Induction of apoptosis by penta- O-galloyl-β- d-glucose through activation of caspase-3 in human leukemia HL-60 cells

Abstract

Penta- O-galloyl-β- d-glucose is structurally related to (−)-epigallocatechin gallate and is isolated from hydrolyzed tannin. Penta- O-galloyl-β- d-glucose can inhibit tumor promotion by teleocidin. We investigated the effects of penta- O-galloyl-β- d-glucose and various tea polyphenols on cell viability in human leukemia HL-60 cells. In this study, we demonstrated that penta- O-galloyl-β- d-glucose was able to induce apoptosis in a concentration- and time-dependent manner; however, other polyphenols were less effective. We further investigated the molecular mechanisms of penta- O-galloyl-β- d-glucose-induced apoptosis. Treatment with penta- O-galloyl-β- d-glucose caused induction of caspase-3/CPP32 activity in dose- and time-dependent manner, but not caspase-1 activity, and induced the degradation of poly-(ADP-ribose) polymerase. Pretreatment with acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) and Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK) inhibited penta- O-galloyl-β- d-glucose-induced DNA fragmentation. Furthermore, treatment with penta- O-galloyl-β- d-glucose (50 μM) caused a rapid loss of mitochondrial transmembrane potential, release of mitochondrial cytochrome c into cytosol, and subsequent induction of procaspase-9 processing. Our results indicate that penta- O-galloyl-β- d-glucose allows caspase-activated deoxyribonuclease to enter the nucleus and degrade chromosomal DNA, and induces DFF-45 (DNA fragmentation factor) degradation. These results lead to a working hypothesis that penta- O-galloyl-β- d-glucose-induced apoptosis is triggered by the release of cytochrome c into the cytosol, procaspase-9 processing, activation of caspase-3, degradation of poly-(ADP-ribose) polymerase, and DNA fragmentation caused by the caspase-activated deoxyribonuclease through the digestion of DFF-45. The induction of apoptosis by penta- O-galloyl-β- d-glucose may provide a pivotal mechanism for its cancer chemopreventive action.