Na-Sal treatment of TF-1 cells activates caspase-3 and induces cleavage of PARP and gelsolin. (A and B) Activation of cpp-32 (caspase-3) in response to treatment with Na-Sal. (A) TF-1 cells were treated with 5 mmol/L Na-Sal for the time indicated and the presence of intact cpp-32 and its proteolytic fragment (p20) was shown by immunoblotting using an anti-cpp–32 antibody (Transduction Laboratories) (B) Caspase-3 activity was determined in cells treated with Na-Sal (1 mmol/L, 3 mmol/L, and 5 mmol/L) for 16 hours. (C and D) Na-Sal–induced cleavage of PARP. TF-1 cells were left untreated (0) or were treated with 5 mmol/L Na-Sal for 2, 6, or 9 hours, as indicated (C). Cells were also treated with increasing concentrations of Na-Sal (1, 5, or 10 mmol/L, as indicated) for 5 hours (D). The presence of PARP (116 kD) and its 86-kD proteolytic fragment were detected by immunoblotting using an anti-PARP antibody (Pharmingen). (E) Na-Sal–induced cleavage of gelsolin. TF-1 cells were treated with increasing concentrations of Na-Sal (indicated at the top) for 5 hours; the amount of gelsolin and its proteolytic degradation was analyzed by immunoblotting using an anti-gelsolin antibody (Sigma).