title: Constitutive phosphorylation of inhibitor-1 at Ser67 and Thr75 depresses calcium cycling in cardiomyocytes and leads to remodeling upon aging.
abstract: The activity of protein phosphatase-1 (PP1) inhibitor-1 (I-1) is antithetically modulated by the cAMP-protein kinase A (PKA) and Ca(2+)-protein kinase C (PKC) signaling axes. β-adrenergic (β-AR) stimulation results in PKA-phosphorylation of I-1 at threonine 35 (Thr35) and depressed PP1 activity, while PKC phosphorylation at serine 67 (Ser67) and/or Thr75 increases PP1 activity. In heart failure, pThr35 is decreased while pSer67 and pThr75 are elevated. However, the role of Ser67/Thr75 phosphorylation in vivo and its effects on Ca(2+)-cycling are not known. Thus, our aim was to investigate the functional significance of Ser67 and Thr75 phosphorylation in intact hearts. We generated transgenic mice (TG) with cardiac-specific overexpression of constitutively phosphorylated I-1 at Ser67 and Thr75 (S67D/T75D) and evaluated cardiac function. The S67D/T75D cardiomyocytes exhibited significantly depressed Ca(2+)-kinetics and contractile parameters, compared with wild-type (WT) cells. The decreased Ca(2+)-cycling was associated with a 27 % increase in PP1 activity, no alterations in PP2 activity and impaired phosphorylation of myosin-binding protein-C (MyBPC). Upon aging, there was cardiac remodeling associated with increases in systolic and diastolic left ventricular internal diameter dimensions (at 16 months), compared with WTs. The results indicate that phosphorylation of I-1 at Ser67 and Thr75 is associated with increased PP1 activity and depressed cardiomyocyte Ca(2+)-cycling, which manifests in geometrical alterations over the long term. Thus, hyperphosphorylation of these sites in failing hearts may contribute to deteriorative remodeling.
authors: Department of Pharmacology and Cell Biophysics, College of Medicine, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH 45267, USA.
authors: Stela
authors: S
authors: Florea
authors: Ahmad
authors: A
authors: Anjak
authors: Wen-Feng
authors: WF
authors: Cai
authors: Jiang
authors: J
authors: Qian
authors: Elizabeth
authors: E
authors: Vafiadaki
authors: Sarah
authors: S
authors: Figueria
authors: Kobra
authors: K
authors: Haghighi
authors: Jack
authors: J
authors: Rubinstein
authors: John
authors: J
authors: Lorenz
authors: Evangelia G
authors: EG
authors: Kranias
mesh_terms: D000375:Aging / Q000473:pathology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D054645:Protein Phosphatase 1 / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D020257:Ventricular Remodeling; D000099163:Myosin Binding Protein C
chemical_list: D002118:Calcium; D002352:Carrier Proteins; D054645:Protein Phosphatase 1; D011506:Proteins; D012694:Serine; D013912:Threonine; D000099163:Myosin Binding Protein C; C073882:phosphoprotein phosphatase inhibitor 1