Dual roles of modulatory calcineurin-interacting protein 1 in cardiac hypertrophy

Estrogen inhibits cardiomyocyte hypertrophy in vitro. Antagonism of calcineurin-related hypertrophy through induction of MCIP1

Evidence from in vivo studies suggests that some inputs to cardiac hypertrophy are opposed by the actions of estrogen. However, the mechanisms of E2 action in this respect are mainly unknown. An important pathway that is utilized by multiple hypertrophic stimuli involves the activation of the tyrosine phosphatase, calcineurin (PP2B). Here we show that 17beta-estradiol (E2) significantly prevents angiotensin II (AngII)- or endothelin-1 (ET-1)-induced new protein synthesis, skeletal muscle actin expression, and increased surface area in cultured rat cardiomyocytes. ET-1 stimulated calcineurin phosphatase activity, resulting in new protein synthesis, and both were prevented by E2. E2 induced the MCIP1 gene, an inhibitor of calcineurin activity, via phosphatidylinositol 3-kinase, transcriptional, and mRNA stability mechanisms. Small interfering RNA for MCIP1 significantly reversed both the E2 restraint of protein synthesis and the inhibition of AngII-induced calcineurin activity. AngII-induced the translocation of the hypertrophic transcription factor, NF-AT, to the nucleus of the cardiomyocyte and stimulated NF-AT transcriptional activity. Both were prevented by E2. AngII also stimulated the activation of ERK and protein kinase C, contributing to cardiac hypertrophy. E2 inhibited these pathways, related to the stimulation of atrial natriuretic peptide production and secretion. Thus, restraint of calcineurin and kinase signaling to the hypertrophic program underlie these important effects of E2.

Toward transcriptional therapies for the failing heart: chemical screens to modulate genes

In response to acute and chronic stresses, the heart frequently undergoes a remodeling process that is accompanied by myocyte hypertrophy, impaired contractility, and pump failure, often culminating in sudden death. The existence of redundant signaling pathways that trigger heart failure poses challenges for therapeutic intervention. Cardiac remodeling is associated with the activation of a pathological gene program that weakens cardiac performance. Thus, targeting the disease process at the level of gene expression represents a potentially powerful therapeutic approach. In this review, we describe strategies for normalizing gene expression in the failing heart with small molecules that control signal transduction pathways directed at transcription factors and associated chromatin-modifying enzymes.

Attenuation of cardiac remodeling after myocardial infarction by muscle LIM protein-calcineurin signaling at the sarcomeric Z-disc

Adverse left ventricular (LV) remodeling after myocardial infarction (MI) is a major cause for heart failure. Molecular modifiers of the remodeling process remain poorly defined. Patients with heart failure after MI have reduced LV expression levels of muscle LIM protein (MLP), a component of the sarcomeric Z-disk that is involved in the integration of stress signals in cardiomyocytes. By using heterozygous MLP mutant (MLP+/-) mice, we explored the role of MLP in post-MI remodeling. LV dimensions and function were similar in sham-operated WT and MLP+/- mice. After MI, however, MLP+/- mice displayed more pronounced LV dilatation and systolic dysfunction and decreased survival compared with WT mice, indicating that reduced MLP levels predispose to adverse LV remodeling. LV dilatation in MLP+/- mice was associated with reduced thickening but enhanced elongation of cardiomyocytes. Activation of the stress-responsive, prohypertrophic calcineurin-nuclear factor of activated T-cells (NFAT) signaling pathway was reduced in MLP+/- mice after MI, as shown by a blunted transcriptional activation of NFAT in cardiomyocytes isolated from MLP+/-/NFAT-luciferase reporter gene transgenic mice. Calcineurin was colocalized with MLP at the Z-disk in WT mice but was displaced from the Z-disk in MLP+/- mice, indicating that MLP is essential for calcineurin anchorage to the Z-disk. In vitro assays in cardiomyocytes with down-regulated MLP confirmed that MLP is required for stress-induced calcineurin-NFAT activation. Our study reveals a link between the stress sensor MLP and the calcineurin-NFAT pathway at the sarcomeric Z-disk in cardiomyocytes and indicates that reduced MLP-calcineurin signaling predisposes to adverse remodeling after MI.

The Yins of T Cell Activation

Transcription factors activated in response to T cell receptor (TCR) signaling include nuclear factor of activated T cells (NFAT) family, which is highly phosphorylated and thereby maintained in the cytoplasm of resting T cells, the nuclear factor NF-kappaB, which is kept in the cytoplasm of resting cells through its association with the inhibitor protein IkappaB, and activating protein-1 (AP-1), which is only transcribed after TCR stimulation. Negative regulators of TCR signaling can be divided into two groups: Class 1 regulators help maintain the quiescent state of unstimulated T cells, whereas class 2 regulators are themselves transcriptionally induced in response to TCR signaling and serve to limit and terminate the activating signal. Class 1 regulators include the autoinhibitory domain of the phosphatase calcineurin; IkappaB and its transcriptional activators Foxj1 and Foxo3a; and various transcriptional coregulators that inhibit interleukin-2 (IL-2) production. Class 2 regulators include the calcipressins, which, like NFATp and NFAT4 are feedback inhibitors of calcineurin-NFAT signaling, IkappaB, and the mitogen-activated protein kinase (MAPK) phosphatases, which inhibit MAPK signaling and thus the nuclear localization of AP-1 components.

Calcium-calcineurin signaling in the regulation of cardiac hypertrophy

Cardiac hypertrophy is a leading predicator of progressive heart disease that often leads to heart failure and a loss of cardiac contractile performance associated with profound alterations in intracellular calcium handling. Recent investigation has centered on identifying the molecular signaling pathways that regulate cardiac myocyte hypertrophy, as well as the mechanisms whereby alterations in calcium handling are associated with progressive heart failure. One potential focal regulator of cardiomyocyte hypertrophy that also responds to altered calcium handling is the calmodulin-activated serine/threonine protein phosphatase calcineurin (PP2B). Once activated by increases in calcium, calcineurin mediates the hypertrophic response through its downstream transcriptional effector nuclear factor of activated T cells (NFAT), which is directly dephosphorylated by calcineurin resulting in nuclear translocation. While previous studies have convincingly demonstrated the sufficiency of calcineurin to mediate cardiac hypertrophy and progressive heart failure, its necessity remains an area of ongoing investigation. Here we weigh an increasing body of literature that suggests a causal link between calcineurin signaling and the cardiac hypertrophic response and heart failure through the use of pharmacologic inhibitors (cyclosporine A and FK506) and genetic approaches. We will also discuss the manner in which calcineurin-NFAT signaling is negatively regulated in the heart through a diverse array of kinases and inhibitory proteins. Finally, we will discuss emerging theories as to the mechanisms whereby alterations in intracellular calcium handling might stimulate calcineurin within the context of a contractile cell continually experiencing calcium flux.

VEGF selectively induces Down syndrome critical region 1 gene expression in endothelial cells: a mechanism for feedback regulation of angiogenesis?

The Down syndrome critical region 1 (DSCR1) gene (also known as MCIP1, Adapt78) encodes a regulatory protein that binds to calcineurin catalytic A subunit and acts as a regulator of the calcineurin-mediated signaling pathway. We show in this study that DSCR1 is greatly induced in endothelial cells in response to VEGF, TNF-alpha, and A23187 treatment, and that this up-regulation is inhibited by inhibitors of the calcineurin-NFAT (nuclear factor of activated T cells) signaling pathway as well as by PKC inhibition and a Ca(2+) chelator. We hypothesized that the up-regulation of DSCR1 gene expression in endothelial cells could act as an endogenous feedback inhibitor for angiogenesis by regulating the calcineurin-NFAT signaling pathway. Our transient transfection analyses confirm that the overexpression of DSCR1 abrogates the up-regulation of reporter gene expression driven by both the cyclooxygenase 2 and DSCR1 promoters in response to stimulators. Our results indicate that DSCR1 up-regulation may represent a potential molecular mechanism underlying the regulation of angiogenic genes activated by the calcineurin-NFAT signaling pathway in endothelial cells.

Gene expression changes associated with fibronectin-induced cardiac myocyte hypertrophy

Fibronectin (FN) is an extracellular matrix protein that binds to integrin receptors and couples cardiac myocytes to the basal lamina. Cardiac FN expression is elevated in models of pressure overload, and FN causes cultured cardiac myocytes to hypertrophy by a mechanism that has not been characterized in detail. In this study, we analyzed the gene expression changes induced by FN in purified rat neonatal ventricular myocytes using the Affymetrix RAE230A microarray, to understand how FN affects gene expression in cardiac myocytes and to separate the effects contributed by cardiac nonmyocytes in vivo. Pathway analysis using z-score statistics and comparison with a mouse model of cardiac hypertrophy revealed several pathways stimulated by FN in cardiac myocytes. In addition to the known cardiac myocyte hypertrophy markers, FN significantly induced metabolic pathways including virtually all of the enzymes of cholesterol biosynthesis, fatty acid biosynthesis, and the mitochondrial electron transport chain. FN also increased the expression of genes coding for ribosomal proteins, translation factors, and the ubiquitin-proteasome pathway. Interestingly, cardiac myocytes plated on FN showed elevated expression of the fibrosis-promoting peptides connective tissue growth factor (CTGF), WNT1 inducible signaling pathway protein 2 (WISP2), and secreted acidic cysteine-rich glycoprotein (SPARC). Our data complement in vivo studies and reveal several novel genes and pathways stimulated by FN, pointing to cardiac myocyte-specific mechanisms that lead to development of the hypertrophic phenotype.

Hypertrophy of the heart: a new therapeutic target?

Recent studies call into question the necessity of hypertrophic growth of the heart as a "compensatory" response to hemodynamic stress. These findings, coupled with recent progress in dissecting the molecular bases of hypertrophy, raise the prospect of suppressing hypertrophy without provoking circulatory insufficiency. In this article, we focus on signaling pathways that hold promise as potential targets for therapeutic intervention. We also summarize observations from animal models and clinical trials that suggest benefit from an antihypertrophic strategy.

Down syndrome candidate region 1,a downstream target of VEGF, participates in endothelial cell migration and angiogenesis

Vascular endothelial growth factor (VEGF) is a principal stimulator of angiogenesis. However, the downstream targets of VEGF in endothelial cells (ECs) are not entirely clarified. Survey of downstream targets of VEGF in human ECs identified a number of genes, including Down syndrome candidate region 1 (DSCR1). Here, we confirmed the inducible expression of DSCR1 in ECs by Northern and Western blottings. Moreover, VEGF-stimulated induction of DSCR1 was blocked by anti-VEGF receptor-2 monoclonal antibody (mAb), or the specific calcineurin inhibitors cyclosporin A and FK506. The expression of DSCR1 in ECs of neovessels was further shown by immunohistochemical analysis. We therefore examined whether DSCR1 played any roles in angiogenesis. The specific downregulation of DSCR1 expression by antisense oligonucleotide (AS-ODN) inhibited VEGF-stimulated migration of ECs as well as angiogenesis in vivo. AS-ODN inhibited the spreading of ECs on vitronectin, as well as on the immobilized anti-alphavbeta3 mAb, but not on anti-alphavbeta5 mAb. Moreover, AS-ODN inhibited tyrosine phosphorylation of focal adhesion kinase when ECs were plated on a vitronectin-coated dish. Immunoprecipitation followed by Western blotting showed the coimmunoprecipitation of DSCR1 and integrin alphavbeta3. These results suggest that DSCR1 is involved in angiogenesis by regulating adhesion and migration of ECs via the interaction with integrin alphavbeta3.

Predicting pathway perturbations in Down syndrome

Comparative annotation of human chromosome 21 genomic sequence with homologous regions of mouse chromosomes 16, 17 and 10 has identified 170 orthologous gene pairs. Functional annotation of these genes, based on literature reports and computationally-derived predictions, shows that a broad range of cellular processes are represented. A goal of Down syndrome research is to determine which of these processes are perturbed by overexpression of chromosome 21 genes, and which may, therefore, contribute to the cognitive deficits that characterize Down syndrome. Eleven chromosome 21 genes are annotated to interact with or be affected by components of the MAP Kinase pathway and eight are involved in Ca2+/calcineurin signaling. Both pathways are critical for normal neurological function, and consequently their perturbations are proposed as candidates for phenotypic relevance. We present evidence suggesting that the MAP Kinase pathway is perturbed in the Ts65Dn mouse model of Down syndrome at 4-6 months of age. Analysis is complicated by the observation that overexpression of chromosome 21 genes in trisomy may be affected by method of detection, organism, tissue or brain region, and/or developmental age.

Aggregate formation and synaptic abnormality induced by DSCR1

Aggregation of conformation-abnormal peptides probably plays a key role in the pathogenesis of many neurodegenerative diseases. DSCR1 Down syndrome (DS) critical region 1, was identified from a chromosomal region (21q22.1-q22.2) for the clinical manifestations of DS when an extra-copy is present. We report that expression of DSCR1 in several cell types, including primary neurons, causes microtubule-dependent aggresome-like inclusion body formation. Disease-associated huntingtin (Q148) and ataxin-3 (Q84) co-localize with DSCR1 aggregates. Neurons bearing DSCR1 aggregates show reduced synaptophysin staining in processes. DSCR1 residues 31-90 constitute an aggregation-prone domain that is predicted to form a hydrophobic patch on the protein surface when residues 1-30 are removed. This study identifies a novel function of DSCR1 that may underlie DS neuropathology.

DSCR1 gene expression is dependent on NFATc1 during cardiac valve formation and colocalizes with anomalous organ development in trisomy 16 mice

The Down syndrome critical region 1 (DSCR1) gene is present in the region of human chromosome 21 and the syntenic region of mouse chromosome 16, trisomy of which is associated with congenital heart defects observed in Down syndrome. DSCR1 encodes a regulatory protein in the calcineurin/NFAT signal transduction pathway. During valvuloseptal development in the heart, DSCR1 is expressed in the endocardium of the developing atrioventricular and semilunar valves, the muscular interventricular septum, and the ventricular myocardium. Human DSCR1 contains an NFAT-rich calcineurin-responsive element adjacent to exon 4. Transgenic mice generated with a homologous regulatory region of the mouse DSCR1 gene linked to lacZ (DSCR1(e4)/lacZ) show gene activation in the endocardium of the developing valves and aorticopulmonary septum of the heart, recapitulating a specific subdomain of endogenous DSCR1 cardiac expression. DSCR1(e4)/lacZ expression in the developing valve endocardium colocalizes with NFATc1 and, endocardial DSCR1(e4)/lacZ, is notably reduced or absent in NFATc1(-/-) embryos. Furthermore, expression of the endogenous DSCR1(e4) isoform is decreased in the outflow tract of NFATc1(-/-) hearts, and the DSCR1(e4) intragenic element is trans-activated by NFATc1 in cell culture. In trisomy 16 (Ts16) mice, expression of endogenous DSCR1 and DSCR1(e4)/lacZ colocalizes with anomalous valvuloseptal development, and transgenic Ts16 hearts have increased beta-galactosidase activity. DSCR1 and DSCR1(e4)/lacZ also are expressed in other organ systems affected by trisomy 16 in mice or trisomy 21 in humans including the brain, eye, ear, face, and limbs. Together, these results show that DSCR1(e4) expression in the developing valve endocardium is dependent on NFATc1 and support a role for DSCR1 in normal cardiac valvuloseptal formation as well as the abnormal development of several organ systems affected in individuals with Down syndrome.

A small molecular activator of cardiac hypertrophy uncovered in a chemical screen for modifiers of the calcineurin signaling pathway

The calcium, calmodulin-dependent phosphatase calcineurin, regulates growth and gene expression of striated muscles. The activity of calcineurin is modulated by a family of cofactors, referred to as modulatory calcineurin-interacting proteins (MCIPs). In the heart, the MCIP1 gene is activated by calcineurin and has been proposed to fulfill a negative feedback loop that restrains potentially pathological calcineurin signaling, which would otherwise lead to abnormal cardiac growth. In a high-throughput screen for small molecules capable of regulating MCIP1 expression in muscle cells, we identified a unique 4-aminopyridine derivative exhibiting an embedded partial structural motif of serotonin (5-hydroxytryptamine, 5-HT). This molecule, referred to as pyridine activator of myocyte hypertrophy, acts as a selective agonist for 5-HT(2A/2B) receptors and induces hypertrophy of cardiac muscle cells through a signaling pathway involving calcineurin and a kinase-dependent mechanism that inactivates class II histone deacetylases, which act as repressors of cardiac growth. These findings identify MCIP1 as a downstream target of 5-HT(2A/2B) receptor signaling in cardiac muscle cells and suggest possible uses for 5-HT(2A/2B) agonists and antagonists as modulators of cardiac growth and gene expression.

MCIP1 Overexpression Suppresses Left Ventricular Remodeling and Sustains Cardiac Function After Myocardial Infarction

Pathological remodeling of the left ventricle (LV) after myocardial infarction (MI) is a major cause of heart failure. Although cardiac hypertrophy after increased loading conditions has been recognized as a clinical risk factor for human heart failure, it is unknown whether post-MI hypertrophic remodeling of the myocardium is beneficial for cardiac function over time, nor which regulatory pathways play a crucial role in this process. To address these questions, transgenic (TG) mice engineered to overexpress modulatory calcineurin-interacting protein-1 (MCIP1) in the myocardium were used to achieve cardiac-specific inhibition of calcineurin activation. MCIP1-TG mice and their wild-type (WT) littermates, were subjected to MI and analyzed 4 weeks later. At 4 weeks after MI, calcineurin was activated in the LV of WT mice, which was significantly reduced in MCIP1-TG mice. WT mice displayed a 78% increase in LV mass after MI, which was reduced by 38% in MCIP1-TG mice. Echocardiography indicated marked LV dilation and loss of systolic function in WT-MI mice, whereas TG-MI mice displayed a remarkable preservation of LV geometry and contractility, a pronounced reduction in myofiber hypertrophy, collagen deposition, and beta-MHC expression compared with WT-MI mice. Together, these results reveal a protective role for MCIP1 in the post-MI heart and suggest that calcineurin is a crucial regulator of postinfarction-induced pathological LV remodeling. The improvement in functional, structural, and molecular abnormalities in MCIP1-TG mice challenges the adaptive value of post-MI hypertrophy of the remote myocardium. The full text of this article is available online at http://circres.ahajournals.org.

Endogenous protein inhibitors of calcineurin

A growing family of endogenous inhibitors of calcineurin has been identified in recent years. These endogenous calcineurin inhibitors are throwing new light on the function and regulation of calcineurin in a wide variety of cellular processes and cell types.

Pacing-induced calcineurin activation controls cardiac Ca2+ signalling and gene expression

Calcineurin, a Ca(2+)-calmodulin-dependent protein phosphatase (PP2B) is one of the links between Ca(2+) signals and regulation of gene transcription in cardiac muscle. We studied the Ca(2+) signal specificity of calcineurin activation experimentally and with modelling. In the rat atrial preparation, an increase in pacing frequency increased nuclear activity of the calcineurin-sensitive transcription factor, nuclear factor of activated T-cells (NFAT), 2-fold in a cyclosporin A (CsA)-sensitive manner. In line with this, modelling results predicted that the frequency of cardiac Ca(2+) transients encodes the stimulus for calcineurin activation. We further observed experimentally that calcineurin inhibition by CsA modulated Ca(2+) release in a Ca(2+)-dependent manner. CsA had no effect on [Ca(2+)](i) at a pacing frequency of 1 Hz but it significantly suppressed the amplitude of Ca(2+) transients, systolic [Ca(2+)](i) and time averaged [Ca(2+)](i) at 6 Hz. Calcineurin had a differential role in the expression of immediate-early genes B-type natriuretic peptide (BNP) and c-fos. CsA inhibited the pacing-induced BNP gene expression, whereas pacing alone had no effect on the expression of c-fos. However, in the presence of CsA, c-fos mRNA levels were significantly augmented by increased pacing frequency. These results show that frequency-dependent calcineurin activation has a specific role in [Ca(2+)](i) regulation and gene expression, constantly recruited by varying cardiac Ca(2+) signals.

GSK-3 kinases enhance calcineurin signaling by phosphorylation of RCNs

The conserved RCN family of proteins can bind and directly regulate calcineurin, a Ca(2+)-activated protein phosphatase involved in immunity, heart growth, muscle development, learning, and other processes. Whereas high levels of RCNs can inhibit calcineurin signaling in fungal and animal cells, RCNs can also stimulate calcineurin signaling when expressed at endogenous levels. Here we show that the stimulatory effect of yeast Rcn1 involves phosphorylation of a conserved serine residue by Mck1, a member of the GSK-3 family of protein kinases. Mutations at the GSK-3 consensus site of Rcn1 and human DSCR1/MCIP1 abolish the stimulatory effects on calcineurin signaling. RCNs may therefore oscillate between stimulatory and inhibitory forms in vivo in a manner similar to the Inhibitor-2 regulators of type 1 protein phosphatase. Computational modeling indicates a biphasic response of calcineurin to increasing RCN concentration such that protein phosphatase activity is stimulated by low concentrations of phospho-RCN and inhibited by high concentrations of phospho- or dephospho-RCN. This prediction was verified experimentally in yeast cells expressing Rcn1 or DSCR1/MCIP1 at different concentrations. Through the phosphorylation of RCNs, GSK-3 kinases can potentially contribute to a positive feedback loop involving calcineurin-dependent up-regulation of RCN expression. Such feedback may help explain the large induction of DSCR1/MCIP1 observed in brain of Down syndrome individuals.

The Drosophila homolog of Down's syndrome critical region 1 gene regulates learning: implications for mental retardation

Mental retardation is the most common phenotypic abnormality seen in Down's syndrome (DS) patients, yet the underlying mechanism remains mysterious. DS critical region 1 (DSCR1), located on chromosome 21, is overexpressed in the brain of DS fetus and encodes an inhibitor of calcineurin, but its physiological significance is unknown. To study its functional importance and role in mental retardation in DS, we generated Drosophila mutants of nebula, an ortholog of human DSCR1. Here, we report that both nebula loss-of-function and overexpression mutants exhibit severe learning defects that are attributed by biochemical perturbations rather than maldevelopment of the brain. These results, combined with our data showing that the same biochemical signaling pathway is altered in human DS fetal brain tissue overexpressing DSCR1, suggest that alteration of DSCR1 expression could contribute to mental retardation in DS.

Ca2+/calcineurin signalling in cells of the immune system

Calcineurin is a serine-threonine - phosphatase that is expressed in a wide variety of tissues and has particularly critical functions in neurons, cardiac and skeletal muscle cells, and lymphocytes. This review focuses on recent studies elucidating the role of Ca(2+)/calcineurin signalling of the immune system.

Role of calcineurin in striated muscle: development, adaptation, and disease

Striated muscles, cardiac and skeletal muscles, use calcium as a second messenger to respond and adapt to environmental stimuli. Elevations in intracellular calcium activate calcineurin, a serine/threonine phosphatase, resulting in expression of a set of genes involved in remodeling striated muscle. Activation of calcineurin in hearts produces cardiac hypertrophy, and in skeletal muscle promotes cell differentiation and transforms fiber type specificity. In this review we discuss the effects of calcineurin activity on development, adaptation, and disease of striated muscle.

The threshold pattern of calcineurin-dependent gene expression is altered by loss of the endogenous inhibitor calcipressin

Calcineurin links calcium signaling to transcriptional responses in the immune, nervous and cardiovascular systems. To determine the function of the calcipressins, a family of putative calcineurin inhibitors, we assessed the calcineurin-dependent process of T cell activation in mice engineered to lack the gene encoding calcipressin 1 (Csp1). Csp1 regulated calcineurin in vivo, and genes triggered in an immune response had unique transactivation thresholds for T cell receptor stimulation. In the absence of Csp1, the apparent transactivation thresholds for all these genes were shifted because of enhanced calcineurin activity. This unbridled calcineurin activity drove Fas ligand expression, which normally requires high T cell receptor stimulation and results in the premature death of T helper type 1 cells. Thus, calcipressins modulate the pattern of calcineurin-dependent transcription, and may influence calcineurin activity beyond calcium to integrate a broad array of signals into the cellular response.