Since treatment of ErbB2+ breast cancer cells with Hsp90 inhibitors promotes rapid ubiquitination and proteasome-dependent degradation [23], identification of CHIP as a binding partner and inhibitor of the folding function of Hsc70 [32] suggested that it may serve as a mediator of Hsp90 inhibitor-induced ErbB2 degradation. Here, STUB1 is linked to breast cancer.