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202
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Schwoerer AP, Neuber C, Schmechel A, Melnychenko I, Mearini G, Boknik P, Kirchhefer U, Schmitz W, Ehmke H, Eschenhagen T, El-Armouche A. Mechanical unloading of the rat heart involves marked changes in the protein kinase–phosphatase balance. J Mol Cell Cardiol 2008; 45:846-52. [DOI: 10.1016/j.yjmcc.2008.09.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Revised: 09/08/2008] [Accepted: 09/08/2008] [Indexed: 02/06/2023]
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203
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Sun YB, Lou F, Irving M. Calcium- and myosin-dependent changes in troponin structure during activation of heart muscle. J Physiol 2008; 587:155-63. [PMID: 19015190 DOI: 10.1113/jphysiol.2008.164707] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Each heartbeat is triggered by a pulse of intracellular calcium ions which bind to troponin on the actin-containing thin filaments of heart muscle cells, initiating a change in filament structure that allows myosin to bind and generate force. We investigated the molecular mechanism of calcium regulation in demembranated trabeculae from rat ventricle using polarized fluorescence from probes on troponin C (TnC). Native TnC was replaced by double-cysteine mutants of human cardiac TnC with bifunctional rhodamine attached along either the C helix, adjacent to the regulatory Ca(2+)-binding site, or the E helix in the IT arm of the troponin complex. Changes in the orientation of both troponin helices had the same steep Ca(2+) dependence as active force production, with a Hill coefficient (n(H)) close to 3, consistent with a single co-operative transition controlled by Ca(2+) binding. Complete inhibition of active force by 25 microM blebbistatin had very little effect on the Ca(2+)-dependent structural changes and in particular did not significantly reduce the value of n(H). Binding of rigor myosin heads to thin filaments following MgATP depletion in the absence of Ca(2+) also changed the orientation of the C and E helices, and addition of Ca(2+) in rigor produced further changes characterized by increased Ca(2+) affinity but with n(H) close to 1. These results show that, although myosin binding can switch on thin filaments in rigor conditions, it does not contribute significantly under physiological conditions. The physiological mechanism of co-operative Ca(2+) regulation of cardiac contractility must therefore be intrinsic to the thin filaments.
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Affiliation(s)
- Yin-Biao Sun
- Randall Division of Cell and Molecular Biophysics, King's College London, London SE1 1UL, UK.
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204
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Davis J, Westfall MV, Townsend D, Blankinship M, Herron TJ, Guerrero-Serna G, Wang W, Devaney E, Metzger JM. Designing heart performance by gene transfer. Physiol Rev 2008; 88:1567-651. [PMID: 18923190 DOI: 10.1152/physrev.00039.2007] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.
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Affiliation(s)
- Jennifer Davis
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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205
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Ke L, Qi XY, Dijkhuis AJ, Chartier D, Nattel S, Henning RH, Kampinga HH, Brundel BJ. Calpain mediates cardiac troponin degradation and contractile dysfunction in atrial fibrillation. J Mol Cell Cardiol 2008; 45:685-93. [DOI: 10.1016/j.yjmcc.2008.08.012] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 08/07/2008] [Accepted: 08/20/2008] [Indexed: 10/21/2022]
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206
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207
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Robinson JM. Physical limits on computation by assemblies of allosteric proteins. PHYSICAL REVIEW LETTERS 2008; 101:178104. [PMID: 18999791 DOI: 10.1103/physrevlett.101.178104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Indexed: 05/27/2023]
Abstract
Assemblies of allosteric proteins are the principle information processing devices in biology. Using the Ca2+-sensitive cardiac regulatory assembly as a paradigm for Brownian computation, I examine how system complexity and system resetting impose physical limits on computation. Nearest-neighbor-limited interactions among assembly components constrain the topology of the system's macrostate free energy landscape and produce degenerate transition probabilities. As a result, signaling fidelity and deactivation kinetics cannot be simultaneously optimized. This imposes an upper limit on the rate of information processing by assemblies of allosteric proteins that couple to a single ligand type.
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Affiliation(s)
- John M Robinson
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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208
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Rudy Y, Ackerman MJ, Bers DM, Clancy CE, Houser SR, London B, McCulloch AD, Przywara DA, Rasmusson RL, Solaro RJ, Trayanova NA, Van Wagoner DR, Varró A, Weiss JN, Lathrop DA. Systems approach to understanding electromechanical activity in the human heart: a national heart, lung, and blood institute workshop summary. Circulation 2008; 118:1202-11. [PMID: 18779456 DOI: 10.1161/circulationaha.108.772715] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The National Heart, Lung, and Blood Institute (NHLBI) convened a workshop of cardiologists, cardiac electrophysiologists, cell biophysicists, and computational modelers on August 20 and 21, 2007, in Washington, DC, to advise the NHLBI on new research directions needed to develop integrative approaches to elucidate human cardiac function. The workshop strove to identify limitations in the use of data from nonhuman animal species for elucidation of human electromechanical function/activity and to identify what specific information on ion channel kinetics, calcium handling, and dynamic changes in the intracellular/extracellular milieu is needed from human cardiac tissues to develop more robust computational models of human cardiac electromechanical activity. This article summarizes the workshop discussions and recommendations on the following topics: (1) limitations of animal models and differences from human electrophysiology, (2) modeling ion channel structure/function in the context of whole-cell electrophysiology, (3) excitation-contraction coupling and regulatory pathways, (4) whole-heart simulations of human electromechanical activity, and (5) what human data are currently needed and how to obtain them. The recommendations can be found on the NHLBI Web site at http://www.nhlbi.nih.gov/meetings/workshops/electro.htm.
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Affiliation(s)
- Yoram Rudy
- Cardiac Bioelectricity and Arrhythmia Center, The Fred Saigh Distinguished Professor, Washington University, Campus Box 1097, Whitaker Hall Room 290B, One Brookings Dr, St Louis, MO 63130-4899, USA.
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209
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Ababou A, Rostkova E, Mistry S, Masurier CL, Gautel M, Pfuhl M. Myosin binding protein C positioned to play a key role in regulation of muscle contraction: structure and interactions of domain C1. J Mol Biol 2008; 384:615-30. [PMID: 18926831 PMCID: PMC2631168 DOI: 10.1016/j.jmb.2008.09.065] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Revised: 09/06/2008] [Accepted: 09/10/2008] [Indexed: 01/27/2023]
Abstract
Myosin binding protein C (MyBP-C) is a thick filament protein involved in the regulation of muscle contraction. Mutations in the gene for MyBP-C are the second most frequent cause of hypertrophic cardiomyopathy. MyBP-C binds to myosin with two binding sites, one at its C-terminus and another at its N-terminus. The N-terminal binding site, consisting of immunoglobulin domains C1 and C2 connected by a flexible linker, interacts with the S2 segment of myosin in a phosphorylation-regulated manner. It is assumed that the function of MyBP-C is to act as a tether that fixes the S1 heads in a resting position and that phosphorylation releases the S1 heads into an active state. Here, we report the structure and binding properties of domain C1. Using a combination of site-directed mutagenesis and NMR interaction experiments, we identified the binding site of domain C1 in the immediate vicinity of the S1–S2 hinge, very close to the light chains. In addition, we identified a zinc binding site on domain C1 in close proximity to the S2 binding site. Its zinc binding affinity (Kd of approximately 10–20 μM) might not be sufficient for a physiological effect. However, the familial hypertrophic cardiomyopathy-related mutation of one of the zinc ligands, glutamine 210 to histidine, will significantly increase the binding affinity, suggesting that this mutation may affect S2 binding. The close proximity of the C1 binding site to the hinge, the light chains and the S1 heads also provides an explanation for recent observations that (a) shorter fragments of MyBP-C unable to act as a tether still have an effect on the actomyosin ATPase and (b) as to why the myosin head positions in phosphorylated wild-type mice and MyBP-C knockout mice are so different: Domain C1 bound to the S1–S2 hinge is able to manipulate S1 head positions, thus influencing force generation without tether. The potentially extensive extra interactions of C1 are expected to keep it in place, while phosphorylation dislodges the C1–C2 linker and domain C2. As a result, the myosin heads would always be attached to a tether that has phosphorylation-dependent length regulation.
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Affiliation(s)
- Abdessamad Ababou
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK
| | - Elena Rostkova
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunts House, Guy's Hospital, London SE1 1UL, UK
| | - Shreena Mistry
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK
| | - Clare Le Masurier
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK
| | - Mathias Gautel
- Randall Division of Cell and Molecular Biophysics, King's College London, New Hunts House, Guy's Hospital, London SE1 1UL, UK
| | - Mark Pfuhl
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK
- Corresponding author.
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210
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Abstract
The Ca(2+)-sensitive regulatory switch of cardiac muscle is a paradigmatic example of protein assemblies that communicate ligand binding through allosteric change. The switch is a dimeric complex of troponin C (TnC), an allosteric sensor for Ca(2+), and troponin I (TnI), an allosteric reporter. Time-resolved equilibrium Förster resonance energy transfer (FRET) measurements suggest that the switch activates in two steps: a TnI-independent Ca(2+)-priming step followed by TnI-dependent opening. To resolve the mechanistic role of TnI in activation we performed stopped-flow FRET measurements of activation after rapid addition of a lacking component (Ca(2+) or TnI) and deactivation after rapid chelation of Ca(2+). Time-resolved measurements, stopped-flow measurements, and Ca(2+)-titration measurements were globally analyzed in terms of a new quantitative dynamic model of TnC-TnI allostery. The analysis provided a mesoscopic parameterization of distance changes, free energy changes, and transition rates among the accessible coarse-grained states of the system. The results reveal that 1), the Ca(2+)-induced priming step, which precedes opening, is the rate-limiting step in activation; 2), closing is the rate-limiting step in de-activation; 3), TnI induces opening; 4), there is an incompletely deactivated population when regulatory Ca(2+) is not bound, which generates an accessory pathway of activation; and 5), there is incomplete activation by Ca(2+)-when regulatory Ca(2+) is bound, a 3:2 mixture of dynamically interconverting open (active) and primed-closed (partially active) conformers is observed (15 degrees C). Temperature-dependent stopped-flow FRET experiments provide a near complete thermokinetic parameterization of opening: the enthalpy change (DeltaH = -33.4 kJ/mol), entropy change (DeltaS = -0.110 kJ/mol/K), heat capacity change (DeltaC(p) = -7.6 kJ/mol/K), the enthalpy of activation (delta(double dagger) = 10.6 kJ/mol) and the effective barrier crossing attempt frequency (nu(adj) = 1.8 x 10(4) s(-1)).
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211
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Robertson IM, Baryshnikova OK, Li MX, Sykes BD. Defining the binding site of levosimendan and its analogues in a regulatory cardiac troponin C-troponin I complex. Biochemistry 2008; 47:7485-95. [PMID: 18570382 PMCID: PMC2652250 DOI: 10.1021/bi800438k] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The interaction of Cardiac Troponin C (cTnC) and Cardiac Troponin I (cTnI) plays a critical role in transmitting the Ca (2+) signal to the other myofilament proteins in the activation of cardiac muscle contraction. As such, the cTnC-cTnI interface is a logical target for cardiotonic agents such as levosimendan that can modulate the Ca (2+) sensitivity of the myofilaments. Evidence indicates that drug candidates may exert their effects by targeting a site formed by binding of the switch region of cTnI to the regulatory N domain of cTnC (cNTnC). In this study, we utilized two-dimensional (1)H- (15)N HSQC NMR spectroscopy to monitor the binding of levosimendan and its analogues, CMDP, AMDP, CI-930, imazodan, and MPDP, to cNTnC.Ca (2+) in complex with two versions of the switch region of cTnI (cTnI 147-163 and cTnI 144-163). Levosimendan, CMDP, AMDP, and CI-930 were found to bind to both cNTnC.Ca (2+).cTnI 147-163 and cNTnC.Ca (2+).cTnI 144-163 complexes. These compounds contain a methyl group that is absent in MPDP or imazodan. Thus, the methyl group is one of the pharmacophores responsible for the action of these pyridazinone drugs on cTnC. Furthermore, the results showed that the cNTnC.Ca (2+).cTnI 144-163 complex presents a higher-affinity binding site for these compounds than the cNTnC.Ca (2+).cTnI 147-163 complex. This is consistent with our observation that the affinity of cTnI 144-163 for cNTnC.Ca (2+) is approximately 10-fold stronger than that of cTnI 147-163, likely a result of electrostatic forces between the N-terminal RRV extension in cTnI 144-163 and the acidic residues in the C and D helices of cNTnC. These results will help in the delineation of the mode of action of levosimendan on the important functional unit of cardiac troponin that constitutes the regulatory domain of cTnC and the switch region of cTnI.
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Affiliation(s)
- Ian M Robertson
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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212
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Solaro RJ. Multiplex kinase signaling modifies cardiac function at the level of sarcomeric proteins. J Biol Chem 2008; 283:26829-33. [PMID: 18567577 DOI: 10.1074/jbc.r800037200] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and the Center for Cardiovascular Research, University of Illinois, Chicago, Illinois 60612, USA.
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213
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Yuan C, Sheng Q, Tang H, Li Y, Zeng R, Solaro RJ. Quantitative comparison of sarcomeric phosphoproteomes of neonatal and adult rat hearts. Am J Physiol Heart Circ Physiol 2008; 295:H647-56. [PMID: 18552161 DOI: 10.1152/ajpheart.00357.2008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neonatal hearts respond to stress and function in an environment quite different from adult hearts. There is evidence that these functional differences not only reflect modifications in the abundance and isoforms of sarcomeric proteins but also in the modulation of sarcomeric protein phosphorylation. Yet our understanding of changes in sarcomeric protein phosphorylation in development is incomplete. In the experiments reported here, we first quantified the intact sarcomeric protein phosphorylation status between neonatal and adult rat hearts by employing comparative two-dimensional (2-D) gel electrophoresis in conjunction with phosphoprotein-specific staining. Subsequently, we measured phosphorylation changes at the peptide level by employing high-resolution linear ion trap-Fourier transform (LTQ-FT) mass spectrometry analysis of titanium dioxide-enriched phosphopeptides differentially labeled with (16)O/(18)O during in-gel digestion. We also employed Western blot analysis using phosphorylation site-specific antibodies to measure phosphorylation changes. Our data demonstrated the novel finding that phosphorylation levels of myosin-binding protein C (MyBP-C) at Ser(295) and Ser(315) as well as tropomyosin at Ser(283) increased, whereas phosphorylation levels of MyBP-C at Ser(320) and myosin light chain 2 at Ser(15) decreased in neonatal hearts compared with the same sites in adult hearts. Although our data highlight the significant challenges in understanding relations between protein phosphorylation and cardiac function, they do support the hypothesis that developmental changes in the modulation of protein are functionally significant and correlate with the prevailing physiological state.
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Affiliation(s)
- Chao Yuan
- Department of Physiology and Biophysics, UIC, Chicago, IL 60612, USA
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214
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Sumandea MP, Rybin VO, Hinken AC, Wang C, Kobayashi T, Harleton E, Sievert G, Balke CW, Feinmark SJ, Solaro RJ, Steinberg SF. Tyrosine phosphorylation modifies protein kinase C delta-dependent phosphorylation of cardiac troponin I. J Biol Chem 2008; 283:22680-9. [PMID: 18550549 DOI: 10.1074/jbc.m802396200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Our study identifies tyrosine phosphorylation as a novel protein kinase Cdelta (PKCdelta) activation mechanism that modifies PKCdelta-dependent phosphorylation of cardiac troponin I (cTnI), a myofilament regulatory protein. PKCdelta phosphorylates cTnI at Ser23/Ser24 when activated by lipid cofactors; Src phosphorylates PKCdelta at Tyr311 and Tyr332 leading to enhanced PKCdelta autophosphorylation at Thr505 (its activation loop) and PKCdelta-dependent cTnI phosphorylation at both Ser23/Ser24 and Thr144. The Src-dependent acquisition of cTnI-Thr144 kinase activity is abrogated by Y311F or T505A substitutions. Treatment of detergent-extracted single cardiomyocytes with lipid-activated PKCdelta induces depressed tension at submaximum but not maximum [Ca2+] as expected for cTnI-Ser23/Ser24 phosphorylation. Treatment of myocytes with Src-activated PKCdelta leads to depressed maximum tension and cross-bridge kinetics, attributable to a dominant effect of cTnI-Thr144 phosphorylation. Our data implicate PKCdelta-Tyr311/Thr505 phosphorylation as dynamically regulated modifications that alter PKCdelta enzymology and allow for stimulus-specific control of cardiac mechanics during growth factor stimulation and oxidative stress.
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Affiliation(s)
- Marius P Sumandea
- Department of Internal Medicine, Cardiovascular Research Center, University of Kentucky, Lexington, Kentucky 40536, USA
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215
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Ait Mou Y, le Guennec JY, Mosca E, de Tombe PP, Cazorla O. Differential contribution of cardiac sarcomeric proteins in the myofibrillar force response to stretch. Pflugers Arch 2008; 457:25-36. [PMID: 18449562 DOI: 10.1007/s00424-008-0501-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Revised: 03/18/2008] [Accepted: 03/18/2008] [Indexed: 11/24/2022]
Abstract
The present study examined the contribution of myofilament contractile proteins to regional function in guinea pig myocardium. We investigated the effect of stretch on myofilament contractile proteins, Ca(2+) sensitivity, and cross-bridge cycling kinetics (K (tr)) of force in single skinned cardiomyocytes isolated from the sub-endocardial (ENDO) or sub-epicardial (EPI) layer. As observed in other species, ENDO cells were stiffer, and Ca(2+) sensitivity of force at long sarcomere length was higher compared with EPI cells. Maximal K (tr) was unchanged by stretch, but was higher in EPI cells possibly due to a higher alpha-MHC content. Submaximal Ca(2+)-activated K (tr) increased only in ENDO cells with stretch. Stretch of skinned ENDO muscle strips induced increased phosphorylation in both myosin-binding protein C and myosin light chain 2. We concluded that transmural MHC isoform expression and differential regulatory protein phosphorylation by stretch contributes to regional differences in stretch modulation of activation in guinea pig left ventricle.
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Affiliation(s)
- Younss Ait Mou
- INSERM, U 637, Université MONTPELLIER I, UFR de Médecine, F-34295, Montpellier, France
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216
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Zabrouskov V, Ge Y, Schwartz J, Walker JW. Unraveling molecular complexity of phosphorylated human cardiac troponin I by top down electron capture dissociation/electron transfer dissociation mass spectrometry. Mol Cell Proteomics 2008; 7:1838-49. [PMID: 18445579 DOI: 10.1074/mcp.m700524-mcp200] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cardiac troponin I (cTnI), the inhibitory subunit of the thin filament troponin-tropomyosin regulatory complex, is required for heart muscle relaxation during the cardiac cycle. Expressed only in cardiac muscle, cTnI is widely used in the clinic as a serum biomarker of cardiac injury. In vivo function of cTnI is influenced by phosphorylation and proteolysis; therefore analysis of post-translational modifications of the intact protein should greatly facilitate the understanding of cardiac regulatory mechanisms and may improve cTnI as a disease biomarker. cTnI (24 kDa, pI approximately 9.5) contains twelve serine, eight threonine, and three tyrosine residues, which presents a challenge for unequivocal identification of phosphorylation sites and quantification of positional isomers. In this study, we used top down electron capture dissociation and electron transfer dissociation MS to unravel the molecular complexity of cTnI purified from human heart tissue. High resolution MS spectra of human cTnI revealed a high degree of heterogeneity, corresponding to phosphorylation, acetylation, oxidation, and C-terminal proteolysis. Thirty-six molecular ions of cTnI were detected in a single ESI/FTMS spectrum despite running as a single sharp band on SDS-PAGE. Electron capture dissociation of monophosphorylated cTnI localized two major basal phosphorylation sites: a well known site at Ser(22) and a novel site at Ser(76)/Thr(77), each with partial occupancy (Ser(22): 53%; Ser(76)/Thr(77): 36%). Top down MS(3) analysis of diphosphorylated cTnI revealed occupancy of Ser(23) only in diphosphorylated species consistent with sequential (or ordered) phosphorylation/dephosphorylation of the Ser(22/23) pair. Top down MS of cTnI provides unique opportunities for unraveling its molecular complexity and for quantification of phosphorylated positional isomers thus allowing establishment of the relevance of such modifications to physiological functions and disease status.
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217
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Kobayashi T, Jin L, de Tombe PP. Cardiac thin filament regulation. Pflugers Arch 2008; 457:37-46. [PMID: 18421471 DOI: 10.1007/s00424-008-0511-8] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 03/19/2008] [Accepted: 03/25/2008] [Indexed: 12/17/2022]
Abstract
Myocardial contraction is initiated upon the release of calcium into the cytosol from the sarcoplasmic reticulum following membrane depolarization. The fundamental physiological role of the heart is to pump an amount blood that is determined by the prevailing requirements of the body. The physiological control systems employed to accomplish this task include regulation of heart rate, the amount of calcium release, and the response of the cardiac myofilaments to activator calcium ions. Thin filament activation and relaxation dynamics has emerged as a pivotal regulatory system tuning myofilament function to the beat-to-beat regulation of cardiac output. Maladaptation of thin filament dynamics, in addition to dysfunctional calcium cycling, is now recognized as an important cellular mechanism causing reduced cardiac pump function in a variety of cardiac diseases. Here, we review current knowledge regarding protein-protein interactions involved in the dynamics of thin filament activation and relaxation and the regulation of these processes by protein kinase-mediated phosphorylation.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology & Biophysics, University of Illinois at Chicago, Chicago, IL 60612, USA
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218
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Reece KL, Moss RL. Intramolecular interactions in the N-domain of cardiac troponin C are important determinants of calcium sensitivity of force development. Biochemistry 2008; 47:5139-46. [PMID: 18410130 DOI: 10.1021/bi800164c] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Myocardial contraction is initiated when Ca2+ binds to site II of cardiac troponin C. This 12-residue EF-hand loop (NH2-DEDGSGTVDFDE-COOH) contains six residues (bold) that coordinate Ca2+ binding and six residues that do not appear to influence Ca2+ binding directly. We have introduced six single-cysteine substitutions (italics) within site II of cTnC to investigate whether these residues are essential for Ca2+ binding affinity in isolation and Ca2+ sensitivity of force development in single muscle fibers. Ca2+ binding properties of mutant proteins were examined in solution and after substitution into rat skinned soleus fibers. Except for the serine mutation, cysteine substitution had no effect on Ca2+ binding on cTnC in solution. However, as part of the myofilament, the threonine mutation reduced Ca2+ sensitivity while the phenylalanine mutation increased Ca2+ sensitivity. Analysis of the available crystal and NMR structures reveals specific structural mechanisms for these effects.
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Affiliation(s)
- Karen L Reece
- Department of Physiology, UniVersity of Wisconsin School of Medicine and Public Health, 123 Service Memorial Institute, 1300 University Avenue, Madison, Wisconsin 53706, USA
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219
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Warren CM, Arteaga GM, Rajan S, Ahmed RPH, Wieczorek DF, Solaro RJ. Use of 2-D DIGE analysis reveals altered phosphorylation in a tropomyosin mutant (Glu54Lys) linked to dilated cardiomyopathy. Proteomics 2008; 8:100-5. [PMID: 18095372 DOI: 10.1002/pmic.200700772] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Current electrophoretic methods have not been optimized to fully separate post-translationally modified mutant forms of tropomyosin (Tm) from wild-type cardiac samples. We describe here a method employing a modified 2-D PAGE/2-D DIGE protocol, to fully separate native, mutant (E54K), and phosphorylated forms of Tm. Our data demonstrate the first evidence of a significant (approximately 40%) decrease in Tm phosphorylation in transgenic compared to non-transgenic mouse hearts, and indicate that altered phosphorylation may be a significant factor in the linkage of the E54K mutation to dilated cardiomyopathy.
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Affiliation(s)
- Chad M Warren
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, 835 E. Wolcott Avenue, Chicago, IL 60612, USA
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220
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Tachampa K, Kobayashi T, Wang H, Martin AF, Biesiadecki BJ, Solaro RJ, de Tombe PP. Increased cross-bridge cycling kinetics after exchange of C-terminal truncated troponin I in skinned rat cardiac muscle. J Biol Chem 2008; 283:15114-21. [PMID: 18378675 DOI: 10.1074/jbc.m801636200] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The precise mechanism of cardiac troponin I (cTnI) proteolysis in myocardial stunning is not fully understood. Accordingly, we determined the effect of cTnI C terminus truncation on chemo-mechanical transduction in isolated skinned rat trabeculae. Recombinant troponin complex (cTn), containing either mouse cTnI-(1-193) or human cTnI-(1-192) was exchanged into skinned cardiac trabeculae; Western blot analysis confirmed that 60-70% of the endogenous cTn was replaced by recombinant Tn. Incorporation of truncated cTnI induced significant reductions ( approximately 50%) in maximum force and cooperative activation as well as increases ( approximately 50%) in myofilament Ca(2+) sensitivity and tension cost. Similar results were obtained with either mouse or human truncated cTn. Presence of truncated cTnI increased maximum actin-activated S1 ATPase activity as well as its Ca(2+) sensitivity in vitro. Partial exchange (50%) for truncated cTnI resulted in similar reductions in maximum force and cooperativity; tension cost was increased in proportion to truncated cTnI content. In vitro, to determine the molecular mechanism responsible for the enhanced myofilament Ca(2+) sensitivity, we measured Ca(2+) binding to cTn as reported using a fluorescent probe. Incorporation of truncated cTnI did not affect Ca(2+) binding affinity to cTn alone. However, when cTn was incorporated into thin filaments, cTnI truncation induced a significant increase in Ca(2+) binding affinity to cTn. We conclude that cTnI truncation induces depressed myofilament function. Decreased cardiac function after ischemia/reperfusion injury may directly result, in part, from proteolytic degradation of cTnI, resulting in alterations in cross-bridge cycling kinetics.
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Affiliation(s)
- Kittipong Tachampa
- Center for Cardiovascular Research and Department of Physiology and Biophysics, University of Illinois, Chicago, IL 60612, USA
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221
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Liang B, Chung F, Qu Y, Pavlov D, Gillis TE, Tikunova SB, Davis JP, Tibbits GF. Familial hypertrophic cardiomyopathy-related cardiac troponin C mutation L29Q affects Ca2+ binding and myofilament contractility. Physiol Genomics 2008; 33:257-66. [PMID: 18285522 DOI: 10.1152/physiolgenomics.00154.2007] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The cardiac troponin C (cTnC) mutation, L29Q, has been found in a patient with familial hypertrophic cardiomyopathy. We previously showed that L29, together with neighboring residues, Asp2, Val28, and Gly30, plays an important role in determining the Ca(2+) affinity of site II, the regulatory site of mammalian cardiac troponin C (McTnC). Here we report on the Ca(2+) binding characteristics of L29Q McTnC and D2N/V28I/L29Q/G30D McTnC (NIQD) utilizing the Phe(27) --> Trp (F27W) substitution, allowing one to monitor Ca(2+) binding and release. We also studied the effect of these mutants on Ca(2+) activation of force generation in single mouse cardiac myocytes using cTnC replacement, together with sarcomere length (SL) dependence. The Ca(2+)-binding affinity of site II of L29Q McTnC(F27W) and NIQD McTnC(F27W) was approximately 1.3- and approximately 1.9-fold higher, respectively, than that of McTnC(F27W). The Ca(2+) disassociation rate from site II of L29Q McTnC(F27W) and NIQD McTnC(F27W) was not significantly different than that of control (McTnC(F27W)). However, the rate of Ca(2+) binding to site II was higher in L29Q McTnC(F27W) and NIQD McTnC(F27W) relative to control (approximately 1.5-fold and approximately 2.0-fold respectively). The Ca(2+) sensitivity of force generation was significantly higher in myocytes reconstituted with L29Q McTnC (approximately 1.4-fold) and NIQD McTnC (approximately 2-fold) compared with those reconstituted with McTnC. Interestingly, the change in Ca(2+) sensitivity of force generation in response to an SL change (1.9, 2.1, and 2.3 mum) was significantly reduced in myocytes containing L29Q McTnC or NIQD McTnC. These results demonstrate that the L29Q mutation enhances the Ca(2+)-binding characteristics of cTnC and that when incorporated into cardiac myocytes, this mutant alters myocyte contractility.
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Affiliation(s)
- Bo Liang
- Cardiac Membrane Research Laboratory, Kinesiology, Simon Fraser University, Burnaby, Canada
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222
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Differential effects of a green tea-derived polyphenol (-)-epigallocatechin-3-gallate on the acidosis-induced decrease in the Ca(2+) sensitivity of cardiac and skeletal muscle. Pflugers Arch 2008; 456:787-800. [PMID: 18231806 DOI: 10.1007/s00424-008-0456-y] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Revised: 01/12/2008] [Accepted: 01/14/2008] [Indexed: 10/22/2022]
Abstract
(-)-Epigallocatechin-3-gallate (EGCg), a green tea-derived polyphenol, has received much attention as a protective agent against cardiovascular diseases. In this study, we determined its effects on the acidosis-induced change in the Ca(2+) sensitivity of myofilaments in myofibrils prepared from porcine ventricular myocardium and chicken pectoral muscle. EGCg (0.1 mM) significantly inhibited the decrease caused by lowering the pH from 7.0 to 6.0 in the Ca(2+) sensitivity of myofibrillar ATPase activity in cardiac muscle, but not in skeletal muscle. Studies on recombinant mouse cardiac troponin C (cTnC) and chicken fast skeletal troponin C (sTnC) using circular dichroism and intrinsic and extrinsic fluorescence spectroscopy showed that EGCg bound to cTnC with a dissociation constant of approximately 3-4 muM, but did not bind to sTnC. By presumably binding to the cTnC C-lobe, EGCg decreased Ca(2+) binding to cTnC and overcame the depressant effect of protons on the Ca(2+) sensitivity of the cardiac contractile response. To demonstrate isoform-specific effects of the action of EGCg, the pH sensitivity of the Ca(2+) response was examined in cardiac myofibrils in which endogenous cTnC was replaced with exogenous sTnC or cTnC and in skeletal myofibrils in which the endogenous sTn complex was replaced with whole cardiac Tn complex (cTn). The results suggest that the binding of EGCg to the cardiac isoform-specific TnC or Tn complex alters the effect of pH on myofilament Ca(2+) sensitivity in striated muscle.
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223
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Solaro RJ, Rosevear P, Kobayashi T. The unique functions of cardiac troponin I in the control of cardiac muscle contraction and relaxation. Biochem Biophys Res Commun 2007; 369:82-7. [PMID: 18162178 DOI: 10.1016/j.bbrc.2007.12.114] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2007] [Accepted: 12/11/2007] [Indexed: 01/02/2023]
Abstract
We review development of evidence and current perceptions of the multiple and significant functions of cardiac troponin I in regulation and modulation of cardiac function. Our emphasis is on the unique structure function relations of the cardiac isoform of troponin I, especially regions containing sites of phosphorylation. The data indicate that modifications of specific regions cardiac troponin I by phosphorylations either promote or reduce cardiac contractility. Thus, a homeostatic balance in these phosphorylations is an important aspect of control of cardiac function. A new concept is the idea that the homeostatic mechanisms may involve modifications of intra-molecular interactions in cardiac troponin I.
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics (M/C901) and Center for Cardiovascular Research, 835 South Wolcott Avenue, University of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA
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224
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Chang AN, Parvatiyar MS, Potter JD. Troponin and cardiomyopathy. Biochem Biophys Res Commun 2007; 369:74-81. [PMID: 18157941 DOI: 10.1016/j.bbrc.2007.12.081] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2007] [Accepted: 12/11/2007] [Indexed: 02/08/2023]
Abstract
The troponin complex was discovered over thirty years ago and since then much insight has been gained into how this complex senses fluctuating levels of Ca(2+) and transmits this signal to the myofilament. Advances in genetics methods have allowed identification of mutations that lead to the phenotypically distinct cardiomyopathies: hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM) and dilated cardiomyopathy (DCM). This review serves to highlight key in vivo studies of mutation effects that have followed many years of functional studies and discusses how these mutations alter energetics and promote the characteristic remodeling associated with cardiomyopathic diseases. Studies have been performed that examine alterations in signaling and genomic methods have been employed to isolate upregulated proteins, however these processes are complex as there are multiple roads to hypertrophy or dilation associated with genetic cardiomyopathies. This review suggests future directions to explore in the troponin field that would heighten our understanding of the complex regulation of cardiac muscle contraction.
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Affiliation(s)
- Audrey N Chang
- Department of Molecular and Cellular Pharmacology, University of Miami, Miller School of Medicine, Room 6085A RMSB,1600 NW 10th Avenue, Miami, FL 33136, USA
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225
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Li MX, Robertson IM, Sykes BD. Interaction of cardiac troponin with cardiotonic drugs: a structural perspective. Biochem Biophys Res Commun 2007; 369:88-99. [PMID: 18162171 DOI: 10.1016/j.bbrc.2007.12.108] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2007] [Accepted: 12/11/2007] [Indexed: 11/29/2022]
Abstract
Over the 40 years since its discovery, many studies have focused on understanding the role of troponin as a myofilament based molecular switch in regulating the Ca(2+)-dependent activation of striated muscle contraction. Recently, studies have explored the role of cardiac troponin as a target for cardiotonic agents. These drugs are clinically useful for treating heart failure, a condition in which the heart is no longer able to pump enough blood to other organs. These agents act via a mechanism that modulates the Ca(2+)-sensitivity of troponin; such a mode of action is therapeutically desirable because intracellular Ca(2+) concentration is not perturbed, preserving the regulation of other Ca(2+)-based signaling pathways. This review describes molecular details of the interaction of cardiac troponin with a variety of cardiotonic drugs. We present recent structural work that has identified the docking sites of several cardiotonic drugs in the troponin C-troponin I interface and discuss their relevance in the design of troponin based drugs for the treatment of heart disease.
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Affiliation(s)
- Monica X Li
- Department of Biochemistry, University of Alberta, Edmonton, Alta., Canada
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226
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Abstract
Controversy abounds in the cardiac muscle literature over the rate-limiting steps of cardiac muscle contraction and relaxation. However, the idea of a single biochemical mechanism being the all-inclusive rate-limiting step for cardiac muscle contraction and relaxation may be oversimplified. There is ample evidence that Ca(2+) concentration and dynamics, intrinsic cross-bridge properties, and even troponin C (TnC) Ca(2+) binding and dissociation can all modulate the mechanical events of cardiac muscle contraction and relaxation. However, TnC has generally been thought to play no role in influencing cardiac muscle dynamics due to the idea that Ca(2+) exchange with TnC is very rapid. This definitely is the case for isolated TnC, but not for the more sophisticated biochemical systems of reconstituted thin filaments and myofibrils. This review will discuss the biochemical influences on Ca(2+) exchange with TnC and their physiological implications.
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Affiliation(s)
- Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, 400 Hamilton Hall, Columbus, OH 43210, USA.
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227
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Dong WJ, Xing J, Ouyang Y, An J, Cheung HC. Structural kinetics of cardiac troponin C mutants linked to familial hypertrophic and dilated cardiomyopathy in troponin complexes. J Biol Chem 2007; 283:3424-3432. [PMID: 18063575 DOI: 10.1074/jbc.m703822200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The key events in regulating cardiac muscle contraction involve Ca(2+) binding to and release from cTnC (troponin C) and structural changes in cTnC and other thin filament proteins triggered by Ca(2+) movement. Single mutations L29Q and G159D in human cTnC have been reported to associate with familial hypertrophic and dilated cardiomyopathy, respectively. We have examined the effects of these individual mutations on structural transitions in the regulatory N-domain of cTnC triggered by Ca(2+) binding and dissociation. This study was carried out with a double mutant or triple mutants of cTnC, reconstituted into troponin with tryptophanless cTnI and cTnT. The double mutant, cTnC(L12W/N51C) labeled with 1,5-IAEDANS at Cys-51, served as a control to monitor Ca(2+)-induced opening and closing of the N-domain by Förster resonance energy transfer (FRET). The triple mutants contained both L12W and N51C labeled with 1,5-IAEDANS, and either L29Q or G159D. Both mutations had minimal effects on the equilibrium distance between Trp-12 and Cys-51-AEDANS in the absence or presence of bound Ca(2+). L29Q had no effect on the closing rate of the N-domain triggered by release of Ca(2+), but reduced the Ca(2+)-induced opening rate. G159D reduced both the closing and opening rates. Previous results showed that the closing rate of cTnC N-domain triggered by Ca(2+) dissociation was substantially enhanced by PKA phosphorylation of cTnI. This rate enhancement was abolished by L29Q or G159D. These mutations alter the kinetics of structural transitions in the regulatory N-domain of cTnC that are involved in either activation (L29Q) or deactivation (G159D). Both mutations appear to be antagonistic toward phosphorylation signaling between cTnI and cTnC.
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Affiliation(s)
- Wen-Ji Dong
- School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99164; Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington 99164.
| | - Jun Xing
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Alabama 35294
| | - Yexin Ouyang
- Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, Washington 99164
| | - Jianli An
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Alabama 35294
| | - Herbert C Cheung
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Alabama 35294
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228
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Chen L, Zhang J, Gan TX, Chen-Izu Y, Hasday JD, Karmazyn M, Balke CW, Scharf SM. Left ventricular dysfunction and associated cellular injury in rats exposed to chronic intermittent hypoxia. J Appl Physiol (1985) 2007; 104:218-23. [PMID: 18006871 DOI: 10.1152/japplphysiol.00301.2007] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Obstructive sleep apnea (OSA) increases cardiovascular morbidity and mortality. We have reported that chronic intermittent hypoxia (CIH), a direct consequence during OSA, leads to left ventricular (LV) remodeling and dysfunction in rats. The present study is to determine LV myocardial cellular injury that is possibly associated with LV global dysfunction. Fifty-six rats were exposed either to CIH (nadir O(2) 4-5%) or sham (handled normoxic controls, HC), 8 h/day for 6 wk. At the end of the exposure, we studied LV global function by cardiac catheterization, and LV myocardial cellular injury by in vitro analyses. Compared with HC, CIH animals demonstrated elevations in mean arterial pressure and LV end-diastolic pressure, but reductions in cardiac output (CIH 141.3 +/- 33.1 vs. HC 184.4 +/- 21.2 ml x min(-1) x kg(-1), P < 0.01), maximal rate of LV pressure rise in systole (+dP/dt), and maximal rate of LV pressure fall in diastole (-dP/dt). CIH led to significant cell injury in the left myocardium, including elevated LV myocyte size, measured by cell surface area (CIH 3,564 +/- 354 vs. HC 2,628 +/- 242 microm(2), P < 0.05) and cell length (CIH 148 +/- 23 vs. HC 115 +/- 16 microm, P < 0.05), elevated terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-stained positive cell number (CIH 98 +/- 45 vs. HC 15 +/- 13, P < 0.01), elevated caspase-3 activity (906 +/- 249 vs. 2,275 +/- 1,169 pmol x min(-1) x mg(-1), P < 0.05), and elevated expression of several remodeling gene markers, including c-fos, atrial natriuretic peptide, beta-myosin heavy chain, and myosin light chain-2. However, there was no difference between groups in sarcomere contractility of isolated LV myocytes, or in LV collagen deposition on trichrome-stained slices. In conclusion, CIH-mediated LV global dysfunction is associated with myocyte hypertrophy and apoptosis at the cellular level.
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Affiliation(s)
- Ling Chen
- Div. of Pulmonary and Critical Care Medicine, Univ. of Maryland, Baltimore, 685 West Baltimore St., MSTF 816, Baltimore, MD 21201, USA.
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229
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Blebbistatin: use as inhibitor of muscle contraction. Pflugers Arch 2007; 455:995-1005. [DOI: 10.1007/s00424-007-0375-3] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2007] [Accepted: 10/17/2007] [Indexed: 10/22/2022]
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230
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Tachampa K, Wang H, Farman GP, de Tombe PP. Cardiac troponin I threonine 144: role in myofilament length dependent activation. Circ Res 2007; 101:1081-3. [PMID: 17975107 DOI: 10.1161/circresaha.107.165258] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Myofilament length-dependent activation is the main cellular mechanism responsible for the Frank-Starling law of the heart. All striated muscle display length-dependent activation properties, but it is most pronounced in cardiac muscle and least in slow skeletal muscle. Cardiac muscle expressing slow skeletal troponin (ssTn)I instead of cardiac troponin (cTn)I displays reduced myofilament length-dependent activation. The inhibitory region of troponin (Tn)I differs by a single residue, proline at position 112 in ssTnI versus threonine at position 144 in cTnI. Here we tested whether this substitution was important for myofilament length-dependent activation; using recombinant techniques, we prepared wild-type cTnI, ssTnI, and 2 mutants: cTnI(Thr>Pro) and ssTnI(Pro>Thr). Purified proteins were complexed with recombinant cardiac TnT/TnC and exchanged into skinned rat cardiac trabeculae. Force-Ca2+ relationships were determined to derive myofilament Ca2+ sensitivity (EC50) at 2 sarcomere lengths: 2.0 and 2.2 microm (n=7). Myofilament length-dependent activation was indexed as deltaEC50, the difference in EC50 between sarcomere lengths of 2.0 and 2.2 microm. Incorporation of ssTnI compared with cTnI into the cardiac sarcomere reduced deltaEC50 from 1.26+/-0.30 to 0.19+/-0.04 micromol/L. A similar reduction also could be observed when Tn contained cTnI(Thr>Pro) (deltaEC50=0.24+/-0.04 micromol/L), whereas the presence of ssTnI(Pro>Thr) increased deltaEC50 to 0.94+/-0.12 micromol/L. These results suggest that Thr144 in cardiac TnI modulates cardiac myofilament length-dependent activation.
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Affiliation(s)
- Kittipong Tachampa
- Department of Physiology and Biophysics, University of Illinois, Chicago IL 60612, USA
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231
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Mathur MC, Kobayashi T, Chalovich JM. Negative charges at protein kinase C sites of troponin I stabilize the inactive state of actin. Biophys J 2007; 94:542-9. [PMID: 17872964 PMCID: PMC2157249 DOI: 10.1529/biophysj.107.113944] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Alterations in the troponin complex can lead to increases or decreases in contractile activity. Most mutations of troponin that cause hypertrophic cardiomyopathy increase the activity of cardiac muscle fibers. In at least some cases these mutants stabilize the active state of regulated actin. In contrast, phosphorylation of troponin I at residues 43, 45, and 144 inhibits muscle contractility. To determine if alterations of troponin I that reduce activity do stabilize the inactive state of actin, we introduced negative charges at residues 43, 45, and 144 of troponin I to mimic a constitutively phosphorylated state. At saturating calcium, all mutants decreased ATPase rates relative to wild-type actin-tropomyosin-troponin. Reduced activation of ATPase activity was seen with a single mutation at S45E and was not further altered by mutating the other two sites. In the presence of low concentrations of NEM-S1, wild-type troponin was more active than the mutants. At high NEM-S1, the rates of wild-type and mutants approached the same limiting value. Changes in Ca(2+) affinity also support the idea that the equilibrium between states of actin-tropomyosin-troponin was shifted to the inactive state by mutations that mimic troponin I phosphorylation.
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Affiliation(s)
- Mohit C Mathur
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, USA
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232
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Tou L, Liu Q, Shivdasani RA. Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility. Genes Dev 2007; 24:3132-9. [PMID: 15060137 PMCID: PMC381684 DOI: 10.1128/mcb.24.8.3132-3139.2004] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Histone deacetylases (HDACs) tighten chromatin structure and repress gene expression through the removal of acetyl groups from histone tails. The class I HDACs, HDAC1 and HDAC2, are expressed ubiquitously, but their potential roles in tissue-specific gene expression and organogenesis have not been defined. To explore the functions of HDAC1 and HDAC2 in vivo, we generated mice with conditional null alleles of both genes. Whereas global deletion of HDAC1 results in death by embryonic day 9.5, mice lacking HDAC2 survive until the perinatal period, when they succumb to a spectrum of cardiac defects, including obliteration of the lumen of the right ventricle, excessive hyperplasia and apoptosis of cardiomyocytes, and bradycardia. Cardiac-specific deletion of either HDAC1 or HDAC2 does not evoke a phenotype, whereas cardiac-specific deletion of both genes results in neonatal lethality, accompanied by cardiac arrhythmias, dilated cardiomyopathy, and up-regulation of genes encoding skeletal muscle-specific contractile proteins and calcium channels. Our results reveal cell-autonomous and non-cell-autonomous functions for HDAC1 and HDAC2 in the control of myocardial growth, morphogenesis, and contractility, which reflect partially redundant roles of these enzymes in tissue-specific transcriptional repression.
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Affiliation(s)
- Liqiang Tou
- Department of Medical Oncology and Cancer Biology, Dana-Farber Cancer Institute, Boston, Massachusetts, USA
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233
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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234
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Solzin J, Iorga B, Sierakowski E, Gomez Alcazar DP, Ruess DF, Kubacki T, Zittrich S, Blaudeck N, Pfitzer G, Stehle R. Kinetic mechanism of the Ca2+-dependent switch-on and switch-off of cardiac troponin in myofibrils. Biophys J 2007; 93:3917-31. [PMID: 17704185 PMCID: PMC2099212 DOI: 10.1529/biophysj.107.111146] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The kinetics of Ca2+-dependent conformational changes of human cardiac troponin (cTn) were studied on isolated cTn and within the sarcomeric environment of myofibrils. Human cTnC was selectively labeled on cysteine 84 with N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole and reconstituted with cTnI and cTnT to the cTn complex, which was incorporated into guinea pig cardiac myofibrils. These exchanged myofibrils, or the isolated cTn, were rapidly mixed in a stopped-flow apparatus with different [Ca2+] or the Ca2+-buffer 1,2-Bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid to determine the kinetics of the switch-on or switch-off, respectively, of cTn. Activation of myofibrils with high [Ca2+] (pCa 4.6) induced a biphasic fluorescence increase with rate constants of >2000 s−1 and ∼330 s−1, respectively. At low [Ca2+] (pCa 6.6), the slower rate was reduced to ∼25 s−1, but was still ∼50-fold higher than the rate constant of Ca2+-induced myofibrillar force development measured in a mechanical setup. Decreasing [Ca2+] from pCa 5.0–7.9 induced a fluorescence decay with a rate constant of 39 s−1, which was approximately fivefold faster than force relaxation. Modeling the data indicates two sequentially coupled conformational changes of cTnC in myofibrils: 1), rapid Ca2+-binding (kB ≈ 120 μM−1 s−1) and dissociation (kD ≈ 550 s−1); and 2), slower switch-on (kon = 390s−1) and switch-off (koff = 36s−1) kinetics. At high [Ca2+], ∼90% of cTnC is switched on. Both switch-on and switch-off kinetics of incorporated cTn were around fourfold faster than those of isolated cTn. In conclusion, the switch kinetics of cTn are sensitively changed by its structural integration in the sarcomere and directly rate-limit neither cardiac myofibrillar contraction nor relaxation.
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Affiliation(s)
- Johannes Solzin
- Institut fuer Vegetative Physiologie, University Cologne, Köln, Germany
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235
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Solaro RJ. Translational medicine with a capital T, troponin T, that is. Circ Res 2007; 101:114-5. [PMID: 17641232 DOI: 10.1161/circresaha.107.157420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
MESH Headings
- Amino Acid Sequence
- Animals
- Calcium/metabolism
- Cardiomyopathy, Dilated/drug therapy
- Cardiomyopathy, Dilated/genetics
- Cardiomyopathy, Dilated/metabolism
- Cardiomyopathy, Dilated/pathology
- Cardiomyopathy, Dilated/physiopathology
- Cardiotonic Agents/pharmacology
- Cardiotonic Agents/therapeutic use
- Cell Membrane Permeability/drug effects
- Cell Membrane Permeability/genetics
- Death, Sudden, Cardiac/pathology
- Disease Models, Animal
- Genetic Diseases, Inborn/drug therapy
- Genetic Diseases, Inborn/genetics
- Genetic Diseases, Inborn/metabolism
- Genetic Diseases, Inborn/pathology
- Genetic Diseases, Inborn/physiopathology
- Humans
- Mice
- Mice, Knockout
- Mice, Mutant Strains
- Muscle Contraction/drug effects
- Muscle Contraction/genetics
- Muscle Fibers, Skeletal/metabolism
- Muscle Fibers, Skeletal/pathology
- Myocardium/metabolism
- Myocardium/pathology
- Pyridazines/pharmacology
- Pyridazines/therapeutic use
- Sarcomeres/genetics
- Sarcomeres/metabolism
- Sarcomeres/pathology
- Sequence Deletion
- Troponin C/genetics
- Troponin C/metabolism
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236
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Stelzer JE, Patel JR, Walker JW, Moss RL. Differential roles of cardiac myosin-binding protein C and cardiac troponin I in the myofibrillar force responses to protein kinase A phosphorylation. Circ Res 2007; 101:503-11. [PMID: 17641226 DOI: 10.1161/circresaha.107.153650] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The heart is remarkably adaptable in its ability to vary its function to meet the changing demands of the circulatory system. During times of physiological stress, cardiac output increases in response to increased sympathetic activity, which results in protein kinase A (PKA)-mediated phosphorylations of the myofilament proteins cardiac troponin (cTn)I and cardiac myosin-binding protein (cMyBP)-C. Despite the importance of this mechanism, little is known about the relative contributions of cTnI and cMyBP-C phosphorylation to increased cardiac contractility. Using engineered mouse lines either lacking cMyBP-C (cMyBP-C(-/-)) or expressing a non-PKA phosphorylatable cTnI (cTnI(ala2)), or both (cMyBP-C(-/-)/cTnI(ala2)), we investigated the roles of cTnI and cMyBP-C phosphorylation in the regulation of the stretch-activation response. PKA treatment of wild-type and cTnI(ala2) skinned ventricular myocardium accelerated stretch activation such that the response was indistinguishable from stretch activation of cMyBP-C(-/-) or cMyBP-C(-/-)/cTnI(ala2) myocardium; however, PKA had no effect on stretch activation in cMyBP-C(-/-) or cMyBP-C(-/-)/cTnI(ala2) myocardium. These results indicate that the acceleration of stretch activation in wild-type and cTnI(ala2) myocardium is caused by phosphorylation of cMyBP-C and not cTnI. We conclude that the primary effect of PKA phosphorylation of cTnI is reduced Ca(2+) sensitivity of force, whereas phosphorylation of cMyBP-C accelerates the kinetics of force development. These results predict that PKA phosphorylation of myofibrillar proteins in living myocardium contributes to accelerated relaxation in diastole and increased rates of force development in systole.
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Affiliation(s)
- Julian E Stelzer
- Department of Physiology, University of Wisconsin School of Medicine, Madison, WI 53711, USA.
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237
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Montgomery RL, Davis CA, Potthoff MJ, Haberland M, Fielitz J, Qi X, Hill JA, Richardson JA, Olson EN. Histone deacetylases 1 and 2 redundantly regulate cardiac morphogenesis, growth, and contractility. Genes Dev 2007; 21:1790-802. [PMID: 17639084 PMCID: PMC1920173 DOI: 10.1101/gad.1563807] [Citation(s) in RCA: 546] [Impact Index Per Article: 32.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2007] [Accepted: 06/13/2007] [Indexed: 11/24/2022]
Abstract
Histone deacetylases (HDACs) tighten chromatin structure and repress gene expression through the removal of acetyl groups from histone tails. The class I HDACs, HDAC1 and HDAC2, are expressed ubiquitously, but their potential roles in tissue-specific gene expression and organogenesis have not been defined. To explore the functions of HDAC1 and HDAC2 in vivo, we generated mice with conditional null alleles of both genes. Whereas global deletion of HDAC1 results in death by embryonic day 9.5, mice lacking HDAC2 survive until the perinatal period, when they succumb to a spectrum of cardiac defects, including obliteration of the lumen of the right ventricle, excessive hyperplasia and apoptosis of cardiomyocytes, and bradycardia. Cardiac-specific deletion of either HDAC1 or HDAC2 does not evoke a phenotype, whereas cardiac-specific deletion of both genes results in neonatal lethality, accompanied by cardiac arrhythmias, dilated cardiomyopathy, and up-regulation of genes encoding skeletal muscle-specific contractile proteins and calcium channels. Our results reveal cell-autonomous and non-cell-autonomous functions for HDAC1 and HDAC2 in the control of myocardial growth, morphogenesis, and contractility, which reflect partially redundant roles of these enzymes in tissue-specific transcriptional repression.
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Affiliation(s)
- Rusty L. Montgomery
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Christopher A. Davis
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Matthew J. Potthoff
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Michael Haberland
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Jens Fielitz
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Xiaoxia Qi
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Joseph A. Hill
- Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - James A. Richardson
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
- Department of Pathology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
| | - Eric N. Olson
- Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
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238
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Sheehan KA, Ke Y, Solaro RJ. p21-Activated kinase-1 and its role in integrated regulation of cardiac contractility. Am J Physiol Regul Integr Comp Physiol 2007; 293:R963-73. [PMID: 17609315 DOI: 10.1152/ajpregu.00253.2007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We review here a novel concept in the regulation of cardiac contractility involving variations in the activity of the multifunctional enzyme, p21-activated kinase 1 (Pak1), a member of a family of proteins in the small G protein-signaling pathway that is activated by Cdc42 and Rac1. There is a large body of evidence from studies in noncardiac tissue that Pak1 activity is key in regulation of a number of cellular functions, including cytoskeletal dynamics, cell motility, growth, and proliferation. Although of significant potential impact, the role of Pak1 in regulation of the heart has been investigated in only a few laboratories. In this review, we discuss the structure of Pak1 and its sites of posttranslational modification and molecular interactions. We assemble an overview of the current data on Pak1 signaling in noncardiac tissues relative to similar signaling pathways in the heart, and we identify potential roles of Pak1 in cardiac regulation. Finally, we discuss the current state of Pak1 research in the heart in regard to regulation of contractility through functional myofilament and Ca(2+)-flux modification. An important aspect of this regulation is the modulation of kinase and phosphatase activity. We have focused on Pak1 regulation of protein phosphatase 2A (PP2A), which is abundant in cardiac muscle, thereby mediating dephosphorylation of sarcomeric proteins and sensitizing the myofilaments to Ca(2+). We present a model for Pak1 signaling that provides a mechanism for specifically affecting cardiac cellular processes in which regulation of protein phosphorylation states by PP2A dephosphorylation predominates.
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Affiliation(s)
- Katherine A Sheehan
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612-7342, USA.
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239
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Daniels MCG, Naya T, Rundell VLM, de Tombe PP. Development of contractile dysfunction in rat heart failure: hierarchy of cellular events. Am J Physiol Regul Integr Comp Physiol 2007; 293:R284-92. [PMID: 17363676 DOI: 10.1152/ajpregu.00880.2006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The cellular mechanisms underlying the development of congestive heart failure (HF) are not well understood. Accordingly, we studied myocardial function in isolated right ventricular trabeculae from rats in which HF was induced by left ventricular myocardial infarction (MI). Both early-stage (12 wk post-MI; E-pMI) and late, end-stage HF (28 wk post-Mi; L-pMI) were studied. HF was associated with decreased sarcoplasmic reticulum Ca2+ ATPase protein levels (28% E-pMI; 52% L-pMI). HF affected neither sodium/calcium exchange, ryanodine receptor, nor phospholamban protein levels. Twitch force at saturating extracellular [Ca2+] was depressed in HF (30% E-pMI; 38% L-pMI), concomitant with a marked increase in sensitivity of twitch force toward extracellular [Ca2+] (26% E-pMI; 68% L-pMI). Ca2+-saturated myofilament force development in skinned trabeculae was unchanged in E-pMI but significantly depressed in L-pMI (45%). Tension-dependent ATP hydrolysis rate was depressed in L-pMI (49%), but not in E-pMI. Our results suggest a hierarchy of cellular events during the development of HF, starting with altered calcium homeostasis during the early phase followed by myofilament dysfunction at end-stage HF.
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Affiliation(s)
- Marcel C G Daniels
- Department of Physiology and Biophysics MC901, Center for Cardiovascular Research, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612, USA
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240
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Du CK, Morimoto S, Nishii K, Minakami R, Ohta M, Tadano N, Lu QW, Wang YY, Zhan DY, Mochizuki M, Kita S, Miwa Y, Takahashi-Yanaga F, Iwamoto T, Ohtsuki I, Sasaguri T. Knock-in mouse model of dilated cardiomyopathy caused by troponin mutation. Circ Res 2007; 101:185-94. [PMID: 17556660 DOI: 10.1161/circresaha.106.146670] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We created knock-in mice in which a deletion of 3 base pairs coding for K210 in cardiac troponin (cTn)T found in familial dilated cardiomyopathy patients was introduced into endogenous genes. Membrane-permeabilized cardiac muscle fibers from mutant mice showed significantly lower Ca(2+) sensitivity in force generation than those from wild-type mice. Peak amplitude of Ca(2+) transient in cardiomyocytes was increased in mutant mice, and maximum isometric force produced by intact cardiac muscle fibers of mutant mice was not significantly different from that of wild-type mice, suggesting that Ca(2+) transient was augmented to compensate for decreased myofilament Ca(2+) sensitivity. Nevertheless, mutant mice developed marked cardiac enlargement, heart failure, and frequent sudden death recapitulating the phenotypes of dilated cardiomyopathy patients, indicating that global functional defect of the heart attributable to decreased myofilament Ca(2+) sensitivity could not be fully compensated by only increasing the intracellular Ca(2+) transient. We found that a positive inotropic agent, pimobendan, which directly increases myofilament Ca(2+) sensitivity, had profound effects of preventing cardiac enlargement, heart failure, and sudden death. These results verify the hypothesis that Ca(2+) desensitization of cardiac myofilament is the absolute cause of the pathogenesis of dilated cardiomyopathy associated with this mutation and strongly suggest that Ca(2+) sensitizers are beneficial for the treatment of dilated cardiomyopathy patients affected by sarcomeric regulatory protein mutations.
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MESH Headings
- Amino Acid Sequence
- Animals
- Calcium/metabolism
- Cardiomyopathy, Dilated/drug therapy
- Cardiomyopathy, Dilated/genetics
- Cardiomyopathy, Dilated/metabolism
- Cardiomyopathy, Dilated/pathology
- Cardiomyopathy, Dilated/physiopathology
- Cardiotonic Agents/pharmacology
- Cardiotonic Agents/therapeutic use
- Cell Membrane Permeability/drug effects
- Cell Membrane Permeability/genetics
- Death, Sudden, Cardiac/pathology
- Disease Models, Animal
- Genetic Diseases, Inborn/drug therapy
- Genetic Diseases, Inborn/genetics
- Genetic Diseases, Inborn/metabolism
- Genetic Diseases, Inborn/pathology
- Genetic Diseases, Inborn/physiopathology
- Humans
- Mice
- Mice, Knockout
- Mice, Mutant Strains
- Muscle Contraction/drug effects
- Muscle Contraction/genetics
- Muscle Fibers, Skeletal/metabolism
- Muscle Fibers, Skeletal/pathology
- Myocardium/metabolism
- Myocardium/pathology
- Pyridazines/pharmacology
- Pyridazines/therapeutic use
- Sarcomeres/genetics
- Sarcomeres/metabolism
- Sarcomeres/pathology
- Sequence Deletion
- Troponin C/genetics
- Troponin C/metabolism
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Affiliation(s)
- Cheng-Kun Du
- Department of Clinical Pharmacology, Kyushu University Graduate School of Medicine, Maidashi, Higashi-ku, Fukuoka, Japan
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241
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Hinken AC, Solaro RJ. A dominant role of cardiac molecular motors in the intrinsic regulation of ventricular ejection and relaxation. Physiology (Bethesda) 2007; 22:73-80. [PMID: 17420299 DOI: 10.1152/physiol.00043.2006] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Molecular motors housed in myosins of the thick filament react with thin-filament actins and promote force and shortening in the sarcomeres. However, other actions of these motors sustain sarcomeric activation by cooperative feedback mechanisms in which the actin-myosin interaction promotes thin-filament activation. Mechanical feedback also affects the actin-myosin interaction. We discuss current concepts of how these relatively under-appreciated actions of molecular motors are responsible for modulation of the ejection time and isovolumic relaxation in the beating heart.
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Affiliation(s)
- Aaron C Hinken
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, IL, USA
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242
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Biesiadecki BJ, Kobayashi T, Walker JS, Solaro RJ, de Tombe PP. The Troponin C G159D Mutation Blunts Myofilament Desensitization Induced by Troponin I Ser23/24 Phosphorylation. Circ Res 2007; 100:1486-93. [PMID: 17446435 DOI: 10.1161/01.res.0000267744.92677.7f] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Striated muscle contraction is regulated by the binding of Ca
2+
to the N-terminal regulatory lobe of the cardiac troponin C (cTnC) subunit in the troponin complex. In the heart, β-adrenergic stimulation induces protein kinase A phosphorylation of cardiac troponin I (cTnI) at Ser23/24 to alter the interaction of cTnI with cTnC in the troponin complex and is critical to the regulation of cardiac contractility. We investigated the effect of the dilated cardiomyopathy linked cTnC Gly159 to Asp (cTnC-G159D) mutation on the development of Ca
2+
-dependent tension and ATPase rate in whole troponin-exchanged skinned rat trabeculae. Even though this mutation is located in the C-terminal lobe of cTnC, the G159D mutation was demonstrated to depress ATPase activation and filament sliding in vitro. The effects of this mutation within the cardiac myofilament are unknown. Our results demonstrate that the cTnC-G159D mutation by itself does not alter the myofilament response to Ca
2+
in the cardiac muscle lattice. However, in the presence of cTnI phosphorylated at Ser23/24, which reduced Ca
2+
sensitivity and enhanced cross-bridge cycling in controls, cTnC-G159D specifically blunted the phosphorylation induced decrease in Ca
2+
-sensitive tension development without altering cross-bridge cycling. Measurements in purified troponin confirmed that this cTnC-G159D blunting of myofilament desensitization results from altered Ca
2+
-binding to cTnC. Our results provide novel evidence that modification of the cTnC-cTnI interaction has distinct effects on troponin Ca
2+
-binding and cross-bridge kinetics to suggest a novel role for thin filament mutations in the modulation of myofilament function through β-adrenergic signaling as well as the development of cardiomyopathy.
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Affiliation(s)
- Brandon J Biesiadecki
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, IL 60612, USA
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243
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Solaro RJ, Arteaga GM. Heart failure, ischemia/reperfusion injury and cardiac troponin. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 592:191-200. [PMID: 17278366 DOI: 10.1007/978-4-431-38453-3_17] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Over the forty years since its discovery, there has been a profound transition in thinking with regard to the role of troponin in the control of cardiac function. This transition involved a change in perception oftroponin as a passive molecular switch responding to membrane controlled fluctuations in cytoplasmic Ca2+ to a perception of troponin as a critical element in signaling cascades that actively engage in control of cardiac function. Evidence demonstrating functionally significant developmental and mutant isoform switches and post-translational modifications of cardiac troponin complex proteins, troponin I (cTnI) and troponin T (cTnT) provided convincing evidence for a more complicated role of troponin in control of cardiac function and dynamics. The physiological role of these modifications of troponin is reviewed in this monograph and has also been reviewed elsewhere (Solaro and Rarick, 1998; Gordon et al., 2000; Solaro et al., 2002a; Kobayashi and Solaro, 2005). Our focus here is on studies related to modifications in troponin that appear important in the processes leading from compensated hypertrophy to heart failure. These studies reveal the potentially significant role of post-translational modifications of troponin in these processes. Another focus is on troponin as a target for inotropic agents. Pharmacological manipulation of troponin by small molecules remains an important avenue of approach for the treatment of acute and chronic heart failure (Kass and Solaro, 2006).
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics (M/C 901), University of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA
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244
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Kruglov EA, Correa PRAV, Arora G, Yu J, Nathanson MH, Dranoff JA. Molecular basis for calcium signaling in hepatic stellate cells. Am J Physiol Gastrointest Liver Physiol 2007; 292:G975-82. [PMID: 17204544 DOI: 10.1152/ajpgi.00401.2006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Progressive liver fibrosis (with the resultant cirrhosis) is the primary cause of chronic liver failure. Hepatic stellate cells (HSCs) are critically important mediators of liver fibrosis. In the healthy liver, HSCs are quiescent lipid-storing cells limited to the perisinusoidal endothelium. However, in the injured liver, HSCs undergo myofibroblastic transdifferentiation (activation), which is a critical step in the development of organ fibrosis. HSCs express P2Y receptors linking extracellular ATP to inositol (1,4,5)-trisphosphate-mediated cytosolic Ca(2+) signals. Here, we report that HSCs express only the type I inositol (1,4,5)-trisphosphate receptor and that the receptor shifts into the nucleus and cell extensions upon activation. These cell extensions, furthermore, express sufficient machinery to enable local application of ATP to evoke highly localized Ca(2+) signals that induce localized contractions. These autonomous units of subcellular signaling and response reveal a new level of subcellular organization, which, in turn, establishes a novel paradigm for the local control of fibrogenesis in the liver.
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MESH Headings
- Active Transport, Cell Nucleus
- Adenosine Triphosphate/metabolism
- Animals
- Calcium Signaling
- Calreticulin/metabolism
- Cell Nucleus/metabolism
- Cell Shape
- Cell Surface Extensions/metabolism
- Cells, Cultured
- Endoplasmic Reticulum/metabolism
- Inositol 1,4,5-Trisphosphate Receptors/genetics
- Inositol 1,4,5-Trisphosphate Receptors/metabolism
- Liver/cytology
- Liver/metabolism
- Liver Cirrhosis/metabolism
- Male
- Microscopy, Confocal
- Microscopy, Video
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptors, Purinergic P2/metabolism
- Time Factors
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Affiliation(s)
- Emma A Kruglov
- Section of Digestive Diseases, Department of Internal Medicine, Yale University School of Medicine, 333 Cedar St., LMP 1080, New Haven, CT 06520, USA
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245
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Gao WD, Murphy AM. Local control in thin filament activation of cardiac muscle. J Physiol 2007; 580:358. [PMID: 17347259 PMCID: PMC2075562 DOI: 10.1113/jphysiol.2007.131672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Wei Dong Gao
- Department of Anaesthesia and Critical Care Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
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246
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Solaro RJ. Nitroxyl effects on myocardium provide new insights into the significance of altered myofilament response to calcium in the regulation of contractility. J Physiol 2007; 580:697. [PMID: 17347260 PMCID: PMC2075453 DOI: 10.1113/jphysiol.2007.131649] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- R John Solaro
- Center for Cardiovascular Research, Department of Physiology and Biophysics, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612-7342, USA.
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247
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Yumoto F, Tanokura M. Structural and functional analysis of troponins from scallop striated and human cardiac muscles. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2007; 592:163-73. [PMID: 17278364 DOI: 10.1007/978-4-431-38453-3_15] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Affiliation(s)
- Fumiaki Yumoto
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan
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248
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Davis JP, Norman C, Kobayashi T, Solaro RJ, Swartz DR, Tikunova SB. Effects of thin and thick filament proteins on calcium binding and exchange with cardiac troponin C. Biophys J 2007; 92:3195-206. [PMID: 17293397 PMCID: PMC1852344 DOI: 10.1529/biophysj.106.095406] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Understanding the effects of thin and thick filament proteins on the kinetics of Ca(2+) exchange with cardiac troponin C is essential to elucidating the Ca(2+)-dependent mechanisms controlling cardiac muscle contraction and relaxation. Unlike labeling of the endogenous Cys-84, labeling of cardiac troponin C at a novel engineered Cys-53 with 2-(4'-iodoacetamidoanilo)napthalene-6-sulfonic acid allowed us to accurately measure the rate of calcium dissociation from the regulatory domain of troponin C upon incorporation into the troponin complex. Neither tropomyosin nor actin alone affected the Ca(2+) binding properties of the troponin complex. However, addition of actin-tropomyosin to the troponin complex decreased the Ca(2+) sensitivity ( approximately 7.4-fold) and accelerated the rate of Ca(2+) dissociation from the regulatory domain of troponin C ( approximately 2.5-fold). Subsequent addition of myosin S1 to the reconstituted thin filaments (actin-tropomyosin-troponin) increased the Ca(2+) sensitivity ( approximately 6.2-fold) and decreased the rate of Ca(2+) dissociation from the regulatory domain of troponin C ( approximately 8.1-fold), which was completely reversed by ATP. Consistent with physiological data, replacement of cardiac troponin I with slow skeletal troponin I led to higher Ca(2+) sensitivities and slower Ca(2+) dissociation rates from troponin C in all the systems studied. Thus, both thin and thick filament proteins influence the ability of cardiac troponin C to sense and respond to Ca(2+). These results imply that both cross-bridge kinetics and Ca(2+) dissociation from troponin C work together to modulate the rate of cardiac muscle relaxation.
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Affiliation(s)
- Jonathan P Davis
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio 43210, USA.
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249
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Eichmüller C, Skrynnikov NR. Observation of microsecond time-scale protein dynamics in the presence of Ln3+ ions: application to the N-terminal domain of cardiac troponin C. JOURNAL OF BIOMOLECULAR NMR 2007; 37:79-95. [PMID: 17180551 DOI: 10.1007/s10858-006-9105-y] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 10/02/2006] [Indexed: 05/13/2023]
Abstract
The microsecond time-scale motions in the N-terminal domain of cardiac troponin C (NcTnC) loaded with lanthanide ions have been investigated by means of a (1)H(N) off-resonance spin-lock experiment. The observed relaxation dispersion effects strongly increase along the series of NcTnC samples containing La(3+), Ce(3+), and Pr(3+) ions. This rise in dispersion effects is due to modulation of long-range pseudocontact shifts by micros time-scale dynamics. Specifically, the motion in the coordination sphere of the lanthanide ion (i.e. in the NcTnC EF-hand motif) causes modulation of the paramagnetic susceptibility tensor which, in turn, causes modulation of pseudocontact shifts. It is also probable that opening/closing dynamics, previously identified in Ca(2+)-NcTnC, contributes to some of the observed dispersions. On the other hand, it is unlikely that monomer-dimer exchange in the solution of NcTnC is directly responsible for the dispersion effects. Finally, on-off exchange of the lanthanide ion does not seem to play any significant role. The amplification of dispersion effects by Ln(3+) ions is a potentially useful tool for studies of micros-ms motions in proteins. This approach makes it possible to observe the dispersions even when the local environment of the reporting spin does not change. This happens, for example, when the motion involves a 'rigid' structural unit such as individual alpha-helix. Even more significantly, the dispersions based on pseudocontact shifts offer better chances for structural characterization of the dynamic species. This method can be generalized for a large class of applications via the use of specially designed lanthanide-binding tags.
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250
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Vahebi S, Ota A, Li M, Warren CM, de Tombe PP, Wang Y, Solaro RJ. p38-MAPK induced dephosphorylation of alpha-tropomyosin is associated with depression of myocardial sarcomeric tension and ATPase activity. Circ Res 2007; 100:408-15. [PMID: 17234967 DOI: 10.1161/01.res.0000258116.60404.ad] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Our objective in work presented here was to understand the mechanisms by which activated p38alpha MAPK depresses myocardial contractility. To test the hypothesis that activation of p38 MAPK directly influences sarcomeric function, we used transgenic mouse models with hearts in which p38 MAPK was constitutively turned on by an upstream activator (MKK6bE). These hearts demonstrated a significant depression in ejection fraction after induction of the transgene. We also studied hearts of mice expressing a dominant negative p38alpha MAPK. Simultaneous determination of tension and ATPase activity of detergent-skinned fiber bundles from left ventricular papillary muscle demonstrated a significant inhibition of both maximum tension and ATPase activity in the transgenic-MKK6bE hearts. Fibers from hearts expressing dominant negative p38alpha MAPK demonstrated no significant change in tension or ATPase activity. There were no significant changes in phosphorylation level of troponin-T3 and troponin-T4, or myosin light chain 2. However, compared with controls, there was a significant depression in levels of phosphorylation of alpha-tropomyosin and troponin I in fiber bundles from transgenic-MKK6bE hearts, but not from dominant negative p38alpha MAPK hearts. Our experiments also showed that p38alpha MAPK colocalizes with alpha-actinin at the Z-disc and complexes with protein phosphatases (PP2alpha, PP2beta). These data are the first to indicate that chronic activation of p38alpha MAPK directly depresses sarcomeric function in association with decreased phosphorylation of alpha-tropomyosin.
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Affiliation(s)
- Susan Vahebi
- Department of Physiology and Biophysics, Center for Cardiovascular Research, College of Medicine, University of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612-7342, USA
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