Down-regulation of the c-Jun N-terminal kinase (JNK) phosphatase M3/6 and activation of JNK by hydrogen peroxide and pyrrolidine dithiocarbamate

Oxidative stress activates the c-Jun N-terminal kinase (JNK) pathway. Howev er, the exact mechanisms by which reactive oxygen species (ROS) activate JN K are unclear. We found that the ability of hydrogen peroxide (H2O2) to ind uce JNK activation varied in different cell types. Pyrrolidine dithiocarbam ate (PDTC), a presumed antioxidant, induced JNK activation on its own and e nhanced JNK activation by H2O2 in many cell types, including Jurkat, HEK293 , and LNCaP and Tsu-Prl prostate cancer cells. The activation of JNK by PDT C, in the presence or absence of exogenous H2O2, was dependent on its chela ting ability to metal ions, most likely copper ions, Despite the strong JNK -activating ability, H2O2 plus PDTC did not induce significant activation o f the upstream kinases, SEK1/MKK4 and MKK7. However, the JNK inactivation r ate was slower in cells treated with H2O2 pins PDTC compared with the rate in cells treated with ultraviolet C CUV-C), Treatment of H2O2 pins PDTC sig nificantly decreased the expression levels of a JNK phosphatase, M3/6 (also named hVH-5), but not the levels of other phosphatases (PP2A and PP4), In contrast, UV-C irradiation did not cause the down-regulation of M3/6, These results suggest that JNK activation by H2O2 plus PDTC resulted from the do wn-regulation of JNK phosphatases. Our data also reveal a necessity to care fully evaluate the pharmacological and biochemical properties of PDTC.