Nuclear CaMKII enhances histone H3 phosphorylation and remodels chromatin during cardiac hypertrophy.

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a central role in pathological cardiac hypertrophy, but the mechanisms by which it modulates gene activity in the nucleus to mediate hypertrophic signaling remain unclear. Here, we report that nuclear CaMKII activates cardiac transcription by directly binding to chromatin and regulating the phosphorylation of histone H3 at serine-10. These specific activities are demonstrated both in vitro and in primary neonatal rat cardiomyocytes. Activation of CaMKII signaling by hypertrophic agonists increases H3 phosphorylation in primary cardiac cells and is accompanied by concomitant cellular hypertrophy. Conversely, specific silencing of nuclear CaMKII using RNA interference reduces both H3 phosphorylation and cellular hypertrophy. The hyper-phosphorylation of H3 associated with increased chromatin binding of CaMKII occurs at specific gene loci reactivated during cardiac hypertrophy. Importantly, H3 Ser-10 phosphorylation and CaMKII recruitment are associated with increased chromatin accessibility and are required for chromatin-mediated transcription of the Mef2 transcription factor. Unlike phosphorylation of H3 by other kinases, which regulates cellular proliferation and immediate early gene activation, CaMKII-mediated signaling to H3 is associated with hypertrophic growth. These observations reveal a previously unrecognized function of CaMKII as a kinase signaling to histone H3 and remodeling chromatin. They suggest a new epigenetic mechanism controlling cardiac hypertrophy.

Critical role of nuclear calcium/calmodulin-dependent protein kinase IIdeltaB in cardiomyocyte survival in cardiomyopathy.

Calcium/calmodulin-dependent protein kinase II (CaMKII) plays a central role in cardiac contractility and heart disease. However, the specific role of alternatively spliced variants of CaMKII in cardiac disease and apoptosis remains poorly explored. Here we report that the deltaB subunit of CaMKII (CaMKIIdeltaB), which is the predominant nuclear isoform of calcium/calmodulin-dependent protein kinases in heart muscle, acts as an anti-apoptotic factor and is a novel target of the antineoplastic and cardiomyopathic drug doxorubicin (Dox (adriamycin)). Hearts of rats that develop cardiomyopathy following chronic treatment with Dox also show down-regulation of CaMKIIdeltaB mRNA, which correlates with decreased cardiac function in vivo, reduced expression of sarcomeric proteins, and increased tissue damage associated with Dox cardiotoxicity. Overexpression of CaMKIIdeltaB in primary cardiac cells inhibits Dox-mediated apoptosis and prevents the loss of the anti-apoptotic protein Bcl-2. Specific silencing of CaMKIIdeltaB by small interfering RNA prevents the formation of organized sarcomeres and decreases the expression of Bcl-2, which all mimic the effect of Dox. CaMKIIdeltaB is required for GATA-4-mediated co-activation and binding to the Bcl-2 promoter. These results reveal that CaMKIIdeltaB plays an essential role in cardiomyocyte survival and provide a mechanism for the protective role of CaMKIIdeltaB. These results suggest that selective targeting of CaMKII in the nuclear compartment might represent a strategy to regulate cardiac apoptosis and to reduce Dox-mediated cardiotoxicity.

Phosphorylation-dependent degradation of p300 by doxorubicin-activated p38 mitogen-activated protein kinase in cardiac cells.

p300 and CBP are general transcriptional coactivators implicated in different cellular processes, including regulation of the cell cycle, differentiation, tumorigenesis, and apoptosis. Posttranslational modifications such as phosphorylation are predicted to select a specific function of p300/CBP in these processes; however, the identification of the kinases that regulate p300/CBP activity in response to individual stimuli and the physiological significance of p300 phosphorylation have not been elucidated. Here we demonstrate that the cardiotoxic anticancer agent doxorubicin (adriamycin) induces the phosphorylation of p300 in primary neonatal cardiomyocytes. Hyperphosphorylation precedes the degradation of p300 and parallels apoptosis in response to doxorubicin. Doxorubicin-activated p38 kinases alpha and beta associate with p300 and are implicated in the phosphorylation-mediated degradation of p300, as pharmacological blockade of p38 prevents p300 degradation. p38 phosphorylates p300 in vitro at both the N and C termini of the protein, and enforced activation of p38 by the constitutively active form of its upstream kinase (MKK6EE) triggers p300 degradation. These data support the conclusion that p38 mitogen-activated protein kinase regulates p300 protein stability and function in cardiomyocytes undergoing apoptosis in response to doxorubicin.

Calcium phosphate coprecipitation greatly enhances transduction of cardiac myocytes and vascular smooth muscle cells by lentivirus vectors.

BACKGROUND: Lentivirus vectors provide a delivery system that can both transduce nondividing cells and integrate transgenes into the genome of target cells without cytotoxicity. However, their relatively low transduction efficiency presents a significant obstacle to progress. OBJECTIVES: In the present paper, a simple and easy method using calcium phosphate (CaPi) to enhance the efficiency of lentivirus gene transfer in both vascular smooth muscle cells and cardiac myocytes is reported. METHODS AND RESULTS: Delivery of lentivirus vectors in the presence of CaPi coprecipitates increased vector-encoded transgene expression up to 13-fold. Of interest, the magnitudes of enhancement of transgene expression by CaPi coprecipitates in 293T cells, vascular smooth muscle cells and cardiac myocytes were greater during brief periods (10 min and 120 min) of virus-cell contact than during long periods (16 h). Moreover, with a short duration of incubation with CaPi coprecipitates (up to 120 min), there was little evidence of direct cell toxicity. CaPi coprecipitates had no effect on host range specificity of ecotropic viruses and thus appears to enhance transduction efficiency physiologically by facilitating physical interaction between virus and cell. CONCLUSIONS: These data show that lentivirus with CaPi coprecipitates increases both the efficiency and the speed of gene transfer. These approaches provide an efficient method and an improved tool for research and possibly for therapy of cardiovascular diseases.

HERP1 inhibits myocardin-induced vascular smooth muscle cell differentiation by interfering with SRF binding to CArG box.

OBJECTIVE: Myocardin is a coactivator of serum response factor (SRF) required for vascular smooth muscle cell (VSMC) differentiation. HERP1 is a transcriptional repressor, which is abundantly expressed in vascular system and is known to function as a target gene of Notch. However, the role of HERP1 in the pathogenesis of vascular lesions remains unknown. The present study characterizes the expression of HERP1 in normal and diseased vessels, and tests the hypothesis that HERP1 inhibits SRF/myocardin-dependent SMC gene expression. METHODS AND RESULTS: Immunohistochemistry revealed that HERP1 and myocardin expression was localized to SMC in the neointima of balloon-injured rat aorta and in human coronary atherosclerotic lesions. Expression of both HERP1 and myocardin was elevated in cultured VSMCs compared with medial SMC. Overexpressed HERP1 inhibited the myocardin-induced SMC marker gene expression in 10T1/2 cells. HERP1 protein interfered with the SRF/CArG-box interaction in vivo and in vitro. Immunoprecipitation assays showed that HERP1 physically interacts with SRF. CONCLUSIONS: HERP1 expression was associated with the SMC proliferation and dedifferentiation in vitro and in vivo. HERP1 may play a role in promoting the phenotypic modulation of VSMCs during vascular injury and atherosclerotic process by interfering with SRF binding to CArG-box through physical association between HERP1 and SRF.

Washout of transplanted cells from the heart: a potential new hurdle for cell transplantation therapy.

OBJECTIVE: The number of viable transplanted cells in the heart is sharply decreased shortly after cell injection. The exact mechanics of cell loss are unclear. We hypothesized that immature cardiac cells transplanted directly into rat heart could be washed out via the cardiac vasculature, and carried to other organs. METHODS: Female Fischer rats were subjected to 60 min of coronary artery occlusion followed by 3 h of reperfusion (OR group) or 4 h or permanent coronary artery occlusion (PO group). Neonatal rat cardiac cells (5x10(6)) were injected directly into the free wall of the left ventricle at either 15 min post-reperfusion (OR group) or 75 min after occlusion (PO group). At the end of the protocol, a histological analysis for transplanted cells in the heart (i.e. microscopic examination for cells in approximately 790 histogic fields within each heart) and polymerase chain reaction (PCR)-based determination of the Sry gene (a male cell marker) in the heart and other organs were performed. RESULTS: In the OR group, only 3.39+/-0.69% fields contained immature cells compared to 6.57+/-1.33% fields in the PO group (p<0.05). Cardiac blood vessels contained round, immature cardiomyocytes. PCR analysis revealed that 100% of the animals (5 of 5) in both groups had cells present in their hearts and lungs, 40% of the OR group and 60% of the PO group demonstrated cells in the liver and kidneys, and 40% of the PO group had cells in the spleen. CONCLUSION: Neonatal cardiomyocytes injected directly into the area at risk of the heart escape acutely from the infract to other organs through the vascular system of the heart; loss of cells is more prominent with reperfusion.

Rebuilding a damaged heart: long-term survival of transplanted neonatal rat cardiomyocytes after myocardial infarction and effect on cardiac function.

BACKGROUND: The long-term effects of cardiac cell transplantation on cardiac function are unknown. Therefore, we tested the survival and functional impact of rat neonatal cardiac myocytes up to 6 months after transplantation into infarcted hearts. METHODS AND RESULTS: Cardiomyocytes from male neonatal Fischer 344 rats (1 to 2 days, 3 to 5x10(6)) or medium was injected into the infarcts of adult syngeneic female animals 1 week after left coronary artery ligation. Six months later, implanted cardiomyocytes were still present by quantitative TaqMan polymerase chain reaction and histology. In all treated hearts, discrete lumps of cells were present within the infarct scar, which was not observed in media-injected hearts typified by a transmural infarct scar. Infarct thickness was greater in treated animals versus control animals (909+/-97 versus 619+/-43 microm, P<0.02), whereas infarct size and left ventricular volumes were similar. By biplane angiography, left ventricular ejection fractions at 6 months were greater (0.36+/-0.03 versus 0.25+/-0.02, P<0.01) and significantly less infarct zone dyskinesis was seen (0.30+/-0.08 versus 0.55+/-0.07, P=0.035, lateral projection) in treated animals versus control animals. CONCLUSIONS: Grafted neonatal cardiomyocytes were present in infarcts 6 months after transplantation; they thickened the wall of the left ventricle and were associated with enhanced ejection fraction and reduced paradoxical systolic bulging of the infarct. Therefore, neonatal cardiac cell transplants exhibit long-term survival in a myocardial infarct model and contribute to long-term improved cardiac function. These results suggest that a damaged heart can be rebuilt.

Notch signaling in vascular development.

Notch signaling is an extremely conserved and widely used mechanism regulating cell fate in metazoans. Interaction of Notch receptors (Notch) with their ligands (Delta-like or Jagged) leads to cleavage of the Notch intracellular domain (NICD) that migrates into the nucleus. In the nucleus, NICD associates with a transcription factor, RBP-Jk. The NICD-RBP-Jk complex, in turn, upregulates expression of primary target genes of Notch signaling, such as hairy and enhancer of split (HES) and HES-related repressor protein (HERP) transcriptional repressors. Recent evidence has demonstrated that the Notch pathway is involved in multiple aspects of vascular development, including proliferation, migration, smooth muscle differentiation, angiogenic processes, and arterial-venous differentiation. In this brief review, we focus on ligands, receptors, and target genes of Notch signaling in the vascular system and discuss (1) tissue distribution; (2) gain- and loss-of-function studies; and (3) the role of Notch components in human diseases involving the vascular system.

Brief episode of ischemia activates protective genetic program in rat heart: a gene chip study.

OBJECTIVE: Brief episodes of ischemia of 20 min or less have the potential to protect the heart. Such episodes are associated primarily with reversible ischemic injury yet they induce changes in gene expression. The purpose of the study was to determine whether activation of protective genes takes place within 4 h following a brief episode of ischemia that would mimic angina pectoris. METHODS: Three groups of rats were studied. In the control (Ctrl) group, hearts were immediately excised following anesthesia; in the sham-operated (SO) group, opened-chest rats received 4 h and 20 min of no intervention; and in the group subjected to ischemia (SI) hearts received 20 min of proximal coronary occlusion followed by 4 h of reperfusion. Hearts from the SI group were divided into nonischemic (NI) and ischemic (Isc) areas. Changes in gene expression pattern were analyzed by using Affymetrix Gene Chips. RESULTS: Ischemia led to strong upregulation of mRNA transcripts for heat shock proteins 70, 27, 105, 86 and 40 kDa, vascular endothelial growth factor, brain-derived neurotrophic factor, plasminogen activator inhibitor-1, activating transcription factor 3, B-cell translocation gene 2, and growth arrest and DNA damage inducible 45 alpha protein compared to the NI tissue. The majority of mRNAs whose levels increased following brief ischemia were of a protective nature. CONCLUSION: Genetic reprogramming emerging during or following brief episodes of ischemia that simulate angina, can be characterized as protective in nature. Developing new therapeutic strategies aimed to promote this protective response represents a legitimate target for future research.

Development of abnormal tissue architecture in transplanted neonatal rat myocytes.

BACKGROUND: Most myocardial cell transplant studies focus on demonstration of improved function; however, such improvement depends on the development of appropriate tissue structure. Thus, our aim was to assess the architectural changes that occurred after cell transplant into normal and infarcted myocardium. METHODS: Male neonatal cells (1 to 2 days old) were injected into the left ventricular free wall of adult female rats. The tissue was examined 0 to 1 days and 1 to 2, 4 to 6, and 12 weeks later in noninfarcted hearts and 6 months after transplant into infarcts. In histologic sections, we assessed the cells' retardation of polarized light (to measure development of contractile elements), two-dimensional cell orientation, cell nuclear morphology, and collagen content. RESULTS: The transplant cells' retardation of polarized light gradually increased to 81% of that of host cells after 6 months (p < 0.001). The transplant cells were disorganized and although their nuclei increased in size, they always had a rounded appearance. Collagen content in the transplant was 210% to 430% higher than in host tissue (p < 0.01). In addition, scar collagen always separated transplant and host cells. CONCLUSIONS: One architectural feature, the rounded nuclei, provided a distinctive marker to identify transplanted cells. Nevertheless, the transplants' inhibited muscle development together with disorganization, separation from the host muscle, and a substantial increase in collagen resulted in a structure unlikely to play an active role in systolic function.

The new date, new format, new goals and new sponsor of the Archon Genomics X PRIZE competition.

The Archon Genomics X PRIZE presented by MEDCO is a $10 million prize for whole human genome sequencing that will test 100 samples and establish a defined method for determining quality and cost per genome. The contest will entail a head-to-head competition starting on 3 January 2013. The $10 million grand prize will be awarded to the first team to meet all the quality standards. If there is no grand prize winner, lesser awards will be made for single achievements in the three categories of accuracy, completeness and haplotype phasing. Similar to the open comment period offered earlier this year for the validation protocol, the X PRIZE Foundation seeks commentary from the scientific community on the revised competition format and judging criteria prior to publishing final rules as part of a master agreement with competing teams next year. The official validation protocol will make the competition judging transparent and fair using multiple standard techniques and robust bioinformatics. With sponsorship from Medco Health Solutions (MEDCO), the 100 samples will be derived from genomes of appropriately consented centenarian subjects. At the conclusion of the contest, the data from the redundantly sequenced genomes will be deposited into a scientific database and provide a heretofore unrealized depth of sequence data based on multiple technologies. The sample set and the bioinformatic pipeline will also be made available to the scientific community.

Lentiviral vector-mediated gene transfer to endotherial cells compared with adenoviral and retroviral vectors.

Human immunodeficiency virus (HIV, lentivirus) vector has attractive features for gene therapy, including the ability to transduce non-dividing cells and long-term transgene expression. We have already reported that lentivirus vector can transduce well-differentiated rat cardiac myocytes. Endothelial cells (EC) are an attractive target for gene therapy, both for the treatment of cardiovascular disease and for the systemic delivery of recombinant gene products directly into the circulation. There are several reports regarding application of adenovirus and retrovirus based vectors to EC. However, there have been few reports which show the effect to lentivirus-mediated gene transfer efficiency, compared with adenovirus and retrovirus. In this study, bovine aortic endothelial cells (BAECs) were infected, in vitro, with these virus vectors. Transduction efficiency (TE) of beta-Gal gene transfer in BAECs by adenovirus, lentivirus, or retrovirus at MOI10 (Multiplicity of infection) (determined on Hela cells) is 69+/-11, 33+/-8, or 22+/-6% respectively. In adenovirus and lentivirus, almost 100% of BAECs were transduced at MOI 50. However, in retrovirus, TE showed only 48+/-6% at MOI 50 and no increase at MOI 100. The percentage of beta-Gal positive cells was decreased rapidly at longer passage of cells after being transduced by adenovirus. However, lentivirus and retrovirus showed sustained higher percentage of positive cells. Furthermore, transduction by lentiviral vectors had no significant effect on viability of BAECs. Our results indicate that lentivirus showed high-level and long term gene expression in BAECs. Lentivirus can be an effective vector for the ex vivo, genetically modified EC implantation and in vivo gene therapy.

Leucine 135 of tropomodulin-1 regulates its association with tropomyosin, its cellular localization, and the integrity of sarcomeres.

Tropomodulin-1 (Tmod-1) is a well defined actin-capping protein that interacts with tropomyosin (TM) at the pointed end of actin filaments. Previous studies by others have mapped its TM-binding domain to the amino terminus from amino acid 39 to 138. In this study, we have identified several amino acid residues on Tmod-1 that are important for its interaction with TM5 (a nonmuscle TM isoform). Glutathione S-transferase affinity chromatography and immunoprecipitation assays reveal that Tmod sense mutations of either amino acid 134, 135, or 136 causes various degrees of loss of function of Tmod TM-binding ability. The reduction of TM-binding ability was relatively mild (reduced approximately 20-40%) from the G136A Tmod mutant but more substantially (reduced approximately 50-100%) from the I134D, L135E, and L135V Tmod mutants. In addition, mutation at any of these three sites dramatically alters the subcellular location of Tmod-1 when introduced into mammalian cells. Further analysis of these three mutants uncovered a previously unknown nuclear trafficking function of Tmod-1, and residues 134, 135, and 136 are located within a nuclear export signal motif. As a result, mutation on either residue 134 or residue 135 not only will cause a significant reduction of the Tmod-1 ability to bind to TM5 but also lead to predominant nuclear localization of Tmod-1 by crippling its nuclear export mechanism. The failure of the Tmod mutations to fully associate with TM5 when introduced into neonatal rat cardiomyocytes was also associated with an accelerated and severe fragmentation of sarcomeric structures compared with overexpression of wild type Tmod-1. The multiple losses of function of Tmod engendered by these missense mutations are most severe with the single substitution of residue 135.

Nuclear Rho kinase, ROCK2, targets p300 acetyltransferase.

Rho-associated coiled-coil protein kinase (ROCK) is an effector for the small GTPase Rho and plays a pivotal role in diverse cellular activities, including cell adhesion, cytokinesis, and gene expression, primarily through an alteration of actin cytoskeleton dynamics. Here, we show that ROCK2 is localized in the nucleus and associates with p300 acetyltransferase both in vitro and in cells. Nuclear ROCK2 is present in a large protein complex and partially cofractionates with p300 by gel filtration analysis. By immunofluorescence, ROCK2 partially colocalizes with p300 in distinct insoluble nuclear structures. ROCK2 phosphorylates p300 in vitro, and nuclear-restricted expression of constitutively active ROCK2 induces p300 phosphorylation in cells. p300 acetyltransferase activity is dependent on its phosphorylation status in cells, and p300 phosphorylation by ROCK2 results in an increase in its acetyltransferase activity in vitro. These observations suggest that nucleus-localized ROCK2 targets p300 for phosphorylation to regulate its acetyltransferase activity.

Nuclear hormone receptor coregulator GRIP1 suppresses, whereas SRC1A and p/CIP coactivate, by domain-specific binding of MyoD.

p160 coregulators were initially identified as nuclear hormone receptor coactivators. In this study, functional data demonstrate that members of the three p160 families can have opposing roles in regulating gene expression by the same transcription factor. Both SRC1A and p/CIP function as coactivators for MyoD-mediated transcription whereas GRIP1 acts negatively as a (co)repressor. SRC1A and p/CIP predominantly interact with distinct sites on the NH2-terminal activation domain of MyoD. GRIP1 binds to both these regions but it alone, and neither SRC1A nor p/CIP, also interacts with specific sites on MyoD that are critical for the binding of the essential MyoD coactivator, p300. This suggests that competition by GRIP1 for SRC1A, p/CIP, and p300 binding sites on a transcription factor may regulate the activity of the factor.

Cytoplasmic nuclear transfer of the actin-capping protein tropomodulin.

Tropomodulin (Tmod) is a cytoskeletal actin-capping protein that interacts with tropomyosin at the pointed end of actin filaments. E-Tmod is an isoform that expresses predominantly in cardiac cells and slow skeletal muscle fibers. We unexpectedly discovered significant levels of Tmod in nuclei and then defined peptide domains in Tmod responsible for nuclear import and export. These domains resemble, and function as, a nuclear export signal (NES) and a pattern 4 nuclear localization signal (NLS). Both motifs are conserved in other Tmod isoforms and across species. Comparisons of wild-type Tmod and Tmod carrying mutations in these peptide domains revealed that Tmod normally traffics through the nucleus. These observations logically presuppose that Tmod functions may include a nuclear role. Indeed, increasing Tmod in the nucleus severely hampered myogenic differentiation and selectively suppressed muscle-specific gene expression (endogenous p21, myosin heavy chain, myogenin, and Tmod) but did not affect endogenous glyceraldehyde-3-phosphate dehydrogenase or expression from a transfected E-GFP vector. These results suggest that, at least in myogenic cells, nuclear Tmod may be involved in the differentiation process.

HES and HERP families: multiple effectors of the Notch signaling pathway.

Notch signaling dictates cell fate and critically influences cell proliferation, differentiation, and apoptosis in metazoans. Multiple factors at each step-ligands, receptors, signal transducers and effectors-play critical roles in executing the pleiotropic effects of Notch signaling. Ligand-binding results in proteolytic cleavage of Notch receptors to release the signal-transducing Notch intracellular domain (NICD). NICD migrates into the nucleus and associates with the nuclear proteins of the RBP-Jkappa family (also known as CSL or CBF1/Su(H)/Lag-1). RBP-Jkappa, when complexed with NICD, acts as a transcriptional activator, and the RBP-Jkappa-NICD complex activates expression of primary target genes of Notch signaling such as the HES and enhancer of split [E(spl)] families. HES/E(spl) is a basic helix-loop-helix (bHLH) type of transcriptional repressor, and suppresses expression of downstream target genes such as tissue-specific transcriptional activators. Thus, HES/E(spl) directly affects cell fate decisions as a primary Notch effector. HES/E(spl) had been the only known effector of Notch signaling until a recent discovery of a related but distinct bHLH protein family, termed HERP (HES-related repressor protein, also called Hey/Hesr/HRT/CHF/gridlock). In this review, we summarize the recent data supporting the idea of HERP being a new Notch effector, and provide an overview of the similarities and differences between HES and HERP in their biochemical properties as well as their tissue distribution. One key observation derived from identification of HERP is that HES and HERP form a heterodimer and cooperate for transcriptional repression. The identification of the HERP family as a Notch effector that cooperates with HES/E(spl) family has opened a new avenue to our understanding of the Notch signaling pathway.