An enhancer core element mediates stimulation of the rat beta-myosin heavy chain promoter by an alpha 1-adrenergic agonist and activated beta-protein kinase C in hypertrophy of cardiac myocytes

miR-31-5p suppresses myocardial hypertrophy by targeting Nfatc2ip

Cardiac hypertrophy, worldwide known as an adaptive functional compensatory state of myocardial stress, is mainly believed to proceed to severe heart diseases, even to sudden death. Emerging studies have explored the microRNA alteration during hypertrophy. However, the mechanisms of microRNAs involved in cardiac hypertrophy are still uncertain. We studied young rats to establish abdominal aorta coarctation (AAC) for 4 weeks. With the significant downregulated cardiac function and upregulated hypertrophic biomarkers, AAC-induced rats showed enlarged myocardiocytes and alterations in microRNAs, especially downregulated miR-31-5p. miR-31-5p targets the 3'UTR of Nfatc2ip and inhibits myocardial hypertrophy in vitro and in vivo. Furthermore, we verified that Nfatc2ip is necessary and sufficient for cardiac hypertrophy in neonatal rat cardiomyocytes. Moreover, we found miR-31-5p inhibited the colocalization of Nfatc2ip and hypertrophic gene β-Mhc. Luciferase assay and ChiP-qPCR test demonstrated that Nfatc2ip binded to the core-promoter of β-Mhc and enhanced its transcriptional activity. Above all, our study found a new pathway, mir-31-5p/Nfatc2ip/β-Mhc, which is involved in cardiac hypertrophy, suggesting a potential target for intervention of cardiac hypertrophy.

Vestigial-like 2 contributes to normal muscle fiber type distribution in mice

Skeletal muscle is composed of heterogeneous populations of myofibers that are classified as slow- and fast-twitch fibers. The muscle fiber-type is regulated in a coordinated fashion by multiple genes, including transcriptional factors and microRNAs (miRNAs). However, players involved in this regulation are not fully elucidated. One of the members of the Vestigial-like factors, Vgll2, is thought to play a pivotal role in TEA domain (TEAD) transcription factor-mediated muscle-specific gene expression because of its restricted expression in skeletal muscles of adult mice. Here, we generated Vgll2 null mice and investigated Vgll2 function in adult skeletal muscles. These mice presented an increased number of fast-twitch type IIb fibers and exhibited a down-regulation of slow type I myosin heavy chain (MyHC) gene, Myh7, which resulted in exercise intolerance. In accordance with the decrease in Myh7, down-regulation of miR-208b, encoded within Myh7 gene and up-regulation of targets of miR-208b, Sox6, Sp3, and Purβ, were observed in Vgll2 deficient mice. Moreover, we detected the physical interaction between Vgll2 and TEAD1/4 in neonatal skeletal muscles. These results suggest that Vgll2 may be both directly and indirectly involved in the programing of slow muscle fibers through the formation of the Vgll2-TEAD complex.

Alpha-1-adrenergic receptors in heart failure: the adaptive arm of the cardiac response to chronic catecholamine stimulation

Alpha-1-adrenergic receptors (ARs) are G protein-coupled receptors activated by catecholamines. The alpha-1A and alpha-1B subtypes are expressed in mouse and human myocardium, whereas the alpha-1D protein is found only in coronary arteries. There are far fewer alpha-1-ARs than beta-ARs in the nonfailing heart, but their abundance is maintained or increased in the setting of heart failure, which is characterized by pronounced chronic elevation of catecholamines and beta-AR dysfunction. Decades of evidence from gain and loss-of-function studies in isolated cardiac myocytes and numerous animal models demonstrate important adaptive functions for cardiac alpha-1-ARs to include physiological hypertrophy, positive inotropy, ischemic preconditioning, and protection from cell death. Clinical trial data indicate that blocking alpha-1-ARs is associated with incident heart failure in patients with hypertension. Collectively, these findings suggest that alpha-1-AR activation might mitigate the well-recognized toxic effects of beta-ARs in the hyperadrenergic setting of chronic heart failure. Thus, exogenous cardioselective activation of alpha-1-ARs might represent a novel and viable approach to the treatment of heart failure.

Essential role of TEA domain transcription factors in the negative regulation of the MYH 7 gene by thyroid hormone and its receptors

MYH7 (also referred to as cardiac myosin heavy chain β) gene expression is known to be repressed by thyroid hormone (T3). However, the molecular mechanism by which T3 inhibits the transcription of its target genes (negative regulation) remains to be clarified, whereas those of transcriptional activation by T3 (positive regulation) have been elucidated in detail. Two MCAT (muscle C, A, and T) sites and an A/T-rich region in the MYH7 gene have been shown to play a critical role in the expression of this gene and are known to be recognized by the TEAD/TEF family of transcription factors (TEADs). Using a reconstitution system with CV-1 cells, which has been utilized in the analysis of positive as well as negative regulation, we demonstrate that both T3 receptor (TR) β1 and α1 inhibit TEAD-dependent activation of the MYH7 promoter in a T3 dose-dependent manner. TRβ1 bound with GC-1, a TRβ-selective T3 analog, also repressed TEAD-induced activity. Although T3-dependent inhibition required the DNA-binding domain (DBD) of TRβ1, it remained after the putative negative T3-responsive elements were mutated. A co-immunoprecipitation study demonstrated the in vivo association of TRβ1 with TEAD-1, and the interaction surfaces were mapped to the DBD of the TRβ1 and TEA domains of TEAD-1, both of which are highly conserved among TRs and TEADs, respectively. The importance of TEADs in MYH7 expression was also validated with RNA interference using rat embryonic cardiomyocyte H9c2 cells. These results indicate that T3-bound TRs interfere with transactivation by TEADs via protein-protein interactions, resulting in the negative regulation of MYH7 promoter activity.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

Genome-wide computational prediction and analysis of core promoter elements across plant monocots and dicots

Transcription initiation, essential to gene expression regulation, involves recruitment of basal transcription factors to the core promoter elements (CPEs). The distribution of currently known CPEs across plant genomes is largely unknown. This is the first large scale genome-wide report on the computational prediction of CPEs across eight plant genomes to help better understand the transcription initiation complex assembly. The distribution of thirteen known CPEs across four monocots (Brachypodium distachyon, Oryza sativa ssp. japonica, Sorghum bicolor, Zea mays) and four dicots (Arabidopsis thaliana, Populus trichocarpa, Vitis vinifera, Glycine max) reveals the structural organization of the core promoter in relation to the TATA-box as well as with respect to other CPEs. The distribution of known CPE motifs with respect to transcription start site (TSS) exhibited positional conservation within monocots and dicots with slight differences across all eight genomes. Further, a more refined subset of annotated genes based on orthologs of the model monocot (O. sativa ssp. japonica) and dicot (A. thaliana) genomes supported the positional distribution of these thirteen known CPEs. DNA free energy profiles provided evidence that the structural properties of promoter regions are distinctly different from that of the non-regulatory genome sequence. It also showed that monocot core promoters have lower DNA free energy than dicot core promoters. The comparison of monocot and dicot promoter sequences highlights both the similarities and differences in the core promoter architecture irrespective of the species-specific nucleotide bias. This study will be useful for future work related to genome annotation projects and can inspire research efforts aimed to better understand regulatory mechanisms of transcription.

Diversity of the protein kinase C gene family Implications for cardiovascular disease

All eukaryotic cells are capable of responding to a changing intracellular environment and to extracellular stimuli. These functional responses are highly regulated by diverse means; one of the most common mechanisms of regulation requires the covalent phosphorylation of intracellular proteins, which when phosphorylated, mediate many functional events. The general class of enzymes that catalyzes the phosphorylation of effectors (substrates), the protein kinases, may be divided into two broad categories, depending on whether they phosphorylate serine and threonine residues or tyrosine residues. Evidence has accumulated that implicates abnormal activation of protein kinase C (PKC), which is one family of serine-threonine protein kinases, in cells and tissues from patients or models of cardiovascular disease. In this review, we present the molecular and biochemical basis for the diversity of the PKC family, and briefly summarize the evidence that PKC is implicated in cardiovascular pathology and the potential therapeutic implications and approaches.

The role of transcription enhancer factors in cardiovascular biology

The transcriptional enhancer factor (TEF) multigene family is primarily functional in muscle-specific genes through binding to MCAT elements that activate or repress transcription of many genes in response to physiological and pathological stimuli. Among the TEF family, TEF-1, RTEF-1, and DTEF-1 are critical regulators of cardiac and smooth muscle-specific genes during cardiovascular development and cardiac disorders including cardiac hypertrophy. Emerging evidence suggests that in addition to functioning as muscle-specific transcription factors, members of the TEF family may be key mediators of gene expression induced by hypoxia in endothelial cells by virtue of its multidomain organization, potential for post-translational modifications, and interactions with numerous transcription factors, which represent a cell-selective control mediator of nuclear signaling. We review the recent literature demonstrating the involvement of the TEF family of transcription factors in the regulation of differential gene expression in cardiovascular physiology and pathology.

Dysfunctional ryanodine receptor and cardiac hypertrophy: role of signaling molecules

Mice with three amino acid mutations in the calmodulin binding domain of type-2 ryanodine receptor ion channel (Ryr2(ADA/ADA) mice) have impaired intracellular Ca(2+) handling and cardiac hypertrophy with death at an early age. In this report, the role of signaling molecules implicated in cardiac hypertrophy of Ryr2(ADA/ADA) mice was investigated. Calcineurin A-β (CNA-β) and nuclear factor of activated T cell (NFAT) signaling were monitored in mice carrying either luciferase transgene driven by NFAT-dependent promoter or knockout of CNA-β. NFAT transcriptional activity in Ryr2(ADA/ADA) hearts was not markedly upregulated at embryonic day 16.5 compared with wild-type but significantly increased at postnatal days 1 and 10. Ablation of CNA-β extended the life span of Ryr2(ADA/ADA) mice and enhanced cardiac function without improving sarcoplasmic reticulum Ca(2+) handling or suppressing the expression of genes implicated in cardiac hypertrophy. Embryonic day 16.5 Ryr2(ADA/ADA) mice had normal heart weights with no major changes in Akt1 and class II histone deacetylase phosphorylation and myocyte enhancer factor-2 activity. In contrast, phosphorylation levels of Erk1/2, p90 ribosomal S6 kinases (p90RSKs), and GSK-3β were increased in hearts of embryonic day 16.5 homozygous mutant mice. The results indicate that an impaired calmodulin regulation of RyR2 was neither associated with an altered CNA-β/NFAT, class II histone deacetylase (HDAC)/MEF2, nor Akt signaling in embryonic day 16.5 hearts; rather increased Erk1/2 and p90RSK phosphorylation levels likely leading to reduced GSK-3β activity were found to precede development of cardiac hypertrophy in mice expressing dysfunctional ryanodine receptor ion channel.

TEAD-1 overexpression in the mouse heart promotes an age-dependent heart dysfunction

TEA domain transcription factor-1 (TEAD-1) is essential for proper heart development and is implicated in cardiac specific gene expression and the hypertrophic response of primary cardiomyocytes to hormonal and mechanical stimuli, and its activity increases in the pressure-overloaded hypertrophied rat heart. To investigate whether TEAD-1 is an in vivo modulator of cardiac specific gene expression and hypertrophy, we developed transgenic mice expressing hemagglutinin-tagged TEAD-1 under the control of the muscle creatine kinase promoter. We show that a sustained increase in TEAD-1 protein leads to an age-dependent dysfunction. Magnetic resonance imaging revealed decreases in cardiac output, stroke volume, ejection fraction, and fractional shortening. Isolated TEAD-1 hearts revealed decreased left ventricular power output that correlated with increased betaMyHC protein. Histological analysis showed altered alignment of cardiomyocytes, septal wall thickening, and fibrosis, although electrocardiography displayed a left axis shift of mean electrical axis. Transcripts representing most members of the fetal heart gene program remained elevated from fetal to adult life. Western blot analyses revealed decreases in p-phospholamban, SERCA2a, p-CX43, p-GSK-3alpha/beta, nuclear beta-catenin, GATA4, NFATc3/c4, and increased NCX1, nuclear DYKR1A, and Pur alpha/beta protein. TEAD-1 mice did not display cardiac hypertrophy. TEAD-1 mice do not tolerate stress as they die over a 4-day period after surgical induction of pressure overload. These data provide the first in vivo evidence that increased TEAD-1 can induce characteristics of cardiac remodeling associated with cardiomyopathy and heart failure.

The transcriptional co-activator TAZ interacts differentially with transcriptional enhancer factor-1 (TEF-1) family members

Members of the highly related TEF-1 (transcriptional enhancer factor-1) family (also known as TEAD, for TEF-1, TEC1, ABAA domain) bind to MCAT (muscle C, A and T sites) and A/T-rich sites in promoters active in cardiac, skeletal and smooth muscle, placenta, and neural crest. TEF-1 activity is regulated by interactions with transcriptional co-factors [p160, TONDU (Vgl-1, Vestigial-like protein-1), Vgl-2 and YAP65 (Yes-associated protein 65 kDa)]. The strong transcriptional co-activator YAP65 interacts with all TEF-1 family members, and, since YAP65 is related to TAZ (transcriptional co-activator with PDZ-binding motif), we wanted to determine if TAZ also interacts with members of the TEF-1 family. In the present study, we show by GST (glutathione S-transferase) pull-down assays, by co-immunoprecipitation and by modified mammalian two-hybrid assays that TEF-1 interacts with TAZ in vitro and in vivo. Electrophoretic mobility-shift assays with purified TEF-1 and GST-TAZ fusion protein showed that TAZ interacts with TEF-1 bound to MCAT DNA. TAZ can interact with endogenous TEF-1 proteins, since exogenous TAZ activated MCAT-dependent reporter promoters. Like YAP65, TAZ interacted with all four TEF-1 family members. GST pull-down assays with increasing amounts of [35S]TEF-1 and [35S]RTEF-1 (related TEF-1) showed that TAZ interacts more efficiently with TEF-1 than with RTEF-1. This differential interaction also extended to the interaction of TEF-1 and RTEF-1 with TAZ in vivo, as assayed by a modified mammalian two-hybrid experiment. These data show that differential association of TEF-1 proteins with transcriptional co-activators may regulate the activity of TEF-1 family members.

Phosphoinositide 3-kinase Akt signaling pathway interacts with protein kinase Cbeta2 in the regulation of physiologic developmental hypertrophy and heart function

The phosphoinositide 3-kinase (PI3-kinase)-protein kinase B (Akt) signaling pathway is essential in the induction of physiological cardiac hypertrophy. In contrast, protein kinase C beta2 (PKCbeta2) is implicated in the development of pathological cardiac hypertrophy and heart failure. Thus far, no clear association has been demonstrated between these two pathways. In this study, we examined the potential interaction between the PI3-kinase and PKCbeta2 pathways by crossing transgenic mice with cardiac specific expression of PKCbeta2, constitutively active (ca) PI3-kinase, and dominant-negative (dn) PI3-kinase. In caPI3-kinase/PKCbeta2 and dnPI3-kinase/PKCbeta2 double-transgenic mice, the heart weight-to-body weight ratios and cardiomyocyte sizes were similar to those observed in caPI3-kinase and dnPI3-kinase transgenic mice, respectively, suggesting that the regulation of physiological developmental hypertrophy via modulation of cardiomyocyte size proceeds through the PI3-kinase pathway. In addition, we observed that caPI3-kinase/PKCbeta2 mice showed improved cardiac function while the function of dnPI3-kinase/PKCbeta2 mice was similar to that of the PKCbeta2 group. PKCbeta2 protein levels in both dnPI3-kinase/PKCbeta2 and PKCbeta2 mice were significantly upregulated. Interestingly, however, PKCbeta2 protein expression was significantly attenuated in caPI3-kinase/PKCbeta2 mice. PI3-kinase activity measured by Akt phosphorylation was not affected by PKCbeta2 overexpression. These data suggest a potential interaction between these two pathways in the heart, where PI3-kinase is predominantly responsible for the regulation of physiological developmental hypertrophy and may act as an upstream modulator of PKCbeta2 with the potential for rescuing the pathological cardiac dysfunction induced by overexpression of PKCbeta.

Inhibitory effect of D1-like and D3 dopamine receptors on norepinephrine-induced proliferation in vascular smooth muscle cells

The sympathetic nervous system plays an important role in the regulation of blood pressure. There is increasing evidence for positive and negative interactions between dopamine and adrenergic receptors; the activation of the alpha-adrenergic receptor induces vasoconstriction, whereas the activation of dopamine receptor induces vasorelaxation. We hypothesize that the D1-like receptor and/or D3 receptor also inhibit alpha1-adrenergic receptor-mediated proliferation in vascular smooth muscle cells (VSMCs). In this study, VSMC proliferation was determined by measuring [3H]thymidine incorporation, cell number, and uptake of 3-(4,5-dimethylthiazol-2-yl)-diphenyltetrazolium bromide (MTT). Norepinephrine increased VSMC number and MTT uptake, as well as [3H]thymidine incorporation via the alpha1-adrenergic receptor in aortic VSMCs from Sprague-Dawley rats. The proliferative effects of norepinephrine were attenuated by the activation of D1-like receptors or D3 receptors, although a D1-like receptor agonist, fenoldopam, and a D3 receptor agonist, PD-128907, by themselves, at low concentrations, had no effect on VSMC proliferation. Simultaneous stimulation of both D1-like and D3 receptors had an additive inhibitory effect. The inhibitory effect of D3 receptor was via protein kinase A, whereas the D1-like receptor effect was via protein kinase C-zeta. The interaction between alpha1-adrenergic and dopamine receptors, especially D1-like and D3 receptors in VSMCs, could be involved in the pathogenesis of hypertension.

Sox6 is required for normal fiber type differentiation of fetal skeletal muscle in mice

Sox6, a member of the Sox family of transcription factors, is highly expressed in skeletal muscle. Despite its abundant expression, the role of Sox6 in muscle development is not well understood. We hypothesize that, in fetal muscle, Sox6 functions as a repressor of slow fiber type-specific genes. In the wild-type mouse, differentiation of fast and slow fibers becomes apparent during late fetal stages (after approximately embryonic day 16). However, in the Sox6 null-p(100H) mutant mouse, all fetal muscle fibers maintain slow fiber characteristics, as evidenced by expression of the slow myosin heavy chain MyHC-beta. Knockdown of Sox6 expression in wild-type myotubes results in a significant increase in MyHC-beta expression, supporting our hypothesis. Analysis of the MyHC-beta promoter revealed a Sox consensus sequence that likely functions as a negative cis-regulatory element. Together, our results suggest that Sox6 plays a critical role in the fiber type differentiation of fetal skeletal muscle.

MCAT elements and the TEF-1 family of transcription factors in muscle development and disease

MCAT elements are located in the promoter-enhancer regions of cardiac, smooth, and skeletal muscle-specific genes including cardiac troponin T, beta-myosin heavy chain, smooth muscle alpha-actin, and skeletal alpha-actin, and play a key role in the regulation of these genes during muscle development and disease. The binding factors of MCAT elements are members of the transcriptional enhancer factor-1 (TEF-1) family. However, it has not been fully understood how these transcription factors confer cell-specific expression in muscle, because their expression patterns are relatively broad. Results of recent studies revealed multiple mechanisms whereby TEF-1 family members control MCAT element-dependent muscle-specific gene expression, including posttranslational modifications of TEF-1 family members, the presence of muscle-selective TEF-1 cofactors, and cell-selective control of TEF-1 accessibility to MCAT elements. In addition, of particular interest, recent studies regarding MCAT element-dependent transcription of the myocardin gene and the smooth muscle alpha-actin gene in muscle provide evidence for the transcriptional diversity among distinct cell types and subtypes. This article summarizes the role of MCAT elements and the TEF-1 family of transcription factors in muscle development and disease, and reviews recent progress in our understanding of the transcriptional regulatory mechanisms involved in MCAT element-dependent muscle-specific gene expression.

Factors controlling cardiac myosin-isoform shift during hypertrophy and heart failure

Myosin is a molecular motor, which interacts with actin to convert the energy from ATP hydrolysis into mechanical work. In cardiac myocytes, two myosin isoforms are expressed and their relative distribution changes in different developmental and pathophysiologic conditions of the heart. It has been realized for a long time that a shift in myosin isoforms plays a major role in regulating myocardial contractile activity. With the recent evidence implicating that alteration in myosin isoform ratio may be eventually beneficial for the treatment of a stressed heart, a new interest has developed to find out ways of controlling the myosin isoform shift. This article reviews the published data describing the role of myosin isoforms in the heart and highlighting the importance of various factors shown to influence myosin isofrom shift during physiology and disease states of the heart.

Characterization of cardiac gene promoter activity: reporter constructs and heterologous promoter studies

Cardiac gene promoter analysis remains an integral method in molecular cardiology and continues to provide novel insights into the transcriptional mechanisms that regulate gene expression in the myocardium. Initial studies focused on the regulated expression of contractile genes, since their transcripts are abundant and their cDNAs were among the first to be cloned. More recent studies have focused on the promoters of genes expressed at much lower levels, including those that encode ion channels, signaling proteins, and the cardiac transcription factors. The standard approach to analyze myocardial gene promoters has been to transfect reporter plasmids into cultured neonatal rat cardiac myocytes. This approach has the unique advantage of allowing the exploration of different signaling mechanisms by supplementing culture media with different agonists and inhibitors. In addition, cis-elements that control gene expression under different physiological stresses have been further characterized in the context of heterologous promoters to demonstrate their "stand-alone" functional properties in the absence of confounding influences from other cis-elements and their cognate transcription factors. Here we illustrate the characterization of cardiac gene promoter activity using reporter constructs and heterologous promoter studies in cultured cardiac myocytes.

Transcriptional regulation of tissue-specific genes by the ERK5 mitogen-activated protein kinase

The ERK5 mitogen-activated protein kinase (MAPK) differs from other MAPKs in possessing a potent transcriptional activation domain. ERK5-/- embryos die from angiogenic defects, but the precise physiological role of ERK5 remains poorly understood. To elucidate molecular functions of ERK5 in the development of vasculature and other tissues, we performed gene profile analyses of erk5-/- mouse embryos and erk5-/- fibroblast cells reconstituted with ERK5 or ERK5(1-740), which lacks the transactivation domain. These experiments revealed several potential ERK5 target genes, including a proapoptotic gene bnip3, known angiogenic genes flt1 and lklf (lung Krüppel-like factor), and genes that regulate cardiovascular development. Among these, LKLF, known for its roles in angiogenesis, T-cell quiescence, and survival, was found to be absolutely dependent on ERK5 for expression in endothelial and T cells. We show that ERK5 drives lklf transcription by activating MEF2 transcription factors. Expression of erk5 short hairpin or a dominant-negative form of the ERK5 upstream activator, MEK5, in T cells led to downregulation of LKLF, increased cell size and upregulation of activation markers. Thus, through its kinase and transcriptional activation domains, ERK5 regulates transcriptional responses of cell survival and quiescence critical for angiogenesis and T-cell function.

Distinct pathways regulate proapoptotic Nix and BNip3 in cardiac stress

Up-regulation of myocardial Nix and BNip3 is associated with apoptosis in cardiac hypertrophy and ischemia, respectively. To identify mechanisms of gene regulation for these critical cardiac apoptosis effectors, the determinants of Nix and BNip3 promoter activation were elucidated by luciferase reporter gene expression in neonatal rat cardiac myocytes. BNip3 transcription was increased by hypoxia but not by phenylephrine (10 microM), angiotensin II (100 nM), or isoproterenol (10 microM). In contrast, Nix transcription was increased by phenylephrine but not by isoproterenol, angiotensin II, or hypoxia. Since phenylephrine stimulates cardiomyocyte hypertrophy via protein kinase C (PKC), the effects of phorbol myristate acetate (PMA, 10 nM for 24 h) and adenoviral PKC expression were assessed. PMA and PKC alpha, but not PKC epsilon or dominant negative PKC alpha, increased Nix transcription. Multiple Nix promoter GC boxes bound transcription factor Sp-1, and basal and PMA- or PKC alpha-stimulated Nix promoter activity was suppressed by mithramycin inhibition of Sp1-DNA interactions. In vivo determinants of Nix expression were evaluated in Nix promoter-luciferase (NixP) transgenic mice that underwent ischemia-reperfusion (1 h/24 h), transverse aortic coarctation (TAC), or cross-breeding with the G(q) overexpression model of hypertrophy. Luciferase activity increased in G alpha(q)-NixP hearts 3.2 +/- 0.4-fold and in TAC hearts 2.8 +/- 0.4-fold but did not increase with infarction-reperfusion. NixP activity was proportional to the extent of TAC hypertrophy and was inhibited by mithramycin. These studies revealed distinct mechanisms of transcriptional regulation for cardiac Nix and BNip3. BNip3 is hypoxia-inducible, whereas Nix expression was induced by G alpha(q)-mediated hypertrophic stimuli. PKC alpha, a G(q) effector, transduced Nix transcriptional induction via Sp1.

Determinants of inducible brain natriuretic peptide promoter activity

Atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are polypeptide hormones belonging to the cardiac-derived mammalian natriuretic peptide system. These hormones share the same biological properties and receptors and both play important roles in the maintenance of fluid and electrolyte balance and in cardiovascular growth. Most hemodynamic and neurohumoral stimuli can coordinately increase ANF and BNP gene expression. However, instances of discoordinated ANF and BNP gene expression have been described, providing an opportunity for investigating the mechanisms that differentially regulate the expression of the natriuretic peptide genes. For example, exposure of cardiocytes in culture to certain pro-inflammatory cytokines and conditioned medium from mixed lymphocyte cultures upregulate BNP but not ANF gene expression. BNP promoter activity is also upregulated under these conditions but the cis-acting elements involved in this phenomenon are not known. In comparison to the ANF gene, less is known about BNP promoter consensus elements that regulate gene expression by mechanical or neurohumoral agonists. A number of cis-acting elements for GATA, Nkx2.5, NF-kappaB and TEF transcription factors have recently been identified within the BNP promoter that regulate BNP expression in response to specific agonists. This review focuses on the information available regarding cis-acting determinants responsible for inducible BNP transcription.

Myosin heavy chain isoforms expression and cyclic AMP concentrations in hypoxia-induced hypertrophied right ventricle in rats

We have previously demonstrated that the relative expression of myosin heavy chain-beta (MHC-beta) in both ventricles of rats exposed to long-term hypobaric hypoxia correlated significantly with the relative ventricular mass. In the present study, we investigated whether an increased expression of MHC-beta was accompanied by a reduction in cyclic AMP (cAMP) activity in hypoxia-induced hypertrophied right ventricle (RV). We used male Wistar-Kyoto rats born and raised at simulated altitudes (2200 m: H2 group or 4000 m: H4 group) compared to age-matched sea level controls (SC group). There were no significant differences between the groups in basal and forskolin-stimulated adenylyl cyclase (AC) activities. The basal and IBMX-inhibited phosphodiesterase (PDE) activities were slightly higher in both hypoxic groups (p>0.05), except that the H2 group had a higher basal PDE activity than the SC group (p<0.05). The AC/PDE activity ratios were significantly decreased in both hypoxic groups (p<0.05), suggesting that low concentrations of cellular cAMP were maintained in the RV under hypoxic conditions. However, there were no correlations between MHC-beta expression and either AC activity, PDE activity, or AC/PDE activity ratio. These results provided evidence against the causal role for cAMP concentration in the expression of MHC-beta associated with hypoxia-induced ventricular hypertrophy.

Nutritional modulation of parathyroid hormone secretion may influence risk for left ventricular hypertrophy

Recent studies demonstrate low serum levels of 25-hydroxyvitamin D in patients with congestive heart failure (CHF). Although this may in part reflect reduced capacity for outdoor exercise, the possibility that poor vitamin D status increases risk for left ventricular hypertrophy (LVH), and its common sequel CHF, merits consideration. In cardiomyocytes, hormones which activate protein kinase C (PKC) -- including norepinephrine, angiotensin II, and endostatin, implicated in the pathogenesis of LVH -- induce a hypertrophic response analogous to that seen in LVH. Transgenic mice overexpressing PKC-beta2 or its upstream activator Galphaq in cardiac myofibers develop a syndrome similar to LVH. Parathyroid hormone (PTH) also activates Galphaq and PKC in cardiomyocytes, and provokes the expected hypertrophic response. Both primary and secondary hyperparathyroidism are associated with high risk for LVH. Moreover, in uncomplicated essential hypertension, left ventricular mass index has been shown to correlate very tightly with serum PTH levels, independent of blood pressure. This latter finding suggests that variations of PTH within the normal range can influence induction of LVH in at-risk subjects. If so, nutritional and lifestyle measures which modulate PTH secretion may have an impact on LVH risk. PTH secretion should be down-regulated by good vitamin D status -- achieved through supplementation or regular uv exposure -- and by vegan diets moderately low in bioavailable phosphate. Although high calcium intakes can likewise suppress PTH, they also boost renin secretion, which could have a countervailing effect on risk for LVH. Whether these nutritional measures do indeed influence LVH risk could be examined in prospective studies targeting patients at high risk, such as hypertensives.

Protein Kinase C in Cardiac Disease and as a Potential Therapeutic Target

Protein kinase C (PKC) is a member of a large family of serine/threonine kinases that plays an integral role in many of the signaling cascades that govern cellular behavior. As such, it is intricately involved in the processes that mediate disease pathogenesis. Strategies that serve to alter PKC function may prove to be useful in the treatment of numerous disease states. This article reviews the various roles PKC may play in cardiovascular disease, specifically with regard to ischemic heart disease, cardiac hypertrophy, heart failure, hypertension, and atherosclerosis, and suggests the potential for developing therapeutic approaches that can target PKC activity.

Regulation of naturally occurring antisense RNA of myosin heavy chain (MyHC) in neonatal cardiomyocytes

Naturally occurring antisense RNA has been detected for a range of eukaryotic genes. Its abundance compared to levels of its complementary sense mRNA appears to be a factor indicating its possible regulatory function. In previous studies, we detected appreciable levels of antisense RNA against the two isoforms (alpha and beta) of the heavy myosin-chain (MyHC) in the myocardium of rats. If this is to play a significant role in gene expression antisense levels should vary in response to external and internal cellular influences. Recently, a bidirectional promoter located in the alpha/beta MyHC intergenic region was described, which was proposed to regulate coordinated transcription of alpha-MyHC sense and beta-MyHC antisense. To study MyHC antisense regulation in neonatal heart, we investigated cultivated myocytes stimulated with either trijodthyronin (T3) as an inductor of alpha-MyHC or phenylephrine with stimulation of beta-MyHC. RNA-quantification of sense and antisense transcripts of both isoforms was performed by real-time RT-PCR. Stimulation by T3 led to an induction of both sense and antisense of alpha-MyHC and to a decrease of beta-MyHC sense and antisense. Phenylephrine increased sense and antisense beta-MyHC but reduced antisense alpha-MyHC. The sense/antisense of alpha- and beta-MyHC ratio was unchanged compared to control. Results indicate a coregulation of sense and antisense MyHC RNA under stimulation of T3 and phenylephrine in neonatal cardiomyocytes.

RTEF-1, a Novel Transcriptional Stimulator of Vascular Endothelial Growth Factor in Hypoxic Endothelial Cells

Vascular endothelial growth factor (VEGF) is an angiogenic growth factor known to be up-regulated in ischemic heart and hypoxic endothelial cells. However, the transcriptional regulation of VEGF in hypoxia-induced angiogenesis is not fully understood. Transcriptional enhancer factor-1 (TEF-1) is a transcriptional factor family that can regulate many genes expressed in cardiac and skeletal muscle cells by binding to myocyte-specific chloramphenicol acetyltransferase heptamer elements in the promoters of these genes. In this study, we demonstrated that related TEF-1 (RTEF-1), a member of the TEF-1 family, is up-regulated in hypoxic endothelial cells. Overexpression of RTEF-1 increases VEGF promoter activity and VEGF expression. Sequential deletion and site-directed mutation analyses of the VEGF promoter demonstrated that a GC-rich region containing four Sp1 response elements, located between -114 and -50, was essential for RTEF-1 function. This region is beyond the hypoxia-inducible factor-1alpha binding site and does not consist of M-CAT-related elements. By electrophoretic mobility shift assay, RTEF-1 was found to interact with the first Sp1 residue (-97 to -87) of the four consecutive Sp1 elements. Binding activity of RTEF-1 to VEGF promoter is also confirmed by chromatin immunoprecipitation. In addition, induction of VEGF promoter activity by RTEF-1 results in an increase of angiogenic processes including endothelial cells proliferation and vascular structure formation. These results indicate that RTEF-1 acts as a transcriptional stimulator of VEGF by regulating VEGF promoter activity through binding to Sp1 site. In addition, RTEF-1-induced VEGF promoter activity was enhanced in a hypoxic condition, indicating that RTEF-1 may play an important role in the regulation of VEGF under hypoxia.

Cell-specific expression of SERCA, the exogenous Ca2+transport ATPase, in cardiac myocytes

We evaluated various constructs to obtain cell-specific expression of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) gene in cardiac myocytes after cDNA transfer by means of transfections or infections with adenovirus vectors. Expression of exogenous enhanced green fluorescent protein (EGFP) and SERCA genes was studied in cultured chicken embryo and neonatal rat cardiac myocytes, skeletal and smooth muscle cells, fibroblasts, and hepatocytes. Whereas the cytomegalovirus (CMV) promoter yielded high levels of protein expression in all cells studied, cardiac troponin T (cTnT) promoter segments demonstrated high specificity for cardiac myocytes. Their efficiency for protein expression was lower than that of the CMV promoter, but higher than that of cardiac myosin light chain or β-myosin heavy chain promoter segments. A double virus system for Cre-dependent expression under control of the CMV promoter and Cre expression under control of a cardiac-specific promoter yielded high protein levels in cardiac myocytes, but only partial cell specificity due to significant Cre expression in hepatocytes. Specific intracellular targeting of gene products was demonstrated in situ by specific immunostaining of exogenous SERCA1 and endogenous SERCA2 and comparative fluorescence microscopy. The -374 cTnT promoter segment was the most advantageous of the promoters studied, producing cell-specific SERCA expression and a definite increase over endogenous Ca2+-ATPase activity as well as faster removal of cytosolic calcium after membrane excitation. We conclude that analysis of promoter efficiency and cell specificity is of definite advantage when cell-specific expression of exogenous SERCA is wanted in cardiac myocytes after cDNA delivery to mixed cell populations.

Maternal methamphetamine administration during pregnancy influences on fetal rat heart development

Methamphetamine (MAP) is one of the most abused drugs in Japan. The rate of MAP abuse by young women has recently reached more than 50 percent in adolescents. A major health concern is that these women will continue to use MAP during pregnancy. The purpose of this study was to investigate whether MAP administered to the mother during pregnancy would change the expression of alpha- and beta- myosin heavy chain (MHC) mRNA in rat neonatal hearts, as detected by quantitative RT-PCR. In addition, morphological changes in the rat neonatal ventricles were examined. Pregnant rats were injected intraperitoneally with MAP (1 mg/kg/day) starting at day 0 of gestation and ending at day 21. There was a significant increase in alpha-MHC mRNA expression in the neonatal ventricular muscle in the experimental group compared with the control at postnatal day (P) 0 and 5. alpha-MHC mRNA expression in both groups was similar after P9. beta-MHC mRNA expression was similar in both groups at P0. Postnatal beta-MHC mRNA expression decreased rapidly, but significant alteration was not detected. Neonatal rats at P0 exhibited some cardiac changes, including hypertrophy, degeneration, and disarrangement of myofibers, but these lesions disappeared by P14. We conclude that chronic maternal administration of MAP changes the alpha- and beta-MHC mRNA expression pattern in fetal and neonatal hearts, correlating with abnormal development, plasma level of hormones, and myocardial damage. At the same time, it is indicated that neonatal cardiomyocytes have reversibility.

In vivo regulation of the chicken cardiac troponin T gene promoter in zebrafish embryos

The chicken cardiac troponin T (cTnT) gene is representative of numerous cardiac and skeletal muscle-specific genes that contain muscle-CAT (MCAT) elements within their promoters. We examined the regulation of the chicken cTnT gene in vivo in zebrafish embryos, and in vitro in cardiomyocyte, myoblast, and fibroblast cultures. Defined regions of the cTnT promoter were linked to the green fluorescent protein (GFP) gene for in vivo analysis, and the luciferase gene for in vitro analysis. Injection of the cTnT promoter constructs into fertilized zebrafish eggs resulted in GFP expression in both heart and skeletal muscle cells reproducing the pattern of expression of the endogenous cTnT gene in the chicken embryo. Promoter deletion analysis revealed that the cis-regulatory regions responsible for cardiac and skeletal muscle-specific expression functioned in an equivalent manner in both in vitro and in vivo environments. In addition, we show that mutation of the poly-ADP ribose polymerase-I (PARP-I) binding site adjacent to the distal MCAT element in the chicken cTnT promoter produced a non-cell-specific promoter in vitro and in the zebrafish. Thus, the PARP-I transcriptional regulatory mechanism that governs muscle specificity of the chicken cTnT promoter is conserved across several chordate classes spanning at least 350 million years of evolution.

Cocaine produces cardiac hypertrophy by protein kinase C dependent mechanisms

BACKGROUND

Chronic cocaine users can have as much as a 69% increase in left ventricular muscle mass without associated increases in arterial blood pressure, heart rate, renin, aldosterone, or cortisol. We determined whether cocaine directly increases cardiomyocyte protein content and whether protein kinase C is important in this process.

METHODS AND RESULTS

Adult rat cardiomyocytes were isolated and grown in cultures. In Series I experiments, cocaine, 10(-8) to 10(-6) M, or vehicle, in the absence or presence of phentolamine or metoprolol, was added to each culture and the cells were subsequently harvested. In Series II, cocaine, 10(-6) M, cocaine, 10(-6) M, plus bisindolylmaleimide, 10(-6) M, a protein kinase C inhibitor, or vehicle were added to each culture and the cells subsequently harvested. We determined the total protein content, the content of alpha-myosin and fetal beta-myosin heavy-chain protein, and the presence of protein kinase C isoforms in the cardiomyocyte soluble and particulate fractions. Protein kinase C translocation from the soluble to particulate fraction is indicative of activation. In Series III, we determined the cocaine effects on ERK, SAPK/JNK, and p38. In Series I, cocaine, 10(-8) to 10(-6) M, dose-dependently increased myocyte protein content by as much as 28%+/-2% (P<.001) and fetal beta-myosin heavy-chain protein content by 80%+/-2% (P<.001). Neither phentolamine nor metoprolol inhibited this process. In Series II, we determined that ventricular myocytes contain alpha (alpha), beta (beta), delta (delta), epsilon (epsilon), and zeta (zeta) protein kinase C isoforms. Cocaine, 10(-6) M, caused a 45+/-5% increase (P<.001) in protein kinase Calpha in the particulate fraction. The addition of a protein kinase C inhibitor to the myocyte cultures prevented the cocaine-induced translocation of protein kinase Calpha and limited the increase in beta-myosin heavy-chain protein content by >75% (P<.001). However, cocaine did not increase the phosphorylation of ERK, SAPK/JNK or p38 in Series III.

CONCLUSIONS

Cocaine increases adult cardiomyocyte protein content by protein kinase Calpha-dependent mechanisms, and this process can contribute to the cardiac hypertrophy and cardiomyopathy that results from chronic cocaine use.

Transcriptional regulation of the type I myosin heavy chain gene in denervated rat soleus

Denervation (DEN) of rat soleus is associated with a decreased expression of slow type I myosin heavy chain (MHC) and an increased expression of the faster MHC isoforms. The molecular mechanisms behind these shifts remain unclear. We first investigated endogenous transcriptional activity of the type I MHC gene in normal and denervated soleus muscles via pre-mRNA analysis. Our results suggest that the type I MHC gene is regulated via transcriptional processes in the denervated soleus. Deletion and mutational analysis of the rat type I MHC promoter was then used to identify cis elements or regions of the promoter involved in this response. DEN significantly decreased in vivo activity of the -3,500, -2,500, -914, -408, -299, and -215 bp type I MHC promoters, relative to the alpha-skeletal actin promoter. In contrast, normalized -171 promoter activity was unchanged. Mutation of the betae3 element (-214/-190) in the -215 promoter and deletion of this element (-171 promoter) blunted type I downregulation with DEN. In contrast, betae3 mutation in the -408 promoters was not effective in attenuating the DEN response, suggesting the existence of additional DEN-responsive sites between -408 and -215. Western blotting and gel mobility supershift assays demonstrated decreased expression and DNA binding of transcription enhancer factor 1 (TEF-1) with DEN, suggesting that this decrease may contribute to type I MHC downregulation in denervated muscle.

Regulation of the S100B gene by alpha 1-adrenergic stimulation in cardiac myocytes

We previously reported that S100B, a 20-kDa Ca(2+)-binding homodimer, inhibited the postinfarct myocardial hypertrophic response mediated by alpha(1)-adrenergic stimulation through the protein kinase C (PKC) signaling pathway. In the present study, we examined whether the same pathway induced the S100B gene, supporting the hypothesis that S100B is a feedback negative regulator of this pathway. We transfected cultured neonatal rat cardiac myocytes with a luciferase reporter gene driven by the maximal human S100B promoter and progressively shorter segments of this promoter sequentially deleted from the 5' end. We identified a basic promoter essential for transcription spanning 162 bp upstream of the transcription initiation site and positive (at -782/-162 and -6,689/-4,463) and negative (at -4,463/-782) myocyte-selective regulatory elements. We showed that the basic and maximal S100B promoters were activated specifically by alpha(1)-adrenergic agonists through the alpha(1A)-adrenergic receptor, but not by any other trophic hormonal stimuli. The activation of the S100B promoter was mediated through the PKC signaling pathway. Transcription enhancer factor-1 (TEF-1) and related to TEF-1 (RTEF-1) influenced transcription from the maximal, but not the basic, promoter implicating active MCAT elements upstream from the basic promoter. Acting in opposing fashions, TEF-1 transrepressed the S100B promoter and RTEF-1 transactivated the promoter. Our results suggest that alpha(1)-adrenergic stimulation induces the S100B gene after myocardial infarction through the PKC signaling pathway and that this induction is modulated by TEF-1 and RTEF-1.

Divergence in species and regulatory role of beta -myosin heavy chain proximal promoter muscle-CAT elements

We examined the functional role of distinct muscle-CAT (MCAT) elements during non-weight-bearing (NWB) regulation of a wild-type 293-base pair beta-myosin heavy chain (beta MyHC) transgene. Electrophoretic mobility shift assays (EMSA) revealed decreased NTEF-1, poly(ADP-ribose) polymerase, and Max binding at the human distal MCAT element when using NWB soleus vs. control soleus nuclear extract. Compared with the wild-type transgene, expression assays revealed that distal MCAT element mutation decreased basal transgene expression, which was decreased further in response to NWB. EMSA analysis of the human proximal MCAT (pMCAT) element revealed low levels of NTEF-1 binding that did not differ between control and NWB extract, whereas the rat pMCAT element displayed robust NTEF-1 binding that decreased when using NWB soleus extracts. Differences in binding between human and rat pMCAT elements were consistent whether using rat or mouse nuclear extract or in vitro synthesized human TEF-1 proteins. Our results provide the first evidence that 1) different binding properties and likely regulatory functions are served by the human and rat pMCAT elements, and 2) previously unrecognized beta MyHC proximal promoter elements contribute to NWB regulation.

Inhibition of angiotensin-converting enzyme reduces susceptibility of hypertrophied rat myocardium to ventricular fibrillation

Left ventricular (LV) hypertrophy increases susceptibility to reperfusion arrhythmias and the angiotensin-converting enzyme inhibitor, ramipril, may reduce that susceptibility via regression of LV hypertrophy. Rats (n=12 per group) were subjected to abdominal aortic constriction (AC) or sham-operation (SH) and from 3 to 6 weeks after surgery, 3 AC groups received ramipril (0.01, 0.1, or 1 mg/kg per day p.o.) while the SH and 1 AC group received vehicle. Six weeks after surgery (ie after 3 weeks of treatment), the hearts were excised and subjected to independent Langendorf perfusion of left and right coronary beds. The left coronary bed was then subjected to ischemia (7 min) and reperfusion (5 min). Hypertrophied hearts from the vehicle AC group showed a significant increase in the incidence of reperfusion-induced ventricular fibrillation (VF) compared with control hearts from the SH group (92%* vs 33%: *p<0.05); this difference was abolished by ramipril (42%, 50%, and 42%, at 0.01, 0.1, or 1 mg/kg per day, respectively). The LV weight/body weight ratio was significantly increased in all AC groups (regardless of ramipril treatment) relative to the SH group. At the cellular level, myocyte length was significantly increased in the vehicle AC group, but was normalized by ramipril treatment (1 mg/kg per day). At the molecular level, atrial natriuretic factor (ANF) mRNA expression was also significantly increased in the vehicle AC group, but was again normalized by ramipril treatment (1 mg/kg per day). In conclusion, short-term treatment with ramipril reduced susceptibility to severe ventricular arrhythmias in hypertrophied rat hearts. This protection was achieved in the absence of a significant reduction in LV weight, but was accompanied by regression of myocyte hypertrophy, as reflected by reductions in cell size and ANF expression.

Alpha(1)-adrenergic activation of the cardiac ankyrin repeat protein gene in cardiac myocytes

Cardiac ankyrin repeat protein (CARP) is a nuclear transcription cofactor that is activated by multiple signaling pathways in hypertrophic cardiac myocytes. Since CARP has been reported to be a transcriptional co-repressor, its activation during hypertrophy might contribute to the deregulation of gene expression leading to heart failure. Here, we found that alpha(1)-adrenergic signaling activates CARP mRNA expression in rat cardiac myocytes. To examine how alpha(1)-adrenergic signaling activates the CARP gene, a 660 bp fragment of the mouse CARP promoter was cloned. Previous reports suggested that the mouse CARP promoter was dependent on the GATA4 transcription factor whereas the human CARP promoter was dependent on transcriptional enhancer factor-1 (TEF-1). TEF-1 and GATA4 transcription factors, known mediators of alpha(1)-adrenergic signaling, bound to the mouse CARP promoter at several sites as determined by gel mobility shift assays. These sites are highly conserved between the mouse and human promoters, suggesting that they are functionally important in both. Mutation analysis showed that binding of TEF-1 factors is required for basal activity of the CARP promoter in cardiac myocytes. However, over-expression of TEF-1 factors could not potentiate the response of the CARP promoter to alpha(1)-adrenergic stimulation. On the other hand, the alpha(1)-adrenergic response was potentiated by GATA4 over-expression. Taken together, our results demonstrate that alpha(1)-adrenergic signaling regulates CARP expression in cardiac myocytes, in part through the transcription factor GATA4.

Mouse DTEF-1 (ETFR-1, TEF-5) is a transcriptional activator in alpha 1-adrenergic agonist-stimulated cardiac myocytes

alpha(1)-Adrenergic signaling in cardiac myocytes activates the skeletal muscle alpha-actin gene through an MCAT cis-element, the binding site of the transcriptional enhancer factor-1 (TEF-1) family of transcription factors. TEF-1 accounts for more than 85% of the MCAT binding activity in neonatal rat cardiac myocytes. Other TEF-1 family members account for the rest. Although TEF-1 itself has little effect on the alpha(1)-adrenergic activation of skeletal muscle alpha-actin, the related factor RTEF-1 augments the response and is a target of alpha(1)-adrenergic signaling. Here, we examined another TEF-1 family member expressed in cardiac muscle, DTEF-1, and observed that it also augmented the alpha(1)-adrenergic response of skeletal muscle alpha-actin. A DTEF-1 peptide-specific antibody revealed that endogenous DTEF-1 accounts for up to 5% of the MCAT binding activity in neonatal rat cardiac myocytes. A TEF-1/DTEF-1 chimera suggests that alpha(1)-adrenergic signaling modulates DTEF-1 function. Orthophosphate labeling and immunoprecipitation of an epitope-tagged DTEF-1 showed that DTEF-1 is phosphorylated in vivo. alpha(1)-Adrenergic stimulation increased while phosphatase treatment lowered the MCAT binding by DTEF-1 and the endogenous non-TEF-1 MCAT-binding factor. In contrast, alpha(1)-adrenergic stimulation did not alter, and phosphatase treatment increased, MCAT binding of TEF-1 and RTEF-1. Taken together, these results suggest that DTEF-1 is a target for alpha(1)-adrenergic activation of the skeletal muscle alpha-actin gene in neonatal rat cardiac myocytes.

Functional overload increases beta-MHC promoter activity in rodent fast muscle via the proximal MCAT (betae3) site

Functional overload (OL) of the rat plantaris muscle by the removal of synergistic muscles induces a shift in the myosin heavy chain (MHC) isoform expression profile from the fast isoforms toward the slow type I, or, beta-MHC isoform. Different length rat beta-MHC promoters were linked to a firefly luciferase reporter gene and injected in control and OL plantaris muscles. Reporter activities of -3,500, -914, -408, and -215 bp promoters increased in response to 1 wk of OL. The smallest -171 bp promoter was not responsive to OL. Mutation analyses of putative regulatory elements within the -171 and -408 bp region were performed. The -408 bp promoters containing mutations of the betae1, distal muscle CAT (MCAT; betae2), CACC, or A/T-rich (GATA), were still responsive to OL. Only the proximal MCAT (betae3) mutation abolished the OL response. Gel mobility shift assays revealed a significantly higher level of complex formation of the betae3 probe with nuclear protein from OL plantaris compared with control plantaris. These results suggest that the betae3 site functions as a putative OL-responsive element in the rat beta-MHC gene promoter.

Transcriptional regulation of the type I myosin heavy chain promoter in inactive rat soleus

Chronic muscle inactivity with spinal cord isolation (SI) decreases expression of slow type I myosin heavy chain (MHC) while increasing expression of the faster MHC isoforms, primarily IIx. The purpose of this study was to determine whether type I MHC downregulation in the soleus muscle of SI rats is regulated transcriptionally and to identify cis-acting elements or regions of the rat type I MHC gene promoter involved in this response. One week of SI significantly decreased in vivo activity of the -3500-, -408-, -299-, -215-, and -171-bp type I MHC promoters. The activity of all tested deletions of the type I MHC promoter, relative to the human skeletal alpha-actin promoter, were significantly reduced in the SI soleus, except activity of the -171-bp promoter, which increased. Mutation of the betae3 element (-214/-190 bp) in the -215- and -408-bp promoters and deletion of this element (-171-bp promoter) attenuated type I downregulation with SI. Gel mobility shift assays demonstrated a decrease in transcription enhancer factor-1 binding to the betae3 element with SI, despite an increase in total binding to this region. These results demonstrate that type I MHC downregulation with SI is transcriptionally regulated and suggest that interactions between transcription enhancer factor-1 and the betae3 element are likely involved in this response.

Involvement of reactive oxygen species-mediated NF-kappa B activation in TNF-alpha-induced cardiomyocyte hypertrophy

We examined the intracellular signaling mechanism for tumor necrosis factor-alpha (TNF-alpha)-induced cardiac hypertrophy in isolated rat neonatal cardiomyocytes. TNF-alpha enhanced the expression of a kappa B-dependent reporter gene construct in a dose-dependent manner, which was transiently transfected in cardiomyocytes. Electrophoretic mobility shift assay demonstrated that TNF-alpha induced nuclear factor- kappa B (NF-kappa B)-specific DNA binding. Cultured cardiomyocytes were infected with a recombinant adenoviral vector expressing a degradation-resistant mutant of I kappa B alpha (AdI kappa B alpha 32/36A). The I kappa B alpha mutant suppressed NF-kappa B activation induced by TNF- alpha. In cardiomyocytes infected with AdI kappa B alpha 32/36A, TNF-alpha-induced hypertrophic responses, including increases in cell size, protein synthesis and atrial natriuretic factor production and enhancement of sarcomeric organization, were remarkably attenuated compared to the cells infected with an adenovirus expressing bacterial beta-galactosidase. Using a reactive oxygen species (ROS)-sensitive fluorescent dye, 2', 7'-dichlorofluorescin, we observed an increase in fluorescent signal in cardiomyocytes over time, upon addition of TNF-alpha. Preincubation of n-acetyl cysteine (NAC), an antioxidant, prior to TNF-alpha treatment, abolished TNF-alpha -induced ROS generation. NAC abolished TNF-alpha-induced NF-kappa B activation and hypertrophic responses. These findings indicated that TNF-alpha-induced cardiomyocyte hypertrophy is mediated through NF-kappa B activation via the generation of ROS.

Enhanced PKC beta II translocation and PKC beta II-RACK1 interactions in PKC epsilon-induced heart failure: a role for RACK1

Recent investigations have established a role for the beta II-isoform of protein kinase C (PKC beta II) in the induction of cardiac hypertrophy and failure. Although receptors for activated C kinase (RACKs) have been shown to direct PKC signal transduction, the mechanism through which RACK1, a selective PKC beta II RACK, participates in PKC beta II-mediated cardiac hypertrophy and failure remains undefined. We have previously reported that PKC epsilon activation modulates the expression of RACKs, and that altered epsilon-isoform of PKC (PKC epsilon)-RACK interactions may facilitate the genesis of cardiac phenotypes in mice. Here, we present evidence that high levels of PKC epsilon activity are commensurate with impaired left ventricular function (dP/dt = 6,074 +/- 248 mmHg/s in control vs. 3,784 +/- 269 mmHg/s in transgenic) and significant myocardial hypertrophy. More importantly, we demonstrate that high levels of PKC epsilon activation induce a significant colocalization of PKC beta II with RACK1 (154 +/- 7% of control) and a marked redistribution of PKC beta II to the particulate fraction (17 +/- 2% of total PKC beta II in control mice vs. 49 +/- 5% of total PKC beta II in hypertrophied mice), without compensatory changes of the other eight PKC isoforms present in the mouse heart. This enhanced PKC beta II activation is coupled with increased RACK1 expression and PKC beta II-RACK1 interactions, demonstrating PKC epsilon-induced PKC beta II signaling via a RACK1-dependent mechanism. Taken together with our previous findings regarding enhanced RACK1 expression and PKC epsilon-RACK1 interactions in the setting of cardiac hypertrophy and failure, these results suggest that RACK1 serves as a nexus for at least two isoforms of PKC, the epsilon-isoform and the beta II-isoform, thus coordinating PKC-mediated hypertrophic signaling.

Regulation of thyroid hormone receptor isoforms in physiological and pathological cardiac hypertrophy

Physiological and pathological cardiac hypertrophy have directionally opposite changes in transcription of thyroid hormone (TH)-responsive genes, including alpha- and beta-myosin heavy chain (MyHC) and sarcoplasmic reticulum Ca(2+)-ATPase (SERCA), and TH treatment can reverse molecular and functional abnormalities in pathological hypertrophy, such as pressure overload. These findings suggest relative hypothyroidism in pathological hypertrophy, but serum levels of TH are usually normal. We studied the regulation of TH receptors (TRs) beta1, alpha1, and alpha2 in pathological and physiological rat cardiac hypertrophy models with hypothyroid- and hyperthyroid-like changes in the TH target genes, alpha- and beta-MyHC and SERCA. All 3 TR subtypes in myocytes were downregulated in 2 hypertrophy models with a hypothyroid-like mRNA phenotype, phenylephrine in culture and pressure overload in vivo. Myocyte TRbeta1 was upregulated in models with a hyperthyroid-like phenotype, TH (triiodothyronine, T3), in culture and exercise in vivo. In myocyte culture, TR overexpression, or excess T3, reversed the effects of phenylephrine on TH-responsive mRNAs and promoters. In addition, TR cotransfection and treatment with the TRbeta1-selective agonist GC-1 suggested different functional coupling of the TR isoforms, TRbeta1 to transcription of beta-MyHC, SERCA, and TRbeta1, and TRalpha1 to alpha-MyHC transcription and increased myocyte size. We conclude that TR isoforms have distinct regulation and function in rat cardiac myocytes. Changes in myocyte TR levels can explain in part the characteristic molecular phenotypes in physiological and pathological cardiac hypertrophy.

Glycogen synthase kinase 3beta regulates GATA4 in cardiac myocytes

Inactivation of glycogen synthase kinase 3beta (GSK3beta) is critical for transcription of atrial natriuretic factor (ANF) by beta-adrenergic receptors in cardiac myocytes. We examined the mechanism by which GSK3beta regulates ANF transcription. Stimulation of beta-adrenergic receptors induced nuclear accumulation of GATA4, whereas beta-adrenergic ANF transcription was suppressed by dominant negative GATA4, suggesting that GATA4 plays an important role in beta-adrenergic ANF transcription. Interestingly, GATA4-mediated transcription was markedly attenuated by GSK3beta. GSK3beta physically associates with GATA4 and phosphorylates GATA4 in vitro. Overexpression of GSK3beta suppressed both basal and beta-adrenergic increases in nuclear expression of GATA4, whereas inhibition of GSK3beta by LiCl caused nuclear accumulation of GATA4, suggesting that GSK3beta negatively regulates nuclear expression of GATA4. The nuclear exportin Crm1 reduced nuclear expression of GATA4, and the reduction was enhanced by GSK3beta but not by kinase-inactive GSK3beta. Leptomycin B, an inhibitor for Crm1, increased basal nuclear GATA4 and suppressed GSK3beta-induced decreases in nuclear GATA4. These results suggest that GSK3beta negatively regulates nuclear expression of GATA4 by stimulating Crm1-dependent nuclear export. Inhibition of GSK3beta by beta-adrenergic stimulation abrogates GSK3beta-induced nuclear export of GATA4, causing nuclear accumulation of GATA4, which may represent an important signaling mechanism mediating cardiac hypertrophy.

DNA binding of TEA/ATTS domain factors is regulated by protein kinase C phosphorylation in human choriocarcinoma cells

Transcription enhancer factor 1 (TEF-1) controls the expression of a diverse set of genes. Previous studies implicated protein kinase C (PKC)-mediated signal transduction in modulating TEF function. We demonstrate that in human choriocarcinoma BeWo cells, the PKC activator 12-O-tetradecanoyl phorbol 13-acetate and PKC inhibitor bisindolylmaleimide reciprocally down- and up-regulate, respectively, TEF-mediated GGAATG core enhancer activity. In vitro TEF-1 phosphorylation with several PKC isozymes and phosphoamino acid analysis confirmed that TEF-1 is a potential PKC substrate. TEF-1.DNA complexes formed by BeWo nuclear extracts are supershifted by phosphoserine- and phosphothreonine- but not phosphotyrosine-specific antibodies, indicating that TEF-1 is phosphorylated in vivo at serine and threonine residues. The TEF-1 phosphorylation domain was localized to the third alpha-helix of the DNA binding domain and adjacent hinge region by phosphopeptide analysis. TEF-1 phosphorylation significantly reduced its DNA binding activity both in vitro and in vivo, providing a possible mechanism for the inhibitory action of PKC. Finally, BeWo cells contained abundant levels of gamma and delta PKC isoforms, and their overexpression resulted in even greater inhibition of GGAATG core enhancer activity after 12-O-tetradecanoyl phorbol 13-acetate treatment. These data strongly suggest that PKC-mediated phosphorylation is a key factor controlling TEF function.

In vivo regulation of the beta-myosin heavy chain gene in hypertensive rodent heart

The main goal of this study was to examine the transcriptional activity of different-length beta-myosin heavy chain (beta-MHC) promoters in the hypertensive rodent heart using the direct gene transfer approach. A hypertensive state was induced by abdominal aortic constriction (AbCon) sufficient to elevate mean arterial pressure by approximately 45% relative to control. Results show that beta-MHC promoter activity of all tested wild-type constructs, i.e., -3500, -408, -299, -215, -171, and -71 bp, was significantly increased in AbCon hearts. In the normal control hearts, expression of the -71-bp construct was comparable to that of the promoterless vector, but its induction by AbCon was comparable to that of the other constructs. Additional results, based on mutation analysis and DNA gel mobility shift assays targeting betae1, betae2, GATA, and betae3 elements, show that these previously defined cis-elements in the proximal promoter are indeed involved in maintaining basal promoter activity; however, none of these elements, either individually or collectively, appear to be major players in mediating the hypertension response of the beta-MHC gene. Collectively, these results indicate that three separate regions on the beta-MHC promoter are involved in the induction of the gene in response to hypertension: 1) a distal region between -408 and -3500 bp, 2) a proximal region between -299 and -215 bp, and 3) a basal region within -71 bp of the transcription start site. Future research needs to further characterize these responsive regions to more fully delineate beta-MHC transcriptional regulation in response to pressure overload.

Cloning and characterization of the mouse alpha1C/A-adrenergic receptor gene and analysis of an alpha1C promoter in cardiac myocytes: role of an MCAT element that binds transcriptional enhancer factor-1 (TEF-1)

alpha1-Adrenergic receptor (AR) subtypes in the heart are expressed by myocytes but not by fibroblasts, a feature that distinguishes alpha1-ARs from beta-ARs. Here we studied myocyte-specific expression of alpha1-ARs, focusing on the subtype alpha1C (also called alpha1A), a subtype implicated in cardiac hypertrophic signaling in rat models. We first cloned the mouse alpha1C-AR gene, which consisted of two exons with an 18 kb intron, similar to the alpha1B-AR gene. The receptor coding sequence was >90% homologous to that of rat and human. alpha1C-AR transcription in mouse heart was initiated from a single Inr consensus sequence at -588 from the ATG; this and a putative polyadenylation sequence 8.5 kb 3' could account for the predominant 11 kb alpha1C mRNA in mouse heart. A 5'-nontranscribed fragment of 4.4 kb was active as a promoter in cardiac myocytes but not in fibroblasts. Promoter activity in myocytes required a single muscle CAT (MCAT) element, and this MCAT bound in vitro to recombinant and endogenous transcriptional enhancer factor-1. Thus, alpha1C-AR transcription in cardiac myocytes shares MCAT dependence with other cardiac-specific genes, including the alpha- and beta-myosin heavy chains, skeletal alpha-actin, and brain natriuretic peptide. However, the mouse alpha1C gene was not transcribed in the neonatal heart and was not activated by alpha1-AR and other hypertrophic agonists in rat myocytes, and thus differed from other MCAT-dependent genes and the rat alpha1C gene.

Reactive oxygen species modulate angiotensin II-induced beta-myosin heavy chain gene expression via Ras/Raf/extracellular signal-regulated kinase pathway in neonatal rat cardiomyocytes

Angiotensin II (Ang II) causes cardiomyocytes hypertrophy. Cardiac beta-myosin heavy chain (beta-MyHC) gene expression can be altered by Ang II. The molecular mechanisms are not completely known. Reactive oxygen species (ROS) are involved in signal transduction pathways of Ang II. However, the role of ROS on Ang II-induced beta-MyHC gene expression remains unclear. Here we found that Ang II increased beta-MyHC promoter activity and it was blocked by Ang II type 1 receptor antagonist losartan. Ang II dose-dependently increased the intracellular ROS. Cardiomyocytes cotransfected with a dominant negative mutant of Ras (RasN17), Raf-1 (Raf301), or a catalytically inactive mutant of extracellular signal regulated kinase (mERK2) inhibited Ang II-induced beta-MyHC promoter activity, indicating Ras/Raf/ERK pathway was involved. Antioxidants such as catalase or N-acetyl-cysteine decreased Ang II-activated ERK phosphorylation and inhibited Ang II-induced beta-MyHC promoter activity. These data indicate that Ang II increases beta-MyHC gene expression in part via the generation of ROS.