title: AMPK activation stimulates myofibrillar protein degradation and expression of atrophy-related ubiquitin ligases by increasing FOXO transcription factors in C2C12 myotubes.
abstract: In skeletal muscle, AMP-activated protein kinase (AMPK) is a metabolic master switch regulating glucose and lipid metabolism. Recently, AMPK has been implicated in the control of protein synthesis in skeletal muscle, but the effect of AMPK activation on myofibrillar protein degradation has yet to be elucidated. The present study was designed to examine the effect of 5-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR)-induced AMPK signaling on effector mechanisms of myofibrillar protein degradation and the expression of atrophy-related genes (atrogin-1/MAFbx, MuRF1, proteasome C2 subunit, calpains, cathepsin B, and caspase-3) in C2C12 myotubes. AICAR stimulated myofibrillar protein degradation (as measured by N(tau)-methylhistidine release), while also increasing the levels of atrogin-1/MAFbx and MuRF1 mRNA, but the expression of other atrophy-related genes was not enhanced by AICAR treatment in C2C12 myotubes. AICAR also stimulated the level of FOXO transcription factors mRNA and protein in C2C12 myotubes. These results indicate that activation of AMPK stimulates myofibrillar protein degradation through the expression of atrogin-1/MAFbx and MuRF1 by increasing FOXO transcription factors in skeletal muscles.
authors.affiliation: Molecular Nutrition Research Team, National Institute of Livestock and Grassland Science, Ikenoda, Tsukuba, Japan. kaznaka@affrc.go.jp
authors.forename: Kazuki
authors.initials: K
authors.lastname: Nakashima
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yakabe
mesh_terms: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000502:physiology; D051858:Forkhead Transcription Factors / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology; D051379:Mice; D009097:Multienzyme Complexes / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000201:enzymology*; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics*; D009133:Muscular Atrophy / Q000201:enzymology*; D009210:Myofibrils / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D012265:Ribonucleotides / Q000502:physiology; D044843:SKP Cullin F-Box Protein Ligases / Q000096:biosynthesis / Q000235:genetics*; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D051858:Forkhead Transcription Factors; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D012265:Ribonucleotides; D000070584:Tripartite Motif Proteins; D000620:Aminoimidazole Carboxamide; C486691:Fbxo32 protein, mouse; D044843:SKP Cullin F-Box Protein Ligases; C499084:Trim63 protein, mouse; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide