Recent studies have determined that a variety of protein tyrosine kinases can be activated by the exposure of cells to oxidative stress (1 –3 ). The stress may arise from chemical agents such as hydrogen peroxide, as well as from irradiation with ultraviolet or ionizing radiation. Oxidative stress can activate tyrosine phosphorylation signaling pathways normally regulated by cell-surface receptors. Because tyrosine kinases are frequently the proximal signaling enzyme to cell-surface receptors, their activation by stress can lead to activation of signal cascades, including the activation of serine/threonine kinases (4 ). However, because this activation occurs in the absence of a natural ligand, oxidative stress is capable of activating the receptor signal pathways outside of normal receptor control. This process has been extensively characterized in lymphocytes, where oxidative stress from hydrogen peroxide or ultraviolet (UV) radiation has been found to activate tyrosine kinases associated with the antigen receptor in T- and B-cells, giving rise to signaling patterns similar to those induced by direct antigen-receptor stimulation (5 –8 ).
