title: Phosphorylation of human inhibitor-1 at Ser67 and/or Thr75 attenuates stimulatory effects of protein kinase A signaling in cardiac myocytes.
abstract: The depressed function of failing hearts has been partially attributed to increased protein phosphatase-1 through its impaired regulation by inhibitor-1. Phosphorylation of inhibitor-1 at Thr35 by PKA results in potent inhibition of protein phosphatase-1 activity, while phosphorylation at Ser67 or Thr75 by PKC attenuates the inhibitory activity. To examine the functional role of dual-site (Ser67, Thr75) phosphorylation of inhibitor-1 by PKC, the constitutively phosphorylated Ser67 (S67D) and/or Thr75 (T75D) human inhibitor-1 forms were expressed in adult cardiomyocytes. Expression of either single or double phosphorylated inhibitor-1 was associated with similar decreases in cardiac contractility, indicating that maximal inhibition can be elicited by each of these sites alone and that their inhibitory effects are not additive. Notably, activation of the cAMP pathway could only partially reverse the depressed contractile parameters. Accordingly, protein phosphatase-1 activity remained elevated, phosphorylation of phospholamban at Ser16 was decreased, and the EC(50) values of the sarcoplasmic reticulum calcium transport system were higher compared with controls. Thus phosphorylation of Ser67 and/or Thr75 in inhibitor-1 may mitigate the stimulatory effects of the cAMP pathway, resulting in compromised cardiac function.
authors.affiliation: Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0575, USA.
authors.forename: Patricia
authors.initials: P
authors.lastname: Rodriguez
authors.forename: Bryan
authors.initials: B
authors.lastname: Mitton
authors.forename: Persoulla
authors.initials: P
authors.lastname: Nicolaou
authors.forename: Guoli
authors.initials: G
authors.lastname: Chen
authors.forename: Evangelia G
authors.initials: EG
authors.lastname: Kranias
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013912:Threonine / Q000378:metabolism
chemical_list: C448783:HIAF-1 protein, human; D011506:Proteins; D013912:Threonine; D012694:Serine; D017868:Cyclic AMP-Dependent Protein Kinases