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Activation of an MDM2-specific caspase by p53 in the absence of apoptosis
R Pochampally1, B Fodera, L Chen
1Louisiana State University Medical Center, Department of Microbiology, Stanley S. Scott Cancer Center, New Orleans, Louisiana 70112, USA.
Abstract:
Cells undergoing p53-mediated apoptosis activate caspase 3-like activities, resulting in the cleavage of the MDM2 oncoprotein and other apoptotic substrates such as poly(ADP-ribose) polymerase. To investigate the mechanism of p53-mediated apoptosis and to determine whether cleavage of MDM2 has a potential role in regulating p53, we examined caspase activation and cleavage of MDM2 in a cell line undergoing p53-mediated growth arrest and delayed apoptosis. We found that in H1299 cells expressing a temperature-sensitive human p53, a distinct caspase activity specific for the MDM2 cleavage site DVPD is induced by p53 prior to the onset of apoptosis and loss of viability. This is accompanied by the cleavage of MDM2 but not the apoptotic substrate poly(ADP-ribose) polymerase. The cleaved MDM2 loses the ability to promote p53 degradation and may potentially function in a dominant-negative fashion to stabilize p53. These results suggest that p53 activation may induce a positive feedback effect by cleavage of MDM2 through a unique caspase.
Insights
p53 activation induces a unique caspase that cleaves MDM2, inhibiting p53 degradation and stabilizing p53. This creates a positive feedback loop during p53-mediated apoptosis.
Area of Science:
- Cellular biology
- Molecular oncology
- Apoptosis research
Background:
- p53-mediated apoptosis involves caspase activation, leading to cleavage of substrates like MDM2 and PARP.
- The precise role of MDM2 cleavage in regulating p53 during apoptosis remains unclear.
Purpose of the Study:
- To investigate the mechanism of p53-mediated apoptosis.
- To determine if MDM2 cleavage regulates p53 activity.
Main Methods:
- Utilized H1299 cells expressing temperature-sensitive human p53.
- Examined caspase activation and MDM2 cleavage.
- Assessed cleavage of poly(ADP-ribose) polymerase (PARP) as an apoptotic marker.
Main Results:
- A specific caspase activity targeting the MDM2 cleavage site (DVPD) was induced by p53 before apoptosis.
- MDM2 cleavage occurred, but PARP cleavage was not observed.
- Cleaved MDM2 lost its ability to degrade p53, potentially stabilizing p53.
Conclusions:
- p53 activation induces a unique caspase that cleaves MDM2.
- MDM2 cleavage by this caspase may create a positive feedback loop, stabilizing p53 during apoptosis.