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Quercetin abrogates taxol-mediated signaling by inhibiting multiple kinases
M Marone1, G D'Andrilli, N Das
1Laboratory of Anti-neoplastic Pharmacology, Catholic University, Rome, Italy.
Abstract:
Cell cycle block in G(2)/M initiates apoptosis, but the mechanism of this signaling cascade are largely unknown. The microtubule-perturbing agent Taxol has multiple effects on this signaling pathway and is a potent inducer of apoptosis. The specific pathways activated by low, clinically relevant concentrations of the drug are still largely unknown and are dependent on cell type and drug concentration. In this work, we have investigated why HeLa cells respond to Taxol by undergoing complete apoptosis, whereas MCF-7 cells remain in an intermediate phase with reduced death. Three phases were distinguished in these apoptotic pathways. The initial phase characterized by cellular detachment is followed by a second phase which includes the onset of apoptotic morphology, and p38 and Bcl-2 phosphorylation. These two phases are common to both cell lines. HeLa cells then proceed to the third and final execution phase, which culminates in death, whereas MCF-7 cells do not progress. Interestingly, the isoflavonoid Quercetin, a known general kinase inhibitor and an antioxidant, was able to prevent the onset of Taxol-induced cellular detachment and to protect from cell death. Moreover, it blocked Taxol-induced phosphorylation of p38 and Bcl-2, and prevented a Taxol-induced change in relative mobility of the apoptosis signal-regulating kinase 1 (Ask1). Our data elucidate the signaling pathways activated by Taxol at low clinically relevant concentrations.
Insights
Taxol induces apoptosis via cell cycle arrest, but pathways differ by cell type. Quercetin inhibits Taxol-induced cell death by blocking key signaling events like p38 and Bcl-2 phosphorylation.
Area of Science:
- Cell Biology
- Molecular Biology
- Pharmacology
Background:
- Apoptosis initiation via G(2)/M cell cycle arrest is known, but downstream mechanisms remain unclear.
- Taxol (paclitaxel) is a microtubule-targeting agent that induces apoptosis, yet its precise signaling pathways at low concentrations are cell-type dependent.
- Understanding differential cellular responses to Taxol is crucial for its clinical application.
Purpose of the Study:
- Investigate the differential mechanisms of Taxol-induced apoptosis in HeLa and MCF-7 cells.
- Elucidate the specific signaling pathways activated by low, clinically relevant concentrations of Taxol.
- Determine the role of Quercetin in modulating Taxol's apoptotic effects.
Main Methods:
- Comparative analysis of Taxol-treated HeLa and MCF-7 cell lines.
- Observation of cellular morphology and cell cycle progression.
- Western blot analysis to assess protein phosphorylation (p38, Bcl-2) and kinase activity (Ask1).
- Treatment with Quercetin to evaluate its inhibitory effects.
Main Results:
- Both cell lines exhibited initial phases of Taxol treatment including cellular detachment and apoptotic morphology onset, with p38 and Bcl-2 phosphorylation.
- HeLa cells progressed to a complete apoptotic execution phase, while MCF-7 cells remained in an intermediate state.
- Quercetin inhibited Taxol-induced cellular detachment, protected against cell death, and blocked phosphorylation of p38 and Bcl-2, and altered Apoptosis Signal-Regulating Kinase 1 (Ask1) mobility.
Conclusions:
- Differential progression to apoptosis in response to Taxol is cell-type specific.
- Taxol-induced apoptosis involves p38 and Bcl-2 phosphorylation and Ask1 activation.
- Quercetin acts as a protective agent by inhibiting key signaling nodes in the Taxol-induced apoptotic pathway.