Fig. 2. High ERK-MAPK activity prevents proteasome-dependent degradation of FRA-1. (A) Immunoblot analysis of FRA-1, ERK2 and phospho-ERK1/2 protein expression in HCT-116 and BE cells 16 hours after addition of the proteasome inhibitor lactacystin. (B) Immunoblot analysis of FRA-1, RAF:ER, ERK2 and phospho-ERK1/2 proteins in the HCT-116-RAF:ER cell line 2 and 24 hours after activation of the RAF:ER construct with tamoxifen (4-OHT), or ethanol (EtOH) in control experiments. (C) Northern blot analysis of FRA-1 and GAPDH mRNA accumulation in the HCT-116-RAF:ER cell line 2 and 24 hours after activation of the RAF:ER construct with tamoxifen, or ethanol in control experiments.