Initial PKC activation is required for potentiation of paclitaxel-induced TNF-α induction and apoptosis by bryostatin 1.

(A) U937 cells were treated with bryostatin 1 (10 nM) alone (○) or in combination with paclitaxel (5 nM, ●). Total cellular PKC activity was assessed as described in “Materials and methods.” (B) U937 cells were exposed to paclitaxel/bryostatin 1 in the presence or absence of GFX (1 μM) for 3 hours. Total RNA was isolated, and TNF-α mRNA levels were determined by RT-PCR. (C) U937 cells were treated with GFX (1 μM) before (−30 or 0 minutes) or after (3 or 6 hours) administration of paclitaxel (5 nM) and bryostatin 1 (10 nM). Cell death was assessed after 24 hours by annexin and PI staining as described in “Materials and methods.” Results for panels A and C correspond to 3 separate experiments (means ± SE).