Modulation of myosin phosphatase targeting subunit and protein phosphatase 1 in the heart

Ravi Rajashree, Bradford C. Blunt, Polly Hofmann

Research output: Contribution to journalArticle

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Abstract

Myosin light chain 2 (LC2) phosphorylation is of both physiological and pathological importance to myocardial function. The phosphatase that directly dephosphorylates LC2 is a type 1 protein phosphatase (PP1) that contains a catalytic subunit that complexes with a myosin-binding phosphatase targeting subunit (MYPT). The goal of the present study was to examine the role of MYPT in the regulation of PP1 in ventricular myocytes, In the first part of the study, regional distribution of MYPT expression and phosphorylation were determined in unstimulated hearts. The pattern of MYPT phosphorylation was inversely related to the LC2 phosphorylation spatial gradient as described by Epstein and colleagues (Davis JS, Hassanzadeh S, Winitsky S, Lin H, Satorius C, Vemuri R, Aletras AH, Wen H, and Epstein ND. Cell 107: 631-641, 2001). In the second part of the study, adult rat isolated ventricular myocytes were exposed to an α-adrenergic receptor agonist, and properties of MYPT, PP1, and LC2 were studied. We found MYPT associates with cardiac myofilaments, and this association increases upon α-adrenergic receptor stimulation. Activation of α-adrenergic receptors also led to a decrease in the PP1-myofilament association. Furthermore, α-adrenergic receptor stimulation results in phosphorylation of MYPT and LC2 and an increase in myocyte Ca 2+ sensitivity of tension that all depend on Rho kinase activation. These data support the hypothesis that α-adrenergic receptor activation works through Rho kinase to phosphorylate MYPT, and phosphorylated MYPT dissociates from PP1 so that PP1 is no longer physically associated with LC2. Hence, we propose a pathway for the dynamic modulation of LC2 phosphorylation through receptor-dependent phosphorylation of MYPT, and a spatial gradient of LC2 phosphorylation under basal conditions that occurs due to varied levels of phosphorylation of MYPT in ventricles.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume289
Issue number4 58-4
DOIs
StatePublished - Oct 1 2005

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Myosin-Light-Chain Phosphatase
Protein Phosphatase 1
Phosphorylation
Light
Adrenergic Receptors
Muscle Cells
rho-Associated Kinases
Myofibrils
Adrenergic Agonists
Phosphoric Monoester Hydrolases
Catalytic Domain

All Science Journal Classification (ASJC) codes

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)

Cite this

Modulation of myosin phosphatase targeting subunit and protein phosphatase 1 in the heart. / Rajashree, Ravi; Blunt, Bradford C.; Hofmann, Polly.

In: American Journal of Physiology - Heart and Circulatory Physiology, Vol. 289, No. 4 58-4, 01.10.2005.

Research output: Contribution to journalArticle

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AB - Myosin light chain 2 (LC2) phosphorylation is of both physiological and pathological importance to myocardial function. The phosphatase that directly dephosphorylates LC2 is a type 1 protein phosphatase (PP1) that contains a catalytic subunit that complexes with a myosin-binding phosphatase targeting subunit (MYPT). The goal of the present study was to examine the role of MYPT in the regulation of PP1 in ventricular myocytes, In the first part of the study, regional distribution of MYPT expression and phosphorylation were determined in unstimulated hearts. The pattern of MYPT phosphorylation was inversely related to the LC2 phosphorylation spatial gradient as described by Epstein and colleagues (Davis JS, Hassanzadeh S, Winitsky S, Lin H, Satorius C, Vemuri R, Aletras AH, Wen H, and Epstein ND. Cell 107: 631-641, 2001). In the second part of the study, adult rat isolated ventricular myocytes were exposed to an α-adrenergic receptor agonist, and properties of MYPT, PP1, and LC2 were studied. We found MYPT associates with cardiac myofilaments, and this association increases upon α-adrenergic receptor stimulation. Activation of α-adrenergic receptors also led to a decrease in the PP1-myofilament association. Furthermore, α-adrenergic receptor stimulation results in phosphorylation of MYPT and LC2 and an increase in myocyte Ca 2+ sensitivity of tension that all depend on Rho kinase activation. These data support the hypothesis that α-adrenergic receptor activation works through Rho kinase to phosphorylate MYPT, and phosphorylated MYPT dissociates from PP1 so that PP1 is no longer physically associated with LC2. Hence, we propose a pathway for the dynamic modulation of LC2 phosphorylation through receptor-dependent phosphorylation of MYPT, and a spatial gradient of LC2 phosphorylation under basal conditions that occurs due to varied levels of phosphorylation of MYPT in ventricles.

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