Relationship between degradation of AKT1 or RAF1 and killing of mutant KRAS-dependent cancer cells by HSP90 inhibitors. (a) Immunoblots of MDA-MB-231 cells incubated with 1 µM PU-H71 for the indicated times showing depletion of AKT1 and RAF1. (b and c) PARP cleavage in mutant KRAS-dependent lung cancer (A549), breast cancer (MDA-MB-231), and colon cancer (HCT-116) cell lines transduced with shRNAs targeting AKT1 (c) and RAF1 (b), respectively, or a nontargeting control shRNA. (d) Immunoblots of A549, MDA-MB-231, and HCT-116 cells stably transduced with empty vector (EV), AKT1, or RAF1 and incubated with 1 µM PU-H71 for 24 h. All results were confirmed in at least one additional independent experiment.