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Regulation of bad phosphorylation and association with Bcl-x(L) by the MAPK/Erk kinase
M P Scheid1, K M Schubert, V Duronio
1Jack Bell Research Centre, University of British Columbia, Vancouver, British Columbia V6H 3Z6, Canada.
Abstract:
Phosphorylation of the Bcl-2 family protein Bad may represent an important bridge between survival signaling by growth factor receptors and the prevention of apoptosis. Bad phosphorylation was examined following cytokine stimulation, which revealed phosphorylation on a critical residue, serine 112, in a MEK-dependent manner. Furthermore, Bad phosphorylation also increased on several sites distinct from serine 112 but could not be detected on serine 136, previously thought to be a protein kinase B/Akt-targeted residue. Serine 112 phosphorylation was shown to be absolutely required for dissociation of Bad from Bcl-x(L). These results demonstrate for the first time in mammalian cells the involvement of the Ras-MAPK pathway in the phosphorylation of Bad and the regulation of its function.
Insights
Growth factor receptor signaling prevents apoptosis by phosphorylating the Bad protein. This study reveals the Ras-MAPK pathway
Area of Science:
- Cellular signaling pathways
- Apoptosis regulation
- Protein phosphorylation
Background:
- The Bcl-2 family protein Bad plays a crucial role in apoptosis.
- Growth factor receptors initiate survival signals that can inhibit apoptosis.
- The precise mechanisms linking survival signaling to Bad regulation are under investigation.
Purpose of the Study:
- To investigate the role of cytokine stimulation in Bad phosphorylation.
- To identify the specific signaling pathways involved in Bad phosphorylation.
- To determine the functional consequences of Bad phosphorylation on its interaction with Bcl-x(L).
Main Methods:
- Cytokine stimulation of cells.
- Analysis of Bad protein phosphorylation at specific residues (serine 112 and serine 136).
- Investigation of the involvement of the MEK (Mitogen-activated protein kinase kinase) and Ras-MAPK (Ras-Mitogen-activated protein kinase) pathways.
- Assessment of Bad and Bcl-x(L) protein interactions.
Main Results:
- Cytokine stimulation induced Bad phosphorylation at serine 112 in a MEK-dependent manner.
- Phosphorylation occurred at additional sites distinct from serine 112.
- Phosphorylation at serine 136, previously linked to protein kinase B/Akt, was not detected.
- Phosphorylation of serine 112 was essential for the dissociation of Bad from Bcl-x(L).
Conclusions:
- The Ras-MAPK pathway is involved in the phosphorylation of Bad in mammalian cells.
- MEK-dependent phosphorylation of serine 112 is critical for regulating Bad's interaction with Bcl-x(L).
- This study elucidates a novel mechanism linking growth factor signaling to apoptosis prevention via Bad regulation.