AJP - Heart and Circulatory Physiology, Vol 270, Issue 4 1159-H1164, Copyright © 1996 by American Physiological Society

ARTICLES

Evidence for presence and hormonal regulation of protein phosphatase inhibitor-1 in ventricular cardiomyocyte

R. C. Gupta, J. Neumann, A. M. Watanabe, M. Lesch and H. N. Sabbah
Department of Medicine, Henry Ford Heart and Vascular Institute, Henry Ford Hospital, Detroit, Michigan 48202, USA.

Protein phosphatase inhibitor-1 (PPI-1) has been shown to be present in heart tissue and smooth muscle. Whether PPI-1 is present in cardiomyocytes is not known. The purpose of this study was to determine whether PPI-1 is present and is hormonally regulated in cardiomyocytes. A trichloroacetic acid (TCA) extract enriched in PPI-1 was isolated from guinea pig ventricular cardiomyocytes. The TCA extract inhibited the activity of type 1 protein phosphatase by 20 +/- 4% (n = 3 expts). On phosphorylation by the catalytic subunit of adenosine 3', 5'-cyclic monophosphate-dependent protein kinase, the extent of this inhibition was augmented to 4.5-fold. Dephosphorylation of the phosphorylated TCA extract by type 2 protein phosphatase reduced inhibition to 2 +/- 0.2% (n = 3 expts). To determine whether isoproterenol increases phosphorylation of PPI-1 in cardiomyocytes, the TCA extracts were prepared from cardiomyocytes treated with 1 microM isoproterenol and from untreated cardiomyocytes. The inhibitory activity of the TCA extract in untreated cardiomyocytes was 25 +/- 3% (n = 3 expts) and increased to 75 +/- 2% (n = 3 expts) in isoproterenol-treated cardiomyocytes. With the use of a rabbit skeletal muscle PPI-1 antibody, immunoblots of the TCA extract of cardiomyocytes identified a 28-kDa protein. A 28-kDa protein was also immunoprecipitated from a TCA extract isolated from isoproterenol-treated 32P-labeled cardiomyocytes. The immunoprecipitation was blocked by the addition of excess amounts of purified rabbit skeletal muscle PPI-1. Isoproterenol-treated cardiomyocytes increased the phosphorylation of the 28-kDa protein by 232 +/- 20% (n = 3 expts) compared with untreated cardiomyocytes. We conclude that 1) the 28-kDa protein is PPI-1, 2) PPI-1 is present in ventricular cardiomyocytes, and 3) PPI-1 is hormonally regulated. A decrease in type 1 protein phosphatase activity through phosphorylation of PPI-1 may be an important pathway for augmenting cardiac contractility.

This article has been cited by other articles:

				N. Bruchert, N. Mavila, P. Boknik, H. A. Baba, L. Fabritz, U. Gergs, U. Kirchhefer, P. Kirchhof, M. Matus, W. Schmitz, et al. Inhibitor-2 prevents protein phosphatase 1-induced cardiac hypertrophy and mortality Am J Physiol Heart Circ Physiol, October 1, 2008; 295(4): H1539 - H1546. [Abstract] [Full Text] [PDF]

				W. H. duBell and T. B. Rogers Protein phosphatase 1 and an opposing protein kinase regulate steady-state L-type Ca2+ current in mouse cardiac myocytes J. Physiol., April 1, 2004; 556(1): 79 - 93. [Abstract] [Full Text] [PDF]

				T. Peng, X. Lu, M. Lei, and Q. Feng Endothelial Nitric-oxide Synthase Enhances Lipopolysaccharide-stimulated Tumor Necrosis Factor-alpha Expression via cAMP-mediated p38 MAPK Pathway in Cardiomyocytes J. Biol. Chem., February 28, 2003; 278(10): 8099 - 8105. [Abstract] [Full Text] [PDF]

				A. N. Carr, A. G. Schmidt, Y. Suzuki, F. del Monte, Y. Sato, C. Lanner, K. Breeden, S.-L. Jing, P. B. Allen, P. Greengard, et al. Type 1 Phosphatase, a Negative Regulator of Cardiac Function Mol. Cell. Biol., June 15, 2002; 22(12): 4124 - 4135. [Abstract] [Full Text] [PDF]

				S. Herzig and J. Neumann Effects of Serine/Threonine Protein Phosphatases on Ion Channels in Excitable Membranes Physiol Rev, January 1, 2000; 80(1): 173 - 210. [Abstract] [Full Text] [PDF]

				R.-P. Xiao, H. Cheng, Y.-Y. Zhou, M. Kuschel, and E. G. Lakatta Recent Advances in Cardiac {beta}2-Adrenergic Signal Transduction Circ. Res., November 26, 1999; 85(11): 1092 - 1100. [Abstract] [Full Text] [PDF]

				J. H. Connor, H. N. Quan, N. T. Ramaswamy, L. Zhang, S. Barik, J. Zheng, J. F. Cannon, E. Y. C. Lee, and S. Shenolikar Inhibitor-1 Interaction Domain That Mediates the Inhibition of Protein Phosphatase-1 J. Biol. Chem., October 16, 1998; 273(42): 27716 - 27724. [Abstract] [Full Text] [PDF]

				L. Vittone, C. Mundina-Weilenmann, M. Said, and A. Mattiazzi Mechanisms Involved in the Acidosis Enhancement of the Isoproterenol-induced Phosphorylation of Phospholamban in the Intact Heart J. Biol. Chem., April 17, 1998; 273(16): 9804 - 9811. [Abstract] [Full Text] [PDF]

				D. Hagemann, M. Kuschel, T. Kuramochi, W. Zhu, H. Cheng, and R.-P. Xiao Frequency-encoding Thr17 Phospholamban Phosphorylation Is Independent of Ser16 Phosphorylation in Cardiac Myocytes J. Biol. Chem., July 14, 2000; 275(29): 22532 - 22536. [Abstract] [Full Text] [PDF]

				M. Zheng, S.-J. Zhang, W.-Z. Zhu, B. Ziman, B. K. Kobilka, and R.-P. Xiao beta 2-Adrenergic Receptor-induced p38 MAPK Activation Is Mediated by Protein Kinase A Rather than by Gi or Gbeta gamma in Adult Mouse Cardiomyocytes J. Biol. Chem., December 15, 2000; 275(51): 40635 - 40640. [Abstract] [Full Text] [PDF]