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Activation of p53 by roscovitine-mediated suppression of MDM2 expression
1Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, Florida, FL 33612, USA.
Abstract:
The p53 tumor suppressor is regulated by the MDM2 oncoprotein. Overexpression of MDM2 maintains p53 at low levels and contributes to the functional inactivation of p53 in a subset of tumors. We found that treatment with roscovitine and olomoucin, which were originally developed as cyclin-dependent kinase (CDK) inhibitors, can efficiently stabilize and activate nuclear p53 in tumor cells with MDM2 amplification or cytoplasmic p53. These inhibitors block the degradation of p53 without affecting p53-MDM2 binding and the nuclear shuttling function of p53 and MDM2. Roscovitine also induces stabilization of the p53 Ala-315 mutant, indicating that it does not act by regulating the CDK phosphorylation of serine 315. Roscovitine induces down-regulation of MDM2 expression at both protein and mRNA levels. Ectopic expression of MDM2 can abrogate the ability of roscovitine to induce p53 stabilization. Low concentrations of roscovitine cooperate with the DNA-damaging agent camptothecin to activate p53 in a synergistic fashion. These results show that the small molecule CDK inhibitors can be used to activate p53 through their potent inhibitory effect on MDM2 expression and may be useful as sensitizing agents for other DNA-damaging drugs.
Insights
Small molecule cyclin-dependent kinase (CDK) inhibitors, roscovitine and olomoucin, activate the p53 tumor suppressor by downregulating MDM2 expression. These drugs offer a new strategy for cancer therapy.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- The p53 tumor suppressor is crucial for preventing cancer, but its function is often compromised by the MDM2 oncoprotein.
- MDM2 overexpression leads to low p53 levels and functional inactivation, contributing to tumor development.
- Targeting the p53-MDM2 interaction is a key strategy in cancer therapy.
Purpose of the Study:
- To investigate the potential of small molecule cyclin-dependent kinase (CDK) inhibitors, roscovitine and olomoucin, in reactivating p53 tumor suppressor function.
- To elucidate the mechanism by which these CDK inhibitors affect p53 and MDM2 levels and activity.
- To evaluate the therapeutic potential of these inhibitors in cancer cells with dysregulated p53-MDM2 pathways.
Main Methods:
- Treatment of tumor cells with roscovitine and olomoucin.
- Assessment of p53 and MDM2 protein and mRNA levels.
- Analysis of p53-MDM2 binding and nuclear shuttling.
- Investigation of p53 stabilization in the presence of MDM2 overexpression or specific p53 mutants.
- Evaluation of synergistic effects with DNA-damaging agents.
Main Results:
- Roscovitine and olomoucin efficiently stabilize and activate nuclear p53 in tumor cells with MDM2 amplification or cytoplasmic p53.
- These inhibitors block p53 degradation without disrupting p53-MDM2 binding or nuclear shuttling.
- Roscovitine induces down-regulation of MDM2 at both protein and mRNA levels, independent of CDK phosphorylation at serine 315.
- Ectopic MDM2 expression abrogates roscovitine-induced p53 stabilization.
- Low-dose roscovitine synergizes with camptothecin to activate p53.
Conclusions:
- Small molecule CDK inhibitors can activate the p53 tumor suppressor by inhibiting MDM2 expression.
- These findings highlight a novel therapeutic approach for cancers with defective p53 pathways.
- Roscovitine and olomoucin show promise as sensitizing agents for DNA-damaging chemotherapy.