Reactive oxygen species (ROS) such as superoxide anion and hydrogen peroxide are generated during cellular metabolism or by external factors. It has been known that low concentration of ROS can stimulate cellular proliferation as a second messenger. Phenazine methosulfate (PMS) is used to generate intracellular ROS. Treatment with 3 μM PMS in Chinese hamster lung fibroblast (V79) cells stimulated cellular proliferation by 50% increase and also activated c-Jun N- terminal kinase (JNK) and p38 mitogen- activated protein kinase (MAPK) but did not activate extracellular signal regulated kinase (ERK) 1/2 and ERK5. The phosphorylation of c-Jun and ATF-2, transcription factors which are mediated by JNK and p38 MAPK, were also increased by the treatment with PMS. The increased proliferation was blocked by SB203580 (an inhibitor of p38 MAPK) but not by PD98059 (an inhibitor of ERK). The sequence of electron reductions can make superoxide anion and hydrogen peroxide to hydroxyl radical. Because of mild capabilities of superoxide anion and hydrogen peroxide, most of the damages caused by ROS are thought to be due to their metal iron-dependent conversion into highly reactive species, hydroxyl radials (HO-). Treatment with deferoxamine (an iron chelator) and benzoic acid (a hydroxyl radical scavenger) diminished the activation of JNK and p38 MAPK, and also suppressed cellular proliferation. These results suggest that superoxide anion generation by the treatment with PMS, related to hydroxyl radicals somewhat, increased cellular proliferation through the activation of JNK and p38 MAPK and components of AP-1 transcription factors c-Jun and ATF-2.
