Enhanced ROS production in oncogenically transformed cells potentiates c-Jun N-terminal kinase and p38 mitogen-activated protein kinase activation and sensitization to genotoxic stress

Many primary tumors as well as transformed cell lines display high sensitiv ity to chemotherapeutic drugs and radiation. The molecular mechanisms that underlie this sensitivity are largely unknown. Here we show that the sensit ization of transformed cells to stress stimuli is due to the potentiation o f the c-Jun N-terminal kinase (JNK) and p38 nitrogen-activated protein kina se pathways. Activation of these pathways by the antitumor drug cis-platin (CDDP) and by other stress agents is markedly enhanced and is induced by lo wer stress doses in NIH 3T3 cells overexpressing epidermal growth factor re ceptor, HER1-2 kinase, or oncogenic Ras than in nontransformed NIH 3T3 cell s. Inhibition of stress kinase activity by specific inhibitors reduces CDDP -mediated cell death in transformed cells, whereas overactivation of stress kinase pathways augments cells death. Potentiation of stress kinases is a common feature of cells transformed by different oncogenes, including cells derived front human tumors, and is shown here to be independent of the act ivity of the particular transforming oncoprotein. We further show that the mechanism that underlies potentiation of stress kinases in transformed cell s involves reactive oxygen species (ROS), whose production is elevated in t hese cells. JNK/p38 activation is inhibited by antioxidants and in particul ar by inhibitors of the mitochondrial respiratory chain and NADPH oxidase. Conversely, by artificially elevating ROS levels in nontransformed NIH 3T3 cells we were able to induce potentiation of JNK/p38 activation. Taken toge ther, our findings suggest that ROS-dependent potentiation of stress kinase pathways accounts for the sensitization of transformed cells to stress and anticancer drugs.