FIGURE 7.

Impaired ERK1/2 activation in oxidant-exposed senescent cells. A–C, ERK1/2 phosphorylation induced by oxidative stress in senescent cells. Control and senescent cells were exposed to 100 μm H₂O₂ (A) or 50 μm menadione (Mena, B) for the indicated times and subjected to Western blot analysis of p-ERK1/2 and ERK1/2. C, cells were exposed to 50 μm menadione for the indicated time and subjected to Northern blot analysis of c-Fos and Ho-1. GAPDH was used as a loading control. D and E, involvement of p53 in the regulation of ERK1/2 phosphorylation. D, control and senescent cells were treated with 50 μm menadione for the indicated time and subjected to Western blot analysis of p-MEK1 and MKP-3. β-Actin was used as a loading control. E, control cells were treated with 1 μg/ml ETO in the absence or presence of 5 μm PFT for 3 days, and then cells were exposed to 50 μm menadione for the indicated time. Cell lysates were subjected to Western blot analysis of p-ERK1/2 and ERK1/2.