title: S165F mutation of junctophilin 2 affects Ca2+ signalling in skeletal muscle.
abstract: JPs (junctophilins) contribute to the formation of junctional membrane complexes in muscle cells by physically linking the t-tubule (transverse-tubule) and SR (sarcoplasmic reticulum) membranes. In humans with HCM (hypertrophic cardiomyopathy), mutations in JP2 are linked to altered Ca2+ signalling in cardiomyocytes; however, the effects of these mutations on skeletal muscle function have not been examined. In the present study, we investigated the role of the dominant-negative JP2-S165F mutation (which is associated with human HCM) in skeletal muscle. Consistent with the hypertrophy observed in human cardiac muscle, overexpression of JP2-S165F in primary mouse skeletal myotubes led to a significant increase in myotube diameter and resting cytosolic Ca2+ concentration. Single myotube Ca2+ imaging experiments showed reductions in both the excitation-contraction coupling gain and RyR (ryanodine receptor) 1-mediated Ca2+ release from the SR. Immunoprecipitation assays revealed defects in the PKC (protein kinase C)-mediated phosphorylation of the JP2-S165F mutant protein at Ser165 and in binding of JP2-S165F to the Ca2+ channel TRPC3 (transient receptor potential cation canonical-type channel 3) on the t-tubule membrane. Therefore both the hypertrophy and altered intracellular Ca2+ signalling in the JP2-S165F-expressing skeletal myotubes can be linked to altered phosphorylation of JP2 and/or altered cross-talk among Ca2+ channels on the t-tubule and SR membranes.
authors.affiliation: Department of Physiology, College of Medicine, The Catholic University of Korea, Seoul 137-701, Republic of Korea.
authors.forename: Jin Seok
authors.initials: JS
authors.lastname: Woo
authors.forename: Ji-Hye
authors.initials: JH
authors.lastname: Hwang
authors.forename: Jae-Kyun
authors.initials: JK
authors.lastname: Ko
authors.forename: Noah
authors.initials: N
authors.lastname: Weisleder
authors.forename: Do Han
authors.initials: DH
authors.lastname: Kim
authors.forename: Jianjie
authors.initials: J
authors.lastname: Ma
authors.forename: Eun Hui
authors.initials: EH
authors.lastname: Lee
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D015398:Signal Transduction; D050052:TRPC Cation Channels / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D010726:Phosphodiesterase Inhibitors; D019837:Ryanodine Receptor Calcium Release Channel; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; C412507:junctophilin; D002110:Caffeine; D011493:Protein Kinase C