A Smac-mimetic sensitizes prostate cancer cells to TRAIL-induced apoptosis via modulating both IAPs and NF-kappaB

BMC Cancer. 2009 Nov 6;9:392. doi: 10.1186/1471-2407-9-392.

Abstract

Background: Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent for human cancer therapy, prostate cancer still remains resistant to TRAIL. Both X-linked inhibitor of apoptosis (XIAP) and nuclear factor-kappaB function as key negative regulators of TRAIL signaling. In this study, we evaluated the effect of SH122, a small molecule mimetic of the second mitochondria-derived activator of caspases (Smac), on TRAIL-induced apoptosis in prostate cancer cells.

Methods: The potential of Smac-mimetics to bind XIAP or cIAP-1 was examined by pull-down assay. Cytotoxicity of TRAIL and/or Smac-mimetics was determined by a standard cell growth assay. Silencing of XIAP or cIAP-1 was achieved by transient transfection of short hairpin RNA. Apoptosis was detected by Annexin V-PI staining followed by flow cytometry and by Western Blot analysis of caspases, PARP and Bid. NF-kappaB activation was determined by subcellular fractionation, real time RT-PCR and reporter assay.

Results: SH122, but not its inactive analog, binds to XIAP and cIAP-1. SH122 significantly sensitized prostate cancer cells to TRAIL-mediated cell death. Moreover, SH122 enhanced TRAIL-induced apoptosis via both the death receptor and the mitochondrial pathway. Knockdown of both XIAP and cIAP-1 sensitized cellular response to TRAIL. XIAP-knockdown attenuated sensitivity of SH122 to TRAIL-induced cytotoxicity, confirming that XIAP is an important target for IAP-inhibitor-mediated TRAIL sensitization. SH122 also suppressed TRAIL-induced NF-kappaB activation by preventing cytosolic IkappaB-alpha degradation and RelA nuclear translocation, as well as by suppressing NF-kappaB target gene expression.

Conclusion: These results demonstrate that SH122 sensitizes human prostate cancer cells to TRAIL-induced apoptosis by mimicking Smac and blocking both IAPs and NF-kappaB. Modulating IAPs may represent a promising approach to overcoming TRAIL-resistance in human prostate cancer with constitutively active NF-kappaB signaling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins
  • Cell Line, Tumor
  • Humans
  • Inhibitor of Apoptosis Proteins / genetics
  • Inhibitor of Apoptosis Proteins / metabolism*
  • Intracellular Signaling Peptides and Proteins / agonists*
  • Intracellular Signaling Peptides and Proteins / pharmacology
  • Male
  • Mitochondrial Proteins / agonists*
  • Mitochondrial Proteins / pharmacology
  • NF-kappa B / genetics
  • NF-kappa B / metabolism*
  • Prostatic Neoplasms / drug therapy
  • Prostatic Neoplasms / genetics
  • Prostatic Neoplasms / metabolism*
  • Protein Binding
  • TNF-Related Apoptosis-Inducing Ligand / pharmacology*
  • X-Linked Inhibitor of Apoptosis Protein / genetics
  • X-Linked Inhibitor of Apoptosis Protein / metabolism

Substances

  • Apoptosis Regulatory Proteins
  • DIABLO protein, human
  • Inhibitor of Apoptosis Proteins
  • Intracellular Signaling Peptides and Proteins
  • Mitochondrial Proteins
  • NF-kappa B
  • TNF-Related Apoptosis-Inducing Ligand
  • X-Linked Inhibitor of Apoptosis Protein