Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

RIP2 is a serine-threonine kinase associated with the tumor necrosis factor (TNF) receptor complex and is implicated in the activation of NF-kappaB and cell death in mammalian cells. However, the function of its kinase domain is still enigmatic as it is not required in engaging these responses. Here we show that RIP2 activates the extracellular signal-regulated kinase (ERK) pathway and that the kinase activity of RIP2 appears to be important in this process. RIP2 activates AP-1 and serum response element regulated expression by inducing the activation of the Elk1 transcription factor. RIP2 directly phosphorylates and activates ERK2 in vivo and in vitro. RIP2 in turn is activated through its interaction with Ras-activated Raf1. Kinase-defective point and deletion variants of RIP2 also significantly blocked the activation of ERK2 by TNFalpha but not epidermal growth factor. These results describe a novel pathway of ERK activation and the first catalytic function ascribed to any of the RIP-like kinases associated with the TNF receptor superfamily.
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PMID:RIP2 is a Raf1-activated mitogen-activated protein kinase kinase. 1055 58

Epithelial cells are refractory to extracellular lipopolysaccharide (LPS), yet when presented inside the cell, it is capable of initiating an inflammatory response. Using invasive Shigella flexneri to deliver LPS into the cytosol, we examined how this factor, once intracellular, activates both NF-kappaB and c-Jun N-terminal kinase (JNK). Surprisingly, the mode of activation is distinct from that induced by toll-like receptors (TLRs), which mediate LPS responsiveness from the outside-in. Instead, our findings demonstrate that this response is mediated by a cytosolic, plant disease resistance-like protein called CARD4/Nod1. Biochemical studies reveal enhanced oligomerization of CARD4 upon S. flexneri infection, an event necessary for NF-kappaB induction. Dominant-negative versions of CARD4 block activation of NF-kappaB and JNK by S. flexneri as well as microinjected LPS. Finally, we showed that invasive S. flexneri triggers the formation of a transient complex involving CARD4, RICK and the IKK complex. This study demonstrates that in addition to the extracellular LPS sensing system mediated by TLRs, mammalian cells also possess a cytoplasmic means of LPS detection via a molecule that is related to plant disease-resistance proteins.
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PMID:CARD4/Nod1 mediates NF-kappaB and JNK activation by invasive Shigella flexneri. 1146 46

The neurotrophins are growth factors that play critical roles in the development, maintenance, survival, and death of the nervous system. The signal transducing systems that mediate the diverse biological functions of the neurotrophins are initiated by their interactions with two categories of cell surface receptors, the Trk family of tyrosine kinases and the p75 neurotrophin receptor (p75NTR). While the Trk receptors are responsible for most of the survival and growth properties of the neurotrophins, the actions of p75NTR fall into two categories. First, p75NTR is a Trk co-receptor that can enhance or suppress neurotrophin-mediated Trk receptor activity. Second, p75NTR autonomously activates signaling cascades that result in the induction of apoptosis or in the promotion of survival. The signaling cascades activated by p75NTR remain elusive, but structural and functional differences between p75NTR and other tumor necrosis factor receptor (TNFR) superfamily members suggest that p75NTR employs distinct signaling pathways. p75NTR has been shown to activate the NF-kappaB, Akt, and JNK pathways and interacts with several adaptor proteins. Of these, NRAGE, NADE, and NRIF have been associated with the induction of apoptosis, and FAP-1, RIP2, and TRAF6 appear to promote cellular survival. It remains a major challenge to link the various p75NTR binding proteins to specific p75NTR-dependent functions, but the identification of p75NTR interactors and signaling pathways has sparked new directions in p75NTR research, and will provide a better understanding of this enigmatic receptor.
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PMID:Neurotrophin signaling through the p75 neurotrophin receptor. 1216 97

RIP1 and its homologs, RIP2 and RIP3, form part of a family of Ser/Thr kinases that regulate signal transduction processes leading to NF-kappa B activation. Here, we identify RIP4 (DIK/PKK) as a novel member of the RIP kinase family. RIP4 contains an N-terminal RIP-like kinase domain and a C-terminal region characterized by the presence of 11 ankyrin repeats. Overexpression of RIP4 leads to activation of NF-kappa B and JNK. Kinase inactive RIP4 or a truncated version containing the ankyrin repeats have a dominant negative (DN) effect on NF-kappa B induction by multiple stimuli. RIP4 binds to several members of the TRAF protein family, and DN versions of TRAF1, TRAF3 and TRAF6 inhibit RIP4-induced NF-kappa B activation. Moreover, RIP4 is cleaved after Asp340 and Asp378 during Fas-induced apoptosis. These data suggest that RIP4 is involved in NF-kappa B and JNK signaling and that caspase-dependent processing of RIP4 may negatively regulate NF-kappa B-dependent pro-survival or pro-inflammatory signals.
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PMID:RIP4 (DIK/PKK), a novel member of the RIP kinase family, activates NF-kappa B and is processed during apoptosis. 1244 64

Nod2 (CARD15) is a macrophage-specific protein containing two CARD domains, a large nucleotide binding domain and leucine-rich repeats. Human genetic studies have linked mutations in NOD2/CARD15 with Crohn's disease, although the mechanisms involved are unknown. However, Nod2 has been proposed to directly bind bacterial lipopolysaccharide (LPS) and subsequently act as an activator of NF-kappaB via the association of the CARD domains with Rip2/RICK/CARDIAK. This is hypothesized to constitute a pathogen recognition pathway distinct from Toll-like receptor 4-mediated recognition of LPS. Using targeted mutagenesis, we introduced a mutation to delete the CARD domains of mouse Nod2. Mice lacking Nod2 were indistinguishable from controls and showed no signs of intestinal pathology. Macrophages responded normally to multiple Toll-like receptor agonists in terms of NF-kappaB target activation, mitogen-activated protein kinase activation, and cytokine secretion. However, Nod2(-/-) mice were significantly protected in endotoxin challenge experiments, and Nod2(-/-) macrophages were refractory to muramyl dipeptide stimulation. These results argue that Nod2 does not play an essential, nonredundant role in the response of macrophages to bacterial products but rather plays unexpected roles in regulating systemic responses to pathogens.
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PMID:Role of nod2 in the response of macrophages to toll-like receptor agonists. 1456 1

The proteolytic activity of caspases is involved in apoptosis and inflammation. In this regard, caspase-1 is required for pro-interleukin (IL)-1beta and pro-IL-18 maturation. We report here on a novel function of caspase-1 as an activator of nuclear factor of the kappa-enhancer in B-cells (NF-kappaB) and p38 mitogen-activated protein kinase (MAPK). This function is not shared by the murine caspase-1 homologues caspase-11 and -12. In contrast to pro-IL-1beta maturation, caspase-1-induced NF-kappaB activation is not inhibited by the virus-derived caspase-1 inhibitor cytokine response modifier A and is equally induced by the enzymatically inactive caspase-1 C285A mutant. Although the general NF-kappaB-inhibiting protein A20 inhibits caspase-1-derived activation of NF-kappaB, dominant-negative forms of TRAF2 and RIP1 have no effect. We demonstrate that caspase-1 interacts with RIP2 and that dominant-negative forms of RIP2 and IkappaB kinase complex-beta inhibit caspase-1-mediated NF-kappaB activation. Structure-function analysis shows that the caspase recruitment domain of caspase-1 mediates the activation of NF-kappaB and p38 MAPK. These data demonstrate that caspase-1 contributes to inflammation by two distinct pathways: proteolysis of pro-IL-1beta, and RIP2-dependent activation of NF-kappaB and p38 MAPK mediated by the caspase recruitment domain.
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PMID:Caspase-1 activates nuclear factor of the kappa-enhancer in B cells independently of its enzymatic activity. 1503 21

Lipopolysaccharide (LPS) and muramyl dipeptide (MDP) are components of microbial cell walls that cause innate immune responses and inflammation. Toll-like receptor 4 (TLR4) is a receptor for LPS and transduces signals through myeloid differentiation factor 88 (MyD88), which plays essential roles in the TLR/IL-1R signaling and activates NF-kappaB and MAP kinase pathways to induce RANKL expression in osteoblasts. Osteoblasts express NOD2, an intracellular sensor for MDP, in response to LPS, IL-1 and TNF. NOD2 binds RIP2, a serine/threonine kinase which transduces NF-kappaB signaling. Thus MDP synergistically enhances osteoclast formation induced by LPS, IL-1 and TNF through RANK ligand up-regulation in osteoblasts. In summary, innate immune receptors, TLR4 and NOD2, recognize bacterial components on cell surfaces and inside cells, respectively, and these signals cross-talk to induce RANKL expression in osteoblasts, which results in enhancing osteoclast formation and function.
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PMID:[Osteoclastogenesis through TLR/NOD signaling]. 1616 10

Nod1 is a member of the NLR/Nod/CATERPILLER family. It acts as a sensor for intracellular bacteria by recognizing specific glycopeptides derived from peptidoglycan. Nod1 activation mediates distinct cellular responses including activation of MAP kinases, IL-8 release, apoptosis and suppression of several estrogen-dependent responses in MCF-7 cells. Here we have extended these studies by identifying key regulatory steps in Nod1-dependent signaling pathways. We provide multiple lines of data showing that Nod1-dependent apoptosis is a caspase 8-mediated event and that apoptosis requires RIP2. In contrast, several lines of evidence show that Nod1-dependent JNK activation and IL-8 production did not require the presence of caspase 8 but required activation of TAK1 as well as RIP2. Thus, we have identified several key control points that lie downstream of Nod1. This work provides the basis for further studies of the biological significance and regulation of the Nod1 pathway.
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PMID:Regulation of Nod1-mediated signaling pathways. 1718 25

MDP (muramyl dipeptide), a component of peptidoglycan, interacts with NOD2 (nucleotide-binding oligomerization domain 2) stimulating the NOD2-RIP2 (receptor-interacting protein 2) complex to activate signalling pathways important for antibacterial defence. Here we demonstrate that the protein kinase activity of RIP2 has two functions, namely to limit the strength of downstream signalling and to stabilize the active enzyme. Thus pharmacological inhibition of RIP2 kinase with either SB 203580 [a p38 MAPK (mitogen-activated protein kinase) inhibitor] or the Src family kinase inhibitor PP2 induces a rapid and drastic decrease in the level of the RIP2 protein, which may explain why these RIP2 inhibitors block MDP-stimulated downstream signalling and the production of IL-1beta (interleukin-1beta) and TNFalpha (tumour necrosis factor-alpha). We also show that RIP2 induces the activation of the protein kinase TAK1 (transforming-growth-factor-beta-activated kinase-1), that a dominant-negative mutant of TAK1 inhibits RIP2-induced activation of JNK (c-Jun N-terminal kinase) and p38alpha MAPK, and that signalling downstream of NOD2 or RIP2 is reduced by the TAK1 inhibitor (5Z)-7-oxozeaenol or in TAK1-deficient cells. We also show that MDP activates ERK1 (extracellular-signal-regulated kinase 1)/ERK2 and p38alpha MAPK in human peripheral-blood mononuclear cells and that the activity of both MAPKs and TAK1 are required for MDP-induced signalling and production of IL-1beta and TNFalpha in these cells. Taken together, our results indicate that the MDP-NOD2/RIP2 and LPS (lipopolysaccharide)-TLR4 (Toll-like receptor 4) signalling pathways converge at the level of TAK1 and that many subsequent events that lead to the production of pro-inflammatory cytokines are common to both pathways.
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PMID:Molecular mechanisms involved in the regulation of cytokine production by muramyl dipeptide. 1734 59

The Crohn's-disease-susceptibility protein, NOD2, coordinates signaling responses upon intracellular exposure to bacteria. Although NOD2 is known to activate NFkappaB, little is known about the molecular mechanisms by which NOD2 coordinates functionally separate signaling pathways such as NFkappaB, JNK, and p38 to regulate cytokine responses. Given that one of the characteristics of Crohn's disease is an altered cytokine response to normal bacterial flora, the coupling of signaling pathways could be important for Crohn's-disease pathophysiology. We find that a MAP3K, MEKK4, binds to RIP2 to sequester RIP2 from the NOD2 signaling pathway. This MEKK4:RIP2 complex dissociates upon exposure to the NOD2 agonist, MDP, allowing NOD2 to bind to RIP2 and activate NFkappaB. MEKK4 thus sequesters RIP2 to inhibit the NOD2:RIP2 complex from activating NFkappaB signaling pathways, and Crohn's-disease-associated NOD2 polymorphisms cannot compete with MEKK4 for RIP2 binding. Lastly, we find that MEKK4 helps dictate signal specificity downstream of NOD2 activation as knockdown of MEKK4 in macrophages exposed to MDP causes increased NFkappaB activity, absent p38 activity, and hyporesponsiveness to TLR2 and TLR4 agonists. These biochemical findings suggest that basal inhibition of the NOD2-driven NFkappaB pathway by MEKK4 could be important in the pathogenesis of Crohn's disease.
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PMID:MEKK4 sequesters RIP2 to dictate NOD2 signal specificity. 1877 59


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