Molecular Basis for the Direct Inhibition of AP-1 DNA Binding by 15-Deoxy-Δ12,14-prostaglandin J2

Alexander disease GFAP R239C mutant shows increased susceptibility to lipoxidation and elicits mitochondrial dysfunction and oxidative stress

Alexander disease is a fatal neurological disorder caused by mutations in the intermediate filament protein Glial Fibrillary Acidic Protein (GFAP), which is key for astrocyte homeostasis. These mutations cause GFAP aggregation, astrocyte dysfunction and neurodegeneration. Remarkably, most of the known GFAP mutations imply a change by more nucleophilic amino acids, mainly cysteine or histidine, which are more susceptible to oxidation and lipoxidation. Therefore, we hypothesized that a higher susceptibility of Alexander disease GFAP mutants to oxidative or electrophilic damage, which frequently occurs during neurodegeneration, could contribute to disease pathogenesis. To address this point, we have expressed GFP-GFAP wild type or the harmful Alexander disease GFP-GFAP R239C mutant in astrocytic cells. Interestingly, GFAP R239C appears more oxidized than the wild type under control conditions, as indicated both by its lower cysteine residue accessibility and increased presence of disulfide-bonded oligomers. Moreover, GFP-GFAP R239C undergoes lipoxidation to a higher extent than GFAP wild type upon treatment with the electrophilic mediator 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2). Importantly, GFAP R239C filament organization is altered in untreated cells and is earlier and more severely disrupted than GFAP wild type upon exposure to oxidants (diamide, H2O2) or electrophiles (4-hydroxynonenal, 15d-PGJ2), which exacerbate GFAP R239C aggregation. Furthermore, H2O2 causes reversible alterations in GFAP wild type, but irreversible damage in GFAP R239C expressing cells. Finally, we show that GFAP R239C expression induces a more oxidized cellular status, with decreased free thiol content and increased mitochondrial superoxide generation. In addition, mitochondria show decreased mass, increased colocalization with GFAP and altered morphology. Notably, a GFP-GFAP R239H mutant recapitulates R239C-elicited alterations whereas an R239G mutant induces a milder phenotype. Together, our results outline a deleterious cycle involving altered GFAP R239C organization, mitochondrial dysfunction, oxidative stress, and further GFAP R239C protein damage and network disruption, which could contribute to astrocyte derangement in Alexander disease.

15-Deoxy-Delta-12,14-prostaglandin J2 modulates pro-labour and pro-inflammatory responses in human myocytes, vaginal and amnion epithelial cells

BACKGROUND

Prematurity is the leading cause of childhood death under the age of five. The aetiology of preterm birth is multifactorial; however, inflammation and infection are the most common causal factors, supporting a potential role for immunomodulation as a therapeutic strategy. 15-Deoxy-Delta-12,14-prostaglandin J2 (15dPGJ2) is an anti-inflammatory prostaglandin and has been shown to delay lipopolysaccharide (LPS) induced preterm labour in mice and improve pup survival. This study explores the immunomodulatory effect of 15dPGJ2 on the transcription factors NF-κB and AP-1, pro-inflammatory cytokines, and contraction associated proteins in human cultured myocytes, vaginal epithelial cell line (VECs) and primary amnion epithelial cells (AECs).

METHODS

Cells were pre-incubated with 32µM of 15dPGJ2 and stimulated with 1ng/mL of IL-1β as an in vitro model of inflammation. Western immunoblotting was used to detect phosphorylated p-65 and phosphorylated c-Jun as markers of NF-κB and AP-1 activation, respectively. mRNA expression of the pro-inflammatory cytokines IL-6, IL-8, and TNF-α was examined, and protein expression of COX-2 and PGE2 were detected by western immunoblotting and ELISA respectively. Myometrial contractility was examined ex-vivo using a myograph.

RESULTS

15dPGJ2 inhibited IL-1β-induced activation of NF-κB and AP-1, and expression of IL-6, IL-8, TNF-α, COX-2 and PGE2 in myocytes, with no effect on myometrial contractility or cell viability. Despite inhibiting IL-1β-induced activation of NF-κB, expression of IL-6, TNF-α, and COX-2, 15dPGJ2 led to activation of AP-1, increased production of PGE2 and increased cell death in VECs and AECs.

CONCLUSION

We conclude that 15dPGJ2 has differential effects on inflammatory modulation depending on cell type and is therefore unlikely to be a useful therapeutic agent for the prevention of preterm birth.

15-Deoxy-Δ-12,14-prostaglandin J2 effects in vascular smooth muscle cells: Implications in vascular smooth muscle cell proliferation and contractility

15-Deoxy-Δ-12,14-prostaglandin J2 (15d-PGJ2) is an endogenous agonist of the ligand dependent transcriptional factor, peroxisome proliferator-activated receptor -gamma (PPAR-γ). Although PPAR-γ mediates some actions of 15d-PGJ2, many actions of 15d-PGJ2 are independent of PPAR-γ. The PPAR-γ signaling pathway has beneficial effects on tumor progression, inflammation, oxidative stress, and angiogenesis in numerous studies. In this review, various studies were analyzed to understand the effects of 15d-PGJ2 in vascular smooth muscle cells (VSMC)s. 15d-PGJ2 inhibits proliferation of VSMCs during vascular remodeling and it alters the expression of contractile proteins and inflammatory components within these cells as well. However, the effects of 15d-PGJ2 as well as its ability to induce PPAR-γ activation remains controversial as contradictory effects of this prostaglandin in VSMCs exist. Understanding the mechanisms by which 15d-PGJ2 elicit beneficial actions whether by PPAR-γ activation or independently, will aid in developing new therapeutic strategies for diseases such as hypertension with an inflammatory component. Although great advances are being made, more research is needed to reach definitive conclusions.

STAT3 as a Potential Target for Tumor Suppressive Effects of 15-Deoxy-Δ12,14-prostaglandin J2 in Triple Negative Breast Cancer

STAT3 plays a prominent role in proliferation and survival of tumor cells. Thus, STAT3 has been considered to be a prime target for development of anti-cancer therapeutics. The electrophilic cyclopentenone prostaglandin,15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) has been well recognized for its capability to modulate intracellular signaling pathways involved in cancer cell growth and progression. We previously reported that 15d-PGJ₂ had potent cytotoxicity against harvey-ras transformed human mammary epithelial cells through direct interaction with STAT3. In this study, we have attempted to verify the inhibitory effects of 15d-PGJ₂ on STAT3 signaling in human breast tumor cells. The triple negative breast cancer cell lines, MDA-MB-231 and MDA-MB-468 displaying constitutive phosphorylation of STAT3 on the tyrosine 705 (Tyr705) residue, underwent apoptosis upon inhibition of STAT3 by 15d-PGJ₂. In contrast, estrogen receptor positive MCF-7 breast cancer cells that do not exhibit elevated STAT3 phosphorylation were much less susceptible to 15d-PGJ₂-induced apoptosis as assessed by PARP cleavage. Furthermore, 15d-PGJ₂ inhibited interleukin-6-induced tyrosine phosphorylation of STAT3 in LNCaP cells. According to molecular docking studies, 15d-PGJ₂ may preferentially bind to the cysteine 259 residue (Cys259) present in the coiled-coil domain of STAT3. Site-directed mutagenesis of STAT3 identified Cys259 to be the critical amino acid for the 15d-PGJ₂-induced apoptosis as well as epithelial-to-mesenchymal transition. Taken together, these findings suggest STAT3 inactivation through direct chemical modification of its Cys259 as a potential therapeutic approach for treatment of triple negative breast cancer treatment.

Cyclopentenone Prostaglandins: Biologically Active Lipid Mediators Targeting Inflammation

Cyclopentenone prostaglandins (cyPGs) are biologically active lipid mediators, including PGA2, PGA1, PGJ2, and its metabolites. cyPGs are essential regulators of inflammation, cell proliferation, apoptosis, angiogenesis, cell migration, and stem cell activity. cyPGs biologically act on multiple cellular targets, including transcription factors and signal transduction pathways. cyPGs regulate the inflammatory response by interfering with NF-κB, AP-1, MAPK, and JAK/STAT signaling pathways via both a group of nuclear receptor peroxisome proliferator-activated receptor-gamma (PPAR-γ) dependent and PPAR-γ independent mechanisms. cyPGs promote the resolution of chronic inflammation associated with cancers and pathogen (bacterial, viral, and parasitic) infection. cyPGs exhibit potent effects on viral infections by repressing viral protein synthesis, altering viral protein glycosylation, inhibiting virus transmission, and reducing virus-induced inflammation. We summarize their anti-proliferative, pro-apoptotic, cytoprotective, antioxidant, anti-angiogenic, anti-inflammatory, pro-resolution, and anti-metastatic potential. These properties render them unique therapeutic value, especially in resolving inflammation and could be used in adjunct with other existing therapies. We also discuss other α, β -unsaturated carbonyl lipids and cyPGs like isoprostanes (IsoPs) compounds.

15-Deoxy-Δ12,14-prostaglandin J2 Upregulates VEGF Expression via NRF2 and Heme Oxygenase-1 in Human Breast Cancer Cells

There is a plethora of evidence to support that inflammation is causally linked to carcinogenesis. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme in the biosynthesis of prostaglandins, is inappropriately overexpressed in various cancers and hence recognized as one of the hallmarks of chronic inflammation-associated malignancies. However, the mechanistic role of COX-2 as a link between inflammation and cancer remains largely undefined. In this study, we found that 15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), one of the final products of COX-2, induced upregulation of vascular endothelial growth factor (VEGF) and capillary formation and migration through nuclear factor erythroid 2-related factor 2 (NRF2)-dependent heme oxygenase-1 (HO-1) induction in MCF-7 cells. Analysis of the publicly available TCGA data set showed that high mRNA levels of both COX-2 and NRF2 correlated with the poor clinical outcomes in breast cancer patients. Moreover, human tissue analysis showed that the levels of 15d-PGJ₂ as well the expression of COX-2, NRF2, and HO-1 were found to be increased in human breast cancer tissues. In conclusion, the elevated levels of 15d-PGJ₂ during inflammatory response activate VEGF expression through NRF2-driven induction of HO-1 in human breast cancer cells, proposing a novel mechanism underlying the oncogenic function of 15d-PGJ₂.

Protein Lipoxidation: Basic Concepts and Emerging Roles

Protein lipoxidation is a non-enzymatic post-translational modification that consists of the covalent addition of reactive lipid species to proteins. This occurs under basal conditions but increases in situations associated with oxidative stress. Protein targets for lipoxidation include metabolic and signalling enzymes, cytoskeletal proteins, and transcription factors, among others. There is strong evidence for the involvement of protein lipoxidation in disease, including atherosclerosis, neurodegeneration, and cancer. Nevertheless, the involvement of lipoxidation in cellular regulatory mechanisms is less understood. Here we review basic aspects of protein lipoxidation and discuss several features that could support its role in cell signalling, including its selectivity, reversibility, and possibilities for regulation at the levels of the generation and/or detoxification of reactive lipids. Moreover, given the great structural variety of electrophilic lipid species, protein lipoxidation can contribute to the generation of multiple structurally and functionally diverse protein species. Finally, the nature of the lipoxidised proteins and residues provides a frameshift for a complex interplay with other post-translational modifications, including redox and redox-regulated modifications, such as oxidative modifications and phosphorylation, thus strengthening the importance of detailed knowledge of this process.

15-Deoxy-Δ12,14 -prostaglandin J2 binds and inactivates STAT3 via covalent modification of cysteine 259 in H-Ras-transformed human breast epithelial cells

Signal transducer and activator of transcription 3 (STAT3) has been considered as a potential target for development of anticancer therapeutics. Here, we report a novel mechanism by which the cyclopentenone prostaglandin, 15-deoxy-Δ^12,14 -prostaglandin J₂ (15d-PGJ₂ ) functions as an allosteric inhibitor of STAT3. 15d-PGJ₂ inhibits phosphorylation, dimerization, nuclear translocation, and transcriptional activity of STAT3 in H-Ras-transformed human mammary epithelial cells (MCF10A-Ras) through the Michael addition reaction at cysteine 259 of STAT3. Comparative studies with 15d-PGJ₂ analogues reveal that both C12-C13 and C9-C10 double bonds conjugated to the carbonyl group in the cyclopentenone ring of 15d-PGJ₂ are essential for STAT3 binding. Antiproliferative and pro-apoptotic activities of 15d-PGJ₂ in MCF10A-Ras cells are attributable to covalent modification of STAT3 on Cys259, and mimic the effects induced by mutation of this amino acid.

Activation of phospholipase A2 by prostaglandin in vitro

Prostaglandins are a diverse family of biological active molecules that are synthesized after liberation of arachnidonic or linolenic acid from the plasma membrane by phospholipase A2 (PLA2). Specific prostaglandins may be pro-inflammatory or anti-inflammatory due to a poorly understood biochemical equilibrium. Some of the anti-inflammatory prostaglandins namely, prostaglandin A1 (PGA1) and prostaglandin E1 (PGE1) have a cyclopentenone moiety that can react and modify a protein's activity. These two prostaglandins are electrophilic reactive lipid species and are formed as a result of the reaction cascade initiated by PLA2. It was of interest to study the interaction with these prostaglandins as they could either amplify or block this enzyme's activity. We found that the former is true initially as there is a shorter time to activate the protein on the lipid membrane and an overall increase in hydrolysis was observed when PGA1 and PGE1 prostaglandin was added with PLA2 and liposomes. The interfacial activation model was further explored in which there is a modification of the enzyme rather than a modifcation of the substrate. However, after a time the protein was shown to form amyloid like fibrils thereby blocking further hydrolysis. The fibrillization kinetics in the presence of the one of the prostaglandins was monitored using thioflavin T (ThT) and the resulting fibrils were characterized using transmission electron microscopy (TEM) and atomic force microscopy (AFM). Modification of PLA2 by these prostaglandins leading to amyloid like fibrils gives an additional perspective of control of the interfacial activation mechanism of this enzyme.

15-Deoxy-Δ12,14-prostaglandin J2 Induces Apoptosis in Ha-ras-transformed Human Breast Epithelial Cells by Targeting IκB kinase-NF-κB Signaling

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), an endogenous ligand for PPARγ, has differential effects on cancer cell proliferation and survival depending on the dose and the type of cells. In the present study, we have investigated the effects of 15d-PGJ₂ on apoptosis of the Ha-ras transformed human breast epithelial (MCF10A-ras) cells. When MCF10A-ras cells were treated with 15d-PGJ₂ (10 μM) for 24 hours, they underwent apoptosis as evidenced by characteristic morphological features, an increased proportion of sub-G₀/G₁ cell population, a typical pattern of annexin V/propidium iodide staining, perturbation of mitochondrial transmembrane potential (Δψ_m), and cleavage of caspase-3 and its substrate PARP. A pan-caspase inhibitor, Z-Val-Ala-Asp (OCH₃)-fluoromethyl ketone attenuated cytotoxicity and proteolytic cleavage of caspase-3 induced by 15d-PGJ₂. The 15d-PGJ₂-induced apoptosis was accompanied by enhanced intracellular accumulation of reactive oxygen species (ROS), which was abolished by the antioxidant N-acetyl-L-cysteine (NAC). 15d-PGJ₂ inhibited the DNA binding activity of NF-κB which was associated with inhibition of expression and catalytic activity of IκB kinase β (IKKβ). 15d-PGJ₂-mediated inhibition of IKKβ and nuclear translocation of phospho-p65 was blocked by NAC treatment. 9,10-Dihydro-PGJ₂, a non-electrophilic analogue of 15d-PGJ₂, failed to produce ROS, to inhibit NF-κB DNA binding, and to induce apoptosis, suggesting that the electrophilic α,β-unsaturated carbonyl group of 15d-PGJ₂ is essential for its pro-apoptotic activity. 15d-PGJ₂-induced inactivation of IKKβ was also attributable to its covalent thiol modification at the cysteine 179 residue of IKKβ. Based on these findings, we propose that 15d-PGJ₂ inactivates IKKβ–ΝF-κB signaling through oxidative or covalent modification of IKKβ, thereby inducing apoptosis in Ha-ras transformed human breast epithelial cells.

Integrated approaches to unravel the impact of protein lipoxidation on macromolecular interactions

Protein modification by lipid derived reactive species, or lipoxidation, is increased during oxidative stress, a common feature observed in many pathological conditions. Biochemical and functional consequences of lipoxidation include changes in the conformation and assembly of the target proteins, altered recognition of ligands and/or cofactors, changes in the interactions with DNA or in protein-protein interactions, modifications in membrane partitioning and binding and/or subcellular localization. These changes may impact, directly or indirectly, signaling pathways involved in the activation of cell defense mechanisms, but when these are overwhelmed they may lead to pathological outcomes. Mass spectrometry provides state of the art approaches for the identification and characterization of lipoxidized proteins/residues and the modifying species. Nevertheless, understanding the complexity of the functional effects of protein lipoxidation requires the use of additional methodologies. Herein, biochemical and biophysical methods used to detect and measure functional effects of protein lipoxidation at different levels of complexity, from in vitro and reconstituted cell-like systems to cells, are reviewed, focusing especially on macromolecular interactions. Knowledge generated through innovative and complementary technologies will contribute to comprehend the role of lipoxidation in pathophysiology and, ultimately, its potential as target for therapeutic intervention.

Lipoxidation and cancer immunity

Lipoxidation is a well-known reaction between electrophilic carbonyl species, formed during oxidation of lipids, and specific proteins that, in most cases, causes an alteration in proteins function. This can occur under physiological conditions but, in many cases, it has been associated to pathological process, including cancer. Lipoxidation may have an effect in cancer development through their effects in tumour cells, as well as through the alteration of immune components and the consequent modulation of the immune response. The formation of protein adducts affects different proteins in cancer, triggering different mechanism, such as proliferation, cell differentiation and apoptosis, among others, altering cancer progression. The divergent results obtained documented that the formation of lipoxidation adducts can have either anti-carcinogenic or pro-carcinogenic effects, depending on the cell type affected and the specific adduct formed. Moreover, lipoxidation adducts may alter the immune response, consequently causing either positive or negative alterations in cancer progression. Therefore, in this review, we summarize the effects of lipoxidation adducts in cancer cells and immune components and their consequences in the evolution of different types of cancer.

Modulation of nuclear receptor function: Targeting the protein-DNA interface

Nuclear receptors (NRs) are a superfamily of ligand-dependent transcription factors that modulate several biological processes. Traditionally, modulation of NRs has been focused on the development of ligands that recognize and bind to the ligand binding domain (LBD), resulting in activation or repression of transcription through the recruitment of coregulators. However, for more severe diseases, such as breast and prostate cancer, the conventional treatment addressing LBD modulation is not always successful, due to tumor resistance. To overcome these challenges and aiming to modulate NR activity by inhibiting the NR-DNA interaction, new studies focus on the development of molecules targeting alternative sites and domains on NRs. Here, we discuss two different approaches for this alternative NR modulation: one targeting the NR DNA binding domain (DBD); and the other targeting the DNA sites recognized by NRs. Our aim is to present the challenges and perspectives for developing specific inhibitors for each purpose, alongside with already reported examples.

1,8-Cineole Ameliorates LPS-Induced Vascular Endothelium Dysfunction in Mice via PPAR-γ Dependent Regulation of NF-κB

1,8-Cineole (eucalyptol), a monoterpene, has been widely reported for the anti-inflammatory effects. Our previous data confirmed that 1,8-cineole ameliorated the inflammatory phenotype of human umbilical vein endothelial cells (HUVECs) by mediating NF-κB expression in vitro. At present, we investigated the protection effects of 1,8-cineole on vascular endothelium in lipopolysaccharide (LPS)-induced acute inflammatory injury mice and the potential mechanisms involved in the protection in HUVECs. Results from enzyme linked immunosorbent assays revealed that 1,8-cineole suppressed the secretion of interleukin (IL)-6 and IL-8 and increased the expression of IL-10 in the serum of LPS-induced mice. 1,8-Cineole reduced the inflammatory infiltration and the expression of vascular cell adhesion molecular 1 (VCAM-1) in the sections of thoracic aorta in LPS-induced acute inflammatory mice. Western blotting indicated that 1,8-cineole significantly decreased the phosphorylation of NF-κB p65 and increased the expression of PPAR-γ in the thoracic aorta tissue. 1,8-Cineole increased the expression of PPAR-γ in LPS-induced HUVECs. 1,8-Cineole and rosiglitazone reduced the protein and mRNA levels of VCAM-1, E-selectin, IL-6, and IL-8 in LPS-induced HUVECs, which could be reversed by the action of GW9662 (inhibitor of PPAR-γ). 1,8-Cineole and rosiglitazone blocked the LPS-induced IκBα degradation and NF-κB p65 nucleus translocation, which could be reversed by the pretreatment of GW9662 or silence of PPAR-γ gene. In conclusion, 1,8-cineole attenuated LPS-induced vascular endothelial cells injury via PPAR-γ dependent modulation of NF-κB.

Biological Activities, Health Benefits, and Therapeutic Properties of Avenanthramides: From Skin Protection to Prevention and Treatment of Cerebrovascular Diseases

Oat (Avena sativa) is a cereal known since antiquity as a useful grain with abundant nutritional and health benefits. It contains distinct molecular components with high antioxidant activity, such as tocopherols, tocotrienols, and flavanoids. In addition, it is a unique source of avenanthramides, phenolic amides containing anthranilic acid and hydroxycinnamic acid moieties, and endowed with major beneficial health properties because of their antioxidant, anti-inflammatory, and antiproliferative effects. In this review, we report on the biological activities of avenanthramides and their derivatives, including analogs produced in recombinant yeast, with a major focus on the therapeutic potential of these secondary metabolites in the treatment of aging-related human diseases. Moreover, we also present recent advances pointing to avenanthramides as interesting therapeutic candidates for the treatment of cerebral cavernous malformation (CCM) disease, a major cerebrovascular disorder affecting up to 0.5% of the human population. Finally, we highlight the potential of foodomics and redox proteomics approaches in outlining distinctive molecular pathways and redox protein modifications associated with avenanthramide bioactivities in promoting human health and contrasting the onset and progression of various pathologies. The paper is dedicated to the memory of Adelia Frison.

15-Deoxy-Δ12,14-prostaglandin J2 activates PI3K-Akt signaling in human breast cancer cells through covalent modification of the tumor suppressor PTEN at cysteine 136

15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), one of the terminal products of cyclooxygenase-2-catalized arachidonic acid metabolism, has been shown to stimulate breast cancer cell proliferation and migration through Akt activation, but the underlying mechanisms remain poorly understood. In the present study, we investigated the effects of 15d-PGJ₂ on the activity of PTEN, the inhibitor of the phosphoinositide 3-kinase (PI3K)-Akt axis, in human breast cancer (MCF-7) cells. Since the α,β-unsaturated carbonyl moiety in the cyclopentenone ring of 15d-PGJ₂ is electrophilic, we hypothesized that 15d-PGJ₂-induced Akt phosphorylation might result from the covalent modification and subsequent inactivation of PTEN that has several critical cysteine residues. When treated to MCF-7 cells, 15d-PGJ₂ bound to PTEN, and this was abolished in the presence of the thiol-reducing agent dithiothreitol. A mass spectrometric analysis by using recombinant and endogenous PTEN protein revealed that the cysteine 136 residue (Cys¹³⁶) of PTEN is covalently modified upon treatment with 15d-PGJ₂. Notably, the ability of 15d-PGJ₂ to covalently bind to PTEN as well as to induce Akt phosphorylation was abolished in the cells expressing a mutant form of PTEN in which Cys¹³⁶ was replaced by serine (C136S-PTEN). The present study demonstrates for the first time that electrophilic 15d-PGJ₂ directly binds to cysteine 136 of PTEN and provides new insight into PTEN loss in cancer progression associated with chronic inflammation. These observations suggest that 15d-PGJ₂ can undergo nucleophilic addition to PTEN, presumably at Cys¹³⁶, thereby inactivating this tumor suppressor protein with concomitant Akt activation.

Anti-cancer effect of snake venom toxin through down regulation of AP-1 mediated PRDX6 expression

Snake venom toxin (SVT) from Vipera lebetina turanica contains a mixture of different enzymes and proteins. Peroxiredoxin 6 (PRDX6) is known to be a stimulator of lung cancer cell growth. PRDX6 is a member of peroxidases, and has calcium-independent phospholipase A2 (iPLA2) activities. PRDX6 has an AP-1 binding site in its promoter region of the gene. Since AP-1 is implicated in tumor growth and PRDX6 expression, in the present study, we investigated whether SVT inhibits PRDX6, thereby preventing human lung cancer cell growth (A549 and NCI-H460) through inactivation of AP-1. A docking model study and pull down assay showed that SVT completely fits on the basic leucine zipper (bZIP) region of c-Fos of AP-1. SVT (0–10 μg/ml) inhibited lung cancer cell growth in a concentration dependent manner through induction of apoptotic cell death accompanied by induction of cleaved caspase-3, -8, -9, Bax, p21 and p53, but decreased cIAP and Bcl2 expression via inactivation of AP-1. In an xenograft in vivo model, SVT (0.5 mg/kg and 1 mg/kg) also inhibited tumor growth accompanied with the reduction of PRDX6 expression, but increased expression of proapoptotic proteins. These data indicate that SVT inhibits tumor growth via inhibition of PRDX6 activity through interaction with its transcription factor AP-1.

PGA1-induced apoptosis involves specific activation of H-Ras and N-Ras in cellular endomembranes

The cyclopentenone prostaglandin A₁ (PGA₁) is an inducer of cell death in cancer cells. However, the mechanism that initiates this cytotoxic response remains elusive. Here we report that PGA₁ triggers apoptosis by a process that entails the specific activation of H- and N-Ras isoforms, leading to caspase activation. Cells without H- and N-Ras did not undergo apoptosis upon PGA₁ treatment; in these cells, the cellular demise was rescued by overexpression of either H-Ras or N-Ras. Consistently, the mutant H-Ras-C118S, defective for binding PGA₁, did not produce cell death. Molecular analysis revealed a key role for the RAF-MEK-ERK signaling pathway in the apoptotic process through the induction of calpain activity and caspase-12 cleavage. We propose that PGA₁ evokes a specific physiological cell death program, through H- and N-Ras, but not K-Ras, activation at endomembranes. Our results highlight a novel mechanism that may be of potential interest for tumor treatment.

Milk-derived bioactive peptides and their health promoting effects: a potential role in atherosclerosis

Bioactive peptides derived from milk proteins are food components that, in addition to their nutritional value, retain many biological properties and have therapeutic effects in several health disorders, including cardiovascular disease. Amongst these, atherosclerosis is the underlying cause of heart attack and strokes. It is a progressive dyslipidaemic and inflammatory disease where accumulation of oxidized lipids and inflammatory cells leads to the formation of an atherosclerotic plaque in the vessel wall. Milk-derived bioactive peptides can be released during gastrointestinal digestion, food processing or by enzymatic and bacterial fermentation and are considered to promote diverse beneficial effects such as lipid lowering, antihypertensive, immnomodulating, anti-inflammatory and antithrombotic effects. In this review, an overview of the diverse biological effects of these compounds is given, particularly focusing on their beneficial properties on cardiovascular disease and proposing novel mechanisms of action responsible for their bioactivity. Attempts to prevent cardiovascular diseases target modifications of several risk factors such as high blood pressure, obesity, high blood concentrations of lipids or insulin resistance. Milk-derived bioactive peptides are a source of health-enhancing components and the potential health benefit of these compounds has a growing commercial potential. Consequently, they have been incorporated as ingredients in functional foods, as dietary supplements and as pharmaceuticals to promote health and reduce risk of chronic diseases.

Synthesis and in vitro cytotoxicity of cross-conjugated prostaglandin A and J series and their hydroxy derivatives

The synthesis of two cross-conjugated prostaglandin analogues of known neurotrophic activity and their new hydroxy derivatives was accomplished starting from the diastereoisomeric (+)-camphor protected 3-[(dimethoxyphosphoryl)methyl]-4,5-dihydroxycyclopent-2-enones. The cytotoxicity of these compounds was determined against HeLa, K562, HL-60 human cancer cell lines and normal human cells (HUVEC). We found that NEPP11 and its C7-hydroxy derivative demonstrated high anticancer activity against the HeLa and HL-60 human cancer cell lines at concentrations ranging from 1 to 2 μM. Moreover, the C7-hydroxy derivative of NEPP11 displayed high cytotoxic selectivity between cancer cell lines and normal human cells. On the other hand, the J-type prostaglandin analogue of NEPP11 and its C13-hydroxy derivatives were much less toxic or nontoxic against the cancer and normal cells at concentrations up to 1 mM.

The role of cyclooxygenase-2, interleukin-1β and fibroblast growth factor-2 in the activation of matrix metalloproteinase-1 in sheared-chondrocytes and articular cartilage

MMP-1 expression is detected in fluid shear stress (20 dyn/cm²)-activated and osteoarthritic human chondrocytes, however, the precise mechanisms underlying shear-induced MMP-1 synthesis remain unknown. Using primary chondrocytes and T/C-28a2 chondrocytic cells as model systems, we report that prolonged application of high fluid shear to human chondrocytes induced the synthesis of cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β) and fibroblast growth factor-2 (FGF-2), which led to a marked increase in MMP-1 expression. IL-1β, COX-2-dependent PGE₂ activated the PI3-K/AKT and p38 signaling pathways, which were in turn responsible for MMP-1 synthesis via NF-κB- and c-Jun-transactivating pathways. Prolonged shear stress exposure (>12 h) induced 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) synthesis. Although 15d-PGJ₂ suppressed PI3-K/AKT and p38 signaling pathways, it stimulated MMP-1 expression via activating heme oxygenase 1 (HO-1). The critical role of COX-2 in regulating MMP-1 expression in articular cartilage in vivo was demonstrated using COX-2^+/− transgenic mice in the absence or presence of rofecoxib oral administration. These findings provide novel insights for developing therapeutic strategies to combat OA.

MAP kinase phosphatase-1 expression is regulated by 15-deoxy-Δ12,14-prostaglandin J2 via a HuR-dependent post-transcriptional mechanism

In the present study, we demonstrate a mechanism through which 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) induces MKP-1 expression in rat primary astrocytes, leading to the regulation of inflammatory responses. We show that 15d-PGJ2 enhances the efficiency of MKP-1 pre-mRNA processing (constitutive splicing and 3'-end processing) and increases the stability of the mature mRNA. We further report that this occurs via the RNA-binding protein, Hu antigen R (HuR). Our experiments show that HuR knockdown abrogates the 15d-PGJ2-induced increases in the pre-mRNA processing and mature mRNA stability of MKP-1, whereas HuR overexpression further enhances the 15d-PGJ2-induced increases in these parameters. Using cysteine (Cys)-mutated HuR proteins, we show that the Cys-245 residue of HuR (but not Cys-13 or Cys-284) is critical for the direct binding of HuR with 15d-PGJ2 and the effects downstream of this interaction. Collectively, our data show that HuR is a novel target of 15d-PGJ2 and reveal HuR-mediated pre-mRNA processing and mature mRNA stabilization as important regulatory steps in the 15d-PGJ2-induced expression of MKP-1. The potential to use a small molecule such as 15d-PGJ2 to regulate the induction of MKP-1 at multiple levels of gene expression could be exploited as a novel therapeutic strategy aimed at combating a diverse range of MKP-1-associated pathologies.

Milk-derived bioactive peptides inhibit human endothelial-monocyte interactions via PPAR-γ dependent regulation of NF-κB

Background

Milk-derived bioactive peptides retain many biological properties and have therapeutic effects in cardiovascular disorders such as atherosclerosis. Under inflammatory conditions the expression of endothelial cells adhesion molecules is induced, increasing monocyte adhesion to human vessel wall, a critical step in the pathogenesis of atherosclerosis. In the present work we explored the effects of milk-derived bioactive peptides on the expression of the inflammatory phenotype of human endothelial cells and their effects on monocyte adherence to endothelial cells.

Results

Treatment of endothelial cells with milk-derived hydrolysate inhibited their production of inflammatory proteins MCP-1 and IL-8 and expression of VCAM-1, ICAM-1 and E-selectin. Milk derived hydrolysate also attenuated the adhesion of human monocytes to activated endothelial cells. The effect was similar to that obtained in endothelial cells treated with troglitazone, a ligand of peroxisome proliferators-activator receptor-gamma (PPAR-γ). PPAR-γ is a transcription factor which when activated antagonises the pro-inflammatory capability of nuclear factor κB (NF-κB). We further examined whether the effects of milk-derived hydrolysates on endothelial cells may be mediated through NF-κB activation via a PPAR-γ dependent mechanism. The specific PPAR-γ inhibitor, GW9662 blocked the effects of the hydrolysate on the NF-κB-mediated chemokines and adhesion molecules expression in endothelial cells.

Conclusions

These results suggest that milk-derived bioactive peptides work as anti-atherogenic agents through the inhibition of endothelial-dependent adhesive interactions with monocytes by inhibiting the NF-κB pathway through a PPAR-γ dependent mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-014-0044-1) contains supplementary material, which is available to authorized users.

Electrophilic lipid mediator 15-deoxy-Δ12,14-prostaglandin j2 modifies glucocorticoid signaling via receptor SUMOylation

Cortisol, the central stress hormone in humans, activates the glucocorticoid receptor (GR). Anti-inflammatory effects are the most important pharmaceutical effects mediated by the GR. Inasmuch as electrophilic cyclopentenone prostaglandin 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) has potent anti-inflammatory properties and activates the SUMOylation pathway, we have investigated the effect of 15d-PGJ2 on glucocorticoid signaling and receptor SUMOylation. To this end, we studied isogenic HEK293 cells expressing either wild-type GR or SUMOylation-defective GR. Interestingly, 15d-PGJ2 triggered SUMO-2 and -3 (SUMO-2/3) modification in the primary SUMOylation sites of the GR. Gene expression profiling and pathway analyses indicate that 15d-PGJ2 inhibits GR signaling in a genome-wide fashion that is significantly dependent on the GR SUMOylation sites. Chromatin immunoprecipitation assays showed that the repressive effect of 15d-PGJ2 on GR target gene expression occurs in parallel with the inhibition of receptor binding to the target gene chromatin. Furthermore, depletion of UBC9, the sole SUMO E2 conjugase, from HEK293 cells confirmed the involvement of active SUMOylation in the regulatory process. Taken together, our data indicate that GR SUMOylation modulates the glucocorticoid signaling during acute cell stress. Our data also suggest that GR SUMOylation modulates cross talk of the glucocorticoid signaling with other transcription factors that are responsive to cell stress.

Anti-inflammatory prostaglandins for the prevention of preterm labour

Preterm birth occurs in 10-12% of pregnancies and is the primary cause of neonatal mortality and morbidity. Tocolytic therapies have long been the focus for the prevention of preterm labour, yet they do not significantly improve neonatal outcome. A direct causal link exists between infection-induced inflammation and preterm labour. As inflammation and infection are independent risk factors for poor neonatal outcome, recent research focus has been shifted towards exploring the potential for anti-inflammatory strategies. Nuclear factor kappa B (NFκB) is a transcription factor that controls the expression of many labour-associated genes including PTGS2 (COX2), prostaglandins (PGs) and the oxytocin receptor (OXTR) as well as key inflammatory genes. Targeting the inhibition of NFκB is therefore an attractive therapeutic approach for both the prevention of preterm labour and for reducing neonatal exposure to inflammation. While PGs are considered to be pro-labour and pro-inflammatory, the cyclopentenone PG 15-deoxy-Δ(12,14)PGJ2 (15d-PGJ2) exhibits anti-inflammatory properties via the inhibition of NFκB in human amniocytes, myocytes and peripheral blood mononuclear cells in vitro. 15d-PGJ2 also delays inflammation-induced preterm labour in the mouse and significantly increases pup survival. This review examines the current understanding of inflammation in the context of labour and discusses how anti-inflammatory PGs may hold promise for the prevention of preterm labour and improved neonatal outcome.

Prostaglandin E2 modifies SMAD2 and promotes SMAD2-SMAD4 complex formation

We report that PGE2 promotes Smad2-Smad4 complex formation and this phenomenon could be blocked by DIDS, an anion transporter inhibitor. Our data suggest that PGE2 had no effects on Smad2 phosphorylation, suggesting that PGE2-mediated Smad2-Smad4 complex formation is independent of TGF-β signaling and that PGE2 induced Smad2 modification which is different from TGF-β-mediated phosphorylation. We demonstrate that in primary human glomerular mesangial cells PGE2 caused modification of Smad2 as detected by Smad2N antibody, raised against a peptide near the N-terminus of Smad2. We hypothesize that Smad2 protein is post-translationaly modified by PGE2. Direct evidence of Smad2 modification by PGE2 was achieved by avidin pulldown assay which showed that endogenous Smad2 and recombinant Smad2 protein were attached by biotin-labeled PGE2. Taken together, our results provided evidence that post-translational modification of Smad2 could be a mechanism for the action of PGE2 in the pathogenesis of human pathologies.

15-Deoxy-Δ12,14-prostaglandin J2 induces PPARγ- and p53-independent apoptosis in rabbit synovial cells

A ligand of peroxisome proliferator-activated receptor γ (PPARγ), 15-deoxy-Δ(12,14)-prostaglandin J2 (15d-PGJ2) induces apoptosis in various cells. However, the mechanism appears to be complex and cell-type specific. We investigated the mechanism of 15d-PGJ2-induced apoptosis of rabbit synovial cells. Exposure to 15d-PGJ2 resulted in DNA fragmentation accompanied by caspase-3 and -9 activations in the cells, suggesting occurrence of mitochondria-mediated apoptosis. Although the exposure also induced remarkable increase in p53 protein, its transcriptional activity was rather reduced, suggesting non-necessity of p53 in 15d-PGJ2-induced apoptosis. Covalent binding of 15d-PGJ2 to cellular proteins including p53 resulted in their insolubilization. N-acetylcysteine inhibited not only the 15d-PGJ2-induced apoptotic events but also the protein insolubilizations via its interaction with 15d-PGJ2. The studies using a PPARγ-agonist and -antagonist showed noninvolvement of PPARγ in 15d-PGJ2-induced apoptosis. The pre-exposure to pro-inflammatory cytokines did not affect the cytotoxicity of 15d-PGJ2 in synovial cells. Taken together, these results show that 15d-PGJ2 induces a mitochondria-mediated apoptotic pathway in p53- and PPARγ-independent manners.

Modification of cysteine residues by cyclopentenone prostaglandins: interplay with redox regulation of protein function

Cyclopentenone prostaglandins (cyPG) are endogenous lipid mediators involved in the resolution of inflammation and the regulation of cell proliferation and cellular redox status. Upon exogenous administration they have shown beneficial effects in models of inflammation and tissue injury, as well as potential antitumoral actions, which have raised a considerable interest in their study for the development of therapeutic tools. Due to their electrophilic nature, the best-known mechanism of action of these mediators is the covalent modification of proteins at cysteine residues through Michael addition. Identification of cyPG targets through proteomic approaches, including MS/MS analysis to pinpoint the modified residues, is proving critical to characterize their mechanisms of action. Among the targets of cyPG are proinflammatory transcription factors, proteins involved in cell defense, such as the regulator of the antioxidant response Keap1 and detoxifying enzymes like GST, and key signaling proteins like Ras proteins. Moreover, cyPG may interact with redox-active small molecules, such as glutathione and hydrogen sulfide. Much has been learned about cyPG in the past few years and this knowledge has also contributed to clarify both pharmacological actions and signaling mechanisms of these and other electrophilic lipids. Given the fact that many cyPG targets are involved in or are targets for redox regulation, there is a complex interplay with redox-induced modifications. Here we address the modification of protein cysteine residues by cyPG elucidated by proteomic studies, paying special attention to the interplay with redox signaling.

Detection of electrophile-sensitive proteins

BACKGROUND

Redox signaling is an important emerging mechanism of cellular function. Dysfunctional redox signaling is increasingly implicated in numerous pathologies, including atherosclerosis, diabetes, and cancer. The molecular messengers in this type of signaling are reactive species which can mediate the post-translational modification of specific groups of proteins, thereby effecting functional changes in the modified proteins. Electrophilic compounds comprise one class of reactive species which can participate in redox signaling. Electrophiles modulate cell function via formation of covalent adducts with proteins, particularly cysteine residues.

SCOPE OF REVIEW

This review will discuss the commonly used methods of detection for electrophile-sensitive proteins, and will highlight the importance of identifying these proteins for studying redox signaling and developing novel therapeutics.

MAJOR CONCLUSIONS

There are several methods which can be used to detect electrophile-sensitive proteins. These include the use of tagged model electrophiles, as well as derivatization of endogenous electrophile-protein adducts.

GENERAL SIGNIFICANCE

In order to understand the mechanisms by which electrophiles mediate redox signaling, it is necessary to identify electrophile-sensitive proteins and quantitatively assess adduct formation. Strengths and limitations of these methods will be discussed. This article is part of a Special Issue entitled Current methods to study reactive oxygen species - pros and cons and biophysics of membrane proteins. Guest Editor: Christine Winterbourn.

Lipoxidation adducts with peptides and proteins: deleterious modifications or signaling mechanisms?

Protein lipoxidation refers to the modification by electrophilic lipid oxidation products to form covalent adducts, which for many years has been considered as a deleterious consequence of oxidative stress. Oxidized lipids or phospholipids containing carbonyl moieties react readily with lysine to form Schiff bases; alternatively, oxidation products containing α,β-unsaturated moieties are susceptible to nucleophilic attack by cysteine, histidine or lysine residues to yield Michael adducts, overall corresponding to a large number of possible protein adducts. The most common detection methods for lipoxidized proteins take advantage of the presence of reactive carbonyl groups to add labels, or use antibodies. These methods have limitations in terms of specificity and identification of the modification site. The latter question is satisfactorily addressed by mass spectrometry, which enables the characterization of the adduct structure. This has allowed the identification of lipoxidized proteins in physiological and pathological situations. While in many cases lipoxidation interferes with protein function, causing inhibition of enzymatic activity and increased immunogenicity, there are a small number of cases where lipoxidation results in gain of function or activity. For certain proteins lipoxidation may represent a form of redox signaling, although more work is required to confirm the physiological relevance and mechanisms of such processes. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.

Design of small molecules targeting transcriptional activation by NF-κB: overview of recent advances

BACKGROUND

The transcription factor NF-κB plays a central role in immune signaling and the inflammatory response. It also activates transcription of antiapoptotic factors in tumor cells, leading to enhanced cell survival. Because of the importance of NF-κB in inflammation and cancer, there is considerable interest in development of drugs that inhibit NF-κB activation or NF-κB-directed transcription. Recent elucidation of the intracellular pathways that activate NF-κB and mechanisms for transcriptional regulation by NF-κB has identified molecular targets for rational design of such drugs.

OBJECTIVE

This review provides an update on NF-κB signaling and an overview of three classes of NF-κB inhibitors: i) inhibitors of IκB kinase-β (also called IKK2), an essential link in the inflammatory response; ii) agents that react with NF-κB and prevent its binding to DNA; and iii) ligands for nuclear receptors such as the glucocorticoid receptor, PPARs and liver X receptor, which interfere with NF-κB-mediated transcription through a mechanism termed ligand-dependent transrepression. Recent progress in development of glucocorticoid receptor, PPAR and liver X receptor ligands with dissociated activity, which retain transrepression but have reduced transactivation potency, is also described.

CONCLUSIONS

NF-κB inhibitors have yielded promising results in rodent models of inflammatory disease and cancer. Some of these are currently advancing into clinical trials.

Genotoxic properties of cyclopentenone prostaglandins and the onset of glutathione depletion

Prostaglandins are endogenous mediators formed from arachidonic acid by cyclooxygenases and prostaglandin synthases during inflammatory processes. The five-membered ring can be dehydrated, and α,β-unsaturated cyclopentenone PGs (cyPGs) are generated. Recent studies have been focused on their potential pharmacological use against inflammation and cancer. However, little is known so far about possible adverse health effects of cyPGs. We addressed the question whether selected cyPGs at a concentration range of 0.1-10 μM exhibit mutagenic and genotoxic properties in the hamster lung fibroblast V79 cell line and whether these effects are accompanied by a depletion of intracellular glutathione (GSH). The cyPGs 15-deoxy-Δ12,14-prostaglandin J2 (15dPGJ2) and prostaglandin A2 (PGA2) significantly induced DNA damage in V79 cells after 1 h of incubation. Furthermore, a more pronounced increase in formamidopyrimidine-DNA glycosylase (FPG) sensitive sites, indicative of oxidative DNA-damage, was observed. The findings on DNA-damaging properties were supported by our results that 15dPGJ(2) acts as an aneugenic agent which induces the amount of kinetochore positive micronuclei associated with an increase of apoptosis. The strong potency of cyPGs to rapidly bind GSH measured in a chemical assay and to significantly reduce the GSH level after only 1 h of incubation may contribute to the observed oxidative DNA strand breaks, whereas directly induced oxidative stress via reactive oxygen species could be excluded. However, after an extended incubation time of 24 h no genotoxicity could be measured, this may contribute to the lack of mutagenicity in the hypoxanthine phosphorybosyltransferase (HPRT) assay. In conclusion, potential in vitro genotoxicity of cyPG and a strong impact on GSH homeostasis have been demonstrated, which may be involved in carcinogenesis mediated by chronic inflammation.

Prostaglandin 15d-PGJ(2) inhibits androgen receptor signaling in prostate cancer cells

Androgen signaling, in particular overexpression of the androgen receptor (AR), is critical for the growth and progression of prostate cancer. Because the AR is amenable to targeting by small-molecule inhibitors, it remains the major druggable target for the advanced disease. Inflammation has also been implicated in the cancerous growth in the prostate. Here we show that 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), an endogenously produced antiinflammatory prostaglandin, targets the AR and acts as a potent AR inhibitor, rapidly repressing AR target genes, such as FKBP51 and TMPRSS2 in prostate cancer cells. However, exposure of prostate cancer cells to 15d-PGJ(2) does not simply evoke a general inhibition of nuclear receptor activity or transcription because under the same conditions, peroxisome proliferator-activated receptor-γ is activated by 15d-PGJ(2). Moreover, 15d-PGJ(2) rapidly triggers modifications of AR by small ubiquitin-related modifier-2/3 (SUMO-2/3), which may modulate the repressing effect of 15d-PGJ(2) on AR-dependent transcription. Chromatin immunoprecipitation assays indicate that the inhibitory effect of 15d-PGJ(2) on FKBP51 and TMPRSS2 expression occurs in parallel with the inhibition of the AR binding to the regulatory regions of these genes. However, the DNA-binding activity is not the only AR function targeted by 15d-PGJ(2) because the prostaglandin also blunted the androgen-dependent interaction between the AR amino and carboxy termini. In conclusion, our results identify 15d-PGJ(2) as a potent and direct inhibitor of androgen signaling, suggesting novel possibilities in restricting the AR activity in prostate cancer cells.

Small molecule activators of the heat shock response: chemical properties, molecular targets, and therapeutic promise

All cells have developed various mechanisms to respond and adapt to a variety of environmental challenges, including stresses that damage cellular proteins. One such response, the heat shock response (HSR), leads to the transcriptional activation of a family of molecular chaperone proteins that promote proper folding or clearance of damaged proteins within the cytosol. In addition to its role in protection against acute insults, the HSR also regulates lifespan and protects against protein misfolding that is associated with degenerative diseases of aging. As a result, identifying pharmacological regulators of the HSR has become an active area of research in recent years. Here, we review progress made in identifying small molecule activators of the HSR, what cellular targets these compounds interact with to drive response activation, and how such molecules may ultimately be employed to delay or reverse protein misfolding events that contribute to a number of diseases.

The antagonistic actions of endogenous interleukin-1β and 15-deoxy-Δ12,14-prostaglandin J2 regulate the temporal synthesis of matrix metalloproteinase-9 in sheared chondrocytes

Mechanical overloading of articular cartilage producing hydrostatic stress, tensile strain, and fluid flow results in irreversible cartilage erosion and osteoarthritis (OA). Application of high fluid shear to chondrocytes recapitulates the earmarks of OA as evidenced by the induction of proinflammatory cytokines and prostaglandins, which are capable of inducing the expression of matrix-degrading enzymes. Matrix metalloproteinase-9 (MMP-9) synthesis is detected at early but not late stages of OA. However, the underlying mechanism(s) of the MMP-9 temporal regulation remains unknown. Using the T/C-28a2 chondrocyte cell line as a model system, we demonstrated that high fluid shear induces a marked increase in MMP-9 expression at short shear exposure times (3-6 h), which falls below basal levels after prolonged shear exposure (12-48 h). High fluid shear stress induced the rapid and sustained synthesis of IL-1β, activating PI3K, ERK1/2, and JNK, which are in turn responsible for MMP-9 expression. Prolonged shear exposure (>12 h) induced 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)) synthesis, which exerted an antagonistic effect on IL-1β-mediated PI3K-, ERK1/2-, and JNK-dependent NF-κB activation, thereby suppressing MMP-9 expression in human chondrocytes. Reconstructing the signaling network that regulates shear-mediated MMP-9 expression in human chondrocytes may provide insights for developing strategies to treat arthritic disorders.

Cell signalling by reactive lipid species: new concepts and molecular mechanisms

The process of lipid peroxidation is widespread in biology and is mediated through both enzymatic and non-enzymatic pathways. A significant proportion of the oxidized lipid products are electrophilic in nature, the RLS (reactive lipid species), and react with cellular nucleophiles such as the amino acids cysteine, lysine and histidine. Cell signalling by electrophiles appears to be limited to the modification of cysteine residues in proteins, whereas non-specific toxic effects involve modification of other nucleophiles. RLS have been found to participate in several physiological pathways including resolution of inflammation, cell death and induction of cellular antioxidants through the modification of specific signalling proteins. The covalent modification of proteins endows some unique features to this signalling mechanism which we have termed the ‘covalent advantage’. For example, covalent modification of signalling proteins allows for the accumulation of a signal over time. The activation of cell signalling pathways by electrophiles is hierarchical and depends on a complex interaction of factors such as the intrinsic chemical reactivity of the electrophile, the intracellular domain to which it is exposed and steric factors. This introduces the concept of electrophilic signalling domains in which the production of the lipid electrophile is in close proximity to the thiol-containing signalling protein. In addition, we propose that the role of glutathione and associated enzymes is to insulate the signalling domain from uncontrolled electrophilic stress. The persistence of the signal is in turn regulated by the proteasomal pathway which may itself be subject to redox regulation by RLS. Cell death mediated by RLS is associated with bioenergetic dysfunction, and the damaged proteins are probably removed by the lysosome-autophagy pathway.

The tobacco smoke component, acrolein, suppresses innate macrophage responses by direct alkylation of c-Jun N-terminal kinase

The respiratory innate immune system is often compromised by tobacco smoke exposure, and previous studies have indicated that acrolein, a reactive electrophile in tobacco smoke, may contribute to the immunosuppressive effects of smoking. Exposure of mice to acrolein at concentrations similar to those in cigarette smoke (5 ppm, 4 h) significantly suppressed alveolar macrophage responses to bacterial LPS, indicated by reduced induction of nitric oxide synthase 2, TNF-α, and IL-12p40. Mechanistic studies with bone marrow-derived macrophages or MH-S macrophages demonstrated that acrolein (1-30 μM) attenuated these LPS-mediated innate responses in association with depletion of cellular glutathione, although glutathione depletion itself was not fully responsible for these immunosuppressive effects. Inhibitory actions of acrolein were most prominent after acute exposure (<2 h), indicating the involvement of direct and reversible interactions of acrolein with critical signaling pathways. Among the key signaling pathways involved in innate macrophage responses, acrolein marginally affected LPS-mediated activation of nuclear factor (NF)-κB, and significantly suppressed phosphorylation of c-Jun N-terminal kinase (JNK) and activation of c-Jun. Using biotin hydrazide labeling, NF-κB RelA and p50, as well as JNK2, a critical mediator of innate macrophage responses, were revealed as direct targets for alkylation by acrolein. Mass spectrometry analysis of acrolein-modified recombinant JNK2 indicated adduction to Cys(41) and Cys(177), putative important sites involved in mitogen-activated protein kinase (MAPK) kinase (MEK) binding and JNK2 phosphorylation. Our findings indicate that direct alkylation of JNK2 by electrophiles, such as acrolein, may be a prominent and hitherto unrecognized mechanism in their immunosuppressive effects, and may be a major factor in smoking-induced effects on the immune system.

Celastrol inhibits Tat-mediated human immunodeficiency virus (HIV) transcription and replication

Current drugs used for antiretroviral therapy against human immunodeficiency virus (HIV) have a narrow spectrum of activity and, more often, have associated toxicities and severe side effects in addition to developing resistance. Thus, there is a need to develop new therapeutic strategies against HIV/AIDS to complement the already existing ones. Surprisingly, transactivator of transcription (Tat), an early virus-encoded protein required for the efficient transcription of the HIV genome, has not been developed as a target for small molecular therapeutics. We have previously described the ability of an endogenous Michael acceptor electrophile (MAE), 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), to inhibit Tat-dependent transcription by targeting its cysteine (Cys)-rich domain. In an effort to identify other MAEs possessing inhibitory activity against HIV-1 Tat, we tested a collection of plant-derived compounds with electrophilic properties, including curcumin, rosmarinic acid, and gambogic acid, for their ability to inhibit Tat. Celastrol (Cel), a triterpenoid MAE isolated from Tripterygium wilfordii, exhibited the highest inhibitory activity against Tat. Using biochemical techniques, we demonstrate that Cel, by covalently modifying the cysteine thiols, inhibits Tat transactivation function. Using circular dichroism spectroscopy, we show that alkylation of Tat brought about a change in the secondary structure of Tat, which inhibited the transcription elongation of the HIV proviral genome by effecting mechanisms other than Tat-TAR (transactivation-responsive region) interaction. Our results demonstrate the underlying mechanism of antiretroviral activity of the plant-derived MAEs and suggest that Cel could serve as a lead compound to develop novel antiviral therapeutics.

Identification of aldo-keto reductase AKR1B10 as a selective target for modification and inhibition by prostaglandin A(1): implications for antitumoral activity

Cyclopentenone prostaglandins (cyPG) are reactive eicosanoids that may display anti-inflammatory and antiproliferative actions, possibly offering therapeutic potential. Here we report the identification of members of the aldo-keto reductase (AKR) family as selective targets of the cyPG prostaglandin A(1) (PGA(1)). AKR enzymes metabolize aldehydes and drugs containing carbonyl groups and are involved in inflammation and tumorigenesis. Thus, these enzymes represent a class of targets to develop small molecule inhibitors with therapeutic activity. Molecular modeling studies pointed to the covalent binding of PGA(1) to Cys299, close to the active site of AKR, with His111 and Tyr49, which are highly conserved in the AKR family, playing a role in PGA(1) orientation. Among AKR enzymes, AKR1B10 is considered as a tumor marker and contributes to tumor development and chemoresistance. We validated the direct modification of AKR1B10 by biotinylated PGA(1) (PGA(1)-B) in cells, and confirmed that mutation of Cys299 abolishes PGA(1)-B incorporation, whereas substitution of His111 or Tyr49 reduced the interaction. Modification of AKR1B10 by PGA(1) correlated with loss of enzymatic activity and both effects were increased by depletion of cellular glutathione. Moreover, in lung cancer cells PGA(1) reduced tumorigenic potential and increased accumulation of the AKR substrate doxorubicin, potentiating cell-cycle arrest induced by this chemotherapeutic agent. Our findings define PGA(1) as a new AKR inhibitor and they offer a framework to develop compounds that could counteract cancer chemoresistance.

Proteomic identification of protein targets for 15-deoxy-Δ(12,14)-prostaglandin J2 in neuronal plasma membrane

15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)) is one of factors contributed to the neurotoxicity of amyloid β (Aβ), a causative protein of Alzheimer's disease. Type 2 receptor for prostaglandin D(2) (DP2) and peroxysome-proliferator activated receptorγ (PPARγ) are identified as the membrane receptor and the nuclear receptor for 15d-PGJ(2), respectively. Previously, we reported that the cytotoxicity of 15d-PGJ(2) was independent of DP2 and PPARγ, and suggested that 15d-PGJ(2) induced apoptosis through the novel specific binding sites of 15d-PGJ(2) different from DP2 and PPARγ. To relate the cytotoxicity of 15d-PGJ(2) to amyloidoses, we performed binding assay [(3)H]15d-PGJ(2) and specified targets for 15d-PGJ(2) associated with cytotoxicity. In the various cell lines, there was a close correlation between the susceptibilities to 15d-PGJ(2) and fibrillar Aβ. Specific binding sites of [(3)H]15d-PGJ(2) were detected in rat cortical neurons and human bronchial smooth muscle cells. When the binding assay was performed in subcellular fractions of neurons, the specific binding sites of [(3)H]15d-PGJ(2) were detected in plasma membrane, nuclear and cytosol, but not in microsome. A proteomic approach was used to identify protein targets for 15d-PGJ(2) in the plasma membrane. By using biotinylated 15d-PGJ(2), eleven proteins were identified as biotin-positive spots and classified into three different functional proteins: glycolytic enzymes (Enolase2, pyruvate kinase M1 (PKM1) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH)), molecular chaperones (heat shock protein 8 and T-complex protein 1 subunit α), cytoskeletal proteins (Actin β, F-actin-capping protein, Tubulin β and Internexin α). GAPDH, PKM1 and Tubulin β are Aβ-interacting proteins. Thus, the present study suggested that 15d-PGJ(2) plays an important role in amyloidoses not only in the central nervous system but also in the peripheral tissues.

The C-terminus of H-Ras as a target for the covalent binding of reactive compounds modulating Ras-dependent pathways

Ras proteins are crucial players in differentiation and oncogenesis and constitute important drug targets. The localization and activity of Ras proteins are highly dependent on posttranslational modifications at their C-termini. In addition to an isoprenylated cysteine, H-Ras, but not other Ras proteins, possesses two cysteine residues (C181 and C184) in the C-terminal hypervariable domain that act as palmitoylation sites in cells. Cyclopentenone prostaglandins (cyPG) are reactive lipidic mediators that covalently bind to H-Ras and activate H-Ras dependent pathways. Dienone cyPG, such as 15-deoxy-Δ^12,14-PGJ₂ (15d-PGJ₂) and Δ¹²-PGJ₂ selectively bind to the H-Ras hypervariable domain. Here we show that these cyPG bind simultaneously C181 and C184 of H-Ras, thus potentially altering the conformational tendencies of the hypervariable domain. Based on these results, we have explored the capacity of several bifunctional cysteine reactive small molecules to bind to the hypervariable domain of H-Ras proteins. Interestingly, phenylarsine oxide (PAO), a widely used tyrosine phosphatase inhibitor, and dibromobimane, a cross-linking agent used for cysteine mapping, effectively bind H-Ras hypervariable domain. The interaction of PAO with H-Ras takes place in vitro and in cells and blocks modification of H-Ras by 15d-PGJ₂. Moreover, PAO treatment selectively alters H-Ras membrane partition and the pattern of H-Ras activation in cells, from the plasma membrane to endomembranes. These results identify H-Ras as a novel target for PAO. More importantly, these observations reveal that small molecules or reactive intermediates interacting with spatially vicinal cysteines induce intramolecular cross-linking of H-Ras C-terminus potentially contributing to the modulation of Ras-dependent pathways.

Prostaglandins antagonistically control Bax activation during apoptosis

The Bax protein (Bcl-2-associated X protein) is pivotal for the apoptotic process. Bax, which resides in an inactive form in the cytosol of healthy cells, is activated during the early stages of apoptosis and becomes associated with mitochondria through poorly understood mechanisms. In this study, we show that a family of bioactive lipids, namely prostaglandins, regulates Bax-dependent apoptosis. The prostaglandin E(2) (PGE(2)) or its derivative PGA(2) binds to Bax, induces its change of conformation, and thereby triggers apoptosis. A cysteine present in the loop between the two transmembrane α-helices of Bax, Cys126 is critical for its activation. PGD(2) inhibits PGE(2) binding to Bax and PGE(2)-induced apoptosis, as well as cell death induced by staurosporine and UV-B in various cell lines. This result is consistent with the fact that apoptosis is accompanied during these treatments by an increase in PGE(2). This process is distinct, yet cooperative, from that involving the BH3-only protein Bid. Our results establish that the PGE(2)/PGD(2) balance is involved in a new early mechanism of control in the activation of Bax during apoptosis.