PARP cleavage in B-CLL cells. (A) Time course of dexamethasone-induced PARP cleavage. B-CLL lymphocytes were incubated with or without 10 μmol/L dexamethasone for the indicated times. (B) Dose response of PARP cleavage. Cells were incubated for 48 hours with various concentrations of dexamethasone as indicated. PARP cleavage was analyzed by Western blot as described in Materials and Methods. The position of the native PARP (116 kD) and the proteolytic fragment (85 kD) is indicated.