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Junctophilins 1, 2, and 3 all support voltage-induced Ca2+ release despite considerable divergence
1Department of Physiology and Biophysics, University of Colorado, Anschutz Medical Campus, Aurora, CO.
The Journal of General Physiology
|January 28, 2022
Summary
Juncopphilins (JPHs) 1 and 3, like JPH2, support voltage-induced calcium release by forming essential ER-PM junctions. JPH4, however, does not support this process, highlighting isoform-specific functions in calcium signaling.
Area of Science:
- Cellular Biology
- Molecular Physiology
- Biophysics
Background:
- Skeletal muscle depolarization triggers calcium release from the sarcoplasmic reticulum (SR) via voltage-induced calcium release (VICR).
- Junctophilins (JPHs) are critical for forming the specialized structures, SR-plasma membrane (PM) junctions, where VICR occurs.
- Previous studies confirmed JPH2's role in VICR, but the functions of other JPH isoforms remained unclear.
Purpose of the Study:
- To investigate whether JPH1, JPH3, and JPH4 can mediate voltage-induced calcium release (VICR) in HEK293 cells.
- To explore the role of different JPH isoforms in the recruitment of CaV1.1 and RYR1 to ER-PM junctions.
- To understand the functional implications of JPH isoform divergence in skeletal muscle calcium signaling.
Main Methods:
- Coexpression of JPH isoforms (JPH1-4) with CaV1.1, β1a, Stac3, and RYR1 in HEK293 cells.
- Confocal microscopy to assess the colocalization of CaV1.1 and RYR1 at ER-PM junctions.
- Potassium-induced depolarization to elicit cytoplasmic calcium transients, using both wild-type and calcium-impermeant CaV1.1 mutants.
Main Results:
- JPH1, JPH2, and JPH3 successfully recruited CaV1.1 and RYR1 to ER-PM junctions, recapitulating VICR even with a calcium-impermeant CaV1.1 mutant.
- JPH4 expression led to ER-PM junctions containing CaV1.1 but not RYR1, and failed to support depolarization-induced calcium transients.
- These findings indicate that JPH1, JPH2, and JPH3 support VICR, while JPH4 does not.
Conclusions:
- JPH1, JPH2, and JPH3 are functionally capable of supporting voltage-induced calcium release by forming functional ER-PM junctions and recruiting necessary proteins.
- JPH4, while capable of forming ER-PM junctions with CaV1.1, does not support RYR1 recruitment or VICR.
- JPH isoforms primarily function in organizing junctional structures and protein recruitment, rather than directly mediating the CaV1.1-RYR1 interaction in VICR.
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