Experimental cell research
TNF-related apoptosis-inducing ligand (TRAIL) is a potential chemotherapeutic agent with high selectivity for malignant cells. Many tumors, however, are resistant to TRAIL cytotoxicity. Although cellular inhibitors of apoptosis 1 and 2 (cIAP-1 and -2) are often over-expressed in cancers, their role in mediating TRAIL resistance remains unclear. Here, we demonstrate that TRAIL-induced apoptosis of liver cancer cells is associated with degradation of cIAP-1 and X-linked IAP (XIAP), whereas cIAP-2 remains unchanged. Lower concentrations of TRAIL causing minimal or no apoptosis do not alter cIAP-1 or XIAP protein levels. Silencing of cIAP-1 expression, but not XIAP or cIAP-2, as well as co-treatment with a second mitochondrial activator of caspases (SMAC) mimetic (which results in rapid depletion of cIAP-1), sensitizes the cells to TRAIL. TRAIL-induced loss of cIAP-1 and XIAP requires caspase activity. In particular, caspase 8 knockdown stabilizes both cIAP-1 and XIAP, while caspase 9 knockdown prevents XIAP, but not cIAP-1 degradation. Cell-free experiments confirmed cIAP-1 is a substrate for caspase 8, with likely multiple cleavage sites. These results suggest that TRAIL-mediated apoptosis proceeds through caspase 8-dependent degradation of cIAP-1. Targeted depletion of cIAP-1 by SMAC mimetics in conjunction with TRAIL may be beneficial for the treatment of human hepatobiliary malignancies.
Apoptosis, Caspase 8, Caspase 9, Caspase Inhibitors, Gene Knockdown Techniques, Humans, Inhibitor of Apoptosis Proteins, Protein Processing, Post-Translational, RNA, Small Interfering, Signal Transduction, TNF-Related Apoptosis-Inducing Ligand, Tumor Cells, Cultured, X-Linked Inhibitor of Apoptosis Protein
Guicciardi, Maria Eugenia; Mott, Justin L.; Bronk, Steven F.; Kurita, Satoshi; Fingas, Christian D.; and Gores, Gregory J., "Cellular inhibitor of apoptosis 1 (cIAP-1) degradation by caspase 8 during TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis." (2011). Journal Articles: Biochemistry & Molecular Biology. 23.