The proteasome inhibitor bortezomib promotes mitochondrial injury and apoptosis induced by the small molecule Bcl-2 inhibitor HA14-1 in multiple myeloma cells

Abstract

Interactions between the small molecule Bcl-2 inhibitor HA14-1 and proteasome inhibitors, including bortezomib (Velcadet; formerly known as PS-341) and MG-132, have been examined in human multiple myeloma cells. Sequential (but not simultaneous) exposure of MM.1S cells to bortezomib or MG-132 (10 h) followed by HA14-1 (8 h) resulted in a marked increase in mitochondrial injury (loss of DW m , cytochrome c, Smac/DIA-BLO, and apoptosis-inducing factor release), activation of procaspases-3, -8, and -9, and Bid, induction of apoptosis, and loss of clonogenicity. Similar interactions were observed in U266 and MM.1R dexamethasone-resistant myeloma cells. These events were associated with Bcl-2 cleavage, Bax, Bak, and Bad accumulation, mitochondrial translocation of Bax, abrogation of Mcl-1, Bcl-xL, and XIAP upregulation, and a marked induction of JNK and p53. Bortezomib/HA14-1 treatment triggered an increase in reactive oxygen species (ROS), which, along with apoptosis, was blocked by the free radical scavenger N-acetyl-L-cysteine (L-NAC). L-NAC also opposed bortezomib/HA14-1-mediated JNK activation, upregulation of p53 and Bax, and release of cytochrome c and Smac/DIABLO. Finally, bortezomib/HA14-1-mediated apoptosis was unaffected by exogenous IL-6. Together, these findings indicate that sequential exposure of myeloma cells to proteasome and small molecule Bcl-2 inhibitors such as HA14-1 may represent a novel therapeutic strategy in myeloma.

Proteasome inhibitor‐induced apoptosis in human monocyte‐derived dendritic cells

“…These mainly include the anti-apoptotic Bcl-2 and the pro-apoptotic Bcl-2-associated X protein (Bax) [1,2,13,[33][34][35][36][37]. While Bcl-2 levels were not found to be substantially altered by treatment of DC with bortezomib (data not shown), Bax protein levels were increased (Fig.…”

Analysis of changes in the proteome of HL-60 promyeloid leukemia cells induced by the proteasome inhibitor PSI

“…Prominent events in proteasome inhibitor induced apoptosis include the production of reactive oxygen species (ROS) [20,21], activation of the stress kinases JNK [22][23][24] and p38 [8,10,25,26] as well as abrogation of cytoprotective p42/p44 MAPK signaling [27,28]. Furthermore, transcriptional activation of NFκB dependent survival promoting genes, such as cIAP-1 and cIAP-2 [29], XIAP [30], A1 and A20 [31,32] and Bcl-xL [33] is inhibited by blocking the degradation of IκB [34,35].…”

Specific downregulation of bcl-2 and xIAP by RNAi enhances the effects of chemotherapeutic agents in MCF-7 human breast cancer cells

“…More recently, considerable attention has been drawn to small organic molecules or short peptides that antagonize or mimic the function of apoptosis-regulating gene products. Promising examples of this approach are the inhibitors of Bcl-2 and Bcl-x L [9][10][11] and the short peptides that substitute for the mitochondrial proapoptotic Smac protein. 12 Finally, the successful use of small interfering RNAs (siRNAs) to downregulate gene expression in several model systems [13][14][15][16][17][18] has led to many attempts to explore this methodology in potentially therapeutic settings.…”