Fig. 7. Dexamethasone does not inhibit MKP-1 degradation by the proteasome in NIH-3T3 fibroblasts. NIH-3T3 fibroblasts were treated for the indicated time [(A and B)] or for 5 h (C) with dexamethasone (Dex, 0.1 µM) or solvent alone (ethanol). For the last 3 h of the treatment period, solvent alone (DMSO), the proteasome inhibitors MG132 or LLnL, or the cysteine proteinase inhibitor E-64d were added (C). The cells were then stimulated with TPA as indicated (A). Expression of MKP-1 and phosphorylation of Erk-1/2 (p-Erk) were assessed by immunoblotting as described in Materials and methods. The results are representative of two different experiments.