Association of rolipram/forskolin-induced CLL apoptosis with caspase-9 activation.

Rolipram/forskolin-induced CLL apoptosis is associated with caspase-9 activation and is inhibited by a caspase-9 inhibitor but not a caspase-8 inhibitor. (A) CLL cells were incubated with media alone (CT) or with 10 μM rolipram and 40 μM forskolin alone (R/F) or in the presence of the caspase-8 inhibitor Z-IETD-Fmk (C8-I) or the caspase-9 inhibitor Z-LEHD-Fmk (C9-I). After 48 hours, apoptosis was quantitated as hypodiploid events on propidium iodide flow cytometry. These data are representative of results obtained with leukemic cells from 4 of 5 CLL patients. (B) Caspase-mediated cleavage of PARP to p85 was assessed by immunoblotting CLL cells cultured for 18 hours as in panel A. (C) CLL cells treated for 18 hours with 40 μM forskolin and the indicated concentration of rolipram (R) were assessed for cleavage of procaspase-9 to p10 (arrow) by immunoblotting. Similar results were obtained in 5 of 6 CLL patients.