EGR-1/Bax pathway plays a role in vitamin E δ-tocotrienol-induced apoptosis in pancreatic cancer cells

The anticancer activity of delta-tocotrienol, a bioactive vitamin E present in whole grain cereals, annatto beans and palm fruit, is strongly dependent on its effect on the induction of apoptosis. delta-Tocotrienol-induced apoptosis is associated with consistent induction in the expression of the proapoptotic protein BcI-2-associated X protein (Bax). The molecular mechanism by which delta-tocotrienol regulates Bax expression is unknown. We carried out a DNA microarray study that identified delta-tocotrienol induction of the zinc finger transcription factor EGR-1 in pancreatic cancer cells. Here, we provide evidence linking delta-tocotrienol-induced apoptosis in pancreatic cancer cells to EGR-1 regulation of Bax expression. Forced expression of EGR-1 induces Bax expression and apoptosis in pancreatic cancer cells. In contrast, knockdown of delta-tocotrienol-induced EGR-1 by small interfering RNA attenuated delta-tocotrienol-induced Bax expression and reduced delta-tocotrienol-induced apoptosis. Further analyses showed that de nova protein synthesis was not required for delta-tocotrienol-induced EGR-1 expression, suggesting a direct effect of delta-tocotrienol on EGR-1 expression. Furthermore, a chromatin immunoprecipitation assay demonstrated that EGR-1 binds to the Bax gene promoter. Finally, delta-tocotrienol treatment induced Bax expression and activated EGR-1 in the pancreatic neoplastic cells of the PDX-Cre Kras genetically engineered model of pancreatic cancer. Our study provides the first evidence for EGR-1 as a direct target of vitamin E delta-tocotrienol, suggesting that EGR-1 may act as a proapoptotic factor in pancreatic cancer cells via induction of Bax. (C) 2015 Elsevier Inc. All rights reserved.