Another leap for EMM into a new era

No abstract available.

Transient exposure to hydrogen peroxide inhibits the ubiquitination of phosphorylated IkappaBalpha in TNFalpha-stimulated HEK293 cells

During ischemia-reperfusion injury, brief pre-exposure to oxidative stress renders organs resistant to subsequent severe damage. NF-kappaB is a transcription factor that is involved in reperfusion-induced inflammatory and immune responses. The activity of NF-kappaB has been shown to be modulated by oxidative stress in various cell types through different pathways. We studied the effect of pre-exposure to oxidative stress on subsequent NF-kappaB activation in TNFalpha-stimulated HEK293 cells. The cells were transiently exposed to 0.5 mM H2O2 for 20 min, prior to stimulation with TNFalpha, and the subsequent expression of NF-kappaB-dependent genes and the levels of NF-kappaB signaling molecules were measured. Pre-exposure to H2O2 significantly delayed the TNFalpha-induced expression of an NF-kappaB reporter gene and inflammatory proteins (intercellular adhesion molecule-1 and IL-1beta). The degradation of inhibitor of NF-kappaB alpha (IkappaBalpha) and the nuclear translocation of NF-kappaB were also delayed by H2O2 treatment, whereas IkappaBalpha phosphorylation and IkappaB kinase activity were not changed. When we examined the ubiquitin/proteosome pathway in H2O2-treated cells, we could not detect significant changes in proteosomal peptidase activities, but we were able to detect a delay of IkappaBalpha poly-ubiquitination. Our results suggest that transient exposure to oxidative stress temporally inhibits NF-kappaB-dependent gene expression by suppressing the poly-ubiquitination of phosphorylated IkappaBalpha in HEK293 cells.

Cysteine-179 of I kappa B kinase beta plays a critical role in enzyme activation by promoting phosphorylation of activation loop serines

I kappa B kinase beta (IKK beta) subunit of IKK complex is essential for the activation of NF-kappa B in response to various proinflammatory signals. Cys-179 in the activation loop of IKK beta is known to be the target site for IKK inhibitors such as cyclopentenone prostaglandins, arsenite, and antirheumatic gold compounds. Here we show that a mutant IKK beta in which Cys-179 is substituted with alanine had decreased activity when it was expressed in HEK-293 cells, and TNF stimulation did not restore the activity. Phosphorylation of activation loop serines (Ser-177 and Ser-181) which is required for IKK beta activation was reduced in the IKK beta (C179A) mutant. The activity of IKK beta (C179A) was partially recovered when its phosphorylation was enforced by coexpression with mitogen-activated protein kinase kinase kinases (MAPKKK) such as NF-kappa B inducing kinase (NIK) and MAPK/extracellular signal-regulated kinase kinase kinase 1(MEKK1) or when the serine residues were replaced with phospho-mimetic glutamate. The IKK beta (C179A) mutant was normal in dimer formation, while its activity abnormally responded to the change in the concentration of substrate ATP in reaction mixture. Our results suggest that Cys-179 of IKK beta plays a critical role in enzyme activation by promoting phosphorylation of activation-loop serines and interaction with ATP.

Regulation of Interleukin-17 Production in Patients with Rheumatoid Arthritis by Phosphoinositide 3-kinase (PI3K)/ Akt and Nuclear Factor KappaB (NF-kappaB) Dependent Signal Transduction Pathway

Inflammatory mediators has been recognized as an important role in the pathogenesis of rheumatoid arthritis (RA). IL-17 is increasingly recognized as an important regulator of immune and inflammatory responses, including induction of proinflammatory cytokines and osteoclastic bone resorption. Evidence of the expression and proinflammatory activity of IL-17 has been demonstrated in RA synovium and in animal models of RA. However, the signaling pathways that regulate IL-17 production remain unknown. In the present study, we investigated the role of the phosphatidylinositol 3 kinase (PI3K)-Akt pathway in the regulation of IL-17 production in RA. PBMC were separated from RA (n=24) patients, and stimulated with various agents (anti CD3, anti CD28, PHA, ConA, IL-15). IL-17 levels were determined by sandwich ELISA and RT-PCR. The production of IL-17 was significantly increased in cells treated with anti-CD3 antibody, PHA, IL-15 or MCP-1 (P<0.05). ConA also strongly induced IL-17 production (P<0.001), whereas TNF-alpha, IL-1beta, IL-18 or TGF-beta did not. IL-17 was detected in the PBMC of patients with osteoarthritis (OA) but their expression levels were much lower than those of RA PBMC. Anti-CD3 antibody activated the PI3K-Akt pathway and activation of the PI3K-Akt pathway resulted in a pronounced augmentation of nuclear factor kappaB (NF-kappaB). IL-17 production by activated PBMC in RA is completely or partially blocked in the presence of NF-kappaB inhibitor PDTC and PI3K- Akt inhibitor, wortmannin and LY294002, respectively. Whereas the inhibition of AP-1 and extracellular signal-regulated kinase (ERK)1/2 did not affect IL-17 production. These results provide new insight into that PI3K/Akt and NF-kappaB dependent signal transduction pathway could be involved in the overproduction of key inflammatory cytokine, IL-17 in rheumatoid arthritis.

Gold compound auranofin inhibits I kappaB kinase (IKK) by modifying Cys-179 of IKK beta subunit

Antirheumatic gold compounds have been shown to inhibit NF-kB activation by blocking IkB kinase (IKK) activity. To examine the possible inhibitory mechanism of gold compounds, we expressed wild type and mutant forms of IKk alpha and beta subunits in COS-7 cells and determined the effect of gold on the activity of these enzymes both in vivo and in vitro. Substitution of Cys-179 of IKK beta with alanine (C179A) rendered the enzyme to become resistant to inhibition by a gold compound auranofin, however, similar protective effect was not observed with an equivalent level of IKK alpha (C178A) mutant expressed in the cells. Auranofin inhibited constitutively active IKK alpha and beta and variants; IKK alpha (S176E, S180E) or IKK beta (S177E, S181E), suggesting that gold directly cause inhibition of activated enzyme. The different inhibitory effect of auranofin on IKK alpha (C178A) and IKK beta (C179A) mutants indicates that gold could inhibit the two subunits of IKK in a different mode, and the inhibition of NF- kB and IKK activation induced by inflammatory signals in gold-treated cells appears through its interaction with Cys-179 of IKK beta.

Dual effect of oxidative stress on NF-kappaB activation in HeLa cells

Reactive oxygen species (ROS) has been implicated as an inducer of NF-kappaB activity in numbers of cell types where exposure of cells to ROS such as H2O2 leads to NF-kappaB activation. In contrast, exposure to oxidative stress in certain cell types induced reduction of tumor necrosis factor (TNF)-induced NF-kappaB activation. And various thiol-modifying agents including gold compounds and cyclopentenone prostaglandins inhibit NF-kappaB activation by blocking IkappaB kinase (IKK). To understand such conflicting effect of oxidative stress on NF-kappaB activation, HeLa cells were incubated with H2O2 or diamide and TNF-induced expression of NF-kappaB reporter gene was measured. NF-kappaB activation was significantly blocked by these oxidizing agents, and the inhibition was accompanied with reduced nuclear NF-kappaB and inappropriate cytosolic IkappaB degradation. H2O2 and diamide also inhibited IKK activation in HeLa and RAW 264.7 cells stimulated with TNF and lipopolysaccharide, respectively, and directly blocked IKK activity in vitro. In cells treated with H2O2 alone, nuclear NF-kappaB was induced after 2 h without detectible degradation of cytosolic IkBa or activation of IKK. Our results suggest that ROS has a dual effect on NF-kappaB activation in the same HeLa cells: it inhibits acute IKK-mediated NF-kappaB activation induced by inflammatory signals, while longer-term exposure to ROS induces NF-kappaB activity through an IKK-independent pathway.

Murine pro-tumor necrosis factor expressed in Saccharomyces cerevisiae HF7c localizes to membrane/particulate

Tumor necrosis factor (TNF) is a cytokine that is produced by immune cells in response to bacterial and viral stimuli and plays important roles in various inflammatory diseases. TNF is produced as a membrane-bound precursor, which is then cleaved to release soluble mature protein. We expressed murine pro-TNF in Saccharomyces cerevisiae and examined processing and cellular localization of the recombinant protein. Yeast cells were transformed with an expression construct carrying the pro-TNF gene under the control of alcohol dehydrogenase promoter. Immunoblotting analysis of cell homogenate revealed expression of 26 kD pro-TNF in transformed cells. Upon centrifugation, pro-TNF transformed cells fractionated into the membrane/particulate. In a clone that expresses a high level of pro-TNF, mature 17 kD TNF was detected in the culture medium, although the amount was far smaller than that of cell-associated pro-TNF. Flow cytometric analysis of yeast spheroplasts demonstrated the presence of TNF on the cell surface. Our results show that pro-TNF expressed in yeast mainly resides in the cellular membrane with an orientation similar to that of pro-TNF produced in mammalian cells. Our data suggest that the transformed yeast cells can be used for the genetic analysis of pro-TNF processing machinery in immune cells.

Measurement of Serum Fas Ligand (FasL), FasL-Fas Complex and FasL-IgG Complex in Patients with Rheumatic Diseases / 대한류마티스학회지

OBJECTIVE: To quantify the soluble Fas ligand (sFasL) and to measure FasL-Fas complex and FasL-IgG complex in the sera of patients with various rheumatic diseases: systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc), and adult onset Still? disease (AOSD). METHODS: Serum samples were obtained from 37 patients with SLE, 40 with RA, 30 with SSc, 20 with AOSD, and 40 healthy controls. The serum sFasL, FasL-Fas complex, and FasL-IgG complex were measured using a sandwich enzyme-linked immunoabsorbent assay. Hospital medical records were retrospectively reviewed for clinical and laboratory characteristics in patients with SLE. Disease activity in SLE patients was assessed by the SLE Disease Activity Index (SLEDAI) score. RESULTS: In patients with SLE, serum sFasL levels (383.1+/-208.9pg/ml) were significantly higher (p<0.001) than those of healthy controls (192.0+/-84.7pg/ml). sFasL levels in patients with RA (150.8+/-30.7pg/ml, p=0.014), SSc (115.4+/-13.5pg/ml, p<0.001), and AOSD (137.5+/-12.9pg/ml, p=0.001) were significantly lower compared with healthy controls. The frequencies of positive FasL-Fas complex and FasL-IgG complex were higher in patients with SLE (56.8%, 56.8% respectively) than in healthy controls (2.5%, 0% respectively) (p<0.001). All patients with RA or AOSD were negative for FasL-Fas complex and FasL-IgG complex. No patients with SSc were positive for FasL-Fas complex. On the other hand, the positive frequency of FasL-IgG complex was greater in patients with SSc (16.7%) than in healthy controls (0%)(p=0.012). Serum levels of FasL-IgG complexes in active SLE patients (OD 0.467+/-0.050) were tended to be lower than those in inactive SLE patients (OD 0.509+/-0.055)(p=0.060). SLEDAI score was tended to be negatively correlated with the serum levels of FasL-IgG complex in patients with SLE (r=-0.308, p=0.068). CONCLUSION: These results suggest that FasL may possibly play a role in the pathogenesis of SLE.

Measurement of Serum Fas Ligand (FasL), FasL-Fas Complex and FasL-IgG Complex in Patients with Rheumatic Diseases / 대한류마티스학회지

OBJECTIVE: To quantify the soluble Fas ligand (sFasL) and to measure FasL-Fas complex and FasL-IgG complex in the sera of patients with various rheumatic diseases: systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc), and adult onset Still? disease (AOSD). METHODS: Serum samples were obtained from 37 patients with SLE, 40 with RA, 30 with SSc, 20 with AOSD, and 40 healthy controls. The serum sFasL, FasL-Fas complex, and FasL-IgG complex were measured using a sandwich enzyme-linked immunoabsorbent assay. Hospital medical records were retrospectively reviewed for clinical and laboratory characteristics in patients with SLE. Disease activity in SLE patients was assessed by the SLE Disease Activity Index (SLEDAI) score. RESULTS: In patients with SLE, serum sFasL levels (383.1+/-208.9pg/ml) were significantly higher (p<0.001) than those of healthy controls (192.0+/-84.7pg/ml). sFasL levels in patients with RA (150.8+/-30.7pg/ml, p=0.014), SSc (115.4+/-13.5pg/ml, p<0.001), and AOSD (137.5+/-12.9pg/ml, p=0.001) were significantly lower compared with healthy controls. The frequencies of positive FasL-Fas complex and FasL-IgG complex were higher in patients with SLE (56.8%, 56.8% respectively) than in healthy controls (2.5%, 0% respectively) (p<0.001). All patients with RA or AOSD were negative for FasL-Fas complex and FasL-IgG complex. No patients with SSc were positive for FasL-Fas complex. On the other hand, the positive frequency of FasL-IgG complex was greater in patients with SSc (16.7%) than in healthy controls (0%)(p=0.012). Serum levels of FasL-IgG complexes in active SLE patients (OD 0.467+/-0.050) were tended to be lower than those in inactive SLE patients (OD 0.509+/-0.055)(p=0.060). SLEDAI score was tended to be negatively correlated with the serum levels of FasL-IgG complex in patients with SLE (r=-0.308, p=0.068). CONCLUSION: These results suggest that FasL may possibly play a role in the pathogenesis of SLE.

Nuclear factor kappaB (NF-kappaB) pathway as a therapeutic target in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by persistent joint swelling and progressive destruction of cartilage and bone. Current RA treatments are largely empirical in origin and their precise mechanism of action is uncertain. Increasing evidence shows that chronic inflammatory diseases such as RA are caused by prolonged production of proinflammatory cytokines including tumor necrosis factor (TNF) and interleukin 1 (IL-1). The nuclear factor kappaB (NF-kappaB) plays an essential role in transcriptional activation of TNF and IL-1. NF-kappaB is induced by many stimuli including TNF and IL-1, forming a positive regulatory cycle that may amplify and maintain RA disease process. NF-kappaB and enzymes involved in its activation can be a target for anti-inflammatory treatment. Aspirin and sodium salicylate inhibit activation of NF-KB by blocking IkappaB kinase, a key enzyme in NF-kappaB activation. Glucocorticoids suppress expression of inflammatory genes by binding glucocorticoid receptor with NF-kappaB, and increasing expression of inhibitory protein of NF-kappaB, IkappaBalpha. Sulfasalazine and gold compounds also inhibit NF-kappaB activation. Continuing advances in our understanding of action mechanism of antirheumatic agents will benefit the future development of RA regimens with greater efficacy and less toxicity.