Taurine monochloramine activates a cell death pathway involving Bax and caspase-9

Taurine is an abundant free amino acid that interacts with the potent oxidant hypochlorous acid to form the less toxic and more stable oxidant taurine monochloramine (TauNHCl). TauNHCl has diverse cellular effects ranging from inhibiting the production of proinflammatory mediators to inhibiting cell proliferation and inducing cell death. We hypothesized that TauNHCl could activate a cell death pathway involving Bcl-2 members and the activation of caspase proteases. FL5.12 cells are lymphocytic cells that undergo apoptosis following interleukin-3 (IL-3) withdrawal. Therefore, cell death following TauNHCl treatment of FL5.12 cells was compared and contrasted with IL-3 withdrawal. We found that TauNHCI treatment activates a cell death pathway with kinetics very similar to IL-3 withdrawal. TauNHCl-treated cells undergo an annexin V-positive/propidium iodide-negative phase of death consistent with apoptosis. TauNHCl treatment results in a conformational change in BAX that is associated with its activation. Both Bcl-2 and, to a lesser degree, the dominant negative form of caspase-9 inhibit cell death following TauNHCI treatment. In contrast with IL-3 withdrawal, TauNHCI treatment of FL5.12 cells results in a rapid cell cycle arrest that is cell cycle phase-independent. These results demonstrate that TauNHCI treatment induces a rapid, cell cycle-independent proliferative arrest followed by the activation of a cell death pathway involving Bcl-2 family members and caspase activation.