Effects of Phosphorylation and Mutation R145G on Human Cardiac Troponin I Function

Deng, Yi; Schmidtmann, Anja; Redlich, Alexander; Westerdorf, Barbara; Jaquet, Kornélia; Thieleczek, Rolf

doi:10.1021/bi0115232

Cited by 67 publications

(83 citation statements)

References 34 publications

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“…In addition, we have demonstrated that the Ca 2ϩ sensitivity of E99K actin-containing thin filaments was uncoupled from the PKA-dependent phosphorylation of troponin I. Uncoupling has been reported with other HCM-or DCM-causing mutations in thin filament proteins (16,28,46), and in DCM it seems to be the only consistent effect of disease-causing mutations (21). In contrast, HCM mutations are always associated with higher myofibrillar Ca 2ϩ sensitivity.…”

Section: Actc E99k Mouse Model Of Hcm-we Developed Thementioning

confidence: 60%

“…Uncoupling was previously reported in the TNNTI3 R145G mutation (46) and the TNNC1 L29Q mutation (40) that cause HCM but also in DCM mutations (ACTC E361G, TNNC1 G149D, and TPM1 E40K (16,21,28)) and in troponin from human myectomy samples (56). Thus, it appears that uncoupling may be a default consequence of structural perturbations.…”

Section: Actc E99k Mouse Model Of Hcm-we Developed Thementioning

confidence: 70%

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Molecular Mechanism of the E99K Mutation in Cardiac Actin (ACTC Gene) That Causes Apical Hypertrophy in Man and Mouse

Song

Dyer

Stuckey

et al. 2011

Journal of Biological Chemistry

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We generated a transgenic mouse model expressing the apical hypertrophic cardiomyopathy-causing mutation ACTC E99K at 50% of total heart actin and compared it with actin from patients carrying the same mutation. The actin mutation caused a higher Ca 2؉ sensitivity in reconstituted thin filaments measured by in vitro motility assay (2.3-fold for mice and 1.3-fold for humans) and in skinned papillary muscle. The mutation also abolished the change in Ca 2؉ sensitivity normally linked to troponin I phosphorylation. MyBP-C and troponin I phosphorylation levels were the same as controls in transgenic mice and human carrier heart samples. ACTC E99K mice exhibited a high death rate between 28 and 45 days (48% females and 22% males). At 21 weeks, the hearts of the male survivors had enlarged atria, increased interstitial fibrosis, and sarcomere disarray. MRI showed hypertrophy, predominantly at the apex of the heart. End-diastolic volume and end-diastolic pressure were increased, and relaxation rates were reduced compared with nontransgenic littermates. End-systolic pressures and volumes were unaltered. ECG abnormalities were present, and the contractile response to ␤-adrenergic stimulation was much reduced. Older mice (29-week-old females and 38-week-old males) developed dilated cardiomyopathy with increased end-systolic volume and continuing increased end-diastolic pressure and slower contraction and relaxation rates. ECG showed atrial flutter and frequent atrial ectopic beats at rest in some ACTC E99K mice. We propose that the ACTC E99K mutation causes higher myofibrillar Ca 2؉ sensitivity that is responsible for the sudden cardiac death, apical hypertrophy, and subsequent development of heart failure in humans and mice.

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Section: Actc E99k Mouse Model Of Hcm-we Developed Thementioning

confidence: 60%

Section: Actc E99k Mouse Model Of Hcm-we Developed Thementioning

confidence: 70%

Molecular Mechanism of the E99K Mutation in Cardiac Actin (ACTC Gene) That Causes Apical Hypertrophy in Man and Mouse

Song

Dyer

Stuckey

et al. 2011

Journal of Biological Chemistry

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“…A recent report by Deng et al (46) showed that the TnI R145G mutation renders the actomyosin system at maximum Ca 2ϩ activation insensitive to protein kinase A phosphorylation suggesting that muscles containing this TnI mutation might have an altered response to this intracellular phosphorylation pathway.…”

Section: Discussionmentioning

confidence: 99%

Functional Analysis of a Troponin I (R145G) Mutation Associated with Familial Hypertrophic Cardiomyopathy

Lang¹,

Gomes²,

Zhao³

et al. 2002

Journal of Biological Chemistry

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Familial hypertrophic cardiomyopathy has been associated with several mutations in the gene encoding human cardiac troponin I (HCTnI). A missense mutation in the inhibitory region of TnI replaces an arginine residue at position 145 with a glycine and cosegregates with the disease. Results from several assays indicate that the inhibitory function of HCTnI R145G is significantly reduced. When HCTnI R145G was incorporated into whole troponin, Tn R145G (HCTnT⅐HCTnI R145G ⅐HCTnC), only partial inhibition of the actin-tropomyosin-myosin ATPase activity was observed in the absence of Ca 2؉ compared with wild type Tn (HCTnT⅐HCTnI⅐HCTnC). Maximal activation of actin-tropomyosin-myosin ATPase in the presence of Ca 2؉ was also decreased in Tn R145G when compared with Tn. Using skinned cardiac muscle fibers, we determined that in comparison with the wild type complex 1) the complex containing HCTnI R145G only inhibited 84% of Ca 2؉ -unregulated force, 2) the recovery of Ca 2؉ -activated force was decreased, and 3) there was a significant increase in the Ca 2؉ sensitivity of force development. Computer modeling of troponin C and I variables predicts that the primary defect in TnI caused by these mutations would lead to diastolic dysfunction. These results suggest that severe diastolic dysfunction and somewhat decreased contractility would be prominent clinical features and that hypertrophy could arise as a compensatory mechanism. Familial hypertrophic cardiomyopathy (FHC)1 has been linked to mutations in genes of nine different sarcomeric proteins. These mutations have been found in the genes for ␣-myosin heavy chain (1), cardiac myosin essential light chain and cardiac myosin regulatory light chain (2), ␣-tropomyosin, cardiac troponin T (TnT) (3), cardiac myosin-binding protein C (4, 5), troponin I (TnI) (6), ␣-actin (7), as well as titin (8), and possibly troponin C (TnC) (9). This disease has recently gained significant attention due to several highly publicized reports of sudden death and fainting spells in young athletes who were asymptomatic and otherwise healthy individuals. In general, patients with FHC demonstrate an increase in heart muscle mass and sometimes an irregular echocardiogram (10). Kimura et al. (6) reported five missense mutations in TnI, R145G, R145Q, R162W, G203S, and K206Q, that cosegregate with FHC (Fig. 1). Three other TnI FHC mutants (S199N, Lys-183 deletion, and an exon 8 deletion mutant encompassing the stop codon of the cardiac TnI gene) have recently been discovered (11, 12). Functionally TnI is the inhibitory subunit of the troponin (Tn) complex that controls the interaction between actin and myosin in a Ca 2ϩ -dependent manner (13-15). Studies using proteolytic fragments of fast skeletal TnI identified the central TnI sequence (residues 96 -116) as being responsible for its inhibitory activity. Residues 104 -115 of fast skeletal TnI (comparable to residues 136 -147 in cardiac TnI) formed the minimum sequence necessary for inhibition of muscle contraction (16 -19). Two of these mutations occ...

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“…These studies suggest that the R145G mutation prevents the inhibitory region of cTnI from properly interacting with actin-tropomyosin in the thin filament. In addition, cTnI carrying the R145G mutation is insensitive to phosphorylation of the two adjacent Ser residues in the cardiac N-extension [52]. Thus, replacement of a basic Arg residue in the inhibitory region of cTnI with Gly appears to disrupt the effect of PKA phosphorylation at Ser-23/Ser-24 in the cardiac N-extension.…”

Section: Molecular Mechanisms Of the Effects Of Ctni Phosphorylation mentioning

confidence: 99%

The unique functions of cardiac troponin I in the control of cardiac muscle contraction and relaxation

Solaro

Rosevear

Kobayashi

2008

Biochemical and Biophysical Research Communications

105

119

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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. KeywordsCardiac; Sarcomeres; Adrenergic stimulation; Mechanics; Kinases; Phosphatases In the time since the troponin discovery and naming by the laboratory of Setsuro Ebashi [1], there has been a constant stream of evidence indicating the substantial role of modifications in cardiac troponin (cTn) as a critical control element in the body's response to physiological stressors such as the hemodynamic demands of exercise. It is now widely recognized that regulatory processes at the level of the sarcomeres and the hetero-trimeric Tn complex involve not only the reception of Ca 2+ by cTnC, but also transduction of this Ca-binding signal by cTnI and cTnT [2,3]. Multiple interactions of cTnI and cTnT with actin and tropomyosin (Tm) control the number and kinetics of interactions of cross-bridges with the thin filament. Our focus here on cTnI serves to highlight the significant impact of modifications in the function of Tn in working cardiac myocytes and in the integrated physiological responses to exercise, which we have reviewed previously [4,5]. Evidence summarized below indicates that phosphorylation of cTnI by adrenergic signaling cascades is an indispensable control mechanism in matching cardiac output to venous return and myocyte dynamics to heart rate. Specific modifications in troponin I affect the dynamics and intensity of the heart beatElucidation of the function of an N-terminal extension of ~30 amino acids with sites (Ser-23, Ser-24) of phosphorylation by protein kinase A (PKA), not present in the fast skeletal (fsTnI) or slow skeletal isoforms (ssTnI), provided the first evidence that cTnI may have a special role * Corresponding

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Effects of Phosphorylation and Mutation R145G on Human Cardiac Troponin I Function

Cited by 67 publications

References 34 publications

Molecular Mechanism of the E99K Mutation in Cardiac Actin (ACTC Gene) That Causes Apical Hypertrophy in Man and Mouse

Molecular Mechanism of the E99K Mutation in Cardiac Actin (ACTC Gene) That Causes Apical Hypertrophy in Man and Mouse

Functional Analysis of a Troponin I (R145G) Mutation Associated with Familial Hypertrophic Cardiomyopathy

The unique functions of cardiac troponin I in the control of cardiac muscle contraction and relaxation

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