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Regional expression of protein phosphatase type 1 and 2A catalytic subunit isoforms in the human heart
H Lüss1, O Klein-Wiele, P Bokník
1Institut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität Münster, Germany. luss@uni-muenster.de
Insights
Protein phosphatase 1 (PP1) and 2A (PP2A) isoforms are expressed in the human heart. Their regional differences in expression may explain faster atrial relaxation compared to ventricles.
Area of Science:
- Cardiology
- Molecular Biology
- Biochemistry
Background:
- Myocardial contraction duration differs between mammalian atria and ventricles.
- Cardiac regulatory protein phosphorylation/dephosphorylation influences contraction time.
- Protein phosphatases (PPs), primarily PP1 and PP2A, mediate dephosphorylation.
Purpose of the Study:
- To identify PP1 and PP2A isoforms in human myocardium.
- To determine if PP1 and PP2A expression differs regionally within the human heart.
Main Methods:
- Reverse transcription polymerase chain reaction (RT-PCR) for gene expression.
- Northern blotting for mRNA expression analysis.
- Protein level analysis and phosphorylation state assessment.
Main Results:
- All known PP1 and PP2A isoforms are expressed in the human heart.
- PP1 alpha, delta, gamma, and PP2A alpha showed higher expression in right ventricles vs. atria.
- PP2A protein levels were 56% higher in right ventricles compared to atria, with lower TnI phosphorylation.
Conclusions:
- PP1 and PP2A isoforms are regionally regulated in the human heart.
- Lower PP2A expression in atria may contribute to faster relaxation via increased TnI phosphorylation.
Abstract:
In mammalian species, including man, the duration of myocardial contraction is shorter in atria than ventricles. Total contraction time depends at least in part on phosphorylation and dephosphorylation of cardiac regulatory proteins. Dephosphorylation reactions are mediated by protein phosphatases. In the mammalian heart more than 90% of the protein phosphatase (PP) activity consists of PP1 and PP2A. Therefore, the aim of this study was to investigate which isoforms of PP1 and PP2A are present in human myocardium and whether their expression is regionally different. RT-PCR and Northern blotting revealed that all isoforms of PP1 and PP2A presently known are expressed in the human heart. Expression levels of PP1 alpha, delta, and gamma as well as 2A alpha were higher in right ventricles than in right atria. However, there was no such difference for PP2A beta. At the protein level PP1 alpha was unchanged, whereas PP2A was by 56% higher in right ventricles compared to atria. The phosphorylation state of TnI was lower in right ventricle than in right atrium. Thus, lower protein expression of PP2A in atrium could contribute to the faster relaxation by increasing the phosphorylation state of TnI. We conclude that expression of PP1 and PP2A isoforms is regionally regulated in the human heart.