Down-regulation of dcr3 enhances TRAIL-mediated apoptosis in pancreatic cancer

827 Introduction: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a critical pro-apoptotic molecule on the cell surface, has been identified as a promising anti-cancer agent. However, most human pancreatic cancer cells are resistant to TRAIL-induced apoptosis. This study is focused on revealing the underlying mechanisms by which pancreatic cancer cells utilize their extracellular molecules to counteract the pro-apoptotic signaling mediated by the TNF family. Methods: The binding of DcR3 (Decoy Receptor 3) with TRAIL was determined with several assays including Flow cytometry analysis, Western blotting and ELISA-like binding assay using recombinant DcR3 and TRAIL. The binding assays were also performed in both culture media and cell lysate from AsPC-1 and MiaPaCa-2 human pancreatic cancer cells. The biological function of this binding was studied with several indices for apoptosis including sub-G1 population, caspase 3 activity and cleaved PARP. Gemcitabine and siRNA for DcR3 were used to regulate the expression levels of DcR3 and TRAIL to confirm the function of the interaction of these two molecules. Results: In this study, we demonstrate for the first time that DcR3, a secreted decoy receptor expressed at a high level by malignant pancreatic cancer cells, acts as an extracellular anti-apoptotic molecule by binding to TRAIL, thus counteracting the death-promoting function of TRAIL. The reduction of DcR3 with siRNA unmasks TRAIL and greatly enhances TRAIL-induced apoptosis. Gemcitabine, a first line drug for pancreatic cancer, also reduces the level of DcR3. The addition of DcR3 siRNA could further enhance the apoptosis induced by Gemcitabine. Importantly, the in vivo studies demonstrate that the therapeutic effect of Gemcitabine is enhanced via further reduction of DcR3, suggesting that down-regulation of DcR3 in tumor cells could tip the balance from survival to death and serve as a new strategy for pancreatic cancer therapy. Conclusion: DcR3 is utilized by cancer cells for their survival upon the various stresses, including chemotherapy. The binding of DcR3 to TRAIL blocks the apoptosis induced by TRAIL. The down-regulation of DcR3 is a new strategy for enhancement of anti-cancer therapy.