FIGURE 2.
Oxidative stress activates ERK MAPK signaling but inhibits IGF-I activation of Akt in normal human chondrocytes. Chondrocytes cultured in monolayer were treated with 250 μm tBHP for 30 min, followed by a 30-min stimulation with 50 ng/ml IGF-I. A, immunoblotting was performed to determine the phosphorylation of IRS-1, Akt, p70S6K, MEK1/2 (S/S, Ser-217/Ser-221), and ERK1/2 (T/Y, Thr-202/Tyr-204) using antibodies specific to their phosphorylated forms. B and C, the relative phosphorylation levels (normalized to their total proteins) of IRS-1, Akt, and ERK1/2 were determined by densitometric analysis of the bands and were expressed as a percentage of the IGF-I-stimulated sample. The results shown represent the means ± S.D. of three normal donors. *, p < 0.05; **, p < 0.01; ***, p < 0.005.