title: Dexamethasone stimulates store-operated calcium entry and protein degradation in cultured L6 myotubes through a phospholipase A(2)-dependent mechanism.
abstract: Muscle wasting in various catabolic conditions is at least in part regulated by glucocorticoids. Increased calcium levels have been reported in atrophying muscle. Mechanisms regulating calcium homeostasis in muscle wasting, in particular the role of glucocorticoids, are poorly understood. Here we tested the hypothesis that glucocorticoids increase intracellular calcium concentrations in skeletal muscle and stimulate store-operated calcium entry (SOCE) and that these effects of glucocorticoids may at least in part be responsible for glucocorticoid-induced protein degradation. Treatment of cultured myotubes with dexamethasone, a frequently used in vitro model of muscle wasting, resulted in increased intracellular calcium concentrations determined by fura-2 AM fluorescence measurements. When SOCE was measured by using calcium "add-back" to muscle cells after depletion of intracellular calcium stores, results showed that SOCE was increased 15-25% by dexamethasone and that this response to dexamethasone was inhibited by the store-operated calcium channel blocker BTP2. Dexamethasone treatment stimulated the activity of calcium-independent phospholipase A(2) (iPLA(2)), and dexamethasone-induced increase in SOCE was reduced by the iPLA(2) inhibitor bromoenol lactone (BEL). In additional experiments, treatment of myotubes with the store-operated calcium channel inhibitor gadolinium ion or BEL reduced dexamethasone-induced increase in protein degradation. Taken together, the results suggest that glucocorticoids increase calcium concentrations in myocytes and stimulate iPLA(2)-dependent SOCE and that glucocorticoid-induced muscle protein degradation may at least in part be regulated by increased iPLA(2) activity, SOCE, and cellular calcium levels.
authors.affiliation: Dept. of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Itagaki
authors.forename: Michael
authors.initials: M
authors.lastname: Menconi
authors.forename: Bozena
authors.initials: B
authors.lastname: Antoniu
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhang
authors.forename: Patricia
authors.initials: P
authors.lastname: Gonnella
authors.forename: David
authors.initials: D
authors.lastname: Soybel
authors.forename: Carl
authors.initials: C
authors.lastname: Hauser
authors.forename: Per-Olof
authors.initials: PO
authors.lastname: Hasselgren
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation; D020868:Gene Silencing; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D054467:Phospholipases A2 / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D046509:Tissue Culture Techniques
chemical_list: D012333:RNA, Messenger; D034741:RNA, Small Interfering; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D054467:Phospholipases A2