Bortezomib was shown to evoke mitochondrial apoptosis in MM cells by upregulation of BH3-only proteins and activation of BAX/BAK [48, 50], following upregulation of pro-apoptotic terminal UPR signaling components including PERK and its downstream effectors ATF4 and CHOP [51]. This evidence concerns the gene ATF4 and Miyoshi myopathy.