PXN

Paxillin (PXN) is a focal adhesion scaffold protein that couples integrin-based adhesion and mechanical inputs to actin remodeling, cell migration, and tumor progression (PMID:37846507, PMID:34466738). Its disordered N-terminal domain undergoes conformational compaction upon binding the C-terminal FAT domain of FAK, forming a multi-state fuzzy complex that is necessary and sufficient to localize FAK to focal adhesions [PMID:bio_10.1101_2025.01.01.630265]. PXN function is gated by competing phosphorylation: FAK/Src phosphorylate tyrosine residues to promote focal adhesion assembly, while ULK1/2 directly phosphorylate S32 and S119 to weaken PXN homotypic interactions and liquid-liquid phase separation, thereby opposing focal adhesion assembly, stress fiber formation, and migration (PMID:37846507). At adhesions, substrate stiffness drives FAK/PXN phosphorylation that activates Rac1 and downstream YAP nuclear translocation to specify endothelial tip cells, and PXN sits functionally upstream of focal-adhesion and adherens-junction tension buildup (PMID:34466738). In cancer, multiple upstream inputs converge on PXN phosphorylation and expression to drive migration and invasion: ANGPTL4 binding NRP1 triggers ABL1-dependent PXN phosphorylation (PMID:37169211), CXCL5 activates a PXN/AKT cascade that upregulates PD-L1 for immune evasion (PMID:39034411), and integrin β1 feeds a PXN/YWHAZ/AKT axis (PMID:34977001, PMID:34589278). PXN expression is transcriptionally controlled by STAT3, ETV4, and LSD1 and is suppressed by miR-212, while PXN reciprocally activates STAT3 via SRC and stabilizes YB-1 against ubiquitin-mediated degradation, establishing feed-forward loops in tumor cells (PMID:25285406, PMID:41872167, PMID:26693054, PMID:28468300, PMID:31670855).

1. 2012 Low

   Established a tissue-specific expression context for PXN as a focal adhesion scaffold, showing it is selectively present in pillar cells of the developing organ of Corti.

   Evidence Reporter expression analysis and in situ hybridization in mouse inner ear

   PMID:22446079

   Open questions at the time

   • No functional consequence of pillar-cell expression established
   • No mechanism linking PXN to inner ear development
   • Localization-only, single study
2. 2014 Medium

   Connected chromatin-level regulation to PXN, showing the demethylase LSD1 controls PXN transcription and a LSD1→PXN phosphorylation→migration axis.

   Evidence ChIP-seq, transcriptome, siRNA knockdown and migration assays in prostate cancer cells

   PMID:25285406

   Open questions at the time

   • Whether LSD1 acts directly at the PXN locus versus indirectly not fully resolved
   • Kinase responsible for the downstream PXN phosphorylation not identified
3. 2015 Medium

   Identified a post-transcriptional brake on PXN, demonstrating miR-212 directly targets the PXN 3'UTR to suppress invasion.

   Evidence Luciferase 3'UTR reporter, miRNA mimic/inhibitor, rescue, in vitro/in vivo invasion in gastric cancer

   PMID:26693054

   Open questions at the time

   • Other miR-212 targets contributing to phenotype not excluded
   • Does not address PXN protein-level activity changes
4. 2017 Medium

   Mapped a direct transcriptional input by showing STAT3 binds the PXN promoter to drive PXN-mediated tumor angiogenesis.

   Evidence EMSA and ChIP at the PXN promoter, HUVEC angiogenesis assay in ER+ breast cancer cells

   PMID:28468300

   Open questions at the time

   • Direction of causality within Src/FAK/STAT3 loop not fully dissected
   • Pharmacological agent (nobiletin) may have off-target effects
5. 2018 Medium

   Placed PXN within a YAP1-FAK/PXN signaling module governing the switch from collective to mesenchymal invasion.

   Evidence IHC correlation, invasion assays, Src-family inhibition in nasopharyngeal carcinoma

   PMID:30504771

   Open questions at the time

   • PXN's specific contribution versus FAK/YAP1 not separated
   • Direct molecular link between cytoplasmic LIF and PXN unresolved
6. 2019 Medium

   Added a second direct transcriptional activator, showing ETV4 upregulates PXN to drive proliferation and migration.

   Evidence Luciferase reporter, microarray, gain/loss-of-function in NSCLC cells

   PMID:31670855

   Open questions at the time

   • ETV4 binding site within PXN regulatory region not mapped precisely
   • PXN inhibition only partially abolishes ETV4 effects
7. 2021 Medium

   Defined the mechanotransduction output of PXN phosphorylation, linking substrate stiffness through FAK/PXN to Rac1 activation and YAP-driven endothelial tip cell specification.

   Evidence Tunable hydrogels, phospho-WB, Rac1 GTP-pulldown, YAP imaging, loss-of-function in endothelial cells

   PMID:34466738

   Open questions at the time

   • Specific phospho-residues mediating Rac1 activation not defined
   • How p-PXN loosens intercellular junctions mechanistically unclear
8. 2021 Medium

   Embedded PXN in integrin and small-GTPase signaling cascades, placing it downstream of ITGB1 and CDC42/ITGB1 in AKT-coupled migration and cell-cycle pathways.

   Evidence siRNA knockdown, phospho-WB, CDC42 rescue, migration/invasion, xenograft in HCC and gastric cancer

   PMID:34589278 PMID:34977001

   Open questions at the time

   • Direct versus indirect regulation of PXN by ITGB1 not distinguished in HCC study (Low confidence)
   • Mechanism of YWHAZ involvement in the axis not detailed
9. 2023 High

   Revealed an antagonistic regulatory logic on PXN, showing ULK1/2 directly phosphorylate S32/S119 to weaken PXN phase separation and oppose FAK/Src-driven focal adhesion assembly.

   Evidence In vitro kinase assay, S32/S119 mutagenesis, phase separation assay, FA imaging, KO/KD migration phenotypes

   PMID:37846507

   Open questions at the time

   • How the ULK1/2 versus FAK/Src balance is set in cells not defined
   • Physiological signals controlling ULK1/2 phosphorylation of PXN unknown
10. 2023 Medium

    Identified an upstream receptor-kinase route to PXN phosphorylation, showing ANGPTL4/NRP1/ABL1 drives PXN phosphorylation and migration.

    Evidence Co-receptor binding, siRNA of NRP1/ABL1, dasatinib, phospho-PXN WB, migration in HNSCC

    PMID:37169211

    Open questions at the time

    • ABL1 phospho-target residues on PXN not mapped
    • dasatinib inhibits multiple kinases beyond ABL1
11. 2024 Medium

    Linked PXN to immune evasion, showing CXCL5 drives a PXN/AKT cascade that upregulates PD-L1 in a positive feedback loop.

    Evidence Gene silencing, p-PXN/p-AKT WB, PD-L1 flow cytometry, xenograft in lung cancer

    PMID:39034411

    Open questions at the time

    • Direct biochemical link between p-PXN and AKT activation not shown
    • Mechanism by which PXN/AKT controls PD-L1 transcription unresolved
12. 2025 Medium

    Resolved the structural basis of FAK recruitment, showing the disordered PXN N-terminus forms a multi-state fuzzy complex with the FAK FAT domain that is necessary and sufficient to localize FAK to adhesions.

    Evidence NMR and SAXS ensemble analysis of the PXN–FAT disordered complex (preprint)

    PMID:bio_10.1101_2025.01.01.630265

    Open questions at the time

    • Preprint, not yet peer-reviewed
    • Functional consequence of individual fuzzy states in cells not tested
    • How phosphorylation reshapes the fuzzy ensemble not addressed
13. 2025 Low

    Positioned PXN upstream of force buildup in early transformation, showing PXN is required for transient FA and adherens-junction tension and the proliferative advantage of Src-activated cells.

    Evidence siRNA, FRET tension biosensors at FAs/AJs, FAK inhibition, proliferation assays (preprint)

    PMID:bio_10.1101_2025.07.05.663275

    Open questions at the time

    • Preprint, single lab, not peer-reviewed
    • Molecular link between PXN and adherens-junction tension not defined
    • Connection to EGFR-ERK/MRTF-A-SRF axis correlative
14. 2026 Medium

    Established a self-reinforcing transcriptional circuit and a protein-stabilization role, showing STAT3 drives PXN, PXN reactivates STAT3 via SRC, and PXN stabilizes YB-1 against ubiquitin-mediated degradation.

    Evidence qRT-PCR, WB, mRNA-seq, knockdown, ubiquitination assay in IDH-wildtype GBM

    PMID:41872167

    Open questions at the time

    • Whether PXN regulates YB-1 ubiquitination directly or via an intermediary unknown
    • Mechanism by which PXN controls SRC transcription unresolved

• How the competing FAK/Src and ULK1/2 phosphorylation inputs, the fuzzy PXN-FAT ensemble, and PXN phase separation are integrated to set adhesion dynamics in physiological versus tumor contexts remains unresolved.
• No unified model coupling phosphorylation state to fuzzy-complex conformation and phase behavior
• In vivo physiological role of PXN phase separation untested
• Cytoplasmic versus nuclear/transcriptional functions of PXN not mechanistically reconciled