PKC-δ mediates activation of ERK1/2 and induction of iNOS by IL-1β in vascular smooth muscle cells

PKCα and PKCδ: Friends and Rivals

PKC comprises a large family of serine/threonine kinases that share a requirement for allosteric activation by lipids. While PKC isoforms have significant homology, functional divergence is evident among subfamilies and between individual PKC isoforms within a subfamily. Here, we highlight these differences by comparing the regulation and function of representative PKC isoforms from the conventional (PKCα) and novel (PKCδ) subfamilies. We discuss how unique structural features of PKCα and PKCδ underlie differences in activation and highlight the similar, divergent, and even opposing biological functions of these kinases. We also consider how PKCα and PKCδ can contribute to pathophysiological conditions and discuss challenges to targeting these kinases therapeutically.

[Effects of protein kinase C and motigen-activated protein kinase kinase/extracellular regulated protein kinases signaling pathway on mRNA level of inducible nitric oxide synthase in Tca8113 cells]

OBJECTIVE

To explore the regulatory mechanism of inducible nitric oxide synthase (NOS-2) expression related to proliferation of Tca8113 cells.

METHODS

RNAi mediated by short hairpin RNAs was utilized to knock down NOS-2, protein kinase C (PKC)-α, PKC-β and PKC-δ. Griess Reagent played a significant role on the detection of NO product after NOS-2 silence. The cell proliferation was determined by CCK8 method. Quantitative real-time polymerase chain reaction (q-PCR) was recruited to check the mRNA level of NOS-2, PKC-α, PKC-β and PKC-δ after treated by a variety of ways. Eventually, the measure of phosphorylation of extracellular regulated protein kinases (ERK)1/2 was performed by Western blotting in PMA-treated Tca8113 cells.

RESULTS

The cell viability of Tca8113 decreased obviously after transfected with NOS-2 siRNA (P<0.01). PKC reduced the expression level of NOS-2 mRNA (P<0.05). PKC-α, PKC-β and PKC-δ worked together to regulate the level of NOS-2 mRNA (P<0.01). Motigen-activated protein kinase kinase (MEK)/ERK signaling pathway regulated the level of NOS-2 mRNA negatively (P<0.05). PKC down regulated the level of NOS-2 mRNA through MEK/ERK signaling pathway (P<0.05).

CONCLUSIONS

PKC regulates the mRNA level of NOS-2 related to proliferation through MEK/ERK signaling pathway in Tca8113 cells.

Excessive Glutamate Stimulation Impairs ACE2 Activity Through ADAM17-Mediated Shedding in Cultured Cortical Neurons

The excitotoxicity of glutamate plays an important role in the progression of various neurological disorders via participating in inflammation and neuronal damage. In this study, we identified the role of excessive glutamate stimulation in the modulation of angiotensin-converting enzyme type 2 (ACE2), a critical component in the compensatory axis of the renin-angiotensin system (RAS). In primary cultured cortical neurons, high concentration of glutamate (100 µM) significantly reduced the enzymatic activity of ACE2. The elevated activity of ADAM17, a member of the 'A Disintegrin And Metalloprotease' (ADAM) family, was found to contribute to this glutamate-induced ACE2 down-regulation. The decrease of ACE2 activity could be prevented by pre-treatment with antagonists targeting ionotropic glutamate receptors. In addition, the glutamate-induced decrease in ACE2 activity was significantly attenuated when the neurons were co-treated with MitoTEMPOL or blockers that target oxidative stress-mediated signaling pathway. In summary, our study reveals a strong relationship between excessive glutamate stimulation and ADAM17-mediated impairment in ACE2 activity, suggesting a possible cross-talk between glutamate-induced excitotoxicity and dysregulated RAS.

Protein kinase Cδ upregulation in microglia drives neuroinflammatory responses and dopaminergic neurodegeneration in experimental models of Parkinson's disease

Chronic microglial activation has been linked to the progressive degeneration of the nigrostriatal dopaminergic neurons evidenced in Parkinson's disease (PD) pathogenesis. The exact etiology of PD remains poorly understood. Although both oxidative stress and neuroinflammation are identified as co-contributors in PD pathogenesis, signaling mechanisms underlying neurodegenerative processes have yet to be defined. Indeed, we recently identified that protein kinase C delta (PKCδ) activation is critical for induction of dopaminergic neuronal loss in response to neurotoxic stressors. However, it remains to be defined whether PKCδ activation contributes to immune signaling events driving microglial neurotoxicity. In the present study, we systematically investigated whether PKCδ contributes to the heightened microglial activation response following exposure to major proinflammatory stressors, including α-synuclein, tumor necrosis factor α (TNFα), and lipopolysaccharide (LPS). We report that exposure to the aforementioned inflammatory stressors dramatically upregulated PKCδ with a concomitant increase in its kinase activity and nuclear translocation in both BV-2 microglial cells and primary microglia. Importantly, we also observed a marked upregulation of PKCδ in the microglia of the ventral midbrain region of PD patients when compared to age-matched controls, suggesting a role for microglial PKCδ in neurodegenerative processes. Further, shRNA-mediated knockdown and genetic ablation of PKCδ in primary microglia blunted the microglial proinflammatory response elicited by the inflammogens, including ROS generation, nitric oxide production, and proinflammatory cytokine and chemokine release. Importantly, we found that PKCδ activated NFκB, a key mediator of inflammatory signaling events, after challenge with inflammatory stressors, and that transactivation of NFκB led to translocation of the p65 subunit to the nucleus, IκBα degradation and phosphorylation of p65 at Ser536. Furthermore, both genetic ablation and siRNA-mediated knockdown of PKCδ attenuated NFκB activation, suggesting that PKCδ regulates NFκB activation subsequent to microglial exposure to inflammatory stimuli. To further investigate the pivotal role of PKCδ in microglial activation in vivo, we utilized pre-clinical models of PD. We found that PKCδ deficiency attenuated the proinflammatory response in the mouse substantia nigra, reduced locomotor deficits and recovered mice from sickness behavior in an LPS-induced neuroinflammation model of PD. Likewise, we found that PKCδ knockout mice treated with MPTP displayed a dampened microglial inflammatory response. Moreover, PKCδ knockout mice exhibited reduced susceptibility to the neurotoxin-induced dopaminergic neurodegeneration and associated motor impairments. Taken together, our studies propose a pivotal role for PKCδ in PD pathology, whereby sustained PKCδ activation drives sustained microglial inflammatory responses and concomitant dopaminergic neurotoxicity consequently leading to neurobehavioral deficits. We conclude that inhibiting PKCδ activation may represent a novel therapeutic strategy in PD treatment.

Dexmedetomidine-Induced Contraction in the Isolated Endothelium-Denuded Rat Aorta Involves PKC-δ-mediated JNK Phosphorylation

Vasoconstriction mediated by the highly selective alpha-2 adrenoceptor agonist dexmedetomidine leads to transiently increased blood pressure and severe hypertension. The dexmedetomidine-induced contraction involves the protein kinase C (PKC)-mediated pathway. However, the main PKC isoform involved in the dexmedetomidine-induced contraction remains unknown. The goal of this in vitro study was to examine the specific PKC isoform that contributes to the dexmedetomidine-induced contraction in the isolated rat aorta. The endothelium-denuded rat aorta was suspended for isometric tension recording. Dexmedetomidine dose-response curves were generated in the presence or absence of the following inhibitors: the pan-PKC inhibitor, chelerythrine; the PKC-α and -β inhibitor, Go6976; the PKC-α inhibitor, safingol; the PKC-β inhibitor, ruboxistaurin; the PKC-δ inhibitor, rottlerin; the c-Jun NH2-terminal kinase (JNK) inhibitor, SP600125; and the myosin light chain kinase inhibitor, ML-7 hydrochloride. Western blot analysis was used to examine the effect of rottlerin on dexmedetomidine-induced PKC-δ expression and JNK phosphorylation in rat aortic vascular smooth muscle cells (VSMCs) and to investigate the effect of dexmedetomidine on PKC-δ expression in VSMCs transfected with PKC-δ small interfering RNA (siRNA) or control siRNA. Chelerythrine as well as SP600125 and ML-7 hydrochloride attenuated the dexmedetomidine-induced contraction. Go6976, safingol, and ruboxistaurin had no effect on the dexmedetomidine-induced contraction, whereas rottlerin inhibited the dexmedetomidine-induced contraction. Dexmedetomidine induced PKC-δ expression, whereas rottlerin and PKC-δ siRNA transfection inhibited dexmedetomidine-induced PKC-δ expression. Dexmedetomidine also induced JNK phosphorylation, which was inhibited by rottlerin. Taken together, these results suggest that the dexmedetomidine-induced contraction involves PKC-δ-dependent JNK phosphorylation in the isolated rat aorta.

ENaC activity and expression is decreased in the lungs of protein kinase C-α knockout mice

We used a PKC-α knockout model to investigate the regulation of alveolar epithelial Na(+) channels (ENaC) by PKC. Primary alveolar type II (ATII) cells were subjected to cell-attached patch clamp. In the absence of PKC-α, the open probability (Po) of ENaC was decreased by half compared with wild-type mice. The channel density (N) was also reduced in the knockout mice. Using in vivo biotinylation, membrane localization of all three ENaC subunits (α, β, and γ) was decreased in the PKC-α knockout lung, compared with the wild-type. Confocal microscopy of lung slices showed elevated levels of reactive oxygen species (ROS) in the lungs of the PKC-α knockout mice vs. the wild-type. High levels of ROS in the knockout lung can be explained by a decrease in both cytosolic and mitochondrial superoxide dismutase activity. Elevated levels of ROS in the knockout lung activates PKC-δ and leads to reduced dephosphorylation of ERK1/2 by MAP kinase phosphatase, which in turn causes increased internalization of ENaC via ubiquitination by the ubiquitin-ligase Nedd4-2. In addition, in the knockout lung, PKC-δ activates ERK, causing a decrease in ENaC density at the apical alveolar membrane. PKC-δ also phosphorylates MARCKS, leading to a decrease in ENaC Po. The effects of ROS and PKC-δ were confirmed with patch-clamp experiments on isolated ATII cells in which the ROS scavenger, Tempol, or a PKC-δ-specific inhibitor added to patches reversed the observed decrease in ENaC apical channel density and Po. These results explain the decrease in ENaC activity in PKC-α knockout lung.

Small GTPase and regulation of inflammation response in atherogenesis

Small GTPases are key signal transducers from extracellular stimuli to the nucleus that regulate a variety of cellular responses, including changes in gene expression and cell adhesion and migration. Accumulating data have demonstrated that abnormal activation of these small GTPases plays a critical role in the atherosclerosis characterized by vascular abnormalities, especially endothelial dysfunction and inflammation. Here, we discuss the linkage between small GTPases, inflammation, and atherogenesis. First, small GTPases affect gene expression of inflammatory cytokines through proinflammatory signaling pathways, such as nuclear factor-κB, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, interlukin-8, and monocyte chemoattractant protein-1. Then, these molecules regulate the vascular inflammation through cell adhesion and migration. In turn, small GTPases are also regulated by extracellular stimuli, such as L-selectin, thrombin, oxidized phospholipids, and interleukins. Thus, these inflammatory cytokines generate a vicious cycle for small GTPases and inflammatory responses in the atherogenesis.

Protein kinase C and its inhibitors in the regulation of inflammation: inducible nitric oxide synthase as an example

Protein kinase C (PKC) is a family of ten isoenzymes that play a crucial role in cellular signal transduction. Studies with PKC knockout animals have revealed that many of the isoenzymes are involved in cell growth, proliferation and differentiation. Several PKC isoenzymes have also been shown to be important mediators in inflammation and immunity, particularly in lymphocyte responses. However, less is known about the role of PKC in the regulation of the expression of inflammatory genes. In inflammatory processes, nitric oxide is primarily produced by inducible nitric oxide synthase (iNOS) in inflammatory cells, such as macrophages. In innate immunity, nitric oxide functions as an effector molecule towards the infectious organisms. Increased levels of nitric oxide are also produced by inflammatory and tissue cells in inflammatory diseases, such as asthma and arthritis. In this MiniReview, the role of PKC isoenzymes in the pathogenesis and as a potential drug target in inflammation will be discussed presenting iNOS as an example of an inflammatory gene regulated by the pleiotropic PKC signalling pathway.

NADPH oxidase 4 is required for interleukin-1β-mediated activation of protein kinase Cδ and downstream activation of c-jun N-terminal kinase signaling in smooth muscle

Reactive oxygen species (ROS) are generated in the vascular wall upon stimulation by proinflammatory cytokines and are important mediators of diverse cellular responses that occur as a result of vascular injury. Members of the NADPH oxidase (NOX) family of proteins have been identified in vascular smooth muscle (VSM) cells as important sources of ROS. In this study, we tested the hypothesis that NOX4 is a proximal mediator of IL-1β-dependent activation of PKCδ and increases IL-1β-stimulated c-Jun kinase (JNK) signaling in primary rat aortic VSM cells. We found that stimulation of VSM cells with IL-1β increased PKCδ activity and intracellular ROS generation. SiRNA silencing of NOX4 but not NOX1 ablated the IL-1β-dependent increase in ROS production. Pharmacological inhibition of PKCδ activity as well as siRNA depletion of PKCδ or NOX4 blocked the IL-1β-dependent activation of JNK. Further studies showed that the IL-1β-dependent upregulation of inducible NO synthase expression was inhibited through JNK inhibition and NOX4 silencing. Taken together, these results indicate that IL-1β-dependent activation of PKCδ is modulated by NOX4-derived ROS. Our study positions PKCδ as an important redox-sensitive mediator of IL-1β-dependent signaling and downstream activation of inflammatory mediators in VSM cells.

MEKK1-MKK4-JNK-AP1 pathway negatively regulates Rgs4 expression in colonic smooth muscle cells

BACKGROUND

Regulator of G-protein Signaling 4 (RGS4) plays an important role in regulating smooth muscle contraction, cardiac development, neural plasticity and psychiatric disorder. However, the underlying regulatory mechanisms remain elusive. Our recent studies have shown that upregulation of Rgs4 by interleukin (IL)-1β is mediated by the activation of NFκB signaling and modulated by extracellular signal-regulated kinases, p38 mitogen-activated protein kinase, and phosphoinositide-3 kinase. Here we investigate the effect of the c-Jun N-terminal kinase (JNK) pathway on Rgs4 expression in rabbit colonic smooth muscle cells.

METHODOLOGY/PRINCIPAL FINDINGS

Cultured cells at first passage were treated with or without IL-1β (10 ng/ml) in the presence or absence of the selective JNK inhibitor (SP600125) or JNK small hairpin RNA (shRNA). The expression levels of Rgs4 mRNA and protein were determined by real-time RT-PCR and Western blot respectively. SP600125 or JNK shRNA increased Rgs4 expression in the absence or presence of IL-1β stimulation. Overexpression of MEKK1, the key upstream kinase of JNK, inhibited Rgs4 expression, which was reversed by co-expression of JNK shRNA or dominant-negative mutants for MKK4 or JNK. Both constitutive and inducible upregulation of Rgs4 expression by SP600125 was significantly inhibited by pretreatment with the transcription inhibitor, actinomycin D. Dual reporter assay showed that pretreatment with SP600125 sensitized the promoter activity of Rgs4 in response to IL-1β. Mutation of the AP1-binding site within Rgs4 promoter increased the promoter activity. Western blot analysis confirmed that IL-1β treatment increased the phosphorylation of JNK, ATF-2 and c-Jun. Gel shift and chromatin immunoprecipitation assays validated that IL-1β increased the in vitro and ex vivo binding activities of AP1 within rabbit Rgs4 promoter.

CONCLUSION/SIGNIFICANCE

Activation of MEKK1-MKK4-JNK-AP1 signal pathway plays a tonic inhibitory role in regulating Rgs4 transcription in rabbit colonic smooth muscle cells. This negative regulation may aid in maintaining the transient level of RGS4 expression.

Protein kinase C δ (PKCδ)-extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascade regulates glycogen synthase kinase-3 (GSK-3) inhibition-mediated interleukin-10 (IL-10) expression in lipopolysaccharide (LPS)-induced endotoxemia

Glycogen synthase kinase-3 (GSK-3) modulates a wide array of cellular processes, including embryonic development, cell differentiation, survival, and apoptosis. Recently, it was reported that a GSK-3 inhibitor attenuates lipopolysaccharide (LPS)-induced septic shock and regulates the mortality of endotoxemic mice. However, the detailed mechanism of reduced mortality via GSK-3 inhibition is not well defined. Herein, we showed that GSK-3 inhibition induces extracellular signal-regulated kinase 1/2 (ERK1/2) activation under LPS-stressed conditions via protein kinase C δ (PKCδ) activation. Furthermore, PKCδ-induced ERK1/2 activation by the inhibition of GSK-3 provoked the production of interleukin (IL)-10, playing a crucial role in regulating endotoxemia. Using a mitogen-activated protein kinase kinase-1 (MEK-1) and PKCδ inhibitor, we confirmed that GSK-3 inhibition induces PKCδ and subsequent ERK1/2 activation, resulting in increased IL-10 expression under LPS-treated conditions. We verified that septic shock caused by LPS is attenuated by GSK-3 inhibition using a GSK-3 inhibitor. This relieved endotoxemia induced by GSK-3 inhibition was restored in an ERK1/2-dependent manner. Taken together, IL-10 expression produced by GSK-3 inhibition-induced ERK1/2 activation via PKCδ relieved LPS-mediated endotoxemia. This finding suggests that IL-10 hyperexpression resulting from GSK-3 inhibition-induced ERK activation could be a new therapeutic pathway for endotoxemia.

Rottlerin increases cardiac contractile performance and coronary perfusion through BKCa++ channel activation after cold cardioplegic arrest in isolated hearts

BACKGROUND

Cardioplegia and cardiopulmonary bypass (CP/CPB) subjects myocardium to complex injurious stimuli that can result in cardiomyocyte and vascular contractile abnormalities. Rottlerin, originally identified as a delta-protein kinase C inhibitor, has a number of known additional effects that may be beneficial in the setting of CP/CPB. We tested the hypothesis that rottlerin mitigates deleterious effects associated with CP/CPB.

METHODS AND RESULTS

Langendorff-perfused isolated rat hearts were subjected to 2 hours intermittent cold (10°C) CP (St Thomas II) followed by 30 minutes normothermic reperfusion. CP was delivered every 30 minutes for 1 minute. Hearts were treated with rottlerin 1 μmol/L (CP+R) (n=7) or without rottlerin (CP) (n=9), and the BK(Ca++) channel inhibitor paxilline 100 nmol/L was supplied in the CP. Hearts constantly perfused with KHB served as controls (n=6). Baseline parameters of cardiac function were similar between groups. CP resulted in reduced cardiac function (left ventricular diastolic pressure, 39 ± 3.8%; ± dP/dt, 32 ± 4.4%, -41 ± 5.1% decrease compared to baseline). Treatment with rottlerin 1 μmol/L significantly improved CP-induced cardiac function (left ventricular diastolic pressure, 20 ± 5.9%; ± dP/dt, 5.2 ± 4.5%, -11.6 ± 4.7% decrease versus baseline; P<0.05 CP+R versus CP). Rottlerin also caused a significant increase in coronary flow postreperfusion (CP, 34 ± 4.2% decrease from baseline; CP+R, 26 ± 9.6% increase over baseline; P=0.01). Independent of vascular effects, CP significantly decreased isolated myocyte contraction, which was restored by rottlerin treatment. The BK(Ca++) channel inhibitor greatly reduced the majority of beneficial effects associated with rottlerin.

CONCLUSIONS

Rottlerin significantly improves cardiac performance after CP arrest through improved cardiomyocyte contraction and coronary perfusion.

Vascular plasticity in cerebrovascular disorders

Cerebral ischemia remains a major cause of morbidity and mortality with little advancement in subacute treatment options. This review aims to cover and discuss novel insight obtained during the last decade into plastic changes in the vasoconstrictor receptor profiles of cerebral arteries and microvessels that takes place after different types of stroke. Receptors like the endothelin type B, angiotensin type 1, and 5-hydroxytryptamine type 1B/1D receptors are upregulated in the smooth muscle layer of cerebral arteries after different types of ischemic stroke as well as after subarachnoid hemorrhage, yielding rather dramatic changes in the contractility of the vessels. Some of the signal transduction processes mediating this receptor upregulation have been elucidated. In particular the extracellular regulated kinase 1/2 pathway, which is activated early in the process, has proven to be a promising therapeutic target for prevention of vasoconstrictor receptor upregulation after stroke. Together, those findings provide new perspectives on the pathophysiology of ischemic stroke and point toward a novel way of reducing vasoconstriction, neuronal cell death, and thus neurologic deficits after stroke.

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.

Akt-mediated signaling is induced by cytokines and cyclic adenosine monophosphate and suppresses hepatocyte inducible nitric oxide synthase expression independent of MAPK P44/42

Cyclic AMP inhibits the expression of nitric oxide synthase (Harbrecht et al., 1995 [1]) in hepatocytes but the mechanism for this effect is incompletely understood. Cyclic AMP can activate several intracellular signaling pathways in hepatocytes including Protein Kinase A (PKA), cAMP regulated guanine nucleotide exchange factors (cAMP-GEFs), and calcium-mediated Protein Kinases. There is considerable overlap and cross-talk between many of these signaling pathways, however, and how these cascades regulate hepatocyte iNOS is not known. We hypothesized that Akt mediates the effect of cAMP on hepatocyte iNOS expression. Hepatocytes cultured with cytokines and dbcAMP increased Akt phosphorylation up to 2h of culture. Akt phosphorylation was inhibited by the PI3K inhibitor LY294002 (10μM), farnyltranferase inhibitor FTI-276, or transfection with a dominant negative Akt. The cyclic AMP-induced suppression of cytokine-stimulated iNOS was partially reversed by LY294002 and FTI-276. LY294002 also increased NFκB nucleus translocation by Western blot analysis in nuclear extracts. Cyclic AMP increased phosphorylation of Raf1 at serine 259 which was blocked by LY294002 and associated with decreased MAPK P44/42 phosphorylation. However, inhibition of MAPK P44/42 signaling with PD98059 failed to suppress cytokine-induced hepatocyte iNOS expression and did not enhance the inhibitory effect of dbcAMP on iNOS production. A constitutively active MAPK P44/42 plasmid had no effect on cytokine-stimulated NO production. These data demonstrate that dbcAMP regulates hepatocyte iNOS expression through an Akt-mediated signaling mechanism that is independent of MAPK P44/42.

A phosphoinositide 3-kinase-gamma inhibitor, AS605240 prevents bleomycin-induced pulmonary fibrosis in rats

Phosphoinositide 3-kinase-gamma (PI3Kgamma) has been identified to play the critical roles in inflammatory cells activation and recruitment in multiply inflammatory diseases and it promised to be a prospective target for relevant inflammatory diseases therapy. AS605240, a selective PI3Kgamma inhibitor, has been proved effective on several inflammatory diseases. In this study, we investigated the protective effect of AS605240 on bleomycin-induced pulmonary fibrosis in rats. Our results showed that orally administration of AS605240 significantly prevented lung inflammation and reduced collagen deposition. AS605240 also inhibited augmented expression of TNF-alpha and IL-1beta induced by bleomycin instillation. Moreover, the mRNA levels of TNF-alpha and IL-1beta in lung were remarkably suppressed. Histological assessment found that AS605240 reduced the expression of TGF-beta(1) and prevented T lymphocytes infiltration to lung. Phospho-Akt level in inflammatory cells by blocking PI3Kgamma was down-regulated and the inhibition of Akt phosphorylation was further confirmed by Western blot. Our findings illustrated that AS605240 was effective for preventing pulmonary fibrosis by suppressing inflammatory cells recruitment and production of inflammatory cytokines. These findings also suggest that PI3Kgamma may be a useful target in treating inflammation diseases and AS605240 may represent a promising novel agent for the future therapy of pulmonary fibrosis.

Raf-1 kinase regulates smooth muscle contraction in the rat mesenteric arteries

We investigated the potential role of Raf-1 kinase in mesenteric arterial contraction. Inhibitors of Raf-1 kinase, GW5074, L779450 and ZM 336372 reversed phenylephrine (PE)-induced mesenteric vascular contraction. Studies in vivo in rats showed that GW5074 inhibited PE-induced increase in mean arterial pressure in adult female Sprague-Dawley rats. Isometric tension studies in mesenteric arteries of rats showed that GW5074 did not change the KCl-evoked contraction but significantly inhibited the contractions to PE, 5-HT, U46619, endothelin 1, angiotensin II and phorbol 12, 13-dibutyrate (PDBu). In mesenteric vascular smooth muscle cells (VSMCs), PE stimulated increase in Raf-1 phosphorylation which was inhibited by GW5074. Measurement of [Ca(2+)](i) with Fura-2 showed that GW5074-mediated inhibition of PE-induced contraction was not associated with decreases in [Ca(2+)](i). VSMCs treated with PE exhibited higher levels of the contractile proteins, p-MYPT1 and p-MLC(20), which was inhibited by GW5074. Similarly, PDBu induced increases in phosphorylation of Raf-1, MLC(20) and MYPT1 and this was inhibited by GW5074. However, GW5074 did not have any significant effect on PE/PDBu-induced MEK/ERK activation. The results indicate that Raf-1 kinase plays an important role in the regulation of vascular contractility through regulation of calcium sensitization.

Protease-activated receptor-2 stimulates intestinal epithelial chloride transport through activation of PLC and selective PKC isoforms

Serine proteases play important physiological roles through their activity at G protein-coupled protease-activated receptors (PARs). We examined the roles that specific phospholipase (PL) C and protein kinase (PK) C (PKC) isoforms play in the regulation of PAR(2)-stimulated chloride secretion in intestinal epithelial cells. Confluent SCBN epithelial monolayers were grown on Snapwell supports and mounted in modified Ussing chambers. Short-circuit current (I(sc)) responses to basolateral application of the selective PAR(2) activating peptide, SLIGRL-NH(2), were monitored as a measure of net electrogenic ion transport caused by PAR(2) activation. SLIGRL-NH(2) induced a transient I(sc) response that was significantly reduced by inhibitors of PLC (U73122), phosphoinositol-PLC (ET-18), phosphatidylcholine-PLC (D609), and phosphatidylinositol 3-kinase (PI3K; LY294002). Immunoblot analysis revealed the phosphorylation of both PLCbeta and PLCgamma following PAR(2) activation. Pretreatment of the cells with inhibitors of PKC (GF 109203X), PKCalpha/betaI (Gö6976), and PKCdelta (rottlerin), but not PKCzeta (selective pseudosubstrate inhibitor), also attenuated this response. Cellular fractionation and immunoblot analysis, as well as confocal immunocytochemistry, revealed increases of PKCbetaI, PKCdelta, and PKCepsilon, but not PKCalpha or PKCzeta, in membrane fractions following PAR(2) activation. Pretreatment of the cells with U73122, ET-18, or D609 inhibited PKC activation. Inhibition of PI3K activity only prevented PKCdelta translocation. Immunoblots revealed that PAR(2) activation induced phosphorylation of both cRaf and ERK1/2 via PKCdelta. Inhibition of PKCbetaI and PI3K had only a partial effect on this response. We conclude that basolateral PAR(2)-induced chloride secretion involves activation of PKCbetaI and PKCdelta via a PLC-dependent mechanism resulting in the stimulation of cRaf and ERK1/2 signaling.

Bee venom suppresses LPS-mediated NO/iNOS induction through inhibition of PKC-alpha expression

ETHNOPHARMACOLOGICAL RELEVANCE

Bee venom (BV) is a traditional Korean medicine that has been widely used with satisfactory results in the treatment of some immune-related diseases, especially rheumatoid arthritis.

AIM OF THE STUDY

The purpose of this study is to elucidate the molecular mechanism underlying the anti-inflammatory effects of BV, which is used in the treatment of various inflammatory diseases in traditional Korean medicine. We evaluated the anti-inflammatory effect of BV on NO generation and iNOS expression by LPS in rat C6 glioma cells.

MATERIAL AND METHODS

BV was obtained from the National Institute of Agricultural Science and Technology (NIAST) of Korea. Nitrite measurement, Immuno blot analysis, Reverse transcriptase-PCR and Electrophoretic mobility shift assay (EMSA) were used for assessment.

RESULTS

BV suppressed the LPS-induced NO generation and iNOS expression, and it also inhibited the expressions of LPS-induced pro-inflammatory molecules including Cox-2 and IL-1 beta in rat C6 glioma cells. Then, BV inhibited LPS-induced expression of PKC-alpha and MEK/ERK, not p38 and JNK. Moreover, inhibition of LPS-induced iNOS expression by BV was dependent on transcriptional activities of AP-1/NF-kappaB through MEK/ERK pathway.

CONCLUSION

These results indicate that BV suppresses LPS-induced iNOS activation through regulation of PKC-alpha. Accordingly, BV exerts a potent suppressive effect on pro-inflammatory responses in rat C6 glioma cells.

Upregulation of RGS4 expression by IL-1beta in colonic smooth muscle is enhanced by ERK1/2 and p38 MAPK and inhibited by the PI3K/Akt/GSK3beta pathway

Initial Ca(2+)-dependent contraction of intestinal smooth muscle is inhibited upon IL-1beta treatment. The decrease in contraction reflects the upregulation of regulator of G protein signaling-4 (RGS4) via the canonical inhibitor of NF-kappaB kinase-2 (IKK2)/IkappaB-alpha/NF-kappaB pathway. Here, we show that the activation of various protein kinases, including ERK1/2, p38 MAPK, and phosphoinositide 3-kinase (PI3K), differentially modulates IL-1beta-induced upregulation of RGS4 in rabbit colonic muscle cells. IL-1beta treatment caused a transient phosphorylation of ERK1/2 and p38 MAPK. It also caused the phosphorylation of Akt and glycogen synthase kinase-3beta (GSK3beta), sequential downstream effectors of PI3K. Pretreatment with PD-98059 (an ERK inhibitor) and SB-203580 (a p38 MAPK inhibitor) significantly inhibited IL-1beta-induced RGS4 expression. In contrast, LY-294002 (a PI3K inhibitor) augmented, whereas GSK3beta inhibitors inhibited, IL-1beta-induced RGS4 expression. PD-98059 blocked IL-1beta-induced phosphorylation of IKK2, degradation of IkappaB-alpha, and phosphorylation and nuclear translocation of NF-kappaB subunit p65, whereas SB-203580 had a marginal effect, implying that the effect of ERK1/2 is exerted on the canonical IKK2/IkappaB-alpha/p65 pathway of NF-kappaB activation but that the effect of p38 MAPK may not predominantly involve NF-kappaB signaling. The increase in RGS4 expression enhanced by LY-294002 was accompanied by an increase in the phosphorylation of IKK2/IkappaB-alpha/p65 and blocked by pretreatment with inhibitors of IKK2 (IKK2-IV) and IkappaB-alpha (MG-132). Inhibition of GSK3beta abolished IL-1beta-induced phosphorylation of IKK2/p65. These findings suggest that ERK1/2 and p38 MAPK enhance IL-1beta-induced upregulation of RGS4; the effect of ERK1/2 reflects its ability to promote IKK2 phosphorylation and increase NF-kappaB activity. GSK3beta acts normally to augment the activation of the canonical NF-kappaB signaling. The PI3K/Akt/GSK3beta pathway attenuates IL-1beta-induced upregulation of RGS4 expression by inhibiting NF-kappaB activation.

Role of protein kinase C β2 activation in TNF-α-induced human vascular endothelial cell apoptosis

The circulatory inflammatory cytokine tumor necrosis factor alpha (TNF-α) is increased in pathologic conditions that initiate or exacerbate vascular endothelial injury, such as diabetes. Protein kinase C (PKC) has been shown to play a critical role in TNF-α-induced human endothelial cell apoptosis. However, the relative roles played by specific isoforms of PKC in TNF-α-induced human endothelial cell apoptosis have not been addressed. We investigated the effects of a selective PKCβ2 inhibitor (CGP53353) on TNF-α-induced apoptosis in human vascular endothelial cells (cell line ECV304) and on the production of reactive oxygen species and nitric oxide, and compared its effects with rottlerin, a reagent that has been shown to reduce PKCδ protein levels. Cultured human vascular endothelial cells (ECV304) were treated for 24 h with one of 4 regimes: 40 ng/mL TNF-α alone (TNF-α), TNF-α with 10 µmol/L rottlerin (T+rottlerin), TNF-α with 1 µmol/L CGP53353 (T+CGP), or untreated (control). Cell viability was measured by MTT assay, and cell apoptosis was assessed by flow cytometry. TNF-α-induced endothelial cell apoptosis was associated with dramatic increases in production of intracellular hydrogen peroxide (approximately 20 times greater than control) and superoxide (approximately 16 times greater than control), as measured by dichlorofluorescein and dihydroethidium fluorescent staining, respectively. This increase was accompanied by reduced activity of superoxide dismutase and glutathione peroxidase and, subsequently, an increase in the lipid peroxidation product malondialdehyde. CGP53353, but not rottlerin, abolished or attenuated all these changes. We conclude that PKCβ2 plays a major role in TNF-α-induced human vascular endothelial cell apoptosis.

Epigallocatechin-3-gallate augments antioxidant activities and inhibits inflammation during bleomycin-induced experimental pulmonary fibrosis through Nrf2-Keap1 signaling

The mechanism involved in the enhancement of antioxidant activities and resolved inflammation after epigallocatechin-3-gallate (EGCG) treatment during bleomycin-induced pulmonary fibrosis is investigated in this study. The levels of reactive-oxygen species (ROS), lipid peroxidation (LPO), hydroxyproline and the activity of myeloperoxidase (MPO) were increased due to bleomycin challenge and were brought back to near normal status on EGCG supplementation. The decreased antioxidant status due to bleomycin challenge was also restored upon EGCG treatment. Bleomycin-induced rats showed increased cell counts as compared to control and EGCG-treated rats. Histopathological analysis showed increased inflammation and alveolar damage, while picrosirius red staining showed an increased collagen deposition in bleomycin-challenged rats that were decreased upon EGCG treatment. Immunohistochemical, immunofluorescent and immunoblot studies revealed that EGCG supplementation decreased the levels of nuclear factor-kappaB (NF-kappaB), tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), which were increased upon bleomycin induction. The declined activities of Phase II enzymes such as glutathione-S-transferase (GST) and NAD(P)H:quinone oxidoreductase 1 (NQO1) in bleomycin-injured rats were restored upon EGCG treatment. Confocal microscopy, immunoblot and RT-PCR studies confirm that EGCG is a potent inducer of NF-E2-related factor 2 (Nrf2). Expression of Kelch like ECH-associated protein (Keap)-1, a vital factor in Nrf2 signaling cascade was analyzed by immunoblotting. However, there was no significant change in the expression of Keap1 in control and experimental groups. This study demonstrates the involvement of Nrf2-Keap1 signaling through which EGCG enhances antioxidant activities and Phase II enzymes with subsequent restraint inflammation during bleomycin-induced pulmonary fibrosis.

Activating deltaPKC antagonizes the protective effect of ERK1/2 inhibition against stroke in rats

Two pathways that have been shown to mediate cerebral ischemic damage are the MEK/ERK cascade and the pro-apoptotic deltaPKC pathway. We investigated the relationship between these pathways in a rat model of focal ischemia by observing and modifying the activation state of each pathway. The ERK1/2 inhibitor, U0126, injected at ischemia onset, attenuated the increase in phosphorylated ERK1/2 (P-ERK1/2) after reperfusion. The deltaPKC inhibitor, deltaV1-1, delivered at reperfusion, did not significantly change P-ERK1/2 levels. In contrast, the deltaPKC activator, psi deltaRACK, injected at reperfusion, reduced ERK1/2 phosphorylation measured 4 h after reperfusion. Additionally, U0126 pretreatment at ischemia onset reduced infarct size compared with vehicle, but U0126 injected at the onset of reperfusion had no protection. Finally, combination of U0126 injection at ischemia onset plus deltaV1-1 injection at reperfusion further reduced infarct size, while combination of U0126 delivered at ischemia onset with psi deltaRACK injected at reperfusion increased infarct size compared with U0126 alone. In conclusion, we find that inhibiting both the MEK/ERK and the deltaPKC pathways offers greater protection than either alone, indicating they likely act independently.

Exogenous corticosterone reduces L-DOPA-induced dyskinesia in the hemi-parkinsonian rat: role for interleukin-1beta

While the etiology of Parkinson's disease (PD) remains unknown, there is overwhelming evidence that neuroinflammation plays a critical role in the progressive loss of dopamine (DA) neurons. Because nearly all persons suffering from PD receive l-DOPA, it is surprising that inflammation has not been examined as a potential contributor to the abnormal involuntary movements (AIMs) that occur as a consequence of chronic l-DOPA treatment. As an initial test of this hypothesis, we examined the effects of exogenously administered corticosterone (CORT), an endogenous anti-inflammatory agent, on the expression and development of l-DOPA-induced dyskinesia (LID) in unilateral DA-depleted rats. To do this, male Sprague-Dawley rats received unilateral medial forebrain bundle 6-hydroxydopamine lesions. Three weeks later, l-DOPA primed rats received acute injections of CORT (0-3.75 mg/kg) prior to l-DOPA to assess the expression of LID. A second group of rats was used to examine the development of LID in l-DOPA naïve rats co-treated with CORT and l-DOPA for 2 weeks. AIMs and rotations were recorded. Exogenous CORT dose-dependently attenuated both the expression and development of AIMs without affecting rotations. Real-time reverse-transcription polymerase chain reaction of striatal tissue implicated a role for interleukin-1 (IL-1) beta in these effects as its expression was increased on the lesioned side in rats treated with l-DOPA (within the DA-depleted striatum) and attenuated with CORT. In the final experiment, interleukin-1 receptor antagonist (IL-1ra) was microinjected into the striatum of l-DOPA-primed rats to assess the impact of IL-1 signaling on LID. Intrastriatal IL-1ra reduced the expression of LID without affecting rotations. These findings indicate a novel role for neuroinflammation in the expression of LID, and may implicate the use of anti-inflammatory agents as a potential adjunctive therapy for the treatment of LID.

Regulation of smooth muscle by inducible nitric oxide synthase and NADPH oxidase in vascular proliferative diseases

Inflammation plays a critical role in promoting smooth muscle migration and proliferation during vascular diseases such as postangioplasty restenosis and atherosclerosis. Another common feature of many vascular diseases is the contribution of reactive oxygen (ROS) and reactive nitrogen (RNS) species to vascular injury. Primary sources of ROS and RNS in smooth muscle are several isoforms of NADPH oxidase (Nox) and the cytokine-regulated inducible nitric oxide (NO) synthase (iNOS). One important example of the interaction between NO and ROS is the reaction of NO with superoxide to yield peroxynitrite, which may contribute to the pathogenesis of hypertension. In this review, we discuss the literature that supports an alternate possibility: Nox-derived ROS modulate NO bioavailability by altering the expression of iNOS. We highlight data showing coexpression of iNOS and Nox in vascular smooth muscle demonstrating the functional consequences of iNOS and Nox during vascular injury. We describe the relevant literature demonstrating that the mitogen-activated protein kinases are important modulators of proinflammatory cytokine-dependent expression of iNOS. A central hypothesis discussed is that ROS-dependent regulation of the serine/threonine kinase protein kinase Cdelta is essential to understanding how Nox may regulate signaling pathways leading to iNOS expression. Overall, the integration of nonphagocytic NADPH oxidase with cytokine signaling in general and in vascular smooth muscle in particular is poorly understood and merits further investigation.

Epigallocatechin-3-gallate inhibits interleukin-1beta-induced MUC5AC gene expression and MUC5AC secretion in normal human nasal epithelial cells

It has been reported that the proinflammatory cytokine interleukin-1beta (IL-1beta) induces mucus hypersecretion in normal human nasal epithelial (NHNE) cells and that the MAP kinase pathway may be an important signal pathway in IL-1beta-induced MUC5AC gene expression. Green tea (Camellia sinensis) polyphenols are potent anti-inflammatory agents and have been shown to inhibit inflammation in tumor cell lines and cultured respiratory epithelial cells. In this study, we examined the effect of (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol, on IL-1beta-induced MUC5AC gene expression and secretion in NHNE cells. After cells had been treated with IL-1beta (10 ng/ml) and pretreated with EGCG (10, 50 and 100 microM), mRNA expression of MUC5AC was determined by real-time polymerase chain reaction. The suppression of each signal pathway protein was determined by Western blot analysis after treatment with IL-1beta and EGCG, respectively. IL-1beta increased MUC5AC gene expression and MUC5AC secretion. EGCG markedly suppressed IL-1beta-induced MUC5AC gene expression and MUC5AC secretion via suppression of the phosphorylation of ERK MAP kinase, MSK1, and transcription factor, cAMP response element-binding protein. IL-1beta increased the number of cells staining positive with MUC5AC antibodies, and EGCG treatment decreased this number. Our data suggest that EGCG may be an effective inhibitor of IL-1beta-induced mucus hypersecretion.

Src suppressed C kinase substrate regulates the lipopolysaccharide-induced TNF-α biosynthesis in rat astrocytes

The protein kinase C (PKC) is known to be a critical component in the signaling cascades that lead to astrocyte-activation. To further understand the mechanism of PKC signaling in astrocyte-activation, we investigated the effect of SSeCKS, a PKC substrate, on LPS-induced cytokine expression in astrocytes by RT-PCR and enzyme-linked immunosorbent assay. Exposure of the cells to LPS induced rapid translocation of SSeCKS to the perinuclear sides, ERK activation and pronounced TNF-alpha production, which can be inhibited by the PKC inhibitor Gö6983. By using siRNA knockdown of SSeCKS expression, LPS-induced signaling events were partly inhibited, including ERK activation, inducible TNF-alpha biosynthesis and secretion. These results suggest that SSeCKS is involved in the LPS-induced TNF-alpha expression in astrocytes mediated by PKC.

Reactive oxygen species, cell growth, cell cycle progression and vascular remodeling in hypertension

Reactive oxygen species (ROS) include superoxide, hygrogen peroxide and hydroxyl radical. Under physiological conditions, all vascular cell types produce ROS in a controlled and regulated fashion, mainly through nonphagocyte NADPH oxidase. An imbalance between pro-oxidants and antioxidants results in oxidative stress. ROS are important intracellular signaling molecules. There is growing evidence that increased oxidative stress and associated oxidative damage are mediators of vascular injury in hypertension, as well as in other cardiovascular diseases. Oxidative stress causes vascular injury by reducing nitric oxide bioavailability, altering endothelial function and vascular contraction/dilation, promoting vascular smooth muscle cell proliferation and hypertrophy, and increasing extracellular matrix deposition and inflammation. The present review focuses on the regulatory role of ROS on cell growth and cell cycle progression and discusses implications of these events in vascular remodeling in hypertension.