The IKK/NF-κB pathway:

Cell‐Based Assays Using Primary Endothelial Cells to Study Multiple Steps in Inflammation

Cell-based assays are powerful tools for drug discovery and provide insight into complex signal transduction pathways in higher eukaryotic cells. Information gleaned from assays that monitor a cellular phenotype can be used to elucidate the details of a single pathway and to establish patterns of cross talk between pathways. By selecting the appropriate cell model, cell-based assays can be used to understand the function of a specific cell type in a complex disease process such as inflammation. We have used human umbilical vein endothelial cells to establish three cell-based, phenotypic assays that query different stages of a major signaling pathway activated in inflammation. One assay analyzes the tumor necrosis factor alpha (TNFalpha)-induced translocation of the transcription factor NF-kappaB from the cytoplasm into the nucleus 20 min after stimulation with TNFalpha. Two more assays monitor the expression of E-selectin and VCAM-1, 4 and 24 h after stimulation with TNFalpha. Indirect immunofluorescence and high-throughput automated microscopy were used to analyze cells. Imaging was performed with the IN Cell Analyzer 3000. All assays proved to be highly robust. Z' values between 0.7 and 0.8 make each of the three assays well suited for use in high-throughput screening for drug or probe discovery.

Alterations in Cell Signaling in Sepsis

Multiple intracellular signaling pathways involving kinases, transcriptional factors, and the expression of immunoregulatory mediators are altered in sepsis. Recent data have shown stable patterns of activation among peripheral blood mononuclear cells and neutrophils in healthy human subjects. Although polymorphisms in Toll-like receptors play a contributory role in determining cellular activation, other factors are involved as well. Increased activation of the mitogen-activated protein kinase protein 38, Akt, and nuclear factor (NF)-kappa B in neutrophils and other cell populations obtained at early time points in the clinical course of sepsis-induced acute lung injury or after accidental trauma is associated with a more-severe clinical course, suggesting that a proinflammatory cellular phenotype contributes to organ system dysfunction in such settings. Identification of patients with cellular phenotypes characterized by increased activation of NF-kappa B, Akt, and protein 38, as well as discrete patterns of gene activation, may permit identification of patients with sepsis who are likely to have a worse clinical outcome, thereby permitting early institution of therapies that modulate deleterious signaling pathways before organ system dysfunction develops, reducing morbidity and improving survival.

The C-terminal activating region 2 of the Epstein-Barr virus-encoded latent membrane protein 1 activates NF-kappaB through TRAF6 and TAK1

Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) is oncogenic and indispensable for EBV-mediated B cell transformation. LMP1 is capable of activating several intracellular signaling pathways including the NF-kappaB pathway, which contributes to the EBV-mediated cell transformation. Two regions in the cytoplasmic carboxyl tail of LMP1, namely C-terminal activating regions 1 and 2 (CTAR1 and CTAR2), are responsible for NF-kappaB activation, with CTAR2 being the main NF-kappaB activator. Although the CTAR1-mediated NF-kappaB activation was previously shown to be TRAF3-dependent, we showed here that the CTAR2-mediated NF-kappaB activation is mainly TRAF6-dependent but TRAF2/5-independent. In contrast to the interleukin-1 receptor/toll-like receptor-mediated NF-kappaB pathways, the CTAR2-mediated NF-kappaB pathway does not require MyD88, IRAK1, or IRAK4 for TRAF6 engagement. Furthermore, we showed that TAK1 is required for NF-kappaB activation by LMP1. Thus, LMP1 utilizes two distinct pathways to activate NF-kappaB: a major one through CTAR2/TRAF6/TAK1/IKKbeta (canonical pathway) and a minor one through CTAR1/TRAF3/NIK/IKKalpha (noncanonical pathway).

The NF-κB pathway blockade by the IKK inhibitor PS1145 can overcome Imatinib resistance

Imatinib represents at present the most attractive therapy for BCR-ABL positive leukemias, even though a percentage of CML patients develop resistance to this compound. For these resistant patients a therapeutic approach based on a combination of drugs is more likely to be effective. In the last years, constitutive NF-kappaB/Rel activity has been demonstrated in several hematological malignancies. As a result, NFkB/Rel-blocking approaches have been proposed as antineoplastic strategies. Furthermore, the identification of specific kinases within the NF-kappaB activation pathway offers a selective target to address tailored therapies. In the current study, we show that the IKK inhibitor PS1145 is able to inhibit the proliferation of CML cell lines and primary BM cells. Moreover, the addition of Imatinib increases the effects of PS1145 in resistant cell lines and BM cells from resistant patients, with a further increase of apoptosis and inhibition of proliferation and colony growth. Our data provide the rational for a new therapeutic approach, which combines Imatinib and the IKK inhibitor PS1145 in CML resistant patients.

The Anti-Death Machinery in IKK/NF-κB Signaling

The most extensively studied function of NF-kappaB is its ability to promote cell survival through induction of target genes, whose products inhibit various aspects of the apoptotic machinery in both normal and malignant cells. Recent studies, however, indicate that NF-kappaB activation can also suppress programmed necrosis through induction of genes encoding anti-oxidant proteins. Since tumor cells often use NF-kappaB pathway as a shield to escape the killing of conventional anti-cancer therapies, intervention of IKK/NF-kappaB signaling would be a promising option to improve the efficacy of cancer treatment.

The ethyl pyruvate analogues, diethyl oxaloproprionate, 2-acetamidoacrylate, and methyl-2-acetamidoacrylate, exhibit anti-inflammatory properties in vivo and/or in vitro

Ethyl pyruvate (EP) is a simple aliphatic ester derived from the endogenous metabolite, pyruvic acid. EP has been shown to decrease the expression of various pro-inflammatory mediators, including nitric oxide (NO*), tumor necrosis factor (TNF), cyclooxygenase-2, and interleukin (IL)-6, in a variety of in vitro and in vivo model systems. In an effort to better understand the chemical features that might explain the anti-inflammatory properties of EP, we screened 15 commercially available compounds for cytoprotective or anti-inflammatory effects using two in vitro assay systems: TNF and NO* production by lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophage-like cells and changes in the permeability of Caco-2 human enterocyte-like monolayers stimulated with a cocktail of pro-inflammatory cytokines called cytomix (1000U/ml IFN-gamma plus 10ng/ml TNF-alpha plus 1ng/ml IL-1beta). Two compounds, namely diethyl oxaloproprionate (DEOP) and 2-acetamidoacrylate (2AA), demonstrated consistent anti-inflammatory or cytoprotective pharmacological properties in this screening process. Treatment of mice with either of these compounds ameliorated LPS-induced ileal mucosal hyperpermeability to the fluorescent probe, fluorescein isothiocyanate-labeled dextran (average molecular mass 4kDa), and bacterial translocation to mesenteric lymph nodes. Treatment with either of these compounds also improved survival in mice challenged with a lethal dose of LPS. Finally, in a study that compared 2AA to its methyl ester, we showed that methyl-2-acetamidoacrylate is at least 100-fold more potent than the parent carboxylate as an inhibitor of LPS-induced NO* production by RAW 264.7 cells. Collectively, these data are consistent with the view that anti-inflammatory activity is demonstrable for a number of compounds that either incorporate an olefinic linkage conjugated to a carbonyl moiety or are capable of undergoing tautomeric rearrangement to form such a structure. Moreover, our findings suggest that esters with these general characteristics, perhaps because of their greater lipophilicity or electrophilicity, are more potent anti-inflammatory agents than are the parent carboxylates.

Reoxygenation of hypoxic mice with 100% oxygen induces brain nuclear factor-kappa B

Oxidative stress is closely related to inflammation, a pathologic process characterized by activation of the transcriptional factor nuclear factor-kappa B (NF-kappaB). We have used transgenic NF-kappaB luciferase reporter mice to assess brain NF-kappaB activity noninvasively in living mice. We have studied NF-kappaB activation in hypoxic mice reoxygenated with either 21% O2 (room air) or 100% O2. Forty-one mice exposed for 2 h to 4% oxygen and then randomized to reoxygenation with pure oxygen or room air were investigated. A control mouse was dedicated to every mouse exposed to hypoxia. In vivo luminescence originated from brain was measured from mice 2 d before hypoxia, and 3 h after reoxygenation. A change in luminescence between the mouse exposed to hypoxia and its control demonstrates an alteration in NF-kappaB activity. Because of high mortality among males, only females were included. Six female mice died. Nineteen female mice were reoxygenated with room air, 16 with pure oxygen. We observed a significantly higher luminescence in the brain of the 100% O2 group versus the 21% O2 group. Our data indicate that brain NF-kappaB activity is increased in mice subjected to 4% oxygen followed by reoxygenation with 100% oxygen. However, when reoxygenation occurs with 21% O2 (room air), no elevation in NF-kappaB activity is observed. Thus, reoxygenation with room air may induce less brain inflammation than reoxygenation with pure oxygen.

Inhibition of IKK-2 by 2-[(aminocarbonyl)amino]-5-acetylenyl-3-thiophenecarboxamides

A series of 21 novel 2-[(aminocarbonyl)amino]-5-acetylenyl-3-thiophenecarboxamides were synthesized and evaluated for the inhibition of IKK-2. In spite of their often modest activity on the enzyme, six selected analogs showed significant inhibition of the production of inflammatory cytokine IL-8 in IL-1beta stimulated rheumatoid arthritis-derived synovial fibroblasts, demonstrating their potential usefulness as NF-kappaB regulators.

Adenovirus-mediated gene transfer of mutated IkappaB kinase and IkappaBalpha reveal NF-kappaB-dependent as well as NF-kappaB-independent pathways of HAS1 activation

It has become increasingly clear that hyaluronan is more than the simple matrix molecule it was once thought to be but instead takes part in a multitude of biological functions. Three genes encode for hyaluronan synthases (HAS). We demonstrated earlier that HAS2 and HAS3 are constitutively activated in type-B synoviocytes (fibroblast-like synoviocytes) and, furthermore, that the only gene that readily responds to stimulation with a series of proinflammatory cytokines is HAS1. Here we probe the involvement of the transcription factor NF-kappaB in induced and noninduced HAS activation. Transforming growth factor (TGF) beta1 as well as interleukin (IL)-1beta are both strong inducers of HAS1 transcription. Stimulation of fibroblast-like synoviocytes with IL-1beta resulted in rapid degradation of IkappaBalpha, an event that was preceded by IkappaBalpha phosphorylation. Interestingly, TGFbeta1 neither affected IkappaBalpha levels, nor did it cause phosphorylation of IkappaBalpha. In addition, TGFbeta1 had no effect on IkappaBbeta and IkappaBepsilon levels. Electrophorectic mobility shift assays demonstrate that IL-1beta is a potent inducer of NF-kappaB translocation; however, TGFbeta1 treatment did not result in shifting bands. Two adenovirus constructs were used to further clarify differences in TGFbeta1- and IL-1beta-induced HAS1 activation. Overexpressing IkappaBalpha completely abolished the IL-1beta effect on HAS1 but did not interfere with TGFbeta1-induced HAS1 mRNA accumulation. Identical results were obtained when a dominant negative IKK was overexpressed. Interestingly, neither overexpression of IkappaBalpha nor of IKK had any effect on HAS2 and HAS3 mRNA levels. Taken together, HAS1 can be activated by distinct pathways; IL-1beta utilizes NF-kappaB, and TGFbeta1 does not. Furthermore, HAS2 and HAS3 are activated without the involvement of NF-kappaB.

Human serum from patients with septic shock activates transcription factors STAT1, IRF1, and NF-kappaB and induces apoptosis in human cardiac myocytes

Proinflammatory cytokines have been linked to depression of myocardial contractility in vivo in patients with acute septic shock and in vitro models employing isolated myocytes exposed to serum from such patients. The key pathways involved in mediating this septic organ dysfunction (cell adhesion molecule expression, inducible nitric-oxide synthase induction, and apoptosis) are known to be regulated by transcription factors STAT1, IRF1, and NF-kappaB. Utilizing a model that mimics human disease, we have demonstrated activation of the transcription factors STAT1, IRF1, and NF-kappaB in human fetal myocytes exposed to human septic serum. Both reporter and electrophoretic mobility shift assays demonstrated a 5-19-fold increase in activation of transcription factors STAT1, IRF1, and NF-kappaB in response to incubation with human septic serum. The addition of human septic serum to human fetal myocytes induced apoptosis in human fetal myocytes and activation of the mitogen-activated protein kinase c-Jun NH -terminal kinase and caspase 1 as measured by Western blot. These data suggest that transcription factor activation and early myocyte apoptosis play a mechanistic role in septic myocardial depression and sepsis-induced organ dysfunction.

Topical vitamin C: a useful agent for treating photoaging and other dermatologic conditions

BACKGROUND

Cosmeceuticals containing antioxidants are among the most popular antiaging remedies. Topically applied antioxidants exert their benefits by offering protection from damaging free radicals produced when skin is exposed to ultraviolet light or allowed to age naturally. Vitamin C is a naturally occurring potent water-soluble antioxidant. Accordingly, it has been incorporated into a variety of cosmeceuticals designed to protect and rejuvenate photoaged skin.

OBJECTIVE

This article reviews the scientific data and clinical studies supporting the use of topically applied vitamin C for treating photoaged skin. Other innovative uses for vitamin C cosmeceuticals are also discussed.

CONCLUSION

A significant body of scientific research supports the use of cosmeceuticals containing vitamin C. Cutaneous benefits include promoting collagen synthesis, photoprotection from ultraviolet A and B, lightening hyperpigmentation, and improvement of a variety of inflammatory dermatoses. Because of the diverse biologic effects of this compound, topical vitamin C has become a useful part of the dermatologist's armamentarium.

Angiotensin II induces the expression of tissue factor and its mechanism in human monocytes

The renin-angiotensin system (RAS) is linked with the vascular motion and the secretion of aldosterone. The purpose of the present study was to elucidate whether angiotensin II (Ang II) induces monocytes (Mo) to express tissue factor (TF) and if Ang II subtype 1 receptor (AT1R) antagonists inhibit the effect of Ang II. The roles of different intracellular signal transduction pathways and IkappaB/NF-kappaB in Ang II-induced TF expression of Mo were also studied to explore the mechanisms involved. Mo were isolated from heparinized human blood by a two-step gradient centrifugation, cultured in RPMI-1640 and exposed to Ang II and other test reagents. Mo TF activity and TF antigen were determined with a one-stage clotting method and ELISA, respectively, after the culture. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the TF mRNA levels in Mo. The level of IkappaBalpha in Mo was detected by Western blot analysis. Electrophoresis mobility shift assay (EMSA) was performed to evaluate the binding activity of NF-kappaB in Mo. The experiment results are as follows: (1) Ang II (10(-10)-10(-7) M) induced Mo to express TF activity but had no marked effect on other mononuclear cells. Ang II 10(-10)-10(-7) M) also caused increased TF mRNA expression and TF antigen from Mo in a dose-dependent manner. The TF antigen of Mo was elevated at 4 h after Mo was exposed to Ang II (10(-7) M) in culture, reached the peak at 6 h, and then declined from 12 h. The changes of TF activity were positively correlated with those of TF antigen. TF mRNA expression was elevated at 1 h, peaked at 3 h, and declined after 8 h. (2) Losartan (10(-6)-10(-5) M) significantly inhibited the stimulative effects of Ang II on TF activity, TF antigen and TF mRNA in Mo in a dose-dependent manner. (3) The protein kinase C (PKC) inhibitor, staurosporine, and the protein tyrosine kinase (PTK) inhibitor, genistein, both lowered TF levels in Mo, but the inhibitory effect of staurosporine was stronger than that of genistein. The effect of mitogen-activated protein kinase (MAPK) inhibitor, U0126, on monocytic TF expression was not significant. (4) Western blot analysis revealed that after Ang II (10(-7) M)exposure, levels of IkappaBalpha began to decrease at 15 min, reached a nadir at 60 min (P<.01), and recovered at 180 min. (5) EMSA showed that NF-kappaB binding activity started to increase at 15 min, reached a peak at 60 min, and returned to baseline at 180 min. The present data suggest that Ang II can directly induce TF expression in human Mo and this effect is mediated by AT1R. PKC may play the most important role in Ang II-induced TF expression among the three signal pathways detected. In addition, activation of NF-kappaB is also involved in the TF expression of Mo induced by Ang II.

Type 1 diabetes is associated with increased cyclooxygenase- and cytokine-mediated inflammation

OBJECTIVE

The extent of involvement of cyclooxygenase (COX)-mediated inflammation in type 1 diabetes is unknown, and the association between the COX- and cytokine-mediated inflammatory responses in type 1 diabetes is not fully understood.

RESEARCH DESIGN AND METHODS

Plasma high-sensitivity C-reactive protein (CRP), 24-h urinary and plasma 15-keto-dihydro-prostaglandin F(2alpha) (a metabolite of prostaglandin F(2alpha) [PGF(2alpha)] and an indicator of COX-mediated inflammation), serum amyloid protein A (SAA), and interleukin (IL)-6 (indicators of inflammation) were measured in 38 subjects with type 1 diabetes and 41 healthy age- and sex-matched control subjects.

RESULTS

The inflammatory indicators (urinary 15-keto-dihydro-PGF(2alpha), P < 0.01; IL-6, P < 0.04) were increased in men with diabetes. CRP and SAA did not show any significant difference between the diabetic and the control subjects. Urinary levels of 15-keto-dihydro-PGF(2alpha) correlated with the degree of glycemic control, HbA(1c) (r = 0.42, P < 0.0005). No correlation was found between the duration of diabetes and the inflammatory biomarkers or metabolic measurements.

CONCLUSIONS

These results suggest that an early low-grade inflammatory process reflected by elevated levels of PGF(2alpha) and IL-6 is involved in type 1 diabetes. Thus, both COX- and cytokine-mediated inflammatory pathways are significantly related to type 1 diabetes.

Ethacrynic acid inhibits multiple steps in the NF-kappaB signaling pathway

Ethacrynic acid has been used as a safe and effective diuretic for more than 30 years. In this study, we tested the hypothesis that ethacrynic acid is also an anti-inflammatory agent that inhibits signaling by the proinflammatory transcription factor NF-kappaB. We showed that ethacrynic acid inhibited luciferase expression in lipopolysaccharide-stimulated macrophage-like RAW 264.7 cells transfected with an NF-kappaB-dependent luciferase reporter vector and also inhibited NF-kappaB DNA binding in lipopolysaccharide-stimulated RAW 264.7 cells (electrophoretic mobility shift assay). Ethacrynic acid inhibited degradation of IkappaBalpha and IkappaBbeta in lipopolysaccharide-stimulated RAW 264.7 cells. Ethacrynic acid impaired DNA binding of wild-type p65 subunits of NF-kappaB in cells. However, DNA binding of a Cys--> Ser p65 mutant was not inhibited by ethacrynic acid, suggesting that ethacrynic acid inhibits DNA binding by alkylating p65 at Cys. In a cell-free system, binding of p50 homodimers to an NF-kappaB consensus sequence was inhibited by ethacrynic acid at concentrations from 10 to 100 microM, indicating that ethacrynic acid probably also covalently modifies the p50 subunit. These data indicate that ethacrynic acid inhibits activation of the NF-kappaB pathway at multiple points and suggest that this well-studied drug warrants further investigation as a potential therapeutic for various conditions that are associated with excessive inflammation.

The intriguing biology of the tumour necrosis factor/tumour necrosis factor receptor superfamily: players, rules and the games

The members of the tumour necrosis factor (TNF)/tumour necrosis factor receptor (TNFR) superfamily are critically involved in the maintenance of homeostasis of the immune system. The biological functions of this system encompass beneficial and protective effects in inflammation and host defence as well as a crucial role in organogenesis. At the same time, members of this superfamily are responsible for host damaging effects in sepsis, cachexia, and autoimmune diseases. This review summarizes recent progress in the immunobiology of the TNF/TNFR superfamily focusing on results obtained from animal studies using gene targeted mice. The different modes of signalling pathways affecting cell proliferation, survival, differentiation, apoptosis, and immune organ development as well as host defence are reviewed. Molecular and cellular mechanisms that demonstrate a therapeutic potential by targeting individual receptors or ligands for the treatment of chronic inflammatory or autoimmune diseases are discussed.

Increased expression of toll-like receptor-2 and -4 on leukocytes from patients with sepsis

The reduced responsiveness of monocytes or granulocytes toward endotoxin (endotoxin tolerance) during sepsis may depend on Toll-like receptors (TLR). The expression of TLR-2 and TLR-4 was measured on neutrophils (PMN) and monocytes from patients with sepsis (n = 21) or healthy controls (n = 12). Leukocytes (1 x 10/mL) were incubated at 37 degrees C with or without a TLR-4 (LPS 1 microg/mL) or a TLR-2 ligand (MALP-2 2 nM). Surface expression of TLR-2 and TLR-4 at 0, 4, and 16 h was determined in FACS after staining with specific antibodies. The release of IL-8 and TNF-alpha was measured by ELISA. Freshly isolated PMN from patients with sepsis exhibited significantly (P < 0.05) higher mean fluorescence for TLR-2 (78.0 +/- 18.6) and TLR-4 (11.4 +/- 2.3) than controls (12.8 +/- 2.2 and 2.3 +/- 0.4). Similarly, monocytes from patients exhibited higher TLR-2 and TLR-4 expression (300.8 +/- 40.6 and 92.7 +/- 12.1) than cells from controls (149.5 +/- 27.1 and 52.2 +/- 7.6). In patients with sepsis, expression of TLR-2 and TLR-4 on PMN increased during 16 h of incubation (106.2 +/- 22.1 and 34.5 +/- 5.3), whereas it remained unchanged in controls (19.3 +/- 6.1 and 5.4 +/- 1.9). Incubation with LPS or MALP-2 had no effect on TLR-4 or TLR-2 expression in cells from either controls or patients. Despite increased TLR expression in cells from patients with sepsis, the endotoxin-induced release of TNF-alpha and IL-8 was indistinguishable from that in controls. Therefore, the endotoxin tolerance seen in patients with sepsis does not depend solely on TLR-2 or TLR-4 expression, and other mechanisms must be involved.

Inhibition of IKK down-regulates antigen + IgE-induced TNF production by mast cells: a role for the IKK-IκB-NF-κB pathway in IgE-dependent mast cell activation

Mast cells (MC) are major effector cells for allergic diseases. Cross-linking of immunoglobulin E (IgE) and its high-affinity receptor, FcepsilonRI, by antigen initiates a cascade of signaling events leading to nuclear factor (NF)-kappaB activation and tumor necrosis factor (TNF) production. Here, we demonstrated that inhibition of inhibitor of kappaB (IkappaB) kinase (IKK) by a peptide IKK inhibitor or by four individual chemical IKK inhibitors including 15-deoxy-prostaglandin J(2), BMS-345541, SC-514, or sulindac significantly blocked IgE + trinitrophenyl (TNP)-induced TNF production by mouse bone marrow-derived MC (BMMC). Moreover, IgE + TNP induced a rapid phosphorylation of IKKalpha but not IKKbeta in BMMC. IgE + TNP-induced phosphorylation of IKKalpha was accompanied with phosphorylation and degradation of IkappaBalpha, subsequent NF-kappaB activation, and TNF production. Inhibition of IKK by sulindac decreased IKKalpha phosphorylation, IkappaBalpha phosphorylation and degradation, NF-kappaB activation, and TNF production by BMMC. It is interesting that IgE + TNP stimulation also induced a prominent synthesis of IKKalpha and IkappaBalpha. Inhibition of NF-kappaB activity by pyrrolidine dithiocarbomate (PDTC) blocked IgE + TNP-induced IkappaBalpha synthesis. NF-kappaB activity and TNF production were also inhibited when PDTC was used even after IgE + TNP stimulation, suggesting a potential role for the newly synthesized IkappaBalpha in MC activation. In addition, IgE + TNP-induced IKKalpha and IkappaBalpha phosphorylation was inhibited by a protein kinase C (PKC) inhibitor Ro 31-8220. Taken together, our results support a role for the IKK-IkappaB-NF-kappaB pathway, which likely involves PKC in IgE-dependent TNF production by MC. Thus, IKK may serve as a new target for the regulation of MC function in allergy.

Cyclic mechanical strain inhibits skeletal myogenesis through activation of focal adhesion kinase, Rac-1 GTPase, and NF-kappaB transcription factor

Myogenesis is a multistep developmental program that generates and regenerates skeletal muscles. Several extracellular factors have been identified that participate in the regulation of myogenesis. Although skeletal muscles are always subjected to mechanical stress in vivo, the role of mechanical forces in the regulation of myogenesis remains unknown. We have investigated the molecular mechanisms by which cyclic mechanical strain modulates myogenesis. Application of cyclic mechanical strain using the computer-controlled Flexcell Strain Unit increased the proliferation of C2C12 cells and inhibited their differentiation into myotubes. Cyclic strain increased the activity of cyclin-dependent kinase 2 (cdk2) and the cellular level of cyclin A, and inhibited the expression of myosin heavy chain and formation of myotubes in C2C12 cultures. The activity of nuclear factor-kappa B (NF-kappaB) transcription factor and the expression of NF-kappaB-regulated genes, cyclin D1 and IL-6, were augmented in response to mechanical strain. Cyclic strain also increased the activity of Rho GTPases, especially Rac-1. The inhibition of Rho GTPases activity, by overexpression of Rho GDP dissociation inhibitor (Rho-GDI), inhibited the strain-induced activation of NF-kappaB in C2C12 cells. Overexpression of either NF-kappaB inhibitory protein IkappaBalphaDeltaN (a degradation resistant mutant IkappaBalpha) or Rho-GDI blocked the strain-induced proliferation of C2C12 cells. Furthermore, overexpression of FRNK, a dominant negative mutant of focal adhesion kinase (FAK), inhibited the strain-induced proliferation of C2C12 cells. Our study demonstrates that cyclic mechanical strain inhibits myogenesis through the activation of FAK, Rac-1, and NF-kappaB.

NF-kappaB: a multifaceted transcription factor regulated at several levels

NF-kappaB is a generic name for an evolutionarily conserved transcription-factor system that contributes to the mounting of an effective immune response but is also involved in the regulation of cell proliferation, development, and apoptosis. The implication of NF-kappaB in central biological processes and its extraordinary connectivity to other signaling pathways raise a need for highly controlled regulation of NF-kappaB activity at several levels. While all NF-kappaB activation pathways share a central and critical proteasome-mediated step that leads to the degradation of inhibitory proteins and the release of DNA-binding subunits, there is evidence for a downstream level of NF-kappaB regulation that employs several mechanisms. These include promoter-specific exchange of dimers and modification of the transactivating p65 subunit by phosphorylation, acetylation, ubiquitination, or prolyl isomerization. The signaling pathways and enzymes controlling this second level of regulation and their potential use as therapeutic targets for the treatment of NF-kappaB-associated pathologies are discussed here.

Mechanotransduction by integrin is essential for IL-6 secretion from endothelial cells in response to uniaxial continuous stretch

We previously reported that uniaxial continuous stretch in human umbilical vein endothelial cells (HUVECs) induced interleukin-6 (IL-6) secretion via IkappaB kinase (IKK)/nuclear factor-kappaB (NF-kappaB) activation. The aim of the present study was to clarify the upstream signaling mechanism responsible for this phenomenon. Stretch-induced IKK activation and IL-6 secretion were inhibited by application of alpha(5)beta(1) integrin-inhibitory peptide (GRGDNP), phosphatidylinositol 3-kinase inhibitor (LY-294002), phospholipase C-gamma inhibitor (U-73122), or protein kinase C inhibitor (H7). Although depletion of intra- or extracellular Ca(2+) pool using thapsigargin (TG) or EGTA, respectively, showed little effect, a TG-EGTA mixture significantly inhibited stretch-induced IKK activation and IL-6 secretion. An increase in the intracellular Ca(2+) concentration ([Ca(2+)](i)) upon continuous stretch was observed even in the presence of TG, EGTA, or GRGDNP, but not in a solution containing the TG-EGTA mixture, indicating that both integrin activation and [Ca(2+)](i) rise are crucial factors for stretch-induced IKK activation and after IL-6 secretion in HUVECs. Furthermore, while PKC activity was inhibited by the TG-EGTA mixture, GRGDNP, LY-294002, or U-73122, PLC-gamma activity was retarded by GRGDNP or LY-294002. These results indicate that continuous stretch-induced IL-6 secretion in HUVECs depends on outside-in signaling via integrins followed by a PI3-K-PLC-gamma-PKC-IKK-NF-kappaB signaling cascade. Another crucial factor, [Ca(2+)](i) increase, may at least be required to activate PKC needed for NF-kappaB activation.

Ethyl Pyruvate Inhibits Nuclear Factor-κB-Dependent Signaling by Directly Targeting p65

Ethyl pyruvate has been shown to have anti-inflammatory properties in numerous cell culture and animal studies. In this series of experiments, we tested the hypothesis that ethyl pyruvate inhibits signaling by the pro-inflammatory transcription factor, NF-kappaB. Ethyl pyruvate inhibited luciferase expression in lipopolysaccharide-stimulated murine macrophage-like RAW 264.7 cells transfected with an NF-kappaB-dependent luciferase reporter vector. Ethyl pyruvate also decreased NF-kappaB DNA-binding activity in lipopolysaccharide-stimulated RAW 264.7 cells and decreased lipopolysaccharide-induced expression of an NF-kappaB-dependent gene, inducible nitric oxide synthase. Ethyl pyruvate had no effect on the degradation of IkappaBalpha or IkappaBbeta in lipopolysaccharide-stimulated RAW 264.7 cells, suggesting that ethyl pyruvate acts distally to this step in the activation of NF-kappaB. In a cell-free system, binding of p50 homodimers to an NF-kappaB consensus oligonucleotide sequence was unaffected by ethyl pyruvate over a wide range of concentrations, indicating that ethyl pyruvate probably does not modify or interact with the p50 subunit of NF-kappaB. In contrast, ethyl pyruvate inhibited DNA binding by ectopically overexpressed wild-type p65 homodimers. However, ethyl pyruvate failed to inhibit the DNA-binding activity of homodimers of an overexpressed mutant form of a p65 with substitution of serine for cysteine 38. Taken together, these results suggest that ethyl pyruvate inhibits DNA-binding by covalently modifying p65 at Cys(38). We conclude that some of the beneficial anti-inflammatory effects of ethyl pyruvate may be due to modification of p65, thereby inhibiting signaling via the NF-kappaB pathway.

IκB Kinase-β (IKKβ) Modulation of Epithelial Sodium Channel Activity

Using the yeast two-hybrid system, we identified a number of proteins that interacted with the carboxyl termini of murine epithelial sodium channel (ENaC) subunits. Initial screens indicated an interaction between the carboxyl terminus of beta-ENaC and IkappaB kinase-beta (IKKbeta), the kinase that phosphorylates Ikappabeta and results in nuclear targeting of NF-kappaB. A true two-hybrid reaction employing full-length IKKbeta and the carboxyl termini of all three subunits confirmed a strong interaction with beta-ENaC, a weak interaction with gamma-ENaC, and no interaction with alpha-ENaC. Co-immunoprecipitation studies for IKKbeta were performed in a murine cortical collecting duct cell line that endogenously expresses ENaC. Immunoprecipitation with beta-ENaC, but not gamma-ENaC, resulted in co-immunoprecipitation of IKKbeta. To examine the direct effects of IKKbeta on ENaC activity, co-expression studies were performed using the two-electrode voltage clamp technique in Xenopus oocytes. Oocytes were injected with cRNAs for alphabetagamma-ENaC with or without cRNA for IKKbeta. Co-injection of IKKbeta significantly increased the amiloride-sensitive current above controls. Using cell surface ENaC labeling, we determined that an increase of ENaC in the plasma membrane accounted for the increase in current. The injection of kinase-dead IKKbeta (K44A) in ENaC-expressing oocytes resulted in a significant decrease in current. Treatment of mpkCCD(c14) cells with aldosterone increased whole cell amounts of IKKbeta. Because this result suggested that aldosterone might activate NF-kappaB, mpkCCD(c14) cells were transiently transfected with a luciferase reporter gene responsive to NF-kappaB activation. Both aldosterone and tumor necrosis factor-alpha (TNFalpha) stimulation caused a similar and significant increase in luciferase activity as compared with controls. We conclude that IKKbeta interacts with ENaC by up-regulating ENaC at the plasma membrane and that the presence of IKKbeta is at very least permissive to ENaC function. These studies also suggest a previously unexpected interaction between the NF-kappaB transcription pathway and steroid regulatory pathways in epithelial cells.

IMMUNOMODULATION AND SEPSIS: IMPACT OF THE PATHOGEN

Infection begins when microorganisms overcome host barriers and multiply within host tissues. To contain the infection, the host mounts an inflammatory response that mobilizes defense systems and kills the invading microorganisms. A focal inflammatory response is usually sufficient to eradicate the organisms. However, when it fails to contain the infection, the organisms, their toxins, and numerous host mediators are released into the bloodstream, producing a systemic inflammatory response and organ failure. Microorganisms have coevolved with their hosts, thereby acquiring means of overcoming host defense mechanisms or even taking advantage of innate host responses. Many pathogens avoid recognition by the host or dampen host immune responses via sophisticated pathogen-host interactions. Some pathogens benefit from the inflammatory response. According to current hypotheses regarding the pathogenesis of sepsis, the host generates both an innate immune response identical for all pathogens and an adaptive pathogen-specific response. Determining whether the innate response benefits the pathogen or the host is essential for understanding host-pathogen interactions. In this review, we discuss how pathogens interfere with innate and adaptive immune responses to escape eradication by the host.

HTLV-I Tax induces a novel interaction between p65/RelA and p53 that results in inhibition of p53 transcriptional activity

Nuclear factor kappaB (NF-kappaB) activation plays a critical role in oncogenesis by human T-cell lymphotrophic virus type I (HTLV-I), the etiologic agent of adult T-cell leukemia (ATL), and is indispensable for maintenance of the malignant phenotype. In T lymphocytes, Tax-mediated p53 inhibition is dependent on Tax activation of the NF-kappaB pathway and is linked to p53 phosphorylation. We now report that blocking NF-kappaB transcriptional activation in HTLV-I-transformed cells restores p53 activity. Further, using mouse embryo fibroblast (MEF) null cells and antisense oligonucleotides to inhibit expression of NF-kappaB family members, we demonstrate that the p65 subunit of NF-kappaB is uniquely involved in p53 inhibition. Coimmunoprecipitation assays demonstrate an interaction between p65 and p53 in HTLV-I-transformed cells. In transient transfection assays, we demonstrate that Tax induces the p53-p65 interaction. Phosphorylation of p53 at serines 15 and 392 is critical for complex formation. Importantly, Tax-mediated p53 inhibition correlates with p65 and p53 interaction. By using chromatin immunoprecipitation (ChIP) assays, we find that in HTLV-I-transformed cells p53 and p65 form a complex on the inactive, p53-responsive murine double minute 2 (MDM2) promoter. Consistent with reduced transcriptional activity, transcription factor IID (TFIID) binding is not observed. These studies identify a unique mechanism for p53 regulation by the p65/RelA subunit of NF-kappaB.

TNAP, a novel repressor of NF-kappaB-inducing kinase, suppresses NF-kappaB activation

NF-kappaB-inducing kinase (NIK) has been implicated as an essential component of NF-kappaB activation. However, the regulatory mechanism of NIK signaling remains elusive. We have identified a novel NIK interacting protein, TNAP (for TRAFs and NIK-associated protein). In mammalian cells, TNAP physically interacts with NIK, TRAF2, and TRAF3 but not IKK1 or IKK2. TNAP specifically inhibits NF-kappaB activation induced by tumor necrosis factor (TNF)-alpha, TNF receptor 1, TRADD, RIP, TRAF2, and NIK but does not affect IKK1- and IKK2-mediated NF-kappaB activation. Knockdown of TNAP by lentiviral-mediated small interference RNA potentiates TNF-alpha-induced NF-kappaB activation. TNAP suppresses NIK kinase activity and subsequently reduces p100 processing, p65 phosphorylation, and IkappaBalpha degradation. These data suggest that TNAP is a repressor of NIK activity and regulates both the classical and alternative NF-kappaB signaling pathways.

Synthesis and structure–activity relationships of novel IKK-β inhibitors. Part 3: Orally active anti-inflammatory agents

A series of 2-amino-3-cyano-4-alkyl-6-(2-hydroxyphenyl)pyridine derivatives was synthesized and evaluated as I kappaB kinase beta (IKK-beta) inhibitors. Modification of a novel IKK-beta inhibitor 1 (IKK-beta IC(50)=1500 nM, Cell IC(50)=8000 nM) at the 4-phenyl ring and 6-phenol group on the pyridine core ring resulted in a marked increased in biological activities. An optimized compound, 2-amino-6-[2-(cyclopropylmethoxy)-6-hydroxyphenyl]-4-piperidin-4-yl nicotinonitrile, exhibited excellent in vitro profiles (IKK-beta IC(50)=8.5 nM, Cell IC(50)=60 nM) and a strong oral efficacy in in vivo anti-inflammatory assays (significant effects at 1mg/kg, po in arachidonic acid-induced ear edema model in mice).

Research: advances in cell biology relevant to critical illness

During the past decade, enormous advances have been made in cell biology. Major advances included the publication of the human genome sequence, the development of proteomics, and DNA microarray technologies and techniques to selectively "silence" genes using short strands of double-stranded RNA. Some areas of great progress that are particularly relevant to critical care medicine include huge improvements in our understanding of the signal transduction pathways involved in the innate immune response and adaptation to hypoxia. Other areas of important progress include improvements in our understanding of how inflammation causes derangements in epithelial structure and function and impairs cellular utilization of oxygen.

Formyl-Met-Leu-Phe induces calcium-dependent tyrosine phosphorylation of Rel-1 in neutrophils

Chemoattractant priming and activation of PMNs results in changes in cytosolic Ca2+ concentration, tyrosine kinase activity, and gene expression. We hypothesize that the initial signaling for the activation of a 105kDa protein (Rel-1) requires Ca2+-dependent tyrosine phosphorylation. A rapid and time-dependent tyrosine phosphorylation of Rel-1 occurred following formyl-Met-Leu-Phe (fMLP) stimulation of human PMNs at concentrations that primed or activated the NADPH oxidase (10(-9) to 10(-6)M), becoming maximal after 30s. Pretreatment with pertussis toxin (Ptx) or tyrosine kinase inhibitors abrogated this phosphorylation and inhibited fMLP activation of the oxidase. The fMLP concentrations employed also caused a rapid increase in cytosolic Ca2+ but chelation negated the effects, including the cytosolic Ca2+ flux, oxidase activation, and the tyrosine phosphorylation of Rel-1. Conversely, chelation of extracellular Ca2+ decreased the fMLP-mediated Ca2+ flux, had no affect on the oxidase, and augmented tyrosine phosphorylation of Rel-1. Phosphorylation of Rel-1 was inhibited when PMNs were preincubated with a p38 MAP kinase (MAPK) inhibitor (SB203580). In addition, fMLP elicited rapid activation of p38 MAPK which was abrogated by chelation of cytosolic Ca2+. Thus, fMLP concentrations that prime or activate the oxidase cause a rapid Ca2+-dependent tyrosine phosphorylation of Rel-1 involving p38 MAPK activation.

Fatiguing exercise reduces DNA binding activity of NF-kappaB in skeletal muscle nuclei

This study tested the hypothesis that skeletal muscle contraction activates nuclear factor-kappaB (NF-kappaB), a putative regulator of muscle protein breakdown. Muscle biopsies were obtained from the vastus lateralis of healthy humans before, immediately after, and 1 h after fatiguing resistance exercise of the lower limbs. Biopsies were analyzed for nuclear NF-kappaB DNA binding activity by using electrophoretic mobility shift assay. NF-kappaB activity, measured immediately after exercise, was less than preexercise activity; after 1-h recovery, activity returned to preexercise levels. In follow-up studies in adult mice, basal NF-kappaB activity varied among individual muscles. NF-kappaB activity in diaphragm fiber bundles was decreased after a 10-min bout of fatiguing tetanic contractions in vitro. NF-kappaB activity in soleus was increased by 12 days of unloading by hindlimb suspension; this increase was reversed by 10 min of fatiguing exercise. These data provide no support for our original hypothesis. Instead, acute fatiguing exercise appears to decrease NF-kappaB activity in muscle under a variety of conditions.

Vitamin A status significantly alters nuclear factor-kappaB activity assessed by in vivo imaging

Our study aimed to investigate, in vivo, the relationship between vitamin A status and NF-kappaB activity, a transcription factor central in regulating inflammatory and immune responses. We used a novel transgenic murine NF-kappaB-luciferase reporter model that enabled molecular imaging of NF-kappaB activity in live mice via an intensified image-capture apparatus. Whole-body luminescence, which reflects overall NF-kappaB activity, was elevated 2.2-fold in vitamin A-deficient (VAD) mice compared with control mice. Specifically, NF-kappaB activity in VAD mice was increased 1.8-fold in the lymph nodes and 1.4-fold in the thymus and, NF-kappaB induction in UVB radiation-exposed skin was also enhanced in VAD mice compared with control mice. The administration of all-trans retinoic acid to VAD mice resulted in a transient reduction in NF-kappaB activity and, conversely, a single dose of the RAR-pan-antagonist, AGN 194310, administered to control mice, led to a marked, transient induction of whole-body luminescence. Our results suggest that vitamin A status, and vitamin A itself, affects NF-kappaB activity in vivo and that the elevated NF-kappaB activity in VAD may be a mechanism underlying some of the features of VAD syndrome.

Protein kinase C family functions in B-cell activation

Members of the protein kinase C (PKC) family play important but distinct roles in B-cell activation, as demonstrated by emerging genetic and biochemical studies. PKCbeta is indispensable for B-cell antigen receptor (BCR)-induced NF-kappaB activation and B-cell survival. Recent evidence indicates that PKCbeta might regulate inhibitor of kappaB kinase (IKK) and NF-kappaB activation through interaction with the CARMA1/Bcl10/MALT signaling complex in BCR microdomains. By contrast, the novel PKC isoform PKCdelta is specifically required to maintain the tolerance of self-reactive B cells.

The puzzle of sepsis: fitting the pieces of the inflammatory response with treatment

Sepsis is a complex syndrome characterized by simultaneous activation of inflammation and coagulation in response to microbial insult. These events manifest as systemic inflammatory response syndrome (SIRS)/sepsis symptoms through release of proinflammatory cytokines, procoagulants, and adhesion molecules from immune cells and/or damaged endothelium.Conventional treatments have focused on source control, antimicrobials, vasopressors, and fluid resuscitation; however, a new treatment paradigm exists: that of treating the host response to infection with adjunct therapies including early goal directed therapy, drotrecogin alfa (activated), and immunonutrition. The multimechanistic drotrecogin alfa (activated) has been shown to reduce mortality in the severely septic patient when combined with traditional treatment. Therapies targeting improved oxygen and blood flow and reduction of apoptosis and free radicals are under investigation. Early sepsis diagnosis through detection of pro calcitonin, C reactive protein, sublingual CO2, and genetic factors may be beneficial. Ultimately, intervention timing may be the most important factor in reducing severe sepsis mortality.

Inhibition of NF-kappa B activation and its target genes by heparin-binding epidermal growth factor-like growth factor

Many cells upon injury mount extensive, compensatory responses that increase cell survival; however, the intracellular signals that regulate these responses are not completely understood. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) has been implicated as a cytoprotective agent. We have previously demonstrated that pretreatment of human intestinal epithelial cells with HB-EGF significantly decreased cytokine-induced activation of inducible NO synthase mRNA expression and NO production and protected the cells from apoptosis and necrosis. However, the mechanisms by which HB-EGF exerts these effects are not known. Here we show that cytokine exposure (IL-1beta and IFN-gamma) induced NF-kappaB activation and IL-8 and NO production in DLD-1 cells. Transient expression of a dominant negative form of IkappaBalpha decreased NO production, suggesting that the cytokines stimulated NO production in part through activation of NF-kappaB. HB-EGF dramatically suppressed NF-kappaB activity and IL-8 release and decreased NO production in cells pretreated with HB-EGF. HB-EGF blocked NF-kappaB activation by inhibiting IkappaB kinase activation and IkappaB phosphorylation and degradation, thus interfering with NF-kappaB nuclear translocation, DNA-binding activity, and NF-kappaB-dependent transcriptional activity. The data demonstrate that HB-EGF decreases inflammatory cytokine and NO production by interfering with the NF-kappaB signaling pathway. Inhibition of NF-kappaB may represent one of the mechanisms by which HB-EGF exerts its potent anti-inflammatory and cytoprotective effects.

Human T-cell lymphotropic virus type 1 tax induction of biologically Active NF-kappaB requires IkappaB kinase-1-mediated phosphorylation of RelA/p65

Activation of the NF-kappaB/Rel family of transcription factors proceeds through a catalytic complex containing IkappaB kinase (IKK)-1 and IKK2. Targeted disruption of each of the IKK genes suggests that these two kinases may mediate distinct functions in the activation pathway. In our studies of the human T-cell lymphotropic virus type 1 (HTLV-1) Tax oncoprotein, we have uncovered a new function of IKK1 required for complete activation of the NF-kappaB transcriptional program. In IKK1(-/-) murine embryonic fibroblasts (MEFs), Tax normally induced early NF-kappaB activation events. However, NF-kappaB induced by Tax in these IKK1(-/-) cells was functionally impaired. In IKK1(-/-) (but not wild-type) MEFs, Tax failed to activate several different kappaB reporter constructs or to induce the endogenous IkappaBalpha gene. In contrast, Tax normally activated the cAMP-responsive element-binding protein/activating transcription factor pathway, leading to full stimulation of an HTLV-1 long terminal repeat reporter construct in IKK1(-/-) cells. Furthermore, reconstitution of IKK1(-/-) cells with kinase-proficient (but not kinase-deficient) forms of IKK1 restored the Tax induction of full NF-kappaB transactivation. We further found that the defect in NF-kappaB action in IKK1(-/-) cells correlated with a failure of Tax to induce phosphorylation of the RelA/p65 subunit of NF-kappaB at Ser(529) and Ser(536). Such phosphorylation of RelA/p65 was readily detected in wild-type MEFs. Phosphorylation of Ser(536) was required for a complete response to Tax expression, whereas phosphorylation of Ser(529) appeared to be less critical. Together, these findings highlight distinct roles for the IKK1 and IKK2 kinases in the activation of NF-kappaB in response to HTLV-1 Tax. IKK2 plays a dominant role in signaling for IkappaBalpha degradation, whereas IKK1 appears to play an important role in enhancing the transcriptional activity of NF-kappaB by promoting RelA/p65 phosphorylation.

Disruption of the actin cytoskeleton results in nuclear factor‐κB activation and inflammatory mediator production in cultured human intestinal epithelial cells

The cytoskeleton in eukaryotic cells is composed of two major filament systems, the microtubule system and the actin cytoskeleton. The microtubule system has recently emerged as an important regulator of NF-kappaB function. However, the role that the actin microfilament system plays in controlling NF-kappaB activation is incompletely understood. In this study, we examined the effect of actin cytoskeleton disruption on NF-kappaB activation in human intestinal epithelial cells. Treatment of HT-29 or Caco-2 cells with the prototypic actin disrupting agents cytochalasin D or latrunculin B resulted in increased NF-kappaB DNA binding and NF-kappaB-dependent transcriptional activity. This NF-kappaB activation by cytochalasin D was secondary to an effect on IkappaB, because cytochalasin D-induced IkappaB degradation and the cytochalasin D-induced increase in NF-kappaB-dependent transcriptional activity was prevented by a dominant negative IkappaB mutant. Exposure of the cells to cytochalasins or latrunculin B increased gene expression and release of the NF-kappaB-dependent chemokines IL-8 and GRO-alpha. Cytochalasin D also activated p38 MAP kinase, which pathway contributed to the cytochalasin D-induced increase in IL-8 production. These results demonstrate that the actin cytoskeleton plays an important role in the regulation of NF-kappaB activation and inflammatory events in intestinal epithelial cells.

Endotoxin tlerance inhibits lipopolysaccharide-initiated acute pulmonary inflammation and lung injury in rats by the mechanism of nuclear factor-kappaB

In this study, the effect of endotoxin tolerance on lipopolysaccharide (LPS)-initiated pulmonary inflammation, the local production of tumour necrosis factor-alpha (TNF-alpha) and the cytokine-induced neutrophil attractant (CINC), as well as the activation of nuclear factor-kappaB (NF-kappaB) and its subunit composition, were examined in vivo. Endotoxin tolerance was reproduced by four consecutive daily intraperitoneal injections of 0.6 mg/kg of Escherichia coli 055:B5 LPS. Compared with control rats, endotoxin-tolerant rats failed to increase the permeability of pulmonary microvascular or recruit neutrophil to lung tissue upon restimulation with 6 mg/kg of LPSs. Pretreatment with LPSs inhibited the protein level of TNF-alpha in bronchoalveolar lavage fluid (BALF) and mRNA expression of CINC in lung tissue in response to subsequent LPS stimulation. These changes were accompanied by the suppression of activation of NF-kappaB, including the low level of total amount of DNA-binding activity and high percentage of non-transactive p50 homodimers. These data demonstrate that endotoxin tolerance can alleviate the LPS-induced acute neutrophilic pulmonary inflammation in rats and can inhibit the proinflammatory cytokines in lung and suggest that endotoxin tolerance might result from the unresponsiveness of NF-kappaB and persistent high percentage of p50 homodimers. Therefore, the phenomenon of endotoxin tolerance might be used as a strategy for the prevention or treatment of LPS-associated acute respiratory distress syndrome in which excessive or dysregulated inflammation leads to acute lung injury.

[Role of the innate immune response in sepsis]

The innate immune system succeeds against the majority of infections before the adaptive immune system is activated. New findings contribute to a better understanding of the pathophysiology of sepsis and lead to the development of new therapeutic strategies. The innate immune system, being responsible for the first response to infections, can trigger adaptive immune responses in case the initial response is ineffective. Both arms of the immune system interact with each other, mainly via cell-cell-interactions but also by soluble factors, such as cytokines and chemokines. Two sub-populations of helper T-cells direct both balanced activation and inhibition of the two arms of the immune systems using specific patterns of cytokine release. Results obtained in new animal models of sepsis, taking a progressive growth of bacteria into account, have implied that existing knowledge has to be reanalyzed. The idea of sepsis as a mere "over-reaction to inflammation" has to be abandoned. Various so-called pattern recognition receptors (e.g. toll-like receptors, TLRs, NOD proteins) are located intracellularly or in the plasma membrane of innate immune cells and recognize certain patterns expressed exclusively by extracellular pathogens. Upon receptor engagement, intracellular signaling pathways lead to cellular activation, followed by release of various cytokines and anti-microbial substances. During the course of sepsis a cytokine shift towards increasing immune suppression occurs. The innate immune system also contributes to the migration of leukocytes in inflammed tissue, involving chemokines and adhesion molecules. Leukocytes also secrete the tissue factor leading to formation of thrombin. The environment in sepsis can cause disseminated intravascular coagulation (DIC), but at the same time thrombin triggers the release of chemokines and adhesion molecules through endothelial cells, which represents a positive feedback mechanism for innate immune responses. New therapeutic strategies for sepsis try to establish a well-balanced immune response. Intervention is accomplished through inhibition of inflammatory cytokines, their receptors or through activation of immunostimulatory responses.

Overexpression of MEKK3 confers resistance to apoptosis through activation of NFkappaB

Many cancers have constitutively activated NFkappaB, the elevation of which contributes to cancer cell resistance to chemotherapeutic agent-induced apoptosis. Although mitogen-activated protein kinase/extracellular-regulated kinase kinase kinase-3 (MEKK3) has been shown to participate in the activation of NFkappaB, its relations to apoptosis and cancer are unclear. In this study, we established cell model systems to examine whether stable expression of MEKK3 could lead to increased NFkappaB activity and confer resistance to apoptosis. In addition, we investigated in breast and ovarian cancers whether MEKK3 expression may be altered and correlated with aberrant NFkappaB activity. We show that stable cell lines overexpressing MEKK3 not only had elevated levels of NFkappaB binding activity but also were more responsive to cytokine stimulation. These stable cells showed 2-4-fold higher basal expression of Bcl-2 and xIAP than the parental cells. Consistent with this increased expression of cell survival genes, MEKK3 stable cells showed reduced activation of caspases 3 and 8 and poly(ADP-ribose) polymerase cleavage and dramatically increased resistance to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand, doxorubicin, daunorubicin, camptothecin, and paclitaxel. Intriguingly, analysis of human breast and ovarian cancers showed that a significant fraction of these samples have elevated MEKK3 protein levels with corresponding increases in NFkappaB binding activities. Thus, our results established that elevated expression of MEKK3 appears to be a frequent occurrence in breast and ovarian cancers and that overexpression of MEKK3 in cells leads to increased NFkappaB activity and increased expression of cell survival factors and ultimately contributes to their resistance to apoptosis. As such, MEKK3 may serve as a therapeutic target to control cancer cell resistance to cytokine- or drug-induced apoptosis.

Epicatechin, catechin, and dimeric procyanidins inhibit PMA-induced NF-kappaB activation at multiple steps in Jurkat T cells

The capacity of the flavan-3-ols [(-)-epicatechin (EC) and (+)-catechin (CT)] and a B dimeric procyanidin (DP-B) to modulate phorbol 12-myristate 13-acetate (PMA)-induced NF-kappaB activation in Jurkat T cells was investigated. The classic PMA-triggered increase in cell oxidants was prevented when cells were preincubated for 24 h with EC, CT, or DP-B (1.7-17.2 microM). PMA induced the phosphorylation of IKKbeta and the subsequent degradation of IkappaBalpha. These events were inhibited in cells pretreated with the flavonoids. PMA induced a 4.6-fold increase in NF-kappaB nuclear binding activity in control cells. Pretreatment with EC, CT, or DP-B decreased PMA-induced NF-kappaB binding activity and the transactivation of the NF-kappaB-driven gene IL-2. EC, CT, and DP-B inhibited, in vitro, NF-kappaB binding to its DNA consensus sequence, but they had no effect on the binding activity of CREB or OCT-1. Thus, EC, CT, or DP-B can influence the immune response by modulating NF-kappaB activation. This modulation can occur at early (regulation of oxidant levels, IKK activation) as well as late (binding of NF-kappaB to DNA) stages of the NF-kappaB activation cascade. A model is presented for possible interactions between DP-B and NF-kappaB proteins, which could lead to the inhibition of NF-kappaB binding to kappaB sites.

Mechanical stretch activates nuclear factor-kappaB, activator protein-1, and mitogen-activated protein kinases in lung parenchyma: implications in asthma

We investigated the effects of mechanical stretch and induced stimulation of lung parenchyma on the activation of proinflammatory transcription factors in normal mice and in a mouse model of asthma. Mechanical stretching of lung parenchyma led to increased activation of NF-kappaB and AP-1 transcription factors. Incubation of lung parenchyma with methacholine increased the activation of NF-kappaB, which was further augmented by stretch. Activation of NF-kappaB in response to mechanical stretch was associated with the phosphorylation and degradation of IkappaBalpha and the activation of IkappaB kinase. Stretch-induced activation of NF-kappaB involves activation of stretch-activated (SA) channels and the production of free radicals. Mechanical stretch and/or treatment with methacholine resulted in an increased activation of ERK1/2 and p38 MAP kinase, and the inhibition of the activity of these kinases partially blocked the stretch-induced NF-kappaB and AP-1 activation. A greater level of NF-kappaB and ERK1/2 activity was observed in the asthmatic mice, which was further increased by mechanical stretching. The level of cyclooxygenase-2, an NF-kappaB-regulated enzyme, was also higher in lung parenchyma from asthmatic mice than in normal mice. Our data suggest that mechanical stretching of lung parenchyma activates NF-kappaB and AP-1, at least in part, through the activation of MAP kinase signaling pathways.

How not to get bugged by bugs: mechanisms of cellular tolerance to microorganisms

PURPOSE OF REVIEW

Advances in the characterization of the receptors and signaling pathways involved in the response to infection have led to a more detailed understanding of cellular tolerance to endotoxin and other microbial components. This review summarizes recent progress in the field, particularly in relation to the molecular mechanisms that underlie the development of tolerance to microorganisms.

RECENT FINDINGS

The identification of Toll-like receptors as major sensors of microbial molecules has led to numerous studies of their function in tolerant cells. Decreased Toll-like receptor expression, altered interactions between the Toll-like receptors and intracellular signal transducers, and decreased expression or activity of downstream signaling molecules have all been implicated. Upregulation of specific proteins that inhibit Toll-like receptor signaling has also been described. Apart from these general mechanisms, special features of the intestinal microenvironment and its resident cells also contribute to making the gut hyporesponsive to microorganisms.

SUMMARY

The application of gene knockout technology has highlighted the importance of macrophage tolerance in regulating innate immunity to microbial infection. Such studies have indicated that the failure of tolerance can lead to exaggerated inflammatory responses to intestinal bacteria, raising the possibility that defects in tolerance may be linked to conditions such as inflammatory bowel disease. Further characterization of this link will help in elucidating the pathogenesis of such conditions and in devising new approaches to treatment.

Reduction of chemokine IL-8 and RANTES expression in human bronchial epithelial cells by a sea-water derived saline through inhibited nuclear factor-kappaB activation

The NaCl content of airway surface fluid is believed to be of central importance in lung pathology. To test whether the Na+ concentration could influence the inflammatory response in human bronchial epithelial cells (BECs), we investigated the interleukin (IL)-8 and RANTES expression in BECs exposed to an isotonic sea-water derived low Na+ (ISW) saline compared to isotonic 0.9% NaCl saline. Exposure of BECs to ISW saline caused a significant decrease in IL-8 and RANTES gene expression and protein production as compared to that observed with 0.9% NaCl saline. Furthermore, we observed a concomitant reduction of phosphorylated IkappaBalpha associated with a marked inhibition of NF-kappaB-DNA binding activity in BECs exposed to ISW saline as compared to 0.9% NaCl saline. These findings support a new role for Na+ in the pathogenesis of airway inflammatory disorders. Therapies targeted at lowering Na+ level in airway epithelium may be beneficial in treating inflammatory lung diseases.

A selective IKK-2 inhibitor blocks NF-kappa B-dependent gene expression in interleukin-1 beta-stimulated synovial fibroblasts

NF-kappa B-induced gene expression contributes significantly to the pathogenesis of inflammatory diseases such as arthritis. I kappa B kinase (IKK) is the converging point for the activation of NF-kappa B by a broad spectrum of inflammatory agonists and is thus a novel target for therapeutic intervention. We describe a small molecule, selective inhibitor of IKK-2, SC-514, which does not inhibit other IKK isoforms or other serine-threonine and tyrosine kinases. SC-514 inhibits the native IKK complex or recombinant human IKK-1/IKK-2 heterodimer and IKK-2 homodimer similarly. IKK-2 inhibition by SC-514 is selective, reversible, and competitive with ATP. SC-514 inhibits transcription of NF-kappa B-dependent genes in IL-1 beta-induced rheumatoid arthritis-derived synovial fibroblasts in a dose-dependent manner. When the mechanism of NF-kappa B activation was evaluated in the presence of this inhibitor, several interesting observations were found. First, SC-514 did not inhibit the phosphorylation and activation of the IKK complex. Second, there was a delay but not a complete blockade in I kappa B alpha phosphorylation and degradation; likewise there was a slightly slowed, decreased import of p65 into the nucleus and a faster export of p65 from the nucleus. Finally, both I kappa B alpha and p65 were comparable substrates for IKK-2, with similar Km and Kcat values, and SC-514 inhibited the phosphorylation of either substrate similarly. Thus, the effect of SC-514 on cytokine gene expression may be a combination of inhibiting I kappa B alpha phosphorylation/degradation, affecting NF-kappa B nuclear import/export as well as the phosphorylation and transactivation of p65.

Nuclear factor-kappaB and its role in sepsis-associated organ failure

Nuclear factor (NF)-kappaB is involved in regulating the transcription of many of the immunomodulatory mediators involved in the development of sepsis-induced organ failure. Kinase pathways involving p38 and Akt and initiated by engagement of Toll-like receptors modulate transcriptional activity of NF-kappaB, but apparently through different mechanisms. Increased activation of NF-kappaB occurs with sepsis, and greater levels of nuclear accumulation of NF-kappaB are associated with higher rates of mortality and worse clinical outcome. The percentage of apoptotic neutrophils is reduced in sepsis, and inhibition of nuclear translocation of NF-kappaB restores neutrophil apoptosis to baseline levels. In models of sepsis, suppression of NF-kappaB activation decreases acute inflammatory processes and organ dysfunction. Because NF-kappaB occupies a central role in signaling pathways important in sepsis, modulation of NF-kappaB activity may be an appropriate therapeutic target in patients with sepsis.

Endothelial activation by angiotensin II through NFkappaB and p38 pathways: Involvement of NFkappaB-inducible kinase (NIK), free oxygen radicals, and selective inhibition by aspirin

Angiotensin-II (AII), the dominant effector of the renin-angiotensin system, is involved in the pathogenesis of cardiovascular diseases, such as atherosclerosis. Upregulation of the adhesion molecules VCAM-1, ICAM-1, and E-selectin in endothelial cells by inflammatory cytokines through nuclear factor kappa B (NFkappaB) activation is implicated in formation and progression of atherosclerotic plaque. Here we show that AII induces NFkappaB-dependent transcription in primary endothelial cell lines, leading to the upregulation of ICAM-1 and VCAM-1 expression. NFkappaB activation by AII is mediated by the NFkappaB-inducing kinase (NIK), a common mediator of NFkappaB activation by inflammatory cytokines, such as TNF-alpha. However, NFkappaB stimulation by AII differs from that of TNF-alpha since a TNF-receptor associated factor 2 (TRAF-2) dominant negative mutant does not prevent AII-mediated NFkappaB activation. In analogy with TNF-alpha-dependent activation of NFkappaB, treatment with either the anti-oxidant N-acetyl cysteine (NAC) or the cyclooxygenase (COX) inhibitor acetyl salicylic acid (aspirin), but not indometacin, prevents the induction of NFkappaB-dependent transcription by AII. Thus, production of reactive oxygen species, aspirin (asp)-sensitive enzymes of the arachidonate metabolism, and NIK are common transducers of AII- and TNF-dependent pathways to NFkappaB. AII also activates the inflammatory p38 kinase in endothelial cells, an effect inhibited by exposure to either NAC or asp. Pharmacological interference of the p38 pathway, with the inhibitor SB 202190, prevented AII-mediated activation of the NFkappaB target V-CAM, without affecting degradation of IkappaBalpha. These results support a pro-inflammatory effect of the vasoactive peptide AII in endothelial cells, through at least two pathways-NFkappaB and p38-both of which are sensitive to asp and antioxidants.

Role of the MyD88 transduction signaling pathway in endothelial activation by antiphospholipid antibodies

Antiphospholipid syndrome (APS) is an autoimmune disease characterized by the persistent presence of antiphospholipid antibodies (aPLs) and recurrent thrombosis or fetal loss. The thrombophilic state has been partially related to the induction of a proinflammatory and procoagulant endothelial cell (EC) phenotype induced by anti-beta(2)-glycoprotein I (beta(2)-GPI) antibodies that bind beta(2)-GPI expressed on the EC surface. Anti-beta(2)-GPI antibody binding has been shown to induce nuclear factor-kappa B (NF-kappa B) translocation leading to a proinflammatory EC phenotype similar to that elicited by interaction with microbial products (lipopolysaccharide [LPS]) and proinflammatory cytokines (interleukin 1 beta [IL-1 beta], tumor necrosis factor alpha [TNF-alpha]). However, the upstream signaling events are not characterized yet. To investigate the endothelial signaling cascade activated by anti-beta(2)-GPI antibodies, we transiently cotransfected immortalized human microvascular endothelial cells (HMEC-1) with dominant-negative constructs of different components of the pathway (Delta TRAF2, Delta TRAF6, Delta MyD88) together with reporter genes (NF-kappa B luciferase and pCMV-beta-galactosidase). Results showed that both human anti-beta(2)-GPI IgM monoclonal antibodies as well as polyclonal affinity-purified anti-beta(2)-GPI IgG display a signaling cascade comparable to that activated by LPS or IL-1. Delta TRAF6 and Delta MyD88 significantly abrogate antibody-induced as well as IL-1- or LPS-induced NF-kappa B activation, whereas Delta TRAF2 (involved in NF-kappa B activation by TNF) does not affect it. Moreover, anti- beta(2)-GPI antibodies and LPS followed the same time kinetic of IL-1 receptor-activated kinase (IRAK) phosphorylation, suggesting an involvement of the toll-like receptor (TLR) family. Our findings demonstrate that anti-beta(2)-GPI antibodies react with their antigen likely associated to a member of the TLR/IL-1 receptor family on the EC surface and directly induce activation.