title: Knocking down type 2 but not type 1 calsequestrin reduces calcium sequestration and release in C2C12 skeletal muscle myotubes.
abstract: We examined the roles of type 1 and type 2 calsequestrins (CSQ1 and CSQ2) in stored Ca2+ release of C2C12 skeletal muscle myotubes. Transduction of C2C12 myoblasts with CSQ1 or CSQ2 small interfering RNAs effectively reduced the expression of targeted CSQ protein to near undetectable levels. As compared with control infected or CSQ1 knockdown myotubes, CSQ2 and CSQ1/CSQ2 knockdown myotubes had significantly reduced stored Ca2+ release evoked by activators of intracellular Ca2+ release channel/ryanodine receptor (10 mM caffeine, 200 microM 4-chloro-m-cresol, or 10 mM KCl). Thus, CSQ1 is not essential for effective stored Ca2+ release in C2C12 myotubes despite our in vitro studies suggesting that CSQ1 may enhance ryanodine receptor channel activity. To determine the basis of the reduced stored Ca2+ release in CSQ2 knockdown myotubes, we performed immunoblot analyses and found a significant reduction in both sarco/endoplasmic reticulum Ca2+-ATPase and skeletal muscle ryanodine receptor proteins in CSQ2 and CSQ1/CSQ2 knockdown myotubes. Moreover, these knockdown myotubes exhibited reduced Ca2+ uptake and reduced stored Ca2+ release by UTP (400 microM) that activates a different family of intracellular Ca2+ release channels (inositol 1,4,5-trisphosphate receptors). Taken together, our data suggest that knocking down CSQ2, but not CSQ1, leads to reduced Ca2+ storage and release in C2C12 myotubes.
authors.affiliation: Department of Biochemistry and Biophysics, Gene Therapy Center, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Le
authors.initials: L
authors.lastname: Xu
authors.forename: Hongzhe
authors.initials: H
authors.lastname: Duan
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Pasek
authors.forename: Jerry P
authors.initials: JP
authors.lastname: Eu
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meissner
mesh_terms: D000818:Animals; D001483:Base Sequence; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002155:Calsequestrin / Q000037:antagonists & inhibitors* / Q000145:classification / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D011817:Rabbits
chemical_list: D002135:Calcium-Binding Proteins; D002155:Calsequestrin; C503130:Casq1 protein, mouse; D034741:RNA, Small Interfering