Thrombin induces nitric-oxide synthase via Galpha12/13-coupled protein kinase C-dependent I-kappaBalpha phosphorylation and JNK-mediated I-kappaBalpha degradation

GPCR-Gα13 Involvement in Mitochondrial Function, Oxidative Stress, and Prostate Cancer

Gα13 and Gα12, encoded by the GNA13 and GNA12 genes, respectively, are members of the G12 family of Gα proteins that, along with their associated Gβγ subunits, mediate signaling from specific G protein-coupled receptors (GPCRs). Advanced prostate cancers have increased expression of GPCRs such as CXC Motif Chemokine Receptor 4 (CXCR4), lysophosphatidic acid receptor (LPAR), and protease activated receptor 1 (PAR-1). These GPCRs signal through either the G12 family, or through Gα13 exclusively, often in addition to other G proteins. The effect of Gα13 can be distinct from that of Gα12, and the role of Gα13 in prostate cancer initiation and progression is largely unexplored. The oncogenic effect of Gα13 on cell migration and invasion in prostate cancer has been characterized, but little is known about other biological processes such as mitochondrial function and oxidative stress. Current knowledge on the link between Gα13 and oxidative stress is based on animal studies in which GPCR-Gα13 signaling decreased superoxide levels, and the overexpression of constitutively active Gα13 promoted antioxidant gene activation. In human samples, mitochondrial superoxide dismutase 2 (SOD2) correlates with prostate cancer risk and prognostic Gleason grade. However, overexpression of SOD2 in prostate cancer cells yielded conflicting results on cell growth and survival under basal versus oxidative stress conditions. Hence, it is necessary to explore the effect of Gα13 on prostate cancer tumorigenesis, as well as the effect of Gα13 on SOD2 in prostate cancer cell growth under oxidative stress conditions.

Gα12 and endoplasmic reticulum stress-mediated pyroptosis in a single cycle of dextran sulfate-induced mouse colitis

Inflammatory bowel disease (IBD) pathogenesis involves complex inflammatory events and cell death. Although IBD involves mainly necrosis in the digestive tract, pyroptosis has also been recognized. Nonetheless, the underlying basis is elusive. Gα12/13 overexpression may affect endoplasmic reticulum (ER) stress. This study examined how Gα12/13 and ER stress affect pyroptosis using dextran sulfate sodium (DSS)-induced colitis models. Gα12/13 levels were increased in the distal and proximal colons of mice exposed to a single cycle of DSS, as accompanied by increases of IRE1α, ATF6, and p-PERK. Moreover, Il-6, Il-1β, Ym1, and Arg1 mRNA levels were increased with caspase-1 and IL-1β activation, supportive of pyroptosis. In the distal colon, RIPK1/3 levels were enhanced to a greater degree, confirming necroptosis. By contrast, the mice subjected to three cycles of DSS treatments showed decreases of Gα12/13, as accompanied by IRE1α and ATF6 suppression, but increases of RIPK1/3 and c-Cas3. AZ2 treatment, which inhibited Gα12, has an anti-pyroptotic effect against a single cycle of colitis. These results show that a single cycle of DSS-induced colitis may cause ER stress-induced pyroptosis as mediated by Gα12 overexpression in addition to necroptosis, but three cycles model induces only necroptosis, and that AZ2 may have an anti-pyroptotic effect.

Effects of toxicants on endoplasmic reticulum stress and hepatic cell fate determination

Toxicant-induced injury is a significant global health issue. However, the mechanisms through which toxicants such as carbon tetrachloride, acetaminophen, dimethylformamide, cocaine, and morphine induce the death of multiple cell types and contribute to liver toxicity are highly complex. This phenomenon involves intricate signaling pathways in association with oxidative stress, inflammation, and activation of death receptors, which are closely linked to endoplasmic reticulum (ER) stress. ER stress initially triggers the unfolded protein response, which either promotes cell survival or causes cell death at later times, depending on the severity and duration of the stress. Thus, comprehending the molecular basis governing cell fate determination in the context of ER stress may provide key insights into the prevention and treatment of toxicant-induced injury. This review summarizes our current understanding of agents that trigger different forms of ER stress-mediated cell death, necroptosis, ferroptosis, pyroptosis, and apoptosis, and covers the underlying molecular basis of toxicant-induced ER stress, as well as potential target molecules.

PAR-1 signaling on macrophages is required for effective in vivo delayed-type hypersensitivity responses

Delayed-type hypersensitivity (DTH) responses underpin chronic inflammation. Using a model of oxazolone-induced dermatitis and a combination of transgenic mice, adoptive cell transfer, and selective agonists/antagonists against protease activated receptors, we show that that PAR-1 signaling on macrophages by thrombin is required for effective granuloma formation. Using BM-derived macrophages (BMMs) in vitro, we show that thrombin signaling induced (a) downregulation of cell membrane reverse cholesterol transporter ABCA1 and (b) increased expression of IFNγ receptor and enhanced co-localization within increased areas of cholesterol-rich membrane microdomains. These two key phenotypic changes combined to make thrombin-primed BMMs sensitive to M1 polarization by 1000-fold less IFNγ, compared to resting BMMs. We confirm that changes in ABCA1 expression were directly responsible for the exquisite sensitivity to IFNγ in vitro and for the impact on granuloma formation in vivo. These data indicate that PAR-1 signaling plays a hitherto unrecognized and critical role in DTH responses.

Effects of Long-term Thrombin Inhibition (Dabigatran Etexilate) on Spontaneous Thrombolytic Activity during the Progression of Atherosclerosis in ApoE-/--LDLR-/- Double-Knockout Mice

Background and Objectives

Atherosclerosis is characterized by a hypercoagulable state, during which coagulation and fibrinolytic factors are activated simultaneously. However, details regarding the thrombolytic pathway in this context remain unknown. Here we investigated how direct long-term inhibition of thrombin influenced spontaneous thrombolytic activity during atherosclerotic progression in apolipoprotein E (ApoE)^–/^––low density lipoprotein receptor (LDLR)^–/^– double-knockout mice.

Methods

All mice received either standard chow (placebo group) or dabigatran-containing chow for 22 weeks, after which we evaluated them. The amount of atherosclerosis was estimated as the ratio of the atherosclerotic area to the total aortic intimal area. In addition, we used immunohistochemistry to analyze the expression of tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1), thrombin activatable fibrinolysis inhibitor (TAFI), and endothelial nitric oxide synthase (eNOS) in atherosclerotic regions. To evaluate thrombolysis, we used a He–Ne laser to induce thrombosis in vessels of the cremaster muscle and then measured the thrombus volume over time.

Results

The atherosclerotic area was smaller and thrombolytic activity greater in the dabigatran-treated group than in the placebo group. Furthermore, according to the thrombolysis model, spontaneous thrombolytic activity was increased in the dabigatran-treated mice compared with the placebo mice. In support of these results, immunohistochemistry demonstrated decreased expression of PAI-1 and TAFI but increased expression of eNOS in the dabigatran group compared with the placebo group. However, t-PA expression did not differ between groups.

Conclusions

Direct long-term inhibition by dabigatran etexilate of thrombin led to an increase in spontaneous thrombolytic activity decreasing the expression of PAI-1 and TAFI.

Gα12/13 signaling in metabolic diseases

As the key governors of diverse physiological processes, G protein-coupled receptors (GPCRs) have drawn attention as primary targets for several diseases, including diabetes and cardiovascular disease. Heterotrimeric G proteins converge signals from ~800 members of the GPCR family. Among the members of the G protein α family, the Gα₁₂ family members comprising Gα₁₂ and Gα₁₃ have been referred to as gep oncogenes. Gα_12/13 levels are altered in metabolic organs, including the liver and muscles, in metabolic diseases. The roles of Gα_12/13 in metabolic diseases have been investigated. In this review, we highlight findings demonstrating Gα_12/13 amplifying or dampening regulators of phenotype changes. We discuss the molecular basis of G protein biology in the context of posttranslational modifications to heterotrimeric G proteins and the cell signaling axis. We also highlight findings providing insights into the organ-specific, metabolic and pathological roles of G proteins in changes associated with specific cells, energy homeostasis, glucose metabolism, liver fibrosis and the immune and cardiovascular systems. This review summarizes the currently available knowledge on the importance of Gα_12/13 in the physiology and pathogenesis of metabolic diseases, which is presented according to the basic understanding of their metabolic actions and underlying cellular and molecular bases.

Understanding the activities of two members of a vital category of proteins called G proteins, which initiate metabolic changes when signaling molecules bind to cells, could lead to new therapies for many diseases. Researchers in South Korea and Japan, led by Sang Geon Kim at Seoul National University, review the significance of the Gα12 and Gα13 proteins in diseases characterised by significant changes in metabolism, including liver conditions and disorders of the cardiovascular and immune systems. Specific roles for the proteins have been identified by a variety of methods, including studying the effect of disabling the genes that code for them in mice. Recent insights suggest that drugs interfering with the activity of these Gα proteins might help treat many conditions in which the molecular signalling networks involving the proteins are disrupted.

Thrombin Induces Angiotensin II-Mediated Senescence in Atrial Endothelial Cells: Impact on Pro-Remodeling Patterns

BACKGROUND

Besides its well-known functions in hemostasis, thrombin plays a role in various non-hemostatic biological and pathophysiologic processes. We examined the potential of thrombin to promote premature atrial endothelial cells (ECs) senescence.

METHODS AND RESULTS

Primary ECs were isolated from porcine atrial tissue. Endothelial senescence was assessed by measuring beta-galactosidase (SA-β-gal) activity using flow cytometry, oxidative stress using the redox-sensitive probe dihydroethidium, protein level by Western blot, and matrix metalloproteinases (MMPs) activity using zymography. Atrial endothelial senescence was induced by thrombin at clinically relevant concentrations. Thrombin induced the up-regulation of p53, a key regulator in cellular senescence and of p21 and p16, two cyclin-dependent kinase inhibitors. Nicotinamide adenine dinucleotide phosphate NADPH oxidase, cyclooxygenases and the mitochondrial respiration complex contributed to oxidative stress and senescence. Enhanced expression levels of vascular cell adhesion molecule (VCAM)-1, tissue factor, transforming growth factor (TGF)-β and MMP-2 and 9 characterized the senescence-associated secretory phenotype of atrial ECs. In addition, the pro-senescence endothelial response to thrombin was associated with an overexpression of both angiotensin converting enzyme and AT1 receptors and was inhibited by perindoprilat and losartan.

CONCLUSIONS

Thrombin promotes premature ageing and senescence of atrial ECs and may pave the way to deleterious remodeling of atrial tissue by a local up-regulation of the angiotensin system and by promoting pro-inflammatory, pro-thrombotic, pro-fibrotic and pro-remodeling responses. Hence, targeting thrombin and/or angiotensin systems may efficiently prevent atrial endothelial senescence.

The Signaling Pathways in Nitric Oxide Production by Neutrophils Exposed to N-nitrosodimethylamine

Background:

Polymorphonuclear neutrophils (PMNs) play a crucial role in the innate immune system’s response to microbial pathogens through the release of reactive nitrogen species, including Nitric Oxide (NO). </P><P> Methods: In neutrophils, NO is produced by the inducible Nitric Oxide Synthase (iNOS), which is regulated by various signaling pathways and transcription factors. N-nitrosodimethylamine (NDMA), a potential human carcinogen, affects immune cells. NDMA plays a major part in the growing incidence of cancers. Thanks to the increasing knowledge on the toxicological role of NDMA, the environmental factors that condition the exposure to this compound, especially its precursors- nitrates arouse wide concern.

Results:

In this article, we present a detailed summary of the molecular mechanisms of NDMA’s effect on the iNOS-dependent NO production in human neutrophils.

Conclusion:

This research contributes to a more complete understanding of the mechanisms that explain the changes that occur during nonspecific cellular responses to NDMA toxicity.

Gα12 overexpression induced by miR-16 dysregulation contributes to liver fibrosis by promoting autophagy in hepatic stellate cells

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) have a role in liver fibrosis. Guanine nucleotide-binding α-subunit 12 (Gα12) converges signals from G-protein-coupled receptors whose ligand levels are elevated in the environment during liver fibrosis; however, information is lacking on the effect of Gα12 on HSC trans-differentiation. This study investigated the expression of Gα12 in HSCs and the molecular basis of the effects of its expression on liver fibrosis.

METHODS

Gα12 expression was assessed by immunostaining, and immunoblot analyses of mouse fibrotic liver tissues and primary HSCs. The role of Gα12 in liver fibrosis was estimated using a toxicant injury mouse model with Gα12 gene knockout and/or HSC-specific Gα12 delivery using lentiviral vectors, in addition to primary HSCs and LX-2 cells using microRNA (miR) inhibitors, overexpression vectors, or adenoviruses. miR-16, Gα12, and LC3 were also examined in samples from patients with fibrosis.

RESULTS

Gα12 was overexpressed in activated HSCs and fibrotic liver, and was colocalised with desmin. In a carbon tetrachloride-induced fibrosis mouse model, Gα12 ablation prevented increases in fibrosis and liver injury. This effect was attenuated by HSC-specific lentiviral delivery of Gα12. Moreover, Gα12 activation promoted autophagy accompanying c-Jun N-terminal kinase-dependent ATG12-5 conjugation. In addition, miR-16 was found to be a direct inhibitor of the de novo synthesis of Gα12. Modulations of miR-16 altered autophagy in HSCs. In a fibrosis animal model or patients with severe fibrosis, miR-16 levels were lower than in their corresponding controls. Consistently, cirrhotic patient liver tissues showed Gα12 and LC3 upregulation in desmin-positive areas.

CONCLUSIONS

miR-16 dysregulation in HSCs results in Gα12 overexpression, which activates HSCs by facilitating autophagy through ATG12-5 formation. This suggests that Gα12 and its regulatory molecules could serve as targets for the amelioration of liver fibrosis.

LAY SUMMARY

Guanine nucleotide-binding α-subunit 12 (Gα12) is upregulated in activated hepatic stellate cells (HSCs) as a consequence of the dysregulation of a specific microRNA that is abundant in HSCs, facilitating the progression of liver fibrosis. This event is mediated by c-Jun N-terminal kinase-dependent ATG12-5 formation and the promotion of autophagy. We suggest that Gα12 and its associated regulators could serve as new targets in HSCs for the treatment of liver fibrosis.

Gα12 overexpressed in hepatocellular carcinoma reduces microRNA-122 expression via HNF4α inactivation, which causes c-Met induction

MicroRNA-122 (miR-122) is implicated as a regulator of physiological and pathophysiological processes in the liver. Overexpression of Gα₁₂ is associated with overall survival in patients with hepatocellular carcinoma (HCC). Array-based miRNA profiling was performed on Huh7 stably transfected with activated Gα₁₂ to find miRNAs regulated by the Gα₁₂ pathway; among them, miR-122 was most greatly repressed. miR-122 directly inhibits c-Met expression, playing a role in HCC progression. Gα₁₂ destabilized HNF4α by accelerating ubiquitination, impeding constitutive expression of miR-122. miR-122 mimic transfection diminished the ability of Gα₁₂ to increase c-Met and to activate ERK, STAT3, and Akt/mTOR, suppressing cell proliferation with augmented apoptosis. Consistently, miR-122 transfection prohibited tumor cell colony formation and endothelial tube formation. In a xenograft model, Gα₁₂ knockdown attenuated c-Met expression by restoring HNF4α levels, and elicited tumor cell apoptosis but diminished Ki67 intensities. In human HCC samples, Gα₁₂ levels correlated to c-Met and were inversely associated with miR-122. Both miR-122 and c-Met expression significantly changed in tumor node metastasis (TNM) stage II/III tumors. Moreover, changes in Gα₁₂ and miR-122 levels discriminated recurrence-free and overall survival rates of HCC patients. Collectively, Gα₁₂ overexpression in HCC inhibits MIR122 transactivation by inactivating HNF4α, which causes c-Met induction, contributing to cancer aggressiveness.

Gα12 gep oncogene deregulation of p53-responsive microRNAs promotes epithelial-mesenchymal transition of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a poor prognosis owing to aggressive phenotype. Gα12 gep oncogene product couples to G-protein-coupled receptors, whose ligand levels are frequently increased in tumor microenvironments. Here, we report Gα12 overexpression in human HCC and the resultant induction of zinc-finger E-box-binding homeobox 1 (ZEB1) as mediated by microRNA deregulation. Gα12 expression was higher in HCC than surrounding non-tumorous tissue. Transfection of Huh7 cell with an activated mutant of Gα12 (Gα12QL) deregulated microRNA (miRNA or miR)-200b/a/429, -194-2/192 and -194-1/215 clusters in the miRNome. cDNA microarray analyses disclosed the targets affected by Gα12 gene knockout. An integrative network of miRNAs and mRNA changes enabled us to predict ZEB1 as a key molecule governed by Gα12. Decreases of miR-200a/b, -192 and -215 by Gα12 caused ZEB1 induction. The ability of Gα12 to decrease p53 levels, as a result of activating protein-1 (AP-1)/c-Jun-mediated mouse double minute 2 homolog induction, contributed to transcriptional deregulation of the miRNAs. Gα12QL induced ZEB1 and other epithelial-mesenchymal transition markers with fibroblastoid phenotype change. Consistently, transfection with miR-200b, -192 or -215 mimic prevented the ability of Gα12QL to increase tumor cell migration/invasion. In xenograft studies, sustained knockdown of Gα12 decreased the overall growth rate and average volume of tumors derived from SK-Hep1 cell (mesenchymal-typed). In HCC patients, miR-192, -215 and/or -200a were deregulated with microvascular invasion or growth advantage. In the HCC samples with higher Gα12 level, a correlation existed in the comparison of relative changes of Gα12 and ZEB1. In conclusion, Gα12 overexpressed in HCC causes ZEB1 induction by deregulating p53-responsive miRNAs, which may facilitate epithelial-mesenchymal transition and growth of liver tumor. These findings highlight the significance of Gα12 upregulation in liver tumor progression, implicating Gα12 as an attractive therapeutic target.

Autophagy and microRNA dysregulation in liver diseases

Autophagy is a catabolic process through which organelles and cellular components are sequestered into autophagosomes and degraded via fusion with lysosomes. Autophagy plays a role in many physiological processes, including stress responses, energy homeostasis, elimination of cellular organelles, and tissue remodeling. In addition, autophagy capacity changes in various disease states. A series of studies have shown that autophagy is strictly controlled to maintain homeostatic balance of energy metabolism and cellular organelle and protein turnover. These studies have also shown that this process is post-transcriptionally controlled by small noncoding microRNAs that regulate gene expression through complementary base pairing with mRNAs. Conversely, autophagy regulates the expression of microRNAs. Therefore, dysregulation of the link between autophagy and microRNA expression exacerbates the pathogenesis of various diseases. In this review, we summarize the roles of autophagy and microRNA dysregulation in the course of liver diseases, with the aim of understanding how microRNAs modify key autophagic effector molecules, and we discuss how this dysregulation affects both physiological and pathological conditions. This article may advance our understanding of the cellular and molecular bases of liver disease progression and promote the development of strategies for pharmacological intervention.

The role of MAP kinases in the induction of iNOS expression in neutrophils exposed to NDMA: the involvement transcription factors

PURPOSE

The role of MAP kinases in the activation of AP-1 (c-Jun, c-Fos) and NF-κB p65 engaged in the regulation of iNOS expression in human neutrophils (PMNs) exposed to N-nitrosodimethylamine (NDMA) was analyzed in the study.

MATERIAL AND METHODS

The study included a group of 20 healthy individuals. Isolated human PMN were incubated in the presence of NDMA. Selective MAP kinases inhibitors were used. The expression of proteins in the cytoplasmic and nuclear fractions was assessed using Western blot method.

RESULTS

The results show that NDMA intensifies iNOS, c-Jun, NF-κB p65 and IκB-α expression in the analyzed PMNs. The blocking of the p38 pathway led to lower iNOS expression, and higher expression of c-Jun and c-Fos in the cytoplasmic fraction, and also lower c-Jun expression in the nuclear fraction of PMNs exposed to NDMA. A decrease in iNOS expression in the cytoplasmic fraction, and also c-Jun in both fractions of the examined cells, was observed as a result of JNK pathway inhibition. The blocking of the ERK5 pathway led to higher iNOS, c-Jun and c-Fos expression in the cytoplasmic fraction, and higher c-Jun expression in the nuclear fraction of PMNs exposed to NDMA. The study also demonstrated that blocking of the p38 and JNK pathways resulted in higher expression of NF-κB p65 and IκB-α in the cytoplasmic fraction and their lower expression in the nuclear fraction of these cells.

CONCLUSION

Our data indicate the role of MAP kinases p38 and JNK in the activation of c-Jun and NF-κB p65 transcription factors engaged in the regulation of iNOS expression in human neutrophils exposed to NDMA. However ERK5 kinase is not involved in the regulation of iNOS and NO production by those cells.

Induction in gastric mucosal prostaglandin and nitric oxide by Helicobacter pylori is dependent on MAPK/ERK-mediated activation of IKK-β and cPLA2: modulatory effect of ghrelin

Among the key factors defining the extent of gastric mucosal inflammatory involvement in response to Helicobacter pylori is the excessive generation of prostaglandin (PGE2) and nitric oxide (NO), caused by the overexpression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), and triggered by the activation of mitogen-activated protein kinase (MAPK)/c-Jun N-terminal kinase, p38 and ERK, and nuclear translocation of the cognate transcription factors. In this study, we report on the role of MAPK/ERK in the regulation of H. pylori LPS-induced gastric mucosal expression of COX-2 and iNOS. We show that ERK activation by the LPS leads to phosphorylation of the inhibitory κB kinase-β (IKK-β) and cytosolic phospholipase A2 (cPLA2), and is reflected in the upsurge in NF-κB nuclear translocation, induction in COX-2 and iNOS expression, and up-regulation in cPLA2 activity. The modulatory effect of peptide hormone, ghrelin, on the LPS-induced changes, although associated with further enhancement in ERK, IKK-β, and cPLA2 phosphorylation, was reflected in the suppression of IKK-β and cPLA2 activity through S-nitrosylation. While the effect of ghrelin on S-nitrosylation was susceptible to suppression by the inhibitors of Src/Akt pathway, the inhibition of ERK activation caused the blockage in IKK-β and cPLA2 phosphorylation as well as S-nitrosylation. Taken together, our data show that H. pylori-induced ERK activation plays a critical role in up-regulation of gastric mucosal PGE2 and NO generation at the level of IKK-β and cPLA2 activation, and that ghrelin counters these proinflammatory consequences of the LPS through Src/Akt-dependent S-nitrosylation.

Rivaroxaban modulates electrical and mechanical characteristics of left atrium

Background

Rivaroxaban reduces stroke in patients with atrial fibrillation (AF). Left atrium (LA) plays a critical role in the pathophysiology of AF. However, the electromechanical effects of rivaroxaban on LA are not clear.

Results

Conventional microelectrodes and a whole-cell patch-clamp were used to record the action potentials (APs) and ionic currents in rabbit LA preparations and isolated single LA cardiomyocytes before and after the administration of rivaroxaban. Rivaroxaban (10, 30, 100, and 300 nM) concentration-dependently reduced LA (n = 7) AP durations at 90% repolarization (APD₉₀) from 76 ± 2 to 79 ± 3, 67 ± 4 (P < 0.05, vs. control), 59 ± 5, (P < 0.01, vs. control), and 56 ± 4 ms (P < 0.005, vs. control), respectively. Rivaroxaban (10, 30, 100, and 300 nM) concentration-dependently increased the LA (n = 7) diastolic tension by 351 ± 69 (P < 0.05, vs. control), 563 ± 136 (P < 0.05, vs. control), 582 ± 119 (P < 0.05, vs. control), and 603 ± 108 mg (P < 0.005, vs. control), respectively, but did not change LA contractility. In the presence of L-NAME (100 μM) and indomethacin (10 μM), additional rivaroxaban (300 nM) treatment did not significantly further increase the LA (n = 7) diastolic tension, but shortened the APD₉₀ from 73 ± 2 to 60 ± 6 ms (P < 0.05, vs. control). Rivaroxaban (100 nM) increased the L-type calcium current and ultra-rapid delayed rectifier potassium current, but did not change the transient outward potassium current in isolated LA cardiomyocytes.

Conclusions

Rivaroxaban modulates LA electrical and mechanical characteristics with direct ionic current effects.

Involvement of p38 MAPK-dependent activator protein (AP-1) activation in modulation of gastric mucosal inflammatory responses to Helicobacter pylori by ghrelin

A peptide hormone, ghrelin, plays an important role in modulation of gastric mucosal inflammatory responses to Helicobacter pylori infection by controlling the cross-talk between nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems. In this study, we report that H. pylori LPS-elicited induction in gastric mucosal COX-2 and inducible (i) iNOS protein expression, and the impairment in constitutive (c) cNOS phosphorylation, was associated with mitogen-activated protein kinase, c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase and p38 activation, and occurred with the involvement of transcription factors, CCATT/enhancer-binding protein (C/EBP) δ, cAMP response element-binding protein, activator protein-1 (AP-1), and NF-κB. The modulatory effect of ghrelin on the LPS-induced changes was manifested in the inhibition of nuclear translocation of p65 NF-κB and C/EBPδ, and suppression in AP-1 activation, and the inhibition in phosphorylation of JNK and p38, as well as their respective downstream targets, c-Jun and ATF-2. However, only the inhibition of p38-mediated ATF-2 phosphorylation was reflected in the reduced expression of COX-2 protein. Further, the effect of ghrelin of the LPS-induced changes was reflected in the increase in Src/Akt-dependent cNOS activation through phosphorylation and the inhibition of cNOS-mediated IKK-β S-nitrosylation. Our findings indicate ghrelin counters the proinflammatory consequences of H. pylori by interfering with the p38/ATF-2-induced AP-1 activation in association with concurrent up-regulation in Src/Akt-dependent cNOS phosphorylation.

Tissue factor pathway inhibitor 2 is induced by thrombin in human macrophages

Tissue factor pathway inhibitor 2 (TFPI2) is a serine protease inhibitor critical for the regulation of extracellular matrix remodeling and atherosclerotic plaque stability. Previously, we demonstrated that TFPI2 expression is increased in monocytes from patients with familial combined hyperlipidemia (FCH). To gain insight into the molecular mechanisms responsible for this upregulation, we examined TFPI2 expression in THP-1 macrophages exposed to lipoproteins and thrombin. Our results showed that TFPI2 expression was not affected by treatment with very low density lipoproteins (VLDL), but was induced by thrombin (10 U/ml) in THP-1 (1.9-fold increase, p<0.001) and human monocyte-derived macrophages (2.3-fold increase, p<0.005). The specificity of the inductive effect was demonstrated by preincubation with the thrombin inhibitors hirudin and PPACK, which ablated thrombin effects. TFPI2 induction was prevented by pre-incubation with MEK1/2 and JNK inhibitors, but not by the EGF receptor antagonist AG1478. In the presence of parthenolide, an inhibitor of NFκB, but not of SR-11302, a selective AP-1 inhibitor, thrombin-mediated TFPI2 induction was blunted. Our results also show that thrombin treatment increased ERK1/2, JNK and IκBα phosphorylation. Finally, we ruled out the possibility that TFPI2 induction by thrombin was mediated by COX-2, as preincubation with a selective COX-2 inhibitor did not prevent the inductive effect. In conclusion, thrombin induces TFPI2 expression by a mechanism involving ERK1/2 and JNK phosphorylation, leading finally to NFkB activation. In the context of atherosclerosis, thrombin-induced macrophage TFPI2 expression could represent a means of avoiding excessive activation of matrix metalloproteases at sites of inflammation.

Thrombin-dependent NF-{kappa}B activation and monocyte/endothelial adhesion are mediated by the CARMA3·Bcl10·MALT1 signalosome

Thrombin is a potent modulator of endothelial function and, through stimulation of NF-κB, induces endothelial expression of intracellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). These cell surface adhesion molecules recruit inflammatory cells to the vessel wall and thereby participate in the development of atherosclerosis, which is increasingly recognized as an inflammatory condition. The principal receptor for thrombin on endothelial cells is protease-activated receptor-1 (PAR-1), a member of the G protein-coupled receptor superfamily. Although it is known that PAR-1 signaling to NF-κB depends on initial PKC activation, the subsequent steps leading to stimulation of the canonical NF-κB machinery have remained unclear. Here, we demonstrate that a complex of proteins containing CARMA3, Bcl10, and MALT1 links PAR-1 activation to stimulation of the IκB kinase complex. IκB kinase in turn phosphorylates IκB, leading to its degradation and the release of active NF-κB. Further, we find that although this CARMA3·Bcl10·MALT1 signalosome shares features with a CARMA1-containing signalosome found in lymphocytes, there are significant differences in how the signalosomes communicate with their cognate receptors. Specifically, whereas the CARMA1-containing lymphocyte complex relies on 3-phosphoinositide-dependent protein kinase 1 for assembly and activation, the CARMA3-containing endothelial signalosome functions completely independent of 3-phosphoinositide-dependent protein kinase 1 and instead relies on β-arrestin 2 for assembly. Finally, we show that thrombin-dependent adhesion of monocytes to endothelial cells requires an intact endothelial CARMA3·Bcl10·MALT1 signalosome, underscoring the importance of the signalosome in mediating one of the most significant pro-atherogenic effects of thrombin.

Thrombin induces cyclooxygenase-2 expression and prostaglandin E2 release via PAR1 activation and ERK1/2- and p38 MAPK-dependent pathway in murine macrophages

Thrombin levels increase at sites of vascular injury and during acute coronary syndromes. It is also increased several fold by sepsis with a reciprocal decrease in the anti-thrombin III levels. In this study we investigate the effects of thrombin on the induction of cyclooxygenase-2 (COX-2) and prostaglandin (PG) production in macrophages. Thrombin-induced COX-2 protein and mRNA expression in RAW264.7 and primary cultured peritoneal macrophages. A serine proteinase, trypsin, also exerted a similar effect. The inducing effect by thrombin in macrophages was not affected by a lipopolysaccharide (LPS)-binding antibiotic, polymyxin B, excluding the possibility of LPS contamination. The increase of COX-2 expression by thrombin was functionally linked to release of PGE(2) and PGI(2) but not thromboxane A(2) into macrophage culture medium. Thrombin-induced COX-2 expression and PGE(2) production were significantly attenuated by PD98059 and SB202190 but not by SP600125, suggesting that ERK1/2 and p38 MAPK activation were involved in this process. This was supported by the observation that thrombin could directly activate ERK1/2 and p38 MAPK in macrophages. A further analysis indicated that the proteinase-activated receptor 1 (PAR1)-activating agonist induced effects similar to those induced by thrombin in macrophages and the PAR1 antagonist-SCH79797 could attenuate thrombin-induced COX-2 expression and PGE(2) release. Taken together, we provided evidence demonstrating that thrombin can induce COX-2 mRNA and protein expression and PGE(2) production in macrophages through PAR1 activation and ERK1/2 and p38 MAPK-dependent pathway. The results presented here may explain, at least in part, the possible contribution of thrombin and macrophages in these pathological conditions.

Galpha12 is critical for TCR-induced IL-2 production and differentiation of T helper 2 and T helper 17 cells

G12 family have been known to modulate a variety of cellular events such as cell migration, B cell activation and maturation, cytokine production, and cell differentiation. In particular, Galpha12 modulates IgG production, thus induces IgG antibody-mediated immune responses. However, it is largely unknown whether Galpha12 is required for T cell-mediated immune functions. In this study, we investigated the effects of Galpha12 in the activation and differentiation of CD4+ T cells. While PMA plus ionomycin induced equal levels of IL-2 production in WT and Galpha12-deficient lymphocytes, TCR-triggered IL-2 production was significantly attenuated in Galpha12 KO lymphocytes. In particular, CD4+ T cells and effector Th cells lacking of Galpha12 revealed diminished IL-2 production, but not IFNgamma production, upon TCR stimulation. In addition, supplement of IL-2 preferentially induced Galpha12-deficient CD4+ T cells into Th2 and Th17 cells; however, the expression of specific transcription factors was unchanged in Galpha12 KO Th cells. While IL-2 expression was still diminished by the re-stimulation with anti-CD3, PMA plus ionomycin restored IL-2 production in Galpha12-deficient Th1 and Th2 cells. These results suggest that Galpha12 may be a critical signaling molecule in TCR-induced IL-2 production and also relay a signal to suppress Th2 and Th17 cell differentiation.

Essential role of mitogen-activated protein kinase pathways in protease activated receptor 2-mediated nitric-oxide production from rat primary astrocytes

Protease-activated receptors (PARs) play important roles in the regulation of brain function such as neuroinflammation by transmitting the signal from proteolytic enzymes such as thrombin and trypsin. We and others have reported that a member of the family, PAR-2 is activated by trypsin, whose involvement in the neurophysiological process is increasingly evident, and is involved in the neuroinflammatory processes including morphological changes of astrocytes. In this study, we investigated the role of PAR-2 in the production of nitric oxide (NO) in rat primary astrocytes. Treatment of PAR-2 agonist trypsin increased NO production in a dose-dependent manner, which was mediated by the induction of inducible nitric-oxide synthase. The trypsin-mediated production of NO was mimicked by PAR-2 agonist peptide and reduced by either pharmacological PAR-2 antagonist peptide or by siRNA-mediated inhibition of PAR-2 expression, which suggests the critical role of PAR-2 in this process. NO production by PAR-2 was mimicked by PMA, a PKC activator, and was attenuated by Go6976, a protein kinase C (PKC) inhibitor. PAR-2 stimulation activated three subtypes of mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. NO production by PAR-2 was blocked by inhibition of ERK, p38, and JNK pathways. PAR-2 stimulation also activated nuclear factor-kappaB (NF-kappaB) DNA binding and transcriptional activity as well as IkappaBalpha phosphorylation. Inhibitors of NF-kappaB pathway inhibited PAR-2-mediated NO production. In addition, inhibitors of MAPK pathways prevented transcriptional activation of NF-kappaB reporter constructs. These results suggest that PAR-2 activation-mediated NO production in astrocytes is transduced by the activation of MAPKs followed by NF-kappaB pathways.

Galpha13 regulates methacholine-induced contraction of bronchial smooth muscle via phosphorylation of MLC20

Reversible airway constriction is induced by an increase in airway smooth muscle contractility in response to methacholine likely as a bronchospastic stimulus. Despite the finding of Galpha12 and Galpha13 up-regulation in airway hyperresponsive animals, their functional role of contraction in airway smooth muscle has not been directly explored. This study investigated the differential regulatory role of Galpha12/Galpha13 in methacholine-induced contraction of trachea and bronchus in Galpha12 or Galpha13 gene knockout mice after ovalbumin sensitization and challenges. Organ bath assays and videomicroscopy revealed that Galpha13 deficiency delayed methacholine-induced contractile response of bronchiolar smooth muscle, but not that of tracheal smooth muscle. In primary bronchial smooth muscle cells, knockdown of Galpha13 blocked methacholine-induced phosphorylation of 20 kDa regulatory light chain of myosin II (MLC20), a prerequisite step for the contractile initiation of actin and myosin. Galpha13-dependent MLC20 phosphorylation was confirmed in murine embryonic fibroblasts. After ovalbumin sensitization and challenges, wild type mice exhibited methacholine-induced bronchial contraction of lung tissue. Heterozygous absence of the Galpha13 gene abrogated methacholine-induced contractions, whereas homozygous absence of the Galpha12 gene failed to do so. Our findings indicate that Galpha13, but not Galpha12, specifically regulates cholinergic bronchial contraction in airway responsiveness via controlling phosphorylation of MLC20 by methacholine.

The gep oncogenes, Galpha(12) and Galpha(13), upregulate the transforming growth factor-beta1 gene

Transforming growth factor-beta1 (TGFbeta1) plays a role in neoplastic transformation and transdifferentiation. Galpha(12) and Galpha(13), referred to as the gep oncogenes, stimulate mitogenic pathways. Nonetheless, no information is available regarding their roles in the regulation of the TGFbeta1 gene and the molecules linking them to gene transcription. Knockdown or knockout experiments using murine embryonic fibroblasts and hepatic stellate cells indicated that a Galpha(12) and Galpha(13) deficiency reduced constitutive, auto-stimulatory or thrombin-inducible TGFbeta1 gene expression. In contrast, transfection of activated mutants of Galpha(12) and Galpha(13) enabled the knockout cells to promote TGFbeta1 induction. A promoter deletion analysis suggested that activating protein 1 (AP-1) plays a role in TGFbeta1 gene transactivation, which was corroborated by the observation that a deficiency of the G-proteins decreased the AP-1 activity, whereas their activation enhanced it. Moreover, mutation of the AP-1-binding site abrogated the ability of Galpha(12) and Galpha(13) to induce the TGFbeta1 gene. Transfection of a dominant-negative mutant of Rho or Rac, but not Cdc42, prevented gene transactivation and decreased AP-1 activity downstream of Galpha(12) and Galpha(13). In summary, Galpha(12) and Galpha(13) regulate the expression of the TGFbeta1 gene through an increase in Rho/Rac-dependent AP-1 activity, implying that the G-protein-coupled receptor (GPCR)-Galpha(12) pathway is involved in the TGFbeta1-mediated transdifferentiation process.

A novel mitogen-activated protein kinase phosphatase-1 and glucocorticoid receptor (GR) interacting protein-1-dependent combinatorial mechanism of gene transrepression by GR

Glucocorticoids have major antiinflammatory effects. Because COX-2 is the rate-limiting enzyme for proinflammatory prostaglandins, this study investigated the combinatorial inhibitory role of glucocorticoid receptor (GR) in COX-2 gene induction in macrophages and sought to identify the molecular mechanisms for that inhibition. Glucocorticoid-activated GR repressed COX-2 gene induction by lipopolysaccharide (LPS). Activated GR inhibited LPS-induced activator protein 1 activity, which in turn decreased activating transcription factor 2/c-Jun phosphorylation. The inhibition of MAPK-dependent activating transcription factor 2/c-Jun phosphorylation by GR in COX-2 repression was a result of MAPK phosphatase-1 (MKP-1) induction. Although GR did not inhibit LPS-induced p65 phosphorylation or nuclear factor-kappaB DNA binding activity, deletion of the nuclear factor-kappaB binding site in the COX-2 gene suppressed the ability of glucocorticoid to attenuate COX-2 induction. Chromatin immunoprecipitation and transfection assays revealed that a p65 DNA complex involving GR-bound GR-interacting protein 1 (GRIP1) also contributed to COX-2 repression. Additional knockdown and transfection assays identified other inflammatory genes coordinately regulated by MKP-1 and GRIP1. In summary, activated GR was found to antagonize the LPS-dependent induction of the COX-2 gene via a novel combinatorial mechanism involving MKP-1-mediated activator protein 1 inhibition and GR/GRIP1 recruitment to the p65 DNA complex; moreover, this work facilitated the identification of other GR-responding MKP-1/GRIP1-regulated genes.

Regulation of thymus-dependent and thymus-independent production of immunoglobulin G subclasses by Galpha12 and Galpha13

Background

A previous study from this laboratory showed that Gα₁₂ members participate in the production of inflammatory cytokines. In spite of the identification of B cell homeostasis responses regulated by Gα₁₃, the functional roles of Gα₁₂ members in the production of immunoglobulin (Ig) isotypes remained unknown. This study investigated whether Gα₁₂ members are involved in the Ig isotype antibody production with the purpose of establishing their functions in thymus-dependent and thymus-independent humoral responses.

Results

Mice lacking Gα₁₂ and/or Gα₁₃ showed an impaired antigen-specific antibody production promoted by challenge(s) of ovalbumin or trinitrophenyl-lipopolysaccharide (TNP-LPS), used for thymus-dependent and thymus-independent stimuli, respectively. Homozygous knockout (KO) of Gα₁₂ or double heterozygous KO of Gα₁₂/Gα₁₃ significantly reduced the antigen-specific total IgG level after multiple ovalbumin immunizations with decreases in the production of IgG1, IgG2a and IgG2b subclasses, as compared to wild type control. In contrast, IgM production was not decreased. Moreover, mice deficient in Gα₁₂ or partially deficient in Gα₁₃ or Gα₁₂/Gα₁₃ showed significantly low production of IgG2b in response to TNP-LPS. In TNP-LPS-injected mice, IgG1 and IgG2a productions were unaffected by the G protein KOs.

Conclusion

Our results demonstrate that both Gα₁₂ and Gα₁₃ are essentially involved in thymus-dependent and independent production of IgG subclasses, implying that the G-proteins contribute to the process of antigen-specific IgG antibody production.

G alpha 12/13 basally regulates p53 through Mdm4 expression

G alpha(12/13), which belongs to the G alpha(12) family, participates in the regulation of diverse physiologic processes. In view of the control of G alpha(12/13) in cell proliferation, this study investigated the role of G alpha(12/13) in the regulation of p53 and mdm4. Immunoblotting and immunocytochemistry revealed that p53 was expressed in control embryonic fibroblasts and was largely localized in the nuclei. G alpha(12) deficiency decreased p53 levels and its DNA binding activity, accompanying p21 repression with Bcl(2) induction, whereas G alpha(13) deficiency exerted weak effects. G alpha(12) or G alpha(13) deficiency did not change p53 mRNA expression. ERK1/2 or Akt was not responsible for p53 repression due to G alpha(12) deficiency. Mdm4, a p53-stabilizing protein, was repressed by G alpha(12) deficiency and to a lesser extent by G alpha(13) deficiency, whereas mdm2, PTEN, beta-catenin, ATM, and Chk2 were unaffected. p53 accumulation by proteasomal inhibition during G alpha(12) deficiency suggested the role of G alpha(12) in p53 stabilization. Constitutively active G alpha(12) (G alpha(12)QL) or G alpha(13) (G alpha(13)QL) promoted p53 accumulation with mdm4 induction in MCF10A cells. p53 accumulation by mdm4 overexpression, but no mdm4 induction by p53 overexpression, and small interfering RNA knockdown verified the regulatory role of mdm4 for p53 downstream of G alpha(12/13). In control or G alpha(12)/G alpha(13)-deficient cells, genotoxic stress led to p53 accumulation. At concentrations increasing the flow cytometric pre-G(1) phase, doxorubicin or etoposide treatment caused serine phosphorylations in G alpha(12)-/- or G alpha(12/13)-/- cells, but did not induce mdm4. G alpha(12/13)QL transfection failed to phosphorylate p53 at serines. Our results indicate that G alpha(12/13) regulate basal p53 levels via mdm4, which constitutes a cell signaling pathway distinct from p53 phosphorylations elicited by genotoxic stress.

Role of Galpha12 and Galpha13 as novel switches for the activity of Nrf2, a key antioxidative transcription factor

Galpha12 and Galpha13 function as molecular regulators responding to extracellular stimuli. NF-E2-related factor 2 (Nrf2) is involved in a protective adaptive response to oxidative stress. This study investigated the regulation of Nrf2 by Galpha12 and Galpha13. A deficiency of Galpha12, but not of Galpha13, enhanced Nrf2 activity and target gene transactivation in embryo fibroblasts. In mice, Galpha12 knockout activated Nrf2 and thereby facilitated heme catabolism to bilirubin and its glucuronosyl conjugations. An oligonucleotide microarray demonstrated the transactivation of Nrf2 target genes by Galpha12 gene knockout. Galpha12 deficiency reduced Jun N-terminal protein kinase (JNK)-dependent Nrf2 ubiquitination required for proteasomal degradation, and so did Galpha13 deficiency. The absence of Galpha12, but not of Galpha13, increased protein kinase C delta (PKC delta) activation and the PKC delta-mediated serine phosphorylation of Nrf2. Galpha13 gene knockout or knockdown abrogated the Nrf2 phosphorylation induced by Galpha12 deficiency, suggesting that relief from Galpha12 repression leads to the Galpha13-mediated activation of Nrf2. Constitutive activation of Galpha13 promoted Nrf2 activity and target gene induction via Rho-mediated PKC delta activation, corroborating positive regulation by Galpha13. In summary, Galpha12 and Galpha13 transmit a JNK-dependent signal for Nrf2 ubiquitination, whereas Galpha13 regulates Rho-PKC delta-mediated Nrf2 phosphorylation, which is negatively balanced by Galpha12.

Molecular mechanisms of thrombin-induced interleukin-8 (IL-8/CXCL8) expression in THP-1-derived and primary human macrophages

Under normal conditions, macrophages provide essential innate immune surveillance in tissues. These cells also play key functions during wound healing and in pathological conditions. When macrophages are exposed to thrombin, an enzyme released from leaky blood vessels, they are stimulated to produce inflammatory cytokines, which are critical for wound healing and can also facilitate tumor growth and invasion. Using antibody cytokine arrays, we identified IL-8/CXCL8, a chemokine that plays important functions in inflammation and angiogenesis and consequently in healing and tumor development, as one of the cytokines that is highly stimulated in macrophages by thrombin. Here, we investigated the signal transduction mechanism by which thrombin stimulates IL-8/CXCL8 expression in THP-1-derived and primary human macrophages. We show that JNK is a crucial mediator of the thrombin signaling pathways in macrophages, and the activation of JNK is dependent on stimulation of the Rho small GTPase. The thrombin-induced Rho/JNK cascade is a novel signaling cascade for IL-8/CXCL8 transcription activation. Understanding the molecular mechanism by which thrombin controls the expression of inflammatory cytokines in macrophages can lead to therapeutic interventions, which can provide better management of healing, inflammation, and tumorigenesis.

Inflammatory effect of endosulfan via NF-κB activation in macrophages

Macrophages are essential for the inflammatory response process because they release a wide variety of proinflammatory mediators. Endosulfan is extremely toxic to invertebrates and has been implicated in various mammalian toxicities. However, its influence on production of cytokine or on the functions of macrophages is unclear. This study examined the effects of endosulfan on the production of nitric oxide (NO) and proinflammatory cytokines (IL-1beta, IL-6, TNF-alpha), and examined the molecular mechanism in macrophages. Exposing macrophages to endosulfan induced the production of NO and proinflammatory cytokines and the expression of these genes. The transient transfection and electrophoretic mobility shift assays with the NF-kappaB binding sites showed that the NF-kappaB transcription factor mediated the endosulfan-induced increase in the expression levels of iNOS and proinflammatory cytokines. These results show that endosulfan stimulates the production of NO and proinflammatory cytokines and can up-regulate the gene expression levels through NF-kappaB transactivation. Overall, these results suggest that endosulfan has inflammatory potential.

Novel role of IL-6/SIL-6R signaling in the expression of inducible nitric oxide synthase (iNOS) in murine B16, metastatic melanoma clone F10.9, cells

Inducible nitric oxide synthase (iNOS) has been shown to be frequently expressed in melanomas; up-regulation of this enzyme is though to be associated with tumor progression. In this study, we investigated whether diverse cytokines such as: IL-6, TNF-alpha, IL-1beta, IFN-gamma and IL6RIL6 (a highly active fusion protein of the soluble form of the IL-6R (sIL-6R) and IL-6) enhance the iNOS gene expression in B16/F10.9 murine metastatic melanoma cells. An increase at iNOS expression and NO production was observed with the co-treatment of IL6RIL6 plus TNF-alpha. Gel shift and reporter gene analyses revealed that IL6RIL6 selectively activated AP-1; while TNF-alpha increased the activities of both NF-kappaB and AP-1. Persistent activation of AP-1 was also seen in cells treated with IL6RIL6 plus TNF-alpha. Stimulation of cells with IL6RIL6/TNF-alpha resulted in the activation of mitogen-activated protein kinases (MAPK) such as c-Jun N-terminal kinase (JNK) and p38, and the abrogation by pretreatment with JNK or p38 MAPK inhibitor. IL6RIL6 or IL6RIL6/TNFalpha-inducible AP-1 binding increase was supershifted by anti-c-Jun or c-Fos antibodies, and the activation of c-Jun and c-Fos was dependent on JNK and p38, respectively. These results suggest that IL-6/sIL-6R/gp130 complex signaling has an unexpected positive effect on iNOS gene expression through JNK/p38 MAPK mediated-AP-1 activation in melanoma cells.

Galpha12 specifically regulates COX-2 induction by sphingosine 1-phosphate. Role for JNK-dependent ubiquitination and degradation of IkappaBalpha

Cyclooxygenase-2 (COX-2) plays a critical role in vasodilatation and local inflammatory responses during platelet aggregation and thrombosis. Sphingosine 1-phosphate (S1P), a sphingolipid released from activated platelets, stimulates COX-2 induction and activates G-protein-coupled receptors coupled to Galpha family members. In this study, we investigated whether Galpha(12) family regulates COX-2 induction by S1P and investigated the molecular basis of this COX-2 regulation. Gene knock-out and chemical inhibitor experiments revealed that the S1P induction of COX-2 requires Galpha(12) but not Galpha(13), Galpha(q), or Galpha(i/o). The specific role of Galpha(12) in COX-2 induction by S1P was verified by promoter luciferase assay, Galpha(12) transfection, and knockdown experiments. Experiments using siRNAs specifically directed against S1P(1-5) showed that S1P(1), S1P(3), and S1P(5) are necessary for the full activation of COX-2 induction. Gel shift, immunocytochemistry, chromatin immunoprecipitation, and NF-kappaB site mutation analyses revealed the role of NF-kappaBin COX-2 gene transcription by S1P. Galpha(12) deficiency did not affect S1P-mediated IkappaBalpha phosphorylation but abrogated IkappaBalpha ubiquitination and degradation. Moreover, the inhibition of S1P activation of JNK abolished IkappaBalpha ubiquitination. Consistently, JNK transfection restored the ability of S1P to degrade IkappaBalpha during Galpha(12) deficiency. S1P injection induced COX-2 in the lungs and livers of mice and increased plasma prostaglandin E(2), and these effects were prevented by Galpha(12) deficiency. Our data indicate that, of the Galpha proteins coupled to S1P receptors, Galpha(12) specifically regulates NF-kappaB-mediated COX-2 induction by S1P downstream of S1P(1), S1P(3), and S1P(5), in a process mediated by the JNK-dependent ubiquitination and degradation of IkappaBalpha.

Potent inhibition of the inductions of inducible nitric oxide synthase and cyclooxygenase-2 by taiwaniaflavone

The improper productions of nitric oxide and prostaglandins following the inductions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) are involved in the pathogenesis of chronic inflammation. Selaginella tamariscina is used as an oriental medicine for its anti-inflammatory effects. Here, we isolated taiwaniaflavone from S. tamariscina and investigated whether taiwaniaflavone affects the induction of iNOS and COX-2 in RAW264.7 macrophages stimulated with lipopolysaccharide. We found that taiwaniaflavone blocks the transactivations of iNOS and COX-2 genes by blocking the nuclear translocation of p65 and subsequent nuclear factor-kappaB inactivation. It is known that NF-kappaB activation is controlled by the phosphorylation and subsequent degradation of I-kappaBalpha, and in the present study, we found that the phosphorylation and degradation of I-kappaBalpha were also inhibited by taiwaniaflavone. Our findings indicate that taiwaniaflavone may provide a developmental basis for an agent against inflammatory diseases.

7,7'-Dihydroxy bursehernin inhibits the expression of inducible nitric oxide synthase through NF-kappaB DNA binding suppression

This study isolated a lignan, 7,7'-dihydroxy bursehernin, from Geranium thunbergii and investigated whether or not the lignan affects the induction of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in RAW264.7 macrophages stimulated with lipopolysaccharide (LPS). The gel shift analysis and luciferase reporter gene assays using the iNOS promoter and nuclear factor-kappaB (NF-kappaB) minimal promoter showed that a treatment with 7,7'-dihydroxy bursehernin reduced the reporter activities and binding of NF-kappaB to the NF-kappaB consensus sequence, while it had no effect on the nuclear translocation of p65 and the phosphorylation/degradation of I-kappaBalpha. It was reported that a few natural compounds directly suppressed the binding activity of the NF-kappaB components to DNA. The NF-kappaB binding activity was not reversed by the in vitro exposure of the nuclear extracts to 7,7'-dihydroxy bursehernin, which suggest that a metabolite(s) of 7,7'-dihydroxy bursehernin might target the binding of the NF-kappaB complex to the DNA binding domain region in the promoter region of the iNOS gene. After incubation of RAW264.7 cells with 7,7-dihydroxy bursehernin for 18h, the levels of parent compound were negligible; while a main metabolite, 4-[4-(n-hydroxy-phenyl)-2,3-dimethyl-buta-1,3-dienyl]-benzene-1,2-diol was detected in cell lysates and culture medium.

Bifunctional effects of fucoidan on the expression of inducible nitric oxide synthase

Algal fucoidan is a marine sulfated polysaccharide with a wide variety of biological activities including anti-thrombotic and anti-inflammatory effects. This study evaluated the effect of fucoidan on the expression of inducible nitric oxide synthase (iNOS) in a macrophage cell line, RAW264.7. Low concentration range of fucoidan (10 microg/ml) increased the basal expression level of iNOS in quiescent macrophages. However, we found for the first time that fucoidan inhibited the release of nitric oxide (NO) in RAW264.7 cells stimulated with lipopolysaccharide (LPS). Western blot analysis revealed that fucoidan suppressed the LPS-induced expression of the inducible nitric oxide synthase (iNOS) gene. Moreover, the activation of both nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1) are key steps in the transcriptional activation of the iNOS gene. Here, it was revealed that fucoidan selectively suppressed AP-1 activation, and that the activation of AP-1 appears to be essential for the induction of iNOS in activated macrophages. This inhibitory effect on AP-1 activation by fucoidan might be associated with its NO blocking and anti-inflammatory effects.

Inhibition of inducible nitric oxide synthase by sumaflavone isolated from Selaginella tamariscina

We previously reported that amentoflavone isolated from Selaginella tamariscina inhibits the production of nitric oxide (NO) in macrophages via nuclear factor-kappaB (NF-kappaB) inactivation. Here, we isolated two other bi-flavonoid compounds (sumaflavone and robustaflavone) from Selaginella tamariscina and studied their effects on inducible nitric oxide synthase (iNOS) gene expression. Sumaflavone inhibited NO production in a concentration-dependent manner and blocked the lipopolysaccharide (LPS)-induced expression of iNOS. In contrast, robustaflavone only marginally affected iNOS gene expression and NO production. To identify the transcriptional factors affected by sumaflavone, we investigated NF-kappaB and AP-1 activation. Reporter gene analysis using AP-1-specific luciferase reporter and gel shift analysis showed that enhanced AP-1 activity by LPS was significantly diminished in macrophages pretreated with sumaflavone. However, sumaflavone did not inhibit LPS-inducible NF-kappaB reporter activity. Western blot analyses also confirmed that the extent of I-kappaBalpha phosphorylation and the nuclear level of p65 were unaffected by sumaflavone. These results suggest that the inhibitory effect of sumaflavone on AP-1 activation may be associated with the potent NO blocking and anti-inflammatory effects of Selaginella tamariscina extract.

Inhibition of p38 mitogen-activated protein kinase enhances c-Jun N-terminal kinase activity: implication in inducible nitric oxide synthase expression

Background

Nitric oxide (NO) is an inflammatory mediator, which acts as a cytotoxic agent and modulates immune responses and inflammation. p38 mitogen-activated protein kinase (MAPK) signal transduction pathway is activated by chemical and physical stress and regulates immune responses. Previous studies have shown that p38 MAPK pathway regulates NO production induced by inflammatory stimuli. The aim of the present study was to investigate the mechanisms involved in the regulation of inducible NO synthesis by p38 MAPK pathway.

Results

p38 MAPK inhibitors SB203580 and SB220025 stimulated lipopolysaccharide (LPS)-induced inducible nitric oxide synthase (iNOS) expression and NO production in J774.2 murine macrophages. Increased iNOS mRNA expression was associated with reduced degradation of iNOS mRNA. Treatment with SB220025 increased also LPS-induced c-Jun N-terminal kinase (JNK) activity. Interestingly, JNK inhibitor SP600125 reversed the effect of SB220025 on LPS-induced iNOS mRNA expression and NO production.

Conclusion

The results suggest that inhibition of p38 MAPK by SB220025 results in increased JNK activity, which leads to stabilisation of iNOS mRNA, to enhanced iNOS expression and to increased NO production.

Inhibition of Nuclear Factor-.KAPPA.B Activation by 2',8"-Biapigenin

Inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) play a key role in the inflammatory processes. Improper overproduction of NO and prostaglandins by both enzymes are also believed to be involved in the pathogenesis of certain human cancers. Crude extracts of Selaginella tamariscina are used as an oriental medicine, which has been reported to inhibit the production of proinflammatory cytokines and cause cell cycle arrest. We isolated 2',8''-biapigenin from S. tamariscina and investigated whether it modulates iNOS and COX-2 expressions in Raw264.7 macrophages stimulated with lipopolysaccharide (LPS). We found that 2',8''-biapigenin blocked the transactivations of iNOS and COX-2 genes via the inactivation of nuclear factor-kappaB by preventing the nuclear translocation of p65. Hence, it may be possible to develop S. tamariscina extracts or 2',8''-biapigenin as a useful agent for cancer chemoprevention or for the treatment of inflammatory diseases.

PAR1-mediated NFkappaB activation promotes survival of prostate cancer cells through a Bcl-xL-dependent mechanism

We have previously reported that protease-activated receptor 1 (PAR1 or thrombin receptor) is over-expressed in metastatic prostate cancer cell lines compared to prostate epithelial cells. In this study, we examined 1,074 prostate biopsies by tissue microarray analysis and demonstrated that PAR1 expression is significantly increased in prostate cancer compared to normal prostate epithelial cells and benign prostatic hyperplasia. We hypothesized that PAR1 activation contributed to prostate cancer cell progression. We demonstrated that stimulation of PAR1 by thrombin or thrombin receptor activating peptide (TRAP6), in androgen-independent DU145 and PC-3 cells resulted in increased DNA binding activity of the NFkappaB p65 subunit. IL-6 and IL-8 levels were also elevated in conditioned media by at least two-fold within 4-6 h of PAR1 activation. This induction of cytokine production was abrogated by pretreatment of cells with the NFkappaB inhibitor caffeic acid phorbol ester. The p38 and ERK1/2 MAPK signaling cascades were also activated by PAR1 stimulation, whereas the SAPK/JNK pathway was unaffected. Inhibition of p38 and ERK1/2 by SB-203589 and PD-098059, respectively, did not abrogate NFkappaB activity, suggesting an independent induction of NFkappaB by PAR1 stimulation. Furthermore, TUNEL assay showed that activation of PAR1 attenuated docetaxel induced apoptosis through the upregulation of the Bcl-2 family protein Bcl-xL. Akt activation was not observed, suggesting that drug resistance induced by PAR1 was independent of PI3K signaling pathway. Because thrombin and PAR1 are over-expressed in prostate cancer patients, targeting the inhibition of their interaction may attenuate NFkappaB signaling transduction resulting in decreased drug resistance and subsequent survival of prostate cancer cells.

G-protein signaling in iNOS gene expression

Heterotrimeric G proteins are the molecular switches in the receptor-mediated transmembrane signaling system. Inducible nitric oxide synthase (iNOS) is inducible by a variety of inflammatory stimuli, which leads to vascular hyporeactivity. In this chapter, the system to study the cell signaling pathways downstream of the GPCR coupling to G proteins is described for the study of iNOS gene expression. The cellular signaling pathways by which ligand induces iNOS may serve as the pharmacological targets for preventing or treating vascular hyporeactivity.

Chrysoeriol potently inhibits the induction of nitric oxide synthase by blocking AP-1 activation

Chrysoeriol is a flavonoid with antioxidant and anti-inflammatory activities. Despite the large number of studies performed on its biological activities, no clear picture of its mode of action has emerged. In the present study, we isolated chrysoeriol from the leaves of Digitalis purpurea (foxglove), and studied its effect on the induction of the inducible nitric oxide synthase (iNOS) gene, and the mechanism of this induction in Raw264.7 macrophages. Chrysoeriol pretreatment potently inhibited the release of NO in the cells treated with lipopolysaccharide (LPS), and Western blot and RT-PCR analyses revealed that chrysoeriol inhibited the LPS-induced inductions of iNOS gene. Moreover, it is known that the activations of nuclear factor-kappaB (NF-kappaB) and activator protein 1 (AP-1) are crucial steps in the transcriptional activation of the iNOS gene. Here, we found that chrysoeriol selectively suppressed AP-1 activation, and that activation of AP-1 is likely to be essential for iNOS induction in LPS-treated macrophages. This presumed inhibitory effect on AP-1 activation by chrysoeriol may be associated with its potent NO blocking and anti-inflammatory effects.

Amentoflavone inhibits the induction of nitric oxide synthase by inhibiting NF-κB activation in macrophages

Amentoflavone is a bi-flavonoid compound with anti-fungal and anti-inflammatory activities. We isolated amentoflavone from Selaginella tamariscina (Selaginellaceae) and studied its effects on nuclear factor-kappaB (NF-kappaB)-mediated inducible nitric oxide synthase (iNOS) gene expression in RAW 264.7 cells. Amentoflavone inhibited the production of nitric oxide in a concentration-dependent manner and also blocked the lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase (iNOS). To clarify the mechanistic basis for its inhibition of iNOS induction, we examined the effect of amentoflavone on the transactivation of iNOS gene by luciferase reporter activity using -1.59 kb flanking region. Amentoflavone potently suppressed the reporter gene activity. The LPS-induced activation of NF-kappaB was also found to be significantly blocked by amentoflavone, but AP-1 activation was unaffected. Furthermore, the nuclear translocation of p65 by LPS was inhibited by amentoflavone. NF-kappaB activation is controlled by the phosphorylation and subsequent degradation of I-kappaBalpha, and the cytosolic degradation of I-kappaBalpha was found to be inhibited by amentoflavone. These findings suggest that the inhibition of LPS-induced NO formation by amentoflavone is due to its inhibition of NF-kappaB by blocking I-kappaBalpha degradation, which may be the mechanistic basis of the anti-inflammatory effects of amentoflavone.

Ginsenoside Rg3 inhibits phenylephrine-induced vascular contraction through induction of nitric oxide synthase

Ginsenoside Rg3 (Rg3) isolated from Panax ginseng relaxes vessels and exerts a cytoprotective effect. In view of the fact that nitric oxide (NO) is involved in vascular hyporeactivity and immunostimulation, the effects of total ginsenosides (GS) and Rg3 on the vascular responses and the expression of inducible nitric oxide synthase (iNOS) were investigated. Vasocontraction of endothelium-denuded aortic ring was induced by phenylephrine with or without GS or Rg3. The expression of iNOS was assessed by Western blot and RT-PCR analyses. NF-kappaB activation was monitored by gel shift, immunoblot and immunocytochemical analyses. Incubation of the endothelium-denuded aortic ring with GS or Rg3 inhibited phenylephrine-induced vasocontraction, which was abrogated by NOS inhibition. GS or Rg3 increased NO production in aortic rings, but Rb1, Rc, Re and Rg1 had no effect. Aortic rings obtained from rats treated with GS or Rg3 responded to phenylnephrine to a lesser extent, while producing NO to a larger extent, than those from control animals. GS or Rg3 induced iNOS in vascular smooth muscle. Rg3 induced iNOS with increase in NO production in Raw264.7 cells. Rg3 increased NF-kappaB DNA binding, whose band was supershifted with anti-p65 and anti-p50 antibodies, and elicited p65 nuclear translocation, which was accompanied by phosphorylation and degradation of I-kappaBalpha. PKC regulated iNOS induction by Rg3. In conclusion, Rg3 relaxes vessels as a consequence of NO production, to which iNOS induction contributes, and iNOS induction by Rg3 accompanied NF-kappaB activation, which involves phosphorylation and degradation of I-kappaBalpha and nuclear translocation of p65.

Pkc downstream of pi3-kinase regulates peroxynitrite formation for nrf2-mediated gsta2 induction

The protective adaptive response to electrophiles and reactive oxygen species is mediated by the induction of phase II detoxifying genes including glutathione S-transferases (GSTs). NF-E2-related factor-2 (Nrf2) phosphorylation by protein kinase C (PKC) is a critical event for its nuclear translocation in response to oxidative stress. Previously, we have shown that peroxynitrite plays a role in activation of Nrf2 and Nrf2 binding to the antioxidant response element (ARE) via the pathway of phosphatidylinositol 3-kinase (Pl3-kinase) and that nitric oxide synthase in hepatocytes is required for GSTA2 induction. In view of the importance of PKC and Pl3-kinase in Nrf2-mediated GST induction, we investigated the role of these kinases in peroxynitrite formation for GSTA2 induction by oxidative stress and determined the relationship between PKC and Pl3-kinase. Although PKC activation by phorbol 12-myristate-13-acetate (PMA) did not increase the extents of constitutive and inducible GSTA2 expression, either PKC depletion by PMA or PKC inhibition by staurosporine significantly inhibited GSTA2 induction by tert-butylhydroquinone (t-BHQ) a prooxidant chemical. Therefore, the basal PKC activity is requisite for GSTA2 induction. 3-Morpholinosydnonimine (SIN-1), which decomposes and yields peroxynitrite, induced GSTA2, which was not inhibited by PKC depletion, but slightly enhanced by PKC activation, suggesting that PKC promotes peroxynitrite formation for Nrf2-mediated GSTA2 induction. Treatment of cells with S-nitroso-N-acetyl-penicillamine (SNAP), an exogenous NO donor, in combination with t-BHQ may produce peroxynitrite. GSTA2 induction by SNAP + t-BHQ was not decreased by PKC depletion, but rather enhanced by PKC activation, showing that the activity of PKC might be required for peroxynitrite formation. LY294002 a Pl3-kinase inhibitor blocked GSTA2 induction by t-BHQ, which was reversed by PMA-induced PKC activation. These results provide evidence that PKC may play a role in formation of peroxynitrite that activates Nrf2 for GSTA2 induction and that PKC may serve an activator for GSTA2 induction downstream of Pl3-kinase.