Role of calcineurin and protein phosphatase-2A in the regulation of phosphatase inhibitor-1 in cardiac myocytes.
Inhibitor 1 (I-1) is a protein inhibitor of protein phosphatase 1 (PP1), the predominating Ser/Thr phosphatase in the heart. Non-phosphorylated I-1 is inactive, whereas I-1 phosphorylated by protein kinase A (PKA) at Thr35 is a potent PP1 inhibitor. The phosphatases that dephosphorylate I-1Thr35 and thus deactivate I-1 in the heart are not established. Here we overexpressed I-1 in neonatal rat cardiac myocytes with recombinant adenovirus and determined phosphorylation of I-1, and one of the major target proteins of PKA/PP1 in the heart, phospholamban (PLB), by Western blot with phospho-specific antibodies. Incubation with the calcineurin inhibitor cyclosporine A or okadaic acid, used at a concentration preferentially inhibiting phosphatase 2A (PP2A), increased significantly I-1Thr35 (approximately 2- to 6-fold) and PLB Ser16 phosphorylation (approximately 2-fold). The results indicate that calcineurin and PP2A act to maintain a low basal level of phosphorylated (active) I-1 in living cardiac myocytes. Calcineurin may constitute a cross-talk between calcium- and cAMP-dependent pathways.
El-Armouche
Ali
A
Institute of Experimental and Clinical Pharmacology, Medical Center Hamburg-Eppendorf, Hamburg, Germany.
Bednorz
Anna
A
Pamminger
Torsten
T
Ditz
Diana
D
Didié
Michael
M
Dobrev
Dobromir
D
Eschenhagen
Thomas
T
D000818:Animals; D000831:Animals, Newborn; D019703:Calcineurin / Q000378:metabolism*; D002478:Cells, Cultured; D016572:Cyclosporine / Q000494:pharmacology; D005786:Gene Expression Regulation; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D051381:Rats; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism
D047908:Intracellular Signaling Peptides and Proteins; C021042:protein phosphatase inhibitor-1; D019319:Okadaic Acid; D013912:Threonine; D012694:Serine; D016572:Cyclosporine; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2