title: Suppression of atrogin-1 and MuRF1 prevents dexamethasone-induced atrophy of cultured myotubes.
abstract: OBJECTIVE
  The mechanistic role of the ubiquitin ligases atrogin-1 and MuRF1 in glucocorticoid-induced muscle wasting is not fully understood. Here, we tested the hypothesis that glucocorticoid-induced muscle atrophy is at least in part linked to atrogin-1 and MuRF1 expression and that the ubiquitin ligases are regulated by compensatory mechanisms.
  
  
  METHODS
  The expression of atrogin-1 and MuRF1 was suppressed individually or in combination in cultured L6 myotubes by using siRNA technique. Myotubes were treated with dexamethasone followed by determination of mRNA and protein levels for atrogin-1 and MuRF1, protein synthesis and degradation rates, and myotube morphology.
  
  
  RESULTS
  Suppression of atrogin-1 resulted in increased expression of MuRF1 and vice versa, suggesting that the ubiquitin ligases are regulated by compensatory mechanisms. Simultaneous suppression of atrogin-1 and MuRF1 resulted in myotube hypertrophy, mainly reflecting stimulated protein synthesis, and prevented dexamethasone-induced myotube atrophy, mainly reflecting inhibited protein degradation.
  
  
  CONCLUSIONS
  The results provide evidence for a link between upregulated atrogin-1 and MuRF1 expression and glucocorticoid-induced muscle atrophy. The study also suggests that atrogin-1 and MuRF1 levels are regulated by compensatory mechanisms and that inhibition of both ubiquitin ligases may be needed to prevent glucocorticoid-induced muscle proteolysis and atrophy.
authors.affiliation: Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA.
authors.forename: Estibaliz
authors.initials: E
authors.lastname: Castillero
authors.forename: Nima
authors.initials: N
authors.lastname: Alamdari
authors.forename: Stewart H
authors.initials: SH
authors.lastname: Lecker
authors.forename: Per-Olof
authors.initials: PO
authors.lastname: Hasselgren
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D005938:Glucocorticoids / Q000494:pharmacology; D032342:Muscle Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D009133:Muscular Atrophy / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D014176:Protein Biosynthesis / Q000187:drug effects / Q000235:genetics; D059748:Proteolysis / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics* / Q000378:metabolism*; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D005938:Glucocorticoids; D009124:Muscle Proteins; D012333:RNA, Messenger; D000070584:Tripartite Motif Proteins; D025801:Ubiquitin; D003907:Dexamethasone; C486692:Fbxo32 protein, rat; D044843:SKP Cullin F-Box Protein Ligases; C499086:Trim63 protein, rat; D044767:Ubiquitin-Protein Ligases
keywords: Glucocorticoids; MAFbx; MuRF1; MuRF2; Muscle wasting; NF-κB; PCR; Protein synthesis; Proteolysis; SEM; TCA; TNF; Ubiquitin ligases; eIF3-f; eukaryotic initiation factor 3 subunit 5; muscle RING finger 1; muscle RING finger 2; muscle atrophy F-box; nuclear factor kappa B; polymerase chain reaction; siRNA; small interfering RNA; standard error of the mean; trichloroacetic acid; tumor necrosis factor