Inhibition of ERK oscillations by ionizing radiation and reactive oxygen species

The shuttling of activated protein kinases between the cytoplasm and nucleus is an essential feature of normal growth factor signaling cascades. Here we demonstrate that transforming growth factor alpha (TGFα) induces oscillations in extracellular signal regulated kinase (ERK) cytoplasmic‐nuclear translocations in human keratinocytes. TGFα‐dependent ERK oscillations mediated through the epidermal growth factor receptor (EGFR) are inhibited by low dose X‐irradiation (10 cGy) and low concentrations of hydrogen peroxide (0.32–3.26 µM H₂O₂) used as a model reactive oxygen species (ROS). A fluorescent indicator dye (H2‐DCFDA) was used to measure cellular ROS levels following X‐irradiation, 12‐O‐tetradecanoyl phorbol‐13‐acetate (TPA) and H₂O₂. X‐irradiation did not generate significant ROS production while 0.32 µM H₂O₂ and TPA induced significant increases in ROS levels with H₂O₂ > TPA. TPA alone induced transactivation of the EGFR but did not induce ERK oscillations. TPA as a cotreatment did not inhibit TGFα‐stimulated ERK oscillations but qualitatively altered TGFα‐dependent ERK oscillation characteristics (amplitude, time‐period). Collectively, these observations demonstrate that TGFα‐induced ERK oscillations are inhibited by ionizing radiation/ROS and perturbed by epigenetic carcinogen in human keratinocytes. © 2010 Wiley‐Liss, Inc.