Biomedical subjects

R S Jope

Publications and source records attributed to R S Jope.

At least 37 records · Page 2Linked to original sources

PubMed1999

Muscarinic M3 and epidermal growth factor receptors activate mutually inhibitory signaling cascades in human neuroblastoma SH-SY5Y cells.

Regulatory interactions among individual receptor-coupled signal transduction systems are critically important for establishing cellular responses in the face of multiple stimuli. In this study, potential regulatory interactions between signal transduction systems activated by growth factor receptors and by G-protein-coupled receptors were examined using human neuroblastoma SH-SY5Y cells which express endogenous epidermal growth factor (EGF) and muscarinic M3 receptors. Activation of muscarinic receptors with carbachol was found to inhibit EGF-induced signaling, including tyrosine phosphorylation of the adaptor protein Cbl and of the EGF receptor, and complex formation between Shc proteins and the EGF receptor and Grb2. Protein kinase C, which is activated by muscarinic M3 receptors, mediated this inhibitory cross-talk. Activation of EGF receptors was found to inhibit muscarinic receptor-induced tyrosine phosphorylation of focal adhesion kinase and paxillin. Reactive oxygen species, which are formed as components of the EGF signaling cascade, mediated this inhibitory cross-talk. These mutual inhibitory interactions demonstrate novel mechanisms for neuronal integration of multiple signals generated by activation of receptors by neurotransmitters and growth factors.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Oxidative stress oppositely modulates protein tyrosine phosphorylation stimulated by muscarinic G protein-coupled and epidermal growth factor receptors.

This study's goals were to more fully define the activation of protein tyrosine phosphorylation stimulated by muscarinic receptors, to test if this signaling process is affected by oxidative stress induced by H2O2, and to compare the effects of H2O2 on protein tyrosine phosphorylation activated by epidermal growth factor (EGF) receptors. Experiments used human neuroblastoma SH-SY5Y cells which express endogenous M3 muscarinic and EGF receptors. Carbachol induced time-dependent increases in phosphotyrosine immunoreactivity of several protein bands, which were quantitated, and immunoprecipitation was used to identify the adhesion-related proteins focal adhesion kinase, p130Cas/HEF1, and paxillin, and three shc adapter proteins. Carbachol-induced tyrosine phosphorylation of the adhesion-related proteins was mediated by muscarinic receptors, and was inhibited by a src family kinase inhibitor, PP1. That carbachol can activate src family kinases was indicated further by the finding that carbachol induced an increase in tyrosine phosphorylation of p120-src substrate, which was inhibited by PP1. Oxidative stress induced by H2O2 concentration dependently inhibited carbachol-induced tyrosine phosphorylation of each of the adhesion-related proteins. EGF increased the phosphotyrosine immunoreactivity of 180- and 116-kDa proteins, identified as the EGF receptor and Cbl, respectively. In contrast to the results with carbachol, H2O2 potentiated EGF-induced tyrosine phosphorylation. These results demonstrate that muscarinic receptor activation induces previously unrecognized increases in tyrosine phosphorylation, and that this signaling process is impaired by H2O2, whereas protein tyrosine phosphorylation stimulated by EGF is increased by H2O2. Thus, oxidative stress can oppositely modulate protein tyrosine phosphorylation induced by activation of G protein-coupled and growth factor receptors in the same cells.

Carbachol↗

PubMed1999

Glycogen synthase kinase-3beta, beta-catenin, and tau in postmortem bipolar brain.

Therapeutic concentrations of the anti-bipolar drug lithium inhibit the activity of glycogen synthase kinase-3beta, which raises the possibility that this enzyme and its substrates may be altered in the brain of subjects with bipolar disorder. Therefore, in prefrontal cortical samples from subjects with bipolar disorder and age-matched control subjects, we examined the levels of glycogen synthase kinase 3beta and of two proteins modified by it, beta-catenin and the microtubule associated protein tau. There were no significant differences between subject groups among these measurements, but there was a tendency for the tau isoform profile to be modified in bipolar tissue. Thus, while there are no differences between bipolars and controls in prefrontal cortical levels of glycogen synthase kinase-3beta, beta-catenin, or tau, tau isoform levels or phosphorylation states may be modified in bipolar disorder.

Adult↗

PubMed1999

Bisindolylmaleimide VIII facilitates Fas-mediated apoptosis and inhibits T cell-mediated autoimmune diseases.

Fas-mediated apoptosis is essential for the elimination of cells, and impaired apoptosis can have severe detrimental consequences. Bisindolylmaleimide VIII potentiated Fas-mediated apoptosis in human astrocytoma 1321N1 cells and in Molt-4T cells, both of which were devoid of apoptosis induced by anti-Fas antibody in the absence of bisindolylmaleimide VIII, and in Jurkat and CEM-6 T cells, which showed slight and moderate apoptotic responses, respectively, to low levels of Fas stimulation. Potentiation of Fas-mediated apoptosis by bisindolylmaleimide VIII was selective for activated, rather than non-activated, T cells, and was Fas-dependent, as it was not observed in T cells from Fas-deficient lpr/lpr mice. Administration of bisindolylmaleimide VIII to rats during autoantigen stimulation prevented the development of symptoms of T cell-mediated autoimmune diseases in two models, the Lewis rat model of experimental allergic encephalitis and the Lewis adjuvant arthritis model. Thus, the use of agents such as bisindolylmaleimide VIII may be therapeutically useful for supporting more effective elimination of detrimental cells through enhancement of Fas-dependent apoptosis signaling.

Animals↗

PubMed1999

A bimodal model of the mechanism of action of lithium.

Investigations of the biochemical actions of lithium have identified many individual reactions that are affected, especially within cellular signaling systems, but the actions of lithium at different sites often appear opposing and difficult to integrate into a general mechanism of action. A bimodal mechanism of action of lithium is proposed which is in accord with many of the apparently contradictory results that have been published. This model describes the critical effect of lithium as that of a stabilizer of the magnitude of fluctuations of signaling processes. This is achieved by lithium balancing positive and negative regulators of signaling processes which results in lithium raising basal activities and diminishing maximal activities, thereby stabilizing signaling activities within an optimal range and preventing fluctuations either above or below this optimum. This model is shown to be applicable to many published results concerning the activation of AP-1 DNA binding and cyclic AMP production. Diverse sites of action of lithium are proposed to ultimately converge on the regulation of gene expression to contribute to mood stabilization.

Affect↗

PubMed1999

Anti-bipolar therapy: mechanism of action of lithium.

This review introduces the concepts that multiple actions of lithium are critical for its therapeutic effect, and that these complex effects stabilize neuronal activities, support neural plasticity, and provide neuroprotection. Three interacting systems appear most critical. (i) Modulation of neurotransmitters by lithium likely readjusts balances between excitatory and inhibitory activities, and decreased glutamatergic activity may contribute to neuroprotection. (ii) Lithium modulates signals impacting on the cytoskeleton, a dynamic system contributing to neural plasticity, at multiple levels, including glycogen synthase kinase-3beta, cyclic AMP-dependent kinase, and protein kinase C, which may be critical for the neural plasticity involved in mood recovery and stabilization. (iii) Lithium adjusts signaling activities regulating second messengers, transcription factors, and gene expression. The outcome of these effects appears likely to result in limiting the magnitudes of fluctuations in activities, contributing to a stabilizing influence induced by lithium, and neuroprotective effects may be derived from its modulation of gene expression.

Animals↗

PubMed1999

Insulin transiently increases tau phosphorylation: involvement of glycogen synthase kinase-3beta and Fyn tyrosine kinase.

The modulation of tau phosphorylation in response to insulin was examined in human neuroblastoma SH-SY5Y cells. Insulin treatment resulted in a transient increase in tau phosphorylation followed by a decrease in tau phosphorylation that correlated directly with a sequential activation and deactivation of glycogen synthase kinase-3beta (GSK-3beta). The insulin-induced increase in tau phosphorylation and concurrent activation of GSK-3beta was rapid (<2 min) and transient, and was associated with increased tyrosine phosphorylation of GSK-3beta. The increase in GSK-3beta tyrosine phosphorylation corresponded directly to an increase in the association of Fyn tyrosine kinase with GSK-3beta, and Fyn immunoprecipitated from cells treated with insulin for 1 min phosphorylated GSK-3beta to a significantly greater extent than Fyn immunoprecipitated from control cells. Subsequent to the increase in GSK-3beta activation and tau phosphorylation, treatment of cells with insulin for 60 min resulted in a dephosphorylation of tau and a decrease in GSK-3beta activity. Thus, insulin rapidly and transiently activated GSK-3beta and modulated tau phosphorylation, alterations that may contribute to neuronal plasticity.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed1999

Cholinergic stimulation of early growth response-1 DNA binding activity requires protein kinase C and mitogen-activated protein kinase kinase activation and is inhibited by sodium valproate in SH-SY5Y cells.

Activation of muscarinic receptors in human neuroblastoma SH-SY5Y cells with carbachol stimulated a rapid and large increase in early growth response-1 (Egr-1, also called zif268 and NGF1-A) protein levels and DNA binding activity. Egr-1 DNA binding activity was stimulated within 15 min of treatment with carbachol and maintained a maximum 20-fold increase over basal between 1 and 2 h after treatment, and the EC50 was approximately 1 microM carbachol. Carbachol-stimulated Egr-1 DNA binding activity was dependent on protein kinase C, as it was potently inhibited by GF109203X (IC50 approximately 0.1 microM) and was reduced by 85 +/- 5% by down-regulation of protein kinase C. Inhibitors of increases in intracellular calcium levels reduced carbachol-induced Egr-1 DNA binding activity by 25-35%. Carbachol-stimulated activation of Egr-1 was reduced 35% by genistein, a tyrosine kinase inhibitor, and 60% by PD098059, an inhibitor of mitogen-activated protein kinase kinases 1/2 (MEK1/2) that activates extracellular-regulated kinases 1/2 (ERK1/2). A novel inhibitory action was caused by chronic (7-day) administration of sodium valproate but not by two other bipolar disorder therapeutic agents, lithium and carbamazepine. Valproate treatment reduced carbachol-stimulated Egr-1 DNA binding activity by 60% but did not alter carbachol-induced activation of ERK1/2 or p38 or increases in Egr-1 protein levels. These results reveal that muscarinic receptors activate Egr-1 through a signaling cascade primarily encompassing protein kinase C, MEK1/2, and ERK1/2 and that valproate substantially inhibits Egr-1 DNA binding activity stimulated by carbachol or protein kinase C.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed1999

Cholinergic muscarinic receptor signaling by the phosphoinositide signal transduction system in Alzheimer's disease.

Recent years have seen the advent of new methods capable of measuring the activity of receptor-coupled, G-protein-mediated, phosphoinositide second messenger production in membranes prepared from postmortem human brain. Considering the interest in treating Alzheimer's disease (AD) patients with cholinergic agonists, several investigations have used this new methodology to analyze the functional state of cholinergic muscarinic receptors coupled to phosphoinositide signaling directly in AD brain. Several, but not all, reports indicate that cholinergic agonist-induced phosphoinositide signaling is severely impaired in AD, potentially due to impaired activation of the receptor-coupled G-protein. Additionally, deficits in AD also have been reported in the two second messenger pathways activated following phosphoinositide hydrolysis, inositol-1,4,5,-triphosphate receptor binding and protein kinase C activation, indicating further that phosphoinositide signaling is impaired in AD. Sources of limitations in current methodologies and issues for further exploration are discussed. Speculation concerning potential links between cholinergic receptor-linked signaling and early events in the formation of amyloid plaques and neurofibrillary tangles is provided. Especially intriguing is the potential for the development of synergistic neurotoxicity where deficits of phosphoinositide signaling and increased production of A beta interact to exacerbate alterations in each process that occur in AD, leading to a feed-forward cycle of progressive neuronal dysfunction.

Journal Article↗

PubMed1998

The interrelationship between selective tau phosphorylation and microtubule association.

The purpose of this study was to examine the modulation of tau phosphorylation mediated by protein kinase A, a kinase with low intrinsic activity, and by the constitutively active glycogen synthase kinase, as well as to examine the subsequent effects on tau-microtubule association in differentiated human SH-SY5Y neuroblastoma cells. Activation of protein kinase A with forskolin and rolipram significantly increased tau phosphorylation at Ser262/356 only in the presence of okadaic acid, indicating that phosphates at these sites are normally turned over rapidly. In contrast, glycogen synthase kinase appears to maintain tau phosphorylation at Thr181 and Ser396/404 since inhibition of glycogen synthase kinase with lithium reduced phosphorylation at these sites. Lithium treatment also significantly decreased tau and tyrosinated alpha-tubulin levels. Perturbation of microtubules with nocodazole or taxol induced tau dephosphorylation at Tau-1 sites, Thr181 and Ser396/404, indicating that both constitutive kinase activity and microtubule state modulate tau phosphorylation at these sites. Nocodazole- or taxol-induced tau dephosphorylation was blocked by the protein phosphatase 2A/1 inhibitor okadaic acid, but not by the protein phosphatase 2B inhibitor cyclosporin A. In addition, osmotic stress, such as treatment with 20 mM NaCl, selectively increased tau phosphorylation at the Tau-1 epitope. To investigate the effect of phosphorylation on tau association with microtubules and microtubule stability in situ, a Triton X-100 extraction assay was utilized to separate the detergent-soluble cytosolic components from the detergent-insoluble cytoskeletal components. In control cells or cells treated with lithium very little tau was detected in the cytosolic fraction. Activation of protein kinase A in the presence of okadaic acid elevated tau levels in the detergent-soluble fraction, which contained all the tau phosphorylated at Ser262/356, and also decreased microtubule stability, as indicated by decreased acetylated alpha-tubulin levels. In conclusion, the phosphorylation state of tau in differentiated SH-SY5Y cells is regulated by glycogen synthase kinase, microtubule dynamics and osmotic stress at overlapping sites which apparently have little influence on tau-microtubule association. In contrast, phosphorylation of tau at Ser262/356 within the microtubule-binding, which was mediated in part by protein kinase A, prevented the association of tau with microtubules in situ.

Amino Acid Sequence↗

PubMed1998

Peroxynitrite modulates tyrosine phosphorylation and phosphoinositide signalling in human neuroblastoma SH-SY5Y cells: attenuated effects in human 1321N1 astrocytoma cells.

Peroxynitrite may contribute to oxidative stress involving neurodegeneration in several disorders, including Alzheimer's disease. As with other reactive oxygen species, peroxynitrite might affect neuronal signalling systems, actions that could contribute to adaptive or deleterious cellular outcomes, but such effects have not previously been studied. To address this issue directly, peroxynitrite (50-500 microM) was administered to human neuroblastoma SH-SY5Y cells to assess its effects on protein tyrosine nitration, phosphoinositide signalling and protein tyrosine phosphorylation. Peroxynitrite rapidly increased the nitrotyrosine immunoreactivity of numerous proteins, primarily in the cytosol. Peroxynitrite inhibited, in a concentration-dependent manner, phosphoinositide hydrolysis stimulated by activation of muscarinic receptors with carbachol and the inhibition was greater after the depletion of cellular glutathione. In comparison, muscarinic receptor-stimulated phosphoinositide hydrolysis in human astrocytoma 1321N1 cells was less vulnerable to inhibition by peroxynitrite either without or with prior depletion of glutathione. There was a large, rapid and reversible increase in the tyrosine phosphorylation of the p120 Src substrate in peroxynitrite-treated SH-SY5Y cells, a response that was potentiated by glutathione depletion; in contrast, peroxynitrite decreased the tyrosine phosphorylation of focal adhesion kinase and paxillin. Tyrosine phosphorylation of p120 in 1321N1 astrocytoma cells was less sensitive to modulation by peroxynitrite. Thus alterations in phosphoinositide signalling and protein tyrosine phosphorylation were greater in neuroblastoma than astrocytoma cells, and modulation of these signalling processes probably contributes to neuronal mechanisms of the response to peroxynitrite.

Astrocytoma↗

PubMed1998

Phosphoinositide hydrolysis activated by muscarinic or glutamatergic, but not adrenergic, receptors is impaired in ApoE-deficient mice and by hydrogen peroxide and peroxynitrite.

Apolipoprotein E (apoE)-deficient (knockout) mice, 4 and 12 months old, were used to test if activation of the phosphoinositide signal transduction system coupled with muscarinic, adrenergic, or glutamatergic metabotropic receptors or inhibition by hydrogen peroxide or peroxynitrite was affected by apoE-deficiency in cerebral cortical slices. In 4-month-old apoE knockout mice, glutamatergic metabotropic receptor-stimulated phosphoinositide hydrolysis was 57% lower than age-matched wild-type mice, whereas the responses to muscarinic and adrenergic receptor stimulation were not different from wild-type mice. In 12-month-old mice, the response to glutamatergic metabotropic receptor stimulation remained impaired in apoE knockout mice, and an impairment in phosphoinositide hydrolysis activated by muscarinic receptors (36% decrease), but not by adrenergic receptors, also was evident. Oxidative stress induced by hydrogen peroxide or peroxynitrite inhibited phosphoinositide hydrolysis activated by muscarinic or glutamatergic metabotropic receptors equivalently (41 to 52%) in 4- and 12-month-old wild-type mice. In contrast, these oxidative agents had no effect on phosphoinositide hydrolysis activated by adrenergic receptors. The inhibitory effects of oxidative stress were not enhanced in apoE knockout mice. These results demonstrate that apoE-deficiency and oxidative stress have receptor-selective inhibitory effects on the phosphoinositide signal transduction system. These differential sensitivities to apoE and to oxidative stress may contribute to selective impairments in signaling activity in neurodegenerative conditions associated with apoE isoform-sensitivity or oxidative stress, such as Alzheimer's disease.

Animals↗

PubMed1998

Glutathione depletion exacerbates impairment by oxidative stress of phosphoinositide hydrolysis, AP-1, and NF-kappaB activation by cholinergic stimulation.

Oxidative stress appears to contribute to neuronal dysfunction associated with Alzheimer's disease and other CNS neurodegenerative disorders. This investigation examined if oxidative stress might contribute to impairments in cholinergic receptor-linked signaling systems and if intracellular glutathione levels modulated responses to oxidative stress. To do this the activation of the AP-1 and NF-kappaB transcription factors and of the phosphoinositide second-messenger system was measured in human neuroblastoma SH-SY5Y cells after exposure to the oxidants H2O2 or diamide, with or without prior depletion of cellular glutathione. H2O2 concentration-dependently inhibited carbachol-stimulated AP-1 activation and this inhibition was potentiated in glutathione-depleted cells. Carbachol-stimulated NF-kappaB activation was unaffected by H2O2 unless glutathione was depleted, in which case there was a H2O2 concentration-dependent inhibition. Glutathione depletion also potentiated the inhibition by H2O2 of carbachol- or G-protein (NaF)-stimulated phosphoinositide hydrolysis, whereas phospholipase C activated by the calcium ionophore ionomycin was not inhibited. The thiol-oxidizing agent diamide also inhibited phosphoinositide hydrolysis stimulated by carbachol or NaF, and glutathione depletion potentiated the diamide concentration-dependent inhibition. Unlike H2O2, diamide also inhibited ionomycin-stimulated phosphoinositide hydrolysis. Activation of both AP-1 and NF-kappaB stimulated by carbachol was inhibited by diamide, and glutathione depletion potentiated the inhibitory effects of diamide. Thus, diamide inhibited a wider range of signaling processes than did H2O2, but glutathione depletion increased the susceptibility of phosphoinositide hydrolysis and of transcription factor activation to inhibition by both H2O2 and diamide. These results demonstrate that the vulnerability of signaling systems to oxidative stress is influenced by intracellular glutathione levels, indicating that cell-selective susceptibility to inhibition of signal transduction systems by oxidative stress can arise from cellular variations in antioxidant capacity.

Analysis of Variance↗

PubMed1998

Selective increases in phosphoinositide signaling activity and G protein levels in postmortem brain from subjects with schizophrenia or alcohol dependence.

Comparisons of the activity of the G protein-mediated phosphoinositide signal transduction system and of G protein levels were made in two regions of frontal cortex from eight schizophrenic, alcohol-dependent, and control subjects. G protein-mediated phosphoinositide hydrolysis was measured by stimulating cortical membranes incubated with [3H]phosphatidylinositol with 0.3-10 microM guanosine 5'-O-(3-thio)triphosphate (GTPgammaS). In frontal cortex areas 8/9, GTPgammaS-induced phosphoinositide hydrolysis was 50% greater in schizophrenic than control or alcohol-dependent subjects, whereas there were no differences among these groups of subjects in the response to GTPgammaS in frontal cortex area 10. Agonists for dopaminergic, cholinergic, purinergic, serotonergic, histaminergic, and glutamatergic receptors coupled to the phosphoinositide signaling system increased [3H]phosphatidylinositol hydrolysis in a GTPgammaS-dependent manner. Responses to most agonists were similar in all three subject groups in both cortical regions, with the largest difference being a 40% greater response to dopaminergic receptor stimulation in frontal cortex 8/9 from schizophrenic subjects. Measurements of the levels of phospholipase C-beta, and of alpha-subunits of Gq, Go, Gi1, Gi2, and Gs, made by immunoblot analyses revealed no differences among the groups of subjects except for increased G alpha(o) in schizophrenic subjects and increased G alpha(o) and G alpha(i1) in alcohol-dependent subjects. These results demonstrate that schizophrenia is associated with increased activity of the phosphoinositide signal transduction system and increased levels of G alpha(o), whereas the phosphoinositide system was unaltered in alcohol dependence, but G alpha(o) and G alpha(i1) were increased.

Adult↗

PubMed1997

Ectopically expressed CAG repeats cause intranuclear inclusions and a progressive late onset neurological phenotype in the mouse.

The mutations responsible for several human neurodegenerative disorders are expansions of translated CAG repeats beyond a normal size range. To address the role of repeat context, we have introduced a 146-unit CAG repeat into the mouse hypoxanthine phosphoribosyltransferase gene (Hprt). Mutant mice express a form of the HPRT protein that contains a long polyglutamine repeat. These mice develop a phenotype similar to the human translated CAG repeat disorders. Repeat containing mice show a late onset neurological phenotype that progresses to premature death. Neuronal intranuclear inclusions are present in affected mice. Our results show that CAG repeats do not need to be located within one of the classic repeat disorder genes to have a neurotoxic effect.

Animals↗

PubMed1997

AP-1 and NF-kappaB stimulated by carbachol in human neuroblastoma SH-SY5Y cells are differentially sensitive to inhibition by lithium.

In order to identify potential actions of lithium, the primary therapeutic agent for bipolar affective disorder, on processes regulating gene expression, its effects on two transcription factors, AP-1 and NF-kappaB, were measured in human neuroblastoma SH-SY5Y cells. The cholinergic agonist carbachol concentration-dependently stimulated AP-1 (EC50 = 2 microM) and NF-kappaB (EC50 = 14 microM). Pretreatment for 24 h with a therapeutically relevant concentration of lithium (1 mM) substantially inhibited (30-35%) carbachol-stimulation AP-1 but not NF-kappaB. Inhibition of carbachol-induced AP-1 was directly related to the concentration of lithium (1-20 mM). Besides being differentially sensitive to inhibition by lithium, activation of AP-1 and NF-kappaB demonstrated different carbachol EC50 concentrations, and carbachol-induced activation of AP-1, but not NF-kappaB, was inhibited by treating cells with Ni2+, which blocks receptor-mediated calcium influx. These findings demonstrate that one mechanism by which lithium can influence the expression of specific genes is through the selective modulation of signaling processes which emanate from cholinergic receptor stimulation.

Carbachol↗

PubMed1997

Glucocorticoids modulate G-protein alpha-subunit levels in PC12 cells.

Regulation by the synthetic glucocorticoid hormone, dexamethasone, of the levels of several G-protein alpha-subunits was studied during differentiation in PC12 cells. Similar patterns, although with different magnitudes, were observed in the changes in the levels of alpha il, alpha s, and alpha q induced by the treatments studied, whereas alpha o differed from the other alpha-subunits. Thus, nerve growth factor (NGF) treatment increased alpha il, alpha s, and alpha q, and forskolin increased alpha il and alpha q, with the increase in alpha il being greater than the increases in the other two alpha-subunits after both treatments. The increases in alpha il, alpha s, and alpha q induced by NGF were dependent on signaling through ras, since they did not occur in NGF-treated M17 cells, which express a dominant inhibitory Ha-ras. Treatment of PC12 cells with dexamethasone antagonized the increases in alpha il, alpha s, and alpha q induced by NGF or forskolin, almost completely blocking any changes from control levels. The level of alpha o also was increased in PC12 cells by treatment with NGF or forskolin, but, in contrast to the other G-protein alpha-subunits, the response to NGF was not antagonized by dexamethasone in PC12 cells, or by the deficient ras activity in M17 cells. However, ras influenced the alternative splicing that regulates the levels of the two alpha o subtypes, beta o1 and alpha o2, so they were expressed in a ratio of 1:2 in PC12 cells but 2:1 in ras-deficient M17 cells. These results demonstrated marked, and subtype-selective, influences of dexamethasone on the levels of G-protein alpha-subunits, an effect that may contribute to the effects of conditions that increase the levels of glucocorticoid hormones, such as stress or certain diseases, on signal transduction processes in brain.

Animals↗

PubMed1997

Dexamethasone attenuates NF-kappa B DNA binding activity without inducing I kappa B levels in rat brain in vivo.

This investigation tested if glucocorticoid hormones modulate activation of the NF-kappa B transcription factor in rat brain in vivo. Dexamethasone (2 mg/kg) administration decreased NF-kappa B DNA binding in cerebral cortex and hippocampus nuclear extracts, maximally at 3-6 h after dexamethasone, followed by recovery at 24 h. Dexamethasone did not inhibit NF-kappa B by increasing the level of the inhibitory protein I kappa B alpha, as occurs in some peripheral cells, but instead lowered I kappa B alpha levels. Direct protein-protein inhibition by glucocorticoids was indicated by co-precipitation of glucocorticoid receptors with the p65 NF-kappa B subunit. Thus, glucocorticoids inhibit NF-kappa B DNA binding in rat brain, apparently by complexing with NF-kappa B subunits, which may contribute to the detrimental effects of glucocorticoids on neuronal function associated with oxidative stress and excitotoxicity.

Animals↗