HSP90 inhibition targets BTK and IKKα to overcome BTK resistance. (A) Immunoblotting of MCL lines for the indicated targets after 48-hour exposure to AUY922 50 nM or vehicle. (B) Viable cell counts of splenic B cells from LMP1-CD40//CD19-Cre mice prior to exposure (pre) or upon exposure to the indicated agents for 20 hours. P value based on 2-sided unpaired Student t test. Error bars indicate standard deviation (SD). (C) Immunoblotting of the cells described in panel B for the indicated targets. (D) Immunoblotting of 293T cells expressing wt BTK or BTK C481S and treated for 20 hours with the indicated agents. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.