Because several studies have suggested that the buildup of mitogen-activated protein kinase phosphatase-1 (MKP-1) may account for the chemoresistance of cancer cells to proteasome inhibitors33, 34, 35, we assessed the effect of MLN9708 on the induction of MKP-1 expression in the eight breast cancer cell lines. This evidence concerns the gene DUSP1 and breast cancer.