Maximal Inhibition of SERCA2 Ca2+ Affinity by Phospholamban in Transgenic Hearts Overexpressing a Non-phosphorylatable Form of Phospholamban

Phospholamban is a phosphoprotein in the cardiac sarcoplasmic reticulum (SR) which regulates the apparent Ca2+ affinity of the SR Ca2+-ATPase (SERCA2). To determine the levels of phospholamban which are associated with maximal inhibition of SERCA2, several lines of transgenic mice were generated whi...

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Veröffentlicht in:The Journal of biological chemistry 2000-04, Vol.275 (16), p.12129-12135
Hauptverfasser: Brittsan, Angela G., Carr, Andrew N., Schmidt, Albrecht G., Kranias, Evangelia G.
Format: Artikel
Sprache:eng
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Zusammenfassung:Phospholamban is a phosphoprotein in the cardiac sarcoplasmic reticulum (SR) which regulates the apparent Ca2+ affinity of the SR Ca2+-ATPase (SERCA2). To determine the levels of phospholamban which are associated with maximal inhibition of SERCA2, several lines of transgenic mice were generated which expressed increasing levels of a non-phosphorylatable form of phospholamban (S16A,T17A) specifically in the heart. This mutant form of phospholamban was chosen to prevent phosphorylation as a compensatory mechanism in vivo. Quantitative immunoblotting revealed increased phospholamban protein levels of 1.8-, 2.6-, 3.7-, and 4.7-fold in transgenic hearts compared with wild types. There were no changes in the expression levels of SERCA2, calsequestrin, calreticulin, and ryanodine receptor. Assessment of SR Ca2+ uptake in hearts of transgenic mice indicated increases in the inhibition of the affinity of SERCA2 for Ca2+ with increased phospholamban expression. Maximal inhibition was obtained at phospholamban expression levels of 2.6-fold or higher. Transgenic hearts with functional saturation in phospholamban:SERCA2 (≥2.6:1) exhibited increases in β-myosin heavy chain expression, associated with cardiac hypertrophy. These findings demonstrate that overexpression of a non-phosphorylatable form of phospholamban in transgenic mouse hearts resulted in saturation of the functional phospholamban:SERCA2 ratio at 2.6:1 and suggest that approximately 40% of the SR Ca2+pumps are functionally regulated by phospholamban in vivo.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.275.16.12129