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erk + kinase)

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Life Sciences	50%

Selected Abstracts

Caspase-8- and JNK-dependent AP-1 activation is required for Fas ligand-induced IL-8 production

FEBS JOURNAL, Issue 9 2007
Norihiko Matsumoto
Despite a dogma that apoptosis does not induce inflammation, Fas ligand (FasL), a well-known death factor, possesses pro-inflammatory activity. For example, FasL induces nuclear factor ,B (NF-,B) activity and interleukin 8 (IL-8) production by engagement of Fas in human cells. Here, we found that a dominant negative mutant of c-Jun, a component of the activator protein-1 (AP-1) transcription factor, inhibits FasL-induced AP-1 activity and IL-8 production in HEK293 cells. Selective inhibition of AP-1 did not affect NF-,B activation and vice versa, indicating that their activations were not sequential events. The FasL-induced AP-1 activation could be inhibited by deleting or introducing the lymphoproliferation (lpr) -type point mutation into the Fas death domain (DD), knocking down the Fas-associated DD protein (FADD), abrogating caspase-8 expression with small interfering RNAs, or using inhibitors for pan-caspase and caspase-8 but not caspase-1 or caspase-3. Furthermore, wildtype, but not a catalytically inactive mutant, of caspase-8 reconstituted the FasL-induced AP-1 activation in caspase-8-deficient cells. Fas ligand induced the phosphorylation of two of the three major mitogen-activated protein kinases (MAPKs): extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) but not p38 MAPK. Unexpectedly, an inhibitor for JNK but not for MAPK/ERK kinase inhibited the FasL-induced AP-1 activation and IL-8 production. These results demonstrate that FasL-induced AP-1 activation is required for optimal IL-8 production, and this process is mediated by FADD, caspase-8, and JNK. [source]

Epidermal growth factor stimulates proton efflux from chondrocytic cells

JOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2002
Kevin E.H. Lui
Proton efflux from chondrocytes alters the extracellular pH and ionic composition of cartilage, and influences the synthesis and degradation of extracellular matrix. Epidermal growth factor (EGF) promotes chondrocyte proliferation during skeletal development and accumulates in the synovial fluid in rheumatoid arthritis. The purpose of this study was to investigate the effect of EGF on proton efflux from chondrocytes. When monitored using a Cytosensor microphysiometer, EGF was found to rapidly activate proton efflux from CFK2 chondrocytic cells and rat articular chondrocytes. The actions of EGF were concentration-dependent with half-maximal effects at 0.3,0.7 ng/ml. Partial desensitization and time-dependent recovery of the response were observed following repeated exposures to EGF. EGF-induced proton efflux was dependent on extracellular glucose, and inhibitors of Na+/H+ exchange (NHE) markedly attenuated the initial increase in proton efflux. The response was diminished by inhibitors of phosphatidylinositol 3-kinase and phospholipase C, but not by inhibitors of MEK (MAPK/ERK kinase) or protein kinase A or C. Thus, EGF-induced proton efflux involves glucose metabolism and NHE, and is regulated by a discrete subset of EGF-activated signaling pathways. In vivo, proton efflux induced by EGF may lead to an acidic environment, enhancing turnover of cartilage matrix during development and in rheumatoid arthritis. © 2002 Wiley-Liss, Inc. [source]

Translation of striatal-enriched protein tyrosine phosphatase (STEP) after ,1-adrenergic receptor stimulation

JOURNAL OF NEUROCHEMISTRY, Issue 2 2007
Yaer Hu
Abstract The ,-adrenergic system is implicated in long-term synaptic plasticity in the CNS, a process that requires protein synthesis. To identify proteins that are translated in response to ,-adrenergic receptor stimulation and the pathways that regulate this process, we investigated the effects of isoproterenol on the translation of striatal-enriched protein tyrosine phosphatase (STEP) in both cortico-striatal slices and primary neuronal cultures. Isoproterenol stimulation induced a rapid dose-dependent increase in STEP expression. Anisomycin blocked the increase in STEP expression while actinomycin D had no effect, suggesting a translation-dependent mechanism. Isoproterenol-induced STEP translation required activation of ,1-receptors. Application of the MAPK/ERK kinase (MEK) inhibitor SL327 blocked both isoproterenol-induced activation of pERK and subsequent STEP translation. Inhibitors of PI3K (LY294002) or mTOR (rapamycin) also completely blocked STEP translation. These results suggest that co-activation of both the ERK and PI3K-Akt-mTOR pathways are required for STEP translation. As one of the substrates of STEP includes ERK itself, these results suggest that STEP is translated upon ,-adrenergic activation as part of a negative feedback mechanism. [source]

Acute activation of Erk1/Erk2 and protein kinase B/akt proceed by independent pathways in multiple cell types

FEBS JOURNAL, Issue 17 2005
Doris Chiu
We used two inhibitors of the signaling enzyme phosphatidylinositol 3-kinase (PtdIns3K), wortmannin and LY294002, to evaluate the potential involvement of PtdIns3K in the activation of the MAP kinases (MAPK), Erk1 and Erk2. In dose,response studies carried out on six different cell lines and a primary cell culture, we analyzed the ability of the inhibitors to block phosphorylation of protein kinase B/akt (PKB/akt) at Ser473 as a measure of PtdIns3K activity, or the phosphorylation of Erk1/2 at activating Thr/Tyr sites as a measure of the extent of activation of MAPK/Erk kinase (MEK/Erk). In three different hemopoietic cell lines stimulated with cytokines, and in HEK293 cells, stimulated with serum, either wortmannin or LY294002, but never both, could partially block phosphorylation of Erks. The same observations were made in a B-cell line and in primary fibroblasts. In only one cell type, the A20 B cells, was there a closer correlation between the PtdIns3K inhibition by both inhibitors, and their corresponding effects on Erk phosphorylation. However, this stands out as an exception that gives clues to the mechanism by which cross-talk might occur. In all other cells, acute activation of the pathway leading to Erk phosphorylation could proceed independently of PtdIns3K activation. In a biological assay comparing these two pathways, the ability of LY294002 and the MEK inhibitor, U0126, to induce apoptosis were tested. Whereas LY294002 caused death of cytokine-dependent hemopoietic cells, U0126 had little effect, but both inhibitors together had a synergistic effect. The data show that these two pathways are regulating very different downstream events involved in cell survival. [source]