PDLIM5

PDLIM5 (ENH) is a cytoplasmic PDZ-LIM scaffold/adaptor protein that organizes signaling at the cytoskeleton and synapse and tunes multiple signal transduction outputs (PMID:12665800, PMID:10833443). Through its PDZ domain it binds actin and α-actinin and co-localizes with α-actinin at the cardiomyocyte Z-disk, anchoring it to the actin cytoskeleton (PMID:10833443). Its three C-terminal LIM domains mediate the protein-protein interactions that define its signaling roles: the second LIM domain assembles a Ca²⁺-dependent PKCε–ENH–N-type Ca²⁺ channel ternary complex that enables selective PKC-mediated potentiation of channel activity in neurons, with rising Ca²⁺ strengthening channel binding while dissociating PKCε (PMID:12665800, PMID:15979848). The LIM domains also bind the helix-loop-helix region of Id2, sequestering it in the cytoplasm during neural differentiation to inactivate its transcriptional and cell-cycle functions (PMID:16549780). At the postsynaptic density PDLIM5 interacts with SPAR to control dendritic spine morphology, and PKC activation drives its delivery into spines (PMID:19900557). PDLIM5 is a direct AMPK substrate: phosphorylation at Ser177 suppresses peripheral Rac1 activity, displaces the Arp2/3 complex from the leading edge, and inhibits lamellipodia formation and cell migration, a brake that operates in vascular smooth muscle cells downstream of metformin-AMPK signaling (PMID:25635515, PMID:34368251). In carcinoma contexts it stabilizes TGFβ signaling by binding SMAD3 and competitively blocking its STUB1-mediated proteasomal degradation, thereby sustaining TGFβ-induced EMT (PMID:32737199). Pdlim5 is required for development, as homozygous knockout is embryonic lethal, and reduced dosage produces neurobehavioral phenotypes (PMID:23593136).

1. 2000 High

   Established the cytoskeletal anchoring function of PDLIM5 by showing its PDZ domain links it to the actin/α-actinin Z-disk, defining it as a structural scaffold.

   Evidence GST pulldown and immunofluorescence co-localization in rat neonatal cardiomyocytes, plus identification of LIM-less splice isoforms

   PMID:10833443

   Open questions at the time

   • Functional role of the negatively-modulating short isoforms not tested
   • Does not address signaling outputs of the LIM domains
2. 2003 High

   Answered how PKCε achieves substrate selectivity at neuronal channels by showing ENH acts as an adaptor bridging PKCε to N-type Ca²⁺ channels for selective channel potentiation.

   Evidence Reciprocal co-IP, pulldowns, electrophysiology, and peptide-mediated complex disruption in neurons

   PMID:12665800

   Open questions at the time

   • Which LIM domain mediates the interaction not yet resolved
   • Physiological/behavioral consequence of channel potentiation untested
3. 2005 High

   Refined the ternary complex mechanism by mapping the second LIM domain as the Ca²⁺-dependent binding module and revealing opposing Ca²⁺ effects on channel vs PKCε binding.

   Evidence LIM-domain mutagenesis, Ca²⁺-titrated in vitro binding, co-IP, and demonstration of ENH dimerization

   PMID:15979848

   Open questions at the time

   • Structural basis of Ca²‚ sensing not determined
   • Role of dimerization in complex assembly unclear
4. 2006 High

   Showed PDLIM5 controls neural differentiation non-structurally by using its LIM domains to sequester Id2 in the cytoplasm, inactivating its nuclear functions.

   Evidence Co-IP, GST pulldown, RNAi rescue, and immunofluorescence in retinoic-acid-differentiated neuroblastoma cells

   PMID:16549780

   Open questions at the time

   • Whether other HLH/Id proteins are similarly sequestered untested
   • Link to downstream cell-cycle targets indirect
5. 2009 High

   Placed PDLIM5 at the postsynaptic density as a regulator of dendritic spine shape via SPAR, with PKC controlling its synaptic delivery.

   Evidence Co-IP, RNAi, overexpression, interaction disruption, and spine morphometry in neurons

   PMID:19900557

   Open questions at the time

   • Molecular link between SPAR binding and actin remodeling not defined
   • Whether spine effects require the PKCε/channel complex unknown
6. 2013 Medium

   Provided in vivo evidence that PDLIM5 dosage is essential for development and modulates neurobehavioral phenotypes, connecting its PKCε scaffold role to CNS function.

   Evidence Pdlim5 heterozygous/homozygous knockout mice, behavioral assays, and PKCε translocation-block phenocopy

   PMID:23593136

   Open questions at the time

   • Biochemical mechanism underlying behavioral effects not resolved
   • Embryonic lethal cause of homozygous KO not characterized
7. 2015 High

   Identified PDLIM5 as a direct AMPK substrate and defined a phosphorylation switch (Ser177) that brakes cell migration through Rac1-Arp2/3 suppression.

   Evidence In vitro kinase assay, phosphomimetic/phospho-dead mutants, migration and Rac1 pulldown assays, and immunofluorescence

   PMID:25635515

   Open questions at the time

   • How phospho-Ser177 disrupts Rac-GEF association mechanistically unclear
   • Relationship to the cytoskeletal scaffold function not integrated
8. 2017 Medium

   Suggested a reciprocal relationship in which PDLIM5 binds AMPK and influences its activation/degradation, with knockdown suppressing prostate cancer proliferation and invasion.

   Evidence Co-IP, shRNA knockdown, cell-cycle and invasion assays, and xenograft in prostate cancer cells

   PMID:29228678

   Open questions at the time

   • Mechanism of AMPK regulation by PDLIM5 not resolved
   • Single lab; binding not mapped to specific domains
9. 2020 High

   Defined a TGFβ-pathway function by showing PDLIM5 binds SMAD3 and competitively protects it from STUB1-mediated degradation to sustain signaling and EMT.

   Evidence Reciprocal co-IP, competitive binding, shRNA epistasis with STUB1, proteasome inhibition, migration/invasion, and in vivo metastasis in NSCLC

   PMID:32737199

   Open questions at the time

   • Domain mediating SMAD3 binding not mapped
   • Why SMAD2 is excluded not explained
10. 2021 Medium

    Validated the AMPK-PDLIM5 migration brake in vivo, showing the Ser177 phospho-switch mediates metformin's protection against neointima and atherosclerosis.

    Evidence Phosphomimetic/unphosphorylatable Pdlim5 mutant expression, adenoviral delivery in ApoE-/- mice, wire-injury model, and lineage tracing in VSMCs

    PMID:34368251

    Open questions at the time

    • Largely replicates the 2015 phosphorylation mechanism
    • Endogenous regulation of Ser177 in vivo not directly measured

• How PDLIM5's distinct scaffold functions (cytoskeletal anchoring, PKCε/channel signaling, Id2 sequestration, SMAD3 stabilization, AMPK-Rac1 migration control) are coordinated within a cell, and how isoform composition selects among them, remains unresolved.
• No structural model integrating PDZ and LIM functions
• Isoform-specific functional assignment incomplete
• Tissue-specific partner selection mechanism unknown