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The broad specificity of dominant inhibitory protein kinase C mutants infers a common step in phosphorylation
P Garcia-Paramio1, Y Cabrerizo, F Bornancin
1Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.
Abstract:
Dominant negative properties are conferred on protein kinase (PK) Calpha by mutation of the phosphorylation site in the activation loop of the kinase domain. To address the universality and/or specificity of such mutations, analogous alterations were introduced in other members of the PKC family and tested for their effects on the function of co-transfected activated PKC. For all three subclasses of the PKC family, mutations of the predicted activation loop phosphorylation sites resulted in dominant negative properties. These properties were not restricted to the cognate PKC isotypes, but were effective across the different subclasses. For example, two PKCzeta mutants (atypical isotype) inhibited both PKCalpha (classical isotype) and PKCepsilon (novel isotype). For all these mutants, inhibition correlated with an ability to prevent the accumulation of phosphorylated PKCalpha, consistent with the expected mode of action. In the case of the PKCalpha mutant, it was shown that inhibition required the full-length mutant protein. The results provide evidence for the involvement of a common step in the phosphorylation of all PKC isotypes.
Insights
Mutations in protein kinase C (PKC) activation loops create dominant negative effects across all PKC subclasses. This suggests a common phosphorylation step is crucial for the function of all PKC isotypes.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Signaling
Background:
- Protein Kinase C (PKC) isozymes play critical roles in cellular signaling.
- The activation loop phosphorylation site is essential for PKC catalytic activity.
Purpose of the Study:
- To investigate the universality and specificity of dominant negative properties conferred by mutations at the PKC activation loop phosphorylation site.
- To determine if these mutations affect other PKC isotypes across different subclasses.
Main Methods:
- Site-directed mutagenesis was used to alter the activation loop phosphorylation site in various PKC isotypes.
- Co-transfection experiments were performed to assess the dominant negative effects of mutant PKCs on activated wild-type PKCs.
Main Results:
- Mutations at the activation loop phosphorylation sites of all tested PKC isotypes resulted in dominant negative properties.
- These dominant negative effects were observed across different PKC subclasses, indicating a lack of isotype specificity.
- Mutant PKCzeta inhibited both PKCalpha and PKCepsilon, demonstrating cross-subclass inhibition.
- Inhibition correlated with the prevention of phosphorylated PKCalpha accumulation, supporting the proposed mechanism of action.
Conclusions:
- The findings provide strong evidence for a common, conserved step in the phosphorylation and activation of all protein kinase C isotypes.
- Dominant negative mutations targeting the activation loop phosphorylation site represent a conserved mechanism to inhibit PKC family members.