{"gene":"PKN1","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":1996,"finding":"PKN (PKN1) was identified as a direct binding partner and downstream effector of RhoA. GTP-bound RhoA physically interacted with and activated PKN in vitro and in COS-7 cells, and PKN was phosphorylated in Swiss 3T3 cells stimulated with lysophosphatidic acid in a Rho-dependent manner, establishing PKN as the first serine/threonine kinase target of Rho GTPase.","method":"Co-immunoprecipitation, in vitro kinase assay, botulinum C3 exoenzyme inhibition in cells","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution plus cell-based validation, foundational discovery replicated extensively","pmids":["8571127"],"is_preprint":false},{"year":1996,"finding":"The amino-terminal region of PKN1 (residues 33–111, particularly residues 74–113) is sufficient for RhoA binding, and this interaction inhibits the GTPase activity of RhoA, suggesting a reciprocal regulatory mechanism that sustains GTP-bound active RhoA.","method":"Yeast two-hybrid, in vitro binding assay with synthetic peptide competition","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — in vitro binding with deletion/peptide mapping, multiple orthogonal methods","pmids":["8647255"],"is_preprint":false},{"year":1996,"finding":"PKN1 phosphorylates MARCKS at the same PKC sites (serine 152, 156, and 163) in cell extracts and in vitro, identifying MARCKS as a shared substrate for PKN1 and PKC signaling pathways.","method":"In vitro kinase assay with cell extracts, phosphopeptide mapping","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation with site identification by mass spectrometry/sequencing","pmids":["8557118"],"is_preprint":false},{"year":1996,"finding":"PKN1 undergoes stress-induced nuclear translocation: under heat shock (42°C), sodium arsenite, or serum starvation, PKN1 redistributes from the cytoplasm to the nucleus in NIH 3T3, BALB/c 3T3, and Rat-1 cells, and returns to the cytoplasm after recovery, indicating PKN1 may relay stress signals to the nucleus.","method":"Immunofluorescence confocal microscopy, biochemical subcellular fractionation and immunoblotting","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — direct localization experiment with functional context, two orthogonal methods","pmids":["8816775"],"is_preprint":false},{"year":1997,"finding":"PKN1 interacts with alpha-actinin via its N-terminal region (outside the RhoA-binding domain), binding specifically to the third spectrin-like repeats of both skeletal and non-muscle alpha-actinin. The interaction with non-muscle alpha-actinin's EF-hand motifs is Ca2+-sensitive, and phosphatidylinositol 4,5-bisphosphate stimulates binding of full-length alpha-actinin to PKN1, linking PKN1 to the cytoskeletal network.","method":"Yeast two-hybrid, in vitro binding with truncation mutants, co-immunoprecipitation from COS7 cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus in vitro domain mapping, multiple binding partners characterized","pmids":["9030526"],"is_preprint":false},{"year":1997,"finding":"PKN1 associates with and phosphorylates the head-rod domain of neurofilament L, M, and H subunits. PKN1 binding was mapped to the amino-terminal regulatory region of PKN1 and the head-rod domain of neurofilaments. Phosphorylation of neurofilament L by PKN1 inhibited its polymerization in vitro.","method":"Yeast two-hybrid, GST pulldown, in vitro kinase assay with purified neurofilaments, polymerization assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution, functional consequence (inhibition of polymerization), multiple methods","pmids":["8621664"],"is_preprint":false},{"year":1997,"finding":"PKN1 phosphorylates vimentin and GFAP in the head domain, and this phosphorylation nearly completely inhibits filament formation of both intermediate filament proteins in vitro. The interaction was mapped by yeast two-hybrid and in vitro binding assay to the regulatory domain of PKN1.","method":"Yeast two-hybrid, in vitro binding assay, in vitro kinase assay, filament assembly assay","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation with functional consequence (inhibition of filament formation)","pmids":["9175763"],"is_preprint":false},{"year":1998,"finding":"PRK1/PKN1 contains two HR1 repeats (HR1a and HR1b) that both bind RhoA independently; HR1a binds exclusively to GTP-RhoA, while HR1b binds both GTP- and GDP-RhoA, indicating two independent contact sites on RhoA. The related HR1 motif in PRK2 also confers RhoA binding, and a C. elegans HR1a sequence similarly binds RhoA.","method":"In vitro binding assays with truncation mutants, Rho/Rac chimeras, nucleotide-loaded RhoA variants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic in vitro domain mapping with multiple protein variants and nucleotide-state specificity","pmids":["9446575"],"is_preprint":false},{"year":1998,"finding":"PKN1 is cleaved by caspase-3 at specific aspartate residues during apoptosis (Fas ligation, staurosporin, etoposide treatment), generating a constitutively active kinase fragment. The major cleavage occurs between the N-terminal regulatory and C-terminal catalytic domains. Site-directed mutagenesis of the aspartate cleavage sites prevented fragment generation.","method":"In vitro caspase-3 cleavage assay, site-directed mutagenesis, immunoblotting of apoptotic cells with caspase inhibitor","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro cleavage plus mutagenesis confirming sites, replicated in multiple cell lines","pmids":["9751706"],"is_preprint":false},{"year":1999,"finding":"Drosophila Pkn (ortholog of mammalian PKN1) binds specifically to GTP-activated Rho1 and Rac1 through distinct binding sites, and binding to either GTPase increases kinase activity. Loss-of-function pkn mutants show defects specifically in epidermal cell shape changes during dorsal closure, acting in a Rho1-dependent pathway independent of the Rac-JNK transcriptional cascade.","method":"Genetic loss-of-function mutant analysis, in vitro binding and kinase assays, epistasis in Drosophila embryogenesis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo genetic epistasis plus in vitro biochemistry, Drosophila ortholog with conserved domain architecture","pmids":["10323867"],"is_preprint":false},{"year":1999,"finding":"PKN1 contains an autoinhibitory domain within residues 455–511 that inhibits kinase activity in a substrate-competitive manner (Ki = 0.6 µM) and is selectively relieved by arachidonic acid (IC50 raised ~100-fold). Autophosphorylation at Thr64, Ser374, and Thr531 in the regulatory region and Thr774 in the activation loop are required for full PKN1 kinase activity.","method":"In vitro kinase assay with deletion/point mutants expressed in insect cells, competitive inhibition analysis","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic mutagenesis and reconstituted in vitro assays defining autoinhibitory mechanism","pmids":["10467162"],"is_preprint":false},{"year":1999,"finding":"CG-NAP (later known as AKAP450/AKAP9) was identified as a PKN1-interacting scaffolding protein that co-localizes with PKN1 at the centrosome and Golgi apparatus. CG-NAP also binds PKA regulatory subunit RIIα, PP2A catalytic subunit, and PP1, establishing it as a multi-enzyme scaffold at these organelles.","method":"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence microscopy","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — co-IP plus colocalization, multiple binding partners verified","pmids":["10358086"],"is_preprint":false},{"year":2000,"finding":"PKN1 phosphorylates tau at microtubule-binding domain sites Ser258, Ser320, and Ser352; Ser320 is a PKN1-specific site not phosphorylated by any PKC subtype. PKN1 activation disrupts microtubule arrays both in vitro and in vivo, and dephosphorylation at Ser320 is regulated by calcineurin (PP2B).","method":"In vitro kinase assay, site-directed mutagenesis, phosphorylation-specific antibody (HIA3), cell-based tubulin polymerization assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation with site identification, novel PKN1-specific site validated with phospho-specific antibody in cells","pmids":["11104762"],"is_preprint":false},{"year":2000,"finding":"PKN1 (as a Rho effector) stimulates ANF gene transcription via a serum response element (SRE) in cardiomyocytes. Constitutively active PKN1 robustly activated a luciferase reporter driven by the ANF promoter SRE, and this effect required dominant-active Rho; dominant-negative Rho blocked both phenylephrine-induced and PKN1-stimulated ANF expression.","method":"Luciferase reporter assay in neonatal rat ventricular myocytes, dominant-negative/constitutively active mutant expression","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 — cell-based reporter assay with genetic epistasis, single lab","pmids":["10843871"],"is_preprint":false},{"year":2001,"finding":"PKN1 inhibits Cdc25C phosphatase activity by direct phosphorylation, thereby delaying mitotic timing. Active PKN1 microinjected into Xenopus embryos caused cleavage arrest; in cycling egg extracts, active PKN1 delayed Tyr15 dephosphorylation of Cdc2 and Cdc2/cyclin B activation. The kinase-negative form had no effect.","method":"Xenopus microinjection, cell-free cycling extract assay, in vitro kinase assay of Cdc25C by PKN1","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — in vitro direct phosphorylation plus in vivo Xenopus epistasis, kinase-dead control","pmids":["11134534"],"is_preprint":false},{"year":2003,"finding":"PKN1 is one of three mammalian isoforms (PKNα/PAK-1/PRK-1, PKNβ, and PRK2/PAK-2/PKNγ) of a serine/threonine kinase family with a catalytic domain homologous to PKC and a unique regulatory region containing antiparallel coiled-coil (ACC/HR1) domains. PKN1 is the first identified serine/threonine kinase activated by a small GTPase (Rho) and also activated by fatty acids such as arachidonic acid in vitro.","method":"Review synthesizing biochemical characterization across isoforms","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1 — review consolidating prior reconstitution and in vitro data from multiple independent studies","pmids":["12761194"],"is_preprint":false},{"year":2004,"finding":"PRK1/PKN1 exists as an integral plasma membrane pool in mammalian cells. Phosphorylation of Ser377 of PRK1 is required for membrane integration. Only the membrane-associated form of PRK1 can mediate RhoA-dependent androgen receptor transcriptional activation in prostate epithelial cells and RhoA-induced neurite retraction in neuronal cells.","method":"Membrane fractionation, site-directed mutagenesis (S377A), functional reporter assays, neurite retraction assay","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis of functional site coupled with two distinct cellular functional readouts","pmids":["15375078"],"is_preprint":false},{"year":2006,"finding":"The Salmonella effector SspH1 interacts with PKN1 via its leucine-rich repeat domain. Expression of constitutively active PKN1 decreases NF-κB-dependent reporter gene expression, while siRNA depletion of PKN1 increases NF-κB activity, identifying PKN1 as a negative regulator of NF-κB signaling that is exploited by SspH1.","method":"Yeast two-hybrid screen, co-immunoprecipitation, NF-κB luciferase reporter assay, siRNA knockdown","journal":"Cellular microbiology","confidence":"High","confidence_rationale":"Tier 2 — yeast two-hybrid plus co-IP plus functional reporter with both gain- and loss-of-function","pmids":["16611232"],"is_preprint":false},{"year":2007,"finding":"The HR1b domain of PRK1/PKN1 binds exclusively to Rac1 (not RhoA), while HR1a binds both. NMR solution structure of the HR1b–Rac1 complex reveals that HR1b contacts the C-terminal effector loop, switch 2, and the polybasic C-terminal region of Rac1. The Rac1 polybasic region forms a novel recognition element for effector binding.","method":"NMR structure determination, mutational analysis of binding interface","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional validation of binding interface","pmids":["18006505"],"is_preprint":false},{"year":2007,"finding":"PKN1 mRNA and protein expression are dramatically increased in pregnant human myometrium, and PKN1 phosphorylates CPI-17 (PPP1R14A) to inhibit myosin phosphatase, contributing to calcium sensitization and uterine contractile activity. Elevated GTP-bound RhoA correlates with increased PKN1 signaling in spontaneous preterm labor.","method":"Immunoblotting, phosphorylation assays, immunohistochemistry on human myometrial tissue","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2–3 — functional phosphorylation mechanism in human tissue but primarily correlative; single lab","pmids":["17301291"],"is_preprint":false},{"year":2007,"finding":"Constitutively active PKN1 expressed in transgenic mouse mammary epithelium impairs tight junction sealing at parturition (demonstrated by paracellular sucrose permeability assay) and causes precocious involution, while dominant-negative PKN1 accelerates tight junction sealing in EpH4 cells, revealing PKN1 as a negative regulator of tight junction sealing via glucocorticoid signaling.","method":"Transgenic mouse model, intraductal injection permeability assay, EpH4 cell tight junction assay, dominant-negative/constitutively active mutants","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — in vivo transgenic phenotype plus in vitro gain/loss-of-function with functional readout","pmids":["17591691"],"is_preprint":false},{"year":2008,"finding":"PKN1 is cleaved and activated by caspase in SOD1-G93A transgenic mice (ALS model) and by glutamate treatment in neurons. A constitutively active (cleaved) form of PKN1, but not wild-type PKN1, disrupts neurofilament organization and impairs axonal transport in neurons, suggesting that deregulated PKN1 contributes to ALS pathology.","method":"Immunoblotting of SOD1G93A mice, neuronal cell culture with glutamate, axonal transport assay, expression of cleaved vs. wild-type PKN1","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — disease model plus functional assay, single lab","pmids":["18519042"],"is_preprint":false},{"year":2009,"finding":"A 15-amino-acid peptide (PRL) derived from residues 485–499 of the C2-like domain of PKN1 selectively inhibits all PKN isoforms (Ki = 0.7 µM) in vitro without inhibiting PKC. Cell-permeable delivery of PRL inhibited PKN1-mediated tau phosphorylation at the PKN1-specific site Ser320 in vivo.","method":"In vitro kinase assay with peptide inhibitor, cell-based phosphorylation assay with phospho-specific antibody, cell-penetrating peptide delivery","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro characterization plus in-cell functional validation with specific readout","pmids":["19857203"],"is_preprint":false},{"year":2010,"finding":"PKN1 is activated during myocardial ischemia/reperfusion (I/R), evidenced by Thr774 phosphorylation. Cardiac-specific overexpression of constitutively active PKN1 in transgenic mice significantly reduces myocardial infarct size and apoptosis after I/R, while dominant-negative PKN1 worsens injury. PKN1 mediates phosphorylation of αB-crystallin and stimulates proteasome activity as part of its cytoprotective mechanism.","method":"Transgenic mouse I/R model, TUNEL assay, in vivo and in vitro kinase assays, proteasome activity assay, pharmacological proteasome inhibition","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 — transgenic gain/loss-of-function in vivo with mechanistic downstream targets identified","pmids":["20595653"],"is_preprint":false},{"year":2010,"finding":"PKN1 is activated by hypotonic swelling in cardiac myocytes through a Src→RhoA→PKN1 cascade, and PKN1 in turn activates ERK via MEK to promote cell survival. Knockdown of PKN1 inhibited HS-induced ERK phosphorylation and reduced myocyte survival under hypotonic stress.","method":"siRNA knockdown, constitutively active PKN1 overexpression, co-immunoprecipitation (PKN1–RhoA), kinase activity assays, cell viability assay","journal":"American journal of physiology. Heart and circulatory physiology","confidence":"Medium","confidence_rationale":"Tier 2 — pathway placement by knockdown/overexpression with defined downstream readouts, single lab","pmids":["21037231"],"is_preprint":false},{"year":2011,"finding":"PKN1 and PKN2 substrate recognition requires an arginine at position −3 relative to the phosphoserine, while arginines at +1 (PKN1) or −1 (PKN3) are not tolerated. Using a peptide library and protein array approach, 22 novel PKN1 substrates were identified, and EGFR Thr654 was confirmed as a PKN1 phosphorylation site in vitro and in vivo.","method":"Oriented peptide library screen, protein array, in vitro kinase assay, in vivo phosphorylation with PKN modulation","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 — systematic substrate specificity determination plus novel substrate validation in vitro and in vivo","pmids":["21749319"],"is_preprint":false},{"year":2011,"finding":"PKN2 but not PKN1 or PKN3 is required for cell migration and invasion in 5637 bladder tumor cells. Using chimeric PKN constructs swapping regulatory domains between isoforms, PKN isoform-specific migration functions are conferred by their distinct N-terminal regulatory domains, indicating that different upstream signals are selectively coupled to PKN isoforms.","method":"siRNA knockdown, rescue with wild-type and chimeric PKN constructs, migration and invasion assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — domain-swap rescue experiment defining regulatory specificity, single lab","pmids":["21754995"],"is_preprint":false},{"year":2013,"finding":"PKN1 represses Wnt/β-catenin signaling in melanoma cells. siRNA depletion of PKN1 enhances β-catenin-activated reporter activity and increases WNT3A-induced apoptosis. Affinity purification–mass spectrometry revealed that PKN1 resides in a protein complex with Frizzled 7 and associated proteins, placing PKN1 upstream of β-catenin as a signaling repressor.","method":"siRNA screen, β-catenin luciferase reporter assay, affinity purification–mass spectrometry","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — functional siRNA with reporter plus interactome data, single lab","pmids":["24114839"],"is_preprint":false},{"year":2014,"finding":"PRK1/PKN1 kinase activity is required for migration and invasion of androgen-independent prostate cancer cells. PKN1 regulates migration-relevant gene expression via interaction with scaffold protein SPAG9/JIP4, leading to p38 phosphorylation; depletion of ELK1 (p38 effector) or p38 recapitulates PKN1 depletion phenotypes. A PRK1 inhibitor prevented metastasis in mice.","method":"siRNA knockdown, transcriptome and interactome analysis, co-immunoprecipitation, in vivo mouse metastasis model with pharmacological inhibitor","journal":"Oncotarget","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, in vivo validation, epistasis establishing pathway","pmids":["25504435"],"is_preprint":false},{"year":2016,"finding":"PKN2 knockout in mice causes lethality at embryonic day 10 due to failure of embryonic mesoderm expansion and cardiovascular defects. PKN1 and PKN3 single knockouts are viable, establishing PKN2 as specifically non-redundant. Mouse embryonic fibroblasts (mesodermal origin) require PKN2 for proliferation and motility, and PKN2 is required for neural crest migration in vivo.","method":"Conditional and constitutive knockout mice, embryonic phenotyping, MEF proliferation/motility assays, in vivo neural crest migration analysis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — complete knockout phenotyping across all three isoforms in vivo with cellular mechanism","pmids":["26774483"],"is_preprint":false},{"year":2017,"finding":"PKN1 phosphorylates RPH3A, which enhances RPH3A binding to GTP-bound RAB21. This PKN1→RPH3A→RAB21 phosphorylation cascade drives polarized vesicle trafficking in neutrophils, leading to PIP5K1C90 polarization, integrin activation, and adhesion to endothelial cells. Myeloid-specific loss of PKN1 decreases tissue injury in renal ischemia-reperfusion in vivo.","method":"In vitro kinase assay, co-immunoprecipitation, neutrophil polarization/adhesion assay, conditional PKN1 knockout mice, ischemia-reperfusion model","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1–2 — direct phosphorylation demonstrated in vitro, functional consequence in cells and in vivo, multiple methods","pmids":["28636945"],"is_preprint":false},{"year":2010,"finding":"PKCβI is recruited to AR target gene promoters by PRK1/PKN1 as a 'gatekeeper kinase,' and this PKCβI phosphorylates histone H3 at threonine 6 (H3T6ph) to prevent LSD1 from demethylating H3K4 during androgen-dependent gene expression. PRK1 activation is required for the androgen-stimulated recruitment of PKCβI to promoters.","method":"ChIP, RNAi knockdown, in vitro histone phosphorylation assay, prostate cancer xenograft model","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — chromatin biochemistry plus in vitro reconstitution, in vivo cancer model validation","pmids":["20228790"],"is_preprint":false},{"year":2023,"finding":"In GNAQ-mutant uveal melanoma, PKN/PRK (downstream of the Gαq–RhoA axis) converges with ROCK to control FAK activity. Darovasertib inhibits both PKC and PKN/PRK and synergizes with FAK inhibitors to halt uveal melanoma growth in vitro and in preclinical metastatic mouse models, identifying PKN as part of a non-canonical Gαq signaling vulnerability.","method":"High-throughput chemogenetic drug screen, kinase inhibitor profiling, in vitro cell viability assays, preclinical mouse metastasis models","journal":"Cell reports. Medicine","confidence":"Medium","confidence_rationale":"Tier 2 — chemogenetic screen with in vivo validation, but PKN isoform-specific mechanistic details are limited","pmids":["37858338"],"is_preprint":false}],"current_model":"PKN1 (PRK1) is a Rho/Rac-activated AGC-family serine/threonine kinase whose N-terminal HR1 repeats directly bind GTP-RhoA and GTP-Rac1 to relieve autoinhibition (mediated by residues 455–511) and activate the C-terminal catalytic domain (requiring Thr774 phosphorylation); it is also activated by arachidonic acid, caspase-3 cleavage (generating a constitutively active fragment), and hypo-osmotic or ischemic stress via a Src–RhoA–PDK1 cascade. Established substrates include neurofilament subunits, vimentin, GFAP, tau (Ser320-specific), MARCKS, alpha-actinin, Cdc25C (inhibiting mitotic entry), CPI-17 (promoting myosin phosphatase inhibition and smooth muscle contraction), EGFR Thr654, and RPH3A (driving polarized RAB21 vesicle trafficking in neutrophils). PKN1 scaffolds at the centrosome/Golgi via CG-NAP, translocates to the nucleus under stress, represses NF-κB and Wnt/β-catenin signaling, regulates ANF gene transcription via SRE, and acts as a gatekeeper upstream of PKCβI-mediated H3T6 phosphorylation during androgen receptor-driven transcription; in the heart it protects against ischemia/reperfusion injury by phosphorylating αB-crystallin and stimulating proteasome activity."},"narrative":{"teleology":[{"year":1996,"claim":"Identification of PKN1 as the first serine/threonine kinase directly activated by a Rho-family GTPase established a new effector arm downstream of RhoA signaling, answering how Rho could regulate serine/threonine phosphorylation.","evidence":"Co-immunoprecipitation, in vitro kinase assays, and C3 exoenzyme inhibition in COS-7 and Swiss 3T3 cells","pmids":["8571127","8647255"],"confidence":"High","gaps":["Mechanism of kinase activation by RhoA binding not yet resolved","Physiological substrates unknown at this stage"]},{"year":1996,"claim":"Discovery that PKN1 phosphorylates MARCKS at PKC sites and undergoes stress-induced nuclear translocation placed PKN1 at the intersection of PKC-like signaling and nuclear stress responses, expanding its functional scope beyond a simple Rho effector.","evidence":"In vitro kinase assays with phosphopeptide mapping (MARCKS); immunofluorescence and subcellular fractionation under heat shock, arsenite, and serum starvation","pmids":["8557118","8816775"],"confidence":"High","gaps":["Nuclear targets of translocated PKN1 not identified","Whether nuclear translocation is kinase-activity-dependent was unknown"]},{"year":1997,"claim":"Demonstration that PKN1 phosphorylates intermediate filament proteins (neurofilament subunits, vimentin, GFAP) and inhibits their polymerization in vitro established a direct role for PKN1 in cytoskeletal remodeling, answering how Rho signaling controls intermediate filament dynamics.","evidence":"In vitro kinase and filament assembly assays with purified neurofilaments, vimentin, and GFAP; yeast two-hybrid and GST pulldown mapping","pmids":["8621664","9175763"],"confidence":"High","gaps":["In vivo relevance of intermediate filament phosphorylation by PKN1 not demonstrated","Specific phosphorylation sites on vimentin/GFAP not fully mapped"]},{"year":1998,"claim":"Structural dissection of the HR1 repeats showed that HR1a and HR1b independently bind RhoA with different nucleotide-state preferences, and that caspase-3 cleaves PKN1 to generate a constitutively active fragment during apoptosis, resolving two key regulatory mechanisms: GTPase-selective activation and irreversible proteolytic activation.","evidence":"In vitro binding with truncation mutants and nucleotide-loaded GTPases; in vitro caspase-3 cleavage with site-directed mutagenesis in apoptotic cells","pmids":["9446575","9751706"],"confidence":"High","gaps":["Whether caspase-generated fragment has distinct substrates in vivo unknown","Crystal structure of HR1a–RhoA complex not yet available"]},{"year":1999,"claim":"Identification of a pseudosubstrate autoinhibitory domain (residues 455–511) relieved by arachidonic acid, and key autophosphorylation sites including activation-loop Thr774, defined the intramolecular regulation of PKN1 kinase activity, answering how the enzyme stays inactive in the absence of upstream signals.","evidence":"In vitro kinase assays with deletion/point mutants expressed in insect cells, competitive inhibition kinetics","pmids":["10467162"],"confidence":"High","gaps":["Whether arachidonic acid activates PKN1 physiologically in cells was not resolved","Full interplay between GTPase binding and autoinhibition release not structurally defined"]},{"year":1999,"claim":"Discovery that PKN1 is scaffolded at the centrosome and Golgi via CG-NAP/AKAP450 alongside PKA, PP2A, and PP1 revealed a spatially organized signaling platform, answering how PKN1 is positioned near specific substrates in dividing cells.","evidence":"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence colocalization","pmids":["10358086"],"confidence":"High","gaps":["Functional consequence of centrosomal PKN1 not directly tested","Whether CG-NAP scaffolding is regulated by Rho-GTP unknown"]},{"year":1999,"claim":"Drosophila Pkn loss-of-function mutants showed defective dorsal closure (epidermal cell shape changes) in a Rho1-dependent but Rac-JNK-independent pathway, providing the first in vivo genetic evidence that PKN family kinases act specifically in Rho-driven morphogenesis.","evidence":"Genetic loss-of-function and epistasis analysis in Drosophila embryos combined with in vitro kinase assays","pmids":["10323867"],"confidence":"High","gaps":["Mammalian in vivo requirement for PKN1 in morphogenesis not established at this stage","Substrates of Drosophila Pkn during dorsal closure unknown"]},{"year":2000,"claim":"PKN1 was shown to phosphorylate tau at the novel PKN1-specific site Ser320 (disrupting microtubules) and to stimulate ANF gene transcription via SRE in cardiomyocytes, broadening PKN1's substrate repertoire to include microtubule-associated proteins and revealing a role in cardiac gene regulation.","evidence":"In vitro kinase assays with phospho-specific antibodies and cell-based tubulin polymerization assays (tau); luciferase reporter assays with dominant-active/negative Rho in neonatal cardiomyocytes (ANF)","pmids":["11104762","10843871"],"confidence":"High","gaps":["Whether PKN1-mediated tau phosphorylation contributes to tauopathy in vivo unknown","Transcriptional targets beyond ANF in cardiomyocytes not identified"]},{"year":2001,"claim":"Direct phosphorylation of Cdc25C by PKN1, which delayed Cdc2 dephosphorylation and mitotic entry in Xenopus extracts and embryos, answered how a Rho effector kinase could regulate cell cycle progression.","evidence":"Xenopus microinjection, cycling egg extract assays, in vitro kinase assay with kinase-dead control","pmids":["11134534"],"confidence":"High","gaps":["Cdc25C phosphorylation site by PKN1 not identified","Whether this mitotic delay function operates in mammalian somatic cells untested"]},{"year":2004,"claim":"Discovery of a Ser377-phosphorylation-dependent plasma membrane pool of PKN1 that is required for both RhoA-dependent androgen receptor transactivation and neurite retraction resolved the question of how spatial compartmentalization controls PKN1 function.","evidence":"Membrane fractionation, S377A mutagenesis, AR reporter and neurite retraction assays","pmids":["15375078"],"confidence":"High","gaps":["Kinase responsible for Ser377 phosphorylation not identified","Whether membrane-integrated PKN1 has distinct substrates unknown"]},{"year":2006,"claim":"PKN1 was identified as a negative regulator of NF-κB signaling, exploited by the Salmonella effector SspH1 to suppress host immunity, answering how Rho-dependent kinase activity intersects with innate immune transcription.","evidence":"Yeast two-hybrid, co-immunoprecipitation, NF-κB reporter with PKN1 overexpression and siRNA depletion","pmids":["16611232"],"confidence":"High","gaps":["Direct phosphorylation target linking PKN1 to NF-κB inhibition not identified","In vivo relevance to Salmonella infection in animals untested"]},{"year":2007,"claim":"NMR structure of the HR1b–Rac1 complex revealed a novel recognition mechanism involving Rac1's polybasic C-terminal region, resolving the structural basis for PKN1's dual GTPase specificity and answering how a single kinase integrates Rho and Rac inputs.","evidence":"NMR solution structure with mutational validation of binding interface","pmids":["18006505"],"confidence":"High","gaps":["How simultaneous Rho and Rac binding is coordinated on full-length PKN1 is unresolved","No full-length PKN1 structure available"]},{"year":2007,"claim":"PKN1 phosphorylation of CPI-17 in pregnant human myometrium linked Rho–PKN1 signaling to calcium sensitization and smooth muscle contraction, while PKN1 regulation of tight junction sealing in mammary epithelium revealed tissue-specific roles in epithelial barrier function.","evidence":"Immunohistochemistry and phosphorylation assays on human myometrial tissue; transgenic mouse mammary model with dominant-negative and constitutively active PKN1","pmids":["17301291","17591691"],"confidence":"Medium","gaps":["CPI-17 phosphorylation site specificity by PKN1 not mapped","Myometrial data are correlative with preterm labor rather than causal","Tight junction mechanism downstream of PKN1 not molecularly resolved"]},{"year":2010,"claim":"PKN1 was established as a cardioprotective kinase during ischemia/reperfusion via phosphorylation of αB-crystallin and stimulation of proteasome activity, activated through a Src→RhoA→PKN1 cascade under osmotic and ischemic stress, answering how Rho signaling promotes cardiomyocyte survival.","evidence":"Cardiac-specific transgenic mice with constitutively active/dominant-negative PKN1 in I/R models; siRNA and overexpression with ERK readout in hypotonic stress","pmids":["20595653","21037231"],"confidence":"High","gaps":["αB-crystallin phosphorylation site(s) by PKN1 not identified","Whether PKN1 and PKN2 have redundant roles in cardiac protection unknown"]},{"year":2010,"claim":"PKN1 was shown to act as a gatekeeper kinase that recruits PKCβI to androgen receptor target promoters, enabling H3T6 phosphorylation that prevents LSD1-mediated H3K4 demethylation, establishing PKN1 as a chromatin-level regulator of hormone-dependent transcription.","evidence":"ChIP, RNAi, in vitro histone phosphorylation, prostate cancer xenograft model","pmids":["20228790"],"confidence":"High","gaps":["Whether PKN1 directly phosphorylates a chromatin substrate at AR promoters or acts solely as a scaffold is unclear","Generalizability to other nuclear receptor targets untested"]},{"year":2011,"claim":"Systematic substrate specificity profiling defined the PKN1 consensus motif (requiring Arg at −3) and validated EGFR Thr654 as a direct PKN1 substrate, broadening the kinase's substrate landscape to include receptor tyrosine kinases.","evidence":"Oriented peptide library, protein array, in vitro and in vivo phosphorylation of EGFR Thr654","pmids":["21749319"],"confidence":"High","gaps":["Functional consequence of EGFR Thr654 phosphorylation by PKN1 not determined","Many of the 22 novel array-identified substrates remain unvalidated in cells"]},{"year":2017,"claim":"Discovery that PKN1 phosphorylates RPH3A to enhance its binding to GTP-RAB21, driving polarized vesicle trafficking, integrin activation, and neutrophil adhesion, answered how PKN1 controls immune cell polarity and provided the first in vivo loss-of-function phenotype for mammalian PKN1 (reduced renal ischemia-reperfusion injury in myeloid-specific knockouts).","evidence":"In vitro kinase assay, co-immunoprecipitation, neutrophil polarization/adhesion assays, conditional PKN1 knockout mice, renal I/R model","pmids":["28636945"],"confidence":"High","gaps":["Whether RPH3A phosphorylation by PKN1 operates in non-myeloid contexts unknown","Specific phosphorylation site(s) on RPH3A not reported"]},{"year":2023,"claim":"In GNAQ-mutant uveal melanoma, PKN/PRK was placed in a non-canonical Gαq–RhoA signaling arm that converges with ROCK to control FAK, identifying PKN as a therapeutic vulnerability synergizing with FAK inhibition.","evidence":"Chemogenetic drug screen, kinase inhibitor profiling, preclinical mouse metastasis models","pmids":["37858338"],"confidence":"Medium","gaps":["PKN isoform specificity (PKN1 vs PKN2/3) in uveal melanoma not resolved","Direct PKN substrates mediating FAK regulation not identified","Darovasertib inhibits both PKC and PKN, confounding isoform-specific conclusions"]},{"year":null,"claim":"A full-length structure of PKN1 showing how HR1-mediated GTPase binding, autoinhibitory domain relief, and activation-loop phosphorylation are coordinated remains unavailable, and tissue-specific non-redundant functions relative to PKN2 and PKN3 are incompletely mapped despite single-knockout viability data.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length PKN1 crystal or cryo-EM structure","Tissue-specific conditional knockout phenotypes for PKN1 beyond myeloid cells are lacking","Nuclear substrates mediating PKN1's transcriptional effects are mostly unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,5,6,10,12,14,19,22,23,25,30,31]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,2,5,6,12,14,25,30]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[17,27,31]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[4,5,6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,31]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[16]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[11]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[11]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,7,9,17,18,24,27,32]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[14]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[8,21]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[13,31]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[17,30]},{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[19]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[30]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[28,32]}],"complexes":["CG-NAP/AKAP450 scaffold complex"],"partners":["RHOA","RAC1","AKAP9","ACTN1","MAPT","RPH3A","SPAG9","FZD7"],"other_free_text":[]},"mechanistic_narrative":"PKN1 is a Rho/Rac-activated AGC-family serine/threonine kinase that transduces small GTPase signals into cytoskeletal remodeling, cell cycle control, transcriptional regulation, and stress-protective responses. Its N-terminal HR1a domain binds GTP-RhoA while HR1b binds both Rac1 and RhoA, relieving an internal autoinhibitory segment (residues 455–511) to activate a C-terminal catalytic domain that phosphorylates intermediate filament proteins (neurofilament L, vimentin, GFAP) to inhibit their polymerization, tau at the PKN1-specific site Ser320 to disrupt microtubules, Cdc25C to delay mitotic entry, CPI-17 to promote myosin phosphatase inhibition, RPH3A to drive polarized RAB21-dependent vesicle trafficking in neutrophils, and EGFR at Thr654 [PMID:8571127, PMID:8621664, PMID:11104762, PMID:11134534, PMID:17301291, PMID:28636945, PMID:21749319]. PKN1 also functions as a gatekeeper kinase that recruits PKCβI to androgen receptor target promoters, enabling H3T6 phosphorylation that protects H3K4 methylation marks from LSD1 demethylation, and it represses NF-κB and Wnt/β-catenin signaling [PMID:20228790, PMID:16611232, PMID:24114839]. Under stress, PKN1 translocates to the nucleus and, in the heart, protects against ischemia/reperfusion injury by phosphorylating αB-crystallin and stimulating proteasome activity through a Src–RhoA–PDK1 activation cascade [PMID:8816775, PMID:20595653, PMID:21037231]."},"prefetch_data":{"uniprot":{"accession":"Q16512","full_name":"Serine/threonine-protein kinase N1","aliases":["Protease-activated kinase 1","PAK-1","Protein kinase C-like 1","Protein kinase C-like PKN","Protein kinase PKN-alpha","Protein-kinase C-related kinase 1","Serine-threonine protein kinase N"],"length_aa":942,"mass_kda":103.9,"function":"PKC-related serine/threonine-protein kinase involved in various processes such as regulation of the intermediate filaments of the actin cytoskeleton, cell migration, tumor cell invasion and transcription regulation. Part of a signaling cascade that begins with the activation of the adrenergic receptor ADRA1B and leads to the activation of MAPK14. Regulates the cytoskeletal network by phosphorylating proteins such as VIM and neurofilament proteins NEFH, NEFL and NEFM, leading to inhibit their polymerization. Phosphorylates 'Ser-575', 'Ser-637' and 'Ser-669' of MAPT/Tau, lowering its ability to bind to microtubules, resulting in disruption of tubulin assembly. Acts as a key coactivator of androgen receptor (AR)-dependent transcription, by being recruited to AR target genes and specifically mediating phosphorylation of 'Thr-11' of histone H3 (H3T11ph), a specific tag for epigenetic transcriptional activation that promotes demethylation of histone H3 'Lys-9' (H3K9me) by KDM4C/JMJD2C. Phosphorylates HDAC5, HDAC7 and HDAC9, leading to impair their import in the nucleus. Phosphorylates 'Thr-38' of PPP1R14A, 'Ser-159', 'Ser-163' and 'Ser-170' of MARCKS, and GFAP. Able to phosphorylate RPS6 in vitro","subcellular_location":"Cytoplasm; Nucleus; Endosome; Cell membrane; Cleavage furrow; Midbody","url":"https://www.uniprot.org/uniprotkb/Q16512/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PKN1","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000123143","cell_line_id":"CID001239","localizations":[{"compartment":"cytoplasmic","grade":3}],"interactors":[{"gene":"PKN2","stoichiometry":0.2},{"gene":"RB1CC1","stoichiometry":0.2},{"gene":"NUP85","stoichiometry":0.2},{"gene":"RNF40","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001239","total_profiled":1310},"omim":[{"mim_id":"610714","title":"PROTEIN KINASE N3; PKN3","url":"https://www.omim.org/entry/610714"},{"mim_id":"601032","title":"PROTEIN KINASE N1; PKN1","url":"https://www.omim.org/entry/601032"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytokinetic bridge","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PKN1"},"hgnc":{"alias_symbol":["DBK","PRK1","PKN","MGC46204","PAK1"],"prev_symbol":["PRKCL1"]},"alphafold":{"accession":"Q16512","domains":[{"cath_id":"1.10.287.160","chopping":"17-99","consensus_level":"medium","plddt":74.7053,"start":17,"end":99},{"cath_id":"1.10.287,1.10.287","chopping":"213-295","consensus_level":"medium","plddt":81.4727,"start":213,"end":295},{"cath_id":"2.60.40.150","chopping":"322-341_390-483","consensus_level":"medium","plddt":83.6572,"start":322,"end":483},{"cath_id":"3.30.200.20","chopping":"616-699_919-936","consensus_level":"high","plddt":90.9827,"start":616,"end":936},{"cath_id":"1.10.510.10","chopping":"702-895","consensus_level":"high","plddt":92.1411,"start":702,"end":895}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16512","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q16512-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q16512-F1-predicted_aligned_error_v6.png","plddt_mean":72.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PKN1","jax_strain_url":"https://www.jax.org/strain/search?query=PKN1"},"sequence":{"accession":"Q16512","fasta_url":"https://rest.uniprot.org/uniprotkb/Q16512.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q16512/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q16512"}},"corpus_meta":[{"pmid":"9395435","id":"PMC_9395435","title":"Human 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H3K4.","date":"2010","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/20228790","citation_count":243,"is_preprint":false,"source_track":"gene2pubmed"},{"pmid":"10358086","id":"PMC_10358086","title":"Characterization of a novel giant scaffolding protein, CG-NAP, that anchors multiple signaling enzymes to centrosome and the golgi apparatus.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10358086","citation_count":216,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":48530,"output_tokens":6748,"usd":0.123405},"stage2":{"model":"claude-opus-4-6","input_tokens":10462,"output_tokens":3954,"usd":0.22674},"total_usd":0.783509,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":60790,"output_tokens":8487,"usd":0.154837},"round2_rules_fired":"R2","round2_stage2":{"model":"claude-opus-4-6","input_tokens":12197,"output_tokens":4988,"usd":0.278527}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2003,\n      \"finding\": \"PKN1 (PKNalpha/PAK-1/PRK-1) is a serine/threonine protein kinase with a catalytic domain homologous to PKC, a unique regulatory region containing antiparallel coiled-coil (ACC) domains, and is the first identified serine/threonine kinase that binds to and is activated by the small GTPase RhoA; it can also be activated by fatty acids such as arachidonic acid in vitro.\",\n      \"method\": \"Biochemical characterization, in vitro kinase assays, domain analysis\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — foundational biochemical characterization replicated across multiple studies\",\n      \"pmids\": [\"12761194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PKN1 binds to and phosphorylates neurofilament proteins (NF-L, NF-M, NF-H) via direct interaction between the amino-terminal regulatory region of PKN1 and the head-rod domains of neurofilament subunits; phosphorylation of neurofilament L by PKN inhibits its polymerization in vitro.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay (GST pulldown), in vitro kinase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods (two-hybrid, GST pulldown, in vitro phosphorylation assay)\",\n      \"pmids\": [\"8621664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PKN1 directly interacts with alpha-actinin via its N-terminal region (outside the RhoA-binding domain), specifically binding to the third spectrin-like repeats of both skeletal and non-skeletal muscle alpha-actinin; binding to non-skeletal muscle alpha-actinin EF-hand-like motifs is Ca2+-sensitive. Phosphatidylinositol 4,5-bisphosphate stimulates binding of full-length alpha-actinin to PKN1.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including co-IP and in vitro binding with truncation mutants\",\n      \"pmids\": [\"9030526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PKN1 interacts with vimentin via its regulatory domain and phosphorylates vimentin in the head domain, resulting in nearly complete inhibition of vimentin filament formation in vitro; PKN1 similarly phosphorylates GFAP.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, in vitro kinase assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with functional readout (filament formation inhibition)\",\n      \"pmids\": [\"9175763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PKN1 (PRK1) binds to RhoA through two HR1 repeat motifs (HR1a and HR1b) with distinct nucleotide-bound-state dependencies: HR1a binds only GTP-RhoA, while HR1b binds both GTP- and GDP-bound RhoA, indicating two independent contact sites on RhoA.\",\n      \"method\": \"In vitro binding assay with truncation mutants, Rho/Rac chimeras\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — detailed mutational and biochemical dissection of binding domains\",\n      \"pmids\": [\"9446575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The amino acid residues 33-111 of PKN1 are sufficient for association with RhoA; peptides corresponding to residues 74-93 and 94-113 inhibit PKN1-RhoA interaction; PKN1 binding to RhoA inhibits the endogenous and GAP-stimulated GTPase activity of RhoA.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, GTPase activity assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods including functional GTPase inhibition assay\",\n      \"pmids\": [\"8647255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PKN1 is cleaved at specific sites by caspase-3 (or a related protease) during apoptosis, with the major cleavage occurring between the amino-terminal regulatory domain and the carboxyl-terminal catalytic domain, generating a constitutively active kinase fragment; site-directed mutagenesis of specific aspartate residues prevented the appearance of cleavage fragments.\",\n      \"method\": \"In vitro cleavage with recombinant caspase-3, site-directed mutagenesis, immunoblotting of apoptotic cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with recombinant caspase-3 plus mutagenesis validation\",\n      \"pmids\": [\"9751706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The regulatory region of PKN1 contains an arachidonic acid-sensitive autoinhibitory domain (residues 455-511); a peptide comprising this region (His-Ialpha) inhibits PKN1 catalytic activity in a substrate-competitive manner (Ki = 0.6 μM) and arachidonic acid relieves this autoinhibition; phosphorylation at Thr64, Ser374, Thr531 (regulatory region) and Thr774 (activation loop) are important for PKN1 kinase activity.\",\n      \"method\": \"Deletion/site-directed mutagenesis, in vitro kinase assays with insect cell-expressed proteins\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with defined mutants and in vitro peptide inhibition assays\",\n      \"pmids\": [\"10467162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PKN1 phosphorylates tau at Ser-258, Ser-320, and Ser-352 (in microtubule-binding domains), with Ser-320 being a PKN1-specific phosphorylation site; PKN1 activation disrupts the microtubule array in vitro and in vivo, and calcineurin (PP2B) may dephosphorylate tau at Ser-320.\",\n      \"method\": \"In vitro kinase assays, phospho-specific antibody (HIA3), expression of active/inactive PKN1 in CHO cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro phosphorylation mapped to specific sites, validated with phospho-specific antibody in vivo\",\n      \"pmids\": [\"11104762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PKN1 (PRK1) acts as a downstream effector of RhoA to regulate ANF gene transcription in cardiomyocytes through a serum response element (SRE); this effect is inhibited by dominant negative RhoA and requires an intact SRE in the ANF promoter.\",\n      \"method\": \"Luciferase reporter assays, dominant-negative RhoA co-expression, SRE mutagenesis\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis via dominant-negative with reporter readout, single study\",\n      \"pmids\": [\"10843871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PKN1 delays mitotic timing by directly phosphorylating and inhibiting Cdc25C, thereby suppressing Cdc2/cyclin B kinase activation; active PKN1 injected into Xenopus embryos causes cleavage arrest and delays mitotic timing in Xenopus egg cycling extracts in a kinase-activity-dependent manner.\",\n      \"method\": \"Microinjection into Xenopus embryos, Xenopus egg extract cycling assay, in vitro Cdc25C phosphorylation assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay for Cdc25C phosphorylation, plus functional Xenopus system with kinase-dead controls\",\n      \"pmids\": [\"11134534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PKN1 (PRK1) phosphorylates MARCKS at the same serine residues (Ser-152, Ser-156, Ser-163) as protein kinase C in vitro, identifying MARCKS as a PKN1 substrate.\",\n      \"method\": \"In vitro kinase assay, phosphopeptide mapping\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro phosphorylation with site identification\",\n      \"pmids\": [\"8557118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The Salmonella effector SspH1 interacts with human PKN1 via its leucine-rich repeat domain; constitutively active PKN1 decreases NF-κB-dependent gene expression, while RNAi depletion of PKN1 increases NF-κB-dependent reporter activity, indicating PKN1 negatively regulates NF-κB signaling.\",\n      \"method\": \"Yeast two-hybrid screen, reporter gene assays, RNAi knockdown\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — binding demonstrated by yeast two-hybrid, functional role by reporter assay and RNAi in single study\",\n      \"pmids\": [\"16611232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PRK1/PKN1 has an integral plasma membrane pool (distinct from cytosolic pool) whose membrane integration requires phosphorylation of Ser-377; only the integral membrane form of PRK1 mediates RhoA-dependent androgen receptor transcriptional activation and RhoA-induced neurite retraction.\",\n      \"method\": \"Subcellular fractionation, mutagenesis (Ser377), reporter assays, neuronal cell model\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — localization linked to functional consequence with mutagenesis, single lab\",\n      \"pmids\": [\"15375078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PKN1 undergoes stress-induced nuclear translocation: under heat shock (42°C), sodium arsenite treatment, or serum starvation, PKN1 redistributes from the cytoplasm to the nucleus in NIH 3T3, BALB/c 3T3, and Rat-1 cells; this is reversible upon return to 37°C.\",\n      \"method\": \"Immunofluorescence confocal microscopy, subcellular fractionation, immunoblotting\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment with multiple orthogonal methods (imaging + fractionation) across multiple cell lines\",\n      \"pmids\": [\"8816775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Deregulation (cleavage) of PKN1 disrupts neurofilament organisation and axonal transport; in SOD1-G93A ALS model mice and in glutamate-treated neurons, PKN1 is cleaved and activated by caspase activity, and expression of the cleaved (constitutively active) form, but not wild-type PKN1, disrupts neurofilament organisation and axonal transport.\",\n      \"method\": \"SOD1-G93A transgenic mouse model, neuronal glutamate treatment, overexpression of truncated/wild-type PKN1\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function with specific functional readout in multiple models, single lab\",\n      \"pmids\": [\"18519042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The HR1b domain of PRK1/PKN1 binds exclusively to Rac1 (not RhoA), with binding mediated by the C-terminal end of the effector loop, switch 2, and the C-terminal polybasic region of Rac1; this structural basis was determined by NMR solution structure of the HR1b-Rac1 complex.\",\n      \"method\": \"NMR solution structure determination, mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — atomic-resolution NMR structure with functional validation\",\n      \"pmids\": [\"18006505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKN1 is activated during cardiac ischemia/reperfusion (phosphorylated at Thr774), and protects cardiac myocytes from cell death; PKN1-mediated protection involves phosphorylation of alphaB-crystallin and stimulation of proteasome activity; cardiac-specific overexpression of constitutively active PKN1 reduces myocardial infarction size.\",\n      \"method\": \"Transgenic mouse (cardiac-specific CA-PKN1 and DN-PKN1), I/R model, in vitro H2O2 treatment, proteasome activity assay\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transgenic mouse models with reciprocal gain/loss-of-function and identified downstream substrate (alphaB-crystallin phosphorylation)\",\n      \"pmids\": [\"20595653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKN1 is activated by hypotonic swelling in cardiac myocytes via a Src/RhoA/PKN1 signaling cascade; activated PKN1 promotes ERK phosphorylation via MEK, and PKN1-ERK signaling promotes cardiac myocyte survival under hypotonic stress.\",\n      \"method\": \"In vitro hypotonic stress model, dominant-negative constructs, MEK inhibitor (U-0126), Src inhibitor (PP1)\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic epistasis establishing pathway position, single lab\",\n      \"pmids\": [\"21037231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKN1 (PRK1) regulates cell migration through isoform-specific regulatory domain properties linked to selective upstream signals; PKN1 is not simply redundant with PKN2 in supporting migration in bladder tumor cells.\",\n      \"method\": \"siRNA knockdown, wild-type and chimeric PKN rescue strategy, migration/invasion assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — chimeric rescue strategy distinguishes isoform-specific regulatory domain function, single lab\",\n      \"pmids\": [\"21754995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKN1 phosphorylates RPH3A, which enhances RPH3A binding to GTP-bound RAB21; this promotes polarized localization of RAB21 and RPH3A in neutrophils, leading to PIP5K1C90 polarization, integrin activation, and neutrophil adhesion to endothelial cells; myeloid-specific PKN1 loss decreases tissue injury in renal ischemia-reperfusion.\",\n      \"method\": \"In vitro phosphorylation assay, co-IP, PKN1 knockout mouse, myeloid-specific conditional knockout, inflammatory models\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro phosphorylation, protein interaction assays, and in vivo genetic models with defined phenotype\",\n      \"pmids\": [\"28636945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKN1 phosphorylates the substrate consensus motif with arginine at the -3 position of serine (not tolerating arginine at +1); PKN1 phosphorylates CLIP-170 and EGFR at Thr654 (which has arginine at -3); constitutive EGFR Thr654 phosphorylation is modulated by PKN1 in vivo.\",\n      \"method\": \"Combinatorial peptide library, protein array, site-directed mutagenesis, in vitro kinase assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — peptide library for motif determination plus identification and validation of specific substrate sites\",\n      \"pmids\": [\"21749319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKN1 (PRK1) is required for migration and gene expression in androgen-independent prostate cancer cells; PKN1 interacts with the scaffold protein SPAG9/JIP4, and this interaction is required for p38 phosphorylation and cell migration; ELK1 and p38 act downstream of PKN1 to regulate migration-relevant gene expression.\",\n      \"method\": \"siRNA knockdown, in vivo mouse metastasis model with PKN1 inhibitor, transcriptome and interactome analyses\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with defined interactors and in vivo validation, single lab\",\n      \"pmids\": [\"25504435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKN1 represses Wnt/β-catenin signaling in melanoma cells and is present in a protein complex with the WNT receptor Frizzled 7; siRNA depletion of PKN1 enhances β-catenin-activated transcription.\",\n      \"method\": \"siRNA screen, phosphoproteomics, affinity purification-mass spectrometry, β-catenin reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — AP-MS for complex identification, reporter assay for function, single lab\",\n      \"pmids\": [\"24114839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A selective PKN inhibitory peptide (PRL, residues 485-499 of PKN1 C2-like domain) inhibits all PKN isoforms (Ki = 0.7 μM) but not PKC; cell-permeable PRL inhibits PKN1-mediated phosphorylation of tau at Ser-320 in vivo.\",\n      \"method\": \"In vitro kinase assay, cell-permeable peptide, phospho-specific antibody for tau Ser-320\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical characterization of inhibitory mechanism with in vivo substrate validation\",\n      \"pmids\": [\"19857203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PKN1 constitutive activation in mammary epithelial cells impairs tight junction sealing (not tight junction formation per se), leading to precocious involution; glucocorticoid-stimulated tight junction sealing is highly impaired by constitutively active PKN1 and accelerated by dominant-negative PKN1 in EpH4 cells.\",\n      \"method\": \"Transgenic mouse model, intraductal [14C]sucrose injection, immunofluorescence of tight junction proteins, in vitro EpH4 cell model\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal gain/loss of function (CA and DN) with functional tight junction assay in vivo and in vitro\",\n      \"pmids\": [\"17591691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Drosophila Pkn (ortholog of mammalian PKN1) binds GTP-activated Rho1 and Rac1 through distinct binding sites, with binding to either GTPase increasing kinase activity; Pkn loss-of-function shows it is required for epidermal cell shape changes during dorsal closure, acting via a RhoA-mediated pathway independent of the Rac-JNK cascade.\",\n      \"method\": \"Binding assays, in vitro kinase assay, Drosophila loss-of-function genetics, epistasis with Rac-JNK pathway\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic epistasis in Drosophila with biochemical characterization; ortholog with conserved domain architecture\",\n      \"pmids\": [\"10323867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PKN2 knockout results in embryonic lethality at E10 with mesoderm collapse; PKN1 and PKN3 single knockouts are viable, demonstrating that PKN1 is non-essential for early development in mice; mouse embryonic fibroblasts depend on PKN2 (not PKN1) for proliferation and motility.\",\n      \"method\": \"PKN isoform-specific knockout mice, conditional/inducible deletion, MEF proliferation and motility assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout of all three isoforms with defined phenotypic readouts distinguishing isoform-specific roles\",\n      \"pmids\": [\"26774483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PKN1 expression and CPI-17 (PPP1R14A) phosphorylation are dramatically increased in pregnant human myometrium; PKN1, as a RhoA effector, phosphorylates CPI-17 to inhibit myosin phosphatase, increasing calcium-independent myosin light chain phosphorylation (calcium sensitization) in uterine smooth muscle.\",\n      \"method\": \"Western blotting of human myometrial tissue, immunohistochemistry, measurement of GTP-RhoA levels\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — biochemical evidence from tissue samples establishing PKN1 as a RhoA effector in smooth muscle calcium sensitization, single study\",\n      \"pmids\": [\"17301291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Downstream of the Gαq-RhoA signaling axis in uveal melanoma, PKN/PRK converges with ROCK to control FAK (focal adhesion kinase) signaling; pharmacological inhibition of PKN by darovasertib synergizes with FAK inhibitors in uveal melanoma.\",\n      \"method\": \"High-throughput chemogenetic screen, pharmacological inhibition, in vitro and in vivo mouse metastasis models\",\n      \"journal\": \"Cell reports. Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pathway placement established by drug combination studies with in vivo validation, single study\",\n      \"pmids\": [\"37858338\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PKN1 is a RhoA/Rac1-activated serine/threonine kinase (also activated by arachidonic acid and caspase-3 cleavage) that, downstream of Rho GTPases, phosphorylates multiple cytoskeletal substrates (neurofilaments, vimentin, GFAP, tau at Ser-320, alpha-actinin, MARCKS, EGFR Thr654, CPI-17, RPH3A) to regulate intermediate filament assembly, microtubule dynamics, and actin organization; undergoes stress-induced nuclear translocation; mediates cardiac myocyte survival during ischemia/reperfusion via alphaB-crystallin phosphorylation and proteasome activation; controls mitotic timing by inhibiting Cdc25C; regulates tight junction sealing in mammary epithelium; directs polarized RAB21 vesicle trafficking in neutrophils; and represses NF-κB and Wnt/β-catenin signaling, with its autoinhibitory domain (residues 455–511) relieved by fatty acids or Rho binding.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll classify each paper first, then extract discoveries only from KEPT papers (those about PKN1/PRK1, the canonical protein kinase N1).\n\n**Classification summary:**\n- Papers about PAK1 (p21-activated kinase 1, gene PAK1) are ALIAS COLLISIONS — PAK1 is a completely different protein from PKN1/PRK1. Most of the retrieved papers (1-6, 8, 10-12, 15, 17-20, 22, 24-28, 33, 36, 39-42, 44-53, 55, 58-59, 61-62, 64, 69-72, 75, 78-82, 87-88, 94, 98-100) are about PAK1.\n- Papers [73] and [97] describe bacterial/fission yeast kinases with no relation to mammalian PKN1.\n- Papers [21] is about Ark/Prk family in yeast endocytosis — EXCLUDE.\n- Papers clearly about PKN1/PRK1: [7, 9, 13, 14, 16, 23, 29, 31, 32, 34, 35, 37, 38, 43, 44, 54, 56, 57, 60, 63, 65, 66, 68, 74, 76, 77, 80, 83, 84, 85, 89, 90, 92, 93, 96] and from curated list [20, 29, 30].\n- High-citation proteomics/interactome papers without PKN1-specific mechanistic findings: EXCLUDE for discovery extraction.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"PKN (PKN1) was identified as a direct binding partner and downstream effector of RhoA. GTP-bound RhoA physically interacted with and activated PKN in vitro and in COS-7 cells, and PKN was phosphorylated in Swiss 3T3 cells stimulated with lysophosphatidic acid in a Rho-dependent manner, establishing PKN as the first serine/threonine kinase target of Rho GTPase.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, botulinum C3 exoenzyme inhibition in cells\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus cell-based validation, foundational discovery replicated extensively\",\n      \"pmids\": [\"8571127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The amino-terminal region of PKN1 (residues 33–111, particularly residues 74–113) is sufficient for RhoA binding, and this interaction inhibits the GTPase activity of RhoA, suggesting a reciprocal regulatory mechanism that sustains GTP-bound active RhoA.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay with synthetic peptide competition\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro binding with deletion/peptide mapping, multiple orthogonal methods\",\n      \"pmids\": [\"8647255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PKN1 phosphorylates MARCKS at the same PKC sites (serine 152, 156, and 163) in cell extracts and in vitro, identifying MARCKS as a shared substrate for PKN1 and PKC signaling pathways.\",\n      \"method\": \"In vitro kinase assay with cell extracts, phosphopeptide mapping\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation with site identification by mass spectrometry/sequencing\",\n      \"pmids\": [\"8557118\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"PKN1 undergoes stress-induced nuclear translocation: under heat shock (42°C), sodium arsenite, or serum starvation, PKN1 redistributes from the cytoplasm to the nucleus in NIH 3T3, BALB/c 3T3, and Rat-1 cells, and returns to the cytoplasm after recovery, indicating PKN1 may relay stress signals to the nucleus.\",\n      \"method\": \"Immunofluorescence confocal microscopy, biochemical subcellular fractionation and immunoblotting\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment with functional context, two orthogonal methods\",\n      \"pmids\": [\"8816775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PKN1 interacts with alpha-actinin via its N-terminal region (outside the RhoA-binding domain), binding specifically to the third spectrin-like repeats of both skeletal and non-muscle alpha-actinin. The interaction with non-muscle alpha-actinin's EF-hand motifs is Ca2+-sensitive, and phosphatidylinositol 4,5-bisphosphate stimulates binding of full-length alpha-actinin to PKN1, linking PKN1 to the cytoskeletal network.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding with truncation mutants, co-immunoprecipitation from COS7 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus in vitro domain mapping, multiple binding partners characterized\",\n      \"pmids\": [\"9030526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PKN1 associates with and phosphorylates the head-rod domain of neurofilament L, M, and H subunits. PKN1 binding was mapped to the amino-terminal regulatory region of PKN1 and the head-rod domain of neurofilaments. Phosphorylation of neurofilament L by PKN1 inhibited its polymerization in vitro.\",\n      \"method\": \"Yeast two-hybrid, GST pulldown, in vitro kinase assay with purified neurofilaments, polymerization assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution, functional consequence (inhibition of polymerization), multiple methods\",\n      \"pmids\": [\"8621664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"PKN1 phosphorylates vimentin and GFAP in the head domain, and this phosphorylation nearly completely inhibits filament formation of both intermediate filament proteins in vitro. The interaction was mapped by yeast two-hybrid and in vitro binding assay to the regulatory domain of PKN1.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, in vitro kinase assay, filament assembly assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation with functional consequence (inhibition of filament formation)\",\n      \"pmids\": [\"9175763\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PRK1/PKN1 contains two HR1 repeats (HR1a and HR1b) that both bind RhoA independently; HR1a binds exclusively to GTP-RhoA, while HR1b binds both GTP- and GDP-RhoA, indicating two independent contact sites on RhoA. The related HR1 motif in PRK2 also confers RhoA binding, and a C. elegans HR1a sequence similarly binds RhoA.\",\n      \"method\": \"In vitro binding assays with truncation mutants, Rho/Rac chimeras, nucleotide-loaded RhoA variants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic in vitro domain mapping with multiple protein variants and nucleotide-state specificity\",\n      \"pmids\": [\"9446575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PKN1 is cleaved by caspase-3 at specific aspartate residues during apoptosis (Fas ligation, staurosporin, etoposide treatment), generating a constitutively active kinase fragment. The major cleavage occurs between the N-terminal regulatory and C-terminal catalytic domains. Site-directed mutagenesis of the aspartate cleavage sites prevented fragment generation.\",\n      \"method\": \"In vitro caspase-3 cleavage assay, site-directed mutagenesis, immunoblotting of apoptotic cells with caspase inhibitor\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro cleavage plus mutagenesis confirming sites, replicated in multiple cell lines\",\n      \"pmids\": [\"9751706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Drosophila Pkn (ortholog of mammalian PKN1) binds specifically to GTP-activated Rho1 and Rac1 through distinct binding sites, and binding to either GTPase increases kinase activity. Loss-of-function pkn mutants show defects specifically in epidermal cell shape changes during dorsal closure, acting in a Rho1-dependent pathway independent of the Rac-JNK transcriptional cascade.\",\n      \"method\": \"Genetic loss-of-function mutant analysis, in vitro binding and kinase assays, epistasis in Drosophila embryogenesis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo genetic epistasis plus in vitro biochemistry, Drosophila ortholog with conserved domain architecture\",\n      \"pmids\": [\"10323867\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"PKN1 contains an autoinhibitory domain within residues 455–511 that inhibits kinase activity in a substrate-competitive manner (Ki = 0.6 µM) and is selectively relieved by arachidonic acid (IC50 raised ~100-fold). Autophosphorylation at Thr64, Ser374, and Thr531 in the regulatory region and Thr774 in the activation loop are required for full PKN1 kinase activity.\",\n      \"method\": \"In vitro kinase assay with deletion/point mutants expressed in insect cells, competitive inhibition analysis\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic mutagenesis and reconstituted in vitro assays defining autoinhibitory mechanism\",\n      \"pmids\": [\"10467162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CG-NAP (later known as AKAP450/AKAP9) was identified as a PKN1-interacting scaffolding protein that co-localizes with PKN1 at the centrosome and Golgi apparatus. CG-NAP also binds PKA regulatory subunit RIIα, PP2A catalytic subunit, and PP1, establishing it as a multi-enzyme scaffold at these organelles.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence microscopy\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus colocalization, multiple binding partners verified\",\n      \"pmids\": [\"10358086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PKN1 phosphorylates tau at microtubule-binding domain sites Ser258, Ser320, and Ser352; Ser320 is a PKN1-specific site not phosphorylated by any PKC subtype. PKN1 activation disrupts microtubule arrays both in vitro and in vivo, and dephosphorylation at Ser320 is regulated by calcineurin (PP2B).\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis, phosphorylation-specific antibody (HIA3), cell-based tubulin polymerization assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation with site identification, novel PKN1-specific site validated with phospho-specific antibody in cells\",\n      \"pmids\": [\"11104762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"PKN1 (as a Rho effector) stimulates ANF gene transcription via a serum response element (SRE) in cardiomyocytes. Constitutively active PKN1 robustly activated a luciferase reporter driven by the ANF promoter SRE, and this effect required dominant-active Rho; dominant-negative Rho blocked both phenylephrine-induced and PKN1-stimulated ANF expression.\",\n      \"method\": \"Luciferase reporter assay in neonatal rat ventricular myocytes, dominant-negative/constitutively active mutant expression\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-based reporter assay with genetic epistasis, single lab\",\n      \"pmids\": [\"10843871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PKN1 inhibits Cdc25C phosphatase activity by direct phosphorylation, thereby delaying mitotic timing. Active PKN1 microinjected into Xenopus embryos caused cleavage arrest; in cycling egg extracts, active PKN1 delayed Tyr15 dephosphorylation of Cdc2 and Cdc2/cyclin B activation. The kinase-negative form had no effect.\",\n      \"method\": \"Xenopus microinjection, cell-free cycling extract assay, in vitro kinase assay of Cdc25C by PKN1\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro direct phosphorylation plus in vivo Xenopus epistasis, kinase-dead control\",\n      \"pmids\": [\"11134534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PKN1 is one of three mammalian isoforms (PKNα/PAK-1/PRK-1, PKNβ, and PRK2/PAK-2/PKNγ) of a serine/threonine kinase family with a catalytic domain homologous to PKC and a unique regulatory region containing antiparallel coiled-coil (ACC/HR1) domains. PKN1 is the first identified serine/threonine kinase activated by a small GTPase (Rho) and also activated by fatty acids such as arachidonic acid in vitro.\",\n      \"method\": \"Review synthesizing biochemical characterization across isoforms\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — review consolidating prior reconstitution and in vitro data from multiple independent studies\",\n      \"pmids\": [\"12761194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PRK1/PKN1 exists as an integral plasma membrane pool in mammalian cells. Phosphorylation of Ser377 of PRK1 is required for membrane integration. Only the membrane-associated form of PRK1 can mediate RhoA-dependent androgen receptor transcriptional activation in prostate epithelial cells and RhoA-induced neurite retraction in neuronal cells.\",\n      \"method\": \"Membrane fractionation, site-directed mutagenesis (S377A), functional reporter assays, neurite retraction assay\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis of functional site coupled with two distinct cellular functional readouts\",\n      \"pmids\": [\"15375078\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The Salmonella effector SspH1 interacts with PKN1 via its leucine-rich repeat domain. Expression of constitutively active PKN1 decreases NF-κB-dependent reporter gene expression, while siRNA depletion of PKN1 increases NF-κB activity, identifying PKN1 as a negative regulator of NF-κB signaling that is exploited by SspH1.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, NF-κB luciferase reporter assay, siRNA knockdown\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — yeast two-hybrid plus co-IP plus functional reporter with both gain- and loss-of-function\",\n      \"pmids\": [\"16611232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The HR1b domain of PRK1/PKN1 binds exclusively to Rac1 (not RhoA), while HR1a binds both. NMR solution structure of the HR1b–Rac1 complex reveals that HR1b contacts the C-terminal effector loop, switch 2, and the polybasic C-terminal region of Rac1. The Rac1 polybasic region forms a novel recognition element for effector binding.\",\n      \"method\": \"NMR structure determination, mutational analysis of binding interface\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional validation of binding interface\",\n      \"pmids\": [\"18006505\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PKN1 mRNA and protein expression are dramatically increased in pregnant human myometrium, and PKN1 phosphorylates CPI-17 (PPP1R14A) to inhibit myosin phosphatase, contributing to calcium sensitization and uterine contractile activity. Elevated GTP-bound RhoA correlates with increased PKN1 signaling in spontaneous preterm labor.\",\n      \"method\": \"Immunoblotting, phosphorylation assays, immunohistochemistry on human myometrial tissue\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — functional phosphorylation mechanism in human tissue but primarily correlative; single lab\",\n      \"pmids\": [\"17301291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Constitutively active PKN1 expressed in transgenic mouse mammary epithelium impairs tight junction sealing at parturition (demonstrated by paracellular sucrose permeability assay) and causes precocious involution, while dominant-negative PKN1 accelerates tight junction sealing in EpH4 cells, revealing PKN1 as a negative regulator of tight junction sealing via glucocorticoid signaling.\",\n      \"method\": \"Transgenic mouse model, intraductal injection permeability assay, EpH4 cell tight junction assay, dominant-negative/constitutively active mutants\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo transgenic phenotype plus in vitro gain/loss-of-function with functional readout\",\n      \"pmids\": [\"17591691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PKN1 is cleaved and activated by caspase in SOD1-G93A transgenic mice (ALS model) and by glutamate treatment in neurons. A constitutively active (cleaved) form of PKN1, but not wild-type PKN1, disrupts neurofilament organization and impairs axonal transport in neurons, suggesting that deregulated PKN1 contributes to ALS pathology.\",\n      \"method\": \"Immunoblotting of SOD1G93A mice, neuronal cell culture with glutamate, axonal transport assay, expression of cleaved vs. wild-type PKN1\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — disease model plus functional assay, single lab\",\n      \"pmids\": [\"18519042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A 15-amino-acid peptide (PRL) derived from residues 485–499 of the C2-like domain of PKN1 selectively inhibits all PKN isoforms (Ki = 0.7 µM) in vitro without inhibiting PKC. Cell-permeable delivery of PRL inhibited PKN1-mediated tau phosphorylation at the PKN1-specific site Ser320 in vivo.\",\n      \"method\": \"In vitro kinase assay with peptide inhibitor, cell-based phosphorylation assay with phospho-specific antibody, cell-penetrating peptide delivery\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro characterization plus in-cell functional validation with specific readout\",\n      \"pmids\": [\"19857203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKN1 is activated during myocardial ischemia/reperfusion (I/R), evidenced by Thr774 phosphorylation. Cardiac-specific overexpression of constitutively active PKN1 in transgenic mice significantly reduces myocardial infarct size and apoptosis after I/R, while dominant-negative PKN1 worsens injury. PKN1 mediates phosphorylation of αB-crystallin and stimulates proteasome activity as part of its cytoprotective mechanism.\",\n      \"method\": \"Transgenic mouse I/R model, TUNEL assay, in vivo and in vitro kinase assays, proteasome activity assay, pharmacological proteasome inhibition\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — transgenic gain/loss-of-function in vivo with mechanistic downstream targets identified\",\n      \"pmids\": [\"20595653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKN1 is activated by hypotonic swelling in cardiac myocytes through a Src→RhoA→PKN1 cascade, and PKN1 in turn activates ERK via MEK to promote cell survival. Knockdown of PKN1 inhibited HS-induced ERK phosphorylation and reduced myocyte survival under hypotonic stress.\",\n      \"method\": \"siRNA knockdown, constitutively active PKN1 overexpression, co-immunoprecipitation (PKN1–RhoA), kinase activity assays, cell viability assay\",\n      \"journal\": \"American journal of physiology. Heart and circulatory physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pathway placement by knockdown/overexpression with defined downstream readouts, single lab\",\n      \"pmids\": [\"21037231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKN1 and PKN2 substrate recognition requires an arginine at position −3 relative to the phosphoserine, while arginines at +1 (PKN1) or −1 (PKN3) are not tolerated. Using a peptide library and protein array approach, 22 novel PKN1 substrates were identified, and EGFR Thr654 was confirmed as a PKN1 phosphorylation site in vitro and in vivo.\",\n      \"method\": \"Oriented peptide library screen, protein array, in vitro kinase assay, in vivo phosphorylation with PKN modulation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic substrate specificity determination plus novel substrate validation in vitro and in vivo\",\n      \"pmids\": [\"21749319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKN2 but not PKN1 or PKN3 is required for cell migration and invasion in 5637 bladder tumor cells. Using chimeric PKN constructs swapping regulatory domains between isoforms, PKN isoform-specific migration functions are conferred by their distinct N-terminal regulatory domains, indicating that different upstream signals are selectively coupled to PKN isoforms.\",\n      \"method\": \"siRNA knockdown, rescue with wild-type and chimeric PKN constructs, migration and invasion assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — domain-swap rescue experiment defining regulatory specificity, single lab\",\n      \"pmids\": [\"21754995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKN1 represses Wnt/β-catenin signaling in melanoma cells. siRNA depletion of PKN1 enhances β-catenin-activated reporter activity and increases WNT3A-induced apoptosis. Affinity purification–mass spectrometry revealed that PKN1 resides in a protein complex with Frizzled 7 and associated proteins, placing PKN1 upstream of β-catenin as a signaling repressor.\",\n      \"method\": \"siRNA screen, β-catenin luciferase reporter assay, affinity purification–mass spectrometry\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional siRNA with reporter plus interactome data, single lab\",\n      \"pmids\": [\"24114839\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PRK1/PKN1 kinase activity is required for migration and invasion of androgen-independent prostate cancer cells. PKN1 regulates migration-relevant gene expression via interaction with scaffold protein SPAG9/JIP4, leading to p38 phosphorylation; depletion of ELK1 (p38 effector) or p38 recapitulates PKN1 depletion phenotypes. A PRK1 inhibitor prevented metastasis in mice.\",\n      \"method\": \"siRNA knockdown, transcriptome and interactome analysis, co-immunoprecipitation, in vivo mouse metastasis model with pharmacological inhibitor\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, in vivo validation, epistasis establishing pathway\",\n      \"pmids\": [\"25504435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PKN2 knockout in mice causes lethality at embryonic day 10 due to failure of embryonic mesoderm expansion and cardiovascular defects. PKN1 and PKN3 single knockouts are viable, establishing PKN2 as specifically non-redundant. Mouse embryonic fibroblasts (mesodermal origin) require PKN2 for proliferation and motility, and PKN2 is required for neural crest migration in vivo.\",\n      \"method\": \"Conditional and constitutive knockout mice, embryonic phenotyping, MEF proliferation/motility assays, in vivo neural crest migration analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — complete knockout phenotyping across all three isoforms in vivo with cellular mechanism\",\n      \"pmids\": [\"26774483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PKN1 phosphorylates RPH3A, which enhances RPH3A binding to GTP-bound RAB21. This PKN1→RPH3A→RAB21 phosphorylation cascade drives polarized vesicle trafficking in neutrophils, leading to PIP5K1C90 polarization, integrin activation, and adhesion to endothelial cells. Myeloid-specific loss of PKN1 decreases tissue injury in renal ischemia-reperfusion in vivo.\",\n      \"method\": \"In vitro kinase assay, co-immunoprecipitation, neutrophil polarization/adhesion assay, conditional PKN1 knockout mice, ischemia-reperfusion model\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct phosphorylation demonstrated in vitro, functional consequence in cells and in vivo, multiple methods\",\n      \"pmids\": [\"28636945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKCβI is recruited to AR target gene promoters by PRK1/PKN1 as a 'gatekeeper kinase,' and this PKCβI phosphorylates histone H3 at threonine 6 (H3T6ph) to prevent LSD1 from demethylating H3K4 during androgen-dependent gene expression. PRK1 activation is required for the androgen-stimulated recruitment of PKCβI to promoters.\",\n      \"method\": \"ChIP, RNAi knockdown, in vitro histone phosphorylation assay, prostate cancer xenograft model\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — chromatin biochemistry plus in vitro reconstitution, in vivo cancer model validation\",\n      \"pmids\": [\"20228790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In GNAQ-mutant uveal melanoma, PKN/PRK (downstream of the Gαq–RhoA axis) converges with ROCK to control FAK activity. Darovasertib inhibits both PKC and PKN/PRK and synergizes with FAK inhibitors to halt uveal melanoma growth in vitro and in preclinical metastatic mouse models, identifying PKN as part of a non-canonical Gαq signaling vulnerability.\",\n      \"method\": \"High-throughput chemogenetic drug screen, kinase inhibitor profiling, in vitro cell viability assays, preclinical mouse metastasis models\",\n      \"journal\": \"Cell reports. Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — chemogenetic screen with in vivo validation, but PKN isoform-specific mechanistic details are limited\",\n      \"pmids\": [\"37858338\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PKN1 (PRK1) is a Rho/Rac-activated AGC-family serine/threonine kinase whose N-terminal HR1 repeats directly bind GTP-RhoA and GTP-Rac1 to relieve autoinhibition (mediated by residues 455–511) and activate the C-terminal catalytic domain (requiring Thr774 phosphorylation); it is also activated by arachidonic acid, caspase-3 cleavage (generating a constitutively active fragment), and hypo-osmotic or ischemic stress via a Src–RhoA–PDK1 cascade. Established substrates include neurofilament subunits, vimentin, GFAP, tau (Ser320-specific), MARCKS, alpha-actinin, Cdc25C (inhibiting mitotic entry), CPI-17 (promoting myosin phosphatase inhibition and smooth muscle contraction), EGFR Thr654, and RPH3A (driving polarized RAB21 vesicle trafficking in neutrophils). PKN1 scaffolds at the centrosome/Golgi via CG-NAP, translocates to the nucleus under stress, represses NF-κB and Wnt/β-catenin signaling, regulates ANF gene transcription via SRE, and acts as a gatekeeper upstream of PKCβI-mediated H3T6 phosphorylation during androgen receptor-driven transcription; in the heart it protects against ischemia/reperfusion injury by phosphorylating αB-crystallin and stimulating proteasome activity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PKN1 is a RhoA- and Rac1-activated serine/threonine kinase that functions as a central effector of Rho GTPase signaling to regulate cytoskeletal organization, cell cycle progression, vesicle trafficking, and cell survival. Its catalytic domain is related to PKC, and its N-terminal regulatory region contains HR1 repeats that bind GTP-RhoA (via HR1a) and Rac1 (via HR1b), while an internal autoinhibitory domain (residues 455–511) is relieved by arachidonic acid or Rho binding; caspase-3 cleavage during apoptosis removes the regulatory region to generate a constitutively active kinase fragment [PMID:12761194, PMID:18006505, PMID:9751706, PMID:10467162]. PKN1 phosphorylates intermediate filament proteins (neurofilaments, vimentin, GFAP) to inhibit their polymerization, phosphorylates tau at Ser-320 to disrupt microtubules, phosphorylates Cdc25C to delay mitotic entry, and phosphorylates CPI-17 and RPH3A to modulate myosin phosphatase activity and polarized RAB21 vesicle trafficking in neutrophils, respectively [PMID:8621664, PMID:9175763, PMID:11104762, PMID:11134534, PMID:28636945, PMID:17301291]. PKN1 also protects cardiac myocytes from ischemia/reperfusion injury through alphaB-crystallin phosphorylation and proteasome activation, regulates tight junction sealing in mammary epithelium, and represses NF-κB and Wnt/β-catenin signaling [PMID:20595653, PMID:17591691, PMID:16611232, PMID:24114839].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Identifying PKN1 as a Rho-activated kinase with cytoskeletal substrates established it as a direct effector linking Rho GTPase signaling to intermediate filament regulation — previously no serine/threonine kinase was known to be a Rho target.\",\n      \"evidence\": \"Yeast two-hybrid, GST pulldown, in vitro kinase and GTPase assays; neurofilament phosphorylation inhibits polymerization; MARCKS phosphorylation at PKC sites\",\n      \"pmids\": [\"8621664\", \"8647255\", \"8557118\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKN1-mediated neurofilament phosphorylation occurs in intact neurons\", \"Relative contribution of PKN1 vs. PKC to MARCKS phosphorylation in vivo\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Discovery that PKN1 phosphorylates vimentin/GFAP to block filament assembly and binds alpha-actinin broadened PKN1's role from neurofilaments to a general regulator of cytoskeletal architecture, connecting it to actin crosslinking as well as intermediate filaments.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding with truncation mutants, in vitro kinase assays showing inhibition of vimentin filament formation\",\n      \"pmids\": [\"9175763\", \"9030526\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether alpha-actinin binding modulates PKN1 kinase activity\", \"In vivo relevance of vimentin phosphorylation by PKN1\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Mapping the two HR1 repeats to distinct RhoA-binding modes and discovering caspase-3 cleavage-mediated constitutive activation defined the dual regulatory logic of PKN1 — GTPase-dependent activation in healthy cells and proteolytic activation during apoptosis.\",\n      \"evidence\": \"Truncation mutants with Rho/Rac chimeras for HR1a/HR1b binding; recombinant caspase-3 cleavage with site-directed mutagenesis\",\n      \"pmids\": [\"9446575\", \"9751706\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of caspase-generated kinase fragment in apoptotic cells beyond cleavage observation\", \"Whether HR1a vs. HR1b selectivity applies to all Rho family members\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of the autoinhibitory domain (residues 455–511) and key phosphorylation sites (including activation loop Thr774) explained how PKN1 is kept inactive and how fatty acids bypass GTPase-dependent activation, completing the intramolecular regulation model.\",\n      \"evidence\": \"Deletion and site-directed mutagenesis with in vitro kinase assays using insect cell–expressed protein; inhibitory peptide Ki determination\",\n      \"pmids\": [\"10467162\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the upstream kinase(s) responsible for Thr774 phosphorylation\", \"Structural basis of autoinhibition at atomic resolution\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Drosophila Pkn genetics demonstrated that the Rho-PKN axis is an evolutionarily conserved morphogenetic pathway controlling epithelial cell shape changes, independent of the Rac-JNK cascade — establishing in vivo developmental relevance.\",\n      \"evidence\": \"Drosophila loss-of-function mutants, epistasis with Rac-JNK pathway, in vitro Rho1/Rac1 binding and kinase assays\",\n      \"pmids\": [\"10323867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific substrates mediating dorsal closure downstream of Pkn\", \"Whether mammalian PKN1 plays analogous roles in epithelial morphogenesis\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstrating that PKN1 phosphorylates tau at Ser-320 to disrupt microtubules extended its substrate repertoire beyond intermediate filaments to the microtubule cytoskeleton, connecting PKN1 to neurodegeneration-relevant tau phosphorylation.\",\n      \"evidence\": \"In vitro kinase assay with phospho-specific antibody (HIA3), active/inactive PKN1 expression in CHO cells disrupting microtubule array\",\n      \"pmids\": [\"11104762\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKN1-mediated tau phosphorylation occurs in human neurodegenerative disease\", \"Relative contribution of PKN1 vs. other tau kinases in vivo\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"PKN1 was shown to delay mitotic entry by phosphorylating and inhibiting Cdc25C, establishing a cell cycle regulatory function beyond cytoskeletal control.\",\n      \"evidence\": \"Microinjection into Xenopus embryos causing cleavage arrest, cycling extract assays, in vitro Cdc25C phosphorylation with kinase-dead controls\",\n      \"pmids\": [\"11134534\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific Cdc25C phosphorylation site(s) targeted by PKN1\", \"Whether this mechanism operates in mammalian somatic cells\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery that a phospho-Ser377-dependent integral membrane pool of PKN1 mediates RhoA-dependent androgen receptor transactivation and neurite retraction revealed that subcellular compartmentalization is critical for PKN1 signaling specificity.\",\n      \"evidence\": \"Subcellular fractionation, Ser377 mutagenesis, reporter assays, neuronal cell neurite retraction model\",\n      \"pmids\": [\"15375078\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which Ser377 phosphorylation promotes membrane integration\", \"Identity of Ser377 kinase\", \"Not independently confirmed by other laboratories\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"NMR structure of HR1b–Rac1 showed that PKN1 is a bona fide dual Rho/Rac effector with structurally distinct binding interfaces, and functional studies demonstrated that PKN1 regulates tight junction sealing and smooth muscle calcium sensitization through CPI-17 phosphorylation.\",\n      \"evidence\": \"NMR solution structure of HR1b-Rac1 complex; transgenic mouse mammary gland model with CA/DN PKN1; human myometrial tissue biochemistry\",\n      \"pmids\": [\"18006505\", \"17591691\", \"17301291\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Rac1 and RhoA binding to PKN1 are mutually exclusive\", \"How tight junction sealing is molecularly disrupted by PKN1 activity\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linking caspase-mediated PKN1 cleavage to neurofilament disruption and axonal transport failure in ALS models connected the 1998 caspase-cleavage discovery to a specific neurodegenerative pathomechanism.\",\n      \"evidence\": \"SOD1-G93A transgenic mice, glutamate-treated neurons, overexpression of truncated vs. wild-type PKN1\",\n      \"pmids\": [\"18519042\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether preventing PKN1 cleavage rescues axonal transport in ALS models\", \"Confirmation in human ALS tissue\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"In vivo transgenic mouse studies established PKN1 as a cardioprotective kinase during ischemia/reperfusion, acting through alphaB-crystallin phosphorylation and proteasome activation — the first defined pro-survival signaling pathway for PKN1.\",\n      \"evidence\": \"Cardiac-specific CA-PKN1 and DN-PKN1 transgenic mice, I/R injury model, proteasome activity assay, Src/RhoA epistasis with pharmacological inhibitors\",\n      \"pmids\": [\"20595653\", \"21037231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific alphaB-crystallin phosphorylation site(s) targeted by PKN1\", \"How proteasome activation mechanistically confers cardioprotection\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defining the PKN1 substrate consensus motif (Arg at -3 of Ser) and identification of EGFR Thr654 and RPH3A as substrates, together with myeloid-specific knockout showing reduced ischemic injury, expanded PKN1's functional repertoire to receptor signaling and polarized vesicle trafficking in innate immune cells.\",\n      \"evidence\": \"Combinatorial peptide library, protein array, in vitro kinase assays; PKN1 conditional knockout mouse with renal I/R model; co-IP showing RPH3A-RAB21 interaction enhancement\",\n      \"pmids\": [\"21749319\", \"28636945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full in vivo substrate spectrum of PKN1\", \"Whether PKN1 regulates neutrophil trafficking in human inflammatory disease\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identifying PKN1 as a negative regulator of both NF-κB and Wnt/β-catenin signaling — and as a Frizzled 7 complex component — positioned PKN1 at the intersection of inflammatory and developmental signaling pathways beyond cytoskeletal regulation.\",\n      \"evidence\": \"RNAi/reporter assays for NF-κB; AP-MS identifying Frizzled 7 complex; β-catenin reporter assay after PKN1 depletion in melanoma cells\",\n      \"pmids\": [\"16611232\", \"24114839\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct phosphorylation targets mediating Wnt/β-catenin repression\", \"Mechanism connecting PKN1 to NF-κB pathway suppression\", \"Independent replication of Frizzled 7 complex membership\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Systematic knockout of all three PKN isoforms revealed PKN1 is dispensable for mouse viability (unlike essential PKN2), clarifying that PKN1's physiological roles involve tissue-specific or stress-responsive functions rather than core developmental requirements.\",\n      \"evidence\": \"PKN1, PKN2, PKN3 single and conditional knockout mice; MEF proliferation and motility assays\",\n      \"pmids\": [\"26774483\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Compensatory mechanisms between PKN isoforms\", \"Phenotypes of PKN1/PKN3 double knockout\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placing PKN alongside ROCK as convergent Gαq-RhoA effectors controlling FAK signaling in uveal melanoma, and demonstrating drug synergy with FAK inhibitors, provided a therapeutic framework for targeting PKN-dependent cancers.\",\n      \"evidence\": \"High-throughput chemogenetic screen, darovasertib treatment, in vitro and in vivo uveal melanoma models\",\n      \"pmids\": [\"37858338\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contribution of PKN1 vs. PKN2/PKN3 to FAK regulation in uveal melanoma\", \"Direct PKN1 substrates in the FAK pathway\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The full in vivo substrate spectrum, the structural basis of autoinhibition at atomic resolution, and the extent to which PKN1 functions are compensated by PKN2/PKN3 in specific tissues remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length PKN1 crystal or cryo-EM structure\", \"Tissue-specific functions versus isoform redundancy not systematically mapped\", \"Upstream kinase for activation loop Thr774 not definitively identified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 3, 8, 10, 11, 20, 21]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [1, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 4, 5, 16, 18, 29]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [25]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"RHOA\",\n      \"RAC1\",\n      \"ACTN1\",\n      \"MAPT\",\n      \"VIM\",\n      \"CDC25C\",\n      \"RPH3A\",\n      \"SPAG9\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"PKN1 is a Rho/Rac-activated AGC-family serine/threonine kinase that transduces small GTPase signals into cytoskeletal remodeling, cell cycle control, transcriptional regulation, and stress-protective responses. Its N-terminal HR1a domain binds GTP-RhoA while HR1b binds both Rac1 and RhoA, relieving an internal autoinhibitory segment (residues 455–511) to activate a C-terminal catalytic domain that phosphorylates intermediate filament proteins (neurofilament L, vimentin, GFAP) to inhibit their polymerization, tau at the PKN1-specific site Ser320 to disrupt microtubules, Cdc25C to delay mitotic entry, CPI-17 to promote myosin phosphatase inhibition, RPH3A to drive polarized RAB21-dependent vesicle trafficking in neutrophils, and EGFR at Thr654 [PMID:8571127, PMID:8621664, PMID:11104762, PMID:11134534, PMID:17301291, PMID:28636945, PMID:21749319]. PKN1 also functions as a gatekeeper kinase that recruits PKCβI to androgen receptor target promoters, enabling H3T6 phosphorylation that protects H3K4 methylation marks from LSD1 demethylation, and it represses NF-κB and Wnt/β-catenin signaling [PMID:20228790, PMID:16611232, PMID:24114839]. Under stress, PKN1 translocates to the nucleus and, in the heart, protects against ischemia/reperfusion injury by phosphorylating αB-crystallin and stimulating proteasome activity through a Src–RhoA–PDK1 activation cascade [PMID:8816775, PMID:20595653, PMID:21037231].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of PKN1 as the first serine/threonine kinase directly activated by a Rho-family GTPase established a new effector arm downstream of RhoA signaling, answering how Rho could regulate serine/threonine phosphorylation.\",\n      \"evidence\": \"Co-immunoprecipitation, in vitro kinase assays, and C3 exoenzyme inhibition in COS-7 and Swiss 3T3 cells\",\n      \"pmids\": [\"8571127\", \"8647255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of kinase activation by RhoA binding not yet resolved\", \"Physiological substrates unknown at this stage\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Discovery that PKN1 phosphorylates MARCKS at PKC sites and undergoes stress-induced nuclear translocation placed PKN1 at the intersection of PKC-like signaling and nuclear stress responses, expanding its functional scope beyond a simple Rho effector.\",\n      \"evidence\": \"In vitro kinase assays with phosphopeptide mapping (MARCKS); immunofluorescence and subcellular fractionation under heat shock, arsenite, and serum starvation\",\n      \"pmids\": [\"8557118\", \"8816775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear targets of translocated PKN1 not identified\", \"Whether nuclear translocation is kinase-activity-dependent was unknown\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Demonstration that PKN1 phosphorylates intermediate filament proteins (neurofilament subunits, vimentin, GFAP) and inhibits their polymerization in vitro established a direct role for PKN1 in cytoskeletal remodeling, answering how Rho signaling controls intermediate filament dynamics.\",\n      \"evidence\": \"In vitro kinase and filament assembly assays with purified neurofilaments, vimentin, and GFAP; yeast two-hybrid and GST pulldown mapping\",\n      \"pmids\": [\"8621664\", \"9175763\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo relevance of intermediate filament phosphorylation by PKN1 not demonstrated\", \"Specific phosphorylation sites on vimentin/GFAP not fully mapped\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Structural dissection of the HR1 repeats showed that HR1a and HR1b independently bind RhoA with different nucleotide-state preferences, and that caspase-3 cleaves PKN1 to generate a constitutively active fragment during apoptosis, resolving two key regulatory mechanisms: GTPase-selective activation and irreversible proteolytic activation.\",\n      \"evidence\": \"In vitro binding with truncation mutants and nucleotide-loaded GTPases; in vitro caspase-3 cleavage with site-directed mutagenesis in apoptotic cells\",\n      \"pmids\": [\"9446575\", \"9751706\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether caspase-generated fragment has distinct substrates in vivo unknown\", \"Crystal structure of HR1a–RhoA complex not yet available\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of a pseudosubstrate autoinhibitory domain (residues 455–511) relieved by arachidonic acid, and key autophosphorylation sites including activation-loop Thr774, defined the intramolecular regulation of PKN1 kinase activity, answering how the enzyme stays inactive in the absence of upstream signals.\",\n      \"evidence\": \"In vitro kinase assays with deletion/point mutants expressed in insect cells, competitive inhibition kinetics\",\n      \"pmids\": [\"10467162\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether arachidonic acid activates PKN1 physiologically in cells was not resolved\", \"Full interplay between GTPase binding and autoinhibition release not structurally defined\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovery that PKN1 is scaffolded at the centrosome and Golgi via CG-NAP/AKAP450 alongside PKA, PP2A, and PP1 revealed a spatially organized signaling platform, answering how PKN1 is positioned near specific substrates in dividing cells.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, immunofluorescence colocalization\",\n      \"pmids\": [\"10358086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of centrosomal PKN1 not directly tested\", \"Whether CG-NAP scaffolding is regulated by Rho-GTP unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Drosophila Pkn loss-of-function mutants showed defective dorsal closure (epidermal cell shape changes) in a Rho1-dependent but Rac-JNK-independent pathway, providing the first in vivo genetic evidence that PKN family kinases act specifically in Rho-driven morphogenesis.\",\n      \"evidence\": \"Genetic loss-of-function and epistasis analysis in Drosophila embryos combined with in vitro kinase assays\",\n      \"pmids\": [\"10323867\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian in vivo requirement for PKN1 in morphogenesis not established at this stage\", \"Substrates of Drosophila Pkn during dorsal closure unknown\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"PKN1 was shown to phosphorylate tau at the novel PKN1-specific site Ser320 (disrupting microtubules) and to stimulate ANF gene transcription via SRE in cardiomyocytes, broadening PKN1's substrate repertoire to include microtubule-associated proteins and revealing a role in cardiac gene regulation.\",\n      \"evidence\": \"In vitro kinase assays with phospho-specific antibodies and cell-based tubulin polymerization assays (tau); luciferase reporter assays with dominant-active/negative Rho in neonatal cardiomyocytes (ANF)\",\n      \"pmids\": [\"11104762\", \"10843871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKN1-mediated tau phosphorylation contributes to tauopathy in vivo unknown\", \"Transcriptional targets beyond ANF in cardiomyocytes not identified\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Direct phosphorylation of Cdc25C by PKN1, which delayed Cdc2 dephosphorylation and mitotic entry in Xenopus extracts and embryos, answered how a Rho effector kinase could regulate cell cycle progression.\",\n      \"evidence\": \"Xenopus microinjection, cycling egg extract assays, in vitro kinase assay with kinase-dead control\",\n      \"pmids\": [\"11134534\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cdc25C phosphorylation site by PKN1 not identified\", \"Whether this mitotic delay function operates in mammalian somatic cells untested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery of a Ser377-phosphorylation-dependent plasma membrane pool of PKN1 that is required for both RhoA-dependent androgen receptor transactivation and neurite retraction resolved the question of how spatial compartmentalization controls PKN1 function.\",\n      \"evidence\": \"Membrane fractionation, S377A mutagenesis, AR reporter and neurite retraction assays\",\n      \"pmids\": [\"15375078\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for Ser377 phosphorylation not identified\", \"Whether membrane-integrated PKN1 has distinct substrates unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"PKN1 was identified as a negative regulator of NF-κB signaling, exploited by the Salmonella effector SspH1 to suppress host immunity, answering how Rho-dependent kinase activity intersects with innate immune transcription.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, NF-κB reporter with PKN1 overexpression and siRNA depletion\",\n      \"pmids\": [\"16611232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation target linking PKN1 to NF-κB inhibition not identified\", \"In vivo relevance to Salmonella infection in animals untested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"NMR structure of the HR1b–Rac1 complex revealed a novel recognition mechanism involving Rac1's polybasic C-terminal region, resolving the structural basis for PKN1's dual GTPase specificity and answering how a single kinase integrates Rho and Rac inputs.\",\n      \"evidence\": \"NMR solution structure with mutational validation of binding interface\",\n      \"pmids\": [\"18006505\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How simultaneous Rho and Rac binding is coordinated on full-length PKN1 is unresolved\", \"No full-length PKN1 structure available\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"PKN1 phosphorylation of CPI-17 in pregnant human myometrium linked Rho–PKN1 signaling to calcium sensitization and smooth muscle contraction, while PKN1 regulation of tight junction sealing in mammary epithelium revealed tissue-specific roles in epithelial barrier function.\",\n      \"evidence\": \"Immunohistochemistry and phosphorylation assays on human myometrial tissue; transgenic mouse mammary model with dominant-negative and constitutively active PKN1\",\n      \"pmids\": [\"17301291\", \"17591691\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"CPI-17 phosphorylation site specificity by PKN1 not mapped\", \"Myometrial data are correlative with preterm labor rather than causal\", \"Tight junction mechanism downstream of PKN1 not molecularly resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"PKN1 was established as a cardioprotective kinase during ischemia/reperfusion via phosphorylation of αB-crystallin and stimulation of proteasome activity, activated through a Src→RhoA→PKN1 cascade under osmotic and ischemic stress, answering how Rho signaling promotes cardiomyocyte survival.\",\n      \"evidence\": \"Cardiac-specific transgenic mice with constitutively active/dominant-negative PKN1 in I/R models; siRNA and overexpression with ERK readout in hypotonic stress\",\n      \"pmids\": [\"20595653\", \"21037231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"αB-crystallin phosphorylation site(s) by PKN1 not identified\", \"Whether PKN1 and PKN2 have redundant roles in cardiac protection unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"PKN1 was shown to act as a gatekeeper kinase that recruits PKCβI to androgen receptor target promoters, enabling H3T6 phosphorylation that prevents LSD1-mediated H3K4 demethylation, establishing PKN1 as a chromatin-level regulator of hormone-dependent transcription.\",\n      \"evidence\": \"ChIP, RNAi, in vitro histone phosphorylation, prostate cancer xenograft model\",\n      \"pmids\": [\"20228790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PKN1 directly phosphorylates a chromatin substrate at AR promoters or acts solely as a scaffold is unclear\", \"Generalizability to other nuclear receptor targets untested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Systematic substrate specificity profiling defined the PKN1 consensus motif (requiring Arg at −3) and validated EGFR Thr654 as a direct PKN1 substrate, broadening the kinase's substrate landscape to include receptor tyrosine kinases.\",\n      \"evidence\": \"Oriented peptide library, protein array, in vitro and in vivo phosphorylation of EGFR Thr654\",\n      \"pmids\": [\"21749319\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of EGFR Thr654 phosphorylation by PKN1 not determined\", \"Many of the 22 novel array-identified substrates remain unvalidated in cells\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery that PKN1 phosphorylates RPH3A to enhance its binding to GTP-RAB21, driving polarized vesicle trafficking, integrin activation, and neutrophil adhesion, answered how PKN1 controls immune cell polarity and provided the first in vivo loss-of-function phenotype for mammalian PKN1 (reduced renal ischemia-reperfusion injury in myeloid-specific knockouts).\",\n      \"evidence\": \"In vitro kinase assay, co-immunoprecipitation, neutrophil polarization/adhesion assays, conditional PKN1 knockout mice, renal I/R model\",\n      \"pmids\": [\"28636945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RPH3A phosphorylation by PKN1 operates in non-myeloid contexts unknown\", \"Specific phosphorylation site(s) on RPH3A not reported\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"In GNAQ-mutant uveal melanoma, PKN/PRK was placed in a non-canonical Gαq–RhoA signaling arm that converges with ROCK to control FAK, identifying PKN as a therapeutic vulnerability synergizing with FAK inhibition.\",\n      \"evidence\": \"Chemogenetic drug screen, kinase inhibitor profiling, preclinical mouse metastasis models\",\n      \"pmids\": [\"37858338\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PKN isoform specificity (PKN1 vs PKN2/3) in uveal melanoma not resolved\", \"Direct PKN substrates mediating FAK regulation not identified\", \"Darovasertib inhibits both PKC and PKN, confounding isoform-specific conclusions\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length structure of PKN1 showing how HR1-mediated GTPase binding, autoinhibitory domain relief, and activation-loop phosphorylation are coordinated remains unavailable, and tissue-specific non-redundant functions relative to PKN2 and PKN3 are incompletely mapped despite single-knockout viability data.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length PKN1 crystal or cryo-EM structure\", \"Tissue-specific conditional knockout phenotypes for PKN1 beyond myeloid cells are lacking\", \"Nuclear substrates mediating PKN1's transcriptional effects are mostly unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 5, 6, 10, 12, 14, 19, 22, 23, 25, 30, 31]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 2, 5, 6, 12, 14, 25, 30]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [17, 27, 31]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [4, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 31]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [16]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 7, 9, 17, 18, 24, 27, 32]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [8, 21]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [13, 31]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [17, 30]},\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [30]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [28, 32]}\n    ],\n    \"complexes\": [\n      \"CG-NAP/AKAP450 scaffold complex\"\n    ],\n    \"partners\": [\n      \"RHOA\",\n      \"RAC1\",\n      \"AKAP9\",\n      \"ACTN1\",\n      \"MAPT\",\n      \"RPH3A\",\n      \"SPAG9\",\n      \"FZD7\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}