Objective. To examine the effect of TRIB3 on endoplasmic reticulum stress induced beta-cell apoptosis and to investigate the mechanism with a specific emphasis on the role of NF-kappa B pathway. Materials/Methods. We investigated the effect of TRIB3 on ER stress-induced beta-cell apoptosis in INS-1 cells and primary rodent islets. The potential role of TRIB3 in ER stress inducer thapsigargin (Tg)-induced beta-cell apoptosis was assessed using overexpression and siRNA knockdown approaches. Inducible TRIB3 beta-cells, regulated by the tet-on system, were used for sub-renal capsule transplantation in streptozotocin (STZ)-diabetic mice, to study the effect of TRIB3 on ER stress-induced beta-cell apoptosis in vivo. Apoptosis was determined by TUNEL staining both in vivo and in vitro, while the molecular mechanisms of NF-kappa B activation were investigated. Results. TRIB3 was induced in ER-stressed INS-1 cells and rodent islets, and its overexpression was accompanied by increased beta-cell apoptosis. Specifically, TRIB3 overexpression enhanced Tg-induced INS-1 derived beta-cell apoptosis both in vitro and in sub-renal capsular transplantation animal model. Additionally, knockdown of Trib3 blocked Tg-induced apoptosis. Mechanistically, the induction of TRIB3 during ER stress resulted in the activation of NF-kappa B and aggravated INS-1 derived beta-cell apoptosis, while inhibiting the NF-kappa B pathway significantly abrogated this response and prevented beta-cell apoptosis, both in vitro and in sub-renal capsular transplantation animal model. Conclusion. TRIB3 mediated ER stress-induced beta-cell apoptosis via the NF-kappa B pathway. (C) 2014 Elsevier Inc. All rights reserved.