Stimulation of myofibrillar protein degradation and expression of mRNA encoding the ubiquitin-proteasome system in C(2)C(12) myotubes by dexamethasone: effect of the proteasome inhibitor MG-132.
Addition of the synthetic glucocorticoid, dexamethasone (Dex) to serum-deprived C(2)C(12) myotubes elicited time- and concentration-dependent changes in N(tau)-methylhistidine (3-MH), a marker of myofibrillar protein degradation. Within 24 h, 100 nM Dex significantly decreased the cell content of 3-MH and increased release into the medium. Both of these responses had increased in magnitude by 48 h and then declined toward basal values by 72 h. The increase in the release of 3-MH closely paralleled its loss from the cell protein. Furthermore, Dex also decreased the 3-MH:total cell protein ratio, suggesting that myofibrillar proteins were being preferentially degraded. Incubation of myotubes with the peptide aldehyde, MG-132, an inhibitor of proteolysis by the (ATP)-ubiquitin (Ub)-dependent proteasome, prevented both the basal release of 3-MH (>95%) and the increased release of 3-MH into the medium in response to Dex (>95%). Northern hybridization studies demonstrated that Dex also elicited similar time- and concentration-dependent increases in the expression of mRNA encoding two components (14 kDa E(2) Ub-conjugating enzyme and Ub) of the ATP-Ub-dependent pathway. The data demonstrate that Dex stimulates preferential hydrolysis of myofibrillar proteins in C(2)C(12) myotubes and suggests that the ATP-Ub-dependent pathway is involved in this response.
Thompson
M G
MG
Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
Thom
A
A
Partridge
K
K
Garden
K
K
Campbell
G P
GP
Calder
G
G
Palmer
R M
RM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000235:genetics*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D007976:Leupeptins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000235:genetics*; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D009210:Myofibrils / Q000187:drug effects / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D014452:Ubiquitins / Q000235:genetics*
D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D012333:RNA, Messenger; D014452:Ubiquitins; D003907:Dexamethasone; D000255:Adenosine Triphosphate; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde