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Acute Activation (acute + activation)
Selected AbstractsAcute Activation of Hippocampal Glucocorticoid Receptors Results in Different Waves of Gene Expression Throughout TimeJOURNAL OF NEUROENDOCRINOLOGY, Issue 4 2006M. C. Morsink Abstract Several aspects of hippocampal cell function are influenced by adrenal-secreted glucocorticoids in a delayed, genomic fashion. Previously, we used Serial Analysis of Gene Expression to identify glucocorticoid receptor (GR)-induced transcriptional changes in the hippocampus at a fixed time point. However, because changes in mRNA levels are transient and most likely precede the effects on hippocampal cell function, the aim of the current study was to assess the transcriptional changes in a broader time window by generating a time curve of GR-mediated gene expression changes. Therefore, we used rat hippocampal slices obtained from adrenalectomised rats, substituted in vivo with low corticosterone pellets, predominantly occupying the hippocampal mineralocorticoid receptors. To activate GR, slices were treated in vitro with a high (100 nM) dose of corticosterone and gene expression was profiled 1, 3 and 5 h after GR-activation. Using Affymetrix GeneChips, a striking pattern with different waves of gene expression was observed, shifting from exclusively down-regulated genes 1 h after GR-activation to both up and down regulated genes 3 h after GR-activation. After 5 h, the response was almost back to baseline. Additionally, real-time quantitative polymerase chain reaction was used for validation of a selection of responsive genes including genes involved in neurotransmission and synaptic plasticity such as the corticotropin releasing hormone receptor 1, monoamine oxidase A, LIMK1 and calmodulin 2. This permitted confirmation of GR-responsiveness of 15 out of 18 selected genes. In conclusion, direct activation of GR in hippocampal slices results in transient changes in gene expression. The pattern in which gene expression was modulated suggests that the fast genomic effects of glucocorticoids may be realised via transrepression, preceding a later wave of transactivation. Furthermore, we identified a number of interesting candidate genes which may underlie the glucocorticoid-mediated effects on hippocampal cell function. [source] Acute activation of Erk1/Erk2 and protein kinase B/akt proceed by independent pathways in multiple cell typesFEBS JOURNAL, Issue 17 2005Doris Chiu We used two inhibitors of the signaling enzyme phosphatidylinositol 3-kinase (PtdIns3K), wortmannin and LY294002, to evaluate the potential involvement of PtdIns3K in the activation of the MAP kinases (MAPK), Erk1 and Erk2. In dose,response studies carried out on six different cell lines and a primary cell culture, we analyzed the ability of the inhibitors to block phosphorylation of protein kinase B/akt (PKB/akt) at Ser473 as a measure of PtdIns3K activity, or the phosphorylation of Erk1/2 at activating Thr/Tyr sites as a measure of the extent of activation of MAPK/Erk kinase (MEK/Erk). In three different hemopoietic cell lines stimulated with cytokines, and in HEK293 cells, stimulated with serum, either wortmannin or LY294002, but never both, could partially block phosphorylation of Erks. The same observations were made in a B-cell line and in primary fibroblasts. In only one cell type, the A20 B cells, was there a closer correlation between the PtdIns3K inhibition by both inhibitors, and their corresponding effects on Erk phosphorylation. However, this stands out as an exception that gives clues to the mechanism by which cross-talk might occur. In all other cells, acute activation of the pathway leading to Erk phosphorylation could proceed independently of PtdIns3K activation. In a biological assay comparing these two pathways, the ability of LY294002 and the MEK inhibitor, U0126, to induce apoptosis were tested. Whereas LY294002 caused death of cytokine-dependent hemopoietic cells, U0126 had little effect, but both inhibitors together had a synergistic effect. The data show that these two pathways are regulating very different downstream events involved in cell survival. [source] Serum and forskolin cooperate to promote G1 progression in Schwann cells by differentially regulating cyclin D1, cyclin E1, and p27Kip expressionGLIA, Issue 16 2007Jared Iacovelli Abstract Proliferation of Schwann cells in vitro, unlike most mammalian cells, is not induced by serum alone but additionally requires cAMP elevation and mitogenic stimulation. How these agents cooperate to promote progression through the G1 phase of the cell cycle is unclear. We studied the integrative effects of these compounds on receptor-mediated signaling pathways and regulators of G1 progression. We show that serum alone induces strong cyclical expression of cyclin D1 and E1, 6 and 12 h after addition, respectively. Serum also promotes strong but transient erbB2, ERK, and Akt phosphorylation, but Schwann cells remain arrested in G1 due to high levels of the inhibitor, p27Kip. Forskolin with serum promotes G1 progression in 22% of Schwann cells between 18 and 24 h by inducing a steady decline in p27Kip levels that reaches a nadir at 12 h coinciding with peak cyclin E1 expression. Forskolin also delays neuregulin-induced loss of erbB2 receptors allowing strong acute activation of PI3K, sustained erbB2 phosphorylation and G1 progression in 31% of Schwann cells. We find that the ability of forskolin to decrease p27Kip is associated with its ability to decrease Krox-20 expression that is induced by serum and further increased by neuregulin. Our results explain why serum is required but insufficient to stimulate proliferation and identify two routes by which forskolin promotes proliferation in the presence of serum and neuregulin. These findings provide insights into how G1 progression and, cell cycle arrest leading to myelination are regulated in Schwann cells. © 2007 Wiley-Liss, Inc. [source] Trade-offs between longevity and pathogen resistance in Drosophila melanogaster are mediated by NF,B signalingAGING CELL, Issue 6 2006Sergiy Libert Summary The innate immune response protects numerous organisms, including humans, from the universe of pathogenic molecules, viruses and micro-organisms. Despite its role in promoting pathogen resistance, inappropriate activation and expression of NF,B and other immunity-related effector molecules can lead to cancer, inflammation, and other diseases of aging. Understanding the mechanisms leading to immune system activation as well as the short- and long-term consequences of such activation on health and lifespan is therefore critical for the development of beneficial immuno-modulating and longevity-promoting interventions. Mechanisms of innate immunity are highly conserved across species, and we take advantage of genetic tools in the model organism, Drosophila melanogaster, to study the effects of acute and chronic activation of immunity pathways on pathogen resistance and general fitness of adult flies. Our findings indicate that fat body specific overexpression of a putative pathogen recognition molecule, peptidoglycan recognition protein (PGRP-LE), is sufficient for constitutive up-regulation of the immune response and for enhanced pathogen resistance. Primary components of fitness are unaffected by acute activation, but chronic activation leads to an inflammatory state and reduced lifespan. These phenotypes are dependent on the NF,B-related transcriptional factor, Relish, and they establish a mechanistic basis for a link between immunity, inflammation, and longevity. [source] The effects of experimental muscle and skin pain on the static stretch sensitivity of human muscle spindles in relaxed leg musclesTHE JOURNAL OF PHYSIOLOGY, Issue 11 2008Ingvars Birznieks Animal studies have shown that noxious inputs onto ,-motoneurons can cause an increase in the activity of muscle spindles, and it has been proposed that this causes a fusimotor-driven increase in muscle stiffness that is believed to underlie many chronic pain syndromes. To test whether experimental pain also acts on the fusimotor system in humans, unitary recordings were made from 19 spindle afferents (12 Ia, 7 II) located in the ankle and toe extensors or peronei muscles of awake human subjects. Muscle pain was induced by bolus intramuscular injection of 0.5 ml 5% hypertonic saline into tibialis anterior (TA); skin pain was induced by 0.2 ml injection into the overlying skin. Changes in fusimotor drive to the muscle spindles were inferred from changes in the mean discharge frequency and discharge variability of spindle endings in relaxed muscle. During muscle pain no afferents increased their discharge activity: seven afferents (5 Ia, 2 II) showed a decrease and six (4 Ia, 2 II) afferents were not affected. During skin pain of 13 afferents discharge rate increased in one (Ia) and decreased in two (1 Ia, 1 II). On average, the overall discharge rate decreased during muscle pain by 6.1% (P < 0.05; Wilcoxon), but remained essentially the same during skin pain. There was no detectable correlation between subjective pain level and the small change in discharge rate of muscle spindles. Irrespective of the type of pain, discharge variability parameters were not influenced (P > 0.05; Wilcoxon). We conclude that, contrary to the ,vicious cycle' hypothesis, acute activation of muscle or skin nociceptors does not cause a reflex increase in fusimotor drive in humans. Rather, our results are more aligned with the pain adaptation model, based on clinical studies predicting pain-induced reductions of agonist muscle activity. [source] Stem cell factor and H2O2 induce GLUT1 translocation in M07e cellsBIOFACTORS, Issue 2 2004Tullia Maraldi Abstract This work aims to elucidate the mechanisms involved in the early activation of glucose transport in hematopoietic M07e cells by stem cell factor (SCF) and a reactive oxygen species (ROS) as H2O2. SCF and H2O2 increase Vmax for glucose transport; this enhancement is due to a higher content in GLUT1 in plasma membranes, possibly through a translocation from intracellular stores. Inhibitors of tyrosine kinases or phospholipase C (PLC) remove glucose transport enhancement and prevent translocation. The inhibitory effect of STI-571 suggests a role for c-kit tyrosine kinase on glucose transport activation not only by SCF, but also by H2O2. On the other hand, neither protein kinase C nor phosphoinositide-3-kinase appear to be involved in the acute activation of glucose transport. Our data suggest that i) in M07e cells, SCF and exogenous H2O2 elicit a short-term activation of glucose transport through a translocation of GLUT1 from intracellular stores to plasma membranes; ii) both stimuli could share at least some signaling pathways leading to glucose uptake activation, involving protein tyrosine kinases and PLC iii) H2O2 could act increasing the level of tyrosine phosphorylation through the inhibition of tyrosine phosphatases and mimicking the regulation role of endogenous ROS. [source] | ||||||||||