valinomycin and Lymphoma--B-Cell

Taurine chloramine (TN-Cl) is one of the most abundant compounds generated by activated neutrophils. In contrast to HOCl, which causes necrosis, TN-Cl is a potent inducer of apoptosis in tumor cells. Here we show that the apoptosis induced by TN-Cl in human B lymphoma cells is dependent upon oxidant-mediated mitochondrial damage, a decrease in mitochondrial membrane potential, and caspase-9 activation. Further, we show that TN-Cl is taken up into the cells and is concentrated in the mitochondria, where it induces opening of the permeability transition pore and mitochondrial swelling. Identical activity is seen upon treatment of isolated mitochondria with TN-Cl and is blocked by the permeability transition pore inhibitors bongkrekic acid and cyclosporin A, as well as by the sulfhydryl-reducing agent tris(2-carboxyethyl)-phosphine. The data suggest that TN-Cl causes apoptosis through direct damage to the mitochondria.

Topics: Anti-Bacterial Agents; Apoptosis; Bongkrekic Acid; Caspase 9; Caspases; Cell Death; Cell Line, Tumor; Cyclosporine; Enzyme Inhibitors; Humans; Indicators and Reagents; Inflammation Mediators; Intracellular Membranes; Lymphoma, B-Cell; Membrane Potentials; Microscopy, Confocal; Mitochondria; Neutrophils; Oxidants; Oxygen; Permeability; Propidium; Sulfhydryl Compounds; Taurine; Time Factors; Valinomycin

The resting membrane potential of parental, neomycin control, and Bcl-2 transfected cells was measured, and the effect of membrane hyperpolarization or depolarization on radiosensitivity was studied. Bcl-2 transfected cells were significantly more radioresistant than control cells and were significantly hyperpolarized compared to parental and neomycin control transfected PW and HL60 cells. Hyperpolarization of the parental and neomycin control transfected cells by valinomycin significantly increased the radioresistance of these cells to such an extent that there was no longer a significant difference in the survival of the valinomycin treated and irradiated control cells compared to similarly irradiated Bcl-2 transfected cells. In contrast, depolarization of the Bcl-2 transfected PW and HL60 cells decreased the radioresistance of the Bcl-2 transfectants to a level similar to that of the control cells. The data presented here suggest that overexpression of Bcl-2 affects membrane potential and that this hyperpolarization is associated with increased radioresistance of cells that overexpress Bcl-2. Furthermore, Bcl-2 transfected cells were also less susceptible to the specific Na+/K(+)-ATPase inhibitor ouabain, suggesting that Bcl-2 may act at the level of the Na+/K(+)-ATPase pump.

Topics: Apoptosis; Cell Membrane; Cell Survival; HL-60 Cells; Humans; Lymphoma, B-Cell; Membrane Potentials; Ouabain; Potassium Chloride; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2; Sodium-Potassium-Exchanging ATPase; Tumor Cells, Cultured; Valinomycin