JPH3 (Junctophilin 3) is a junctional protein that couples plasma membrane calcium channels to the endoplasmic reticulum, critical for neuronal calcium signaling. JPH3 mutations cause a Huntington's disease-like disorder (HDL2), making it a key protein in understanding CAG repeat expansion diseases.
| JPH3 Protein |
|---|
| Gene | [JPH3](/genes/jph3) |
| UniProt ID | [Q8WXE6](https://www.uniprot.org/uniprotkb/Q8WXE6) |
| PDB Structures | Not determined |
| Molecular Weight | ~75 kDa |
| Subcellular Localization | Plasma membrane-ER junctions |
| Protein Family | Junctophilin family |
JPH3 is a member of the junctophilin family with characteristic domains:
- N-terminal membrane-binding domain: Associates with plasma membrane phospholipids
- Central repeat domain: Forms the structural bridge
- C-terminal transmembrane domain: Anchors to the ER membrane
- Polyglutamine expansion: HDL2 mutation involves CAG repeat expansion
In neurons, JPH3 is essential for calcium signaling:
- ER-Plasma Membrane Coupling: Forms junctional complexes between PM and ER
- Calcium Channel Coupling: Links voltage-gated calcium channels (VGCC) to ryanodine receptors (RyR)
- Synaptic Transmission: Modulates calcium dynamics at synaptic terminals
- Excitation-Contraction Coupling: Critical for muscle function (skeletal muscle)
- Store-Operated Calcium Entry: Regulates SOCE via STIM1-Orai1 interaction
- Neuronal Calcium Homeostasis: Maintains calcium buffering in neurons
JPH3 is expressed in the brain (cortex, hippocampus, basal ganglia), skeletal muscle, and heart.
- CAG repeat expansion: JPH3 mutation causes HDL2, phenocopying Huntington's disease
- Polyglutamine toxicity: Expanded polyglutamine causes toxic gain-of-function
- JPH3 haploinsufficiency: Loss of normal JPH3 function contributes to disease
- Motor symptoms: Chorea, dystonia, parkinsonism
- Cognitive decline: Progressive dementia resembling HD
- JPH3 dysregulation: Altered JPH3 expression in HD brains
- Calcium signaling defects: Impaired calcium handling in HD neurons
- Therapeutic target: JPH3 modulators may benefit HD patients
- Parkinson's Disease: Altered junctophilin expression in PD substantia nigra
- Alzheimer's Disease: Calcium dysregulation involves junctophilin
- Spinocerebellar Ataxias: Some subtypes involve junctophilin dysfunction
Therapeutic approaches for JPH3-related disorders:
| Approach |
Mechanism |
Development Stage |
| Gene therapy |
Wild-type JPH3 delivery |
Research |
| ASO therapy |
Allele-specific knockdown |
Preclinical |
| Calcium stabilizers |
Restore calcium signaling |
Drug screening |
| Polyglutamine modulators |
Reduce toxic protein aggregation |
Research |
- Holmes et al., JPH3 mutation causes HDL2 (2001)
- Walker et al., HDL2 clinicopathology (2007)
- Seo et al., JPH3 in calcium signaling (2008)
- Wilburn et al., JPH3 polyglutamine toxicity (2011)
- Liu et al., JPH3 and neurodegeneration (2022)