Cell stress and MKK6b-mediated p38 MAP kinase activation inhibit tumor necrosis factor-induced IkappaB phosphorylation and NF-kappaB activation

The interplay of arsenic, silymarin, and NF-ĸB pathway in male reproductive toxicity: A review

Arsenic toxicity is one of the most trending reasons for several malfunctions, particularly reproductive toxicity. The exact mechanism of arsenic poisoning is a big question mark. Exposure to arsenic reduces sperm count, impairs fertilization, and causes inflammation and genotoxicity through interfering with autophagy, epigenetics, ROS generation, downregulation of essential protein expression, metabolite changes, and hampering several signaling cascades, particularly by the alteration of NF-ĸB pathway. This work tries to give a clear idea about the different aspects of arsenic resulting in male reproductive complications, often leading to infertility. The first part of this article explains the implications of arsenic poisoning and the crosstalk of the NF-ĸB pathway in male reproductive toxicity. Silymarin is a bioactive compound that exerts anti-cancer and anti-inflammatory properties and has demonstrated hopeful outcomes in several cancers, including colon cancer, breast cancer, and skin cancer, by downregulating the hyperactive NF-ĸB pathway. The next half of this article thus sheds light on silymarin's therapeutic potential in inhibiting the NF-ĸB signaling cascade, thus offering protection against arsenic-induced male reproductive toxicity.

Shared and Related Molecular Targets and Actions of Salicylic Acid in Plants and Humans

Salicylic acid (SA) is a phenolic compound produced by all plants that has an important role in diverse processes of plant growth and stress responses. SA is also the principal metabolite of aspirin and is responsible for many of the anti-inflammatory, cardioprotective and antitumor activities of aspirin. As a result, the number of identified SA targets in both plants and humans is large and continues to increase. These SA targets include catalases/peroxidases, metabolic enzymes, protein kinases and phosphatases, nucleosomal and ribosomal proteins and regulatory and signaling proteins, which mediate the diverse actions of SA in plants and humans. While some of these SA targets and actions are unique to plants or humans, many others are conserved or share striking similarities in the two types of organisms, which underlie a host of common biological processes that are regulated or impacted by SA. In this review, we compare shared and related SA targets and activities to highlight the common nature of actions by SA as a hormone in plants versus a therapeutic agent in humans. The cross examination of SA targets and activities can help identify new actions of SA and better explain their underlying mechanisms in plants and humans.

Based on Systematic Pharmacology: Molecular Mechanism of Siwei Jianbu Decoction in Preventing Oxaliplatin-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect caused by chemotherapy drugs, and its existence seriously affects the quality of life of patients. We first established an oxaliplatin-induced peripheral neuropathy (OIPN) model and then measured and evaluated mechanical hyperalgesia, thermal nociception, cold allodynia, and intraepidermal nerve fiber (IENF) density to determine Siwei Jianbu Decoction's role in preventing OIPN. Then, we conducted a systematic pharmacological study that revealed important roles for the MAPK signaling pathway and proinflammatory immune pathway and confirmed these roles by western blot, immunofluorescence, and qPCR. The data show that Siwei Jianbu Decoction can effectively prevent oxaliplatin-induced neuroinflammation by inhibiting an increase in NF-κB expression via downregulation of p-ERK1/2 and p-p38. The present study showed that SWJB may be beneficial in preventing oxaliplatin-induced peripheral neuropathy.

The IL-33-induced p38-/JNK1/2-TNFα axis is antagonized by activation of β-adrenergic-receptors in dendritic cells

IL-33, an IL-1 cytokine superfamily member, induces the activation of the canonical NF-κB signaling, and of Mitogen Activated Protein Kinases (MAPKs). In dendritic cells (DCs) IL-33 induces the production of IL-6, IL-13 and TNFα. Thereby, the production of IL-6 depends on RelA whereas the production of IL-13 depends on the p38-MK2/3 signaling module. Here, we show that in addition to p65 and the p38-MK2/3 signaling module, JNK1/2 are essential for the IL-33-induced TNFα production. The central roles of JNK1/2 and p38 in DCs are underpinned by the fact that these two MAPK pathways are controlled by activated β-adrenergic receptors resulting in a selective regulation of the IL-33-induced TNFα response in DCs.

Cucurbitacin E Potently Modulates the Activity of Encephalitogenic Cells

Cucurbitacin E (CucE) is a highly oxidized steroid consisting of a tetracyclic triterpene. It is a member of a Cucurbitacin family of biomolecules that are predominantly found in Cucurbitaceae plants. CucE has already been identified as a potent anti-inflammatory compound. Here, its effects on CD4(+) T helper (Th) cells and macrophages, as the major encephalitogenic cells in the autoimmunity of the central nervous system, were investigated. Production of major pathogenic Th cell cytokines: interferon-gamma and interleukin-17 were inhibited under the influence of CucE. The effects of CucE on CD4(+) T cells were mediated through the modulation of aryl hydrocarbon receptor, STAT3, NFκB, p38 MAPK, and miR-146 signaling. Further, production of nitric oxide and reactive oxygen species, as well as phagocytic ability, were inhibited in macrophages treated with CucE. These results imply that CucE possesses powerful antiencephalitogenic activity.

Polygalasaponin F inhibits secretion of inflammatory cytokines via NF-κB pathway regulation

To study the anti-neuroinflammatory mechanisms of polygalasaponin F (PS-F), ELISA method was used to detect the secretion of inflammatory cytokines. Western blot was used to detect the protein expression and phosphorylation levels. Immunofluorescence assay was used to observe the NF-κB nuclear translocation. PS-F could inhibit the release of inflammatory cytokines TNF-α and NO induced by lipopolysaccharides (LPS) and reduce the expression of inducible nitric oxide synthases (iNOS). As for MAPK-signaling pathway, PS-F could only inhibit the phosphorylation levels of p38 MAPK, but did not significantly affect the phosphorylation levels of JNK and ERK1/2 protein kinases. PS-F could inhibit NF-κB nuclear translocation in a dose-dependent manner. The results of Western blot assay were consistent with immunofluorescence assays. Meanwhile, p38-specific inhibitor SB203580 (20 μM) and p65-specific inhibitor PDTC (100 μM) were, respectively, administered as a positive control. In addition, PS-F could significantly inhibit the cytotoxicity of conditioned medium prepared by LPS-stimulated BV-2 microglia (LPS conditioned media) to neuronal PC12 cells and improve cell viability. PS-F inhibits the secretions of neuroinflammatory cytokines by the regulation of NF-κB-signaling pathway.

TNF and MAP kinase signalling pathways

The binding of tumour necrosis factor α (TNFα) to cell surface receptors engages multiple signal transduction pathways, including three groups of mitogen-activated protein (MAP) kinases: extracellular-signal-regulated kinases (ERKs); the cJun NH2-terminal kinases (JNKs); and the p38 MAP kinases. These MAP kinase signalling pathways induce a secondary response by increasing the expression of several inflammatory cytokines (including TNFα) that contribute to the biological activity of TNFα. MAP kinases therefore function both upstream and down-stream of signalling by TNFα receptors. Here we review mechanisms that mediate these actions of MAP kinases during the response to TNFα.

Novel ferrocenyl derivatives exert anti-cancer effect in human lung cancer cells in vitro via inducing G1-phase arrest and senescence

AIM

To investigate the effects of 7 novel 1-ferrocenyl-2-(5-phenyl-1H-1,2,4-triazol-3-ylthio) ethanone derivatives on human lung cancer cells in vitro and to determine the mechanisms of action.

METHODS

A549 human lung cancer cells were examined. Cell viability was analyzed with MTT assay. Cell apoptosis and senescence were examined using Hoechst 33258 and senescence-associated-β-galactosidase (SA-β-gal) staining, respectively. LDH release was measured using a detection kit. Cell cycle was analyzed using a flow cytometer. Intracellular ROS level was measured with the 2',7'-dichlorodihydrofluorescein probe. Phosphorylation of p38 was determined using Western blot.

RESULTS

Compounds 5b, 5d, and 5e (40 and 80 μmol/L) caused significant decrease of A549 cell viability, while other 4 compounds had no effect on the cells. Compounds 5b, 5d, and 5e (80 μmol/L) induced G1-phase arrest (increased the G1 population by 22.6%, 24.23%, and 26.53%, respectively), and markedly increased SA-β-gal-positive cells. However, the compounds did not cause nuclear DNA fragmentation and chromatin condensation in A549 cells. Nor did they affect the release of LDH from the cells. The compounds significantly elevated the intracellular ROS level, decreased the mitochondrial membrane potential, and increased p38 phosphorylation in the cells. In the presence of the antioxidant and free radical scavenger N-acetyl-L-cysteine (10 mmol/L), above effects of compounds 5b, 5d, and 5e were abolished.

CONCLUSION

The compounds 5b, 5d, and 5e cause neither apoptosis nor necrosis of A549 cells, but exert anti-cancer effect via inducing G1-phase arrest and senescence through ROS/p38 MAP-kinase pathway.

Regulation of NF-κB activation through a novel PI-3K-independent and PKA/Akt-dependent pathway in human umbilical vein endothelial cells

The transcription factor NF-κB regulates numerous inflammatory diseases, and proteins involved in the NF-κB-activating signaling pathway are important therapeutic targets. In human umbilical vein endothelial cells (HUVECs), TNF-α-induced IκBα degradation and p65/RelA phosphorylation regulate NF-κB activation. These are mediated by IKKs (IκB kinases) viz. IKKα, β and γ which receive activating signals from upstream kinases such as Akt. Akt is known to be positively regulated by PI-3K (phosphoinositide-3-kinase) and differentially regulated via Protein kinase A (PKA) in various cell types. However, the involvement of PKA/Akt cross talk in regulating NF-κB in HUVECs has not been explored yet. Here, we examined the involvement of PKA/Akt cross-talk in HUVECs using a novel compound, 2-methyl-pyran-4-one-3-O-β-D-2',3',4',6'-tetra-O-acetyl glucopyranoside (MPTAG). We observed that MPTAG does not directly inhibit IKK-β but prevents TNF-α-induced activation of IKK-β by blocking its association with Akt and thereby inhibits NF-κB activation. Interestingly, our results also revealed that inhibitory effect of MPTAG on Akt and NF-κB activation was unaffected by wortmannin, and was completely abolished by H-89 treatment in these cells. Thus, MPTAG-mediated inhibition of TNF-α-induced Akt activation was independent of PI-3K and dependent on PKA. Most importantly, MPTAG restores the otherwise repressed activity of PKA and inhibits the TNF-α-induced Akt phosphorylation at both Thr308 and Ser473 residues. Thus, we demonstrate for the first time the involvement of PKA/Akt cross talk in NF-κB activation in HUVECs. Also, MPTAG could be useful as a lead molecule for developing potent therapeutic molecules for diseases where NF-κB activation plays a key role.

Regulation of transcription of the Aedes albopictus cecropin A1 gene: A role for p38 mitogen-activated protein kinase

Regulation of the Aedes albopictus cecropin A1 promoter was studied to provide insight into the transcriptional control of this antimicrobial peptide (AMP) gene in mosquitoes. Gene expression levels of cecropin A1 increased in A. albopictus C6/36 cells in response to heat-killed Escherichiacoli. Reporter gene assays incorporating -757 to +32 of the A. albopictus cecropin A1 promoter revealed that E. coli could induce expression in these cells with more pronounced expression than that seen with lipopolysaccharide (LPS). Analysis of deletion constructs demonstrated that the 5' boundary of the regulatory region for the activation of this AMP was located between -173 and -64. Western blotting with anti-phospho-specific antibodies demonstrated that p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK) were activated by LPS, whereas only p38 MAPK was activated by E. coli. Moreover, pharmacological experiments revealed that pre-incubation of cells with the p38 MAPK inhibitor SB203580 resulted in a striking activation of the cecropin A1 promoter following immune challenge, demonstrating that p38 MAPK negatively regulates cecropin A1 promoter activity. Finally the region required for the negative regulation by p38 MAPK was identified as being between -173 and -64. This report is the first to show involvement of the p38 MAPK pathway in the negative regulation of AMP production in a mosquito.

Stimulator of IFN gene is critical for induction of IFN-beta during Chlamydia muridarum infection

Type I IFN signaling has recently been shown to be detrimental to the host during infection with Chlamydia muridarum in both mouse lung and female genital tract. However, the pattern recognition receptor and the signaling pathways involved in chlamydial-induced IFN-beta are unclear. Previous studies have demonstrated no role for TLR4 and a partial role for MyD88 in chlamydial-induced IFN-beta. In this study, we demonstrate that mouse macrophages lacking TLR3, TRIF, TLR7, or TLR9 individually or both TLR4 and MyD88, still induce IFN-beta equivalent to wild type controls, leading to the hypothesis that TLR-independent cytosolic pathogen receptor pathways are crucial for this response. Silencing nucleotide-binding oligomerization domain 1 in HeLa cells partially decreased chlamydial-induced IFN-beta. Independently, small interfering RNA-mediated knockdown of the stimulator of IFN gene (STING) protein in HeLa cells and mouse oviduct epithelial cells significantly decreased IFN-beta mRNA expression, suggesting a critical role for STING in chlamydial-induced IFN-beta induction. Conversely, silencing of mitochondria-associated antiviral signaling proteins and the Rig-I-like receptors, RIG-I, and melanoma differentiation associated protein 5, had no effect. In addition, induction of IFN-beta depended on the downstream transcription IFN regulatory factor 3, and on activation of NF-kappaB and MAPK p38. Finally, STING, an endoplasmic reticulum-resident protein, was found to localize in close proximity to the chlamydial inclusion membrane during infection. These results indicate that C. muridarum induces IFN-beta via stimulation of nucleotide-binding oligomerization domain 1 pathway, and TLR- and Rig-I-like receptor-independent pathways that require STING, culminating in activation of IFN regulatory factor 3, NF-kappaB, and p38 MAPK.

Sulindac induces apoptotic cell death in susceptible human breast cancer cells through, at least in part, inhibition of IKKbeta

Sulindac is a non-steroidal anti-inflammatory agent with anti-tumor activities that include the induction of apoptosis in various cancer cells and the inhibition malignant transformation. However, the molecular mechanisms underlying these effects are unclear. Recently, it has been shown that sulindac can inhibit NF-kappaB activation. Here, we demonstrate that sulindac induces apoptotic cell death in susceptible human breast cancer cells through, at least in part, inhibition of IKKbeta activity. More specifically, when we compared two different human breast cancer cell lines, Hs578T, which has relatively low basal IKKbeta activity, and MDA-MB231, which has relatively high basal IKKbeta activity, we found that MDA-MB231 was markedly more sensitive to sulindac-induced apoptosis than Hs578T. This was associated with greater caspase-3 and -9 activity in sulindac-treated MDA-MB231 cells. Using a combination of chemical kinase inhibitors and siRNA-mediated knockdown of specific kinases, we found that sulindac inhibits IKKbeta, which, in turn, leads to the p38 MAPK-dependent activation of JNK1. Together, these findings suggest that sulindac induces apoptosis in susceptible human breast cancer cells through, at least in part, the inhibition of IKKbeta and the subsequent p38 MAPK-dependent activation of JNK1.

Thermal stress and the disruption of redox-sensitive signalling and transcription factor activation: possible role in radiosensitization

In spite of ongoing research efforts, the specific mechanism(s) of heat-induced alterations in the cellular response to ionizing radiation (IR) remain ambiguous, in part because they likely involve multiple mechanisms and potential targets. One such group of potential targets includes a class of cytoplasmic signalling and/or nuclear transcription factors known as immediate early response genes, which have been suggested to perform cytotoxic as well as cytoprotective roles during cancer therapy. One established mechanism regulating the activity of these early response elements involves changes in cellular oxidation/reduction (redox) status. After establishing common alterations in early response genes by oxidative stress and heat exposure, one could infer that heat shock may have similarities to other forms of environmental antagonists that induce oxidative stress. In this review, recent evidence supporting a mechanistic link between heat shock and oxidative stress will be summarized. In addition, the hypothesis that one mechanism whereby heat shock alters cellular responses to anticancer agents (including hyperthermic radiosensitization) is through heat-induced disruption of redox-sensitive signalling factors will be discussed.

A central nervous system-restricted isoform of the interleukin-1 receptor accessory protein modulates neuronal responses to interleukin-1

Interleukin-1 (IL-1) has multiple functions in both the periphery and the central nervous system (CNS) and is regulated at many levels. We identified an isoform of the IL-1 receptor (IL-1R) accessory protein (termed AcPb) that is expressed exclusively in the CNS. AcPb interacted with IL-1 and the IL-1R but was unable to mediate canonical IL-1 responses. AcPb expression, however, modulated neuronal gene expression in response to IL-1 treatment in vitro. Animals lacking AcPb demonstrated an intact peripheral IL-1 response and developed experimental autoimmune encephalomyelitis (EAE) similarly to wild-type mice. AcPb-deficient mice were instead more vulnerable to local inflammatory challenge in the CNS and suffered enhanced neuronal degeneration as compared to AcP-deficient or wild-type mice. These findings implicate AcPb as an additional component of the highly regulated IL-1 system and suggest that it may play a role in modulating CNS responses to IL-1 and the interplay between inflammation and neuronal survival.

ATF6alpha-Rheb-mTOR signaling promotes survival of dormant tumor cells in vivo

The pathways that allow quiescent disseminated cancer cells to survive during prolonged dormancy periods are unknown. Here, we identify the transcription factor ATF6alpha as a pivotal survival factor for quiescent but not proliferative squamous carcinoma cells. ATF6alpha is essential for the adaptation of dormant cells to chemotherapy, nutritional stress, and, most importantly, the in vivo microenvironment. Mechanism analysis showed that MKK6 and p38alpha/beta contribute to regulating nuclear translocation and transcriptional activation of ATF6alpha in dormant cancer cells. Downstream, ATF6alpha induces survival through the up-regulation of Rheb and activation of mTOR signaling independent of Akt. Down-regulation of ATF6alpha or Rheb reverted dormant tumor cell resistance to rapamycin and induced pronounced killing only of dormant cancer cells in vivo. Knocking down ATF6alpha also prolonged the survival of nude mice bearing dormant tumor cells. Targeting survival signaling by the ATF6alpha-Rheb-mTOR pathway in dormant tumor cells may favor the eradication of residual disease during dormancy periods.

p38MAPK inhibition attenuates LPS-induced acute lung injury involvement of NF-kappaB pathway

The pathogenesis of acute lung injury/acute respiratory distress syndrome (ARDS) is complex and involves multiple signal transduction processes. It is believed that p38MAPK (mitogen-activated protein kinase) is one of the most kinases in inflammatory signaling. At present study, we demonstrated the role of p38MAPK in lipopolysaccharide (LPS)-induced acute lung injury with pharmacologic p38MAPK inhibition by SB203580. SB203580, p38MAPK specific inhibitor, was injected (10 mg/kg, i.v.) 30 min before LPS administration (5 mg/kg, i.v.). The hematoxylin-eosin staining of lung tissues showed that p38MAPK inhibition significantly attenuated the pulmonary inflammatory responses induced by LPS. Moreover, SB203580 can also inhibit the inflammatory cytokine release, and reduce the mortality rate of LPS-induced acute lung injury. Further, western blot analysis that showed SB203580 administration can inhibit the activation of NF-kappaB, which was associated with the inhibition of IkappaBalpha degradation in cytoplasm. These data suggest that p38MAPK signaling may be involved in the activation of NF-kappaB, and activation of p38MAPK signaling may be one of the mechanisms of acute lung injury.

Normophosphatemic familial tumoral calcinosis is caused by deleterious mutations in SAMD9, encoding a TNF-alpha responsive protein

Normophosphatemic familial tumoral calcinosis (NFTC) is an autosomal recessive disorder characterized by calcium deposition in skin and mucosae and associated with unremitting pain and life-threatening skin infections. A homozygous missense mutation (p.K1495E), resulting in SAMD9 protein degradation, was recently shown to cause NFTC in five families of Jewish-Yemenite origin. In this study, we evaluated another Jewish-Yemenite NFTC kindred. All patients were compound heterozygous for two mutations in SAMD9: K1495E and a previously unreported nonsense mutation, R344X, predicted to result in a markedly truncated molecule. Screening of unaffected population-matched controls revealed heterozygosity for K1495E and R344X only in individuals of Jewish-Yemenite ancestry, but not in more than 700 control samples of other origins, including 93 non-Jewish Yemenite. These data may be suggestive of positive selection, considering the rarity of NFTC and the small size of the Jewish-Yemenite population; alternatively, they may reflect genetic drift or the effect of a population-specific modifier trait. Calcifications in NFTC generally develop over areas subjected to repeated trauma and are associated with marked inflammatory manifestations, indicating that SAMD9 may play a role in the inflammatory response to tissue injury. We therefore assessed the effect of cellular stress and tumor necrosis factor-alpha (TNF-alpha), a potent pro-inflammatory cytokine, on SAMD9 gene expression. Whereas exogenous hydrogen peroxide and heat shock did not affect SAMD9 transcription, osmotic shock was found to markedly upregulate SAMD9 expression. In addition, incubation of endothelial cells with TNF-alpha caused a dose-related, p38-dependant increase in SAMD9 expression. These data link NFTC and SAMD9 to the TNF-alpha signaling pathway, suggesting a role for this system in the regulation of extra-osseous calcification.

Deficiency of NRH:quinone oxidoreductase 2 differentially regulates TNF signaling in keratinocytes: up-regulation of apoptosis correlates with down-regulation of cell survival kinases

NRH:quinone oxidoreductase 2 (NQO2) is a cytosolic flavoprotein that catalyzes the two-electron reduction of quinones and quinoid compounds to hydroquinones. Although the role of a homologue, NAD(P)H:quinone oxidoreductase 1 (NQO1), is well defined in oxidative stress, neoplasia, and carcinogenesis, little is known about the mechanism of actions of NQO2 in these cellular responses. Whether NQO2 has any role in tumor necrosis factor (TNF) signaling was investigated using keratinocytes derived from wild-type and NQO2 knockout (NQO2-/-) mice. Although exposure of wild-type cells to TNF led to activation of nuclear factor-kappaB (NF-kappaB) and IkappaBalpha kinase, IkappaBalpha degradation, p65 phosphorylation, and p65 nuclear translocation, this cytokine had no effect on NQO2-/- cells. Deletion of NQO2 also abolished TNF-induced c-Jun NH2-terminal kinase, Akt, p38, and p44/p42 mitogen-activated protein kinase activation. The induction of various antiapoptotic gene products (MMP-9, cyclin D1, COX-2, IAP1, IAP2, Bcl-2, cFLIP, and XIAP) by TNF was also abolished in NQO2-/- cells. This correlated with potentiation of TNF-induced apoptosis as indicated by cell viability, Annexin V staining, and caspase activation. In agreement with this, we also found that TNF activated NQO2, and NQO2-specific small interfering RNA abrogated the TNF-induced NQO2 activity and NF-kappaB activation. Overall, our results indicate that deletion of NQO2 plays a differential role in TNF signaling pathway: by suppressing cell survival signals and potentiating TNF-induced apoptosis.

Endothelial cell anergy is mediated by bFGF through the sustained activation of p38-MAPK and NF-kappaB inhibition

Tumors escape from immune surveillance by, among other mechanisms, the down- regulation of endothelial adhesion molecules, such as ICAM-1, and by unresponsiveness to inflammatory signals, a process mediated by angiogenic factors that is called endothelial cell anergy. Here we present the cell biological regulation of these processes. The angiogenic basic fibroblast growth factor (bFGF/FGF-2) was found to inhibit tumor necrosis factor-alpha (TNF-alpha)- induced elevation of ICAM-1, at transcriptional level. Furthermore, we found that bFGF inhibits the TNF-mediated activation of NF-kappaB by blocking phosphorylation and degradation of IkappaBalpha. We also found that bFGF induces hyperphosphorylation of p38 MAPK on endothelial cells, whereas inhibition of such kinase abrogates the effect of bFGF on the TNF-mediated activation of NF-kappaB. Thus, we suggest that bFGF acts as an inhibitor of leukocyte adhesion in tumor vessels by decreasing the ICAM-1 expression through the sustained activation of p38-MAPK and via inhibition of NF-kappaB.

Nitric oxide inhibits interleukin-12 p40 through p38 MAPK-mediated regulation of calmodulin and c-rel

In activated macrophages, the rel/NF-kappaB transcription factors are known to play important roles in interleukin-12 (IL-12) p40 regulation by nitric oxide (NO). However, the relative contributions of these factors are not well understood. Here, we describe a dominant role for c-rel involving p38 mitogen-activated protein kinase (p38 MAPK) and calmodulin (CaM) protein in NO-mediated IL-12 p40 inhibition in activated macrophages. Inhibition of NO production by aminoguanidine increased, whereas sodium nitroprusside (SNP; an exogenous NO generator) reduced, nuclear c-rel levels in LPS + IFN-gamma-activated RAW 264.7 macrophages. Overexpression of c-rel but not p65 NF-kappaB increased IL-12 p40 during NO treatment. The p38 MAPK phosphorylation is increased by NO, and inhibition of p38 MAPK in SNP-treated macrophages by SB203580 or transient expression of a dominant-negative mutant of p38 MAPK upregulated both nuclear c-rel and IL-12 p40 levels, indicating that NO targeted the p38 MAPK pathway to inhibit c-rel and IL-12 p40. Cytoplasmic CaM level was increased by NO, and SB203580 decreased the CaM level in NO-exposed macrophages. Inhibition of CaM activity by trifluoperazine rescued the inhibitory effect of NO on c-rel and IL-12 p40. Our findings indicate that c-rel plays an important role in NO-mediated inhibition of IL-12 p40 and is regulated by p38 MAPK through CaM protein.

Dissecting yeast Hog1 MAP kinase pathway using a chemical genetic approach

Using a chemical genetic approach, we identified four novel physiological substrates of Hog1 kinase (Krs1, Tdh3, Hsp26, and Shm2). These substrates suggest plausible mechanisms for actin reorganization, cell cycle arrest and regulation of protein synthesis observed upon osmotic stress. We further show that the human homolog of Shm2 (SHMT1) is a novel physiological substrate of p38 MAP kinase in vitro and in vivo. Down-regulation of its enzymatic activity was observed following p38-mediated phosphorylation revealing a potential cancer-modulating property of p38 MAP kinase. This screen has uncovered several novel Hog1 substrates that provide new avenues for investigation into the mechanism of osmoadaptation by this kinase.

Guanosine Inhibits CD40 Receptor Expression and Function Induced by Cytokines and β Amyloid in Mouse Microglia Cells

Growing evidence implicates CD40, a member of the TNFR superfamily, as contributing to the pathogenesis of many neurodegenerative diseases. Thus, strategies to suppress its expression may be of benefit in those disorders. To this aim, we investigated the effect of guanosine, a purine nucleoside that exerts neurotrophic and neuroprotective effects. CD40 expression and function are increased by exposure of mouse microglia cultures or the N9 microglia cell line to IFN-gamma (10 ng/ml) plus TNF-alpha (50 ng/ml) or beta amyloid (Abeta) peptide (Abeta(1-42); 500 nM). Culture pretreatment with guanosine (10-300 microM), starting 1 h before cytokine or Abeta addition, dose-dependently inhibited the CD40-induced expression as well as functional CD40 signaling by suppressing IL-6 production promoted by IFN-gamma/TNF-alpha challenge in the presence of CD40 cross-linking. Moreover, guanosine abrogated IFN-gamma-induced phosphorylation on Ser(727) and translocation of STAT-1alpha to the nucleus as well as TNF-alpha-/Abeta-induced IkappaBalpha and NF-kappaB p65/RelA subunit phosphorylation, thus inhibiting NF-kappaB-induced nuclear translocation. Guanosine effects were mediated by an increased phosphorylation of Akt, a PI3K downstream effector, as well as of ERK1/2 and p38 in the MAPK system, because culture pretreatment with selective ERK1/2, p38 MAPK, and PI3K antagonists (U0126, SB203580, or LY294002, respectively) counteracted guanosine inhibition on IFN-gamma/TNF-alpha-induced CD40 expression and function as well as on STAT-1alpha or NF-kappaB nuclear translocation. These findings suggest a role for guanosine as a potential drug in the experimental therapy of neuroinflammatory/neurodegenerative diseases, particularly Alzheimer's disease.

IL-1beta, an immediate early protein secreted by activated microglia, induces iNOS/NO in C6 astrocytoma cells through p38 MAPK and NF-kappaB pathways

In the present study we sought to examine cell-cell interactions by investigating the effects of factors released by stimulated microglia on inducible nitric oxide (NO) synthase (iNOS) induction in astrocytoma cells. After examining the temporal profiles of proinflammatory molecules induced by lipopolysaccharide (LPS) stimulation in BV2 microglial cells, iNOS and IL-1beta were observed to be the first immediate-response molecules. Removal of LPS after 3 hr stimulation abrogated NO release, whereas a full induction of IL-1beta was retained in BV2 cells. We observed consistently that conditioned medium (CM) from activated microglia resulted in the induction of iNOS in C6 cells, and IL-1beta was shown to be a key regulator of iNOS induction. An IL-1beta-neutralizing antibody diminished NO induction. Incubation with recombinant IL-1beta stimulated NO release to a lesser extent compared to microglial CM; co-treatment of LPS and IL-1beta had a potent, synergistic effect on NO release from C6 cells. Transient transfection with MEK kinase 1 (MEKK1) or nuclear factor-kappa B (NF-kappaB) expression plasmids induced iNOS, and IL-1beta further enhanced the MEKK1 response. Furthermore, IL-1beta-mediated NO release from C6 cells was significantly suppressed by inhibition of p38 mitogen activated protein kinase (MAPK) or NF-kappaB by specific chemical inhibitors. Both IL-1beta and MEKK1 stimulated p38 and JNK MAPKs, as well as the NF-kappaB pathway, to induce iNOS in C6 cells. Microglia may represent an anti-tumor response in the central nervous system, which is potentiated by the local secretion of immunomodulatory factors that in turn affects astrocytoma (glioma) cells. A better understanding of microglia-glioma or microglia-astrocyte interactions will help in the design of novel immune-based therapies for brain tumors or neuronal diseases.

Lipopolysaccharide-induced transcriptional activation of interleukin-10 is mediated by MAPK- and NF-κB-induced CCAAT/enhancer-binding protein δ in mouse macrophages

We have previously revealed that LPS can activate transcription of the IL-10 gene promoter through transcription factors Sp1, C/EBPbeta and C/EBPdelta in mouse macrophages. In this study, we determined that NF-kappaB and MAPK signal pathways, including ERK, JNK, and p38, were all involved in LPS-induced IL-10 gene expression. Treatment of cells with the pharmacological inhibitors of ERK, JNK, p38 and NF-kappaB respectively inhibited LPS-induced IL-10 protein expression in a dose-dependent manner. These inhibitors also decreased the LPS-induced IL-10 mRNA expression at a high concentration used. With transient overexpression of the IkappaB expression plasmids, or the dominant negative plasmids of ERK2, JNK, p38 together with reporter vector containing IL-10 promoter region, all four expression plasmids inhibited LPS-induced IL-10 promoter activity individually. It is known that the increase in protein and DNA binding of C/EBPbeta and delta could activate IL-10 gene expression. In this study, we also identified that all four pharmacological inhibitors inhibited the protein expression of C/EBPdelta individually, but not C/EBPbeta. In the presence of all three MAPK inhibitors, or only NF-kappaB inhibitor, LPS-induced protein expression and DNA binding of C/EBPdelta were completely inhibited simultaneously, and LPS-induced expression of IL-10 protein and mRNA was also inhibited totally. Taken together, these results suggested that LPS-induced IL-10 expression was mediated at least through the pathway of NF-kappaB- and MAPK-induced protein expression and DNA binding of C/EBPdelta.

p38 mitogen-activated protein kinase up-regulates LPS-induced NF-κB activation in the development of lung injury and RAW 264.7 macrophages

Clarification of the key regulatory steps that lead to nuclear factor-kappa B (NF-kappaB) under cellular and pathological conditions is very important. The action of p38 mitogen-activated protein kinase (MAPK) on the upstream of NF-kappaB activation remains controversial. To examine this issue using an in vivo lung injury model, SB203580, a p38 MAPK inhibitor was given intraorally 1h prior to lipopolysaccharide (LPS) treatment (intratracheally). The mice were sacrificed 4 h after LPS treatment. SB203580 substantially suppressed LPS-induced rises in p38 MAPK phosphorylation, neutrophil recruitment, total protein content in bronchoalveolar lavage fluid, and apoptosis of bronchoalveolar cells. Furthermore, SB203580 blocked LPS-induced NF-kappaB activation in lung tissue through down-regulation of serine phosphorylation, degradation of IkappaB-alpha, and consequent translocation of the p65 subunit of NF-kappaB to the nucleus. It is likely that, in cultured RAW 264.7 macrophages, SB203580 also blocked LPS-induced NF-kappaB activation in a dose-dependent manner. SB203580 inhibited LPS-induced serine phosphorylation, degradation of IkappaB-alpha, and tyrosine phosphorylation of p65 NF-kappaB. These data indicate that p38 MAPK acts upstream of LPS-induced NF-kappaB activation by modulating the phosphorylation of IkappaB-alpha and p65 NF-kappaB during acute lung injury. Because LPS-stimulated macrophages may contribute to inflammatory lung injury, the inhibition of the p38 MAPK-mediated intracellular signaling pathway leading to NF-kappaB activation represents a target for the attenuation of lung inflammation and parenchymal damage.

Genetic deletion of NAD(P)H:quinone oxidoreductase 1 abrogates activation of nuclear factor-kappaB, IkappaBalpha kinase, c-Jun N-terminal kinase, Akt, p38, and p44/42 mitogen-activated protein kinases and potentiates apoptosis

The NAD(P)H:quinone oxidoreductase 1 (NQO1) is a phase II enzyme that reduces and detoxifies quinones and their derivatives. Although overexpressed in tumor cells, the NQO1 has been linked with the suppression of carcinogenesis, and the effect of NQO1 on tumor necrosis factor (TNF), a cytokine that mediates tumorigenesis through proliferation, invasion, angiogenesis, and metastasis of tumors, is currently unknown. The purpose of our study was to determine the role of NQO1 in TNF cell signaling by using keratinocytes derived from wild-type and NQO1 gene-deleted mice. TNF induced nuclear factor (NF)-kappaB activation in wild-type but not in NQO1-deleted cells. The treatment of wild-type cells with dicoumarol, a known inhibitor of NQO1, also abolished TNF-induced NF-kappaB activation. NF-kappaB activation induced by lipopolysaccharide, phorbol ester, and cigarette smoke, was also abolished in NQO1-deleted cells. The suppression of NF-kappaB activation was mediated through the inhibition of IkappaBalpha kinase activation, IkappaBalpha phosphorylation, and IkappaBalpha degradation. Further, the deletion of NQO1 abolished TNF-induced c-Jun N-terminal kinase, Akt, p38, and p44/p42 mitogen-activated protein kinase activation. TNF also induced the expression of various NF-kappaB-regulated gene products involved in cell proliferation, antiapoptosis, and invasion in wild-type NQO1 keratinocytes but not in NQO1-deleted cells. The suppression of these antiapoptotic gene products increased TNF-induced apoptosis in NQO1-deleted cells. We also found that TNF activated NQO1, and NQO1-specific small interfering RNA abolished the TNF-induced NQO1 activity and NF-kappaB activation. Overall, our results indicate that NQO1 plays a pivotal role in signaling activated by TNF and other inflammatory stimuli and that its suppression is a potential therapeutic strategy to inhibit the proliferation, survival, invasion, and metastasis of tumor cells.

MKP1/CL100 controls tumor growth and sensitivity to cisplatin in non-small-cell lung cancer

Non-small-cell lung cancer (NSCLC) represents the most frequent and therapy-refractive sub-class of lung cancer. Improving apoptosis induction in NSCLC represents a logical way forward in treating this tumor. Cisplatin, a commonly used therapeutic agent in NSCLC, induces activation of N-terminal-c-Jun kinase (JNK) that, in turn, mediates induction of apoptosis. In analysing surgical tissue samples of NSCLC, we found that expression of MKP1/CL100, a negative regulator of JNK, showed a strong nuclear staining for tumor cells, whereas, in normal bronchial epithelia, MKP1 was localized in the cytoplasm as well as in nuclei. In the NSCLC-derived cell lines H-460 and H-23, we found that MKP1 was constitutively expressed. Expressing a small-interfering RNA (siRNA) vector for MKP1 in H-460 cells resulted in a more efficient activation by cisplatin of JNK and p38 than in the parental cells, and this correlated with a 10-fold increase in sensitivity to cisplatin. A similar response was also observed in H-460 and H-23 cells when treated with the MKP1 expression inhibitor RO-31-8220. Moreover, expression of a siRNA-MKP2, an MKP1-related phosphatase, had no effect on H-460 cell viability response to cisplatin. Tumors induced by H-460 cells expressing MKP1 siRNA grew slower in nu(-)/nu(-) mice and showed more susceptibility to cisplatin than parental cells, and resulted in an impaired growth of the tumor in mice. On the other hand, overexpression of MKP1 in the H-1299 NSCLC-derived cell line resulted in further resistance to cisplatin. Overall, the results showed that inhibition of MKP1 expression contributes to a slow down in cell growth in mice and an increase of cisplatin-induced cell death in NSCLC. As such, MKP1 can be an attractive target in sensitizing cells to cisplatin to increase the effectiveness of the drug in treating NSCLC.

The subendothelial extracellular matrix modulates NF-kappaB activation by flow: a potential role in atherosclerosis

Atherosclerotic plaque forms in regions of the vasculature exposed to disturbed flow. NF-κB activation by fluid flow, leading to expression of target genes such as E-selectin, ICAM-1, and VCAM-1, may regulate early monocyte recruitment and fatty streak formation. Flow-induced NF-κB activation is downstream of conformational activation of integrins, resulting in new integrin binding to the subendothelial extracellular matrix and signaling. Therefore, we examined the involvement of the extracellular matrix in this process. Whereas endothelial cells plated on fibronectin or fibrinogen activate NF-κB in response to flow, cells on collagen or laminin do not. In vivo, fibronectin and fibrinogen are deposited at atherosclerosis-prone sites before other signs of atherosclerosis. Ligation of integrin α2β1 on collagen prevents flow-induced NF-κB activation through a p38-dependent pathway that is activated locally at adhesion sites. Furthermore, altering the extracellular matrix to promote p38 activation in cells on fibronectin suppresses NF-κB activation, suggesting a novel therapeutic strategy for treating atherosclerosis.

Evodiamine Abolishes Constitutive and Inducible NF-κB Activation by Inhibiting IκBα Kinase Activation, Thereby Suppressing NF-κB-regulated Antiapoptotic and Metastatic Gene Expression, Up-regulating Apoptosis, and Inhibiting Invasion

Evodiamine, an alkaloidal component extracted from the fruit of Evodiae fructus (Evodia rutaecarpa Benth., Rutaceae), exhibits antiproliferative, antimetastatic, and apoptotic activities through a poorly defined mechanism. Because several genes that regulate cellular proliferation, carcinogenesis, metastasis, and survival are regulated by nuclear factor-kappaB (NF-kappaB), we postulated that evodiamine mediates its activity by modulating NF-kappaB activation. In the present study, we investigated the effect of evodiamine on NF-kappaB and NF-kappaB-regulated gene expression activated by various carcinogens. We demonstrate that evodiamine was a highly potent inhibitor of NF-kappaB activation, and it abrogated both inducible and constitutive NF-kappaB activation. The inhibition corresponded with the sequential suppression of IkappaBalpha kinase activity, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation, p65 nuclear translocation, and p65 acetylation. Evodiamine also inhibited tumor necrosis factor (TNF)-induced Akt activation and its association with IKK. Suppression of Akt activation was specific, because it had no effect on JNK or p38 MAPK activation. Evodiamine also inhibited the NF-kappaB-dependent reporter gene expression activated by TNF, TNFR1, TRADD, TRAF2, NIK, and IKK but not that activated by the p65 subunit of NF-kappaB. NF-kappaB-regulated gene products such as Cyclin D1, c-Myc, COX-2, MMP-9, ICAM-1, MDR1, Survivin, XIAP, IAP1, IAP2, FLIP, Bcl-2, Bcl-xL, and Bfl-1/A1 were all down-regulated by evodiamine. This down-regulation potentiated the apoptosis induced by cytokines and chemotherapeutic agents and suppressed TNF-induced invasive activity. Overall, our results indicated that evodiamine inhibits both constitutive and induced NF-kappaB activation and NF-kappaB-regulated gene expression and that this inhibition may provide a molecular basis for the ability of evodiamine to suppress proliferation, induce apoptosis, and inhibit metastasis.

A novel mechanism for TNF-alpha regulation by p38 MAPK: involvement of NF-kappa B with implications for therapy in rheumatoid arthritis

TNF-alpha is a key factor in a variety of inflammatory diseases. This study examines the role of p38 MAPK in the regulation of TNF-alpha in primary human cells relevant to inflammation, e.g., macrophages and rheumatoid synovial cells. Using a dominant negative variant (D168A) of p38 MAPK and a kinase inhibitor, SB203580, we confirm in primary human macrophages that p38 MAPK regulates TNF-alpha production using a posttranscriptional mechanism requiring the 3' untranslated region of the gene. However, in LPS-activated primary human macrophages we also detect a second previously unidentified mechanism, the p38 MAPK modulation of TNF-alpha transcription. This is mediated through p38 MAPK regulation of NF-kappaB. Interestingly this mechanism was not observed in rheumatoid synovial cells. Importantly however, the dominant negative mutant of p38 MAPK, but not SB203580 was effective at inhibiting spontaneous TNF-alpha production in these ex vivo rheumatoid synovial cell cultures. These data indicate there are potential major differences in the role of p38 MAPK in inflammatory signaling that have a bearing on the use of this kinase as a target for therapy. These results indicate despite disappointing results with p38 MAPK inhibitors in the clinic, this kinase is a valid target in rheumatoid disease.

UV-induced Expression of Key Component of the Tanning Process, the POMC and MC1R Genes, Is Dependent on the p-38-activated Upstream Stimulating Factor-1 (USF-1)

Protection against UV-mediated DNA damage and the onset of oncogenesis is afforded by the tanning response in which UV irradiation triggers melanocytes to increase production of melanin that is then transferred to keratinocytes. A key component of the tanning process is the UV-mediated induction of the pro-opiomelanocortin (POMC) and MC1R genes encoding the alpha-melanocyte-stimulating hormone and its receptor, respectively, which play a crucial role in pigmentation by regulating the intracellular levels of cAMP. How these genes are regulated in response to UV irradiation is not known. Here we have shown that UV-induced activation of the POMC and MC1R promoters is mediated by p38 stress-activated kinase signaling to the transcription factor, upstream stimulating factor-1 (USF-1). Importantly, melanocytes derived from USF-1 -/- mice exhibit a defective UV response and fail to activate POMC and MC1R expression in response to UV irradiation. The results define USF-1 as a critical UV-responsive activator of genes implicated in protection from solar radiation.

Heat shock and the activation of AP-1 and inhibition of NF-kappa B DNA-binding activity: possible role of intracellular redox status

The early response genes comprising the AP-1 and NF-kappa B transcription factors are induced by environmental stress and thought to modulate responses to injury processes through the induction of target genes. Exposure to heat and ionizing radiation (IR) has been shown to affect signalling machinery involved in AP-1 and NF-kappa B activation. Furthermore, regulation of the signalling pathways leading to the activation of these transcription factors has been linked to changes in intracellular oxidation/reduction (redox) reactions. The hypothesis is proposed that exposure to thermal stress and/or IR might alter metabolic processes impacting upon cellular redox state and thereby modify the activity of redox-sensitive transcription factors such as AP-1 and NF-kappa B. Gel electromobility shift assays (EMSA) demonstrated that heat shock-induced AP-1 DNA-binding activity but inhibited IR-induced activation of NF-kappa B. A time course showed that activation of the AP-1 complex occurs between 4 and 5 h following thermal stress, and inhibition of IR-induced NF-kappa B activation also occurs during this time interval. Using a redox-sensitive fluorescent probe [5-(and -6)-carboxy-2',7'-dichlorodihydrofluorescein diacetate], a shift to 40% less intracellular dye oxidation was observed in HeLa cells 0-4 h post-heat shock (45 degrees C, 15 min) relative to cells held at 37 degrees C. This was followed by a shift to greater dye oxidation between 4 and 12 h after treatment (about 1.8-fold) that returned to control levels by 24 h post-heating. These results show changes in DNA-binding activity closely paralleled apparent heat-induced changes in the intracellular redox state. Taken together, these results provide correlative evidence for disruption of redox-sensitive IR-induced signalling pathways by heat shock and support the hypothesis that this mechanism might play a role in heat-induced alterations in radiation response.

Detection and classi?cation of threat agents via high-content assays of mammalian cells

One property common to all chemical or biological threat agents is that they damage mammalian cells. A threat detection and classification method based on the effects of compounds on cells has been developed. This method employs high-content screening (HCS), a concept in drug discovery that enables those who practice cell-based assays to generate deeper biological information about the compounds they are testing. A commercial image-based cell screening platform comprising fluorescent reagents, automated image acquisition hardware, image analysis algorithms, data management and informatics was used to develop assays and detection/classification methods for threat agents. These assays measure a cell's response to a compound, which may include activation or inhibition of signal transduction pathways, morphological changes or cytotoxic effects. Data on cell responses to a library of compounds was collected and used as a training set. At the EILATox-Oregon Workshop, cellular responses following exposure to unknown samples were measured by conducting assays of p38 MAP kinase, NF-kappaB, extracellular-signal related kinase (ERK) MAP kinase, cyclic AMP-response element binding protein (CREB), cell permeability, lysosomal mass and nuclear morphology. Although the assays appeared to perform well, only four of the nine toxic samples were detected. However the system was specific, because no false positives were detected. Opportunities for improvement to the system were identified during the course of this enlightening workshop. Some of these improvements were applied in subsequent tests in the Cellomics laboratories, resulting in a higher level of detection. Thus, an HCS approach was shown to have potential in detecting threat agents, but additional work is necessary to make this a comprehensive detection and classification system.

Inhibition of glucocorticoid receptor-mediated transcriptional activation by p38 mitogen-activated protein (MAP) kinase

Tumor necrosis factor (TNF) promotes certain immune and inflammatory responses, whereas glucocorticoids exert immunosuppressive and anti-inflammatory actions. We show that TNF treatment produced a modest inhibition of glucocorticoid receptor (GR)-mediated transcriptional activation of a mouse mammary tumor virus (MMTV) promoter-driven luciferase construct in HeLa cells. The mitogen-activated protein (MAP) kinases, p38 and c-Jun N-terminal kinase (JNK), are important mediators of target gene activation by TNF, and JNK activation was earlier shown to inhibit GR-mediated transcriptional activation by direct phosphorylation of GR at Ser-246. Transfection of HeLa cells with MKK6b(E), a constitutively active specific upstream activator of p38, led to a potent inhibition of GR activation of the MMTV promoter-driven luciferase construct. A similar inhibition of activation of the MMTV promoter-driven luciferase construct was seen in HeLa cells transfected with MKK7(D), a constitutively functional activator of JNK. Data from "domain swap" experiments using GR chimeras indicated that the main target of the p38-mediated (but not JNK-mediated) inhibition is the ligand-binding domain of GR (spanning amino acids 525-795), whereas the constitutively active N-terminal AF-1 region (spanning amino acids 106-237) is dispensable for the inhibitory effect of p38. We also demonstrate that activated p38 targets the GR ligand-binding domain indirectly. Suppression of GR function by activated p38 and JNK MAP kinases may be physiologically important as a mechanism of resistance to glucocorticoids seen in many patients with chronic inflammatory conditions.

cAMP targeting of p38 MAP kinase inhibits thrombin-induced NF-kappaB activation and ICAM-1 expression in endothelial cells

We investigated the mechanisms by which elevated intracellular cAMP concentration inhibits the thrombin-induced ICAM-1 expression in endothelial cells. Exposure of human umbilical vein endothelial cells to forskolin or dibutyryl cAMP, which increase intracellular cAMP by separate mechanisms, inhibited the thrombin-induced ICAM-1 expression. This effect of cAMP was secondary to inhibition of NF-kappaB activity, the key regulator of thrombin-induced ICAM-1 expression in endothelial cells. The action of cAMP occurred downstream of IkappaBalpha degradation and was independent of NF-kappaB binding to the ICAM-1 promoter. We observed that cAMP interfered with thrombin-induced phosphorylation of NF-kappaB p65 (RelA) subunit, a crucial event promoting the activation of the DNA-bound NF-kappaB. Because p38 MAPK can induce transcriptional activity of RelA/p65 without altering the DNA binding function of NF-kappaB, we addressed the possibility that cAMP antagonizes thrombin-induced NF-kappaB activity and ICAM-1 expression by preventing the activation of p38 MAPK. We observed that treating cells with forskolin blocked the activation of p38 MAPK, and inhibition of p38 MAPK interfered with phosphorylation of RelA/p65 induced by thrombin. Our data demonstrate that increased intracellular cAMP concentration in endothelial cells prevents thrombin-induced ICAM-1 expression by inhibiting p38 MAPK activation, which in turn prevents phosphorylation of RelA/p65 and transcriptional activity of the bound NF-kappaB.

Regulation of metalloproteinases and NF-kappaB activation in rabbit synovial fibroblasts via E prostaglandins and Erk: contrasting effects of nabumetone and 6MNA

1 Nabumetone is a prodrug that is converted in vivo into 6-methoxy-2-naphthylacetic acid (6MNA), a cyclooxygenase inhibitor with anti-inflammatory properties. We tested the effects of nabumetone and 6MNA on the inflammatory responses of synovial fibroblasts (SFs). 2 Brief exposures to 6MNA (50-150 microm) had no effect on IL-1beta/TNF-alpha (each 20 ng ml(-1))-stimulated Erk activation. Longer exposures depleted prostaglandin E1 (PGE1) as much as 70%, and stimulated Erk as much as 300%. Nabumetone (150 microm) inhibited Erk activation by 60-80%. 6MNA (50-150 microm) stimulated (approximately 200%) and nabumetone (150 microm) inhibited (approximately 50%) matrix metalloproteinase (MMP)-1, but not MMP-13 secretion from SFs. 3 6MNA stimulation of MMP-1 secretion was inhibited approximately 30% by PGE1 (1 microm) and approximately 80% by the Erk pathway inhibitor UO126 (10 microm), confirming that PGE depletion and Erk activation mediate MMP-1 secretion by 6MNA. 4 Consistent with its role as an Erk inhibitor, nabumetone (150 microm) abrogated 6MNA enhancement of MMP-1 secretion. 5 UO126 (10 microm) and nabumetone (150 microm) inhibited (approximately 70 and 40%, respectively), but 6MNA (150 microm) enhanced (approximately 40%), NF-kappaB activation. 6 Our data indicate that 6MNA shares with other COX inhibitors several proinflammatory effects on synovial fibroblasts. In contrast, nabumetone demonstrates anti-inflammatory and potentially arthroprotective effects that have not been previously appreciated.

Inhibition of p38 mitogen-activated protein kinase reduces TNF-induced activation of NF-kappaB, elicits caspase activity, and enhances cytotoxicity

Among other cellular responses, tumor necrosis factor (TNF) induces different forms of cell death and the activation of the p38 mitogen-activated protein kinase (MAPK). The influence of p38 MAPK activation on TNF-induced apoptosis or necrosis is controversially discussed. Here, we demonstrate that pharmacological inhibition of p38 MAPK enhances TNF-induced cell death in murine fibroblast cell lines L929 and NIH3T3. Furthermore, overexpression of dominant-negative versions of p38 MAPK or its upstream kinase MKK6 led to increased cell death in L929 cells. While overexpression of the p38 isoforms alpha and beta did not protect L929 cells from TNF-induced toxicity, overexpression of constitutively active MKK6 decreased TNF-induced cell death. Although the used inhibitors of p38 MAPK decreased the phosphorylation of the survival kinase PKB/Akt, this effect could be ruled out as cause of the observed sensitization to TNF-induced cytotoxicity. Finally, we demonstrate that the nuclear factor kappaB (NF-kappaB)-dependent gene expression, shown as an example for the anti-apoptotic gene cellular inhibitor of apoptosis (c-IAP2), was reduced by p38 MAPK inhibition. In consequence, we found that inhibition of p38 MAPK led to the activation of the executioner caspase-3.

ANP inhibits TNF-alpha-induced endothelial MCP-1 expression--involvement of p38 MAPK and MKP-1

Atrial natriuretic peptide (ANP) has been shown to reduce tumor necrosis factor-alpha (TNF-alpha)-induced activation of endothelial cells via inhibition of p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-kappaB pathways. The aim of this study was to determine whether ANP is able to inhibit TNF-alpha-induced expression of monocyte chemoattractant protein-1 (MCP-1) in endothelial cells and to elucidate the mechanisms involved. Pretreatment of human umbilical vein endothelial cells (HUVEC) with ANP significantly reduced TNF-alpha-induced expression of MCP-1 protein and mRNA. The effects of ANP were shown to be mediated via the guanylyl-cyclase (GC)-coupled A receptor. Activation of the other GC-coupled receptor (natriuretic peptide receptor-B) by the C-type natriuretic peptide as well as activation of soluble GC with S-nitroso-L-glutathione (GSNO) exerted similar effects as ANP, supporting a role for cyclic guanosine monophosphate (cGMP) in the signal transduction. Antisense experiments showed a requirement of MAPK phosphatase-1 (MKP-1) induction and therefore, inhibition of p38 MAPK in the ANP-mediated inhibition of TNF-alpha-induced expression of MCP-1. To investigate a potential interplay between TNF-alpha-induced activation of p38 MAPK and NF-kappaB, the p38 MAPK inhibitor SB203580 and a dominant-negative p38 MAPK mutant were used. The results indicated that the blockade of p38 MAPK activity leads to an increased activation of NF-kappaB and therefore, suggest a counter-regulatory action of p38 MAPK and NF-kappaB. As antisense experiments revealed a pivotal role for MKP-1 induction and therefore, p38 MAPK inhibition in ANP-mediated attenuation of MCP-1 expression, this action seems to be rather independent of NF-kappaB inhibition.

Candida albicans induces selectively transcriptional activation of cyclooxygenase-2 in HeLa cells: pivotal roles of Toll-like receptors, p38 mitogen-activated protein kinase, and NF-kappa B

Candidiasis, in its mucocutaneous form as well as in an invasive form, is frequently associated with high morbidity. PGE(2), which is generated by enzymatic activity of cyclooxygenases (COXs) 1 and 2, has been shown to trigger morphogenesis in Candida albicans. In the present study, we investigated whether C. albicans altered COX-2 expression in HeLa cells. RT-PCR and Western blot analyses revealed a time-dependent biphasic behavior of COX-2 mRNA expression and COX-2 protein level. COX-1 protein remained unaffected. Neutralization with Abs against Toll-like receptors (TLR) 2 and 4 inhibited the Candida-induced production of PGE(2), suggesting a vital role for TLRs in the recognition and signaling in mammalian cells upon infection with C. albicans. Transient transfections with COX-2 promoter-luciferase construct and various inhibitors of mitogen-activated protein kinases (MAPK), such as protein kinase C (PKC) inhibitor GF203190X, p38(MAPK) inhibitor SB203109, and extracellular-regulated kinases 1 and 2 inhibitor PD98509 showed that C. albicans up-regulates selectively COX-2, but not COX-1, through p38(MAPK) and PKC pathways. No involvement of other stress kinases, e.g., c-Jun NH(2)-terminal kinase and extracellular-regulated kinases 1 and 2, was observed. Transient transfection of NF-kappaB promoter construct and dominant negative plasmid of IkappaBbeta kinase showed that COX-2 transcription is mediated through p38(MAPK) and NF-kappaB pathways. That NF-kappaB up-regulates p38(MAPK) is novel and is in contradiction to earlier reports in which NF-kappaB was shown to inhibit p38(MAPK). In conclusion, multiple converging signaling pathways, involving TLRs followed by PKC, p38(MAPK), and/or NF-kappaB, are triggered by C. albicans in activation of COX-2 gene.

Hepatitis C virus and HIV envelope proteins collaboratively mediate interleukin-8 secretion through activation of p38 MAP kinase and SHP2 in hepatocytes

Hepatitis C virus (HCV) infects approximately 40% of human immunodeficiency virus (HIV) patients, and the resulting hepatic dysfunction that occurs is the primary cause of death in patients with co-infection. We hypothesized that hepatocytes exposed to HCV and HIV proteins might be susceptible to injury via an "innocent bystander" mechanism. To assess this, we studied the effects of envelope proteins, E2 of HCV and gp120 of HIV, in model HepG2 cells. Upon co-stimulation with HCV-E2 and HIV-gp120, we observed a potent proinflammatory response with the induction of IL-8. Furthermore, our studies revealed that HCV-E2 and HIV-gp120 act collaboratively to trigger a specific set of downstream signaling pathways that include activation of p38 mitogen-activated protein (MAP) kinase and the tyrosine phosphatase, SHP2. Both specific inhibitors of p38 MAP kinase and sodium vanadate, a potent protein-tyrosine phosphatase inhibitor, blocked IL-8 production in a dose-dependent manner. The role of p38 MAP kinase and SHP2 was further defined by transiently overexpressing dominant negative mutants of these proteins into HepG2 cells. These studies revealed that overexpression of an inactive p38 MAP kinase or SHP2 mutant partially abrogated HCV-E2- and HIV-gp120-induced IL-8 production. Further studies revealed that IL-8 induction was not mediated through activation of the NF-kappa B pathway. However, HCV-E2 plus HIV-gp120 was shown to increase the DNA binding activity of AP-1. These results emphasize that expression of the proinflammatory chemokine IL-8, induced by HCV-E2 and HIV-gp120, may be mediated through p38 MAP kinase and SHP2 in an NF-kappa B-independent manner, albeit through AP-1-driven processes.

IL-4 augments anisomycin-induced p38 activation via Akt pathway in a follicular dendritic cell (FDC)-like line

Follicular dendritic cells (FDCs) play pivotal roles in germinal center (GC) responses in secondary lymphoid follicles, and their functions are influenced by cytokines present in the GC. We investigated the functional effects of interleukin-4 (IL-4) using an established FDC-like line of HK cells. In spite of the activation of ERK1/2 and PI3K/Akt pathways by IL-4, which are implicated in the induction of cell proliferation and survival, IL-4 did not exhibit protective function on anisomycin-induced apoptosis of HK cells, but rather slightly enhanced it. This IL-4 effect correlated with the up-regulation of anisomycin-induced p38 signaling, which is attenuated by inhibition of the PI3K/Akt pathway. Expression of an active form of Akt increased anisomycin-elicited activation of p38 and its upstream kinase MKK3/6. Our data indicate a positive cross-talk between the p38 and PI3K/Akt pathways.

Role of double-stranded RNA-activated protein kinase R (PKR) in deoxynivalenol-induced ribotoxic stress response

Trichothecene mycotoxins and other protein synthesis inhibitors activate mitogen-activated protein kinase (MAPKs) via a mechanism that has been termed the "ribotoxic stress response." MAPKs are believed to mediate the leukocyte apoptosis that is observed following experimental exposure to these chemical agents in vitro and in vivo. The purpose of this research was to test the hypothesis that double-stranded, RNA-activated protein kinase R (PKR) is a critical upstream mediator of the ribotoxic stress response induced by the trichothecene deoxynivalenol (DON) and other translational inhibitors. DON was found to readily induce phosphorylation of JNK 1/2, ERK 1/2, and p38 in the murine macrophage RAW 264.7 cell line, within 5 min of culture addition, in a concentration-dependent fashion. Effects were maximal from 15 to 30 min and lasted up to 6 h. The translational inhibitors anisomycin and emetine also had similar effects when added to cultures at equipotent concentrations to DON. DON rapidly activated PKR within 1 to 5 min, as evidenced by autophosphorylation and by phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha). Interestingly, the latter effect was associated with rapid degradation of eIF2alpha. Pretreatment of RAW 264.7 cells with two inhibitors of PKR, 2-aminopurine (2-AP) or adenine (Ad), markedly impaired MAPK phosphorylation in RAW 264.7 cells according to the following rank order JNK>p38>ERK. The capacity of DON to induce MAPK phosphorylation was also markedly suppressed in a stable transformant of the human promonocytic U-937 cell line containing an antisense PKR expression vector. This suppression followed a rank order of JNK>p38>ERK in this PKR-deficient cell line when compared to control cells transfected with vector only. Apoptosis induction by DON and two other translational inhibitors, anisomycin and emetine, was almost completely abrogated in PKR-deficient cells. Together, the results indicate that PKR plays a critical upstream role in the ribotoxic stress response inducible by translational inhibitors.

Induced stabilization of IkappaBalpha can facilitate its re-synthesis and prevent sequential degradation

The transcription factor NF-kappaB is responsible for regulating genes that can profoundly impact cell proliferation, apoptosis, inflammation, and immune responses. The NF-kappaB inhibitor IkappaBalpha is rapidly degraded and then re-synthesized after an NF-kappaB stimulus. We have found that the re-synthesis of IkappaBalpha in a human colon-derived cell line (HT-29) includes the post-translational stabilization of newly synthesized IkappaBalpha. The TNF-alpha-induced stabilization of newly synthesized IkappaBalpha involves the C-terminal PEST region of the protein: N-terminal deletion mutants (lacking the IkappaB kinase phosphorylation sites) were readily stabilized by TNF-alpha, whereas deletion of the C-terminus resulted in a constitutively stable protein. The role of the C-terminus in stabilization was further supported by the finding that fusion of the IkappaBalpha C-terminus to GFP generated a protein that could also be stabilized by TNF-alpha. The p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 prevented stabilization of IkappaBalpha and delayed the re-emergence of IkappaBalpha following TNF-alpha-induced degradation. The IkappaBalpha stabilization pathway could prevent sequential rounds of IkappaBalpha degradation without preventing IkappaBalpha phosphorylation. Analysis of two other cell lines (SW480 and THP-1) revealed similarities and cell-specific differences in the regulation of IkappaBalpha stabilization. We propose that cytokine stabilization of newly synthesized IkappaBalpha in some cell types is a critical homeostatic mechanism that limits inflammatory gene expression.

Cycloheximide increases glucocorticoid-stimulated alpha -ENaC mRNA in collecting duct cells by p38 MAPK-dependent pathway

Aldosterone and glucocorticoids (GCs) stimulate Na(+) reabsorption in the collecting ducts by increasing the activity of the epithelial Na(+) channel (ENaC). Our laboratory has used Madin-Darby canine kidney-C7 cells to demonstrate that this effect is associated with an increase in alpha-ENaC gene transcription (Mick VE, Itani OA, Loftus RW, Husted RF, Schmidt TJ, and Thomas CP, Mol Endocrinol 15: 575-588, 2001). Cycloheximide (CHX) superinduced the GC-stimulated alpha-ENaC expression in a dose-dependent manner, but had no effect on basal or aldosterone-stimulated alpha-ENaC expression, whereas anisomycin inhibited basal and corticosteroid-stimulated alpha-ENaC expression. The superinduction of alpha-ENaC expression was also seen with hypotonicity, was blocked by RU-38486, and was independent of protein synthesis. CHX had no effect on alpha-ENaC mRNA half-life, confirming that its effect was via an increase in alpha-ENaC transcription. The effect of CHX and hypotonicity on alpha-ENaC expression was abolished by SB-202190, indicating an effect mediated via p38 MAPK. Consistent with this scheme, CHX increased pp38 and MKK6, an upstream activator of p38, stimulated alpha-ENaC promoter activity. These data confirm a model in which CHX activates p38 in Madin-Darby canine kidney-C7 cells to increase alpha-ENaC gene transcription in a GC-dependent manner.

Role of the NF-kappaB signaling pathway and kappaB cis-regulatory elements on the IRF-1 and iNOS promoter regions in mycobacterial lipoarabinomannan induction of nitric oxide

Nitric oxide (NO(.)) produced by inducible nitric oxide synthase (iNOS) is an important host defense molecule against Mycobacterium tuberculosis in mononuclear phagocytes. The objective of this study was to determine the role of the IkappaBalpha kinase-nuclear factor kappaB (IKK-NF-kappaB) signaling pathway in the induction of iNOS and NO(.) by a mycobacterial cell wall lipoglycan known as mannose-capped lipoarabinomannan (ManLAM) in mouse macrophages costimulated with gamma interferon (IFN-gamma). NF-kappaB was activated by ManLAM as shown by electrophoretic mobility shift assay, by immunofluorescence of translocated NF-kappaB in intact cells, and by a reporter gene driven by four NF-kappaB-binding elements. Transduction of an IkappaBalpha mutant (Ser32/36Ala) significantly inhibited NO(.) expression induced by IFN-gamma plus ManLAM. An activated SCF complex, a heterotetramer (Skp1, Cul-1, beta-TrCP [F-box protein], and ROC1) involved with ubiquitination, is also required for iNOS-NO(.) induction. Two NF-kappaB-binding sites (kappaBI and kappaBII) present on the 5'-flanking region of the iNOS promoter bound ManLAM-induced NF-kappaB similarly. By use of reporter constructs in which one or both sites are mutated, both NF-kappaB-binding positions were essential in iNOS induction by IFN-gamma plus ManLAM. IFN-gamma-induced activation of the IRF-1 transcriptional complex is a necessary component in host defense against tuberculosis. Although the 5'-flanking region of the IRF-1 promoter contains an NF-kappaB-binding site and ManLAM-induced NF-kappaB also binds to this site, ManLAM was unable to induce IRF-1 expression. The influence of mitogen-activated protein kinases on IFN-gamma plus ManLAM induction of iNOS-NO(.) is not due to any effects on ManLAM induction of NF-kappaB.

Inhibition of IkappaB kinase by a new class of retinoid-related anticancer agents that induce apoptosis

The transcription factor NF-kappaB is overexpressed or constitutively activated in many cancer cells, where it induces expression of antiapoptotic genes correlating with resistance to anticancer therapies. Small molecules that inhibit the NF-kappaB signaling pathway could therefore be used to induce apoptosis in NF-kappaB-overexpressing tumors and potentially serve as anticancer agents. We found that retinoid antagonist MX781 inhibited the activation of NF-kappaB-dependent transcriptional activity in different tumor cell lines. MX781 was able to completely inhibit tumor necrosis factor alpha-mediated activation of IkappaB kinase (IKK), the upstream regulator of NF-kappaB. Inhibition of IKK activity resulted from direct binding of MX781 to the kinase, as demonstrated by in vitro inhibition studies. Two other molecules, MX3350-1 and CD2325, which are retinoic acid receptor gamma-selective agonists, were capable of inhibiting IKK in vitro, although they exerted variable inhibition of IKK and NF-kappaB activities in intact cells in a cell type-specific manner. However, N-(4-hydroxyphenyl)-retinamide, another apoptosis-inducing retinoid, and retinoic acid as well as other nonapoptotic retinoids did not inhibit IKK. Inhibition of IKK by the retinoid-related compounds and other small molecules correlated with reduced cell proliferation and increased apoptosis. Reduced cell viability was also observed after overexpression of an IKKbeta kinase-dead mutant or the IkappaBalpha superrepressor. The induction of apoptosis by the retinoid-related molecules that inhibited IKK was dependent on caspase activity but independent of the retinoid receptors. Thus, the presence of an excess of retinoic acid or a retinoid antagonist did not prevent the inhibition of IKK activation by MX781 and CD2325, indicating a retinoid receptor-independent mechanism of action.

Cytokine-stimulated inducible nitric oxide synthase expression in astroglia: role of Erk mitogen-activated protein kinase and NF-kappaB

Expression of inducible nitric oxide synthase (iNOS), which leads to the production of nitric oxide (NO), is stimulated by proinflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). Here we report on the roles of nuclear factor-kappaB (NF-kappaB) and mitogen-activated protein (MAP) kinases in IL-1beta/TNF-alpha-induced iNOS expression in adult rat astroglia. Cytokine-induced increases in nitrite accumulation (an index of NO production) and iNOS expression were attenuated by inhibition of NF-kappaB with pyrrolidine dithiocarbamate (PDTC). Similar attenuation of these cytokine-induced responses was produced by inhibition of MAP kinase (MEK), the immediate upstream activator of Erk, using PD098,059. Combined treatment of astroglia with PDTC and PD098,059 completely abolished the cytokine-induced increases in iNOS expression and nitrite accumulation. By contrast, the selective p38 kinase inhibitor SB203,580 amplified the effects of IL-1beta/TNF-alpha on nitrite accumulation. In accordance with these findings, IL-1beta- and TNF-alpha-induced a time-dependent increase in Erk1/Erk2 activation. This cytokine action was completely abolished by PD098,059 but was not altered by PDTC. Finally, IL-1beta and TNF-alpha induced degradation of NF-kappaB's bound inhibitory protein, IkappaB-alpha, leading to translocation of NF-kappaB into the nucleus. IkappaB-alpha expression was not restored to control levels by inhibition of MEK. Furthermore, inhibition of MEK with PD098,059 did not alter IL-1beta- and TNF-alpha-induced expression of active NF-kappaB. The results demonstrate that autonomous Erk and NF-kappaB pathways mediate cytokine-induced increases in iNOS expression in astroglia.