Junctophilin 1 and 2 proteins interact with the L-type Ca2+ channel dihydropyridine receptors (DHPRs) in skeletal muscle.
Junctophilins (JPs) anchor the endo/sarcoplasmic reticulum to the plasma membrane, thus contributing to the assembly of junctional membrane complexes in striated muscles and neurons. Recent studies have shown that JPs may be also involved in regulating Ca2+ homeostasis. Here, we report that in skeletal muscle, JP1 and JP2 are part of a complex that, in addition to ryanodine receptor 1 (RyR1), includes caveolin 3 and the dihydropyridine receptor (DHPR). The interaction between JPs and DHPR was mediated by a region encompassing amino acids 230-369 and amino acids 216-399 in JP1 and JP2, respectively. Immunofluorescence studies revealed that the pattern of DHPR and RyR signals in C2C12 cells knocked down for JP1 and JP2 was rather diffused and characterized by smaller puncta in contrast to that observed in control cells. Functional experiments revealed that down-regulation of JPs in differentiated C2C12 cells resulted in a reduction of intramembrane charge movement and the L-type Ca2+ current accompanied by a reduced number of DHPRs at the plasma membrane, whereas there was no substantial alteration in Ca2+ release from the sterol regulatory element-binding protein. Altogether, these results suggest that JP1 and JP2 can facilitate the assembly of DHPR with other proteins of the excitation-contraction coupling machinery.
Molecular Medicine Section, Department of Neuroscience, and Interuniversity Institute of Myology, University of Siena, 53100 Siena, Italy.
Lucia
L
Golini
Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Université Lyon 1, UMR CNRS 5534, 69622 Villeurbanne cedex, France.
Christophe
C
Chouabe
Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Université Lyon 1, UMR CNRS 5534, 69622 Villeurbanne cedex, France.
Christine
C
Berthier
Molecular Medicine Section, Department of Neuroscience, and Interuniversity Institute of Myology, University of Siena, 53100 Siena, Italy.
Vincenza
V
Cusimano
Molecular Medicine Section, Department of Neuroscience, and Interuniversity Institute of Myology, University of Siena, 53100 Siena, Italy.
Mara
M
Fornaro
Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Université Lyon 1, UMR CNRS 5534, 69622 Villeurbanne cedex, France.
Robert
R
Bonvallet
Molecular Medicine Section, Department of Neuroscience, and Interuniversity Institute of Myology, University of Siena, 53100 Siena, Italy.
Luca
L
Formoso
Molecular Medicine Section, Department of Neuroscience, and Interuniversity Institute of Myology, University of Siena, 53100 Siena, Italy.
Emiliana
E
Giacomello
Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Université Lyon 1, UMR CNRS 5534, 69622 Villeurbanne cedex, France.
Vincent
V
Jacquemond
Molecular Medicine Section, Department of Neuroscience, and Interuniversity Institute of Myology, University of Siena, 53100 Siena, Italy. Electronic address: vincenzo.sorrentino@unisi.it.
Vincenzo
V
Sorrentino
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000378:metabolism; D020013:Calcium Signaling; D002454:Cell Differentiation; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry*; D051379:Mice; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism
D020746:Calcium Channels, L-Type; D008565:Membrane Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C412507:junctophilin; D005982:Glutathione Transferase; D002118:Calcium