Proteasome Inhibitors Sensitize Colon Carcinoma Cells to TRAIL-Induced Apoptosis via Enhanced Release of Smac/DIABLO from the Mitochondria

Katalin NAGY1, Kinga SZÉKELY-SZÜTS5, Kamel IZERADJENE5, Leslie DOUGLAS5, Mike TILLMAN5, Helga BARTI-JUHÁSZ1, Massimo DOMINICI4, Carlotta SPANO4, Gian LUCA CERVO4, Pierfranco CONTE4, Janet A HOUGHTON5, Rudolf MIHALIK2, László KOPPER3, István PETÁK1

1Ist Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest, Hungary
2Molecular Pathology Research Group, Joint Research Organization of the Hungarian Academy of Science and Semmelweis University, Budapest, Hungary
3Szentágothai János Knowledge Center, Budapest, Hungary
4Department of Oncology and Hematology, University of Modena and Reggio Emilia, Modena, Italy
5Division of Molecular Therapeutics, Department of Hematology-Oncology, St. Jude Children’s Research Hospital, Memphis, USA


The synergistic interaction between proteasome inhibitors and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a promising approach to induce cell death in tumor cells. However, the molecular and biochemical mechanisms of this synergism have been proven to be cell type specific. We therefore focused our investigation on TRAIL-resistant colon carcinoma cells in this study. DNA fragmentation, mitochondrial membrane depolarization and increased caspase-3-like enzyme activity was exclusively induced only by combined treatment with proteasome inhibitors (epoxomicin, MG132, bortezomib/PS-341) and TRAIL. The expression level of anti-apoptotic proteins (XIAP, survivin, Bcl-2, Bcl-XL), regulated by NF-κB transcription factor, was not effected by any of these treatments. TRAIL alone induced only partial activation of caspase-3 (p20), while the combination of TRAIL and proteasome inhibition led to the full proteolytic activation of caspase-3 (p17). Only the combination treatment induced marked membrane depolarization and the release of cytochrome c, HtrA2/Omi and Smac/DIABLO. Apoptosis-inducing factor (AIF) was not released in any of these conditions. These results are consistent with a model where the full activation of caspase-3 by caspase-8 is dependent on the release of Smac/DIABLO in response to the combined treatment. This molecular mechanism, independent of the inhibition NF-κB activity, may provide rationale for the combination treatment of colon carcinomas with proteasome inhibitors and recombinant TRAIL or agonistic antibody of TRAIL receptors. Pathology & Oncology Research, Vol 12, Nr 3, 133-142, 2006

Key words: TRAIL; epoxomicin; MG132; bortezomib/PS-341; Smac/DIABLO; colon carcinoma

Received: Aug 15, 2006; accepted: Sep 8, 2006
Correspondence: István PETÁK, Ist Department of Pathology and Experimental Cancer Research, Semmelweis University, Üllõi út 26. Budapest H-1085, Hungary; Tel: (36-1)-4591500/4453, Fax: (36-1)-4591500/4453; E-mail:

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