Carbachol activates IkappaB kinase in isolated canine gastric parietal cells

Retinoic acid attenuates nuclear factor kappaB mediated induction of NLRP3 inflammasome

BACKGROUND

Acetylcholine (ACh), a neurotransmitter and a part of the cholinergic system, can modify immune responses. Expression of acetylcholine receptors (AChR) in immune cells, including macrophages, leads to modulation of their function. Inflammasomes are part of the innate immune system and have been linked to a variety of inflammatory diseases. The NLRP3/ASC/caspase-1/IL-1 axis has emerged as a critical signaling pathway in inflammation process initiation. The role of ACh in modulating inflammasomes in macrophages remains relatively under-explored.

METHODS

The effect of AChR agonist carbachol on inflammasome expression was investigated using murine and human macrophages. Cell lysates were assessed by western blot for protein analysis. Immunofluorescence studies were used to study the translocation of p65. The experiments were conducted in the presence of NF-ĸB inhibitor, AChR antagonists, and retinoic acid (RA) to study the role of NF-ĸB, ACh receptors, and RA, respectively.

RESULTS

We found that carbachol increased the expression of NLRP3 inflammasome (NLRP3, ASC, cleaved caspase-1, IL-1β, and IL-18). The treated cells also showed an increase in NF-ĸB activation. The effect of carbachol was diminished by NF-ĸB inhibitor and atropine, a mAChR antagonist. The addition of RA also significantly reduced the effect of carbachol on NLRP3 inflammasomes.

CONCLUSIONS

Our current study suggests that carbachol induces NLRP3 inflammasome activation through mAChR and NF-ĸB, and that RA abolishes the inflammatory response. It reveals the potentials of co-administration of RA with cholinergic drugs to prevent inflammatory responses during cholinergic medications.

Impact of prenatal and postnatal exposure to the pesticide chlorpyrifos on the contraction of rat ileal muscle strips: involvement of an inducible nitric oxide synthase-dependent pathway

BACKGROUND

Prenatal/postnatal exposure to insecticides has been linked to developmental disorders in adulthood. Chlorpyrifos (CPF) is a widely used organophosphorus acetylcholinesterase (AChE)-inhibiting insecticide. The present study established whether prenatal and postnatal exposure to CPF is associated with intestinal motor dysfunction in adult rats.

METHODS

Three groups of pregnant rats were exposed to either CPF (1 or 5 mg/kg/day; the CPF1 and CPF5 groups) or vehicle (the control group) by gavage from gestational day 1 until weaning. At weaning, the pups were separated from their dams and individually gavaged (with the same dose) until postnatal day 60. We then measured in vivo intestinal transit and the in vitro contractile responses of ileal smooth muscle strips to electrical field stimulation. Expression of inducible nitric oxide synthase (iNOS) in the ileum was determined using qRT-PCR and immunoblots. Morphometry and AChE assays were also performed.

KEY RESULTS

At adulthood, the mean body mass was lower in the CPF1 and CPF5 groups than in controls. CPF5 exposure was associated with weaker in vitro contraction of ileal muscle strips, which was reversed by adding the NOS inhibitor (L-NAME). There was no significant intergroup difference in the mean in vivo transit time. Exposure to CPF was associated with greater iNOS expression, lower AChE activity and reduced circular and longitudinal smooth muscle thickness.

CONCLUSIONS & INFERENCES

Prenatal and postnatal exposure to CPF in the rat is associated with weaker contraction of ileal longitudinal smooth muscle via a nitrergic mechanism with increased iNOS expression.

Mycobacterial HBHA induces endoplasmic reticulum stress-mediated apoptosis through the generation of reactive oxygen species and cytosolic Ca2+ in murine macrophage RAW 264.7 cells

Mycobacterial heparin-binding haemagglutinin antigen (HBHA) is a virulence factor that induces apoptosis of macrophages. Endoplasmic reticulum (ER) stress-mediated apoptosis is an important regulatory response that can be utilised to study the pathogenesis of tuberculosis. In the present study, HBHA stimulation induced ER stress sensor molecules in a caspase-dependent manner. Pre-treatment of RAW 264.7 cells with an IκB kinase 2 inhibitor reduced not only C/EBP homology protein expression but also IL-6 and monocyte chemotactic protein-1 (MCP-1) production. BAPTA-AM reduced both ER stress responses and caspase activation and strongly suppressed HBHA-induced IL-6 and MCP-1 production in RAW 264.7 cells. Enhanced reactive oxygen species (ROS) production and elevated cytosolic [Ca(2+)]i levels were essential for HBHA-induced ER stress responses. Collectively, our data suggest that HBHA induces cytosolic [Ca(2+)]i, which influences the generation of ROS associated with the production of proinflammatory cytokines. These concerted and complex cellular responses induce ER stress-associated apoptosis during HBHA stimulation in macrophages. These results indicate that the ER stress pathway has an important role in the HBHA-induced apoptosis during mycobacterial infection.

M3 subtype of muscarinic acetylcholine receptor promotes cardioprotection via the suppression of miR-376b-5p

The M₃ subtype of muscarinic acetylcholine receptors (M₃-mAChR) plays a protective role in myocardial ischemia and microRNAs (miRNAs) participate in many cardiac pathophysiological processes, including ischemia-induced cardiac injury. However, the role of miRNAs in M₃-mAChR mediated cardioprotection remains unexplored. The present study was designed to identify miRNAs that are involved in cardioprotective effects of M₃-mAChR against myocardial ischemia and elucidate the underlying mechanisms. We established rat model of myocardial ischemia and performed miRNA microarray analysis to identify miRNAs involved in the cardioprotection of M₃-mAChR. In H9c2 cells, the viability, intracellular free Ca²⁺ concentration ([Ca²⁺]i), intracellular reactive oxygen species (ROS), miR-376b-5p expression level, brain derived neurophic factor (BDNF) and nuclear factor kappa-B (NF-κB) levels were measured. Our results demonstrated that M₃-mAChR protected myocardial ischemia injury. Microarray analysis and qRT-PCR revealed that miR-376b-5p was significantly up-regulated in ischemic heart tissue and the M₃-mAChRs agonist choline reversed its up-regulation. In vitro, miR-376b-5p promoted H₂O₂-induced H9c2 cell injuries measured by cells viability, [Ca²⁺]i and ROS. Western blot and luciferase assay identified BDNF as a direct target of miR-376b-5p. M₃-mAChR activated NF-κB and thereby inhibited miR-376b-5p expression. Our data show that a novel M₃-mAChR/NF-κB/miR-376b-5p/BDNF axis plays an important role in modulating cardioprotection. MiR-376b-5p promotes myocardial ischemia injury possibly by inhibiting BDNF expression and M₃-mAChR provides cardioprotection at least partially mediated by the downregulation of miR-376b-5p through NF-κB. These findings provide new insight into the potential mechanism by which M₃-mAChR provides cardioprotection against myocardial ischemia injury.

Revisiting the parietal cell

The parietal cell is responsible for secreting concentrated hydrochloric acid into the gastric lumen. To fulfill this task, it is equipped with a broad variety of functionally coupled apical and basolateral ion transport proteins. The concerted scientific effort over the last years by a variety of researchers has provided us with the molecular identity of many of these transport mechanisms, thereby contributing to the clarification of persistent controversies in the field. This article will briefly review the current model of parietal cell physiology and ion transport in particular and will update the existing models of apical and basolateral transport in the parietal cell.

Sustained activation of nuclear factor-kappaB by reactive oxygen species is involved in the pathogenesis of stress-induced gastric damage in rats

OBJECTIVE

Stress ulceration is a common complication in critically ill patients, but the mechanisms involved are poorly understood. In this study we investigated the temporal activation of the redox-sensitive transcription factor nuclear factor-kappaB and its roles in an experimental model of cold immobilization stress-induced gastric mucosal lesions.

DESIGN

Prospective, controlled, and randomized animal study.

SETTING

University research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

The rats were subjected to cold immobilization stress for a total of 6 hrs. The temporal profiles of nuclear factor-kappaB activation and expression of tumor necrosis factor-alpha, interleukin-1beta, cytokine-induced neutrophil chemoattractant-1 (CINC-1), intercellular adhesion molecule-1 (ICAM-1), and inducible nitric oxide synthase (iNOS) were determined in the gastric corpus mucosa of stressed rats. To study the roles of nuclear factor-kappaB activation, rats received an intravenous bolus of a specific nuclear factor-kappaB inhibitor Bay 11-7082 (20 mg/kg) 1 hr before stress. For antioxidant administration, rats were treated with intravenous injection of a free radical scavenger pyrrolidine dithiocarbamate (50, 100, and 200 mg/kg) 1 hr before stress.

MEASUREMENTS AND MAIN RESULTS

Exposure of rats to 6 hrs of stress led to a rapid and persistent activation of nuclear factor-kappaB, which was associated with transient degradation of inhibitory protein IkappaBalpha and slower but sustained degradation of IkappaBbeta. Nuclear factor-kappaB activation preceded the induction of tumor necrosis factor-alpha, interleukin-1beta, CINC-1, ICAM-1, and iNOS messenger RNAs, all of which were linearly increased with the duration of stress. Bay 11-7082 selectively blocked the stress-induced nuclear factor-kappaB activation and up-regulation of tumor necrosis factor-alpha, interleukin-1beta, CINC-1, ICAM-1, and iNOS messenger RNAs. Inhibition of expression of these proinflammatory genes prevented the increases in myeloperoxidase activity (an indicator of neutrophil infiltration) in gastric mucosa and the development of gastric damage. Pyrrolidine dithiocarbamate dose-dependently inhibited the stress-induced nuclear factor-kappaB pathway activation and consequential proinflammatory gene expression, neutrophil infiltration, and gastric damage, suggesting the involvement of reactive oxygen species in these processes.

CONCLUSIONS

Sustained activation of nuclear factor-kappaB by reactive oxygen species is an important in vivo mechanism mediating stress-induced gastric inflammatory damage in rats.

Transcriptional up-regulation of nitric oxide synthase II by nuclear factor-kappaB at rostral ventrolateral medulla in a rat mevinphos intoxication model of brain stem death

As the origin of a 'life-and-death' signal that reflects central cardiovascular regulatory failure during brain stem death, the rostral ventrolateral medulla (RVLM) is a suitable neural substrate for mechanistic delineation of this vital phenomenon. Using a clinically relevant animal model that employed the organophosphate pesticide mevinphos (Mev) as the experimental insult, we evaluated the hypothesis that transcriptional up-regulation of nitric oxide synthase I or II (NOS I or II) gene expression by nuclear factor-kappaB (NF-kappaB) on activation of muscarinic receptors in the RVLM underlies brain stem death. In Sprague-Dawley rats maintained under propofol anaesthesia, co-microinjection of muscarinic M2R (methoctramine) or M4R (tropicamide), but not M1R (pirenzepine) or M3R (4-diphenylacetoxy-N-dimethylpiperidinium) antagonist significantly reduced the enhanced NOS I-protein kinase G signalling ('pro-life' phase) or augmented NOS II-peroxynitrite cascade ('pro-death' phase) in ventrolateral medulla, blunted the biphasic increase and decrease in baroreceptor reflex-mediated sympathetic vasomotor tone that reflect the transition from life to death, and diminished the elevated DNA binding activity or nucleus-bound translocation of NF-kappaB in RVLM neurons induced by microinjection of Mev into the bilateral RVLM. However, NF-kappaB inhibitors (diethyldithiocarbamate or pyrrolidine dithiocarbamate) or double-stranded kappaB decoy DNA preferentially antagonized the augmented NOS II-peroxynitrite cascade and the associated cardiovascular depression exhibited during the 'pro-death' phase. We conclude that transcriptional up-regulation of NOS II gene expression by activation of NF-kappaB on selective stimulation of muscarinic M2 or M4 subtype receptors in the RVLM underlies the elicited cardiovascular depression during the 'pro-death' phase in our Mev intoxication model of brain stem death.

Characterization, localization and possible anti-inflammatory function of rat histone H4 mRNA variants

Two histone H4 mRNA variants, H4-v.1 and histogranin mRNAs, were detected in the rat genome and measured in various tissues and isolated alveolar macrophages. Medium to high levels of both mRNAs were present in the liver, adrenal glands, thymus, bone marrow and alveolar macrophages. H4-v.1 cDNA contained an open reading frame that coded for unmodified whole histone H4, whereas histogranin cDNA lacked the first ATG codon and contained an open reading frame that coded for modified (Thr89) H4-(84-102). The two genes displayed a sequence homologous (> 80%) to the open reading frame of core H4 somatic (H4s) and H4 germinal (H4g) and their variant nature was supported by the absence of histone consensus palindromic and purine-rich sequences in the proximal 3'UTR, and the presence of a polyadenylation signal in the distal 3'UTR and of specific upstream transcription factor-binding sites. H4-v.1 and histogranin transcripts, but not H4s transcript, were selectively induced by lipopolysaccharide and/or interferon gamma in alveolar macrophages. In vitro transcription/translation experiments with H4-v.1 and histogranin cDNA pCMV constructs produced peptides with the molecular mass (2 kDa) of the alternative histone H4 translation product which, like synthetic H4-(86-100) and [Thr89]H4-(86-100) or rat histogranin, inhibited lipopolysaccharide-induced prostaglandin E(2) release from rat alveolar macrophages. The synthetic peptides also inhibited the secretion of the CXC chemokine interleukin-8 (GRO/CINC-1) in response to lipopolysaccharide. The presence of H4-v.1 and histogranin mRNAs in tissues wherein immune reactions take place and the inhibitory effects of their translation products on prostaglandin E(2) and interkeukin-8 secretion by activated alveolar macrophages suggest an anti-inflammatory function.

Nuclear factor-kappaB activated by capacitative Ca2+ entry enhances muscarinic receptor-mediated soluble amyloid precursor protein (sAPPalpha) release in SH-SY5Y cells

G(q/11) protein-coupled muscarinic receptors are known to regulate the release of soluble amyloid precursor protein (sAPPalpha) produced by alpha-secretase processing; however, their signaling mechanisms remain to be elucidated. It has been reported that a muscarinic agonist activates nuclear factor (NF)-kappaB, a transcription factor that has been shown to play an important role in the Alzheimer disease brain, and that NF-kappaB activation is regulated by intracellular Ca2+ level. In the present study, we investigated whether NF-kappaB activation plays a role in muscarinic receptor-mediated sAPPalpha release enhancement and contributes to a changed capacitative Ca2+ entry (CCE), which was suggested to be involved in the muscarinic receptor-mediated stimulation of sAPPalpha release. Muscarinic receptor-mediated NF-kappaB activation was confirmed by observing the translocation of the active subunit (p65) of NF-kappaB to the nucleus by the muscarinic agonist, oxotremorine M (oxoM), in SH-SY5Y neuroblastoma cells expressing muscarinic receptors that are predominantly of the M3 subtype. NF-kappaB activation and sAPPalpha release enhancement induced by oxoM were inhibited by NF-kappaB inhibitors, such as an NF-kappaB peptide inhibitor (SN50), an IkappaB alpha kinase inhibitor (BAY11-7085), a proteasome inhibitor (MG132), the inhibitor of proteasome activity and IkappaB phosphorylation, pyrrolidine dithiocarbamate, the novel NF-kappaB activation inhibitor (6-amino-4-(4-phenoxyphenylethylamino) quinazoline), and by an intracellular Ca2+ chelator (TMB-8). Furthermore, both oxoM-induced NF-kappaB activation and sAPPalpha release were antagonized by CCE inhibitors (gadolinium or SKF96365) but not by voltage-gated Ca2+-channel blockers. On the other hand, treatment of cells with NF-kappaB inhibitors (SN50, BAY11-7085, MG132, or pyrrolidine dithiocarbamate) did not inhibit muscarinic receptor-mediated CCE. These findings provide evidence for the involvement of NF-kappaB regulated by CCE in muscarinic receptor-mediated sAPPalpha release enhancement.

beta-Arrestin inhibits NF-kappaB activity by means of its interaction with the NF-kappaB inhibitor IkappaBalpha

In addition to their roles in desensitization and signaling of seven-membrane-spanning receptors, beta-arrestins have been more recently implicated in regulating non-seven-membrane-spanning receptor pathways. By using a yeast two-hybrid screen, we identified the inhibitor of NF-kappaB, IkappaBalpha, as a binding partner of beta-arrestin 1. Both beta-arrestin 1 and 2 interact with IkappaBalpha in transfected cells as assessed by immunoprecipitation experiments. Additionally, upstream kinases known to regulate the function of IkappaBalpha, such as IkappaB kinase alpha and beta and NF-kappaB-inducing kinase, were also shown to interact with beta-arrestin. Overexpression of either beta-arrestin 1 or beta-arrestin 2 led to marked inhibition of NF-kappaB activity, as measured by reporter gene activity. Inhibition of NF-kappaB activity was independent of the type of stimulus used for NF-kappaB activation. Conversely, suppression of beta-arrestin 1, but not beta-arrestin 2, expression by using RNA interference led to a 3-fold increase in tumor necrosis factor-stimulated NF-kappaB activity as measured by NF-kappaB mobility-shift analysis. These data uncover a role of beta-arrestins in the regulation of NF-kappaB-mediated gene regulation.

Enzyme fragment complementation: a flexible high throughput screening assay technology

High-affinity complementation of a small fragment of beta-galactosidase to an inactive deletion mutant of the enzyme forms a stable heteromeric enzyme complex capable of hydrolyzing substrates to produce either chemiluminescent or fluorescent signals. This review describes a series of screening assays in which the small beta-galactosidase fragment, Enzyme Donor or ProLabel, is either chemically conjugated or recombinantly fused to small molecules or proteins, respectively. Chemical conjugation forms the basis of several HitHunter HTS assays in which competitive displacement of the ProLabel conjugate from either a binding protein (receptor or antibody) is induced by the analyte in question. In this manner, a calibration curve is generated, to measure cellular analytes including 3',5'-cyclic AMP. Changes in this second messenger, occurring due to G protein-coupled receptor (GPCR) activation, can thus be easily measured in a homogeneous assay. Similar assays have been developed for tyrosine kinases, serine threonine kinases, nuclear hormone receptors, and proteases. A second form of assay technology involves measurement of cellular protein expression, in which the protein is fused to ProLabel. Analysis can be undertaken in crude cell lysates, or with intact cells, using beta-galactosidase complementation in a microtiter plate. This homogeneous technology is highly sensitive and has been developed to measure protein expression changes occurring in response to pathway activation by targets such as GPCRs, tyrosine kinase receptors, and proteases. In summary, the DiscoveRx technology using beta-galactosidase complementation provides a robust and flexible assay technology for use in cell-free and cell-based HTS.

Tumor necrosis factor-alpha promotes survival of opossum kidney cells via Cdc42-induced phospholipase C-gamma1 activation and actin filament redistribution

Although the renal proximal tubular epithelial cells are targeted in a variety of inflammatory diseases of the kidney, the signaling mechanism by which tumor necrosis factor (TNF)-alpha exerts its effects in these cells remains unclear. Here, we report that TNF-alpha elicits antiapoptotic effects in opossum kidney cells and that this response is mediated via actin redistribution through a novel signaling mechanism. More specifically, we show that TNF-alpha prevents apoptosis by inhibiting the activity of caspase-3 and this effect depends on actin polymerization state and nuclear factor-kappaB activity. We also demonstrate that the signaling cascade triggered by TNF-alpha is governed by the phosphatidylinositol-3 kinase, Cdc42/Rac1, and phospholipase (PLC)-gamma1. In this signaling cascade, Cdc42 was found to be selectively essential for PLC-gamma1 activation, whereas phosphatidylinositol-3,4,5-triphosphate alone is not sufficient to activate the phospholipase. Moreover, PLC-gamma1 was found to associate in vivo with the small GTPase(s). Interestingly, PLC-gamma1 was observed to associate with constitutively active (CA) Cdc42V12, but not with CA Rac1V12, whereas no interaction was detected with Cdc42(T17N). The inactive Cdc42(T17N) and the PLC-gamma1 inhibitor U73122 prevented actin redistribution and depolymerization, confirming that both signaling molecules are responsible for the reorganization of actin. Additionally, the actin filament stabilizer phallacidin potently blocked the nuclear translocation of nuclear factor-kappaB and its binding activity, resulting in abrogation of the TNF-alpha-induced inhibition of caspase-3. To conclude, our findings suggest that actin may play a pivotal role in the response of opossum kidney cells to TNF-alpha and implicate Cdc42 in directly regulating PLC-gamma1 activity.

Nuclear factor kappaB activation by muscarinic receptors in astroglial cells: effect of ethanol

Activation of muscarinic receptors leads to proliferation of astroglial cells and this effect is inhibited by ethanol. Among the intracellular pathways involved in the mitogenic action of muscarinic agonists, activation of the atypical protein kinase C zeta (PKC zeta) appears to be of most importance, and is also affected by low ethanol concentrations. PKC zeta has been reported to activate nuclear factor kappaB (NF-kappaB), a transcription factor that has been shown to play an important role in cell proliferation. The aim of this study was, therefore, to determine whether muscarinic receptors would activate NF-kappaB in astroglial cells, whether such activation would play a role in the mitogenic action of muscarinic agonists, and whether it would represent a possible target for ethanol. Carbachol activated NF-kappaB in human 1321N1 astrocytoma cells, as evidenced by translocation of the p65 subunit of NF-kappaB to the nucleus, phosphorylation and degradation of IkappaBalpha in the cytosol, and increase NF-kappaB binding to DNA. Carbachol also induced translocation of p65 to the nucleus in primary rat astrocytes. Carbachol-induced NF-kappaB activation was mediated by the M3 subtype of muscarinic receptors and appeared to involve Ca(2+) mobilization and activation of PKC epsilon and PKC zeta, but not PI3-kinase and mitogen-activated protein kinase. The NF-kappaB peptide inhibitor SN50, but not the inactive peptide SN50M, strongly inhibited carbachol-induced astrocytoma cells proliferation and p65 translocation to the nucleus. Increased DNA synthesis was also antagonized by the IkappaBalpha kinase inhibitor BAY 11-7082. Ethanol (25-100 mM) inhibited the translocation of p65 and the binding of NF-kappaB to DNA in both 1321N1 astrocytoma cells and primary rat cortical astrocytes. Together, these results suggest that activation of NF-kappaB by muscarinic receptors in astroglial cells is important for carbachol-induced DNA synthesis and that ethanol-mediated inhibition of cell proliferation may be due in part to inhibition of NF-kappaB activation.

Enhancement of lipopolysaccharide-stimulated JNK activity in rat aortic smooth muscle cells by pharmacological and adenovirus-mediated inhibition of inhibitory kappa B kinase signalling

1. In rat aortic smooth muscle cells (RASMCs), the putative nuclear factor kappa B (NFkappaB) inhibitor Pyrrolidine dithiocarbamate (PDTC) was found to inhibit lipopolysaccharide (LPS)-stimulated NFkappaB DNA-binding. However, further investigation identified the site of inhibition as being at, or upstream of, the inhibitory kappa B kinases (IKKs) as their kinase activity was substantially reduced. 2. In addition, PDTC potentiated LPS-stimulated c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAP kinase) and MAP kinase-activated protein kinase-2 activity (the downstream target of p38 MAP kinase). 3. Another inhibitor of NFkappaB signalling, the serine protease inhibitor Nalphap-tosyl-L-lysine chloro-methylketone (TLCK), also inhibited LPS-stimulated IKK activity and potentiated JNK activity in response to LPS, suggesting that cross-talk may occur between the NFkappaB and stress-activated protein kinase pathways at the level of IKK or at a common point upstream. 4. Infection of RASMCs with an adenovirus encoding either inhibitory kappa Balpha or a dominant-negative IKKbeta potentiated LPS-stimulated JNK activity. 5. These studies therefore suggest that the loss of NFkappaB DNA-binding and resultant transcriptional activity, rather than the loss of IKK activity, is sufficient to cause an increase in JNK activity. This shows that either pharmacological or molecular inhibition of NFkappaB DNA-binding enhances JNK activation in vascular smooth muscle cells, an effect that may contribute to the pathophysiological effects of LPS.

Cell biology of acid secretion by the parietal cell

Acid secretion by the gastric parietal cell is regulated by paracrine, endocrine, and neural pathways. The physiological stimuli include histamine, acetylcholine, and gastrin via their receptors located on the basolateral plasma membranes. Stimulation of acid secretion typically involves an initial elevation of intracellular calcium and/or cAMP followed by activation of a cAMP-dependent protein kinase cascade that triggers the translocation and insertion of the proton pump enzyme, H,K-ATPase, into the apical plasma membrane of parietal cells. Whereas the H,K-ATPase contains a plasma membrane targeting motif, the stimulation-mediated relocation of the H,K-ATPase from the cytoplasmic membrane compartment to the apical plasma membrane is mediated by a SNARE protein complex and its regulatory proteins. This review summarizes the progress made toward an understanding of the cell biology of gastric acid secretion. In particular we have reviewed the early signaling events following histaminergic and cholinergic activation, the identification of multiple factors participating in the trafficking and recycling of the proton pump, and the role of the cytoskeleton in supporting the apical pole remodeling, which appears to be necessary for active acid secretion by the parietal cell. Emphasis is placed on identifying protein factors that serve as effectors for the mechanistic changes associated with cellular activation and the secretory response.

Role of Ca(2+) on TNF-alpha and IL-6 secretion from RBL-2H3 mast cells

Ca2+ acts as an important second messenger in mast cells. However, the mechanisms involved in the secretion of inflammatory cytokines from activated mast cells are unknown. In this study, we examined the signaling pathway involved in calcium-related cytokine secretion in a mast cell line, RBL-2H3 cells. We report that treatment with 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM), a chelator of intracellular calcium, can inhibit IgE-stimulated TNF-alpha and IL-6 secretion in a concentration-dependent manner with IC50 values of 0.41 and 0.014 microM, respectively. Maximal inhibition of TNFalpha- and IL-6 secretion was 58.5 +/- 3% and 87 +/- 8% in BAPTA-AM, respectively. BAPTA-AM also completely inhibited the IgE-induced TNF-alpha and IL-6 mRNA levels. In activated RBL-2H3 cells, the expression level of NF-kappaB/Rel A protein increased in the nucleus. However, the level of NF-kappaB/Rel A in nucleus was decreased by treatment of BAPTA-AM. In addition, BAPTA-AM completely inhibited the IgE-induced IkappaB kinase beta (IKKbeta) activation and IkappaBalpha phosphorylation. These observations demonstrate that the intracellular Ca2+ may play an important role in IgE-induced TNF-alpha and IL-6 secretion from mast cells via IKKbeta activation.

Regulation and function of COX-2 gene expression in isolated gastric parietal cells

We examined expression, function, and regulation of the cyclooxygenase (COX)-2 gene in gastric parietal cells. COX-2-specific mRNA was isolated from purified (>95%) canine gastric parietal cells in primary culture and measured by Northern blots using a human COX-2 cDNA probe. Carbachol was the most potent inducer of COX-2 gene expression. Gastrin and histamine exhibited minor stimulatory effects. Carbachol-stimulated expression was inhibited by intracellular Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (90%), protein kinase C (PKC) inhibitor GF-109203X (48%), and p38 kinase inhibitor SB-203580 (48%). Nuclear factor (NF)-kappaB inhibitor 1-pyrrolidinecarbodithioic acid inhibited carbachol-stimulated expression by 80%. Similar results were observed in the presence of adenoviral vector Ad.dom.neg.IkappaB, which expresses a repressor of NF-kappaB. Addition of SB-203580 with Ad.dom.neg.IkappaB almost completely blocked carbachol stimulation of COX-2 gene expression. We examined the effect of carbachol on PGE(2) release by enzyme-linked immunoassay. Carbachol induced PGE(2) release. Ad.dom.neg.IkappaB, alone or with SB-203580, produced, respectively, partial (70%) and almost complete (>80%) inhibition of carbachol-stimulated PGE(2) production. Selective COX-2 inhibitor NS-398 blocked carbachol-stimulated PGE(2) release without affecting basal PGE(2) production. In contrast, indomethacin inhibited both basal and carbachol-stimulated PGE(2) release. Carbachol induces COX-2 gene expression in the parietal cells through signaling pathways that involve intracellular Ca(2+), PKC, p38 kinase, and activation of NF-kappaB. The functional significance of these effects seems to be stimulation of PGE(2) release.

Sphingosine 1-phosphate activates nuclear factor-kappa B through Edg receptors. Activation through Edg-3 and Edg-5, but not Edg-1, in human embryonic kidney 293 cells

Sphingosine 1-phosphate (S1P) exerts a variety of actions as a second messenger or as an agonist that binds to one or more members of the Edg family of G protein-coupled receptors. By using human embryonic kidney 293 cells, we show that S1P activates nuclear factor-kappa B (NF-kappa B) in a receptor-dependent fashion. Edg-3 and Edg-5, which are coupled to G(i), G(q), and G(13), affect activation of NF-kappa B, whereas Edg-1, which is coupled to G(i) alone, does not. We find that the activation of NF-kappa B requires protein kinase C and Ca(2+), probably downstream of G(q), but that the activation of Rho alone by S1P, whether through G(q) or G(13), does not translate into the activation of NF-kappa B. G beta gamma has little effect of its own but potentiates the activation of NF-kappa B achieved through other G proteins. We conclude that the activation of NF-kappa B by S1P is a receptor-mediated process that relies primarily on the activation of a phospholipase C by G(q) and secondarily on effector regulation through other G proteins.

Inhibition of NF-kappaB-mediated gene transcription by the human A2B adenosine receptor in Chinese hamster ovary cells

NF-kappaB is a transcription factor that plays a vital role in regulating inducible gene expression in immune and inflammatory responses. In view of the well documented effects of adenosine on immune and inflammatory responses, we have explored whether adenosine A1, A2B and A3 receptors regulate NF-kappaB activity in transfected Chinese hamster ovary (CHO) cells using a luciferase reporter gene construct. No increases in NF-kappaB activity were observed in CHO-A1, -A2B and -A3 cells stimulated with the non-selective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine. Elevating intracellular cyclic AMP (cAMP) levels using forskolin (direct activator of adenylyl cyclase) and rolipram (type IV, cAMP-specific phosphodiesterase inhibitor), inhibited NF-kappaB activity in CHO cells. Adenosine A2B receptor stimulation also inhibited NF-kappaB activity, whereas adenosine A1 and A3 receptor activation had no effect. These data reflect the known coupling of adenosine A2B receptors to increases in cAMP. In conclusion, adenosine A1, A2B and A3 receptors do not directly activate NF-kappaB in CHO cells. However, adenosine A2B receptor activation significantly inhibited NF-kappaB activity. Inhibition of NF-kappaB activity by the adenosine A2B receptor may contribute to the anti-inflammatory effects of adenosine.

Activation of NF-kappa B by bradykinin through a Galpha(q)- and Gbeta gamma-dependent pathway that involves phosphoinositide 3-kinase and Akt

Recent work has suggested a role for the serine/threonine kinase Akt and IkappaB kinases (IKKs) in nuclear factor (NF)-kappaB activation. In this study, the involvement of these components in NF-kappaB activation through a G protein-coupled pathway was examined using transfected HeLa cells that express the B2-type bradykinin (BK) receptor. The function of IKK2, and to a lesser extent, IKK1, was suggested by BK-induced activation of their kinase activities and by the ability of their dominant negative mutants to inhibit BK-induced NF-kappaB activation. BK-induced NF-kappaB activation and IKK2 activity were markedly inhibited by RGS3T, a regulator of G protein signaling that inhibits Galpha(q), and by two Gbetagamma scavengers. Co-expression of Galpha(q) potentiated BK-induced NF-kappaB activation, whereas co-expression of either an activated Galpha(q)(Q209L) or Gbeta(1)gamma(2) induced IKK2 activity and NF-kappaB activation without BK stimulation. BK-induced NF-kappaB activation was partially blocked by LY294002 and by a dominant negative mutant of phosphoinositide 3-kinase (PI3K), suggesting that PI3K is a downstream effector of Galpha(q) and Gbeta(1)gamma(2) for NF-kappaB activation. Furthermore, BK could activate the PI3K downstream kinase Akt, whereas a catalytically inactive mutant of Akt inhibited BK-induced NF-kappaB activation. Taken together, these findings suggest that BK utilizes a signaling pathway that involves Galpha(q), Gbeta(1)gamma(2), PI3K, Akt, and IKK for NF-kappaB activation.

N-acetylcysteine suppresses TNF-induced NF-kappaB activation through inhibition of IkappaB kinases

Here, we used a reductant, N-acetyl-L-cysteine (NAC), to investigate the redox-sensitive step(s) in the signalling pathway from the tumor necrosis factor (TNF) receptor to nuclear factor kappaB (NF-kappaB). We found that NAC suppressed NF-kappaB activation triggered by TNF or by overexpression of either the TNF receptor-associated death domain protein, TNF receptor-associated factor 2, NF-kappaB-inducing kinase (NIK), or IkappaB kinases (IKKalpha and IKKbeta). NAC also suppressed the TNF-induced activation of IKKalpha and IKKbeta, phosphorylation and degradation of IkappaB, and nuclear translocation of NF-kappaB. Furthermore, NAC suppressed the activation of IKKalpha and IKKbeta triggered by the overexpression of NIK. These results indicate that IKKalpha and IKKbeta are subject to redox regulation in the cells, and that NAC inhibits NF-kappaB activation through the suppression of these kinases.