GPC6

GPC6 is a GPI-anchored, heparan sulfate-bearing glypican that acts at the cell surface to modulate developmental morphogen signaling, with roles spanning skeletal growth, oncogenic proliferation, and neuronal homeostasis (PMID:10329016, PMID:19481194). Recessive loss-of-function mutations that disrupt both the heparan sulfate-binding site and the GPI-membrane anchor impair endochondral ossification and cause omodysplasia, consistent with Gpc6 expression in proliferative growth-plate chondrocytes (PMID:19481194). Mechanistically, GPC6 stimulates Hedgehog pathway activity, and a missense variant that diminishes this stimulation produces a milder skeletal phenotype (PMID:37353964); in SHH-subgroup medulloblastoma cells GPC6 upregulates GLI1, supports the ciliogenesis required for signal transduction, and facilitates SHH ligand release via extracellular vesicles, driving proliferation, migration, and invasion (PMID:41320180). In the nervous system GPC6 instead potentiates canonical Wnt signaling: its surface levels are restrained by the GPI-anchor-cleaving enzyme GDE2, and excess GPC6 disrupts nuclear pore complex integrity, Ran-dependent nucleocytoplasmic trafficking, and TDP-43 nuclear localization, with genetic reduction of GPC6 in GDE2-deficient neurons rescuing these defects—defining a GDE2–GPC6–Wnt axis controlling NPC integrity [PMID:bio_10.1101_2025.09.24.678385]. The Drosophila ortholog Dlp is a target of TDP-43 and C9orf72 proteinopathy whose restoration mitigates synaptic and behavioral deficits, and a CRISPRi screen confirmed GPC6 as a contributor to TDP-43-dependent synaptic loss in human neurons (PMID:33762006, PMID:42182325).

1. 1999 Medium

   Defined the basic identity of GPC6 as a member of the glypican family, establishing it as a candidate cell-surface regulator of growth and differentiation before any functional role was known.

   Evidence cDNA cloning, sequence analysis, and Northern blot tissue profiling

   PMID:10329016

   Open questions at the time

   • No functional pathway assignment
   • No identification of signaling partners or substrates
2. 2009 Medium

   Established GPC6 as essential for skeletal growth by linking loss-of-function mutations that ablate both the heparan sulfate and GPI-anchor domains to recessive omodysplasia and localizing expression to proliferative growth-plate chondrocytes.

   Evidence Human mutation identification, protein domain analysis, and microdissected mouse growth-plate expression

   PMID:19481194

   Open questions at the time

   • Did not define which signaling pathway GPC6 acts through in chondrocytes
   • Mechanism connecting surface proteoglycan to ossification unresolved
3. 2019 Low

   Extended GPC6 beyond development by showing it promotes a malignant phenotype in nasopharyngeal carcinoma, raising the possibility of a proliferative signaling role in cancer.

   Evidence Proliferation, migration, and invasion assays in NPC cell lines with GPC6 manipulation

   PMID:31417636

   Open questions at the time

   • No molecular mechanism or pathway placement
   • Single-lab cell-line evidence only
4. 2021 Medium

   First implicated the GPC6 ortholog in neurodegenerative proteinopathy by identifying Dlp/GPC6 as a TDP-43 target affecting synaptic compartments, connecting the gene to Wnt-related synaptic biology.

   Evidence TRAP, immunofluorescence, and genetic interaction analysis in a Drosophila TDP-43 proteinopathy model

   PMID:33762006

   Open questions at the time

   • Ortholog-based; human GPC6 not directly tested here
   • Causal direction between Dlp loss and synaptic dysfunction not isolated
5. 2023 Medium

   Pinned the disease-relevant molecular activity of GPC6 to Hedgehog pathway stimulation by showing a hypomorphic missense variant reduces Hh reporter activity and yields a milder skeletal phenotype.

   Evidence Hedgehog reporter assay comparing wild-type and mutant GPC6

   PMID:37353964

   Open questions at the time

   • Did not resolve how GPC6 mechanistically engages the Hh pathway
   • Single method and lab
6. 2025 Medium

   Defined a GDE2–GPC6–Wnt axis in neurons, showing GPC6 surface levels are restrained by GDE2 and that GPC6 excess disrupts nuclear pore integrity and TDP-43 localization, providing a mechanistic bridge between glypican signaling and neurodegeneration.

   Evidence In vivo mouse genetics (GDE2 KO, GPC6 reduction), NPC integrity and nucleocytoplasmic trafficking assays, TDP-43 localization (preprint)

   PMID:bio_10.1101_2025.09.24.678385

   Open questions at the time

   • Preprint, not peer-reviewed
   • Molecular link between Wnt potentiation and NPC disruption not defined
7. 2026 Medium

   Resolved how GPC6 stimulates Hedgehog signaling in cancer—via GLI1 upregulation, ciliogenesis support, and EV-mediated SHH ligand release—while also confirming its synaptic role in human neurons through CRISPRi.

   Evidence Cancer cell-line knockdown/overexpression with GLI1, ciliogenesis and EV assays; Drosophila rescue and CRISPRi in TDP-43 knockdown iNeurons (one preprint)

   PMID:41320180 PMID:42182325

   Open questions at the time

   • One source is a preprint
   • Direct biochemical interaction between GPC6 and Hh/Wnt components not demonstrated
   • Mechanism distinguishing Hh vs Wnt context-specificity unresolved

• How a single surface glypican selectively engages Hedgehog signaling in skeletal/tumor contexts versus canonical Wnt in neurons, and the structural basis of these interactions, remains unresolved.
• No structural model of GPC6 with Hh or Wnt ligands
• No direct binding data for proposed pathway partners
• Context-determining factors for Hh vs Wnt output unknown