title: Functional consequences of stably expressing a mutant calsequestrin (CASQ2D307H) in the CASQ2 null background.
abstract: The role of calsequestrin (CASQ2) in cardiac sarcoplasmic reticulum (SR) calcium (Ca(2+)) transport has gained significant attention since point mutations in CASQ2 were reported to cause ventricular arrhythmia. In the present study, we have critically evaluated the functional consequences of expressing the CASQ2(D307H) mutant protein in the CASQ2 null mouse. We recently reported that the mutant CASQ2(D307H) protein can be stably expressed in CASQ2 null hearts, and it targets appropriately to the junctional SR (Kalyanasundaram A, Bal NC, Franzini-Armstrong C, Knollmann BC, Periasamy M. J Biol Chem 285: 3076-3083, 2010). In this study, we found that introduction of CASQ2(D307H) protein in the CASQ2 null background partially restored triadin 1 levels, which were decreased in the CASQ2 null mice. Despite twofold expression (relative to wild-type CASQ2), the mutant protein failed to increase SR Ca(2+) load. We also found that the Ca(2+) transient decays slower in the CASQ2 null and CASQ2(D307H) cells. CASQ2(D307H) myocytes, when rhythmically paced and challenged with isoproterenol, exhibit spontaneous Ca(2+) waves similar to CASQ2 null myocytes; however, the stability of Ca(2+) cycling was increased in the CASQ2(D307H) myocytes. In the presence of isoproterenol, Ca(2+)-transient amplitude in CASQ2(D307H) myocytes was significantly decreased, possibly indicating an inherent defect in Ca(2+) buffering capacity and release from the mutant CASQ2 at high Ca(2+) concentrations. We also observed polymorphic ventricular tachycardia in the CASQ2(D307H) mice, although lesser than in the CASQ2 null mice. These data suggest that CASQ2(D307H) point mutation may affect Ca(2+) buffering capacity and Ca(2+) release. We propose that poor interaction between CASQ2(D307H) and triadin 1 could affect ryanodine receptor 2 stability, thereby increasing susceptibility to delayed afterdepolarizations and triggered arrhythmic activity.
authors: Department of Physiology and Cell Biology, The Ohio State University College of Medicine, Columbus, USA.
authors: Anuradha
authors: A
authors: Kalyanasundaram
authors: Serge
authors: S
authors: Viatchenko-Karpinski
authors: Andriy E
authors: AE
authors: Belevych
authors: Veronique A
authors: VA
authors: Lacombe
authors: Hyun Seok
authors: HS
authors: Hwang
authors: Björn C
authors: BC
authors: Knollmann
authors: Sandor
authors: S
authors: Gyorke
authors: Muthu
authors: M
authors: Periasamy
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002155:Calsequestrin / Q000235:genetics / Q000378:metabolism*; D002304:Cardiac Pacing, Artificial; D002316:Cardiotonic Agents / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D004562:Electrocardiography; D005838:Genotype; D047908:Intracellular Signaling Peptides and Proteins; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009124:Muscle Proteins / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D010641:Phenotype; D017354:Point Mutation; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D017180:Tachycardia, Ventricular / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D000098850:Polymorphic Catecholaminergic Ventricular Tachycardia
chemical_list: D002155:Calsequestrin; D002316:Cardiotonic Agents; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C498270:Trdn protein, mouse; C514388:casq2 protein, mouse; D007545:Isoproterenol; D002118:Calcium