RANTES-mediated chemokine transcription in astrocytes involves activation and translocation of p90 ribosomal S6 protein kinase (RSK)

Effects of aspirin on colon cancer using quantitative proteomic analysis

Background

Colon cancer is one of the most prevalent digestive cancers worldwide. Results of epidemiological, experimental, and clinical studies suggest that aspirin inhibits the development of colon cancer. This study aimed to systematically elucidate the molecular mechanisms by which aspirin prevents colon carcinogenesis.

Methods

We determined the global protein expression profiles of colorectal cancer and aspirin-treated cells using quantitative proteomic analysis. We analyzed the proteomic results using bioinformatics (including differential proteins, protein annotation, Kyoto Encyclopedia of Genes and Genomes [KEGG] pathways, and protein-protein interaction [PPI] network). The viability of the colon cancer cell line and HT29 ​cells treated with aspirin was determined using the cell counting kit-8 assay. The differentially expressed proteins, such as p53 and cyclin-dependent kinase 1 (CDK1), were quantified using real-time polymerase chain reaction (PCR) and Western blotting. We measured cell cycle distribution and apoptosis in HT29 ​cells exposed to aspirin using fluorescence-activated cell sorting (FACS).

Results

We found that 552 proteins were significantly dysregulated, of which 208 and 334 were upregulated and downregulated, respectively, in colon cancer cells exposed to 10 ​mmol/L of aspirin (95% confidence interval [CI]: -1.269 to -0.106, P ​< ​0.05). Further gene enrichment analysis revealed that cell cycle-related proteins, such as p53 and CDK1, were significantly differentially expressed. Proteomic analysis showed that after 24 ​h of aspirin exposure, the level of p53 increased by 2.52-fold and CDK1 was downregulated to half that of the controls in HT29 ​cells (95% CI: -0.619 to -0.364, P ​< ​0.05). Real-time PCR and Western blotting results showed that p53 was upregulated (95%CI: -3.088 to -1.912, P ​< ​0.001) and CDK1 was significantly downregulated after aspirin exposure in colon cancer cells (95% CI: 0.576 to 1.045, P ​< ​0.05). We observed that aspirin promoted G1/S cell cycle arrest in HT29 ​cells. We confirmed that aspirin induces apoptosis in human HT29 colon cancer cells in a concentration-dependent manner.

Conclusions

These results indicate that aspirin induces G1 arrest and apoptosis in colorectal cancer cells via the p53-CDK1 pathway. Aspirin may be a promising drug candidate for colon cancer prevention.

Cyclic AMP response element-binding protein (CREB) transcription factor in astrocytic synaptic communication

Astrocytes are known to actively participate in synaptic communication by forming structures called tripartite synapses. These synapses consist of presynaptic axon terminals, postsynaptic dendritic spines, and astrocytic processes where astrocytes release and receive transmitters. Although the transcription factor cyclic AMP response element (CRE)-binding protein (CREB) has been actively studied as an important factor for mediating synaptic activity-induced responses in neurons, its role in astrocytes is relatively unknown. Synaptic signals are known to activate various downstream pathways in astrocytes, which can activate the CREB transcription factor. Therefore, there is a need to summarize studies on astrocytic intracellular pathways that are induced by synaptic communication resulting in activation of the CREB pathway. In this review, we discuss the various neurotransmitter receptors and intracellular pathways that can induce CREB activation and CREB-induced gene regulation in astrocytes.

Impact of Plasma IP-10/CXCL10 and RANTES/CCL5 Levels on Neurocognitive Function in HIV Treatment-Naive Patients

Immune activation, which is accompanied by the production of proinflammatory cytokines, is a strong predictor of disease progression in HIV infection. Inflammation is critical in neuronal damage linked to HIV-associated neurocognitive disorders. We examined the relationship between plasma cytokine levels and deficits in neurocognitive function. Multiplex profiling by Luminex^® technology was used to quantify 27 cytokines/chemokines from 139 plasma samples of people living with HIV (PLWH). The relationship of plasma cytokine markers, clinical parameters, and cognitive impairment, was assessed using Spearman correlations. Partial least squares regression and variable importance in projection scores were used for further evaluation of the association. Forty-nine (35.3%) participants exhibited neurocognitive impairment based on a global deficit score (GDS) of at least 0.5 and 90 (64.7%) were classified as nonimpaired. Twenty-three (16.5%) initiated on combination antiretroviral therapy for 4 weeks before cognitive assessment and 116 (83.5%) were not on treatment. We identified five proinflammatory cytokines that were significant predictors of GDS namely, IP-10 (β = 0.058; p = .007), RANTES (β = 0.049; p = .005), IL-2 (β = 0.047, p = .006), Eotaxin (β = 0.042, p = .003), and IL-7 (β = 0.039, p = .003). IP-10 and RANTES were the strongest predictors of GDS. Both cytokines correlated with plasma viral load and lymphocyte proviral load and were inversely correlated with CD4⁺ T cell counts. IP-10 and RANTES formed a separate cluster with highest proximity. Study findings describe novel associations among IP-10, RANTES, cognitive status, plasma viral load, and cell-associated viral load.

Fingolimod phosphate inhibits astrocyte inflammatory activity in mucolipidosis IV

Mucolipidosis IV (MLIV) is an orphan neurodevelopmental disease that causes severe neurologic dysfunction and loss of vision. Currently there is no therapy for MLIV. It is caused by loss of function of the lysosomal channel mucolipin-1, also known as TRPML1. Knockout of the Mcoln1 gene in a mouse model mirrors clinical and neuropathologic signs in humans. Using this model, we previously observed robust activation of microglia and astrocytes in early symptomatic stages of disease. Here we investigate the consequence of mucolipin-1 loss on astrocyte inflammatory activation in vivo and in vitro and apply a pharmacologic approach to restore Mcoln1-/- astrocyte homeostasis using a clinically approved immunomodulator, fingolimod. We found that Mcoln1-/- mice over-express numerous pro-inflammatory cytokines, some of which were also over-expressed in astrocyte cultures. Changes in the cytokine profile in Mcoln1-/- astrocytes are concomitant with changes in phospho-protein signaling, including activation of PI3K/Akt and MAPK pathways. Fingolimod promotes cytokine homeostasis, down-regulates signaling within the PI3K/Akt and MAPK pathways and restores the lysosomal compartment in Mcoln1-/- astrocytes. These data suggest that fingolimod is a promising candidate for preclinical evaluation in our MLIV mouse model, which, in case of success, can be rapidly translated into clinical trial.

Melanocortin 4 receptor activates ERK-cFos pathway to increase brain-derived neurotrophic factor expression in rat astrocytes and hypothalamus

Melanocortins are neuropeptides with well recognized anti-inflammatory and anti-apoptotic effects in the brain. Of the five melanocortin receptors (MCR), MC4R is abundantly expressed in the brain and is the only MCR present in astrocytes. We have previously shown that MC4R activation by the α-melanocyte stimulating hormone (α-MSH) analog, NDP-MSH, increased brain-derived neurotrophic factor (BDNF) expression through the classic cAMP-Protein kinase A-cAMP responsive element binding protein pathway in rat astrocytes. Now, we examined the participation of the mitogen activated protein kinases pathway in MC4R signaling. Rat cultured astrocytes treated with NDP-MSH 1 µM for 1 h showed increased BDNF expression. Inhibition of extracellular signal-regulated kinase (ERK) and ribosomal p90 S6 kinase (RSK), an ERK substrate, but not of p38 or JNK, prevented the increase in BDNF expression induced by NDP-MSH. Activation of MC4R increased cFos expression, a target of both ERK and RSK. ERK activation by MC4R involves cAMP, phosphoinositide-3 kinase (PI3K) and the non receptor tyrosine kinase, Src. Both PI3K and Src inhibition abolished NDP-MSH-induced BDNF expression. Moreover, we found that intraperitoneal injection of α-MSH induces BDNF and MC4R expression and activates ERK and cFos in male rat hypothalamus. Our results show for the first time that MC4R-induced BDNF expression in astrocytes involves ERK-RSK-cFos pathway which is dependent on PI3K and Src, and that melanocortins induce BDNF expression and ERK-cFos activation in rat hypothalamus.

Information theoretic approach to complex biological network reconstruction: application to cytokine release in RAW 264.7 macrophages

BACKGROUND

High-throughput methods for biological measurements generate vast amounts of quantitative data, which necessitate the development of advanced approaches to data analysis to help understand the underlying mechanisms and networks. Reconstruction of biological networks from measured data of different components is a significant challenge in systems biology.

RESULTS

We use an information theoretic approach to reconstruct phosphoprotein-cytokine networks in RAW 264.7 macrophage cells. Cytokines are secreted upon activation of a wide range of regulatory signals transduced by the phosphoprotein network. Identifying these components can help identify regulatory modules responsible for the inflammatory phenotype. The information theoretic approach is based on estimation of mutual information of interactions by using kernel density estimators. Mutual information provides a measure of statistical dependencies between interacting components. Using the topology of the network derived, we develop a data-driven parsimonious input-output model of the phosphoprotein-cytokine network.

CONCLUSIONS

We demonstrate the applicability of our information theoretic approach to reconstruction of biological networks. For the phosphoprotein-cytokine network, this approach not only captures most of the known signaling components involved in cytokine release but also predicts new signaling components involved in the release of cytokines. The results of this study are important for gaining a clear understanding of macrophage activation during the inflammation process.

The p38-MSK1 signaling cascade influences cytokine production through CREB and C/EBP factors in human neutrophils

Neutrophils influence innate and adaptative immunity by generating numerous cytokines and chemokines whose regulation largely depends on transcriptional activators such as NF-κB and C/EBP factors. In this study, we describe the critical involvement of CREB transcription factors (CREB1 and activating transcription factor-1) in this functional response as well as relevant upstream signaling components. Neutrophil stimulation with LPS or TNF led to the phosphorylation, DNA binding activity, and chemokine promoter association of CREB1 and activating transcription factor-1. These responses occurred downstream of the p38-MSK1 signaling axis, as did the phosphorylation and promoter association of another bZIP factor, C/EBPβ. Conversely, inhibition of RSK1 failed to alter the phosphorylation of either CREB1 or C/EBPβ in neutrophils. From a more functional standpoint, the inhibition of p38 MAPK or MSK1 interfered with cytokine generation in neutrophils. Likewise, overexpression of a dominant-negative CREB1 mutant (K-CREB) or of a point mutant (S133A) resulted in a decreased ability of human neutrophil-like PLB-985 cells to generate inflammatory cytokines (CXCL8, CCL3, CCL4, and TNF-α). Collectively, our data show the involvement of CREB1 in neutrophil cytokine production, the key role of its S133 residue, important upstream signaling events, and the parallel activation of another bZIP factor. These are all potential molecular targets that could be exploited in the context of several chronic inflammatory diseases that prominently feature neutrophils and their products.

Increased abscess formation and defective chemokine regulation in CREB transgenic mice

Cyclic AMP-response element-binding protein (CREB) is a transcription factor implicated in growth factor-dependent cell proliferation and survival, glucose homeostasis, spermatogenesis, circadian rhythms, and synaptic plasticity associated with memory. To study the phenotype of CREB overexpression in vivo, we generated CREB transgenic (TG) mice in which a myeloid specific hMRP8 promoter drives CREB expression. CREB TG mice developed spontaneous skin abscesses more frequently than wild type (WT) mice. To understand the role of CREB in myeloid function and innate immunity, chemokine expression in bone marrow derived macrophages (BMDMs) from CREB TG mice were compared with BMDMs from WT mice. Our results demonstrated decreased Keratinocyte-derived cytokine (KC) in CREB TG BMDMs but not TNFα protein production in response to lipid A (LPA). In addition, mRNA expression of KC and IL-1β (Interleukin)-1β was decreased in CREB TG BMDMs; however, there was no difference in the mRNA expression of TNFα, MCP-1, IL-6 and IL-12p40. The mRNA expression of IL-1RA and IL-10 was decreased in response to LPA. Nuclear factor kappa B (NFκB) expression and a subset of its target genes were upregulated in CREB TG mouse BMDMs. Although neutrophil migration was the same in both CREB TG and WT mice, Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity was significantly increased in neutrophils from CREB TG mice. Taken together, CREB overexpression in myeloid cells results in increased abscess formation in vivo and aberrant cytokine and chemokine response, and neutrophil function in vitro.

Curcumin enhances neuronal survival in N-methyl-d-aspartic acid toxicity by inducing RANTES expression in astrocytes via PI-3K and MAPK signaling pathways

OBJECT

Neuroinflammation, which is characterized by the overproduction of cytokines and chemokines, plays an important role in neurodegenerative diseases, especially in Alzheimer's disease (AD). In the brain, chemokines are predominantly released by astrocytes and microglias. Expression of RANTES, as well as other cytokines, is involved in the inflammatory cascade that contributes to neurodegeneration in AD. Expression of RANTES may also have a neuroprotective effect. We sought to investigate whether curcumin exhibited neuroprotective and antioxidant activity via enhanced RANTES expression by astrocytes in cortical neuron cultures. We evaluated the neuroprotective and anti-neurodegenerative effects of curcumin in NMDA toxicity and in long-term cultures.

METHODS

Pregnant female Sprague-Dawley (SD) rats were used for primary culture of cortical neurons, and neonatal 0- to 2-day-old SD rats were used for primary culture of astrocytes. Cultured astrocytes were conditioned with curcumin to prepare astrocyte-conditioned medium (ACM). Real-time polymerase chain reaction was performed to assess RANTES and iNOS mRNA expression in astrocytes following curcumin treatment. ELISA was used to detect astrocyte-secreted RANTES protein in ACM with curcumin treatment. JAK/STAT, PI-3K, PKC and MAPK inhibitors were used to ascertain whether the effects of curcumin involved these signaling pathways. To evaluate the effects of curcumin-enhanced astrocytes on neuronal survival, cultured cortical neurons treated or untreated with NMDA were incubated in ACM with or without curcumin treatment. Long-term culture (15days in vitro, DIV) was performed to investigate the effects of curcumin-treated astrocytes on the survival of cultured cortical neurons. Neuronal survival rate was assessed by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction activity assay (for cell viability), and the lactate dehydrogenase (LDH) release assay (for cell death).

RESULTS

We demonstrated that curcumin enhanced RANTES expression in primary cultured astrocytes, and that this effect was related to activation of PI-3K and MAPK signaling pathways. We found that curcumin inhibited iNOS expression in primary cultured astrocytes in non-stressed condition. We also found that neurons exposed to NMDA and cultured with curcumin treated ACM, which characteristically exhibited elevated RANTES expression showed higher level of cell viability and lower level of cell death. Using a small interfering RNA (siRNA) knockdown model, we found evidence that the basal level of RANTES expression in non-stimulated astrocytes provided neuroprotection.

CONCLUSION

We postulate that the enhanced neuronal survival by curcumin treatment in NMDA toxicity and long-term cultures was in part attributable to elevated astrocyte-derived RANTES expression via activation of PI3K/MAPK signaling pathways.

RANTES release by human adipose tissue in vivo and evidence for depot-specific differences

Obesity is associated with elevated inflammatory signals from various adipose tissue depots. This study aimed to evaluate release of regulated on activation, normal T cell expressed and secreted (RANTES) by human adipose tissue in vivo and ex vivo, in reference to monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6) release. Arteriovenous differences of RANTES, MCP-1, and IL-6 were studied in vivo across the abdominal subcutaneous adipose tissue in healthy Caucasian subjects with a wide range of adiposity. Systemic levels and ex vivo RANTES release were studied in abdominal subcutaneous, gastric fat pad, and omental adipose tissue from morbidly obese bariatric surgery patients and in thoracic subcutaneous and epicardial adipose tissue from cardiac surgery patients without coronary artery disease. Arteriovenous studies confirmed in vivo RANTES and IL-6 release in adipose tissue of lean and obese subjects and release of MCP-1 in obesity. However, in vivo release of MCP-1 and RANTES, but not IL-6, was lower than circulating levels. Ex vivo release of RANTES was greater from the gastric fat pad compared with omental (P = 0.01) and subcutaneous (P = 0.001) tissue. Epicardial adipose tissue released less RANTES than thoracic subcutaneous adipose tissue in lean (P = 0.04) but not obese subjects. Indexes of obesity correlated with epicardial RANTES but not with systemic RANTES or its release from other depots. In conclusion, RANTES is released by human subcutaneous adipose tissue in vivo and in varying amounts by other depots ex vivo. While it appears unlikely that the adipose organ contributes significantly to circulating levels, local implications of this chemokine deserve further investigation.

CCL5/RANTES gene deletion attenuates opioid-induced increases in glial CCL2/MCP-1 immunoreactivity and activation in HIV-1 Tat-exposed mice

To assess the role of CC-chemokine ligand 5 (CCL5)/RANTES in opiate drug abuse and human immunodeficiency virus type 1 (HIV-1) comorbidity, the effects of systemic morphine and intrastriatal HIV-1 Tat on macrophage/microglial and astroglial activation were assessed in wild-type and CCL5 knockout mice. Mice were injected intrastriatally with vehicle or Tat and assessed after 7 days. Morphine was administered to some Tat-injected mice via time-release implant (5 mg/day, s.c. for 5 days) starting at 2 days post injection. Glial activation was significantly reduced in CCL5(-/-) compared to wild-type mice at 7 days following combined Tat and morphine exposure. Moreover, the percentage of 3-nitrotyrosine immunopositive macrophages/microglia was markedly reduced in CCL5(-/-) mice injected with Tat +/- morphine compared to wild-type counterparts, suggesting that CCL5 contributes to nitrosative stress in HIV-1 encephalitis. In CCL5(-/-) mice, the reductions in Tat +/- morphine-induced gliosis coincided with significant declines in the proportion of CCL2/MCP-1-immunoreactive astrocytes and macrophages/microglia compared to wild-type counterparts. In knockout mice, neither Tat alone nor in combination with morphine increased the proportion of CCL2-immunoreactive astrocytes above percentages seen in vehicle-injected controls. Macrophages/microglia differed showing modest, albeit significant, increases in the proportion of CCL2-positive cells with combined Tat and morphine exposure, suggesting that CCL5 preferentially affects CCL2 expression by astroglia. Thus, CCL5 mediates glial activation caused by Tat and morphine, thereby aggravating HIV-1 neuropathogenesis in opiate abusers and non-abusers. CCL5 is implicated as mediating the cytokine-driven amplification of CCL2 production by astrocytes and resultant macrophage/microglial recruitment and activation.

The nucleotide receptor P2RX7 mediates ATP-induced CREB activation in human and murine monocytic cells

Nucleotide receptors serve as sensors of extracellular ATP and are important for immune function. The nucleotide receptor P2RX7 is a cell-surface, ligand-gated cation channel that has been implicated in many diseases, including arthritis, granuloma formation, sepsis, and tuberculosis. These disorders are often exacerbated by excessive mediator release from activated macrophages in the inflammatory microenvironment. Although P2RX7 activation can modulate monocyte/macrophage-induced inflammatory events, the relevant molecular mechanisms are poorly understood. Previous studies suggest that MAPK cascades and transcriptional control via CREB-linked pathways regulate the inflammatory capacity of monocytic cells. As P2RX7 promotes MAPK activation and inflammatory mediator production, we examined the involvement MAPK-induced CREB activation in P2RX7 action. Our data reveal that stimulation of multiple monocytic cell lines with P2RX7 agonists induces rapid CREB phosphorylation. In addition, we observed a lack of nucleotide-induced CREB phosphorylation in RAW 264.7 cells expressing nonfunctional P2RX7 and a gain of nucleotide-induced CREB phosphorylation in human embryonic kidney-293 cells that heterologously express human P2RX7. Furthermore, our results indicate that P2RX7 agonist-induced CREB phosphorylation is partly mediated via Ca(2+) fluxes and the MEK/ERK system. Mechanistic analyses revealed that macrophage stimulation with a P2RX7 agonist induces CREB/CREB-binding protein complex formation, which is necessary for CREB transcriptional activation. Also, we demonstrate that P2RX7 activation induces a known CREB-dependent gene (c-fos) and that dominant-negative CREB constructs attenuate this response. These studies support the idea that P2RX7 stimulation can directly regulate protein expression that is not dependent on costimulation with other immune modulators such as LPS.

Mechanisms for suppression of interleukin-6 expression in peritoneal macrophages from docosahexaenoic acid-fed mice

Consumption of the trichothecene mycotoxin deoxynivalenol (DON) induces interleukin-6 (IL-6)-dependent IgA nephropathy (IgAN) in mice. This effect can be prevented by feeding long-chain n-3 polyunsaturated fatty acids (PUFAs) found in fish oil. The purpose of this study was to identify the signal transduction pathways by which DON up-regulates IL-6 in the peritoneal macrophage and how consumption of fish oil enriched with the n-3 PUFA docosahexaenoic acid (DHA) suppresses these processes. Incubation with DON induced IL-6 expression in naïve macrophages maximally at 3 h. Knockdown of the transcription factor cAMP response element-binding protein (CREB) or pharmacologic inhibition of the CREB kinases Akt1/2, MSK1 and RSK1 down-regulated this expression. Inhibition of double-stranded RNA-activated protein kinase (PKR) suppressed not only IL-6 expression but also phosphorylation of CREB and its upstream kinases, Akt1, MSK1 and RSK1. Phosphorylations of PKR, CREB kinases and CREB were markedly impaired in peritoneal macrophages isolated from mice that consumed DHA-enriched fish oil for 6 to 8 weeks. DHA's effects were not explainable by increased activity of protein phosphatase 1 and 2A since both were suppressed in mice consuming the DHA diet. Although cells cultured directly with DHA expressed less IL-6 compared to cells cultured with arachidonic acid (AA), neither fatty acid treatment affected DON-induced protein phosphorylation. Furthermore, DHA and AA similarly inhibited cell-free protein kinase activity. These data suggest that DON-induced IL-6 expression is CREB mediated and PKR dependent, and that requisite kinase activities for these pathways were suppressed in macrophages from mice fed DHA for an extended period.

Increased Membrane/Nuclear Translocation and Phosphorylation of p90 KD Ribosomal S6 Kinase in the Brain of Hypoxic Preconditioned Mice

Our previous studies have demonstrated that hypoxic precondition (HPC) increased membrane translocation of protein kinase C isoforms and decreased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in the brain of mice. The goal of this study was to determine the involvement of p90 KD ribosomal S6 kinase (RSK) in cerebral HPC of mice. Using Western-blot analysis, we found that the levels of membrane/nuclear translocation, but not protein expression of RSK increased significantly in the frontal cortex and hippocampus of HPC mice. In addition, we found that the phosphorylation levels of RSK at the Ser227 site (a PDK1 phosphorylation site), but not at the Thr359/Ser363 sites (ERK1/2 phosphorylated sites) increased significantly in the brain of HPC mice. Similar results were confirmed by an immunostaining study of total RSK and phospho-Ser227 RSK. To further define the cellular populations to express phospho-Ser227 RSK, we found that the expression of phospho-Ser227 RSK co-localized with neurogranin, a neuron-specific marker, in cortex and hippocampus of HPC mice by using double-labeled immunofluorescent staining method. These results suggest that increased RSK membrane/nuclear translocation and PDK1 mediated neuron-specific phosphorylation of RSK at Ser227 might be involved in the development of cerebral HPC of mice.

Retinoic acid-inducible gene-I mediates RANTES/CCL5 expression in U373MG human astrocytoma cells stimulated with double-stranded RNA

Retinoic acid-inducible gene-I (RIG-I) mediates part of the cell signaling in response to viral infection. Polyinosinic-polycytidilic acid (poly IC) is a synthetic double-stranded RNA (dsRNA) and mimics viral infection when applied to cell cultures. The CC chemokine, RANTES (regulated on activation, normal T-cell expressed and secreted), is a potent attractant for inflammatory cells such as memory T-lymphocytes, monocytes and eosinophils. In the present study, we demonstrated that poly IC enhances the expression of RIG-I in U373MG human astrocytoma cells. The RNA interference of RIG-I resulted in the suppression of the poly IC-induced RANTES expression. Pretreatment of the cells with SB203580, an inhibitor of p38 mitogen-activated protein kinase, and dexamethasone inhibited the poly IC-induced expression of RIG-I. Furthermore, poly IC upregulated RIG-I in normal human astrocytes in culture and the in vivo injection of poly IC into the striatum of the mouse brain induced the expression of RIG-I in astrocytes. We conclude that RIG-I may be involved in immune reactions against viral infection, at least in part, through the regulation of RANTES expression in astrocytes.

Oxidative stress and mitogen-activated protein kinase phosphorylation mediate ammonia-induced cell swelling and glutamate uptake inhibition in cultured astrocytes

Hepatic encephalopathy (HE) is a major neurological complication in patients with severe liver failure. Elevated levels of ammonia have been strongly implicated as a factor in HE, and astrocytes appear to be the primary target of its neurotoxicity. Mechanisms mediating key aspects of ammonia-induced astrocyte dysfunction such as cell swelling and inhibition of glutamate uptake are not clear. We demonstrated previously that cultured astrocytes exposed to ammonia increase free radical production. We now show that treatment with antioxidants significantly prevents ammonia-induced astrocyte swelling as well as glutamate uptake inhibition. Because one consequence of oxidative stress is the phosphorylation of mitogen-activated protein kinases (MAPKs), we investigated whether phosphorylation of MAPKs may mediate astrocyte dysfunction. Primary cultured astrocytes exposed to 5 mm NH4Cl for different time periods (1-72 h) significantly increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38(MAPK), and c-Jun N-terminal kinase (JNK) 1/2/3, which was inhibited by appropriate MAPK inhibitors 1, 4-diamino-2, 3-dicyano-1, 4-bis (2-aminophenylthio) butadiene (UO126; for ERK1/2), trans-1-(4-hydroxyclyclohexyl)-4-(4-fluorophenyl)-5-(2-methoxypyrimidin-4-yl)imidazole (SB 239063; for p38(MAPK)), and anthra[1,9-cd]pyrazol-6(2H)-one (SP600125; for JNK1/2/3), as well as by antioxidants. Kinase inhibitors partially or completely prevented astrocyte swelling. Although SB239063 and SP600125 significantly reversed glutamate uptake inhibition and ammonia-induced decline in glutamate-aspartate transporter protein levels, UO126 did not, indicating a differential effect of these kinases in ammonia-induced astrocyte swelling and glutamate transport impairment. These studies strongly suggest the involvement of oxidative stress and phosphorylation of MAPKs in the mechanism of ammonia-induced astrocyte dysfunction associated with ammonia neurotoxicity.

Integration of G protein signals by extracellular signal-regulated protein kinases in SK-N-MC neuroepithelioma cells

Mammalian cells often receive multiple extracellular stimuli under physiological conditions, and the various signaling inputs have to be integrated for the processing of complex biological responses. G protein-coupled receptors (GPCRs) are critical players in converting extracellular stimuli into intracellular signals. In this report, we examined the integration of different GPCR signals by mitogen-activated protein kinases (MAPKs) using the SK-N-MC human brain neuroepithelioma cells as a neuronal model. Stimulation of the Gi-coupled neuropeptide Y1 and Gq-coupled muscarinic M1 acetylcholine receptors, but not the Gs-coupled dopamine D1 receptor, led to the activation of extracellular signal-regulated kinase (ERK). All three receptors were also capable of stimulating c-Jun NH2-terminal kinases (JNK) and p38 MAPK. The Gi-mediated ERK activation was completely suppressed upon inhibition of Src tyrosine kinases by PP1, while the Gq-induced response was suppressed by both PP1 and the Ca2+ chelator, BAPTA-AM. In contrast, activations of JNK and p38 by Gs-, Gi-, and Gq-coupled receptors were sensitive to PP1 and BAPTA-AM pretreatments. Simultaneous stimulation of Gi- and Gq-coupled receptors resulted in the synergistic activation of ERK, but not JNK or p38 MAPK. The Gi/Gq-induced synergistic ERK activation was PTX-sensitive, and appeared to be a co-operative effect between Ca2+ and Src family tyrosine kinases. Enhanced ERK activation was associated with an increase in CREB phosphorylation, while the JNK and p38-responsive transcription factor ATF-2 was weakly enhanced upon Gi/Gq-induction. This report provides evidence that G protein signals can be integrated at the level of MAPK, resulting in differential effects on ERK, JNK and p38 MAPK in SK-N-MC cells.

Macrophage inflammatory protein 2 inhibits beta-amyloid peptide (1-42)-mediated hippocampal neuronal apoptosis through activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinase signaling pathways

beta-Amyloid peptide accumulation in senile plaques in the brains of patients with Alzheimer's disease has been considered as a major cause of neuronal death. The present study demonstrated that the CXCR2 ligands macrophage inflammatory protein 2 (MIP-2), CXCL1, and CXCL8, protected hippocampal neurons against beta-amyloid (1-42) induced death. MIP-2-activated extracellular signal-regulated kinase (ERK)1/2 and Akt and both the mitogen-activated protein kinase kinase 1 (MEK1) and phosphatidylinositol 3-kinase (PI3K) inhibitors 2'-amino-3'-methoxyflavone (PD98059) and wortmannin reduced the neuroprotective effect of MIP-2. MIP-2 induced weak phosphorylation of ribosomal S6 kinase (RSK) 1 but remarkable phosphorylation and nuclear translocation of RSK2. MIP-2-induced phosphorylation of RSK2 was inhibited by PD98059 but not by wortmannin. MIP-2 treatment of the neuronal cells resulted in phosphorylation of Bad at both the Ser-112 and Ser-136. The phosphorylation at Ser-112 was blocked by PD98059, whereas the phosphorylation at Ser-136 was blocked by wortmannin. The transcription factor cyclic AMP response element binding protein (CREB) was phosphorylated by MIP-2 stimulation of the neuronal cells. MIP-2-induced CREB phosphorylation was reduced by both PD98059 and wortmannin. These data demonstrate that both MEK1-ERK1/2 and PI3K-Akt signaling pathways are involved in CXCR2-mediated neuroprotection and that multiple downstream signaling events, including RSKs, Bad, and CREB, are activated in this process.

Repression of hsp90β Gene by p53 in UV Irradiation-induced Apoptosis of Jurkat Cells

Tumor suppressor p53 has been implicated in cell stress response and determines cell fate of either growth arrest or apoptosis. Heat shock proteins (Hsps) expressed under stress usually confer survival protection to the cell or interruption in the apoptotic pathways. Although Hsp90 can physically interact with p53, whether or not the hsp90 gene is influenced downstream of p53 in UV irradiation-induced apoptosis remains unclear. We have found that the level of p53 is elevated with the decline of Hsp90 in UV-irradiated cells and that malfunction of Hsp90, as inhibited by geldanamycin, enhances the p53-involved UV irradiation-induced apoptosis. In addition, the expression of the hsp90beta gene was reduced in both UV-irradiated and wild type p53-transfected cells. These results suggest a negative correlation between the trans factor p53 and a chaperone gene hsp90beta in apoptotic cells. Mutation analysis demonstrated that the p53 binding site in the first exon was indispensable for p53 regulation on the hsp90beta gene. In addition, with p53 bound at the promoter of the hsp90beta gene, mSin3a and p300 were differentially recruited in UV irradiation-treated or untreated Jurkat cells in vivo. The evidence of p53-repressed hsp90beta gene expression in UV-irradiated cells shed light on a novel pathway of Hsp90 in the survival control of the stressed cells.

Macrophages and lymphocytes differentially modulate the ability of RANTES to inhibit HIV-1 infection

The beta-chemokines MIP-1alpha, MIP-1beta, and RANTES inhibit HIV-1 infection of CD4+ T cells by inhibiting interactions between the virus and CCR5 receptors. However, while beta-chemokine-mediated inhibition of HIV-1 infection of primary lymphocytes is well documented, conflicting results have been obtained using primary macrophages as the virus target. Here, we show that the beta-chemokine RANTES inhibits virus entry into both cellular targets of the virus, lymphocytes and macrophages. However, while virus entry is inhibited at the moment of infection in both cell types, the amount of virus progeny is lowered only in lymphocytes. In macrophages, early-entry restriction is lost during long-term cultivation, and the amount of virus produced by RANTES-treated macrophages is similar to the untreated cultures, suggesting an enhanced virus replication. We further show that at least two distinct cellular responses to RANTES treatment in primary lymphocytes and macrophages contribute to this phenomenon. In lymphocytes, exposure to RANTES significantly increases the pool of inhibitory beta-chemokines through intracellular signals that result in increased production of MIP-1alpha and MIP-1beta, thereby amplifying the antiviral effects of RANTES. In macrophages this amplification step does not occur. In fact, RANTES added to the macrophages is efficiently cleared from the culture, without inducing synthesis of beta-chemokines. Our results demonstrate dichotomous effects of RANTES on HIV-1 entry at the moment of infection, and on production and spread of virus progeny in primary macrophages. Since macrophages serve as a reservoir of HIV-1, this may contribute to the failure of endogenous chemokines to successfully eradicate the virus.

Induction of MUC8 gene expression by interleukin-1 beta is mediated by a sequential ERK MAPK/RSK1/CREB cascade pathway in human airway epithelial cells

Mucins are the major components of the mucus layer that covers and protects the respiratory, digestive, and reproductive tracts. Our previous studies showed that MUC8 gene expression was overexpressed in in vivo polyp epithelium in chronic sinusitis and was also increased by treatment with inflammatory mediators in an in vitro culture condition. However, the mechanisms by which the inflammatory mediators-induced MUC8 gene expression in normal nasal epithelial cells evolved remain unclear. We examined the mechanism by which the important proinflammatory mediator, interleukin (IL)-1 beta, increases MUC8 gene expression levels. We found that pharmacologic and genetic inhibition of ERK MAPK pathway abolished IL-1 beta-induced MUC8 gene expression in normal human nasal epithelial cells. Moreover, the overexpression of wide-type or of the dominant-negative mutant of p90 ribosomal S6 protein kinase 1 (RSK1) enhanced or suppressed, respectively, IL-1 beta-induced MUC8 gene expression. RSK1 was found to directly phosphorylate cAMP-response element-binding protein (CREB), and this event led to the stimulation of subsequent CRE-mediated gene transcription. In conclusion, IL-1 beta was found to induce MUC8 gene expression via a sequential ERK/RSK1/CREB pathway in human airway epithelial cells.

RSK2 activity is regulated by its interaction with PEA-15

The ERK MAP (mitogen-activated protein) kinase cascade modulates many cellular processes including transcription, adhesion, growth, survival, and proliferation. One target substrate of ERK involved in regulating transcription is the p90 ribosomal S6 kinase (RSK) isozyme, RSK2. Here we demonstrate that a small death effector domain-containing protein called PEA-15 binds RSK2. RSK2 and PEA-15 (phosphoprotein enriched in astrocytes, 15 kDa) co-precipitated from cells and were colocalized in the cytoplasm. Furthermore, purified PEA-15 bound in vitro translated RSK2, suggesting that these proteins interact directly. PEA-15 does not bind to RSK1 and therefore exhibits some binding specificity. RSK2 binds the COOH terminus of PEA-15 and does not interact with its NH2-terminal death effector domain. We show that this interaction has functional consequences including the inhibition of RSK2-dependent CREB transcription. PEA-15 expression also blocks histone H3 phosphorylation, an RSK2-dependent event that may contribute to effects on gene expression. These results can be attributed to two effects of PEA-15 on RSK2. First, PEA-15 blocks nuclear accumulation of RSK2 after epidermal growth factor stimulation. Second, PEA-15 inhibits RSK2 kinase activity by 50%. A mutant of PEA-15 that binds RSK2 but is localized to the nucleus had no effect on RSK2-dependent transcription. Interestingly, this mutant also did not affect RSK2 kinase activity. This may indicate that cytoplasmic retention of RSK2 is also required for PEA-15 to impair kinase activity. PEA-15 does not alter ERK phosphorylation of RSK2 and is not itself a substrate of RSK2. Hence the effects of PEA-15 on RSK2 represent a novel mechanism for the regulation of RSK2-mediated signaling.

Tumor necrosis factor is required for RANTES-induced astrocyte monocyte chemoattractant protein-1 production

Astrocytes respond to stimulation with the chemokine RANTES (regulated on activation, normal T cell expressed) by production of a series of cytokines and chemokines, including tumor necrosis factor-alpha (TNF-alpha) and monocyte chemoattractant protein-1 (MCP-1). In the present study we demonstrate that RANTES induces TNF, which in turn stimulates subsequent production of MCP-1. TNF-R1 (p55) serves as the principal receptor responsible for MCP-1 synthesis. The results define an astrocyte proinflammatory cascade that amplifies synthesis of proinflammatory mediators. The implications of these findings to inflammatory diseases of the central nervous system are discussed.

Negative role of cAMP-dependent protein kinase A in RANTES-mediated transcription of proinflammatory mediators through Raf

The chemokine RANTES (regulated on activation normal T cell expressed and secreted) is expressed in several inflammatory diseases of the central nervous system and is a powerful stimulus for astrocyte production of proinflammatory mediators. The mechanism of RANTES-mediated astrocyte activation was investigated. RANTES stimulation decreased both intracellular cyclic AMP (cAMP) levels and cAMP-dependent protein kinase A (PKA) activity in cultures of primary mouse astrocytes. H-89, a potent inhibitor of PKA, mimicked RANTES-mediated chemokine and cytokine transcription. RANTES treatments activated Raf-1 kinase activity, and conversely a dominant negative Raf and a Raf-1 inhibitor blocked RANTES-induced chemokine transcription. Transfection with a constitutively active Raf was sufficient to induce transcription of proinflammatory mediators. The combined data indicate that Raf-1 is required for RANTES-mediated astrocyte activation. Decreases of cAMP and PKA activity contributed to the transcription of proinflammatory mediators by cross-talk with the Raf-1/mitogen-activated protein kinase pathway. The results identify an upstream signaling pathway for amplification of proinflammatory mediators in the central nervous system.