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Induction of apoptosis by quercetin: involvement of heat shock protein
Abstract:
Quercetin, a widely distributed bioflavonoid, inhibits the growth of tumor cells. The present study was designed to investigate the possible involvement of apoptosis and heat shock protein in the antitumor activity of quercetin. Treatment with quercetin of K562, Molt-4, Raji, and MCAS tumor cell lines resulted in morphological changes, including propidium iodide-stained condensed nuclei (intact or fragmented), condensation of nuclear chromatin, and nuclear fragmentation. Agarose gel electrophoresis of quercetin-treated tumor cells demonstrated a typical ladder-like pattern of DNA fragments. In addition, the hypodiploid DNA peak of propidium iodide-stained nuclei was revealed by flow cytometry. Quercetin induced apoptosis in cells at G1 and S in a dose- and time-dependent manner. The apoptosis-inducing activity of quercetin was enhanced by cycloheximide and actinomycin D. A nuclease inhibitor, aurintricarboxylic acid, inhibited quercetin-induced apoptosis, whereas deprivation of intracellular calcium by EGTA had no effect. 12-O-Tetradecanoylphorbol-13-acetate and H-7 did not affect the induction of apoptosis by quercetin. The synthesis of HSP70 was inhibited by quercetin when determined by immunocytochemistry, Western blot analysis, and Northern blot analysis. Quercetin-treated tumor cells were not induced to show aggregation of HSP70 in the nuclei and nucleolus in response to heat shock, resulting in apoptosis. By contrast, when tumor cells were first exposed to heat shock, no apoptosis was induced by quercetin. In addition, pretreatment of tumor cells with HSP70 antisense oligomer that specifically inhibited the synthesis of HSP70 enhanced the subsequent induction of apoptosis by quercetin. These results suggest that quercetin displays antitumor activity by triggering apoptosis and that HSP70 may affect quercetin-induced apoptosis.
Insights
Quercetin, a bioflavonoid, inhibits tumor cell growth by inducing apoptosis. Heat shock protein 70 (HSP70) synthesis is inhibited by quercetin, suggesting HSP70 plays a role in quercetin-mediated apoptosis.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Quercetin is a bioflavonoid with known antitumor properties.
- The mechanisms underlying quercetin's antitumor activity, particularly apoptosis and heat shock proteins, require further investigation.
Purpose of the Study:
- To investigate the role of apoptosis in quercetin's antitumor activity.
- To explore the involvement of heat shock protein 70 (HSP70) in quercetin-induced apoptosis.
Main Methods:
- Treatment of K562, Molt-4, Raji, and MCAS tumor cell lines with quercetin.
- Morphological analysis, DNA fragmentation assays (agarose gel electrophoresis), and flow cytometry to detect apoptosis.
- Western blot, Northern blot, and immunocytochemistry to assess HSP70 synthesis.
- Experiments involving apoptosis inducers/inhibitors (cycloheximide, actinomycin D, aurintricarboxylic acid, EGTA) and HSP70 modulation (antisense oligomer).
Main Results:
- Quercetin induced apoptosis in tumor cells, characterized by DNA fragmentation and hypodiploid DNA content.
- Apoptosis induction was dose- and time-dependent and enhanced by cycloheximide and actinomycin D.
- Quercetin inhibited HSP70 synthesis, and HSP70 inhibition via antisense oligomer enhanced quercetin-induced apoptosis.
- Heat shock pretreatment abrogated quercetin's apoptosis-inducing effect.
Conclusions:
- Quercetin exhibits antitumor activity by triggering apoptosis in tumor cells.
- HSP70 plays a significant role in modulating quercetin-induced apoptosis, with its inhibition enhancing the process.