Biomedical subjects

Eric N Olson

Publications and source records attributed to Eric N Olson.

At least 55 records · Page 3Linked to original sources

PubMed2006

Local InsP3-dependent perinuclear Ca2+ signaling in cardiac myocyte excitation-transcription coupling.

Previous work showed that calmodulin (CaM) and Ca2+-CaM-dependent protein kinase II (CaMKII) are somehow involved in cardiac hypertrophic signaling, that inositol 1,4,5-trisphosphate receptors (InsP3Rs) in ventricular myocytes are mainly in the nuclear envelope, where they associate with CaMKII, and that class II histone deacetylases (e.g., HDAC5) suppress hypertrophic gene transcription. Furthermore, HDAC phosphorylation in response to neurohumoral stimuli that induce hypertrophy, such as endothelin-1 (ET-1), activates HDAC nuclear export, thereby regulating cardiac myocyte transcription. Here we demonstrate a detailed mechanistic convergence of these 3 issues in adult ventricular myocytes. We show that ET-1, which activates plasmalemmal G protein-coupled receptors and InsP3 production, elicits local nuclear envelope Ca2+ release via InsP3R. This local Ca2+ release activates nuclear CaMKII, which triggers HDAC5 phosphorylation and nuclear export (derepressing transcription). Remarkably, this Ca2+-dependent pathway cannot be activated by the global Ca2+ transients that cause contraction at each heartbeat. This novel local Ca2+ signaling in excitation-transcription coupling is analogous to but separate (and insulated) from that involved in excitation-contraction coupling. Thus, myocytes can distinguish simultaneous local and global Ca2+ signals involved in contractile activation from those targeting gene expression.

Active Transport, Cell Nucleus↗

PubMed2006

Control of cardiac hypertrophy and heart failure by histone acetylation/deacetylation.

The adult heart responds to acute and chronic stresses by a remodelling process that is accompanied by myocyte hypertrophy, impaired contractility, and pump failure, often culminating in sudden death. Pathological growth and remodelling of the adult heart is often associated with the reactivation of a fetal cardiac gene program that further weakens cardiac performance. Recent studies have revealed key roles for histone deacetylases (HDACs) in the control of pathological cardiac growth. Class II HDACs associate with the MEF2 transcription factor, and other factors, to maintain normal cardiac size and function. Stress signals lead to the phosphorylation of class II HDACs and their export from the nucleus to the cytoplasm, with consequent activation of genes involved in cardiac growth. HDAC knockout mice are hypersensitive to stress signalling and develop massively enlarged hearts in response to various pathological stress stimuli due to an inability to counteract pathological signalling to MEF2. Strategies for normalizing gene expression in the failing heart by regulating HDAC phosphorylation and function represent potentially powerful therapeutic approaches.

Acetylation↗

PubMed2005

MicroRNA1 influences cardiac differentiation in Drosophila and regulates Notch signaling.

MicroRNAs (miRNAs) are genomically encoded small RNAs that hybridize with messenger RNAs, resulting in degradation or translational inhibition of targeted transcripts. The potential for miRNAs to regulate cell-lineage determination or differentiation from pluripotent progenitor or stem cells is unknown. Here, we show that microRNA1 (miR-1) is an ancient muscle-specific gene conserved in sequence and expression in Drosophila. Drosophila miR-1 (dmiR-1) is regulated through a serum response factor-like binding site in cardiac progenitor cells. Loss- and gain-of-function studies demonstrated a role for dmiR-1 in modulating cardiogenesis and in maintenance of muscle-gene expression. We provide in vivo evidence that dmiR-1 targets transcripts encoding the Notch ligand Delta, providing a potential mechanism for the expansion of cardiac and muscle progenitor cells and failure of progenitor cell differentiation in some dmiR-1 mutants. These findings demonstrate that dmiR-1 may "fine-tune" critical steps involved in differentiation of cardiac and somatic muscle progenitors and targets a pathway required for progenitor cell specification and asymmetric cell division.

3' Untranslated Regions↗

PubMed2005

A WW domain protein TAZ is a critical coactivator for TBX5, a transcription factor implicated in Holt-Oram syndrome.

The T-box transcription factor TBX5 plays essential roles in cardiac and limb development. Various mutations in the TBX5 gene have been identified in patients with Holt-Oram syndrome, which is characterized by congenital defects in the heart and upper extremities. In this study, we identified a WW-domain-containing transcriptional regulator TAZ as a potent TBX5 coactivator. TAZ directly associates with TBX5 and markedly stimulates TBX5-dependent promoters by interacting with the histone acetyltransferases p300 and PCAF. YAP, a TAZ-related protein with conserved functional domains, also stimulates TBX5-dependent transcription, possibly by forming a heterodimer with TAZ. TBX5 lacks a PY motif, which mediates the association of other proteins with TAZ, and interacts with TAZ through multiple domains including its carboxyl-terminal structure. Truncation mutants of TBX5 identified in patients with Holt-Oram syndrome were markedly impaired in their ability to associate with and be stimulated by TAZ. These findings reveal key roles for TAZ and YAP in the control of TBX5-dependent transcription and suggest the involvement of these coactivators in cardiac and limb development.

Abnormalities, Multiple↗

PubMed2005

Stem cells and their derivatives can bypass the requirement of myocardin for smooth muscle gene expression.

The Serum Response Factor (SRF) coactivator myocardin stimulates the transcription of multiple muscle genes during cardiac and smooth muscle development. Mouse embryos lacking myocardin die during the earliest stages of smooth muscle development and fail to express multiple smooth muscle marker genes in the embryonic dorsal aorta and other vascular structures. In this study, we used mutant embryonic stem cell lines to further define the role of myocardin in smooth muscle differentiation and vascular development. Misexpression of myocardin in undifferentiated muscle stem cells resulted in efficient activation of smooth muscle genes, and weaker activation of genes involved in cardiac and skeletal muscle differentiation. Remarkably, myocardin(-/-) embryonic stem cell lines differentiated into smooth muscle cells in vitro, although these cells expressed significantly decreased levels of smooth muscle contractile genes. Moreover, genetically labeled myocardin(-/-) ES cells were able to contribute to smooth muscle lineages in vivo. These results indicate that while myocardin function is sufficient for activation of SRF-dependent muscle gene expression in multiple cell types, myocardin-independent mechanism(s) can suffice for expression in some smooth muscle lineages.

Animals↗

PubMed2005

Class II histone deacetylases confer signal responsiveness to the ankyrin-repeat proteins ANKRA2 and RFXANK.

Class II histone deacetylases (HDACs) contain unique amino-terminal extensions that mediate interactions with members of the myocyte enhancer factor-2 (MEF2) family of transcription factors and responsiveness to kinases, including Ca2+/calmodulin-dependent kinase (CaMK). Despite intense investigation of class II HDACs, little is known of MEF2-independent mechanisms for transcriptional repression by these chromatin-modifying enzymes. Here, we demonstrate that class II HDACs 4 and 5 physically associate with ankyrin-repeat proteins ANKRA2 and RFXANK (RFX-B/Tvl-1/ANKRA1). ANKRA2 is a megalin- and BKCa potassium channel-interacting factor, whereas RFXANK is a positive regulator of major histocompatibility complex II (MHC II) gene expression. HDAC4 and HDAC5 interact with the ankyrin repeats of ANKRA2 and RFXANK and, through association with RFXANK, repress MHC II promoter activation. HDACs 4 and 5 also repress endogenous HLA-DRA gene expression induced by CIITA. Phosphorylation of class II HDACs by CaMK results in CRM1-dependent nuclear export of HDAC/RFXANK complexes. These results define a novel transcriptional pathway under the control of class II HDACs and suggest a role for these transcriptional repressors as signal-responsive regulators of antigen presentation.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Requirement of myocardin-related transcription factor-B for remodeling of branchial arch arteries and smooth muscle differentiation.

Myocardin and the myocardin-related transcription factors (MRTFs) A and B act as coactivators for serum response factor, which plays a key role in cardiovascular development. To determine the functions of MRTF-B in vivo, we generated MRTF-B mutant mice by targeted inactivation of the MRTF-B gene. We show that mice homozygous for an MRTF-B loss-of-function mutation die during mid-gestation from a spectrum of cardiovascular defects that includes abnormal patterning of the branchial arch arteries, double-outlet right ventricle, ventricular septal defects, and thin-walled myocardium. These abnormalities are accompanied by a failure in differentiation of smooth muscle cells within the branchial arch arteries, which are derived from the neural crest. The phenotype of MRTF-B mutant mice is distinct from that of mice lacking myocardin, revealing unique roles for these serum response factor coactivators in the development of different subsets of smooth muscle cells in vivo.

Animals↗

PubMed2005

Centronuclear myopathy in mice lacking a novel muscle-specific protein kinase transcriptionally regulated by MEF2.

Myocyte enhancer factor 2 (MEF2) plays essential roles in transcriptional control of muscle development. However, signaling pathways acting downstream of MEF2 are largely unknown. Here, we performed a microarray analysis using Mef2c-null mouse embryos and identified a novel MEF2-regulated gene encoding a muscle-specific protein kinase, Srpk3, belonging to the serine arginine protein kinase (SRPK) family, which phosphorylates serine/arginine repeat-containing proteins. The Srpk3 gene is specifically expressed in the heart and skeletal muscle from embryogenesis to adulthood and is controlled by a muscle-specific enhancer directly regulated by MEF2. Srpk3-null mice display a new entity of type 2 fiber-specific myopathy with a marked increase in centrally placed nuclei; while transgenic mice overexpressing Srpk3 in skeletal muscle show severe myofiber degeneration and early lethality. We conclude that normal muscle growth and homeostasis require MEF2-dependent signaling by Srpk3.

Amino Acid Sequence↗

PubMed2005

Regulation of vertebrate myotome development by the p38 MAP kinase-MEF2 signaling pathway.

Biochemical and cell culture studies have characterized the myocyte enhancer factor 2 (MEF2) transcriptional regulatory proteins as obligatory partners for the myogenic regulatory factors (MRFs) in the differentiation of myogenic cells in culture. However, the role of MEF2 activation in somitic myogenesis has not been fully characterized. Here, we report a critical interaction between the p38 mitogen-activated protein kinase (p38 MAPK) and MEF2 in the developing somite myotome. We document expression of MEF2A and p38 MAPK proteins in the somite of 9.5 dpc mouse embryos concurrent with Myf 5 protein expression. We also observed that abrogation of p38 MAPK signaling blocks MEF2 activation using a MEF2 transgenic 'sensor' mouse. Inhibition of p38 MAPK signaling concurrently inhibited myogenic differentiation in somite cultures and in embryos in vivo using transplacental injection of a p38 inhibitor (SB203580). Finally, we document that commitment to the myogenic lineage is not appreciably affected by p38 MAPK inhibition since the activation of an early marker of myogenic commitment (Myf 5) occurs normally when p38 MAPK signaling is inhibited. Thus, we present novel evidence indicating a crucial role for p38 MAPK signaling to the MEF2 transcriptional regulators during early mammalian somite development and myotome formation.

Animals↗

PubMed2005

Hand is a direct target of Tinman and GATA factors during Drosophila cardiogenesis and hematopoiesis.

The existence of hemangioblasts, which serve as common progenitors for hematopoietic cells and cardioblasts, has suggested a molecular link between cardiogenesis and hematopoiesis in Drosophila. However, the molecular mediators that might link hematopoiesis and cardiogenesis remain unknown. Here, we show that the highly conserved basic helix-loop-helix (bHLH) transcription factor Hand is expressed in cardioblasts, pericardial nephrocytes and hematopoietic progenitors. The homeodomain protein Tinman and the GATA factors Pannier and Serpent directly activate Hand in these cell types through a minimal enhancer, which is necessary and sufficient to drive Hand expression in these different cell types. Hand is activated by Tinman and Pannier in cardioblasts and pericardial nephrocytes, and by Serpent in hematopoietic progenitors in the lymph gland. These findings place Hand at a nexus of the transcriptional networks that govern cardiogenesis and hematopoiesis, and indicate that the transcriptional pathways involved in development of the cardiovascular, excretory and hematopoietic systems may be more closely related than previously appreciated.

Animals↗

PubMed2005

An expression screen reveals modulators of class II histone deacetylase phosphorylation.

Class II histone deacetylases (HDACs) repress transcription by associating with a variety of transcription factors and corepressors. Phosphorylation of a set of conserved serine residues in the N-terminal extensions of class II HDACs creates binding sites for 14-3-3 chaperone proteins, which trigger nuclear export of these HDACs, thereby derepressing specific target genes in a signal-dependent manner. To identify intracellular signaling pathways that control phosphorylation of HDAC5, a class II HDAC, we designed a eukaryotic cDNA expression screen in which a GAL4-dependent luciferase reporter was expressed with the DNA-binding domain of GAL4 fused to the N-terminal extension of HDAC5 and the VP16 transcription activation domain fused to 14-3-3. The transfection of COS cells with cDNA expression libraries results in activation of luciferase expression by cDNAs encoding HDAC5 kinases or modulators of such kinases that enable phosphorylated GAL4-HDAC5 to recruit 14-3-3-VP16 with consequent reconstitution of a functional transcriptional complex. Our results reveal a remarkable variety of signaling pathways that converge on the signal-responsive phosphorylation sites in HDAC5, thereby enabling HDAC5 to connect extracellular signals to the genome.

Animals↗

PubMed2005

Unveiling the mechanisms of cell-cell fusion.

Cell-cell fusion is fundamental to the development and physiology of multicellular organisms, but little is known of its mechanistic underpinnings. Recent studies have revealed that many proteins involved in cell-cell fusion are also required for seemingly unrelated cellular processes such as phagocytosis, cell migration, axon growth, and synaptogenesis. We review advances in understanding cell-cell fusion by contrasting it with virus-cell and intracellular vesicle fusion. We also consider how proteins involved in general aspects of membrane dynamics have been co-opted to control fusion of diverse cell types by coupling with specialized proteins involved in cell-cell recognition, adhesion, and signaling.

Animals↗

PubMed2005

Altered vascular remodeling in fibulin-5-deficient mice reveals a role of fibulin-5 in smooth muscle cell proliferation and migration.

Fibulin (fbln)-5 is an elastin-binding protein required for assembly and organization of elastic fibers. To examine the potential role of fbln-5 in vascular remodeling and neointima formation, we induced vascular injury by carotid artery ligation in fbln-5(-/-) mice. Mutant mice displayed an exaggerated vascular remodeling response that was accompanied by severe neointima formation with thickened adventitia. These abnormalities were not observed in elastin(+/-) mice that exhibited a comparable reduction of vessel extensibility to fbln-5(-/-) mice. Thus, the severe remodeling response could not be attributed to altered extensibility of the vessel wall alone. Vascular smooth muscle cells cultured from fbln-5(-/-) mice displayed enhanced proliferative and migratory responses to mitogenic stimulation relative to wild-type cells, and these responses were inhibited by overexpression of fbln-5. These findings demonstrate the importance of the elastic laminae in vascular injury, and reveal an unexpected role of fbln-5 as an inhibitor of vascular smooth muscle cell proliferation and migration.

Animals↗

PubMed2005

Histone deacetylase 9 couples neuronal activity to muscle chromatin acetylation and gene expression.

Electrical activity arising from motor innervation influences skeletal muscle physiology by controlling the expression of many muscle genes, including those encoding acetylcholine receptor (AChR) subunits. How electrical activity is converted into a transcriptional response remains largely unknown. We show that motor innervation controls chromatin acetylation in skeletal muscle and that histone deacetylase 9 (HDAC9) is a signal-responsive transcriptional repressor which is downregulated upon denervation, with consequent upregulation of chromatin acetylation and AChR expression. Forced expression of Hdac9 in denervated muscle prevents upregulation of activity-dependent genes and chromatin acetylation by linking myocyte enhancer factor 2 (MEF2) and class I HDACs. By contrast, Hdac9-null mice are supersensitive to denervation-induced changes in gene expression and show chromatin hyperacetylation and delayed perinatal downregulation of myogenin, an activator of AChR genes. These findings show a molecular mechanism to account for the control of chromatin acetylation by presynaptic neurons and the activity-dependent regulation of skeletal muscle genes by motor innervation.

Acetylation↗

PubMed2005

Identification of direct serum-response factor gene targets during Me2SO-induced P19 cardiac cell differentiation.

Serum-response factor (SRF) is an obligatory transcription factor, required for the formation of vertebrate mesoderm leading to the origin of the cardiovascular system. Protein A-TEV-tagged chromatin immunoprecipitation technology was used to collect direct SRF-bound gene targets from pluripotent P19 cells, induced by Me2SO treatment into an enriched cardiac cell population. From 242 sequenced DNA fragments, we identified 188 genomic DNA fragments as potential direct SRF targets that contain CArG boxes and CArG-like boxes. Of the 92 contiguous genes that were identified, a subgroup of 43 SRF targets was then further validated by co-transfection assays with SRF. Expression patterns of representative candidate genes were compared with the LacZ reporter expression activity of the endogenous SRF gene. According to the Unigene data base, 84% of the SRF target candidates were expressed, at least, in the heart. In SRF null embryonic stem cells, 81% of these SRF target candidates were greatly affected by the absence of SRF. Among these SRF-regulated genes, Raf1, Map4k4, and Bicc1 have essential roles in mesoderm formation. The 12 regulated SRF target genes, Mapk10 (JNK3), Txnl2, Azi2, Tera, Sema3a, Lrp4, Actc1, Myl3, Hspg2, Pgm2, Hif3a, and Asb5, have been implicated in cardiovascular formation, and the Ski and Hes6 genes have roles in muscle differentiation. SRF target genes related to cell mitosis and cycle, E2f5, Npm1, Cenpb, Rbbp6, and Scyl1, expressed in the heart tissue were differentially regulated in SRF null ES cells.

Amino Acid Motifs↗

PubMed2005

Myocardin is sufficient and necessary for cardiac gene expression in Xenopus.

Myocardin is a cardiac- and smooth muscle-specific cofactor for the ubiquitous transcription factor serum response factor (SRF). Using gain-of-function approaches in the Xenopus embryo, we show that myocardin is sufficient to activate transcription of a wide range of cardiac and smooth muscle differentiation markers in non-muscle cell types. We also demonstrate that, for the myosin light chain 2 gene (MLC2), myocardin cooperates with the zinc-finger transcription factor Gata4 to activate expression. Inhibition of myocardin activity in Xenopus embryos using morpholino knockdown methods results in inhibition of cardiac development and the absence of expression of cardiac differentiation markers and severe disruption of cardiac morphological processes. We conclude that myocardin is an essential component of the regulatory pathway for myocardial differentiation.

Amino Acid Sequence↗

PubMed2005

Requirement for serum response factor for skeletal muscle growth and maturation revealed by tissue-specific gene deletion in mice.

Serum response factor (SRF) controls the transcription of muscle genes by recruiting a variety of partner proteins, including members of the myocardin family of transcriptional coactivators. Mice lacking SRF fail to form mesoderm and die before gastrulation, precluding an analysis of the roles of SRF in muscle tissues. To investigate the functions of SRF in skeletal muscle development, we conditionally deleted the Srf gene in mice by skeletal muscle-specific expression of Cre recombinase. In mice lacking skeletal muscle SRF expression, muscle fibers formed, but failed to undergo hypertrophic growth after birth. Consequently, mutant mice died during the perinatal period from severe skeletal muscle hypoplasia. The myopathic phenotype of these mutant mice resembled that of mice expressing a dominant negative mutant of a myocardin family member in skeletal muscle. These findings reveal an essential role for the partnership of SRF and myocardin-related transcription factors in the control of skeletal muscle growth and maturation in vivo.

Animals↗

PubMed2005

Phenotypic modulation of smooth muscle cells through interaction of Foxo4 and myocardin.

Smooth muscle cells (SMCs) modulate their phenotype between proliferative and differentiated states in response to physiological and pathological cues. Insulin-like growth factor-I stimulates differentiation of SMCs by activating phosphoinositide-3-kinase (PI3K)-Akt signaling. Foxo forkhead transcription factors act as downstream targets of Akt and are inactivated through phosphorylation by Akt. We show that Foxo4 represses SMC differentiation by interacting with and inhibiting the activity of myocardin, a transcriptional coactivator of smooth muscle genes. PI3K/Akt signaling promotes SMC differentiation, at least in part, by stimulating nuclear export of Foxo4, thereby releasing myocardin from its inhibitory influence. Accordingly, reduction of Foxo4 expression in SMCs by siRNA enhances myocardin activity and SMC differentiation. We conclude that signal-dependent interaction of Foxo4 with myocardin couples extracellular signals with the transcriptional program for SMC differentiation.

Active Transport, Cell Nucleus↗