prostaglandin-a1 and Inflammation

The signaling lipid molecule 15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) has multiple cellular functions, including anti-inflammatory and antineoplastic activities. Here, we report that 15d-PGJ2 blocks translation through inactivation of translational initiation factor eIF4A. Binding of 15d-PGJ2 to eIF4A blocks the interaction between eIF4A and eIF4G that is essential for translation of many mRNAs. Cysteine 264 in eIF4A is the target site of 15d-PGJ2. The antineoplastic activity of 15d-PGJ2 is likely attributed to inhibition of translation. Moreover, inhibition of translation by 15d-PGJ2 results in stress granule (SG) formation, into which TRAF2 is sequestered. The sequestration of TRAF2 contributes to the anti-inflammatory activity of 15d-PGJ2. These findings reveal a novel cross-talk between translation and inflammatory response, and offer new approaches to develop anticancer and anti-inflammatory drugs that target translation factors including eIF4A.

Topics: Anti-Inflammatory Agents; Arachidonic Acid; Arsenites; Chromans; Cyclopentanes; Cytoplasmic Granules; Dinoprostone; Emetine; Enzyme Inhibitors; Eukaryotic Initiation Factor-2; Eukaryotic Initiation Factor-4A; Gene Expression Regulation; HeLa Cells; Humans; Hypoglycemic Agents; Inflammation; Poly(A)-Binding Proteins; PPAR gamma; Prostaglandin D2; Prostaglandins A; Protein Biosynthesis; Protein Synthesis Inhibitors; Rosiglitazone; Signal Transduction; Sodium Compounds; T-Cell Intracellular Antigen-1; Thiazolidinediones; TNF Receptor-Associated Factor 2; Troglitazone; Tumor Necrosis Factor-alpha

Herpes simplex viruses (HSVs) are able to hijack the host-cell IkappaB kinase (IKK)/NF-kappaB pathway, which regulates critical cell functions from apoptosis to inflammatory responses; however, the molecular mechanisms involved and the outcome of the signaling dysregulation on the host-virus interaction are mostly unknown. Here we show that in human keratinocytes HSV-1 attains a sophisticated control of the IKK/NF-kappaB pathway, inducing two distinct temporally controlled waves of IKK activity and disrupting the NF-kappaB autoregulatory mechanism. Using chromatin immunoprecipitation we demonstrate that dysregulation of the NF-kappaB-response is mediated by a virus-induced block of NF-kappaB recruitment to the promoter of the IkappaBalpha gene, encoding the main NF-kappaB-inhibitor. We also show that HSV-1 redirects NF-kappaB recruitment to the promoter of ICP0, an immediate-early viral gene with a key role in promoting virus replication. The results reveal a new level of control of cellular functions by invading viruses and suggest that persistent NF-kappaB activation in HSV-1-infected cells, rather than being a host response to the virus, may play a positive role in promoting efficient viral replication.

Topics: Blotting, Western; Cell Line; Chromatin Immunoprecipitation; DNA Primers; Gene Expression Regulation; Genes, Viral; Herpesvirus 1, Human; Humans; I-kappa B Proteins; Immediate-Early Proteins; Inflammation; Keratinocytes; Models, Genetic; NF-kappa B; NF-KappaB Inhibitor alpha; Plasmids; Promoter Regions, Genetic; Prostaglandins A; RNA, Messenger; Signal Transduction; Simplexvirus; Time Factors; Transcription, Genetic; Transfection; Ubiquitin-Protein Ligases; Ultraviolet Rays

For many years, cyclooxygenase-2 (COX-2), a critical enzyme for PG production, has been the favorite target for anti-inflammatory drug development. However, recent revelations regarding the adverse effects of selective COX-2 inhibitors have stimulated intense debate. Interestingly, in the early phase of inflammation, COX-2 facilitates inflammatory PG production while in the late phase it has anti-inflammatory effects. Moreover, although some PGs are proinflammatory, others have anti-inflammatory effects. Thus, it is likely that PGs with opposing effects maintain homeostasis, although the molecular mechanism(s) remains unclear. We report here that an inflammatory PG, PGD2, via its receptor, mediates the activation of NF-kappaB stimulating COX-2 gene expression. Most interestingly, an anti-inflammatory PG (PGA1) suppresses NF-kappaB activation and inhibits COX-2 gene expression. We propose that while pro- and anti-inflammatory PGs counteract each other to maintain homeostasis, selective COX-2 inhibitors may disrupt this balance, thereby resulting in reported adverse effects.

Topics: Animals; Cyclooxygenase 2; Cyclooxygenase 2 Inhibitors; Gene Expression; Homeostasis; Inflammation; Mice; NF-kappa B; NIH 3T3 Cells; Prostaglandin D2; Prostaglandins; Prostaglandins A; RNA, Messenger

To investigate molecular mechanisms linking inflammation with neurodegeneration, we treated neuronal cultures with prostaglandins (PGs), which are mediators of inflammation. PGA1, D2, J2, and Delta12-PGJ2, but not PGE2, reduced the viability and raised the levels of ubiquitinated proteins in the neuronal cells. PGJ2 and its metabolite, Delta12-PGJ2, were the most potent of the four neurotoxic PGs tested in inducing both effects. To address the mechanism by which these agents lead to the accumulation of ubiquitinated proteins, we tested their effects on neuronal ubiquitin hydrolases UCH-L1 and UCH-L3 as well as on proteasome activity. Notably, Delta12-PGJ2 inhibited the activities of UCH-L1 (K(i) approximately 3.5 microM) and UCH-L3 (K(i) approximately 8.1 microM) without affecting proteasome activity. Intracellular aggregates containing ubiquitinated proteins were detected in Delta12-PGJ2-treated cells, indicating that these aggregates can form independently of proteasome inhibition. In conclusion, impairment of ubiquitin hydrolase activity, such as triggered by Delta12-PGJ2, may be an important contributor to neurodegeneration associated with accumulation of ubiquitinated proteins and inflammation.

Topics: Animals; Antineoplastic Agents; Cells, Cultured; Cysteine Endopeptidases; Dinoprostone; Enzyme Inhibitors; Inflammation; Mice; Molecular Structure; Multienzyme Complexes; Neurons; Prostaglandin D2; Prostaglandins A; Proteasome Endopeptidase Complex; Rats; Ubiquitin; Ubiquitin Thiolesterase

During inflammation the balance between cell activation and cell death is determined by the tight regulation of multiple intracellular enzyme cascades. Key regulatory steps often involve protein kinases. We show that the prototypical pro-inflammatory molecule, bacterial lipopolysaccharide, activates multiple protein kinases such as p38, JNK, IKK-beta, and PKB/Akt via transforming growth factor beta-activated kinase-1 (TAK1). We also show that TAK1 plays an important role in similar activation pathways triggered by interleukin-1. Thus TAK1 must be considered as an important component of intracellular pathways in cells involved in host responses to physiological and/or environmental stress signals during inflammation.

Topics: Androstadienes; Animals; Apoptosis; Cell Line; Chromones; Cysteine Proteinase Inhibitors; Enzyme Activation; Enzyme Inhibitors; Flavonoids; Humans; Hydrogen Peroxide; Hypertonic Solutions; I-kappa B Kinase; Imidazoles; Inflammation; Insulin-Like Growth Factor I; Interleukin-1; JNK Mitogen-Activated Protein Kinases; Lipopolysaccharides; MAP Kinase Kinase Kinases; MAP Kinase Signaling System; Mice; Mitogen-Activated Protein Kinases; Morpholines; NF-kappa B; Okadaic Acid; p38 Mitogen-Activated Protein Kinases; Phosphatidylinositol 3-Kinases; Prostaglandins A; Protein Kinases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Pyridines; Recombinant Fusion Proteins; Signal Transduction; Stress, Physiological; Transfection; Tumor Cells, Cultured; Wortmannin

I-kappaBalpha is an intracellular protein that functions as a primary inhibitor of the proinflammatory transcription factor NF-kappaB. Induction of the stress response with heat shock was previously demonstrated to induce I-kappaBalpha gene expression. Because the stress response can also be induced by nonthermal stimuli, we determined whether induction of the stress response with prostaglandin A1 (PGA1) would induce I-kappaBalpha gene expression. Treatment of human bronchial epithelium (BEAS-2B cells) with PGA1 induced nuclear translocation of heat shock factor 1, thus confirming that PGA1 induces the stress response in BEAS-2B cells. Induction of the stress response with PGA1 increased I-kappaBalpha mRNA expression in a time-dependent manner and increased I-kappaBalpha peptide expression. Transient transfection assays involving a human I-kappaBalpha promoter-luciferase reporter construct demonstrated that induction of the stress response with PGA1 activated the I-kappaBalpha promoter. Induction of the stress response with PGA1 and concomitant induction of I-kappaBalpha were associated with inhibition of TNF-alpha-mediated secretion of interleukin 8 and with inhibition of TNF-alpha-mediated nuclear translocation and activation of NF-kappaB. These data demonstrate that induction of the stress response, by a nonthermal stimulus, increases I-kappaBalpha gene expression by a mechanism involving activation of the I-kappaBalpha promoter. Coupled with previous data demonstrating heat shock-mediated induction of I-kappaBalpha gene expression, these data suggest that I-kappaBalpha may be considered to be one of the stress proteins. The functional consequences of stress response-mediated I-kappaBalpha gene expression may involve attenuation of cellular proinflammatory responses.

Topics: Cell Line, Transformed; DNA-Binding Proteins; Gene Expression Regulation; Heat Shock Transcription Factors; Humans; I-kappa B Proteins; Inflammation; Interleukin-8; NF-kappa B; NF-KappaB Inhibitor alpha; Prostaglandins A; Stimulation, Chemical; Stress, Physiological; Transcription Factors; Transcription, Genetic; Tumor Necrosis Factor-alpha