Bryostatin 1–induced CLL differentiation requires STAT1 activation. (A) DNA binding activity of nuclear extracts from CLL cells was examined by EMSA using a radiolabeled probe containing a GAS sequence. Cells were untreated or treated for 15 minutes with 500 U/mL IFNγ. For competition experiments, 50 to 100 molar excess of STAT1 decoy ODNs (S1 decoy) or mismatch control STAT1 ODNs (S1m) was incubated with nuclear extracts from IFNγ-treated cells prior to incubation with the radiolabeled probe. (B) CLL cells were transduced with or without 10 μM STAT1 decoy (S1) or 10 μM mismatch control STAT1 ODNs (S1m) by electroporation. All cells were electroporated and then treated with or without (Untx) 10 nM Bryostatin 1 for 24 hours. CD5/CD19⁺ cells were analyzed for CD22 expression by immunostaining and flow cytometric analysis. Values of CD22 expression were normalized to the level of CD22 expression in the Bryostatin 1–treated cells and are expressed as the mean percentage ± SEM from 3 patients. (C) IgM ELISA was performed on 200 μL culture supernatants from CLL cells treated with or without (Untx) 10 nM Bryostatin 1 for 48 hours following transduction with STAT1 decoy (S1) or mismatch control STAT1 ODNs (S1m) as described in panel B. The values of IgM production were normalized to the level of IgM produced by the Bryostatin 1–treated cells and are the mean percentage ± SEM from 3 patients.