TRAIL induces apoptosis but not necroptosis in colorectal and pancreatic cancer cells preferentially via the TRAIL-R2/DR5 receptor
Abstract
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine capable of inducing apoptosis in various human cancer cells by binding to its pro-apoptotic receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5). In addition to apoptosis, TRAIL can activate other signaling pathways, including stress kinases, canonical NF-κB signaling, and necroptosis. Although both receptors are widely expressed, their specific roles in TRAIL-induced signaling remain unclear. To investigate receptor-specific signaling, we developed Strep-tagged, trimerized forms of recombinant human TRAIL that selectively bind with high affinity to either DR4 or DR5. Using these ligands, we explored how each receptor contributes to TRAIL-induced signaling pathways. In TRAIL-resistant colorectal HT-29 cells, but not in pancreatic PANC-1 cells, DISC formation and initial caspase-8 processing occurred similarly through both DR4 and DR5 activation. However, TRAIL-induced apoptosis, enhanced by the Bcl-2 family inhibitor ABT-737 or the translation inhibitor homoharringtonine, predominantly relied on the DR5 receptor in both cell lines. Additionally, shRNA-mediated knockdown of DR4 or DR5 in HT-29 cells revealed a stronger role for DR5 in apoptosis induction. In contrast, necroptotic signaling was similarly activated by both DR4- and DR5-specific ligands. Under apoptotic conditions, activation of additional signaling pathways, including NF-κB and stress kinases, was mainly DR5-dependent, while these pathways were similarly triggered by either ligand during necroptosis. This study provides the first comprehensive analysis of DR4- and DR5-specific signaling in colorectal and pancreatic cancer cells.