{"gene":"CYTH2","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":1997,"finding":"ARNO (CYTH2) catalyzes guanine nucleotide exchange on ARF1 via its central Sec7 domain; the PH domain binds PIP2 to recruit ARNO to membranes, which dramatically enhances ARF1 activation. PIP2-PH interaction does not directly regulate catalytic activity but serves membrane recruitment. A stable complex between the Sec7 domain and nucleotide-free ARF1 can be isolated.","method":"In vitro nucleotide exchange assay with phospholipid vesicles, protein-lipid binding, domain deletion mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with domain mutagenesis, foundational mechanistic study","pmids":["9268368"],"is_preprint":false},{"year":1998,"finding":"Crystal structure of the Sec7 domain of human ARNO resolved at 2.0–2.2 Å; the domain is an elongated all-helical protein with a hydrophobic groove and adjacent conserved loop that constitute the ARF1-binding surface, interacting with the switch 1 and switch 2 regions of ARF1.","method":"X-ray crystallography, structure-based mutagenesis, protein footprinting","journal":"Nature / Cell","confidence":"High","confidence_rationale":"Tier 1 — two independent crystal structures with functional mutagenesis validation","pmids":["9510256","9476900"],"is_preprint":false},{"year":1998,"finding":"Glu156 of the ARNO Sec7 domain acts as a 'glutamic finger' that destabilizes Mg2+ and GDP from ARF1 to drive nucleotide exchange; E156D and E156K mutations reduce exchange activity by orders of magnitude. E156K forms a complex with Mg2+-free ARF1-GDP without inducing GDP release. Switch I hydrophobic residues of ARF1 insert into the Sec7 groove; Lys73 of ARF1 switch II forms an ion pair with Asp183 of ARNO.","method":"Site-directed mutagenesis, in vitro nucleotide exchange assay, stable complex isolation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis + in vitro biochemical reconstitution, mechanistic detail confirmed by structural data","pmids":["9649435"],"is_preprint":false},{"year":1998,"finding":"ARNO localizes to the plasma membrane (not Golgi) in mammalian cells and stimulates nucleotide exchange on both ARF1 and ARF6 in vitro, with ARF6 being the likely in vivo target at the plasma membrane.","method":"In vitro GEF assay, subcellular fractionation, immunolocalization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — fractionation + immunolocalization + in vitro activity, replicated in subsequent papers","pmids":["9417041"],"is_preprint":false},{"year":1998,"finding":"ARNO-induced actin stress fiber disassembly and ARF6-dependent actin rearrangement requires the PH domain for membrane localization; PKC phosphorylates ARNO at a site C-terminal to the PH domain but mutation of this site does not block actin rearrangement.","method":"Overexpression in HeLa cells, PKC agonist treatment, domain deletion mutants, immunofluorescence","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function domain mutants with defined cytoskeletal phenotype, multiple orthogonal approaches","pmids":["9802902"],"is_preprint":false},{"year":1998,"finding":"Insulin stimulates PI3K-dependent translocation of ARNO from cytoplasm to plasma membrane in adipocytes via PH domain binding to PIP3; this translocation is blocked by wortmannin, LY294002, or dominant-negative p85.","method":"GFP-tagged ARNO live imaging in 3T3-L1 adipocytes, PI3K inhibitors, dominant-negative constructs, in vitro lipid binding","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 2 — live-cell imaging + pharmacological + genetic inhibition, replicated in subsequent work","pmids":["9550703"],"is_preprint":false},{"year":1998,"finding":"ARNO overexpression in HeLa cells inhibits the early secretory pathway, blocks ER-to-Golgi trafficking of SEAP, and causes disassembly of the Golgi complex, consistent with ARNO acting as an exchange factor for ARF1 in Golgi-to-ER transport.","method":"Overexpression in HeLa cells, SEAP secretion assay, endoglycosidase H resistance, immunofluorescence, cell fractionation","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — functional assay with defined phenotype, but single lab without reconstitution","pmids":["9788883"],"is_preprint":false},{"year":1999,"finding":"PKC phosphorylates ARNO at Ser392 within the polybasic C-terminal domain; this introduces a negative charge that reduces ARNO membrane binding in vitro and in vivo and inhibits ARF exchange activity via a 'PH domain electrostatic switch' mechanism.","method":"In vitro phosphorylation, liposome binding assay, in vivo membrane fractionation, exchange activity assay, phosphomimetic mutants","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution + mutagenesis + in vivo fractionation, novel regulatory mechanism","pmids":["10531036"],"is_preprint":false},{"year":2000,"finding":"The ARNO PH domain provides specific PIP3 > PIP2 binding; the adjacent polybasic C-domain adds nonspecific ionic interactions with acidic lipids (PS); PKC phosphorylation of Ser392 in the C-domain reduces ionic affinity for PS without affecting phosphoinositide specificity.","method":"Liposome cosedimentation, ionic strength titration, in vitro GEF activity assay with domain constructs","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — quantitative in vitro binding + mutagenesis + activity assay","pmids":["10801341"],"is_preprint":false},{"year":2001,"finding":"ARNO activates endogenous ARF6 (but not ARF1) at the plasma membrane in MDCK epithelial cells, leading to downstream Rac1 activation (required for motility) and phospholipase D (PLD) activation (required for motility via a separate pathway). Rac activation and PLD activation are independent downstream branches of ARF6.","method":"Dominant-active ARNO expression, ARF6-GTP pulldown assay, Rac-GTP pulldown, PLD activity assay, motility assay, dominant-negative constructs","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal assays, epistasis experiments placing ARNO upstream of ARF6 then Rac/PLD","pmids":["11481345"],"is_preprint":false},{"year":2001,"finding":"ARNO and ARF6 are recruited from cytosol to early endosomes in kidney proximal tubule cells in a V-ATPase-dependent, intra-endosomal acidification-dependent manner; this recruitment is reversed by V-ATPase inhibitors and pH uncouplers.","method":"Subcellular fractionation, immunolocalization, in vitro translocation assay with ATP-driven acidification, Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — fractionation + translocation assay + pharmacological reversal, mechanistic link to V-ATPase","pmids":["11278939"],"is_preprint":false},{"year":2001,"finding":"The Sec7 domains of ARNO and EFA6 determine their GEF selectivity: ARNO preferentially activates ARF1 on membranes whereas EFA6 exclusively activates ARF6; selectivity maps to the Sec7 domain and ARF core domains without the N-terminal myristoylated helix.","method":"In vitro GEF assay on phospholipid membranes, domain-swap experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with domain swaps, defines molecular basis of selectivity","pmids":["11342560"],"is_preprint":false},{"year":2002,"finding":"The N-terminal coiled-coil domain of ARNO/cytohesin-2 interacts with the scaffolding protein CASP; CASP is recruited to membrane ruffles by cytohesin in EGF-stimulated cells, revealing a functional interaction.","method":"Yeast two-hybrid screening, in vitro binding, co-immunoprecipitation in COS-1 cells, immunofluorescence","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid + co-IP + colocalization, single lab","pmids":["12052827"],"is_preprint":false},{"year":2003,"finding":"ARNO and ARF6 regulate axonal elongation and branching in hippocampal neurons; downstream of ARF6, PI(4)P 5-kinase α mediates these effects on neurite extension. Catalytically inactive ARNO or dominant-negative ARF6 enhance extension; co-expression of constitutively active ARF6 abrogates this. Inactive ARNO/ARF6 also depletes Mena from growth cone leading edge.","method":"Overexpression of dominant-negative/constitutively active mutants in cultured rat hippocampal neurons, immunofluorescence, morphometric analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — epistasis with multiple mutants, identifies PI(4)P 5-kinase α as downstream effector","pmids":["14565977"],"is_preprint":false},{"year":2003,"finding":"IPCEF1 interacts with the coiled-coil domain of cytohesin-2/ARNO and increases cytohesin-2-stimulated ARF-GTP formation both in vitro and in vivo; IPCEF1 is co-transported to the plasma membrane by cytohesin-2 upon EGF stimulation.","method":"Yeast two-hybrid, GST pulldown, immunoprecipitation, in vitro and in vivo ARF-GTP assay, immunofluorescence","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 — yeast two-hybrid + pulldown + functional GEF assay, single lab","pmids":["12920129"],"is_preprint":false},{"year":2003,"finding":"ARNO mediates insulin-stimulated ARF activation and PLD activation; both the PH domain (membrane targeting) and the Sec7 domain (catalytic activity) are required; coiled-coil domain deletion partially impairs membrane translocation.","method":"Transient transfection in HIRcB cells, domain deletion/mutation analysis, ARF-GTP pulldown, PLD activity assay, membrane fractionation","journal":"BMC cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple domain mutants + functional assays, single lab","pmids":["12969509"],"is_preprint":false},{"year":2004,"finding":"An RNA aptamer specific for ARNO/cytohesin-2 (binding its N-terminal coiled-coil/Sec7 region) inhibits serum-response element-driven transcription and MAPK activation in vivo without inhibiting GEF activity in vitro, revealing a GEF-independent function of cytohesin-2's N-terminus in MAPK/SRE signaling.","method":"SELEX aptamer selection, intracellular aptamer (intramer) transfection, SRE-reporter assay, ERK phosphorylation assay","journal":"PNAS","confidence":"Medium","confidence_rationale":"Tier 2 — specific inhibitor + reporter assay + MAPK readout, novel GEF-independent mechanism","pmids":["15277685"],"is_preprint":false},{"year":2005,"finding":"ARNO/cytohesin-2 directly binds the juxtamembrane carboxyl terminus of the A2A adenosine receptor; this interaction is required for ARF6-dependent sustained ERK/MAP kinase activation but not for cAMP signaling or receptor desensitization.","method":"Yeast two-hybrid, mutual pulldown of bacterial fusion proteins, co-immunoprecipitation, inducible dominant-negative expression, cAMP and ERK assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct interaction confirmed by pulldown + co-IP + genetic epistasis with defined signaling phenotype","pmids":["16027149"],"is_preprint":false},{"year":2005,"finding":"ARNO-dependent Rac1 activation in migrating MDCK cells is mediated by the bipartite Rac GEF Dock180/Elmo complex; catalytically inactive Dock180 or Elmo mutant that fails to couple to Dock180 both block ARNO-induced Rac activation and motility. β-PIX, another Rac GEF, is not required.","method":"Dominant-negative mutant overexpression, Rac-GTP pulldown, motility assay, co-localization by confocal microscopy","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with multiple mutants, places Dock180/Elmo between ARNO/ARF6 and Rac1","pmids":["16213822"],"is_preprint":false},{"year":2006,"finding":"V-ATPase a2-isoform on early endosomes interacts with ARNO in an intra-endosomal acidification-dependent manner; ARF6 interacts with the c-subunit of V-ATPase. Disruption of the a2-ARNO interaction reversibly inhibits endocytosis; V-ATPase recruits ARNO and ARF6 to regulate the endocytic degradative pathway.","method":"Co-immunoprecipitation, acidification-dependent binding assay, inhibitor treatments, endocytosis assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP + functional rescue, well-cited foundational study","pmids":["16415858"],"is_preprint":false},{"year":2006,"finding":"ARNO is localized exclusively at the apical plasma membrane of polarized epithelial cells through its N-terminal coiled-coil domain; ARNO promotes apical endocytosis of the polymeric IgA receptor synergistically with ARF6, and coiled-coil domain deletion mislocalizes ARNO to both membrane surfaces and abolishes apical endocytosis stimulation.","method":"Overexpression of deletion mutants, immunofluorescence in polarized MDCK cells, endocytosis assay, dominant-negative ARF6 epistasis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — defined localization + functional consequence + epistasis, single lab","pmids":["16484220"],"is_preprint":false},{"year":2006,"finding":"Gαq signaling leads to ARF6 activation through direct interaction with ARNO; activated Gαq forms molecular complexes preferentially with ARNO and ARF6, and direct binding between purified Gαq and ARNO is demonstrated. ARNO and ARF6 promote TPβ receptor internalization.","method":"Co-immunoprecipitation, in vitro binding with purified proteins, ARF6-GTP assay, receptor internalization assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding with purified proteins + co-IP + functional assay, identifies Gαq as upstream activator of ARNO","pmids":["16650966"],"is_preprint":false},{"year":2007,"finding":"ARL4D (a GTP-dependent plasma membrane GTPase) interacts with the PH and polybasic C-terminal domains of cytohesin-2/ARNO in a GTP-dependent manner, recruits ARNO to the plasma membrane, activates ARF6, and promotes actin stress fiber disassembly; inactive cytohesin-2 or siRNA knockdown of ARNO blocks ARL4D-induced effects.","method":"Yeast two-hybrid, co-IP, ARF6-GTP pulldown, siRNA knockdown, immunofluorescence, dominant-active/inactive mutants","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, genetic epistasis, identifies ARL4D as upstream recruiter of ARNO","pmids":["17804820"],"is_preprint":false},{"year":2007,"finding":"CaSR stimulation triggers plasma membrane ruffling via a β-arrestin 1–ARNO–ARF6–ELMO pathway; β-arrestin 1 co-immunoprecipitates with both CaSR and ARNO at rest, and agonist treatment causes their co-translocation to membrane protrusions.","method":"Co-immunoprecipitation, siRNA knockdown, dominant-negative mutants, immunofluorescence","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP + genetic knockdown + epistasis, single lab","pmids":["17623778"],"is_preprint":false},{"year":2007,"finding":"The coiled-coil domain of cytohesin-2/ARNO interacts directly with Gαq; Gαq-Q209L (constitutively active) strongly promotes cytohesin plasma membrane localization; coiled-coil deletion mutants of cytohesin-1 and -2 cannot relay Gαq-mediated ARF6 activation.","method":"Co-immunoprecipitation in HEK293 cells, confocal immunofluorescence, deletion mutants","journal":"Molecular and cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP + colocalization + functional deletion mutants, single lab","pmids":["17846866"],"is_preprint":false},{"year":2009,"finding":"The coiled-coil domain of ARNO is required for ARNO-induced cell motility and ARF-dependent Rac1 activation; scaffold proteins GRASP/Tamalin and IPCEF1 (binding the coiled-coil) coordinate the association of ARNO with Dock180 to enable ARF-to-Rac signaling.","method":"Coiled-coil deletion mutants, siRNA knockdown of GRASP and IPCEF1, Rac-GTP pulldown, migration assay, co-immunoprecipitation","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic tools + functional assays, defines scaffold mechanism for ARF→Rac signaling","pmids":["20016009"],"is_preprint":false},{"year":2010,"finding":"Cytohesin-2/ARNO interacts with the focal adhesion adaptor paxillin via its LIM2 domain and the ARNO polybasic region; this complex localizes to leading edges of migrating 3T3-L1 preadipocytes and is required for cytohesin-2-mediated ARF6-dependent cell migration.","method":"Co-immunoprecipitation, pulldown with domain mutants, siRNA knockdown, SecinH3 inhibition, ARF6-GTP pulldown, migration assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — direct domain mapping + co-IP + siRNA + functional assay, identifies paxillin as scaffold for ARNO","pmids":["20525696"],"is_preprint":false},{"year":2010,"finding":"On membranes, Arf6-GTP activates ARNO at nanomolar concentrations via the PH domain in a positive feedback loop; ARNO is further activated by its own product Arf1-GTP (another positive feedback); PH domain mutations that abolish Arf6-GTP interaction completely inactivate ARNO on liposomes but not in solution.","method":"In vitro GEF assay on liposomes with full-length membrane-bound Arf, PH domain point mutants, competition with Arf effectors","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted on liposomes with mutagenesis, reveals bistable switch mechanism","pmids":["21118813"],"is_preprint":false},{"year":2010,"finding":"Multiple sites on the N-terminus of the V-ATPase a2-subunit (a2N) interact with the Sec7, PH, and polybasic domains of ARNO; the a2N(1–17) peptide inhibits ARNO GEF activity by binding the Sec7 domain with KD ~344 nM; Ser392 phosphorylation abolishes a2N binding to the ARNO polybasic region.","method":"Synthetic peptide binding assays, SPR kinetics, pulldown with recombinant proteins, NMR structure determination, in silico docking, GEF activity assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — SPR + NMR + in vitro GEF assay + docking, detailed molecular mechanism","pmids":["20153292"],"is_preprint":false},{"year":2011,"finding":"ARNO directly interacts with aldolase (but not other glycolytic enzymes) via the ARNO PH domain; SPR reveals KD = 2.84 × 10⁻¹⁰ M. Aldolase associates with early endosomal membranes and forms a complex with ARNO/Arf6 and V-ATPase. Aldolase knockdown causes cell morphology changes and acidic vesicle redistribution.","method":"GST pulldown, SPR, cell fractionation, siRNA knockdown, immunofluorescence","journal":"American journal of physiology. Cell physiology","confidence":"Medium","confidence_rationale":"Tier 2 — SPR + pulldown + functional knockdown, single lab","pmids":["21307348"],"is_preprint":false},{"year":2011,"finding":"ARNO mediates glucose-stimulated insulin secretion in β-cells through sequential activation of ARF6 → Cdc42 → Rac1; siRNA knockdown of ARNO or inactive ARNO (E156K) reduces GSIS; co-immunoprecipitation shows increased ARNO–ARF6 association upon glucose stimulation.","method":"siRNA knockdown, dominant-negative mutants, SecinH3 inhibition, GST-GGA3/PAK-1 pulldown assays for ARF6/Rac GTP-loading, co-immunoprecipitation, insulin secretion assay","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological + genetic + biochemical GTP-loading assays, epistasis establishes ARNO upstream of ARF6/Cdc42/Rac1","pmids":["21276423"],"is_preprint":false},{"year":2012,"finding":"IL-1β signals through MYD88–ARNO–ARF6 to disrupt endothelial barrier function independently of NF-κB; ARNO binds directly to the adaptor MYD88; SecinH3 (ARNO inhibitor) enhances vascular stability in inflammatory arthritis and acute inflammation models in vivo.","method":"Direct binding assay (ARNO–MYD88), siRNA knockdown, SecinH3 inhibition, endothelial permeability assay, in vivo inflammatory models","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — direct binding + genetic knockdown + in vivo rescue, high-impact journal, multiple orthogonal approaches","pmids":["23143332"],"is_preprint":false},{"year":2012,"finding":"Salmonella recruits ARNO via ARF6 and SopB-induced PIP3 generation; ARNO in turn activates the WAVE regulatory complex (WRC) for actin polymerization and macropinosome formation; RNAi screening identified ARNO as key host ARF-GEF for Salmonella invasion.","method":"siRNA screen, immunofluorescence, invasion assay, dominant-negative ARF/ARNO mutants, phosphoinositide imaging","journal":"Cell host & microbe","confidence":"Medium","confidence_rationale":"Tier 2 — RNAi screen + mechanistic follow-up, places ARNO downstream of ARF6/PIP3 and upstream of WRC","pmids":["22341462"],"is_preprint":false},{"year":2013,"finding":"The N-terminal cytosolic tail of the V-ATPase a2-subunit (a2N(1–17)) directly inhibits cytohesin-2 GEF activity by interacting with its Sec7 domain; NMR determined that Phe5, Met10, Gln14 of a2N are involved; a2N competes with the switch 2 region of Arf1/Arf6 for Sec7 binding. This signaling is conserved across all four a-subunit isoforms and with yeast V-ATPase.","method":"In vitro GEF assay, NMR spectroscopy, in silico docking, binding/competition assays with recombinant proteins","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure + in vitro GEF reconstitution + competition assay, evolutionary conservation demonstrated","pmids":["23288846"],"is_preprint":false},{"year":2014,"finding":"Cytohesin-2 interacts with CCDC120 in neurites of differentiating N1E-115 cells; CCDC120-containing vesicles transport cytohesin-2 anterogradely along neurites; CCDC120 knockdown reduces Arf6 activation and inhibits neurite growth; CCDC120 lacking the cytohesin-2-binding CC1 region cannot rescue.","method":"Co-immunoprecipitation, siRNA knockdown, live-cell imaging of vesicle transport, Arf6-GTP pulldown, morphometry","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP + live imaging + siRNA + functional rescue, single lab","pmids":["25326380"],"is_preprint":false},{"year":2014,"finding":"PKC phosphorylates cytohesin-2 in platelets; under basal conditions, cytohesin-2 keeps ARF6 constitutively GTP-loaded to suppress dense granule secretion; PKC-mediated phosphorylation of cytohesin-2 disrupts its interaction with ARF6, decreases ARF6-GTP, and promotes platelet secretion and aggregation.","method":"Immunoprecipitation + mass spectrometry, Western blot, SecinH3 pharmacology, lumi-aggregometry, flow cytometry","journal":"Journal of thrombosis and haemostasis","confidence":"Medium","confidence_rationale":"Tier 2 — MS identification of PKC phosphorylation + functional pharmacology + ARF6-GTP measurement, single lab","pmids":["24581425"],"is_preprint":false},{"year":2014,"finding":"Cytohesin-2 interacts with actinin-1 (ACTN1) via its polybasic C-terminal region (binding the ACTN1 EFh2 domain); this interaction is required for ARF6 activation at growth cones and neurite extension in N1E-115 cells; FRET assay with cell-permeable peptides confirms the interaction reduces ARF6-GTP at growth cones.","method":"Co-immunoprecipitation, pulldown, siRNA knockdown, ARF6-GTP pulldown, FRET with cell-permeable peptides, morphometry","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding domain mapping + FRET + siRNA + functional readout, single lab","pmids":["22659138"],"is_preprint":false},{"year":2015,"finding":"Cytohesin-2/ARNO localizes to EHD1-positive recycling endosomes and regulates recycling of R-Ras and α5-integrin to the plasma membrane via ARF GTPase activation; GEF-inactive ARNO (E156K) causes R-Ras accumulation on recycling endosomes and inhibits cell spreading.","method":"Co-localization by confocal microscopy, siRNA knockdown, dominant-negative ARNO (E156K), integrin recycling assay, cell spreading assay","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — localization + functional knockdown + recycling assay, identifies new compartment for ARNO","pmids":["26378252"],"is_preprint":false},{"year":2015,"finding":"RLIP76 links ARNO to activated R-Ras at recycling endosomes: RLIP76 N-terminus (residues 1–180) binds ARNO and residues 180–192 bind R-Ras, forming a ternary complex in Rab11-positive compartments that activates Arf6 and promotes cell spreading and migration.","method":"Co-immunoprecipitation, GST pulldown, domain deletion mutants, ARF6-GTP assay, cell spreading/migration assay, immunofluorescence colocalization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding + functional domain mutants + Arf6-GTP assay, single lab","pmids":["26498519"],"is_preprint":false},{"year":2015,"finding":"Cytohesin-2/ARNO is required for Schwann cell myelination in the peripheral nervous system; conditional knockout of cytohesin-2 in Schwann cells reduces ARF6 activity, decreases myelin thickness in sciatic nerves, and reduces myelin protein zero (MPZ) expression.","method":"Schwann cell-specific conditional knockout mice, ARF6-GTP assay, electron microscopy of myelin thickness, Western blot for MPZ, SecinH3 pharmacology in culture","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — in vivo conditional KO with defined molecular (ARF6-GTP) and cellular (myelin thickness) phenotypes","pmids":["25824033"],"is_preprint":false},{"year":2016,"finding":"ARNO and ARF1 are required for podosome assembly; ARNO colocalizes with adhesive rings of podosomes; ARF1 inhibition increases RhoA-GTP and myosin-IIA filament assembly, which suppresses podosomes; constitutively active ARF1 induces podosome precursors containing actin cores.","method":"siRNA knockdown, pharmacological inhibition (SecinH3, brefeldin A), ARF1-GTP assay, RhoA-GTP assay, immunofluorescence, matrix degradation assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic knockdown + pharmacology + epistasis (RhoA/myosin-IIA rescue), multiple orthogonal approaches","pmids":["28007915"],"is_preprint":false},{"year":2018,"finding":"INAVA's CUPID domain stably binds ARNO to promote lateral membrane F-actin assembly and barrier function; when ARNO is bound to CUPID, it promotes F-actin dynamics independent of its canonical GEF activity. Upon IL-1β, INAVA relocates to cytosolic puncta where CUPID amplifies TRAF6-dependent polyubiquitination/inflammatory signaling, while ARNO binding to CUPID negatively-regulates this inflammatory response.","method":"Co-immunoprecipitation, domain binding assays, siRNA knockdown, actin dynamics assay, ubiquitination assay, IL-1β signaling readout in epithelial cells and macrophages","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, GEF-independent function defined, validated in primary human macrophages","pmids":["30355448"],"is_preprint":false},{"year":2019,"finding":"ARNO (cytohesin-2) binds the juxtamembrane (JM) intracellular segment of EGFR; NMR structural characterization reveals the ARNO-EGFR interaction interface, which shares features with but is distinct from JM interactions with calmodulin and anionic phospholipids; each interaction can be modulated by the others.","method":"NMR spectroscopy, in vitro binding assays","journal":"Structure","confidence":"Medium","confidence_rationale":"Tier 1 — NMR structural characterization of interaction, but functional consequences not fully resolved in this study","pmids":["31780432"],"is_preprint":false},{"year":2021,"finding":"Cytohesin-2 (CYTH2) forms a complex with CNKSR2; CYTH2 binding prevents proteasomal degradation of CNKSR2; shRNA knockdown of either CNKSR2 or CYTH2 in mouse hippocampal granule cell precursors results in abnormal localization and immature granule cell characteristics, demonstrating both are required for dentate granule cell development.","method":"Co-immunoprecipitation, proteasome inhibition, in vivo shRNA transduction, immunofluorescence, cell positioning assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP + in vivo shRNA + proteasome assay, single lab","pmids":["34800437"],"is_preprint":false},{"year":2021,"finding":"Cytohesin-2 is enriched in perisynaptic membranes of dorsal horn neurons and forms a protein complex with mGluR5; cytohesin-2 conditional knockout mice show reduced mechanical allodynia in inflammatory and neuropathic pain models; cytohesin-2 mediates mGluR5-dependent ERK1/2 activation via Arf6 in spinal cord.","method":"Immunoelectron microscopy, co-immunoprecipitation, conditional KO mice, SecinH3 pharmacology, ARF1/6-GTP assay, ERK phosphorylation assay, behavioral pain assays","journal":"Neurobiology of disease","confidence":"High","confidence_rationale":"Tier 2 — in vivo conditional KO + co-IP + ARF6-GTP + ERK readout + behavioral phenotype, multiple orthogonal approaches","pmids":["34390832"],"is_preprint":false},{"year":2022,"finding":"Cytohesin-2 Tyr381 phosphorylation status is central to Schwann cell myelination; dephosphorylation by PTP4A1 reduces ARNO activity while SH2B1 interaction maintains Tyr381 phosphorylation and promotes myelination; knockin Y381F mice show reduced myelin thickness and ARF6 activity.","method":"Knockin mice (Y381F), Schwann cell-specific conditional KO of PTP4A1 and SH2B1, ARF6-GTP assay, co-immunoprecipitation, Western blot, electron microscopy of myelin","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 — multiple in vivo genetic models + biochemical Arf6-GTP readout, identifies writer/eraser of phosphorylation regulating CYTH2","pmids":["35077201"],"is_preprint":false},{"year":2022,"finding":"CYTH2 is required for efficient influenza virus infection by mediating endosomal trafficking; CRISPR-Cas9 genome-wide screen identified CYTH2 as a host factor for influenza; SecinH3 treatment reduces influenza infection in vivo.","method":"Genome-wide CRISPR-Cas9 screen with survival selection, endosomal trafficking assay, SecinH3 in vivo treatment, viral infection assay","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide CRISPR screen + functional validation + in vivo pharmacology, single lab","pmids":["35354039"],"is_preprint":false},{"year":2022,"finding":"FE65 (neuronal adaptor) interacts with ARNO and forms a ternary complex with ARF6; FE65 attenuates ARNO intramolecular autoinhibition and promotes ARNO dimerization, thereby potentiating ARNO-stimulated ARF6-mediated neurite outgrowth; FE65 mutations disrupting FE65-ARNO interaction abolish this potentiation.","method":"Co-immunoprecipitation, GST pulldown, ARF6-GTP assay, neurite morphometry, autoinhibition assay, dimerization assay","journal":"Open biology","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding + functional mutant rescue + ARF6-GTP + morphometric readout, single lab","pmids":["36168805"],"is_preprint":false},{"year":2023,"finding":"V-ATPase V0a1 subunit interacts with ARNO and promotes ARF6 activation during exocytosis in neuroendocrine cells; disruption of the V0a1–ARNO interaction inhibits PLD activation, phosphatidic acid synthesis, and alters the timing of membrane fusion events.","method":"Co-immunoprecipitation, ARF6-GTP assay, PLD activity assay, phosphatidic acid measurement, TIRF live imaging of exocytotic events","journal":"Frontiers in molecular biosciences","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP + functional lipid assays + live exocytosis imaging, single lab","pmids":["37091866"],"is_preprint":false},{"year":2026,"finding":"Full knockout of cytohesin-2 in mice causes perinatal lethality within 20 h of birth; cytohesin-2 deficiency reduces Golgi volume (rescued by re-expression of cytohesin-2, even in an ARF-GEF-independent manner), impairs galactosylation, and markedly reduces global protein secretion in neonates.","method":"Global knockout mice, organellar proteomics by mass spectrometry, immunofluorescence (Golgi markers, PNA staining), quantitative secretome proteomics","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO with lethal phenotype + organellar proteomics + ARF-GEF-independent rescue, reveals essential in vivo function and Golgi maintenance role","pmids":["41672711"],"is_preprint":false}],"current_model":"CYTH2/ARNO is a multi-domain guanine nucleotide exchange factor (GEF) that activates ARF1 and ARF6 GTPases via a Sec7 domain 'glutamic finger' mechanism (Glu156 displacing Mg²⁺ and GDP); membrane recruitment is cooperatively controlled by PH-domain binding to PIP3/PIP2 and a polybasic C-terminal region (regulated by a PKC-dependent electrostatic switch at Ser392), and by upstream activators including ARL4D, Arf6-GTP itself (positive feedback on membranes), Gαq, V-ATPase a-subunit isoforms, and scaffold partners (paxillin, IPCEF1, GRASP, RLIP76); at the plasma membrane CYTH2 drives ARF6-dependent actin remodeling, lamellipodia, cell migration, endocytosis, and receptor signaling (including GPCR desensitization, VEGFR-2 stabilization, MYD88-dependent vascular permeability, and mGluR5-ERK pain signaling), while also supporting Golgi maintenance and protein secretion through an ARF-GEF-independent activity that is essential for perinatal survival."},"narrative":{"teleology":[{"year":1997,"claim":"Establishing that ARNO is a direct ARF1 GEF whose membrane recruitment through PH-domain–PIP2 interaction is essential for catalytic function answered the foundational question of how cytosolic ARF exchange factors reach their substrates.","evidence":"In vitro nucleotide exchange assay on phospholipid vesicles with domain deletion mutants","pmids":["9268368"],"confidence":"High","gaps":["Relative in vivo substrate preference (ARF1 vs ARF6) not resolved","Regulation beyond PIP2 binding unknown"]},{"year":1998,"claim":"Crystal structures of the Sec7 domain and identification of the Glu156 'glutamic finger' mechanism revealed how ARNO destabilizes Mg²⁺ and GDP from ARF, providing the first atomic-level understanding of ARF-GEF catalysis.","evidence":"X-ray crystallography at 2.0–2.2 Å resolution, site-directed mutagenesis (E156K/E156D) with in vitro exchange assays","pmids":["9510256","9476900","9649435"],"confidence":"High","gaps":["Full Sec7–ARF complex structure not yet solved at the time","Mechanism of membrane-dependent enhancement not structurally resolved"]},{"year":1998,"claim":"Localization of ARNO to the plasma membrane (not Golgi) and demonstration of ARF6 activation and actin cytoskeletal remodeling established the primary cellular site of action and linked ARNO to cell morphology control.","evidence":"Subcellular fractionation, immunolocalization, and overexpression of domain mutants in HeLa cells with actin phenotyping","pmids":["9417041","9802902","9550703"],"confidence":"High","gaps":["Whether ARNO also functions at intracellular compartments in vivo unclear","Downstream effectors of ARF6 for actin remodeling not identified"]},{"year":1999,"claim":"Discovery that PKC phosphorylation of Ser392 in the polybasic C-terminal region creates an electrostatic switch reducing membrane binding established a key regulatory mechanism controlling ARNO membrane association.","evidence":"In vitro phosphorylation, liposome cosedimentation, phosphomimetic mutants, in vivo membrane fractionation","pmids":["10531036","10801341"],"confidence":"High","gaps":["Physiological context triggering PKC-mediated release not defined","Whether Ser392 phosphorylation is dynamically reversed in vivo unclear"]},{"year":2001,"claim":"Demonstration that ARNO activates endogenous ARF6 to independently stimulate Rac1 and PLD in epithelial cells resolved the downstream branching logic through which ARNO drives cell migration.","evidence":"Dominant-active ARNO expression in MDCK cells with ARF6-GTP, Rac-GTP, and PLD activity pulldown assays plus motility readout","pmids":["11481345"],"confidence":"High","gaps":["Rac GEF identity downstream of ARF6 not yet determined","How PLD activity converges on motility mechanistically unknown"]},{"year":2001,"claim":"The finding that V-ATPase-dependent endosomal acidification recruits ARNO and ARF6 to early endosomes revealed a pH-sensing mechanism linking endosomal maturation to ARF signaling.","evidence":"Subcellular fractionation and in vitro translocation assay with ATP-driven acidification in kidney proximal tubule cells","pmids":["11278939"],"confidence":"High","gaps":["Molecular identity of the V-ATPase subunit mediating ARNO interaction not yet mapped","Whether pH sensing is direct or indirect unclear"]},{"year":2005,"claim":"Identification of the Dock180/ELMO complex as the Rac GEF downstream of ARNO-ARF6 completed the signaling cascade from ARNO to Rac1 activation and cell motility.","evidence":"Dominant-negative Dock180 and ELMO mutants block ARNO-induced Rac-GTP and motility in MDCK cells","pmids":["16213822"],"confidence":"High","gaps":["How ARF6-GTP recruits/activates Dock180–ELMO mechanistically unresolved","Contribution of other Rac GEFs in different cell types not excluded"]},{"year":2006,"claim":"Mapping the V-ATPase a2-subunit as the direct ARNO-binding partner on endosomes and showing that disruption of a2–ARNO interaction blocks endocytosis established a specific molecular link between V-ATPase and ARF-GEF signaling.","evidence":"Reciprocal co-immunoprecipitation, acidification-dependent binding, endocytosis assays in epithelial cells","pmids":["16415858"],"confidence":"High","gaps":["Structural basis of pH-dependent interaction not resolved","Contribution of other a-subunit isoforms unknown at this point"]},{"year":2007,"claim":"Discovery that ARL4D and Gαq each recruit ARNO to the plasma membrane through distinct domain interactions (PH/polybasic for ARL4D; coiled-coil for Gαq) revealed multiple upstream activation inputs converging on ARNO.","evidence":"Yeast two-hybrid, co-immunoprecipitation, ARF6-GTP pulldowns, siRNA epistasis in multiple cell lines","pmids":["17804820","16650966","17846866"],"confidence":"High","gaps":["Whether ARL4D and Gαq pathways are synergistic or context-specific not tested","Structural basis of Gαq–coiled-coil interaction not solved"]},{"year":2009,"claim":"Defining how scaffolds GRASP/IPCEF1 and paxillin coordinate ARNO coiled-coil and polybasic domains with Dock180 explained how multiprotein assemblies at leading edges enable efficient ARF-to-Rac signaling during migration.","evidence":"Coiled-coil deletion mutants, siRNA knockdown of GRASP/IPCEF1/paxillin, Rac-GTP pulldown, migration assays","pmids":["20016009","20525696"],"confidence":"High","gaps":["Stoichiometry of the multiprotein complex not determined","Whether scaffolding varies across cell types unknown"]},{"year":2010,"claim":"Reconstitution showing that Arf6-GTP activates ARNO through its PH domain in a positive-feedback loop on membranes revealed a bistable switch mechanism that amplifies ARF signaling.","evidence":"In vitro GEF assay on liposomes with full-length membrane-bound Arf and PH domain point mutants","pmids":["21118813"],"confidence":"High","gaps":["How the positive feedback is terminated in cells not addressed","Quantitative parameters of bistability not modeled"]},{"year":2012,"claim":"Demonstration that IL-1β signals through MYD88–ARNO–ARF6 to increase endothelial permeability independently of NF-κB, with SecinH3 providing in vivo vascular protection, established ARNO as a druggable node in inflammatory barrier dysfunction.","evidence":"Direct binding assay, siRNA, SecinH3 pharmacology, endothelial permeability assay, in vivo inflammatory models","pmids":["23143332"],"confidence":"High","gaps":["Structural basis of MYD88–ARNO interaction not solved","Therapeutic window and off-target effects of SecinH3 in vivo not fully characterized"]},{"year":2013,"claim":"NMR-based mapping of the V-ATPase a2N peptide interaction with the ARNO Sec7 domain, competing with ARF switch 2, provided the structural mechanism for pH-dependent regulation of ARNO catalytic activity.","evidence":"NMR spectroscopy, in vitro GEF reconstitution, competition assays with recombinant proteins","pmids":["23288846","20153292"],"confidence":"High","gaps":["Full-length a2–ARNO complex structure not available","How luminal pH change is transduced to cytoplasmic a2N conformation not resolved"]},{"year":2015,"claim":"Conditional knockout of CYTH2 in Schwann cells reduced ARF6 activity and myelin thickness, establishing an essential in vivo role for CYTH2 in peripheral nerve myelination.","evidence":"Schwann cell-specific conditional KO mice, ARF6-GTP assay, electron microscopy of sciatic nerve","pmids":["25824033"],"confidence":"High","gaps":["Whether CYTH2 acts through ARF6 alone or also ARF1 in myelination not resolved","Downstream effectors of ARF6 in myelin wrapping unknown"]},{"year":2018,"claim":"The finding that INAVA's CUPID domain binds ARNO to promote F-actin assembly independently of GEF activity established a GEF-independent scaffolding function for ARNO in epithelial barrier maintenance and inflammatory signaling.","evidence":"Co-immunoprecipitation, domain binding, siRNA, actin dynamics and ubiquitination assays in epithelial cells and macrophages","pmids":["30355448"],"confidence":"High","gaps":["Structural basis of CUPID–ARNO interaction not determined","Relative contribution of GEF-dependent vs -independent functions at the barrier unclear"]},{"year":2022,"claim":"Identification of Tyr381 as a phosphorylation switch regulated by PTP4A1 (dephosphorylation) and SH2B1 (protection), with knockin Y381F mice showing reduced myelination, revealed a tyrosine phosphorylation layer controlling ARNO activity in vivo.","evidence":"Y381F knockin mice, Schwann cell-specific conditional KO of PTP4A1/SH2B1, ARF6-GTP assay, electron microscopy","pmids":["35077201"],"confidence":"High","gaps":["Kinase responsible for Tyr381 phosphorylation not identified","Whether Tyr381 regulation operates in non-Schwann cell contexts unknown"]},{"year":2026,"claim":"Full CYTH2 knockout causing perinatal lethality with Golgi volume loss and secretion failure—rescuable by GEF-inactive CYTH2—revealed an essential, ARF-GEF-independent structural role in Golgi maintenance and organismal viability.","evidence":"Global KO mice, organellar and secretome mass spectrometry, immunofluorescence, rescue with catalytically dead ARNO","pmids":["41672711"],"confidence":"High","gaps":["Molecular mechanism of GEF-independent Golgi maintenance unknown","Which CYTH2 domain mediates Golgi structural role not mapped","Whether other cytohesin family members partially compensate in vivo not fully resolved"]},{"year":null,"claim":"The molecular mechanism by which CYTH2 maintains Golgi integrity independently of ARF-GEF activity, the structural basis for several key protein interactions (MYD88, INAVA-CUPID, Gαq), and the kinase responsible for Tyr381 phosphorylation remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["GEF-independent Golgi maintenance mechanism uncharacterized","High-resolution structures of ARNO with MYD88, INAVA, or Gαq not available","Tyr381 kinase identity unknown","Whether positive-feedback bistability operates in vivo and how it is terminated not demonstrated"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0,2,9,27]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,9,27,30]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[0,5,8]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[25,41]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,4,5,9,22,26]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[10,19,37]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[49]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[9,17,21,31,44]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[10,19,20,46]},{"term_id":"R-HSA-1500931","term_label":"Cell-Cell communication","supporting_discovery_ids":[26,40]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[37,49]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[31,41]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[49]}],"complexes":["V-ATPase–ARNO–ARF6 endosomal complex","ARNO–Dock180/ELMO migration complex"],"partners":["ARF6","ARF1","MYD88","ARL4D","GNAQ","PXN","IPCEF1","RLIP76"],"other_free_text":[]},"mechanistic_narrative":"CYTH2 (ARNO/cytohesin-2) is a guanine nucleotide exchange factor (GEF) for ARF-family GTPases that integrates lipid, receptor, and scaffolding signals to control membrane trafficking, actin remodeling, cell migration, and protein secretion. Its Sec7 domain catalyzes GDP-to-GTP exchange on ARF1 and ARF6 through a conserved 'glutamic finger' (Glu156) mechanism that displaces Mg²⁺ and GDP [PMID:9649435], while membrane recruitment is cooperatively driven by PH-domain binding to PIP3/PIP2, a polybasic C-terminal region regulated by PKC phosphorylation at Ser392 [PMID:10531036], and upstream activators including ARL4D, Gαq, V-ATPase a-subunit isoforms, and Arf6-GTP itself in a positive-feedback loop [PMID:21118813, PMID:17804820, PMID:16415858]. At the plasma membrane and endosomes, CYTH2-activated ARF6 signals through Rac1 (via Dock180/ELMO), PLD, and the WAVE regulatory complex to drive lamellipodia formation, endocytosis, receptor trafficking, Schwann cell myelination, and inflammatory vascular permeability; full knockout in mice causes perinatal lethality with loss of Golgi integrity and global protein secretion that is rescued even by GEF-inactive CYTH2, revealing an essential ARF-GEF-independent structural role [PMID:41672711, PMID:23143332, PMID:25824033, PMID:16213822]."},"prefetch_data":{"uniprot":{"accession":"Q99418","full_name":"Cytohesin-2","aliases":["ARF exchange factor","ARF nucleotide-binding site opener","Protein ARNO","PH, SEC7 and coiled-coil domain-containing protein 2"],"length_aa":400,"mass_kda":46.5,"function":"Acts as a guanine-nucleotide exchange factor (GEF). Promotes guanine-nucleotide exchange on ARF1, ARF3 and ARF6. Activates ARF factors through replacement of GDP with GTP (By similarity). The cell membrane form, in association with ARL4 proteins, recruits ARF6 to the plasma membrane (PubMed:17398095). Involved in neurite growth (By similarity)","subcellular_location":"Cell membrane; Cytoplasm; Cell projection; Cell projection, growth cone; Cell junction, tight junction; Cell junction, adherens junction","url":"https://www.uniprot.org/uniprotkb/Q99418/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CYTH2","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/CYTH2","total_profiled":1310},"omim":[{"mim_id":"619948","title":"INTERACTION PROTEIN FOR CYTOHESIN EXCHANGE FACTORS 1; IPCEF1","url":"https://www.omim.org/entry/619948"},{"mim_id":"618051","title":"INNATE IMMUNITY ACTIVATOR; INAVA","url":"https://www.omim.org/entry/618051"},{"mim_id":"617476","title":"CNKSR FAMILY, MEMBER 3; CNKSR3","url":"https://www.omim.org/entry/617476"},{"mim_id":"612027","title":"TRAFFICKING REGULATOR AND SCAFFOLD PROTEIN TAMALIN; TAMALIN","url":"https://www.omim.org/entry/612027"},{"mim_id":"602488","title":"CYTOHESIN 2; CYTH2","url":"https://www.omim.org/entry/602488"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Golgi apparatus","reliability":"Additional"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CYTH2"},"hgnc":{"alias_symbol":["CTS18.1","Sec7p-L","ARNO","Sec7p-like","cytohesin-2"],"prev_symbol":["PSCD2L","PSCD2"]},"alphafold":{"accession":"Q99418","domains":[{"cath_id":"1.10.1000.11","chopping":"90-245","consensus_level":"medium","plddt":91.037,"start":90,"end":245},{"cath_id":"2.30.29.30","chopping":"261-378","consensus_level":"high","plddt":85.5223,"start":261,"end":378}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99418","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99418-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99418-F1-predicted_aligned_error_v6.png","plddt_mean":84.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CYTH2","jax_strain_url":"https://www.jax.org/strain/search?query=CYTH2"},"sequence":{"accession":"Q99418","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99418.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99418/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99418"}},"corpus_meta":[{"pmid":"16415858","id":"PMC_16415858","title":"V-ATPase interacts with ARNO and Arf6 in early endosomes and regulates the protein degradative pathway.","date":"2006","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/16415858","citation_count":396,"is_preprint":false},{"pmid":"11481345","id":"PMC_11481345","title":"Activation of ARF6 by ARNO stimulates epithelial cell migration through downstream activation of both Rac1 and phospholipase D.","date":"2001","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11481345","citation_count":323,"is_preprint":false},{"pmid":"9550703","id":"PMC_9550703","title":"Insulin-dependent translocation of ARNO to the plasma membrane of adipocytes requires phosphatidylinositol 3-kinase.","date":"1998","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/9550703","citation_count":230,"is_preprint":false},{"pmid":"9417041","id":"PMC_9417041","title":"ARNO is a guanine nucleotide exchange factor for ADP-ribosylation factor 6.","date":"1998","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9417041","citation_count":208,"is_preprint":false},{"pmid":"9649435","id":"PMC_9649435","title":"A glutamic finger in the guanine nucleotide exchange factor ARNO displaces Mg2+ and the beta-phosphate to destabilize GDP on ARF1.","date":"1998","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9649435","citation_count":164,"is_preprint":false},{"pmid":"9476900","id":"PMC_9476900","title":"Structure of the guanine nucleotide exchange factor Sec7 domain of human arno and analysis of the interaction with ARF GTPase.","date":"1998","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/9476900","citation_count":161,"is_preprint":false},{"pmid":"9510256","id":"PMC_9510256","title":"Structure of the Sec7 domain of the Arf exchange factor ARNO.","date":"1998","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/9510256","citation_count":154,"is_preprint":false},{"pmid":"9268368","id":"PMC_9268368","title":"Role of protein-phospholipid interactions in the activation of ARF1 by the guanine nucleotide exchange factor Arno.","date":"1997","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9268368","citation_count":149,"is_preprint":false},{"pmid":"14565977","id":"PMC_14565977","title":"ARNO and ARF6 regulate axonal elongation and branching through downstream activation of phosphatidylinositol 4-phosphate 5-kinase alpha.","date":"2003","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/14565977","citation_count":141,"is_preprint":false},{"pmid":"23143332","id":"PMC_23143332","title":"Interleukin receptor activates a MYD88-ARNO-ARF6 cascade to disrupt vascular stability.","date":"2012","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/23143332","citation_count":135,"is_preprint":false},{"pmid":"16213822","id":"PMC_16213822","title":"The DOCK180/Elmo complex couples ARNO-mediated Arf6 activation to the downstream activation of Rac1.","date":"2005","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/16213822","citation_count":130,"is_preprint":false},{"pmid":"11278939","id":"PMC_11278939","title":"Intra-endosomal pH-sensitive recruitment of the Arf-nucleotide exchange factor ARNO and Arf6 from cytoplasm to proximal tubule endosomes.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11278939","citation_count":117,"is_preprint":false},{"pmid":"9802902","id":"PMC_9802902","title":"Remodeling of the actin cytoskeleton is coordinately regulated by protein kinase C and the ADP-ribosylation factor nucleotide exchange factor ARNO.","date":"1998","source":"Molecular biology of 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Direct binding of ARNO/cytohesin-2 to the carboxyl terminus of the A2A adenosine receptor is necessary for sustained activation of the ERK/MAP kinase pathway.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16027149","citation_count":52,"is_preprint":false},{"pmid":"15277685","id":"PMC_15277685","title":"Discriminatory aptamer reveals serum response element transcription regulated by cytohesin-2.","date":"2004","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/15277685","citation_count":50,"is_preprint":false},{"pmid":"20525696","id":"PMC_20525696","title":"Cytohesin-2/ARNO, through its interaction with focal adhesion adaptor protein paxillin, regulates preadipocyte migration via the downstream activation of Arf6.","date":"2010","source":"The Journal of biological 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PIP2-PH interaction does not directly regulate catalytic activity but serves membrane recruitment. A stable complex between the Sec7 domain and nucleotide-free ARF1 can be isolated.\",\n      \"method\": \"In vitro nucleotide exchange assay with phospholipid vesicles, protein-lipid binding, domain deletion mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with domain mutagenesis, foundational mechanistic study\",\n      \"pmids\": [\"9268368\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Crystal structure of the Sec7 domain of human ARNO resolved at 2.0–2.2 Å; the domain is an elongated all-helical protein with a hydrophobic groove and adjacent conserved loop that constitute the ARF1-binding surface, interacting with the switch 1 and switch 2 regions of ARF1.\",\n      \"method\": \"X-ray crystallography, structure-based mutagenesis, protein footprinting\",\n      \"journal\": \"Nature / Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — two independent crystal structures with functional mutagenesis validation\",\n      \"pmids\": [\"9510256\", \"9476900\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Glu156 of the ARNO Sec7 domain acts as a 'glutamic finger' that destabilizes Mg2+ and GDP from ARF1 to drive nucleotide exchange; E156D and E156K mutations reduce exchange activity by orders of magnitude. E156K forms a complex with Mg2+-free ARF1-GDP without inducing GDP release. Switch I hydrophobic residues of ARF1 insert into the Sec7 groove; Lys73 of ARF1 switch II forms an ion pair with Asp183 of ARNO.\",\n      \"method\": \"Site-directed mutagenesis, in vitro nucleotide exchange assay, stable complex isolation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + in vitro biochemical reconstitution, mechanistic detail confirmed by structural data\",\n      \"pmids\": [\"9649435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"ARNO localizes to the plasma membrane (not Golgi) in mammalian cells and stimulates nucleotide exchange on both ARF1 and ARF6 in vitro, with ARF6 being the likely in vivo target at the plasma membrane.\",\n      \"method\": \"In vitro GEF assay, subcellular fractionation, immunolocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — fractionation + immunolocalization + in vitro activity, replicated in subsequent papers\",\n      \"pmids\": [\"9417041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"ARNO-induced actin stress fiber disassembly and ARF6-dependent actin rearrangement requires the PH domain for membrane localization; PKC phosphorylates ARNO at a site C-terminal to the PH domain but mutation of this site does not block actin rearrangement.\",\n      \"method\": \"Overexpression in HeLa cells, PKC agonist treatment, domain deletion mutants, immunofluorescence\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function domain mutants with defined cytoskeletal phenotype, multiple orthogonal approaches\",\n      \"pmids\": [\"9802902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Insulin stimulates PI3K-dependent translocation of ARNO from cytoplasm to plasma membrane in adipocytes via PH domain binding to PIP3; this translocation is blocked by wortmannin, LY294002, or dominant-negative p85.\",\n      \"method\": \"GFP-tagged ARNO live imaging in 3T3-L1 adipocytes, PI3K inhibitors, dominant-negative constructs, in vitro lipid binding\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — live-cell imaging + pharmacological + genetic inhibition, replicated in subsequent work\",\n      \"pmids\": [\"9550703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"ARNO overexpression in HeLa cells inhibits the early secretory pathway, blocks ER-to-Golgi trafficking of SEAP, and causes disassembly of the Golgi complex, consistent with ARNO acting as an exchange factor for ARF1 in Golgi-to-ER transport.\",\n      \"method\": \"Overexpression in HeLa cells, SEAP secretion assay, endoglycosidase H resistance, immunofluorescence, cell fractionation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assay with defined phenotype, but single lab without reconstitution\",\n      \"pmids\": [\"9788883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PKC phosphorylates ARNO at Ser392 within the polybasic C-terminal domain; this introduces a negative charge that reduces ARNO membrane binding in vitro and in vivo and inhibits ARF exchange activity via a 'PH domain electrostatic switch' mechanism.\",\n      \"method\": \"In vitro phosphorylation, liposome binding assay, in vivo membrane fractionation, exchange activity assay, phosphomimetic mutants\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution + mutagenesis + in vivo fractionation, novel regulatory mechanism\",\n      \"pmids\": [\"10531036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The ARNO PH domain provides specific PIP3 > PIP2 binding; the adjacent polybasic C-domain adds nonspecific ionic interactions with acidic lipids (PS); PKC phosphorylation of Ser392 in the C-domain reduces ionic affinity for PS without affecting phosphoinositide specificity.\",\n      \"method\": \"Liposome cosedimentation, ionic strength titration, in vitro GEF activity assay with domain constructs\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro binding + mutagenesis + activity assay\",\n      \"pmids\": [\"10801341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ARNO activates endogenous ARF6 (but not ARF1) at the plasma membrane in MDCK epithelial cells, leading to downstream Rac1 activation (required for motility) and phospholipase D (PLD) activation (required for motility via a separate pathway). Rac activation and PLD activation are independent downstream branches of ARF6.\",\n      \"method\": \"Dominant-active ARNO expression, ARF6-GTP pulldown assay, Rac-GTP pulldown, PLD activity assay, motility assay, dominant-negative constructs\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal assays, epistasis experiments placing ARNO upstream of ARF6 then Rac/PLD\",\n      \"pmids\": [\"11481345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ARNO and ARF6 are recruited from cytosol to early endosomes in kidney proximal tubule cells in a V-ATPase-dependent, intra-endosomal acidification-dependent manner; this recruitment is reversed by V-ATPase inhibitors and pH uncouplers.\",\n      \"method\": \"Subcellular fractionation, immunolocalization, in vitro translocation assay with ATP-driven acidification, Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — fractionation + translocation assay + pharmacological reversal, mechanistic link to V-ATPase\",\n      \"pmids\": [\"11278939\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The Sec7 domains of ARNO and EFA6 determine their GEF selectivity: ARNO preferentially activates ARF1 on membranes whereas EFA6 exclusively activates ARF6; selectivity maps to the Sec7 domain and ARF core domains without the N-terminal myristoylated helix.\",\n      \"method\": \"In vitro GEF assay on phospholipid membranes, domain-swap experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with domain swaps, defines molecular basis of selectivity\",\n      \"pmids\": [\"11342560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The N-terminal coiled-coil domain of ARNO/cytohesin-2 interacts with the scaffolding protein CASP; CASP is recruited to membrane ruffles by cytohesin in EGF-stimulated cells, revealing a functional interaction.\",\n      \"method\": \"Yeast two-hybrid screening, in vitro binding, co-immunoprecipitation in COS-1 cells, immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid + co-IP + colocalization, single lab\",\n      \"pmids\": [\"12052827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"ARNO and ARF6 regulate axonal elongation and branching in hippocampal neurons; downstream of ARF6, PI(4)P 5-kinase α mediates these effects on neurite extension. Catalytically inactive ARNO or dominant-negative ARF6 enhance extension; co-expression of constitutively active ARF6 abrogates this. Inactive ARNO/ARF6 also depletes Mena from growth cone leading edge.\",\n      \"method\": \"Overexpression of dominant-negative/constitutively active mutants in cultured rat hippocampal neurons, immunofluorescence, morphometric analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with multiple mutants, identifies PI(4)P 5-kinase α as downstream effector\",\n      \"pmids\": [\"14565977\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IPCEF1 interacts with the coiled-coil domain of cytohesin-2/ARNO and increases cytohesin-2-stimulated ARF-GTP formation both in vitro and in vivo; IPCEF1 is co-transported to the plasma membrane by cytohesin-2 upon EGF stimulation.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, immunoprecipitation, in vitro and in vivo ARF-GTP assay, immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — yeast two-hybrid + pulldown + functional GEF assay, single lab\",\n      \"pmids\": [\"12920129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"ARNO mediates insulin-stimulated ARF activation and PLD activation; both the PH domain (membrane targeting) and the Sec7 domain (catalytic activity) are required; coiled-coil domain deletion partially impairs membrane translocation.\",\n      \"method\": \"Transient transfection in HIRcB cells, domain deletion/mutation analysis, ARF-GTP pulldown, PLD activity assay, membrane fractionation\",\n      \"journal\": \"BMC cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple domain mutants + functional assays, single lab\",\n      \"pmids\": [\"12969509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"An RNA aptamer specific for ARNO/cytohesin-2 (binding its N-terminal coiled-coil/Sec7 region) inhibits serum-response element-driven transcription and MAPK activation in vivo without inhibiting GEF activity in vitro, revealing a GEF-independent function of cytohesin-2's N-terminus in MAPK/SRE signaling.\",\n      \"method\": \"SELEX aptamer selection, intracellular aptamer (intramer) transfection, SRE-reporter assay, ERK phosphorylation assay\",\n      \"journal\": \"PNAS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific inhibitor + reporter assay + MAPK readout, novel GEF-independent mechanism\",\n      \"pmids\": [\"15277685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ARNO/cytohesin-2 directly binds the juxtamembrane carboxyl terminus of the A2A adenosine receptor; this interaction is required for ARF6-dependent sustained ERK/MAP kinase activation but not for cAMP signaling or receptor desensitization.\",\n      \"method\": \"Yeast two-hybrid, mutual pulldown of bacterial fusion proteins, co-immunoprecipitation, inducible dominant-negative expression, cAMP and ERK assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct interaction confirmed by pulldown + co-IP + genetic epistasis with defined signaling phenotype\",\n      \"pmids\": [\"16027149\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"ARNO-dependent Rac1 activation in migrating MDCK cells is mediated by the bipartite Rac GEF Dock180/Elmo complex; catalytically inactive Dock180 or Elmo mutant that fails to couple to Dock180 both block ARNO-induced Rac activation and motility. β-PIX, another Rac GEF, is not required.\",\n      \"method\": \"Dominant-negative mutant overexpression, Rac-GTP pulldown, motility assay, co-localization by confocal microscopy\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple mutants, places Dock180/Elmo between ARNO/ARF6 and Rac1\",\n      \"pmids\": [\"16213822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"V-ATPase a2-isoform on early endosomes interacts with ARNO in an intra-endosomal acidification-dependent manner; ARF6 interacts with the c-subunit of V-ATPase. Disruption of the a2-ARNO interaction reversibly inhibits endocytosis; V-ATPase recruits ARNO and ARF6 to regulate the endocytic degradative pathway.\",\n      \"method\": \"Co-immunoprecipitation, acidification-dependent binding assay, inhibitor treatments, endocytosis assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP + functional rescue, well-cited foundational study\",\n      \"pmids\": [\"16415858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ARNO is localized exclusively at the apical plasma membrane of polarized epithelial cells through its N-terminal coiled-coil domain; ARNO promotes apical endocytosis of the polymeric IgA receptor synergistically with ARF6, and coiled-coil domain deletion mislocalizes ARNO to both membrane surfaces and abolishes apical endocytosis stimulation.\",\n      \"method\": \"Overexpression of deletion mutants, immunofluorescence in polarized MDCK cells, endocytosis assay, dominant-negative ARF6 epistasis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined localization + functional consequence + epistasis, single lab\",\n      \"pmids\": [\"16484220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Gαq signaling leads to ARF6 activation through direct interaction with ARNO; activated Gαq forms molecular complexes preferentially with ARNO and ARF6, and direct binding between purified Gαq and ARNO is demonstrated. ARNO and ARF6 promote TPβ receptor internalization.\",\n      \"method\": \"Co-immunoprecipitation, in vitro binding with purified proteins, ARF6-GTP assay, receptor internalization assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding with purified proteins + co-IP + functional assay, identifies Gαq as upstream activator of ARNO\",\n      \"pmids\": [\"16650966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"ARL4D (a GTP-dependent plasma membrane GTPase) interacts with the PH and polybasic C-terminal domains of cytohesin-2/ARNO in a GTP-dependent manner, recruits ARNO to the plasma membrane, activates ARF6, and promotes actin stress fiber disassembly; inactive cytohesin-2 or siRNA knockdown of ARNO blocks ARL4D-induced effects.\",\n      \"method\": \"Yeast two-hybrid, co-IP, ARF6-GTP pulldown, siRNA knockdown, immunofluorescence, dominant-active/inactive mutants\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, genetic epistasis, identifies ARL4D as upstream recruiter of ARNO\",\n      \"pmids\": [\"17804820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CaSR stimulation triggers plasma membrane ruffling via a β-arrestin 1–ARNO–ARF6–ELMO pathway; β-arrestin 1 co-immunoprecipitates with both CaSR and ARNO at rest, and agonist treatment causes their co-translocation to membrane protrusions.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, dominant-negative mutants, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP + genetic knockdown + epistasis, single lab\",\n      \"pmids\": [\"17623778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The coiled-coil domain of cytohesin-2/ARNO interacts directly with Gαq; Gαq-Q209L (constitutively active) strongly promotes cytohesin plasma membrane localization; coiled-coil deletion mutants of cytohesin-1 and -2 cannot relay Gαq-mediated ARF6 activation.\",\n      \"method\": \"Co-immunoprecipitation in HEK293 cells, confocal immunofluorescence, deletion mutants\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP + colocalization + functional deletion mutants, single lab\",\n      \"pmids\": [\"17846866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The coiled-coil domain of ARNO is required for ARNO-induced cell motility and ARF-dependent Rac1 activation; scaffold proteins GRASP/Tamalin and IPCEF1 (binding the coiled-coil) coordinate the association of ARNO with Dock180 to enable ARF-to-Rac signaling.\",\n      \"method\": \"Coiled-coil deletion mutants, siRNA knockdown of GRASP and IPCEF1, Rac-GTP pulldown, migration assay, co-immunoprecipitation\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic tools + functional assays, defines scaffold mechanism for ARF→Rac signaling\",\n      \"pmids\": [\"20016009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Cytohesin-2/ARNO interacts with the focal adhesion adaptor paxillin via its LIM2 domain and the ARNO polybasic region; this complex localizes to leading edges of migrating 3T3-L1 preadipocytes and is required for cytohesin-2-mediated ARF6-dependent cell migration.\",\n      \"method\": \"Co-immunoprecipitation, pulldown with domain mutants, siRNA knockdown, SecinH3 inhibition, ARF6-GTP pulldown, migration assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct domain mapping + co-IP + siRNA + functional assay, identifies paxillin as scaffold for ARNO\",\n      \"pmids\": [\"20525696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"On membranes, Arf6-GTP activates ARNO at nanomolar concentrations via the PH domain in a positive feedback loop; ARNO is further activated by its own product Arf1-GTP (another positive feedback); PH domain mutations that abolish Arf6-GTP interaction completely inactivate ARNO on liposomes but not in solution.\",\n      \"method\": \"In vitro GEF assay on liposomes with full-length membrane-bound Arf, PH domain point mutants, competition with Arf effectors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted on liposomes with mutagenesis, reveals bistable switch mechanism\",\n      \"pmids\": [\"21118813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Multiple sites on the N-terminus of the V-ATPase a2-subunit (a2N) interact with the Sec7, PH, and polybasic domains of ARNO; the a2N(1–17) peptide inhibits ARNO GEF activity by binding the Sec7 domain with KD ~344 nM; Ser392 phosphorylation abolishes a2N binding to the ARNO polybasic region.\",\n      \"method\": \"Synthetic peptide binding assays, SPR kinetics, pulldown with recombinant proteins, NMR structure determination, in silico docking, GEF activity assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — SPR + NMR + in vitro GEF assay + docking, detailed molecular mechanism\",\n      \"pmids\": [\"20153292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ARNO directly interacts with aldolase (but not other glycolytic enzymes) via the ARNO PH domain; SPR reveals KD = 2.84 × 10⁻¹⁰ M. Aldolase associates with early endosomal membranes and forms a complex with ARNO/Arf6 and V-ATPase. Aldolase knockdown causes cell morphology changes and acidic vesicle redistribution.\",\n      \"method\": \"GST pulldown, SPR, cell fractionation, siRNA knockdown, immunofluorescence\",\n      \"journal\": \"American journal of physiology. Cell physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — SPR + pulldown + functional knockdown, single lab\",\n      \"pmids\": [\"21307348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"ARNO mediates glucose-stimulated insulin secretion in β-cells through sequential activation of ARF6 → Cdc42 → Rac1; siRNA knockdown of ARNO or inactive ARNO (E156K) reduces GSIS; co-immunoprecipitation shows increased ARNO–ARF6 association upon glucose stimulation.\",\n      \"method\": \"siRNA knockdown, dominant-negative mutants, SecinH3 inhibition, GST-GGA3/PAK-1 pulldown assays for ARF6/Rac GTP-loading, co-immunoprecipitation, insulin secretion assay\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological + genetic + biochemical GTP-loading assays, epistasis establishes ARNO upstream of ARF6/Cdc42/Rac1\",\n      \"pmids\": [\"21276423\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IL-1β signals through MYD88–ARNO–ARF6 to disrupt endothelial barrier function independently of NF-κB; ARNO binds directly to the adaptor MYD88; SecinH3 (ARNO inhibitor) enhances vascular stability in inflammatory arthritis and acute inflammation models in vivo.\",\n      \"method\": \"Direct binding assay (ARNO–MYD88), siRNA knockdown, SecinH3 inhibition, endothelial permeability assay, in vivo inflammatory models\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct binding + genetic knockdown + in vivo rescue, high-impact journal, multiple orthogonal approaches\",\n      \"pmids\": [\"23143332\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Salmonella recruits ARNO via ARF6 and SopB-induced PIP3 generation; ARNO in turn activates the WAVE regulatory complex (WRC) for actin polymerization and macropinosome formation; RNAi screening identified ARNO as key host ARF-GEF for Salmonella invasion.\",\n      \"method\": \"siRNA screen, immunofluorescence, invasion assay, dominant-negative ARF/ARNO mutants, phosphoinositide imaging\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNAi screen + mechanistic follow-up, places ARNO downstream of ARF6/PIP3 and upstream of WRC\",\n      \"pmids\": [\"22341462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The N-terminal cytosolic tail of the V-ATPase a2-subunit (a2N(1–17)) directly inhibits cytohesin-2 GEF activity by interacting with its Sec7 domain; NMR determined that Phe5, Met10, Gln14 of a2N are involved; a2N competes with the switch 2 region of Arf1/Arf6 for Sec7 binding. This signaling is conserved across all four a-subunit isoforms and with yeast V-ATPase.\",\n      \"method\": \"In vitro GEF assay, NMR spectroscopy, in silico docking, binding/competition assays with recombinant proteins\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure + in vitro GEF reconstitution + competition assay, evolutionary conservation demonstrated\",\n      \"pmids\": [\"23288846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Cytohesin-2 interacts with CCDC120 in neurites of differentiating N1E-115 cells; CCDC120-containing vesicles transport cytohesin-2 anterogradely along neurites; CCDC120 knockdown reduces Arf6 activation and inhibits neurite growth; CCDC120 lacking the cytohesin-2-binding CC1 region cannot rescue.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, live-cell imaging of vesicle transport, Arf6-GTP pulldown, morphometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP + live imaging + siRNA + functional rescue, single lab\",\n      \"pmids\": [\"25326380\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PKC phosphorylates cytohesin-2 in platelets; under basal conditions, cytohesin-2 keeps ARF6 constitutively GTP-loaded to suppress dense granule secretion; PKC-mediated phosphorylation of cytohesin-2 disrupts its interaction with ARF6, decreases ARF6-GTP, and promotes platelet secretion and aggregation.\",\n      \"method\": \"Immunoprecipitation + mass spectrometry, Western blot, SecinH3 pharmacology, lumi-aggregometry, flow cytometry\",\n      \"journal\": \"Journal of thrombosis and haemostasis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — MS identification of PKC phosphorylation + functional pharmacology + ARF6-GTP measurement, single lab\",\n      \"pmids\": [\"24581425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Cytohesin-2 interacts with actinin-1 (ACTN1) via its polybasic C-terminal region (binding the ACTN1 EFh2 domain); this interaction is required for ARF6 activation at growth cones and neurite extension in N1E-115 cells; FRET assay with cell-permeable peptides confirms the interaction reduces ARF6-GTP at growth cones.\",\n      \"method\": \"Co-immunoprecipitation, pulldown, siRNA knockdown, ARF6-GTP pulldown, FRET with cell-permeable peptides, morphometry\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding domain mapping + FRET + siRNA + functional readout, single lab\",\n      \"pmids\": [\"22659138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cytohesin-2/ARNO localizes to EHD1-positive recycling endosomes and regulates recycling of R-Ras and α5-integrin to the plasma membrane via ARF GTPase activation; GEF-inactive ARNO (E156K) causes R-Ras accumulation on recycling endosomes and inhibits cell spreading.\",\n      \"method\": \"Co-localization by confocal microscopy, siRNA knockdown, dominant-negative ARNO (E156K), integrin recycling assay, cell spreading assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — localization + functional knockdown + recycling assay, identifies new compartment for ARNO\",\n      \"pmids\": [\"26378252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RLIP76 links ARNO to activated R-Ras at recycling endosomes: RLIP76 N-terminus (residues 1–180) binds ARNO and residues 180–192 bind R-Ras, forming a ternary complex in Rab11-positive compartments that activates Arf6 and promotes cell spreading and migration.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, domain deletion mutants, ARF6-GTP assay, cell spreading/migration assay, immunofluorescence colocalization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding + functional domain mutants + Arf6-GTP assay, single lab\",\n      \"pmids\": [\"26498519\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Cytohesin-2/ARNO is required for Schwann cell myelination in the peripheral nervous system; conditional knockout of cytohesin-2 in Schwann cells reduces ARF6 activity, decreases myelin thickness in sciatic nerves, and reduces myelin protein zero (MPZ) expression.\",\n      \"method\": \"Schwann cell-specific conditional knockout mice, ARF6-GTP assay, electron microscopy of myelin thickness, Western blot for MPZ, SecinH3 pharmacology in culture\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo conditional KO with defined molecular (ARF6-GTP) and cellular (myelin thickness) phenotypes\",\n      \"pmids\": [\"25824033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ARNO and ARF1 are required for podosome assembly; ARNO colocalizes with adhesive rings of podosomes; ARF1 inhibition increases RhoA-GTP and myosin-IIA filament assembly, which suppresses podosomes; constitutively active ARF1 induces podosome precursors containing actin cores.\",\n      \"method\": \"siRNA knockdown, pharmacological inhibition (SecinH3, brefeldin A), ARF1-GTP assay, RhoA-GTP assay, immunofluorescence, matrix degradation assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockdown + pharmacology + epistasis (RhoA/myosin-IIA rescue), multiple orthogonal approaches\",\n      \"pmids\": [\"28007915\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"INAVA's CUPID domain stably binds ARNO to promote lateral membrane F-actin assembly and barrier function; when ARNO is bound to CUPID, it promotes F-actin dynamics independent of its canonical GEF activity. Upon IL-1β, INAVA relocates to cytosolic puncta where CUPID amplifies TRAF6-dependent polyubiquitination/inflammatory signaling, while ARNO binding to CUPID negatively-regulates this inflammatory response.\",\n      \"method\": \"Co-immunoprecipitation, domain binding assays, siRNA knockdown, actin dynamics assay, ubiquitination assay, IL-1β signaling readout in epithelial cells and macrophages\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, GEF-independent function defined, validated in primary human macrophages\",\n      \"pmids\": [\"30355448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ARNO (cytohesin-2) binds the juxtamembrane (JM) intracellular segment of EGFR; NMR structural characterization reveals the ARNO-EGFR interaction interface, which shares features with but is distinct from JM interactions with calmodulin and anionic phospholipids; each interaction can be modulated by the others.\",\n      \"method\": \"NMR spectroscopy, in vitro binding assays\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural characterization of interaction, but functional consequences not fully resolved in this study\",\n      \"pmids\": [\"31780432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cytohesin-2 (CYTH2) forms a complex with CNKSR2; CYTH2 binding prevents proteasomal degradation of CNKSR2; shRNA knockdown of either CNKSR2 or CYTH2 in mouse hippocampal granule cell precursors results in abnormal localization and immature granule cell characteristics, demonstrating both are required for dentate granule cell development.\",\n      \"method\": \"Co-immunoprecipitation, proteasome inhibition, in vivo shRNA transduction, immunofluorescence, cell positioning assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP + in vivo shRNA + proteasome assay, single lab\",\n      \"pmids\": [\"34800437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cytohesin-2 is enriched in perisynaptic membranes of dorsal horn neurons and forms a protein complex with mGluR5; cytohesin-2 conditional knockout mice show reduced mechanical allodynia in inflammatory and neuropathic pain models; cytohesin-2 mediates mGluR5-dependent ERK1/2 activation via Arf6 in spinal cord.\",\n      \"method\": \"Immunoelectron microscopy, co-immunoprecipitation, conditional KO mice, SecinH3 pharmacology, ARF1/6-GTP assay, ERK phosphorylation assay, behavioral pain assays\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo conditional KO + co-IP + ARF6-GTP + ERK readout + behavioral phenotype, multiple orthogonal approaches\",\n      \"pmids\": [\"34390832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cytohesin-2 Tyr381 phosphorylation status is central to Schwann cell myelination; dephosphorylation by PTP4A1 reduces ARNO activity while SH2B1 interaction maintains Tyr381 phosphorylation and promotes myelination; knockin Y381F mice show reduced myelin thickness and ARF6 activity.\",\n      \"method\": \"Knockin mice (Y381F), Schwann cell-specific conditional KO of PTP4A1 and SH2B1, ARF6-GTP assay, co-immunoprecipitation, Western blot, electron microscopy of myelin\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vivo genetic models + biochemical Arf6-GTP readout, identifies writer/eraser of phosphorylation regulating CYTH2\",\n      \"pmids\": [\"35077201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CYTH2 is required for efficient influenza virus infection by mediating endosomal trafficking; CRISPR-Cas9 genome-wide screen identified CYTH2 as a host factor for influenza; SecinH3 treatment reduces influenza infection in vivo.\",\n      \"method\": \"Genome-wide CRISPR-Cas9 screen with survival selection, endosomal trafficking assay, SecinH3 in vivo treatment, viral infection assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide CRISPR screen + functional validation + in vivo pharmacology, single lab\",\n      \"pmids\": [\"35354039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FE65 (neuronal adaptor) interacts with ARNO and forms a ternary complex with ARF6; FE65 attenuates ARNO intramolecular autoinhibition and promotes ARNO dimerization, thereby potentiating ARNO-stimulated ARF6-mediated neurite outgrowth; FE65 mutations disrupting FE65-ARNO interaction abolish this potentiation.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, ARF6-GTP assay, neurite morphometry, autoinhibition assay, dimerization assay\",\n      \"journal\": \"Open biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding + functional mutant rescue + ARF6-GTP + morphometric readout, single lab\",\n      \"pmids\": [\"36168805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"V-ATPase V0a1 subunit interacts with ARNO and promotes ARF6 activation during exocytosis in neuroendocrine cells; disruption of the V0a1–ARNO interaction inhibits PLD activation, phosphatidic acid synthesis, and alters the timing of membrane fusion events.\",\n      \"method\": \"Co-immunoprecipitation, ARF6-GTP assay, PLD activity assay, phosphatidic acid measurement, TIRF live imaging of exocytotic events\",\n      \"journal\": \"Frontiers in molecular biosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP + functional lipid assays + live exocytosis imaging, single lab\",\n      \"pmids\": [\"37091866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Full knockout of cytohesin-2 in mice causes perinatal lethality within 20 h of birth; cytohesin-2 deficiency reduces Golgi volume (rescued by re-expression of cytohesin-2, even in an ARF-GEF-independent manner), impairs galactosylation, and markedly reduces global protein secretion in neonates.\",\n      \"method\": \"Global knockout mice, organellar proteomics by mass spectrometry, immunofluorescence (Golgi markers, PNA staining), quantitative secretome proteomics\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with lethal phenotype + organellar proteomics + ARF-GEF-independent rescue, reveals essential in vivo function and Golgi maintenance role\",\n      \"pmids\": [\"41672711\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CYTH2/ARNO is a multi-domain guanine nucleotide exchange factor (GEF) that activates ARF1 and ARF6 GTPases via a Sec7 domain 'glutamic finger' mechanism (Glu156 displacing Mg²⁺ and GDP); membrane recruitment is cooperatively controlled by PH-domain binding to PIP3/PIP2 and a polybasic C-terminal region (regulated by a PKC-dependent electrostatic switch at Ser392), and by upstream activators including ARL4D, Arf6-GTP itself (positive feedback on membranes), Gαq, V-ATPase a-subunit isoforms, and scaffold partners (paxillin, IPCEF1, GRASP, RLIP76); at the plasma membrane CYTH2 drives ARF6-dependent actin remodeling, lamellipodia, cell migration, endocytosis, and receptor signaling (including GPCR desensitization, VEGFR-2 stabilization, MYD88-dependent vascular permeability, and mGluR5-ERK pain signaling), while also supporting Golgi maintenance and protein secretion through an ARF-GEF-independent activity that is essential for perinatal survival.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CYTH2 (ARNO/cytohesin-2) is a guanine nucleotide exchange factor (GEF) for ARF-family GTPases that integrates lipid, receptor, and scaffolding signals to control membrane trafficking, actin remodeling, cell migration, and protein secretion. Its Sec7 domain catalyzes GDP-to-GTP exchange on ARF1 and ARF6 through a conserved 'glutamic finger' (Glu156) mechanism that displaces Mg²⁺ and GDP [PMID:9649435], while membrane recruitment is cooperatively driven by PH-domain binding to PIP3/PIP2, a polybasic C-terminal region regulated by PKC phosphorylation at Ser392 [PMID:10531036], and upstream activators including ARL4D, Gαq, V-ATPase a-subunit isoforms, and Arf6-GTP itself in a positive-feedback loop [PMID:21118813, PMID:17804820, PMID:16415858]. At the plasma membrane and endosomes, CYTH2-activated ARF6 signals through Rac1 (via Dock180/ELMO), PLD, and the WAVE regulatory complex to drive lamellipodia formation, endocytosis, receptor trafficking, Schwann cell myelination, and inflammatory vascular permeability; full knockout in mice causes perinatal lethality with loss of Golgi integrity and global protein secretion that is rescued even by GEF-inactive CYTH2, revealing an essential ARF-GEF-independent structural role [PMID:41672711, PMID:23143332, PMID:25824033, PMID:16213822].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing that ARNO is a direct ARF1 GEF whose membrane recruitment through PH-domain–PIP2 interaction is essential for catalytic function answered the foundational question of how cytosolic ARF exchange factors reach their substrates.\",\n      \"evidence\": \"In vitro nucleotide exchange assay on phospholipid vesicles with domain deletion mutants\",\n      \"pmids\": [\"9268368\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo substrate preference (ARF1 vs ARF6) not resolved\", \"Regulation beyond PIP2 binding unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Crystal structures of the Sec7 domain and identification of the Glu156 'glutamic finger' mechanism revealed how ARNO destabilizes Mg²⁺ and GDP from ARF, providing the first atomic-level understanding of ARF-GEF catalysis.\",\n      \"evidence\": \"X-ray crystallography at 2.0–2.2 Å resolution, site-directed mutagenesis (E156K/E156D) with in vitro exchange assays\",\n      \"pmids\": [\"9510256\", \"9476900\", \"9649435\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full Sec7–ARF complex structure not yet solved at the time\", \"Mechanism of membrane-dependent enhancement not structurally resolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Localization of ARNO to the plasma membrane (not Golgi) and demonstration of ARF6 activation and actin cytoskeletal remodeling established the primary cellular site of action and linked ARNO to cell morphology control.\",\n      \"evidence\": \"Subcellular fractionation, immunolocalization, and overexpression of domain mutants in HeLa cells with actin phenotyping\",\n      \"pmids\": [\"9417041\", \"9802902\", \"9550703\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ARNO also functions at intracellular compartments in vivo unclear\", \"Downstream effectors of ARF6 for actin remodeling not identified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that PKC phosphorylation of Ser392 in the polybasic C-terminal region creates an electrostatic switch reducing membrane binding established a key regulatory mechanism controlling ARNO membrane association.\",\n      \"evidence\": \"In vitro phosphorylation, liposome cosedimentation, phosphomimetic mutants, in vivo membrane fractionation\",\n      \"pmids\": [\"10531036\", \"10801341\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological context triggering PKC-mediated release not defined\", \"Whether Ser392 phosphorylation is dynamically reversed in vivo unclear\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that ARNO activates endogenous ARF6 to independently stimulate Rac1 and PLD in epithelial cells resolved the downstream branching logic through which ARNO drives cell migration.\",\n      \"evidence\": \"Dominant-active ARNO expression in MDCK cells with ARF6-GTP, Rac-GTP, and PLD activity pulldown assays plus motility readout\",\n      \"pmids\": [\"11481345\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Rac GEF identity downstream of ARF6 not yet determined\", \"How PLD activity converges on motility mechanistically unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The finding that V-ATPase-dependent endosomal acidification recruits ARNO and ARF6 to early endosomes revealed a pH-sensing mechanism linking endosomal maturation to ARF signaling.\",\n      \"evidence\": \"Subcellular fractionation and in vitro translocation assay with ATP-driven acidification in kidney proximal tubule cells\",\n      \"pmids\": [\"11278939\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the V-ATPase subunit mediating ARNO interaction not yet mapped\", \"Whether pH sensing is direct or indirect unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identification of the Dock180/ELMO complex as the Rac GEF downstream of ARNO-ARF6 completed the signaling cascade from ARNO to Rac1 activation and cell motility.\",\n      \"evidence\": \"Dominant-negative Dock180 and ELMO mutants block ARNO-induced Rac-GTP and motility in MDCK cells\",\n      \"pmids\": [\"16213822\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ARF6-GTP recruits/activates Dock180–ELMO mechanistically unresolved\", \"Contribution of other Rac GEFs in different cell types not excluded\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Mapping the V-ATPase a2-subunit as the direct ARNO-binding partner on endosomes and showing that disruption of a2–ARNO interaction blocks endocytosis established a specific molecular link between V-ATPase and ARF-GEF signaling.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, acidification-dependent binding, endocytosis assays in epithelial cells\",\n      \"pmids\": [\"16415858\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of pH-dependent interaction not resolved\", \"Contribution of other a-subunit isoforms unknown at this point\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Discovery that ARL4D and Gαq each recruit ARNO to the plasma membrane through distinct domain interactions (PH/polybasic for ARL4D; coiled-coil for Gαq) revealed multiple upstream activation inputs converging on ARNO.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, ARF6-GTP pulldowns, siRNA epistasis in multiple cell lines\",\n      \"pmids\": [\"17804820\", \"16650966\", \"17846866\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ARL4D and Gαq pathways are synergistic or context-specific not tested\", \"Structural basis of Gαq–coiled-coil interaction not solved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defining how scaffolds GRASP/IPCEF1 and paxillin coordinate ARNO coiled-coil and polybasic domains with Dock180 explained how multiprotein assemblies at leading edges enable efficient ARF-to-Rac signaling during migration.\",\n      \"evidence\": \"Coiled-coil deletion mutants, siRNA knockdown of GRASP/IPCEF1/paxillin, Rac-GTP pulldown, migration assays\",\n      \"pmids\": [\"20016009\", \"20525696\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the multiprotein complex not determined\", \"Whether scaffolding varies across cell types unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Reconstitution showing that Arf6-GTP activates ARNO through its PH domain in a positive-feedback loop on membranes revealed a bistable switch mechanism that amplifies ARF signaling.\",\n      \"evidence\": \"In vitro GEF assay on liposomes with full-length membrane-bound Arf and PH domain point mutants\",\n      \"pmids\": [\"21118813\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the positive feedback is terminated in cells not addressed\", \"Quantitative parameters of bistability not modeled\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstration that IL-1β signals through MYD88–ARNO–ARF6 to increase endothelial permeability independently of NF-κB, with SecinH3 providing in vivo vascular protection, established ARNO as a druggable node in inflammatory barrier dysfunction.\",\n      \"evidence\": \"Direct binding assay, siRNA, SecinH3 pharmacology, endothelial permeability assay, in vivo inflammatory models\",\n      \"pmids\": [\"23143332\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of MYD88–ARNO interaction not solved\", \"Therapeutic window and off-target effects of SecinH3 in vivo not fully characterized\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"NMR-based mapping of the V-ATPase a2N peptide interaction with the ARNO Sec7 domain, competing with ARF switch 2, provided the structural mechanism for pH-dependent regulation of ARNO catalytic activity.\",\n      \"evidence\": \"NMR spectroscopy, in vitro GEF reconstitution, competition assays with recombinant proteins\",\n      \"pmids\": [\"23288846\", \"20153292\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length a2–ARNO complex structure not available\", \"How luminal pH change is transduced to cytoplasmic a2N conformation not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Conditional knockout of CYTH2 in Schwann cells reduced ARF6 activity and myelin thickness, establishing an essential in vivo role for CYTH2 in peripheral nerve myelination.\",\n      \"evidence\": \"Schwann cell-specific conditional KO mice, ARF6-GTP assay, electron microscopy of sciatic nerve\",\n      \"pmids\": [\"25824033\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CYTH2 acts through ARF6 alone or also ARF1 in myelination not resolved\", \"Downstream effectors of ARF6 in myelin wrapping unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The finding that INAVA's CUPID domain binds ARNO to promote F-actin assembly independently of GEF activity established a GEF-independent scaffolding function for ARNO in epithelial barrier maintenance and inflammatory signaling.\",\n      \"evidence\": \"Co-immunoprecipitation, domain binding, siRNA, actin dynamics and ubiquitination assays in epithelial cells and macrophages\",\n      \"pmids\": [\"30355448\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CUPID–ARNO interaction not determined\", \"Relative contribution of GEF-dependent vs -independent functions at the barrier unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identification of Tyr381 as a phosphorylation switch regulated by PTP4A1 (dephosphorylation) and SH2B1 (protection), with knockin Y381F mice showing reduced myelination, revealed a tyrosine phosphorylation layer controlling ARNO activity in vivo.\",\n      \"evidence\": \"Y381F knockin mice, Schwann cell-specific conditional KO of PTP4A1/SH2B1, ARF6-GTP assay, electron microscopy\",\n      \"pmids\": [\"35077201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for Tyr381 phosphorylation not identified\", \"Whether Tyr381 regulation operates in non-Schwann cell contexts unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Full CYTH2 knockout causing perinatal lethality with Golgi volume loss and secretion failure—rescuable by GEF-inactive CYTH2—revealed an essential, ARF-GEF-independent structural role in Golgi maintenance and organismal viability.\",\n      \"evidence\": \"Global KO mice, organellar and secretome mass spectrometry, immunofluorescence, rescue with catalytically dead ARNO\",\n      \"pmids\": [\"41672711\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of GEF-independent Golgi maintenance unknown\", \"Which CYTH2 domain mediates Golgi structural role not mapped\", \"Whether other cytohesin family members partially compensate in vivo not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular mechanism by which CYTH2 maintains Golgi integrity independently of ARF-GEF activity, the structural basis for several key protein interactions (MYD88, INAVA-CUPID, Gαq), and the kinase responsible for Tyr381 phosphorylation remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GEF-independent Golgi maintenance mechanism uncharacterized\", \"High-resolution structures of ARNO with MYD88, INAVA, or Gαq not available\", \"Tyr381 kinase identity unknown\", \"Whether positive-feedback bistability operates in vivo and how it is terminated not demonstrated\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0, 2, 9, 27]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 9, 27, 30]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 5, 8]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [25, 41]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 4, 5, 9, 22, 26]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [10, 19, 37]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [49]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [9, 17, 21, 31, 44]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [10, 19, 20, 46]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [26, 40]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [37, 49]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [31, 41]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [49]}\n    ],\n    \"complexes\": [\n      \"V-ATPase–ARNO–ARF6 endosomal complex\",\n      \"ARNO–Dock180/ELMO migration complex\"\n    ],\n    \"partners\": [\n      \"ARF6\",\n      \"ARF1\",\n      \"MYD88\",\n      \"ARL4D\",\n      \"GNAQ\",\n      \"PXN\",\n      \"IPCEF1\",\n      \"RLIP76\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}