Bryostatin 1–induced STAT1 activation is dependent on PKC activation in CLL cells. (A) CLL cells were left untreated or treated with 10 nM Bryostatin 1 for 3 or 24 hours. Whole cell lysates were analyzed by Western blotting for the presence of different PKC isoforms. Data are representative of 3 experiments using 3 different patients' cells. (B) CLL cells were treated with 10 nM Bryostatin 1 for 30 minutes. Cells were lysed, and PKC kinase activity was measured after immunoprecipitation in an in vitro kinase assay. Values represent the means ± SEMs of assays performed on CLL cells from 3 patients. (C) CLL cells were pretreated with the indicated concentrations of GF109203X (GFX) or Gö6976 for 1 hour prior to addition of 10 nM Bryostatin 1 for 3 hours. Whole-cell lysates were analyzed by Western blotting for tyrosine phosphorylation of STAT1 (Tyr-P-STAT1). Blots were stripped and reprobed for total STAT1. Data are representative of 4 experiments using 3 different patients' cells.