Ca2+-induced PARP-1 activation and ANF expression are coupled events in cardiomyocytes.

The nuclear protein PARP-1 [poly(ADP-ribose) polymerase-1] is activated in cardiomyocytes exposed to hypoxia causing DNA breaks. Unlike this stress-induced PARP-1 activation, our results provide evidence for Ca(2+)-induced PARP-1 activation in contracting newborn cardiomyocytes treated with growth factors and hormones that increased their contraction rate, induced intracellular Ca(2+) mobilization and its rhythmical and transient translocation into the nucleus. Furthermore, activated PARP-1 up-regulated the activity of phosphorylated ERK (extracellular-signal-regulated kinase) in the nucleus, promoting expression of the Elk1 target gene c-fos. Up-regulation of the transcription factor c-Fos/GATA-4 promoted ANF (atrial natriuretic factor) expression. Given that expression of ANF is known to be implicated in morphological changes, growth and development of cardiomyocytes, these results outline a PARP-1-dependent signal transduction mechanism that links contraction rate and Ca(2+) mobilization with the expression of genes underlying morphological changes in cardiomyocytes.

Related papers:

title: Sarcoplasmic reticulum gene expression in cardiac hypertrophy and heart failure.
abstract: In cardiac and skeletal muscle, the sarcoplasmic reticulum (SR) plays a central role in the contraction relaxation cycle of the muscle by virtue of its ability to regulate the intracellular free Ca'+ concentration [Ca'+],. Ca'+ release from the SR increases [Ca'+] (10`mol/L), thus inducing contraction, whereas Ca2` uptake by the SR reduces [Ca'+] (=10-7 mol/L), producing muscle relaxation. In cardiac muscle, the beatto-beat rhythm (contraction-relaxation cycle) is tightly controlled by the regulated release and removal of Ca'+ by the SR. In view of this key role in excitationcontraction coupling, alterations in the SR function are expected to significantly affect cardiac performance. Over the past three decades, varying degrees of defects in the SR Ca'+ uptake function have been identified in different experimental models of heart disease, and the literature has been reviewed  ~5More recent analyses using animal models and human failing heart samples suggest that alterations in SR function may be primarily due to alterations in the expression level of mRNAs encoding key SR Ca2' transport proteins. The purpose of this review is to highlight recent advances concerning the regulation of SR gene expression during cardiac hypertrophy and heart failure.

title: Cardiomyocyte Ca2+ overload in atrial tachycardia: is blockade of L-type Ca2+ channels a promising approach to prevent electrical remodeling and arrhythmogenesis?
abstract: Electrical remodeling paradigm has important implications for the understanding of atrial fibrillation (AF) and improvement of current treatment. Cardiomyocyte Ca2+ overload is generally accepted as the initiating signal for the tachycardia-induced changes in atrial electrical properties (electrical remodeling). The precise role of cardiomyocyte Ca2+ overload in AF-related ion channel alterations that contribute to AF maintenance is not fully understood. Clinically, patients with AF are often treated with Ca2+ channel blockers such as verapamil to control their ventricular rate and to improve the success rate of cardioversion procedures. However, verapamil may produce an increased L-type Ca2+ channel current (ICa,L) that may reinforce Ca2+ overload thereby promoting AF in the atrium. Ca2+ channel blockers which target T-type Ca2+ channels in addition to ICa,L (for instance, efonidipine) may be more efficient at preventing Ca2+ overload and arrhythmogenic electrical remodeling, but the potential benefits of these drugs have usually been tested in experimental models where drug administration preceded the initiation of electrical remodeling. Studies in animal models with established atrial tachycardia remodeling and in patients with AF are clearly warranted to prove the efficacy of Ca2+ channel blockers that additionally target T-type Ca2+ channels.

title: Alterations of sarcoplasmic reticulum proteins in failing human dilated cardiomyopathy.
abstract: Previous studies provide considerable evidence that excitation-contraction coupling may be disturbed at the level of the sarcoplasmic reticulum (SR) in the failing human heart. Disturbed SR function may result from altered expression of calcium-handling proteins.



Levels of SR proteins involved in calcium release (ryanodine receptor), calcium binding (calsequestrin, calreticulin), and calcium uptake (calcium ATPase, phospholamban) were measured by Western blot analysis in nonfailing human myocardium (n = 7) and in end-stage failing myocardium due to dilated cardiomyopathy (n = 14). The levels of the ryanodine receptor, calsequestrin, and calreticulin were not significantly different in nonfailing and failing human myocardium. Phospholamban protein levels (pentameric form) normalized per total protein were decreased by 18% in the failing myocardium (P < .05). However, phospholamban protein levels were not significantly different in failing and nonfailing myocardium when normalization was performed per calsequestrin. Protein levels of SR calcium ATPase, normalized per total protein or per calsequestrin, were decreased by 41% (P < .001) or 33% (P < .05), respectively, in the failing myocardium. Furthermore, SR calcium ATPase was decreased relative to ryanodine receptor by 37% (P < .05) and relative to phospholamban by 28% (P < .05).



Levels of SR proteins involved in calcium binding and release are unchanged in failing dilated cardiomyopathy. In contrast, protein levels of calcium ATPase involved in SR calcium uptake are reduced in the failing myocardium. Moreover, SR calcium ATPase is decreased relative to its inhibitory protein, phospholamban.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Calcium and cardiac rhythms: physiological and pathophysiological.
abstract: Calcium plays two pivotal roles in cardiac excitation-contraction (E-C) coupling.1 Ca2+ drives myofilament activation and carries or regulates ionic currents that are responsible for normal electrical rhythms2 as well as life-threatening arrhythmias.3 In this editorial, I will focus on Ca2+ and pacemaker activity and arrhythmogenesis.

Ca2+ entry via Ca2+ current ( I Ca) triggers sarcoplasmic reticulum (SR) Ca2+ release via ryanodine receptors (RyRs), and relaxation is driven by Ca2+ transport by the SR Ca2+-ATPase and Na+-Ca2+ exchange. Two I Ca types occur in cardiac myocytes: L-type ( I Ca,L) activated at Em>−40 mV and T-type ( I Ca,T) activated at Em>−60 mV (near the pacemaker range). Inward I Ca,T and I Ca,L can contribute importantly to both normal and abnormal cardiac depolarization. I Ca,L is crucial in E-C coupling in all cardiac myocytes. I Ca,T is absent in most ventricular myocytes but is present in neonatal ventricular myocytes, some atrial myocytes, and in conducting and pacemaker cells. β-Adrenergic receptors (β-ARs) and cAMP-dependent protein kinase (PKA) increase I Ca,L amplitude and shift activation to more negative Em (closer to the pacemaker range). Parasympathetic stimulation of the heart (via muscarinic receptors) can offset the β-AR effect. Withdrawal of muscarinic activation can also cause a rebound overshoot in I Ca,L and may contribute directly to postvagal tachycardia.4,5⇓ I Ca,L is rapidly inactivated by local [Ca2+] at the inner channel mouth (mediated by calmodulin associated with the channel).6,7⇓ As [Ca2+]i declines, I Ca,L can recover partially from inactivation, even at depolarized Em.8 This can allow I Ca,L reactivation before the action potential (AP) fully repolarizes, inducing early afterdepolarizations (EADs).

Resting myocytes exhibit spontaneous, localized SR Ca …

title: PolyADP-Ribosylation Is Involved in Neurotrophic Activity
abstract: PolyADP-ribosylation is a transient posttranslational modification of proteins, mainly catalyzed by poly(ADP-ribose)polymerase-1 (PARP-1). This highly conserved nuclear protein is activated rapidly in response to DNA nick formation and promotes a fast DNA repair. Here, we examine a possible association between polyADP-ribosylation and the activity of neurotrophins and neuroprotective peptides taking part in life-or-death decisions in mammalian neurons. The presented results indicate an alternative mode of PARP-1 activation in the absence of DNA damage by neurotrophin-induced signaling mechanisms. PARP-1 was activated in rat cerebral cortical neurons briefly exposed to NGF-related nerve growth factors and to the neuroprotective peptides NAP (the peptide NAPVSIPQ, derived from the activity-dependent neuroprotective protein ADNP) and ADNF-9 (the peptide SALLRSIPA, derived from the activity-dependent neurotrophic factor ADNF) In addition, polyADP-ribosylation was involved in the neurotrophic activity of NGF-induced and NAP-induced neurite outgrowth in differentiating pheochromocytoma 12 cells as well as in the neuroprotective activity of NAP in neurons treated with the Alzheimer's disease neurotoxin β-amyloid. A fast loosening of the highly condensed chromatin structure by polyADP-ribosylation of histone H1, which renders DNA accessible to transcription and repair, may underlie the role of polyADP-ribosylation in neurotrophic activity.

title: The PARP superfamily
abstract: Poly(ADP‐ribosyl)ation is an immediate DNA‐damage‐dependent post‐translational modification of histones and other nuclear proteins that contributes to the survival of injured proliferating cells. Poly(ADP‐ribose) polymerases (PARPs) now constitute a large family of 18 proteins, encoded by different genes and displaying a conserved catalytic domain in which PARP‐1 (113 kDa), the founding member, and PARP‐2 (62 kDa) are so far the sole enzymes whose catalytic activity has been shown to be immediately stimulated by DNA strand breaks. A large repertoire of sequences encoding novel PARPs now extends considerably the field of poly(ADP‐ribosyl)ation reactions to various aspects of the cell biology including cell proliferation and cell death. Some of these new members interact with each other, share common partners and common subcellular localizations suggesting possible fine tuning in the regulation of this post‐translational modification of proteins. This review summarizes our present knowledge of this emerging superfamily, which might ultimately improve pharmacological strategies to enhance both antitumor efficacy and the treatment of a number of inflammatory and neurodegenerative disorders. A provisional nomenclature is proposed. BioEssays 26:882–893, 2004.

title: Chromatin Loosening by Poly(ADP)-Ribose Polymerase (PARP) at Drosophila Puff Loci
abstract: Steroid response and stress-activated genes such ashsp70 undergo puffing in Drosophila larval salivary glands, a local loosening of polytene chromatin structure associated with gene induction. We find that puffs acquire elevated levels of adenosine diphosphate (ADP)-ribose modified proteins and that poly(ADP)-ribose polymerase (PARP) is required to produce normal-sized puffs and normal amounts of Hsp70 after heat exposure. We propose that chromosomal PARP molecules become activated by developmental or environmental cues and strip nearby chromatin proteins off DNA to generate a puff. Such local loosening may facilitate transcription and may transiently make protein complexes more accessible to modification, promoting chromatin remodeling during development.

title: DNA-independent PARP-1 activation by phosphorylated ERK2 increases Elk1 activity: a link to histone acetylation.
abstract: PolyADP-ribose polymerases (PARPs) catalyze a posttranslational modification of nuclear proteins by polyADP-ribosylation. The catalytic activity of the abundant nuclear protein PARP-1 is stimulated by DNA strand breaks, and PARP-1 activation is required for initiation of DNA repair. Here we show that PARP-1 also acts within extracellular signal-regulated kinase (ERK) signaling cascade that mediates growth and differentiation. The findings reveal an alternative mode of PARP-1 activation, which does not involve binding to DNA or DNA damage. In a cell-free system, recombinant PARP-1 was intensively activated and thereby polyADP-ribosylated by a direct interaction with phosphorylated ERK2, and the activated PARP-1 dramatically increased ERK2-catalyzed phosphorylation of the transcription factor Elk1. In cortical neurons treated with nerve growth factors and in stimulated cardiomyocytes, PARP-1 activation enhanced ERK-induced Elk1-phosphorylation, core histone acetylation, and transcription of the Elk1-target gene c-fos. These findings constitute evidence for PARP-1 activity within the ERK signal-transduction pathway.

title: PARP-1 activation in the ERK signaling pathway.
abstract: PARP-1 is a highly conserved DNA-binding protein, the most abundant member of the polyADP-ribose polymerases (PARP) family, which catalyzes post-translational modification of proteins by polyADP-ribosylation. This modification affects protein-protein and protein-DNA interactions. Binding of PARP-1 to breakages in damaged DNA causes its activation and auto-polyADP-ribosylation in a process that is pivotal for DNA repair. Our recent findings outlined an alternative mechanism of PARP-1 activation via a direct interaction with phosphorylated ERK2 (externally regulated kinase), which is unrelated to DNA damage and does not involve PARP-1 binding to DNA. Furthermore, ERK2-induced PARP-1 activation dramatically amplifies ERK-signals, enhancing ERK-induced phosphorylation of the transcription factor Elk1 and enhancing core histone acetylation and expression of the Elk1 target gene, c-fos. Thus, PARP-1 activation in the ERK signaling pathway mediates epigenetic mechanisms promoting growth, proliferation and differentiation regulated by the Raf-MEK-ERK phosphorylation cascade.

title: Activating the PARP-1 Sensor Component of the Groucho/ TLE1 Corepressor Complex Mediates a CaMKinase IIδ-Dependent Neurogenic Gene Activation Pathway
abstract: Switching specific patterns of gene repression and activation in response to precise temporal/spatial signals is critical for normal development. Here we report a pathway in which induction of CaMKIIdelta triggers an unexpected switch in the function of the HES1 transcription factor from a TLE-dependent repressor to an activator required for neuronal differentiation. These events are based on activation of the poly(ADP-ribose) polymerase1 (PARP-1) sensor component of the groucho/TLE-corepressor complex mediating dismissal of the corepressor complex from HES1-regulated promoters. In parallel, CaMKIIdelta mediates a required phosphorylation of HES1 to permit neurogenic gene activation, revealing the ability of a specific signaling pathway to modulate both the derepression and the subsequent coactivator recruitment events required for transcriptional activation of a neurogenic program. The identification of PARP-1 as a regulated promoter-specific exchange factor required for activation of specific neurogenic gene programs is likely to be prototypic of similar molecular mechanisms.

title: Transcriptional control by PARP-1: chromatin modulation, enhancer-binding, coregulation, and insulation.
abstract: The regulation of gene expression requires a wide array of protein factors that can modulate chromatin structure, act at enhancers, function as transcriptional coregulators, or regulate insulator function. Poly(ADP-ribose) polymerase-1 (PARP-1), an abundant and ubiquitous nuclear enzyme that catalyzes the NAD(+)-dependent addition of ADP-ribose polymers on a variety of nuclear proteins, has been implicated in all of these functions. Recent biochemical, genomic, proteomic, and cell-based studies have highlighted the role of PARP-1 in each of these processes and provided new insights about the molecular mechanisms governing PARP-1-dependent regulation of gene expression. In addition, these studies have demonstrated how PARP-1 functions as an integral part of cellular signaling pathways that culminate in gene-regulatory outcomes.

title: Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins
abstract: This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

title: Ets ternary complex transcription factors.
abstract: The three ternary complex factors (TCFs) Elk-1, Net and Sap-1 form a subfamily of the E twenty-six (Ets) domain transcription factors. Their characteristic property is the ability to form a ternary nucleoprotein complex with the serum response factor (SRF) over the serum response element (SRE) of the c-fos promoter. The molecular mechanisms that underlie the function and regulation of these factors have been extensively studied and the TCFs are a paradigm for the study of transcriptional regulation in response to extracellular signalling through the mitogen-activated protein (MAP) kinase pathway. As final effectors of multiple signalling pathways and components of protein complexes on immediate early promoters, they represent key elements in the complex and dynamic regulation of gene expression. This review summarises the molecular, structural and biochemical studies that have led to the understanding of the functional domains of the TCFs, ternary complex formation, transcriptional regulation, protein partners and target genes in cell lines. Finally, the emerging studies of the biological roles of the TCFs in vivo will be discussed.

title: Tissue-specific GATA factors are transcriptional effectors of the small GTPase RhoA.
abstract: Rho-like GTPases play a pivotal role in the orchestration of changes in the actin cytoskeleton in response to receptor stimulation, and have been implicated in transcriptional activation, cell growth regulation, and oncogenic transformation. Recently, a role for RhoA in the regulation of cardiac contractility and hypertrophic cardiomyocyte growth has been suggested but the mechanisms underlying RhoA function in the heart remain undefined. We now report that transcription factor GATA-4, a key regulator of cardiac genes, is a nuclear mediator of RhoA signaling and is involved in the control of sarcomere assembly in cardiomyocytes. Both RhoA and GATA-4 are essential for sarcomeric reorganization in response to hypertrophic growth stimuli and overexpression of either protein is sufficient to induce sarcomeric reorganization. Consistent with convergence of RhoA and GATA signaling, RhoA potentiates the transcriptional activity of GATA-4 via a p38 MAPK-dependent pathway that phosphorylates GATA-4 activation domains and GATA binding sites mediate RhoA activation of target cardiac promoters. Moreover, a dominant-negative GATA-4 protein abolishes RhoA-induced sarcomere reorganization. The identification of transcription factor GATA-4 as a RhoA mediator in sarcomere reorganization and cardiac gene regulation provides a link between RhoA effects on transcription and cell remodeling.

title: GATA factors and transcriptional regulation of cardiac natriuretic peptide genes
abstract: The A- and B-natriuretic peptides (ANP and BNP) are the heart major secretory products. ANF and BNP expression is a marker of cardiomyocyte differentiation, and is regulated spatially, developmentally and hormonally. Analysis of the ANP and BNP promoters has contributed in a major way to our present understanding of the key regulators of cardiac development. It has also started to unravel the complex combinatorial interactions required for proper regulation of the cardiac genetic program. The GATA family of transcription factors initially identified as essential regulators of the two natriuretic peptide genes appears to be at the heart of the molecular circuits governing cardiac growth and differentiation. In particular, GATA-4 has emerged as the nuclear effector of several signaling pathways which modulate its function through post-translational modifications and protein-protein interactions. This review will cover our current knowledge of cardiac transcription and the role of GATA factors in embryonic and postnatal heart development.

title: Determinants of Natriuretic Peptide Production by the Heart
abstract: The cardiac natriuretic peptides (NPs) atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are polypeptide hormones synthesized, stored, and secreted by cardiac muscle cells (cardiocytes). The NPs modulate extracellular fluid volume and blood pressure and have potent growth-regulating properties, which make them of great interest for cardiac remodeling in acute myocardial infarction and congestive heart failure. We have observed that the production of NP can be coordinately or discoordinately regulated. In the former type, muscle stretch-elicited secretion triggers signals mediated by Gi/o protein, whereas agonists such as endothelin 1 independently signal through Gq. Discoordinated regulation is observed following stimulations by some cytokines, which selectively up-regulate BNP. This regulation takes place at the translational and transcriptional levels and is dependent on a p38 signaling pathway. Further details of processes regulating NP secretion need to be defined to develop a comprehensive view of the endocrine function of the heart. Nevertheless, translational research in the area of NPs has demonstrated the usefulness of these hormones as a marker of disease and as potential therapeutic agents. The latter application of NP is particularly attractive given that ANF and BNP possess pharmacologic actions that require polypharmacy in the treatment of acute myocardial infarction and congestive heart failure.

title: A Triad of Serum Response Factor and the GATA and NK Families Governs the Transcription of Smooth and Cardiac Muscle Genes*
abstract: Serum response factor and the (CC(A/T)6GG) (CArG) box interact to promote the transcription of c-fos and muscle genes; this tissue-specific activity may require co-regulators for serum response factor. The α1 integrin promoter contains twocis-elements besides the CArG box: a TAAT sequence, a consensus binding site for homeoproteins, and a GATA-binding box. As a candidate TAAT-binding factor, we cloned an NK family homeobox gene,Nkx-3.2, which is expressed mainly in smooth muscle tissues and skeletal structures. Nkx-3.2, serum response factor, and GATA-6 were co-expressed only in the medial smooth muscle layer of arteries. These three transcription factors formed a complex with their corresponding cis-elements and cooperatively transactivated smooth muscle genes, including α1 integrin,SM22α, and caldesmon. Cardiac muscle-specific members of the NK and GATA families exist, and the triad of Nkx-2.5, serum response factor, and GATA-4 also transactivated the cardiac atrial natriuretic factor gene, which contains a CArG-like box, a GATA-binding box, and an NK-binding element. Our findings demonstrate that smooth and cardiac muscle have a shared transcriptional machinery and that the GATA and NK families confer muscle specificity on the serum response factor/CArG interaction.

title: Expression of immediate early genes, GATA‐4, and Nkx‐2.5 in adrenergic‐induced cardiac hypertrophy and during regression in adult mice
abstract: Adrenoreceptor agonists induce a hypertrophic phenotype in vitro and in vivo. To investigate the molecular remodeling in chronic cardiac hypertrophy we infused adult male mice with vehicle, isoproterenol, phenylephrine or both agonists for 3, 7 or 14 days. All drugs increased cardiac mass. After minipump removal cardiac mass regressed to control levels within 7 days after PE and ISO treatment whereas ISO+PE treated hearts were incompletely regressed. ANF and β‐MHC, but not α‐MHC, expression were increased by agonists at all time points. GATA‐4, Nkx‐2.5, Egr‐1, c‐jun and c‐fos expression were increased after 3, 7 and 14 days of treatment. Expression was greatest after ISO+PE>>ISO>PE>vehicle infusion suggesting a synergistic effect of adrenoreceptor stimulation and indicating a greater effect of β‐ than α‐adrenergic action in vivo. After PE or ISO drug withdrawal the HW/BW was normal and Egr‐1, c‐jun, c‐fos and GATA‐4, but not Nkx2.5, expression dropped to control levels. HW/BW regression was incomplete after ISO+PE and elevated levels of Egr‐1, c‐jun and Nkx2.5 expression remained. A hydralazine‐mediated reduction in blood pressure had no effect on the agonist‐induced cardiac hypertrophy or gene expression. In conclusion, we found that continued agonist stimulation, and not blood pressure, is responsible for the maintained increase in gene expression. Further, we found the decrease in gene expression in the regression after drug withdrawal was gene specific.

title: Regulation of A1 adenosine receptors by amiodarone and electrical stimulation in rat myocardial cells in vitro.
abstract: The effects of conditions that either increase or decrease heart rate on the pharmacological properties of adenosine receptors in cultured rat myocytes were examined. Levels of A1 adenosine receptors, following prolonged treatment with electrical stimulation (ES) or the antiarrhythmic drug amiodarone, were determined using radioligand binding with the specific A1 receptor antagonist [3H]1,3-dipropyl-8-cyclopentylxanthine (CPX). The effects of lowering temperature were also explored. Exposure to amiodarone for 4 days reduced the density of A1 receptors by 19% (from 24.7 +/- 0.4 to 20.09 +/- 0.3 fmol/dish) and inhibited the rate of contraction by 60% (from 188 +/- 16 to 76 +/- 30 beats/min), without changing the receptor affinity, protein content, creatine kinase (CK) activity or cell number. Electrical stimulation at 25 degrees C elevated the density of A1 adenosine receptors by 185% (from 4.1 +/- 0.4 to 11.69 +/- 2.1 fmol/dish). Four days of reduced temperature (from 37 degrees C to either 30 or 25 degrees C) lowered the density of A1 adenosine receptors by 69 or 86%, respectively (from 24.1 +/- 1.2 to 7.4 +/- 0.4 or 3.4 +/- 0.3 fmol/dish), with no significant change in the receptor affinity, activity of CK, or lactate dehydrogenase (LDH), protein content or cell number. The observed up- and down-regulation of A1 adenosine receptors in primary myocyte cultures in response to conditions that exogenously alter the rate of contraction, is indicative of the role of adenosine receptors in adaptation of heart cells to stress.

title: Evidence for Endogenous ADP-ribosylation of GTP-binding Proteins in Neuronal Cell Nucleus
abstract: GTP-binding protein(s) recognized by antibodies against the α-subunits of Gi- and Go-proteins were detected in crude nuclei isolated from rat brain stem and cortex. Immunohistochemical staining indicated that in the cortex these proteins are perinuclear, or are embedded in the nuclear membrane. Evidence is presented for an endogenous ADP-ribosylation of these proteins, which competes with their PTX-catalyzed ADP-ribosylation. The endogenous reaction has the characteristics of nonenzymatic ADP-ribosylation of cysteine residues, known to involve NAD-glycohydrolase activity. In vitro experiments showed that the α-subunit of Go-proteins in the cell membrane also acts as a substrate of this endogenous ADP-ribosylation. The in situ effect of membrane depolarization on the nuclear GTP-binding proteins may be attributable to their depolarization-induced endogenous ADP-ribosylation, suggesting a novel signaling mechanism in neuronal cells in the central nervous system.

title: Cardioprotective effects of adenosine A1 and A 3 receptor activation during hypoxia in isolated rat cardiac myocytes
abstract: Adenosine (ADO) is a well-known regulator of a variety of physiological functions in the heart. In stress conditions, like hypoxia or ischemia, the concentration of adenosine in the extracellular fluid rises dramatically, mainly through the breakdown of ATP. The degradation of adenosine in the ischemic myocytes induced damage in these cells, but it may simultaneously exert protective effects in the heart by activation of the adenosine receptors. The contribution of ADO to stimulation of protective effects was reported in human and animal hearts, but not in rat hearts. The aim of this study was to evaluate the role of adenosine A1 and A3 receptors (A1R and A3R), in protection of isolated cardiac myocytes of newborn rats from ischemic injury. The hypoxic conditions were simulated by exposure of cultured rat cardiomyocytes (4–5 days in vitro), to an atmosphere of a N2 (95%) and CO2 (5%) mixture, in glucose-free medium for 90 min. The cardiotoxic and cardioprotective effects of ADO ligands were measured by the release of lactate dehydrogenase (LDH) into the medium. Morphological investigation includes immunohistochemistry, image analysis of living and fixed cells and electron microscopy were executed. Pretreatment with the adenosine deaminase considerably increased the hypoxic damage in the cardiomyocytes indicating the importance of extracellular adenosine. Blocking adenosine receptors with selective A1 and A3 receptor antagonists abolished the protective effects of adenosine. A1R and A3R activation during the hypoxic insult delays onset of irreversible cell injury and collapse of mitochondrial membrane potential as assessed using DASPMI fluorochrom. Cardioprotection induced by the A1R agonist, CCPA, was abolished by an A1R antagonist, DPCPX, and was not affected by an A3R antagonist, MRS1523. Cardioprotection caused by the A3R agonist, Cl-IB-MECA, was antagonized completely by MRS1523 and only partially by DPCPX. Activation of both A1R and A3R together was more efficient in protection against hypoxia than by each one alone. Our study indicates that activation of either A1 or A3 adenosine receptors in the rat can attenuate myocyte injury during hypoxia. Highly selective A1R and A3R agonists may have potential as cardioprotective agents against ischemia or heart surgery.

title: Involvement of UTP in protection of cardiomyocytes from hypoxic stress.
abstract: Massive amounts of nucleotides are released during ischemia in the cardiovascular system. Although the effect of the purine nucleotide ATP has been intensively studied in myocardial infarction, the cardioprotective role of the pyrimidine nucleotide UTP is still unclear, especially in the cardiovascular system. The purpose of our study was to elucidate the protective effects of UTP receptor activation and describe the downstream cascade for the cardioprotective effect. Cultured cardiomyocytes and left anterior descending (LAD)-ligated rat hearts were pretreated with UTP and exposed to hypoxia-ischemia. In vitro experiments revealed that UTP reduced cardiomyocyte death induced by hypoxia, an effect that was diminished by suramin. UTP caused several effects that could trigger a cardioprotective response: a transient increase of [Ca2+]i, an effect that was abolished by PPADS or RB2; phosphorylation of the kinases ERK and Akt, which was abolished by U0126 and LY294002, respectively; and reduced mitochondrial calcium elevation after hypoxia. In vivo experiments revealed that UTP maintained ATP levels, improved mitochondrial activity, and reduced infarct size. In conclusion, UTP administrated before ischemia reduced infarct size and improved myocardial function. Reduction of mitochondrial calcium overload can partially explain the protective effect of UTP after hypoxic-ischemic injury.

title: Thiamine deficiency in cardiac cells in culture.
abstract: Rat heart cells in culture were found to be a unique model for studying biochemical and pharmacological aspects of thiamine deficiency. When thiamine was excluded from the growth medium, the following effects were observed: (1) Morphological examination did not show any difference between control and thiamine-deprived cells during the first 10 days. However, after 10-11 days spontaneous contractions ceased, accompanied by initiation of cell degeneration; (2) Intensive degeneration and cell death were observed after 14-16 days. (3) Thiamine pyrophosphate (TPP) concentration in thiamine-deprived cells was decreased gradually, with an elimination half-life of 4-5 days. (4) [3H]deoxyglucose uptake by the cells was increased, even after 1 day of thiamine deprivation. (5) ATP level decreased after 8 days and reached 50% of control cells after 10 days. (6) In thiamine-deprived cells, thiamine addition caused a 60% rise in contraction amplitude but contraction rate was not altered significantly. (7) All these effects were reversible if thiamine was supplied before the initiation of the degeneration processes.

title: Transcriptional activation of the rat liver S14 gene during postnatal development.
abstract: The mRNA coding for the rat liver S14 protein (Mr 17,000, pI 4.9) shows profound increases during postnatal development. In an effort to define the molecular basis for the postnatal rise in mRNAs14 we examined the chromatin organization of the S14 gene, its DNA methylation state, the hepatic expression of mRNAs14, and the in vitro S14 "run-on" activity prior to and after weaning at 21 days postpartum. In animals less than or equal to 15 days of age, the hepatic S14 gene is transcriptionally inactive, mRNAs14 levels are less than or equal to 0.5% of adult levels, and the chromatin organization within 11 kilobases of the 5' end of the S14 gene is similar to that found in tissues not expressing mRNAs14. From 18 to 22 days postpartum, the transcriptional activity of the S14 gene increases greater than or equal to 40-fold and mRNAs14 increases greater than or equal to 100-fold approaching adult levels of expression. Highly specific changes in S14 chromatin structure accompany gene activation. The formation of Hss-1 near the S14 cap site (-65 to -265 base pairs) and Hss-3 -3.3 kilobases upstream from the S14 cap site suggests that changes in DNA-protein interaction at these sites may function in both the tissue-specific and developmental regulation of S14 gene expression. The methylation studies suggest HhaI sites may be a cue for the tissue-specific expression of S14. However, the maintenance of hypermethylated HpaII sites throughout S14 gene activation argues against a role for these sites in either the tissue-specific or developmental regulation of S14 gene expression. These studies show that the principal molecular mechanism accounting for the major rise in mRNAs14 during postnatal development is activation of gene transcription and not stabilization of S14 RNA.

title: Adenovirus vectors differentially modulate proliferation of pituitary lactotrophs in primary culture in a mitogen and infection time-dependent manner.
abstract: Adenoviruses are powerful, widely utilized vectors for gene transfer. Limitations to their application, however, have not been well described. We used rat pituitary lactotrophs in primary culture as a model for studying how adenovirus vector infection modulates mitogen-induced proliferation and the activities of mitogen signaling pathways. Infection with adenovirus vectors expressing beta-galactosidase (betagal) raised basal proliferative levels and blocked fetal bovine serum (FBS)-induced proliferation of lactotrophs, but did not influence the changes in proliferation induced by forskolin, IGF-I, and bromocriptine. The betagal-expressing adenoviruses did not alter the inhibitory action of 17beta-estradiol (E(2)) in the presence of IGF-I; however, they blocked the stimulatory action of E(2) in the presence of dextran-coated charcoal-striped serum or forskolin. An adenovirus expressing no protein failed to block FBS-induced proliferation, but was effective in modulating basal proliferative levels and the stimulatory actions of E(2). The increased basal proliferative level and the blockade of FBS-induced proliferation were transient, and lost 5 days after infection while the blockade of the stimulatory action of E(2) in the presence of forskolin persisted. Adenovirus infection raised basal protein levels of the phosphorylated forms of cAMP response element-binding protein (pCREB) and ERK1/2 and increased the proportion of pCREB-immunoreactive lactotrophs. Adenoviruses also altered estrogen-induced responses in mRNA expression of several estrogen-responsive genes in a gene-specific manner. The results demonstrate that an adenovirus vector differentially interferes with lactotroph proliferation in response to various mitogens. Our results suggest that the effects of the adenovirus that are independent of the genes transferred must be considered when performing adenoviral gene transfer in the primary cultures of normal cells.

title: Convergence of Protein Kinase C and JAK-STAT Signaling on Transcription Factor GATA-4
abstract: Angiotensin II (AII), a potent vasoactive hormone, acts on numerous organs via G-protein-coupled receptors and elicits cell-specific responses. At the level of the heart, AII stimulation alters gene transcription and leads to cardiomyocyte hypertrophy. Numerous intracellular signaling pathways are activated in this process; however, which of these directly link receptor activation to transcriptional regulation remains undefined. We used the atrial natriuretic factor (ANF) gene (NPPA) as a marker to elucidate the signaling cascades involved in AII transcriptional responses. We show that ANF transcription is activated directly by the AII type 1 receptor and precedes the development of myocyte hypertrophy. This response maps to STAT and GATA binding sites, and the two elements transcriptionally cooperate to mediate signaling through the JAK-STAT and protein kinase C (PKC)-GATA-4 pathways. PKC phosphorylation enhances GATA-4 DNA binding activity, and STAT-1 functionally and physically interacts with GATA-4 to synergistically activate AII and other growth factor-inducible promoters. Moreover, GATA factors are able to recruit STAT proteins to target promoters via GATA binding sites, which are sufficient to support synergy. Thus, STAT proteins can act as growth factor-inducible coactivators of tissue-specific transcription factors. Interactions between STAT and GATA proteins may provide a general paradigm for understanding cell specificity of cytokine and growth factor signaling.

title: Th1-specific cell surface protein Tim-3 regulates macrophage activation and severity of an autoimmune disease
abstract: Activation of naive CD4+ T-helper cells results in the development of at least two distinct effector populations, Th1 and Th2 cells. Th1 cells produce cytokines (interferon (IFN)-γ, interleukin (IL)-2, tumour-necrosis factor (TNF)-α and lymphotoxin) that are commonly associated with cell-mediated immune responses against intracellular pathogens, delayed-type hypersensitivity reactions, and induction of organ-specific autoimmune diseases. Th2 cells produce cytokines (IL-4, IL-10 and IL-13) that are crucial for control of extracellular helminthic infections and promote atopic and allergic diseases. Although much is known about the functions of these two subsets of T-helper cells, there are few known surface molecules that distinguish between them. We report here the identification and characterization of a transmembrane protein, Tim-3, which contains an immunoglobulin and a mucin-like domain and is expressed on differentiated Th1 cells. In vivo administration of antibody to Tim-3 enhances the clinical and pathological severity of experimental autoimmune encephalomyelitis (EAE), a Th1-dependent autoimmune disease, and increases the number and activation level of macrophages. Tim-3 may have an important role in the induction of autoimmune diseases by regulating macrophage activation and/or function.

title: Characterizing transcription factor binding sites using formaldehyde crosslinking and immunoprecipitation.
abstract: In their article, A.S. Weinmann and P.J. Farnham (2002, ) described new techniques for isolating in vivo binding sites for any DNA-binding protein. In this article, we describe complementary methods for detailed in vivo characterizations of such identified protein-DNA interactions. First, we describe how formaldehyde crosslinking and chromatin immunoprecipitation (ChIP), in conjunction with transient transfections or the use of cell lines containing stably integrated constructs or episomes, can be employed to identify which specific nucleotides of a region of DNA are required for recruitment of a particular transcription factor. In contrast to in vivo footprinting, this method not only specifies which nucleotides are bound, but also identifies the protein(s) involved in binding. Next, we discuss the use of the ChIP assay to study how binding of a transcription factor is altered by passage through the cell cycle, by overexpression or deletion of another factor, or during tumorigenesis. Finally, a look toward the future suggests that the ChIP assay may be combined with Western blot analysis or mass spectrometry to identify additional proteins that interact with a transcription factor of interest.

title: Adenosine A2A and beta-adrenergic calcium transient and contractile responses in rat ventricular myocytes.
abstract: The adenosine A2A receptor (A2AR) enhances cardiac contractility, and the adenosine A1R receptor (A1R) is antiadrenergic by reducing the adrenergic beta1 receptor (beta1R)-elicited increase in contractility. In this study we compared the A2AR-, A1R-, and beta1R-elicited actions on isolated rat ventricular myocytes in terms of Ca transient and contractile responses involving PKA and PKC. Stimulation of A2AR with 2 microM (approximately EC50) CGS-21680 (CGS) produced a 17-28% increase in the Ca transient ratio (CTR) and maximum velocities (Vmax) of transient ratio increase (+MVT) and recovery (-MVT) but no change in the time-to-50% recovery (TTR). CGS increased myocyte sarcomere shortening (MSS) and the maximum velocities of shortening (+MVS) and relaxation (-MVS) by 31-34% with no change in time-to-50% relengthening (TTL). beta1R stimulation using 2 nM (approximately EC50) isoproterenol (Iso) increased CTR, +MVT, and -MVT by 67-162% and decreased TTR by 43%. Iso increased MSS, +MVS, and -MVS by 153-174% and decreased TTL by 31%. The A2AR and beta1R Ca transient and contractile responses were not additive. The PKA inhibitor Rp-adenosine 3',5'-cyclic monophosphorothioate triethylamonium salt prevented both the CGS- and Iso-elicited contractile responses. The PKC inhibitors chelerythrine and KIE1-1 peptide (PKCepsilon specific) prevented the antiadrenergic action of A1R but did not influence A2AR-mediated increases in contractile variables. The findings suggest that cardiac A2AR utilize cAMP/PKA like beta1R, but the Ca transient and contractile responses are less in magnitude and not equally affected. Although PKC is important in the A1R antiadrenergic action, it does not seem to play a role in A2AR-elicited Ca transient and contractile events.

title: Spatiotemporal Dynamics of β-Adrenergic cAMP Signals and L-Type Ca2+ Channel Regulation in Adult Rat Ventricular Myocytes: Role of Phosphodiesterases
abstract: Steady-state activation of cardiac β-adrenergic receptors leads to an intracellular compartmentation of cAMP resulting from localized cyclic nucleotide phosphodiesterase (PDE) activity. To evaluate the time course of the cAMP changes in the different compartments, brief (15 seconds) pulses of isoprenaline (100 nmol/L) were applied to adult rat ventricular myocytes (ARVMs) while monitoring cAMP changes beneath the membrane using engineered cyclic nucleotide-gated channels and within the cytosol with the fluorescence resonance energy transfer–based sensor, Epac2-camps. cAMP kinetics in the two compartments were compared to the time course of the L-type Ca2+ channel current (ICa,L) amplitude. The onset and recovery of cAMP transients were, respectively, 30% and 50% faster at the plasma membrane than in the cytosol, in agreement with a rapid production and degradation of the second messenger at the plasma membrane and a restricted diffusion of cAMP to the cytosol. ICa,L amplitude increased twice slower than cAMP at the membrane, and the current remained elevated for ≈5 minutes after cAMP had already returned to basal level, indicating that cAMP changes are not rate-limiting in channel phosphorylation/dephosphorylation. Inhibition of PDE4 (with 10 &mgr;mol/L Ro 20-1724) increased the amplitude and dramatically slowed down the onset and recovery of cAMP signals, whereas PDE3 blockade (with 1 &mgr;mol/L cilostamide) had a minor effect only on subsarcolemmal cAMP. However, when both PDE3 and PDE4 were inhibited, or when all PDEs were blocked using 3-isobutyl-l-methylxanthine (300 &mgr;mol/L), cAMP signals and ICa,L declined with a time constant >10 minutes. cAMP-dependent protein kinase inhibition with protein kinase inhibitor produced a similar effect as a partial inhibition of PDE4 on the cytosolic cAMP transient. Consistently, cAMP-PDE assay on ARVMs briefly (15 seconds) exposed to isoprenaline showed a pronounced (up to ≈50%) dose-dependent increase in total PDE activity, which was mainly attributable to activation of PDE4. These results reveal temporally distinct β-adrenergic receptor cAMP compartments in ARVMs and shed new light on the intricate roles of PDE3 and PDE4.

title: Hypertrophic responses of cardiomyocytes induced by endothelin-1 through the protein kinase C-dependent but Src and Ras-independent pathways.
abstract: We have previously shown that endothelin-1 (ET-1) modulates mechanical stretch-induced hypertrophic responses such as extracellular signal-regulated protein kinase (ERK) activation in cardiac myocytes. This study was undertaken to elucidate the ET-1-evoked signal transduction pathways leading to ERK activation. ET-1 was added to cultured cardiac myocytes of neonatal rats with or without a variety of inhibitors. ET-1 activated ERKs, which were followed by an increase in protein synthesis, and inhibition of protein kinase C activities by calphostin C completely suppressed the ET-1-induced ERK activation. We next examined whether tyrosine kinases or Ras are involved in ET-1-induced signaling pathways in cardiomyocytes. Pretreatment with a receptor tyrosine kinase inhibitor did not attenuate ET-1-induced activation of ERKs. Also, co-transfection of the dominant-negative mutant of Ras or active mutant of C-terminal Src kinase, a tyrosine kinase which inhibits Src family tyrosine kinases, with hemagglutinin-tagged ERK2 had no effects on ET-1-induced ERK2 activation. On the other hand, blockade of Raf-1 kinase function by overexpression of the dominant-negative mutant of Raf-1 kinase completely inhibited ET-1-induced ERK2 activation. These results suggest that protein kinase C and Raf-1 kinase, but not Src or Ras, are critical to ET-1-induced ERK activation in cardiac myocytes.

title: The extracellular signal-regulated kinase: Multiple substrates regulate diverse cellular functions
abstract: The extracellular signal-regulated kinase (ERK) cascade is a central pathway that transmits signals from many extracellular agents to regulate cellular processes such as proliferation, differentiation and cell cycle progression. The signaling via the ERK cascade is mediated by sequential phosphorylation and activation of protein kinases in the different tiers of the cascade. Although the main core phosphorylation chain of the cascade includes Raf kinases, MEK1/2, ERK1/2 (ERKs) and RSKs, other alternatively spliced forms and distinct components exist in the different tiers, and participate in ERK signaling under specific conditions. These components enhance the complexity of the ERK cascade and thereby, enable the wide variety of functions that are regulated by it. Another factor that is important for the dissemination of ERKs' signals is the multiplicity of the cascade's substrates, which include transcription factors, protein kinases and phosphatases, cytoskeletal elements, regulators of apoptosis, and a variety of other signaling-related molecules. About 160 substrates have already been discovered for ERKs, and the list of these substrates, as well as the function and mechanism of activation of representative substrates, are described in the current review. Many of these substrates are localized in the nucleus, and seem to participate in the regulation of transcription upon stimulation. However, other substrates are found in the cytosol as well as in other cellular organelles, and those are responsible for processes such as translation, mitosis and apoptosis. Understanding of these processes may provide a full picture of the distinct, and even opposing cellular processes that are regulated by the ERK cascade.

title: Interaction with GATA transcription factors provides a mechanism for cell-specific effects of c-Fos
abstract: c-Fos is a multifunctional transcription factor that is involved in cellular proliferation, differentiation and apoptosis. Fos is rapidly induced by a variety of hormones, growth factors and other extracellular stimuli, resulting in cell-specific responses. One potential mechanism underlying the cell-specific effects of c-Fos may be its ability to regulate gene expression through interaction with tissue-restricted transcription factors. We report here that c-Fos interacts with the cell-specific GATA proteins to potentiate their ability to transactivate target promoters, via GATA-binding sites. c-Fos is recruited to GATA proteins through direct interaction with their N-terminal activation domain. Neither the leucine zipper nor the DNA-binding domain of c-Fos is required for physical interaction with GATA proteins. Instead, a C-terminal domain located between amino acids 235 and 296, which is conserved in FosB but not in the nontransforming Fos family members, FosB/SF or Fra-1, is essential for c-Fos-GATA interaction. These data suggest that c-Fos may act as an inducible cofactor for cell-specific transcription factors and unravel a novel mechanism for transcriptional regulation by c-Fos, independent of the well-studied AP-1 pathway. The results also raise the possibility that dysregulated interaction with cell-specific transcription factors may be an important component in cellular transformation by nuclear oncogenes.

title: Decoding calcium signals involved in cardiac growth and function
abstract: Calcium is central in the regulation of cardiac contractility, growth and gene expression. Variations in the amplitude, frequency and compartmentalization of calcium signals are decoded by calcium/calmodulin-dependent enzymes, ion channels and transcription factors. Understanding the circuitry for calcium signaling creates opportunities for pharmacological modification of cardiac function.

title: Pacing‐induced calcineurin activation controls cardiac Ca2+ signalling and gene expression
abstract: Calcineurin, a Ca2+–calmodulin‐dependent protein phosphatase (PP2B) is one of the links between Ca2+ signals and regulation of gene transcription in cardiac muscle. We studied the Ca2+ 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 Ca2+ transients encodes the stimulus for calcineurin activation. We further observed experimentally that calcineurin inhibition by CsA modulated Ca2+ release in a Ca2+‐dependent manner. CsA had no effect on [Ca2+]i at a pacing frequency of 1 Hz but it significantly suppressed the amplitude of Ca2+ transients, systolic [Ca2+]i and time averaged [Ca2+]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 [Ca2+]i regulation and gene expression, constantly recruited by varying cardiac Ca2+ signals.

title: Calcium and heart failure: the cycle game
abstract: Three new studies examine how a regulator of calcium homeostasis contributes to heart failure in humans and mice.

title: Ca2+ oscillation frequency decoding in cardiac cell hypertrophy: Role of calcineurin/NFAT as Ca2+ signal integrators
abstract: The role of Ca2+ signaling in triggering hypertrophy was investigated in neonatal rat cardiomyocytes in vitro. We show that an increase in cell size and sarcomere reorganization were elicited by receptor agonists such as Angiotensin II, aldosterone, and norepinephrine and by a small rise in medium KCl concentration, a treatment devoid of direct effects on receptor functions. All these treatments increased the frequency of spontaneous [Ca2+] transients, caused nuclear translocation of transfected NFAT(GFP), and increased the expression of a NFAT-sensitive reporter gene. There was no increase in Ca2+ spark frequency in the whole cell or in the perinuclear region under these conditions. Hypertrophy and NFAT translocation but not the increased frequency of [Ca2+] transients were inhibited by the calcineurin inhibitor cyclosporine A. Hypertrophy by the different stimuli was insensitive to inhibition of myofilament contraction. We concluded that calcineurin–NFAT can act as integrators of the contractile Ca2+ signal, and that they can decode alterations in the frequency even of rapid Ca2+ oscillations.

title: An autocrine role for leptin in mediating the cardiomyocyte hypertrophic effects of angiotensin II and endothelin-1.
abstract: Leptin is a 16 kDa product of the obesity gene secreted primarily by adipocytes. We recently identified cardiomyocytes as a target for the direct hypertrophic effects of leptin and suggested that leptin may be a biological link between obesity and cardiovascular pathologies. Activation of the renin-angiotensin and endothelin systems is associated with development of cardiovascular diseases and plasma renin levels are elevated in obese individuals. We therefore determined possible interaction between these factors in mediating hypertrophy in cultured neonatal rat ventricular myocytes. Treatment for 24 h with leptin (3.1 nM), angiotensin II (100 nM) or endothelin-1 (ET-1, 10 nM) significantly increased cell area by 37%, 36% and 35%, respectively and significantly increased gene expression of myosin light chain-2 and alpha-skeletal actin as well as leucine incorporation. The hypertrophic effects of all three agents were prevented by leptin and a leptin triple mutant receptor antagonist whereas the AT(1) receptor blocker (Sar1-lle(8))-Ang II or the ET(A) receptor blocker BQ123 was ineffective against leptin-induced hypertrophy. Both angiotensin II and ET-1 significantly increased leptin levels in the culture medium by fivefold. Moreover, both angiotensin II and ET-1 increased the gene expression of the short form (OBRa) by 180% and long form (OBRb) of leptin receptors by 200%, and this increase was abolished by both leptin receptor and leptin antibodies and leptin triple mutant. Although both angiotensin II and ET-1 increased phosphorylation of MAPK (p38, ERK1/2 and JNK) and NF-kappaB, the ability of leptin blockade to attenuate the hypertrophic responses was generally dissociated from these effects suggesting an alternate, yet to be identified cellular pathway mediating this role of leptin. Our studies therefore suggest a novel autocrine function for leptin in mediating the hypertrophic effects of both angiotensin II and ET-1 in cardiac myocytes.

title: Mode of Induction of Ventricular Tachycardia and Prognosis in Patients with Coronary Disease: The Multicenter UnSustained Tachycardia Trial (MUSTT)
abstract: Programmed stimulation is an important prognostic tool in the evaluation of patients with an ejection fraction ≤40% after myocardial infarction. Many believe that ventricular tachycardia (VT) requiring 3 ventricular extrastimuli (VES) for induction is less likely to occur spontaneously and has less predictive value. However, it is unknown whether the mode of VT induction is associated with long‐term prognosis.