Nur77-mimicking peptide induces Bcl-B–dependent apoptosis of myeloma cells. (A) Schematic representation of Nur77 protein and the corresponding Nur77 9′mer peptide. “GX” corresponds to the linker, and “r8” corresponds to 8 arginines that endow the peptide with cell penetration activity. (B) A serial concentration of GST or GST–Bcl-2, GST–Bcl-X_L, or GST–Bcl-B (left panel) or GST–Bcl-W, GST–Bfl-1, (right panel) or GST–Mcl-1 was incubated with 20 nM FITC–Nur77 peptides in PBS buffer. Fluorescence polarization was measured after 10 minutes. (C) RPMI 8226 cells were electroporated with either control or Bcl-B siRNA. After 72 hours, cells were treated for 18 hours with either Nur77 peptide or corresponding inactive mutant (3 to 12 μM). Then, cells were washed with PBS, fixed with 3.7% formaldehyde, and stained with DAPI to visualize nuclei by UV microscopy. The percentages of apoptotic cells were determined by counting 200 GFP-positive cells (mean ± SE; n = 3).