Skeletal troponin C reduces contractile sensitivity to acidosis in cardiac myocytes from transgenic mice.

Protooncogenes such as c-myc have been implicated in the transduction of growth signals in the cardiac myocyte. We examined whether increases in c-myc expression occur in murine heart in vivo as a generalized response to the pharmacological stimulation of myocyte growth. Both triiodothyronine (T3) and the beta-adrenergic agonist isoproterenol were demonstrated to induce a rapid and transient increase in cardiac c-myc mRNA abundance, which preceded an increase in cardiac mass. We then examined whether myocyte growth could be modulated by selectively altering cardiac c-myc expression. The model system used was a strain of transgenic mice exhibiting a 20-fold increase in cardiac c-myc expression. Although in nontransgenic mice the administration of T3 and isoproterenol resulted in similar increases in cardiac mass, in transgenic mice the degree of myocardial growth induced with T3 was significantly greater than that induced with isoproterenol (P less than 0.001). This study demonstrates that increasing the basal expression of c-myc in cardiac myocytes alters the growth response of the heart in vivo to certain hypertrophic stimuli and implicates the c-myc protooncogene in the transduction of selective hypertrophic growth signals in differentiated cardiac myocytes.

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Increasing mammalian cardiomyocyte contractility with residues identified in trout troponin C

Physiological Genomics ◽

10.1152/physiolgenomics.00007.2005 ◽

2005 ◽

Vol 22 (1) ◽

pp. 1-7 ◽

Cited By ~ 22

Author(s):

Todd E. Gillis ◽

Bo Liang ◽

Franca Chung ◽

Glen F. Tibbits

Keyword(s):

Amino Acid ◽

Cardiac Myocytes ◽

Cardiac Troponin ◽

Troponin C ◽

Force Generation ◽

Wild Type ◽

Cardiac Troponin C ◽

Cardiomyocyte Contractility

The Ca2+ sensitivity of force generation in trout cardiac myocytes is significantly greater than that from mammalian hearts. One mechanism that we have suggested to be responsible, at least in part, for this high Ca2+ sensitivity is the isoform of cardiac troponin C (cTnC) found in trout hearts (ScTnC), which has greater than twice the Ca2+ affinity of mammalian cTnC (McTnC). Here, through a series of mutations, the residues in ScTnC responsible for its high Ca2+ affinity have been identified as being Asn2, Ile28, Gln29, and Asp30. When these residues in McTnC were mutated to the trout-equivalent amino acid, the Ca2+ affinity of the molecule, determined by monitoring the fluorescence of a Trp inserted for a Phe at residue 27, is comparable to that of ScTnC. To determine how a McTnC mutant containing Asn2, Ile28, Gln29, and Asp30 (NIQD McTnC) affects the Ca2+ sensitivity of force generation, endogenous cTnC in single, chemically skinned rabbit cardiomyocytes was replaced with either wild-type McTnC or NIQD McTnC. Our results demonstrate that the cardiomyocytes containing NIQD McTnC were approximately twice as sensitive to Ca2+, illustrating that a McTnC mutant with similar Ca2+ affinity as ScTnC can be used to sensitize mammalian cardiac myocytes to Ca2+.

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Beta-MHC and SMLC1 transgene induction in overloaded skeletal muscle of transgenic mice

AJP Cell Physiology ◽

10.1152/ajpcell.1996.270.4.c1111 ◽

1996 ◽

Vol 270 (4) ◽

pp. C1111-C1121 ◽

Cited By ~ 15

Author(s):

J. L. Wiedenman ◽

I. Rivera-Rivera ◽

D. Vyas ◽

G. Tsika ◽

L. Gao ◽

...

Keyword(s):

Transgenic Mice ◽

Troponin C ◽

Type I ◽

Initial Attempt ◽

Specific Expression ◽

Slow Type ◽

Transgenic Lines ◽

Fast Twitch Muscle ◽

Mechanical Overload

The hypertrophic responses of white fast-twitch muscle to mechanical overload has been investigated using transgenic mice. After 7 wk of overload, endogenous beta-myosin heavy chain (MHC) and slow myosin light chain 1 and 2 (SMLC1, SMLC2) protein were increased in the overloaded plantaris (OP) muscle compared with sham-operated control plantaris (CP)muscle. Concurrently, the levels of endogenous beta-MHC, SMLC1, SMLC2, and cardiac/slow troponin C (CTnC) mRNA transcripts were significantly increased in OP muscles, whereas skeletal troponin C (sTnC) mRNA transcript levels decreased. As an initial attempt to locate DNA sequence(s) that governs beta-MHC induction in response to mechanical overload, multiple independent transgenic lines harboring four different human beta-MHC transgenes (beta 1286, beta 988, beta 450, beta 141) were generated. Except for transgene beta 141, muscle-specific expression and induction (3- to 22-fold) in OP muscles were observed by measuring chloramphenicol acetyltransferase activity (CAT assay). Induction of a SMLC1 transgene (3920SMLC1) in OP muscles was also observed. Collectively, these in vivo data provide evidence that 1) a mechanical overload inducible element(s) is located between nucleotides -450 and +120 of the human beta-MHC transgene, 2) 3,900 bp of 5' sequence is sufficient to confer mechanical overload induction of a SMLC1 transgene, and 3) the increased expression of slow/type I isomyosin (beta-MHC, SMLC1, SMLC2) in response to mechanical overload is regulated, in part, transcriptionally.

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beta-MHC transgene expression in suspended and mechanically overloaded/suspended soleus muscle of transgenic mice

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1997.272.5.r1552 ◽

1997 ◽

Vol 272 (5) ◽

pp. R1552-R1561 ◽

Cited By ~ 22

Author(s):

J. J. McCarthy ◽

A. M. Fox ◽

G. L. Tsika ◽

L. Gao ◽

R. W. Tsika

Keyword(s):

Transgenic Mice ◽

Soleus Muscle ◽

Transgene Expression ◽

Specific Activity ◽

Fiber Type ◽

Weight Bearing ◽

Troponin C ◽

Hindlimb Suspension ◽

Regulatory Sequences ◽

Type I

Non-weight-bearing (NWB) activity [space flight and hindlimb suspension (HS)] results in the loss of soleus muscle mass, a slow-to-fast fiber-type conversion, and decreased beta-myosin heavy chain (beta-MHC) protein and mRNA expression. To identify beta-MHC promoter sequences required for decreased beta-MHC expression in response to HS, we have modified an existing noninvasive hindlimb unweighting model to accommodate the use of (transgenic) mice. After 2 wk of HS, body and muscle (soleus > gastrocnemius > plantaris) weights were decreased as was the proportion of histochemically classified type I fibers in HS soleus muscle. Northern blot analysis revealed decreases in endogenous mRNA representing beta-MHC, slow myosin light chain 1 and 2, and cardiac/slow troponin C, whereas those representing skeletal troponin C, muscle creatine kinase, and glyceraldehyde-3-phosphate dehydrogenase increased. Protein extracts prepared from HS soleus (SS) muscle of mice harboring transgenes comprised of 5.6 or 0.6 kilobase of wild type (wt) mouse beta-MHC promoter (beta 5.6 wt, beta 0.6wt) and those carrying the simultaneous mutation (mut) of the MCAT, C-rich, and beta e3 subregions (beta 5.6mut3, beta 0.6mut3) revealed decreases in chloramphenicol acetyltransferase (CAT) specific activity relative to respective controls. Decreased CAT mRNA was observed for transgene beta 5.6mut3, line 85. Two weeks of the simultaneous imposition of mechanical overload (synergist ablation) and HS (MOV/HS) countermanded the loss in absolute and normalized SS weight but did not decrease beta 0.6wt transgene expression. These transgenic results demonstrate that regulatory sequences within a 600-base pair beta-MHC promoter are sufficient to direct decreased transcription of beta-MHC transgenes after 2 wk of HS.

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Phospholamban-to-SERCA2 ratio controls the force-frequency relationship

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.3.h779 ◽

1999 ◽

Vol 276 (3) ◽

pp. H779-H785 ◽

Cited By ~ 17

Author(s):

Markus Meyer ◽

Wolfgang F. Bluhm ◽

Huaping He ◽

Steven R. Post ◽

Frank J. Giordano ◽

...

Keyword(s):

Sarcoplasmic Reticulum ◽

Transgenic Mice ◽

Cardiac Myocytes ◽

Cardiac Contractility ◽

Adult Rabbit ◽

Force Frequency ◽

Papillary Muscles ◽

Inhibitory Protein ◽

Frequency Relationship ◽

Myocyte Contractility

The force-frequency relationship (FFR) describes the frequency-dependent potentiation of cardiac contractility. The interaction of the sarcoplasmic reticulum Ca2+-adenosinetriphosphatase (SERCA2) with its inhibitory protein phospholamban (PLB) might be involved in the control of the FFR. The FFR was analyzed in two systems in which the PLB-to-SERCA2 ratio was modulated. Adult rabbit cardiac myocytes were transduced with adenovirus encoding for SERCA2, PLB, and β-galactosidase (control). After 3 days, the relative PLB/SERCA2 values were significantly different between groups (SERCA2, 0.5; control, 1.0; PLB, 4.5). SERCA2 overexpression shortened relaxation by 23% relative to control, whereas PLB prolonged relaxation by 39% and reduced contractility by 47% (0.1 Hz). When the stimulation frequency was increased to 1.5 Hz, myocyte contractility was increased by 30% in control myocytes. PLB-overexpressing myocytes showed an augmented positive FFR (+78%), whereas SERCA2-transduced myocytes displayed a negative FFR (−15%). A more negative FFR was also found in papillary muscles from SERCA2 transgenic mice. These findings demonstrate that the ratio of phospholamban to SERCA2 is an important component in the control of the FFR.

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The GATA-4 transcription factor transactivates the cardiac muscle-specific troponin C promoter-enhancer in nonmuscle cells.

Molecular and Cellular Biology ◽

10.1128/mcb.14.11.7517 ◽

1994 ◽

Vol 14 (11) ◽

pp. 7517-7526 ◽

Cited By ~ 133

Author(s):

H S Ip ◽

D B Wilson ◽

M Heikinheimo ◽

Z Tang ◽

C N Ting ◽

...

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Transcription Factors ◽

Cardiac Muscle ◽

Binding Site ◽

Cardiac Myocytes ◽

Specific Binding ◽

Troponin C ◽

Specific Gene ◽

Cardiac Muscle Cells

The unique contractile phenotype of cardiac myocytes is determined by the expression of a set of cardiac muscle-specific genes. By analogy to other mammalian developmental systems, it is likely that the coordinate expression of cardiac genes is controlled by lineage-specific transcription factors that interact with promoter and enhancer elements in the transcriptional regulatory regions of these genes. Although previous reports have identified several cardiac muscle-specific transcriptional elements, relatively little is known about the lineage-specific transcription factors that regulate these elements. In this report, we demonstrate that the slow/cardiac muscle-specific troponin C (cTnC) enhancer contains a specific binding site for the lineage-restricted zinc finger transcription factor GATA-4. This GATA-4-binding site is required for enhancer activity in primary cardiac myocytes. Moreover, the cTnC enhancer can be transactivated by overexpression of GATA-4 in non-cardiac muscle cells such as NIH 3T3 cells. In situ hybridization studies demonstrate that GATA-4 and cTnC have overlapping patterns of expression in the hearts of postimplantation mouse embryos and that GATA-4 gene expression precedes cTnC expression. Indirect immunofluorescence reveals GATA-4 expression in cultured cardiac myocytes from neonatal rats. Taken together, these results are consistent with a model in which GATA-4 functions to direct tissue-specific gene expression during mammalian cardiac development.

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Improved calcium imaging in transgenic mice expressing a troponin C–based biosensor

Nature Methods ◽

10.1038/nmeth1009 ◽

2007 ◽

Vol 4 (2) ◽

pp. 127-129 ◽

Cited By ~ 135

Author(s):

Nicola Heim ◽

Olga Garaschuk ◽

Michael W Friedrich ◽

Marco Mank ◽

Ruxandra I Milos ◽

...

Keyword(s):

Transgenic Mice ◽

Calcium Imaging ◽

Troponin C

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2me‐SATP activates P2X4R and induces a secondary increase of Na+ pump and Na+/Ca++ currents in cardiac myocytes of P2X4R overexpression transgenic mice

The FASEB Journal ◽

10.1096/fasebj.26.1_supplement.1048.9 ◽

2012 ◽

Vol 26 (S1) ◽

Author(s):

Jian Bing Shen ◽

Achilles J Pappano ◽

Bruce T Liang

Keyword(s):

Transgenic Mice ◽

Cardiac Myocytes ◽

Na Pump ◽

Ca Currents

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The GATA-4 transcription factor transactivates the cardiac muscle-specific troponin C promoter-enhancer in nonmuscle cells

Molecular and Cellular Biology ◽

10.1128/mcb.14.11.7517-7526.1994 ◽

1994 ◽

Vol 14 (11) ◽

pp. 7517-7526

Author(s):

H S Ip ◽

D B Wilson ◽

M Heikinheimo ◽

Z Tang ◽

C N Ting ◽

...

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Transcription Factors ◽

Cardiac Muscle ◽

Binding Site ◽

Cardiac Myocytes ◽

Specific Binding ◽

Troponin C ◽

Specific Gene ◽

Cardiac Muscle Cells

The unique contractile phenotype of cardiac myocytes is determined by the expression of a set of cardiac muscle-specific genes. By analogy to other mammalian developmental systems, it is likely that the coordinate expression of cardiac genes is controlled by lineage-specific transcription factors that interact with promoter and enhancer elements in the transcriptional regulatory regions of these genes. Although previous reports have identified several cardiac muscle-specific transcriptional elements, relatively little is known about the lineage-specific transcription factors that regulate these elements. In this report, we demonstrate that the slow/cardiac muscle-specific troponin C (cTnC) enhancer contains a specific binding site for the lineage-restricted zinc finger transcription factor GATA-4. This GATA-4-binding site is required for enhancer activity in primary cardiac myocytes. Moreover, the cTnC enhancer can be transactivated by overexpression of GATA-4 in non-cardiac muscle cells such as NIH 3T3 cells. In situ hybridization studies demonstrate that GATA-4 and cTnC have overlapping patterns of expression in the hearts of postimplantation mouse embryos and that GATA-4 gene expression precedes cTnC expression. Indirect immunofluorescence reveals GATA-4 expression in cultured cardiac myocytes from neonatal rats. Taken together, these results are consistent with a model in which GATA-4 functions to direct tissue-specific gene expression during mammalian cardiac development.

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