Inhibiting RBM39-MEK5 enhances the cytotoxicity of bortezomib by inhibiting p65. (A) p65, RSK1, and c-Myc were decreased under the condition of MEK5 knockdown, which was detected 48 hours after infection by western blotting. (B) MEK5, p65, RSK1, and c-Myc were decreased under the condition of RBM39 knockdown, which was detected 48 hours after infection by western blotting. (C) MEK5, p65, RSK1, and c-Myc were decreased under the condition of indisulam treatment, which was detected 48 hours after treatment by western blotting. (D) H929 or MM1.S cells were treated by single indisulam/Btz or both the drugs, followed by western blotting to detect the protein level of PARP, p65, and p-p65. Indisulam and Btz synergistically inhibited p65. (E) Kaplan-Meier overall survival of indisulam/Btz-treated mice in LP-1-luc disseminated xenograft mice. Mice were transplanted with LP-1 luciferase cells and treated with single indisulam/Btz or both of the drugs. The mice received indisulam every other day by intraperitoneal administration at a dose of 20 mg/kg, for a total of 10 doses. Btz was given at days 1, 4, 8, and 11 via tail vein at dosage of 1 mg/kg. (F) Bioluminescent imaging of LP-1-luc cell transplanted mice treated with single indisulam/Btz or both the drugs. Representative images of 3 mice/group are shown (vehicle group, n = 5; indisulam group, n = 4; Btz group, n = 4; combine group, n = 5). (G) Quantification of bioluminescence signals in panel F at indicated time points. (H) p65, RSK1, and c-Myc were decreased on the condition of MEK5 inhibitor BIX 02189 treatment, which was detected 48 hours after treatment by western blotting. (I) H929 cells were treated by either or both of drugs and cell apoptosis was detected by annexin V/PI 48 hours later. (J) BIX 02189 and Btz synergistically inhibited the expression of p65 and p-p65 and induced PARP cleavage in H929. ∗∗∗∗P < .0001. PI, propidium iodide.