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cAMP-dependent protein kinase phosphorylates and activates nuclear Ca2+-ATPase
P J Rogue1, J P Humbert, A Meyer
1Laboratoire de Neurobiologie Moléculaire des Interactions Cellulaires, UPR 416 du Centre National de la Recherche Scientifique, 5 rue Blaise Pascal, 67084 Strasbourg, France.
Summary
cAMP-dependent protein kinase (PKA) enhances nuclear calcium transport by phosphorylating nuclear Ca2+-ATPase (NCA). This crosstalk between signaling pathways regulates calcium-dependent transport across the nuclear envelope.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- A Ca2+-pump ATPase (NCA) is present on the outer membrane of rat liver nuclei.
- The role of cAMP-dependent protein kinase (PKA) in regulating NCA activity was previously unknown.
Purpose of the Study:
- To investigate the effect of PKA on nuclear Ca2+-ATPase (NCA) activity.
- To determine if PKA-mediated phosphorylation influences nuclear transport.
Main Methods:
- Purified rat liver nuclei were treated with the catalytic unit of PKA.
- Phosphorylation was analyzed using immunoblotting with antibodies specific for sarcoplasmic reticulum Ca2+-ATPase type 2b.
- ATP-dependent 45Ca2+ uptake and transport of fluorescent-labeled dextrans across the nuclear envelope were measured.
Main Results:
- PKA treatment resulted in the phosphorylation of a 105-kDa protein identified as NCA.
- PKA phosphorylation significantly enhanced the Ca2+-pumping activity of NCA.
- PKA phosphorylation of NCA increased the transport of 10-kDa fluorescent-labeled dextrans across the nuclear envelope.
Conclusions:
- PKA directly phosphorylates and activates NCA in rat liver nuclei.
- Signaling pathway crosstalk between cAMP/PKA and Ca2+ extends to the nucleus.
- This crosstalk plays a role in regulating calcium-dependent nuclear envelope transport.