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Excessive Activation (excessive + activation)
Selected AbstractsCigarette smoke suppresses in vitro allergic activation of mouse mast cellsCLINICAL & EXPERIMENTAL ALLERGY, Issue 5 2009E. Mortaz Summary Background Mast cells are important effector cells in innate or acquired immunity that contribute to host defence. Excessive activation of mast cells can result in the development of allergic diseases, including atopic asthma. Mast cell activation by IgE and specific antigen induces the cells to release spasmogenic, vasoactive and pro-inflammatory mediators, which enhance airway smooth muscle contraction, vascular permeability and inflammatory cell recruitment. Recently, we have demonstrated that exposure of mast cells to cigarette smoke medium (CSM) triggered mast cells to produce chemokines. On the other hand, smoking may decrease the risk of allergic sensitization, which could be explained by a reduced IgE production or a diminished response of mast cells to activation of the IgE receptor. Objective In this study, we investigated the effect of CSM on the allergic activation of mast cells through IgE and antigen. Methods Primary cultured murine mast cells were exposed to CSM and activated with IgE and antigen or lipopolysaccharide (LPS). The release of granules, production of leukotrienes, chemokines and cytokines was determined in the supernatants by ELISA. The effect of CSM exposure on intracellular signalling, especially the nuclear factor (NF)-,B and extracellular signal-regulated kinase (Erk)1/2 pathways, was analysed by Western blotting. Results CSM suppressed IgE-mediated degranulation and cytokine release, but no effect was observed on leukotriene release. CSM induced phosphorylation of Erk1/2 in mast cells. In CSM-exposed mast cells, activating transcription factor (ATF)-1 was phosphorylated after stimulation with IgE/Ag. LPS-activated mast cells were not influenced by CSM. Conclusion Our study suggests that exposure to cigarette smoke may lead to a reduced allergic activation of mast cells without affecting their response to activation via e.g. bacterial-derived LPS. [source] Activated Rac1, but not the tumorigenic variant Rac1b, is ubiquitinated on Lys 147 through a JNK-regulated processFEBS JOURNAL, Issue 2 2008Orane Visvikis Ubiquitination and proteasomal degradation have recently emerged as an additional level of regulation of activated forms of Rho GTPases. To characterize this novel regulatory pathway and to gain insight into its biological significance, we studied the ubiquitination of two constitutively activated forms of Rac1, i.e. the mutationally activated Rac1L61, and the tumorigenic splice variant Rac1b, which is defective for several downstream signaling pathways, including JNK activation. Whereas Rac1L61 undergoes polyubiquitination and subsequent proteasomal degradation in HEK293 cells, Rac1b is poorly ubiquitinated and appears to be much more resistant to proteasomal degradation than Rac1L61. Mutational analysis of all lysine residues in Rac1 revealed that the major target site for Rac1 ubiquitination is Lys147, a solvent-accessible residue that has a similar conformation in Rac1b. Like Rac1L61, Rac1b was found to be largely associated with plasma membrane, a known prerequisite for Rac1 ubiquitination. Interestingly, Rac1b ubiquitination could be stimulated by coexpression of Rac1L61, suggesting positive regulation of Rac1 ubiquitination by Rac1 downstream signaling. Indeed, ubiquitination of Rac1L61 is critically dependent on JNK activation. In conclusion: (a) Rac1b appears to be more stable than Rac1L61 with regard to the ubiquitin,proteasome system, and this may be of importance for the expression and tumorigenic capacity of Rac1b; and (b) ubiquitination of activated Rac1 occurs through a JNK-activated process, which may explain the defective ubiquitination of Rac1b. The JNK-dependent activation of Rac1 ubiquitination would create a regulatory loop allowing the cell to counteract excessive activation of Rac1 GTPase. [source] The interleukin-6 (IL6),174 G/C promoter genotype is associated with the presence of septic shock and the ex vivo secretion of IL6INTERNATIONAL JOURNAL OF IMMUNOGENETICS, Issue 6 2007J. J. W. Tischendorf Summary Septic shock is associated with a high mortality and an excessive activation of immune cascades. Interleukin (IL)-6 has been found to be a key cytokine in the pathogenesis of severe sepsis, but the importance of a regulatory polymorphism within the IL6 promoter has been controversial in these patients. The aim of the study was therefore to systematically investigate the IL6,174 G/C promoter genotype with regard to the presence of shock in patients with sepsis, the IL6 serum levels, and the ex vivo secretion of IL6, respectively. Overall, 112 consecutive subjects with severe sepsis and septic shock according to consensus criteria were enrolled. The ex vivo secretion of IL6 after stimulation with lipopolysaccharide (LPS) in a whole blood assay and the IL6 serum concentrations were determined after admission of the patients. Among the 112 subjects with severe sepsis, 85 patients fulfilled the criteria of septic shock. In these patients, the frequency of the mutated C-allele of the IL6 promoter polymorphism was significantly (P = 0.04) higher compared to that in individuals without shock. IL6 serum concentrations were highest in patients with the GG genotype (mean 2209 pg mL,1), followed by CG genotype (mean 1113 pg mL,1), and lowest in individuals with the CC genotype (mean 256 pg mL,1). Interestingly, a significantly (P = 0.005) higher ex vivo secretion of IL6 is detected in heterozygote individuals (535 pg mL,1) and patients with the IL6 CC genotype (555 pg mL,1) compared to patients with the ,174 GG genotype (276 pg mL,1). In conclusion, the IL6,174 G/C promoter genotype is associated with shock in patients with sepsis. Functionally, the mutated C-allele is correlated with low IL6 serum concentrations, but a high ex vivo secretion after LPS stimulation. These results further indicate a complex regulation of the expression of IL6 during infection and have implications for the design of immune intervention trials. [source] Stat1-mediated cytoplasmic attenuation in osteoimmunologyJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2005Hiroshi Takayanagi Abstract Signal transducer and activator of transcription 1 (Stat1) is a critical mediator of gene transcription in type I interferon (IFN-,/,) signaling that is essential for host defense against viruses. In the skeletal system, type I IFNs (IFN-,/,) also play an important physiological role in the inhibition of receptor activator of NF-,B ligand (RANKL)-induced osteoclast differentiation and bone resorption: mice deficient in IFN signaling exhibit decreased bone mass accompanied by the activation of osteoclastogenesis. On the other hand, an unexpected increase in bone mass was observed in Stat1-deficient mice, indicating that Stat1 has a hitherto unknown function in the regulation of bone formation. Indeed, Stat1 was found to have a unique, non-canonical function as a cytoplasmic attenuator of Runx2, a key transcription factor for osteoblast differentiation. Thus, the loss of Stat1 results in excessive activation of Runx2 and osteoblast differentiation, thereby tipping the balance in favor of bone formation over bone resorption. This is an interesting example in which a latent transcription factor attenuates the activity of another transcription factor in the cytoplasm, and reveals a novel regulatory mechanism of bone remodeling by immunomodulatory molecules. Here, we summarize recent advances in the study of Stat1 and IFNs in the context of osteoimmunology, including latest reports that question whether the inhibitory function of Stat1 in chondrocytes is responsible for dwarfism in achondroplasia. © 2004 Wiley-Liss, Inc. [source] Neuroprotective effect of asymmetric dimethylarginine against 1-methyl-4-phenylpyridinium ion-induced damage in PC12 cellsCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 5-6 2010Xiao-Qing Tang Summary 1. Asymmetric dimethylarginine (ADMA) is a well-known endogenous nitric oxide synthase (NOS) inhibitor. Although it has been shown to be a novel risk marker in cardiovascular medicine and chronic kidney disease, we speculated that in some states associated with excess of nitric oxide (NO), such as 1-methyl-4-phenylpyridinium ion (MPP+)-induced neuronal injury, ADMA might be protective by limiting the toxic effect of high concentrations of NO. 2. The aim of the present study is to explore the protection of ADMA against MPP+ -induced apoptosis and the molecular mechanisms underlying in PC12 cells. 3. We found that exogenous application of ADMA obviously protected PC12 cells against MPP+ -induced cytotoxicity and apoptosis not only by reducing the loss of mitochondrial membrane potential, but also by attenuating an increase in intracellular reactive oxygen species. Moreover, ADMA attenuated MPP+ -induced excessive activation of nitric oxide synthase and overproduction of NO. 4. The results of the present study suggest that the protection caused by ADMA is related to preserving mitochondrial membrane potential and attenuating the MPP+ -induced intracellular reactive oxygen species generation through inhibiting nitric oxide synthase activity and limiting NO generation. [source] | ||||||||||