The role of hydroxyl radical as a messenger in Cr(VI)-induced p53 activation

The present study investigates whether reactive oxygen species (ROS)are involved in p53 activation, and if they are, which species isresponsible for the activation. Our hypothesis is that hydroxyl radical(·OH) functions as a messenger for the activation of this tumorsuppressor protein. Human lung epithelial cells (A549) were used totest this hypothesis. Cr(VI) was employed as the source of ROS due toits ability to generate a whole spectrum of ROS inside the cell. Cr(VI)is able to activate p53 by increasing the protein levels and enhancingboth the DNA binding activity and transactivation ability of theprotein. Increased cellular levels of superoxide radicals(O₂·), hydrogen peroxide(H₂O₂), and ·OH radicals were detected on theaddition of Cr(VI) to the cells. Superoxide dismutase, by enhancing theproduction of H₂O₂ from O₂·radicals, increased p53 activity. Catalase, anH₂O₂ scavenger, eliminated ·OH radicalgeneration and inhibited p53 activation. Sodium formate and aspirin,·OH radical scavengers, also suppressed p53 activation. Deferoxamine,a metal chelator, inhibited p53 activation by chelating Cr(V) to makeit incapable of generating radicals from H₂O₂.NADPH, which accelerated the one-electron reduction of Cr(VI) to Cr(V)and increased ·OH radical generation, dramatically enhanced p53activation. Thus ·OH radical generated from Cr(VI) reduction in A549cells is responsible for Cr(VI)-induced p53 activation.