REACTIVE OXYGEN SPECIES MEDIATE CYTOKINE ACTIVATION OF C-JUN NH2-TERMINAL KINASES

Interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF alpha) are k nown to induce production of reactive oxygen species (ROS), which have been suggested to act as second messengers. Here we demonstrate that ROS production by bovine chondrocytes upon cytokine stimulation induce s c-jun expression. Since c-jun expression is regulated by its own gen e product via phosphorylation by c-Jun NH2-terminal kinases (JNKs), we investigated if cytokines and ROS could modulate JNK activity in chon drocyte monolayer cultures. Treatment of bovine chondrocytes with both IL-1 and TNF alpha leads to rapid induction of JNK activity, stimulat ing JNK activity 7- and 20-fold, respectively. Importantly, the observ ation that antioxidant treatment antagonizes IL-1 and TNF alpha activa tion of JNK provides strong evidence that ROS can act as mediators of JNK activity. Moreover, potent activation of JNK is also observed by d irect addition of the ROS hydrogen peroxide (H2O2) to the chondrocyte cultures. Nitric oxide (NO), a multifunctional ROS, also appears to si mulate JNK albeit to a lesser extent. These findings identify JNK as a nother molecular target for the actions of NO and H2O2. In addition, t he inhibitory effect of diphenyleneiodonium on JNK activation implicat es the involvement of flavonoid-containing enzymes in the ROS-mediated signaling process. Overstimulation of JNK activity by excessive produ ction of ROS may, therefore, underlie pathological conditions such as arthritis and cancer.