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Dissecting p53 tumor suppressor functions in vivo
Clemens A Schmitt1, Jordan S Fridman, Meng Yang
1Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, New York 11724, USA.
Abstract:
Although the p53 tumor suppressor acts in a plethora of processes that influence cellular proliferation and survival, it remains unclear which p53 functions are essential for tumor suppression and, as a consequence, are selected against during tumor development. Using a mouse model harboring primary, genetically modified myc-driven lymphomas, we show that disruption of apoptosis downstream of p53 by Bcl2 or a dominant-negative caspase 9 confers-like p53 loss-a selective advantage, and completely alleviates pressure to inactivate p53 during lymphomagenesis. Despite their p53-null-like aggressive phenotype, apoptosis-defective lymphomas that retain intact p53 genes do not display the checkpoint defects and gross aneuploidy that are characteristic of p53 mutant tumors. Therefore, apoptosis is the only p53 function selected against during lymphoma development, whereas defective cell-cycle checkpoints and aneuploidy are mere byproducts of p53 loss.
Insights
Disrupting apoptosis downstream of the p53 tumor suppressor gene provides a selective advantage in lymphoma development. This indicates apoptosis is the key p53 function selected against, not cell-cycle checkpoints.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- The p53 tumor suppressor protein regulates critical cellular processes like proliferation and survival.
- The specific functions of p53 that are essential for tumor suppression and are selected against during tumor development are not fully understood.
Purpose of the Study:
- To identify which p53 functions are essential for tumor suppression by examining selective pressures during lymphoma development.
- To determine if apoptosis or cell-cycle checkpoints are the primary p53 functions targeted during lymphomagenesis.
Main Methods:
- Utilized a mouse model with genetically modified myc-driven lymphomas.
- Investigated the impact of disrupting apoptosis downstream of p53 using Bcl2 or dominant-negative caspase 9.
- Compared the phenotypes of apoptosis-defective lymphomas with p53-null lymphomas.
Main Results:
- Disruption of apoptosis downstream of p53 conferred a selective advantage, mimicking p53 loss.
- Apoptosis-defective lymphomas with intact p53 showed an aggressive phenotype but lacked the characteristic checkpoint defects and aneuploidy of p53 mutant tumors.
- Inactivation of p53 was not required for lymphomagenesis when apoptosis was disrupted.
Conclusions:
- Apoptosis is the sole p53 function selected against during lymphoma development.
- Cell-cycle checkpoint defects and aneuploidy observed in p53 mutant tumors are byproducts, not primary targets, of p53 loss during lymphomagenesis.