Fig. 5. Dexamethasone inhibits MKP-1-targeted degradation by the proteasome in RBL-2H3 mast cells. RBL-2H3 mast cells were treated for the indicated time with dexamethasone (Dex, 0.1 µM) or solvent alone (ethanol) (A). Cells were also treated for 3 h with solvent alone (DMSO), the proteasome inhibitors MG132 or LLnL, or the cysteine proteinase inhibitor E-64d (B). The cells were sensitized with anti-DNP IgE, then stimulated with DNP-BSA [(A) and (B)]. Phosphorylation of Erk-1/2 (p-Erk) and expression of MKP-1 were assessed by immunoblotting as described in Materials and methods. The results are representative of two different experiments.