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MDM2 antagonist Nutlin-3 suppresses the proliferation and differentiation of human pre-osteoclasts through a
Giorgio Zauli1, Erika Rimondi, Federica Corallini
1Department of Biomedicine, University of Trieste, Trieste, Italy.
Unlabelled:
Exposure of human pre-osteoclasts to the MDM2 antagonist Nutlin-3 activated the p53 pathway and significantly decreased the entry of pre-osteoclasts in the S phase in response to RANKL. Moreover, repeated exposure to Nutlin-3 suppressed osteoclastic differentiation, without affecting cell survival at any culture time.
Introduction:
The p53 oncosuppressor coordinates an intracellular network involved in protection from malignant transformation and cell cycle control; its activation is tightly regulated by the murine double minute 2 (MDM2) gene and p53-MDM2 interaction can be disrupted by selective small molecule inhibitors, the Nutlins. Although the ability of Nutlins to suppress the growth of wildtype p53 tumors has been clearly established, their biological activity in normal cells and tissues has not been extensively studied.
Materials And Methods:
Peripheral blood mononuclear cell pre-osteoclasts were cultured with macrophage-colony stimulating factor (M-CSF) + RANKL or co-cultured with SaOS-2 osteosarcoma cells in the presence of IL-1beta to induce osteoclastic differentiation. Cell cycle was analyzed by BrdU incorporation. The degree of osteoclastic differentiation was monitored at different culture times by TRACP and DAPI staining, as well as by TRACP-5b ELISA. Finally, the role of p53 in mediating the biological activity of Nutlin-3 was studied using specific siRNA.
Results:
Exposure of human pre-osteoclasts to RANKL induced an early (24 h) increase in the percentage of cells in the S phase, followed by the exit from the cell cycle at later time-points. The simultaneous addition of Nutlin-3 and RANKL dose-dependently decreased the percentage of pre-osteoclasts in the S phase and induced a rapid accumulation of p53 protein coupled with the induction of p53 target genes. Unexpectedly, the administration of Nutlin-3 to pre-osteoclasts at early culture times significantly suppressed the final output of osteoclasts at day 14 of culture. The role of p53 in mediating this biological activity of Nutlin-3 was underscored by gene knockdown experiments, in which the anti-osteoclastic activity of Nutlin-3 was significantly counteracted by siRNA specific for p53. Nutlin-3 also significantly decreased the formation of osteoclasts in a co-culture system of SaOS-2 osteosarcoma and pre-osteoclastic cells.
Conclusions:
These findings indicate that Nutlin-3 abrogates both pre-osteoclastic proliferation and differentiation through a p53-dependent pathway and may have therapeutic implications for those neoplastic diseases characterized by an abnormal osteoclastic activity.
Insights
The MDM2 antagonist Nutlin-3 inhibits osteoclast proliferation and differentiation via the p53 pathway. This discovery offers potential therapeutic strategies for diseases involving abnormal osteoclast activity.
Area of Science:
- Cell Biology
- Oncology
- Pharmacology
Background:
- The p53 tumor suppressor is crucial for cell cycle control and preventing malignancy.
- MDM2 regulates p53 activity; Nutlins inhibit this interaction.
- Nutlin's effects on normal cells are less understood than on tumors.
Purpose of the Study:
- Investigate Nutlin-3's impact on human pre-osteoclast proliferation and differentiation.
- Elucidate the role of the p53 pathway in mediating Nutlin-3's effects.
- Explore potential therapeutic applications of Nutlin-3 in osteoclast-related diseases.
Main Methods:
- Human pre-osteoclasts were cultured and stimulated with M-CSF and RANKL.
- Cell cycle progression was assessed using BrdU incorporation.
- Osteoclast differentiation was quantified via TRACP staining and ELISA.
- p53's role was confirmed using siRNA knockdown experiments.
Main Results:
- Nutlin-3 activated the p53 pathway and reduced pre-osteoclast entry into S phase.
- Repeated Nutlin-3 exposure suppressed osteoclast differentiation without affecting cell survival.
- p53 knockdown partially reversed Nutlin-3's anti-osteoclastic effects.
- Nutlin-3 reduced osteoclast formation in a co-culture system.
Conclusions:
- Nutlin-3 inhibits pre-osteoclast proliferation and differentiation through a p53-dependent mechanism.
- These findings suggest Nutlin-3 as a potential therapeutic agent for neoplastic diseases with aberrant osteoclast activity.
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