TPA-induced differentiation of U937 cells is associated with caspase activation.

U937 cells were treated with 20 nM TPA for indicated times. (A) Adhesion of cells to the culture flasks (mean ± SD of 3 independent experiments). (B) Flow cytometry analysis of CD11b expression on the plasma membrane (1 representative of 3 experiments). (C) DEVD-AMC, VDVAD-AFC, IETD-AFC, and LEHD-AFC peptide cleavage activity in TPA-treated cells (mean ± SD of 3 independent experiments in triplicate). (D) Flow cytometry analysis of caspase-3 active fragments using a cell-signaling Ab (white curves indicate untreated cells; gray curves, TPA-treated cells; dashed line, control immunoglobulin G [IgG]). (E) Western blot analysis of caspase-3 in whole-cell extracts. VP16 indicates U937 cells exposed to 50 μM etoposide for 4.5 hours. Numbers on the right indicate molecular weight in kilodaltons; *indicates cleavage products.