title: Dexamethasone-induced protein degradation in cultured myotubes is p300/HAT dependent.
abstract: Muscle proteolysis during sepsis and other catabolic conditions is, at least in part, regulated by glucocorticoids. Dexamethasone-treated myotubes are a commonly used in vitro model of muscle wasting. We reported recently that treatment of cultured L6 myotubes with dexamethasone resulted in increased gene and protein expression of the nuclear cofactor p300 but it is not known whether glucocorticoids upregulate p300 histone acetyl transferase (HAT) activity in muscle and whether p300/HAT activity regulates glucocorticoid-induced muscle proteolysis. Here, we found that treatment of cultured L6 myotubes with dexamethasone resulted in increased nuclear p300/HAT activity. Treatment of myotubes with p300 siRNA or transfection of muscle cells with a plasmid expressing p300 that was mutated in its HAT activity domain blocked the dexamethasone-induced increase in protein degradation, supporting a role of p300/HAT in glucocorticoid-induced muscle proteolysis. In addition to increased HAT activity, treatment of the myotubes with dexamethasone resulted in reduced nuclear expression and activity of histone deacetylases (HDACs) 3 and 6. When myotubes were treated with the HDAC inhibitor trichostatin A, protein degradation increased to the same degree as in dexamethasone-treated myotubes. The results suggest that glucocorticoids increase HAT and decrease HDAC activities in muscle, changes that both favor hyperacetylation. The results also provide evidence that dexamethasone-induced protein degradation in cultured myotubes is, at least in part, regulated by p300/HAT activity.
authors.affiliation: Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Yang
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.forename: Michael
authors.initials: M
authors.lastname: Menconi
authors.forename: Per-Olof
authors.initials: PO
authors.lastname: Hasselgren
mesh_terms: D000107:Acetylation; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051548:Histone Acetyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006655:Histone Deacetylases / Q000378:metabolism; D006877:Hydroxamic Acids / Q000494:pharmacology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010957:Plasmids / Q000276:immunology; D011506:Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014162:Transfection; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor
chemical_list: D000893:Anti-Inflammatory Agents; D018797:Cell Cycle Proteins; D003907:Dexamethasone; D004791:Enzyme Inhibitors; D051548:Histone Acetyltransferases; D006655:Histone Deacetylases; D006877:Hydroxamic Acids; D011506:Proteins; D034741:RNA, Small Interfering; D014157:Transcription Factors; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor; C012589:trichostatin A