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Phosphorylation of Bcl-2 protein and association with p21Ras in Ras-induced apoptosis
1Cancer Research Center, Boston University School of Medicine, Massachusetts 02118, USA.
Abstract:
p21Ras mediates mitogenic responses and also renders cells susceptible to apoptosis after inhibition of protein kinase C (PKC) activity. Ras-induced apoptosis can be blocked by the proto-oncogene bcl-2, but the biochemical or functional nature of Bcl-2 regulation of Ras-induced apoptosis is not understood. We demonstrate that Bcl-2 and p21Ras molecules can be co-immunoprecipitated in Jurkat cells. The level of this association is enhanced when an apoptotic stimulus (inhibition of PKC activity) is delivered. Bcl-2/p21Ras association is coincident with new phosphorylation of the Bcl-2 protein. Inhibition of this phosphorylation prevents protection from apoptosis by Bcl-2, providing a functional correlation to the phosphorylation event. The Bcl-2/p21Ras association cannot be competed by exogenous glutathione S-transferase-Ras fusion protein, suggesting that the endogenous complex may be formed before cell lysis. These results provide a possible mechanism of regulation of Ras-induced apoptosis by Bcl-2.
Insights
The proto-oncogene Bcl-2 (B-cell lymphoma 2) protein can block Ras-induced apoptosis. This study shows Bcl-2 interacts with p21Ras, and this interaction is enhanced by apoptotic stimuli, suggesting a novel regulatory mechanism.
Area of Science:
- Cellular biology
- Molecular oncology
- Apoptosis research
Background:
- p21Ras proteins are key mediators of cell proliferation and can induce apoptosis upon inhibition of protein kinase C (PKC).
- The proto-oncogene Bcl-2 (B-cell lymphoma 2) is known to inhibit apoptosis, including Ras-induced cell death, but the underlying mechanism remains unclear.
- Understanding the interaction between Bcl-2 and Ras is crucial for elucidating cancer development and cell death pathways.
Purpose of the Study:
- To investigate the molecular mechanism by which Bcl-2 regulates Ras-induced apoptosis.
- To determine if Bcl-2 and p21Ras physically interact and how this interaction is affected by apoptotic stimuli.
- To explore the role of Bcl-2 phosphorylation in its protective function against Ras-induced cell death.
Main Methods:
- Co-immunoprecipitation assays were used to detect the association between Bcl-2 and p21Ras in Jurkat cells.
- Apoptotic stimuli, specifically inhibition of PKC activity, were applied to assess changes in Bcl-2/p21Ras complex formation.
- Phosphorylation of Bcl-2 was monitored in conjunction with the association studies.
- Competition assays using glutathione S-transferase-Ras fusion protein were performed to investigate the nature of the Bcl-2/p21Ras interaction.
Main Results:
- Bcl-2 and p21Ras proteins were found to co-immunoprecipitate in Jurkat cells, indicating a physical association.
- The association between Bcl-2 and p21Ras was significantly enhanced upon inhibition of PKC activity, an apoptotic stimulus.
- This enhanced association coincided with the phosphorylation of the Bcl-2 protein.
- Inhibition of Bcl-2 phosphorylation abolished its protective effect against Ras-induced apoptosis, establishing a functional link.
- Competition assays suggested that the Bcl-2/p21Ras complex forms within the cell prior to lysis.
Conclusions:
- Bcl-2 directly interacts with p21Ras, and this interaction is modulated by apoptotic signals.
- Phosphorylation of Bcl-2 is a critical event, functionally linked to its ability to protect cells from Ras-induced apoptosis.
- These findings propose a novel mechanism for Bcl-2-mediated regulation of Ras-induced apoptosis, involving direct physical interaction and phosphorylation-dependent modulation.