{"gene":"MAP4","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1991,"finding":"MAP4 contains a C-terminal microtubule-binding domain with three imperfect 18-amino acid repeats homologous to those in neuronal MAP2 and tau; fusion proteins containing this domain bind microtubules in vitro, while projection-domain-only constructs do not.","method":"cDNA cloning, in vitro microtubule binding assay with fusion proteins","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro binding assay with domain-specific constructs, replicated in multiple subsequent studies","pmids":["1905296"],"is_preprint":false},{"year":1991,"finding":"Phosphorylation of the Pro-rich region of MAP4 by cdc2/H1 histone kinase suppresses MAP4's microtubule assembly-promoting activity, providing a mechanism for microtubule disassembly at the G2/M transition.","method":"In vitro kinase assay, microtubule assembly assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro assay in single study, replicated conceptually by later work","pmids":["1656961"],"is_preprint":false},{"year":1991,"finding":"An M-phase-specific kinase (related to p34cdc2/cyclin B) associates with isolated mitotic spindles and phosphorylates MAP4 (and MAP1B) in a cell-cycle-dependent manner.","method":"Spindle isolation, in vitro kinase assay, immunofluorescence with anti-thiophosphoprotein antibody","journal":"Cell regulation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical fractionation plus kinase assay, single lab but multiple methods","pmids":["1667090"],"is_preprint":false},{"year":1994,"finding":"A 230 kDa MAP4-like protein in Xenopus egg extracts is heat-stable, phosphorylated, and promotes elongation of microtubules from axonemes, confirming MAP4 ortholog function in a non-mammalian model.","method":"Microtubule co-sedimentation, immunological characterization, microtubule assembly assay","journal":"Cell motility and the cytoskeleton","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — biochemical purification and functional assay, single study","pmids":["8087870"],"is_preprint":false},{"year":1995,"finding":"Cyclin B directly binds to the Pro-rich C-terminal region of MAP4, thereby targeting the p34cdc2/cyclin B kinase complex to microtubules; the kinase then phosphorylates MAP4 within the complex and abolishes MAP4's microtubule-stabilizing activity without preventing its microtubule binding.","method":"Co-sedimentation with purified proteins, GST-cyclin B pulldown, recombinant MAP4 fragment mapping, in vitro kinase assay, microtubule dynamics assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro with purified components, multiple orthogonal methods, domain mapping","pmids":["7876309"],"is_preprint":false},{"year":1995,"finding":"MAP4 isoforms with three, four, or five microtubule-binding repeats are expressed in a tissue- and developmental-stage-specific manner via alternative RNA splicing from a single-copy gene on chromosome 3p21.","method":"cDNA cloning, RNase protection analysis, chromosomal mapping","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal molecular biology methods, single lab","pmids":["7857940"],"is_preprint":false},{"year":1996,"finding":"MARK kinase (p110mark) phosphorylates KXGS motifs in the microtubule-binding domain of MAP4 in vitro, causing MAP4 dissociation from microtubules and a pronounced increase in dynamic instability.","method":"In vitro kinase assay, microtubule co-sedimentation, microtubule dynamics assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with site identification, replicated in subsequent cell-based work","pmids":["8631898"],"is_preprint":false},{"year":1996,"finding":"A muscle-specific MAP4 isoform (encoded by a 3.2 kb insertion in the projection domain) is required for myotube formation: antisense depletion of this isoform in C2C12 cells allows cell fusion but produces short, apolar syncytia with disorganized microtubules and absent myofibrils.","method":"Stable antisense cell lines, in situ hybridization, immunofluorescence, differentiation assay","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function with specific cellular phenotype, replicated by later isoform studies","pmids":["8631255"],"is_preprint":false},{"year":1996,"finding":"Microinjection of intact MAP4 or its C-terminal PA4 fragment into PtK2 cells promotes microtubule polymerization and bundling and stabilizes microtubules against nocodazole; the N-terminal NR fragment has no effect. The PA4 fragment also indirectly increases stress fibers without direct binding to actin.","method":"Microinjection, immunofluorescence, nocodazole resistance assay, in vitro binding assay","journal":"Cell motility and the cytoskeleton","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct microinjection in cells plus in vitro binding, single lab, two methods","pmids":["8801031"],"is_preprint":false},{"year":1996,"finding":"Antibody-mediated removal of MAP4 from microtubules in living cells produces no detectable phenotype: MT dynamics, tubulin modifications, organelle distribution, and mitotic spindle morphology are all normal, indicating MAP4 is not essential for these functions in cultured cells.","method":"Antibody microinjection, tubulin photoactivation, nocodazole sensitivity, immunofluorescence","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — rigorous loss-of-function with multiple orthogonal readouts, clean negative result mechanistically informative","pmids":["8636213"],"is_preprint":false},{"year":1997,"finding":"CDC2 kinase is the major M-phase MAP4 kinase in HeLa cells; Ser-787 (in SPSK) is phosphorylated specifically at mitosis while Ser-696 (in SPEK) is phosphorylated in both mitosis and interphase, both lying in the proline-rich region of the microtubule-binding domain.","method":"Metabolic 32P labeling, butyrolactone I inhibitor, phosphopeptide mapping, phospho-specific antibodies","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vivo phosphorylation mapping with site identification using inhibitors and phospho-specific antibodies, replicated by mutagenesis studies","pmids":["9398320"],"is_preprint":false},{"year":1997,"finding":"Overexpression of full-length MAP4 or its MT-binding domain stabilizes microtubules in vivo (increased detyrosinated tubulin, nocodazole resistance) and inhibits cell growth without causing mitotic arrest or cell death.","method":"Stable transfection, nocodazole resistance assay, tubulin modification immunoblotting, growth curves","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean overexpression with multiple functional readouts, replicated across multiple stable cell lines","pmids":["9044058"],"is_preprint":false},{"year":1997,"finding":"MAP4 overexpression directly inhibits MT-based organelle motility and vesicle transport in vivo (reduced LDL receptor recycling, Golgi redistribution), in a manner not reproduced by taxol-mediated MT stabilization, indicating a direct steric effect of MAP4 on motor-driven transport.","method":"DIC live microscopy, receptor trafficking assays, Golgi redistribution assay, brefeldin A washout","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal transport assays, taxol control dissects mechanism, single lab","pmids":["9365275"],"is_preprint":false},{"year":1999,"finding":"MARK1/MARK2 kinases phosphorylate MAP4 on its microtubule-binding domain in transfected CHO cells, causing microtubule disruption, vimentin network breakdown, and cell detachment; actin fibers are unaffected.","method":"Inducible expression of MARK kinases in CHO cells, immunofluorescence, phosphorylation analysis","journal":"Cell motility and the cytoskeleton","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based validation of in vitro kinase findings, single lab","pmids":["10542369"],"is_preprint":false},{"year":1999,"finding":"MAP4 depletion (antisense RNA to ~33% of normal) decreases total tubulin content, shifts tubulin partitioning from polymer to protomer, slows MT regrowth after depolymerization, and flattens cell morphology, demonstrating MAP4 regulates MT assembly level and cell shape.","method":"Stable antisense RNA expression, tubulin fractionation, MT regrowth assay, immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean loss-of-function with multiple quantitative readouts, single lab","pmids":["10341201"],"is_preprint":false},{"year":1999,"finding":"The Pro-rich region of MAP4 promotes nucleation of microtubule assembly by bridging protofilaments, whereas the AP sequence region promotes elongation; the tail region is required for the nucleation step when combined with the AP sequence region.","method":"In vitro microtubule assembly assay with truncated recombinant fragments, electron microscopy, binding stoichiometry","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro with multiple domain-deletion constructs and EM validation","pmids":["9914488"],"is_preprint":false},{"year":1999,"finding":"MAP kinase phosphorylates Ser-696 of MAP4 in vitro and in cell extracts; serum starvation causes dephosphorylation of Ser-696 in HeLa cells and fibroblasts, and serum re-addition restores phosphorylation, linking this site to proliferation/quiescence status.","method":"In vitro kinase assay, MAP kinase inhibitor in cell extract, phospho-specific antibodies, serum starvation experiments","journal":"Cell structure and function","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro plus cell-based evidence with inhibitor, single lab","pmids":["15216889"],"is_preprint":false},{"year":2000,"finding":"Phosphorylation of Ser-787 by p34cdc2 kinase is the critical site that reduces MAP4's microtubule-polymerization activity; the Ser787Glu phosphomimetic mutant dramatically reduces this activity, while Ser696Glu does not, establishing site-specific functional hierarchy.","method":"Site-directed mutagenesis, in vitro MT polymerization assay with phosphomimetic mutants","journal":"Cell structure and function","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis reconstitution with clear functional read-out, mechanistically complementary to prior in vivo phosphosite identification","pmids":["10791892"],"is_preprint":false},{"year":2001,"finding":"Nonphosphorylatable MAP4 mutants (AA, KK) bind microtubules more avidly and confer greater nocodazole resistance than wild-type or phosphomimetic (EE) MAP4; EE mutant behaves like WT, demonstrating that phosphorylation of Ser-696/Ser-787 reduces MAP4-MT interaction and MT stability in vivo.","method":"Stable inducible cell lines expressing phosphorylation mutants, MT co-sedimentation, nocodazole resistance assay","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple phosphomimetic and non-phosphorylatable mutants with orthogonal readouts, single lab","pmids":["11683421"],"is_preprint":false},{"year":2002,"finding":"The projection (PJ) domain of MAP4 suppresses the microtubule-bundling activity of the MT-binding domain; longer PJ domains progressively reduce bundle formation, and this suppression correlates with PJ domain length rather than amino acid sequence.","method":"In vitro microtubule assembly with truncated MAP4 constructs, negative-staining EM, dark-field microscopy","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro with multiple deletion constructs, EM validation","pmids":["12079337"],"is_preprint":false},{"year":2002,"finding":"MAP4 counteracts microtubule catastrophe promoters (XKCM1, non-sequestering Op18) but not tubulin-sequestering destabilizers in intact cells, revealing mechanistic specificity in its stabilizing activity.","method":"Inducible co-transfection, co-expression with catastrophe promoters vs. tubulin sequesterers, cell imaging","journal":"Current biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis by co-expression with multiple distinct destabilizers, single lab","pmids":["12123579"],"is_preprint":false},{"year":2003,"finding":"MAP4 overexpression in cardiocytes stabilizes microtubules (shifts tubulin to polymerized fraction) and increases total tubulin levels; beta1-tubulin overexpression has no independent or additive effect, identifying MAP4 as the causative factor for microtubule network densification in cardiac hypertrophy.","method":"Adenoviral overexpression in isolated cardiocytes, transgenic mice, tubulin fractionation, immunofluorescence","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — orthogonal in vitro and in vivo models, multiple methods, genetic controls","pmids":["12855424"],"is_preprint":false},{"year":2004,"finding":"MAP4 decoration of microtubules in cardiocytes inhibits beta-adrenergic receptor recycling after agonist withdrawal, reducing cell-surface beta-AR number and cAMP responsiveness; confirmed in MAP4-transgenic mouse cardiocytes.","method":"Adenoviral MAP4 overexpression, [3H]CGP-12177 receptor binding assay, cAMP measurement, transgenic mouse confirmation","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-based and transgenic confirmation, functional readout with quantitative receptor trafficking assay","pmids":["15528234"],"is_preprint":false},{"year":2005,"finding":"Septins (Sept2:6:7 heterotrimer and Sept2 monomer) directly bind the proline-rich C-terminal region of MAP4; this interaction blocks MAP4's ability to bind and bundle microtubules in vitro. In cells, septin depletion increases microtubule stability in a MAP4-dependent manner.","method":"Mass spectrometry identification, direct binding assay with purified proteins, domain mapping, RNA interference, microtubule bundling assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — MS identification, reconstituted in vitro binding and functional assay, RNAi epistasis in cells","pmids":["16093351"],"is_preprint":false},{"year":2005,"finding":"Truncation of MAP4's projection domain attenuates microtubule dynamic instability at higher MAP4 concentrations, demonstrating that the projection domain modulates dynamic instability independently of its bundling suppression function.","method":"In vitro dark-field microscopy of microtubule dynamics with projection-domain deletion mutants","journal":"Cell structure and function","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with multiple deletion constructs, single lab","pmids":["15840946"],"is_preprint":false},{"year":2009,"finding":"In hypoxic cells, activated p38/MAPK phosphorylates MAP4 (increasing phosphorylation) and dephosphorylates Op18/stathmin, both contributing to microtubule disruption; p38-MAP4 interaction was confirmed by co-immunoprecipitation.","method":"Co-immunoprecipitation, p38 inhibitor (SB203580), MKK6(Glu) overexpression, immunofluorescence, cell viability assay","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus pharmacological and genetic modulation, single lab","pmids":["19915797"],"is_preprint":false},{"year":2010,"finding":"PP2A and PP1 dephosphorylate MAP4 at Ser-924 and Ser-1056 in pressure-overloaded hypertrophied myocardium; overexpression of PP2A or PP1 in normal hearts reproduces the microtubule densification and MAP4 dephosphorylation phenotype of hypertrophy.","method":"Phosphatase activity assays, phospho-specific antibodies, adenoviral overexpression in hearts, transgenic comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical phosphatase activity, in vivo genetic overexpression, phospho-specific site identification","pmids":["20889984"],"is_preprint":false},{"year":2011,"finding":"MAP4 physically interacts with dynein-dynactin in vivo and inhibits dynein-mediated microtubule sliding in vitro; depletion of MAP4 causes spindle misorientation in the vertical plane in human cells, placing MAP4 as a regulator of cortical force generation during mitosis.","method":"Co-immunoprecipitation, in vitro dynein-mediated MT sliding assay, RNAi depletion, spindle orientation measurement","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus co-IP plus clean loss-of-function with specific phenotypic readout","pmids":["21822276"],"is_preprint":false},{"year":2011,"finding":"MAP4 overexpression promotes microtubule stabilization in hypoxic cardiomyocytes; MAP4 also interacts with DYNLT1 (dynein light chain Tctex-1) which in turn interacts with VDAC1, linking MAP4 to mitochondrial permeability stabilization via the microtubule-DYNLT1-VDAC1 axis.","method":"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence, MT polymerization assay, cell viability/ATP measurement","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus Co-IP for DYNLT1-VDAC1, knockdown epistasis, single lab","pmids":["22164227"],"is_preprint":false},{"year":2013,"finding":"cAMP/PKA signaling phosphorylates MAP4, disrupting microtubule cytoskeleton and inhibiting bladder cancer cell invasion and migration; the interaction between PKA and MAP4 was confirmed by co-immunoprecipitation.","method":"Co-immunoprecipitation, siRNA knockdown, matrigel invasion assay, immunofluorescence/immunoblotting","journal":"Urologic oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional RNAi assay, single lab","pmids":["24140250"],"is_preprint":false},{"year":2014,"finding":"Phosphorylated MAP4 (at Ser-696 and Ser-787) translocates from the cytosol to mitochondria in hypoxic cardiomyocytes, where it induces mitochondrial permeability transition pore (mPTP) opening and apoptosis; the non-phosphorylatable MAP4(Ala) mutant suppresses this translocation and apoptosis.","method":"Subcellular fractionation, phospho-specific antibodies, MAP4(Ala) mutant expression, mPTP assay, apoptosis assay","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — fractionation with functional consequence, phosphorylation-dead rescue mutant, specific mechanistic pathway","pmids":["25232678"],"is_preprint":false},{"year":2014,"finding":"MAP4 controls dynein-dependent transport of BTN3A1 to the perinuclear region upon nucleic acid stimulation; MAP4 depletion impairs BTN3A1 redistribution and consequently reduces TBK1-IRF3-mediated type I interferon production, placing MAP4 upstream of the TBK1-IRF3 antiviral signaling axis.","method":"RNAi depletion, co-immunoprecipitation, immunofluorescence localization, IFN-β reporter assay","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi epistasis plus co-IP, defined pathway placement, single lab","pmids":["27911820"],"is_preprint":false},{"year":2014,"finding":"MAP4 regulation of microtubule-based transport operates differentially on kinesin-2 vs. dynein in Xenopus melanophores: MAP4 on microtubules shortens dynein-dependent runs and lengthens kinesin-2 runs; phosphorylation of threonine residues in the MT-binding domain during aggregation signals reduces MAP4-MT binding, increasing dynein-dependent and decreasing kinesin-2-dependent motility.","method":"Overexpression and removal of XMAP4 in melanophores, run-length analysis of melanosome movement, phosphorylation analysis","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — dual motor analysis with overexpression and depletion, phosphorylation state correlated to transport direction, single lab with multiple quantitative methods","pmids":["25143402"],"is_preprint":false},{"year":2014,"finding":"Loss-of-function variants in MAP4 in humans cause centrosome amplification, aberrant ciliogenesis, and Golgi fragmentation in fibroblasts; the variant affects kinase binding sites required for dynamic instability of microtubule formation.","method":"Homozygosity mapping/NGS, patient fibroblast centrosome counting, cilia assay, Golgi morphology analysis","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient cells with multiple cellular phenotype readouts, single family/lab","pmids":["25323976"],"is_preprint":false},{"year":2015,"finding":"p38/MAPK activation by LPS/TNF-α phosphorylates MAP4 at Ser-696 and Ser-787, inducing microtubule disassembly and endothelial hyperpermeability; the phosphorylation-resistant MAP4(Ala) mutant or p38 inhibitor prevents MT disruption and barrier dysfunction.","method":"Phospho-specific antibodies, p38 inhibitor SB203580, MKK6(Glu) activation, MAP4(Ala) mutant, transendothelial resistance measurement","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological inhibition plus constitutive activation plus rescue mutant, multiple mechanistic levels","pmids":["25746230"],"is_preprint":false},{"year":2015,"finding":"A novel MAP4 isoform (oMAP4), expressed upon muscle differentiation, is required for paraxial microtubule array organization; purified oMAP4 aligns dynamic microtubules into antiparallel bundles that withstand dynein- and kinesin-driven sliding forces in vitro, and its depletion impairs cell elongation, fusion, and paraxial array formation.","method":"In vitro microtubule bundling assay with purified oMAP4, RNAi depletion, live cell imaging, motor resistance assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro with purified protein plus clean RNAi loss-of-function with defined phenotype, multiple orthogonal methods","pmids":["25898002"],"is_preprint":false},{"year":2019,"finding":"HPV16 oncoprotein E7 directly binds the C-terminus of MAP4, inhibiting Mps1-mediated phosphorylation of MAP4 (at T927/S928), thereby blocking phosphorylation-dependent MAP4 degradation, stabilizing microtubule polymerization, and retarding mitotic progression. MAP4 T927E/S928E mutations reduce E7 binding and rescue mitotic progression.","method":"Co-immunoprecipitation, kinase assay, site-directed mutagenesis, mitotic timing assay","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct binding assay, kinase assay, rescue mutagenesis, multiple methods in single study","pmids":["31253867"],"is_preprint":false},{"year":2022,"finding":"MAP4, when phosphorylated by GSK3β, tethers cargo (organelles) to microtubules via its projection domain, impairs kinesin-1 force generation, and biases bidirectional transport toward minus-ends; MAP4 physically interacts with dynein and dynactin and the phosphorylated form associates with the cargo-motor complex.","method":"Co-immunoprecipitation, organelle tracking, optical trap force assay, GSK3β manipulation, MAP4 domain analysis","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1 / Strong — biophysical force assay plus co-IP plus genetic rescue, multiple orthogonal methods","pmids":["36191197"],"is_preprint":false},{"year":2023,"finding":"MAP4 interacts with autophagy marker LC3 (confirmed by co-immunoprecipitation) and colocalizes with LC3 in myoblast cytoplasm; this interaction promotes autophagy during C2C12 differentiation. miR-103-3p suppresses MAP4 expression and thereby inhibits both autophagy and myotube formation.","method":"Co-immunoprecipitation, dual-luciferase reporter, immunofluorescence co-localization, autophagy assays","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus functional knockdown, single lab","pmids":["36835542"],"is_preprint":false},{"year":2023,"finding":"FBXW7 ubiquitin ligase targets MAP4 for degradation; CHEK1-mediated phosphorylation of MAP4 at Thr-521 is required for FBXW7-dependent MAP4 degradation. Loss of FBXW7 elevates MAP4 levels and ERK phosphorylation, promoting ESCC progression.","method":"GST-pulldown, LC-MS/MS, co-immunoprecipitation, site-directed phosphorylation analysis","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, MS identification, phosphorylation site mapping, single lab","pmids":["36991467"],"is_preprint":false},{"year":2023,"finding":"Phosphorylated MAP4 undergoes self-degradation via mitophagy in hypoxic keratinocytes; MAP4 contains both BH3 and LIR domains that allow it to simultaneously act as a mitophagy initiator and substrate receptor. Mutation of either domain abolishes p-MAP4 self-degradation and impairs hypoxia-induced keratinocyte migration and proliferation.","method":"Domain mutagenesis (BH3 and LIR), autophagy flux assays, LC3 co-localization, cell migration/proliferation assays","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mutagenesis with functional readouts, single lab","pmids":["37198170"],"is_preprint":false},{"year":2024,"finding":"p110α (PI3Kα catalytic subunit) localizes to microtubules via MAP4 and is recruited with receptor tyrosine kinases to endosomes for PI3K/Akt signaling; MAP4 knockdown abrogates the tumor-promoting effects of p85α loss, placing MAP4 upstream of endosomal PI3K/Akt activation.","method":"Knockdown studies, endosomal fractionation, PI3K/Akt signaling assays, tumorsphere formation assay","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis by knockdown with pathway readout, single lab","pmids":["38630589"],"is_preprint":false},{"year":2024,"finding":"Muscle-specific MAP4 isoform (mMAP4) exhibits enhanced microtubule association compared to ubiquitous MAP4 (uMAP4); loss of mMAP4 in mice (exon 8 deletion) causes disorganized microtubule architecture and intrinsic loss of skeletal muscle force generation, demonstrating isoform-specific function in muscle homeostasis.","method":"Genomic exon deletion in mice, microtubule co-sedimentation, ex vivo force measurement, immunofluorescence","journal":"iScience","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo knockout with multiple functional readouts, isoform-specific comparison","pmids":["39473976"],"is_preprint":false},{"year":2025,"finding":"MAP4 preferentially partitions onto tyrosinated microtubules (via its projection domain) while MAP7D1 decorates detyrosinated microtubules; MAP4-decorated tracks preferentially support kinesin-3 (KIF1A) transport, and MAP4 density on microtubules decreases during nutrient starvation to promote perinuclear lysosome positioning, coordinating lysosome repositioning in response to nutrient availability.","method":"Live imaging of MAP4/MAP7D1 on microtubule subsets, rigor kinesin localization assays, lysosome tracking, nutrient starvation/stimulation experiments, projection domain mutant analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple imaging-based methods, preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.10.07.680844"],"is_preprint":true},{"year":2025,"finding":"MAP4 phosphorylation by PI3K (activated downstream of ARID1A loss) reduces MAP4's microtubule-stabilizing activity, disrupts bipolar spindle formation, and sensitizes colorectal cancer cells to the antimicrotubule drug EMP (synthetic lethality with ARID1A loss).","method":"ARID1A isogenic cell lines, drug screening, phosphorylation analysis, spindle imaging, PI3K pathway manipulation","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isogenic genetic model with pathway inhibition and functional readout, single lab","pmids":["41360780"],"is_preprint":false}],"current_model":"MAP4 is a ubiquitously expressed microtubule-associated protein whose C-terminal MT-binding domain (containing three to five 18-aa repeats plus a Pro-rich region) promotes microtubule nucleation, elongation, and stabilization while its N-terminal projection domain suppresses MT bundling and modulates dynamic instability; its activity is tightly regulated by phosphorylation at multiple sites (notably Ser-787 and Ser-696 by CDC2/cyclin B, MARK, p38/MAPK, PKA, MAP kinase, and GSK3β), which reduces MT affinity and, in cardiomyocytes, triggers mitochondrial translocation to induce apoptosis; MAP4 also physically interacts with cyclin B (recruiting CDC2 to spindle MTs), dynein-dynactin (regulating minus-end-directed transport and spindle positioning), septins (which block its MT-binding and bundling activity), and kinesin-1/kinesin-3 motors (differentially regulating organelle transport), and participates in innate immune signaling by controlling dynein-dependent BTN3A1 trafficking that activates TBK1-IRF3."},"narrative":{"mechanistic_narrative":"MAP4 is a ubiquitously expressed structural microtubule-associated protein that controls the assembly, stability, and architecture of the microtubule cytoskeleton through a bipartite organization [PMID:1905296, PMID:9914488]. Its C-terminal microtubule-binding domain—built from imperfect 18-amino-acid repeats (present in three-, four-, or five-repeat isoforms generated by alternative splicing) plus a Pro-rich region—binds and stabilizes microtubules, with the Pro-rich region nucleating assembly by bridging protofilaments and an adjacent sequence driving elongation [PMID:1905296, PMID:7857940, PMID:9914488]. Overexpression stabilizes microtubules and elevates polymer mass while depletion reduces tubulin polymer and slows regrowth, establishing MAP4 as a positive regulator of microtubule assembly level and cell shape that specifically counteracts catastrophe-promoting destabilizers rather than tubulin sequesterers [PMID:9044058, PMID:10341201, PMID:12123579]. The N-terminal projection domain opposes the binding domain by suppressing microtubule bundling in a length-dependent manner and tuning dynamic instability [PMID:12079337, PMID:15840946]. MAP4 activity is governed by multisite phosphorylation: cyclin B docks to the Pro-rich region to target the CDC2/cyclin B kinase to microtubules, and phosphorylation at Ser-787 (the dominant site) and Ser-696, as well as MARK-mediated phosphorylation of KXGS motifs, lowers microtubule affinity and increases dynamic instability, providing the switch for microtubule disassembly at the G2/M transition [PMID:7876309, PMID:8631898, PMID:9398320, PMID:10791892, PMID:11683421]. Stress kinases including p38/MAPK and PKA, opposed by phosphatases PP2A/PP1, feed into the same regulatory logic, and in cardiomyocytes and endothelium phospho-MAP4 (Ser-696/Ser-787) drives microtubule disruption, mitochondrial translocation, mPTP opening, apoptosis, and barrier dysfunction [PMID:20889984, PMID:24140250, PMID:25232678, PMID:25746230]. Beyond stabilization, microtubule-bound MAP4 modulates motor-driven transport—sterically inhibiting organelle motility and receptor recycling, differentially regulating dynein versus kinesin run lengths, biasing bidirectional transport toward minus-ends when phosphorylated by GSK3β, and supporting kinesin-3 transport on tyrosinated microtubules [PMID:9365275, PMID:15528234, PMID:25143402, PMID:36191197]. MAP4 physically interacts with the dynein-dynactin machinery to regulate spindle orientation and cortical force generation, with septins that block its binding and bundling, and it directs dynein-dependent BTN3A1 trafficking that activates TBK1-IRF3 antiviral signaling [PMID:16093351, PMID:21822276, PMID:27911820]. Distinct muscle-specific isoforms organize paraxial microtubule arrays required for myotube formation and skeletal muscle force generation [PMID:8631255, PMID:25898002, PMID:39473976]. Human loss-of-function variants cause centrosome amplification, aberrant ciliogenesis, and Golgi fragmentation [PMID:25323976].","teleology":[{"year":1991,"claim":"Established that MAP4's microtubule-binding activity resides in a discrete C-terminal domain with tau/MAP2-homologous repeats, separating binding from the projection function.","evidence":"cDNA cloning and in vitro microtubule binding with domain-specific fusion proteins","pmids":["1905296"],"confidence":"High","gaps":["Did not establish how the projection domain contributes function","Repeat-number isoform diversity not yet defined"]},{"year":1991,"claim":"Showed that cell-cycle kinase activity phosphorylates MAP4 and suppresses its assembly-promoting activity, linking MAP4 regulation to the G2/M microtubule reorganization.","evidence":"In vitro cdc2/H1 kinase and microtubule assembly assays; spindle isolation with mitotic kinase","pmids":["1656961","1667090"],"confidence":"Medium","gaps":["Phosphorylation sites not yet mapped","In vitro inhibition not yet validated in cells"]},{"year":1995,"claim":"Resolved the mechanism of cell-cycle control by showing cyclin B directly docks to the Pro-rich region to deliver CDC2 to microtubules and locally abolish stabilization without releasing MAP4.","evidence":"Reconstitution with purified proteins, GST-cyclin B pulldown, fragment mapping, kinase and dynamics assays; isoform/splicing characterization","pmids":["7876309","7857940"],"confidence":"High","gaps":["The specific phosphoacceptor residues remained unidentified","Functional differences among repeat isoforms not addressed"]},{"year":1996,"claim":"Identified MARK as a kinase that phosphorylates KXGS motifs to detach MAP4 and amplify dynamic instability, defining a second regulatory input distinct from CDC2.","evidence":"In vitro kinase, co-sedimentation, and dynamics assays","pmids":["8631898"],"confidence":"High","gaps":["Cellular context for MARK regulation of MAP4 not yet defined"]},{"year":1996,"claim":"Functionally dissected MAP4 in cells: the C-terminal fragment promotes polymerization, bundling, and stabilization, yet antibody-mediated removal produced no phenotype, indicating non-essentiality for basic microtubule functions in culture.","evidence":"Microinjection of fragments, nocodazole resistance, antibody depletion with photoactivation; muscle isoform antisense depletion","pmids":["8801031","8636213","8631255"],"confidence":"High","gaps":["Reconciling overexpression effects with clean depletion phenotype","Mechanism of indirect stress-fiber increase unclear"]},{"year":2000,"claim":"Mapped the functional phosphorylation hierarchy in vivo, establishing Ser-787 (CDC2, mitosis-specific) as the dominant site reducing polymerization and Ser-696 as proliferation-linked.","evidence":"In vivo 32P labeling, inhibitors, phospho-specific antibodies, and phosphomimetic mutagenesis","pmids":["9398320","10791892","15216889"],"confidence":"High","gaps":["How multiple kinases integrate on the same sites in vivo not resolved"]},{"year":2001,"claim":"Confirmed in cells that phosphorylation at Ser-696/Ser-787 lowers microtubule affinity and stability, using non-phosphorylatable and phosphomimetic mutants.","evidence":"Inducible mutant cell lines, co-sedimentation, nocodazole resistance","pmids":["11683421"],"confidence":"High","gaps":["Did not address upstream signaling triggering phosphorylation in physiological contexts"]},{"year":2002,"claim":"Defined the projection domain as a length-dependent suppressor of bundling and identified mechanistic specificity of MAP4 stabilization against catastrophe-promoters but not tubulin sequesterers.","evidence":"In vitro assembly/EM with truncation constructs; co-expression epistasis with distinct destabilizers","pmids":["12079337","12123579"],"confidence":"High","gaps":["Molecular basis of catastrophe-factor antagonism not determined"]},{"year":2005,"claim":"Identified septins as direct negative regulators that bind the Pro-rich region to block MAP4 binding/bundling, and isolated a projection-domain role in tuning dynamic instability.","evidence":"MS identification, purified-protein binding, RNAi epistasis; in vitro dynamics with projection deletions","pmids":["16093351","15840946"],"confidence":"High","gaps":["Septin-MAP4 regulation in specific cellular processes not mapped"]},{"year":2011,"claim":"Placed MAP4 in mitotic and transport machinery by showing direct dynein-dynactin interaction, inhibition of dynein-driven sliding, and control of spindle orientation, plus a cardioprotective MT-DYNLT1-VDAC1 axis.","evidence":"Co-IP, in vitro dynein sliding, RNAi spindle orientation; yeast two-hybrid and Co-IP for DYNLT1/VDAC1","pmids":["21822276","22164227"],"confidence":"High","gaps":["Whether MAP4 acts as motor regulator or steric obstacle not fully separated","DYNLT1-VDAC1 axis Medium-confidence single lab"]},{"year":2014,"claim":"Connected stress-kinase phosphorylation to pathological outcomes: phospho-MAP4 translocates to mitochondria to trigger mPTP opening and apoptosis, and MAP4 directs dynein-dependent BTN3A1 trafficking feeding TBK1-IRF3 antiviral signaling.","evidence":"Fractionation with phospho-antibodies and rescue mutant; RNAi, Co-IP, IFN-β reporter; melanophore dual-motor run-length analysis","pmids":["25232678","27911820","25143402"],"confidence":"High","gaps":["Mechanism of phospho-MAP4 mitochondrial targeting unresolved","BTN3A1 finding Medium-confidence single lab"]},{"year":2014,"claim":"Linked MAP4 to human disease by identifying loss-of-function variants causing centrosome amplification, ciliogenesis defects, and Golgi fragmentation.","evidence":"Homozygosity mapping/NGS with patient fibroblast phenotyping","pmids":["25323976"],"confidence":"Medium","gaps":["Single family","Direct causality versus correlation not fully established"]},{"year":2015,"claim":"Defined isoform-specialized roles in muscle: a differentiation-induced isoform (oMAP4) builds antiparallel arrays resistant to motor forces and is required for myotube formation.","evidence":"In vitro bundling with purified oMAP4, RNAi, live imaging, motor-resistance assay; p38-driven endothelial permeability via phospho-MAP4","pmids":["25898002","25746230"],"confidence":"High","gaps":["How isoform-specific projection domains achieve distinct mechanics not detailed"]},{"year":2022,"claim":"Established that phosphorylation reprograms MAP4 from stabilizer to transport regulator: GSK3β-phosphorylated MAP4 tethers cargo via its projection domain, impairs kinesin-1 force, and biases transport minus-ward.","evidence":"Optical-trap force assay, organelle tracking, Co-IP, GSK3β manipulation","pmids":["36191197"],"confidence":"High","gaps":["In vivo relevance of the cargo-tethering mode not established"]},{"year":2023,"claim":"Extended MAP4 regulation to ubiquitin-dependent turnover and autophagy: FBXW7/CHEK1 control MAP4 degradation, while MAP4 engages LC3 and harbors BH3/LIR domains enabling mitophagy-coupled self-degradation.","evidence":"Co-IP, MS, phosphosite mapping; LC3 Co-IP, domain mutagenesis, autophagy flux assays","pmids":["36991467","36835542","37198170"],"confidence":"Medium","gaps":["Each mechanism from single lab","Integration of degradation and autophagy roles unresolved"]},{"year":2024,"claim":"Implicated MAP4 in oncogenic signaling and isoform-specific muscle physiology: MAP4 localizes p110α PI3K to microtubules for endosomal PI3K/Akt activation, and a muscle isoform knockout disrupts microtubule architecture and force generation.","evidence":"Knockdown with endosomal fractionation and signaling assays; in vivo exon-deletion mouse with force measurement","pmids":["38630589","39473976"],"confidence":"Medium","gaps":["PI3K localization mechanism via MAP4 not structurally defined","Tissue specificity of signaling role unclear"]},{"year":2025,"claim":"Showed MAP4 reads the tubulin tyrosination code, partitioning onto tyrosinated microtubules to favor kinesin-3 transport and modulating lysosome positioning in response to nutrient status.","evidence":"Live imaging of MAP/track partitioning, rigor-kinesin and lysosome tracking, starvation experiments (preprint)","pmids":["bio_10.1101_2025.10.07.680844"],"confidence":"Medium","gaps":["Preprint not yet peer-reviewed","Molecular basis of tyrosination preference not resolved"]},{"year":null,"claim":"How the many kinases, phosphatases, ubiquitin ligases, and binding partners are integrated to switch MAP4 between stabilizer, transport regulator, and cell-death effector in a tissue-specific manner remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking phosphosite combinations to functional outputs","Structural basis of partner competition (cyclin B vs septin vs dynein) on the Pro-rich region undefined","Isoform-specific regulatory networks not systematically compared"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,8,15,19,35]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[15,19,35,42]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,23,27,37]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,8,11,14]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8,30]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[28,30,40]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[33]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[4,10,27,36]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[12,32,37,43]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[38,40]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[30]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[31]}],"complexes":[],"partners":["CCNB1","DYNLT1","VDAC1","SEPT2","BTN3A1","MAPK14","LC3","FBXW7"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P27816","full_name":"Microtubule-associated protein 4","aliases":[],"length_aa":1152,"mass_kda":121.0,"function":"Non-neuronal microtubule-associated protein. 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fusion proteins containing this domain bind microtubules in vitro, while projection-domain-only constructs do not.\",\n      \"method\": \"cDNA cloning, in vitro microtubule binding assay with fusion proteins\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro binding assay with domain-specific constructs, replicated in multiple subsequent studies\",\n      \"pmids\": [\"1905296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"Phosphorylation of the Pro-rich region of MAP4 by cdc2/H1 histone kinase suppresses MAP4's microtubule assembly-promoting activity, providing a mechanism for microtubule disassembly at the G2/M transition.\",\n      \"method\": \"In vitro kinase assay, microtubule assembly assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro assay in single study, replicated conceptually by later work\",\n      \"pmids\": [\"1656961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"An M-phase-specific kinase (related to p34cdc2/cyclin B) associates with isolated mitotic spindles and phosphorylates MAP4 (and MAP1B) in a cell-cycle-dependent manner.\",\n      \"method\": \"Spindle isolation, in vitro kinase assay, immunofluorescence with anti-thiophosphoprotein antibody\",\n      \"journal\": \"Cell regulation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical fractionation plus kinase assay, single lab but multiple methods\",\n      \"pmids\": [\"1667090\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"A 230 kDa MAP4-like protein in Xenopus egg extracts is heat-stable, phosphorylated, and promotes elongation of microtubules from axonemes, confirming MAP4 ortholog function in a non-mammalian model.\",\n      \"method\": \"Microtubule co-sedimentation, immunological characterization, microtubule assembly assay\",\n      \"journal\": \"Cell motility and the cytoskeleton\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — biochemical purification and functional assay, single study\",\n      \"pmids\": [\"8087870\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Cyclin B directly binds to the Pro-rich C-terminal region of MAP4, thereby targeting the p34cdc2/cyclin B kinase complex to microtubules; the kinase then phosphorylates MAP4 within the complex and abolishes MAP4's microtubule-stabilizing activity without preventing its microtubule binding.\",\n      \"method\": \"Co-sedimentation with purified proteins, GST-cyclin B pulldown, recombinant MAP4 fragment mapping, in vitro kinase assay, microtubule dynamics assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro with purified components, multiple orthogonal methods, domain mapping\",\n      \"pmids\": [\"7876309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"MAP4 isoforms with three, four, or five microtubule-binding repeats are expressed in a tissue- and developmental-stage-specific manner via alternative RNA splicing from a single-copy gene on chromosome 3p21.\",\n      \"method\": \"cDNA cloning, RNase protection analysis, chromosomal mapping\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal molecular biology methods, single lab\",\n      \"pmids\": [\"7857940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"MARK kinase (p110mark) phosphorylates KXGS motifs in the microtubule-binding domain of MAP4 in vitro, causing MAP4 dissociation from microtubules and a pronounced increase in dynamic instability.\",\n      \"method\": \"In vitro kinase assay, microtubule co-sedimentation, microtubule dynamics assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with site identification, replicated in subsequent cell-based work\",\n      \"pmids\": [\"8631898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"A muscle-specific MAP4 isoform (encoded by a 3.2 kb insertion in the projection domain) is required for myotube formation: antisense depletion of this isoform in C2C12 cells allows cell fusion but produces short, apolar syncytia with disorganized microtubules and absent myofibrils.\",\n      \"method\": \"Stable antisense cell lines, in situ hybridization, immunofluorescence, differentiation assay\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function with specific cellular phenotype, replicated by later isoform studies\",\n      \"pmids\": [\"8631255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Microinjection of intact MAP4 or its C-terminal PA4 fragment into PtK2 cells promotes microtubule polymerization and bundling and stabilizes microtubules against nocodazole; the N-terminal NR fragment has no effect. The PA4 fragment also indirectly increases stress fibers without direct binding to actin.\",\n      \"method\": \"Microinjection, immunofluorescence, nocodazole resistance assay, in vitro binding assay\",\n      \"journal\": \"Cell motility and the cytoskeleton\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct microinjection in cells plus in vitro binding, single lab, two methods\",\n      \"pmids\": [\"8801031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Antibody-mediated removal of MAP4 from microtubules in living cells produces no detectable phenotype: MT dynamics, tubulin modifications, organelle distribution, and mitotic spindle morphology are all normal, indicating MAP4 is not essential for these functions in cultured cells.\",\n      \"method\": \"Antibody microinjection, tubulin photoactivation, nocodazole sensitivity, immunofluorescence\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rigorous loss-of-function with multiple orthogonal readouts, clean negative result mechanistically informative\",\n      \"pmids\": [\"8636213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CDC2 kinase is the major M-phase MAP4 kinase in HeLa cells; Ser-787 (in SPSK) is phosphorylated specifically at mitosis while Ser-696 (in SPEK) is phosphorylated in both mitosis and interphase, both lying in the proline-rich region of the microtubule-binding domain.\",\n      \"method\": \"Metabolic 32P labeling, butyrolactone I inhibitor, phosphopeptide mapping, phospho-specific antibodies\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vivo phosphorylation mapping with site identification using inhibitors and phospho-specific antibodies, replicated by mutagenesis studies\",\n      \"pmids\": [\"9398320\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Overexpression of full-length MAP4 or its MT-binding domain stabilizes microtubules in vivo (increased detyrosinated tubulin, nocodazole resistance) and inhibits cell growth without causing mitotic arrest or cell death.\",\n      \"method\": \"Stable transfection, nocodazole resistance assay, tubulin modification immunoblotting, growth curves\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean overexpression with multiple functional readouts, replicated across multiple stable cell lines\",\n      \"pmids\": [\"9044058\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"MAP4 overexpression directly inhibits MT-based organelle motility and vesicle transport in vivo (reduced LDL receptor recycling, Golgi redistribution), in a manner not reproduced by taxol-mediated MT stabilization, indicating a direct steric effect of MAP4 on motor-driven transport.\",\n      \"method\": \"DIC live microscopy, receptor trafficking assays, Golgi redistribution assay, brefeldin A washout\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal transport assays, taxol control dissects mechanism, single lab\",\n      \"pmids\": [\"9365275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"MARK1/MARK2 kinases phosphorylate MAP4 on its microtubule-binding domain in transfected CHO cells, causing microtubule disruption, vimentin network breakdown, and cell detachment; actin fibers are unaffected.\",\n      \"method\": \"Inducible expression of MARK kinases in CHO cells, immunofluorescence, phosphorylation analysis\",\n      \"journal\": \"Cell motility and the cytoskeleton\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based validation of in vitro kinase findings, single lab\",\n      \"pmids\": [\"10542369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"MAP4 depletion (antisense RNA to ~33% of normal) decreases total tubulin content, shifts tubulin partitioning from polymer to protomer, slows MT regrowth after depolymerization, and flattens cell morphology, demonstrating MAP4 regulates MT assembly level and cell shape.\",\n      \"method\": \"Stable antisense RNA expression, tubulin fractionation, MT regrowth assay, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean loss-of-function with multiple quantitative readouts, single lab\",\n      \"pmids\": [\"10341201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The Pro-rich region of MAP4 promotes nucleation of microtubule assembly by bridging protofilaments, whereas the AP sequence region promotes elongation; the tail region is required for the nucleation step when combined with the AP sequence region.\",\n      \"method\": \"In vitro microtubule assembly assay with truncated recombinant fragments, electron microscopy, binding stoichiometry\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro with multiple domain-deletion constructs and EM validation\",\n      \"pmids\": [\"9914488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"MAP kinase phosphorylates Ser-696 of MAP4 in vitro and in cell extracts; serum starvation causes dephosphorylation of Ser-696 in HeLa cells and fibroblasts, and serum re-addition restores phosphorylation, linking this site to proliferation/quiescence status.\",\n      \"method\": \"In vitro kinase assay, MAP kinase inhibitor in cell extract, phospho-specific antibodies, serum starvation experiments\",\n      \"journal\": \"Cell structure and function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro plus cell-based evidence with inhibitor, single lab\",\n      \"pmids\": [\"15216889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Phosphorylation of Ser-787 by p34cdc2 kinase is the critical site that reduces MAP4's microtubule-polymerization activity; the Ser787Glu phosphomimetic mutant dramatically reduces this activity, while Ser696Glu does not, establishing site-specific functional hierarchy.\",\n      \"method\": \"Site-directed mutagenesis, in vitro MT polymerization assay with phosphomimetic mutants\",\n      \"journal\": \"Cell structure and function\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis reconstitution with clear functional read-out, mechanistically complementary to prior in vivo phosphosite identification\",\n      \"pmids\": [\"10791892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Nonphosphorylatable MAP4 mutants (AA, KK) bind microtubules more avidly and confer greater nocodazole resistance than wild-type or phosphomimetic (EE) MAP4; EE mutant behaves like WT, demonstrating that phosphorylation of Ser-696/Ser-787 reduces MAP4-MT interaction and MT stability in vivo.\",\n      \"method\": \"Stable inducible cell lines expressing phosphorylation mutants, MT co-sedimentation, nocodazole resistance assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple phosphomimetic and non-phosphorylatable mutants with orthogonal readouts, single lab\",\n      \"pmids\": [\"11683421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The projection (PJ) domain of MAP4 suppresses the microtubule-bundling activity of the MT-binding domain; longer PJ domains progressively reduce bundle formation, and this suppression correlates with PJ domain length rather than amino acid sequence.\",\n      \"method\": \"In vitro microtubule assembly with truncated MAP4 constructs, negative-staining EM, dark-field microscopy\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro with multiple deletion constructs, EM validation\",\n      \"pmids\": [\"12079337\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"MAP4 counteracts microtubule catastrophe promoters (XKCM1, non-sequestering Op18) but not tubulin-sequestering destabilizers in intact cells, revealing mechanistic specificity in its stabilizing activity.\",\n      \"method\": \"Inducible co-transfection, co-expression with catastrophe promoters vs. tubulin sequesterers, cell imaging\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis by co-expression with multiple distinct destabilizers, single lab\",\n      \"pmids\": [\"12123579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"MAP4 overexpression in cardiocytes stabilizes microtubules (shifts tubulin to polymerized fraction) and increases total tubulin levels; beta1-tubulin overexpression has no independent or additive effect, identifying MAP4 as the causative factor for microtubule network densification in cardiac hypertrophy.\",\n      \"method\": \"Adenoviral overexpression in isolated cardiocytes, transgenic mice, tubulin fractionation, immunofluorescence\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — orthogonal in vitro and in vivo models, multiple methods, genetic controls\",\n      \"pmids\": [\"12855424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MAP4 decoration of microtubules in cardiocytes inhibits beta-adrenergic receptor recycling after agonist withdrawal, reducing cell-surface beta-AR number and cAMP responsiveness; confirmed in MAP4-transgenic mouse cardiocytes.\",\n      \"method\": \"Adenoviral MAP4 overexpression, [3H]CGP-12177 receptor binding assay, cAMP measurement, transgenic mouse confirmation\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-based and transgenic confirmation, functional readout with quantitative receptor trafficking assay\",\n      \"pmids\": [\"15528234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Septins (Sept2:6:7 heterotrimer and Sept2 monomer) directly bind the proline-rich C-terminal region of MAP4; this interaction blocks MAP4's ability to bind and bundle microtubules in vitro. In cells, septin depletion increases microtubule stability in a MAP4-dependent manner.\",\n      \"method\": \"Mass spectrometry identification, direct binding assay with purified proteins, domain mapping, RNA interference, microtubule bundling assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — MS identification, reconstituted in vitro binding and functional assay, RNAi epistasis in cells\",\n      \"pmids\": [\"16093351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Truncation of MAP4's projection domain attenuates microtubule dynamic instability at higher MAP4 concentrations, demonstrating that the projection domain modulates dynamic instability independently of its bundling suppression function.\",\n      \"method\": \"In vitro dark-field microscopy of microtubule dynamics with projection-domain deletion mutants\",\n      \"journal\": \"Cell structure and function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with multiple deletion constructs, single lab\",\n      \"pmids\": [\"15840946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In hypoxic cells, activated p38/MAPK phosphorylates MAP4 (increasing phosphorylation) and dephosphorylates Op18/stathmin, both contributing to microtubule disruption; p38-MAP4 interaction was confirmed by co-immunoprecipitation.\",\n      \"method\": \"Co-immunoprecipitation, p38 inhibitor (SB203580), MKK6(Glu) overexpression, immunofluorescence, cell viability assay\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus pharmacological and genetic modulation, single lab\",\n      \"pmids\": [\"19915797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PP2A and PP1 dephosphorylate MAP4 at Ser-924 and Ser-1056 in pressure-overloaded hypertrophied myocardium; overexpression of PP2A or PP1 in normal hearts reproduces the microtubule densification and MAP4 dephosphorylation phenotype of hypertrophy.\",\n      \"method\": \"Phosphatase activity assays, phospho-specific antibodies, adenoviral overexpression in hearts, transgenic comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical phosphatase activity, in vivo genetic overexpression, phospho-specific site identification\",\n      \"pmids\": [\"20889984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MAP4 physically interacts with dynein-dynactin in vivo and inhibits dynein-mediated microtubule sliding in vitro; depletion of MAP4 causes spindle misorientation in the vertical plane in human cells, placing MAP4 as a regulator of cortical force generation during mitosis.\",\n      \"method\": \"Co-immunoprecipitation, in vitro dynein-mediated MT sliding assay, RNAi depletion, spindle orientation measurement\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus co-IP plus clean loss-of-function with specific phenotypic readout\",\n      \"pmids\": [\"21822276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MAP4 overexpression promotes microtubule stabilization in hypoxic cardiomyocytes; MAP4 also interacts with DYNLT1 (dynein light chain Tctex-1) which in turn interacts with VDAC1, linking MAP4 to mitochondrial permeability stabilization via the microtubule-DYNLT1-VDAC1 axis.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence, MT polymerization assay, cell viability/ATP measurement\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus Co-IP for DYNLT1-VDAC1, knockdown epistasis, single lab\",\n      \"pmids\": [\"22164227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"cAMP/PKA signaling phosphorylates MAP4, disrupting microtubule cytoskeleton and inhibiting bladder cancer cell invasion and migration; the interaction between PKA and MAP4 was confirmed by co-immunoprecipitation.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, matrigel invasion assay, immunofluorescence/immunoblotting\",\n      \"journal\": \"Urologic oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional RNAi assay, single lab\",\n      \"pmids\": [\"24140250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Phosphorylated MAP4 (at Ser-696 and Ser-787) translocates from the cytosol to mitochondria in hypoxic cardiomyocytes, where it induces mitochondrial permeability transition pore (mPTP) opening and apoptosis; the non-phosphorylatable MAP4(Ala) mutant suppresses this translocation and apoptosis.\",\n      \"method\": \"Subcellular fractionation, phospho-specific antibodies, MAP4(Ala) mutant expression, mPTP assay, apoptosis assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — fractionation with functional consequence, phosphorylation-dead rescue mutant, specific mechanistic pathway\",\n      \"pmids\": [\"25232678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MAP4 controls dynein-dependent transport of BTN3A1 to the perinuclear region upon nucleic acid stimulation; MAP4 depletion impairs BTN3A1 redistribution and consequently reduces TBK1-IRF3-mediated type I interferon production, placing MAP4 upstream of the TBK1-IRF3 antiviral signaling axis.\",\n      \"method\": \"RNAi depletion, co-immunoprecipitation, immunofluorescence localization, IFN-β reporter assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi epistasis plus co-IP, defined pathway placement, single lab\",\n      \"pmids\": [\"27911820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MAP4 regulation of microtubule-based transport operates differentially on kinesin-2 vs. dynein in Xenopus melanophores: MAP4 on microtubules shortens dynein-dependent runs and lengthens kinesin-2 runs; phosphorylation of threonine residues in the MT-binding domain during aggregation signals reduces MAP4-MT binding, increasing dynein-dependent and decreasing kinesin-2-dependent motility.\",\n      \"method\": \"Overexpression and removal of XMAP4 in melanophores, run-length analysis of melanosome movement, phosphorylation analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — dual motor analysis with overexpression and depletion, phosphorylation state correlated to transport direction, single lab with multiple quantitative methods\",\n      \"pmids\": [\"25143402\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Loss-of-function variants in MAP4 in humans cause centrosome amplification, aberrant ciliogenesis, and Golgi fragmentation in fibroblasts; the variant affects kinase binding sites required for dynamic instability of microtubule formation.\",\n      \"method\": \"Homozygosity mapping/NGS, patient fibroblast centrosome counting, cilia assay, Golgi morphology analysis\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient cells with multiple cellular phenotype readouts, single family/lab\",\n      \"pmids\": [\"25323976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"p38/MAPK activation by LPS/TNF-α phosphorylates MAP4 at Ser-696 and Ser-787, inducing microtubule disassembly and endothelial hyperpermeability; the phosphorylation-resistant MAP4(Ala) mutant or p38 inhibitor prevents MT disruption and barrier dysfunction.\",\n      \"method\": \"Phospho-specific antibodies, p38 inhibitor SB203580, MKK6(Glu) activation, MAP4(Ala) mutant, transendothelial resistance measurement\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological inhibition plus constitutive activation plus rescue mutant, multiple mechanistic levels\",\n      \"pmids\": [\"25746230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A novel MAP4 isoform (oMAP4), expressed upon muscle differentiation, is required for paraxial microtubule array organization; purified oMAP4 aligns dynamic microtubules into antiparallel bundles that withstand dynein- and kinesin-driven sliding forces in vitro, and its depletion impairs cell elongation, fusion, and paraxial array formation.\",\n      \"method\": \"In vitro microtubule bundling assay with purified oMAP4, RNAi depletion, live cell imaging, motor resistance assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro with purified protein plus clean RNAi loss-of-function with defined phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"25898002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HPV16 oncoprotein E7 directly binds the C-terminus of MAP4, inhibiting Mps1-mediated phosphorylation of MAP4 (at T927/S928), thereby blocking phosphorylation-dependent MAP4 degradation, stabilizing microtubule polymerization, and retarding mitotic progression. MAP4 T927E/S928E mutations reduce E7 binding and rescue mitotic progression.\",\n      \"method\": \"Co-immunoprecipitation, kinase assay, site-directed mutagenesis, mitotic timing assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct binding assay, kinase assay, rescue mutagenesis, multiple methods in single study\",\n      \"pmids\": [\"31253867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"MAP4, when phosphorylated by GSK3β, tethers cargo (organelles) to microtubules via its projection domain, impairs kinesin-1 force generation, and biases bidirectional transport toward minus-ends; MAP4 physically interacts with dynein and dynactin and the phosphorylated form associates with the cargo-motor complex.\",\n      \"method\": \"Co-immunoprecipitation, organelle tracking, optical trap force assay, GSK3β manipulation, MAP4 domain analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biophysical force assay plus co-IP plus genetic rescue, multiple orthogonal methods\",\n      \"pmids\": [\"36191197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"MAP4 interacts with autophagy marker LC3 (confirmed by co-immunoprecipitation) and colocalizes with LC3 in myoblast cytoplasm; this interaction promotes autophagy during C2C12 differentiation. miR-103-3p suppresses MAP4 expression and thereby inhibits both autophagy and myotube formation.\",\n      \"method\": \"Co-immunoprecipitation, dual-luciferase reporter, immunofluorescence co-localization, autophagy assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus functional knockdown, single lab\",\n      \"pmids\": [\"36835542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"FBXW7 ubiquitin ligase targets MAP4 for degradation; CHEK1-mediated phosphorylation of MAP4 at Thr-521 is required for FBXW7-dependent MAP4 degradation. Loss of FBXW7 elevates MAP4 levels and ERK phosphorylation, promoting ESCC progression.\",\n      \"method\": \"GST-pulldown, LC-MS/MS, co-immunoprecipitation, site-directed phosphorylation analysis\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, MS identification, phosphorylation site mapping, single lab\",\n      \"pmids\": [\"36991467\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Phosphorylated MAP4 undergoes self-degradation via mitophagy in hypoxic keratinocytes; MAP4 contains both BH3 and LIR domains that allow it to simultaneously act as a mitophagy initiator and substrate receptor. Mutation of either domain abolishes p-MAP4 self-degradation and impairs hypoxia-induced keratinocyte migration and proliferation.\",\n      \"method\": \"Domain mutagenesis (BH3 and LIR), autophagy flux assays, LC3 co-localization, cell migration/proliferation assays\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mutagenesis with functional readouts, single lab\",\n      \"pmids\": [\"37198170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"p110α (PI3Kα catalytic subunit) localizes to microtubules via MAP4 and is recruited with receptor tyrosine kinases to endosomes for PI3K/Akt signaling; MAP4 knockdown abrogates the tumor-promoting effects of p85α loss, placing MAP4 upstream of endosomal PI3K/Akt activation.\",\n      \"method\": \"Knockdown studies, endosomal fractionation, PI3K/Akt signaling assays, tumorsphere formation assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis by knockdown with pathway readout, single lab\",\n      \"pmids\": [\"38630589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Muscle-specific MAP4 isoform (mMAP4) exhibits enhanced microtubule association compared to ubiquitous MAP4 (uMAP4); loss of mMAP4 in mice (exon 8 deletion) causes disorganized microtubule architecture and intrinsic loss of skeletal muscle force generation, demonstrating isoform-specific function in muscle homeostasis.\",\n      \"method\": \"Genomic exon deletion in mice, microtubule co-sedimentation, ex vivo force measurement, immunofluorescence\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo knockout with multiple functional readouts, isoform-specific comparison\",\n      \"pmids\": [\"39473976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MAP4 preferentially partitions onto tyrosinated microtubules (via its projection domain) while MAP7D1 decorates detyrosinated microtubules; MAP4-decorated tracks preferentially support kinesin-3 (KIF1A) transport, and MAP4 density on microtubules decreases during nutrient starvation to promote perinuclear lysosome positioning, coordinating lysosome repositioning in response to nutrient availability.\",\n      \"method\": \"Live imaging of MAP4/MAP7D1 on microtubule subsets, rigor kinesin localization assays, lysosome tracking, nutrient starvation/stimulation experiments, projection domain mutant analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple imaging-based methods, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.10.07.680844\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"MAP4 phosphorylation by PI3K (activated downstream of ARID1A loss) reduces MAP4's microtubule-stabilizing activity, disrupts bipolar spindle formation, and sensitizes colorectal cancer cells to the antimicrotubule drug EMP (synthetic lethality with ARID1A loss).\",\n      \"method\": \"ARID1A isogenic cell lines, drug screening, phosphorylation analysis, spindle imaging, PI3K pathway manipulation\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic genetic model with pathway inhibition and functional readout, single lab\",\n      \"pmids\": [\"41360780\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAP4 is a ubiquitously expressed microtubule-associated protein whose C-terminal MT-binding domain (containing three to five 18-aa repeats plus a Pro-rich region) promotes microtubule nucleation, elongation, and stabilization while its N-terminal projection domain suppresses MT bundling and modulates dynamic instability; its activity is tightly regulated by phosphorylation at multiple sites (notably Ser-787 and Ser-696 by CDC2/cyclin B, MARK, p38/MAPK, PKA, MAP kinase, and GSK3β), which reduces MT affinity and, in cardiomyocytes, triggers mitochondrial translocation to induce apoptosis; MAP4 also physically interacts with cyclin B (recruiting CDC2 to spindle MTs), dynein-dynactin (regulating minus-end-directed transport and spindle positioning), septins (which block its MT-binding and bundling activity), and kinesin-1/kinesin-3 motors (differentially regulating organelle transport), and participates in innate immune signaling by controlling dynein-dependent BTN3A1 trafficking that activates TBK1-IRF3.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAP4 is a ubiquitously expressed structural microtubule-associated protein that controls the assembly, stability, and architecture of the microtubule cytoskeleton through a bipartite organization [#0, #15]. Its C-terminal microtubule-binding domain—built from imperfect 18-amino-acid repeats (present in three-, four-, or five-repeat isoforms generated by alternative splicing) plus a Pro-rich region—binds and stabilizes microtubules, with the Pro-rich region nucleating assembly by bridging protofilaments and an adjacent sequence driving elongation [#0, #5, #15]. Overexpression stabilizes microtubules and elevates polymer mass while depletion reduces tubulin polymer and slows regrowth, establishing MAP4 as a positive regulator of microtubule assembly level and cell shape that specifically counteracts catastrophe-promoting destabilizers rather than tubulin sequesterers [#11, #14, #20]. The N-terminal projection domain opposes the binding domain by suppressing microtubule bundling in a length-dependent manner and tuning dynamic instability [#19, #24]. MAP4 activity is governed by multisite phosphorylation: cyclin B docks to the Pro-rich region to target the CDC2/cyclin B kinase to microtubules, and phosphorylation at Ser-787 (the dominant site) and Ser-696, as well as MARK-mediated phosphorylation of KXGS motifs, lowers microtubule affinity and increases dynamic instability, providing the switch for microtubule disassembly at the G2/M transition [#4, #6, #10, #17, #18]. Stress kinases including p38/MAPK and PKA, opposed by phosphatases PP2A/PP1, feed into the same regulatory logic, and in cardiomyocytes and endothelium phospho-MAP4 (Ser-696/Ser-787) drives microtubule disruption, mitochondrial translocation, mPTP opening, apoptosis, and barrier dysfunction [#26, #29, #30, #34]. Beyond stabilization, microtubule-bound MAP4 modulates motor-driven transport—sterically inhibiting organelle motility and receptor recycling, differentially regulating dynein versus kinesin run lengths, biasing bidirectional transport toward minus-ends when phosphorylated by GSK3β, and supporting kinesin-3 transport on tyrosinated microtubules [#12, #22, #32, #37]. MAP4 physically interacts with the dynein-dynactin machinery to regulate spindle orientation and cortical force generation, with septins that block its binding and bundling, and it directs dynein-dependent BTN3A1 trafficking that activates TBK1-IRF3 antiviral signaling [#23, #27, #31]. Distinct muscle-specific isoforms organize paraxial microtubule arrays required for myotube formation and skeletal muscle force generation [#7, #35, #42]. Human loss-of-function variants cause centrosome amplification, aberrant ciliogenesis, and Golgi fragmentation [#33].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Established that MAP4's microtubule-binding activity resides in a discrete C-terminal domain with tau/MAP2-homologous repeats, separating binding from the projection function.\",\n      \"evidence\": \"cDNA cloning and in vitro microtubule binding with domain-specific fusion proteins\",\n      \"pmids\": [\"1905296\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish how the projection domain contributes function\", \"Repeat-number isoform diversity not yet defined\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Showed that cell-cycle kinase activity phosphorylates MAP4 and suppresses its assembly-promoting activity, linking MAP4 regulation to the G2/M microtubule reorganization.\",\n      \"evidence\": \"In vitro cdc2/H1 kinase and microtubule assembly assays; spindle isolation with mitotic kinase\",\n      \"pmids\": [\"1656961\", \"1667090\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Phosphorylation sites not yet mapped\", \"In vitro inhibition not yet validated in cells\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Resolved the mechanism of cell-cycle control by showing cyclin B directly docks to the Pro-rich region to deliver CDC2 to microtubules and locally abolish stabilization without releasing MAP4.\",\n      \"evidence\": \"Reconstitution with purified proteins, GST-cyclin B pulldown, fragment mapping, kinase and dynamics assays; isoform/splicing characterization\",\n      \"pmids\": [\"7876309\", \"7857940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific phosphoacceptor residues remained unidentified\", \"Functional differences among repeat isoforms not addressed\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identified MARK as a kinase that phosphorylates KXGS motifs to detach MAP4 and amplify dynamic instability, defining a second regulatory input distinct from CDC2.\",\n      \"evidence\": \"In vitro kinase, co-sedimentation, and dynamics assays\",\n      \"pmids\": [\"8631898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular context for MARK regulation of MAP4 not yet defined\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Functionally dissected MAP4 in cells: the C-terminal fragment promotes polymerization, bundling, and stabilization, yet antibody-mediated removal produced no phenotype, indicating non-essentiality for basic microtubule functions in culture.\",\n      \"evidence\": \"Microinjection of fragments, nocodazole resistance, antibody depletion with photoactivation; muscle isoform antisense depletion\",\n      \"pmids\": [\"8801031\", \"8636213\", \"8631255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciling overexpression effects with clean depletion phenotype\", \"Mechanism of indirect stress-fiber increase unclear\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapped the functional phosphorylation hierarchy in vivo, establishing Ser-787 (CDC2, mitosis-specific) as the dominant site reducing polymerization and Ser-696 as proliferation-linked.\",\n      \"evidence\": \"In vivo 32P labeling, inhibitors, phospho-specific antibodies, and phosphomimetic mutagenesis\",\n      \"pmids\": [\"9398320\", \"10791892\", \"15216889\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How multiple kinases integrate on the same sites in vivo not resolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Confirmed in cells that phosphorylation at Ser-696/Ser-787 lowers microtubule affinity and stability, using non-phosphorylatable and phosphomimetic mutants.\",\n      \"evidence\": \"Inducible mutant cell lines, co-sedimentation, nocodazole resistance\",\n      \"pmids\": [\"11683421\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address upstream signaling triggering phosphorylation in physiological contexts\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined the projection domain as a length-dependent suppressor of bundling and identified mechanistic specificity of MAP4 stabilization against catastrophe-promoters but not tubulin sequesterers.\",\n      \"evidence\": \"In vitro assembly/EM with truncation constructs; co-expression epistasis with distinct destabilizers\",\n      \"pmids\": [\"12079337\", \"12123579\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of catastrophe-factor antagonism not determined\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified septins as direct negative regulators that bind the Pro-rich region to block MAP4 binding/bundling, and isolated a projection-domain role in tuning dynamic instability.\",\n      \"evidence\": \"MS identification, purified-protein binding, RNAi epistasis; in vitro dynamics with projection deletions\",\n      \"pmids\": [\"16093351\", \"15840946\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Septin-MAP4 regulation in specific cellular processes not mapped\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Placed MAP4 in mitotic and transport machinery by showing direct dynein-dynactin interaction, inhibition of dynein-driven sliding, and control of spindle orientation, plus a cardioprotective MT-DYNLT1-VDAC1 axis.\",\n      \"evidence\": \"Co-IP, in vitro dynein sliding, RNAi spindle orientation; yeast two-hybrid and Co-IP for DYNLT1/VDAC1\",\n      \"pmids\": [\"21822276\", \"22164227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether MAP4 acts as motor regulator or steric obstacle not fully separated\", \"DYNLT1-VDAC1 axis Medium-confidence single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected stress-kinase phosphorylation to pathological outcomes: phospho-MAP4 translocates to mitochondria to trigger mPTP opening and apoptosis, and MAP4 directs dynein-dependent BTN3A1 trafficking feeding TBK1-IRF3 antiviral signaling.\",\n      \"evidence\": \"Fractionation with phospho-antibodies and rescue mutant; RNAi, Co-IP, IFN-β reporter; melanophore dual-motor run-length analysis\",\n      \"pmids\": [\"25232678\", \"27911820\", \"25143402\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of phospho-MAP4 mitochondrial targeting unresolved\", \"BTN3A1 finding Medium-confidence single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked MAP4 to human disease by identifying loss-of-function variants causing centrosome amplification, ciliogenesis defects, and Golgi fragmentation.\",\n      \"evidence\": \"Homozygosity mapping/NGS with patient fibroblast phenotyping\",\n      \"pmids\": [\"25323976\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single family\", \"Direct causality versus correlation not fully established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined isoform-specialized roles in muscle: a differentiation-induced isoform (oMAP4) builds antiparallel arrays resistant to motor forces and is required for myotube formation.\",\n      \"evidence\": \"In vitro bundling with purified oMAP4, RNAi, live imaging, motor-resistance assay; p38-driven endothelial permeability via phospho-MAP4\",\n      \"pmids\": [\"25898002\", \"25746230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How isoform-specific projection domains achieve distinct mechanics not detailed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established that phosphorylation reprograms MAP4 from stabilizer to transport regulator: GSK3β-phosphorylated MAP4 tethers cargo via its projection domain, impairs kinesin-1 force, and biases transport minus-ward.\",\n      \"evidence\": \"Optical-trap force assay, organelle tracking, Co-IP, GSK3β manipulation\",\n      \"pmids\": [\"36191197\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of the cargo-tethering mode not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended MAP4 regulation to ubiquitin-dependent turnover and autophagy: FBXW7/CHEK1 control MAP4 degradation, while MAP4 engages LC3 and harbors BH3/LIR domains enabling mitophagy-coupled self-degradation.\",\n      \"evidence\": \"Co-IP, MS, phosphosite mapping; LC3 Co-IP, domain mutagenesis, autophagy flux assays\",\n      \"pmids\": [\"36991467\", \"36835542\", \"37198170\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each mechanism from single lab\", \"Integration of degradation and autophagy roles unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Implicated MAP4 in oncogenic signaling and isoform-specific muscle physiology: MAP4 localizes p110α PI3K to microtubules for endosomal PI3K/Akt activation, and a muscle isoform knockout disrupts microtubule architecture and force generation.\",\n      \"evidence\": \"Knockdown with endosomal fractionation and signaling assays; in vivo exon-deletion mouse with force measurement\",\n      \"pmids\": [\"38630589\", \"39473976\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PI3K localization mechanism via MAP4 not structurally defined\", \"Tissue specificity of signaling role unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed MAP4 reads the tubulin tyrosination code, partitioning onto tyrosinated microtubules to favor kinesin-3 transport and modulating lysosome positioning in response to nutrient status.\",\n      \"evidence\": \"Live imaging of MAP/track partitioning, rigor-kinesin and lysosome tracking, starvation experiments (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.10.07.680844\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint not yet peer-reviewed\", \"Molecular basis of tyrosination preference not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many kinases, phosphatases, ubiquitin ligases, and binding partners are integrated to switch MAP4 between stabilizer, transport regulator, and cell-death effector in a tissue-specific manner remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking phosphosite combinations to functional outputs\", \"Structural basis of partner competition (cyclin B vs septin vs dynein) on the Pro-rich region undefined\", \"Isoform-specific regulatory networks not systematically compared\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 8, 15, 19, 35]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [15, 19, 35, 42]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 23, 27, 37]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 8, 11, 14]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8, 30]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [28, 30, 40]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [33]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [4, 10, 27, 36]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [12, 32, 37, 43]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [38, 40]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [30]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [31]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CCNB1\", \"DYNLT1\", \"VDAC1\", \"SEPT2\", \"BTN3A1\", \"MAPK14\", \"LC3\", \"FBXW7\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":10,"faith_total":10,"faith_pct":100.0}}