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

• Published in: BMC cancer 2009-11, Vol.9 (1), p.392-392, Article 392
• Main Authors: Dai, Yao, Liu, Meilan, Tang, Wenhua, Li, Yongming, Lian, Jiqin, Lawrence, Theodore S, Xu, Liang
• Format: Article
• Language: English
• Subjects: Apoptosis - drug effects; Care and treatment; Cell Line, Tumor; Cellular signal transduction; Gene expression; Genetic aspects; 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; Physiological aspects; Prostate cancer; Prostatic Neoplasms - drug therapy; Prostatic Neoplasms - genetics; Prostatic Neoplasms - metabolism; Protein Binding; TNF-Related Apoptosis-Inducing Ligand - pharmacology; Transcription factors; X-Linked Inhibitor of Apoptosis Protein - genetics; X-Linked Inhibitor of Apoptosis Protein - metabolism
• ISSN: 1471-2407; 1471-2407
• DOI: 10.1186/1471-2407-9-392

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. 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. 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. 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.