The proteasome inhibitor PS-341 overcomes TRAIL resistance in Bax and caspase 9-negative or Bcl-xL overexpressing cells

Oncogene. 2003 Aug 7;22(32):4953-63. doi: 10.1038/sj.onc.1206656.


We demonstrate that PS-341, a small molecule inhibitor of the proteasome, markedly sensitizes resistant prostate, colon, and bladder cancer cells to TNF-like apoptosis-inducing ligand (TRAIL)-induced apoptosis irrespective of Bcl-xL overexpression. PS-341 treatment by itself does not affect the levels of Bax, Bak, caspases 3 and 8, c-Flip or FADD, but elevates levels of TRAIL receptors DR4 and DR5. This increase in receptor protein levels is associated with the ubiquitination of the DR5 protein. When PS-341 is combined with TRAIL, the levels of activated caspase 8 and cleaved Bid are substantially increased. In Bax-negative TRAIL-resistant HC-4 colon cancer cells, the combination of PS-341 and TRAIL overcomes the block to activation of the mitochondrial pathway and causes SMAC and cytochrome c release followed by apoptosis. Similarly, murine embryonic fibroblasts lacking Bax undergo apoptosis when exposed to the combination of PS-341 and TRAIL; however, fibroblasts lacking Bak are significantly resistant. Taken together, these findings indicate that PS-341 enhances TRAIL-induced apoptosis by increasing the cleavage of caspase 8, causing Bak-dependent release of mitochondrial proapoptotic proteins.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Apoptosis / drug effects
  • Apoptosis Regulatory Proteins
  • Boronic Acids / pharmacology*
  • Bortezomib
  • Caspase 9
  • Caspases / metabolism
  • Humans
  • Membrane Glycoproteins / drug effects*
  • Protease Inhibitors / pharmacology*
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / drug effects*
  • Pyrazines / pharmacology*
  • TNF-Related Apoptosis-Inducing Ligand
  • Tumor Necrosis Factor-alpha / drug effects*
  • bcl-2-Associated X Protein
  • bcl-X Protein


  • Apoptosis Regulatory Proteins
  • BAX protein, human
  • BCL2L1 protein, human
  • Boronic Acids
  • Membrane Glycoproteins
  • Protease Inhibitors
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Pyrazines
  • TNF-Related Apoptosis-Inducing Ligand
  • TNFSF10 protein, human
  • Tumor Necrosis Factor-alpha
  • bcl-2-Associated X Protein
  • bcl-X Protein
  • Bortezomib
  • CASP9 protein, human
  • Caspase 9
  • Caspases