MG132 is a potent cell-permeable proteasome and calpain inhibitor with IC50 of 0.1 and 1.2 μM for the inhibition of proteasome and calpain, respectively. The Ki of MG132  is 4 nM. MG132 inhibits TNF-α-induced NF-κB activation and IκBα degradation with an IC50 of 3 µM and prevents β-secretase cleavage. MG132  induces neurite outgrowth in PC12 cells and has anticancer properties in vitro. MG132  reduces the degradation of ubiquitin-conjugated proteins in mammalian cells and permeable strains of yeast by the 26S complex without affecting its ATPase or isopeptidase activities. MG132 activates c-Jun N-terminal kinase (JNK1), which initiates apoptosis.