The cyclopentenone-type prostaglandin 15-deoxy-delta 12,14-prostaglandin J2 inhibits CD95 ligand gene expression in T lymphocytes: interference with promoter activation via peroxisome proliferator-activated receptor-gamma-independent mechanisms

Bone Marrow Stromal Cell-Derived IL-8 Upregulates PVR Expression on Multiple Myeloma Cells via NF-kB Transcription Factor

Bone marrow stromal cells (BMSCs) strongly contribute to multiple myeloma (MM) progression, promoting the survival and growth of malignant plasma cells (PCs). However, the possible impact of these cells on the immune-mediated recognition of MM cells remains largely unknown. DNAM-1 activating receptor plays a prominent role in NK cell anti-MM response engaging the ligands poliovirus receptor (PVR) and nectin-2 on malignant PCs. Here, we analysed the role of MM patient-derived BMSCs in the regulation of PVR expression. We found that BMSCs enhance PVR surface expression on MM cells and promote their NK cell-mediated recognition. PVR upregulation occurs at transcriptional level and involves NF-kB transcription factor activation by BMSC-derived soluble factors. Indeed, overexpression of a dominant-negative mutant of IKBα blocked PVR upregulation. IL-8 plays a prominent role in these mechanisms since blockade of CXCR1/2 receptors as well as depletion of the cytokine via RNA interference prevents the enhancement of PVR expression by BMSC-derived conditioned medium. Interestingly, IL-8 is associated with stromal microvesicles which are also required for PVR upregulation via CXCR1/CXCR2 signaling activation. Our findings identify BMSCs as regulators of NK cell anti-MM response and contribute to define novel molecular pathways involved in the regulation of PVR expression in cancer cells.

15-Deoxy-Δ12,14-Prostaglandin J 2 Reinforces the Anti-Inflammatory Capacity of Endothelial Cells With a Genetically Determined NO Deficit

Rationale:

Fluid shear stress (FSS) maintains NOS-3 (endothelial NO synthase) expression. Homozygosity for the C variant of the T-786C single-nucleotide polymorphism of the NOS3 gene, which solely exists in humans, renders the gene less sensitive to FSS, resulting in a reduced endothelial cell (EC) capacity to generate NO. Decreased bioavailability of NO in the arterial vessel wall facilitates atherosclerosis. Consequently, individuals homozygous for the C variant have an increased risk for coronary heart disease (CHD).

Objective:

At least 2 compensatory mechanisms seem to minimize the deleterious effects of this single-nucleotide polymorphism in affected individuals, one of which is characterized herein.

Methods and Results:

Human genotyped umbilical vein ECs and THP-1 monocytes were used to investigate the role of 15-deoxy-Δ12,14-prostaglandin J 2 (15d-PGJ 2 ) in vitro. Its concentration in plasma samples from genotyped patients with CHD and age-matched CHD-free controls was determined using quantitative ultraperformance LC-MS/MS. Exposure of human ECs to FSS effectively reduced monocyte transmigration particularly through monolayers of CC-genotype ECs. Primarily in CC-genotype ECs, FSS elicited a marked rise in COX (cyclooxygenase)-2 and L-PGDS (lipocalin-type prostaglandin D synthase) expression, which appeared to be NO sensitive, and provoked a significant release of 15d-PGJ 2 over baseline. Exogenous 15d-PGJ 2 significantly reduced monocyte transmigration and exerted a pronounced anti-inflammatory effect on the transmigrated monocytes by downregulating, for example, transcription of the IL (interleukin)-1β gene ( IL1B ). Reporter gene analyses verified that this effect is due to binding of Nrf2 (nuclear factor [erythroid-derived 2]–like 2) to 2 AREs (antioxidant response elements) in the proximal IL1B promoter. In patients with CHD, 15d-PGJ 2 plasma levels were significantly upregulated compared with age-matched CHD-free controls, suggesting that this powerful anti-inflammatory prostanoid is part of an endogenous defence mechanism to counteract CHD.

Conclusions:

Despite a reduced capacity to form NO, CC-genotype ECs maintain a robust anti-inflammatory phenotype through an enhanced FSS-dependent release of 15d-PGJ 2 .

17β-Estradiol inhibits TNF-α-induced proliferation and migration of vascular smooth muscle cells via suppression of TRAIL

Atherosclerosis is an inflammatory disease and involves migration of vascular smooth muscle cells (VSMCs). Estrogen inhibits VSMCs migration, while the underlying mechanism remains to be revealed. Recent years, there is emerging evidence showing that TNF-related apoptosis-inducing ligand (TRAIL) increases proliferation and migration of VSMCs. In this study, we investigated the regulatory effect of estrogen on TRAIL expression in VSMCs. TNF-α greatly enhanced TRAIL protein expression and stimulated VSMCs proliferation and migration. This effect was partially inhibited by the addition of TRAIL neutralizing antibody, suggesting that TRAIL is important in TNF-α-induced migration. 17β-estradiol (E2) inhibited TRAIL expression under TNF-α stimulation in a time- and concentration-dependent manner. This effect was was mimicked by ERα agonist 4',4″,4‴-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT), but not ERβ agonist 2,3-bis-(4-hydroxyphenyl)-propionitrile (DPN), indicating that ERα is involved in this action. TNF-α led to nuclear factor kappa B (NF-κB) p65 phosphorylation and the inhibitor pyrrolidine dithiocarbama (PDTC) inhibited TRAIL expression, suggesting that NF-κB signaling is crucial for TARIL production. E2 suppressed p65 phosphorylation in VSMCs and the overexpression of p65 subunit reversed the inhibitory effect of E2 on TRAIL expression and cell proliferation and migration. Taken together, our results indicate that E2 inhibits VSMCs proliferation and migration by downregulation of TRAIL expression via suppression of NF-κB pathway.

Advances in Our Understanding of Oxylipins Derived from Dietary PUFAs

Oxylipins formed from polyunsaturated fatty acids (PUFAs) are the main mediators of PUFA effects in the body. They are formed via cyclooxygenase, lipoxygenase, and cytochrome P450 pathways, resulting in the formation of prostaglandins, thromboxanes, mono-, di-, and tri-hydroxy fatty acids (FAs), epoxy FAs, lipoxins, eoxins, hepoxilins, resolvins, protectins (also called neuroprotectins in the brain), and maresins. In addition to the well-known eicosanoids derived from arachidonic acid, recent developments in lipidomic methodologies have raised awareness of and interest in the large number of oxylipins formed from other PUFAs, including those from the essential FAs and the longer-chain n-3 (ω-3) PUFAs. Oxylipins have essential roles in normal physiology and function, but can also have detrimental effects. Compared with the oxylipins derived from n-3 PUFAs, oxylipins from n-6 PUFAs generally have greater activity and more inflammatory, vasoconstrictory, and proliferative effects, although there are notable exceptions. Because PUFA composition does not necessarily reflect oxylipin composition, comprehensive analysis of the oxylipin profile is necessary to understand the overall physiologic effects of PUFAs mediated through their oxylipins. These analyses should include oxylipins derived from linoleic and α-linolenic acids, because these largely unexplored bioactive oxylipins constitute more than one-half of oxylipins present in tissues. Because collated information on oxylipins formed from different PUFAs is currently unavailable, this review provides a detailed compilation of the main oxylipins formed from PUFAs and describes their functions. Much remains to be elucidated in this emerging field, including the discovery of more oxylipins, and the understanding of the differing biological potencies, kinetics, and isomer-specific activities of these novel PUFA metabolites.

Fluid shear stress-induced osteoarthritis: roles of cyclooxygenase-2 and its metabolic products in inducing the expression of proinflammatory cytokines and matrix metalloproteinases

The mechanical overloading of cartilage is involved in the pathophysiology of osteoarthritis (OA) by both biochemical and mechanical pathways. The application of fluid shear stress to chondrocytes recapitulates the earmarks of OA, as evidenced by the release of proinflammatory cytokines (PICs), matrix metalloproteinases (MMPs), and apoptotic factors. Dysregulations or mutations in these genes might directly cause OA in addition to determining the stage at which OA becomes apparent, the joint sites involved, and the severity of the disease and how rapidly it progresses. However, the underlying mechanisms remain unknown. In this review, we propose that the dysregulation of cyclooxygenase-2 (COX-2) is associated with fluid shear stress-induced OA via its metabolic products at different stages of the disease. Indeed, high fluid shear stress rapidly induces the production of PICs and MMPs via COX-2-derived prostaglandin (PG)E2 at the early stage of OA. In contrast, prolonged shear exposure (>12 h) aggravates the condition by concurrently up-regulating the expression of proapoptotic genes and down-regulating the expression of antiapoptotic genes in a 15-deoxy-Δ (12,14)-prostaglandin J2 (15d-PGJ2)-dependent manner at the late stage of disease. These observations may help to resolve long-standing questions in OA progression and provide insight for development of strategies to treat and combat OA.

Regulation of the human TRAIL gene

TRAIL is a member of the TNF superfamily that induces tumor-selective cell death by engaging the pro-apoptotic death receptors DR4 and DR5. The antitumor potential of the TRAIL pathway has been targeted by several therapeutic approaches including recombinant TRAIL and TRAIL-receptor agonist antibodies among others. Interest in sensitizing tumor cells to TRAIL-mediated apoptosis has driven investigations of TRAIL-receptor gene regulation, though regulation of the TRAIL gene has been less studied. Physiologically, TRAIL serves as a pro-apoptotic effector molecule in the immune surveillance of cancer that is conditionally expressed by immune cells upon stimulation via an interferon-response element that was identified in early studies of the TRAIL gene promoter. Here, we map the TRAIL gene promoter and review studies of TRAIL gene regulation that involve several modalities of gene regulation including transcription factors, epigenetics, single-nucleotide polymorphisms and functionally distinct isoforms.

EGR1 expression: a calcium and ERK1/2 mediated PPARγ-independent event involved in the antiproliferative effect of 15-deoxy-Δ12,14-prostaglandin J2 and thiazolidinediones in breast cancer cells

Our aim was to get new information about the Peroxisome Proliferator Activated Receptor gamma (PPARγ)-independent pathway involved in the antiproliferative action of PPARγ ligands in breast cancer cells. We investigated the effects of Troglitazone (TGZ), Ciglitazone (CGZ), Rosiglitazone (RGZ) and, 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ(2)) on the hormone-dependent breast cancer cell line MCF7. The early transcription factor EGR1 (Early Growth Response gene 1) mRNA and protein levels peaked after 3h of incubation with 25μM TGZ, CGZ or 15d-PGJ(2) and then gradually decreased. RGZ, the most potent activator of PPARγ, did not show this effect. The PPARγ antagonist GW 9662 did not block EGR1 mRNA induction which also still occurred in case of PPARγ silencing as well as in case of treatment with the PPARγ-inactive compound Δ2-TGZ. EGR1 mRNA induction required ERK1/2 phosphorylation which was not blocked by EGF Receptor (EGFR) inhibition. The ERK1/2 pathway was also involved in Δ2-TGZ-induced EGR1 mRNA expression in the hormone-independent breast cancer cell line MDA-MB-231. Using the fluorescent dye Fura2, we showed in MCF7 that TGZ or Δ2-TGZ induced an immediate increase in cytosolic calcium which was required for ERK1/2 phosphorylation and EGR1 mRNA induction as demonstrated by calcium chelation experiments. Furthermore, in MCF7 transfected with siRNA targeting EGR1, Δ2-TGZ inhibited less efficiently cell proliferation.

PPARdelta is a type 1 IFN target gene and inhibits apoptosis in T cells

Peroxisome proliferator-activated receptor beta/delta (PPARdelta) is a nuclear hormone receptor regulating diverse biological processes, including beta-oxidation of fatty acid and epithelial cell differentiation. To date, the role of PPARdelta in the immune system has not been thoroughly studied. Here, we show that PPARdelta is expressed in activated human T cells purified from peripheral blood as well as in T cells isolated from affected psoriasis skin lesions. PPARdelta is induced in T cells on stimulation with type 1 IFN. Functionally, PPARdelta enhances proliferation of primary T cells and blocks apoptosis induced by type 1 IFN and by serum deprivation. We show that these cellular functions are mediated by the activation of extracellular signal-regulated kinase1/2 signaling. Our results (1) establish a direct molecular link between type 1 IFN signaling and PPARdelta, (2) define a functional role for PPARdelta in human T cells, and (3) suggest that the induction of PPARdelta by type 1 IFN contributes to the persistence of activated T cells in psoriasis skin lesions.

Peroxisome proliferator-activated receptor gamma activates fas ligand gene promoter inducing apoptosis in human breast cancer cells

In just over a decade, apart from established metabolic actions, peroxisome proliferator-activated receptor gamma (PPARgamma) has evolved as key therapeutic target in cancer disease. Fas ligand (FasL), a trans-membrane protein, induces apoptosis by crosslinking with the Fas receptor. Despite the FasL relevance, little is available on the regulation of its expression. In the current study, we explored for the first time the potential role of PPARgamma in triggering apoptotic events through the Fas/FasL pathway in breast cancer cells. In MCF7 cells, by reverse transcription-polymerase chain reaction and Western blotting, we showed that the synthetic PPARgamma ligand rosiglitazone (BRL) enhanced FasL expression, that was abrogated by a specific PPARgamma antagonist GW9662. Transient transfection assays demonstrated that BRL transactivated human FasL promoter gene in a PPARgamma-dependent manner. Progressive 5' deletion analysis has identified a minimal promoter fragment spanning nucleotides from -318 to -237 bp, which is still sensitive to BRL treatment. FasL promoter activity was abrogated by mithramycin, suggesting an involvement of Sp1 transcription factor in PPARgamma action. Electrophoretic mobility shift and chromatin immuno-precipitation assays demonstrated that BRL increased the binding of PPARgamma and Sp1 to the Sp1 sequence located within the FasL gene promoter. The role of PPARgamma and Fas/FasL pathways in BRL-induced apoptotic events was assessed by caspase 8 cleavage in the presence of GW as well as PPARgamma and FasL RNA interferences. Our results indicate that PPARgamma positively regulates the FasL gene expression also in MDA-MB231 and in BT20, revealing a new molecular mechanism by which BRL induces apoptosis in breast cancer cells.

Targeting 15d-prostaglandin J2 to hepatic stellate cells: two options evaluated

PURPOSE

Delivery of apoptosis-inducing compounds to hepatic stellate cells (HSC) may be an effective strategy to reverse liver fibrosis. The aim of this study was therefore to examine the selective targeting of the apoptosis-inducing drug 15-deoxy-delta12,14-prostaglandin J2 (15dPGJ2) with two different HSC-carriers: human serum albumin modified with the sugar mannose-6-phosphate (M6PHSA) or albumin modified with PDGF-receptor recognizing peptides (pPBHSA).

METHODS AND RESULTS

After chemical conjugation of 15dPGJ2 to the carriers, the constructs displayed pharmacological activity and specific receptor-mediated binding to HSC in vitro. Unlike 15dPGJ2-pPBHSA, the cellular binding of 15dPGJ2-M6PHSA was reduced by a scavenger receptor antagonist. In vivo, both conjugates rapidly accumulated in fibrotic livers. Intrahepatic analysis revealed that 15dPGJ2-M6PHSA mainly accumulated in HSC, and to a lesser extent in Kupffer cells. 15dPGJ2-pPBHSA also predominantly accumulated in HSC with additional uptake in hepatocytes. Assessment of target receptors in human cirrhotic livers revealed that M6P/IGFII-receptor expression was present in fibrotic areas. PDGF-P receptor expression was abundantly expressed on human fibroblasts.

CONCLUSIONS

These studies show that 15dPGJ2 coupled to either M6PHSA or pPBHSA is specifically taken up by HSC and is highly effective within these cells. Both carriers differ with respect to receptor specificity, leading to differences in intrahepatic distribution. Nevertheless, both carriers can be used to deliver the apoptosis-inducing drug 15dPGJ2 to HSC in vivo.

Inhibition of trail gene expression by cyclopentenonic prostaglandin 15-deoxy-delta12,14-prostaglandin J2 in T lymphocytes

15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is a cyclopentenonic prostaglandin endowed with powerful anti-inflammatory activities, as shown in animal models of inflammatory/autoimmune diseases, where pharmacological administration of this prostanoid can ameliorate inflammation and local tissue damage via activation of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) and/or covalent modifications of cellular proteins. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily expressed in most of the cells, including those of immune system such as T lymphocytes, in which it is up-regulated upon antigen-specific stimulation. This cytokine plays an important role in regulating various physiological and immunopathological processes, such as immunosurveillance of tumors and tissue destruction associated with different inflammatory and autoimmune diseases. Here, we demonstrate that 15d-PGJ(2) inhibits trail mRNA and protein expression by down-regulating the activity of its promoter in human T lymphocytes. Our data indicate that both the chemically reactive cyclopentenone moiety of 15d-PGJ(2) and the activation of PPARgamma may be involved in this repressive mechanism. We identified nuclear factor kappaB (NF-kappaB) as a direct target of the prostanoid. 15d-PGJ(2) significantly decreases the expression and/or DNA binding of c-rel, RelA, and p50 transcription factors to the NF-kappaB1 site of trail promoter. Moreover, 15d-PGJ(2)-mediated activation of the transcription factor heat shock factor-1 may contribute to inhibit trail promoter activity in transfected Jurkat T cells. These results suggest that modulation of TRAIL gene expression by 15d-PGJ(2) in T cells may provide a novel pharmacological tool to modify the onset and the progression of specific autoimmune and inflammatory disorders.

Accumulation of hypoxia-inducible factor-1alpha through a novel electrophilic, thiol antioxidant-sensitive mechanism

15-deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)) is a peroxisome-activated proliferator receptor-gamma (PPARgamma) agonist which contains an alpha,beta-unsaturated electrophilic ketone involved in nucleophilic addition reactions to thiols. Here we studied its effect on hypoxia-inducible factor-1alpha (HIF-1alpha) in human proximal tubular cells HK-2. 15d-PGJ(2) induced stabilization of HIF-1alpha protein, without affecting HIF-1alpha mRNA levels or proteasome activity, leading to its nuclear accumulation and activation of HIF-induced transcription. Accumulation of HIF-1alpha was unaffected by selective PPARgamma blockade nor mimicked by the PPARgamma agonists ciglitazone and 9,10-dihydro-15d-PGJ(2). N-acetylcysteine, reduced glutathione (GSH) or dithiothreitol (i.e. agents that act as thiol reducing agents and/or increase the GSH content), but not reactive oxygen species (ROS) scavengers, prevented 15d-PGJ(2)-induced HIF-1alpha accumulation whereas the inhibitor of GSH synthesis buthionine sulfoximine cooperated with 15d-PGJ(2) to accumulate HIF-1alpha. Finally, HIF-1alpha expression was increased by the electrophilic alpha,beta-unsaturated compounds acrolein and PGA(2), but not by 9,10-dihydro-15d-PGJ(2), which lacks the electrophilic cyclopentenone moiety. Taken together, these results point out to a new mechanism to increase pharmacologically the cell levels of HIF-1alpha through the electrophilic reaction of alpha,beta-unsaturated ketones with thiol groups.

15-deoxy-Delta12,14-prostaglandin J2 negatively regulates rankl gene expression in activated T lymphocytes: role of NF-kappaB and early growth response transcription factors

Receptor activator of NF-kappaB ligand (RANKL) and its receptor RANK are cell surface proteins abundantly expressed in bone and lymphoid tissues, whose interaction triggers different signaling pathways leading to activation and differentiation of osteoclasts, pivotal actors of the normal bone remodeling cycle. Moreover, RANKL may act as an immunomodulator, representing an important dendritic cell survival factor produced by activated T cells. A large body of research has shown that not only does the RANKL/RANK system regulate the physiology of bone development but also plays an important pathological role in bone destruction mediated by inflammatory disorders or bone metastatic tumors. 15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a cyclopentenone-type PG endowed with anti-inflammatory properties and produced by different cells, including those of the immune system. Although 15d-PGJ(2) has been studied as a natural ligand of the peroxisome proliferator-activated receptor-gamma nuclear receptor, relevant peroxisome proliferator-activated receptor-gamma-independent actions mediated by this prostanoid have been described. In this study, we describe the effect of 15d-PGJ(2) on the expression of the rankl gene in T lymphocytes. We show that 15d-PGJ(2) inhibits rankl mRNA expression, protein, and rankl promoter activity by mechanisms mediated by its chemically reactive cyclopentenone moiety. Our data also indicate that 15d-PGJ(2) represses rankl activation by interfering with the expression and/or activity of the transcription factors NF-kappaB, early growth response-2, and early growth response-3, whose altered balancing and transactivation may contribute for the repression of this gene. These results place rankl as a novel molecular target for the different immunoregulatory activities mediated by 15d-PGJ(2). The physiological and pharmacological implications of these observations are discussed.

Peroxisome proliferator-activated receptor gamma promotes lymphocyte survival through its actions on cellular metabolic activities

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a metabolic regulator that plays an important role in sensitizing tissues to the action of insulin and in normalizing serum glucose and free fatty acids in type 2 diabetic patients. The receptor has also been implicated in the modulation of inflammatory responses, and ligands of PPARgamma have been found to induce apoptosis in lymphocytes. However, apoptosis induction may not depend on the receptor, because high doses of PPARgamma agonists are required for this process. Using cells containing or lacking PPARgamma, we reported previously that PPARgamma attenuates apoptosis induced by cytokine withdrawal in a murine lymphocytic cell line via a receptor-dependent mechanism. PPARgamma exerts this effect by enhancing the ability of cells to maintain their mitochondrial membrane potential during cytokine deprivation. In this report, we demonstrate that activation of PPARgamma also protects cells from serum starvation-induced apoptosis in human T lymphoma cell lines. Furthermore, we show that the survival effect of PPARgamma is mediated through its actions on cellular metabolic activities. In cytokine-deprived cells, PPARgamma attenuates the decline in ATP level and suppresses accumulation of reactive oxygen species (ROS). Moreover, PPARgamma regulates ROS through its coordinated transcriptional control of proteins and enzymes involved in ROS scavenging, including uncoupling protein 2, catalase, and copper zinc superoxide dismutase. Our studies identify cell survival promotion as a novel activity of PPARgamma and suggest that PPARgamma may modulate cytokine withdrawal-induced activated T cell death.

Contrary prostaglandins: the opposing roles of PGD2 and its metabolites in leukocyte function

Traditionally, PGD(2) has been considered to be a pro-inflammatory mediator, acting via classical PG receptors, such as the PGD(2) receptor (DP). PGD(2) is degraded rapidly in vitro and in vivo to a variety of metabolites, the majority of which were thought, until recently, to be physiologically inactive. Several "inactive" metabolites, particularly 15d-PGJ(2), have been shown to have wide-ranging effects on leukocytes and other cell types, however, and a potentially important anti-inflammatory role for PGD(2) has now been recognized, and the complexity of PGD(2) signaling is beginning to be elucidated. PGD(2) and its metabolites are biologically active over a broad concentration range, and, intriquingly, it appears that there are marked concentration-dependent variations in the consequences of signaling by these eicosanoids, which have the potential to exert pro- and anti-inflammatory effects. For example, the actions of PGD(2) can influence multiple stages in the life of the mature eosinophil, from causing its release from the bone marrow to inducing its recruitment and activation and, ultimately, regulating its apoptosis. This review is concerned with the diverse responses induced in leukocytes by PGD(2) and its metabolites and the signaling mechanisms which are thought to be responsible for them.

Peroxisome proliferator-activated receptor γ contributes to T lymphocyte apoptosis during sepsis

In the last two decades, extensive research failed to significantly improve the outcome of patients with sepsis. In part, this drawback is based on a gap in our knowledge about molecular mechanisms understanding the pathogenesis of sepsis. During sepsis, T cells are usually depleted. Recent studies in mice and human cells suggested a role of the peroxisome proliferator-activated receptor gamma (PPARgamma) in provoking apoptosis in activated T lymphocytes. Therefore, we studied whether expression/activation of PPARgamma might contribute to T cell death during sepsis. We observed PPARgamma up-regulation in T cells of septic patients. In contrast to controls, PPARgamma expressing cells from septic patients responded with apoptosis when exposed to PPARgamma agonists. Cell demise was attenuated by SR-202, a synthetic PPARgamma antagonist, and specificity was further verified by excluding a proapoptotic response to a PPARalpha agonist. We propose that up-regulation of PPARgamma sensitizes T cells of septic patients to undergo apoptosis. PPARgamma activation in T cells requires an exogenous PPARgamma agonist, which we identified in sera of septic patients. Septic sera were used to study reporter gene expression containing a PPAR-responsive element. We conclude that PPARgamma plays a significant role in T cell apoptosis, contributing to lymphocyte loss in sepsis. Thus, inhibition of PPARgamma may turn out to be beneficial for patients suffering from lymphopenia during sepsis.

Making myc

Myc regulates to some degree every major process in the cell. Proliferation, growth, differentiation, apoptosis, and metabolism are all under myc control. In turn, these processes feed back to adjust the level of c-myc expression. Although Myc is regulated at every level from RNA synthesis to protein degradation, c-myc transcription is particularly responsive to multiple diverse physiological and pathological signals. These signals are delivered to the c-myc promoter by a wide variety of transcription factors and chromatin remodeling complexes. How these diverse and sometimes disparate signals are processed to manage the output of the c-myc promoter involves chromatin, recruitment of the transcription machinery, post-initiation transcriptional regulation, and mechanisms to provide dynamic feedback. Understanding these mechanisms promises to add new dimensions to models of transcriptional control and to reveal new strategies to manipulate Myc levels.

Hyperthermia enhances CD95-ligand gene expression in T lymphocytes

Hyperthermia represents an interesting therapeutic strategy for the treatment of tumors. Moreover, it is able to regulate several aspects of the immune response. Fas (APO-1/CD95) and its ligand (FasL) are cell surface proteins whose interaction activates apoptosis of Fas-expressing targets. In T cells, the Fas-Fas-L system regulates activation-induced cell death, is implicated in diseases in which lymphocyte homeostasis is compromised, and plays an important role during cytotoxic and regulatory actions mediated by these cells. In this study we describe the effect of hyperthermia on activation of the fas-L gene in T lymphocytes. We show that hyperthermic treatment enhances Fas-L-mediated cytotoxicity, fas-L mRNA expression, and fas-L promoter activity in activated T cell lines. Our data indicate that hyperthermia enhances the transcriptional activity of AP-1 and NF-kappaB in activated T cells, and this correlates with an increased expression/nuclear translocation of these transcription factors. Moreover, we found that heat shock factor-1 is a transactivator of fas-L promoter in activated T cells, and the overexpression of a dominant negative form of heat shock factor-1 may attenuate the effect of hyperthermia on fas-L promoter activity. Furthermore, overexpression of dominant negative mutants of protein kinase Cepsilon (PKCepsilon) and PKCtheta; partially inhibited the promoter activation and, more importantly, could significantly reduce the enhancement mediated by hyperthermia, indicating that modulation of PKC activity may play an important role in this regulation. These results add novel information on the immunomodulatory action of heat, in particular in the context of its possible use as an adjuvant therapeutic strategy to consider for the treatment of cancer.

Lysophosphatidic acid accelerates the development of human mast cells

Mast cells (MCs) initiate immune responses from mucosal surfaces and perivascular spaces. Stem cell factor (SCF) regulates MC development and viability, but the role of innate serum factors in MC development is unexplored. Cultured cord blood-derived human MCs (hMCs) express mRNA transcripts for all 4 known receptors for lysophosphatidic acid (LPA), an abundant serum-associated lipid growth factor. In an SCF-dependent serum-free culture system, LPA (2.5-10 microM) increased the total number of hMCs by approximately 10-fold compared with cultures maintained in the absence of LPA under otherwise identical conditions. LPA was comitogenic with SCF but did not prolong MC survival. LPA-mediated proliferation was blocked by VPC-32179, a competitive antagonist of LPA(1) and LPA(3) receptors, and by pertussis toxin, and it was also attenuated by GW9662, a selective antagonist of peroxisome proliferator-activated receptor (PPAR)-gamma. LPA accelerated the acquisition of hMC granules and increased Kit expression. hMCs derived in the presence of LPA were functional, as evidenced by their immunoglobulin E (IgE)-dependent histamine release and by their characteristic proliferative responses to interleukin-3 (IL-3), IL-4, and IL-9 in combination with SCF. Thus, LPA acts through LPA receptor and PPAR-gamma-dependent pathways to accelerate hMC proliferation and differentiation, and it modulates their phenotype without providing cytoprotection. LPA could facilitate MC hyperplasia in inflammation associated with either innate or adaptive immunity.

Protein thiol modification by 15-deoxy-Delta12,14-prostaglandin J2 addition in mesangial cells: role in the inhibition of pro-inflammatory genes

The cyclopentenone prostaglandin and PPARgamma agonist 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) displays anti-inflammatory effects in several experimental models. Direct modification of protein thiols is arising as an important mechanism of cyclopentenone prostaglandin action. However, little is known about the extent or specificity of this process. Mesangial cells (MC) play a key role in glomerulonephritis. In this work, we have studied the selectivity of protein modification by 15d-PGJ(2) in MC, and the correlation with the modulation of several proinflammatory genes. MC incubation with biotinylated 15d-PGJ(2) results in the labeling of a distinct set of proteins as evidenced by two-dimensional electrophoresis. 15d-PGJ(2) binds to nuclear and cytosolic targets as detected by fluorescence microscopy and subcellular fractionation. The pattern of biotinylated 15d-PGJ(2)-modified polypeptides is readily distinguishable from that of total protein staining or labeling with biotinylated iodoacetamide. 15d-PGJ(2) addition requires the double bond in the cyclopentane ring. 9,10-Dihydro-15d-PGJ(2), a 15d-PGJ(2) analog that shows the same potency as peroxisome proliferator-activated receptor (PPAR) agonist in MC but lacks the cyclopentenone moiety, displays reduced ability to modify proteins and to block 15d-PGJ(2) binding. Micromolar concentrations of 15d-PGJ(2) inhibit cytokine-elicited levels of inducible nitricoxide synthase, cyclooxygenase-2, and intercellular adhesion molecule-1 in MC. In contrast, 9,10-dihydro-15d-PGJ(2) does not reproduce this inhibition. 15d-PGJ(2) effect is not blocked by the PPARgamma antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662). Moreover, compounds possessing an alpha,beta-unsaturated carbonyl group, like 2-cyclopenten-1-one and 2-cyclohexen-1-one, reduce pro-inflammatory gene expression. These observations indicate that covalent modification of cellular thiols by 15d-PGJ(2) is a selective process that plays an important role in the inhibition of MC responses to pro-inflammatory stimuli.

15-Deoxy-Δ12,14-Prostaglandin J2 Inhibits Glucocorticoid Binding and Signaling in Macrophages through a Peroxisome Proliferator-Activated Receptor γ-Independent Process

15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is involved in the control of inflammatory reaction. We tested the hypothesis that 15d-PGJ(2) would exert this control in part by modulating the sensitivity of inflammatory cells to glucocorticoids. Human U937cells and mouse RAW 264.7 cells were exposed to 15d-PGJ(2), and binding experiments were performed with [(3)H]dexamethasone as a glucocorticoid receptor (GR) ligand. 15d-PGJ(2) caused a transient and concentration-dependent decrease in [(3)H]dexamethasone-specific binding to either cells through a decrease in the number of GR per cell without significant modification of the K(d) value. These changes were related to functional alteration of the GR rather than to a decrease in GR protein. They did not require the engagement of peroxisome proliferator-activated receptor gamma (PPARgamma), because the response to 15d-PGJ(2) was neither mimicked by the PPARgamma agonist ciglitazone nor prevented by the PPARgamma antagonist bisphenol A diglycidyl ether. 15d-PGJ(2) altered GR possibly through the interaction of its cyclopentenone ring with GR cysteine residues because the cyclopentenone ring per se could mimic the effect of 15d-PGJ(2), and modification of GR cysteine residues with methyl methanethiosulfonate suppressed the response to 15d-PGJ(2). Finally, 15d-PGJ(2)-induced decreases in glucocorticoid binding to GR resulted in parallel decreases in the ability of GR to activate the transcription of a glucocorticoid-inducible reporter gene and to reduce the expression of monocyte chemoattractant protein-1. Together these data suggest that 15d-PGJ(2) limits glucocorticoid binding and signaling in monocytes/macrophages through a PPARgamma-independent and cyclopentenone-dependent mechanism. It provides a way in which 15d-PGJ(2) would exert proinflammatory activities in addition to its known anti-inflammatory activities.

Activation of Peroxisome Proliferator-activated Receptor γ Inhibits Interleukin-1β-induced Membrane-associated Prostaglandin E2 Synthase-1 Expression in Human Synovial Fibroblasts by Interfering with Egr-1

Membrane-associated prostaglandin (PG) E(2) synthase-1 (mPGES-1) catalyzes the conversion of PGH(2) to PGE(2), which contributes to many biological processes. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor and plays an important role in growth, differentiation, and inflammation in different tissues. Here, we examined the effect of PPARgamma ligands on interleukin-1beta (IL-1beta)-induced mPGES-1 expression in human synovial fibroblasts. PPARgamma ligands 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)) and the thiazolidinedione troglitazone (TRO), but not PPARalpha ligand Wy14643, dose-dependently suppressed IL-1beta-induced PGE(2) production, as well as mPGES-1 protein and mRNA expression. 15d-PGJ(2) and TRO suppressed IL-1beta-induced activation of the mPGES-1 promoter. Overexpression of wild-type PPARgamma further enhanced, whereas overexpression of a dominant negative PPARgamma alleviated, the suppressive effect of both PPARgamma ligands. Furthermore, pretreatment with an antagonist of PPARgamma, GW9662, relieves the suppressive effect of PPARgamma ligands on mPGES-1 protein expression, suggesting that the inhibition of mPGES-1 expression is mediated by PPARgamma. We demonstrated that PPARgamma ligands suppressed Egr-1-mediated induction of the activities of the mPGES-1 promoter and of a synthetic reporter construct containing three tandem repeats of an Egr-1 binding site. The suppressive effect of PPARgamma ligands was enhanced in the presence of a PPARgamma expression plasmid. Electrophoretic mobility shift and supershift assays for Egr-1 binding sites in the mPGES-1 promoter showed that both 15d-PGJ(2) and TRO suppressed IL-1beta-induced DNA-binding activity of Egr-1. These data define mPGES-1 and Egr-1 as novel targets of PPARgamma and suggest that inhibition of mPGES-1 gene transcription may be one of the mechanisms by which PPARgamma regulates inflammatory responses.

Cyclopentenone prostaglandins induce lymphocyte apoptosis by activating the mitochondrial apoptosis pathway independent of external death receptor signaling

15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a naturally occurring cyclopentenone metabolite of PGD(2) that possesses both peroxisome proliferator-activated receptor gamma (PPAR-gamma)-dependent and PPAR-gamma-independent anti-inflammatory properties. Recent studies suggest that cyclopentenone PGs may play a role in the down-regulation of inflammation-induced immune responses. In this study, we report that 15d-PGJ(2) as well as synthetic PPAR-gamma agonists inhibit lymphocyte proliferation. However, only 15d-PGJ(2), but not the specific PPAR-gamma activators, induce lymphocyte apoptosis. We found that blocking of the death receptor pathway in Fas-associated death domain(-/-) or caspase-8(-/-) Jurkat T cells has no effect on apoptosis induction by 15d-PGJ(2). Conversely, overexpression of Bcl-2 or Bcl-x(L) completely inhibits the initiation of apoptosis, indicating that 15d-PGJ(2)-mediated apoptosis involves activation of the mitochondrial pathway. In line with these results, 15d-PGJ(2) induces mitochondria disassemblage as demonstrated by dissipation of mitochondrial transmembrane potential (Deltapsi(m)) and cytochrome c release. Both of these events are partially inhibited by the broad spectrum caspase inhibitor benzyloxycarbonil-Val-Ala-Asp-fluoromethylketone, suggesting that caspase activation may amplify the mitochondrial alterations initiated by 15d-PGJ(2). We also demonstrate that 15d-PGJ(2) potently stimulates reactive oxygen species production in Jurkat T cells, and Deltapsi(m) loss induced by 15d-PGJ(2) is prevented by the reactive oxygen species scavenger N-acetyl-L-cysteine. In conclusion, our data indicate that cyclopentenone PGs like 15d-PGJ(2) may modulate immune responses even independent of PPAR-gamma by activating the mitochondrial apoptosis pathway in lymphocytes in the absence of external death receptor signaling.