Scavenging of extracellular H2O2 by catalase inhibits the proliferation of HER-2/Neu-transformed rat-1 fibroblasts through the induction of a stress response

High levels of reactive oxygen species (ROS) are associated with cytotoxicity, Alternatively, nontoxic levels of ROS like hydrogen peroxide (H2O2) can mediate the transmission of many intracellular signals, including those invoked in growth and transformation. To identify pathways downstream of endogenous cellular H2O2 production, the response of Rat-1 fibroblasts exhibiting differential HER-2/Neu receptor tyrosine kinase activity to removal of physiological H2O2 concentrations was investigated. The proliferation of all cells was abolished by addition of the H2O2 scavenger catalase to the culture medium; HER-2/Neu activity was not significantly affected by catalase treatment, suggesting that the target(s) of the H2O2 signal lie downstream of the receptor in our model, ERK1/2 phosphorylation was blocked by catalase in fibroblasts expressing wild type Neu, however such a response did not occur in cells possessing activated mutant Neu, This indicates that the ERK1/2 response contributes little to the growth inhibition observed. By contrast, JNK1 activity increased following the addition of catalase or H2O2, regardless of Neu activity or level of cell transformation. Phosphorylation of p38 MAPK was induced by H2O2 but not by catalase. These observations suggest that scavenging of H2O2 from the cellular environment blocks Rat-1 proliferation primarily through the activation of stress pathways.