1,181 research outputs found
Thrombin induces Egr-1 expression in fibroblasts involving elevation of the intracellular Ca2+ concentration, phosphorylation of ERK and activation of ternary complex factor
<p>Abstract</p> <p>Background</p> <p>The serine protease thrombin catalyzes fibrin clot formation by converting fibrinogen into fibrin. Additionally, thrombin stimulation leads to an activation of stimulus-responsive transcription factors in different cell types, indicating that the gene expression pattern is changed in thrombin-stimulated cells. The objective of this study was to analyze the signaling cascade leading to the expression of the zinc finger transcription factor Egr-1 in thrombin-stimulated lung fibroblasts.</p> <p>Results</p> <p>Stimulation of 39M1-81 fibroblasts with thrombin induced a robust and transient biosynthesis of Egr-1. Reporter gene analysis revealed that the newly synthesized Egr-1 was biologically active. The signaling cascade connecting thrombin stimulation with Egr-1 gene expression required elevated levels of cytosolic Ca<sup>2+</sup>, the activation of diacylgycerol-dependent protein kinase C isoenzymes, and the activation of extracellular signal-regulated protein kinase (ERK). Stimulation of the cells with thrombin triggered the phosphorylation of the transcription factor Elk-1. Expression of a dominant-negative mutant of Elk-1 completely prevented Egr-1 expression in stimulated 39M1-81 cells, indicating that Elk-1 or related ternary complex factors connect the intracellular signaling cascade elicited by activation of protease-activated receptors with transcription of the Egr-1 gene. Lentiviral-mediated expression of MAP kinase phosphatase-1, a dual-specific phosphatase that dephosphorylates and inactivates ERK in the nucleus, prevented Elk-1 phosphorylation and Egr-1 biosynthesis in thrombin stimulated 39M1-81 cells, confirming the importance of nuclear ERK and Elk-1 for the upregulation of Egr-1 expression in thrombin-stimulated lung fibroblasts. 39M1-81 cells additionally express M<sub>1 </sub>muscarinic acetylcholine receptors. A comparison between the signaling cascades induced by thrombin or carbachol showed no differences, except that signal transduction via M<sub>1 </sub>muscarinic acetylcholine receptors required the transactivation of the EGF receptor, while thrombin signaling did not.</p> <p>Conclusion</p> <p>This study shows that stimulus-transcription coupling in thrombin-treated lung fibroblasts relies on the elevation of the intracellular Ca<sup>2+</sup>-concentration and the activation of PKC and ERK. In the nucleus, ternary complex factors function as key proteins linking the intracellular signaling cascade with enhanced transcription of the Egr-1 gene. This study further shows that the dominant-negative Elk-1 mutant is a valuable tool to study Elk-1-mediated gene transcription.</p
TRPM3-Induced Gene Transcription Is under Epigenetic Control
Transient receptor potential M3 (TRPM3) cation channels regulate numerous biological
functions, including gene transcription. Stimulation of TRPM3 channels with pregnenolone sulfate
activates stimulus-responsive transcription factors, which bind to short cognate sequences in the
promoters of their target genes. In addition, coregulator proteins are involved that convert the
chromatin into a configuration that is permissive for gene transcription. In this study, we determined
whether TRPM3-induced gene transcription requires coactivators that change the acetylation pattern
of histones. We used compound A485, a specific inhibitor of the histone acetyltransferases CBP
and p300. In addition, the role of bromodomain proteins that bind to acetylated lysine residues
of histones was analyzed. We used JQ1, an inhibitor of bromodomain and extra terminal domain
(BET) family proteins. The results show that both compounds attenuated the activation of AP-1 and
CREB-regulated gene transcription following stimulation of TRPM3 channels. Inhibition of CBP/p300
and BET proteins additionally reduced the transcriptional activation potential of the transcription
factors c-Fos and Elk-1. Transcriptional upregulation of the interleukin-8 gene was attenuated by
A485 and JQ1, indicating that proinflammatory cytokine expression is controlled by CBP/p300
and bromodomain proteins. We conclude that TRPM3-induced signaling involves transcriptional
coactivators and acetyl-lysine-bound bromodomain proteins for activating gene transcription
Glucose Homeostasis and Pancreatic Islet Size Are Regulated by the Transcription Factors Elk-1 and Egr-1 and the Protein Phosphatase Calcineurin
Pancreatic β-cells synthesize and secrete insulin. A key feature of diabetes mellitus is
the loss of these cells. A decrease in the number of β-cells results in decreased biosynthesis of
insulin. Increasing the number of β-cells should restore adequate insulin biosynthesis leading
to adequate insulin secretion. Therefore, identifying proteins that regulate the number of β-cells
is a high priority in diabetes research. In this review article, we summerize the results of three
sophisticated transgenic mouse models showing that the transcription factors Elk-1 and Egr-1 and the
Ca2+/calmodulin-regulated protein phosphatase calcineurin control the formation of sufficiently large
pancreatic islets. Impairment of the biological activity of Egr-1 and Elk-1 in pancreatic β-cells leads to
glucose intolerance and dysregulation of glucose homeostasis, the process that maintains glucose
concentration in the blood within a narrow range. Transgenic mice expressing an activated calcineurin
mutant also had smaller islets and showed hyperglycemia. Calcineurin induces dephosphorylation
of Elk-1 which subsequently impairs Egr-1 biosynthesis and the biological functions of Elk-1 and
Egr-1 to regulate islet size and glucose homeostasis
Expression of the C-Terminal Domain of Phospholipase Cβ3 Inhibits Signaling via Gαq-Coupled Receptors and Transient Receptor Potential Channels
Transient receptor potential (TRP) channels are cation channels that play a regulatory role
in pain and thermosensation, insulin secretion, and neurotransmission. It has been proposed that
activation of TRP channels requires phosphatidylinositol 4,5-bisphosphate, the major substrate for
phospholipase C (PLC). We investigated whether inhibition of PLCβ has an impact on TRP channel
signaling. A genetic approach was used to avoid off-target effects observed when using a pharmacological PLCβ inhibitor. In this study, we show that expression of PLCβ1ct and PLCβ3ct, truncated
forms of PLCβ1 or PLCβ3 that contain the C-terminal membrane binding domains, almost completely
blocked the signal transduction of a Gαq-coupled designer receptor, including the phosphorylation of
ERK1/2. In contrast, expression of the helix-turn-helix motif (Hα1—Hα2) of the proximal C-terminal
domain of PLCβ3 did not affect Gαq-coupled receptor signaling. PLCβ3ct expression impaired
signaling of the TRP channels TRPM3 and TRPM8, stimulated with either prognenolone sulfate or
icilin. Thus, the C-terminal domain of PLCβ3 interacts with plasma membrane targets, most likely
phosphatidylinositol 4,5-bisphosphate, and in this way blocks the biological activation of TRPM3 and
TRPM8, which require interaction with this phospholipid. PLCβ thus regulates TRPM3 and TRPM8
channels by masking phosphatidylinositol 4,5-bisphosphate with its C-terminal domain
Theoretical study of interacting hole gas in p-doped bulk III-V semiconductors
We study the homogeneous interacting hole gas in -doped bulk III-V
semiconductors. The structure of the valence band is modelled by Luttinger's
Hamiltonian in the spherical approximation, giving rise to heavy and light hole
dispersion branches, and the Coulomb repulsion is taken into account via a
self-consistent Hartree-Fock treatment. As a nontrivial feature of the model,
the self-consistent solutions of the Hartree-Fock equations can be found in an
almost purely analytical fashion, which is not the case for other types of
effective spin-orbit coupling terms. In particular, the Coulomb interaction
renormalizes the Fermi wave numbers for heavy and light holes. As a
consequence, the ground state energy found in the self-consistent Hartree-Fock
approach and the result from lowest-order perturbation theory do not agree. We
discuss the consequences of our observations for ferromagnetic semiconductors,
and for the possible observation of the spin-Hall effect in bulk -doped
semiconductors. Finally, we also investigate elementary properties of the
dielectric function in such systems.Comment: 9 pages, 5 figures, title slightly changed in the course of editorial
process, a few references added, version to appear in Phys. Rev.
Ca2+ Microdomains, Calcineurin and the Regulation of Gene Transcription
Ca2+ ions function as second messengers regulating many intracellular events, including
neurotransmitter release, exocytosis, muscle contraction, metabolism and gene transcription. Cells of a
multicellular organism express a variety of cell-surface receptors and channels that trigger an increase
of the intracellular Ca2+ concentration upon stimulation. The elevated Ca2+ concentration is not
uniformly distributed within the cytoplasm but is organized in subcellular microdomains with high
and low concentrations of Ca2+ at different locations in the cell. Ca2+ ions are stored and released by
intracellular organelles that change the concentration and distribution of Ca2+ ions. A major function of
the rise in intracellular Ca2+ is the change of the genetic expression pattern of the cell via the activation
of Ca2+-responsive transcription factors. It has been proposed that Ca2+-responsive transcription
factors are differently affected by a rise in cytoplasmic versus nuclear Ca2+. Moreover, it has been
suggested that the mode of entry determines whether an influx of Ca2+ leads to the stimulation of
gene transcription. A rise in cytoplasmic Ca2+ induces an intracellular signaling cascade, involving the
activation of the Ca2+/calmodulin-dependent protein phosphatase calcineurin and various protein
kinases (protein kinase C, extracellular signal-regulated protein kinase, Ca2+/calmodulin-dependent
protein kinases). In this review article, we discuss the concept of gene regulation via elevated Ca2+
concentration in the cytoplasm and the nucleus, the role of Ca2+ entry and the role of enzymes as
signal transducers. We give particular emphasis to the regulation of gene transcription by calcineurin,
linking protein dephosphorylation with Ca2+ signaling and gene expression
Insulin-Responsive Transcription Factors
The hormone insulin executes its function via binding and activating of the insulin receptor,
a receptor tyrosine kinase that is mainly expressed in skeletal muscle, adipocytes, liver, pancreatic
β-cells, and in some areas of the central nervous system. Stimulation of the insulin receptor activates
intracellular signaling cascades involving the enzymes extracellular signal-regulated protein kinase 1/2 (ERK1/2), phosphatidylinositol 3-kinase, protein kinase B/Akt, and phospholipase Cγ as signal
transducers. Insulin receptor stimulation is correlated with multiple physiological and biochemical
functions, including glucose transport, glucose homeostasis, food intake, proliferation, glycolysis,
and lipogenesis. This review article focuses on the activation of gene transcription as a result of
insulin receptor stimulation. Signal transducers such as protein kinases or the GLUT4-induced influx
of glucose connect insulin receptor stimulation with transcription. We discuss insulin-responsive
transcription factors that respond to insulin receptor activation and generate a transcriptional network
executing the metabolic functions of insulin. Importantly, insulin receptor stimulation induces
transcription of genes encoding essential enzymes of glycolysis and lipogenesis and inhibits genes
encoding essential enzymes of gluconeogenesis. Overall, the activation or inhibition of insulin responsive transcription factors is an essential aspect of orchestrating a wide range of insulin-induced
changes in the biochemistry and physiology of insulin-responsive tissues
Network synchronization of groups
In this paper we study synchronized motions in complex networks in which
there are distinct groups of nodes where the dynamical systems on each node
within a group are the same but are different for nodes in different groups.
Both continuous time and discrete time systems are considered. We initially
focus on the case where two groups are present and the network has bipartite
topology (i.e., links exist between nodes in different groups but not between
nodes in the same group). We also show that group synchronous motions are
compatible with more general network topologies, where there are also
connections within the groups
Adaptive Detection of Instabilities: An Experimental Feasibility Study
We present an example of the practical implementation of a protocol for
experimental bifurcation detection based on on-line identification and feedback
control ideas. The idea is to couple the experiment with an on-line
computer-assisted identification/feedback protocol so that the closed-loop
system will converge to the open-loop bifurcation points. We demonstrate the
applicability of this instability detection method by real-time,
computer-assisted detection of period doubling bifurcations of an electronic
circuit; the circuit implements an analog realization of the Roessler system.
The method succeeds in locating the bifurcation points even in the presence of
modest experimental uncertainties, noise and limited resolution. The results
presented here include bifurcation detection experiments that rely on
measurements of a single state variable and delay-based phase space
reconstruction, as well as an example of tracing entire segments of a
codimension-1 bifurcation boundary in two parameter space.Comment: 29 pages, Latex 2.09, 10 figures in encapsulated postscript format
(eps), need psfig macro to include them. Submitted to Physica
Spatial patterns of desynchronization bursts in networks
We adapt a previous model and analysis method (the {\it master stability
function}), extensively used for studying the stability of the synchronous
state of networks of identical chaotic oscillators, to the case of oscillators
that are similar but not exactly identical. We find that bubbling induced
desynchronization bursts occur for some parameter values. These bursts have
spatial patterns, which can be predicted from the network connectivity matrix
and the unstable periodic orbits embedded in the attractor. We test the
analysis of bursts by comparison with numerical experiments. In the case that
no bursting occurs, we discuss the deviations from the exactly synchronous
state caused by the mismatch between oscillators
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