Beta-sitosterol induces anti-proliferation and apoptosis in human leukemic U937 cells through activation of caspase-3 and induction of Bax/Bcl-2 ratio.
Beta-sitosterol is the main dietary phytosterol found in plants and has been shown to inhibit proliferation and induce apoptosis in human solid tumors such as colon and breast cancers. However, the mechanism by which beta-sitosterol induces apoptosis is not completely understood in leukemic cells. This study investigated the mechanism of apoptosis induced by beta-sitosterol in human leukemic U937 cells. beta-Sitosterol induced cytotoxicity and apoptosis in U937 cells in a concentration dependent manner, as measured by hemocytometer counts, fluorescence microscopy, agarose gel electrophoresis, and flow cytometry analysis. The increase in apoptosis induced by beta-sitosterol was associated with down-regulation of Bcl-2, degradation of poly-(ADP-ribose) polymerase (PARP) and phospholipase C (PLC)-gamma1 protein, and activation of caspase-3. beta-Sitosterol induced apoptosis was not associated with changes in the expression of Bcl-xL, Bax, or inhibitor of apoptosis proteins (IAPs). z-DEVD-fmk, a caspase-3 specific inhibitor, blocked caspase-3 activation and PARP degradation, and significantly attenuated beta-sitosterol-induced apoptosis. This suggests that caspase-3 activation is partially essential for beta-sitosterol-induced apoptosis. Bcl-2 overexpression also significantly blocked caspase-3 activation and the decrease in PARP cleavage by beta-sitosterol, and effectively attenuated the apoptotic response to beta-sitosterol. These results show that beta-sitosterol potently induces apoptosis in U937 cells and that beta-sitosterol-induced apoptosis is related to the selective activation of caspase-3 and induction of Bax/Bcl-2 ratio.
Park
Cheol
C
Department of Biochemistry, Dongeui University, College of Oriental Medicine, Busan, South Korea.
Moon
Dong-Oh
DO
Rhu
Chung-Ho
CH
Choi
Byung Tae
BT
Lee
Won Ho
WH
Kim
Gi-Young
GY
Choi
Yung Hyun
YH
D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism*; D061945:Caspase Inhibitors; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis*; D012855:Sitosterols / Q000494:pharmacology*; D020298:U937 Cells; D051028:bcl-2-Associated X Protein / Q000032:analysis*
D061945:Caspase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D012855:Sitosterols; D051028:bcl-2-Associated X Protein; C025473:gamma-sitosterol; D053148:Caspase 3