1,147 research outputs found

    MAP Kinase-Mediated Negative Regulation of Symbiotic Nodule Formation in Medicago truncatula

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    Mitogen-activated protein kinase (MAPK) signaling cascades play critical roles in various cellular events in plants, including stress responses, innate immunity, hormone signaling, and cell specificity. MAPK-mediated stress signaling is also known to negatively regulate nitrogen-fixing symbiotic interactions, but the molecular mechanism of the MAPK signaling cas-cades underlying the symbiotic nodule development remains largely unknown. We show that the MtMKK5-MtMPK3/6 signaling module negatively regulates the early symbiotic nodule formation, probably upstream of ERN1 (ERF Required for Nodulation 1) and NSP1 (Nod factor Signaling Pathway 1) in Medicago truncatula. The overexpression of MtMKK5 stimulated stress and defense signaling pathways but also reduced nodule formation in M. truncatula roots. Conversely, a MAPK specific inhibitor, U0126, enhanced nodule formation and the expression of an early nodulation marker gene, MtNIN. We found that MtMKK5 directly activates MtMPK3/6 by phosphorylating the TEY motif within the activation loop and that the MtMPK3/6 proteins physically interact with the early nodulation-related transcription factors ERN1 and NSP1. These data suggest that the stress signaling-mediated MtMKK5/MtMPK3/6 module sup-presses symbiotic nodule development via the action of early nodulation transcription factors.115Ysciescopuskc

    The Regulation Landscape of MAPK Signaling Cascade for Thwarting \u3ci\u3eBacillus thuringiensis\u3c/i\u3e Infection in an Insect Host

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    Host-pathogen interactions are central components of ecological networks where the MAPK signaling pathways act as central hubs of these complex interactions. We have previously shown that an insect hormone modulated MAPK signaling cascade participates as a general switch to trans-regulate differential expression of diverse midgut genes in the diamondback moth, Plutella xylostella (L.) to cope with the insecticidal action of Cry1Ac toxin, produced by the entomopathogenic bacterium Bacillus thuringiensis (Bt). The relationship between topology and functions of this four-tiered phosphorylation signaling cascade, however, is an uncharted territory. Here, we carried out a genome-wide characterization of all the MAPK orthologs in P. xylostella to define their phylogenetic relationships and to confirm their evolutionary conserved modules. Results from quantitative phosphoproteomic analyses, combined with functional validations studies using specific inhibitors and dsRNAs lead us to establish a MAPK “road map”, where p38 and ERK MAPK signaling pathways, in large part, mount a resistance response against Bt toxins through regulating the differential expression of multiple Cry toxin receptors and their non-receptor paralogs in P. xylostella midgut. These data not only advance our understanding of host-pathogen interactions in agricultural pests, but also inform the future development of biopesticides that could suppress Cry resistance phenotypes

    Identification and functional characterization of EseH, a new effector of the type III secretion system of Edwardsiella piscicida

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135199/1/cmi12638_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135199/2/cmi12638.pd

    The Role of Specific Mitogen-Activated Protein Kinase Signaling Cascades in the Regulation of Steroidogenesis

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    Mitogen-activated protein kinases (MAPKs) comprise a family of serine/threonine kinases that are activated by a large variety of extracellular stimuli and play integral roles in controlling many cellular processes, from the cell surface to the nucleus. The MAPK family includes four distinct MAPK cascades, that is, extracellular signal-regulated kinase 1/2 (ERK1/2), p38 MAPK, c-Jun N-terminal kinase or stress-activated protein kinase, and ERK5. These MAPKs are essentially operated through three-tiered consecutive phosphorylation events catalyzed by a MAPK kinase kinase, a MAPK kinase, and a MAPK. MAPKs lie in protein kinase cascades. The MAPK signaling pathways have been demonstrated to be associated with events regulating the expression of the steroidogenic acute regulatory protein (StAR) and steroidogenesis in steroidogenic tissues. However, it has become clear that the regulation of MAPK-dependent StAR expression and steroid synthesis is a complex process and is context dependent. This paper summarizes the current level of understanding concerning the roles of the MAPK signaling cascades in the regulation of StAR expression and steroidogenesis in different steroidogenic cell models

    Brief reoxygenation episodes during chronic hypoxia enhance posthypoxic recovery of LV function: Role of mitogen-activated protein kinase signaling pathways

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    Children with congenital cyanotic heart defects have worse outcomes after surgical repair of their heart defects compared with noncyanotic ones. Institution of extracorporeal circulation in these children exposes the cyanotic heart to reoxygenation injury. Mitogen-activated protein kinase (MAPK) signaling cascades are major regulators of cardiomyocyte function in acute hypoxia and reoxygenation. However, their roles in chronic hypoxia are incompletely understood. We determined myocardial activation of the three major MAPKs, c-Jun NH2-terminal kinase (JNK), extracellular signal-regulated kinase-1/2 (ERK1/2), and p38-MAPK in adult rats exposed to hypoxia (FIO2=0.10) for varying periods of time. Myocardial function was analyzed in isolated perfused hearts. Acute hypoxia stimulated JNK and p38-MAPK activation. Chronic hypoxia (2weeks) was associated with increased p38-MAPK (but not JNK) activation, increased apoptosis, and impaired posthypoxic recovery of LV function. Brief normoxic episodes (1h/day) during chronic hypoxia abolished p38-MAPK activation, stimulated MEK-ERK1/2 activation modestly, and restored posthypoxic LV function. In vivo p38-MAPK inhibition by SB203580 or SB202190 in chronically hypoxic rats restored posthypoxic LV function. These results indicate that sustained hypoxemia maintains p38-MAPK in a chronically activated state that predisposes to myocardial impairment upon reoxygenation. Brief normoxic episodes during chronic hypoxia prevent p38-MAPK activation and restore posthypoxic recovery of myocardial functio

    Molecular Pathways Leading to Development of Epilepsy After Brain Injury and Advanced Optical Methods for Epilepsy Study

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    Epilepsy is regarded as a kind of brain disease caused by the abnormal activities of neurons after brain injuries. Long term severe neuron activities, or excitotoxicity, may lead to the death of neurons, causing irreversible damage to the brain. Epilepsy is not curable and hence its treatment is widely investigated. In this dissertation, in order to understand epilepsy, three main projects are undertaken. These projects are: 1) Insulin-Like Growth Factor-1 (IGF-1) regulation in epileptogenesis; 2) effect of siRNA silencing on axon growth; and 3) optical coherence microscopy (OCM) in the study of epilepsy.The first project is to investigate IGF-1 Signaling in Posttraumatic Epileptogenesis. It is reported that concentration of Insulin-like Growth Factor -1 (IGF-1) increases in the brain tissue after head injury, and the phosphorylation in the receptor of IGF-1 causes activation of mammalian target of rapamycin (mTOR) cascade, which involves epileptogenesis, suggesting that IGF-1 is involved in the downstream regulation of neuronal behavior after traumatic brain injury (TBI). In our experiment, the role of IGF-1 in epileptogenesis in an organotypic hippocampal culture (OHC) model of posttraumatic epilepsy is investigated. Lactate production, lactate dehydrogenase (LDH), electrical activity, and phosphorylation of Akt, MAPK, and S6 proteins were measured and their corresponding inhibitors are applied to investigate epileptogenesis. Results show that short-term application of IGF-1 result in a decreased risk of epileptogenesis while chronic application leads to an increase in ictal activities. In addition, chronic IGF-1 application promotes the activation of the Akt-mTOR signaling cascade, but not the MAPK signaling cascade. The second project uses small interfering RNA (siRNA) silencing to inhibit the epileptic pathway. In neurons, actin binding proteins (ABP) and tubulin binding proteins contribute to axon projection. Expression of these proteins is directly associated with the growth of neural circuits. Since epilepsy is deemed to be caused by the formation of abnormal neural circuits, logically speaking, if these proteins are appropriately silenced, epileptogenesis should be inhibited. In this research, cofilin, as an important ABP, is proposed as a targeted protein to control the growth of axons in order to understand the relationship between axon growth and epilepsy at a neuron level. The third project is to evaluate seizure-induced neural injury using optical coherence microscopy. Since this technology can image living tissue based on an intrinsic scattering index, it can be used to investigate neural activities before and after epilepsy and monitor the development of seizure activities at a tissue level. In this project, we firstly validate neuron imaging by OCM with confocal imaging, demonstrating that OCM can be applied to the study of neuron death in the OHC model. Then, after integrating the OCM system with a perfusion system, we use this system to study neural activities and show that there are different optical signals from neurons and surrounding neuropil. The remaining parts of the thesis include other projects done in collaboration with Dr. Liu’s and Dr. Haas’s laboratories

    CRLF2 rearrangement in Ph-like acute lymphoblastic leukemia predicts relative glucocorticoid resistance that is overcome with MEK or Akt inhibition.

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    Philadelphia chromosome-like (Ph-like) acute lymphoblastic leukemia (ALL) is a genetically heterogeneous subtype of B-cell ALL characterized by chromosomal rearrangements and mutations that result in aberrant cytokine receptor and kinase signaling. In particular, chromosomal rearrangements resulting in the overexpression of cytokine receptor-like factor 2 (CRLF2) occur in 50% of Ph-like ALL cases. CRLF2 overexpression is associated with particularly poor clinical outcomes, though the molecular basis for this is currently unknown. Glucocorticoids (GCs) are integral to the treatment of ALL and GC resistance at diagnosis is an important negative prognostic factor. Given the importance of GCs in ALL therapy and the poor outcomes for patients with CRLF2 overexpression, we hypothesized that the aberrant signal transduction associated with CRLF2 overexpression might mediate intrinsic GC insensitivity. To test this hypothesis, we exposed Ph-like ALL cells from patient-derived xenografts to GCs and found that CRLF2 rearranged (CRLF2R) leukemias uniformly demonstrated reduced GC sensitivity in vitro. Furthermore, targeted inhibition of signal transduction with the MEK inhibitor trametinib and the Akt inhibitor MK2206, but not the JAK inhibitor ruxolitinib, was sufficient to augment GC sensitivity. These data suggest that suboptimal GC responses may in part underlie the poor clinical outcomes for patients with CRLF2 overexpression and provide rationale for combination therapy involving GCs and signal transduction inhibitors as a means of enhancing GC efficacy