beta-Sitosterol induces G2/M arrest, endoreduplication, and apoptosis through the Bcl-2 and PI3K/Akt signaling pathways.
beta-Sitosterol (SITO) is a potentially valuable candidate for cancer chemotherapy, however the cellular and molecular mechanisms responsible for its anti-cancer activity are unknown. Therefore, we attempted to elucidate the mechanisms responsible for SITO-induced anti-proliferation in human leukemia cells. Treatment with SITO increased caspase-3 activation and DNA fragmentation in U937 and HL60 cells. This effect was associated with significant G2/M arrest and endoreduplication. We also demonstrated that SITO treatment significantly increases levels of polymeric alpha-tubulin and promoted microtubule polymerization. We next elucidated that ectopic expression of Bcl-2 accelerates endoreduplication in U937 cells. Furthermore, the specific Bcl-2 inhibitor, HA14-1, prevented endoreduplication through G2 phase arrest. Interestingly, SITO treatment did not significantly promote endoreduplication or decrease cell viability in Bcl-2 null K562 cells. SITO treatment also induced a gradual increase of phosphatidyl-inositol 3-kinase (PI3K) and Akt phosphorylation. Treatment with the selective PI3K/Akt inhibitor LY29004 completely blocked endoreduplication and apoptosis in the presence of SITO. In addition, treatment with SITO-induced phosphorylation of extracellular signal-regulated protein kinase (ERK), however significance of ERK activation in the execution of apoptosis and endoreduplication is unknown. These results suggest that SITO induces endoreduplication by promoting spindle microtubule dynamics through the Bcl-2 and PI3K/Akt signaling pathways.
Moon
Dong-Oh
DO
Faculty of Applied Marine Science, Cheju National University, Jeju Special Self-Governing Province 690-756, South Korea.
Kim
Mun-Ock
MO
Choi
Yung Hyun
YH
Kim
Gi-Young
GY
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053148:Caspase 3 / Q000187:drug effects / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D008870:Microtubules / Q000187:drug effects; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D012855:Sitosterols / Q000494:pharmacology*; D014404:Tubulin / Q000187:drug effects
D000970:Antineoplastic Agents; D019253:Proto-Oncogene Proteins c-bcl-2; D012855:Sitosterols; D014404:Tubulin; C025473:gamma-sitosterol; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D053148:Caspase 3