Tumor necrosis factor alpha rapidly activates the mitogen-activated protein kinase (MAPK) cascade in a MAPK kinase kinase-dependent, c-Raf-1-independent fashion in mouse macrophages

Excessive Supplement of l-Arginine Induces Myopia via Orchestrating the MEK-ERK-NO Signaling Pathway

Myopia can impact an individual's quality of life and induce multiple complications. In this study, we randomly divided guinea pigs into the normal control (NC) group, the lens-induced myopia (LIM) group, the normal control plus l-arginine injection (l-Arg) group, and the normal control plus saline injection (NaCl) group. The animals in each group received the relevant treatments. The results showed that myopia was deeper in the LIM and l-Arg groups compared with the NC and NaCl groups. Our experimental results suggest that the excessive supplement of l-Arg will induce myopia onset and a MEK-ERK cascade that stimulates the downstream nNOS-MMP2 and NRF2-KEAP1 signaling pathways, which is accompanied by inflammatory responses, fibrosis changes, and oxidative stress. After receiving excessive arginine supplements, the experimental individuals showed myopic shifts and a similar pathological state as the LIM group. In conclusion, the supplement of excessive arginine may be a danger factor for myopia onset.

RAF-like protein kinases mediate a deeply conserved, rapid auxin response

The plant-signaling molecule auxin triggers fast and slow cellular responses across land plants and algae. The nuclear auxin pathway mediates gene expression and controls growth and development in land plants, but this pathway is absent from algal sister groups. Several components of rapid responses have been identified in Arabidopsis, but it is unknown if these are part of a conserved mechanism. We recently identified a fast, proteome-wide phosphorylation response to auxin. Here, we show that this response occurs across 5 land plant and algal species and converges on a core group of shared targets. We found conserved rapid physiological responses to auxin in the same species and identified rapidly accelerated fibrosarcoma (RAF)-like protein kinases as central mediators of auxin-triggered phosphorylation across species. Genetic analysis connects this kinase to both auxin-triggered protein phosphorylation and rapid cellular response, thus identifying an ancient mechanism for fast auxin responses in the green lineage.

Berberine Improves TNF-α-Induced Hepatic Insulin Resistance by Targeting MEKK1/MEK Pathway

Berberine (BBR), a natural isoquinoline alkaloid exhibiting insulin sensitizing activity, has been applicated in the treatment of diabetes. However, until now, the exact target of BBR has not been well investigated. Here, primary hepatocytes pre-treated with TNF-α were used to evaluate the role of BBR on hepatic insulin sensitivity. Western blot and immunoprecipitation were used to investigate the effect of BBR on the crosstalk between TNF-α pathway and insulin signaling pathway. Molecular docking was used to verify the interactions between BBR and its potential targets. BBR inhibits the MEKK1 and MEK1/2, and thus suppresses the activation of their downstream ERK1/2. It attenuates the ERK1/2-induced serine phosphorylation of IRS-1 and thus enhances IRS-1 tyrosine phosphorylation and Akt activation. By molecular docking, BBR is proved to efficiently bind MEK1/2. MEKK1 is also considered as BBR target for its similarity in primary structure with MEK1/2. In conclusion, BBR ameliorates TNF-α-induced hepatic insulin resistance by targeting MEKK1 and MEK1/2.

Interleukin-1 Is Overexpressed in Injured Muscles Following Spinal Cord Injury and Promotes Neurogenic Heterotopic Ossification

Neurogenic heterotopic ossifications (NHOs) form in periarticular muscles after severe spinal cord (SCI) and traumatic brain injuries. The pathogenesis of NHO is poorly understood with no effective preventive treatment. The only curative treatment remains surgical resection of pathological NHOs. In a mouse model of SCI-induced NHO that involves a transection of the spinal cord combined with a muscle injury, a differential gene expression analysis revealed that genes involved in inflammation such as interleukin-1β (IL-1β) were overexpressed in muscles developing NHO. Using mice knocked-out for the gene encoding IL-1 receptor (IL1R1) and neutralizing antibodies for IL-1α and IL-1β, we show that IL-1 signaling contributes to NHO development after SCI in mice. Interestingly, other proteins involved in inflammation that were also overexpressed in muscles developing NHO, such as colony-stimulating factor-1, tumor necrosis factor, or C-C chemokine ligand-2, did not promote NHO development. Finally, using NHO biopsies from SCI and TBI patients, we show that IL-1β is expressed by CD68⁺ macrophages. IL-1α and IL-1β produced by activated human monocytes promote calcium mineralization and RUNX2 expression in fibro-adipogenic progenitors isolated from muscles surrounding NHOs. Altogether, these data suggest that interleukin-1 promotes NHO development in both humans and mice. © 2021 American Society for Bone and Mineral Research (ASBMR).

Verification of the Potential Targets of the Herbal Prescription Sochehwan for Drug Repurposing Processes as Deduced by Network Pharmacology

Network pharmacology (NP) is a useful, emerging means of understanding the complex pharmacological mechanisms of traditional herbal medicines. Sochehwan (SCH) is a candidate herbal prescription for drug repurposing as it has been suggested to have beneficial effects on metabolic syndrome. In this study, NP was adopted to complement the shortcomings of literature-based drug repurposing strategies in traditional herbal medicine. We conducted in vitro studies to confirm the effects of SCH on potential pharmacological targets identified by NP analysis. Herbal compounds and molecular targets of SCH were explored and screened from a traditional Chinese medicine systems pharmacology database and analysis platform (TCMSP) and an oriental medicine advanced searching integrated system (OASIS). Forty-seven key targets selected from a protein-protein interaction (PPI) network were analyzed with gene ontology (GO) term enrichment and KEGG pathway enrichment analysis to identify relevant categories. The tumor necrosis factor (TNF) and mitogen-activated protein kinase (MAPK) signaling pathways were presented as significant signaling pathways with lowest p-values by NP analysis, which were downregulated by SCH treatment. The signal transducer and activator of transcription 3 (STAT3) was identified as a core key target by NP analysis, and its phosphorylation ratio was confirmed to be significantly suppressed by SCH. In conclusion, the NP-based approach used for target prediction and experimental data obtained from Raw 264.7 cells strongly suggested that SCH can attenuate inflammatory status by modulating the phosphorylation status of STAT3.

The Underlying Mechanism of Paeonia lactiflora Pall. in Parkinson's Disease Based on a Network Pharmacology Approach

Background: Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, yet as of currently, there is no disease-modifying therapy that could delay its progression. Paeonia lactiflora Pall. is the most frequently used herb in formulas for PD in Traditional Chinese Medicine and also a potential neuroprotective agent for neurodegenerative diseases, while its mechanisms remain poorly understood. In this study, we aim to explore the underlying mechanism of P. lactiflora in treating PD utilizing a network pharmacology approach. Methods: The protein targets of P. lactiflora ingredients and PD were first obtained from several databases. To clarify the key targets, a Protein-Protein-Interaction (PPI) network was constructed and analyzed on the String database, and then enrichment analysis was performed by the Metascape platform to determine the main Gene Ontology biological processes and Kyoto Encyclopedia of Genes and Genomes pathways. Finally, the Ingredient-Target-Pathway (I-T-P) network was constructed and analyzed by Cytoscape software. Results: Six active ingredients of P. lactiflora (kaempferol, ß-sitosterol, betulinic acid, palbinone, paeoniflorin and (+)-catechin) as well as six core targets strongly related to PD treatment [AKT1, interleukin-6, CAT, Tumor necrosis factor (TNF), CASP3, and PTGS2] were identified. The main pathways were shown to involve neuroactive ligand-receptor interaction, Calcium signaling pathway, PI3-Akt signaling pathway, TNF signaling pathway, and apoptosis signaling pathway. The main biological process included the regulation of neurotransmitter levels. Conclusion: P. lactiflora may retard neurodegeneration by reducing neuroinflammation, inhibiting intrinsic and extrinsic apoptosis, and may improve motor and non-motor symptoms by regulating the levels of neurotransmitters. Our study has revealed the mechanism of P. lactiflora in the treatment of PD and may contribute to novel drug development for PD.

Novel Therapeutic Anti-ADAM17 Antibody A9(B8) Enhances EGFR-TKI-Mediated Anticancer Activity in NSCLC

Epidermal growth factor receptor (EGFR) mutations were found in 30%-40% of non-small cell lung cancer (NSCLC) patients, who often responded well to EGFR tyrosine kinase inhibitors (EGFR-TKIs) as exemplified by erlotinib and gefitinib in the past decades. However, EGFR mutation-led drug resistance usually occurred upon prolonged treatment with EGFR-TKI. Herein, we study the anticancer effects of EGFR-TKI in combination with a newly developed antibody, A9(B8), to target a disintegrin and metalloprotease (ADAM) 17 that was overexpressed in NSCLC patients. NSCLC cell lines with different EGFR mutations were used to evaluate the drug combination. We have found that the EGFR-TKI-A9(B8) combination exhibited enhanced anticancer effects in NCI-H1975 cells harboring L858R and T790M mutations, which were due to simultaneous suppression of extracellular signal-regulated kinases phosphorylation. Our results suggested that targeting ADAM17 could potentiate the anticancer effects of EGFR-TKI against NSCLC and overcome drug resistance due to EGFR mutations.

Lyssavirus matrix protein cooperates with phosphoprotein to modulate the Jak-Stat pathway

Phosphoprotein (P) and matrix protein (M) cooperate to undermine the immune response to rabies virus (RABV) infections. While P is involved in the modulation of the Jak-Stat pathway through the cytoplasmic retention of interferon (IFN)-activated STAT1 (pSTAT1), M interacts with the RelAp43-p105-ABIN2-TPL2 complex, to efficiently inhibit the nuclear factor-κB (NF-κB) pathway. Using transfections, protein-complementation assays, reverse genetics and DNA ChIP, we identified a role of M protein in the control of Jak-Stat signaling pathway, in synergy with the P protein. In unstimulated cells, both M and P proteins were found to interact with JAK1. Upon type-I IFN stimulation, the M switches toward pSTAT1 interaction, which results in an enhanced capacity of P protein to interact with pSTAT1 and restrain it in the cytoplasm. Furthermore, the role for M-protein positions 77, 100, 104 and 110 was also demonstrated in interaction with both JAK1 and pY-STAT1, and confirmed in vivo. Together, these data indicate that M protein cooperates with P protein to restrain in parallel, and sequentially, NF-κB and Jak-Stat pathways.

Combination of enzastaurin and ATRA exerts dose-dependent dual effects on ATRA-resistant acute promyelocytic leukemia cells

All-trans retinoic acid (ATRA) resistance continues to be a critical problem in acute promyelocytic leukemia (APL)-relapsed patients. In this study, a clinically achievable concentration of enzastaurin synergized with ATRA to induce differentiation and apoptosis in ATRA-resistant APL cell lines, NB4-R1 and NB4-R2. Mechanistically, although enzastaurin is a protein kinase Cβ (PKCβ) inhibitor, PKCβ may not be required since the activity of PKCβ was not suppressed by enzastaurin-ATRA (enz-ATRA) co-treatment, and another PKCβ-selective inhibitor did not mimic the effects of enzastaurin. An MEK inhibitor but not a RAF-1 inhibitor suppressed enz-ATRA treatment-triggered differentiation, activation of MEK/ERK and up-regulation of CCAAT/enhancer binding protein β (C/EBPβ) and/or PU.1. Therefore, RAF-1-independent MEK/ERK signaling was required for enz-ATRA treatment-induced differentiation via modulation of the protein levels of C/EBPβ and/or PU.1. Enz-ATRA treatment collapsed mitochondrial transmembrane potential without the activation of caspase-3, -6 and -7. Moreover, caspase-3/7- and caspase-6-specific inhibitors had no inhibitory effect on enz-ATRA treatment-triggered apoptosis. Therefore, enz-ATRA treatment-induced apoptosis was mitochondria-dependent but caspase-independent. Enz-ATRA treatment degraded PML-RARα, which may be involved in enz-ATRA treatment-induced dual effects and may also be beneficial for APL eradication. These findings may provide a potential therapy for ATRA-resistant APL patients.

The combination of UCN-01 and ATRA triggers differentiation in ATRA resistant acute promyelocytic leukemia cell lines via RAF-1 independent activation of MEK/ERK

With the introduction of arsenic trioxide and all-trans retinoic acid, the prognosis of acute promyelocytic leukemia has greatly improved. However, all-trans retinoic acid resistance is still unresolved in acute promyelocytic leukemia relapsed patients. In this study, the clinical achievable concentration of 7-hydroxystaurosporine synergized with all-trans retinoic acid to induce terminal differentiation in all-trans retinoic acid resistant acute promyelocytic leukemia cell lines. Though 7-hydroxystaurosporine is a PKC inhibitor, PKC might not be involved in the combination-induced differentiation since other PKC selective inhibitors, Gö 6976 and rottlerin failed to cooperate with all-trans retinoic acid to trigger differentiation. The combination significantly enhanced the protein level of CCAAT/enhancer binding protein β and/or PU.1 as well as activated MEK/ERK. U0126 (MEK specific inhibitor) not only suppressed the combination-induced differentiation but also restored the protein level of CCAAT/enhancer binding protein β and/or PU.1. However, RAF-1 inhibitor had no inhibitory effect on MEK activation and the combination-induced differentiation. Therefore, the combination overcame differentiation block via RAF-1 independent MEK/ERK modulation of the protein level of CCAAT/enhancer binding protein β and/or PU.1. These findings may provide a preclinical rationale for the potential role of this combination in the treatment of all-trans retinoic acid resistant acute promyelocytic leukemia patients.

Alcohol abuse and disorder of granulopoiesis

Granulocytes are the major type of phagocytes constituting the front line of innate immune defense against bacterial infection. In adults, granulocytes are derived from hematopoietic stem cells in the bone marrow. Alcohol is the most frequently abused substance in human society. Excessive alcohol consumption injures hematopoietic tissue, impairing bone marrow production of granulocytes through disrupting homeostasis of granulopoiesis and the granulopoietic response. Because of the compromised immune defense function, alcohol abusers are susceptible to infectious diseases, particularly septic infection. Alcoholic patients with septic infection and granulocytopenia have an exceedingly high mortality rate. Treatment of serious infection in alcoholic patients with bone marrow inhibition continues to be a major challenge. Excessive alcohol consumption also causes diseases in other organ systems, particularly severe alcoholic hepatitis which is life threatening. Corticosteroids are the only therapeutic option for improving short-term survival in patients with severe alcoholic hepatitis. The existence of advanced alcoholic liver diseases and administration of corticosteroids make it more difficult to treat serious infection in alcoholic patients with the disorder of granulopoieis. This article reviews the recent development in understanding alcohol-induced disruption of marrow granulopoiesis and the granulopoietic response with the focus on progress in delineating cell signaling mechanisms underlying the alcohol-induced injury to hematopoietic tissue. Efforts in exploring effective therapy to improve patient care in this field will also be discussed.

Ganglioside GM3 suppresses lipopolysaccharide-induced inflammatory responses in rAW 264.7 macrophage cells through NF-κB, AP-1, and MAPKs signaling

Gangliosides are known to specifically inhibit vascular leukocyte recruitment and consequent interaction with the injured endothelium, the basic inflammatory process. In this study, we have found that the production of nitric oxide (NO), a main regulator of inflammation, is suppressed by GM3 on murine macrophage RAW 264.7 cells, when induced by LPS. In addition, GM3 attenuated the increase in cyclooxyenase-2 (COX-2) protein and mRNA levels in lipopolysaccharide (LPS)-activated RAW 264.7 cells in a dose-dependent manner. Moreover, GM3 inhibited the expression and release of pro-inflammatory cytokines of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β) in RAW 264.7 macrophages. At the intracellular level, GM3 inhibited LPS-induced nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and activator protein (AP)-1 in RAW 264.7 macrophages. We, therefore, investigated whether GM3 affects mitogen-activated protein kinase (MAPK) phosphorylation, a process known as the upstream signaling regulator. GM3 dramatically reduced the expression levels of the phosphorylated forms of ERK, JNK, and p38 in LPS-activated RAW 264.7 cells. These results indicate that GM3 is a promising suppressor of the vascular inflammatory responses and ganglioside GM3 suppresses the LPS-induced inflammatory response in RAW 264.7 macrophages by suppression of NF-κB, AP-1, and MAPKs signaling. Accordingly, GM3 is suggested as a beneficial agent for the treatment of diseases that are associated with inflammation.

Inhibition of cyclic AMP response element-directed transcription by decoy oligonucleotides enhances tumor-specific radiosensitivity

The radiation stress induces cytotoxic responses of cell death as well as cytoprotective responses of cell survival. Understanding exact cellular mechanism and signal transduction pathways is important in improving cancer radiotherapy. Increasing evidence suggests that cyclic AMP response element binding protein (CREB)/activating transcription factor (ATF) family proteins act as a survival factor and a signaling molecule in response to stress. We postulated that CREB inhibition via CRE decoy oligonucleotide increases tumor cell sensitization to γ-irradiation-induced cytotoxic stress. In the present study, we demonstrate that CREB phosphorylation and CREB DNA-protein complex formation increased in time- and radiation dose-dependent manners, while there was no significant change in total protein level of CREB. In addition, CREB was phosphorylated in response to γ-irradiation through p38 MAPK pathway. Further investigation revealed that CREB blockade by decoy oligonucleotides functionally inhibited transactivation of CREB, and significantly increased radiosensitivity of multiple human cancer cell lines including TP53- and/or RB-mutated cells with minimal effects on normal cells. We also demonstrate that tumor cells ectopically expressing dominant negative mutant CREB (KCREB) and the cells treated with p38 MAPK inhibitors were more sensitive to γ-irradiation than wild type parental cells or control-treated cells. Taken together, we conclude that CREB protects tumor cells from γ-irradiation, and combination of CREB inhibition plus ionizing radiation will be a promising radiotherapeutic approach.

A RING to rule them all? Insights into the Map3k1 PHD motif provide a new mechanistic understanding into the diverse roles of Map3k1

Despite the sizable number of components that comprise Mapk cascades, Map3k1 is the only element that contains both a kinase domain and a plant homeodomain (PHD) motif, allowing Map3k1 to regulate the protein phosphorylation and ubiquitin proteasome systems. As such, Map3k1 has complex roles in the regulation of cell death, survival, migration and differentiation. Numerous mouse and human genetic analyses have demonstrated that Map3k1 is of critical importance for the immune system, cardiac tissue, testis, wound healing, tumorigenesis and cancer. Recent gene knockin of Map3k1 to mutate the E2 binding site within the Map3k1 PHD motif and high throughput ubiquitin protein array screening for Map3k1 PHD motif substrates provide critical novel insights into Map3k1 PHD motif signal transduction and bring a brand-new understanding to Map3k1 signaling in mammalian biology.

β-arrestin2 in infiltrated macrophages inhibits excessive inflammation after myocardial infarction

Beta-arrestins (β-arrestin1 and β-arrestin2) are known as cytosolic proteins that mediate desensitization and internalization of activated G protein-coupled receptors. In addition to these functions, β-arrestins have been found to work as adaptor proteins for intracellular signaling pathways. β-arrestin1 and β-arrestin2 are expressed in the heart and are reported to participate in normal cardiac function. However, the physiological and pathological roles of β-arrestin1/2 in myocardial infarction (MI) have not been examined. Here, we demonstrate that β-arrestin2 negatively regulates inflammatory responses of macrophages recruited to the infarct area. β-arrestin2 knockout (KO) mice have higher mortality than wild-type (WT) mice after MI. In infarcted hearts, β-arrestin2 was strongly expressed in infiltrated macrophages. The production of inflammatory cytokines was enhanced in β-arrestin2 KO mice. In addition, p65 phosphorylation in the macrophages from the infarcted hearts of β-arrestin2 KO mice was increased in comparison to that of WT mice. These results suggest that the infiltrated macrophages of β-arrestin2 KO mice induce excessive inflammation at the infarct area. Furthermore, the inflammation in WT mice transplanted with bone marrow cells of β-arrestin2 KO mice is enhanced by MI, which is similar to that in β-arrestin2 KO mice. In contrast, the inflammation after MI in β-arrestin2 KO mice transplanted with bone marrow cells of WT mice is comparable to that in WT mice transplanted with bone marrow cells of WT mice. In summary, our present study demonstrates that β-arrestin2 of infiltrated macrophages negatively regulates inflammation in infarcted hearts, thereby enhancing inflammation when the β-arrestin2 gene is knocked out. β-arrestin2 plays a protective role in MI-induced inflammation.

TNF-α-induces airway hyperresponsiveness to cholinergic stimulation in guinea pig airways

BACKGROUND AND PURPOSE

TNF-α is an inflammatory cytokine implicated in the pathogenesis of asthma and it causes airway inflammation, bronchoconstriction and airway hyperresponsiveness to a number of spasmogens following inhalation.

EXPERIMENTAL APPROACH

We compared contractions of guinea pig isolated trachea incubated with saline or TNF-α for 1, 2 or 4 days to electrical field stimulation (EFS), 5-HT or methacholine. In addition, we compared bronchoconstriction in anaesthetized guinea pigs 6 h after intratracheal instillation of saline or TNF-α to vagal nerve stimulation, i.v. 5-HT or methacholine. Differential counts were performed on the bronchoalvelolar lavage fluid (BALF).

KEY RESULTS

Maximum contractions to methacholine, 5-HT and EFS were not different between freshly prepared and saline-incubated tissues. Exposure to TNF-α concentration-dependently potentiated contractions to 5-HT and EFS, but not methacholine. All contractions were atropine-sensitive, but not hexamethonium-sensitive. 5-HT-evoked contractions were inhibited by ketanserin or epithelial denudation. Only EFS-evoked contractions were tetrodotoxin-sensitive. Vagal stimulation, i.v. 5-HT or MCh caused a significant atropine-sensitive, frequency- and dose-dependent bronchoconstriction and decreased blood pressure similarly in both saline and TNF-α pre-treated animals. TNF-α potentiated the bronchoconstriction to vagal stimulation and 5-HT, but not MCh. The BALF from saline-treated animals contained predominantly macrophages, whereas that from TNF-α-treated animals contained neutrophils.

CONCLUSIONS AND IMPLICATIONS

TNF-α caused airway hyperresponsiveness to nerve stimulation in vivo and increased contractility in vitro. However, responsiveness to MCh was unchanged, suggesting a pre-synaptic action of TNF-α on parasympathetic nerves. TNF-α-induced airway hyperresponsiveness to 5-HT suggested an increased 5-HT(2A) receptor-mediated acetylcholine release from epithelial cells.

Tumor necrosis factor-alpha and the roles it plays in homeostatic and degenerative processes within the central nervous system

Tumor Necrosis Factor-alpha (TNF-α) is a prototypic pro-inflammatory cytokine involved in the innate immune response. TNF-α ligation and downstream signaling with one of its cognate receptors, TNF-RI or TNF-RII, modulates fundamental processes in the brain including synapse formation and regulation, neurogenesis, regeneration, and general maintenance of the central nervous system (CNS). During states of chronic neuroinflammation, extensive experimental evidence implicates TNF-α as a key mediator in disease progression, gliosis, demyelination, inflammation, blood-brain-barrier deterioration, and cell death. This review explores the complex roles of TNF-α in the CNS under normal physiologic conditions and during neurodegeneration. We focus our discussion on Multiple Sclerosis, Parkinson's disease, and Alzheimer's disease, relaying the outcomes of preclinical and clinical testing of TNF-α directed therapeutic strategies, and arguing that despite the wealth of functions attributed to this central cytokine, surprisingly little is known about the cell type- and stage-specific roles of TNF-α in these debilitating disorders.

Silica-induced TNF-alpha and TGF-beta1 expression in RAW264.7 cells are dependent on Src-ERK/AP-1 pathways

The cytokines secreted by lung macrophages have been shown to play a critical role in the pathogenesis of silicosis, tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta1 (TGF-beta1) are prominent cytokines in silicosis, but the underlying mechanism remains to be determined. The aim of the present study was to investigate the roles of Src-mitogen-activated protein kinase (MAPKs)/activator protein-1 (AP-1) signaling pathways in silica-induced TNF-alpha and TGF-beta1 expression in macrophage cells (RAW264.7). It was found that silica activated Src, p38 kinase, and extracellular signal-regulated kinase (ERK) in RAW264.7 cells. The induction of TNF-alpha and TGF-beta1 by silica was suppressed by Src inhibitor (PP1), ERK inhibitor (PD98059), but not by p38 kinase inhibitor (SB203580). Dominant negative mutant c-Jun (TAM67) inhibited silica-induced AP-1 DNA binding activity and downregulated the TNF-alpha and TGF-beta1 expression. In addition, PD98059 but not SB203580 inhibited the AP-1 DNA binding activity induced by silica. Based on these findings, it was conclude that Src-ERK/AP-1 signaling pathways are involved in the TNF-alpha and TGF-beta1 expression induced by silica in macrophages.

Reactive astrocytes in glial scar attract olfactory ensheathing cells migration by secreted TNF-alpha in spinal cord lesion of rat

Background

After spinal cord injury (SCI), the formation of glial scar contributes to the failure of injured adult axons to regenerate past the lesion. Increasing evidence indicates that olfactory ensheathing cells (OECs) implanted into spinal cord are found to migrate into the lesion site and induce axons regeneration beyond glial scar and resumption of functions. However, little is known about the mechanisms of OECs migrating from injection site to glial scar/lesion site.

Methods and Findings

In the present study, we identified a link between OECs migration and reactive astrocytes in glial scar that was mediated by the tumor necrosis factor-α (TNF-α). Initially, the Boyden chamber migration assay showed that both glial scar tissue and reactive astrocyte-conditioned medium promoted OECs migration in vitro. Reactive astrocyte-derived TNF-α and its type 1 receptor TNFR1 expressed on OECs were identified to be responsible for the promoting effect on OECs migration. TNF-α-induced OECs migration was demonstrated depending on activation of the extracellular signal-regulated kinase (ERK) signaling cascades. Furthermore, TNF-α secreted by reactive astrocytes in glial scar was also showed to attract OECs migration in a spinal cord hemisection injury model of rat.

Conclusions

These findings showed that TNF-α was released by reactive astrocytes in glial scar and attracted OECs migration by interacting with TNFR1 expressed on OECs via regulation of ERK signaling. This migration-attracting effect of reactive astrocytes on OECs may suggest a mechanism for guiding OECs migration into glial scar, which is crucial for OECs-mediated axons regrowth beyond the spinal cord lesion site.

TNF signaling inhibition in the CNS: implications for normal brain function and neurodegenerative disease

The role of tumor necrosis factor (TNF) as an immune mediator has long been appreciated but its function in the brain is still unclear. TNF receptor 1 (TNFR1) is expressed in most cell types, and can be activated by binding of either soluble TNF (solTNF) or transmembrane TNF (tmTNF), with a preference for solTNF; whereas TNFR2 is expressed primarily by microglia and endothelial cells and is preferentially activated by tmTNF. Elevation of solTNF is a hallmark of acute and chronic neuroinflammation as well as a number of neurodegenerative conditions including ischemic stroke, Alzheimer's (AD), Parkinson's (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). The presence of this potent inflammatory factor at sites of injury implicates it as a mediator of neuronal damage and disease pathogenesis, making TNF an attractive target for therapeutic development to treat acute and chronic neurodegenerative conditions. However, new and old observations from animal models and clinical trials reviewed here suggest solTNF and tmTNF exert different functions under normal and pathological conditions in the CNS. A potential role for TNF in synaptic scaling and hippocampal neurogenesis demonstrated by recent studies suggest additional in-depth mechanistic studies are warranted to delineate the distinct functions of the two TNF ligands in different parts of the brain prior to large-scale development of anti-TNF therapies in the CNS. If inactivation of TNF-dependent inflammation in the brain is warranted by additional pre-clinical studies, selective targeting of TNFR1-mediated signaling while sparing TNFR2 activation may lessen adverse effects of anti-TNF therapies in the CNS.

Interleukin-18 enhances glucose uptake in 3T3-L1 adipocytes

In order to characterize the potential causative effects of interleukin-18 (IL-18) on insulin resistance, we measured glucose uptake in 3T3-L1 adipocytes treated with mouse recombinant IL-18. IL-18 surprisingly enhanced, rather than reduced insulin-mediated glucose uptake in adipocytes. Moreover IL-18 could counteract the glucose uptake suppression caused by tumor necrosis factor alpha in 3T3-L1 adipocytes. The mechanism dissection showed that the IL-18 upregulated phosphorylated Akt and downregulated phosphorylated P38 MAPK. These findings indicated that the elevated serum IL-18 levels in obesity and diabetes might be a compensatory response to insulin resistance.

Mast cells play a key role in the development of late airway hyperresponsiveness through TNF-alpha in a murine model of asthma

We have investigated the role of TNF-alpha in mast cell-mediated late airway hyperresponsiveness (AHR) using mast cell-deficient WBB6F1-W/W(v) (W/W(v)) mice in a murine model of asthma, which exhibits a biphasic increase in AHR. TNF-alpha levels in the airway and magnitude of late AHR in response to airway allergen challenge were severely impaired in W/W(v) mice compared to their littermates. In addition to TNF-alpha, cytosolic phospholipase A(2) (cPLA(2)) phosphorylation and enzymatic activity in the lungs were also impaired in W/W(v) mice. Either anti-TNF-alpha antibody or an inhibitor of cPLA(2) abolished late AHR in congeneic +/+ mice. Intratracheal administration of TNF-alpha resulted in increases in late AHR, cPLA(2 )phosphorylation, cPLA(2 )activity, and phosphorylation of mitogen-activated protein kinases. Mast cell replacement restored airway TNF-alpha level, cPLA(2 )phosphorylation and enzymatic activity in the lungs as well as late AHR in W/W(v) mice. These data indicate that mast cells play a key role in the development of late AHR through liberation of TNF-alpha.

Chemical Genetic Screening Identifies Critical Pathways in Anthrax Lethal Toxin-Induced Pathogenesis

Anthrax lethal toxin (LT)-induced cell death via mitogen-activated protein kinase kinase (MAPKK) cleavage remains questionable. Here, a chemical genetics approach was used to investigate what pathways mediate LT-induced cell death. Several small molecules were found to protect macrophages from anthrax LT cytotoxicity and MAPKK from cleavage by lethal factor (LF), without inhibiting LF enzymatic activity or cellular proteasome activity. Interestingly, the compounds activated MAPK-signaling molecules, induced proinflammatory cytokine production, and inhibited LT-induced macrophage apoptosis in a concentration-dependent manner. We propose that induction of antiapoptotic responses by MAPK-dependent or -independent pathways and activation of host innate responses may protect macrophages from anthrax LT-induced cell death. Altering host responses through a chemical genetics approach can help identify critical cellular pathways involved in the pathogenesis of anthrax and can be exploited to further explore host-pathogen interactions.

Development of a fluorescent microsphere-based multiplexed high-throughput assay system for profiling of transcription factor activation

Transcription factors (TFs), which play crucial roles in the regulation of gene expression in the human genome, are highly regulated by a variety of mechanisms. A single extracellular stimulus can trigger multiple signaling pathways, and these in turn can activate multiple TFs to mediate the inducible expression of target genes. Alterations in the activities of TFs are often associated with human diseases, such as altered activating factor 1, estrogen receptor, and p53 function in cancer, nuclear factor kappaB in inflammatory diseases, and peroxisome proliferator-activated receptor gamma in obesity. A systematic assay for profiling the activation of TFs will aid in elucidating the mechanisms of TF activation, reveal altered TFs associated with human diseases, and aid in developing assays for drug discovery. Here, we developed a 24-plex fluorescent microsphere-based TF activation assay system with a 96-well plate format. The assay system enabled high-throughput profiling of the DNA binding activity of TFs in multiple samples with high sensitivity.

Regulation of signal transduction through protein cysteine oxidation

The production of reactive oxygen species (ROS) accompanies many signaling events. Antioxidants and ROS scavenging enzymes in general have effects that indicate a critical role for ROS in downstream signaling, but a mechanistic understanding of the contribution of ROS as second messengers is incomplete. Here, the role of reactive oxygen species in cell signaling is discussed, emphasizing the ability of ROS to directly modify signaling proteins through thiol oxidation. Examples are provided of protein thiol modifications that control signal transduction effectors that include protein kinases, phosphatases, and transcription factors. Whereas the effects of cysteine oxidation on these proteins in experimental systems is clear, it has proven more difficult to demonstrate these modifications in response to physiologic stimuli. Improved detection methods for analysis of thiol modification will be essential to define these regulatory mechanisms. Bridging these two areas of research could reveal new regulatory mechanisms in signaling pathways, and identify new therapeutic targets.

Translational event mediates differential production of tumor necrosis factor-α in hyaluronan-stimulated microglia and macrophages

Recent evidence has demonstrated that hyaluronan synthase 2 mRNA is up-regulated after brain ischemia. After a cerebral ischemic event, microglia and macrophages are the major inflammatory cells and are activated by hyaluronan (HA). However, it is unclear how these cells compare with regard to HA responsiveness. We show here that peritoneal macrophages and RAW 264.7 macrophages produced more than five- and 10-fold more tumor necrosis factor-alpha (TNF-alpha) than primary microglia and BV-2 microglia, respectively. Antibody blockade study showed that CD44, Toll-like receptor-4 receptor and the receptor for HA-mediated motility were responsible for HA-induced TNF-alpha release. Furthermore, HA induced higher levels of phosphorylated MAPK in RAW 264.7 cells when compared with BV-2 cells. HA-mediated TNF-alpha production required p38 MAPK, extracellular-regulated kinase and c-Jun N-terminal kinase phosphorylation in both cell types. The levels of HA-induced TNF-alpha mRNA expression in BV-2 cells were only twofold lower compared with RAW 264.7 cells, suggesting that a translational event is involved in the differential production of TNF-alpha. Western blot analysis revealed that HA treatment resulted in more rapid phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and more effective dissociation of 4E-BP1 from eukaryotic initiation factor 4E in RAW 264.7 cells than in BV-2 cells. Additionally, HA-induced phosphorylation of 4E-BP1 was dependent on MAPK signaling, indicating that RAW 264.7 cells exhibited higher levels of hyperphosphorylated 4E-BP1 possibly due to the overactivation of MAPK. The results suggest that resident microglia and blood-derived monocytes/macrophages exhibit differential sensitivities in response to extracellular mediators after brain ischemia.

Gene Expression Changes and Signaling Events Associated with the Direct Antimelanoma Effect of IFN-γ

IFN-gamma plays a role in the response to melanoma indirectly through its effect on the immune system and directly through its antiproliferative and proapoptotic effects on melanoma cells. To understand the molecular basis for the direct antimelanoma effect of IFN-gamma, we studied IFN-induced changes in gene expression and signaling among three human melanoma cell lines (DM6, DM93, and 501mel). These were resistant to the antimelanoma effect of IFN-alpha, and only DM6 cells exhibited growth inhibition and apoptosis with IFN-gamma. Through DNA microarray analysis, we found that the antimelanoma effect of IFN-gamma in DM6 was associated with the down-regulation of multiple genes involved in G-protein signaling and phospholipase C activation (including Rap2B and calpain 3) as well as the down-regulation of genes involved in melanocyte/melanoma survival (MITF and SLUG), apoptosis inhibition (Bcl2A1 and galectin-3), and cell cycling (CDK2). The antimelanoma effect of IFN-gamma was also associated with the up-regulation of the proapoptotic dependence receptor UNC5H2 and the Wnt inhibitor Dkk-1. Whereas both IFNs were able to activate Stat1 in all cell lines, the delayed activation of the extracellular signal-regulated kinase, p38, and c-Jun NH2-terminal kinase mitogen-activated protein kinases occurred only in DM6 with IFN-gamma, and the effect of IFN-gamma on cell growth and survival as well as gene expression in DM6 was dependent on the coordinate activation of MEK1 and p38. These findings provide new insights into the signaling events and gene expression changes associated with growth inhibition and apoptosis in melanoma and may thereby assist in identifying new targets for the treatment of melanoma.

Immunosenescence and macrophage functional plasticity: dysregulation of macrophage function by age-associated microenvironmental changes

The macrophage lineage displays extreme functional and phenotypic heterogeneity, which appears to be because, in large part, of the ability of macrophages to functionally adapt to changes in their tissue microenvironment. This functional plasticity of macrophages plays a critical role in their ability to respond to tissue damage and/or infection and to contribute to clearance of damaged tissue and invading microorganisms, to recruitment of the adaptive immune system, and to resolution of the wound and of the immune response. Evidence has accumulated that environmental influences, such as stromal function and imbalances in hormones and cytokines, contribute significantly to the dysfunction of the adaptive immune system. The innate immune system also appears to be dysfunctional in aged animals and humans. In this review, the hypothesis is presented and discussed that the observed age-associated 'dysfunction' of macrophages is the result of their functional adaptation to the age-associated changes in tissue environments. The resultant loss of orchestration of the manifold functional capabilities of macrophages would undermine the efficacy of both the innate and adaptive immune systems. The macrophages appear to maintain functional plasticity during this dysregulation, making them a prime target of cytokine therapy that could enhance both innate and adaptive immune systems.

Acute cutaneous barrier disruption activates epidermal p44/42 and p38 mitogen-activated protein kinases in human and hairless guinea pig skin

Acute cutaneous barrier disruption of the skin elicits various homeostatic repair responses in the epidermis. Although several candidates for the signaling mechanisms that induce these responses have been reported, e.g. the calcium and ion concentration, peroxisome proliferator-activated receptor-alpha, and TNF-alpha signaling mediated by sphingomyelinases, the exact nature of the signals remains undertermined. Therefore, assuming that an important group of serine/threonine-signaling kinases, mitogen- and SAPK/JNK, might link the barrier disruption to the subsequent homeostatic responses, the activation of three MAPKs in hairless guinea pig or in human skin after barrier disruption was investigated. The epidermal barrier was insulated with tape stripping or organic solvents, and Western blotting, and immune complex kinase assay. In the skin of hairless guinea pigs, p44/42 MAPK and p38 MAPK, but nor SAPK/JNK, were continued to be activated for at least 180 min. The activation of p44/42 which positively correlated with the number of tape strippings, whereas K+ sucrose solution suppressed its activation. The activation of p44/42 MAPK was also induced by treatment of the skin with organic solvents. In similar fashion, p44/42 and p38 MAPKs were found to be activated in human skin after tape stripping. These results for strongly suggest that the activation of p44/42 and p38 MAPKs links the stimuli of barrier disruption to the subsequent homeostatic responses to repair the barrier defect.

Hsp90/p50cdc37 is required for mixed-lineage kinase (MLK) 3 signaling

Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase (MAPK) kinase kinase that activates MAPK pathways, including the c-Jun NH(2)-terminal kinase (JNK) and p38 pathways. MLK3 and its family members have been implicated in JNK-mediated apoptosis. A survey of human cell lines revealed high levels of MLK3 in breast cancer cells. To learn more about MLK3 regulation and its signaling pathways in breast cancer cells, we engineered the estrogen-responsive human breast cancer cell line, MCF-7, to stably, inducibly express FLAG epitope-tagged MLK3. FLAG.MLK3 complexes were isolated by affinity purification, and associated proteins were identified by in-gel trypsin digestion followed by liquid chromatography/tandem mass spectrometry. Among the proteins identified were heat shock protein 90alpha,beta (Hsp90) and its kinase-specific co-chaperone p50(cdc37). We show that endogenous MLK3 complexes with Hsp90 and p50(cdc37). Further experiments demonstrate that MLK3 associates with Hsp90/p50(cdc37) through its catalytic domain in an activity-independent manner. Upon treatment of MCF-7 cells with geldanamycin, an ansamycin antibiotic that inhibits Hsp90 function, MLK3 levels decrease dramatically. Furthermore, tumor necrosis factor alpha-induced activation of MLK3 and JNK in MCF-7 cells is blocked by geldanamycin treatment. Our finding that geldanamycin treatment does not affect the cellular levels of the downstream signaling components, MAPK kinase 4, MAPK kinase 7, and JNK, suggests that Hsp90/p50(cdc37) regulates JNK signaling at the MAPK kinase kinase level. Previously identified Hsp90/p50(cdc37) clients include oncoprotein kinases and protein kinases that promote cellular proliferation and survival. Our findings reveal that Hsp90/p50(cdc37) also regulates protein kinases involved in apoptotic signaling.

Inhibition of MEK/ERK 1/2 pathway reduces pro-inflammatory cytokine interleukin-1 expression in focal cerebral ischemia

It has been proposed that mitogen-activated protein kinase (MAPK) pathways may play a role in the regulation of pro-inflammatory cytokines, such as interlukine-1, during cerebral ischemia. Our previous study showed that extracellular-signal-regulated kinases 1 and 2 (ERK 1/2) were activated during focal cerebral ischemia in mice [J. Cereb. Blood Flow Metab. 20 (2000) 1320]. However, the effect of ERK 1/2 activation in focal cerebral ischemia is still unclear. In this study we reported that in vivo phospho-ERK 1/2 expression increased following 30 min of middle cerebral artery occlusion (MCAO) in the mouse brain in both the ischemic core and perifocal regions. Western blot analysis and immunohistochemistry demonstrated that pro-treatment with 1,4-diamino-2,3-dicyano-1,4-bis butadiene (U0126) [J. Biol. Chem. 273 (1998) 18623] could significantly inhibit mouse brain phospho-MEK 1/2 and phospho-ERK 1/2 expression after 1-2 h of MCAO (p<0.05). Compared to the control group of mice, brain infarct volume was significantly decreased after 24 h of MCAO in the U0126-treated mice (27+/-6 vs. 46+/-9 mm(2), p<0.05). Inhibition of the MEK/ERK 1/2 pathway also prevented downstream kinase Elk-1 phosphorylation, and further reduced cytokine IL-1beta mRNA, but not TNFalpha, IL-1alpha, or chemokine MIP-1alpha mRNA expression. Our data demonstrates that in vivo the close linking of MEK 1/2, ERK 1/2, Elk-1, and IL-1 mRNA expression in the cerebral ischemia animals suggests that ERK 1/2 pathway activation is important in pro-inflammatory cytokine IL-1beta signaling, which induces an inflammatory response and exacerbates ischemic brain injury. Inhibiting the ERK 1/2 pathway may therefore provide a novel approach for the reduction of ischemia-induced IL-1beta overexpression.

PPARγ ligands attenuate mesangial contractile dysfunction in high glucose

BACKGROUND

To elucidate the regulation of peroxisome proliferator-activated receptor gamma (PPARgamma) and its roles in mesangial cells, we examined the expression of PPARgamma1 and effects of its ligands on cell phenotypes and angiotensin II-induced contractile response in cultured rat mesangial cells under a high (20 mmol/L) glucose condition.

METHODS

The effects of tumor necrosis factor alpha (TNFalpha), protein kinase C (PKC) activation, antisense DNA for PPARgamma1, PPARgamma ligands and PD98059 were examined in mesangial cells cultured in either 5 mmol/L or 20 mmol/L glucose. The expressions of PPARgamma1 protein and alpha-smooth muscle actin (alphaSMA) as a marker of phenotype of cells were determined by Western blot. The expression of PPARgamma1 mRNA was determined by a reverse transcription-polymerase chain reaction method. The reduction of cell surface area in response to angiotensin II was measured by microscope to determine cellular contraction.

RESULTS

PKC activation, TNFalpha, and 20 mmol/L glucose decreased PPARgamma1 at both protein and mRNA levels, which was inhibited by PD98059, a specific inhibitor of mitogen-activated protein kinase (MAPK). Decreases of PPARgamma1 protein and contractile response and an increase of alphaSMA occurred simultaneously in the cells treated with 20 mmol/L glucose after 5 days, which were attenuated to the normal levels by PPARgamma ligands. The antisense DNA also induced the decrease of PPARgamma1 protein, contractile dysfunction, and increase of alphaSMA.

CONCLUSION

MAPK suppresses PPARgamma1 at the transcriptional level, and the reduction of PPARgamma1 in cultured rat mesangial cells under the high glucose condition induces phenotypic change and loss of contractile function. PPARgamma ligands recover both reductions of PPARgamma 1 protein and contractile response.

Phosphorylation of tumor necrosis factor receptor 1 (p55) protects macrophages from silica-induced apoptosis

Macrophages play a fundamental role in silicosis in part by removing silica particles and producing inflammatory mediators in response to silica. Tumor necrosis factor alpha (TNFalpha) is a prominent mediator in silicosis. Silica induction of apoptosis in macrophages might be mediated by TNFalpha. However, TNFalpha also activates signal transduction pathways (NF-kappaB and AP-1) that rescue cells from apoptosis. Therefore, we studied the TNFalpha-mediated mechanisms that confer macrophage protection against the pro-apoptotic effects of silica. We will show that exposure to silica induced TNFalpha production by RAW 264.7 cells, but not by IC-21. Silica-induced activation of NF-kappaB and AP-1 was only observed in RAW 264.7 macrophages. ERK activation in response to silica exposure was only observed in RAW 264.7 macrophages, whereas activation of p38 phosphorylation was predominantly observed in IC-21 macrophages. No changes in JNK activity were observed in either cell line in response to silica exposure. Silica induced apoptosis in both macrophage cell lines, but the induction of apoptosis was significantly larger in IC-21 cells. Protection against apoptosis in RAW 264.7 cells in response to silica was mediated by enhanced NF-kappaB activation and ERK-mediated phosphorylation of the p55 TNFalpha receptor. Inhibition of these two protective mechanisms by specific pharmacological inhibitors or transfection of dominant negative mutants that inhibit IkappaBalpha or ERK phosphorylation significantly increased silica-induced apoptosis in RAW 264.7 macrophages. These data suggest that NF-kappaB activation and ERK-mediated phosphorylation of the p55 TNF receptor are important cell survival mechanisms in the macrophage response to silica exposure.

Use of an array technology for profiling and comparing transcription factors activated by TNFalpha and PMA in HeLa cells

Multiple signal transduction pathways are generally triggered simultaneously by a single extracellular stimulus. As a result, multiple transcription factors (TFs) can be activated downstream to mediate the inducible expression of target genes. Profiling the activation of all TFs will aid in the dissection of the numerous pathways of signal transduction. Tumor necrosis factor alpha (TNFalpha) and phorbol 12-myristate 13-acetate (PMA) mediate many biological functions, including cell proliferation and apoptosis, by stimulating signaling pathways. Two TFs, nuclear factor kappaB (NFkappaB) and activating factor 1 (AP1), have been identified as targets of both TNFalpha and PMA activation. Here, we describe the use of a protein/DNA array system to identify additional TFs activated by TNFalpha and PMA in HeLa cells. From a total of 150 targeted TFs, six-CREB, E2F, CETP/CRE, c-Rel, MSP1, and Pax6-were identified whose activities, like NFkappaB and AP1, were regulated by both TNFalpha- and PMA-induced pathways. Interestingly, the TF E47 was shown to be specifically activated by TNFalpha but was not affected by treatment with PMA. In addition, GATA, NF-E1, and ISRE were shown to be specifically activated by PMA but not TNFalpha. These findings suggest that TNFalpha and PMA both stimulate unique signaling pathways while mediating transcriptional activation through common pathways.

In vivo selective inhibition of mitogen-activated protein kinase kinase 1/2 in rabbit experimental osteoarthritis is associated with a reduction in the development of structural changes

OBJECTIVE

The primary aim of this study was to investigate, using an experimental rabbit model of osteoarthritis (OA), the effect of a selective mitogen-activated protein kinase kinase 1/2 (MEK-1/2) inhibitor, PD 198306, on the development of structural changes. Additional aims were to assess the effects of the inhibitor on levels of phosphorylated extracellular signal-regulated kinase 1/2 (phospho-ERK-1/2) and matrix metalloproteinase 1 (MMP-1; collagenase 1) in OA chondrocytes.

METHODS

After surgical sectioning of the anterior cruciate ligament of the right knee joint, rabbits with OA were separated into 3 experimental groups: oral treatment with placebo or with PD 198306 at a therapeutic concentration of 10 mg/kg/day or 30 mg/kg/day. Each treatment started immediately after surgery. The animals were killed 8 weeks after surgery. Macroscopic and histologic studies were performed on the cartilage and synovial membrane. The levels of phospho-ERK-1/2 and MMP-1 in OA cartilage chondrocytes were evaluated by immunohistochemistry. Normal, untreated rabbits were used as controls.

RESULTS

OA rabbits treated with the highest dosage of MEK-1/2 inhibitor showed decreases in the surface area (size) of cartilage macroscopic lesions (P < 0.002) and in osteophyte width on the lateral condyles (P = 0.05). Histologically, the severity of synovial inflammation (villous hyperplasia) was also reduced (P < 0.02). In cartilage from placebo-treated OA rabbits, a significantly higher percentage of chondrocytes in the superficial layer stained positive for phospho-ERK-1/2 and MMP-1 compared with normal controls. Rabbits treated with the highest dosage of PD 198306 demonstrated a significant and dose-dependent reduction in the level of phospho-ERK-1/2 and a lower level of MMP-1.

CONCLUSION

This study demonstrates that, in vivo, PD 198306, a selective inhibitor of MEK-1/2, can partially decrease the development of some of the structural changes in experimental OA. This effect was associated with a reduction in the level of phospho-ERK-1/2 in OA chondrocytes, which probably explains the action of the drug.

Ras and mitogen-activated protein kinase kinase kinase-1 coregulate activator protein-1- and nuclear factor-kappaB-mediated gene expression in airway epithelial cells

In 16HBE14o- human bronchial epithelial cells, maximal tumor necrosis factor (TNF)-alpha-induced interleukin (IL)-8 expression depends on the activation of two distinct signaling pathways, one constituted in part by activator protein (AP)-1 and the other by nuclear factor (NF)-kappaB. We examined the upstream signaling intermediates responsible for IL-8 and granulocyte-macrophage colony-stimulating factor (GM-CSF) expression in this system, hypothesizing that p21 Ras and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase (MEKK)-1 function as common upstream activators of both the AP-1 and NF-kappaB pathways. TNF-alpha treatment induced both Ras and MEKK1 activation. Dominant-negative forms of Ras (N17Ras) and MEKK1 (MEKK1-KM) each inhibited TNF-alpha-induced transcription from IL-8 and GM-CSF promoters. Ras was required for maximal activation of extracellular signal-regulated kinase (ERK) and Jun amino terminal kinase (JNK) as well as AP-1 and NF-kappaB transcriptional activities, but not for activation of IkappaB kinase (IKK)-beta, an upstream activator of NF-kappaB. MEKK1 was required for maximal activation of ERK, JNK, and IKK, as well as for maximal AP-1 and NF-kappaB transcriptional activities. We conclude that Ras regulates TNF-alpha-induced chemokine expression by activating the AP-1 pathway and enhancing transcriptional function of NF-kappaB, whereas MEKK1 activates both the AP-1 and NF-kappaB pathways.

Three mitogen-activated protein kinases inhibit insulin signaling by different mechanisms in 3T3-L1 adipocytes

TNFalpha, which activates three different MAPKs [ERK, p38, and jun amino terminal kinase (JNK)], also induces insulin resistance. To better understand the respective roles of these three MAPK pathways in insulin signaling and their contribution to insulin resistance, constitutively active MAPK/ERK kinase (MEK)1, MAPK kinase (MKK6), and MKK7 mutants were overexpressed in 3T3-L1 adipocytes using an adenovirus-mediated transfection procedure. The MEK1 mutant, which activates ERK, markedly down-regulated expression of the insulin receptor (IR) and its major substrates, IRS-1 and IRS-2, mRNA and protein, and in turn reduced tyrosine phosphorylation of IR as well as IRS-1 and IRS-2 and their associated phosphatidyl inositol 3-kinase (PI3K) activity. The MKK6 mutant, which activates p38, moderately inhibited IRS-1 and IRS-2 expressions and IRS-1-associated PI3K activity without exerting a significant effect on the IR. Finally, the MKK7 mutant, which activates JNK, reduced tyrosine phosphorylation of IRS-1 and IRS-2 and IRS-associated PI3K activity without affecting expression of the IR, IRS-1, or IRS-2. In the context of our earlier report showing down-regulation of glucose transporter 4 by MEK1-ERK and MKK6/3-p38, the present findings suggest that chronic activation of ERK, p38, or JNK can induce insulin resistance by affecting glucose transporter expression and insulin signaling, though via distinctly different mechanisms. The contribution of ERK is, however, the strongest.

Protein kinase Czeta mediated Raf-1/extracellular-regulated kinase activation by daunorubicin

In light of the emerging concept of a protective function of the mitogen-activated protein kinase (MAPK) pathway under stress conditions, we investigated the influence of the anthracycline daunorubicin (DNR) on MAPK signaling and its possible contribution to DNR-induced cytotoxicity. We show that DNR increased phosphorylation of extracellular-regulated kinases (ERKs) and stimulated activities of both Raf-1 and extracellular-regulated kinase 1 (ERK1) within 10 to 30 minutes in U937 cells. ERK1 stimulation was completely blocked by either the mitogen-induced extracellular kinase (MEK) inhibitor PD98059 or the Raf-1 inhibitor 8-bromo-cAMP (cyclic adenosine monophosphate). However, only partial inhibition of Raf-1 and ERK1 stimulation was observed with the antioxidant N-acetylcysteine (N-Ac). Moreover, the xanthogenate compound D609 that inhibits DNR-induced phosphatidylcholine (PC) hydrolysis and subsequent diacylglycerol (DAG) production, as well as wortmannin that blocks phosphoinositide-3 kinase (PI3K) stimulation, only partially inhibited Raf-1 and ERK1 stimulation. We also observed that DNR stimulated protein kinase C zeta (PKCzeta), an atypical PKC isoform, and that both D609 and wortmannin significantly inhibited DNR-triggered PKCzeta activation. Finally, we found that the expression of PKCzeta kinase-defective mutant resulted in the abrogation of DNR-induced ERK phosphorylation. Altogether, these results demonstrate that DNR activates the classical Raf-1/MEK/ERK pathway and that Raf-1 activation is mediated through complex signaling pathways that involve at least 2 contributors: PC-derived DAG and PI3K products that converge toward PKCzeta. Moreover, we show that both Raf-1 and MEK inhibitors, as well as PKCzeta inhibition, sensitized cells to DNR-induced cytotoxicity.

Arterial wall shear stress: observations from the bench to the bedside

Shear stress is the tangential force of the flowing blood on the endothelial surface of the blood vessel. Shear is described mathematically or ideal fluids, and in vitro models have enabled researchers to describe the effects of shear on endothelial cells. High shear stress, as found in laminar flow, promotes endothelial cell survival and quiescence, alignment in the direction of flow, and secretion of substances that promote vasodilation and anticoagulation. Low shear stress, or changing shear stress direction as found in turbulent flow, promotes endothelial proliferation and apoptosis, shape change, and secretion of substances that promote vasoconstriction, coagulation, and platelet aggregation. The precise pathways by which endothelial cells sense shear stress to promote their quiescent or activated pathways are currently unknown. Clinical applications include increasing shear stress via creation of an arteriovenous fistula or vein cuff to promote bypass graft flow and patency. Since an abnormal level of shear stress is implicated in the pathogenesis of atherosclerosis, neointimal hyperplasia, and aneurysmal disease, additional research to understand the effects of shear stress on the blood vessel may provide insight to prevent vascular disease.

Targeting Raf-1 gene expression by a DNA enzyme inhibits juvenile myelomonocytic leukemia cell growth

Juvenile myelomonocytic leukemia (JMML) is an aggressive childhood disorder with few therapeutic options. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) promote JMML cell growth. A hyperactive function of the ras oncogene is a hallmark of JMML. We therefore targeted the protein kinase Raf-1 downstream of Ras using a DNA enzyme that degrades mRNA-Raf-1. Western blots of JMML cell lysates revealed phosphorylated Raf-1 protein, indicating constitutive activation. Addition of GM-CSF, but not TNF-alpha, increased phosphorylation of both Raf-1 and the mitogen-activated protein kinases (MAPKs) JNK-1 and ERK-1. Depletion of Raf-1 protein markedly impaired activation of MAPKs, induced substantial inhibition of JMML cell colony formation, and virtually abolished GM-CSF hypersensitivity in JMML cells. Exogenous TNF-alpha, but not GM-CSF, restored colony formation of JMML cells pretreated with the enzyme. We could not detect any effect of the enzyme on the proliferation of normal bone marrow cells, indicating its specificity and potential safety. When immunodeficient mice engrafted with JMML cells were treated continuously with the enzyme via a peritoneal osmotic mini-pump for 4 weeks, a profound reduction in the JMML cell numbers in the recipient murine bone marrows was found. We conclude that GM-CSF is a chief regulator of JMML growth and exerts its proleukemic effects primarily via the Ras/Raf-1 signaling cascade. TNF-alpha plays a permissive role, being dependent upon GM-CSF to induce JMML cell proliferation. The DNA enzyme efficiently catabolized mRNA-Raf-1 with subsequent inhibition of JMML cell growth, suggesting its potential as a mechanism-based therapy in this fatal leukemia.

Effect of IgA on respiratory burst and cytokine release by human alveolar macrophages: role of ERK1/2 mitogen-activated protein kinases and NF-kappaB

Human alveolar macrophages (HAM) express FcalphaR receptors for immunoglobulin (Ig)A which could link humoral and cellular branches of lung immunity. Here, we investigate the effects of polymeric (p-IgA) and secretory (S-IgA) IgA interaction with Fc(alpha)R on lipopolysaccharide (LPS)- and phorbol myristate acetate (PMA)-activated respiratory burst and TNF-alpha release by HAM. Activation of HAM with LPS and PMA increases the respiratory burst and TNF-alpha release through activation of the extracellular signal-related protein kinases 1 and 2 (ERK1/2) pathway, because these effects are inhibited by treatment of HAM with PD98059, a selective inhibitor of mitogen-activated protein (MAP)/ERK kinases (MEK) pathway. S-IgA and p-IgA downregulate the LPS-increased respiratory burst in HAM through an inhibition of ERK1/2 activity. In contrast, p- and S-IgA induce an increase in the respiratory burst of PMA-treated HAM. This effect is associated with an upregulation by IgA of the PMA-induced phosphorylation of ERK1/2 and is also inhibited by PD98059. Moreover, p-IgA and S-IgA enhance TNF-alpha release by HAM through an alternative pathway distinct from ERK1/2. Because LPS is known to activate nuclear factor-kappaB (NF-kappaB) in HAM, we evaluate the effect of IgA on NF-kappaB. Treatment of HAM with LPS, p- and S-IgA, but not PMA, induces NF-kappaB activation through IkappaBalpha phosphorylation and subsequent proteolysis. Antioxidants, namely N-acetylcysteine (NAC) and glutathione (GSH), have no effects on IgA-mediated NF-kappaB nuclear translocation and only a minor and late effect on that of LPS, suggesting that reactive oxygen intermediates (ROI) play a minor role in HAM activation through NF-kappaB. TNF-alpha release by LPS-activated HAM is sensitive to NF-kappaB inhibition and only partly to oxidant scavenging. In contrast, TNF-alpha release by IgA-treated HAM is not dependent on oxidants and only partly dependent on NF-kappaB. Our results show a differential HAM regulation by IgA through both dependent and independent modulation of ERK pathway. In addition, IgA activates NF-kappaB and this effect was independent on oxidants. These data may help to understand the role of IgA in both lung protection and inflammation.

FcgammaR receptors activate MAP kinase and up-regulate the cyclooxygenase pathway without increasing arachidonic acid release in monocytic cells

THP-1 monocytic cells were stimulated with IgG-ovalbumin equivalence immune complexes (IC) and mAb reacting with both FcgammaRI and FcgammaRIIA. All of these stimuli were capable of activating the cells; however, different patterns of response were observed as regards activation of the p42-MAP/ERK kinase, triggering of the NF-kappaB/Rel system, production of chemotactic cytokines, and induction of the expression of cyclooxygenase-2 (COX-2). Activation of p42-MAP/ERK kinase was a constant finding, which occurred regardless of the type of stimulus applied, for instance, homotypic stimulation of a single type of receptor by cross-linking with specific mAb or heterotypic stimulation with both types of antibodies and IC. However, the activation of the MAP/ERK kinase cascade was not connected to the triggering of cytosolic phospholipase A(2) (cPLA(2)) and arachidonic acid (AA) release. The heterotypic stimulation of FcgammaR induced the expression of COX-2 in a time and dose-dependent manner and activated the NF-kappaB system as judged from the degradation of IkappaB-alpha protein. In summary, the present data indicate that activation of the p42-MAP/ERK pathway occurs after cross-linking FcgammaRI and FcgammaRIIA receptors in monocytic cells; however, this is not coupled to the cPLA(2) route, which leads to the release of AA. Noteworthy,heterotypic activation involving combined cross-linking of both FcgammaRI and FcgammaRIIA has a robust effect on the oxidative metabolism of AA by a mechanism involving kappaB-dependent trans-activation of COX-2.

The ups and downs of MEK kinase interactions

MEK kinases (MEKKs) comprise a family of related serine-threonine protein kinases that regulate mitogen-activated protein kinase (MAPK) signalling pathways leading to c-Jun NH2-terminal kinase (JNK) and p38 activation, induced by cellular stress (e.g., UV and gamma irradiation, osmotic stress, heat shock, protein synthesis inhibitors), inflammatory cytokines (e.g., tumour necrosis factor alpha, TNFalpha, and interleukin-1, IL1) and G protein-coupled receptor agonists (e.g., thrombin). These stress-activated kinases have been implicated in apoptosis, oncogenic transformation, and inflammatory responses in various cell types. At present, the signalling events involving MEKKs are not well understood. This review summarises our current knowledge concerning the regulation and function of MEKK family members, with particular emphasis on those factors capable of directly interacting with distinct MEKK isoforms.

TNF-alpha enhances intracellular glucocorticoid availability

For understanding the mechanism(s) relating inflammation to corticosteroid action, the effect of tumour necrosis factor-alpha (TNF-alpha) on 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the enzyme regulating access of 11beta-hydroxycorticosteroids to receptors, was studied in LLC-PK(1) cells. We observed (i) NAD-dependent enzyme activity and mRNA for 11beta-HSD2, but not 11beta-HSD1, (ii) increasing 11beta-HSD2 activity with increasing degree of differentiation and (iii) a concentration-dependent down-regulation by TNF-alpha, phorbol myristate acetate (PMA) or glucose of activity and mRNA of 11beta-HSD2. The decrease of activity and mRNA by glucose and PMA, but not that by TNF-alpha, was abrogated by the protein kinase C inhibitor GF-109203X. The effect of TNF-alpha on 11beta-HSD2 was reversed by inhibiting the mitogen-activated protein kinases ERK with PD-098050 and p38 by SB-202190, or by activating protein kinase A with forskolin. Overexpression of MEK1, an ERK activator, down-regulated the 11beta-HSD2 activity. In conclusion, TNF-alpha decreases 11beta-HSD2 activity and thereby enhances glucocorticoid access to glucocorticoid receptors to modulate the inflammatory response.

Heterogeneity in the phosphorylation of human death receptors by p42(mapk/erk2)

Phosphorylation of murine CD120a by p42(mapk/erk2) has been shown to inhibit its ability to initiate apoptosis while preserving signaling events such as NF-kappaB activation. Therefore, we sought to determine if p42(mapk/erk2) was also capable of phosphorylating additional human death receptors within the TNF receptor superfamily. These studies showed that CD120a and DR3 are significantly phosphorylated by p42(mapk/erk2) but Fas, DR4 and DR5 are not. Additionally, we demonstrated that (i) the p42(mapk/erk2)-dependent phosphorylation of CD120a and DR3 occurred on Ser and Thr residues, (ii) p42(mapk/erk2) phosphorylated residues located in the membrane proximal regions but not the death domains of CD120a and DR3, (iii) Ser 253 is a preferred site of phosphorylation on CD120a, and (iv) the p42(mapk/erk2)-dependent phosphorylation of the DR3 cytoplasmic domain occurred exclusively at non-p42/44(mapk/erk2/1) consensus sites. These findings suggest that human death receptors segregate into two groups along lines of phylogeny with respect to Ser/Thr phosphorylation by p42(mapk/erk2).

Activation of the EGF receptor signaling pathway in airway epithelial cells exposed to Utah Valley PM

Exposure to ambient particulate matter (PM) in the Utah Valley has previously been associated with a variety of adverse health effects. To investigate intracellular signaling mechanisms for pulmonary responses to Utah Valley PM inhalation, human primary airway epithelial cells were exposed to aqueous extracts of PM collected from the year before (Y1), during (Y2), and after (Y3) the closure of a local steel mill located in the Utah Valley in this study. Transfection with kinase-deficient extracellular signal-regulated kinase (ERK) 1 constructs partially blocked Utah Valley PM-induced interleukin (IL)-8 promoter reporter activity. The mitogen-activated protein kinase/ERK kinase (MEK) activity inhibitor PD-98059 significantly abolished IL-8 released in response to Utah Valley PM, as did the epidermal growth factor (EGF) receptor kinase inhibitor AG-1478. Western blotting showed that Utah Valley PM induced phosphorylation of EGF receptor tyrosine, MEK1/2, and ERK1/2, which could be ablated with AG-1478 or PD-98059. For all findings, the potency of Utah Valley PM collected during Y2 was found to be lower relative to that of Y1 and Y3. These data demonstrate that Utah Valley PM can induce IL-8 expression partially through the activation of the EGF receptor signaling.

MAPK/ERK overrides the apoptotic signaling from Fas, TNF, and TRAIL receptors

The tumor necrosis factor (TNF), Fas, and TNF-related apoptosis-inducing ligand (TRAIL) receptors (R) are highly specific physiological mediators of apoptotic signaling. We observed earlier that a number of FasR-insensitive cell lines could redirect the proapoptotic signal to an anti-apoptotic ERK1/2 signal resulting in inhibition of caspase activation. Here we determine that similar mechanisms are operational in regulating the apoptotic signaling of other death receptors. Activation of the FasR, TNF-R1, and TRAIL-R, respectively, rapidly induced subsequent ERK1/2 activation, an event independent from caspase activity. Whereas inhibition of the death receptor-mediated ERK1/2 activation was sufficient to sensitize the cells to apoptotic signaling from FasR and TRAIL-R, cells were still protected from apoptotic TNF-R1 signaling. The latter seemed to be due to the strong activation of the anti-apoptotic factor NF-kappaB, which remained inactive in FasR or TRAIL-R signaling. However, when the cells were sensitized with cycloheximide, which is sufficient to sensitize the cells also to apoptosis by TNF-R1 stimulation, we noticed that adenovirus-mediated expression of constitutively active MKK1 could rescue the cells from apoptosis induced by the respective receptors by preventing caspase-8 activation. Taken together, our results show that ERK1/2 has a dominant protecting effect over apoptotic signaling from the death receptors. This protection, which is independent of newly synthesized proteins, acts in all cases by suppressing activation of the caspase effector machinery.

Fluid Shear Stress Reduces 11ss-Hydroxysteroid Dehydrogenase Type 2

-In pregnancy, invading trophoblasts represent the inner vascular border of maternal spiral arteries and are exposed to elevated shear stress (ss) in hypertensive disorders. Intracellular cortisol availability is regulated by 11ss-hydroxysteroid dehydrogenases (11ss-HSDs), thus determining body fluid volume and vascular responses. The impact of ss on 11ss-HSD2 activity was studied in the human JEG-3 cell line, a model for trophoblasts. JEG-3 cells do not express 11ss-HSD1; however, 11ss-HSD2 message and activity are measured via cortisol/cortisone conversion in cell lysates, and both are reduced by ss. The reduction in 11ss-HSD2 activity via ss is dose dependent and completely reversible after the discontinuation of ss. cAMP-dependent protein kinase A activation increased the 11ss-HSD2 activity yet did not prevent the ss response. The ss response was completely protein kinase C independent. The mitogen-activated protein kinase kinase inhibitor PD-098059 enhanced 11ss-HSD2 activity in static conditions yet only ameliorated the ss effect. Cytochalasin D disrupts focal adhesion (FA)-cytoskeleton interactions and abolished the ss-induced tyrosine phosphorylation of FA kinase dose-dependently, thus maintaining 11ss-HSD2 activity. The 11ss-HSD2 activity was only partially restored by the tyrosine kinase inhibitor genistein; however, herbimycin A almost completely abolished the ss effect on 11ss-HSD2 activity. In conclusion, JEG-3 cells express 11ss-HSD2, which is downregulated by ss. Regulatory mechanisms involve transcriptional control and require intact FA-cytoskeleton signaling and phosphorylation of FA kinase. Thus, ss adds to an enhanced intracellular availability of cortisol, which may ultimately support a vasoconstrictive vascular response.

Activation, differential localization, and regulation of the stress-activated protein kinases, extracellular signal-regulated kinase, c-JUN N-terminal kinase, and p38 mitogen-activated protein kinase, in synovial tissue and cells in rheumatoid arthritis

OBJECTIVE

To investigate whether stress- and mitogen-activated protein kinases (SAPK/MAPK), such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK, are significantly activated in rheumatoid arthritis (RA) synovial tissue compared with their activation in degenerative joint disease; to assess the localization of SAPK/MAPK activation in rheumatoid synovial tissue; and to search for the factors leading to stress kinase activation in human synovial cells.

METHODS

Immunoblotting and immunohistology by antibodies specific for the activated forms of SAPK/MAPK were performed on synovial tissue samples from patients with RA and osteoarthritis (OA). In addition, untreated and cytokine-treated human synovial cells were assessed for SAPK/MAPK activation and downstream signaling by various techniques.

RESULTS

ERK, JNK, and p38 MAPK activation were almost exclusively found in synovial tissue from RA, but not OA, patients. ERK activation was localized around synovial microvessels, JNK activation was localized around and within mononuclear cell infiltrates, and p38 MAPK activation was observed in the synovial lining layer and in synovial endothelial cells. Tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6 were the major inducers of ERK, JNK, and p38 MAPK activation in cultured human synovial cells.

CONCLUSION

Signaling through SAPK/MAPK pathways is a typical feature of chronic synovitis in RA, but not in degenerative joint disease. SAPK/MAPK signaling is found at distinct sites in the synovial tissue, is induced by proinflammatory cytokines, and could lead to the design of highly targeted therapies.