Stimulation of myofibrillar protein degradation and expression of mRNA encoding the ubiquitin-proteasome system in C2C12 myotubes by dexamethasone: effect of the proteasome inhibitor MG-132
✍ Scribed by Michael G. Thompson; Amanda Thom; Kris Partridge; Karen Garden; Gillian P. Campbell; Graham Calder; Robert M. Palmer
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 147 KB
- Volume
- 181
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Addition of the synthetic glucocorticoid, dexamethasone (Dex) to serum-deprived C 2 C 12 myotubes elicited time-and concentration-dependent changes in Nmethylhistidine (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 (Ͼ95%) and the increased release of 3-MH into the medium in response to Dex (Ͼ95%). 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.