Stimulation of interleukin-8 production by okadaic acid and vanadate in a human promyelocyte cell line, an HL-60 subline. Possible role of mitogen-activated protein kinase on the okadaic acid-induced NF-kappaB activation

Ghrelin rapidly elevates protein synthesis in vitro by employing the rpS6K-eEF2K-eEF2 signalling axis

Activated ghrelin receptor GHS-R1α triggers cell signalling pathways that modulate energy homeostasis and biosynthetic processes. However, the effects of ghrelin on mRNA translation are unknown. Using various reporter assays, here we demonstrate a rapid elevation of protein synthesis in cells within 15–30 min upon stimulation of GHS-R1α by ghrelin. We further show that ghrelin-induced activation of translation is mediated, at least in part, through the de-phosphorylation (de-suppression) of elongation factor 2 (eEF2). The levels of eEF2 phosphorylation at Thr56 decrease due to the reduced activity of eEF2 kinase, which is inhibited via Ser366 phosphorylation by rpS6 kinases. Being stress-susceptible, the ghrelin-mediated decrease in eEF2 phosphorylation can be abolished by glucose deprivation and mitochondrial uncoupling. We believe that the observed burst of translation benefits rapid restocking of neuropeptides, which are released upon GHS-R1α activation, and represents the most time- and energy-efficient way of prompt recharging the orexigenic neuronal circuitry.

Phytoplankton Toxins and Their Potential Therapeutic Applications: A Journey toward the Quest for Potent Pharmaceuticals

Phytoplankton are prominent organisms that contain numerous bioactive substances and secondary metabolites, including toxins, which can be valuable to pharmaceutical, nutraceutical, and biotechnological industries. Studies on toxins produced by phytoplankton such as cyanobacteria, diatoms, and dinoflagellates have become more prevalent in recent years and have sparked much interest in this field of research. Because of their richness and complexity, they have great potential as medicinal remedies and biological exploratory probes. Unfortunately, such toxins are still at the preclinical and clinical stages of development. Phytoplankton toxins are harmful to other organisms and are hazardous to animals and human health. However, they may be effective as therapeutic pharmacological agents for numerous disorders, including dyslipidemia, obesity, cancer, diabetes, and hypertension. In this review, we have focused on the properties of different toxins produced by phytoplankton, as well as their beneficial effects and potential biomedical applications. The anticancer properties exhibited by phytoplankton toxins are mainly attributed to their apoptotic effects. As a result, phytoplankton toxins are a promising strategy for avoiding postponement or cancer treatment. Moreover, they also displayed promising applications in other ailments and diseases such as Alzheimer’s disease, diabetes, AIDS, fungal, bacterial, schizophrenia, inflammation, allergy, osteoporosis, asthma, and pain. Preclinical and clinical applications of phytoplankton toxins, as well as future directions of their enhanced nano-formulations for improved clinical efficacy, have also been reviewed.

Novel Insights on the Toxicity of Phycotoxins on the Gut through the Targeting of Enteric Glial Cells

In vitro and in vivo studies have shown that phycotoxins can impact intestinal epithelial cells and can cross the intestinal barrier to some extent. Therefore, phycotoxins can reach cells underlying the epithelium, such as enteric glial cells (EGCs), which are involved in gut homeostasis, motility, and barrier integrity. This study compared the toxicological effects of pectenotoxin-2 (PTX2), yessotoxin (YTX), okadaic acid (OA), azaspiracid-1 (AZA1), 13-desmethyl-spirolide C (SPX), and palytoxin (PlTX) on the rat EGC cell line CRL2690. Cell viability, morphology, oxidative stress, inflammation, cell cycle, and specific glial markers were evaluated using RT-qPCR and high content analysis (HCA) approaches. PTX2, YTX, OA, AZA1, and PlTX induced neurite alterations, oxidative stress, cell cycle disturbance, and increase of specific EGC markers. An inflammatory response for YTX, OA, and AZA1 was suggested by the nuclear translocation of NF-κB. Caspase-3-dependent apoptosis and induction of DNA double strand breaks (γH2AX) were also observed with PTX2, YTX, OA, and AZA1. These findings suggest that PTX2, YTX, OA, AZA1, and PlTX may affect intestinal barrier integrity through alterations of the human enteric glial system. Our results provide novel insight into the toxicological effects of phycotoxins on the gut.

Lipoxin A4 and Serum Amyloid a Differentially Modulate Phospholipase D in Human Fibroblast-Like Synoviocytes

Lipoxin A4 (LXA4) and scrum amyloid A (SAA) are endogenous negative and positive modulators of inflammation, respectively. Both molecules bind the shared lipoxin A4 receptor (ALX) and elicit opposing effects on the production of inflammatory cytokines and matrix metalloproteinases. The aim of these studies is to examine the divergence of the intracellular signaling pathways triggered by lipid LXA4 (1 nM) and protein SAA (200 nM) ligands of ALX. Phospholipase D (PLD) is a phosphohydrolase enzyme that catalyzes the generation of phosphatidic acid (PA) from membrane phospholipids. Our results showed that in fibroblast-like synoviocytes, activation of PLD occurred only in response to LXA4, and not SAA. PA (30 μM) mimicked LXA4 and demonstrated inhibition of IL-8 production induced by SAA or interleukin-1β. In sharp contrast to LXA4, SAA confirmed the stimulation of IL-8 release as determined previously. Taken together, these findings suggest that two physiologic ligands sharing the common ALX receptor, LXA4 and SAA, differentially regulate the level of PLD activation and differentially modulate IL-8. These results may have important implications for understanding the regulation of inflammatory responses under physiologic and pathological conditions.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Protein phosphatase 2A regulation of markers of extracellular matrix remodelling in hepatocellular carcinoma cells: functional consequences for tumour invasion

BACKGROUND AND PURPOSE

A hallmark of tumour invasion is breakdown of the extracellular matrix due to dysregulation of the matrix metalloproteinase (MMP) system. While our understanding of how this is regulated by kinase signalling pathways is well established, its counter-regulation by protein phosphatases (PP) is poorly understood. Therefore, we investigated the effect of PP inhibition on markers of extracellular remodelling and how PP2A activity modulated MMP-9 abundance and function of Hep3B cells.

EXPERIMENTAL APPROACH

Cells were exposed to okadaic acid (OA), tautomycetin and cyclosporin A, and the expression profile determined using PCR. Effects of OA and a protein inhibitor of PP2A, CIP2A, on MMP-9 abundance, PP2A activity and cell migration were investigated using ELISA, promoter constructs, siRNA knockdown and transwell migration assays.

KEY RESULTS

OA increased expression and abundance of MMP-9 and the tissue inhibitor of MMP, TIMP-1, without affecting other MMPs, TIMPs and ADAMs. The effect on MMP-9 was mimicked by CIP2A overexpression and knockdown of the PPP2CA catalytic, but not PPP2R1A scaffolding, subunit. Cyclosporin A and PPP1CA silencing did not alter MMP-9 expression, while tautomycetin transiently increased it. Mutation of AP-1, but not NF-κB, binding sites inhibited OA-mediated MMP-9 transcriptional activity. OA and CIP2A decreased PP2A activity and increased cell migration.

CONCLUSION AND IMPLICATIONS

OA increased MMP-9 by decreasing PP2A activity and PP2Ac, through AP-1 binding sites on the MMP-9 promoter. The functional consequence of this and CIP2A overexpression was increased cell migration. Hence, PP2A inhibition induced a metastatic phenotype through alterations in MMP-9 in Hep3B cells.

Regulation of Signal Transduction by DJ-1

The ability of DJ-1 to modulate signal transduction has significant effects on how the cell regulates normal processes such as growth, senescence, apoptosis, and autophagy to adapt to changing environmental stimuli and stresses. Perturbations of DJ-1 levels or function can disrupt the equilibrium of homeostatic signaling networks and set off cascades that play a role in the pathogenesis of conditions such as cancer and Parkinson's disease.DJ-1 plays a major role in various pathways. It mediates cell survival and proliferation by activating the extracellular signal-regulated kinase (ERK1/2) pathway and the phosphatidylinositol-3-kinase (PI3K)/Akt pathway. It attenuates cell death signaling by inhibiting apoptosis signal-regulating kinase 1 (ASK1) activation as well as by inhibiting mitogen-activated protein kinase kinase kinase 1 (MEKK1/MAP3K1) activation of downstream apoptotic cascades. It also modulates autophagy through the ERK, Akt, or the JNK/Beclin1 pathways. In addition, DJ-1 regulates the transcription of genes essential for male reproductive function, such as spermatogenesis, by relaying nuclear receptor androgen receptor (AR) signaling. In this chapter, we summarize the ways that DJ-1 regulates these pathways, focusing on how its role in signal transduction contributes to cellular homeostasis and the pathologic states that result from dysregulation.

Pro-inflammatory effects of palytoxin: an in vitro study on human keratinocytes and inflammatory cells

Palytoxin (PLTX) is one of the most harmful marine toxins known so far. Although the ingestion of contaminated seafood is the most dangerous exposure route for humans, cutaneous and inhalational exposures are far more frequent, and can cause strong inflammatory reactions. However, little is known about the inflammatory events that follow the cutaneous exposure to the toxin. In this study, we investigated (1) the effects of both short (2 h) and long (24 h) term exposures of HaCaT keratinocytes to a sub-cytotoxic PLTX concentration on pro-inflammatory mediator gene expression and release and (2) the effect of PLTX-conditioned HaCaT cell media on undifferentiated (monocytes) and differentiated (macrophages; immature dendritic cells, iDCs; mature dendritic cells, mDCs) THP-1 cells. At 10-11 M, PLTX induced interleukin (IL)-6 and IL-8 release from HaCaT keratinocytes after 24 h of continuous exposure to the toxin, as well as after 23 h in toxin-free medium preceded by 1 h exposure to PLTX. Under the same experimental conditions, release of the inflammatory mediators prostaglandin-E2 and histamine was also found after both short and long exposures to the toxin. The conditioned media collected from HaCaT cells treated with PLTX increased the migration of the differentiated and undifferentiated THP-1 cells (potency rank order: monocytes ≥ iDCs > mDCs > macrophages) but did not induce cell differentiation. These results indicate that keratinocytes can be actively involved in the recruitment of inflammatory cells in response to cutaneous contact with PLTX. The lack of a significant effect on monocyte differentiation towards mature immune cells suggests that PLTX is endowed with irritant rather than sensitizing properties.

[Study of cytokine signaling: the quest for immunomodulatory drugs interacting with cytokine production and activity]

I have been engaged in research and education in the fields of immunology and biochemistry at a medical college and college of pharmacy for 40 years. The original reasons why I began studying cytokines and some of the interests that have motivated me to continue working in the field of cytokine research are described: 1) the roles of cytokines in various immunological and inflammatory diseases (e.g., chemokines in bacterial infections and inflammatory diseases, particularly the role of interleukin-5 and eotaxins in eosinophilia); 2) the role of focal adhesion kinase in antiapoptosis and metastasis of melanoma; 3) recent findings on the role of JAK2/STAT pathways, particularly how JAK2V617F mutation induces dysregulated proliferation and tumorigenesis; and 4) the interactions of various chemical compounds and natural products in cytokine gene activation and signaling. Previous discoveries and published findings by my research group are described, along with comments and discussion pertaining to recent developments in the field.

The impact of pneumolysin on the macrophage response to Streptococcus pneumoniae is strain-dependent

Streptococcus pneumoniae is the world's leading cause of pneumonia, bacteremia, meningitis and otitis media. A major pneumococcal virulence factor is the cholesterol-dependent cytolysin, which has the defining property of forming pores in cholesterol-containing membranes. In recent times a clinically significant and internationally successful serotype 1 ST306 clone has been found to express a non-cytolytic variant of Ply (Ply₃₀₆). However, while the pneumococcus is a naturally transformable organism, strains of the ST306 clonal group have to date been virtually impossible to transform, severely restricting efforts to understand the role of non-cytolytic Ply in the success of this clone. In this study isogenic Ply mutants were constructed in the D39 background and for the first time in the ST306 background (A0229467) to enable direct comparisons between Ply variants for their impact on the immune response in a macrophage-like cell line. Strains that expressed cytolytic Ply were found to induce a significant increase in IL-1β release from macrophage-like cells compared to the non-cytolytic and Ply-deficient strains in a background-independent manner, confirming the requirement for pore formation in the Ply-dependent activation of the NLRP3 inflammasome. However, cytolytic activity in the D39 background was found to induce increased expression of the genes encoding GM-CSF (CSF2), p19 subunit of IL-23 (IL23A) and IFNβ (IFNB1) compared to non-cytolytic and Ply-deficient D39 mutants, but had no effect in the A0229467 background. The impact of Ply on the immune response to the pneumococcus is highly dependent on the strain background, thus emphasising the importance of the interaction between specific virulence factors and other components of the genetic background of this organism.

Okadaic acid: more than a diarrheic toxin

Okadaic acid (OA) is one of the most frequent and worldwide distributed marine toxins. It is easily accumulated by shellfish, mainly bivalve mollusks and fish, and, subsequently, can be consumed by humans causing alimentary intoxications. OA is the main representative diarrheic shellfish poisoning (DSP) toxin and its ingestion induces gastrointestinal symptoms, although it is not considered lethal. At the molecular level, OA is a specific inhibitor of several types of serine/threonine protein phosphatases and a tumor promoter in animal carcinogenesis experiments. In the last few decades, the potential toxic effects of OA, beyond its role as a DSP toxin, have been investigated in a number of studies. Alterations in DNA and cellular components, as well as effects on immune and nervous system, and even on embryonic development, have been increasingly reported. In this manuscript, results from all these studies are compiled and reviewed to clarify the role of this toxin not only as a DSP inductor but also as cause of alterations at the cellular and molecular levels, and to highlight the relevance of biomonitoring its effects on human health. Despite further investigations are required to elucidate OA mechanisms of action, toxicokinetics, and harmful effects, there are enough evidences illustrating its toxicity, not related to DSP induction, and, consequently, supporting a revision of the current regulation on OA levels in food.

CXCL8 in thyroid disease: from basic notions to potential applications in clinical practice

CXCL8 was the first chemokine shown to be secreted by thyrocytes. Experimental data suggest that CXCL8 plays a role in thyroid homeostasis but its role in thyroid diseases remains poorly investigated. Clinical studies measuring the serum levels of CXCL8 in patients with autoimmune-thyroid-diseases reported conflicting results. Solid evidences support a role of CXCL8 as a tumor-promoting agent in several human cancers. Studies in thyroid cancer are still in their initial stage, but promising. Several evidences indicate that thyroid cancer may share with other human malignancies some of the effects of CXCL8 and highlight the possibility of using CXCL8 as a marker of aggressiveness. Basic and clinical evidences in favor or against a role for CXCL8 in thyroid diseases are discussed.

Novel low molecular weight lignins as potential anti-emphysema agents: In vitro triple inhibitory activity against elastase, oxidation and inflammation

No molecule has been found to be effective against emphysema to date primarily because of its complex pathogenesis that involves elastolysis, oxidation and inflammation. We here describe novel unsulfated or sulfated low molecular weight lignins (LMWLs) chemo-enzymatically prepared from 4-hydroxycinnamic acids monomers, as the first potent triple-action inhibitors of neutrophil elastase, oxidation and inflammation. The inhibitory potencies of three different cinnamic acid-based LMWLs were determined in vitro using chromogenic substrate hydrolysis assays, radical scavenging and lung cellular oxidative biomarker reduced glutathione (rGSH) assays, and lung cellular inflammatory biomarker NFκB and IL-8 assays, respectively. Each LWML uniquely displayed triple-action inhibition, among which CDSO3, a sulfated caffeic acid-based LMWL, was most potent. The half-maximal anti-human neutrophil elastase (HNE) potency of CDSO3 was 0.43 μM. This high potency arose from lignin-like oligomerization, which was further potentiated by 6.6-fold due to sulfation. Mechanistically, this elastase inhibition was of mixed-type, time-dependent and more selective to positively charged elastases. The half-maximal anti-oxidative potency of CDSO3 was 3.52 μM, 4.8-fold potentiated from that of the monomer, caffeic acid (CA). In contrast, the half-maximal inhibitory potency to TNFα-induced inflammation was 5-10 μM, despite no activity with the monomer. More intriguingly, this anti-inflammatory activity was essentially identical with different stimuli, okadaic acid and hydrogen peroxide (H(2)O(2)), which implied that CDSO3 acts directly on inflammatory cascades within the cells. Overall, oligomerization and sulfation produced or significantly potentiated the activity, in comparison to the monomer. Thus, sulfated and unsulfated LMWLs are novel non-peptidic 2.8-4.1 kDa macromolecules that exhibit for the first time potent triple inhibitory activity against elastase, oxidation and inflammation, the three major pathogenic mechanisms known to cause emphysema.

Interleukin-8 (CXCL8) in tumor associated non-vascular extracellular fluids: its diagnostic and prognostic values. A review

Interleukin-8 (IL-8, CXCL8) was originally discovered as a powerful attractor and activator of polymorphonuclear leukocytes. It was soon recognized that IL-8 also affects proliferation and migration of cancer cells, tumor angiogenesis and metastasis, and that it is expressed in many cancerous cell types. IL-8 protein expression is usually increased in serum of cancer patients, but markedly higher concentrations are found in cancer-associated non-vascular extracellular fluids, such as pleural effusion, ascites and cyst fluid. Elevated concentrations of IL-8 are indicative of malignant processes also in cerebrospinal fluid, urine, saliva, interstitial fluid and cervicovaginal secretions. Higher IL-8 levels are typically found in high-grade peritumoral fluids rather than low-grade tumors and benign conditions, with the exception of inflammatory processes. In line with recent molecular biology investigations, it appears that the local IL-8 production is related to its malignant origin and to tumor progression. Hence, IL-8 in peritumoral fluid is to be taken into consideration while assessing tumor character and monitoring the tumor progression/remission status. Besides, the data here collected justify the attempts to find an IL-8-targeted inhibitory therapy

The oral commensal, Streptococcus gordonii, synergizes with Tat protein to induce HIV-1 promoter activation in monocytes/macrophages

Trans-activator of transcription (Tat) is an HIV-1 protein essential for viral replication. Oral periodontopathogens (e.g. Fusobacterium nucleatum) enhance HIV-1LTR promoter activation in monocytes/macrophages in absence of Tat; however, some oral commensals fail to trigger this response. We sought to determine the effect of Tat on HIV-1LTR promoter activation induced by the representative oral commensal Streptococcus gordonii in monocytes/macrophages. S. gordonii enhanced HIV-1LTR reactivation in THP89GFP (Tat(+)), but not in BF24 (Tat(-)) cells. Interestingly, S. gordonii, but not Streptococcus sanguinis enhanced HIV-1LTR activation in the presence of recombinant Tat in BF24 cells. This response correlated with IL-8 but not TNFα or IL-6 production, and was abrogated by the NFκB inhibitor BAY 11-7082. Kinetics of NFκB-RelA activation did not explain the S. gordonii-induced HIV-1LTR activation in presence of Tat. These results suggest that S. gordonii-induced HIV-1 reactivation in monocytes/macrophages is Tat-dependent and appears to involve NFκB activation.

Progesterone regulates the phosphorylation of protein phosphatases in the brain

Previous studies have shown that progesterone modulates the activity of different kinases and the phosphorylation of Tau in the brain. These actions of progesterone may be involved in the hormonal regulation of neuronal differentiation, neuronal function, and neuroprotection. However, the action of progesterone on protein phosphatases in the nervous system has not been explored previously. In this study we have assessed the effect of the administration of progesterone to adult ovariectomized rats on protein phosphatase 2A (PP2A) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in the hypothalamus, the hippocampus, and the cerebellum. Total levels of PP2A, the state of methylation of PP2A, and total levels of PTEN were unaffected by the hormone in the three brain regions studied. In contrast, progesterone significantly increased the levels of PP2A phosphorylated in tyrosine 307 in the hippocampus and the cerebellum and significantly decreased the levels of PTEN phosphorylated in serine 380 in the hypothalamus and in the hippocampus compared with control values. Estradiol priming blocked the effect of progesterone on PP2A phosphorylation in the hippocampus and on PTEN phosphorylation in the hypothalamus and the hippocampus. In contrast, the action of progesterone on PP2A phosphorylation in the cerebellum was not modified by estradiol priming. These findings suggest that the regulation of the phosphorylation of PP2A and PTEN may be involved in the effects of progesterone on the phosphorylation of Tau and on the activity of phophoinositide-3 kinase and mitogen-activated protein kinase in the brain.

KappaB-Ras is a nuclear-cytoplasmic small GTPase that inhibits NF-kappaB activation through the suppression of transcriptional activation of p65/RelA

NF-κB is an important transcription factor involved in various biological responses, including inflammation, cell differentiation, and tumorigenesis. κB-Ras was identified as an IκB-interacting small GTPase and is reported to disturb cytokine-induced NF-κB activation. In this study, we established that κB-Ras is a novel type of nuclear-cytoplasmic small GTPase that mainly binds to GTP, and its localization seemed to be regulated by its GTP/GDP-binding state. Unexpectedly, the GDP-binding form of the κB-Ras mutant exhibited a more potent inhibitory effect on NF-κB activation, and this inhibitory effect seemed to be due to suppression of the transactivation of a p65/RelA NF-κB subunit. κB-Ras suppressed phosphorylation at serine 276 on the p65/RelA subunit, resulting in decreased interaction between p65/RelA and the transcriptional coactivator p300. Interestingly, the GDP-bound κB-Ras mutant exhibited higher interactive affinity with p65/RelA and inhibited the phosphorylation of p65/RelA more potently than wild-type κB-Ras. Taken together, these findings suggest that the GDP-bound form of κB-Ras in cytoplasm suppresses NF-κB activation by inhibiting its transcriptional activation.

Phosphorylation of p65 is required for zinc oxide nanoparticle-induced interleukin 8 expression in human bronchial epithelial cells

BACKGROUND

Exposure to zinc oxide (ZnO) in environmental and occupational settings causes acute pulmonary responses through the induction of proinflammatory mediators such as interleukin-8 (IL-8).

OBJECTIVE

We investigated the effect of ZnO nanoparticles on IL-8 expression and the underlying mechanisms in human bronchial epithelial cells.

METHODS

We determined IL-8 mRNA and protein expression in primary human bronchial epithelial cells and the BEAS-2B human bronchial epithelial cell line using reverse-transcriptase polymerase chain reaction and the enzyme-linked immunosorbent assay, respectively. Transcriptional activity of IL-8 promoter and nuclear factor kappa B (NFkappaB) in ZnO-treated BEAS-2B cells was measured using transient gene transfection of the luciferase reporter construct with or without p65 constructs. Phosphorylation and degradation of IkappaBalpha, an inhibitor of NF-kappaB, and phosphorylation of p65 were detected using immunoblotting. Binding of p65 to the IL-8 promoter was examined using the chromatin immunoprecipitation assay.

RESULTS

ZnO exposure (2-8 microg/mL) increased IL-8 mRNA and protein expression. Inhibition of transcription with actinomycin D blocked ZnO-induced IL-8 expression, which was consistent with the observation that ZnO exposure increased IL-8 promoter reporter activity. Further study demonstrated that the kappaB-binding site in the IL-8 promoter was required for ZnO-induced IL-8 transcriptional activation. ZnO stimulation modestly elevated IkappaBalpha phosphorylation and degradation. Moreover, ZnO exposure also increased the binding of p65 to the IL-8 promoter and p65 phosphorylation at serines 276 and 536. Overexpression of p65 constructs mutated at serines 276 or 536 significantly reduced ZnO-induced increase in IL-8 promoter reporter activity.

CONCLUSION

p65 phosphorylation and IkappaBalpha phosphorylation and degradation are the primary mechanisms involved in ZnO nanoparticle-induced IL-8 expression in human bronchial epithelial cells.

Optimal Suppression of Protein Phosphatase 2A Activity Is Critical for Maintenance of Human Embryonic Stem Cell Self-Renewal

The self-renewal of embryonic stem cells involves a balance between processes governed by crosstalk between intrinsic and extrinsic factors. We hypothesized that protein serine/threonine phosphatase 2A (PP2A) may play a central role in the signaling pathways that regulate human embryonic stem cell (hESC) self-renewal. Biochemical analyses revealed that PP2A activity gradually increases over the course of hESC differentiation; PP2A/C and PP2A/A levels also increased. The overexpression of PP2A/C or the addition of PP2A activator C2-ceramide promoted hESC differentiation. Accordingly, the addition of PP2A inactivator okadaic acid (OA) maintained hESC self-renewal in the absence of basic fibroblast growth factor (bFGF). The hESCs maintained with OA expressed pluripotency markers and exhibited substantial telomerase activity with normal karyotypes. The hESCs were able to differentiate into derivatives of the three germ layers, both in vitro and in vivo. Furthermore, the addition of OA and bFGF enabled the maintenance of hESC self-renewal without feeder cells, even in chemically defined xeno-free media. These findings shed a light on the role of PP2A in hESC differentiation and provide a novel strategy for maintaining the self-renewal capability of hESC in bFGF-free, feeder cell-free, and xeno-free media through the optimal suppression of PP2A activity using OA.

Molecular evidence for the existence of two distinct IL-8 lineages of teleost CXC-chemokines

Interleukin-8 (IL-8) is a CXC-type chemokine with a chemotactic activity mainly on neutrophils and plays a key role in promoting inflammation. In teleosts, several CXC-chemokines have been cloned and characterized as being IL-8-like. Phylogenetic data however indicate that the reported teleost IL-8-like chemokines are substantially remote from mammalian IL-8, forming a fish-specific clade of IL-8-like chemokines distinct from that of tetrapod IL-8. In the present study, a novel IL-8-like chemokine, designated CaIL-8, has been found in the expressed sequence tags of carp gills and identified as an orthologue of mammalian IL-8. The CaIL-8 transcript encodes 99 amino acids containing a typical CXC motif but lacks an ELR motif, as in most teleost IL-8-like chemokines. Phylogenetic tree constructed by the maximum likelihood method suggests a closer relationship of CaIL-8 with mammalian IL-8 than with other teleost CXC-chemokines reported to be IL-8-like. In a normal unstimulated carp, CaIL-8 mRNA was detected by RT-PCR only in gills, kidney, spleen, heart and peripheral blood leukocytes, in contrast to a previously reported carp IL-8-like chemokine CXCa, which shows ubiquitous basal expression. The results, taken together, are strongly indicative of the presence of two major IL-8-like lineages of CXC-chemokines in teleost.

Crosstalk in inflammation: the interplay of glucocorticoid receptor-based mechanisms and kinases and phosphatases

Glucocorticoids (GCs) are steroidal ligands for the GC receptor (GR), which can function as a ligand-activated transcription factor. These steroidal ligands and derivatives thereof are the first line of treatment in a vast array of inflammatory diseases. However, due to the general surge of side effects associated with long-term use of GCs and the potential problem of GC resistance in some patients, the scientific world continues to search for a better understanding of the GC-mediated antiinflammatory mechanisms. The reversible phosphomodification of various mediators in the inflammatory process plays a key role in modulating and fine-tuning the sensitivity, longevity, and intensity of the inflammatory response. As such, the antiinflammatory GCs can modulate the activity and/or expression of various kinases and phosphatases, thus affecting the signaling efficacy toward the propagation of proinflammatory gene expression and proinflammatory gene mRNA stability. Conversely, phosphorylation of GR can affect GR ligand- and DNA-binding affinity, mobility, and cofactor recruitment, culminating in altered transactivation and transrepression capabilities of GR, and consequently leading to a modified antiinflammatory potential. Recently, new roles for kinases and phosphatases have been described in GR-based antiinflammatory mechanisms. Moreover, kinase inhibitors have become increasingly important as antiinflammatory tools, not only for research but also for therapeutic purposes. In light of these developments, we aim to illuminate the integrated interplay between GR signaling and its correlating kinases and phosphatases in the context of the clinically important combat of inflammation, giving attention to implications on GC-mediated side effects and therapy resistance.

Phosphoglucose isomerase/autocrine motility factor promotes melanoma cell migration through ERK activation dependent on autocrine production of interleukin-8

It is well known that phosphoglucose isomerase/autocrine motility factor (AMF) promotes cell migration in an autocrine manner in various tumor cells. However, it remains unclear whether certain cytokines modulate the effects of AMF on tumor cell migration. Because interleukin (IL)-8, a proinflammatory cytokine, is produced by melanoma cells and has been correlated with melanoma migration, the migratory ability of melanoma cells induced by AMF may also involve induction of IL-8 expression. In the present study, we assessed whether AMF promotes melanoma cell migration through autocrine production of IL-8. We found that AMF stimulation increased IL-8 production through up-regulation of IL-8 mRNA transcription, especially in biologically early stage melanoma cells. AMF-induced migration of these cells was inhibited by a specific neutralizing antibody against IL-8. The IL-8 production induced by AMF was mediated by the ERK1/2 pathways. These findings suggest that melanoma migration induced by AMF is mediated by autocrine production of IL-8 as a novel downstream modulator of the AMF signaling pathway.

Ceramide-dependent PP2A regulation of TNFalpha-induced IL-8 production in respiratory epithelial cells

IL-8 is a key mediator in the pathophysiology of acute lung injury. TNFalpha stimulates IL-8 production in respiratory epithelial cells by activating both the NF-kappaB and MAP kinase pathways. The precise mechanism by which these pathways are downregulated to terminate IL-8 production remains unclear. We studied the regulatory role of the serine/threonine phosphatase, PP2A, on the signaling pathways involved in IL-8 production from respiratory epithelial cells. Inhibition of PP2A using okadaic acid or gene knockdown using siRNA resulted in an augmentation of TNFalpha-induced IL-8 production. We also found that PP2A inhibition resulted in prolonged activation of JNK, p38, and ERK resulting in both increased transcriptional activation of the IL-8 promoter and posttranscriptional stabilization of IL-8 mRNA. Because TNFalpha had been shown to activate ceramide accumulation, and separate studies had linked ceramide with activation of PP2A, we hypothesized the pathway of TNFalpha-inducing ceramide to activate PP2A comprised an endogenous regulatory pathway. Inhibition of the immediate sphingomyelinase-dependent pathway as well as the de novo synthesis pathway of ceramide production reduced serine/threonine phosphatase activity and augmented IL-8 production. These data suggest that ceramide plays a role in activating PP2A to terminate ongoing IL-8 production. In summary, our data suggest that in respiratory epithelium, TNFalpha induces ceramide accumulation, resulting in subsequent activation of PP2A, which targets those kinases responsible for transcriptional activation of IL-8.

Protein phosphatase 2A regulatory subunits and cancer

The serine/threonine protein phosphatase (PP2A) is a trimeric holoenzyme that plays an integral role in the regulation of a number of major signaling pathways whose deregulation can contribute to cancer. The specificity and activity of PP2A are highly regulated through the interaction of a family of regulatory B subunits with the substrates. Accumulating evidence indicates that PP2A acts as a tumor suppressor. In this review we summarize the known effects of specific PP2A holoenzymes and their roles in cancer relevant pathways. In particular we highlight PP2A function in the regulation of MAPK and Wnt signaling.

Berberine suppresses inflammatory agents-induced interleukin-1beta and tumor necrosis factor-alpha productions via the inhibition of IkappaB degradation in human lung cells

Pulmonary inflammation is a characteristic of many lung diseases. Increased levels of pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), have been correlated with lung inflammation. In this study, we demonstrated that various inflammatory agents, including lipopolysaccharide, 12-o-tetradecanoylphorbol-13-acetate, hydrogen peroxide, okadaic acid and ceramide, were able to induce IL-1beta and TNF-alpha productions in human lung epithelial cells (A-549), fibroblasts (HFL1), and lymphoma cells (U-937). Berberine, the protoberberine alkaloid widely distributed in the plant kingdom, was capable of suppressing inflammatory agents-induced cytokine production in lung cells. Inhibition of cytokine production by berberine was dose-dependent and cell type-independent. Moreover, the suppression of berberine on the cytokine production resulted from the inhibition of inhibitory kappaB-alpha phosphorylation and degradation. In conclusion, our findings suggested the potential role of berberine in the treatment of pulmonary inflammation.

Expression and function of protein phosphatase PP2A in malignant testicular germ cell tumours

Testicular germ cell tumours (TGCT) represent the most common malignancy in young males. We reported previously that two prototype members of the mitogen-activated protein kinase (MAPK) family, the MAPK ERK kinase (MEK) and extracellular signal-regulated kinase (ERK), are inactive in malignant testicular germ cells and become active after drug stimulation, leading to apoptosis of tumour cells. In this study, we asked whether the protein phosphatase PP2A, a known inhibitor of the MEK-ERK pathway, participates in the proliferation and/or apoptosis of primary TGCT (n = 48) as well as two TGCT cell lines (NTERA and NCCIT). Quantitative RT-PCR, immunohistochemistry, western blot analyses and phosphatase assay indicate that primary TGCT as well as TGCT cell lines express PP2A and that PP2A is active in TGCT cell lines. The inhibition of PP2A by application of two PP2A inhibitors, cantharidic acid (CA) and okadaic acid (OA), results in a significant increase in caspase-3-mediated apoptosis of TGCT cell lines. Thereby, PP2A inhibition was accompanied by phosphorylation and activation of MEK and ERK. Functional assays using the MEK inhibitor PD98059 demonstrated that the phosphorylation of MEK and ERK was required for the induction of caspase-3-mediated apoptosis of malignant germ cells. Thus, our data suggest that inhibition of PP2A mediates its apoptosis-inducing effect on TGCT through activation of the MEK-ERK signalling pathway that leads to caspase-3-mediated apoptosis of tumour cells. In addition our results support previous observations that PP2A exerts an anti-apoptotic effect on malignant tumour cells.

Focal adhesion kinase determines the fate of death or survival of cells in response to TNFalpha in the presence of actinomycin D

We speculated that focal adhesion kinase (FAK) might play a critical role in the TNFalpha-induced cell death. In this study, we found that FAK-/- cells are more sensitive to TNFalpha-induced apoptosis in the presence of actinomycin D (Act D) compared to FAK+/- cells. Prosurvival pathways are activated by the rapid recruitment of complex I, comprising TNFR1, TRADD, RIP and TRAF2, which leads to the activation of the NF-kappaB pathway. On the other hand, proapoptotic pathways are activated by complex II, the death-inducing signaling complex (DISC), which contains TNFR1, TRADD, RIP, and FADD, and procaspase-8 proteins. As TNFR1, TRADD, and RIP are included in both Complex I and DISC, we speculated that RIP might be a key protein. Coimmunoprecipitation assays revealed that RIP is included in complex I in FAK+/- cells, and FAK was associated with RIP. On the other hand, RIP is included in DISC in FAK-/- cells. FAK might be a key protein in the formation of complex I and the activation of NF-kappaB. Furthermore, Akt was activated in FAK+/- cells, but not FAK-/- cells. In conclusion, we first demonstrated that FAK determines the pathway leading to death or survival in TNFalpha/ActD-stimulated fibroblasts.

Adenovirus RIDalphabeta complex inhibits lipopolysaccharide signaling without altering TLR4 cell surface expression

The transmembrane heterotrimer complex 10.4K/14.5K, also known as RID (for "receptor internalization and degradation"), is encoded by the adenovirus E3 region, and it down-regulates the cell surface expression of several unrelated receptors. We recently showed that RID expression correlates with down-regulation of the cell surface expression of the tumor necrosis factor (TNF) receptor 1 in several human cells. This observation provided the first mechanistic explanation for the inhibition of TNF alpha-induced chemokines by RID. Here we analyze the immunoregulatory activities of RID on lipopolysaccharide (LPS) and interleukin-1 beta (IL-1beta)-mediated responses. Although both signaling pathways are strongly inhibited by RID, the chemokines up-regulated by IL-1beta stimulation are only marginally inhibited. In addition, RID inhibits signaling induced by LPS without affecting the expression of the LPS receptor Toll-like receptor 4, demonstrating that RID need not target degradation of the receptor to alter signal transduction. Taken together, our data demonstrate the inhibitory effect of RID on two additional cell surface receptor-mediated signaling pathways involved in inflammatory processes. The data suggest that RID has intracellular targets that impair signal transduction and chemokine expression without evidence of receptor down-regulation.

C/EBPalpha inactivation in FAK-overexpressed HL-60 cells impairs cell differentiation

We previously demonstrated that focal adhesion kinase (FAK)-overexpressed (HL-60/FAK) cells have marked resistance against various apoptotic stimuli such as oxidative stress, ionizing radiation and TNF-receptor-induced ligand (TRAIL) compared with vector-transfected (HL-60/Vect) cells. Here, we show that HL-60/FAK cells are highly resistant to all-trans retinoic acid (ATRA)-induced differentiation, whereas original HL-60 or HL-60/Vect cells are sensitive. Treatment with ATRA at 1 muM for 5 days markedly inhibited the proliferation and increased the expression of differentiation markers (CD38, CD11b) in HL-60/Vect cells, but showed no such effect in HL-60/FAK cells. Electrophoretic mobility shift assay (EMSA) using an oligonucleotide for the c/EBP consensus binding sequence showed that c/EBPalpha was activated in ATRA-treated HL-60/Vect cells but not in HL-60/FAK cells, indicating that c/EBPalpha activation by ATRA was impaired in HL-60/FAK cells. In addition, the association of retinoblastoma protein (pRb) and c/EBPalpha after treatment with ATRA was seen in HL-60/Vect cells but not in HL-60/FAK cells. Further, hyperphosphorylation of pRb was observed in HL-60/FAK cells. Finally, the introduction of FAK siRNA into HL-60/FAK cells resulted in the recovery of sensitivity to ATRA-induced differentiation, confirming that the inhibition of HL-60/FAK differentiation resulted from both the induction of pRb hyperphosphorylation and the inhibition of association of pRb and c/EBPalpha.

Okadaic acid induces tyrosine phosphorylation of IkappaBalpha that mediated by PKR pathway in human osteoblastic MG63 cells

Treatment of human osteosarcoma cell line MG 63 cells with okadaic acid stimulated phosphorylation of IkappaBalpha, as judged from the results of Western blot analysis and a lambda protein phosphatase dephosphorylation assay. The stimulated phosphorylation of IkappaBalpha was both time- and dose-dependent. The phosphorylation sites of IkappaBalpha were taken to be tyrosine residues because the anti-phospho-tyrosine antibody bound to the samples immunoprecipitated with the anti-IkappaBalpha antibody. In the cells treated with 100 nM okadaic acid consequential translocation of NF-kappaB p65 from the cytosol to the nucleus occurred. Double-stranded RNA-dependent protein kinase (PKR) is a player in the cellular antiviral response and is involved in transcriptional stimulation through activation of NF-kappaB. We investigated the functional relationship between PKR and IkappaBalpha phosphorylation by constructing MG 63 PKR K/R cells that produced a catalytically inactive mutant PKR. NF-kappaB p65 was detected in the nucleus of these cells, even in the unstimulated cells. Although IkappaBalpha was degraded phosphorylation of eIF-2 alpha, a substrate of PKR, did not occur in the mutant cells treated with okadaic acid. Our results suggest that okadaic acid-induced tyrosine phosphorylation of IkappaBalpha was mediated by PKR kinase activity, thus indicating the involvement of this kinase in the control mechanism governing the activation of NF-kappaB.

Okadaic acid induces phosphorylation of p65NF-κB on serine 536 and activates NF-κB transcriptional activity in human osteoblastic MG63 cells

Nuclear factor-kappa B (NF-kappaB) is an essential transcription factor in the control of expression of genes involved in cell growth, differentiation, inflammation, and neoplastic transformation. Previously, we reported that okadaic acid (OA), which is a specific inhibitor of serine/threonine protein phosphatases, induced apoptosis in cells of human osteosarcoma cell line MG63. However, to date, it is not clear whether the phosphorylation status of NF-kappaB could be affected by the treatment with OA. In this report, we demonstrate that treatment of MG63 cells with OA enhanced the phosphorylation level of NF-kappaB, as judged from the results of Western blot analysis and a lambda protein phosphatase dephosphorylation assay. The phosphorylation level of NF-kappaB was enhanced in both time- and dose-dependent manners. In the cells treated with 100 nM OA for 3 h, consequential translocation of NF-kappaB from the cytosol to the nucleus occurred. Western blotting experiments with an anti-phospho-p65NF-kappaB antibody disclosed that the NF-kappaB was phosphorylated on serine 536. Furthermore, OA stimulated the transcriptional activity of NF-kappaB in MG63 cells, as judged from the results of a luciferase assay. Our findings indicate that OA elicit phosphorylation of NF-kappaB on serine 536 in MG63 cells, resulting in the translocation of phospho-NF-kappaB to the nucleus, thereby promoting transcriptional activity of genes.

Insulin-like growth factor-I augments interleukin-8 promoter activity through induction of activator protein-1 complex formation

We previously established that stimulation by IGF-I of interleukin (IL)-8 expression in leukocytes required activation of extracellular-regulated kinase (ERK) and basal activity of c-Jun N-terminal kinase (JNK). In this study, we tested the hypothesis that IGF-I stimulates IL-8 expression at the transcriptional level through induction of Fos/Jun activator protein (AP)-1 complex formation. Inhibition studies using the transcriptional inhibitor actinomycin D and IL-8 promoter activation studies indicate that IGF-I act at the transcriptional level. Using gel shift assays we demonstrate that IGF-I induces the formation of active c-Jun/c-Fos AP-1 complexes. Promoter activation studies using mutated IL-8 promoter constructs show that the AP-1 response element is required for promoter activation by IGF-I whereas CAAT-enhancer binding protein (C/EBP) and nuclear factor of kappa B (NFkappaB) sites were not essential. These results indicate that IGF-I can augment IL-8 expression through activation of AP-1 independent of other inducible transcription factors which have shown to be involved in IL-8 regulation by immune stimuli. This finding is in agreement with our previous observation that IGF-I is able to enhance basal IL-8 production in peripheral blood mononuclear cells (PBMC) in the absence of other stimuli.

Proteomic Analysis of Cellular Response to Microcystin in Human Amnion FL Cells

Microcystins (MC), the potent inhibitor of protein phosphatase 1 and 2A, are hepatotoxins of increasing importance due to its high acute toxicity and potent tumor promoting activity. So far, the exact mechanisms of MC-induced hepatotoxicity and tumor promoting activity have not been fully elucidated. To better understand the mechanisms underlying microcystin-RR (MC-RR) induced toxicity as well as provide the possibility for the establishment of biomarkers for MC-RR exposure, differential proteome analysis on human amnion FL cells treated by MC-RR was carried out using two-dimensional gel electrophoresis (2-DE) followed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Image analysis of silver-stained 2-dimensional gels revealed that 89 proteins showed significant differential expression in MC-RR treated cells compared with control, and 8 proteins were unique to MC-RR treated cells and 8 proteins were only detected in control cells. Sixty-six proteins were further identified with high confidence by peptide mass fingerprinting. Some of the identified differentially expressed proteins have clearly relationship with the process of apoptosis, signal transduction, and cytoskeleton alteration which are consistent with the literature. The functional implications of alterations in the levels of these proteins were discussed. However, most of which have not been reported previously to be involved in cellular processes responded to MC-RR. Therefore, this work will provide new insight into the mechanism of MC-RR toxicity.

Positive regulation of Raf1-MEK1/2-ERK1/2 signaling by protein serine/threonine phosphatase 2A holoenzymes

Protein serine/threonine phosphatase 2A (PP2A) regulates a wide variety of cellular signal transduction pathways. The predominant form of PP2A in cells is a heterotrimeric holoenzyme consisting of a scaffolding (A) subunit, a regulatory (B) subunit, and a catalytic (C) subunit. Although PP2A is known to regulate Raf1-MEK1/2-ERK1/2 signaling at multiple steps in this pathway, the specific PP2A holoenzymes involved remain unclear. To address this question, we established tetracycline-inducible human embryonic kidney 293 cell lines for overexpression of FLAG-tagged Balpha/delta regulatory subunits by approximately 3-fold or knock-down of Balpha by greater than 70% compared with endogenous levels. The expression of functional epitope-tagged B subunits was confirmed by the detection of A and C subunits as well as phosphatase activity in FLAG immune complexes from extracts of cells overexpressing the FLAG-Balpha/delta subunit. Western analysis of the cell extracts using phosphospecific antibodies for MEK1/2 and ERK1/2 demonstrated that activation of these kinases in response to epidermal growth factor was markedly diminished in Balpha knock-down cells but elevated in Balpha- and Bdelta-overexpressing cells as compared with control cells. In parallel with the activation of MEK1/2 and ERK1/2, the inhibitory phosphorylation site of Raf1 (Ser-259) was dephosphorylated in cells overexpressing Balpha or Bdelta. Pharmacological inhibitor studies as well as reporter assays for ERK-dependent activation of the transcription factor Elk1 revealed that the PP2A holoenzymes ABalphaC and ABdeltaC act downstream of Ras and upstream of MEK1 to promote activation of this MAPK signaling cascade. Furthermore both PP2A holoenzymes were found to associate with Raf1 and catalyze dephosphorylation of inhibitory phospho-Ser-259. Together these findings indicate that PP2A ABalphaC and ABdeltaC holoenzymes function as positive regulators of Raf1-MEK1/2-ERK1/2 signaling by targeting Raf1.

IL-4 Inhibits the Expression of Mouse Formyl Peptide Receptor 2, a Receptor for Amyloid β1–42, in TNF-α-Activated Microglia

Microglia are phagocytic cells in the CNS and actively participate in proinflammatory responses in neurodegenerative diseases. We have previously shown that TNF-alpha up-regulated the expression of formyl peptide receptor 2 (mFPR2) in mouse microglial cells, resulting in increased chemotactic responses of such cells to mFPR2 agonists, including amyloid beta1-42 (Abeta42), a critical pathogenic agent in Alzheimer's disease. In the present study, we found that IL-4, a Th2-type cytokine, markedly inhibited TNF-alpha-induced expression of mFPR2 in microglial cells by attenuating activation of ERK and p38 MAPK as well as NF-kappaB. The effect of IL-4 was not dependent on Stat6 but rather required the protein phosphatase 2A (PP2A) as demonstrated by the capacity of PP2A small interfering RNA to reverse the effect of IL-4 in TNF-alpha-activated microglia. Since both IL-4 and TNF-alpha are produced in the CNS under pathophysiological conditions, our results suggest that IL-4 may play an important role in the maintenance of CNS homeostasis by limiting microglial activation by proinflammatory stimulants.

Glycyrrhizin and related compounds down-regulate production of inflammatory chemokines IL-8 and eotaxin 1 in a human lung fibroblast cell line

Glycyrrhizin (GL) is known to have various immunomodulating activities and has long been used clinically as an anti-allergic and anti-hepatitis agent. While the potency of GL against lung inflammatory diseases has been expected, the effect of GL on the lung has been poorly understood. Lung fibroblasts are known as a potent producer of inflammatory chemokines, IL-8 and eotaxin 1, by which neutrophils and eosinophils are strongly attracted during inflammation. Therefore, we studied the effects of GL on the production of these chemokines using a human fetal lung fibroblast cell line, HFL-1, stimulated with TNF-alpha and IL-4. Moreover, we examined the structure-activity relationships of GL to explore more beneficial compounds. 18alpha,beta-GL inhibited IL-8 dose-dependently and inhibited eotaxin 1 slightly. 18alpha,beta-Glycyrrhetic acid (GA) did not inhibit IL-8 but inhibited eotaxin 1. The effect of 18alpha,beta-glycyrrhetic acid monoglucuronide (MGA) resembled that of 18alpha,beta-GL but was weaker. Both 3beta-[(2-O-beta-D-glucopyranuronosyl-beta-D-glucopyranuronosyl)oxy]-18beta-11-deoxo-olean-12-en-30-oic acid (11-deoxo-GL) and 3beta-[(2-O-beta-D-glucopyranuronosyl-beta-D-glucopyranuronosyl)oxy]-olean-11,13,(18)-dien-30-oic acid (hetero-GL) exhibited inhibitory activity with significant cytotoxicity. 3beta-[(2-O-beta-D-Glucopyranuronosyl-beta-D-glucopyranuronosyl)oxy]-18beta-olean-9,12-dien-30-oic acid (homo-GL) did not have cytotoxicity but its activity was mild like that of 18alpha,beta-GL. 3beta-[(2-O-beta-d-Glucopyranuronosyl-beta-D-glucopyranuronosyl)oxy]-olean-11,13(18)-dien-30-ol (hetero-30-OH-GL) and 3beta-[(2-O-beta-D-glucopyranuronosyl-beta-D-glucopyranuronosyl)oxy]-18beta-olean-9,12-dien-30-ol (homo-30-OH-GL) showed potent inhibitory effects, at concentrations lower than 18alpha,beta-GL with no significant cytotoxicity. These results suggest that GL-related compounds are effective in reducing chemokine production and that GL-modified compounds including hetero-30-OH-GL and homo-30-OH-GL appear most beneficial in view of their inhibitory capacity with less cytotoxicity.

Macrophages Survive Hyperoxia via Prolonged ERK Activation Due to Phosphatase Down-regulation

Macrophages exposed to hyperoxia in the lung continue to survive for prolonged periods. We previously reported (Nyunoya, T., Powers, L. S., Yarovinsky, T. O., Butler, N. S., Monick, M. M., and Hunninghake, G. W. (2003) J. Biol. Chem. 278, 36099-36106) that hyperoxia induces cell cycle arrest and sustained extracellular signal-related kinase (ERK) activity in macrophages. In this study, we determined the mechanisms of hyperoxia-induced ERK activation and how ERK activity plays a pro-survival role in hyperoxia-exposed cells. Inhibition of ERK activity decreased survival of hyperoxia-exposed macrophages. This was due, at least in part, to down-regulation of the pro-apoptotic Bcl-2 family member, BimEL. In determining the mechanism of ERK activation by hyperoxia, we found that ERK activation was not associated with hyperoxia-induced activation of the upstream ERK kinase mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2. When we examined the ability of whole cell lysates from hyperoxia-exposed cells to dephosphorylate purified phosphorylated ERK, we found decreased ERK-directed phosphatase activity. Two particular ERK-directed phosphatases (protein phosphatase 2A and MAPK phosphatase-3) demonstrated decreased activity in hyperoxia-exposed cells. Moreover, whole cell lysates from normoxia-exposed cells depleted of PP2A or MAPK phosphatase-3 were also less able to dephosphorylate ERK. These data demonstrate that, in hyperoxia-exposed macrophages, sustained activation of ERK due to phosphatase down-regulation permits macrophage survival via effects on the balance between pro- and anti-apoptotic Bcl-2 family proteins.

Effect of various catechins on the IL-12p40 production by murine peritoneal macrophages and a macrophage cell line, J774.1

Interleukin-12 (IL-12) is a heterodimeric cytokine comprising p40 and p35 subunits produced mainly by monocytes and macrophages, and plays an essential role in the regulation of the differentiation of Th1 cells. Green tea polyphenols exhibit potent anti-oxidative activities and anti-inflammatory effects by modulating cytokine production. We investigated the effect of catechins on IL-12p40 production in murine macrophages induced by bacterial lipopolysaccharide (LPS). Pretreatment with several catechins at doses of 0.3-30 microM suppressed IL-12 p40 production by murine peritoneal exudate cells (PEC) and J774.1 cells in a dose-dependent manner. Decreases in protein production were primarily due to down-regulation of the transcription of IL-12p40 mRNA. Of the various catechins, (-)-epigallocatechin gallate (EGCG) was the most potent inhibitor, followed by (-)-gallocatechin gallate (GCG) and (-)-epicatechin gallate (ECG). EGCG inhibited LPS-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK), but not Jun N-terminal kinase (JNK), while EGCG augmented LPS-induced phosphorylation of p44/p42 extracellular signal-related kinase (ERK). In addition, both EGCG and GCG inhibited LPS-induced degradation of IkappaBalpha with concomitant inhibition of nuclear protein binding to NF-kappaB site and synthesis of IRF-1. These results suggest that gallate-containing catechins, particularly EGCG, inhibits LPS-induced IL-12p40 production in murine macrophages by inhibiting p38 MAPK while enhancing p44/p42 ERK, leading to the inhibition of IkappaBalpha degradation and NF-kappaB activation.

Influence of Radix Isatidis on the endotoxin-induced release of TNF-alpha and IL-8 from HL-60 cells

The effects of active antiendotoxin chemical fraction isolated from Radix Isatidis (fraction D) on TNF-alpha and IL-8 secretion in HL-60 cells induced by lipopolysaccharide (LPS) were studied. The appropriate densities of cell suspension and fraction D solution were determined by MTT colorimetric method. Fraction D and LPS were added to HL-60 cell suspension with three different methods respectively. The contents of TNF-alpha and IL-8 in the cultured supernatant induced by LPS were detected by using ELISA method. The results showed that the absorbance (A) was directly proportional to the number of cells and the linearity was good in the range from 0.25 x 10(5) to 2 x 10(5) cell/mL cell suspension. The fraction D significantly inhibited the oversecretion of TNF-alpha and IL-8 in HL-60 cells induced by LPS at the concentration of 7.812 mg/mL which had no cytotoxicity. It was indicated that the antiendotoxin mechanism of the active fraction from Radix Isatidis was contributed to the inhibition of the oversecretion of cytokines induced by LPS.

Membrane-associated serine/threonine protein phosphatase in endometrial cancer

OBJECTIVE

Reversible serine/threonine protein phosphorylation catalyzed by kinases and phosphatases plays a crucial role in cellular growth and differentiation. We attempted to determine the subcellular location of serine/threonine phosphatase (protein phosphatase type 2A [PP2A]) in endometrial cancer.

STUDY DESIGN

Endometrial cancers surgically removed were examined. PP2A activity was assessed by measuring the dephosphorylation of phosphopeptide highly selective for the PP2A in cytosol and membranes fractionated on a continuous sucrose density gradient. Its protein level was detected by immunoblotting with a specific antibody.

RESULTS

There were three peaks of PP2A enzyme activity and immunoreactivity corresponding by marker enzyme analysis to the cytoplasm, plasma membrane, and endoplasmic reticulum fractions. An enzyme kinetic analysis showed the different activity in cytosol and plasma membrane; K(m) values of 98+/-12 micromol/L for cytosol and 32+/-6.2 micromol/L for plasma membrane (P<.01), respectively. The membrane phosphatase was sensitive to inhibition by okadaic acid and sodium fluoride, characteristics suggestive of PP2A activity.

CONCLUSION

PP2A activity in the plasma membrane of endometrial cancers might be distinct from that present in the cytosol. The plasma membrane PP2A may be responsible for a rapid and initial decrease in intracellular level of phosphoserine and phosphothreonine, interfering with serine/threonine protein phosphorylation-mediated growth of endometrial cancer.

Acute ethanol exposure inhibits macrophage IL-6 production: role of p38 and ERK1/2 MAPK

Acute ethanol consumption has been linked to an increase in infectious complications in trauma and burn patients. Ethanol modifies production of a variety of macrophage-derived immunoregulatory mediators. Lipopolysaccharide (LPS), a potent stimulator of inflammatory responses in macrophages, activates several intracellular signaling pathways, including mitogen-activated protein kinases (MAPK). In the current study, we investigated the effect of acute ethanol exposure on in vivo activation of p38 and extracellularly regulated kinases 1 and 2 (ERK1/2) MAPK in murine macrophages and the corresponding, LPS-stimulated interleukin (IL)-6 production. We demonstrated that a single dose of ethanol transiently down-regulated p38 and ERK1/2 activation levels (3-24 h after treatment) and impaired IL-6 synthesis. Ethanol-related reduction in IL-6 production was not further affected by the presence of inhibitors of p38 and ERK1/2 (SB 202190 and PD 98059, respectively). These results demonstrate that acute ethanol exposure can impair macrophage IL-6 production and indicate that this effect may result from ethanol-induced alterations in intracellular signaling through p38 and ERK1/2.

Integrin alpha2beta1 inhibits Fas-mediated apoptosis in T lymphocytes by protein phosphatase 2A-dependent activation of the MAPK/ERK pathway

The mechanisms by which T lymphocytes escape apoptosis during their activation are still poorly defined. In this study, we elucidated the intracellular signaling pathways through which beta1 integrins modulate Fas-mediated apoptosis in T lymphocytes. In experiments done in Jurkat T cells and activated peripheral blood T lymphocytes, engagement of alpha2beta1 integrin with collagen type I (Coll I) was found to significantly reduce Fas-induced apoptosis and caspase-8 activation; Annexin V binding and DNA fragmentation were reduced by approximately 42 and 38%, respectively. We demonstrated that the protective action of Coll I does not require new protein synthesis but was dependent on the activation of the MAPK/Erk pathway. Furthermore, we found that activation of protein phosphatase 2A (PP2A) by Coll I was required for both Coll I-mediated activation of Erk, and inhibition of Fas-induced caspase-8 activation and apoptosis. Other ligands of beta1 integrins, fibronectin (Fbn), and laminin (Lam), did not sustain significant Erk activation and had no effect on Fas-induced apoptosis. Taken together, these results provide the first evidence of a PP2A-dependent activation of the MAPK/Erk pathway downstream of alpha2beta1 integrin, which has a functional role in regulating Fas-mediated apoptosis in T lymphocytes. As such, this study emphasizes the potential importance that Coll I interactions may have on the control of T lymphocyte homeostasis and their persistence in chronic inflammatory diseases.

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.

Okadaic acid induces sustained activation of NFkappaB and degradation of the nuclear IkappaBalpha in human neutrophils

Human neutrophils differ from other cells by containing high amount of IkappaBalpha in the nucleus, and this increased nuclear IkappaBalpha accumulation is associated with the inhibition of NFkappaB activity and increased apoptosis. However, the mechanisms regulating NFkappaB activation and IkappaBalpha degradation in human neutrophils are little understood. The objective of this study was to provide a further insight into the mechanisms regulating NFkappaB activity and IkappaBalpha degradation in human neutrophils. We show that okadaic acid (OA), an inhibitor of protein phosphatases PP1 and PP2A, induces sustained activation of NFkappaB and degradation of the nuclear IkappaBalpha, and increases interleukin-8 expression in the neutrophils. Furthermore, inhibitors of protein kinase C-delta (PKCdelta) and IkappaB kinase (IKK) inhibit the OA-induced activation of NFkappaB. Collectively, our results indicate that in human neutrophils, the sustained activation of NFkappaB is regulated by a continuous phosphorylation and degradation of the nuclear IkappaBalpha.

Activation of the ERK and JNK signaling pathways caused by neuron-specific inhibition of PP2A in transgenic mice

A reduced activity of protein phosphatase 2A (PP2A) has been shown in brains of patients with Alzheimer's disease (AD), a neurodegenerative disorder characterized histopathologically by amyloid plaques and neurofibrillary tangles. Tau, as the principal component of neurofibrillary tangles, can be hyperphosphorylated by a reduced activity of PP2A in vitro and by pharmacological approaches, suggesting a crucial role of PP2A in tangle formation. To dissect the role of PP2A in vivo, we previously generated transgenic mice with chronically reduced PP2A activity by expressing a dominant-negative mutant form of the PP2A catalytic subunit Calpha, L199P, under the control of a neuron-specific promoter. In these mice, endogenous tau is phosphorylated at the epitopes Ser202/Thr205 and Ser422. In vitro, these tau phospho-epitopes can be phosphorylated by the kinases ERK and JNK, and the kinases themselves are negatively regulated by PP2A. In this study, we show that chronic inhibition of PP2A activity in L199P transgenic mice causes the activation of ERK and JNK as demonstrated by the phosphorylation and nuclear accumulation of the ERK and JNK substrates, Elk-1 and c-Jun. TUNEL staining revealed that activated JNK signaling was not associated with cell death. Our findings imply that PP2A is a negative regulator of the ERK and JNK signaling pathways in vivo, suggesting that in AD, tau hyperphosphorylation may be caused in part by PP2A dysfunction.

Interleukin-10-induced CCR5 expression in macrophage like HL-60 cells: involvement of Erk1/2 and STAT-3

As an immunosuppressive and anti-inflammatory cytokine, IL-10 was recently reported to play roles in CCR5 expression in human monocytes. CCR5 promoter regions contain Oct-2, TCF-1alpha, GATA, and STAT binding sites. Here, we studied the signals involved in the CCR5 expression in IL-10-stimulated cells using the HL-60 cell line. HL-60 cells were stimulated with PMA and differentiated to macrophage-like cells, then stimulated with IL-10. IL-10 induced significant expression of CCR5 protein and CCR5 mRNA in these cells. The induction of CCR5 by IL-10 was inhibited by a MEK-1 inhibitor, PD98059. In addition, IL-10 induced tyrosine (Tyr) phosphorylation of Erk, as well as serine (Ser) and Tyr phosphorylation of STAT-3. Tyr phosphorylation of Erk and Ser phosphorylation of STAT-3 were inhibited by PD98059, while Tyr phosphorylation of STAT-3 was not inhibited by PD98059. DNA binding activity of STAT-3 was observed by the stimulation with IL-10, which was inhibited by PD98059. These results first indicate that Erk1/2 and STAT-3 regulate CCR5 expression, and that Erk-mediated phosphorylation of Ser is required for full stimulation of STAT-3 in CCR5 expression.

PP2A activation by beta2-adrenergic receptor agonists: novel regulatory mechanism of keratinocyte migration

Understanding the mechanisms that regulate cell migration is important for devising novel therapies to control metastasis or enhance wound healing. Previously, we demonstrated that beta2-adrenergic receptor (beta2-AR) activation in keratinocytes inhibited their migration by decreasing the phosphorylation of a critical promigratory signaling component, the extracellular signal-related kinase (ERK). Here we demonstrate that beta2-AR-induced inhibition of migration is mediated by the activation of the serine/threonine phosphatase PP2A. Pretreating human keratinocytes with the PP2A inhibitor, okadaic acid, prevented the beta2-AR-induced inhibition of migration, either as isolated cells or as a confluent sheet of cells repairing an in vitro "wound" and also prevented the beta2-AR-induced reduction in ERK phosphorylation. Similar results were obtained with human corneal epithelial cells. In keratinocytes, immunoprecipitation studies revealed that beta2-AR activation resulted in the rapid association of beta2-AR with PP2A as well as a 37% increase in association of PP2A with ERK2. Finally, beta2-AR activation resulted in a rapid and transient 2-fold increase in PP2A activity. Thus, we provide the first evidence that beta2-AR activation in keratinocytes modulates migration via a novel pathway utilizing PP2A to alter the promigratory signaling cascade. Exploiting this pathway may result in novel therapeutic approaches for control of epithelial cell migration.

FAK overexpression upregulates cyclin D3 and enhances cell proliferation via the PKC and PI3-kinase-Akt pathways

We previously demonstrated that FAK-transfected HL-60 (HL-60/FAK) cells exhibit anti-apoptotic capacity. Here, we report that HL-60/FAK cells proliferate much faster than vector-transfected control (HL-60/Vect) cells with a 1.5-fold faster doubling time. This observation prompted us to investigate the mechanism of how HL-60/FAK cells augment cell proliferation. Since a protein kinase C (PKC) inhibitor, chelerythrine, or a PI3-kinase inhibitor, LY294002, suppressed cell proliferation effectively, both PKC and PI-3-kinase pathways are presumed to be involved in the cell proliferation. Among cyclins and CDKs, cyclin D3 expression was particularly prominent in the HL-60/FAK cells. Among PKC family, particularly PKCalpha, beta and eta isoforms were activated and directly associated with FAK in HL-60/FAK cells. We assumed that FAK activates PKC and PI3-kinase-Akt pathway, which resulted in marked induction of cyclin D3 expression and CDK activity.

TRAF6 and C-SRC induce synergistic AP-1 activation via PI3-kinase-AKT-JNK pathway

Interleukin-1 (IL-1) induces multiple genes via activation of transcription factors that include NF-kappa B and activator protein-1 (AP-1). We found that IL-1-mediated c-Src activation was required for AP-1 activation, but not for NF-kappa B activation and also revealed that c-Src-induced AP-1 activation was enhanced synergistically by the coexpression of TNF receptor associated factor 6 (TRAF6). In addition, c-Src interacts with TRAF6 in response to IL-1 and this interaction is required for c-Src activity. However, neither dominant negative mutants of TRAF6 (TRAF6 DN) nor kinase-dead mutant of c-Src (c-Src KD) counteracted each-induced AP-1 activation, suggesting no hierarchy between these two molecules. During the TRAF6 and c-Src-induced AP-1 activation, phosphatidylinositol 3 (PI3)-kinase, its downstream signaling molecule, Akt and c-Jun N-terminal kinase (JNK) were significantly activated and inhibition of these kinase activities down-regulated AP-1 activation through the suppression of c-fos expression. Furthermore, TRAF6 and c-Src-induced JNK activation was significantly inhibited by PI3-kinase inhibitor or a dominant negative mutant of Akt (Akt DN). Taken together, our results demonstrate that c-Src and TRAF6 are key mediators of IL-1-induced AP-1 activation and provide evidence of cross talk between c-Src and TRAF6 molecules through PI3 kinase-Akt-JNK pathways.