A ternary complex of transcription factors, Nishéd and NFATc4, and co-activator p300 bound to an intronic sequence, intronic regulatory element, is pivotal for the up-regulation of myosin light chain-2v gene in cardiac hypertrophy

Losartan counteracts the effects of cardiomyocyte swelling on glucose uptake and insulin receptor substrate-1 levels

A growing body of evidence demonstrates an association between Angiotensin II (Ang II) receptor blockers (ARBs) and enhanced glucose metabolism during ischemic heart disease. Despite these encouraging results, the mechanisms responsible for these effects during ischemia remain poorly understood. In this study we investigated the influence of losartan, an AT1 receptor blocker, and secreted Ang II (sAng II) on glucose uptake and insulin receptor substrate (IRS-1) levels during cardiomyocyte swelling. H9c2 cells were differentiated to cardiac muscle and the levels of myogenin, Myosin Light Chain (MLC), and membrane AT1 receptors were measured using flow cytometry. Intracellular Ang II (iAng II) was overexpressed in differentiated cardiomyocytes and swelling was induced after incubation with hypotonic solution for 40min. Glucose uptake and IRS-1 levels were monitored by flow cytometry using 2-NBDG fluorescent glucose (10μM) or an anti-IRS-1 monoclonal antibody in the presence or absence of losartan (10^-7M). Secreted Angiotensin II was quantified from the medium using a specific Ang II-EIA kit. To evaluate the relationship between sAng II and losartan effects on glucose uptake, transfected cells were pretreated with the drug for 24h and then exposed to hypotonic solution in the presence or absence of the secreted peptide. The results indicate that: (1) swelling of transfected cardiomyocytes decreased glucose uptake and induced the secretion of Ang II to the extracellular medium; (2) losartan antagonized the effects of swelling on glucose uptake and IRS-1 levels in transfected cardiomyocytes; (3) the effects of losartan on glucose uptake were observed during swelling only in the presence of sAng II in the culture medium. Our study demonstrates that both losartan and sAng II have essential roles in glucose metabolism during cardiomyocyte swelling.

The JAK-STAT pathway in hypertrophic stress signaling and genomic stress response

The JAK-STAT signaling pathway plays a central role in transducing stress and growth signals in the hypertrophic heart. Unlike most signal transducers, JAKs and STATs signal in a number of different ways, both within the JAK-STAT pathway and in collaboration with other signaling pathways. In this review, we discuss how IL-6 activates cells lacking IL-6 receptors through trans-signaling and examine JAK-STAT pathway interaction with GPCR-linked pathways both within and between cells. Finally, we discuss recent studies showing how the JAK-STAT pathway can intersect with a general transcriptional regulatory mechanism to effect transcription of STAT-dependent stress response genes.

Transcriptional regulation of small HSP-HSF1 and beyond

The members of the small heat shock protein (sHSP) family are molecular chaperones that play major roles in development, stress responses, and diseases, and have been envisioned as targets for therapy, particularly in cancer. The molecular mechanisms that regulate their transcription, in normal, stress, or pathological conditions, are characterized by extreme complexity and subtlety. Although historically linked to the heat shock transcription factors (HSFs), the stress-induced or developmental expression of the diverse members, including HSPB1/Hsp27/Hsp25, αA-crystallin/HSPB4, and αB-crystallin/HSPB5, relies on the combinatory effects of many transcription factors. Coupled with remarkably different cis-element architectures in the sHsp regulatory regions, they confer to each member its developmental expression or stress-inducibility. For example, multiple regulatory pathways coordinate the spatio-temporal expression of mouse αA-, αB-crystallin, and Hsp25 genes during lens development, through the action of master genes, like the large Maf family proteins and Pax6, but also HSF4. The inducibility of Hsp27 and αB-crystallin transcription by various stresses is exerted by HSF-dependent mechanisms, by which concomitant induction of Hsp27 and αB-crystallin expression is observed. In contrast, HSF-independent pathways can lead to αB-crystallin expression, but not to Hsp27 induction. Not surprisingly, deregulation of the expression of sHSP is associated with various pathologies, including cancer, neurodegenerative, or cardiac diseases. However, many questions remain to be addressed, and further elucidation of the developmental mechanisms of sHsp gene transcription might help to unravel the tissue- and stage-specific functions of this fascinating class of proteins, which might prove to be crucial for future therapeutic strategies. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Trichostatin A accentuates doxorubicin-induced hypertrophy in cardiac myocytes

Histone deacetylase inhibitors represent a new class of anticancer therapeutics and the expectation is that they will be most effective when used in combination with conventional cancer therapies, such as the anthracycline, doxorubicin. The dose-limiting side effect of doxorubicin is severe cardiotoxicity and evaluation of the effects of combinations of the anthracycline with histone deacetylase inhibitors in relevant models is important. We used a well-established in vitro model of doxorubicin-induced hypertrophy to examine the effects of the prototypical histone deacetylase inhibitor, Trichostatin A. Our findings indicate that doxorubicin modulates the expression of the hypertrophy-associated genes, ventricular myosin light chain-2, the alpha isoform of myosin heavy chain and atrial natriuretic peptide, an effect which is augmented by Trichostatin A. Furthermore, we show that Trichostatin A amplifies doxorubicin-induced DNA double strand breaks, as assessed by γH2AX formation. More generally, our findings highlight the importance of investigating potential side effects that may be associated with emerging combination therapies for cancer.

What causes a broken heart--molecular insights into heart failure

Our understanding of the molecular processes which regulate cardiac function has grown immeasurably in recent years. Even with the advent of β-blockers, angiotensin inhibitors and calcium modulating agents, heart failure (HF) still remains a seriously debilitating and life-threatening condition. Here, we review the molecular changes which occur in the heart in response to increased load and the pathways which control cardiac hypertrophy, calcium homeostasis, and immune activation during HF. These can occur as a result of genetic mutation in the case of hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) or as a result of ischemic or hypertensive heart disease. In the majority of cases, calcineurin and CaMK respond to dysregulated calcium signaling and adrenergic drive is increased, each of which has a role to play in controlling blood pressure, heart rate, and left ventricular function. Many major pathways for pathological remodeling converge on a set of transcriptional regulators such as myocyte enhancer factor 2 (MEF2), nuclear factors of activated T cells (NFAT), and GATA4 and these are opposed by the action of the natriuretic peptides ANP and BNP. Epigenetic modification has emerged in recent years as a major influence cardiac physiology and histone acetyl transferases (HATs) and histone deacetylases (HDACs) are now known to both induce and antagonize hypertrophic growth. The newly emerging roles of microRNAs in regulating left ventricular dysfunction and fibrosis also has great potential for novel therapeutic intervention. Finally, we discuss the role of the immune system in mediating left ventricular dysfunction and fibrosis and ways this can be targeted in the setting of viral myocarditis.

NFATc4 is negatively regulated in miR-133a-mediated cardiomyocyte hypertrophic repression

Activation of NFAT (nuclear factor of activated T cells)-mediated hypertrophic signaling is a major regulatory response to hypertrophic stimuli. A recent study unveiled potential regulatory roles for microRNA-133a (miR-133a) in cardiac hypertrophy. To date, however, no connection has been made between miR-133a and NFAT signaling. In this study, we determined that NFATc4, a hypertrophy-associated mediator, is negatively regulated by miR-133a. Two conserved base-pairing sites between the NFATc4 3'-untranslated region (UTR) and miR-133a were verified. Mutation of these sites in the NFATc4 3'-UTR completely blocked the negative effect of miR-133a on NFATc4, suggesting that NFATc4 is a direct target for miR-133a regulation. Using a gain-of-function approach, we demonstrate that miR-133 significantly reduces the endogenous level of, as well as the hypertrophic stimulus-mediated increase in, NFATc4 gene expression. This latter effect of miR-133a on NFATc4 gene expression was coincided with an attenuated cardiomyocyte hypertrophy induced by an alpha-adrenergic receptor agonist. Conversely, cells treated with miR-133a inhibitor resulted in an increase in NFATc4 expression level. Application of miR-133a had no apparent effect on NFATc4 nuclear localization. We conclude that the negative regulation of NFATc4 expression contributes to miR-133a-mediated hypertrophic repression.

Doxorubicin-mediated apoptosis in glioma cells requires NFAT3

Nuclear factor of activated T cells (NFAT), a family of transcription factors, has been implicated in many cellular processes, including some cancers. Here, we characterize, for the first time, the role of NFAT3 in doxorubicin (DOX)-mediated apoptosis, migration, and invasion in SNB19 and U87 glioma cells. This study demonstrates that the specific knockdown of NFAT3 results in a dramatic inhibition of the apoptotic effect induced by DOX and favors cell survival. Inhibition of NFAT3 activation by shNFAT3 (shNF3) significantly downregulated tumor necrosis factor (TNF)-alpha induction, its receptor TNFR1, caspase 10, caspase 3, and poly (ADP-ribose) polymerase, abrogating DOX-mediated apoptosis in glioma cells. DOX treatment resulted in NFAT3 translocation to the nucleus. Similarly, shNF3 treatment in SNB19 and U87 cells reversed DOX-induced inhibition of cell migration and invasion, as determined by wound healing and matrigel invasion assays. Taken together, these results indicate that NFAT3 is a prerequisite for the induction of DOX-mediated apoptosis in glioma cells.

Repression of the cardiac myosin light chain-2 gene in skeletal muscle requires site-specific association of antithetic regulator, Nished, and HDACs

The transcriptional activation mechanisms that regulate tissue-specific expression of cardiac muscle genes have been extensively investigated, but little is known of the regulatory events involved in repression of cardiac-specific genes in non-cardiac cells. We have previously reported that Nished, a ubiquitous transcription factor, interacts with a positive sequence element, the Intron Regulatory Element (IRE) as well as a negatively acting element, the Cardiac-Specific Sequence (CSS), in myosin light chain-2 (MLC2v) gene to promote activation and repression of the gene in cardiac and skeletal muscle cells respectively. Here, we show that the negative regulation of cardiac MLC2v gene in skeletal muscle cells is mediated via the interaction of Nished with histone deacetylase (HDAC) co-repressor. Treatment of cells with the HDAC inhibitor, Trichostatin A (TSA), alleviates the repressor activity of Nished in a dose-dependent manner. Co-transfection studies in primary muscle cells in culture and in Nished expressing stable skeletal muscle cell line demonstrate that Nished down-regulates the cardiac MLC2 gene expression when its association is restricted to CSS alone. Chromatin immunoprecipitation data suggest that the CSS-mediated repression of cardiac MLC2v gene in skeletal muscle cells excludes the participation of the positive element IRE despite the presence of an identical Nished binding site. Taken together, it appears that the negative control of MLC2v transcription is based on a dual mode of regulations, one that affords inaccessibility of IRE to Nished and second that promotes the formation of the transcription repression complex at the inhibitory CSS site to silence the cardiac gene in skeletal muscle cell.

Positive transcription elongation factor b activity in compensatory myocardial hypertrophy is regulated by cardiac lineage protein-1

Emerging evidence illustrates the importance of the positive transcription elongation factor (P-TEF)b in control of global RNA synthesis, which constitutes a major feature of the compensatory response to diverse hypertrophic stimuli in cardiomyocytes. P-TEFb complex, composed of cyclin T and cdk9, is critical for elongation of nascent RNA chains via phosphorylation of the carboxyl-terminal domain of RNA polymerase (Pol) II. We and others have shown that the activity of P-TEFb is inhibited by its association with cardiac lineage protein (CLP)-1, the mouse homolog of human HEXIM1, in various physiological and pathological conditions. To investigate the mechanism of control of P-TEFb activity by CLP-1 in cardiac hypertrophy, we used a transgenic mouse model of hypertrophy caused by overexpression of calcineurin in the heart. We observed that the level of CLP-1 associated with P-TEFb was reduced markedly in hypertrophic hearts. We also generated bigenic mice (MHC-cyclin T1/CLP-1(+/-)) by crossing MHC-cyclin T1 transgenic mice with CLP-1 heterozygote. The bigenic mice exhibit enhanced susceptibility to hypertrophy that is accompanied with an increase in cdk9 activity via an increase in serine 2 phosphorylation of carboxyl-terminal domain and an increase in GLUT1/GLUT4 ratio. These mice have compensated systolic function without evidence of fibrosis and reduced lifespan. These data suggest that the reduced level of CLP-1 introduced in the background of elevated levels of cyclin T1 elevates derepression of P-TEFb activity and emphasizes the importance of the role of CLP-1 in the mechanism governing compensatory hypertrophy in cardiomyocytes.

Cross-talk between calcineurin/NFAT and Jak/STAT signalling induces cardioprotective alphaB-crystallin gene expression in response to hypertrophic stimuli

Among the stress proteins that are up-regulated in the heart due to imposed biomechanical stress, αB-crystallin (CryAB) is the most abundant and pivotal in rendering protection against stress-induced cell damage. Cardiomyocyte-specific expression of the CryAB gene was shown to be dependent upon an intact αBE4 cis-element located in the CryAB enhancer. To date, there is no evidence on the identity of regulatory proteins and associated signalling molecules that control CryAB expression in cardiomyocytes. In this study, we define a mechanism by which the calcineurin/NFAT and Jak/STAT pathways regulate CryAB gene expression in response to a hypertrophic agonist endothelin-1 (En-1), in hypertrophic hearts of mice with pressure overload (TAC) and in heart-targeted calcineurin over-expressing mice (MHC-CnA). We observed that in response to various hypertrophic stimuli the transcription factors NFAT, Nished and STAT3 form a dynamic ternary complex and interact with the αBE4 promoter element of the CryAB gene. Both dominant negative NFAT and AG490, an inhibitor of the Jak2 phosphorylation, inhibited CryAB gene transcription in transient transfection assays. AG490 was also effective in blocking the nuclear translocation of NFAT and STAT3 in cardiomyocytes treated with En-1. We observed a marked increase in CryAB gene expression in MHC-CnA mouse hearts accompanied with increased phosphorylation of STAT3. We conclude that hypertrophy-dependent CryAB gene expression can be attributed to a functional linkage between the Jak/STAT and calcineurin/NFAT signalling pathways, each of which are otherwise known to be involved independently in the deleterious outcome in cardiac hypertrophy.

Molecular regulation of cardiac hypertrophy

Heart failure is one of the leading causes of mortality in the western world and encompasses a wide spectrum of cardiac pathologies. When the heart experiences extended periods of elevated workload, it undergoes hypertrophic enlargement in response to the increased demand. Cardiovascular disease, such as that caused by myocardial infarction, obesity or drug abuse promotes cardiac myocyte hypertrophy and subsequent heart failure. A number of signalling modulators in the vasculature milieu are known to regulate heart mass including those that influence gene expression, apoptosis, cytokine release and growth factor signalling. Recent evidence using genetic and cellular models of cardiac hypertrophy suggests that pathological hypertrophy can be prevented or reversed and has promoted an enormous drive in drug discovery research aiming to identify novel and specific regulators of hypertrophy. In this review we describe the molecular characteristics of cardiac hypertrophy such as the aberrant re-expression of the fetal gene program. We discuss the various molecular pathways responsible for the co-ordinated control of the hypertrophic program including: natriuretic peptides, the adrenergic system, adhesion and cytoskeletal proteins, IL-6 cytokine family, MEK-ERK1/2 signalling, histone acetylation, calcium-mediated modulation and the exciting recent discovery of the role of microRNAs in controlling cardiac hypertrophy. Characterisation of the signalling pathways leading to cardiac hypertrophy has led to a wealth of knowledge about this condition both physiological and pathological. The challenge will be translating this knowledge into potential pharmacological therapies for the treatment of cardiac pathologies.

Computational identification of the normal and perturbed genetic networks involved in myeloid differentiation and acute promyelocytic leukemia

A dissection of the genetic networks and circuitries is described for two form of leukaemia. Integrating transcription factor binding and gene expression profiling, networks are revealed that underly this important human disease.

Background

Acute myeloid leukemia (AML) comprises a group of diseases characterized by the abnormal development of malignant myeloid cells. Recent studies have demonstrated an important role for aberrant transcriptional regulation in AML pathophysiology. Although several transcription factors (TFs) involved in myeloid development and leukemia have been studied extensively and independently, how these TFs coordinate with others and how their dysregulation perturbs the genetic circuitry underlying myeloid differentiation is not yet known. We propose an integrated approach for mammalian genetic network construction by combining the analysis of gene expression profiling data and the identification of TF binding sites.

Results

We utilized our approach to construct the genetic circuitries operating in normal myeloid differentiation versus acute promyelocytic leukemia (APL), a subtype of AML. In the normal and disease networks, we found that multiple transcriptional regulatory cascades converge on the TFs Rora and Rxra, respectively. Furthermore, the TFs dysregulated in APL participate in a common regulatory pathway and may perturb the normal network through Fos. Finally, a model of APL pathogenesis is proposed in which the chimeric TF PML-RARα activates the dysregulation in APL through six mediator TFs.

Conclusion

This report demonstrates the utility of our approach to construct mammalian genetic networks, and to obtain new insights regarding regulatory circuitries operating in complex diseases in humans.

PAP: a comprehensive workbench for mammalian transcriptional regulatory sequence analysis

Given the recent explosion of publications that employ microarray technology to monitor genome-wide expression and that correlate these expression changes to biological processes or to disease states, the determination of the transcriptional regulation of these co-expressed genes is the next major step toward deciphering the genetic network governing the pathway or disease under study. Although computational approaches have been proposed for this purpose, there is no integrated and user-friendly software application that allows experimental biologists to tackle this problem in higher eukaryotes. We have previously reported a systematic, statistical model of mammalian transcriptional regulatory sequence analysis. We have now made crucial extensions to this model and have developed a comprehensive, user-friendly web application suite termed the Promoter Analysis Pipeline (PAP). PAP is available at: http://bioinformatics.wustl.edu/webTools/portalModule/PromoterSearch.do

Molecular cloning and functional analysis of MRLC2 differential expressed in MeishanxYorkshire F1 crossbreeds and their parents, Meishan pigs

In order to detect the molecular basis of heterosis in pigs, suppression subtractive hybridization was carried out to investigate the difference in gene expression in the Longissimus dorsi muscle tissues between MeishanxYorkshire F1 crossbreeds and their parents, Meishan pigs. The swine myosin regulatory light chain 2 (MRLC2) gene differentially expressed between the crossbreeds and the purebreds was isolated and identified using semi-quantitative reverse transcriptase polymerase chain reaction and its complete cDNA sequence was obtained using the rapid amplification of cDNA ends method. The nucleotide sequence of the gene is not homologous to any of the known porcine genes. The sequence prediction analysis reveals that the open reading frame of this gene encodes a protein of 172 amino acids containing the putative conserved domain of the EF-hand superfamily. This predicted amino acid sequence of porcine MRLC2 protein exhibits 99%, 98%, 98%, 98% and 97% identity with that of cattle, human, dog, rat and mouse, respectively. The homology analysis revealed that the MRLC2 protein was very much conserved in evolution. The tissue expression analysis indicated that the swine MRLC2 gene is highly expressed in muscle, fat, heart, liver, spleen, lung, kidney, stomach, small intestine, ovary and testis, but not expressed in pancreas.

Conditional knockout mice reveal distinct functions for the global transcriptional coactivators CBP and p300 in T-cell development

The global transcriptional coactivators CREB-binding protein (CBP) and the closely related p300 interact with over 312 proteins, making them among the most heavily connected hubs in the known mammalian protein-protein interactome. It is largely uncertain, however, if these interactions are important in specific cell lineages of adult animals, as homozygous null mutations in either CBP or p300 result in early embryonic lethality in mice. Here we describe a Cre/LoxP conditional p300 null allele (p300flox) that allows for the temporal and tissue-specific inactivation of p300. We used mice carrying p300flox and a CBP conditional knockout allele (CBPflox) in conjunction with an Lck-Cre transgene to delete CBP and p300 starting at the CD4- CD8- double-negative thymocyte stage of T-cell development. Loss of either p300 or CBP led to a decrease in CD4+ CD8+ double-positive thymocytes, but an increase in the percentage of CD8+ single-positive thymocytes seen in CBP mutant mice was not observed in p300 mutants. T cells completely lacking both CBP and p300 did not develop normally and were nonexistent or very rare in the periphery, however. T cells lacking CBP or p300 had reduced tumor necrosis factor alpha gene expression in response to phorbol ester and ionophore, while signal-responsive gene expression in CBP- or p300-deficient macrophages was largely intact. Thus, CBP and p300 each supply a surprising degree of redundant coactivation capacity in T cells and macrophages, although each gene has also unique properties in thymocyte development.

A systematic model to predict transcriptional regulatory mechanisms based on overrepresentation of transcription factor binding profiles

An important aspect of understanding a biological pathway is to delineate the transcriptional regulatory mechanisms of the genes involved. Two important tasks are often encountered when studying transcription regulation, i.e., (1) the identification of common transcriptional regulators of a set of coexpressed genes; (2) the identification of genes that are regulated by one or several transcription factors. In this study, a systematic and statistical approach was taken to accomplish these tasks by establishing an integrated model considering all of the promoters and characterized transcription factors (TFs) in the genome. A promoter analysis pipeline (PAP) was developed to implement this approach. PAP was tested using coregulated gene clusters collected from the literature. In most test cases, PAP identified the transcription regulators of the input genes accurately. When compared with chromatin immunoprecipitation experiment data, PAP's predictions are consistent with the experimental observations. When PAP was used to analyze one published expression-profiling data set and two novel coregulated gene sets, PAP was able to generate biologically meaningful hypotheses. Therefore, by taking a systematic approach of considering all promoters and characterized TFs in our model, we were able to make more reliable predictions about the regulation of gene expression in mammalian organisms.