Purification and characterization of a cyclooxygenase-2 and angiogenesis suppressing factor produced by human fibroblasts

5-Methoxytryptophan alleviates atrial structural remodeling in ibrutinib-associated atrial fibrillation

Background

Ibrutinib is an effective and well-tolerated treatment for B-cell lymphomas but is associated with an increased risk of atrial fibrillation (AF) by altering the structure of the atrium. 5-Methoxytryptophan (5-MTP) inhibits inflammatory and fibrotic processes. This study aimed to determine the effects and mechanisms of 5-MTP on the underlying mechanisms of AF caused by ibrutinib.

Methods

The effect of 5-MTP on ibrutinib-related AF was investigated in male Sprague Dawley rats using echocardiographic, electrophysiological, immunofluorescent, Masson staining, and molecular analyses.

Rusults

The ibrutinib+5-MTP group showed (1) a lower incidence and shorter duration of AF and accelerated atrial conduction; (2) a decreased left atrial mass and left atrial diameter; (3) decreased myocardial fibrosis in the left atrium; (4) lower atrial inflammation; (5) increased sarcoplasmic reticulum Ca2+-ATPase 2a protein expression, decreased phosphorylation of phospholamban at Thr17, and decreased sodium/calcium exchanger 1 protein expression and phosphorylation of ryanodine receptor 2 at S2814; and (6) decreased phosphorylation of CaMKII expression. 5-MTP treatment markedly activated the PI3K-Akt signaling. Inhibiting PI3K-Akt signaling significantly reversed the protective effect of 5-MTP on ibrutinib-related AF.

Conclusions

These findings suggest that 5-MTP administration decreases the vulnerability of ibrutinib-related AF mainly caused by ameliorated maladaptive left atrial remodeling and dysregulation of calcium handling proteins. Mechanistically, 5-MTP treatment markedly enhanced the activation of cardiac PI3K-Akt signaling.

Control of Tissue Fibrosis by 5-Methoxytryptophan, an Innate Anti-Inflammatory Metabolite

Tissue fibrosis causes debilitating human diseases such as liver cirrhosis, heart failure, chronic kidney disease and pulmonary insufficiency. It is a dynamic process orchestrated by specific subsets of monocyte-macrophages, fibroblasts, pericytes and hepatic stellate cells. Fibrosis is linked to tissue inflammation. Pro-inflammatory macrophages promote fibrosis by driving myofibroblast differentiation and macrophage myofibroblast transition. Myofibroblasts express α-smooth muscle cell actin (α-SMA) and secrete extracellular matrix (ECM) proteins notably collagen I and III. Deposition of ECM proteins at injury sites and interstitial tissues distorts normal structure and impairs vital functions. Despite advances in the mechanisms of fibrosis at cellular, molecular and genetic levels, prevention and treatment of fibrotic diseases remain poorly developed. Recent reports suggest that 5-methoxytryptophan (5-MTP) is effective in attenuating injury-induced liver, kidney, cardiac and pulmonary fibrosis. It inhibits macrophage activation and blocks fibroblast differentiation to myofibroblasts. Furthermore, it inhibits hepatic stellate cell differentiation into myofibroblasts. As 5-MTP is an endogenous molecule derived from tryptophan catabolism via tryptophan hydroxylase pathway, it is well-suited as a lead compound for developing new anti-fibrotic drugs. This article provides an overview of 5-MTP synthesis, and a critical review of its anti-fibrotic activities. Its mechanisms of actions and potential therapeutic value will be discussed.

Association of Tumor Hydroxyindole O-Methyltransferase and Serum 5-Methoxytryptophan with Long-Term Survival of Hepatocellular Carcinoma

Simple Summary

5-methoxytryptophan (5-MTP) is a tryptophan (Trp) metabolite synthesized by hydroxyindole O-methyltransferase (HIOMT). Expression of HIOMT is decreased in various tumors. However, whether HIOMT expression and serum 5-MTP concentration associate with prognosis of hepatocellular carcinoma (HCC) remains unclear. The aim of this study was to analyze HCC tissue HIOMT mRNA and serum 5-MTP and determine their association with survival following therapeutic liver resection. We found a significant association of serum 5-MTP or tissue HIOMT and serum kynurenine (Kyn) with overall and relapse free (RF) survival of HCC. The combination of serum 5-MTP and Kyn is a potential prognostic biomarker of HCC.

Abstract

5-methoxytryptophan (5-MTP) is a recently discovered tryptophan (Trp) metabolite with anti-inflammatory and tumor-suppressing actions. Its synthesis is catalyzed by hydroxyindole O-methyltransferase (HIOMT). HIOMT levels were reported to be decreased in some patients with colorectal, pancreatic and breast cancer. It is unclear whether tissue HIOMT levels is altered in hepatocellular carcinoma (HCC). It is also unclear whether serum 5-MTP concentration is influenced by HCC. In this study, 150 HCC and adjacent normal liver tissues and serum samples were obtained from the HCC biobank established by a prospective multicenter study. Serum samples from 47 healthy subjects were included as a reference. HIOMT mRNA was measured by real time PCR. Serum 5-MTP and selected Trp metabolites were analyzed by quantitative LC-MS. HCC tissue HIOMT mRNA levels adjusted for adjacent normal tissue HIOMT mRNA levels was associated with overall and relapse-free (RF) survival. Combined serum 5-MTP or tissue HIOMT mRNA and serum kynurenine (Kyn) analysis predicted prolonged overall and RF survival following liver resection. A high serum 5-MTP or tissue HIOMT mRNA and low serum Kyn is associated with long-term survival. In conclusion, tumor tissue HIOMT mRNA and serum 5-MTP are potential biomarkers of HCC, especially when analyzed in combination with serum Kyn.

5-Methoxytryptophan attenuates postinfarct cardiac injury by controlling oxidative stress and immune activation

AIMS

Myocardial infarction (MI) remains a major cause of heart failure. 5-Methoxytryptophan (5-MTP), a 5-methoxyindole metabolite of L-tryptophan, exerts anti-inflammatory and antifibrotic effects, but MI impairs the biosynthesis of cardiac 5-MTP. Therefore, we evaluated the effect of exogenous 5-MTP administration on rescuing post-MI cardiac injury.

METHODS AND RESULTS

After a detailed pharmacokinetic analysis of 5-MTP, Sprague Dawley rats that had undergone left anterior descending coronary artery ligation received intraperitoneal administration of either 17 mg/kg 5-MTP or saline at 0.5 and 24 h after MI. Cardiac systolic function, infarction size, and fibrosis were evaluated using echocardiography, triphenyltetrazolium chloride staining, and Masson trichrome staining, respectively. Myocardial apoptosis was analyzed by staining for caspase-3 and cardiac troponin I. 5-MTP treatment decreased the infarct area and myocardial apoptosis; attenuated systolic dysfunction and left ventricular dilatation; and reduced cardiomyocyte hypertrophy, myocardial fibrosis, and infarct expansion. Crucially, 5-MTP alleviated oxidative stress by preserving mitochondrial antioxidant enzymes and downregulating reactive oxygen species-generating NADPH oxidase isoforms and endothelin-1. Consequently, 5-MTP-treated MI rat hearts exhibited lower levels of chemokines and cytokines, namely interleukin (IL)-1β, IL-18, IL-6, C-C motif chemokine ligand (CCL)-2, and CCL5, accompanied by reduced infiltration of CD11b⁺ cells and CD4⁺ T cells. Notably, 5-MTP protected against H₂O₂-induced damage in HL-1 cardiomyocytes and human umbilical vein endothelial cells in vitro.

CONCLUSION

5-MTP prevented post-MI cardiac injury by promoting mitochondrial stabilization and controlling redox imbalance. This cytoprotective effect ameliorated macrophage and T-cell infiltration, thus reducing the infarct size, attenuating fibrosis, and restoring myocardial function.

Cytoguardin: A Tryptophan Metabolite against Cancer Growth and Metastasis

Cytoguardin was identified in the conditioned medium of fibroblasts as a tryptophan metabolite, 5-methoxytryptophan (5-MTP). It is synthesized via two enzymatic steps: tryptophan hydroxylase (TPH) and hydroxyindole O-methyltransferase (HIOMT). A truncated HIOMT isoform, HIOMT298, catalyzes 5-MTP synthesis. Cancer cells produce scarce 5-MTP due to defective HIOMT298 expression. 5-MTP inhibits cancer cell COX-2 expression and thereby reduces COX-2-mediated cell proliferation and migration. 5-MTP also inhibits MMP-9 expression and thereby reduces cancer cell invasion. 5-MTP exerts its anti-cancer effect by blocking p38 MAPK and p38-mediated NF-κB and p300 HAT activation. The stable transfection of A549 cells with HIOMT298 restores 5-MTP production which renders cancer cells less aggressive. The implantation of HIOMT-transfected A549 into subcutaneous tissues of a murine xenograft tumor model shows that HIOMT-transduced A549 cells form smaller tumors and generate fewer metastatic lung nodules than control A549 cells. HIOMT298 transfection suppresses aromatic amino acid decarboxylase (AADC) expression and serotonin production. Serotonin is a cancer-promoting factor. By restoring 5-MTP and suppressing serotonin production, HIOMT298 overexpression converts cancer cells into less malignant phenotypes. The analysis of HIOMT expression in a human cancer tissue array showed reduced HIOMT levels in a majority of colorectal, pancreatic, and breast cancer. HIOMT298 may be a biomarker of human cancer progression. Furthermore, 5-MTP has the potential to be a lead compound in the development of new therapy for the chemoprevention of certain cancers such as hepatocellular cancer.

Control of Mesenchymal Stromal Cell Senescence by Tryptophan Metabolites

Cellular senescence contributes to aging and age-related disorders. High glucose (HG) induces mesenchymal stromal/stem cell (MSC) senescence, which hampers cell expansion and impairs MSC function. Intracellular HG triggers metabolic shift from aerobic glycolysis to oxidative phosphorylation, resulting in reactive oxygen species (ROS) overproduction. It causes mitochondrial dysfunction and morphological changes. Tryptophan metabolites such as 5-methoxytryptophan (5-MTP) and melatonin attenuate HG-induced MSC senescence by protecting mitochondrial integrity and function and reducing ROS generation. They upregulate the expression of antioxidant enzymes. Both metabolites inhibit stress-induced MSC senescence by blocking p38 MAPK signaling pathway, NF-κB, and p300 histone acetyltransferase activity. Furthermore, melatonin upregulates SIRT-1, which reduces NF-κB activity by de-acetylation of NF-κB subunits. Melatonin and 5-MTP are a new class of metabolites protecting MSCs against replicative and stress-induced cellular senescence. They provide new strategies to improve the efficiency of MSC-based therapy for diverse human diseases.

Endothelium-Derived 5-Methoxytryptophan Protects Endothelial Barrier Function by Blocking p38 MAPK Activation

The endothelial junction is tightly controlled to restrict the passage of blood cells and solutes. Disruption of endothelial barrier function by bacterial endotoxins, cytokines or growth factors results in inflammation and vascular damage leading to vascular diseases. We have identified 5-methoxytryptophan (5-MTP) as an anti-inflammatory factor by metabolomic analysis of conditioned medium of human fibroblasts. Here we postulated that endothelial cells release 5-MTP to protect the barrier function. Conditioned medium of human umbilical vein endothelial cells (HUVECs) prevented endothelial hyperpermeability and VE-cadherin downregulation induced by VEGF, LPS and cytokines. We analyzed the metabolomic profile of HUVEC conditioned medium and detected 5-MTP but not melatonin, serotonin or their catabolites, which was confirmed by enzyme-linked immunosorbent assay. Addition of synthetic pure 5-MTP preserved VE-cadherin and maintained barrier function despite challenge with pro-inflammatory mediators. Tryptophan hydroxylase-1, an enzyme required for 5-MTP biosynthesis, was downregulated in HUVECs by pro-inflammatory mediators and it was accompanied by reduction of 5-MTP. 5-MTP protected VE-cadherin and prevented endothelial hyperpermeability by blocking p38 MAPK activation. A chemical inhibitor of p38 MAPK, SB202190, exhibited a similar protective effect as 5-MTP. To determine whether 5-MTP prevents vascular hyperpermeability in vivo, we evaluated the effect of 5-MTP administration on LPS-induced murine microvascular permeability with Evans blue. 5-MTP significantly prevented Evans blue dye leakage. Our findings indicate that 5-MTP is a new class of endothelium-derived molecules which protects endothelial barrier function by blocking p38 MAPK.

5-methoxyindole metabolites of L-tryptophan: control of COX-2 expression, inflammation and tumorigenesis

Cyclooxygenase-2(COX-2) overexpression promotes inflammation and tumorigenesis. COX-2 expression in response to diverse stimuli is tightly controlled to avoid persistent overexpression. 5-methoxyindole metabolites of L-tryptophan represent a new class of compounds that control COX-2 expression at the transcriptional level. Two of the metabolites, the newly discovered 5-methoxytryptophan (5-MTP, also known as cytoguardin) and N-acetyl 5-methoxytryptamine (melatonin) are the focus of this review. 5-MTP is produced by mesenchymal cells such as fibroblasts via 5-hydroxytryptophan (5-HTP). It inhibits COX-2 transcriptional activation induced by diverse proinflammatory and mitogenic factors. Cancer cells are deficient in cytoguardin production which contributes to COX-2 overexpression. Fibroblast-generated 5-MTP is capable of restoring the control of COX-2 overexpression in cancer cells. 5-MTP blocks cancer cell migration and invasion in vitro and inhibits tumor growth and cancer metastasis in a xenograft model. Melatonin possesses similar COX-2 suppressing and anti-cancer properties albeit at supra-pharmacological concentrations. By contrast, 5-hydroxyindole metabolites of L-tryptophan such as 5-hydroxytryptamine (serotonin), 5-hydroxytryptophol and other serotonin catabolites do not control COX-2 expression. 5-hydroxytryptophan inhibits COX-2 expression through conversion to 5-MTP. The physiological relevance of 5-MTP as an endogenous regulator of inflammation and cancer metastasis remains to be investigated. On the other hand, 5-methoxyindole metabolites of tryptophan are valuable lead compounds for development of new anti-inflammatory drugs and cancer chemoprevention.

Quiescent and proliferative fibroblasts exhibit differential p300 HAT activation through control of 5-methoxytryptophan production

Quiescent fibroblasts possess unique genetic program and exhibit high metabolic activity distinct from proliferative fibroblasts. In response to inflammatory stimulation, quiescent fibroblasts are more active in expressing cyclooxygenase-2 and other proinflammatory genes than proliferative fibroblasts. The underlying transcriptional mechanism is unclear. Here we show that phorbol 12-myristate 13-acetate (PMA) and cytokines increased p300 histone acetyltransferase activity to a higher magnitude (> 2 fold) in quiescent fibroblasts than in proliferative fibroblasts. Binding of p300 to cyclooxygenase-2 promoter was reduced in proliferative fibroblasts. By ultrahigh-performance liquid chromatography coupled with a quadrupole time of flight mass spectrometer and enzyme-immunoassay, we found that production of 5-methoxytryptophan was 2–3 folds higher in proliferative fibroblasts than that in quiescent fibroblasts. Addition of 5-methoxytryptophan and its metabolic precursor, 5-hydroxytryptophan, to quiescent fibroblasts suppressed PMA-induced p300 histone acetyltransferase activity and cyclooxygenase-2 expression to the level of proliferative fibroblasts. Silencing of tryptophan hydroxylase-1 or hydroxyindole O-methyltransferase in proliferative fibroblasts with siRNA resulted in elevation of PMA-induced p300 histone acetyltransferase activity to the level of that in quiescent fibroblasts, which was rescued by addition of 5-hydroxytryptophan or 5-methoxytryptophan. Our findings indicate that robust inflammatory gene expression in quiescent fibroblasts vs. proliferative fibroblasts is attributed to uncontrolled p300 histone acetyltransferase activation due to deficiency of 5-methoxytryptophan production. 5-methoxytryptophan thus is a potential valuable lead compound for new anti-inflammatory drug development.

Quiescent fibroblasts are more active in mounting robust inflammatory responses than proliferative fibroblasts

Quiescent cells are considered to be dormant. However, recent studies suggest that quiescent fibroblasts possess active metabolic profile and certain functional characteristics. We previously observed that serum-starved quiescent fibroblasts respond to proinflammatory stimuli by robust expression of cyclooxygenase-2 (COX-2), which declines after the quiescent fibroblasts are driven to proliferation. In this study, we elucidated the underlying signaling and transcriptional mechanism and identified by microarray genes with similar differential expression. By using pharmacological inhibitors coupled with gene silencing, we uncovered the key role of protein kinase C δ (PKCδ) and extracellular signal regulated protein kinase 1/2 (ERK1/2) signaling in mediating COX-2 expression in quiescent cells. Surprisingly, COX-2 expression in proliferative cells was not blocked by PKCδ or ERK1/2 inhibitors due to intrinsic inhibition of PKCδ and ERK1/2 in proliferative cells. Restrained COX-2 transcription in proliferative cells was attributable to reduced NF-κB binding. Microarray analysis identified 35 genes whose expressions were more robust in quiescent than in proliferative cells. A majority of those genes belong to proinflammatory cytokines, chemokines, adhesive molecules and metalloproteinases, which require NF-κB for transcription. Quiescent fibroblasts had a higher migratory activity than proliferative fibroblasts as determined by the transwell assay. Selective COX-2 inhibition reduced migration which was restored by prostaglandin E(2). As COX-2 and inflammatory mediators induce DNA oxidation, we measured 8-hydroxydeoxyguanosine (8-OHdG) in quiescent vs. proliferative fibroblasts. PMA-induced 8-OHdG accumulation was significantly higher in quiescent than in proliferative fibroblasts. These findings indicate that quiescent fibroblasts (and probably other quiescent cells) are at the forefront in mounting inflammatory responses through expression of an array of proinflammatory genes via the PKCδ/ERK1/2 signaling pathway.

Control of cyclooxygenase-2 expression and tumorigenesis by endogenous 5-methoxytryptophan

Cyclooxygenase-2 (COX-2) expression is induced by mitogenic and proinflammatory factors. Its overexpression plays a causal role in inflammation and tumorigenesis. COX-2 expression is tightly regulated, but the mechanisms are largely unclear. Here we show the control of COX-2 expression by an endogenous tryptophan metabolite, 5-methoxytryptophan (5-MTP). By using comparative metabolomic analysis and enzyme-immunoassay, our results reveal that normal fibroblasts produce and release 5-MTP into the extracellular milieu whereas A549 and other cancer cells were defective in 5-MTP production. 5-MTP was synthesized from L-tryptophan via tryptophan hydroxylase-1 and hydroxyindole O-methyltransferase. 5-MTP blocked cancer cell COX-2 overexpression and suppressed A549 migration and invasion. Furthermore, i.p. infusion of 5-MTP reduced tumor growth and cancer metastasis in a murine xenograft tumor model. We conclude that 5-MTP synthesis represents a mechanism for endogenous control of COX-2 overexpression and is a valuable lead for new anti-cancer and anti-inflammatory drug development.

Quercetin suppresses cyclooxygenase-2 expression and angiogenesis through inactivation of P300 signaling

Quercetin, a polyphenolic bioflavonoid, possesses multiple pharmacological actions including anti-inflammatory and antitumor properties. However, the precise action mechanisms of quercetin remain unclear. Here, we reported the regulatory actions of quercetin on cyclooxygenase-2 (COX-2), an important mediator in inflammation and tumor promotion, and revealed the underlying mechanisms. Quercetin significantly suppressed COX-2 mRNA and protein expression and prostaglandin (PG) E(2) production, as well as COX-2 promoter activation in breast cancer cells. Quercetin also significantly inhibited COX-2-mediated angiogenesis in human endothelial cells in a dose-dependent manner. The in vitro streptavidin-agarose pulldown assay and in vivo chromatin immunoprecipitation assay showed that quercetin considerably inhibited the binding of the transactivators CREB2, C-Jun, C/EBPβ and NF-κB and blocked the recruitment of the coactivator p300 to COX-2 promoter. Moreover, quercetin effectively inhibited p300 histone acetyltransferase (HAT) activity, thereby attenuating the p300-mediated acetylation of NF-κB. Treatment of cells with p300 HAT inhibitor roscovitine was as effective as quercetin at inhibiting p300 HAT activity. Addition of quercetin to roscovitine-treated cells did not change the roscovitine-induced inhibition of p300 HAT activity. Conversely, gene delivery of constitutively active p300 significantly reversed the quercetin-mediated inhibition of endogenous HAT activity. These results indicate that quercetin suppresses COX-2 expression by inhibiting the p300 signaling and blocking the binding of multiple transactivators to COX-2 promoter. Our findings therefore reveal a novel mechanism of action of quercetin and suggest a potential use for quercetin in the treatment of COX-2-mediated diseases such as breast cancers.

Interferon-gamma suppresses cyclooxygenase-2 promoter activity by inhibiting C-Jun and C/EBPbeta binding

OBJECTIVE

Cyclooxygenase-2 (COX-2) and interferon gamma (IFNgamma) are overexpressed in vascular inflammatory and atherosclerotic lesions. We postulated that IFNgamma suppresses COX-2 expression at the transcriptional level.

METHODS AND RESULTS

The effect of IFNgamma on COX-2 expression was evaluated in several types of human cells stimulated with phorbol 12-myristate 13-acetate (PMA), interleukin (IL)-1beta, or tumor necrosis factor (TNF) alpha. IFNgamma concentration-dependently inhibited COX-2 proteins and promoter activities induced by PMA or cytokines in human fibroblasts and monocytic and endothelial cells. PMA and cytokines stimulate binding of C-Jun, C-Fos, CCAAT/enhancer binding protein beta (C/EBPbeta), or NF-kappaB to their respective regulatory elements on COX-2 promoter. IFNgamma blocked C-Jun and C/EBPbeta but not C-Fos or p50 NF-kappaB binding as determined by in vitro binding assays and chromatin immunoprecipitation assay. p300 binding to COX-2 promoter was inhibited by IFNgamma in a manner comparable to C-Jun and C/EBPbeta binding.

CONCLUSIONS

IFNgamma suppresses proinflammatory mediator-induced COX-2 transcription by selective inhibition of C-Jun and C/EBPbeta DNA binding activity and p300 recruitment in human cells. Because IFNgamma is coexpressed with COX-2 in vascular lesions, it may play a role in controlling COX-2-mediated inflammatory changes.

Differential cyclooxygenase-2 transcriptional control in proliferating versus quiescent fibroblasts

Cyclooxygenase-2 (COX-2) overexpression is associated with cancer. One potential mechanism is DNA damage caused by COX-2 derived oxidants. Since DNA in proliferating cells is highly vulnerable to oxidative damage and mutation, we propose that COX-2 transactivation by exogenous stimuli is suppressed in proliferating cells compared to quiescent cells. In this review, we provide evidence for reduced COX-2 transcriptional expression in response to phorbol esters (PMA), lipopolysaccharide (LPS), interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha). Our results show that COX-2 transcription in proliferating fibroblasts is suppressed by a small molecular weight compound produced by proliferating cells. By contrast, COX-2 expression in response to exogenous stimuli is robust in quiescent cells. The quiescent cells in human body may play a primary role in mounting response to exogenous stimuli. Salicylate inhibits COX-2 transcriptional activation in quiescent cells but not in serum-driven proliferating cells by blocking C/EBPbeta DNA binding. These studies suggest that COX-2 expressions in quiescent and proliferating cells are regulated by different mechanisms. Further investigations into their transcriptional control mechanisms will have great impact on the fundamental understanding of the division of cell functions between quiescent and proliferating cells and the design of novel therapeutic strategies.

Regulation of intracellular cyclooxygenase levels by gene transcription and protein degradation

Cyclooxygenases-1 and -2 (COX-1 and -2) catalyze the committed step in prostaglandin formation. Each isozyme subserves different biological functions. This is, at least in part, a consequence of differences in patterns of COX-1 and COX-2 expression. COX-1 is induced during development, and COX-1 mRNA and COX-1 protein are very stable. These latter properties can explain why COX-1 protein levels usually remain constant in those cells that express this isozyme. COX-2 is usually expressed inducibly in association with cell replication or differentiation. Both COX-2 mRNA and COX-2 protein have short half-lives relative to those of COX-1. Therefore, COX-2 protein is typically present for only a few hours after its synthesis. Here we review and develop the concepts that (a) COX-2 gene transcription can involve at least six different cis-acting promoter elements interacting with trans-acting factors generated by multiple, different signaling pathways, (b) the relative contribution of each cis-acting COX-2 promoter element depends on the cell type, the stimulus and the time following the stimulus and (c) a unique 27 amino acid instability element located just upstream of the C-terminus of COX-2 targets this isoform to the ER-associated degradation system and proteolysis by the cytosolic 26S proteasome.

Transcriptional Control of COX-2 via C/EBPbeta

Cyclooxygenase-2 (COX-2) is a highly inducible enzyme exerting diverse actions on cell functions, including proliferation, migration, and DNA damage. Enhanced COX-2 expression may be protective, but excessive expression may be harmful, causing inflammation, atheromatous plaque instability, and intimal hyperplasia. COX-2 transcriptional activation by proinflammatory mediators has been extensively characterized. In this review, the role of C/EBP in regulating COX-2 transcription is highlighted. Recent advances in control of COX-2 transcription by aspirin and salicylate and by a cell cycle-dependent endogenous mechanism are described. The recent progress sheds light on the pathophysiological mechanisms of COX-2 and new transcription-based strategy for controlling COX-2 overexpression and COX-2-mediated cardiovascular diseases.

Regulation of Inducible Nitric Oxide Synthase Expression by p300 and p50 Acetylation

To determine whether p300 is involved in inducible NO synthase (iNOS) transcriptional regulation, we evaluated the effect of p300 overexpression on iNOS expression and characterized p300 binding to iNOS promoter in RAW 264.7 cells. p300 overexpression increased iNOS expression which was abrogated by deletion of the histone acetyltransferase (HAT) domain (Delta1472-1522). DNA-binding and chromatin immunoprecipitation assays revealed binding of p300 to several DNA-bound transactivators at basal state. Following stimulation with LPS plus IFN-gamma, binding of p300, p50/p65 NF-kappaB, and IFN-regulatory factor-1 was increased by approximately 2-fold. Nuclear p50 was complexed with and acetylated by p300 at the basal binding state which was increased by LPS and IFN-gamma stimulation. p300 overexpression resulted in increased p50 acetylation which was reduced by HAT mutation. p50 acetylation correlated with increased NF-kappaB binding and enhanced p300 recruitment. Co-overexpression of E1A abolished the augmentation of p50 acetylation and p50 binding induced by p300 overexpression, and a correlative suppression of p300 recruitment to the complex. We conclude that p300 is essential for iNOS transcription. Our results suggest that p300 HAT acetylates the p50 subunit of NF-kappaB, thereby increasing NF-kappaB binding and NF-kappaB mediated transactivation.

The Potential Contributions of Chronic Inflammation to Lung Carcinogenesis

A number of lines of evidence suggests that chronic inflammation contributes to the process of carcinogenesis. In this article, this theme is explored with particular emphasis on the involvement of inflammation in the development of lung cancer. A number of molecular pathways activated in chronic inflammation may contribute to lung carcinogenesis. The challenge is to conceptualize a cohesive picture of this complex biology that allows for effective pharmaceutical intervention. Initial therapeutic efforts involve strategies to block single pathways, such as with cyclooxygenase (COX) activity. However, the more that is learned about the consequences of COX activity, the more evident are the relationships of this enzyme to other classes of regulatory molecules such as the potent nuclear factor-kB. In light of this emerging picture, more global intervention strategies, such as with drug combinations, may be essential for success. Further basic study is essential to sort out possible molecular relationships and to permit elucidation of the most critical regulatory circuits. Given the complexity of these molecular interactions, well-designed clinical trials that specifically evaluate the precise effects of particular antiinflammatory drugs on lung carcinogenesis will also be critical to sort out the complexity and to validate successful approaches to arresting lung carcinogenesis.

Activation-induced PPARgamma expression sensitizes primary human T cells toward apoptosis

Phytohemagglutinin (PHA) elicited expression of peroxisome proliferator-activated receptor gamma (PPARgamma) in primary human T cells via the PPARgamma3 promoter, as shown by reverse transcription-polymerase chain reaction. Electrophoretic mobility shift assay demonstrated no correlation between PPARgamma expression and its activation. However, addition of specific PPARgamma agonists such as ciglitazone or 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) for 1 h following PHA pretreatment provoked PPARgamma activation verified by supershift analysis. Taking the proapoptotic properties of PPARgamma into consideration, we analyzed induction of apoptosis in activated T cells in response to PPARgamma agonists. Cells exposed to PPARgamma agonists alone revealed minor cell death compared with controls, whereas treatment with 15d-PGJ(2) or ciglitazone for 4 h subsequent to PHA stimulation significantly increased cell demise, which was attenuated by the pan-caspase inhibitor zVAD, pointing to apoptosis as the underlying mechanism. These data may be relevant for pathophysiological conditions accompanied with lymphopenia of T cells under conditions such as sepsis.

Up-regulation of p300 binding and p50 acetylation in tumor necrosis factor-alpha-induced cyclooxygenase-2 promoter activation

It is well established that p300 plays an important role in mediating gene expressions. However, it is less clear how its binding is influenced by physiological stimuli and how its altered binding affects transactivator acetylation and binding. In this study, we determined p300 binding to a core cyclooxygenase-2 (COX-2) promoter region by chromatin immunoprecipitation and streptavidin-agarose pull-down assays in basal and tumor necrosis factor-alpha (TNFalpha)-treated human foreskin fibroblasts. We found basal binding of p300, p50/p65 NF-kappaB, cyclic AMP regulatory element-binding protein-2, CCAAT/enhancer-binding protein beta, and c-Jun. p50/p65 and p300 binding was selectively increased by TNFalpha. Immunoprecipitation confirmed direct interaction of p300 with NF-kappaB and the other involved transactivators. p50 acetylation was detected in resting cells and was increased by TNFalpha or lipopolysaccharide. Overexpression of p300 augmented p50 acetylation, which was attenuated by deletion of its histone acetyltransferase domain. Enhanced p50 acetylation correlated with increased p50 binding to COX-2 promoter and transcriptional activation. Co-transfection of E1A with p300 abrogated p50 acetylation and p50 binding. These findings suggest that up-regulation of p300 binding and its acetylation of NF-kappaB occupies a central position in COX-2 promoter activation.