Ionizing radiation-induced, mitochondria-dependent generation of reactive oxygen/nitrogen.
Transient generation of reactive oxygen or nitrogen (ROS/RNS), detected with dihydrodichlorofluoroscein by fluorescence microscopy, occurs within minutes of exposing cells to ionizing radiation. In the 1-10 Gy dose range, the amount of ROS/RNS produced/cell is constant, but the percentage of producing cells increases with dose (20 to 80%). Reversible depolarization of the mitochondrial membrane potential () and decrease in fluorescence of a mitochondria-entrapped dye, calcein, are observed coincidentally. Radiation-induced ROS/RNS, depolarization, and calcein fluorescence decrease are inhibited by the mitochondrial permeability transition inhibitor, cyclosporin A, but not the structural analogue, cyclosporin H. Radiation-stimulated ROS/RNS is also inhibited by overexpressing the Ca(2+)-binding protein, calbindin 28K, or treating cells with an intracellular Ca(2+) chelator. Radiation-induced ROS/RNS is observed in several cell types with the exception of rho(o) cells deficient in mitochondrial electron transport. rho(o) cells show neither radiation-induced ROS/RNS production nor depolarization. We propose that radiation damage in a few mitochondria is transmitted via a reversible, Ca(2+)-dependent mitochondrial permeability transition to adjacent mitochondria with resulting enhanced ROS/RNS generation. Measurements of radiation-induced mitogen-activated protein kinase activity indicate that this sensing/amplification mechanism is necessary for activation of some cytoplasmic signaling pathways by low doses of radiation.
Leach
J K
JK
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA 23298, USA.
Van Tuyle
G
G
Lin
P S
PS
Schmidt-Ullrich
R
R
Mikkelsen
R B
RB
D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism; D016466:CHO Cells / Q000528:radiation effects; D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000528:radiation effects; D006224:Cricetinae; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation / Q000528:radiation effects; D006801:Humans; D007425:Intracellular Membranes / Q000528:radiation effects; D008297:Male; D008928:Mitochondria / Q000378:metabolism / Q000528:radiation effects*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000528:radiation effects
D017382:Reactive Oxygen Species; D020928:Mitogen-Activated Protein Kinases; D009584:Nitrogen