title: Triiodothyronine but not thyroxine accelerates myofibrillar proteolysis via ATP production in cultured muscle cells.
abstract: These experiments were done to clarify that the differential effects of thyroxine (T(4)) and triiodothyronine (T(3)) on skeletal muscle protein turnover are caused by their roles on ATP production. Primary cultured chick muscle cells were treated with a physiological level of T(4) (60 ng/ml), T(3) (12 ng/ml), or ATP (0.5 mM) for 6 days and the protein content, ATP production, proteasome activity, and myofibrillar protein breakdown were measured. The protein content measured as an index of cell growth was not affected by T(4), T(3), or ATP. The cellular ATP level was increased by T(3) and ATP, but not by T(4). Proteasome activity and N(tau)-methylhistidine (MeHis) release measured as an index of myofiblillar protein breakdown was also increased by T(3) and ATP, but not by T(4). These results indicate that T(3) but not T(4) increases ATP production followed by an increase in proteasome activity, and thus stimulates myofibrillar proteolysis.
authors.affiliation: Department of Biochemical Sciences, Kagoshima University, Korimoto, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Doi
authors.forename: Akane
authors.initials: A
authors.lastname: Ohtsubo
authors.forename: Akira
authors.initials: A
authors.lastname: Ohtsuka
authors.forename: Kunioki
authors.initials: K
authors.lastname: Hayashi
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D002645:Chickens; D003546:Cysteine Endopeptidases / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D009124:Muscle Proteins / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D013974:Thyroxine / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D009097:Multienzyme Complexes; D009124:Muscle Proteins; D014284:Triiodothyronine; D000255:Adenosine Triphosphate; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D013974:Thyroxine