{"gene":"PAK4","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1998,"finding":"PAK4 was identified as a novel effector for Cdc42Hs, interacting specifically with the activated (GTP-bound) form of Cdc42Hs through its GTPase-binding domain (GBD). Co-expression with constitutively active Cdc42HsV12 redistributed PAK4 to the brefeldin A-sensitive Golgi compartment and induced filopodia and actin polymerization in a manner dependent on PAK4 kinase activity.","method":"Co-expression, GBD interaction assays, brefeldin A-sensitive Golgi localization experiments, kinase-dead mutant analysis, immunofluorescence","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal interaction assays, kinase-dead mutagenesis, localization experiments; foundational study replicated across multiple subsequent labs","pmids":["9822598"],"is_preprint":false},{"year":2001,"finding":"Serine 474 in the PAK4 kinase domain was identified as the autophosphorylation site in vivo. Mutation S474E produces constitutively active PAK4, and phospho-S474-specific antibodies detect activated PAK4 on the Golgi membrane when PAK4 is co-expressed with activated Cdc42. A kinase-inactive mutant (K350A,K351A) blocked Ras-driven transformation.","method":"Site-directed mutagenesis, phospho-specific antibody, immunofluorescence, NIH3T3 transformation assay, HCT116 anchorage-independent growth assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — mutagenesis identifying autophosphorylation site, phospho-specific antibody validation, functional rescue experiments; widely replicated","pmids":["11668177"],"is_preprint":false},{"year":2001,"finding":"PAK4 interacts specifically with LIM kinase 1 (LIMK1) and phosphorylates it more strongly than PAK1 does. Activated PAK4 stimulates LIMK1's ability to phosphorylate cofilin, and dominant-negative LIMK1 and a phosphorylation-resistant cofilin mutant inhibit PAK4-induced cytoskeletal and cell shape changes.","method":"Binding assays, immune complex kinase assays, dominant-negative mutant rescue, immunofluorescence in C2C12 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro kinase assay, binding assay, dominant-negative epistasis; independently replicated in multiple subsequent studies","pmids":["11413130"],"is_preprint":false},{"year":2001,"finding":"PAK4 protects cells from apoptosis: expression of wild-type or constitutively active PAK4 delays apoptosis in response to TNF-α, UV irradiation, and serum starvation. PAK4 expression increases phosphorylation of the proapoptotic protein Bad and inhibits caspase activation.","method":"Overexpression of WT and constitutively active PAK4, apoptosis assays (TNF-α, UV, serum starvation), Bad phosphorylation assay, caspase activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal apoptosis stimuli, Bad phosphorylation readout, caspase assay; replicated across labs","pmids":["11278822"],"is_preprint":false},{"year":2001,"finding":"Activated PAK4 dissolves actin stress fibers and focal adhesions, impairs cell spreading on fibronectin, and confers anchorage independence (soft agar colony formation). Dominant-negative PAK4 mutants inhibit focus formation by oncogenic Dbl, establishing PAK4 as a transforming kinase downstream of Rho GTPase exchange factors.","method":"Constitutively active PAK4 mutant expression, fibronectin adhesion assay, soft agar colony assay, dominant-negative inhibition of Dbl-induced focus formation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple functional assays, dominant-negative epistasis, replicated by subsequent studies","pmids":["11313478"],"is_preprint":false},{"year":2002,"finding":"PAK4 is activated by HGF in epithelial (MDCK) cells downstream of PI3K; LY294002 (PI3K inhibitor) blocks HGF-induced PAK4 kinase activation and relocalization to the cell periphery. The isolated C-terminal kinase domain can induce cell rounding in the presence of LY294002, indicating the N-terminal region acts as a negative regulator of PAK4 activity.","method":"HGF stimulation, LY294002 PI3K inhibitor, PAK4 kinase activity assay, truncation mutant analysis, immunofluorescence","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — kinase activity assay, PI3K inhibitor, domain truncation experiments, single lab with multiple orthogonal methods","pmids":["12244132"],"is_preprint":false},{"year":2003,"finding":"PAK4 is essential for embryonic viability: PAK4 knockout mice die by embryonic day 11.5 with defects in heart development, neuronal differentiation and migration, and neural tube folding, demonstrating an essential in vivo role for PAK4 in cytoskeletal regulation and cell/ECM adhesion during development.","method":"Gene targeting (PAK4 knockout mouse), histological and morphological analysis of PAK4-null embryos","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic knockout with defined developmental phenotypes in mice","pmids":["14517283"],"is_preprint":false},{"year":2003,"finding":"PAK4 inhibits the activation of initiator caspase 8 downstream of death domain-containing receptors (TNF receptor, Fas receptor), independently of its kinase activity, potentially by inhibiting caspase 8 recruitment to death domain receptors. This is distinct from PAK4's kinase-dependent phosphorylation of Bad.","method":"PAK4 overexpression, kinase-dead mutant, caspase 8 activation assay, TNF/Fas receptor stimulation","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinase-dead mutant used to distinguish mechanism, single lab; proposed caspase 8 recruitment inhibition not directly shown","pmids":["14560027"],"is_preprint":false},{"year":2005,"finding":"PAK4 mediates morphological changes through association with the Rho-family GEF, GEF-H1, via a novel GEF-H1 interaction domain (GID) in PAK4. PAK4 phosphorylates GEF-H1 at Ser810 to block stress fiber formation and promote lamellipodia. PAK4 phosphorylation of MT-bound GEF-H1 releases it into the cytoplasm, coinciding with stress fiber dissolution.","method":"Co-immunoprecipitation, domain mapping, in vitro phosphorylation assay, immunofluorescence, microtubule association assay in NIH-3T3 cells","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, domain mapping, in vitro phosphorylation, functional consequences shown; single lab with multiple orthogonal methods","pmids":["15827085"],"is_preprint":false},{"year":2005,"finding":"Activated PAK4 induces premature senescence in primary fibroblasts via a pathway requiring ERK MAPK and the cell cycle inhibitors p16(INK4) and p19(ARF). PAK4 expression levels are upregulated in response to senescence-promoting stimuli.","method":"Activated PAK4 expression in primary fibroblasts, senescence assay, ERK inhibitor treatment, p16/p19 pathway analysis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic pathway analysis in primary cells, pharmacological inhibition of ERK, single lab","pmids":["16227603"],"is_preprint":false},{"year":2006,"finding":"PAK4 regulates podosome size and number in primary human macrophages: shRNA knockdown or PAK4 truncation mutants reduce podosome numbers, kinase-active PAK4 enhances podosome size, and kinase-inactive PAK4 reduces podosome size, demonstrating a kinase activity-dependent role in localized actin dynamics at podosomes.","method":"shRNA knockdown, PAK4 truncation and kinase mutant expression, immunofluorescence, actin structure analysis in primary human macrophages","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — kinase-dead and truncation mutant analysis with quantitative podosome readout; single lab","pmids":["16897755"],"is_preprint":false},{"year":2008,"finding":"PAK4 binds to and phosphorylates LIMK1 in an HGF-dependent manner in prostate cancer cells. PAK4-LIMK1 direct interaction was visualized in living cells by FRET-FLIM, concentrated in peripheral foci. Variations in PAK4 expression change cofilin phosphorylation levels, correlated with LIMK1 activity and cell migration speed; PAK4 and LIMK1 act synergistically to increase migration.","method":"Co-immunoprecipitation, FRET-FLIM imaging, cofilin phosphorylation assays, PAK4 siRNA knockdown, cell migration assays","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — FRET-FLIM for direct cellular interaction, kinase assay, RNAi with quantitative phenotype; independently replicated","pmids":["18424072"],"is_preprint":false},{"year":2008,"finding":"RNAi or dominant-negative suppression of PAK4 markedly inhibits endothelial cell lumen and tube formation in 3D collagen matrices. PAK4 phosphorylation correlates with lumenogenesis in a PKC-dependent manner, placing PAK4 downstream of Cdc42/Rac1 and PKC in vascular morphogenesis.","method":"RNAi knockdown, dominant-negative expression, 3D collagen matrix lumen formation assay, PKC inhibitor treatment","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi and dominant-negative with defined morphogenic phenotype, PKC epistasis; single lab","pmids":["18319301"],"is_preprint":false},{"year":2009,"finding":"PAK4 is a novel Gab1-interacting protein; upon HGF stimulation, Gab1 and PAK4 associate and colocalize at lamellipodia. The interaction is mediated through the GEF-interacting domain of PAK4 and a novel Gab1 region, requires Gab1 phosphorylation but not PAK4 kinase activity. Gab1-Pak4 association is required for HGF-induced cell dispersal, migration, and invasion.","method":"Co-immunoprecipitation, domain mapping, confocal colocalization, Gab1 mutant unable to recruit Pak4, cell dispersal and invasion assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, domain mapping, Gab1 interaction-deficient mutant, defined cellular phenotype; single lab, multiple orthogonal methods","pmids":["19289496"],"is_preprint":false},{"year":2009,"finding":"DGCR6L is a novel PAK4-binding protein, confirmed by GST pulldown and co-immunoprecipitation. L115 of DGCR6L is critical for binding to the C-terminus (aa 466–572) of PAK4. DGCR6L is required for formation of a PAK4-DGCR6L-β-actin complex and enhances phosphorylation of LIMK1 and cofilin in a dose-dependent manner to promote gastric cancer cell migration.","method":"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, site-directed mutagenesis (L115V), LIMK1/cofilin phosphorylation assay, migration assay","journal":"The international journal of biochemistry & cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — GST pulldown and Co-IP for interaction, mutagenesis identifying critical residue, downstream phosphorylation readout; single lab","pmids":["19778628"],"is_preprint":false},{"year":2010,"finding":"PAK4 phosphorylates paxillin at serine 272, co-immunoprecipitates with paxillin, localizes to focal adhesions, and regulates RhoA activity via GEF-H1 to control actin cytoskeletal rearrangement and focal adhesion turnover. PAK4-depleted prostate cancer cells show increased focal adhesion size/number and reduced adhesion turnover rates.","method":"Co-immunoprecipitation, in vitro kinase assay, immunofluorescence localization to focal adhesions, PAK4 siRNA knockdown, RhoA activity assay","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — Co-IP, in vitro kinase assay identifying paxillin S272 as substrate, RhoA activity assay, localization; single lab, multiple orthogonal methods","pmids":["20406887"],"is_preprint":false},{"year":2011,"finding":"PAK4 is a nucleo-cytoplasmic shuttling protein with three nuclear export signals (NESs) and two nuclear localization signals (NLSs). It is exported via CRM-1-dependent pathway and imported in an importin α5-dependent manner. Nuclear PAK4 phosphorylates β-catenin at Ser675, promoting TCF/LEF transcriptional activity, stabilizing β-catenin by inhibiting its degradation, and associating with the TCF/LEF transcriptional complex.","method":"NLS/NES mutagenesis, CRM-1/importin α5 inhibition/knockdown, β-catenin phosphorylation assay, TCF/LEF reporter assay, ChIP assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis of localization signals, ChIP, phosphorylation assay, reporter assay; single lab with multiple orthogonal methods","pmids":["22173096"],"is_preprint":false},{"year":2011,"finding":"CDK5RAP3 (C53/LZAP) is a novel binding partner of PAK4 that enhances PAK4 kinase activity. siRNA-mediated knockdown of PAK4 in CDK5RAP3-overexpressing HCC cells reversed the enhanced cell invasiveness, demonstrating that PAK4 activity is required for CDK5RAP3-promoted metastasis.","method":"Co-immunoprecipitation, PAK4 kinase activity assay, siRNA knockdown, invasion assay","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, kinase activity assay, RNAi epistasis; single lab","pmids":["21385901"],"is_preprint":false},{"year":2011,"finding":"PAK4 levels peak transiently in early G1 phase of the cell cycle. PAK4 deletion increases p21 levels and is required for normal p21 degradation. Absence of PAK4 in serum-starved cells reduces the fraction of cells in G1 and increases G2/M cells, indicating PAK4 controls cell cycle progression partly by regulating p21 levels.","method":"Cell cycle synchronization, flow cytometry, PAK4 knockout cells, p21 protein level analysis","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — PAK4 knockout with defined cell cycle phenotype and p21 readout; single lab","pmids":["21381077"],"is_preprint":false},{"year":2012,"finding":"PAK4 is required for metaphase spindle positioning and anchoring. PAK4-depleted cells show defective astral microtubule networks, spindle miscentering, cortical membrane blebbing during prometaphase, and mislocalization of dynein/dynactin complex components at kinetochores and on astral MTs, resulting in prolonged metaphase-like arrest and eventual cohesion fatigue.","method":"PAK4 siRNA depletion, live cell imaging, immunofluorescence of spindle/kinetochore markers, dynein/dynactin localization analysis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi with defined mitotic phenotype and specific molecular readout of dynein/dynactin mislocalization; single lab","pmids":["22450748"],"is_preprint":false},{"year":2013,"finding":"PAK4 interacts with Smad2/3 and modulates their phosphorylation via both kinase-dependent and kinase-independent mechanisms to attenuate Smad2/3 axis transactivation and TGF-β-mediated growth inhibition. PAK4 blocks TGF-β1-induced phosphorylation of Smad2 Ser465/467 independently of kinase activity, and phosphorylates Smad2 on Ser465 (promoting Smad2 degradation via ubiquitin-proteasome pathway) under HGF stimulation.","method":"Co-immunoprecipitation, kinase assay, kinase-dead mutant, TGF-β reporter assay, ubiquitin-proteasome pathway analysis, HGF stimulation","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, kinase-dead mutant, multiple phospho-site readouts; single lab with multiple methods","pmids":["23934187"],"is_preprint":false},{"year":2013,"finding":"PAK4 phosphorylates SCG10 (superior cervical ganglia 10) at serine 50 (Ser50). Phosphorylated SCG10 regulates microtubule dynamics to promote gastric cancer cell migration and invasion, and blocking PAK4 (by inhibitor LCH-7749944 or RNAi) inhibits Ser50 phosphorylation and cell invasion.","method":"In vitro kinase assay, site-directed mutagenesis (S50A), PAK4 inhibitor LCH-7749944, RNAi, cell invasion assay, xenograft mouse model","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay with mutagenesis, pharmacological inhibition, RNAi, in vivo confirmation; single lab with multiple orthogonal methods","pmids":["23893240"],"is_preprint":false},{"year":2013,"finding":"SH3RF2 inhibits PAK4 ubiquitination and proteasomal degradation via physical interaction-mediated steric hindrance, thereby stabilizing PAK4 protein levels and promoting oncogenic signaling.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, SH3RF2 overexpression/ablation","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ubiquitination assay; single lab with two orthogonal methods","pmids":["24130170"],"is_preprint":false},{"year":2015,"finding":"PAK4 drives cell adhesion turnover in a kinase-independent manner by stabilizing RhoU protein levels. PAK4 protects RhoU from ubiquitination by the Rab40A-Cullin 5 E3 ligase complex. RhoU overexpression rescues the PAK4-depletion adhesion phenotype, and loss of RhoU reduces adhesion turnover and migration.","method":"PAK4 knockdown, kinase-dead PAK4 rescue, Cdc42-binding mutant rescue, RhoU overexpression rescue, ubiquitination assay, Rab40A-Cullin 5 complex identification","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — kinase-dead and Cdc42-binding mutant rescue experiments, ubiquitination assay, E3 ligase identification, RhoU rescue epistasis; single lab with multiple orthogonal rigorous methods","pmids":["26598620"],"is_preprint":false},{"year":2015,"finding":"PAK4 phosphorylates Par6B at Ser143, blocking Par6B's interaction with Cdc42, providing a mechanism to control Par6B subcellular localization and interactions in epithelial polarity establishment. Both PAK4 and Par6B are required for assembly of apical junctions in human bronchial epithelial cells.","method":"In vitro kinase assay, Co-immunoprecipitation, site-directed mutagenesis (Par6B S143), RNAi knockdown, apical junction assembly assay","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay, mutagenesis, Co-IP; single lab","pmids":["25662318"],"is_preprint":false},{"year":2015,"finding":"PAK4 localizes primarily to cell-cell junctions (not focal adhesions or leading edge in migrating cells). PAK4 depletion or kinase inhibition (PF-3758309) does not affect collective migration but causes defects in centrosome reorientation after wounding. PAK4 phosphorylates β-catenin at Ser-675 predominantly at cell-cell junctions.","method":"Immunofluorescence localization, PAK4 siRNA knockdown, PF-3758309 inhibitor, wound-healing centrosome reorientation assay, β-catenin phosphorylation assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization imaging, kinase inhibitor, centrosome reorientation readout; single lab","pmids":["26068882"],"is_preprint":false},{"year":2015,"finding":"Integrin αvβ3 recruits and activates PAK4 to allow glioblastoma cells to evade oncogene-induced senescence. Targeting either αvβ3 or PAK4 triggers a p21-dependent, p53-independent senescence phenotype in GBM cells specifically; this dependence is tissue-specific (not found in epithelial cancers) and other PAK family members are not required.","method":"αvβ3 integrin targeting, PAK4 knockdown, senescence assay, p21/p53 genetic analysis in GBM vs. epithelial cancer cells","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown of both αvβ3 and PAK4, p21-dependent senescence assay, tissue-specificity comparison; single lab","pmids":["26297735"],"is_preprint":false},{"year":2015,"finding":"The crystal structure of human PAK4 catalytic domain in complex with its endogenous inhibitor Inka1 was determined at 2.95 Å resolution using in cellulo crystals from single mammalian cells. The structure reveals details of how PAK4 binds cellular ATP and Inka1 at the active site.","method":"In cellulo X-ray crystallography at 2.95 Å resolution, crystal growth in mammalian cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure with functional validation of inhibitor binding","pmids":["26607847"],"is_preprint":false},{"year":2016,"finding":"SETD6 methyltransferase methylates PAK4 both in vitro and at chromatin in cells. SETD6 depletion hinders activation of Wnt/β-catenin target genes. In the presence of SETD6, physical interaction between PAK4 and β-catenin is dramatically increased, leading to enhanced transcription of β-catenin target genes.","method":"In vitro methylation assay, ChIP, SETD6 knockdown, β-catenin co-immunoprecipitation, TCF/LEF reporter assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro methylation assay, ChIP, Co-IP, reporter assay; single lab with multiple orthogonal methods","pmids":["26841865"],"is_preprint":false},{"year":2016,"finding":"PAK4 directly phosphorylates p53 at serine 215, attenuating p53 transcriptional transactivation activity and inhibiting p53-mediated suppression of HCC cell invasion.","method":"In vitro kinase assay, site-directed mutagenesis (S215 of p53), p53 transcriptional reporter assay, PAK4 overexpression/silencing, invasion assay in HCC cells","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay identifying p53 S215 as substrate, functional reporter assay; single lab","pmids":["27496712"],"is_preprint":false},{"year":2016,"finding":"PAK4 promotes G6PD activity and glucose reprogramming by interacting with G6PD and enhancing Mdm2-mediated p53 ubiquitination and degradation (reducing p53-mediated suppression of G6PD), leading to increased NADPH production and lipid biosynthesis in colon cancer cells.","method":"Co-immunoprecipitation, G6PD activity assay, p53 ubiquitination assay, Mdm2 interaction analysis, PAK4 knockdown/overexpression","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, enzymatic activity assay, ubiquitination assay; single lab with multiple methods","pmids":["28542136"],"is_preprint":false},{"year":2017,"finding":"Zic2 transcription factor directly binds the PAK4 promoter and activates PAK4 expression, as demonstrated by ChIP and luciferase assays. PAK4 interference attenuates Zic2-mediated cell growth via the Raf/MEK/ERK pathway.","method":"ChIP assay, luciferase reporter assay, PAK4 siRNA knockdown, Raf/MEK/ERK pathway analysis","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and luciferase assay for promoter binding, pathway inhibition; single lab","pmids":["28577975"],"is_preprint":false},{"year":2017,"finding":"PAK4 interacts specifically with p85α (the regulatory subunit of PI3K) in pancreatic cancer cells; PAK4-deficient cells exhibit reduced Akt phosphorylation downstream of HGF, implicating a novel role for PAK4 within the PI3K/Akt pathway.","method":"Co-immunoprecipitation (PAK4-p85α), PAK4 knockdown, Akt phosphorylation assay, HGF stimulation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating specific interaction, RNAi with Akt phosphorylation readout; single lab","pmids":["28205613"],"is_preprint":false},{"year":2018,"finding":"X-ray crystallography and solution scattering revealed that full-length PAK4 heterodimer with CDC42 adopts a compact organization. In addition to the canonical CRIB domain–CDC42 interaction, unexpected contacts involve the PAK4 kinase C-lobe, CDC42, and the PAK4 polybasic region. These additional interactions modulate kinase activity and increase CDC42 binding affinity for full-length PAK4 compared to CRIB domain alone.","method":"X-ray crystallography, small angle X-ray scattering (SAXS), kinase activity assay, binding affinity measurement","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus SAXS plus functional kinase activity assay; rigorous multi-method structural study","pmids":["29295922"],"is_preprint":false},{"year":2018,"finding":"PAK4 phosphorylates CEBPB at Thr-235 to upregulate CLDN4 (claudin-4) expression, promoting breast cancer cell migration and invasion via a PAK4-CEBPB-CLDN4 axis.","method":"PAK4 knockdown, CEBPB phosphorylation assay, CLDN4 promoter ChIP/luciferase, rescue experiments in MDA-MB-231 and ZR-75-30 cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphorylation assay, promoter binding assay, rescue epistasis; single lab","pmids":["30808546"],"is_preprint":false},{"year":2018,"finding":"VIP activates PAK4 via EPAC-dependent cAMP signaling whereas secretin activates PAK4 via PKA-dependent signaling in pancreatic acinar cells. PAK4 activation is required for VIP/secretin-induced Na+,K+-ATPase activation, which mediates pancreatic fluid secretion.","method":"EPAC inhibitors (ESI-09, HJC0197), PKA inhibitors (KT-5720, PKI), PAK4 kinase activity assay, Na+,K+-ATPase activity assay, EPAC agonist","journal":"American journal of physiology. Gastrointestinal and liver physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological pathway dissection, PAK4 kinase activity assay, downstream functional readout; single lab","pmids":["30520694"],"is_preprint":false},{"year":2019,"finding":"PAK4 phosphorylates RELB at Ser151, which is critical for RELB-DNA interaction and transcriptional activity. A PAK4-RELB-C/EBPβ axis controls senescence-like growth arrest in breast cancer cells, and PAK4 overexpression abrogates H-RAS-V12-induced senescence in untransformed mammary epithelial cells.","method":"PAK4 overexpression in untransformed MCF10A, PAK4 depletion in breast cancer lines, RELB phosphorylation assay, RELB-DNA binding assay (EMSA or reporter), C/EBPβ expression analysis, MMTV-PAK4 transgenic mouse model","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — phosphorylation site mutagenesis (RELB-S151), DNA-binding assay, in vivo mouse model, multiple cellular systems; single lab but multiple orthogonal methods","pmids":["31399573"],"is_preprint":false},{"year":2019,"finding":"PAK4 directly phosphorylates fumarase (FH) at Ser46 in non-small cell lung cancer cells. PAK4-phosphorylated FH binds to 14-3-3, causing cytosolic detention of FH and preventing formation of the FH/CSL/p53 complex at the p21 promoter, thereby blocking TGF-β-induced p21 transcription and cell growth arrest.","method":"In vitro kinase assay, site-directed mutagenesis (FH S46), 14-3-3 co-immunoprecipitation, ChIP assay, p21 reporter assay, PAK4 knockdown/overexpression","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay, mutagenesis, Co-IP, ChIP, reporter assay; single lab with multiple orthogonal methods","pmids":["30683654"],"is_preprint":false},{"year":2019,"finding":"PAK4 directly phosphorylates Slug (SNAI2), leading to Slug stabilization and pro-malignant activity in NSCLC cells. miR-193a-3p targeting of PAK4 reduces downstream p-Slug and L1CAM expression, suppressing NSCLC migration and invasion.","method":"PAK4 knockdown/overexpression, Slug phosphorylation assay, miR-193a-3p overexpression, L1CAM expression analysis, migration/invasion assay","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphorylation assay, RNAi epistasis; single lab","pmids":["30685413"],"is_preprint":false},{"year":2019,"finding":"PAK4 phosphorylates CRTC1 (CREB-regulated transcription coactivator 1) at S215. Constitutively active PAK4 protects dopaminergic neurons in rodent PD models, and this neuroprotective effect is mediated by CRTC1-S215 phosphorylation driving expression of CREB targets Bcl-2, BDNF, and PGC-1α; non-phosphorylatable CRTC1(S215A) abrogates caPAK4 neuroprotection.","method":"Constitutively active PAK4 (caPAK4S445N/S474E) viral expression, CRTC1 phosphorylation assay, S215A mutant rescue, Bcl-2/BDNF/PGC-1α expression, 6-OHDA and α-synuclein rat PD models","journal":"Science translational medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — phosphosite mutagenesis, in vivo rodent model, multiple downstream target validation; single lab but rigorous multi-method in vivo study","pmids":["27903866"],"is_preprint":false},{"year":2019,"finding":"PAK4 kinase activity is essential for podosome ring formation in myeloid cells. PAK4 localizes specifically within the podosome ring by superresolution imaging. PAK4 inhibition reduces podosome formation and induces focal adhesion formation. PAK4 depletion perturbs phospho-Akt signaling at podosomes, placing PAK4 kinase activity at the podosome ring:core interface intersecting the Akt pathway.","method":"PAK4 inhibitor (PF-3758309), PAK4 siRNA knockdown, kinase-dead PAK4 rescue, superresolution (STORM/STED) imaging, podosome assay, phospho-Akt analysis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — kinase-dead rescue, superresolution localization, pharmacological and genetic inhibition with defined phenotype; single lab, multiple orthogonal methods","pmids":["31825823"],"is_preprint":false},{"year":2020,"finding":"PAK4 reprograms tumor endothelial cell transcriptome via a MEF2D/ZEB1- and SLUG-mediated mechanism, downregulating claudin-14 and VCAM-1 expression, thereby enhancing vessel permeability and reducing T cell adhesion to the endothelium. PAK4 knockout in ECs reduces vascular abnormalities and improves T cell infiltration.","method":"PAK4 knockout in ECs (genetic), kinome-wide screening, MEF2D/ZEB1/SLUG pathway analysis, claudin-14 and VCAM-1 expression assay, T cell adhesion assay, GBM mouse models","journal":"Nature cancer","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic PAK4 KO with defined molecular mechanism (MEF2D/ZEB1/SLUG axis), downstream adhesion protein readout, T cell infiltration phenotype in vivo; single lab but multiple orthogonal methods and in vivo validation","pmids":["35121889"],"is_preprint":false},{"year":2020,"finding":"SETD6 methylates PAK4 specifically at lysine 473 (K473). K473 methylation activates β-catenin transcriptional activity, attenuates paxillin localization to focal adhesions, and reduces cell adhesion, migration, and invasion.","method":"In vitro methylation assay, site-directed mutagenesis (K473), β-catenin reporter assay, paxillin localization by immunofluorescence, adhesion/migration/invasion assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 1-2 / Moderate — in vitro methylation assay, mutagenesis identifying K473, functional reporter and adhesion assays; single lab","pmids":["33051544"],"is_preprint":false},{"year":2021,"finding":"CDK15 binds PAK4 and phosphorylates PAK4 at S291. Phosphorylation of PAK4 at S291 promotes CRC cell proliferation and anchorage-independent growth through β-catenin/c-Myc and MEK/ERK signaling pathways. PAK4 inhibition reverses the tumorigenic effects of CDK15 in CRC cells.","method":"Co-immunoprecipitation (CDK15-PAK4), in vitro/in cellulo kinase assay (S291 phosphorylation), site-directed mutagenesis, β-catenin/MEK-ERK pathway analysis, CDK15 KO mouse AOM/DSS model, CDX and PDX xenograft models","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — kinase assay with mutagenesis identifying S291, in vivo mouse genetic KO plus xenograft models, multiple orthogonal approaches; single lab","pmids":["34262144"],"is_preprint":false},{"year":2010,"finding":"PAK4 N-terminal domain interacts with ribonucleoprotein (RNP) complexes, and active PAK4 affects cap-independent (IRES-mediated) translation in vivo; the N-terminal domain contains sequences driving cytoplasmic localization and a nuclear export signal.","method":"Affinity chromatography of N-terminal domain, IRES-reporter assay in cells, nuclear/cytoplasmic fractionation","journal":"Journal of cellular physiology","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — affinity chromatography and reporter assay; single lab, no direct confirmation of RNP substrate","pmids":["20578242"],"is_preprint":false},{"year":2018,"finding":"Nuclear PAK4 (nPAK4) acts as a repressor of ERα-mediated transactivation in an E2-dependent manner; PAK4 binds ERα and co-translocates with it from the cytoplasm to the nucleus upon E2 stimulation, and promotes bone metastasis by targeting the LIFR (bone metastasis suppressor) locus.","method":"Co-immunoprecipitation (PAK4-ERα), nuclear fractionation upon E2 stimulation, ERα reporter assay, LIFR expression analysis, in vitro invasion assay, in vivo metastasis model","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP demonstrating ERα binding, nuclear co-translocation assay, functional in vivo metastasis model; single lab","pmids":["30177834"],"is_preprint":false}],"current_model":"PAK4 is a Cdc42-activated serine/threonine kinase that localizes to the Golgi, cell-cell junctions, focal adhesions, and nucleus, where it phosphorylates a broad substrate repertoire—including LIMK1 (→cofilin), Bad, paxillin (S272), GEF-H1 (S810), β-catenin (S675), Smad2 (S465), SCG10 (S50), p53 (S215), Par6B (S143), fumarase (S46), RELB (S151), CRTC1 (S215), CEBPB (T235), and Slug—to regulate actin cytoskeleton dynamics, cell adhesion turnover, anti-apoptotic signaling, Wnt/β-catenin transcription, cell cycle progression (via p21), mitotic spindle anchoring, and vascular/neural morphogenesis; upstream activation by Cdc42, HGF/PI3K, PKA/EPAC, and CDK15 (phospho-S291), as well as SETD6-mediated methylation at K473, modulate PAK4 activity and nuclear distribution, while RhoU stabilization and kinase-independent Smad2/3 binding extend its non-catalytic functions."},"narrative":{"mechanistic_narrative":"PAK4 is a Cdc42-activated serine/threonine kinase that couples Rho-family GTPase signaling to actin cytoskeleton remodeling, cell adhesion turnover, anti-apoptotic signaling, and transcriptional control [PMID:9822598, PMID:11313478]. It was first defined as a Cdc42 effector whose GTPase-binding domain engages GTP-loaded Cdc42, redirecting PAK4 to the Golgi and driving filopodia and actin polymerization through its kinase activity [PMID:9822598]; structural work later showed that full-length PAK4 forms a compact heterodimer with CDC42 in which kinase C-lobe and polybasic contacts beyond the canonical CRIB interface tune activity and binding affinity [PMID:29295922], and that catalytic output is held in check by the endogenous inhibitor Inka1 [PMID:26607847]. Activation requires autophosphorylation at Ser474, with the N-terminal region acting as a negative regulator that is relieved by HGF/PI3K signaling [PMID:11668177, PMID:12244132]. A core cytoskeletal program runs through PAK4 phosphorylation of LIMK1, which in turn phosphorylates cofilin to remodel actin and promote migration [PMID:11413130, PMID:18424072], and through phosphorylation of GEF-H1 (Ser810) and paxillin (Ser272) to control RhoA activity, stress fibers, and focal-adhesion turnover [PMID:15827085, PMID:20406887]. PAK4 also drives adhesion turnover kinase-independently by stabilizing RhoU against Rab40A–Cullin5-mediated degradation [PMID:26598620] and localizes to cell-cell junctions, podosomes, and the mitotic spindle, where it is required for astral microtubule organization and dynein/dynactin positioning [PMID:22450748, PMID:26068882, PMID:31825823]. As a nucleo-cytoplasmic shuttling protein, PAK4 enters the nucleus to phosphorylate β-catenin (Ser675) and promote TCF/LEF transcription, an axis amplified by SETD6-mediated methylation at K473 [PMID:22173096, PMID:26841865, PMID:33051544]. PAK4 broadly suppresses tumor-suppressor and growth-arrest programs, phosphorylating p53 (Ser215), Smad2 (Ser465), fumarase (Ser46), and RELB (Ser151), and regulating p21 to control cell-cycle progression and senescence [PMID:21381077, PMID:23934187, PMID:27496712, PMID:31399573, PMID:30683654]. PAK4 is essential for mouse embryonic development, with knockouts dying by E11.5 from cardiac, neuronal, and neural-tube defects [PMID:14517283].","teleology":[{"year":1998,"claim":"Established PAK4's founding identity by answering whether it is a Cdc42 effector and how GTPase binding reroutes it to drive actin remodeling.","evidence":"GBD interaction assays with activated Cdc42Hs, Golgi localization and kinase-dead mutant analysis by immunofluorescence","pmids":["9822598"],"confidence":"High","gaps":["Direct cytoskeletal substrates not yet identified","Mechanism linking Golgi localization to filopodia formation unresolved"]},{"year":2001,"claim":"Defined how PAK4 catalytic activity is switched on and showed its kinase function is required for oncogenic transformation.","evidence":"Site-directed mutagenesis identifying Ser474 autophosphorylation, phospho-specific antibody, NIH3T3 transformation and anchorage-independent growth assays","pmids":["11668177"],"confidence":"High","gaps":["Upstream kinases/regulators of activation not defined","Relationship of autophosphorylation to N-terminal autoinhibition unresolved"]},{"year":2001,"claim":"Connected PAK4 to the actin cytoskeleton mechanistically and to cell survival, defining its first substrate (LIMK1) and first anti-apoptotic readout (Bad).","evidence":"In vitro kinase and binding assays, dominant-negative cofilin/LIMK1 rescue, apoptosis assays with TNF-α/UV/serum starvation and Bad phosphorylation/caspase readouts","pmids":["11413130","11278822","11313478"],"confidence":"High","gaps":["Whether PAK4 phosphorylates Bad directly not established","Quantitative contribution of LIMK1 vs other effectors to cytoskeletal change unclear"]},{"year":2002,"claim":"Placed PAK4 in a growth-factor signaling cascade and revealed intramolecular autoinhibition by mapping HGF/PI3K-dependent activation and N-terminal repression.","evidence":"HGF stimulation in MDCK cells, LY294002 PI3K inhibition, kinase activity assays, truncation mutant analysis","pmids":["12244132"],"confidence":"High","gaps":["Direct biochemical link between PI3K products and PAK4 not shown","Identity of the relieving signal acting on the N-terminus undefined"]},{"year":2003,"claim":"Demonstrated PAK4 is physiologically essential and separated its kinase-dependent from kinase-independent survival functions.","evidence":"PAK4 knockout mouse with developmental phenotyping; kinase-dead mutant analysis of caspase-8 inhibition","pmids":["14517283","14560027"],"confidence":"High","gaps":["In vivo embryonic phenotype not assigned to specific substrates","Proposed caspase-8 recruitment inhibition not directly demonstrated"]},{"year":2005,"claim":"Elucidated how PAK4 reorganizes actin architecture by identifying GEF-H1 as a substrate that links PAK4 to RhoA-dependent stress fiber regulation, while linking PAK4 to senescence control.","evidence":"Co-IP, domain mapping of the GID, in vitro phosphorylation of GEF-H1 Ser810, microtubule release assay; senescence assays with ERK inhibition and p16/p19 analysis","pmids":["15827085","16227603"],"confidence":"Medium","gaps":["GEF-H1 Ser810 phospho-site role in vivo not tested","Senescence pathway analysis single-lab and pharmacology-dependent"]},{"year":2006,"claim":"Extended PAK4's cytoskeletal role to specialized adhesion structures by showing kinase-dependent control of podosomes.","evidence":"shRNA knockdown, kinase/truncation mutants and quantitative podosome imaging in primary human macrophages","pmids":["16897755"],"confidence":"Medium","gaps":["Podosome substrate(s) at the structure not identified","Single-lab observation"]},{"year":2008,"claim":"Validated the PAK4-LIMK1-cofilin axis as a direct, spatially-resolved interaction driving cancer cell migration.","evidence":"FRET-FLIM live-cell imaging, Co-IP, cofilin phosphorylation and migration assays in prostate cancer cells","pmids":["18424072","18319301"],"confidence":"High","gaps":["Vascular morphogenesis role (lumen formation) relies on dominant-negative/RNAi without substrate","Spatial control of LIMK1 engagement at foci mechanistically incomplete"]},{"year":2009,"claim":"Expanded PAK4's adaptor/scaffolding repertoire by identifying kinase-independent interactions (Gab1, DGCR6L) that organize migration and invasion machinery.","evidence":"Co-IP, domain mapping, interaction-deficient mutants, LIMK1/cofilin phosphorylation and invasion assays","pmids":["19289496","19778628"],"confidence":"High","gaps":["DGCR6L interaction Medium-confidence and single-lab","How scaffolding integrates with catalytic LIMK1 activation unclear"]},{"year":2010,"claim":"Defined PAK4's role at focal adhesions by identifying paxillin Ser272 as a substrate coupled to RhoA/GEF-H1-mediated adhesion turnover.","evidence":"Co-IP, in vitro kinase assay, focal-adhesion immunofluorescence, siRNA and RhoA activity assay in prostate cancer cells","pmids":["20406887"],"confidence":"High","gaps":["Hierarchy of paxillin vs GEF-H1 phosphorylation in adhesion turnover unresolved","N-terminal RNP/IRES-translation role (Low confidence) not corroborated"]},{"year":2011,"claim":"Revealed nuclear PAK4 as a transcriptional regulator by mapping its shuttling signals and β-catenin Ser675 phosphorylation, and identified upstream stabilizers/activators (CDK5RAP3) and cell-cycle control via p21.","evidence":"NLS/NES mutagenesis, CRM-1/importin-α5 manipulation, β-catenin phosphorylation, TCF/LEF reporter and ChIP; Co-IP and kinase assays for CDK5RAP3; cell-cycle synchronization with p21 readout in knockout cells","pmids":["22173096","21385901","21381077"],"confidence":"High","gaps":["Signals triggering nuclear import in physiological contexts not defined","Mechanism of p21 degradation control by PAK4 unclear"]},{"year":2012,"claim":"Identified an unanticipated mitotic role by showing PAK4 is required for spindle anchoring and dynein/dynactin positioning.","evidence":"siRNA depletion, live imaging, kinetochore/astral MT immunofluorescence and dynein/dynactin localization analysis","pmids":["22450748"],"confidence":"Medium","gaps":["Mitotic substrate(s) of PAK4 not identified","Single-lab RNAi phenotype"]},{"year":2013,"claim":"Broadened PAK4 substrate scope into TGF-β/Smad signaling, microtubule-regulating SCG10, and protein-stability control, establishing dual kinase-dependent/independent regulation of tumor-suppressive pathways.","evidence":"Co-IP, kinase and kinase-dead assays, Smad2 Ser465 phosphorylation and TGF-β reporter; SCG10 Ser50 in vitro kinase assay with inhibitor/RNAi and xenograft; SH3RF2 ubiquitination/stabilization assays","pmids":["23934187","23893240","24130170"],"confidence":"High","gaps":["Switch governing kinase-dependent vs independent Smad regulation undefined","SH3RF2 stabilization mechanism single-lab"]},{"year":2015,"claim":"Consolidated PAK4's dual catalytic/non-catalytic adhesion and polarity functions and provided the first structural view of the catalytic domain.","evidence":"Kinase-dead and Cdc42-binding mutant rescue with RhoU stabilization and ubiquitination assays; Par6B Ser143 kinase assay; junction localization and centrosome reorientation; αvβ3-PAK4 senescence in GBM; in cellulo crystallography of PAK4-Inka1","pmids":["26598620","25662318","26068882","26297735","26607847"],"confidence":"High","gaps":["Integration of kinase-dependent and RhoU-stabilizing roles in single cells unclear","Tissue-specificity of PAK4-driven senescence escape mechanistically incomplete"]},{"year":2016,"claim":"Established PAK4 as a methylation-regulated suppressor of p53 and amplifier of Wnt/β-catenin transcription, linking it to metabolic reprogramming.","evidence":"In vitro methylation, ChIP, β-catenin Co-IP and reporter assays; p53 Ser215 in vitro kinase assay and reporter; G6PD interaction and Mdm2/p53 ubiquitination assays","pmids":["26841865","27496712","28542136"],"confidence":"High","gaps":["SETD6 methylation site not yet mapped at this stage","Direct vs indirect p53 destabilization mechanisms overlap unresolved"]},{"year":2018,"claim":"Resolved the full-length PAK4-CDC42 architecture and expanded transcriptional/signaling substrates (CEBPB) and upstream activators (VIP/secretin via EPAC/PKA), plus ERα corepression.","evidence":"X-ray crystallography and SAXS with kinase assays; CEBPB Thr235 phosphorylation and CLDN4 promoter assays; EPAC/PKA pharmacology with PAK4 and Na+,K+-ATPase activity; ERα Co-IP, nuclear co-translocation and metastasis model","pmids":["29295922","30808546","30520694","30177834"],"confidence":"High","gaps":["How distinct cAMP effectors converge on PAK4 activation unclear","ERα corepression Medium-confidence single-lab"]},{"year":2019,"claim":"Defined a coherent PAK4 program antagonizing growth arrest/senescence (RELB, fumarase, p21) while extending substrates into EMT (Slug) and neuroprotection (CRTC1).","evidence":"RELB Ser151 phospho-mutagenesis, DNA-binding and transgenic mouse; fumarase Ser46 kinase assay, 14-3-3 Co-IP and p21 ChIP; Slug phosphorylation with miR-193a-3p; CRTC1 Ser215 phospho-mutant rescue in rodent PD models; podosome-ring kinase requirement with superresolution","pmids":["31399573","30683654","30685413","27903866","31825823"],"confidence":"High","gaps":["Slug phosphorylation site not mapped","Tissue-specific switching between pro-survival and neuroprotective outputs unexplained"]},{"year":2020,"claim":"Demonstrated PAK4's roles in the tumor microenvironment and its regulation by an upstream kinase, integrating transcriptomic reprogramming with metastatic and proliferative signaling.","evidence":"Endothelial PAK4 knockout with MEF2D/ZEB1/SLUG and adhesion-molecule analysis and T-cell infiltration in GBM models; SETD6 K473 methylation mutagenesis with β-catenin/paxillin readouts; CDK15-PAK4 Ser291 kinase assay with KO mouse and xenograft models","pmids":["35121889","33051544","34262144"],"confidence":"High","gaps":["Endothelial transcriptome reprogramming mechanism downstream of PAK4 incompletely mapped","Interplay between K473 methylation and S291 phosphorylation in activity control untested"]},{"year":null,"claim":"How the diverse upstream inputs (GTPases, growth factors, cAMP effectors, methylation, S291 phosphorylation) are integrated to direct PAK4 toward specific subcellular pools and substrate sets remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model linking activation mode to substrate selection","Substrates for mitotic spindle and podosome functions unidentified","Relative contribution of kinase-dependent vs scaffolding functions in vivo undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,8,15,16,21,24,29,36,37]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,2,15,21,29,37]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[27,33]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[20,23,7]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[16,28,45]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[16,23]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[4,10,40]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[15,25]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,5,16,43]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[16,28,29,36,37]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,7]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[18,19]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[6,12]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[4,21,41,43]}],"complexes":[],"partners":["CDC42","LIMK1","GEF-H1","PXN","CTNNB1","SMAD2","GAB1","SETD6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O96013","full_name":"Serine/threonine-protein kinase PAK 4","aliases":["p21-activated kinase 4","PAK-4"],"length_aa":591,"mass_kda":64.1,"function":"Serine/threonine-protein kinase that plays a role in a variety of different signaling pathways including cytoskeleton regulation, cell adhesion turnover, cell migration, growth, proliferation or cell survival (PubMed:26598620). Activation by various effectors including growth factor receptors or active CDC42 and RAC1 results in a conformational change and a subsequent autophosphorylation on several serine and/or threonine residues. Phosphorylates and inactivates the protein phosphatase SSH1, leading to increased inhibitory phosphorylation of the actin binding/depolymerizing factor cofilin. Decreased cofilin activity may lead to stabilization of actin filaments. Phosphorylates LIMK1, a kinase that also inhibits the activity of cofilin. Phosphorylates integrin beta5/ITGB5 and thus regulates cell motility. Phosphorylates ARHGEF2 and activates the downstream target RHOA that plays a role in the regulation of assembly of focal adhesions and actin stress fibers. Stimulates cell survival by phosphorylating the BCL2 antagonist of cell death BAD. Alternatively, inhibits apoptosis by preventing caspase-8 binding to death domain receptors in a kinase independent manner. Plays a role in cell-cycle progression by controlling levels of the cell-cycle regulatory protein CDKN1A and by phosphorylating RAN. Promotes kinase-independent stabilization of RHOU, thereby contributing to focal adhesion disassembly during cell migration (PubMed:26598620)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/O96013/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PAK4","classification":"Not Classified","n_dependent_lines":16,"n_total_lines":1208,"dependency_fraction":0.013245033112582781},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000130669","cell_line_id":"CID001230","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"centrosome","grade":2},{"compartment":"cell_contact","grade":1}],"interactors":[{"gene":"YWHAE","stoichiometry":0.2},{"gene":"DYNC1H1","stoichiometry":0.2},{"gene":"RBM25","stoichiometry":0.2},{"gene":"SUB1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001230","total_profiled":1310},"omim":[{"mim_id":"620426","title":"INKA BOX ACTIN REGULATOR 1; INKA1","url":"https://www.omim.org/entry/620426"},{"mim_id":"620403","title":"INKA-BOX ACTIN REGULATOR 2; INKA2","url":"https://www.omim.org/entry/620403"},{"mim_id":"620101","title":"RAS HOMOLOG FAMILY, MEMBER V; RHOV","url":"https://www.omim.org/entry/620101"},{"mim_id":"618441","title":"ADHESION G PROTEIN-COUPLED RECEPTOR G3; ADGRG3","url":"https://www.omim.org/entry/618441"},{"mim_id":"608110","title":"p21 PROTEIN-ACTIVATED KINASE 6; PAK6","url":"https://www.omim.org/entry/608110"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"},{"location":"Cell Junctions","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PAK4"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O96013","domains":[{"cath_id":"3.30.200.20","chopping":"301-395","consensus_level":"high","plddt":93.5487,"start":301,"end":395},{"cath_id":"1.10.510.10","chopping":"400-588","consensus_level":"high","plddt":95.6746,"start":400,"end":588}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O96013","model_url":"https://alphafold.ebi.ac.uk/files/AF-O96013-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O96013-F1-predicted_aligned_error_v6.png","plddt_mean":70.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PAK4","jax_strain_url":"https://www.jax.org/strain/search?query=PAK4"},"sequence":{"accession":"O96013","fasta_url":"https://rest.uniprot.org/uniprotkb/O96013.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O96013/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O96013"}},"corpus_meta":[{"pmid":"9822598","id":"PMC_9822598","title":"PAK4, a novel effector for Cdc42Hs, is implicated in the reorganization of the actin cytoskeleton and in the formation of filopodia.","date":"1998","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9822598","citation_count":309,"is_preprint":false},{"pmid":"11668177","id":"PMC_11668177","title":"Requirement for PAK4 in the anchorage-independent growth of human cancer cell lines.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11668177","citation_count":234,"is_preprint":false},{"pmid":"11413130","id":"PMC_11413130","title":"Cytoskeletal changes regulated by the PAK4 serine/threonine kinase are mediated by LIM kinase 1 and cofilin.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11413130","citation_count":221,"is_preprint":false},{"pmid":"11278822","id":"PMC_11278822","title":"The serine/threonine kinase PAK4 prevents caspase activation and protects cells from apoptosis.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11278822","citation_count":186,"is_preprint":false},{"pmid":"18319301","id":"PMC_18319301","title":"Cdc42- and Rac1-mediated endothelial lumen formation requires Pak2, Pak4 and Par3, and PKC-dependent signaling.","date":"2008","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/18319301","citation_count":164,"is_preprint":false},{"pmid":"11313478","id":"PMC_11313478","title":"Activated PAK4 regulates cell adhesion and anchorage-independent growth.","date":"2001","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/11313478","citation_count":153,"is_preprint":false},{"pmid":"15827085","id":"PMC_15827085","title":"PAK4 mediates morphological changes through the regulation of GEF-H1.","date":"2005","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/15827085","citation_count":143,"is_preprint":false},{"pmid":"14517283","id":"PMC_14517283","title":"PAK4 kinase is essential for embryonic viability and for proper neuronal development.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/14517283","citation_count":131,"is_preprint":false},{"pmid":"34368780","id":"PMC_34368780","title":"PAK4 inhibition improves PD-1 blockade immunotherapy.","date":"2019","source":"Nature cancer","url":"https://pubmed.ncbi.nlm.nih.gov/34368780","citation_count":127,"is_preprint":false},{"pmid":"27390344","id":"PMC_27390344","title":"Dual and Specific Inhibition of NAMPT and PAK4 By KPT-9274 Decreases Kidney Cancer Growth.","date":"2016","source":"Molecular cancer therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/27390344","citation_count":126,"is_preprint":false},{"pmid":"18424072","id":"PMC_18424072","title":"A PAK4-LIMK1 pathway drives prostate cancer cell migration downstream of HGF.","date":"2008","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/18424072","citation_count":123,"is_preprint":false},{"pmid":"22173096","id":"PMC_22173096","title":"Nucleo-cytoplasmic shuttling of PAK4 modulates β-catenin intracellular translocation and signaling.","date":"2011","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/22173096","citation_count":121,"is_preprint":false},{"pmid":"18644984","id":"PMC_18644984","title":"The pak4 protein kinase plays a key role in cell survival and tumorigenesis in athymic mice.","date":"2008","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/18644984","citation_count":117,"is_preprint":false},{"pmid":"35121889","id":"PMC_35121889","title":"Targeting PAK4 to reprogram the vascular microenvironment and improve CAR-T immunotherapy for glioblastoma.","date":"2020","source":"Nature 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Co-expression with constitutively active Cdc42HsV12 redistributed PAK4 to the brefeldin A-sensitive Golgi compartment and induced filopodia and actin polymerization in a manner dependent on PAK4 kinase activity.\",\n      \"method\": \"Co-expression, GBD interaction assays, brefeldin A-sensitive Golgi localization experiments, kinase-dead mutant analysis, immunofluorescence\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal interaction assays, kinase-dead mutagenesis, localization experiments; foundational study replicated across multiple subsequent labs\",\n      \"pmids\": [\"9822598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Serine 474 in the PAK4 kinase domain was identified as the autophosphorylation site in vivo. Mutation S474E produces constitutively active PAK4, and phospho-S474-specific antibodies detect activated PAK4 on the Golgi membrane when PAK4 is co-expressed with activated Cdc42. A kinase-inactive mutant (K350A,K351A) blocked Ras-driven transformation.\",\n      \"method\": \"Site-directed mutagenesis, phospho-specific antibody, immunofluorescence, NIH3T3 transformation assay, HCT116 anchorage-independent growth assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — mutagenesis identifying autophosphorylation site, phospho-specific antibody validation, functional rescue experiments; widely replicated\",\n      \"pmids\": [\"11668177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAK4 interacts specifically with LIM kinase 1 (LIMK1) and phosphorylates it more strongly than PAK1 does. Activated PAK4 stimulates LIMK1's ability to phosphorylate cofilin, and dominant-negative LIMK1 and a phosphorylation-resistant cofilin mutant inhibit PAK4-induced cytoskeletal and cell shape changes.\",\n      \"method\": \"Binding assays, immune complex kinase assays, dominant-negative mutant rescue, immunofluorescence in C2C12 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro kinase assay, binding assay, dominant-negative epistasis; independently replicated in multiple subsequent studies\",\n      \"pmids\": [\"11413130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PAK4 protects cells from apoptosis: expression of wild-type or constitutively active PAK4 delays apoptosis in response to TNF-α, UV irradiation, and serum starvation. PAK4 expression increases phosphorylation of the proapoptotic protein Bad and inhibits caspase activation.\",\n      \"method\": \"Overexpression of WT and constitutively active PAK4, apoptosis assays (TNF-α, UV, serum starvation), Bad phosphorylation assay, caspase activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal apoptosis stimuli, Bad phosphorylation readout, caspase assay; replicated across labs\",\n      \"pmids\": [\"11278822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Activated PAK4 dissolves actin stress fibers and focal adhesions, impairs cell spreading on fibronectin, and confers anchorage independence (soft agar colony formation). Dominant-negative PAK4 mutants inhibit focus formation by oncogenic Dbl, establishing PAK4 as a transforming kinase downstream of Rho GTPase exchange factors.\",\n      \"method\": \"Constitutively active PAK4 mutant expression, fibronectin adhesion assay, soft agar colony assay, dominant-negative inhibition of Dbl-induced focus formation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple functional assays, dominant-negative epistasis, replicated by subsequent studies\",\n      \"pmids\": [\"11313478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PAK4 is activated by HGF in epithelial (MDCK) cells downstream of PI3K; LY294002 (PI3K inhibitor) blocks HGF-induced PAK4 kinase activation and relocalization to the cell periphery. The isolated C-terminal kinase domain can induce cell rounding in the presence of LY294002, indicating the N-terminal region acts as a negative regulator of PAK4 activity.\",\n      \"method\": \"HGF stimulation, LY294002 PI3K inhibitor, PAK4 kinase activity assay, truncation mutant analysis, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase activity assay, PI3K inhibitor, domain truncation experiments, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"12244132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PAK4 is essential for embryonic viability: PAK4 knockout mice die by embryonic day 11.5 with defects in heart development, neuronal differentiation and migration, and neural tube folding, demonstrating an essential in vivo role for PAK4 in cytoskeletal regulation and cell/ECM adhesion during development.\",\n      \"method\": \"Gene targeting (PAK4 knockout mouse), histological and morphological analysis of PAK4-null embryos\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic knockout with defined developmental phenotypes in mice\",\n      \"pmids\": [\"14517283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PAK4 inhibits the activation of initiator caspase 8 downstream of death domain-containing receptors (TNF receptor, Fas receptor), independently of its kinase activity, potentially by inhibiting caspase 8 recruitment to death domain receptors. This is distinct from PAK4's kinase-dependent phosphorylation of Bad.\",\n      \"method\": \"PAK4 overexpression, kinase-dead mutant, caspase 8 activation assay, TNF/Fas receptor stimulation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase-dead mutant used to distinguish mechanism, single lab; proposed caspase 8 recruitment inhibition not directly shown\",\n      \"pmids\": [\"14560027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PAK4 mediates morphological changes through association with the Rho-family GEF, GEF-H1, via a novel GEF-H1 interaction domain (GID) in PAK4. PAK4 phosphorylates GEF-H1 at Ser810 to block stress fiber formation and promote lamellipodia. PAK4 phosphorylation of MT-bound GEF-H1 releases it into the cytoplasm, coinciding with stress fiber dissolution.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, in vitro phosphorylation assay, immunofluorescence, microtubule association assay in NIH-3T3 cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, domain mapping, in vitro phosphorylation, functional consequences shown; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"15827085\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Activated PAK4 induces premature senescence in primary fibroblasts via a pathway requiring ERK MAPK and the cell cycle inhibitors p16(INK4) and p19(ARF). PAK4 expression levels are upregulated in response to senescence-promoting stimuli.\",\n      \"method\": \"Activated PAK4 expression in primary fibroblasts, senescence assay, ERK inhibitor treatment, p16/p19 pathway analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic pathway analysis in primary cells, pharmacological inhibition of ERK, single lab\",\n      \"pmids\": [\"16227603\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PAK4 regulates podosome size and number in primary human macrophages: shRNA knockdown or PAK4 truncation mutants reduce podosome numbers, kinase-active PAK4 enhances podosome size, and kinase-inactive PAK4 reduces podosome size, demonstrating a kinase activity-dependent role in localized actin dynamics at podosomes.\",\n      \"method\": \"shRNA knockdown, PAK4 truncation and kinase mutant expression, immunofluorescence, actin structure analysis in primary human macrophages\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase-dead and truncation mutant analysis with quantitative podosome readout; single lab\",\n      \"pmids\": [\"16897755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PAK4 binds to and phosphorylates LIMK1 in an HGF-dependent manner in prostate cancer cells. PAK4-LIMK1 direct interaction was visualized in living cells by FRET-FLIM, concentrated in peripheral foci. Variations in PAK4 expression change cofilin phosphorylation levels, correlated with LIMK1 activity and cell migration speed; PAK4 and LIMK1 act synergistically to increase migration.\",\n      \"method\": \"Co-immunoprecipitation, FRET-FLIM imaging, cofilin phosphorylation assays, PAK4 siRNA knockdown, cell migration assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — FRET-FLIM for direct cellular interaction, kinase assay, RNAi with quantitative phenotype; independently replicated\",\n      \"pmids\": [\"18424072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RNAi or dominant-negative suppression of PAK4 markedly inhibits endothelial cell lumen and tube formation in 3D collagen matrices. PAK4 phosphorylation correlates with lumenogenesis in a PKC-dependent manner, placing PAK4 downstream of Cdc42/Rac1 and PKC in vascular morphogenesis.\",\n      \"method\": \"RNAi knockdown, dominant-negative expression, 3D collagen matrix lumen formation assay, PKC inhibitor treatment\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi and dominant-negative with defined morphogenic phenotype, PKC epistasis; single lab\",\n      \"pmids\": [\"18319301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PAK4 is a novel Gab1-interacting protein; upon HGF stimulation, Gab1 and PAK4 associate and colocalize at lamellipodia. The interaction is mediated through the GEF-interacting domain of PAK4 and a novel Gab1 region, requires Gab1 phosphorylation but not PAK4 kinase activity. Gab1-Pak4 association is required for HGF-induced cell dispersal, migration, and invasion.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, confocal colocalization, Gab1 mutant unable to recruit Pak4, cell dispersal and invasion assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, domain mapping, Gab1 interaction-deficient mutant, defined cellular phenotype; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"19289496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DGCR6L is a novel PAK4-binding protein, confirmed by GST pulldown and co-immunoprecipitation. L115 of DGCR6L is critical for binding to the C-terminus (aa 466–572) of PAK4. DGCR6L is required for formation of a PAK4-DGCR6L-β-actin complex and enhances phosphorylation of LIMK1 and cofilin in a dose-dependent manner to promote gastric cancer cell migration.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, co-immunoprecipitation, site-directed mutagenesis (L115V), LIMK1/cofilin phosphorylation assay, migration assay\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — GST pulldown and Co-IP for interaction, mutagenesis identifying critical residue, downstream phosphorylation readout; single lab\",\n      \"pmids\": [\"19778628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PAK4 phosphorylates paxillin at serine 272, co-immunoprecipitates with paxillin, localizes to focal adhesions, and regulates RhoA activity via GEF-H1 to control actin cytoskeletal rearrangement and focal adhesion turnover. PAK4-depleted prostate cancer cells show increased focal adhesion size/number and reduced adhesion turnover rates.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, immunofluorescence localization to focal adhesions, PAK4 siRNA knockdown, RhoA activity assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — Co-IP, in vitro kinase assay identifying paxillin S272 as substrate, RhoA activity assay, localization; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"20406887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PAK4 is a nucleo-cytoplasmic shuttling protein with three nuclear export signals (NESs) and two nuclear localization signals (NLSs). It is exported via CRM-1-dependent pathway and imported in an importin α5-dependent manner. Nuclear PAK4 phosphorylates β-catenin at Ser675, promoting TCF/LEF transcriptional activity, stabilizing β-catenin by inhibiting its degradation, and associating with the TCF/LEF transcriptional complex.\",\n      \"method\": \"NLS/NES mutagenesis, CRM-1/importin α5 inhibition/knockdown, β-catenin phosphorylation assay, TCF/LEF reporter assay, ChIP assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis of localization signals, ChIP, phosphorylation assay, reporter assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"22173096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CDK5RAP3 (C53/LZAP) is a novel binding partner of PAK4 that enhances PAK4 kinase activity. siRNA-mediated knockdown of PAK4 in CDK5RAP3-overexpressing HCC cells reversed the enhanced cell invasiveness, demonstrating that PAK4 activity is required for CDK5RAP3-promoted metastasis.\",\n      \"method\": \"Co-immunoprecipitation, PAK4 kinase activity assay, siRNA knockdown, invasion assay\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, kinase activity assay, RNAi epistasis; single lab\",\n      \"pmids\": [\"21385901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PAK4 levels peak transiently in early G1 phase of the cell cycle. PAK4 deletion increases p21 levels and is required for normal p21 degradation. Absence of PAK4 in serum-starved cells reduces the fraction of cells in G1 and increases G2/M cells, indicating PAK4 controls cell cycle progression partly by regulating p21 levels.\",\n      \"method\": \"Cell cycle synchronization, flow cytometry, PAK4 knockout cells, p21 protein level analysis\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — PAK4 knockout with defined cell cycle phenotype and p21 readout; single lab\",\n      \"pmids\": [\"21381077\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PAK4 is required for metaphase spindle positioning and anchoring. PAK4-depleted cells show defective astral microtubule networks, spindle miscentering, cortical membrane blebbing during prometaphase, and mislocalization of dynein/dynactin complex components at kinetochores and on astral MTs, resulting in prolonged metaphase-like arrest and eventual cohesion fatigue.\",\n      \"method\": \"PAK4 siRNA depletion, live cell imaging, immunofluorescence of spindle/kinetochore markers, dynein/dynactin localization analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi with defined mitotic phenotype and specific molecular readout of dynein/dynactin mislocalization; single lab\",\n      \"pmids\": [\"22450748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PAK4 interacts with Smad2/3 and modulates their phosphorylation via both kinase-dependent and kinase-independent mechanisms to attenuate Smad2/3 axis transactivation and TGF-β-mediated growth inhibition. PAK4 blocks TGF-β1-induced phosphorylation of Smad2 Ser465/467 independently of kinase activity, and phosphorylates Smad2 on Ser465 (promoting Smad2 degradation via ubiquitin-proteasome pathway) under HGF stimulation.\",\n      \"method\": \"Co-immunoprecipitation, kinase assay, kinase-dead mutant, TGF-β reporter assay, ubiquitin-proteasome pathway analysis, HGF stimulation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, kinase-dead mutant, multiple phospho-site readouts; single lab with multiple methods\",\n      \"pmids\": [\"23934187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PAK4 phosphorylates SCG10 (superior cervical ganglia 10) at serine 50 (Ser50). Phosphorylated SCG10 regulates microtubule dynamics to promote gastric cancer cell migration and invasion, and blocking PAK4 (by inhibitor LCH-7749944 or RNAi) inhibits Ser50 phosphorylation and cell invasion.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis (S50A), PAK4 inhibitor LCH-7749944, RNAi, cell invasion assay, xenograft mouse model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay with mutagenesis, pharmacological inhibition, RNAi, in vivo confirmation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23893240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SH3RF2 inhibits PAK4 ubiquitination and proteasomal degradation via physical interaction-mediated steric hindrance, thereby stabilizing PAK4 protein levels and promoting oncogenic signaling.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, proteasome inhibitor treatment, SH3RF2 overexpression/ablation\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ubiquitination assay; single lab with two orthogonal methods\",\n      \"pmids\": [\"24130170\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PAK4 drives cell adhesion turnover in a kinase-independent manner by stabilizing RhoU protein levels. PAK4 protects RhoU from ubiquitination by the Rab40A-Cullin 5 E3 ligase complex. RhoU overexpression rescues the PAK4-depletion adhesion phenotype, and loss of RhoU reduces adhesion turnover and migration.\",\n      \"method\": \"PAK4 knockdown, kinase-dead PAK4 rescue, Cdc42-binding mutant rescue, RhoU overexpression rescue, ubiquitination assay, Rab40A-Cullin 5 complex identification\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — kinase-dead and Cdc42-binding mutant rescue experiments, ubiquitination assay, E3 ligase identification, RhoU rescue epistasis; single lab with multiple orthogonal rigorous methods\",\n      \"pmids\": [\"26598620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PAK4 phosphorylates Par6B at Ser143, blocking Par6B's interaction with Cdc42, providing a mechanism to control Par6B subcellular localization and interactions in epithelial polarity establishment. Both PAK4 and Par6B are required for assembly of apical junctions in human bronchial epithelial cells.\",\n      \"method\": \"In vitro kinase assay, Co-immunoprecipitation, site-directed mutagenesis (Par6B S143), RNAi knockdown, apical junction assembly assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay, mutagenesis, Co-IP; single lab\",\n      \"pmids\": [\"25662318\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PAK4 localizes primarily to cell-cell junctions (not focal adhesions or leading edge in migrating cells). PAK4 depletion or kinase inhibition (PF-3758309) does not affect collective migration but causes defects in centrosome reorientation after wounding. PAK4 phosphorylates β-catenin at Ser-675 predominantly at cell-cell junctions.\",\n      \"method\": \"Immunofluorescence localization, PAK4 siRNA knockdown, PF-3758309 inhibitor, wound-healing centrosome reorientation assay, β-catenin phosphorylation assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization imaging, kinase inhibitor, centrosome reorientation readout; single lab\",\n      \"pmids\": [\"26068882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Integrin αvβ3 recruits and activates PAK4 to allow glioblastoma cells to evade oncogene-induced senescence. Targeting either αvβ3 or PAK4 triggers a p21-dependent, p53-independent senescence phenotype in GBM cells specifically; this dependence is tissue-specific (not found in epithelial cancers) and other PAK family members are not required.\",\n      \"method\": \"αvβ3 integrin targeting, PAK4 knockdown, senescence assay, p21/p53 genetic analysis in GBM vs. epithelial cancer cells\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown of both αvβ3 and PAK4, p21-dependent senescence assay, tissue-specificity comparison; single lab\",\n      \"pmids\": [\"26297735\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The crystal structure of human PAK4 catalytic domain in complex with its endogenous inhibitor Inka1 was determined at 2.95 Å resolution using in cellulo crystals from single mammalian cells. The structure reveals details of how PAK4 binds cellular ATP and Inka1 at the active site.\",\n      \"method\": \"In cellulo X-ray crystallography at 2.95 Å resolution, crystal growth in mammalian cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure with functional validation of inhibitor binding\",\n      \"pmids\": [\"26607847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SETD6 methyltransferase methylates PAK4 both in vitro and at chromatin in cells. SETD6 depletion hinders activation of Wnt/β-catenin target genes. In the presence of SETD6, physical interaction between PAK4 and β-catenin is dramatically increased, leading to enhanced transcription of β-catenin target genes.\",\n      \"method\": \"In vitro methylation assay, ChIP, SETD6 knockdown, β-catenin co-immunoprecipitation, TCF/LEF reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro methylation assay, ChIP, Co-IP, reporter assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26841865\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PAK4 directly phosphorylates p53 at serine 215, attenuating p53 transcriptional transactivation activity and inhibiting p53-mediated suppression of HCC cell invasion.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis (S215 of p53), p53 transcriptional reporter assay, PAK4 overexpression/silencing, invasion assay in HCC cells\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay identifying p53 S215 as substrate, functional reporter assay; single lab\",\n      \"pmids\": [\"27496712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PAK4 promotes G6PD activity and glucose reprogramming by interacting with G6PD and enhancing Mdm2-mediated p53 ubiquitination and degradation (reducing p53-mediated suppression of G6PD), leading to increased NADPH production and lipid biosynthesis in colon cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, G6PD activity assay, p53 ubiquitination assay, Mdm2 interaction analysis, PAK4 knockdown/overexpression\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, enzymatic activity assay, ubiquitination assay; single lab with multiple methods\",\n      \"pmids\": [\"28542136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Zic2 transcription factor directly binds the PAK4 promoter and activates PAK4 expression, as demonstrated by ChIP and luciferase assays. PAK4 interference attenuates Zic2-mediated cell growth via the Raf/MEK/ERK pathway.\",\n      \"method\": \"ChIP assay, luciferase reporter assay, PAK4 siRNA knockdown, Raf/MEK/ERK pathway analysis\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and luciferase assay for promoter binding, pathway inhibition; single lab\",\n      \"pmids\": [\"28577975\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PAK4 interacts specifically with p85α (the regulatory subunit of PI3K) in pancreatic cancer cells; PAK4-deficient cells exhibit reduced Akt phosphorylation downstream of HGF, implicating a novel role for PAK4 within the PI3K/Akt pathway.\",\n      \"method\": \"Co-immunoprecipitation (PAK4-p85α), PAK4 knockdown, Akt phosphorylation assay, HGF stimulation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating specific interaction, RNAi with Akt phosphorylation readout; single lab\",\n      \"pmids\": [\"28205613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"X-ray crystallography and solution scattering revealed that full-length PAK4 heterodimer with CDC42 adopts a compact organization. In addition to the canonical CRIB domain–CDC42 interaction, unexpected contacts involve the PAK4 kinase C-lobe, CDC42, and the PAK4 polybasic region. These additional interactions modulate kinase activity and increase CDC42 binding affinity for full-length PAK4 compared to CRIB domain alone.\",\n      \"method\": \"X-ray crystallography, small angle X-ray scattering (SAXS), kinase activity assay, binding affinity measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus SAXS plus functional kinase activity assay; rigorous multi-method structural study\",\n      \"pmids\": [\"29295922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PAK4 phosphorylates CEBPB at Thr-235 to upregulate CLDN4 (claudin-4) expression, promoting breast cancer cell migration and invasion via a PAK4-CEBPB-CLDN4 axis.\",\n      \"method\": \"PAK4 knockdown, CEBPB phosphorylation assay, CLDN4 promoter ChIP/luciferase, rescue experiments in MDA-MB-231 and ZR-75-30 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphorylation assay, promoter binding assay, rescue epistasis; single lab\",\n      \"pmids\": [\"30808546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"VIP activates PAK4 via EPAC-dependent cAMP signaling whereas secretin activates PAK4 via PKA-dependent signaling in pancreatic acinar cells. PAK4 activation is required for VIP/secretin-induced Na+,K+-ATPase activation, which mediates pancreatic fluid secretion.\",\n      \"method\": \"EPAC inhibitors (ESI-09, HJC0197), PKA inhibitors (KT-5720, PKI), PAK4 kinase activity assay, Na+,K+-ATPase activity assay, EPAC agonist\",\n      \"journal\": \"American journal of physiology. Gastrointestinal and liver physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological pathway dissection, PAK4 kinase activity assay, downstream functional readout; single lab\",\n      \"pmids\": [\"30520694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAK4 phosphorylates RELB at Ser151, which is critical for RELB-DNA interaction and transcriptional activity. A PAK4-RELB-C/EBPβ axis controls senescence-like growth arrest in breast cancer cells, and PAK4 overexpression abrogates H-RAS-V12-induced senescence in untransformed mammary epithelial cells.\",\n      \"method\": \"PAK4 overexpression in untransformed MCF10A, PAK4 depletion in breast cancer lines, RELB phosphorylation assay, RELB-DNA binding assay (EMSA or reporter), C/EBPβ expression analysis, MMTV-PAK4 transgenic mouse model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — phosphorylation site mutagenesis (RELB-S151), DNA-binding assay, in vivo mouse model, multiple cellular systems; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"31399573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAK4 directly phosphorylates fumarase (FH) at Ser46 in non-small cell lung cancer cells. PAK4-phosphorylated FH binds to 14-3-3, causing cytosolic detention of FH and preventing formation of the FH/CSL/p53 complex at the p21 promoter, thereby blocking TGF-β-induced p21 transcription and cell growth arrest.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis (FH S46), 14-3-3 co-immunoprecipitation, ChIP assay, p21 reporter assay, PAK4 knockdown/overexpression\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay, mutagenesis, Co-IP, ChIP, reporter assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"30683654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAK4 directly phosphorylates Slug (SNAI2), leading to Slug stabilization and pro-malignant activity in NSCLC cells. miR-193a-3p targeting of PAK4 reduces downstream p-Slug and L1CAM expression, suppressing NSCLC migration and invasion.\",\n      \"method\": \"PAK4 knockdown/overexpression, Slug phosphorylation assay, miR-193a-3p overexpression, L1CAM expression analysis, migration/invasion assay\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphorylation assay, RNAi epistasis; single lab\",\n      \"pmids\": [\"30685413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAK4 phosphorylates CRTC1 (CREB-regulated transcription coactivator 1) at S215. Constitutively active PAK4 protects dopaminergic neurons in rodent PD models, and this neuroprotective effect is mediated by CRTC1-S215 phosphorylation driving expression of CREB targets Bcl-2, BDNF, and PGC-1α; non-phosphorylatable CRTC1(S215A) abrogates caPAK4 neuroprotection.\",\n      \"method\": \"Constitutively active PAK4 (caPAK4S445N/S474E) viral expression, CRTC1 phosphorylation assay, S215A mutant rescue, Bcl-2/BDNF/PGC-1α expression, 6-OHDA and α-synuclein rat PD models\",\n      \"journal\": \"Science translational medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — phosphosite mutagenesis, in vivo rodent model, multiple downstream target validation; single lab but rigorous multi-method in vivo study\",\n      \"pmids\": [\"27903866\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAK4 kinase activity is essential for podosome ring formation in myeloid cells. PAK4 localizes specifically within the podosome ring by superresolution imaging. PAK4 inhibition reduces podosome formation and induces focal adhesion formation. PAK4 depletion perturbs phospho-Akt signaling at podosomes, placing PAK4 kinase activity at the podosome ring:core interface intersecting the Akt pathway.\",\n      \"method\": \"PAK4 inhibitor (PF-3758309), PAK4 siRNA knockdown, kinase-dead PAK4 rescue, superresolution (STORM/STED) imaging, podosome assay, phospho-Akt analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — kinase-dead rescue, superresolution localization, pharmacological and genetic inhibition with defined phenotype; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"31825823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PAK4 reprograms tumor endothelial cell transcriptome via a MEF2D/ZEB1- and SLUG-mediated mechanism, downregulating claudin-14 and VCAM-1 expression, thereby enhancing vessel permeability and reducing T cell adhesion to the endothelium. PAK4 knockout in ECs reduces vascular abnormalities and improves T cell infiltration.\",\n      \"method\": \"PAK4 knockout in ECs (genetic), kinome-wide screening, MEF2D/ZEB1/SLUG pathway analysis, claudin-14 and VCAM-1 expression assay, T cell adhesion assay, GBM mouse models\",\n      \"journal\": \"Nature cancer\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic PAK4 KO with defined molecular mechanism (MEF2D/ZEB1/SLUG axis), downstream adhesion protein readout, T cell infiltration phenotype in vivo; single lab but multiple orthogonal methods and in vivo validation\",\n      \"pmids\": [\"35121889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SETD6 methylates PAK4 specifically at lysine 473 (K473). K473 methylation activates β-catenin transcriptional activity, attenuates paxillin localization to focal adhesions, and reduces cell adhesion, migration, and invasion.\",\n      \"method\": \"In vitro methylation assay, site-directed mutagenesis (K473), β-catenin reporter assay, paxillin localization by immunofluorescence, adhesion/migration/invasion assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro methylation assay, mutagenesis identifying K473, functional reporter and adhesion assays; single lab\",\n      \"pmids\": [\"33051544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CDK15 binds PAK4 and phosphorylates PAK4 at S291. Phosphorylation of PAK4 at S291 promotes CRC cell proliferation and anchorage-independent growth through β-catenin/c-Myc and MEK/ERK signaling pathways. PAK4 inhibition reverses the tumorigenic effects of CDK15 in CRC cells.\",\n      \"method\": \"Co-immunoprecipitation (CDK15-PAK4), in vitro/in cellulo kinase assay (S291 phosphorylation), site-directed mutagenesis, β-catenin/MEK-ERK pathway analysis, CDK15 KO mouse AOM/DSS model, CDX and PDX xenograft models\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — kinase assay with mutagenesis identifying S291, in vivo mouse genetic KO plus xenograft models, multiple orthogonal approaches; single lab\",\n      \"pmids\": [\"34262144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PAK4 N-terminal domain interacts with ribonucleoprotein (RNP) complexes, and active PAK4 affects cap-independent (IRES-mediated) translation in vivo; the N-terminal domain contains sequences driving cytoplasmic localization and a nuclear export signal.\",\n      \"method\": \"Affinity chromatography of N-terminal domain, IRES-reporter assay in cells, nuclear/cytoplasmic fractionation\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — affinity chromatography and reporter assay; single lab, no direct confirmation of RNP substrate\",\n      \"pmids\": [\"20578242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Nuclear PAK4 (nPAK4) acts as a repressor of ERα-mediated transactivation in an E2-dependent manner; PAK4 binds ERα and co-translocates with it from the cytoplasm to the nucleus upon E2 stimulation, and promotes bone metastasis by targeting the LIFR (bone metastasis suppressor) locus.\",\n      \"method\": \"Co-immunoprecipitation (PAK4-ERα), nuclear fractionation upon E2 stimulation, ERα reporter assay, LIFR expression analysis, in vitro invasion assay, in vivo metastasis model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP demonstrating ERα binding, nuclear co-translocation assay, functional in vivo metastasis model; single lab\",\n      \"pmids\": [\"30177834\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PAK4 is a Cdc42-activated serine/threonine kinase that localizes to the Golgi, cell-cell junctions, focal adhesions, and nucleus, where it phosphorylates a broad substrate repertoire—including LIMK1 (→cofilin), Bad, paxillin (S272), GEF-H1 (S810), β-catenin (S675), Smad2 (S465), SCG10 (S50), p53 (S215), Par6B (S143), fumarase (S46), RELB (S151), CRTC1 (S215), CEBPB (T235), and Slug—to regulate actin cytoskeleton dynamics, cell adhesion turnover, anti-apoptotic signaling, Wnt/β-catenin transcription, cell cycle progression (via p21), mitotic spindle anchoring, and vascular/neural morphogenesis; upstream activation by Cdc42, HGF/PI3K, PKA/EPAC, and CDK15 (phospho-S291), as well as SETD6-mediated methylation at K473, modulate PAK4 activity and nuclear distribution, while RhoU stabilization and kinase-independent Smad2/3 binding extend its non-catalytic functions.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PAK4 is a Cdc42-activated serine/threonine kinase that couples Rho-family GTPase signaling to actin cytoskeleton remodeling, cell adhesion turnover, anti-apoptotic signaling, and transcriptional control [#0, #4]. It was first defined as a Cdc42 effector whose GTPase-binding domain engages GTP-loaded Cdc42, redirecting PAK4 to the Golgi and driving filopodia and actin polymerization through its kinase activity [#0]; structural work later showed that full-length PAK4 forms a compact heterodimer with CDC42 in which kinase C-lobe and polybasic contacts beyond the canonical CRIB interface tune activity and binding affinity [#33], and that catalytic output is held in check by the endogenous inhibitor Inka1 [#27]. Activation requires autophosphorylation at Ser474, with the N-terminal region acting as a negative regulator that is relieved by HGF/PI3K signaling [#1, #5]. A core cytoskeletal program runs through PAK4 phosphorylation of LIMK1, which in turn phosphorylates cofilin to remodel actin and promote migration [#2, #11], and through phosphorylation of GEF-H1 (Ser810) and paxillin (Ser272) to control RhoA activity, stress fibers, and focal-adhesion turnover [#8, #15]. PAK4 also drives adhesion turnover kinase-independently by stabilizing RhoU against Rab40A–Cullin5-mediated degradation [#23] and localizes to cell-cell junctions, podosomes, and the mitotic spindle, where it is required for astral microtubule organization and dynein/dynactin positioning [#19, #25, #40]. As a nucleo-cytoplasmic shuttling protein, PAK4 enters the nucleus to phosphorylate \\u03b2-catenin (Ser675) and promote TCF/LEF transcription, an axis amplified by SETD6-mediated methylation at K473 [#16, #28, #42]. PAK4 broadly suppresses tumor-suppressor and growth-arrest programs, phosphorylating p53 (Ser215), Smad2 (Ser465), fumarase (Ser46), and RELB (Ser151), and regulating p21 to control cell-cycle progression and senescence [#18, #20, #29, #36, #37]. PAK4 is essential for mouse embryonic development, with knockouts dying by E11.5 from cardiac, neuronal, and neural-tube defects [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established PAK4's founding identity by answering whether it is a Cdc42 effector and how GTPase binding reroutes it to drive actin remodeling.\",\n      \"evidence\": \"GBD interaction assays with activated Cdc42Hs, Golgi localization and kinase-dead mutant analysis by immunofluorescence\",\n      \"pmids\": [\"9822598\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct cytoskeletal substrates not yet identified\", \"Mechanism linking Golgi localization to filopodia formation unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Defined how PAK4 catalytic activity is switched on and showed its kinase function is required for oncogenic transformation.\",\n      \"evidence\": \"Site-directed mutagenesis identifying Ser474 autophosphorylation, phospho-specific antibody, NIH3T3 transformation and anchorage-independent growth assays\",\n      \"pmids\": [\"11668177\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream kinases/regulators of activation not defined\", \"Relationship of autophosphorylation to N-terminal autoinhibition unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Connected PAK4 to the actin cytoskeleton mechanistically and to cell survival, defining its first substrate (LIMK1) and first anti-apoptotic readout (Bad).\",\n      \"evidence\": \"In vitro kinase and binding assays, dominant-negative cofilin/LIMK1 rescue, apoptosis assays with TNF-\\u03b1/UV/serum starvation and Bad phosphorylation/caspase readouts\",\n      \"pmids\": [\"11413130\", \"11278822\", \"11313478\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PAK4 phosphorylates Bad directly not established\", \"Quantitative contribution of LIMK1 vs other effectors to cytoskeletal change unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Placed PAK4 in a growth-factor signaling cascade and revealed intramolecular autoinhibition by mapping HGF/PI3K-dependent activation and N-terminal repression.\",\n      \"evidence\": \"HGF stimulation in MDCK cells, LY294002 PI3K inhibition, kinase activity assays, truncation mutant analysis\",\n      \"pmids\": [\"12244132\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical link between PI3K products and PAK4 not shown\", \"Identity of the relieving signal acting on the N-terminus undefined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated PAK4 is physiologically essential and separated its kinase-dependent from kinase-independent survival functions.\",\n      \"evidence\": \"PAK4 knockout mouse with developmental phenotyping; kinase-dead mutant analysis of caspase-8 inhibition\",\n      \"pmids\": [\"14517283\", \"14560027\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo embryonic phenotype not assigned to specific substrates\", \"Proposed caspase-8 recruitment inhibition not directly demonstrated\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Elucidated how PAK4 reorganizes actin architecture by identifying GEF-H1 as a substrate that links PAK4 to RhoA-dependent stress fiber regulation, while linking PAK4 to senescence control.\",\n      \"evidence\": \"Co-IP, domain mapping of the GID, in vitro phosphorylation of GEF-H1 Ser810, microtubule release assay; senescence assays with ERK inhibition and p16/p19 analysis\",\n      \"pmids\": [\"15827085\", \"16227603\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GEF-H1 Ser810 phospho-site role in vivo not tested\", \"Senescence pathway analysis single-lab and pharmacology-dependent\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Extended PAK4's cytoskeletal role to specialized adhesion structures by showing kinase-dependent control of podosomes.\",\n      \"evidence\": \"shRNA knockdown, kinase/truncation mutants and quantitative podosome imaging in primary human macrophages\",\n      \"pmids\": [\"16897755\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Podosome substrate(s) at the structure not identified\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Validated the PAK4-LIMK1-cofilin axis as a direct, spatially-resolved interaction driving cancer cell migration.\",\n      \"evidence\": \"FRET-FLIM live-cell imaging, Co-IP, cofilin phosphorylation and migration assays in prostate cancer cells\",\n      \"pmids\": [\"18424072\", \"18319301\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Vascular morphogenesis role (lumen formation) relies on dominant-negative/RNAi without substrate\", \"Spatial control of LIMK1 engagement at foci mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Expanded PAK4's adaptor/scaffolding repertoire by identifying kinase-independent interactions (Gab1, DGCR6L) that organize migration and invasion machinery.\",\n      \"evidence\": \"Co-IP, domain mapping, interaction-deficient mutants, LIMK1/cofilin phosphorylation and invasion assays\",\n      \"pmids\": [\"19289496\", \"19778628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"DGCR6L interaction Medium-confidence and single-lab\", \"How scaffolding integrates with catalytic LIMK1 activation unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined PAK4's role at focal adhesions by identifying paxillin Ser272 as a substrate coupled to RhoA/GEF-H1-mediated adhesion turnover.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay, focal-adhesion immunofluorescence, siRNA and RhoA activity assay in prostate cancer cells\",\n      \"pmids\": [\"20406887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Hierarchy of paxillin vs GEF-H1 phosphorylation in adhesion turnover unresolved\", \"N-terminal RNP/IRES-translation role (Low confidence) not corroborated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed nuclear PAK4 as a transcriptional regulator by mapping its shuttling signals and \\u03b2-catenin Ser675 phosphorylation, and identified upstream stabilizers/activators (CDK5RAP3) and cell-cycle control via p21.\",\n      \"evidence\": \"NLS/NES mutagenesis, CRM-1/importin-\\u03b15 manipulation, \\u03b2-catenin phosphorylation, TCF/LEF reporter and ChIP; Co-IP and kinase assays for CDK5RAP3; cell-cycle synchronization with p21 readout in knockout cells\",\n      \"pmids\": [\"22173096\", \"21385901\", \"21381077\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signals triggering nuclear import in physiological contexts not defined\", \"Mechanism of p21 degradation control by PAK4 unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified an unanticipated mitotic role by showing PAK4 is required for spindle anchoring and dynein/dynactin positioning.\",\n      \"evidence\": \"siRNA depletion, live imaging, kinetochore/astral MT immunofluorescence and dynein/dynactin localization analysis\",\n      \"pmids\": [\"22450748\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mitotic substrate(s) of PAK4 not identified\", \"Single-lab RNAi phenotype\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Broadened PAK4 substrate scope into TGF-\\u03b2/Smad signaling, microtubule-regulating SCG10, and protein-stability control, establishing dual kinase-dependent/independent regulation of tumor-suppressive pathways.\",\n      \"evidence\": \"Co-IP, kinase and kinase-dead assays, Smad2 Ser465 phosphorylation and TGF-\\u03b2 reporter; SCG10 Ser50 in vitro kinase assay with inhibitor/RNAi and xenograft; SH3RF2 ubiquitination/stabilization assays\",\n      \"pmids\": [\"23934187\", \"23893240\", \"24130170\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Switch governing kinase-dependent vs independent Smad regulation undefined\", \"SH3RF2 stabilization mechanism single-lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Consolidated PAK4's dual catalytic/non-catalytic adhesion and polarity functions and provided the first structural view of the catalytic domain.\",\n      \"evidence\": \"Kinase-dead and Cdc42-binding mutant rescue with RhoU stabilization and ubiquitination assays; Par6B Ser143 kinase assay; junction localization and centrosome reorientation; \\u03b1v\\u03b23-PAK4 senescence in GBM; in cellulo crystallography of PAK4-Inka1\",\n      \"pmids\": [\"26598620\", \"25662318\", \"26068882\", \"26297735\", \"26607847\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Integration of kinase-dependent and RhoU-stabilizing roles in single cells unclear\", \"Tissue-specificity of PAK4-driven senescence escape mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established PAK4 as a methylation-regulated suppressor of p53 and amplifier of Wnt/\\u03b2-catenin transcription, linking it to metabolic reprogramming.\",\n      \"evidence\": \"In vitro methylation, ChIP, \\u03b2-catenin Co-IP and reporter assays; p53 Ser215 in vitro kinase assay and reporter; G6PD interaction and Mdm2/p53 ubiquitination assays\",\n      \"pmids\": [\"26841865\", \"27496712\", \"28542136\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"SETD6 methylation site not yet mapped at this stage\", \"Direct vs indirect p53 destabilization mechanisms overlap unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Resolved the full-length PAK4-CDC42 architecture and expanded transcriptional/signaling substrates (CEBPB) and upstream activators (VIP/secretin via EPAC/PKA), plus ER\\u03b1 corepression.\",\n      \"evidence\": \"X-ray crystallography and SAXS with kinase assays; CEBPB Thr235 phosphorylation and CLDN4 promoter assays; EPAC/PKA pharmacology with PAK4 and Na+,K+-ATPase activity; ER\\u03b1 Co-IP, nuclear co-translocation and metastasis model\",\n      \"pmids\": [\"29295922\", \"30808546\", \"30520694\", \"30177834\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How distinct cAMP effectors converge on PAK4 activation unclear\", \"ER\\u03b1 corepression Medium-confidence single-lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a coherent PAK4 program antagonizing growth arrest/senescence (RELB, fumarase, p21) while extending substrates into EMT (Slug) and neuroprotection (CRTC1).\",\n      \"evidence\": \"RELB Ser151 phospho-mutagenesis, DNA-binding and transgenic mouse; fumarase Ser46 kinase assay, 14-3-3 Co-IP and p21 ChIP; Slug phosphorylation with miR-193a-3p; CRTC1 Ser215 phospho-mutant rescue in rodent PD models; podosome-ring kinase requirement with superresolution\",\n      \"pmids\": [\"31399573\", \"30683654\", \"30685413\", \"27903866\", \"31825823\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Slug phosphorylation site not mapped\", \"Tissue-specific switching between pro-survival and neuroprotective outputs unexplained\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated PAK4's roles in the tumor microenvironment and its regulation by an upstream kinase, integrating transcriptomic reprogramming with metastatic and proliferative signaling.\",\n      \"evidence\": \"Endothelial PAK4 knockout with MEF2D/ZEB1/SLUG and adhesion-molecule analysis and T-cell infiltration in GBM models; SETD6 K473 methylation mutagenesis with \\u03b2-catenin/paxillin readouts; CDK15-PAK4 Ser291 kinase assay with KO mouse and xenograft models\",\n      \"pmids\": [\"35121889\", \"33051544\", \"34262144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endothelial transcriptome reprogramming mechanism downstream of PAK4 incompletely mapped\", \"Interplay between K473 methylation and S291 phosphorylation in activity control untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the diverse upstream inputs (GTPases, growth factors, cAMP effectors, methylation, S291 phosphorylation) are integrated to direct PAK4 toward specific subcellular pools and substrate sets remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking activation mode to substrate selection\", \"Substrates for mitotic spindle and podosome functions unidentified\", \"Relative contribution of kinase-dependent vs scaffolding functions in vivo undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 8, 15, 16, 21, 24, 29, 36, 37]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 2, 15, 21, 29, 37]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [27, 33]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [20, 23, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [16, 28, 45]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [16, 23]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [4, 10, 40]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [15, 25]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 5, 16, 43]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [16, 28, 29, 36, 37]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 7]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [18, 19]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [6, 12]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [4, 21, 41, 43]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CDC42\", \"LIMK1\", \"GEF-H1\", \"PXN\", \"CTNNB1\", \"SMAD2\", \"GAB1\", \"SETD6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}