Hydrogen Peroxide: A Key Messenger That Modulates Protein Phosphorylation Through Cysteine Oxidation

Ligand-receptor interactions can generate the production of hydrogen peroxide (H2O2) in cells, the implications of which are becoming appreciated. Fluctuations in H2O2 levels can affect the intracellular activity of key signaling components including protein kinases and protein phosphatases. Rhee et al. discuss recent findings on the role of H2O2 in signal transduction. Specifically, H2O2 appears to oxidize active site cysteines in phosphatases, thereby inactivating them. H2O2 also can activate protein kinases; however, although the mechanism of activation for some kinases appears to be similar to that of phosphatase inactivation (cysteine oxidation), it is unclear how H2O2 promotes increased activation of other kinases. Thus, the higher levels of intracellular phosphoproteins observed in cells most likely occur because of the concomitant inhibition of protein phosphatases and activation of protein kinases.