Proteostasis regulation using naturally occurring small molecules has been considered as a promising strategy for manipulating cancer sensitivity and therapy. Here, we identify a small molecule Hsp90 inhibitor radicicol that induces intracellular accumulation of cytotoxic clusterin variant. In the mechanistic basis, this variant proved to be a product disposed from the stressed ER. During this process, inhibitory effect of radicicol on protein degradation results in cytosolic accumulation of glycan-deficient clusterin variant that signals cell death. These results provide a therapeutic insight into the targeted proteostasis perturbation of clusterin as an anti-cancer strategy. (C) 2015 Elsevier Inc. All rights reserved.