Evidence for protein phosphatase inhibitor-1 playing an amplifier role in beta-adrenergic signaling in cardiac myocytes.
The protein phosphatase inhibitor-1 (PPI-1) inhibits phosphatase type-1 (PP1) only when phosphorylated by protein kinase A and could play a pivotal role in the phosphorylation/dephosphorylation balance. Rat cardiac PPI-1 was cloned by reverse transcriptase-polymerase chain reaction, expressed in Eschericia coli, evaluated in phosphatase assays, and used to generate an antiserum. An adenovirus was constructed encoding PPI-1 and green fluorescent protein (GFP) under separate cytomegalovirus promotors (AdPPI-1/GFP). A GFP-only virus (AdGFP) served as control. Engineered heart tissue (EHT) from neonatal rat cardiomyocytes and adult rat cardiac myocytes (ARCMs) were used as model systems. PPI-1 expression was determined in human ventricular samples by Northern blots. Compared with AdGFP, AdPPI-1/GFP-infected neonatal rat cardiomyocytes displayed a 73% reduction in PP1 activity. EHTs infected with AdPPI-1/GFP exhibited a fivefold increase in isoprenaline sensitivity. AdPPI-1/GFP-infected ARCMs displayed enhanced cell shortening as well as enhanced phospholamban phosphorylation when stimulated with 1 nM isoprenaline. PPI-1 mRNA levels were reduced by 57+/-12% in failing hearts with dilated and ischemic cardiomyopathy (n=8 each) compared with nonfailing hearts (n=8). In summary, increased PPI-1 expression enhances myocyte sensitivity to isoprenaline, indicating that PPI-1 acts as an amplifier in beta-adrenergic signaling. Decreased PPI-1 in failing human hearts could participate in desensitization of the cAMP pathway.
El-Armouche
Ali
A
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Universitätsklinikum Hamburg-Eppendorf, Germany.
Rau
Thomas
T
Zolk
Oliver
O
Ditz
Diana
D
Pamminger
Torsten
T
Zimmermann
Wolfram-H
WH
Jäckel
Elmar
E
Harding
Sian E
SE
Boknik
Peter
P
Neumann
Joachim
J
Eschenhagen
Thomas
T
D000256:Adenoviridae / Q000235:genetics; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D003062:Codon; D004722:Endoribonucleases; D005822:Genetic Vectors; D006333:Heart Failure / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007545:Isoproterenol / Q000494:pharmacology*; D008955:Models, Cardiovascular; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D015202:Protein Engineering; D011506:Proteins / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D016601:RNA-Binding Proteins; D051381:Rats; D015398:Signal Transduction
D000318:Adrenergic beta-Agonists; D002352:Carrier Proteins; D003062:Codon; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C021042:protein phosphatase inhibitor-1; C472592:protein phosphatase inhibitor-1, rat; D004722:Endoribonucleases; D010749:Phosphoprotein Phosphatases; C097081:PPP1R8 protein, human; D007545:Isoproterenol