{"gene":"ARL4D","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2007,"finding":"ARL4D interacts with cytohesin-2/ARNO in a GTP-dependent manner, binding to its C-terminal pleckstrin homology (PH) and polybasic c domains. GTP-bound ARL4D localizes to the plasma membrane (requiring N-terminal myristoylation) and recruits cytohesin-2/ARNO there, leading to ARF6 activation, actin stress fiber disassembly, and increased cell migration. Knockdown of cytohesin-2/ARNO or expression of its inactive form (E156K) blocked ARL4D-mediated actin remodeling. ARL4D-induced translocation of cytohesin-2/ARNO did not require PI3K activation.","method":"Co-immunoprecipitation, GTP-dependent binding assays, constitutively active/dominant-negative mutants (Q80L, E156K), siRNA knockdown, cell migration assays, actin staining","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction mapped to specific domains, multiple orthogonal methods (Co-IP, dominant-negative rescue, siRNA KD, GTP-dependence), clear functional phenotype","pmids":["17804820"],"is_preprint":false},{"year":2004,"finding":"GTP-bound ARL4D (Q80L) localizes to the plasma membrane and promotes transport of cargo (e.g., transferrin receptor) to the plasma membrane, while GDP-bound ARL4D (T35N) localizes to endosomes and causes accumulation of transferrin receptors in the endosomal compartment, establishing ARL4D as a regulator of recycling between endosomes and the plasma membrane.","method":"Immunocytochemistry with GTP/GDP-binding mutants (Q80L, T35N), transferrin receptor localization assays","journal":"Cellular and molecular neurobiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — mutant overexpression and localization assays in single study, no in vitro reconstitution","pmids":["15049518"],"is_preprint":false},{"year":2009,"finding":"Arl4D acts upstream of cytohesin-2 and ARF6 to regulate neurite outgrowth in N1E-115 neuroblastoma cells. Constitutively active Arl4D induced neurite outgrowth, Arl4D knockdown inhibited VPA-induced outgrowth, and a cell-permeable peptide corresponding to the cytohesin-2-binding region of Arl4D blocked VPA effects, establishing the Arl4D–cytohesin-2–ARF6 axis in neuronal morphogenesis.","method":"siRNA knockdown, constitutively active mutant overexpression, cell-permeable peptide inhibition, pharmacological inhibition (SecinH3)","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (KD, CA mutant, peptide inhibition) in single lab","pmids":["19327349"],"is_preprint":false},{"year":2012,"finding":"GTP-binding-defective ARL4D (T35N) localizes to mitochondria (requiring N-terminal myristoylation), where it reduces mitochondrial membrane potential (ΔΨm) and causes mitochondrial fragmentation. The C-terminal NLS region of ARL4D(T35N) is required for these mitochondrial effects. A portion of endogenous ARL4D also resides in mitochondria.","method":"Mutant overexpression (T35N), subcellular fractionation, immunofluorescence, mitochondrial membrane potential assays, NLS deletion mutants","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with functional consequence, domain mapping, single lab","pmids":["22927989"],"is_preprint":false},{"year":2008,"finding":"ARL4D (ARF4L) protein expression is controlled post-transcriptionally by the Akt/mTOR pathway downstream of PTEN loss; rapamycin treatment decreased ARF4L protein levels, and the ARF4L transcript preferentially associated with the polysomal compartment following PTEN loss or Akt activation, with no change at the transcript level.","method":"Western blot, Northern blot, qPCR, polysomal fractionation, rapamycin treatment in glioma cell lines with defined PTEN status","journal":"Journal of neurosurgery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — polysomal fractionation plus pharmacological inhibition, single lab, correlative transcript measurements","pmids":["18240926"],"is_preprint":false},{"year":2018,"finding":"Arl4D expression is induced by PD-L1-dependent signals in LSEC-primed CD8 T cells and limits IL-2 production and Akt phosphorylation. Arl4D-deficient T cells overproduced IL-2 upon stimulation, showed enhanced expansion, effector function, and preferential development into KLRG1+CD127- short-lived effector cells during viral infection in vivo.","method":"Genetic knockout (Arl4d-deficient mice), in vitro T cell stimulation, viral infection in vivo, IL-2 ELISA, flow cytometry, Akt phosphorylation assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with defined cellular phenotype, in vivo validation, 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 domain and an SxLP motif in Arl4D. Arl4D colocalizes with γ-tubulin at centrosomes; Arl4D depletion causes centrosomal MT nucleation defects. Arl4D–EB1 interaction promotes centrosomal EB1 recruitment and increases the association between EB1 and the p150 subunit of dynactin, important for MT stabilization.","method":"Co-immunoprecipitation, GTP-dependence assays, domain-mapping mutants (SxLP motif), siRNA depletion, centrosomal MT nucleation assays, immunofluorescence colocalization","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain-level mapping, depletion phenotype with specific MT nucleation readout, multiple orthogonal methods in single study","pmids":["32755434"],"is_preprint":false},{"year":2025,"finding":"Arl4D acts as a scaffolding protein at the plasma membrane that recruits both Erk1/2 and Pak1, assembling them into a functional complex. This complex enables Erk1/2 to phosphorylate Pak1 at the plasma membrane in response to PDGF signaling, driving cell migration. Arl4D thereby functions as a novel regulator of Erk1/2 substrate targeting.","method":"Co-immunoprecipitation, plasma membrane recruitment assays, phosphorylation assays, loss-of-function and rescue experiments, cell migration assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, phosphorylation assays, functional rescue, single lab","pmids":["40309925"],"is_preprint":false},{"year":2026,"finding":"TBC1D15, a known Rab7 GAP, also functions as a GTPase-activating protein (GAP) for Arl4D: it interacts with Arl4D through its TBC domain and promotes GTP hydrolysis of Arl4D. Under serum starvation, GDP-bound Arl4D translocates to mitochondria; knockdown of TBC1D15 increases Arl4D GTP-bound activity and decreases its mitochondrial translocation, placing TBC1D15 as the Arl4D GAP regulating mitochondrial targeting.","method":"Co-immunoprecipitation, GTPase activity assays (GAP activity), TBC1D15 siRNA knockdown, subcellular fractionation, mitochondrial localization assays","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro GAP activity assay, Co-IP, KD with functional readout, single lab","pmids":["41709823"],"is_preprint":false},{"year":2026,"finding":"PI(4,5)P2 promotes GTP-dependent Arl4D self-association at the plasma membrane via a conserved C-terminal polybasic motif. Fibronectin stimulation enhances Arl4D self-association through two cooperative mechanisms: direct PI(4,5)P2 binding and phosphorylation of Arl4D at Ser144 by its effector kinase Pak1 (a positive feedback). Arl4D self-association increases membrane residency and protein stability, and is required for downstream Pak1 activation and cell migration. An AlphaFold-guided mutant defective in self-association but retaining GTP binding and membrane targeting failed to activate Pak1 or support migration; forced self-association of this mutant restored these functions.","method":"AlphaFold structural prediction with mutagenesis, lipid-binding assays, phosphorylation mapping (Ser144), Co-immunoprecipitation for self-association, cell migration assays, GTP-binding assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — structure-guided mutagenesis, lipid binding, phosphorylation mapping, multiple orthogonal functional readouts in single rigorous study","pmids":["41779780"],"is_preprint":false}],"current_model":"ARL4D is a GTP-dependent, N-terminally myristoylated small GTPase that localizes to the plasma membrane in its active (GTP-bound) state, where it (1) recruits cytohesin-2/ARNO to activate ARF6 and remodel the actin cytoskeleton, (2) acts as a scaffolding protein assembling Erk1/2 and Pak1 into a complex for Pak1 phosphorylation and cell migration, (3) self-associates in a PI(4,5)P2- and Pak1-phosphorylation-dependent manner to amplify downstream signaling, and (4) promotes centrosomal EB1 recruitment and microtubule nucleation; in its GDP-bound/inactive state, ARL4D translocates to mitochondria (facilitated by the GAP TBC1D15) to alter mitochondrial morphology and membrane potential, while also cycling through endosomes to regulate recycling to the plasma membrane."},"narrative":{"mechanistic_narrative":"ARL4D is an N-terminally myristoylated small GTPase whose subcellular distribution and effector engagement are governed by its nucleotide state, allowing it to coordinate actin remodeling, cell migration, microtubule organization, and mitochondrial morphology [PMID:17804820, PMID:22927989, PMID:32755434]. In its GTP-bound state ARL4D localizes to the plasma membrane and recruits cytohesin-2/ARNO through that protein's PH and polybasic domains, driving ARF6 activation, actin stress fiber disassembly, and migration; this same axis acts upstream of cytohesin-2 and ARF6 to promote neurite outgrowth [PMID:17804820, PMID:19327349]. At the plasma membrane ARL4D additionally functions as a scaffold that assembles Erk1/2 and Pak1 into a complex, enabling Erk1/2 to phosphorylate Pak1 in response to PDGF and thereby driving migration [PMID:40309925]; this signaling output is amplified by PI(4,5)P2- and Pak1-dependent self-association of ARL4D, which increases its membrane residency and stability and is required for Pak1 activation [PMID:41779780]. GTP-bound ARL4D also binds the microtubule plus-end protein EB1 via an SxLP motif, promoting centrosomal EB1 recruitment, EB1–dynactin association, and microtubule nucleation [PMID:32755434]. Conversely, the GDP-bound/GTP-binding-defective form localizes to endosomes to regulate transferrin receptor recycling and translocates to mitochondria—a transition driven by the GAP TBC1D15—where it lowers mitochondrial membrane potential and causes fragmentation [PMID:15049518, PMID:22927989, PMID:41709823]. ARL4D protein levels are controlled post-transcriptionally by Akt/mTOR signaling downstream of PTEN loss, and ARL4D restrains IL-2 production and Akt phosphorylation in CD8 T cells [PMID:18240926, PMID:30382149].","teleology":[{"year":2004,"claim":"Established that ARL4D's nucleotide state dictates its localization and that it regulates membrane trafficking, the founding observation linking GTP/GDP cycling to function.","evidence":"Immunocytochemistry with Q80L/T35N mutants and transferrin receptor localization assays","pmids":["15049518"],"confidence":"Medium","gaps":["No effector identified for the recycling function","Single study without in vitro reconstitution"]},{"year":2007,"claim":"Identified cytohesin-2/ARNO as a GTP-dependent effector, explaining how active ARL4D drives ARF6 activation, actin remodeling, and migration.","evidence":"Co-IP with domain mapping, GTP-dependent binding, dominant-negative and siRNA rescue, migration and actin assays","pmids":["17804820"],"confidence":"High","gaps":["Did not address how nucleotide state is regulated in vivo","ARF6 downstream targets not enumerated"]},{"year":2008,"claim":"Showed ARL4D abundance is set post-transcriptionally by Akt/mTOR after PTEN loss, connecting it to growth-factor and tumor-suppressor signaling.","evidence":"Western/Northern blot, qPCR, polysomal fractionation, rapamycin treatment in PTEN-defined glioma lines","pmids":["18240926"],"confidence":"Medium","gaps":["Mechanism of translational control not defined","Correlative transcript/polysome data only"]},{"year":2009,"claim":"Extended the ARL4D–cytohesin-2–ARF6 axis to a physiological readout, neuronal morphogenesis, via neurite outgrowth.","evidence":"siRNA KD, constitutively active mutant, cell-permeable peptide inhibition, SecinH3 in N1E-115 cells","pmids":["19327349"],"confidence":"Medium","gaps":["In vivo relevance to neuronal development untested","Single cell-line context"]},{"year":2012,"claim":"Revealed a distinct GDP-bound function: mitochondrial localization with effects on membrane potential and morphology, indicating dual organelle targeting.","evidence":"T35N overexpression, subcellular fractionation, immunofluorescence, membrane potential assays, NLS deletion","pmids":["22927989"],"confidence":"Medium","gaps":["Mitochondrial binding partners unknown at this stage","Mechanism linking ARL4D to membrane potential unresolved"]},{"year":2018,"claim":"Demonstrated an immunoregulatory role in which ARL4D limits CD8 T cell IL-2 production and Akt signaling, broadening its physiological scope.","evidence":"Arl4d-deficient mice, in vitro T cell stimulation, viral infection in vivo, IL-2 ELISA, flow cytometry","pmids":["30382149"],"confidence":"Medium","gaps":["Molecular pathway connecting ARL4D to IL-2/Akt not defined","Whether GTPase activity is required is untested"]},{"year":2020,"claim":"Identified EB1 as a GTP-dependent effector, defining a microtubule/centrosomal function distinct from the actin pathway.","evidence":"Reciprocal Co-IP, SxLP motif mapping, siRNA depletion, centrosomal MT nucleation assays, colocalization","pmids":["32755434"],"confidence":"High","gaps":["How ARL4D is targeted to centrosomes not resolved","Relationship to its plasma-membrane pool unclear"]},{"year":2025,"claim":"Defined ARL4D as a plasma-membrane scaffold that assembles Erk1/2 and Pak1, explaining how it targets Erk1/2 substrate phosphorylation during PDGF-driven migration.","evidence":"Co-IP, plasma membrane recruitment, phosphorylation assays, loss-of-function and rescue, migration assays","pmids":["40309925"],"confidence":"Medium","gaps":["Whether scaffolding requires the cytohesin-2/ARF6 arm is unclear","Single-lab biochemistry"]},{"year":2026,"claim":"Identified TBC1D15 as the ARL4D GAP, providing the regulatory switch that drives GDP-bound ARL4D to mitochondria under serum starvation.","evidence":"Co-IP, in vitro GAP activity assays, TBC1D15 siRNA KD, subcellular fractionation","pmids":["41709823"],"confidence":"Medium","gaps":["GEF for ARL4D still unidentified","Single-lab in vitro GAP assay"]},{"year":2026,"claim":"Showed that PI(4,5)P2- and Pak1-phosphorylation-dependent self-association is a feedback mechanism that stabilizes ARL4D at the membrane and is required for downstream Pak1 activation and migration.","evidence":"AlphaFold-guided mutagenesis, lipid binding, Ser144 phosphorylation mapping, self-association Co-IP, migration assays","pmids":["41779780"],"confidence":"High","gaps":["Stoichiometry/structure of the self-associated oligomer not experimentally determined","Whether self-association applies to non-migratory functions untested"]},{"year":null,"claim":"The activating GEF for ARL4D and how its competing plasma-membrane, centrosomal, endosomal, and mitochondrial pools are spatially partitioned remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No GEF identified","No structural model of full-length ARL4D bound to effectors","Integration of actin, microtubule, and mitochondrial functions unexplained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0,8]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[7]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,6]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,7,9]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[3,8]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,7,9]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5]}],"complexes":[],"partners":["CYTH2","ARF6","EB1","PAK1","MAPK3","TBC1D15"],"other_free_text":[]}},"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":82,"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":19,"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":8,"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":2,"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":"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":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":8664,"output_tokens":3048,"usd":0.035856,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10365,"output_tokens":3415,"usd":0.0686,"stage2_stop_reason":"end_turn"},"total_usd":0.104456,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2007,\n      \"finding\": \"ARL4D interacts with cytohesin-2/ARNO in a GTP-dependent manner, binding to its C-terminal pleckstrin homology (PH) and polybasic c domains. GTP-bound ARL4D localizes to the plasma membrane (requiring N-terminal myristoylation) and recruits cytohesin-2/ARNO there, leading to ARF6 activation, actin stress fiber disassembly, and increased cell migration. Knockdown of cytohesin-2/ARNO or expression of its inactive form (E156K) blocked ARL4D-mediated actin remodeling. ARL4D-induced translocation of cytohesin-2/ARNO did not require PI3K activation.\",\n      \"method\": \"Co-immunoprecipitation, GTP-dependent binding assays, constitutively active/dominant-negative mutants (Q80L, E156K), siRNA knockdown, cell migration assays, actin staining\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction mapped to specific domains, multiple orthogonal methods (Co-IP, dominant-negative rescue, siRNA KD, GTP-dependence), clear functional phenotype\",\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 (e.g., transferrin receptor) to the plasma membrane, while GDP-bound ARL4D (T35N) localizes to endosomes and causes accumulation of transferrin receptors in the endosomal compartment, establishing ARL4D as a regulator of recycling between endosomes and the plasma membrane.\",\n      \"method\": \"Immunocytochemistry with GTP/GDP-binding mutants (Q80L, T35N), transferrin receptor localization assays\",\n      \"journal\": \"Cellular and molecular neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — mutant overexpression and localization assays in single study, no in vitro reconstitution\",\n      \"pmids\": [\"15049518\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Arl4D acts upstream of cytohesin-2 and ARF6 to regulate neurite outgrowth in N1E-115 neuroblastoma cells. Constitutively active Arl4D induced neurite outgrowth, Arl4D knockdown inhibited VPA-induced outgrowth, and a cell-permeable peptide corresponding to the cytohesin-2-binding region of Arl4D blocked VPA effects, establishing the Arl4D–cytohesin-2–ARF6 axis in neuronal morphogenesis.\",\n      \"method\": \"siRNA knockdown, constitutively active mutant overexpression, cell-permeable peptide inhibition, pharmacological inhibition (SecinH3)\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (KD, CA mutant, peptide inhibition) in single lab\",\n      \"pmids\": [\"19327349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GTP-binding-defective ARL4D (T35N) localizes to mitochondria (requiring N-terminal myristoylation), where it reduces mitochondrial membrane potential (ΔΨm) and causes mitochondrial fragmentation. The C-terminal NLS region of ARL4D(T35N) is required for these mitochondrial effects. A portion of endogenous ARL4D also resides in mitochondria.\",\n      \"method\": \"Mutant overexpression (T35N), subcellular fractionation, immunofluorescence, mitochondrial membrane potential assays, NLS deletion mutants\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with functional consequence, domain mapping, single lab\",\n      \"pmids\": [\"22927989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ARL4D (ARF4L) protein expression is controlled post-transcriptionally by the Akt/mTOR pathway downstream of PTEN loss; rapamycin treatment decreased ARF4L protein levels, and the ARF4L transcript preferentially associated with the polysomal compartment following PTEN loss or Akt activation, with no change at the transcript level.\",\n      \"method\": \"Western blot, Northern blot, qPCR, polysomal fractionation, rapamycin treatment in glioma cell lines with defined PTEN status\",\n      \"journal\": \"Journal of neurosurgery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — polysomal fractionation plus pharmacological inhibition, single lab, correlative transcript measurements\",\n      \"pmids\": [\"18240926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Arl4D expression is induced by PD-L1-dependent signals in LSEC-primed CD8 T cells and limits IL-2 production and Akt phosphorylation. Arl4D-deficient T cells overproduced IL-2 upon stimulation, showed enhanced expansion, effector function, and preferential development into KLRG1+CD127- short-lived effector cells during viral infection in vivo.\",\n      \"method\": \"Genetic knockout (Arl4d-deficient mice), in vitro T cell stimulation, viral infection in vivo, IL-2 ELISA, flow cytometry, Akt phosphorylation assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with defined cellular phenotype, in vivo validation, 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 domain and an SxLP motif in Arl4D. Arl4D colocalizes with γ-tubulin at centrosomes; Arl4D depletion causes centrosomal MT nucleation defects. Arl4D–EB1 interaction promotes centrosomal EB1 recruitment and increases the association between EB1 and the p150 subunit of dynactin, important for MT stabilization.\",\n      \"method\": \"Co-immunoprecipitation, GTP-dependence assays, domain-mapping mutants (SxLP motif), siRNA depletion, centrosomal MT nucleation assays, immunofluorescence colocalization\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain-level mapping, depletion phenotype with specific MT nucleation readout, multiple orthogonal methods in single study\",\n      \"pmids\": [\"32755434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Arl4D acts as a scaffolding protein at the plasma membrane that recruits both Erk1/2 and Pak1, assembling them into a functional complex. This complex enables Erk1/2 to phosphorylate Pak1 at the plasma membrane in response to PDGF signaling, driving cell migration. Arl4D thereby functions as a novel regulator of Erk1/2 substrate targeting.\",\n      \"method\": \"Co-immunoprecipitation, plasma membrane recruitment assays, phosphorylation assays, loss-of-function and rescue experiments, cell migration assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, phosphorylation assays, functional rescue, single lab\",\n      \"pmids\": [\"40309925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TBC1D15, a known Rab7 GAP, also functions as a GTPase-activating protein (GAP) for Arl4D: it interacts with Arl4D through its TBC domain and promotes GTP hydrolysis of Arl4D. Under serum starvation, GDP-bound Arl4D translocates to mitochondria; knockdown of TBC1D15 increases Arl4D GTP-bound activity and decreases its mitochondrial translocation, placing TBC1D15 as the Arl4D GAP regulating mitochondrial targeting.\",\n      \"method\": \"Co-immunoprecipitation, GTPase activity assays (GAP activity), TBC1D15 siRNA knockdown, subcellular fractionation, mitochondrial localization assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro GAP activity assay, Co-IP, KD with functional readout, single lab\",\n      \"pmids\": [\"41709823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"PI(4,5)P2 promotes GTP-dependent Arl4D self-association at the plasma membrane via a conserved C-terminal polybasic motif. Fibronectin stimulation enhances Arl4D self-association through two cooperative mechanisms: direct PI(4,5)P2 binding and phosphorylation of Arl4D at Ser144 by its effector kinase Pak1 (a positive feedback). Arl4D self-association increases membrane residency and protein stability, and is required for downstream Pak1 activation and cell migration. An AlphaFold-guided mutant defective in self-association but retaining GTP binding and membrane targeting failed to activate Pak1 or support migration; forced self-association of this mutant restored these functions.\",\n      \"method\": \"AlphaFold structural prediction with mutagenesis, lipid-binding assays, phosphorylation mapping (Ser144), Co-immunoprecipitation for self-association, cell migration assays, GTP-binding assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — structure-guided mutagenesis, lipid binding, phosphorylation mapping, multiple orthogonal functional readouts in single rigorous study\",\n      \"pmids\": [\"41779780\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ARL4D is a GTP-dependent, N-terminally myristoylated small GTPase that localizes to the plasma membrane in its active (GTP-bound) state, where it (1) recruits cytohesin-2/ARNO to activate ARF6 and remodel the actin cytoskeleton, (2) acts as a scaffolding protein assembling Erk1/2 and Pak1 into a complex for Pak1 phosphorylation and cell migration, (3) self-associates in a PI(4,5)P2- and Pak1-phosphorylation-dependent manner to amplify downstream signaling, and (4) promotes centrosomal EB1 recruitment and microtubule nucleation; in its GDP-bound/inactive state, ARL4D translocates to mitochondria (facilitated by the GAP TBC1D15) to alter mitochondrial morphology and membrane potential, while also cycling through endosomes to regulate recycling to the plasma membrane.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ARL4D is an N-terminally myristoylated small GTPase whose subcellular distribution and effector engagement are governed by its nucleotide state, allowing it to coordinate actin remodeling, cell migration, microtubule organization, and mitochondrial morphology [#0, #3, #6]. In its GTP-bound state ARL4D localizes to the plasma membrane and recruits cytohesin-2/ARNO through that protein's PH and polybasic domains, driving ARF6 activation, actin stress fiber disassembly, and migration; this same axis acts upstream of cytohesin-2 and ARF6 to promote neurite outgrowth [#0, #2]. At the plasma membrane ARL4D additionally functions as a scaffold that assembles Erk1/2 and Pak1 into a complex, enabling Erk1/2 to phosphorylate Pak1 in response to PDGF and thereby driving migration [#7]; this signaling output is amplified by PI(4,5)P2- and Pak1-dependent self-association of ARL4D, which increases its membrane residency and stability and is required for Pak1 activation [#9]. GTP-bound ARL4D also binds the microtubule plus-end protein EB1 via an SxLP motif, promoting centrosomal EB1 recruitment, EB1–dynactin association, and microtubule nucleation [#6]. Conversely, the GDP-bound/GTP-binding-defective form localizes to endosomes to regulate transferrin receptor recycling and translocates to mitochondria—a transition driven by the GAP TBC1D15—where it lowers mitochondrial membrane potential and causes fragmentation [#1, #3, #8]. ARL4D protein levels are controlled post-transcriptionally by Akt/mTOR signaling downstream of PTEN loss, and ARL4D restrains IL-2 production and Akt phosphorylation in CD8 T cells [#4, #5].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that ARL4D's nucleotide state dictates its localization and that it regulates membrane trafficking, the founding observation linking GTP/GDP cycling to function.\",\n      \"evidence\": \"Immunocytochemistry with Q80L/T35N mutants and transferrin receptor localization assays\",\n      \"pmids\": [\"15049518\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No effector identified for the recycling function\", \"Single study without in vitro reconstitution\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified cytohesin-2/ARNO as a GTP-dependent effector, explaining how active ARL4D drives ARF6 activation, actin remodeling, and migration.\",\n      \"evidence\": \"Co-IP with domain mapping, GTP-dependent binding, dominant-negative and siRNA rescue, migration and actin assays\",\n      \"pmids\": [\"17804820\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address how nucleotide state is regulated in vivo\", \"ARF6 downstream targets not enumerated\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed ARL4D abundance is set post-transcriptionally by Akt/mTOR after PTEN loss, connecting it to growth-factor and tumor-suppressor signaling.\",\n      \"evidence\": \"Western/Northern blot, qPCR, polysomal fractionation, rapamycin treatment in PTEN-defined glioma lines\",\n      \"pmids\": [\"18240926\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of translational control not defined\", \"Correlative transcript/polysome data only\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended the ARL4D–cytohesin-2–ARF6 axis to a physiological readout, neuronal morphogenesis, via neurite outgrowth.\",\n      \"evidence\": \"siRNA KD, constitutively active mutant, cell-permeable peptide inhibition, SecinH3 in N1E-115 cells\",\n      \"pmids\": [\"19327349\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance to neuronal development untested\", \"Single cell-line context\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Revealed a distinct GDP-bound function: mitochondrial localization with effects on membrane potential and morphology, indicating dual organelle targeting.\",\n      \"evidence\": \"T35N overexpression, subcellular fractionation, immunofluorescence, membrane potential assays, NLS deletion\",\n      \"pmids\": [\"22927989\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mitochondrial binding partners unknown at this stage\", \"Mechanism linking ARL4D to membrane potential unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated an immunoregulatory role in which ARL4D limits CD8 T cell IL-2 production and Akt signaling, broadening its physiological scope.\",\n      \"evidence\": \"Arl4d-deficient mice, in vitro T cell stimulation, viral infection in vivo, IL-2 ELISA, flow cytometry\",\n      \"pmids\": [\"30382149\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular pathway connecting ARL4D to IL-2/Akt not defined\", \"Whether GTPase activity is required is untested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Identified EB1 as a GTP-dependent effector, defining a microtubule/centrosomal function distinct from the actin pathway.\",\n      \"evidence\": \"Reciprocal Co-IP, SxLP motif mapping, siRNA depletion, centrosomal MT nucleation assays, colocalization\",\n      \"pmids\": [\"32755434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ARL4D is targeted to centrosomes not resolved\", \"Relationship to its plasma-membrane pool unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined ARL4D as a plasma-membrane scaffold that assembles Erk1/2 and Pak1, explaining how it targets Erk1/2 substrate phosphorylation during PDGF-driven migration.\",\n      \"evidence\": \"Co-IP, plasma membrane recruitment, phosphorylation assays, loss-of-function and rescue, migration assays\",\n      \"pmids\": [\"40309925\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether scaffolding requires the cytohesin-2/ARF6 arm is unclear\", \"Single-lab biochemistry\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Identified TBC1D15 as the ARL4D GAP, providing the regulatory switch that drives GDP-bound ARL4D to mitochondria under serum starvation.\",\n      \"evidence\": \"Co-IP, in vitro GAP activity assays, TBC1D15 siRNA KD, subcellular fractionation\",\n      \"pmids\": [\"41709823\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GEF for ARL4D still unidentified\", \"Single-lab in vitro GAP assay\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Showed that PI(4,5)P2- and Pak1-phosphorylation-dependent self-association is a feedback mechanism that stabilizes ARL4D at the membrane and is required for downstream Pak1 activation and migration.\",\n      \"evidence\": \"AlphaFold-guided mutagenesis, lipid binding, Ser144 phosphorylation mapping, self-association Co-IP, migration assays\",\n      \"pmids\": [\"41779780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry/structure of the self-associated oligomer not experimentally determined\", \"Whether self-association applies to non-migratory functions untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The activating GEF for ARL4D and how its competing plasma-membrane, centrosomal, endosomal, and mitochondrial pools are spatially partitioned remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No GEF identified\", \"No structural model of full-length ARL4D bound to effectors\", \"Integration of actin, microtubule, and mitochondrial functions unexplained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0, 8]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 7, 9]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [3, 8]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 7, 9]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CYTH2\", \"ARF6\", \"EB1\", \"PAK1\", \"MAPK3\", \"TBC1D15\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}