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Apoptosis regulation by interaction of Bcl-2 protein and Raf-1 kinase
H G Wang1, T Miyashita, S Takayama
1La Jolla Cancer Research Foundation, Cancer Research Center, CA 92037.
Abstract:
The Bcl-2 protein is over-produced in many types of human tumors and suppresses apoptosis induced by a wide-variety of stimuli, including chemotherapeutic drugs and gamma-irradiation. The biochemical mechanism of action of the Bcl-2 protein however remains enigmatic. Here we show that Bcl-2 can be co-immunoprecipitated with the serine/threonine-specific Raf-1 kinase both in a mammalian hemopoietic cell 32D.3 and when the two proteins are produced in Sf9 insect cells using recombinant baculoviruses. Though analysis of Raf-1 deletion mutants suggested that the C-terminal half of the protein which contains the catalytic domain is sufficient for co-immunoprecipitation with Bcl-2, Raf-1 does not appear to induce phosphorylation of Bcl-2 protein in 32D.3 and Sf9 cells. Furthermore, a mutant form of Raf-1 that lacks kinase activity could still be co-immunoprecipitated with Bcl-2 in Sf9 cells, suggesting that the interaction of these proteins does not reflect a kinase-substrate relation. Gene transfer experiments using 32D.3 hemopoietic cells demonstrated functional synergy between Bcl-2 and Raf-1 with regards to suppression of apoptosis induced by growth factor withdrawal. Taken together, these observations for the first time functionally link Bcl-2 to a signal transducing protein and suggest that the interaction of the Bcl-2 and Raf-1 proteins may be responsible for their ability to cooperate in the suppression of apoptosis.
Insights
The anti-apoptotic Bcl-2 protein interacts with Raf-1 kinase, functionally linking them. This interaction, independent of Raf-1
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Bcl-2 protein overexpression is common in human tumors, inhibiting apoptosis.
- The precise biochemical mechanism of Bcl-2's action remains unclear.
- Understanding Bcl-2's interactions is crucial for cancer therapy development.
Purpose of the Study:
- To investigate the biochemical interaction between Bcl-2 and Raf-1 kinase.
- To determine if Raf-1 kinase activity is required for Bcl-2 interaction.
- To explore the functional consequences of Bcl-2 and Raf-1 synergy in apoptosis suppression.
Main Methods:
- Co-immunoprecipitation assays in mammalian (32D.3) and insect (Sf9) cells.
- Analysis of Raf-1 deletion mutants to identify interaction domains.
- Functional gene transfer experiments to assess apoptosis suppression.
Main Results:
- Bcl-2 was successfully co-immunoprecipitated with Raf-1 kinase.
- The C-terminal half of Raf-1, containing the catalytic domain, was sufficient for binding.
- Raf-1 did not appear to phosphorylate Bcl-2, and a kinase-inactive mutant still bound Bcl-2.
- Bcl-2 and Raf-1 exhibited functional synergy in suppressing apoptosis induced by growth factor withdrawal.
Conclusions:
- This study provides the first functional link between Bcl-2 and a signal-transducing protein, Raf-1.
- The interaction between Bcl-2 and Raf-1 is independent of Raf-1's kinase activity.
- Cooperative action of Bcl-2 and Raf-1 in apoptosis suppression is suggested by their interaction.