Endogenous Bcl-B mediates Nur77-induced apoptosis in myeloma cells. (A) RPMI 8226 myeloma cells were electroporated with either control or Bcl-B siRNA. After 72 hours, cells were harvested and lysates (100 μg) were analyzed by SDS-PAGE/immunoblotting using Bcl-B (top blot) and actin (bottom blot) antibodies. (B) RPMI 8226 cells were electroporated with either control, Bcl-B, or Bcl-2 siRNA. Then, 72 hours later, cells were transfected with plasmids (0.1 to 1 μg) encoding GFP or GFP-Nur77ΔDBD proteins. After 18 hours, fixed cells were stained with DAPI to visualize nuclei by UV microscopy and determine percentages of apoptotic cells by counting 200 GFP-positive cells (mean ± SE; n = 3). (C) RPMI 8226 cells were electroporated with either control or Bcl-B siRNA. Cells were treated 72 hours later with staurosporine (0.01 to 0.3 μM) for 18 hours. Apoptosis was determined as in panel B.