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MAPK Kinase (mapk + kinase)
Selected AbstractsDiffering mechanisms of cAMP- versus seawater-induced oocyte maturation in marine nemertean worms I. The roles of serine/threonine kinases and phosphatasesMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 12 2006Stephen A. Stricker Abstract Unlike in most animals, oocytes of marine nemertean worms initiate maturation (=germinal vesicle breakdown, GVBD) following an increase, rather than a decrease, in intraoocytic cAMP. To analyze how serine/threonine (Ser/Thr) kinase cascades involving mitogen-activated protein kinase (MAPK), maturation-promoting factor (MPF), cAMP-dependent protein kinase (PKA), and phosphatidylinositol 3-kinase (PI3K) regulate nemertean GVBD, oocytes of Cerebratulus sp. were treated with pharmacological modulators and stimulated with cAMP-elevating drugs or seawater (SW) alone. Both cAMP elevators and SW triggered GVBD while activating MAPK, its target p90Rsk, and MPF. Similarly, neither cAMP- nor SW-induced GVBD was affected by several Ser/Thr phosphatase inhibitors, and both stimuli apparently accelerated GVBD via a MAPK-independent, PI3K-dependent mechanism. However, inhibitors of Raf-1, a kinase that activates MAPK kinase, blocked GVBD and MAPK activation during SW-, but not cAMP-induced maturation. In addition, MPF blockers more effectively reduced GVBD and MAPK activity in SW versus in cAMP-elevating treatments. Moreover, the two maturation-inducing stimuli yielded disparate patterns of PKA-related MAPK activations and phosphorylations of putative PKA substrates. Collectively, such findings suggest that in maturing oocytes of Cerebratulus sp., Ser/Thr kinase cascades differ during cAMP- versus SW-induced GVBD in several ways, including MAPK activation modes, MPF-feedback loops, and PKA-related signaling pathways. Additional differences in cAMP- versus SW-induced oocyte maturation are also described in the accompanying study that deals with the roles of tyrosine kinase signaling during GVBD. Mol. Reprod. Dev. 73: 1578,1590, 2006. © 2006 Wiley-Liss, Inc. [source] Chloroplast-generated reactive oxygen species are involved in hypersensitive response-like cell death mediated by a mitogen-activated protein kinase cascadeTHE PLANT JOURNAL, Issue 6 2007Yidong Liu Summary Plant defense against pathogens often includes rapid programmed cell death known as the hypersensitive response (HR). Recent genetic studies have demonstrated the involvement of a specific mitogen-activated protein kinase (MAPK) cascade consisting of three tobacco MAPKs, SIPK, Ntf4 and WIPK, and their common upstream MAPK kinase (MAPKK or MEK), NtMEK2. Potential upstream MAPKK kinases (MAPKKKs or MEKKs) in this cascade include the orthologs of Arabidopsis MEKK1 and tomato MAPKKK,. Activation of the SIPK/Ntf4/WIPK pathway induces cell death with phenotypes identical to pathogen-induced HR at macroscopic, microscopic and physiological levels, including loss of membrane potential, electrolyte leakage and rapid dehydration. Loss of membrane potential in NtMEK2DD plants is associated with the generation of reactive oxygen species (ROS), which is preceded by disruption of metabolic activities in chloroplasts and mitochondria. We observed rapid shutdown of carbon fixation in chloroplasts after SIPK/Ntf4/WIPK activation, which can lead to the generation of ROS in chloroplasts under illumination. Consistent with a role of chloroplast-generated ROS in MAPK-mediated cell death, plants kept in the dark do not accumulate H2O2 in chloroplasts after MAPK activation, and cell death is significantly delayed. Similar light dependency was observed in HR cell death induced by tobacco mosaic virus, which is known to activate the same MAPK pathway in an N -gene-dependent manner. These results suggest that activation of the SIPK/Ntf4/WIPK cascade by pathogens actively promotes the generation of ROS in chloroplasts, which plays an important role in the signaling for and/or execution of HR cell death in plants. [source] Function of a mitogen-activated protein kinase pathway in N gene-mediated resistance in tobaccoTHE PLANT JOURNAL, Issue 4 2003Hailing Jin Summary The active defense of plants against pathogens often includes rapid and localized cell death known as hypersensitive response (HR). Protein phosphorylation and dephosphorylation are implicated in this event based on studies using protein kinase and phosphatase inhibitors. Recent transient gain-of-function studies demonstrated that the activation of salicylic acid-induced protein kinase (SIPK) and wounding-induced protein kinase (WIPK), two tobacco mitogen-activated protein kinases (MAPKs) by their upstream MAPK kinase (MAPKK), NtMEK2 leads to HR-like cell death. Here, we report that the conserved kinase interaction motif (KIM) in MAPKKs is required for NtMEK2 function. Mutation of the conserved basic amino acids in this motif, or the deletion of N-terminal 64 amino acids containing this motif significantly compromised or abolished the ability of NtMEK2DD to activate SIPK/WIPK in vivo. These mutants were also defective in interacting with SIPK and WIPK, suggesting protein,protein interaction is required for the functional integrity of this MAPK cascade. To eliminate Agrobacterium that is known to activate a number of defense responses in transient transformation experiments, we generated permanent transgenic plants. Induction of NtMEK2DD expression by dexamethasone induced HR-like cell death in both T1 and T2 plants. In addition, by using PVX-induced gene silencing, we demonstrated that the suppression of all three known components in the NtMEK2,SIPK/WIPK pathway attenuated N gene-mediated TMV resistance. Together with previous report that SIPK and WIPK are activated by TMV in a gene-for-gene-dependent manner, we conclude that NtMEK2,SIPK/WIPK pathway plays a positive role in N gene-mediated resistance, possibly through regulating HR cell death. [source] Activation of AtMEK1, an Arabidopsis mitogen-activated protein kinase kinase, in vitro and in vivo: analysis of active mutants expressed in E. coli and generation of the active form in stress response in seedlingsTHE PLANT JOURNAL, Issue 5 2002Daisuke Matsuoka Summary The mitogen-activated protein kinase (MAPK) cascade, consisting of MAPK, MAPK kinase (MAPKK) and MAPK kinase kinase (MAPKKK), is the signaling system that relays various external signals, including mitogens and stresses in eukaryotes. MAPKK is activated by phosphorylation in the consensus motif, SXXXS/T, in animals, but the regulation mechanism for the plant MAPKK by phosphorylation, having the putative phosphorylation motif of S/TXXXXXS/T, is not yet fully clarified. Here we constructed a series of mutants of AtMEK1, an Arabidopsis MAPKK, having the sequence T218-X-S220-X-X-X-S224 that fits both of the plant- and animal-type motifs. We show that the two double-mutant proteins replacing Thr-218/Ser-224 and Ser-220/Ser-224 by Glu expressed in Escherichia coli show a constitutive activity to phosphorylate the Thr and Tyr residues of the kinase-negative mutant of an Arabidopsis MAPK, named ATMPK4, in vitro. The mutation analysis of AtMEK1 replacing Thr-218 and Ser-220 to Ala suggested that Thr-218 is autophosphorylated by the enzyme. The wild-type ATMPK4 was also phosphorylated by the active mutants of AtMEK1 and showed a high protein kinase activity toward myelin basic proteins. In contrast, ATMPK3, another Arabidopsis MAPK, was a poor substrate of this plant MAPKK, indicating that AtMEK1 has a substrate specificity preferring ATMPK4 to ATMPK3, at least in vitro. Furthermore, AtMEK1 immunoprecipitated from Arabidopsis seedlings stimulated with wounding, cold, drought, and high salt showed an elevated protein kinase activity toward the kinase-negative ATMPK4, while the amounts of the AtMEK1 protein did not change significantly. These data indicate that the AtMEK1 becomes an active form through phosphorylation and activates its downstream target ATMPK4 in stress response in Arabidopsis. [source] Protein kinase C zeta plays an essential role for Mycobacterium tuberculosis -induced extracellular signal-regulated kinase 1/2 activation in monocytes/macrophages via Toll-like receptor 2CELLULAR MICROBIOLOGY, Issue 2 2007Chul-Su Yang Summary This study characterized the upstream signalling molecules involved in extracellular signal-regulated kinase (ERK) 1/2 activation and determined their effects on differential tumour necrosis factor (TNF)-, expression by monocytes/macrophages infected with virulent or avirulent mycobacteria. The avirulent Mycobacterium tuberculosis (MTB) strain H37Ra (MTBRa) induced higher levels of activation of ERK 1/2 and the upstream MAPK kinase (MEK)1 and, subsequently, higher levels of TNF-, expression in human primary monocytes and monocyte-derived macrophages, as compared with MTB strain H37Rv (MTBRv). The MTB-induced activation of ERK 1/2 was not dependent on Ras or Raf. However, inhibition of the activity of atypical protein kinase C (PKC) , decreased the in vitro phosphorylation of MEK, ERK 1/2 activation and subsequent TNF-, induction caused by MTBRv or MTBRa. Toll-like receptor (TLR) 2 was found to play a major role in MTB-induced TNF-, expression and PKC, phosphorylation. Co-immunoprecipitation experiments showed that PKC, interacts physically with TLR2 after MTB stimulation. Moreover, PKC, phosphorylation was increased more in macrophages following MTBRa, versus MTBRv, infection. This is the first demonstration that PKC, interacts with TLR2 to play an essential role in MTB-induced ERK 1/2 activation and subsequent TNF-, expression in monocytes/macrophages. [source] p38 MAPK is a critical regulator of the constitutive and the ,4,integrin-regulated expression of IL-6 in human normal thymic epithelial cellsEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 11 2003Fabrizio Mainiero Abstract Cytokines and adhesion receptors are key mediators in the dialog occurring between thymic epithelial cells (TEC) and thymocytes and regulating T,cell maturation and epithelial embryonic differentiation. Among cytokines, IL-6 can be critical in the thymus, fostering proliferation, differentiation and/or survival of both TEC and thymocytes. We have previously reported in human normal TEC that clustering of the laminin receptor ,6,4 integrin induced by thymocyte contact or monoclonal antibody-mediated cross-linking regulates IL-6 gene expression via activation of NF-,B and NF-IL6 transactivators. Here we show that ,6,4 integrin activates p38 mitogen-activated protein kinase (MAPK) and that p38 is essential for IL-6 gene expression. In fact, ,4 cross-linking activated p38 and extracellular signal-regulated kinase (ERK) MAPK, Rac1, p21-activated protein kinase,1 (PAK1) and MAPK kinases (MKK),3/MKK6. However, pharmacological blockade of p38 or ERK demonstrated that p38 inhibition abrogated both basal and ,4,integrin-induced production of IL-6 preventing NF-,B and NF-IL6 activation, whereas ERK inhibition reduced IL-6 production, hampering only NF-,B activation. Overall, our results indicate that p38 MAPK and ,6,4,integrin, expressed by TEC throughout their life, are critical regulators of the intrathymic availability of a cytokine controlling fate and functions of cells governing development and maintenance of thymic architecture and immune responses. [source] | ||||||||||