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Functional interplay between dual site phospholambam phosphorylation: insights from genetically altered mouse models
Guoxiang Chu1, Evangelia G Kranias
1Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, 231 Albert B. Sabin Way, Cincinnati, OH 45267-0575, USA.
Basic Research in Cardiology
|December 14, 2002
Summary
Phosphorylation of phospholamban (PLB) at Ser16 is sufficient for beta-adrenergic stimulation of cardiac function. Ser16 phosphorylation is required for Thr17 phosphorylation in vivo, revealing insights into cardiac calcium handling.
Area of Science:
- Cardiology
- Molecular Biology
- Biochemistry
Background:
- Phospholamban (PLB) regulates the sarcoplasmic reticulum Ca2+ pump (SERCA2) activity.
- Phosphorylation of PLB by PKA (Ser16) and CaMKII (Thr17) mediates cardiac responses to beta-adrenergic agonists.
- The interplay between these phosphorylation sites is not fully understood.
Purpose of the Study:
- To elucidate the functional significance of dual-site PLB phosphorylation in cardiac function.
- To investigate the interdependence of PKA and CaMKII pathways in PLB phosphorylation during beta-adrenergic stimulation.
Main Methods:
- Generation and characterization of phospholamban knockout mice.
- Expression of wild-type and phosphorylation site-specific PLB mutants (S16A, T17A) in transgenic mice.
- In vivo and in vitro phosphorylation assays.
Main Results:
- Re-expression of PLB in knockout mice reversed hyperdynamic cardiac function.
- Serine-16 phosphorylation of PLB alone mediated maximal cardiac contractile responses to beta-adrenergic stimulation.
- Serine-16 phosphorylation is a prerequisite for Threonine-17 phosphorylation in vivo, though Threonine-17 can be phosphorylated independently in vitro.
Conclusions:
- Phosphorylation of phospholamban at Serine-16 is the primary driver of beta-adrenergic stimulation in the heart.
- The PKA-mediated Serine-16 phosphorylation pathway is critical and precedes CaMKII-mediated Threonine-17 phosphorylation in vivo.
- These findings clarify the hierarchical and functional roles of distinct PLB phosphorylation sites in cardiac regulation.