Stable overexpression of manganese superoxide dismutase in mitochondria identifies hydrogen peroxide as a major oxidant in the AP-1-mediated induction of matrix-degrading metalloprotease-1

Reactive oxygen species (ROS) are important second messengers for the induction of several genes in a variety of physiological and pathological conditions. Here we addressed the question of whether isolated, unbalanced overexpression of the antioxidant enzyme manganese superoxide dismutase (Mn-SOD) may modulate signal transduction cascades, finally leading to connective tissue degradation, a hallmark in carcinogenesis and aging, Therefore, we generated stably Mn-SOD-overexpressing fibroblasts with an up to 4.6-fold increase in Mn-SOD activity. The Mn-SOD-overexpressing cells revealed specific resistance to the superoxide anion (O-2 radical anion)-generating agent paraquat, whereas no resistance to UVA-generated oxidative stress was found. Treatment of the Mn-SOD overexpressing cells with various ROS-generating systems resulted (due to the enhanced dismutation of superoxide anion to hydrogen peroxide) in an up to 9.5-fold increase in matrix-degrading metalloprotease-1 (MMP-1) mRNA levels, A similar increase in MMP-1 mRNA was also seen when the intracellular H2O2 concentration was increased by the inhibition of different H2O2-detoxifying pathways, Furthermore, prooxidant conditions led to a strong induction of c-jun and c-fos mRNA levels resulting in a 4-fold higher transactivation of the transcription factor AP-1 in the Mn-SOD-overexpressing cells. Collectively, we have found that enhanced Mn-SOD activity, via an unbalanced H2O2 overproduction and detoxification, induces MMP-1 mRNA levels, and this effect is at least partly mediated by the DNA recognition sequence AP-1.