RRR‐α‐tocopheryl succinate inhibits el4 thymic lymphoma cell growth by inducing apoptosis and DNA synthesis arrest

Abstract

RRR‐α‐tocopheryl succinate (vitamin E succinate, VES) treatment of murine ElA T lymphoma cells induced the cells to undergo apoptosis. After 48 hours of VES treatment at 20 μg/ml, 95% of cells were apoptotic. Evidence for the induction of apoptosis by VES treatments is based on staining of DNA for detection of chromatin condensation/fragmentation, two‐color flow‐cytometric analyses of DNA content, and end‐labeled DNA and electrophoretic analyses for detection of DNA ladder formation. VES‐treated EL4 cells were blocked in the G1 cell cycle phase; however, apoptotic cells came from all cell cycle phases. Analyses of mRNA expression of genes involved in apoptosis revealed decreased c‐myc and increased bcl‐2, c‐fos, and c‐jun mRNAs within three to six hours after treatment. Western analyses showed increased c‐Jun, c‐Fos, and Bcl‐2 protein levels. Electrophoretic mobility shift assays showed increased AP‐1 binding at 6, 12, and 24 hours after treatment and decreased c‐Myc binding after 12 and 24 hours of VES treatment. Treatments of EL4 cells with VES + RRR‐α‐to‐copherol reduced apoptosis without effecting DNA synthesis arrest. Treatments of ELA cells with VES + rac‐6‐hydroxyl‐2, 5,7,8‐tetramethyl‐chroman‐2‐carboxylic acid, butylated hy‐droxytoluene, or butylated hydroxyanisole had no effect on apoptosis or DNA synthesis arrest caused by VES treatments. Analyses of bcl‐2, c‐myc, c‐jun, and c‐fos mRNA levels in cells receiving VES + RRR‐α‐tocopherol treatments showed no change from cells receiving VES treatments alone, implying that these changes are correlated with VES treatments but are not causal for apoptosis. However, treatments with VES + RRR‐α‐tocopherol decreased AP‐1 binding to consensus DNA oligomer, suggesting AP‐1 involvement in apoptosis induced by VES treatments.