title: Upregulation of IL-6 mRNA by IL-6 in skeletal muscle cells: role of IL-6 mRNA stabilization and Ca2+-dependent mechanisms.
abstract: Skeletal muscle cells have been established as significant producers of IL-6 during exercise. This IL-6 production is discussed as one possible mediator of the beneficial effects of physical activity on glucose and fatty acid metabolism. IL-6 itself could be the exercise-related factor that upregulates and maintains its own production. We investigated this hypothesis and the underlying molecular mechanism in cultured C(2)C(12) cells. IL-6 led to a rapid and prolonged increase in IL-6 mRNA, which was also found in human myotubes. Because IL-6 has been shown to activate AMP-activated kinase (AMPK), we studied whether, in turn, activated AMPK induces IL-6 expression. Pharmacological activation of AMPK with 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside upregulated IL-6 mRNA expression, which was blocked by knockdown of AMPK alpha(1) and alpha(2) using small, interfering RNA (siRNA) oligonucleotides. However, the effect of IL-6 was shown to be independent of AMPK, since the siRNA approach silencing the AMPK alpha-subunits did not reduce the upregulation of IL-6 induced by IL-6 stimulation. The self-stimulatory effect of IL-6 partly involves a Ca(2+)-dependent pathway: IL-6 increased intracellular Ca(2+), and intracellular blockade of Ca(2+) with a Ca(2+) chelator reduced the IL-6-mediated increase in IL-6 mRNA levels. Moreover, inhibition of Ca(2+)/calmodulin-dependent kinase kinase with STO-609 or the siRNA approach decreased IL-6 mRNA levels of control and IL-6-stimulated cells. A major, STO-609-independent mechanism is the IL-6-mediated stabilization of its mRNA. The data suggest that IL-6 could act as autocrine factor upregulating its mRNA levels, thereby supporting its function as an exercise-activated factor in skeletal muscle cells.
authors.affiliation: Dept. of Internal Medicine, Division of Endocrinology, Metabolism, Pathobiochemistry and Clinical Chemistry, Univ. of Tuebingen, Otfried-Mueller-Straaae 10, D-72076 Tuebingen, Germany. cora.weigert@med.uni-tuebingen.de
authors.forename: Cora
authors.initials: C
authors.lastname: Weigert
authors.forename: Martina
authors.initials: M
authors.lastname: Düfer
authors.forename: Perikles
authors.initials: P
authors.lastname: Simon
authors.forename: Evaine
authors.initials: E
authors.lastname: Debre
authors.forename: Heike
authors.initials: H
authors.lastname: Runge
authors.forename: Katrin
authors.initials: K
authors.lastname: Brodbeck
authors.forename: Hans U
authors.initials: HU
authors.lastname: Häring
authors.forename: Erwin D
authors.initials: ED
authors.lastname: Schleicher
mesh_terms: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D019898:Autocrine Communication / Q000187:drug effects / Q000502:physiology; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D015850:Interleukin-6 / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D020871:RNA Stability / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D015854:Up-Regulation / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D007004:Hypoglycemic Agents; D015850:Interleukin-6; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; C526181:PRKAA2 protein, human; D017346:Protein Serine-Threonine Kinases; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D048051:p38 Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases; C526180:PRKAA1 protein, human; D019703:Calcineurin; C031143:AICA ribonucleotide; D002118:Calcium