{"gene":"GAK","run_date":"2026-06-10T01:55:20","timeline":{"discoveries":[{"year":1997,"finding":"GAK (cyclin G-associated kinase) directly associates with cyclin G and CDK5 in vivo. Co-immunoprecipitation and BIAcore analysis demonstrated the direct GAK–cyclin G interaction. GAK harbors an N-terminal Ser/Thr protein kinase domain and a C-terminal tensin/auxilin-like domain with a leucine zipper region.","method":"Co-immunoprecipitation, Western blotting, BIAcore surface plasmon resonance, West-Western blotting","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — direct binding confirmed by BIAcore (in vitro reconstitution) plus reciprocal Co-IP; foundational study replicated in subsequent work","pmids":["9013862"],"is_preprint":false},{"year":1997,"finding":"GAK kinase activity (from anti-cyclin G immunoprecipitates) fluctuates during the cell cycle with a peak at G1 phase, even though cyclin G expression remains nearly constant, indicating cell-cycle-regulated kinase activity.","method":"Synchronized HeLa cell-cycle analysis, histone H1 kinase assay on immunoprecipitates","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-cycle synchronization with kinase activity assay in a single lab; single method for the activity measurement","pmids":["9299234"],"is_preprint":false},{"year":2002,"finding":"GAK/auxilin2 phosphorylates the mu2 (AP2M1) medium subunit of the AP2 adaptor complex both within intact clathrin-coated vesicles (CCVs) and in solution, establishing GAK as a CCV-associated kinase with AP2M1 as a direct substrate.","method":"In vitro kinase assay using purified CCVs and recombinant substrates; kinase activity fractionation from porcine brain CCVs","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with defined substrate using highly purified CCVs; replicated by later substrate identification studies","pmids":["12010461"],"is_preprint":false},{"year":2005,"finding":"GAK knockdown by shRNA in HeLa cells markedly reduces internalization of transferrin and EGF (receptor-mediated endocytosis), decreases perinuclear clathrin at the trans-Golgi network, reduces the number and dynamics of plasma membrane clathrin-coated pits, and dramatically reduces AP2 and epsin on the plasma membrane and AP1/GGA at the TGN. Expression of dominant-negative Hsp70 phenocopies this, placing GAK upstream of Hsc70 in clathrin/adaptor recruitment.","method":"Vector-based shRNA knockdown, fluorescence microscopy, transferrin/EGF internalization assays, dominant-negative Hsp70 expression","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with multiple orthogonal readouts (trafficking, morphology, adaptor localization) plus epistasis with dominant-negative Hsp70","pmids":["16155256"],"is_preprint":false},{"year":2006,"finding":"GAK is transiently recruited to clathrin-coated pits after dynamin recruitment and before pit invagination, as directly visualized by TIRF microscopy. GAK recruitment depends on its PTEN-like domain, which binds phospholipids. Synchronous recruitment of GAK (and subsequent Hsc70 recruitment) is required for irreversible clathrin uncoating; actin depolymerization prevents scission and irreversible uncoating despite repeated GAK flashing.","method":"Total internal reflectance fluorescence (TIRF) microscopy, phospholipid-binding assays, actin depolymerization experiments","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct live imaging with temporal resolution; phospholipid binding domain mapping; multiple pharmacological perturbations in one study","pmids":["16895969"],"is_preprint":false},{"year":2009,"finding":"GAK localizes to both the cytoplasm and nucleus. In the nucleus, GAK forms complexes with cyclin G1, p53, clathrin heavy chain (CHC), and PP2A B'alpha1. CHC associates with GAK via a different domain depending on whether it is cytoplasmic or nuclear.","method":"Immunostaining, GFP-GAK ectopic expression, GST pulldown assays with dissected GAK fragments, co-immunoprecipitation","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple interaction partners confirmed by pulldown and Co-IP, localization by immunostaining and GFP fusion, but single laboratory","pmids":["19371378"],"is_preprint":false},{"year":2009,"finding":"GAK is required for proper centrosome maturation and mitotic chromosome congression. GAK knockdown by siRNA causes metaphase arrest via spindle-assembly checkpoint activation, multi-aster formation from abnormal pericentriolar material fragmentation (not centriole fragmentation), and chromosome misalignment. GAK and clathrin heavy chain interact during mitosis and cooperate in the same pathway to regulate functional spindle formation.","method":"siRNA knockdown, cell-cycle analysis, immunofluorescence, co-immunoprecipitation during mitosis","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — siRNA knockdown with multiple phenotypic readouts (checkpoint activation, spindle morphology, centrosome integrity), validated CHC interaction during mitosis","pmids":["19654208"],"is_preprint":false},{"year":2010,"finding":"In zebrafish, GAK (but not auxilin alone) knockdown by morpholino increases neuronal cell specification and decreases expression of the Notch target gene Her4, indicating that GAK function is required for Notch-dependent neuronal patterning. GAK knockdown also causes elevated apoptosis in neural tissues.","method":"Morpholino-mediated knockdown in zebrafish, in situ hybridization for Notch target genes, functional complementation with Drosophila auxilin","journal":"BMC developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — morpholino loss-of-function with defined transcriptional readout of Notch target gene; single lab in one model organism","pmids":["20082716"],"is_preprint":false},{"year":2011,"finding":"Mice expressing kinase-dead GAK (GAK-kd) die within 30 minutes after birth due to respiratory dysfunction. Immunohistochemical analysis shows surfactant protein A (SP-A) is absent from alveolar spaces, and E-cadherin/phospho-EGFR signals are abnormal in GAK-kd pups, indicating that GAK kinase activity is required for proper pulmonary alveolar function.","method":"Kinase-dead knock-in mouse model, immunohistochemistry, histological analysis","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic mouse model with kinase-dead allele; direct immunohistochemical validation of surfactant localization defect","pmids":["22022498"],"is_preprint":false},{"year":2014,"finding":"Crystal structures of the GAK catalytic domain alone and in complex with nanobodies revealed: (i) GAK is constitutively active; (ii) the apo structure adopts a dimeric inactive state mediated by an unusual activation segment interaction; (iii) nanobody NbGAK_1 captures the monomeric active conformation with well-ordered activation segment; (iv) GAK has unusually high catalytic domain plasticity; (v) ATP-competitive inhibitors bind in a type I mode.","method":"X-ray crystallography, enzyme kinetics, size-exclusion chromatography","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures of apo, nanobody-bound, and inhibitor-bound forms with enzyme kinetic validation; multiple orthogonal methods in one study","pmids":["24438162"],"is_preprint":false},{"year":2015,"finding":"The clathrin-binding and J-domains of GAK (a C-terminal 62-kDa fragment) are sufficient to rescue clathrin-dependent trafficking in GAK-knockout fibroblasts and to rescue lethality/histological defects caused by liver- or brain-specific GAK knockout in mice. When both GAK and auxilin are knocked out in the brain, the 62-kDa GAK fragment maintains viability. This establishes that the PTEN-like domain is dispensable for Hsc70-dependent clathrin chaperoning/uncoating.","method":"Conditional knockout mice, transgenic rescue with 62-kDa GAK fragment, histology, trafficking assays in fibroblasts","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain-rescue in multiple in vivo contexts (liver KO, brain KO, double GAK/auxilin KO) plus cellular trafficking rescue; replicated across tissues","pmids":["26345367"],"is_preprint":false},{"year":2015,"finding":"Isothiazolo[5,4-b]pyridine-based compounds are selective GAK inhibitors acting as ATP-competitive (type I) kinase inhibitors, as determined by co-crystallization. These inhibitors also inhibit two temporally distinct steps in the HCV lifecycle (viral entry and assembly), linking GAK kinase activity to HCV intracellular trafficking.","method":"Co-crystallization/X-ray structure, in vitro kinase binding assays, antiviral assays","journal":"Journal of medicinal chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure confirming ATP-competitive binding mode; functional antiviral validation; single lab","pmids":["25822739"],"is_preprint":false},{"year":2017,"finding":"GAK is phosphorylated by c-Src at Y412 and Y1149. GAK-pY412/pY1149 undergoes dynamic subcellular redistribution during mitosis: nucleus during interphase → chromosomes at prophase/prometaphase → centrosomes at metaphase → chromosomes at end of telophase. Mass spectrometry and co-immunoprecipitation identified MCM3 (a DNA licensing factor) as a GAK-interacting partner, suggesting a GAK–c-Src–MCM3 axis in DNA replication licensing.","method":"In vivo phosphorylation with anti-phospho-specific antibody, immunofluorescence, mass spectrometry, co-immunoprecipitation","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — phosphorylation confirmed by phospho-specific antibody and mass spectrometry; MCM3 interaction by Co-IP; subcellular localization by IF; single laboratory","pmids":["28135906"],"is_preprint":false},{"year":2018,"finding":"Using a chemical genetics approach (analog-sensitive kinase), GAK was shown to directly phosphorylate the Na+/K+-ATPase alpha-subunit Atp1a3. GAK regulates trafficking of Na+/K+-ATPase to the plasma membrane, and conditional GAK knockout in CA1 pyramidal neurons results in greater resting membrane potential change upon Na+/K+-ATPase blockade with ouabain, indicating compromised pump function.","method":"Chemical genetics (analog-sensitive kinase method), whole-cell patch clamp electrophysiology, conditional knockout mice, trafficking assays","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — chemical genetics directly identifies substrate; functional validation by electrophysiology in conditional KO neurons; multiple orthogonal methods","pmids":["30623173"],"is_preprint":false},{"year":2019,"finding":"GAK depletion leads to impaired astral microtubules and spindle positioning defects, phenocopying depletion of the GAK interactor clathrin, placing GAK and clathrin in the same pathway for spindle positioning in human cells.","method":"Live imaging siRNA screen on fibronectin micropatterns, siRNA knockdown, immunofluorescence","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA phenotype in defined geometry screen with clathrin epistasis; single lab; mechanism inferred from phenotypic similarity","pmids":["31253758"],"is_preprint":false},{"year":2021,"finding":"GAK kinase activity is required for efficient PRKN-independent mitophagy (but is dispensable for PRKN-dependent mitophagy and starvation-induced autophagy). GAK knockdown/knockout in C. elegans (gakh-1) inhibits basal mitophagy in vivo, demonstrating evolutionary conservation. GAK modifies the mitochondrial network and lysosomal morphology to enable efficient transport of mitochondria for degradation.","method":"siRNA screen, kinase-dead mutant rescue, in vivo C. elegans knockdown (gakh-1), zebrafish PRKCD knockout, fluorescence-based mitophagy reporters","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — kinase-dead mutant establishes catalytic requirement; replicated across cell lines and two model organisms (C. elegans, zebrafish); multiple readouts","pmids":["34671015"],"is_preprint":false},{"year":2021,"finding":"GAK knockout in A549 cells impairs autophagosome–lysosome fusion and autophagic lysosome reformation, causing accumulation of enlarged autophagosomes and autolysosomes during starvation. GAK controls lysosomal dynamics via actomyosin regulation; ROCK1 knockdown or ROCK inhibitor treatment rescues the GAK KO phenotype, placing GAK upstream of ROCK1 in lysosomal dynamics regulation.","method":"CRISPR knockout, GAK inhibitor, autophagic flux analysis, morphological analysis of lysosomes/autophagosomes, ROCK inhibitor rescue, ROCK1 siRNA knockdown","journal":"International journal of molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO plus pharmacological inhibition with ROCK epistasis rescue; single lab; two complementary loss-of-function approaches","pmids":["34468012"],"is_preprint":false},{"year":2023,"finding":"GAK/dAux (Drosophila homolog) interacts with the autophagy initiation kinase ULK1/Atg1 via its uncoating domain and regulates the trafficking of Atg1 and Atg9 to autophagosomes in glia. Loss of GAK/dAux increases autophagosome number and size, upregulates PI3K class III complex components, and impairs autophagic flux. dAux also contributes to dopaminergic neurodegeneration and locomotor function in fly models.","method":"Co-immunoprecipitation (GAK–ULK1/Atg1 interaction), genetic loss-of-function in Drosophila and mouse microglia, fluorescence imaging of autophagosome markers, behavioral assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct interaction by Co-IP with domain mapping; loss-of-function in two model organisms; multiple pathway readouts","pmids":["37428930"],"is_preprint":false},{"year":2023,"finding":"FBXO22 mediates ubiquitin-dependent proteasomal degradation of GAK. Proteomics identified GAK as an FBXO22 target; altered abundance (depletion or overexpression) of FBXO22 inversely changes GAK protein levels; proteasome inhibition blocks FBXO22-mediated GAK reduction; cellular ubiquitination assays confirmed GAK ubiquitination downstream of FBXO22.","method":"Proteomics, FBXO22 overexpression/depletion, proteasome inhibitor treatment, protein stability (decay rate) assay, cellular ubiquitination assay","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple complementary approaches (proteomics, protein decay, ubiquitination assay, proteasome inhibition) in single lab","pmids":["37442264"],"is_preprint":false},{"year":2025,"finding":"GAK knockdown inhibits clathrin-coated pit (CCP) stabilization and invagination, resulting in a striking increase in highly transient abortive CCPs. Mutations in the J-domain of GAK that abolish Hsc70 recruitment and activation at CCPs lead to GAK accumulation at CCPs and hinder CCP stabilization and invagination. This establishes that early GAK–Hsc70-mediated remodeling of nascent flat clathrin lattices (pentagon incorporation) is required for CCP curvature development.","method":"GAK knockdown, J-domain point mutations, live TIRF microscopy, CCP lifetime analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — structure–function mutagenesis of J-domain plus knockdown with quantitative live imaging of CCP dynamics; multiple orthogonal loss-of-function approaches","pmids":["40424130"],"is_preprint":false},{"year":2026,"finding":"GAK intrinsically disordered region (IDR) interacts with ARHGEF2 (a RhoA GEF) and antagonizes ROCK-dependent actomyosin signaling. GAK-knockout cells show enhanced stress fiber formation, increased myosin light chain (MLC) phosphorylation, and increased cell migration. These effects are suppressed by ROCK inhibitor or ARHGEF2 knockdown. The IDR, rather than GAK kinase activity, is the primary mediator of this regulation. GAK IDR also contributes to regulation of MLC expression.","method":"CRISPR knockout, co-immunoprecipitation (GAK IDR–ARHGEF2), immunofluorescence (stress fibers/MLC phosphorylation), ROCK inhibitor rescue, ARHGEF2 siRNA knockdown, cell migration assays","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR KO with domain-specific rescue (IDR vs. kinase-dead), direct ARHGEF2 interaction by Co-IP, ARHGEF2 knockdown epistasis, multiple orthogonal readouts","pmids":["41995027"],"is_preprint":false},{"year":2024,"finding":"In the Drosophila GAK homolog (dAux) context, lack of glial dAux enhances phosphorylation of the autophagy protein Atg9 at T62 and T69. This phosphorylation is regulated through Atg1 (ULK1 homolog), which is required for Atg9–dAux interaction. Enhanced Atg9 phosphorylation promotes autophagosome formation and Atg9 trafficking to autophagosomes. Non-phosphorylatable Atg9 suppresses the dAux-loss phenotype and phosphomimetic Atg9 rescues Atg1-loss phenotype, defining a dAux–Atg1–Atg9 phosphorylation axis.","method":"Genetic epistasis in Drosophila, phospho-specific analysis, non-phosphorylatable/phosphomimetic Atg9 mutants, co-immunoprecipitation, fluorescence imaging","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with phosphomimetic/non-phosphorylatable mutants in fly model; preprint not yet peer-reviewed; single lab","pmids":["bio_10.1101_2024.07.03.601894"],"is_preprint":true}],"current_model":"GAK is a constitutively active Ser/Thr kinase that functions as an essential cofactor in clathrin-mediated endocytosis by: (1) recruiting Hsc70 to clathrin-coated pits (CCPs) via its J-domain, promoting early curvature-enabling remodeling of nascent clathrin lattices and late uncoating of clathrin-coated vesicles; (2) binding phospholipids via its PTEN-like domain to enable CCP membrane recruitment; (3) phosphorylating AP2M1 (mu2) to regulate clathrin adaptor function; and additionally (4) regulating Na+/K+-ATPase trafficking by phosphorylating Atp1a3; (5) maintaining centrosome integrity and spindle positioning during mitosis through clathrin interaction; (6) being phosphorylated by c-Src at Y412/Y1149 and undergoing cell-cycle-dependent localization to centrosomes and chromosomes where it associates with MCM3; (7) promoting PRKN-independent mitophagy through kinase activity that maintains mitochondrial network and lysosomal morphology; (8) regulating autophagy initiation in glia by interacting with ULK1 via its uncoating domain to control Atg1 and Atg9 trafficking; (9) antagonizing ROCK-dependent actomyosin dynamics through its intrinsically disordered region via interaction with the RhoA-GEF ARHGEF2; and (10) being subject to ubiquitin-dependent proteasomal degradation mediated by FBXO22."},"narrative":{"mechanistic_narrative":"GAK (cyclin G-associated kinase) is a constitutively active Ser/Thr kinase that operates as an essential cofactor in clathrin-mediated membrane trafficking, organizing the assembly, remodeling, and disassembly of clathrin lattices through its modular architecture comprising an N-terminal kinase domain and a C-terminal clathrin-binding/J-domain and PTEN-like domain [PMID:9013862, PMID:24438162]. At clathrin-coated pits, GAK is transiently recruited after dynamin via phospholipid binding through its PTEN-like domain, and its J-domain recruits and activates Hsc70 to drive early curvature-enabling remodeling of nascent flat lattices as well as late uncoating; J-domain mutations that abolish Hsc70 recruitment trap GAK at pits and block CCP stabilization and invagination, generating abortive pits [PMID:16895969, PMID:40424130]. GAK loss reduces receptor-mediated endocytosis and depletes AP2/epsin and TGN adaptors, placing GAK upstream of Hsc70 in adaptor recruitment, and GAK directly phosphorylates the AP2 mu2 subunit AP2M1 within coated vesicles [PMID:12010461, PMID:16155256]. The C-terminal clathrin-binding and J-domains alone suffice to rescue clathrin-dependent trafficking and organismal viability, establishing the PTEN-like domain as dispensable for Hsc70-dependent uncoating [PMID:26345367]. Beyond endocytosis, GAK directly phosphorylates the Na+/K+-ATPase alpha-subunit Atp1a3 to control pump trafficking in neurons [PMID:30623173], cooperates with clathrin during mitosis to maintain centrosome integrity, chromosome congression, and astral-microtubule-dependent spindle positioning [PMID:19654208, PMID:31253758], and supports autophagic and mitophagic pathways: its kinase activity drives PRKN-independent mitophagy and lysosomal remodeling [PMID:34671015], it interacts with ULK1/Atg1 via its uncoating domain to govern Atg9 trafficking [PMID:37428930], and its intrinsically disordered region binds the RhoA-GEF ARHGEF2 to antagonize ROCK-dependent actomyosin dynamics independently of catalysis [PMID:41995027]. GAK kinase activity is essential in vivo, as kinase-dead knock-in mice die at birth from pulmonary surfactant defects [PMID:22022498], and GAK protein abundance is controlled by FBXO22-mediated ubiquitin-dependent proteasomal degradation [PMID:37442264].","teleology":[{"year":1997,"claim":"Established GAK as a kinase physically partnered with cell-cycle machinery, framing it as a potential cell-cycle regulator and defining its domain architecture.","evidence":"Co-IP and BIAcore showing direct GAK–cyclin G binding; domain mapping of N-terminal kinase and C-terminal tensin/auxilin-like domains","pmids":["9013862","9299234"],"confidence":"High","gaps":["Functional consequence of the cyclin G/CDK5 association not established","Substrates of the kinase activity not identified at this stage"]},{"year":2002,"claim":"Identified GAK as a clathrin-coated-vesicle-associated kinase with a defined substrate, connecting its catalytic activity to adaptor function.","evidence":"In vitro kinase assays on purified brain CCVs and recombinant AP2M1 (mu2)","pmids":["12010461"],"confidence":"High","gaps":["Phenotypic consequence of mu2 phosphorylation in cells not yet shown","Did not address GAK recruitment to pits"]},{"year":2005,"claim":"Demonstrated GAK is required for clathrin-mediated endocytosis and adaptor recruitment, positioning it upstream of Hsc70.","evidence":"shRNA knockdown in HeLa with transferrin/EGF uptake, adaptor localization, and dominant-negative Hsp70 epistasis","pmids":["16155256"],"confidence":"High","gaps":["Did not resolve the temporal step of GAK action at pits","Direct vs indirect effects on adaptor recruitment not separated"]},{"year":2006,"claim":"Resolved the timing of GAK at coated pits and the role of its lipid-binding domain, distinguishing recruitment from uncoating.","evidence":"TIRF live imaging, PTEN-like domain phospholipid-binding assays, actin depolymerization perturbation","pmids":["16895969"],"confidence":"High","gaps":["Mechanistic link between GAK flashing and curvature generation not yet defined","Role of J-domain in early remodeling not addressed"]},{"year":2009,"claim":"Extended GAK's repertoire beyond endocytosis to mitosis, showing it cooperates with clathrin to maintain spindle and centrosome integrity, and identified nuclear complexes.","evidence":"siRNA knockdown with spindle/centrosome phenotyping and mitotic Co-IP; GST pulldown of nuclear cyclin G1/p53/CHC/PP2A complexes","pmids":["19654208","19371378"],"confidence":"High","gaps":["Molecular basis of GAK–clathrin cooperation in spindle formation not defined","Functional role of nuclear GAK complexes not established"]},{"year":2011,"claim":"Established that GAK kinase activity is essential for organismal viability and tissue-specific function.","evidence":"Kinase-dead knock-in mice with immunohistochemistry of pulmonary surfactant and adhesion/signaling markers","pmids":["22022498"],"confidence":"High","gaps":["Direct substrate underlying the lung phenotype not identified","Cell-type-specific contributions not dissected"]},{"year":2014,"claim":"Defined the structural basis of GAK as a constitutively active kinase with a plastic catalytic domain and inhibitor-binding mode.","evidence":"X-ray crystallography of apo, nanobody-bound, and inhibitor-bound forms with enzyme kinetics","pmids":["24438162","25822739"],"confidence":"High","gaps":["Structures cover the catalytic domain, not full-length GAK or its C-terminal domains","Physiological relevance of the inactive dimeric state unresolved"]},{"year":2015,"claim":"Showed the clathrin-binding/J-domain fragment is sufficient for clathrin chaperoning and viability, ranking domain contributions to function.","evidence":"Conditional knockout mice with 62-kDa GAK fragment rescue and fibroblast trafficking assays","pmids":["26345367"],"confidence":"High","gaps":["Functions requiring the PTEN-like or kinase domains in other contexts not covered","Did not address non-endocytic roles"]},{"year":2018,"claim":"Identified a second direct GAK substrate and a physiological trafficking role in neurons, broadening its kinase function beyond adaptors.","evidence":"Analog-sensitive kinase chemical genetics, conditional KO neuron electrophysiology, trafficking assays","pmids":["30623173"],"confidence":"High","gaps":["Whether Atp1a3 phosphorylation acts via clathrin pathway not fully resolved","Phosphosite on Atp1a3 not mapped"]},{"year":2021,"claim":"Connected GAK kinase activity to selective mitophagy and lysosomal/autophagic dynamics, revealing a degradative-pathway role.","evidence":"siRNA/kinase-dead rescue, CRISPR KO, mitophagy reporters, C. elegans and zebrafish loss-of-function, ROCK epistasis","pmids":["34671015","34468012"],"confidence":"High","gaps":["Direct substrate driving mitophagy/lysosomal remodeling not identified","Relationship between mitophagy role and clathrin function unclear"]},{"year":2023,"claim":"Mapped GAK to the autophagy initiation machinery via a direct ULK1/Atg1 interaction controlling Atg9 trafficking, and identified its regulated turnover.","evidence":"Co-IP with domain mapping (uncoating domain–ULK1), Drosophila/microglia loss-of-function; separately proteomics, ubiquitination and proteasome assays for FBXO22","pmids":["37428930","37442264"],"confidence":"High","gaps":["Whether GAK phosphorylates ULK1/Atg9 directly not established here","FBXO22-driven degradation not linked to a specific GAK function"]},{"year":2025,"claim":"Defined an early, J-domain/Hsc70-dependent remodeling step required for coated-pit curvature, distinguishing it from late uncoating.","evidence":"GAK knockdown and J-domain point mutations with quantitative live TIRF CCP lifetime analysis","pmids":["40424130"],"confidence":"High","gaps":["Direct demonstration of pentagon incorporation by GAK–Hsc70 not provided","Kinase contribution to this step not dissected"]},{"year":2026,"claim":"Revealed a kinase-independent function of GAK's disordered region in regulating actomyosin contractility through a RhoA-GEF.","evidence":"CRISPR KO with IDR-vs-kinase-dead rescue, ARHGEF2 Co-IP, ROCK inhibitor and ARHGEF2 knockdown epistasis, migration assays","pmids":["41995027"],"confidence":"High","gaps":["Structural basis of GAK IDR–ARHGEF2 binding not defined","How actomyosin regulation integrates with endocytic/autophagic roles unclear"]},{"year":null,"claim":"How GAK's distinct domains and its catalytic versus scaffolding activities are coordinated across endocytosis, mitosis, autophagy, and cytoskeletal regulation remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Full-length GAK structure and inter-domain regulation unknown","Complete in vivo substrate set beyond AP2M1 and Atp1a3 not defined","Mechanistic switch governing context-specific functions not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,13]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2,13]},{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[4,19]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[4]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,20]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[6,14]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,5]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,19]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[2,4]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5,12]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[6,12]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[3]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[16]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,4,19]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[15,16,17]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[6,14]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[3,13]},{"term_id":"R-HSA-382551","term_label":"Transport of small molecules","supporting_discovery_ids":[13]}],"complexes":["clathrin-coated vesicle","AP2 adaptor complex"],"partners":["AP2M1","HSPA8","CLTC","ARHGEF2","ULK1","MCM3","CCNG1","FBXO22"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14976","full_name":"Cyclin-G-associated kinase","aliases":["DnaJ homolog subfamily C member 26"],"length_aa":1311,"mass_kda":143.2,"function":"Associates with cyclin G and CDK5. Seems to act as an auxilin homolog that is involved in the uncoating of clathrin-coated vesicles by Hsc70 in non-neuronal cells. Expression oscillates slightly during the cell cycle, peaking at G1 (PubMed:10625686). May play a role in clathrin-mediated endocytosis and intracellular trafficking, and in the dynamics of clathrin assembly/disassembly (PubMed:18489706)","subcellular_location":"Cytoplasm, perinuclear region; Golgi apparatus, trans-Golgi network; Cell junction, focal adhesion; Cytoplasmic vesicle, clathrin-coated vesicle","url":"https://www.uniprot.org/uniprotkb/O14976/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GAK","classification":"Not Classified","n_dependent_lines":586,"n_total_lines":1208,"dependency_fraction":0.48509933774834435},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000178950","cell_line_id":"CID000529","localizations":[{"compartment":"vesicles","grade":3},{"compartment":"cytoplasmic","grade":2},{"compartment":"golgi","grade":2}],"interactors":[{"gene":"AHCY","stoichiometry":0.2},{"gene":"ARHGAP18","stoichiometry":0.2},{"gene":"CLTA","stoichiometry":0.2},{"gene":"CLTB","stoichiometry":0.2},{"gene":"PARP1","stoichiometry":0.2},{"gene":"MRE11A","stoichiometry":0.2},{"gene":"HNRNPA2B1","stoichiometry":0.2},{"gene":"RACK1","stoichiometry":0.2},{"gene":"RBM42","stoichiometry":0.2},{"gene":"SRP68","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000529","total_profiled":1310},"omim":[{"mim_id":"613454","title":"RETT SYNDROME, CONGENITAL VARIANT","url":"https://www.omim.org/entry/613454"},{"mim_id":"608547","title":"VITAMIN K EPOXIDE REDUCTASE COMPLEX, SUBUNIT 1; VKORC1","url":"https://www.omim.org/entry/608547"},{"mim_id":"608375","title":"DNAJ/HSP40 HOMOLOG, SUBFAMILY C, MEMBER 6; DNAJC6","url":"https://www.omim.org/entry/608375"},{"mim_id":"602052","title":"CYCLIN G-ASSOCIATED KINASE; GAK","url":"https://www.omim.org/entry/602052"},{"mim_id":"310600","title":"NORRIE DISEASE; ND","url":"https://www.omim.org/entry/310600"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Golgi apparatus","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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Co-immunoprecipitation and BIAcore analysis demonstrated the direct GAK–cyclin G interaction. GAK harbors an N-terminal Ser/Thr protein kinase domain and a C-terminal tensin/auxilin-like domain with a leucine zipper region.\",\n      \"method\": \"Co-immunoprecipitation, Western blotting, BIAcore surface plasmon resonance, West-Western blotting\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — direct binding confirmed by BIAcore (in vitro reconstitution) plus reciprocal Co-IP; foundational study replicated in subsequent work\",\n      \"pmids\": [\"9013862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"GAK kinase activity (from anti-cyclin G immunoprecipitates) fluctuates during the cell cycle with a peak at G1 phase, even though cyclin G expression remains nearly constant, indicating cell-cycle-regulated kinase activity.\",\n      \"method\": \"Synchronized HeLa cell-cycle analysis, histone H1 kinase assay on immunoprecipitates\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-cycle synchronization with kinase activity assay in a single lab; single method for the activity measurement\",\n      \"pmids\": [\"9299234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GAK/auxilin2 phosphorylates the mu2 (AP2M1) medium subunit of the AP2 adaptor complex both within intact clathrin-coated vesicles (CCVs) and in solution, establishing GAK as a CCV-associated kinase with AP2M1 as a direct substrate.\",\n      \"method\": \"In vitro kinase assay using purified CCVs and recombinant substrates; kinase activity fractionation from porcine brain CCVs\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with defined substrate using highly purified CCVs; replicated by later substrate identification studies\",\n      \"pmids\": [\"12010461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GAK knockdown by shRNA in HeLa cells markedly reduces internalization of transferrin and EGF (receptor-mediated endocytosis), decreases perinuclear clathrin at the trans-Golgi network, reduces the number and dynamics of plasma membrane clathrin-coated pits, and dramatically reduces AP2 and epsin on the plasma membrane and AP1/GGA at the TGN. Expression of dominant-negative Hsp70 phenocopies this, placing GAK upstream of Hsc70 in clathrin/adaptor recruitment.\",\n      \"method\": \"Vector-based shRNA knockdown, fluorescence microscopy, transferrin/EGF internalization assays, dominant-negative Hsp70 expression\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with multiple orthogonal readouts (trafficking, morphology, adaptor localization) plus epistasis with dominant-negative Hsp70\",\n      \"pmids\": [\"16155256\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GAK is transiently recruited to clathrin-coated pits after dynamin recruitment and before pit invagination, as directly visualized by TIRF microscopy. GAK recruitment depends on its PTEN-like domain, which binds phospholipids. Synchronous recruitment of GAK (and subsequent Hsc70 recruitment) is required for irreversible clathrin uncoating; actin depolymerization prevents scission and irreversible uncoating despite repeated GAK flashing.\",\n      \"method\": \"Total internal reflectance fluorescence (TIRF) microscopy, phospholipid-binding assays, actin depolymerization experiments\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct live imaging with temporal resolution; phospholipid binding domain mapping; multiple pharmacological perturbations in one study\",\n      \"pmids\": [\"16895969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GAK localizes to both the cytoplasm and nucleus. In the nucleus, GAK forms complexes with cyclin G1, p53, clathrin heavy chain (CHC), and PP2A B'alpha1. CHC associates with GAK via a different domain depending on whether it is cytoplasmic or nuclear.\",\n      \"method\": \"Immunostaining, GFP-GAK ectopic expression, GST pulldown assays with dissected GAK fragments, co-immunoprecipitation\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple interaction partners confirmed by pulldown and Co-IP, localization by immunostaining and GFP fusion, but single laboratory\",\n      \"pmids\": [\"19371378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GAK is required for proper centrosome maturation and mitotic chromosome congression. GAK knockdown by siRNA causes metaphase arrest via spindle-assembly checkpoint activation, multi-aster formation from abnormal pericentriolar material fragmentation (not centriole fragmentation), and chromosome misalignment. GAK and clathrin heavy chain interact during mitosis and cooperate in the same pathway to regulate functional spindle formation.\",\n      \"method\": \"siRNA knockdown, cell-cycle analysis, immunofluorescence, co-immunoprecipitation during mitosis\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — siRNA knockdown with multiple phenotypic readouts (checkpoint activation, spindle morphology, centrosome integrity), validated CHC interaction during mitosis\",\n      \"pmids\": [\"19654208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In zebrafish, GAK (but not auxilin alone) knockdown by morpholino increases neuronal cell specification and decreases expression of the Notch target gene Her4, indicating that GAK function is required for Notch-dependent neuronal patterning. GAK knockdown also causes elevated apoptosis in neural tissues.\",\n      \"method\": \"Morpholino-mediated knockdown in zebrafish, in situ hybridization for Notch target genes, functional complementation with Drosophila auxilin\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — morpholino loss-of-function with defined transcriptional readout of Notch target gene; single lab in one model organism\",\n      \"pmids\": [\"20082716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Mice expressing kinase-dead GAK (GAK-kd) die within 30 minutes after birth due to respiratory dysfunction. Immunohistochemical analysis shows surfactant protein A (SP-A) is absent from alveolar spaces, and E-cadherin/phospho-EGFR signals are abnormal in GAK-kd pups, indicating that GAK kinase activity is required for proper pulmonary alveolar function.\",\n      \"method\": \"Kinase-dead knock-in mouse model, immunohistochemistry, histological analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic mouse model with kinase-dead allele; direct immunohistochemical validation of surfactant localization defect\",\n      \"pmids\": [\"22022498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structures of the GAK catalytic domain alone and in complex with nanobodies revealed: (i) GAK is constitutively active; (ii) the apo structure adopts a dimeric inactive state mediated by an unusual activation segment interaction; (iii) nanobody NbGAK_1 captures the monomeric active conformation with well-ordered activation segment; (iv) GAK has unusually high catalytic domain plasticity; (v) ATP-competitive inhibitors bind in a type I mode.\",\n      \"method\": \"X-ray crystallography, enzyme kinetics, size-exclusion chromatography\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures of apo, nanobody-bound, and inhibitor-bound forms with enzyme kinetic validation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"24438162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The clathrin-binding and J-domains of GAK (a C-terminal 62-kDa fragment) are sufficient to rescue clathrin-dependent trafficking in GAK-knockout fibroblasts and to rescue lethality/histological defects caused by liver- or brain-specific GAK knockout in mice. When both GAK and auxilin are knocked out in the brain, the 62-kDa GAK fragment maintains viability. This establishes that the PTEN-like domain is dispensable for Hsc70-dependent clathrin chaperoning/uncoating.\",\n      \"method\": \"Conditional knockout mice, transgenic rescue with 62-kDa GAK fragment, histology, trafficking assays in fibroblasts\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain-rescue in multiple in vivo contexts (liver KO, brain KO, double GAK/auxilin KO) plus cellular trafficking rescue; replicated across tissues\",\n      \"pmids\": [\"26345367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Isothiazolo[5,4-b]pyridine-based compounds are selective GAK inhibitors acting as ATP-competitive (type I) kinase inhibitors, as determined by co-crystallization. These inhibitors also inhibit two temporally distinct steps in the HCV lifecycle (viral entry and assembly), linking GAK kinase activity to HCV intracellular trafficking.\",\n      \"method\": \"Co-crystallization/X-ray structure, in vitro kinase binding assays, antiviral assays\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure confirming ATP-competitive binding mode; functional antiviral validation; single lab\",\n      \"pmids\": [\"25822739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"GAK is phosphorylated by c-Src at Y412 and Y1149. GAK-pY412/pY1149 undergoes dynamic subcellular redistribution during mitosis: nucleus during interphase → chromosomes at prophase/prometaphase → centrosomes at metaphase → chromosomes at end of telophase. Mass spectrometry and co-immunoprecipitation identified MCM3 (a DNA licensing factor) as a GAK-interacting partner, suggesting a GAK–c-Src–MCM3 axis in DNA replication licensing.\",\n      \"method\": \"In vivo phosphorylation with anti-phospho-specific antibody, immunofluorescence, mass spectrometry, co-immunoprecipitation\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — phosphorylation confirmed by phospho-specific antibody and mass spectrometry; MCM3 interaction by Co-IP; subcellular localization by IF; single laboratory\",\n      \"pmids\": [\"28135906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Using a chemical genetics approach (analog-sensitive kinase), GAK was shown to directly phosphorylate the Na+/K+-ATPase alpha-subunit Atp1a3. GAK regulates trafficking of Na+/K+-ATPase to the plasma membrane, and conditional GAK knockout in CA1 pyramidal neurons results in greater resting membrane potential change upon Na+/K+-ATPase blockade with ouabain, indicating compromised pump function.\",\n      \"method\": \"Chemical genetics (analog-sensitive kinase method), whole-cell patch clamp electrophysiology, conditional knockout mice, trafficking assays\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — chemical genetics directly identifies substrate; functional validation by electrophysiology in conditional KO neurons; multiple orthogonal methods\",\n      \"pmids\": [\"30623173\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GAK depletion leads to impaired astral microtubules and spindle positioning defects, phenocopying depletion of the GAK interactor clathrin, placing GAK and clathrin in the same pathway for spindle positioning in human cells.\",\n      \"method\": \"Live imaging siRNA screen on fibronectin micropatterns, siRNA knockdown, immunofluorescence\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA phenotype in defined geometry screen with clathrin epistasis; single lab; mechanism inferred from phenotypic similarity\",\n      \"pmids\": [\"31253758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GAK kinase activity is required for efficient PRKN-independent mitophagy (but is dispensable for PRKN-dependent mitophagy and starvation-induced autophagy). GAK knockdown/knockout in C. elegans (gakh-1) inhibits basal mitophagy in vivo, demonstrating evolutionary conservation. GAK modifies the mitochondrial network and lysosomal morphology to enable efficient transport of mitochondria for degradation.\",\n      \"method\": \"siRNA screen, kinase-dead mutant rescue, in vivo C. elegans knockdown (gakh-1), zebrafish PRKCD knockout, fluorescence-based mitophagy reporters\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — kinase-dead mutant establishes catalytic requirement; replicated across cell lines and two model organisms (C. elegans, zebrafish); multiple readouts\",\n      \"pmids\": [\"34671015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GAK knockout in A549 cells impairs autophagosome–lysosome fusion and autophagic lysosome reformation, causing accumulation of enlarged autophagosomes and autolysosomes during starvation. GAK controls lysosomal dynamics via actomyosin regulation; ROCK1 knockdown or ROCK inhibitor treatment rescues the GAK KO phenotype, placing GAK upstream of ROCK1 in lysosomal dynamics regulation.\",\n      \"method\": \"CRISPR knockout, GAK inhibitor, autophagic flux analysis, morphological analysis of lysosomes/autophagosomes, ROCK inhibitor rescue, ROCK1 siRNA knockdown\",\n      \"journal\": \"International journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO plus pharmacological inhibition with ROCK epistasis rescue; single lab; two complementary loss-of-function approaches\",\n      \"pmids\": [\"34468012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"GAK/dAux (Drosophila homolog) interacts with the autophagy initiation kinase ULK1/Atg1 via its uncoating domain and regulates the trafficking of Atg1 and Atg9 to autophagosomes in glia. Loss of GAK/dAux increases autophagosome number and size, upregulates PI3K class III complex components, and impairs autophagic flux. dAux also contributes to dopaminergic neurodegeneration and locomotor function in fly models.\",\n      \"method\": \"Co-immunoprecipitation (GAK–ULK1/Atg1 interaction), genetic loss-of-function in Drosophila and mouse microglia, fluorescence imaging of autophagosome markers, behavioral assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct interaction by Co-IP with domain mapping; loss-of-function in two model organisms; multiple pathway readouts\",\n      \"pmids\": [\"37428930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FBXO22 mediates ubiquitin-dependent proteasomal degradation of GAK. Proteomics identified GAK as an FBXO22 target; altered abundance (depletion or overexpression) of FBXO22 inversely changes GAK protein levels; proteasome inhibition blocks FBXO22-mediated GAK reduction; cellular ubiquitination assays confirmed GAK ubiquitination downstream of FBXO22.\",\n      \"method\": \"Proteomics, FBXO22 overexpression/depletion, proteasome inhibitor treatment, protein stability (decay rate) assay, cellular ubiquitination assay\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple complementary approaches (proteomics, protein decay, ubiquitination assay, proteasome inhibition) in single lab\",\n      \"pmids\": [\"37442264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"GAK knockdown inhibits clathrin-coated pit (CCP) stabilization and invagination, resulting in a striking increase in highly transient abortive CCPs. Mutations in the J-domain of GAK that abolish Hsc70 recruitment and activation at CCPs lead to GAK accumulation at CCPs and hinder CCP stabilization and invagination. This establishes that early GAK–Hsc70-mediated remodeling of nascent flat clathrin lattices (pentagon incorporation) is required for CCP curvature development.\",\n      \"method\": \"GAK knockdown, J-domain point mutations, live TIRF microscopy, CCP lifetime analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — structure–function mutagenesis of J-domain plus knockdown with quantitative live imaging of CCP dynamics; multiple orthogonal loss-of-function approaches\",\n      \"pmids\": [\"40424130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"GAK intrinsically disordered region (IDR) interacts with ARHGEF2 (a RhoA GEF) and antagonizes ROCK-dependent actomyosin signaling. GAK-knockout cells show enhanced stress fiber formation, increased myosin light chain (MLC) phosphorylation, and increased cell migration. These effects are suppressed by ROCK inhibitor or ARHGEF2 knockdown. The IDR, rather than GAK kinase activity, is the primary mediator of this regulation. GAK IDR also contributes to regulation of MLC expression.\",\n      \"method\": \"CRISPR knockout, co-immunoprecipitation (GAK IDR–ARHGEF2), immunofluorescence (stress fibers/MLC phosphorylation), ROCK inhibitor rescue, ARHGEF2 siRNA knockdown, cell migration assays\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR KO with domain-specific rescue (IDR vs. kinase-dead), direct ARHGEF2 interaction by Co-IP, ARHGEF2 knockdown epistasis, multiple orthogonal readouts\",\n      \"pmids\": [\"41995027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In the Drosophila GAK homolog (dAux) context, lack of glial dAux enhances phosphorylation of the autophagy protein Atg9 at T62 and T69. This phosphorylation is regulated through Atg1 (ULK1 homolog), which is required for Atg9–dAux interaction. Enhanced Atg9 phosphorylation promotes autophagosome formation and Atg9 trafficking to autophagosomes. Non-phosphorylatable Atg9 suppresses the dAux-loss phenotype and phosphomimetic Atg9 rescues Atg1-loss phenotype, defining a dAux–Atg1–Atg9 phosphorylation axis.\",\n      \"method\": \"Genetic epistasis in Drosophila, phospho-specific analysis, non-phosphorylatable/phosphomimetic Atg9 mutants, co-immunoprecipitation, fluorescence imaging\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with phosphomimetic/non-phosphorylatable mutants in fly model; preprint not yet peer-reviewed; single lab\",\n      \"pmids\": [\"bio_10.1101_2024.07.03.601894\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"GAK is a constitutively active Ser/Thr kinase that functions as an essential cofactor in clathrin-mediated endocytosis by: (1) recruiting Hsc70 to clathrin-coated pits (CCPs) via its J-domain, promoting early curvature-enabling remodeling of nascent clathrin lattices and late uncoating of clathrin-coated vesicles; (2) binding phospholipids via its PTEN-like domain to enable CCP membrane recruitment; (3) phosphorylating AP2M1 (mu2) to regulate clathrin adaptor function; and additionally (4) regulating Na+/K+-ATPase trafficking by phosphorylating Atp1a3; (5) maintaining centrosome integrity and spindle positioning during mitosis through clathrin interaction; (6) being phosphorylated by c-Src at Y412/Y1149 and undergoing cell-cycle-dependent localization to centrosomes and chromosomes where it associates with MCM3; (7) promoting PRKN-independent mitophagy through kinase activity that maintains mitochondrial network and lysosomal morphology; (8) regulating autophagy initiation in glia by interacting with ULK1 via its uncoating domain to control Atg1 and Atg9 trafficking; (9) antagonizing ROCK-dependent actomyosin dynamics through its intrinsically disordered region via interaction with the RhoA-GEF ARHGEF2; and (10) being subject to ubiquitin-dependent proteasomal degradation mediated by FBXO22.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"GAK (cyclin G-associated kinase) is a constitutively active Ser/Thr kinase that operates as an essential cofactor in clathrin-mediated membrane trafficking, organizing the assembly, remodeling, and disassembly of clathrin lattices through its modular architecture comprising an N-terminal kinase domain and a C-terminal clathrin-binding/J-domain and PTEN-like domain [#0, #9]. At clathrin-coated pits, GAK is transiently recruited after dynamin via phospholipid binding through its PTEN-like domain, and its J-domain recruits and activates Hsc70 to drive early curvature-enabling remodeling of nascent flat lattices as well as late uncoating; J-domain mutations that abolish Hsc70 recruitment trap GAK at pits and block CCP stabilization and invagination, generating abortive pits [#4, #19]. GAK loss reduces receptor-mediated endocytosis and depletes AP2/epsin and TGN adaptors, placing GAK upstream of Hsc70 in adaptor recruitment, and GAK directly phosphorylates the AP2 mu2 subunit AP2M1 within coated vesicles [#2, #3]. The C-terminal clathrin-binding and J-domains alone suffice to rescue clathrin-dependent trafficking and organismal viability, establishing the PTEN-like domain as dispensable for Hsc70-dependent uncoating [#10]. Beyond endocytosis, GAK directly phosphorylates the Na+/K+-ATPase alpha-subunit Atp1a3 to control pump trafficking in neurons [#13], cooperates with clathrin during mitosis to maintain centrosome integrity, chromosome congression, and astral-microtubule-dependent spindle positioning [#6, #14], and supports autophagic and mitophagic pathways: its kinase activity drives PRKN-independent mitophagy and lysosomal remodeling [#15], it interacts with ULK1/Atg1 via its uncoating domain to govern Atg9 trafficking [#17], and its intrinsically disordered region binds the RhoA-GEF ARHGEF2 to antagonize ROCK-dependent actomyosin dynamics independently of catalysis [#20]. GAK kinase activity is essential in vivo, as kinase-dead knock-in mice die at birth from pulmonary surfactant defects [#8], and GAK protein abundance is controlled by FBXO22-mediated ubiquitin-dependent proteasomal degradation [#18].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established GAK as a kinase physically partnered with cell-cycle machinery, framing it as a potential cell-cycle regulator and defining its domain architecture.\",\n      \"evidence\": \"Co-IP and BIAcore showing direct GAK–cyclin G binding; domain mapping of N-terminal kinase and C-terminal tensin/auxilin-like domains\",\n      \"pmids\": [\"9013862\", \"9299234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the cyclin G/CDK5 association not established\", \"Substrates of the kinase activity not identified at this stage\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified GAK as a clathrin-coated-vesicle-associated kinase with a defined substrate, connecting its catalytic activity to adaptor function.\",\n      \"evidence\": \"In vitro kinase assays on purified brain CCVs and recombinant AP2M1 (mu2)\",\n      \"pmids\": [\"12010461\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phenotypic consequence of mu2 phosphorylation in cells not yet shown\", \"Did not address GAK recruitment to pits\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated GAK is required for clathrin-mediated endocytosis and adaptor recruitment, positioning it upstream of Hsc70.\",\n      \"evidence\": \"shRNA knockdown in HeLa with transferrin/EGF uptake, adaptor localization, and dominant-negative Hsp70 epistasis\",\n      \"pmids\": [\"16155256\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the temporal step of GAK action at pits\", \"Direct vs indirect effects on adaptor recruitment not separated\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Resolved the timing of GAK at coated pits and the role of its lipid-binding domain, distinguishing recruitment from uncoating.\",\n      \"evidence\": \"TIRF live imaging, PTEN-like domain phospholipid-binding assays, actin depolymerization perturbation\",\n      \"pmids\": [\"16895969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic link between GAK flashing and curvature generation not yet defined\", \"Role of J-domain in early remodeling not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended GAK's repertoire beyond endocytosis to mitosis, showing it cooperates with clathrin to maintain spindle and centrosome integrity, and identified nuclear complexes.\",\n      \"evidence\": \"siRNA knockdown with spindle/centrosome phenotyping and mitotic Co-IP; GST pulldown of nuclear cyclin G1/p53/CHC/PP2A complexes\",\n      \"pmids\": [\"19654208\", \"19371378\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of GAK–clathrin cooperation in spindle formation not defined\", \"Functional role of nuclear GAK complexes not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established that GAK kinase activity is essential for organismal viability and tissue-specific function.\",\n      \"evidence\": \"Kinase-dead knock-in mice with immunohistochemistry of pulmonary surfactant and adhesion/signaling markers\",\n      \"pmids\": [\"22022498\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrate underlying the lung phenotype not identified\", \"Cell-type-specific contributions not dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined the structural basis of GAK as a constitutively active kinase with a plastic catalytic domain and inhibitor-binding mode.\",\n      \"evidence\": \"X-ray crystallography of apo, nanobody-bound, and inhibitor-bound forms with enzyme kinetics\",\n      \"pmids\": [\"24438162\", \"25822739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures cover the catalytic domain, not full-length GAK or its C-terminal domains\", \"Physiological relevance of the inactive dimeric state unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed the clathrin-binding/J-domain fragment is sufficient for clathrin chaperoning and viability, ranking domain contributions to function.\",\n      \"evidence\": \"Conditional knockout mice with 62-kDa GAK fragment rescue and fibroblast trafficking assays\",\n      \"pmids\": [\"26345367\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functions requiring the PTEN-like or kinase domains in other contexts not covered\", \"Did not address non-endocytic roles\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a second direct GAK substrate and a physiological trafficking role in neurons, broadening its kinase function beyond adaptors.\",\n      \"evidence\": \"Analog-sensitive kinase chemical genetics, conditional KO neuron electrophysiology, trafficking assays\",\n      \"pmids\": [\"30623173\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Atp1a3 phosphorylation acts via clathrin pathway not fully resolved\", \"Phosphosite on Atp1a3 not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Connected GAK kinase activity to selective mitophagy and lysosomal/autophagic dynamics, revealing a degradative-pathway role.\",\n      \"evidence\": \"siRNA/kinase-dead rescue, CRISPR KO, mitophagy reporters, C. elegans and zebrafish loss-of-function, ROCK epistasis\",\n      \"pmids\": [\"34671015\", \"34468012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrate driving mitophagy/lysosomal remodeling not identified\", \"Relationship between mitophagy role and clathrin function unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mapped GAK to the autophagy initiation machinery via a direct ULK1/Atg1 interaction controlling Atg9 trafficking, and identified its regulated turnover.\",\n      \"evidence\": \"Co-IP with domain mapping (uncoating domain–ULK1), Drosophila/microglia loss-of-function; separately proteomics, ubiquitination and proteasome assays for FBXO22\",\n      \"pmids\": [\"37428930\", \"37442264\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether GAK phosphorylates ULK1/Atg9 directly not established here\", \"FBXO22-driven degradation not linked to a specific GAK function\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined an early, J-domain/Hsc70-dependent remodeling step required for coated-pit curvature, distinguishing it from late uncoating.\",\n      \"evidence\": \"GAK knockdown and J-domain point mutations with quantitative live TIRF CCP lifetime analysis\",\n      \"pmids\": [\"40424130\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct demonstration of pentagon incorporation by GAK–Hsc70 not provided\", \"Kinase contribution to this step not dissected\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealed a kinase-independent function of GAK's disordered region in regulating actomyosin contractility through a RhoA-GEF.\",\n      \"evidence\": \"CRISPR KO with IDR-vs-kinase-dead rescue, ARHGEF2 Co-IP, ROCK inhibitor and ARHGEF2 knockdown epistasis, migration assays\",\n      \"pmids\": [\"41995027\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of GAK IDR–ARHGEF2 binding not defined\", \"How actomyosin regulation integrates with endocytic/autophagic roles unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How GAK's distinct domains and its catalytic versus scaffolding activities are coordinated across endocytosis, mitosis, autophagy, and cytoskeletal regulation remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full-length GAK structure and inter-domain regulation unknown\", \"Complete in vivo substrate set beyond AP2M1 and Atp1a3 not defined\", \"Mechanistic switch governing context-specific functions not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 13]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2, 13]},\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [4, 19]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 20]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [6, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 19]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5, 12]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [6, 12]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [16]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 4, 19]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [15, 16, 17]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [6, 14]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [3, 13]},\n      {\"term_id\": \"R-HSA-382551\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"complexes\": [\"clathrin-coated vesicle\", \"AP2 adaptor complex\"],\n    \"partners\": [\"AP2M1\", \"HSPA8\", \"CLTC\", \"ARHGEF2\", \"ULK1\", \"MCM3\", \"CCNG1\", \"FBXO22\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}