinal cord, SGK1 phosphorylation triggers a GRASP-1/Rab4 cascade that drives GluR1-containing AMPAR recycling to the dorsal horn membrane during inflammatory pain. Coprecipitation demonstrated physical interactions among pSGK1-GRASP-1, GRASP-1-Rab4, and Rab4-GluR1 in hyperalgesic rats, and siRNA targeting Rab4 blocked GluR1 trafficking and pain behavior.","method":"Co-immunoprecipitation, Western blotting, siRNA knockdown, pharmacological inhibition (SGK1 antagonist, AMPAR antagonist), behavioral assays","journal":"Pain","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis established via inhibitors and siRNA with defined behavioral and biochemical phenotypes, single lab","pmids":["22980744"],"is_preprint":false},{"year":2011,"finding":"Prenatal cocaine exposure increases PKC- and Src-mediated phosphorylation of GRIP, which enhances synaptic localization of GRASP-1 and reduces its RasGEF activity by ~40%, while activating RhoA, cdc42/Rac1, and Rap1 small GTPases and increasing F-actin levels.","method":"Co-immunoprecipitation, subcellular fractionation, RasGEF activity assay, Western blotting in rat model","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo model with enzymatic activity measured and protein interactions assessed, single lab","pmids":["21980374"],"is_preprint":false},{"year":2017,"finding":"GRASP1 is required for learning-induced synaptic AMPAR incorporation and spine maintenance in vivo. Mice lacking GRASP1 show abnormal excitatory synapse number, synaptic plasticity, and hippocampal-dependent learning. Two GRASP1 point mutations from intellectual disability patients disrupt AMPAR recycling and glutamate uncaging-induced structural and functional plasticity, and wild-type but not mutant GRASP1 rescues spine loss in CA1 neurons of knockout mice.","method":"Knockout mouse, point mutants from human ID patients, electrophysiology (LTP), two-photon uncaging, spine morphology analysis, surface biotinylation of AMPARs","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — KO with defined plasticity/behavioral phenotypes, human disease mutations tested, multiple orthogonal methods, 52 citations","pmids":["28285821"],"is_preprint":false},{"year":2017,"finding":"CPEB2 enhances translation of GRASP1 mRNA, thereby facilitating recycling and maintenance of surface AMPA receptor levels. Ectopic expression of GRASP1 in CPEB2 cKO hippocampi rescued LTP and spatial memory, placing GRASP1 downstream of CPEB2-mediated translational control in synaptic plasticity.","method":"Conditional knockout mouse, polysome fractionation/translation assay, surface AMPAR biotinylation, electrophysiology (LTP), behavioral assays, in vivo viral rescue","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis via KO and rescue, translational assay, electrophysiology, and behavior, moderate evidence","pmids":["29141213"],"is_preprint":false},{"year":2021,"finding":"GRASP1 is regulated by ubiquitin-dependent proteasomal degradation via K48-linked polyubiquitin chains. Overexpression of ubiquitin reduces GRASP1 protein levels and decreases surface GluA1 AMPAR subunits and mEPSC amplitude in hippocampal neurons; these effects are reversed by co-expression of GRASP1.","method":"Co-transfection in HEK293T cells and hippocampal neurons, ubiquitin mutant (K48R), Western blotting, surface biotinylation, whole-cell patch-clamp (mEPSC recording)","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — ubiquitin mutant and rescue experiments in neurons with electrophysiological readout, single lab","pmids":["34245609"],"is_preprint":false},{"year":2025,"finding":"The E3 ubiquitin ligase UBE3A polyubiquitinates GRASP1 (GRIPAP1) to regulate its protein turnover; loss of UBE3A in human iPSC-derived cortical neurons leads to increased GRASP1 abundance, implicating this pathway in impaired activity-dependent synaptic plasticity in Angelman syndrome.","method":"UBE3A knockout in human iPSC-derived cortical neurons, LC-MS/MS proteomics, ubiquitination assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — proteomic identification plus biochemical ubiquitination assay in human neuronal model, single lab","pmids":["40671377"],"is_preprint":false},{"year":2026,"finding":"GRIPAP1 functions as an endosomal tethering factor in megakaryocytes, binding GTP-loaded Rab4a to recruit endosomal compartments and facilitating trafficking of endocytosed fibrinogen and newly synthesized PF4 to platelet α-granules. GRIPAP1 forms an elongated homodimer biochemically consistent with membrane tethering factors, and artificial mislocalization of GRIPAP1 to mitochondria was sufficient to redirect Rab4a compartments containing internalized transferrin and PF4 to mitochondria. GRIPAP1 deficiency reduces α-granule numbers and cargo levels.","method":"GRIPAP1-deficient megakaryocytes, GTP-loading pulldown (Rab4a binding assay), live imaging, artificial mitochondrial mislocalization, electron microscopy, biochemical analysis (homodimerization)","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods including reconstitution-style mislocalization rescue, KO phenotype, and biochemical characterization of homodimer structure with functional validation","pmids":["41632639"],"is_preprint":false}],"current_model":"GRIPAP1/GRASP-1 is a multifunctional neuronal and ubiquitous scaffold protein that acts as a neuron-specific Rab4 effector and endosomal tethering factor, bridging early (Rab4/Rab5) and recycling (Rab11) endosomal compartments via interaction with syntaxin 13 to drive AMPA receptor recycling and synaptic plasticity; it also contains a RasGEF domain that activates Ras signaling and scaffolds the JNK pathway via MEKK-1/JNK binding, is cleaved by caspase-3 to modulate these activities, and is subject to K48-linked ubiquitin-dependent proteasomal degradation regulated by UBE3A; in non-neuronal megakaryocytes it functions as an elongated homodimeric tethering factor that binds GTP-Rab4a to direct endosomal cargo toward platelet α-granule biogenesis."},"narrative":{"teleology":[{"year":2000,"claim":"Identifying GRIPAP1 as a neuronal RasGEF that associates with the AMPA receptor/GRIP complex established its entry point into receptor trafficking and synaptic function.","evidence":"Co-immunoprecipitation and overexpression in cultured neurons showing reduced synaptic AMPAR targeting","pmids":["10896157"],"confidence":"High","gaps":["RasGEF substrate specificity not fully defined","mechanism by which GRASP-1 overexpression reduces synaptic AMPARs unclear","whether GRASP-1 acts catalytically or as a scaffold not resolved"]},{"year":2002,"claim":"Demonstrating caspase-3 cleavage of GRASP-1 revealed a post-translational mechanism that separates its RasGEF and GRIP-binding domains, with relevance to development and ischemia.","evidence":"Cleavage site-specific antibody and Western blotting in brain tissue and ischemia model","pmids":["12207967"],"confidence":"Medium","gaps":["functional consequences of cleavage on receptor trafficking not directly tested","in vivo cleavage quantification limited to select brain regions"]},{"year":2007,"claim":"Showing that GRASP-1 scaffolds MEKK-1 and JNK to activate the JNK pathway, and that caspase-3 cleavage potentiates this activity, linked its proteolytic processing to a specific signaling output.","evidence":"Co-immunoprecipitation, mutagenesis of caspase site, JNK/ERK activity assays in overexpression system","pmids":["17761173"],"confidence":"Medium","gaps":["JNK scaffolding demonstrated only by overexpression, not in loss-of-function","physiological context for caspase-3-dependent JNK activation in neurons not established"]},{"year":2010,"claim":"Identifying GRASP-1 as a neuron-specific Rab4 effector that tethers early-to-recycling endosome transitions via syntaxin 13 transformed its mechanistic identity from a signaling scaffold to an endosomal tethering factor essential for AMPAR recycling and synaptic plasticity.","evidence":"Live imaging, electron microscopy, shRNA knockdown, co-immunoprecipitation, LTP and spine morphology assays in cultured neurons","pmids":["20098723"],"confidence":"High","gaps":["structural basis of Rab4 binding and syntaxin 13 interaction not resolved","whether RasGEF activity is required for tethering function unclear"]},{"year":2011,"claim":"Prenatal cocaine exposure modulated GRASP-1 synaptic localization and reduced its RasGEF activity via GRIP phosphorylation, linking external stimuli to GRASP-1 regulation of small GTPases.","evidence":"Subcellular fractionation, RasGEF activity assay, and co-immunoprecipitation in rat brain","pmids":["21980374"],"confidence":"Medium","gaps":["causal relationship between reduced RasGEF activity and downstream GTPase changes not established","single model system"]},{"year":2012,"claim":"Placing GRASP-1 downstream of SGK1 phosphorylation in a spinal cord Rab4-dependent AMPAR recycling cascade extended its trafficking role beyond hippocampal synapses to inflammatory pain signaling.","evidence":"Co-immunoprecipitation, siRNA knockdown of Rab4, pharmacological inhibition, behavioral pain assays in rats","pmids":["22980744"],"confidence":"Medium","gaps":["direct phosphorylation of GRASP-1 by SGK1 not demonstrated","specificity of the cascade to pain circuits versus general AMPAR trafficking not resolved"]},{"year":2017,"claim":"Knockout mice and human intellectual disability mutations established that GRASP-1 is required in vivo for learning-induced AMPAR incorporation, spine maintenance, and synaptic plasticity, and that disease-associated point mutations are loss-of-function for these processes.","evidence":"GRASP1 knockout mouse, human ID patient point mutants, electrophysiology, two-photon uncaging, rescue experiments in CA1 neurons","pmids":["28285821"],"confidence":"High","gaps":["molecular basis by which specific point mutations disrupt function not structurally defined","whether JNK scaffolding contributes to the in vivo phenotype not addressed"]},{"year":2017,"claim":"Demonstrating that CPEB2 translationally controls GRASP1 mRNA and that GRASP1 re-expression rescues LTP and memory in CPEB2 knockouts placed GRASP1 as a key effector of translational regulation of plasticity.","evidence":"Conditional knockout mouse, polysome fractionation, in vivo viral rescue, electrophysiology, behavioral assays","pmids":["29141213"],"confidence":"High","gaps":["whether CPEB2 regulation of GRASP1 is activity-dependent not fully resolved","other translationally regulated targets of CPEB2 may contribute to phenotype"]},{"year":2021,"claim":"Identifying K48-linked polyubiquitination as a mechanism for GRASP1 proteasomal degradation that regulates surface AMPAR levels and synaptic transmission established ubiquitin-dependent control of its abundance.","evidence":"Ubiquitin mutant (K48R) co-transfection, surface biotinylation, mEPSC recordings in hippocampal neurons","pmids":["34245609"],"confidence":"Medium","gaps":["E3 ligase responsible not identified in this study","ubiquitination sites on GRASP1 not mapped"]},{"year":2025,"claim":"Identifying UBE3A as the E3 ligase that polyubiquitinates GRASP1 linked its degradation pathway to Angelman syndrome, where UBE3A loss leads to GRASP1 accumulation and impaired activity-dependent plasticity.","evidence":"UBE3A knockout in human iPSC-derived cortical neurons, LC-MS/MS proteomics, ubiquitination assay","pmids":["40671377"],"confidence":"Medium","gaps":["whether GRASP1 accumulation is causally sufficient for Angelman syndrome plasticity deficits not tested by rescue","ubiquitination sites not mapped"]},{"year":2026,"claim":"Characterizing GRIPAP1 as an elongated homodimeric endosomal tethering factor in megakaryocytes that binds GTP-Rab4a and directs cargo to α-granules demonstrated a non-neuronal tethering function and provided the first structural-level insight into its mechanism.","evidence":"GRIPAP1-deficient megakaryocytes, GTP-loading Rab4a pulldown, artificial mitochondrial mislocalization, electron microscopy, biochemical homodimerization analysis","pmids":["41632639"],"confidence":"High","gaps":["atomic-resolution structure of the homodimer not determined","whether the tethering mechanism is identical in neurons not directly tested","relationship between RasGEF domain and tethering function remains unclear"]},{"year":null,"claim":"The structural basis of GRIPAP1's dual function as a RasGEF and endosomal tethering factor, and whether these activities are mechanistically linked or independently regulated, remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["no atomic-resolution structure of full-length GRIPAP1 or its complexes","catalytic activity of the RasGEF domain toward specific Ras-family substrates not definitively assigned","whether JNK scaffolding occurs on endosomal membranes or in the cytosol is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,3,5]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,5]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3,10]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[3,10]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,5]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,10]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[0,3,6]}],"complexes":[],"partners":["GRIP1","RAB4A","STX13","JNK","MAP3K1","UBE3A","CPEB2"],"other_free_text":[]},"mechanistic_narrative":"GRIPAP1 (GRASP-1) is a Rab4-binding endosomal tethering factor and scaffold protein that coordinates recycling endosome maturation and membrane cargo trafficking in neurons and megakaryocytes. In dendrites, GRIPAP1 segregates Rab4 from Rab5/EEA1-positive early endosomes and couples them to Rab11-positive recycling endosomes via interaction with syntaxin 13, thereby driving AMPA receptor recycling to the postsynaptic surface, maintaining dendritic spine morphology, and enabling long-term potentiation and hippocampal-dependent learning [PMID:20098723, PMID:28285821, PMID:29141213]. GRIPAP1 also contains a RasGEF domain that activates Ras signaling and scaffolds the JNK pathway by binding MEKK-1 and JNK, with caspase-3 cleavage separating the RasGEF and GRIP-binding domains to modulate these activities [PMID:10896157, PMID:12207967, PMID:17761173]. GRIPAP1 protein turnover is regulated by K48-linked polyubiquitination mediated by the E3 ligase UBE3A, linking its abundance to activity-dependent plasticity and Angelman syndrome pathogenesis [PMID:34245609, PMID:40671377]. Point mutations in GRIPAP1 identified in intellectual disability patients disrupt AMPA receptor recycling and structural plasticity, establishing GRIPAP1 as a causative gene for intellectual disability [PMID:28285821]."},"prefetch_data":{"uniprot":{"accession":"Q4V328","full_name":"GRIP1-associated protein 1","aliases":[],"length_aa":841,"mass_kda":96.0,"function":"Regulates the endosomal recycling back to the neuronal plasma membrane, possibly by connecting early and late recycling endosomal domains and promoting segregation of recycling endosomes from early endosomal membranes. Involved in the localization of recycling endosomes to dendritic spines, thereby playing a role in the maintenance of dendritic spine morphology. Required for the activity-induced AMPA receptor recycling to dendrite membranes and for long-term potentiation and synaptic plasticity (By similarity) Functions as a scaffold protein to facilitate MAP3K1/MEKK1-mediated activation of the JNK1 kinase by phosphorylation, possibly by bringing MAP3K1/MEKK1 and JNK1 in close proximity","subcellular_location":"Early endosome membrane; Recycling endosome membrane; Cell projection, axon; Cell projection, dendrite; Synapse","url":"https://www.uniprot.org/uniprotkb/Q4V328/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GRIPAP1","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":[],"url":"https://opencell.sf.czbiohub.org/search/GRIPAP1","total_profiled":1310},"omim":[{"mim_id":"300408","title":"GRIP1-ASSOCIATED PROTEIN 1; GRIPAP1","url":"https://www.omim.org/entry/300408"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/GRIPAP1"},"hgnc":{"alias_symbol":["GRASP-1","GRASP1","KIAA1167","MPMGp800B12492Q3","DKFZp434P0630"],"prev_symbol":[]},"alphafold":{"accession":"Q4V328","domains":[{"cath_id":"1.20.5","chopping":"9-58","consensus_level":"medium","plddt":93.3248,"start":9,"end":58}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4V328","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q4V328-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q4V328-F1-predicted_aligned_error_v6.png","plddt_mean":78.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GRIPAP1","jax_strain_url":"https://www.jax.org/strain/search?query=GRIPAP1"},"sequence":{"accession":"Q4V328","fasta_url":"https://rest.uniprot.org/uniprotkb/Q4V328.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q4V328/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q4V328"}},"corpus_meta":[{"pmid":"10896157","id":"PMC_10896157","title":"GRASP-1: a neuronal RasGEF associated with the AMPA receptor/GRIP complex.","date":"2000","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/10896157","citation_count":127,"is_preprint":false},{"pmid":"20098723","id":"PMC_20098723","title":"Neuron specific Rab4 effector GRASP-1 coordinates membrane specialization and maturation of recycling endosomes.","date":"2010","source":"PLoS biology","url":"https://pubmed.ncbi.nlm.nih.gov/20098723","citation_count":89,"is_preprint":false},{"pmid":"28285821","id":"PMC_28285821","title":"GRASP1 Regulates Synaptic Plasticity and Learning through Endosomal Recycling of AMPA Receptors.","date":"2017","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/28285821","citation_count":52,"is_preprint":false},{"pmid":"22980744","id":"PMC_22980744","title":"Spinal SGK1/GRASP-1/Rab4 is involved in complete Freund's adjuvant-induced inflammatory pain via regulating dorsal horn GluR1-containing AMPA receptor trafficking in rats.","date":"2012","source":"Pain","url":"https://pubmed.ncbi.nlm.nih.gov/22980744","citation_count":41,"is_preprint":false},{"pmid":"29141213","id":"PMC_29141213","title":"CPEB2 Activates GRASP1 mRNA Translation and Promotes AMPA Receptor Surface Expression, Long-Term Potentiation, and Memory.","date":"2017","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/29141213","citation_count":31,"is_preprint":false},{"pmid":"21057633","id":"PMC_21057633","title":"GRASP-1 regulates endocytic receptor recycling and synaptic plasticity.","date":"2010","source":"Communicative & integrative biology","url":"https://pubmed.ncbi.nlm.nih.gov/21057633","citation_count":15,"is_preprint":false},{"pmid":"17761173","id":"PMC_17761173","title":"GRASP-1 is a neuronal scaffold protein for the JNK signaling pathway.","date":"2007","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/17761173","citation_count":14,"is_preprint":false},{"pmid":"12207967","id":"PMC_12207967","title":"Physiological and pathological caspase cleavage of the neuronal RasGEF GRASP-1 as detected using a cleavage site-specific antibody.","date":"2002","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/12207967","citation_count":13,"is_preprint":false},{"pmid":"21980374","id":"PMC_21980374","title":"Prenatal cocaine exposure increases synaptic localization of a neuronal RasGEF, GRASP-1 via hyperphosphorylation of AMPAR anchoring protein, GRIP.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21980374","citation_count":12,"is_preprint":false},{"pmid":"15897011","id":"PMC_15897011","title":"Identification of GRASP-1 as a novel 97 kDa autoantigen localized to endosomes.","date":"2005","source":"Clinical immunology (Orlando, Fla.)","url":"https://pubmed.ncbi.nlm.nih.gov/15897011","citation_count":11,"is_preprint":false},{"pmid":"34245609","id":"PMC_34245609","title":"GRASP1 ubiquitination regulates AMPA receptor surface expression and synaptic activity in cultured hippocampal neurons.","date":"2021","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/34245609","citation_count":5,"is_preprint":false},{"pmid":"39523115","id":"PMC_39523115","title":"Analysis of Expression of the GRIPAP1, DLG4, KIF1B, NGFRAP1, and NRF1 Genes in Peripheral Blood of the Patients with Parkinson's Disease in the Early Clinical Stages.","date":"2024","source":"Biochemistry. Biokhimiia","url":"https://pubmed.ncbi.nlm.nih.gov/39523115","citation_count":1,"is_preprint":false},{"pmid":"40671377","id":"PMC_40671377","title":"The Ubiquitin E3 Ligase UBE3A Regulates GRIPAP1 and PACSIN1 Proteins Linked to the Endocytic Recycling of AMPA Receptors.","date":"2025","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/40671377","citation_count":1,"is_preprint":false},{"pmid":"41632639","id":"PMC_41632639","title":"GRIPAP1 is an endosomal tethering factor mediating platelet α-granule biogenesis.","date":"2026","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/41632639","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.16.682426","title":"Beyond the Genotype: A Multi-Omic Analysis of APOEe4’s Role in Alzheimer’s Disease","date":"2025-10-16","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.16.682426","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8710,"output_tokens":2987,"usd":0.035467},"stage2":{"model":"claude-opus-4-6","input_tokens":6326,"output_tokens":2917,"usd":0.156833},"total_usd":0.1923,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"GRASP-1 (GRIPAP1) is a neuronal RasGEF that physically associates with the AMPA receptor/GRIP complex in vivo, and overexpression of GRASP-1 in cultured neurons specifically reduces the synaptic targeting of AMPA receptors. Subcellular distribution of both AMPA receptors and GRASP-1 is rapidly regulated by NMDA receptor activation.\",\n      \"method\": \"Co-immunoprecipitation, overexpression in cultured neurons, subcellular fractionation, immunostaining\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP and neuronal overexpression with defined receptor trafficking phenotype, foundational paper with 127 citations\",\n      \"pmids\": [\"10896157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GRASP-1 is a substrate of caspase-3; cleavage separates the N-terminal RasGEF catalytic domain from the C-terminal GRIP-interacting region, potentially disrupting regulation of RasGEF activity by GRIP. Cleavage occurs in specific brain regions during postnatal development and ischemia.\",\n      \"method\": \"Cleavage site-specific antibody (CGP), Western blotting, in vivo ischemia model\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo demonstration with site-specific antibody, single lab\",\n      \"pmids\": [\"12207967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GRASP-1 acts as a scaffold protein for the JNK signaling pathway by binding both JNK and the upstream activator MEKK-1, thereby potently activating JNK but not ERK signaling. Mutations preventing caspase-3 cleavage of GRASP-1 dramatically inhibit its JNK pathway-activating activity, linking caspase-3 activation to JNK signaling.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/mutagenesis, JNK/ERK activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — binding partners identified by Co-IP and functional pathway activity measured with mutagenesis, single lab\",\n      \"pmids\": [\"17761173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"GRASP-1 is a neuron-specific effector of Rab4 that coordinates recycling endosome maturation in dendrites. GRASP-1 segregates Rab4 from EEA1/Neep21/Rab5-positive early endosomal membranes and coordinates coupling to Rab11-labeled recycling endosomes by interacting with the endosomal SNARE syntaxin 13. GRASP-1 is necessary for AMPA receptor recycling, maintenance of spine morphology, and synaptic plasticity.\",\n      \"method\": \"Co-immunoprecipitation, live imaging, electron microscopy, shRNA knockdown, immunofluorescence co-localization, spine morphology and LTP assays\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, imaging, EM, KD with defined cellular phenotypes), 89 citations, strong mechanistic resolution\",\n      \"pmids\": [\"20098723\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In the spinal cord, SGK1 phosphorylation triggers a GRASP-1/Rab4 cascade that drives GluR1-containing AMPAR recycling to the dorsal horn membrane during inflammatory pain. Coprecipitation demonstrated physical interactions among pSGK1-GRASP-1, GRASP-1-Rab4, and Rab4-GluR1 in hyperalgesic rats, and siRNA targeting Rab4 blocked GluR1 trafficking and pain behavior.\",\n      \"method\": \"Co-immunoprecipitation, Western blotting, siRNA knockdown, pharmacological inhibition (SGK1 antagonist, AMPAR antagonist), behavioral assays\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established via inhibitors and siRNA with defined behavioral and biochemical phenotypes, single lab\",\n      \"pmids\": [\"22980744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Prenatal cocaine exposure increases PKC- and Src-mediated phosphorylation of GRIP, which enhances synaptic localization of GRASP-1 and reduces its RasGEF activity by ~40%, while activating RhoA, cdc42/Rac1, and Rap1 small GTPases and increasing F-actin levels.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, RasGEF activity assay, Western blotting in rat model\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo model with enzymatic activity measured and protein interactions assessed, single lab\",\n      \"pmids\": [\"21980374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GRASP1 is required for learning-induced synaptic AMPAR incorporation and spine maintenance in vivo. Mice lacking GRASP1 show abnormal excitatory synapse number, synaptic plasticity, and hippocampal-dependent learning. Two GRASP1 point mutations from intellectual disability patients disrupt AMPAR recycling and glutamate uncaging-induced structural and functional plasticity, and wild-type but not mutant GRASP1 rescues spine loss in CA1 neurons of knockout mice.\",\n      \"method\": \"Knockout mouse, point mutants from human ID patients, electrophysiology (LTP), two-photon uncaging, spine morphology analysis, surface biotinylation of AMPARs\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — KO with defined plasticity/behavioral phenotypes, human disease mutations tested, multiple orthogonal methods, 52 citations\",\n      \"pmids\": [\"28285821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CPEB2 enhances translation of GRASP1 mRNA, thereby facilitating recycling and maintenance of surface AMPA receptor levels. Ectopic expression of GRASP1 in CPEB2 cKO hippocampi rescued LTP and spatial memory, placing GRASP1 downstream of CPEB2-mediated translational control in synaptic plasticity.\",\n      \"method\": \"Conditional knockout mouse, polysome fractionation/translation assay, surface AMPAR biotinylation, electrophysiology (LTP), behavioral assays, in vivo viral rescue\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via KO and rescue, translational assay, electrophysiology, and behavior, moderate evidence\",\n      \"pmids\": [\"29141213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GRASP1 is regulated by ubiquitin-dependent proteasomal degradation via K48-linked polyubiquitin chains. Overexpression of ubiquitin reduces GRASP1 protein levels and decreases surface GluA1 AMPAR subunits and mEPSC amplitude in hippocampal neurons; these effects are reversed by co-expression of GRASP1.\",\n      \"method\": \"Co-transfection in HEK293T cells and hippocampal neurons, ubiquitin mutant (K48R), Western blotting, surface biotinylation, whole-cell patch-clamp (mEPSC recording)\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ubiquitin mutant and rescue experiments in neurons with electrophysiological readout, single lab\",\n      \"pmids\": [\"34245609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The E3 ubiquitin ligase UBE3A polyubiquitinates GRASP1 (GRIPAP1) to regulate its protein turnover; loss of UBE3A in human iPSC-derived cortical neurons leads to increased GRASP1 abundance, implicating this pathway in impaired activity-dependent synaptic plasticity in Angelman syndrome.\",\n      \"method\": \"UBE3A knockout in human iPSC-derived cortical neurons, LC-MS/MS proteomics, ubiquitination assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — proteomic identification plus biochemical ubiquitination assay in human neuronal model, single lab\",\n      \"pmids\": [\"40671377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GRIPAP1 functions as an endosomal tethering factor in megakaryocytes, binding GTP-loaded Rab4a to recruit endosomal compartments and facilitating trafficking of endocytosed fibrinogen and newly synthesized PF4 to platelet α-granules. GRIPAP1 forms an elongated homodimer biochemically consistent with membrane tethering factors, and artificial mislocalization of GRIPAP1 to mitochondria was sufficient to redirect Rab4a compartments containing internalized transferrin and PF4 to mitochondria. GRIPAP1 deficiency reduces α-granule numbers and cargo levels.\",\n      \"method\": \"GRIPAP1-deficient megakaryocytes, GTP-loading pulldown (Rab4a binding assay), live imaging, artificial mitochondrial mislocalization, electron microscopy, biochemical analysis (homodimerization)\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including reconstitution-style mislocalization rescue, KO phenotype, and biochemical characterization of homodimer structure with functional validation\",\n      \"pmids\": [\"41632639\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GRIPAP1/GRASP-1 is a multifunctional neuronal and ubiquitous scaffold protein that acts as a neuron-specific Rab4 effector and endosomal tethering factor, bridging early (Rab4/Rab5) and recycling (Rab11) endosomal compartments via interaction with syntaxin 13 to drive AMPA receptor recycling and synaptic plasticity; it also contains a RasGEF domain that activates Ras signaling and scaffolds the JNK pathway via MEKK-1/JNK binding, is cleaved by caspase-3 to modulate these activities, and is subject to K48-linked ubiquitin-dependent proteasomal degradation regulated by UBE3A; in non-neuronal megakaryocytes it functions as an elongated homodimeric tethering factor that binds GTP-Rab4a to direct endosomal cargo toward platelet α-granule biogenesis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GRIPAP1 (GRASP-1) is a Rab4-binding endosomal tethering factor and scaffold protein that coordinates recycling endosome maturation and membrane cargo trafficking in neurons and megakaryocytes. In dendrites, GRIPAP1 segregates Rab4 from Rab5/EEA1-positive early endosomes and couples them to Rab11-positive recycling endosomes via interaction with syntaxin 13, thereby driving AMPA receptor recycling to the postsynaptic surface, maintaining dendritic spine morphology, and enabling long-term potentiation and hippocampal-dependent learning [PMID:20098723, PMID:28285821, PMID:29141213]. GRIPAP1 also contains a RasGEF domain that activates Ras signaling and scaffolds the JNK pathway by binding MEKK-1 and JNK, with caspase-3 cleavage separating the RasGEF and GRIP-binding domains to modulate these activities [PMID:10896157, PMID:12207967, PMID:17761173]. GRIPAP1 protein turnover is regulated by K48-linked polyubiquitination mediated by the E3 ligase UBE3A, linking its abundance to activity-dependent plasticity and Angelman syndrome pathogenesis [PMID:34245609, PMID:40671377]. Point mutations in GRIPAP1 identified in intellectual disability patients disrupt AMPA receptor recycling and structural plasticity, establishing GRIPAP1 as a causative gene for intellectual disability [PMID:28285821].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Identifying GRIPAP1 as a neuronal RasGEF that associates with the AMPA receptor/GRIP complex established its entry point into receptor trafficking and synaptic function.\",\n      \"evidence\": \"Co-immunoprecipitation and overexpression in cultured neurons showing reduced synaptic AMPAR targeting\",\n      \"pmids\": [\"10896157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RasGEF substrate specificity not fully defined\", \"mechanism by which GRASP-1 overexpression reduces synaptic AMPARs unclear\", \"whether GRASP-1 acts catalytically or as a scaffold not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Demonstrating caspase-3 cleavage of GRASP-1 revealed a post-translational mechanism that separates its RasGEF and GRIP-binding domains, with relevance to development and ischemia.\",\n      \"evidence\": \"Cleavage site-specific antibody and Western blotting in brain tissue and ischemia model\",\n      \"pmids\": [\"12207967\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"functional consequences of cleavage on receptor trafficking not directly tested\", \"in vivo cleavage quantification limited to select brain regions\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing that GRASP-1 scaffolds MEKK-1 and JNK to activate the JNK pathway, and that caspase-3 cleavage potentiates this activity, linked its proteolytic processing to a specific signaling output.\",\n      \"evidence\": \"Co-immunoprecipitation, mutagenesis of caspase site, JNK/ERK activity assays in overexpression system\",\n      \"pmids\": [\"17761173\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"JNK scaffolding demonstrated only by overexpression, not in loss-of-function\", \"physiological context for caspase-3-dependent JNK activation in neurons not established\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identifying GRASP-1 as a neuron-specific Rab4 effector that tethers early-to-recycling endosome transitions via syntaxin 13 transformed its mechanistic identity from a signaling scaffold to an endosomal tethering factor essential for AMPAR recycling and synaptic plasticity.\",\n      \"evidence\": \"Live imaging, electron microscopy, shRNA knockdown, co-immunoprecipitation, LTP and spine morphology assays in cultured neurons\",\n      \"pmids\": [\"20098723\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"structural basis of Rab4 binding and syntaxin 13 interaction not resolved\", \"whether RasGEF activity is required for tethering function unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Prenatal cocaine exposure modulated GRASP-1 synaptic localization and reduced its RasGEF activity via GRIP phosphorylation, linking external stimuli to GRASP-1 regulation of small GTPases.\",\n      \"evidence\": \"Subcellular fractionation, RasGEF activity assay, and co-immunoprecipitation in rat brain\",\n      \"pmids\": [\"21980374\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"causal relationship between reduced RasGEF activity and downstream GTPase changes not established\", \"single model system\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Placing GRASP-1 downstream of SGK1 phosphorylation in a spinal cord Rab4-dependent AMPAR recycling cascade extended its trafficking role beyond hippocampal synapses to inflammatory pain signaling.\",\n      \"evidence\": \"Co-immunoprecipitation, siRNA knockdown of Rab4, pharmacological inhibition, behavioral pain assays in rats\",\n      \"pmids\": [\"22980744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"direct phosphorylation of GRASP-1 by SGK1 not demonstrated\", \"specificity of the cascade to pain circuits versus general AMPAR trafficking not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Knockout mice and human intellectual disability mutations established that GRASP-1 is required in vivo for learning-induced AMPAR incorporation, spine maintenance, and synaptic plasticity, and that disease-associated point mutations are loss-of-function for these processes.\",\n      \"evidence\": \"GRASP1 knockout mouse, human ID patient point mutants, electrophysiology, two-photon uncaging, rescue experiments in CA1 neurons\",\n      \"pmids\": [\"28285821\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"molecular basis by which specific point mutations disrupt function not structurally defined\", \"whether JNK scaffolding contributes to the in vivo phenotype not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating that CPEB2 translationally controls GRASP1 mRNA and that GRASP1 re-expression rescues LTP and memory in CPEB2 knockouts placed GRASP1 as a key effector of translational regulation of plasticity.\",\n      \"evidence\": \"Conditional knockout mouse, polysome fractionation, in vivo viral rescue, electrophysiology, behavioral assays\",\n      \"pmids\": [\"29141213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"whether CPEB2 regulation of GRASP1 is activity-dependent not fully resolved\", \"other translationally regulated targets of CPEB2 may contribute to phenotype\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying K48-linked polyubiquitination as a mechanism for GRASP1 proteasomal degradation that regulates surface AMPAR levels and synaptic transmission established ubiquitin-dependent control of its abundance.\",\n      \"evidence\": \"Ubiquitin mutant (K48R) co-transfection, surface biotinylation, mEPSC recordings in hippocampal neurons\",\n      \"pmids\": [\"34245609\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"E3 ligase responsible not identified in this study\", \"ubiquitination sites on GRASP1 not mapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identifying UBE3A as the E3 ligase that polyubiquitinates GRASP1 linked its degradation pathway to Angelman syndrome, where UBE3A loss leads to GRASP1 accumulation and impaired activity-dependent plasticity.\",\n      \"evidence\": \"UBE3A knockout in human iPSC-derived cortical neurons, LC-MS/MS proteomics, ubiquitination assay\",\n      \"pmids\": [\"40671377\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"whether GRASP1 accumulation is causally sufficient for Angelman syndrome plasticity deficits not tested by rescue\", \"ubiquitination sites not mapped\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Characterizing GRIPAP1 as an elongated homodimeric endosomal tethering factor in megakaryocytes that binds GTP-Rab4a and directs cargo to α-granules demonstrated a non-neuronal tethering function and provided the first structural-level insight into its mechanism.\",\n      \"evidence\": \"GRIPAP1-deficient megakaryocytes, GTP-loading Rab4a pulldown, artificial mitochondrial mislocalization, electron microscopy, biochemical homodimerization analysis\",\n      \"pmids\": [\"41632639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"atomic-resolution structure of the homodimer not determined\", \"whether the tethering mechanism is identical in neurons not directly tested\", \"relationship between RasGEF domain and tethering function remains unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of GRIPAP1's dual function as a RasGEF and endosomal tethering factor, and whether these activities are mechanistically linked or independently regulated, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"no atomic-resolution structure of full-length GRIPAP1 or its complexes\", \"catalytic activity of the RasGEF domain toward specific Ras-family substrates not definitively assigned\", \"whether JNK scaffolding occurs on endosomal membranes or in the cytosol is unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3, 10]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [3, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 10]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [0, 3, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GRIP1\", \"RAB4A\", \"STX13\", \"JNK\", \"MAP3K1\", \"UBE3A\", \"CPEB2\"],\n    \"other_free_text\": []\n  }\n}\n```"}