PKP2

Plakophilin-2 (PKP2) is a desmosomal armadillo-repeat protein that serves as a multifunctional scaffold at cardiac intercalated discs, integrating mechanical coupling, electrical communication, metabolic regulation, and signaling homeostasis in cardiomyocytes. PKP2 physically bridges desmosomal and adherens junction complexes by interacting with desmoplakin and connexin-43, and its loss disrupts both mechanical integrity and gap junction/sodium channel function, causing arrhythmia and ventricular dysfunction (PMID:19084810, PMID:27412010). PKP2 subcellular localization is regulated by C-TAK1-mediated phosphorylation that creates a 14-3-3 binding site (PMID:12941695), and PRMT1-catalyzed arginine methylation stabilizes β-catenin through USP7 recruitment, linking PKP2 to DNA repair and Wnt pathway modulation (PMID:33742119, PMID:29044515). In cardiomyocytes, PKP2 deficiency compromises nuclear envelope integrity causing DNA damage and paracrine oxidative stress, downregulates oxidative phosphorylation via reduced PGC1α expression, and non-cell-autonomously induces pro-inflammatory senescence in neighboring non-myocyte populations (PMID:35959657, PMID:33536940).

1. 2003 High

   Establishing that PKP2 is post-translationally regulated by phosphorylation revealed how its subcellular distribution is controlled: C-TAK1 phosphorylation generates a 14-3-3 docking site that governs PKP2 localization.

   Evidence In vitro kinase assay with mutagenesis of C-TAK1 binding motifs and localization studies

   PMID:12941695

   Open questions at the time

   • Upstream signals that regulate C-TAK1-PKP2 phosphorylation remain undefined
   • Functional consequence of 14-3-3 binding on desmosome assembly not tested
2. 2008 Medium

   Demonstrating that disease-associated PKP2 truncations disrupt interactions with desmoplakin and connexin-43 established PKP2 as a nexus linking desmosomal adhesion to gap junction and ion channel function in cardiomyocytes.

   Evidence Adenoviral expression of R79x and 179fs PKP2 mutants in neonatal rat ventricular myocytes with co-immunoprecipitation and immunofluorescence

   PMID:19084810

   Open questions at the time

   • Studies used overexpression of truncated constructs rather than endogenous mutation knock-in
   • Whether Cx43 loss is due to direct binding loss or secondary remodeling was not resolved
3. 2016 Medium

   An in vivo transgenic model demonstrated that truncated PKP2 causes dose-dependent remodeling of desmosomal, gap junction, and sodium channel proteins with progressive ventricular dysfunction and arrhythmia, confirming PKP2 as a master organizer of intercalated disc integrity.

   Evidence Transgenic mice expressing PKP2-Ser329 at varying content levels with ultrastructural, protein-level, and electrophysiological characterization

   PMID:27412010

   Open questions at the time

   • Mechanism by which truncated PKP2 dominantly destabilizes native full-length PKP2 not defined
   • Contribution of individual downstream targets (Cx43 vs Nav1.5 vs desmosomal proteins) to arrhythmogenesis not dissected
4. 2017 Medium

   Identification of PKP2 as both a direct transcriptional target of Wnt/β-catenin signaling and an antagonist of Wnt/β-catenin transcriptional activity revealed a negative feedback loop through which PKP2 constrains Wnt pathway output.

   Evidence Reporter assays with TCF binding site mutagenesis, ChIP, and overexpression in HEK-293T cells

   PMID:29044515

   Open questions at the time

   • Feedback loop not validated in cardiomyocytes
   • Molecular mechanism by which PKP2 protein antagonizes β-catenin transcriptional activity not identified
5. 2021 High

   Discovery that PRMT1-mediated arginine methylation of PKP2 recruits USP7 to stabilize β-catenin, thereby inducing LIG4 and radioresistance, expanded PKP2's role beyond structural scaffolding to signaling-dependent regulation of DNA repair.

   Evidence CRISPR screen, mass spectrometry identification of arginine methylation, Co-IP for PRMT1-PKP2 and USP7, functional radioresistance assays in lung cancer cells

   PMID:33742119

   Open questions at the time

   • Relevance of PRMT1-PKP2-USP7 axis in cardiomyocytes not tested
   • Whether other armadillo proteins are similarly methylated by PRMT1 is unknown
6. 2021 Medium

   Cardiomyocyte-specific PKP2 knockout revealed that PKP2 loss cell-autonomously upregulates inflammatory/immune transcripts in cardiomyocytes, establishing an intrinsic inflammatory program independent of immune cell infiltration.

   Evidence Cardiac-specific tamoxifen-activated Pkp2-KO mice with RiboTag ribosome-resident transcriptomics; correlation with human GTEx data

   PMID:33536940

   Open questions at the time

   • Transcription factor(s) driving cardiomyocyte-intrinsic inflammatory gene induction not identified
   • Causal relationship between inflammatory gene expression and disease phenotype not established
7. 2022 High

   Demonstrating that PKP2 deficiency compromises nuclear envelope integrity, causing DNA damage and extracellular H₂O₂ release that damages neighboring cells, revealed a non-cell-autonomous paracrine injury mechanism and identified nuclear envelope disruption as an early mechanistic node.

   Evidence High-resolution mass spectrometry, RNA-seq, TEM of human ARVC biopsies, cardiac-specific Pkp2-KO mice, and iPSC-derived PKP2-deficient cardiomyocytes

   PMID:35959657

   Open questions at the time

   • Molecular link between desmosomal PKP2 loss and nuclear envelope destabilization not fully defined
   • Whether antioxidant intervention can prevent disease progression in vivo not tested
8. 2024 Medium

   Identification of MYZAP as a stabilizer of PKP2 and Nav1.5 levels, and CASK as a repressor of PKP2 accumulation at intercalated discs, defined upstream regulators that control PKP2 protein abundance and localization at cell contacts.

   Evidence AAV-mediated CASK knockdown in rat hearts and iPSC-CMs with proteomics and electron microscopy (preprint); cardiac-specific CCRR/MYZAP transgenic and AAV models with protein level measurements

   PMID:39507261 PMID:bio_10.1101_2024.10.14.618172

   Open questions at the time

   • CASK mechanism is from a preprint awaiting peer review
   • Direct physical interaction between MYZAP and PKP2 not demonstrated
   • Whether CASK and MYZAP pathways converge or act independently is unknown
9. 2025 Medium

   Multiple studies converged to show that PKP2 deficiency causes broad metabolic dysfunction — reduced OXPHOS gene expression via PGC1α, impaired lipid homeostasis and glycolysis — and that metabolic restoration partially rescues contractility but not electrophysiological defects, separating metabolic from structural functions of PKP2.

   Evidence RNA-seq and PGC1α rescue in iPSC-CMs and human PKP2 mutant hearts (preprint); metabolite profiling and AAV9:PKP2 vs metabolic enhancer rescue in mouse and iPSC-CM models (preprint)

   PMID:bio_10.1101_2025.01.17.633239 PMID:bio_10.1101_2025.06.02.656790

   Open questions at the time

   • Both metabolic studies are preprints awaiting peer review
   • Mechanism linking PKP2 protein to PGC1α transcriptional regulation is unknown
   • Whether metabolic impairment is downstream of nuclear envelope disruption or independent is unresolved
10. 2025 Medium

    PKP2 deficiency in cardiomyocytes was shown to non-cell-autonomously induce pro-inflammatory senescence (SASP) in neighboring non-myocyte populations including fibroblasts and epicardium-derived cells, with B cell infiltration contributing to early fibrosis, and AAV9-PKP2 gene therapy reversing fibroblast activation via Ptprc.

    Evidence Cardiomyocyte-specific Pkp2-KO mice with multiplex imaging, scRNA-seq, cytokine arrays, epigenetic clocks (preprints); scRNA-seq of Pkp2-KO rat hearts with AAV9-PKP2 rescue and B cell depletion; iPSC-derived epicardial cells with isogenic controls

    PMID:40979216 PMID:41145823 PMID:41279609 PMID:bio_10.1101_2025.10.22.682160

    Open questions at the time

    • Most senescence studies are preprints
    • Whether paracrine H₂O₂ from cardiomyocytes is the direct trigger for non-myocyte senescence is not confirmed
    • Ptprc mechanism of fibroblast phenotypic conversion is correlative
11. 2025 Medium

    Exercise-induced remodeling of β1-adrenergic receptor distribution and sympathetic innervation in PKP2-deficient hearts revealed a previously unknown link between desmosomal integrity and adrenergic signaling that may explain exercise-triggered arrhythmias.

    Evidence Expansion and structured illumination microscopy of β1-AR localization; OCT3 knockdown and pharmacological dissection of catecholamine response in cardiomyocyte-specific Pkp2-KO mice

    PMID:40383179

    Open questions at the time

    • Mechanism by which PKP2 loss causes β1-AR redistribution not defined
    • OCT3 role is based on shRNA knockdown without genetic confirmation
    • Whether β1-AR remodeling is a direct structural consequence or secondary to metabolic/inflammatory changes is unknown

• The molecular link between desmosomal PKP2 loss and nuclear envelope disruption — the central early node connecting structural, metabolic, oxidative, and inflammatory pathologies — remains uncharacterized, and whether distinct PKP2 functions (scaffolding, signaling, metabolic regulation) are mediated by separate protein domains or interaction surfaces is unknown.
• No structural model of PKP2 in complex with nuclear envelope components exists
• Domain-function mapping for PKP2's non-desmosomal roles (metabolic, signaling) has not been performed
• Therapeutic thresholds for PKP2 restoration (how much protein is sufficient) are not defined