Cardiac SR-coupled PP1 activity and expression are increased and inhibitor 1 protein expression is decreased in failing hearts.
Type 1 protein phosphatase (PP1) is a negative regulator of cardiac function. However, studies on the status and regulation of sarcoplasmic reticulum (SR)-associated PP1 activity in failing hearts are limited. We studied PP1 activity and protein and mRNA expression of the catalytic subunit of PP1 (PP1C) and protein levels of PP1-specific inhibitors [inhibitor 1 (Inh-1) and inhibitor 2 (Inh-2)] in the left ventricular (LV) myocardium of 6 dogs with heart failure (HF; LV ejection fraction, 23 +/- 2%) and 6 normal dogs. In failing LV tissue, PP1 activity values (expressed as pmol 32P. min-1. mg of noncollagen protein-1) in the homogenate, crude membranes, cytosol, and purified SR were increased by 52, 54, 55, and 72%, respectively. Trypsin treatment released PP1 but not type 2A protein phosphatase from the SR. In the supernatant of trypsin-treated SR, PP1 activity was approximately 24% higher in failing hearts than in normal control hearts. A similar increase in protein expression of PP1C was observed in the nontrypsinized SR. Heat-denatured phosphorylated SR inhibited PP1 activity by 30%, which suggests the presence of Inh-1 or -2 or both in the SR. With the use of a specific antibody, both Inh-1 and -2 proteins were found in the SR; the former was decreased by 56% in the failing SR, whereas the latter did not change. These results suggest that protein phosphatase activity bound to the SR is increased and is predominantly type 1. Increased SR-associated PP1 activity in failing hearts appears to be due partly to increased expression of PP1C and partly to reduced levels of Inh-1 but not Inh-2 protein. Thus inhibition of PP1 activity in the SR appears to be a potential therapeutic target for improving LV function in failing hearts, because it may lead to increased SR Ca2+ uptake, which is impaired in failing hearts.
Gupta
Ramesh C
RC
Division of Cardiovascular Medicine, Department of Medicine, Henry Ford Heart and Vascular Institute, Detroit, MI 48202, USA. rgupta1@hfhs.org
Mishra
Sudhish
S
Rastogi
Sharad
S
Imai
Makoto
M
Habib
Omar
O
Sabbah
Hani N
HN
D000818:Animals; D001794:Blood Pressure; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D004285:Dogs; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D006333:Heart Failure / Q000378:metabolism* / Q000503:physiopathology; D006339:Heart Rate; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D054645:Protein Phosphatase 1; D011506:Proteins / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D018487:Ventricular Dysfunction, Left / Q000378:metabolism / Q000503:physiopathology; D000097847:Protein Phosphatase Inhibitory Proteins
D000252:Calcium-Transporting ATPases; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D011506:Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C021042:protein phosphatase inhibitor-1; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins