{"gene":"ARL4D","run_date":"2026-04-28T17:12:37","timeline":{"discoveries":[{"year":2007,"finding":"ARL4D interacts with the C-terminal pleckstrin homology (PH) and polybasic domains of cytohesin-2/ARNO in a GTP-dependent manner, recruits cytohesin-2/ARNO to the plasma membrane, and thereby activates ARF6 to induce actin stress fiber disassembly and cell migration. Plasma membrane localization of ARL4D requires GTP binding and N-terminal myristoylation.","method":"Co-immunoprecipitation, GTP-dependent binding assays, dominant-active/inactive mutants (Q80L, E156K), siRNA knockdown, GTP-bound ARF6 pull-down assay, cell migration assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (co-IP, mutant analysis, siRNA rescue, GTPase activity assay, migration assay) in a single study with rigorous controls","pmids":["17804820"],"is_preprint":false},{"year":2004,"finding":"GTP-bound ARL4D (Q80L) localizes to the plasma membrane and promotes transport of cargo (transferrin receptor) from endosomes to the plasma membrane, whereas GDP-bound ARL4D (T35N) localizes to endosomes and causes retention of transferrin receptors in the endosomal compartment.","method":"Immunocytochemistry with GTPase mutants (Q80L active form, T35N inactive form), transferrin receptor localization assay","journal":"Cellular and molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, single method (immunocytochemistry with mutants), moderate mechanistic detail","pmids":["15049518"],"is_preprint":false},{"year":2009,"finding":"Arl4D acts upstream of cytohesin-2 and ARF6 to promote neurite outgrowth; a cell-permeable peptide encoding the cytohesin-2-binding region of Arl4D blocks VPA-induced neurite outgrowth, and constitutively active Arl4D is sufficient to induce outgrowth.","method":"siRNA knockdown of Arl4D, constitutively active Arl4D overexpression, cell-permeable peptide competition, SecinH3 inhibitor, siRNA knockdown of ARF6 vs ARF1","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal approaches (KD, OE, peptide competition, isoform-specific knockdown) but from a single lab","pmids":["19327349"],"is_preprint":false},{"year":2012,"finding":"GTP-binding-defective ARL4D (T35N) localizes to mitochondria in an N-terminal myristoylation-dependent manner, where it reduces mitochondrial membrane potential and causes mitochondrial fragmentation; the C-terminal NLS region of ARL4D(T35N) is required for these mitochondrial effects.","method":"Subcellular fractionation, confocal immunofluorescence, dominant-negative mutant ARL4D(T35N), membrane potential assay (JC-1), domain deletion mutants","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with functional consequence, multiple domain mutants, single lab","pmids":["22927989"],"is_preprint":false},{"year":2018,"finding":"Arl4D expression is induced by PD-L1 signaling in CD8 T cells and limits IL-2 production and Akt phosphorylation; Arl4D-deficient T cells overproduce IL-2, expand more, and show enhanced effector function including increased SLEC development during viral infection.","method":"Arl4d knockout mice, in vivo viral infection model, IL-2 ELISA, Akt phosphorylation Western blot, flow cytometry","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with defined cellular phenotype and pathway placement (Akt), replicated in vitro and in vivo, single lab","pmids":["30382149"],"is_preprint":false},{"year":2020,"finding":"Arl4D interacts with the microtubule plus-end tracking protein EB1 in a GTP-dependent manner via EB1's C-terminal EB homology region and an SxLP motif on Arl4D. Arl4D colocalizes with γ-tubulin at centrosomes, promotes centrosomal recruitment of EB1, and facilitates microtubule nucleation by enhancing the association between EB1 and the p150 subunit of dynactin.","method":"Co-immunoprecipitation, GST pulldown, mutagenesis (SxLP motif), siRNA depletion, live-cell MT nucleation assay, immunofluorescence co-localization, proximity ligation assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1–2 — reciprocal co-IP, domain mutagenesis, functional MT nucleation assay, and localization with functional consequence, multiple orthogonal methods","pmids":["32755434"],"is_preprint":false},{"year":2008,"finding":"ARL4D (ARF4L) protein levels are controlled post-transcriptionally by the Akt/mTOR pathway downstream of PTEN loss; rapamycin treatment reduces ARL4D protein and ARL4D transcripts preferentially associate with polysomes upon Akt activation.","method":"Western blot across isogenic PTEN-mutant cell lines, rapamycin treatment, polysomal fractionation, Northern blot/qPCR","journal":"Journal of neurosurgery","confidence":"Medium","confidence_rationale":"Tier 2 — polysomal fractionation and pharmacological inhibition establish translational regulation, single lab","pmids":["18240926"],"is_preprint":false},{"year":2025,"finding":"Arl4D functions as a scaffolding protein that recruits both Erk1/2 and Pak1 to the plasma membrane, assembling them into a functional complex that allows Erk1/2 to phosphorylate Pak1, thereby driving cell migration in PDGF signaling.","method":"Co-immunoprecipitation, plasma membrane fractionation, Pak1 phosphorylation assays, dominant-mutant and knockdown approaches, cell migration assay","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, biochemical phosphorylation assay, and migration rescue, multiple orthogonal methods establishing mechanism","pmids":["40309925"],"is_preprint":false},{"year":2026,"finding":"PI(4,5)P2 promotes Arl4D self-association at the plasma membrane via a conserved C-terminal polybasic motif, and Pak1 phosphorylates Arl4D at Ser144 to further enhance this self-association. GTP-dependent Arl4D self-association increases membrane residency and stability, amplifying downstream Pak1 signaling. An AlphaFold-guided Arl4D mutant defective in self-association fails to activate Pak1 or promote cell migration, while forced self-association restores these functions.","method":"In vitro lipid-binding assay, co-immunoprecipitation, phosphomimetic/phosphodeficient mutants, AlphaFold structural prediction with mutagenesis validation, FRAP, cell migration assay, Pak1 kinase assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — structural prediction with mutagenesis, lipid-binding assay, phosphorylation validation, functional rescue, multiple orthogonal methods","pmids":["41779780"],"is_preprint":false},{"year":2026,"finding":"TBC1D15 functions as a GTPase-activating protein (GAP) for Arl4D through its TBC domain, promoting GTP hydrolysis and thereby driving GDP-bound Arl4D to translocate to mitochondria under serum starvation. Knockdown of TBC1D15 increases Arl4D GTP levels and decreases its mitochondrial localization, implicating this GAP activity in mitochondrial homeostasis.","method":"Co-immunoprecipitation (TBC domain interaction), in vitro GAP assay, siRNA knockdown of TBC1D15, GTP-bound Arl4D pull-down (active-state assessment), mitochondrial fractionation/immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro GAP assay plus co-IP and functional KD with defined mitochondrial phenotype","pmids":["41709823"],"is_preprint":false}],"current_model":"ARL4D is a GTP-dependent Ras-family small GTPase that, when GTP-bound, localizes to the plasma membrane via N-terminal myristoylation and acts as a scaffolding hub: it recruits cytohesin-2/ARNO to activate ARF6 for actin remodeling, recruits Pak1 and Erk1/2 into a phosphorylation complex for cell migration, and promotes centrosomal EB1 recruitment for microtubule nucleation; PI(4,5)P2 binding and Pak1-mediated phosphorylation of Arl4D at Ser144 cooperatively drive its self-association to amplify Pak1 signaling, while TBC1D15 serves as its GAP to convert it to the GDP-bound form, which instead translocates to mitochondria to regulate organelle morphology and membrane potential."},"narrative":{"teleology":[{"year":2004,"claim":"Establishing that ARL4D nucleotide state dictates its subcellular compartment—GTP-bound at the plasma membrane versus GDP-bound at endosomes—and that this toggle controls transferrin receptor trafficking, providing the first functional readout for ARL4D's GTPase cycle.","evidence":"Immunocytochemistry with constitutively active (Q80L) and dominant-negative (T35N) ARL4D mutants, transferrin receptor localization assay","pmids":["15049518"],"confidence":"Medium","gaps":["Single imaging-based method without biochemical confirmation of GTP loading","Endogenous ARL4D localization not assessed","Mechanism of endosome-to-PM transport effect unclear"]},{"year":2007,"claim":"Identifying cytohesin-2/ARNO as the first direct effector of GTP-bound ARL4D and establishing a linear ARL4D→cytohesin-2→ARF6 activation cascade that controls actin remodeling and cell migration, thus defining ARL4D's primary signaling axis.","evidence":"Co-immunoprecipitation, GTP-dependent binding assays, dominant-active/inactive mutants, siRNA knockdown, ARF6-GTP pull-down, and cell migration assay in HeLa cells","pmids":["17804820"],"confidence":"High","gaps":["GAP and GEF for ARL4D itself unidentified","Whether ARL4D acts on cytohesins other than ARNO not tested"]},{"year":2008,"claim":"Revealing that ARL4D protein abundance is regulated post-transcriptionally via the Akt/mTOR axis, linking upstream growth-factor signaling to ARL4D expression control.","evidence":"Western blot in isogenic PTEN-mutant glioblastoma lines, rapamycin treatment, polysomal fractionation","pmids":["18240926"],"confidence":"Medium","gaps":["Direct mTOR-regulated translational element on ARL4D mRNA not mapped","Functional consequence of ARL4D upregulation in PTEN-null cells not tested"]},{"year":2009,"claim":"Extending the ARL4D→cytohesin-2→ARF6 pathway to a physiological morphogenesis outcome—neurite outgrowth—and demonstrating that ARL4D is both necessary and sufficient for this process.","evidence":"siRNA knockdown, constitutively active ARL4D overexpression, cell-permeable competing peptide, SecinH3 inhibitor, and isoform-specific ARF knockdown in neuronal differentiation model","pmids":["19327349"],"confidence":"Medium","gaps":["In vivo neural development phenotype not examined","Endogenous regulation of ARL4D during differentiation not characterized"]},{"year":2012,"claim":"Demonstrating that GDP-bound ARL4D translocates to mitochondria in a myristoylation-dependent manner and impairs mitochondrial membrane potential and morphology, establishing a second, nucleotide-state-specific functional compartment distinct from its plasma membrane role.","evidence":"Subcellular fractionation, confocal immunofluorescence, JC-1 membrane potential assay, domain deletion mutants of ARL4D(T35N)","pmids":["22927989"],"confidence":"Medium","gaps":["Mitochondrial target/receptor unknown","Whether endogenous ARL4D reaches mitochondria under physiological conditions not shown","Mechanism linking ARL4D to fission machinery undefined"]},{"year":2018,"claim":"Placing ARL4D as a downstream effector of PD-L1 signaling in CD8 T cells that limits IL-2 production and Akt phosphorylation, defining a new immunological function where ARL4D restrains T cell effector expansion.","evidence":"Arl4d knockout mice, in vivo viral infection, IL-2 ELISA, Akt phosphorylation Western blot, flow cytometry","pmids":["30382149"],"confidence":"Medium","gaps":["Direct molecular target of ARL4D in T cells not identified","Whether ARL4D's GTPase activity is required for this immune phenotype not tested"]},{"year":2020,"claim":"Identifying EB1 as a GTP-dependent interactor of ARL4D through an SxLP motif, and showing that ARL4D promotes centrosomal EB1 recruitment and microtubule nucleation, thus extending ARL4D function beyond actin to the microtubule cytoskeleton.","evidence":"Reciprocal co-IP, GST pulldown, SxLP motif mutagenesis, siRNA depletion, live-cell microtubule nucleation assay, proximity ligation assay","pmids":["32755434"],"confidence":"High","gaps":["Physiological stimulus that activates ARL4D at centrosomes unknown","Whether ARL4D and EB1 interaction is cell-cycle regulated not tested"]},{"year":2025,"claim":"Establishing ARL4D as a scaffolding platform that co-recruits Erk1/2 and Pak1 to the plasma membrane, enabling Erk-mediated Pak1 phosphorylation and PDGF-driven cell migration—expanding ARL4D from a GTPase-cascade activator to a kinase-organizing scaffold.","evidence":"Reciprocal co-IP, plasma membrane fractionation, Pak1 phosphorylation assays, dominant-mutant/knockdown approaches, cell migration assay","pmids":["40309925"],"confidence":"High","gaps":["Whether scaffold function requires simultaneous ARF6 activation not tested","Stoichiometry of the ARL4D–Erk–Pak1 complex not determined"]},{"year":2026,"claim":"Revealing that PI(4,5)P2 binding and Pak1-mediated Ser144 phosphorylation cooperatively drive GTP-dependent ARL4D self-association at the plasma membrane, creating a positive-feedback loop that amplifies Pak1 signaling and cell migration.","evidence":"In vitro lipid-binding assay, co-IP, phosphomimetic/phosphodeficient mutants, AlphaFold-guided mutagenesis, FRAP, Pak1 kinase assay, forced-dimerization rescue","pmids":["41779780"],"confidence":"High","gaps":["Oligomeric state (dimer vs. higher-order cluster) not resolved biophysically","Whether self-association also affects EB1 or cytohesin-2 pathways untested"]},{"year":2026,"claim":"Identifying TBC1D15 as the GAP for ARL4D, showing that TBC1D15-catalyzed GTP hydrolysis promotes ARL4D translocation to mitochondria under serum starvation and thereby closes the regulatory cycle governing ARL4D nucleotide state and compartmental switching.","evidence":"Co-IP mapping TBC domain interaction, in vitro GAP assay, siRNA knockdown of TBC1D15, GTP-Arl4D pull-down, mitochondrial fractionation and immunofluorescence","pmids":["41709823"],"confidence":"High","gaps":["GEF for ARL4D remains unidentified","Physiological signals that regulate TBC1D15 activity toward ARL4D not defined"]},{"year":null,"claim":"The GEF that activates ARL4D, the mitochondrial receptor for GDP-bound ARL4D, and the structural basis of ARL4D self-association all remain unknown, as does how the plasma membrane (actin/migration) and centrosomal (microtubule nucleation) functions of ARL4D are coordinated in space and time.","evidence":"","pmids":[],"confidence":"High","gaps":["No GEF identified","Mitochondrial receptor/tether for GDP-ARL4D unknown","No high-resolution structure of ARL4D oligomer","Coordination between ARF6, Pak1/Erk, and EB1 signaling arms not addressed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0,1,9]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[7,8]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[8]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,7,8]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[3,9]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[5]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,7,8]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[3,9]}],"complexes":[],"partners":["CYTH2","ARF6","MAPRE1","PAK1","MAPK3","TBC1D15"],"other_free_text":[]},"mechanistic_narrative":"ARL4D is a myristoylated Arf-family small GTPase that functions as a GTP-dependent signaling scaffold at the plasma membrane, coordinating actin remodeling, cell migration, and microtubule nucleation. In its GTP-bound state, ARL4D recruits cytohesin-2/ARNO to the plasma membrane to activate ARF6, driving actin stress fiber disassembly, endosome-to-plasma-membrane cargo transport, and neurite outgrowth [PMID:17804820, PMID:15049518, PMID:19327349]; it also assembles Erk1/2 and Pak1 into a membrane-proximal phosphorylation complex that promotes PDGF-stimulated cell migration, with PI(4,5)P2 binding and Pak1-mediated Ser144 phosphorylation driving ARL4D self-association to amplify signaling [PMID:40309925, PMID:41779780]. ARL4D additionally interacts with EB1 via an SxLP motif to promote centrosomal EB1 recruitment and microtubule nucleation [PMID:32755434]. TBC1D15 serves as the GAP that converts ARL4D to its GDP-bound form, which translocates to mitochondria in a myristoylation-dependent manner to reduce membrane potential and induce fragmentation [PMID:41709823, PMID:22927989]."},"prefetch_data":{"uniprot":{"accession":"P49703","full_name":"ADP-ribosylation factor-like protein 4D","aliases":["ADP-ribosylation factor-like protein 4L"],"length_aa":201,"mass_kda":22.2,"function":"Small GTP-binding protein which cycles between an inactive GDP-bound and an active GTP-bound form, and the rate of cycling is regulated by guanine nucleotide exchange factors (GEF) and GTPase-activating proteins (GAP). GTP-binding protein that does not act as an allosteric activator of the cholera toxin catalytic subunit. Recruits CYTH1, CYTH2, CYTH3 and CYTH4 to the plasma membrane in GDP-bound form","subcellular_location":"Nucleus, nucleolus; Cell membrane; Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P49703/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ARL4D","classification":"Not Classified","n_dependent_lines":274,"n_total_lines":1207,"dependency_fraction":0.22700911350455674},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ARL4D","total_profiled":1310},"omim":[{"mim_id":"600732","title":"ADP-RIBOSYLATION FACTOR-LIKE GTPase 4D; ARL4D","url":"https://www.omim.org/entry/600732"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"},{"location":"Golgi apparatus","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ARL4D"},"hgnc":{"alias_symbol":[],"prev_symbol":["ARF4L"]},"alphafold":{"accession":"P49703","domains":[{"cath_id":"3.40.50.300","chopping":"21-198","consensus_level":"high","plddt":95.7751,"start":21,"end":198}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P49703","model_url":"https://alphafold.ebi.ac.uk/files/AF-P49703-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P49703-F1-predicted_aligned_error_v6.png","plddt_mean":89.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ARL4D","jax_strain_url":"https://www.jax.org/strain/search?query=ARL4D"},"sequence":{"accession":"P49703","fasta_url":"https://rest.uniprot.org/uniprotkb/P49703.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P49703/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P49703"}},"corpus_meta":[{"pmid":"17804820","id":"PMC_17804820","title":"ARL4D recruits cytohesin-2/ARNO to modulate actin remodeling.","date":"2007","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/17804820","citation_count":80,"is_preprint":false},{"pmid":"19327349","id":"PMC_19327349","title":"Valproic acid-inducible Arl4D and cytohesin-2/ARNO, acting through the downstream Arf6, regulate neurite outgrowth in N1E-115 cells.","date":"2009","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/19327349","citation_count":29,"is_preprint":false},{"pmid":"22927989","id":"PMC_22927989","title":"GTP-binding-defective ARL4D alters mitochondrial morphology and membrane potential.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22927989","citation_count":18,"is_preprint":false},{"pmid":"30382149","id":"PMC_30382149","title":"The PDL1-inducible GTPase Arl4d controls T effector function by limiting IL-2 production.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30382149","citation_count":16,"is_preprint":false},{"pmid":"18240926","id":"PMC_18240926","title":"Increased expression of the glioma-associated antigen ARF4L after loss of the tumor suppressor PTEN. Laboratory investigation.","date":"2008","source":"Journal of neurosurgery","url":"https://pubmed.ncbi.nlm.nih.gov/18240926","citation_count":14,"is_preprint":false},{"pmid":"9602063","id":"PMC_9602063","title":"Expression of an ADP-ribosylation factor like gene, ARF4L, is induced after transient forebrain ischemia in the gerbil.","date":"1998","source":"Brain research. Molecular brain research","url":"https://pubmed.ncbi.nlm.nih.gov/9602063","citation_count":11,"is_preprint":false},{"pmid":"15049518","id":"PMC_15049518","title":"Role of ARF4L in recycling between endosomes and the plasma membrane.","date":"2004","source":"Cellular and molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/15049518","citation_count":9,"is_preprint":false},{"pmid":"21769420","id":"PMC_21769420","title":"Overexpression of the small GTPase Arl4D suppresses adipogenesis.","date":"2011","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/21769420","citation_count":9,"is_preprint":false},{"pmid":"32755434","id":"PMC_32755434","title":"Arl4D-EB1 interaction promotes centrosomal recruitment of EB1 and microtubule growth.","date":"2020","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/32755434","citation_count":7,"is_preprint":false},{"pmid":"40309925","id":"PMC_40309925","title":"The phosphorylation of Pak1 by Erk1/2 to drive cell migration requires Arl4D acting as a scaffolding protein.","date":"2025","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/40309925","citation_count":1,"is_preprint":false},{"pmid":"41779780","id":"PMC_41779780","title":"Phosphatidylinositol 4,5-bisphosphate mediates Arl4D self-interaction to promote Pak1 signaling.","date":"2026","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/41779780","citation_count":0,"is_preprint":false},{"pmid":"41709823","id":"PMC_41709823","title":"TBC1D15 functions as an Arl4D GAP and promotes the mitochondrial translocation of Arl4D for organelle homeostasis.","date":"2026","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/41709823","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.12.02.626348","title":"The phosphorylation of Pak1 by Erk1/2 for cell migration requires Arl4D acting as a scaffolding protein","date":"2024-12-02","source":"bioRxiv","url":"https://doi.org/10.1101/2024.12.02.626348","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.11.07.622483","title":"Critical role of Spatio-Temporally Regulated Maternal RNAs in Zebrafish Embryogenesis","date":"2024-11-08","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.07.622483","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7896,"output_tokens":2739,"usd":0.032386},"stage2":{"model":"claude-opus-4-6","input_tokens":6055,"output_tokens":2940,"usd":0.155663},"total_usd":0.188049,"stage1_batch_id":"msgbatch_01TqNM6p6FsoMBT2jzQTwKBr","stage2_batch_id":"msgbatch_01Ya473eco8sTHbvRymQaU8o","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"ARL4D interacts with the C-terminal pleckstrin homology (PH) and polybasic domains of cytohesin-2/ARNO in a GTP-dependent manner, recruits cytohesin-2/ARNO to the plasma membrane, and thereby activates ARF6 to induce actin stress fiber disassembly and cell migration. Plasma membrane localization of ARL4D requires GTP binding and N-terminal myristoylation.\",\n      \"method\": \"Co-immunoprecipitation, GTP-dependent binding assays, dominant-active/inactive mutants (Q80L, E156K), siRNA knockdown, GTP-bound ARF6 pull-down assay, cell migration assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (co-IP, mutant analysis, siRNA rescue, GTPase activity assay, migration assay) in a single study with rigorous controls\",\n      \"pmids\": [\"17804820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"GTP-bound ARL4D (Q80L) localizes to the plasma membrane and promotes transport of cargo (transferrin receptor) from endosomes to the plasma membrane, whereas GDP-bound ARL4D (T35N) localizes to endosomes and causes retention of transferrin receptors in the endosomal compartment.\",\n      \"method\": \"Immunocytochemistry with GTPase mutants (Q80L active form, T35N inactive form), transferrin receptor localization assay\",\n      \"journal\": \"Cellular and molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method (immunocytochemistry with mutants), moderate mechanistic detail\",\n      \"pmids\": [\"15049518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Arl4D acts upstream of cytohesin-2 and ARF6 to promote neurite outgrowth; a cell-permeable peptide encoding the cytohesin-2-binding region of Arl4D blocks VPA-induced neurite outgrowth, and constitutively active Arl4D is sufficient to induce outgrowth.\",\n      \"method\": \"siRNA knockdown of Arl4D, constitutively active Arl4D overexpression, cell-permeable peptide competition, SecinH3 inhibitor, siRNA knockdown of ARF6 vs ARF1\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (KD, OE, peptide competition, isoform-specific knockdown) but from a single lab\",\n      \"pmids\": [\"19327349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GTP-binding-defective ARL4D (T35N) localizes to mitochondria in an N-terminal myristoylation-dependent manner, where it reduces mitochondrial membrane potential and causes mitochondrial fragmentation; the C-terminal NLS region of ARL4D(T35N) is required for these mitochondrial effects.\",\n      \"method\": \"Subcellular fractionation, confocal immunofluorescence, dominant-negative mutant ARL4D(T35N), membrane potential assay (JC-1), domain deletion mutants\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with functional consequence, multiple domain mutants, single lab\",\n      \"pmids\": [\"22927989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Arl4D expression is induced by PD-L1 signaling in CD8 T cells and limits IL-2 production and Akt phosphorylation; Arl4D-deficient T cells overproduce IL-2, expand more, and show enhanced effector function including increased SLEC development during viral infection.\",\n      \"method\": \"Arl4d knockout mice, in vivo viral infection model, IL-2 ELISA, Akt phosphorylation Western blot, flow cytometry\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with defined cellular phenotype and pathway placement (Akt), replicated in vitro and in vivo, single lab\",\n      \"pmids\": [\"30382149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Arl4D interacts with the microtubule plus-end tracking protein EB1 in a GTP-dependent manner via EB1's C-terminal EB homology region and an SxLP motif on Arl4D. Arl4D colocalizes with γ-tubulin at centrosomes, promotes centrosomal recruitment of EB1, and facilitates microtubule nucleation by enhancing the association between EB1 and the p150 subunit of dynactin.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, mutagenesis (SxLP motif), siRNA depletion, live-cell MT nucleation assay, immunofluorescence co-localization, proximity ligation assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — reciprocal co-IP, domain mutagenesis, functional MT nucleation assay, and localization with functional consequence, multiple orthogonal methods\",\n      \"pmids\": [\"32755434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ARL4D (ARF4L) protein levels are controlled post-transcriptionally by the Akt/mTOR pathway downstream of PTEN loss; rapamycin treatment reduces ARL4D protein and ARL4D transcripts preferentially associate with polysomes upon Akt activation.\",\n      \"method\": \"Western blot across isogenic PTEN-mutant cell lines, rapamycin treatment, polysomal fractionation, Northern blot/qPCR\",\n      \"journal\": \"Journal of neurosurgery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — polysomal fractionation and pharmacological inhibition establish translational regulation, single lab\",\n      \"pmids\": [\"18240926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Arl4D functions as a scaffolding protein that recruits both Erk1/2 and Pak1 to the plasma membrane, assembling them into a functional complex that allows Erk1/2 to phosphorylate Pak1, thereby driving cell migration in PDGF signaling.\",\n      \"method\": \"Co-immunoprecipitation, plasma membrane fractionation, Pak1 phosphorylation assays, dominant-mutant and knockdown approaches, cell migration assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, biochemical phosphorylation assay, and migration rescue, multiple orthogonal methods establishing mechanism\",\n      \"pmids\": [\"40309925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PI(4,5)P2 promotes Arl4D self-association at the plasma membrane via a conserved C-terminal polybasic motif, and Pak1 phosphorylates Arl4D at Ser144 to further enhance this self-association. GTP-dependent Arl4D self-association increases membrane residency and stability, amplifying downstream Pak1 signaling. An AlphaFold-guided Arl4D mutant defective in self-association fails to activate Pak1 or promote cell migration, while forced self-association restores these functions.\",\n      \"method\": \"In vitro lipid-binding assay, co-immunoprecipitation, phosphomimetic/phosphodeficient mutants, AlphaFold structural prediction with mutagenesis validation, FRAP, cell migration assay, Pak1 kinase assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — structural prediction with mutagenesis, lipid-binding assay, phosphorylation validation, functional rescue, multiple orthogonal methods\",\n      \"pmids\": [\"41779780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TBC1D15 functions as a GTPase-activating protein (GAP) for Arl4D through its TBC domain, promoting GTP hydrolysis and thereby driving GDP-bound Arl4D to translocate to mitochondria under serum starvation. Knockdown of TBC1D15 increases Arl4D GTP levels and decreases its mitochondrial localization, implicating this GAP activity in mitochondrial homeostasis.\",\n      \"method\": \"Co-immunoprecipitation (TBC domain interaction), in vitro GAP assay, siRNA knockdown of TBC1D15, GTP-bound Arl4D pull-down (active-state assessment), mitochondrial fractionation/immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro GAP assay plus co-IP and functional KD with defined mitochondrial phenotype\",\n      \"pmids\": [\"41709823\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARL4D is a GTP-dependent Ras-family small GTPase that, when GTP-bound, localizes to the plasma membrane via N-terminal myristoylation and acts as a scaffolding hub: it recruits cytohesin-2/ARNO to activate ARF6 for actin remodeling, recruits Pak1 and Erk1/2 into a phosphorylation complex for cell migration, and promotes centrosomal EB1 recruitment for microtubule nucleation; PI(4,5)P2 binding and Pak1-mediated phosphorylation of Arl4D at Ser144 cooperatively drive its self-association to amplify Pak1 signaling, while TBC1D15 serves as its GAP to convert it to the GDP-bound form, which instead translocates to mitochondria to regulate organelle morphology and membrane potential.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ARL4D is a myristoylated Arf-family small GTPase that functions as a GTP-dependent signaling scaffold at the plasma membrane, coordinating actin remodeling, cell migration, and microtubule nucleation. In its GTP-bound state, ARL4D recruits cytohesin-2/ARNO to the plasma membrane to activate ARF6, driving actin stress fiber disassembly, endosome-to-plasma-membrane cargo transport, and neurite outgrowth [PMID:17804820, PMID:15049518, PMID:19327349]; it also assembles Erk1/2 and Pak1 into a membrane-proximal phosphorylation complex that promotes PDGF-stimulated cell migration, with PI(4,5)P2 binding and Pak1-mediated Ser144 phosphorylation driving ARL4D self-association to amplify signaling [PMID:40309925, PMID:41779780]. ARL4D additionally interacts with EB1 via an SxLP motif to promote centrosomal EB1 recruitment and microtubule nucleation [PMID:32755434]. TBC1D15 serves as the GAP that converts ARL4D to its GDP-bound form, which translocates to mitochondria in a myristoylation-dependent manner to reduce membrane potential and induce fragmentation [PMID:41709823, PMID:22927989].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing that ARL4D nucleotide state dictates its subcellular compartment—GTP-bound at the plasma membrane versus GDP-bound at endosomes—and that this toggle controls transferrin receptor trafficking, providing the first functional readout for ARL4D's GTPase cycle.\",\n      \"evidence\": \"Immunocytochemistry with constitutively active (Q80L) and dominant-negative (T35N) ARL4D mutants, transferrin receptor localization assay\",\n      \"pmids\": [\"15049518\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single imaging-based method without biochemical confirmation of GTP loading\", \"Endogenous ARL4D localization not assessed\", \"Mechanism of endosome-to-PM transport effect unclear\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identifying cytohesin-2/ARNO as the first direct effector of GTP-bound ARL4D and establishing a linear ARL4D→cytohesin-2→ARF6 activation cascade that controls actin remodeling and cell migration, thus defining ARL4D's primary signaling axis.\",\n      \"evidence\": \"Co-immunoprecipitation, GTP-dependent binding assays, dominant-active/inactive mutants, siRNA knockdown, ARF6-GTP pull-down, and cell migration assay in HeLa cells\",\n      \"pmids\": [\"17804820\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GAP and GEF for ARL4D itself unidentified\", \"Whether ARL4D acts on cytohesins other than ARNO not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealing that ARL4D protein abundance is regulated post-transcriptionally via the Akt/mTOR axis, linking upstream growth-factor signaling to ARL4D expression control.\",\n      \"evidence\": \"Western blot in isogenic PTEN-mutant glioblastoma lines, rapamycin treatment, polysomal fractionation\",\n      \"pmids\": [\"18240926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mTOR-regulated translational element on ARL4D mRNA not mapped\", \"Functional consequence of ARL4D upregulation in PTEN-null cells not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extending the ARL4D→cytohesin-2→ARF6 pathway to a physiological morphogenesis outcome—neurite outgrowth—and demonstrating that ARL4D is both necessary and sufficient for this process.\",\n      \"evidence\": \"siRNA knockdown, constitutively active ARL4D overexpression, cell-permeable competing peptide, SecinH3 inhibitor, and isoform-specific ARF knockdown in neuronal differentiation model\",\n      \"pmids\": [\"19327349\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo neural development phenotype not examined\", \"Endogenous regulation of ARL4D during differentiation not characterized\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrating that GDP-bound ARL4D translocates to mitochondria in a myristoylation-dependent manner and impairs mitochondrial membrane potential and morphology, establishing a second, nucleotide-state-specific functional compartment distinct from its plasma membrane role.\",\n      \"evidence\": \"Subcellular fractionation, confocal immunofluorescence, JC-1 membrane potential assay, domain deletion mutants of ARL4D(T35N)\",\n      \"pmids\": [\"22927989\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mitochondrial target/receptor unknown\", \"Whether endogenous ARL4D reaches mitochondria under physiological conditions not shown\", \"Mechanism linking ARL4D to fission machinery undefined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Placing ARL4D as a downstream effector of PD-L1 signaling in CD8 T cells that limits IL-2 production and Akt phosphorylation, defining a new immunological function where ARL4D restrains T cell effector expansion.\",\n      \"evidence\": \"Arl4d knockout mice, in vivo viral infection, IL-2 ELISA, Akt phosphorylation Western blot, flow cytometry\",\n      \"pmids\": [\"30382149\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target of ARL4D in T cells not identified\", \"Whether ARL4D's GTPase activity is required for this immune phenotype not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identifying EB1 as a GTP-dependent interactor of ARL4D through an SxLP motif, and showing that ARL4D promotes centrosomal EB1 recruitment and microtubule nucleation, thus extending ARL4D function beyond actin to the microtubule cytoskeleton.\",\n      \"evidence\": \"Reciprocal co-IP, GST pulldown, SxLP motif mutagenesis, siRNA depletion, live-cell microtubule nucleation assay, proximity ligation assay\",\n      \"pmids\": [\"32755434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological stimulus that activates ARL4D at centrosomes unknown\", \"Whether ARL4D and EB1 interaction is cell-cycle regulated not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Establishing ARL4D as a scaffolding platform that co-recruits Erk1/2 and Pak1 to the plasma membrane, enabling Erk-mediated Pak1 phosphorylation and PDGF-driven cell migration—expanding ARL4D from a GTPase-cascade activator to a kinase-organizing scaffold.\",\n      \"evidence\": \"Reciprocal co-IP, plasma membrane fractionation, Pak1 phosphorylation assays, dominant-mutant/knockdown approaches, cell migration assay\",\n      \"pmids\": [\"40309925\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether scaffold function requires simultaneous ARF6 activation not tested\", \"Stoichiometry of the ARL4D–Erk–Pak1 complex not determined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealing that PI(4,5)P2 binding and Pak1-mediated Ser144 phosphorylation cooperatively drive GTP-dependent ARL4D self-association at the plasma membrane, creating a positive-feedback loop that amplifies Pak1 signaling and cell migration.\",\n      \"evidence\": \"In vitro lipid-binding assay, co-IP, phosphomimetic/phosphodeficient mutants, AlphaFold-guided mutagenesis, FRAP, Pak1 kinase assay, forced-dimerization rescue\",\n      \"pmids\": [\"41779780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Oligomeric state (dimer vs. higher-order cluster) not resolved biophysically\", \"Whether self-association also affects EB1 or cytohesin-2 pathways untested\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identifying TBC1D15 as the GAP for ARL4D, showing that TBC1D15-catalyzed GTP hydrolysis promotes ARL4D translocation to mitochondria under serum starvation and thereby closes the regulatory cycle governing ARL4D nucleotide state and compartmental switching.\",\n      \"evidence\": \"Co-IP mapping TBC domain interaction, in vitro GAP assay, siRNA knockdown of TBC1D15, GTP-Arl4D pull-down, mitochondrial fractionation and immunofluorescence\",\n      \"pmids\": [\"41709823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GEF for ARL4D remains unidentified\", \"Physiological signals that regulate TBC1D15 activity toward ARL4D not defined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The GEF that activates ARL4D, the mitochondrial receptor for GDP-bound ARL4D, and the structural basis of ARL4D self-association all remain unknown, as does how the plasma membrane (actin/migration) and centrosomal (microtubule nucleation) functions of ARL4D are coordinated in space and time.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No GEF identified\", \"Mitochondrial receptor/tether for GDP-ARL4D unknown\", \"No high-resolution structure of ARL4D oligomer\", \"Coordination between ARF6, Pak1/Erk, and EB1 signaling arms not addressed\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0, 1, 9]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [7, 8]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 7, 8]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [3, 9]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 7, 8]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [3, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CYTH2\",\n      \"ARF6\",\n      \"MAPRE1\",\n      \"PAK1\",\n      \"MAPK3\",\n      \"TBC1D15\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}