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Calmodulin can modulate protein phosphorylation in rat liver cells nuclei
R Bosser1, R Aligué, D Guerini
1Department of Cell Biology, Faculty of Medicine, University of Barcelona, Spain.
The Journal of Biological Chemistry
|July 25, 1993
Summary
Nuclear calmodulin in rat liver cells activates calcineurin and inhibits casein kinase-2. This dual action regulates nuclear protein phosphorylation by promoting dephosphorylation and reducing specific protein phosphorylation.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- A 60-kDa calmodulin-binding protein was previously identified in rat liver cell nuclei.
- Calmodulin is a ubiquitous calcium-binding protein involved in cellular signaling.
Purpose of the Study:
- To identify the 60-kDa nuclear calmodulin-binding protein.
- To investigate the role of nuclear calmodulin in regulating protein phosphorylation.
Main Methods:
- Immunological identification using antibodies.
- Nuclease extraction (DNase and RNase) to isolate nuclear components.
- Enzyme activity assays for calcineurin and casein kinase-2.
- Phosphorylation experiments to identify kinase substrates.
Main Results:
- The 60-kDa nuclear calmodulin-binding protein was identified as calcineurin, a calmodulin-dependent protein phosphatase.
- Calcineurin is associated with nuclease-sensitive nuclear structures like chromatin.
- Calmodulin inhibits the activity of nuclear casein kinase-2.
- Calmodulin reduces the phosphorylation of specific casein kinase-2 substrates (42-44 kDa and 50 kDa bands).
Conclusions:
- Nuclear calmodulin regulates nuclear protein phosphorylation through calcineurin activation and casein kinase-2 inhibition.
- Calmodulin promotes dephosphorylation via calcineurin and reduces phosphorylation by inhibiting casein kinase-2.
- These mechanisms highlight calmodulin's crucial role in modulating nuclear protein phosphorylation states.