Phorbol ester synergistically increases interferon-gamma-induced nitric oxide synthesis in murine microglial cells

CircWAC induces chemotherapeutic resistance in triple-negative breast cancer by targeting miR-142, upregulating WWP1 and activating the PI3K/AKT pathway

BACKGROUND

Chemotherapeutic resistance is the main cause of clinical treatment failure and poor prognosis in triple-negative breast cancer (TNBC). There is no research on chemotherapeutic resistance in TNBC from the perspective of circular RNAs (circRNAs).

METHODS

TNBC-related circRNAs were identified based on the GSE101124 dataset. Quantitative reverse transcription PCR was used to detect the expression level of circWAC in TNBC cells and tissues. Then, in vitro and in vivo functional experiments were performed to evaluate the effects of circWAC in TNBC.

RESULTS

CircWAC was highly expressed in TNBC and was associated with worse TNBC patient prognosis. Subsequently, it was verified that downregulation of circWAC can increase the sensitivity of TNBC cells to paclitaxel (PTX) in vitro and in vivo. The expression of miR-142 was negatively correlated with circWAC in TNBC. The interaction between circWAC and miR-142 in TNBC cells was confirmed by RNA immunoprecipitation assays, luciferase reporter assays, pulldown assays, and fluorescence in situ hybridization. Mechanistically, circWAC acted as a miR-142 sponge to relieve the repressive effect of miR-142 on its target WWP1. In addition, the overall survival of TNBC patients with high expression of miR-142 was significantly better than that of patients with low expression of miR-142, and these results were verified in public databases. MiR-142 regulated the expression of WWP1 and the activity of the PI3K/AKT pathway. It was confirmed that WWP1 is highly expressed in TNBC and that the prognosis of patients with high WWP1 expression is poor.

CONCLUSIONS

CircWAC/miR-142/WWP1 form a competing endogenous RNA (ceRNA) network to regulate PI3K/AKT signaling activity in TNBC cells and affect the chemosensitivity of cells.

The epinephrine-induced PGE2 reduces Na+/K+ ATPase activity in Caco-2 cells via PKC, NF-κB and NO

We showed previously an epinephrine-induced inhibition of the Na⁺/K⁺ ATPase in Caco-2 cells mediated via PGE2. This work is an attempt to further elucidate mediators downstream of PGE2 and involved in the observed inhibitory effect. The activity of the Na⁺/K⁺ ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain, a specific inhibitor of the enzyme. Changes in the protein expression of the Na⁺/K⁺ ATPase were investigated by western blot analysis which revealed a significant decrease in the abundance of the ATPase in plasma membranes. Treating the cells with epinephrine or PGE2 in presence of SC19220, a blocker of EP1 receptors abolished completely the effect of the hormone and the prostaglandin while the effect was maintained unaltered in presence of antagonists to all other receptors. Treatment with calphostin C, PTIO, ODQ or KT5823, respective inhibitors of PKC, NO, soluble guanylate cyclase and PKG, abrogated completely the effect of epinephrine and PGE2, suggesting an involvement of these mediators. A significant inhibition of the ATPase was observed when cells were treated with PMA, an activator of PKC or with 8-Br-cGMP, a cell permeable cGMP analogue. PMA did reduce the protein expression of IκB, as shown by western blot analysis, and its effect on the ATPase was not manifested in presence of an inhibitor of NF-κB while that of SNAP, a nitric oxide donor, was not affected. The results infer that NF-κB is downstream PKC and upstream NO. The data support a pathway in which epinephrine induces the production of PGE2 which binds to EP1 receptors and activates PKC and NF-κB leading to NO synthesis. The latter activates soluble guanylate cyclase resulting in cGMP production and activation of PKG which through direct or indirect phosphorylation inhibits the Na⁺/K⁺ ATPase by inducing its internalization.

Acute toxication of deltamethrin results in activation of iNOS, 8-OHdG and up-regulation of caspase 3, iNOS gene expression in common carp (Cyprinus carpio L.)

Deltamethrin is a widely used synthetic pyrethroid pesticide that protects agricultural yields, including crops, fruits, and vegetables from insect-pests. It is known that deltamethrin toxication leads to metabolic disorders and has detrimental effects on the brain and liver in different organisms. However, the harmful effects of deltamethrin toxication on aquatic animals remain unclear. In the present study, we aimed to evaluate the adverse effects of deltamethrin toxication by performing a histopathological examination, an immunofluorescence assay, and a qRT-PCR on common carp. We observed that a low-dose (0.04μM) and a high-dose (0.08μM) of deltamethrin exposure caused lamellar cells hyperplasia and inflammatory cells infiltration in the gills, hyperemia, diffuse hydropic degenerations and focal necrosis in the hepatocytes, necrotic changes in the neurons, and also induced activation of inducible Nitric Oxide Synthase (iNOS) and 8-hydroxy-2-deoxyguanosine (8-OHdG) in the gills, liver, and brain depending on the exposure time (24h, 48h, 72h and 96h). In addition, deltamethrin toxication caused the up-regulation of caspase-3 and the inducible Nitric Oxide Synthase (iNOS) of the gene expression depending on the dose (0.04μM and 0.08μM) and the exposure time in the brain (p<0.05, p<0.01, p<0.001). Our results indicated that long-term deltamethrin exposure could lead to inflammation, oxidative stress, DNA damage, and apoptosis on the different organs in common carp. Thus, deltamethrin toxication is dangerous for common carp populations, and the usage of deltamethrin should be controlled and restricted in agricultural areas.

Say "no" to spinal cord injury: is nitric oxide an option for therapeutic strategies?

PURPOSE

a literature review was made to investigate the role of nitric oxide (NO) in spinal cord injury, a pathological condition that leads to motor, sensory, and autonomic deficit. Besides, we were interested in potential therapeutic strategies interfering with NO mechanism of secondary damage.

MATERIALS

A literature search using PubMed Medline database has been performed.

RESULTS

excessive NO production after spinal cord injury promotes oxidative damage perpetuating the injury causing neuronal loss at the injured site and in the surrounding area.

CONCLUSION

different therapeutic approaches for contrasting or avoiding NO secondary damage have been studied, these include nitric oxide synthase inhibitors, compounds that interfere with inducible NO synthase expression, and molecules working as antioxidant. Further studies are needed to explain the neuroprotective or cytotoxic role of the different isoforms of NO synthase and the other mediators that take part or influence the NO cascade. In this way, it would be possible to find new therapeutic targets and furthermore to extend the experimentation to humans.

Specific PKC isoforms regulate LPS-stimulated iNOS induction in murine microglial cells

Background

Excessive production of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) in reactive microglia is a major contributor to initiation/exacerbation of inflammatory and degenerative neurological diseases. Previous studies have indicated that activation of protein kinase C (PKC) can lead to iNOS induction. Because of the existence of various PKC isoforms and the ambiguous specificity of PKC inhibitors, it is unclear whether all PKC isoforms or a specific subset are involved in the expression of iNOS by reactive microglia. In this study, we employed molecular approaches to characterize the role of each specific PKC isoform in the regulation of iNOS expression in murine microglia.

Methods

Induction of iNOS in response to bacterial endotoxin lipopolysaccharide (LPS) was measured in BV-2 murine microglia treated with class-specific PKC inhibitors, or transfected with siRNA to silence specific PKC isoforms. iNOS expression and MAPK phosphorylation were evaluated by western blot. The role of NF-κB in activated microglia was examined by determining NF-κB transcriptional response element- (TRE-) driven, promoter-mediated luciferase activity.

Results

Murine microglia expressed high levels of nPKCs, and expressed relatively low levels of cPKCs and aPKCs. All PKC inhibitors attenuated induction of iNOS in LPS-activated microglia. Knockdown of PKC δ and PKC β attenuated ERK1/2 and p38 phosphorylation, respectively, and blocked NF-κB activation that leads to the expression of iNOS in reactive microglia.

Conclusions

Our results identify PKC δ and β as the major PKC isoforms regulating iNOS expression in reactive microglia. The signaling pathways mediated by PKC involve phosphorylation of distinct MAPKs and activation of NF-κB. These results may help in the design of novel and selective PKC inhibitors for the treatment of many inflammatory and neurological diseases in which production of NO plays a pathogenic role.

Inducible nitric oxide synthase (iNOS) in tumor biology: the two sides of the same coin

Inducible nitric oxide synthase (iNOS) is one of three key enzymes generating nitric oxide (NO) from the amino acid l-arginine. iNOS-derived NO plays an important role in numerous physiological (e.g. blood pressure regulation, wound repair and host defence mechanisms) and pathophysiological (inflammation, infection, neoplastic diseases, liver cirrhosis, diabetes) conditions. iNOS is the synthase isoform most commonly associated with malignant disease. Nevertheless, the role of iNOS during tumor development is highly complex, and incompletely understood. Both promoting and deterring actions have been described, presumably depending upon the local concentration of iNOS within the tumor microenvironment. In particular, pivotal effects such as malingnant transformation, angiogenesis, and metastasis are modulated by iNOS. On the other hand, NO derived from macrophages has a potentially cytotoxic/cytostatic effect upon tumor cells. Hence, therapeutical interference with iNOS activity is of considerable interest, especially in tumors where metastatic activity, host defence mechanisms and the level of differentiation seem to be correlated to iNOS expression. This review will aim to summarize the dual actions of iNOS as simultaneous tumor promoter and suppressor.

Distinct signaling pathways for induction of type II NOS by IFNγ and LPS in BV-2 microglial cells

Nitric oxide (NO) release upon microglial cell activation has been implicated in the tissue injury and cell death in many neurodegenerative diseases. Recent studies have indicated the ability of interferon-gamma (IFNgamma) and lipopolysaccharides (LPS) to independently induce type II nitric oxide synthase (iNOS) expression and NO production in BV-2 microglial cells. However, a detailed comparison between the signaling pathways activating iNOS by these two agents has not been accomplished. Analysis of PKC isoforms revealed mainly the presence of PKCdelta, iota and lambda in BV-2 cells. Although both IFNgamma and LPS could specifically enhance the tyrosine phosphorylation of PKCdelta, treatment with IFNgamma induced a steady increase of phospho-PKCdelta for up to 1h, whereas treatment with LPS elevated phospho-PKCdelta levels only transiently, with peak activity at 5 min. Rottlerin, a specific inhibitor for PKCdelta, dose-dependently inhibited IFNgamma- and LPS-induced NO production. Despite the common involvement of PKCdelta, IFNgamma- but not LPS-induced NO production involved extracellular signal-regulated kinases (ERK1/2) cascade and IFNgamma-induced phosphorylation of ERK1/2 was mediated through PKC. On the other hand, LPS- but not IFNgamma-induced NO production was through stimulation of NF-kappaB activation and nuclear translocation to interact with DNA. These results demonstrated distinct signaling pathways for induction of iNOS by IFNgamma and LPS in BV-2 microglial cells.

Gangliosides activate microglia via protein kinase C and NADPH oxidase

Microglia, the major immune effector cells in the central nervous system, are activated when the brain suffers injury. A number of studies indicate that gangliosides activate microglia. However, the signaling mechanisms involved in microglial activation are not yet to be elucidated. Our results show that gangliosides induce the expression of interleukin (IL)-1beta, tumor necrosis factor-alpha (TNF-alpha), and inducible nitric oxide synthase (iNOS) in rat brain microglia and BV2 murine microglia via protein kinase C (PKC) and NADPH oxidase. Expression of IL-1beta, TNF-alpha, and iNOS in ganglioside-treated cells was significantly reduced in the presence of inhibitors of PKC (GF109203X, Go6976, Ro31-8220, and rottlerin) and NADPH oxidase (diphenyleneiodonium chloride [DPI]). In response to gangliosides, PKC-alpha, betaII, and delta and NADPH oxidase p67(phox) translocated from the cytosol to the membrane. ROS generation was also activated within 5 min of ganglioside treatment. Ganglioside-induced ROS generation was blocked by PKC inhibitors. Furthermore, ganglioside-induced activation of NF-kappaB, an essential transcription factor that mediates the expression of IL-1beta, TNF-alpha, and iNOS, was reduced in the presence of GF109203X and DPI. Our results collectively suggest that gangliosides activate microglia via PKC and NADPH oxidase, which regulate activation of NF-kappaB.

P2X7 nucleotide receptor activation enhances IFN gamma-induced type II nitric oxide synthase activity in BV-2 microglial cells

Under normal and pathological conditions, brain cells release nucleotides that regulate a wide range of cellular responses due to activation of P2 nucleotide receptors. In this study, the effect of extracellular nucleotides on IFN gamma-induced NO release in murine BV-2 microglial cells was investigated. BV-2 cells expressed mRNA for metabotropic P2Y and ionotropic P2X receptors. Among the P2 receptor agonists tested, ATP, ADP, 2',3'-O-(4-benzoylbenzoyl)-ATP (BzATP), and 2-methylthio-ATP (2-MeSATP), but not UTP, enhanced IFN gamma-induced iNOS expression and NO production, suggesting that the uridine nucleotide receptors P2Y2 and P2Y6 are not involved in this response. U0126, an antagonist for MEK1/2, a kinase that phosphorylates the extracellular signal-regulated kinases ERK1/2, decreased IFN gamma-induced NO production. BzATP, a potent P2X7 receptor agonist, was more effective than ATP, ADP, or 2-MeSATP at enhancing IFN gamma-induced ERK1/2 phosphorylation. Consistent with activation of the P2X7 receptor, periodate-oxidized ATP, a P2X7 receptor antagonist, and suramin, a non-specific P2 receptor antagonist, inhibited the effect of ATP or BzATP on IFN gamma-induced NO production, whereas pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), an antagonist of several P2X receptor subtypes, was ineffective. These results suggest that activation of P2X7 receptors may contribute to inflammatory responses in microglial cells seen in neurodegenerative diseases.

Identification of protein kinase C isoforms involved in interferon-gamma-induced expression of inducible nitric oxide synthase in murine BV2 microglia

Microglia are major inflammatory cells of the brain. It has been known that interferon-gamma (IFN-gamma) induces nitric oxide (NO)/inducible nitric oxide synthase (iNOS) in microglia, and that protein kinase C (PKC) mediates the action of IFN-gamma. In this study, we investigated isoforms of PKC that are involved in IFN-gamma-induced activation of microglia using BV2 murine microglial cells. NO release/iNOS expression in IFN-gamma -treated BV2 cells was reduced in the presence of PKC inhibitors (Gö 6976 and BIM), and by long-term pre-treatment (48 h) of cells with phorbol-12-myristate-13-acetate (PMA) or thymeleatoxin. PMA depleted alpha, beta, delta, and epsilon isoforms, and thymeleatoxin depleted alpha, beta, and epsilon isoforms although gamma, eta, iota, lambda, theta, mu, and zeta were also detected in these cells. Furthermore, IFN-gamma phosphorylated alpha and epsilon on their tyrosine residues. These results suggested that alpha and epsilon could be the major PKC isoforms involved in signaling pathways of IFN-gamma to induce NO/iNOS expression in BV2 microglia.

Phorbol ester synergistically increases interferon regulatory factor-1 and inducible nitric oxide synthase induction in interferon-gamma-treated RAW 264.7 cells

The roles of PKC in iNOS induction by IFN-gamma have been shown in some cell types. The effect of a PKC activator, phorbol ester, in iNOS induction is thought to be due to multiple mechanisms, and it is necessary to examine the involvement of phorbol ester on IFN-gamma-induced iNOS in detail. In the present study, we investigated the mechanisms of phorbol ester on IFN-gamma-induced iNOS in RAW 264.7 cells. PMA synergistically increased iNOS activity, protein and mRNA levels in IFN-gamma-treated RAW 264.7 cells. PMA together with IFN-gamma increased iNOS mRNA without affecting the iNOS mRNA degradation, suggesting that the synergistic effect of PMA on IFN-gamma-induced iNOS mRNA production may depend on the elevation of the transcription rate rather than a prolongation of mRNA stability. The DNA binding proteins that are involved in the regulation of iNOS expression are mainly NF-kappa B and IRF-1. IRF-1 transcriptionally regulates many IFN-inducible genes such as iNOS whose promoter contains an IRF-1 binding site. PMA might modulate iNOS induction as a cosignal with IFN-gamma in RAW 264.7 cells because the synergistic effect of PMA was mediated through IRF-1, rather than NF-kappa B. Ro 31-8220, a PKC inhibitor, decreased iNOS activity, protein, mRNA levels and IRF-1 activity, indicating that the effect of PMA on iNOS induction might occur via the PKC pathway. It is evidence that PKC plays an important role in IRF-1 activation and that phorbol ester has a synergistic effect on iNOS induction through IRF-1 activation in IFN-gamma-treated RAW 264.7 cells. The synergistic effect of PMA on IFN-gamma-induced IRF-1 binding activity was observed in macrophage cell line J774 cells as well as RAW 264.7 cells, but not in thioglycollate-elicited peritoneal macrophages.

Human chorionic gonadotropin induces nitric oxide synthesis by murine microglia

This study investigated the effects of human chorionic gonadotropin (hCG) on the synthesis of nitric oxide (NO) in murine neonatal microglial cells. When hCG was used in combination with interferon-gamma (IFN-gamma), there was a marked cooperative induction of NO synthesis in a dose-dependent manner. This increase in NO synthesis was reflected as an increased amount of iNOS protein. The increase of NO synthesis by IFN-gamma-plus-hCG was associated with the increase of tumor necrosis factor-alpha (TNF-alpha) secretion and hCG-induced NO production was decreased by the treatment with anti-murine TNF-alpha neutralizing antibody. This study provides evidence that hCG activates expression of iNOS protein in murine microglial cells accompanied by NO accumulation via pathway dependent on L-arginine in the culture medium, and further offers that TNF-alpha acts on the NO synthesis from IFN-gamma-primed murine microglial cells.

Induction of protein kinase Cdelta subspecies in neurons and microglia after transient global brain ischemia

The delayed death of CA1 neurons after global brain ischemia is associated with induction of apoptosis genes and is inhibited by protein synthesis inhibitors, suggesting that the degeneration of CA1 pyramidal neurons is an active process that requires new gene expression. The transient global ischemia model has been extensively used to identify enzymes and other proteins underlying delayed neuronal cell death. The expression of protein kinase C (PKC) subspecies after 20 minutes of global brain ischemia produced by a four-vessel occlusion model in the rat was studied. From the multiple PKC subspecies studied, only PKCdelta mRNA was significantly up-regulated in CA1 pyramidal neurons at 24 hours and in activated microglia at 3 to at least 7 days after ischemia. The induction of PKCdelta mRNA was also found in the cortex at 8 hours and 3 days after ischemia. This cortical but not hippocampal induction was regulated by an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/kainate receptor antagonist, 6-nitro-7-sulfamobenzo[f]quinoxaline-2,3-dione, and glucocorticoids. An N-methyl-D-aspartate receptor antagonist, MK-801, was without effect on the induction of PKCdelta subspecies. The selective and prolonged induction of the PKCdelta mRNA and protein first in CA1 pyramidal neurons and at a later stage in activated microglia suggests that the PKCdelta isozyme may take part in regulation of the delayed death of CA1 neurons after transient global brain ischemia.

Role of iNOS in the vasodilator responses induced by L-arginine in the middle cerebral artery from normotensive and hypertensive rats

1. The substrate of nitric oxide synthase (NOS), L-arginine (L-Arg, 0.01 microM - 1 mM), induced endothelium-independent relaxations in segments of middle cerebral arteries (MCAs) from normotensive Wistar-Kyoto (WKY) and hypertensive rats (SHR) precontracted with prostaglandin F2alpha (PGF2alpha). These relaxations were higher in SHR than WKY arteries. 2. L-N(G)-nitroarginine methyl ester (L-NAME) and 2-amine-5,6-dihydro-6-methyl-4H-1,3-tiazine (AMT), unspecific and inducible NOS (iNOS) inhibitors, respectively, reduced those relaxations, specially in SHR. 3. Four- and seven-hours incubation with dexamethasone reduced the relaxations in MCAs from WKY and SHR, respectively. 4. Polymyxin B and calphostin C, protein kinase C (PKC) inhibitors, reduced the L-Arg-induced relaxation. 5. Lipopolysaccharide (LPS, 7 h incubation) unaltered and inhibited these relaxations in WKY and SHR segments, respectively. LPS antagonized the effect polymyxin B in WKY and potentiated L-Arg-induced relaxations in SHR in the presence of polymyxin B. 6. The contraction induced by PGF2alpha was greater in SHR than WKY arteries. This contraction was potentiated by dexamethasone and polymyxin B although the effect of polymyxin B was higher in SHR segments. LPS reduced that contraction and antagonized dexamethasone- and polymyxin B-induced potentiation, these effects being greater in arteries from SHR. 7. These results suggest that in MCAs: (1) the induction of iNOS participates in the L-Arg relaxation and modulates the contraction to PGF2alpha; (2) that induction is partially mediated by a PKC-dependent mechanism; and (3) the involvement of iNOS in such responses is greater in the hypertensive strain.

Inhibition of the induction of the inducible nitric oxide synthase in murine brain microglial cells by sodium salicylate

The induction of the inducible nitric oxide synthase (iNOS) has been proposed to play a role in a variety of inflammatory diseases. Sodium salicylate (NaSal) is the most commonly used anti-inflammatory agent. We investigated whether NaSal can diminish the induction of iNOS in murine brain microglial cells. In primary cultures, interferon-gamma (IFN-gamma) or lipopolysaccharide (LPS) separately did not stimulate nitric oxide (NO) production, whereas IFN-gamma combined with LPS synergistically induced iNOS. NaSal inhibited both the production of NO and expression of iNOS in microglial cells. Synergy between IFN-gamma and LPS was mainly dependent on tumour necrosis factor-alpha (TNF-alpha) secretion as the increase of the induction of the iNOS by IFN-gamma plus LPS was associated with the increase of TNF-alpha secretion and IFN-gamma plus LPS-induced TNF-alpha secretion by microglial cells was decreased by the treatment with NaSal. These results suggest a possible use of NaSal in managing inflammation of the central nervous system through inhibition of the iNOS induction.

Up-regulation of protein kinase C-epsilon promotes the expression of cytokine-inducible nitric oxide synthase in RAW 264.7 cells

Stimulation of the murine macrophage RAW 264.7 cell line with phorbol esters fails to promote nitric oxide synthesis as occurs in rat hepatocytes or peritoneal macrophages. Transfection of RAW 264.7 cells with plasmids harboring protein kinase C (PKC) -epsilon isotype but not with PKC-alpha, -beta1, -delta, or constitutively active -alpha and -beta1 isotypes resulted in the expression of nitric oxide synthase type II (iNOS), as reflected by the synthesis of nitric oxide measured in the culture medium of transfected cells. cotransfection of RAW 264.7 cells with the -1592 to +121-base pair promoter region of the murine iNOS gene and PKC isotypes specifically induced the transactivation of this promoter in the case of the plasmids containing the PKC-epsilon isotype. The mechanism by which PKC-epsilon induced iNOS expression involved the activation of nuclear factor binding to kappaB sites (NF-kappaB) as deduced by the suppressive effect of pyrrolidine dithiocarbamate on nitric oxide synthesis, an inhibitor of NF-kappaB activation, and by the activation of kappaB sites in cells transfected with a vector containing a kappaB motif linked to a chloramphenicol acetyltransferase reporter gene. These results suggest that PKC-epsilon can regulate a pathway that promotes iNOS expression in macrophages in response to phorbol ester activation.