HF-induced apoptosis in U937 cells is caspase-dependent.

<p>(A) U937 cells were treated for 14 and 24 h with 1.4 µg/ml HF or left untreated. Caspase-8, -9 and -3 activities were determined using IETD-pNA (caspase-8), LEHD-pNA (caspase-9) DEVD-pNA (caspase-3) respectively. The release of pNA was measured at 405 nm. The data are expressed as fold-increase relative to respective untreated samples (basal values for caspase-8, -9 and -3 activities were respectively 23±0.02, 9±0.01 and 13±0.02 pmol pNA/60 min/µg protein). Data are from three determinations ± SD. (B) Lysates from U937, NB4 and OCI cells treated for 24 h with HF (1, 1.4, 2 µg/ml) were examined for PARP-1 expression by immunoblot. The arrows indicate the cleaved form (cf) of PARP-1. (C) U937 cells were incubated with 1.4 µg/ml HF for 48 h after 1 h-pretreatment with 50 µM Z-VAD-fmk (broad spectrum caspase inhibitor), Z-DEVD-fmk (caspase-3 inhibitor), Z-IETD-fmk (caspase-8 inhibitor) or Ac-LEHD-CHO (caspase-9 inhibitor). The percentage of apoptotic cells was determined after annexin-V-FITC/PI staining and flow cytometry (L2+L4 gates). Data are the mean ± SD of results from 3 independent experiments. *<i>P</i><0.05 compared with untreated cells or cells pretreated with caspase inhibitors.