EC:2.7.11.10 - FACTA Search

Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.10 (IKK)
4,900 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The interferon (IFN)-inducible double-stranded-RNA (dsRNA)-activated serine-threonine protein kinase (PKR) is a major mediator of the antiviral and antiproliferative activities of IFNs. PKR has been implicated in different stress-induced signaling pathways including dsRNA signaling to nuclear factor kappa B (NF-kappaB). The mechanism by which PKR mediates activation of NF-kappaB is unknown. Here we show that in response to poly(rI). poly(rC) (pIC), PKR activates IkappaB kinase (IKK), leading to the degradation of the inhibitors IkappaBalpha and IkappaBbeta and the concomitant release of NF-kappaB. The results of kinetic studies revealed that pIC induced a slow and prolonged activation of IKK, which was preceded by PKR activation. In PKR null cell lines, pIC failed to stimulate IKK activity compared to cells from an isogenic background wild type for PKR in accord with the inability of PKR null cells to induce NF-kappaB in response to pIC. Moreover, PKR was required to establish a sustained response to tumor necrosis factor alpha (TNF-alpha) and to potentiate activation of NF-kappaB by cotreatment with TNF-alpha and IFN-gamma. By coimmunoprecipitation, PKR was shown to be physically associated with the IKK complex. Transient expression of a dominant negative mutant of IKKbeta or the NF-kappaB-inducing kinase (NIK) inhibited pIC-induced gene expression from an NF-kappaB-dependent reporter construct. Taken together, these results demonstrate that PKR-dependent dsRNA induction of NF-kappaB is mediated by NIK and IKK activation.
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PMID:NF-kappaB activation by double-stranded-RNA-activated protein kinase (PKR) is mediated through NF-kappaB-inducing kinase and IkappaB kinase. 1064 14

Besides its known role as a translational controlling factor, the double stranded RNA-dependent protein kinase (PKR) is a key transcriptional regulator exerting antiviral and antitumoural activities. We have recently described that induction of NF-kappa B by PKR is involved in apoptosis commitment. To define how PKR mediates NF-kappa B activation by dsRNA, we have used two different approaches, one based on expression of PKR by a vaccinia virus (VV) recombinant and the other based on induction of endogenous PKR by poly I:C (pIC) treatment. We found that NF-kappa B complexes induced by PKR are composed primarily of p50-p65 heterodimers and also of c-rel-p50 heterodimers. As described for other stimuli, following pIC treatment, PKR phosphorylates the NF-kappa B inhibitor I kappa B alpha at serine 32 before degradation. Expression by VV recombinants of IKK1 or IKK2 dominant negative mutants together with PKR showed inhibition of PKR-induced NF-kappa B activation, as measured both by gel shift and luciferase reporter assays. Immunoprecipitation analysis revealed that PKR interacts with the IKK complex. Our findings demonstrate that physiological function(s) of PKR involve activation of the I kappa B kinase complex. Oncogene (2000) 19,1369 - 1378.
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PMID:Activation of NF-kappa B by the dsRNA-dependent protein kinase, PKR involves the I kappa B kinase complex. 1072 27

The interferon (IFN)-induced double-stranded RNA-activated protein kinase PKR mediates inhibition of protein synthesis through phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) and is also involved in the induction of the IFN gene through the activation of the transcription factor NF-kappaB. NF-kappaB is retained in the cytoplasm through binding to its inhibitor IkappaBalpha. The critical step in NF-kappaB activation is the phosphorylation of IkappaBalpha by the IkappaB kinase (IKK) complex. This activity releases NF-kappaB from IkappaBalpha and allows its translocation to the nucleus. Here, we have studied the ability of PKR to activate NF-kappaB in a reporter assay and have shown for the first time that two catalytically inactive PKR mutants, PKR/KR296 and a deletion mutant (PKR/Del42) which lacks the potential eIF2alpha-binding domain, can also activate NF-kappaB. This result indicated that NF-kappaB activation by PKR does not require its kinase activity and that it is independent of the PKR-eIF2alpha relationship. Transfection of either wild-type PKR or catalytically inactive PKR in PKR(0/0) mouse embryo fibroblasts resulted in the activation of the IKK complex. By using a glutathione S-transferase pull-down assay, we showed that PKR interacts with the IKKbeta subunit of the IKK complex. This interaction apparently does not require the integrity of the IKK complex, as it was found to occur with extracts from cells deficient in the NF-kappaB essential modulator, one of the components of the IKK complex. Therefore, our results reveal a novel pathway by which PKR can modulate the NF-kappaB signaling pathway without using its kinase activity.
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PMID:PKR stimulates NF-kappaB irrespective of its kinase function by interacting with the IkappaB kinase complex. 1084 80

The double stranded RNA-dependent protein kinase (PKR), in addition to its role as a translational controlling factor, is a key transcriptional regulator exerting antiviral and antitumoral activities. We have previously shown that induction of NF-kappaB by PKR is involved in apoptosis commitment and this process is mediated through activation of the IKK complex. To gain insights into the mechanism of activation of NF-kappaB by PKR, we have analysed the domains of PKR involved in IKK activation and subsequent NF-kappaB induction. In PKR(0/0) cells infected with a collection of vaccinia virus (VV) recombinants expressing different mutant forms of PKR, we found that only PKR forms conserving the catalytic activity are able to activate NF-kappaB. An inactive PKR mutant (K296R), was unable to induce NF-kappaB activation despite full expression of the protein in a wide range of concentrations, as defined by Western blot, EMSA, IKK kinase activity and NF-kappaB transactivation assays. Moreover, the mutant PKR (K296R) acts as a dominant negative of PKR-induced eIF-2alpha phosphorylation and NF-kappaB activation. However, PKR mutants unable to activate NF-kappaB still retain their ability to associate with the IKK complex, as confirmed by immunoprecipitation analysis. We conclude that the catalytic activity of PKR and not only a protein-protein interaction with the IKK complex, is needed for activation of the transcription factor NF-kappaB.
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PMID:The catalytic activity of dsRNA-dependent protein kinase, PKR, is required for NF-kappaB activation. 1131 68

The vital role of interferons (IFNs) as mediators of innate immunity is well established. It has recently become apparent that one of the pivotal proteins in mediating the antiviral activity of IFNs, the double-stranded RNA (dsRNA)-activated protein kinase (PKR), also functions as a signal transducer in the proinflammatory response to different agents. PKR is a member of a small family of kinases that are activated by extracellular stresses and that phosphorylate the alpha subunit of protein synthesis initiation factor eIF-2, thereby inhibiting protein synthesis. The activation of PKR during infection by viral dsRNA intermediates results in the inhibition of viral replication. PKR also mediates the activation of signal transduction pathways by proinflammatory stimuli, including bacterial lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-alpha), and interleukin 1 (IL-1). PKR is a component of the inhibitor of kappaB (IkappaB) kinase complex and plays either a catalytic or structural role in the activation of IkappaB kinase, depending on the stimulus. The activities of the stress-activated protein kinases p38 and c-Jun NH(2)-terminal kinase (JNK) are also regulated by PKR in a pathway that leads to the production of proinflammatory cytokines. This review will focus on the role of PKR in nuclear factor kappa B (NF-kappaB) and mitogen-activated protein kinase (MAPK) pathways, because these have been the subjects of a series of publications over the past year that have reported conflicting findings. Although the conflicts may not be resolved in this review, suggestions are made for experiments that could lead to a clearer understanding of the mechanisms involved.
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PMID:Signal integration via PKR. 1175 61

Viral infection is one of the leading causes of brain encephalitis and meningitis. Recently, it was reported that Toll-like receptor-3 (TLR3) induces a double-stranded RNA (dsRNA)-mediated inflammatory signal in the cells of the innate immune system, and studies suggested that dsRNA may induce inflammation in the central nervous system (CNS) by activating the CNS-resident glial cells. To explore further the connection between dsRNA and inflammation in the CNS, we have studied the effects of dsRNA stimulation in astrocytes. Our results show that the injection of polyinosinic-polycytidylic acid (poly(I:C)), a synthetic dsRNA, into the striatum of the mouse brain induces the activation of astrocytes and the expression of TNF-alpha, IFN-beta, and IP-10. Stimulation with poly(I:C) also induces the expression of these proinflammatory genes in primary astrocytes and in CRT-MG, a human astrocyte cell line. Furthermore, our studies on the intracellular signaling pathways reveal that poly(I:C) stimulation activates IkappaB kinase (IKK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) in CRT-MG. Pharmacological inhibitors of nuclear factor-kappaB (NF-kappaB), JNK, ERK, glycogen synthase kinase-3beta (GSK-3beta), and dsRNA-activated protein kinase (PKR) inhibit the expression of IL-8 and IP-10 in astrocytes, indicating that the activation of these signaling molecules is required for the TLR3-mediated chemokine gene induction. Interestingly, the inhibition of PI3 kinase suppressed the expression of IP-10, but upregulated the expression of IL-8, suggesting differential roles for PI3 kinase, depending on the target genes. These data suggest that the TLR3 expressed on astrocytes may initiate an inflammatory response upon viral infection in the CNS.
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PMID:TLR3-mediated signal induces proinflammatory cytokine and chemokine gene expression in astrocytes: differential signaling mechanisms of TLR3-induced IP-10 and IL-8 gene expression. 1626 67

The interferon-inducible, double-stranded (ds)RNA-dependent protein kinase (PKR) plays a major role in antiviral defense mechanisms where it down-regulates translation via phosphorylation of eukaryotic translation initiation factor 2alpha. PKR is also involved in the activation of nuclear factor kappaB (NFkappaB) through activation of the IkappaB kinase complex. Activation of PKR can occur in the absence of dsRNA and in such case is controlled by intracellular regulators like the PKR-activating protein (PACT), the PKR inhibitor p58(IPK), or heat-shock proteins (Hsp). These regulators are activated by stress stimuli, supporting a role for PKR in response to stress; however the final outcome of PKR activation in stress situations is unclear. We present here evidence that expression and activation of PKR contributes to an increased cellular resistance to mercury cytotoxicity. In two cell lines constitutively expressing PKR (THP-1 and Molt-3), treatment with the PKR inhibitor 2-aminopurine increases their sensitivity to mercury. In contrast, Ramos cells, which do not constitutively express PKR, present an increased resistance to mercury when PKR expression is induced by polyIC or interferon-beta treatment. This protective effect is inhibited by 2-aminopurine. We also show that exposure of Ramos cells to mercury leads to the induction of Hsp70. Treatment of cells with Hsp70 or NFkappaB inhibitors suppresses the PKR-dependent protection. We propose a model where PKR, modulated by Hsp70, activates a NFkappaB-mediated protective pathway. Because the cytotoxicity of mercury is primarily due to the generation of reactive oxygen species, our results suggest a more general function of PKR in the mechanisms of cellular response to oxidative stress.
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PMID:Double-stranded RNA-dependent protein kinase (PKR) is a stress-responsive kinase that induces NFkappaB-mediated resistance against mercury cytotoxicity. 1632 19

The interferon-induced double-stranded RNA (dsRNA)-activated protein kinase (PKR) has been shown to activate NF-kappaB independently of its kinase function after interaction with the IKK complex. In order to investigate the mechanism of NF-kappaB activation by PKR, we identified the domain of PKR responsible for stimulating the NF-kappaB pathway in PKR-deficient fibroblasts using an NF-kappaB dependent reporter assay. The N-terminal 1-265 AA of PKR activates NF-kappaB, whereas the 1-180 AA N-terminus restricted to the two dsRNA Binding Domains (DRBD), the third basic domain alone (AA 181-265), or the C-terminus of PKR (AA 266-550) were unable to stimulate the expression of the NF-kappaB dependent reporter gene. Using confocal microscopy, we confirmed that PKR full length as well as PKR N-terminus colocalized with IKKbeta. By GST-pulldown analysis, using different PKR domains, we then revealed the specific ability of the PKR N-terminus 1-265 to bind to and activate IKK and showed that this activation requires the integrity of the IKK complex. This activation is not only due to DRBDs since the DRBD fragment 1-180 failed to inhibit PKR 1-265 induced NF-kappaB activation. Our results therefore demonstrate that the ability of PKR to mediate NF-kappaB activation resides in its full N-terminus, and requires both DRBDs and the third basic domain.
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PMID:The N-terminus of PKR is responsible for the activation of the NF-kappaB signaling pathway by interacting with the IKK complex. 1660 May 70

Double-stranded RNA-dependent protein kinase (PKR), a ubiquitously expressed serine/threonine kinase, has been implicated in the regulation or modulation of cell growth through multiple signaling pathways, but how PKR regulates tumor necrosis factor (TNF)-induced signaling pathways is poorly understood. In the present study, we used fibroblasts derived from PKR gene-deleted mice to investigate the role of PKR in TNF-induced activation of nuclear factor-kappaB (NF-kappaB), mitogen-activated protein kinases (MAPKs) and growth modulation. We found that in wild-type mouse embryonic fibroblast (MEF), TNF induced NF-kappaB activation as measured by DNA binding but deletion of PKR abolished this activation. This inhibition was associated with suppression of inhibitory subunit of NF-kappaB (IkappaB)alpha kinase (IKK) activation, IkappaBalpha phosphorylation and degradation, p65 phosphorylation and nuclear translocation, and NF-kappaB-dependent reporter gene transcription. TNF-induced Akt activation needed for IKK activation was also abolished by deletion of PKR. NF-kappaB activation was diminished in PKR-deleted cells transfected with TNF receptor (TNFR) 1, TNFR-associated death domain and TRAF2 plasmids; NF-kappaB activated by NF-kappaB-inducing kinase, IKK or p65, however, was minimally affected. Among the MAPKs, it was interesting that whereas TNF-induced c-Jun N-terminal kinase (JNK) activation was abolished, activation of p44/p42 MAPK and p38 MAPK was potentiated in PKR-deleted cells. TNF induced the expression of NF-kappaB-regulated gene products cyclin D1, c-Myc, matrix metalloproteinase-9, survivin, X-linked inhibitor-of-apoptosis protein (IAP), IAP1, Bcl-x(L), A1/Bfl-1 and Fas-associated death domain protein-like IL-1beta-converting enzyme-inhibitory protein in wild-type MEF but not in PKR-/- cells. Similarly, TNF induced the proliferation of wild-type cells, but this proliferation was completely suppressed in PKR-deleted cells. Overall, our results indicate that PKR differentially regulates TNF signaling; IKK, Akt and JNK were positively regulated, whereas p44/p42 MAPK and p38 MAPK were negatively regulated.
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PMID:Genetic deletion of PKR abrogates TNF-induced activation of IkappaBalpha kinase, JNK, Akt and cell proliferation but potentiates p44/p42 MAPK and p38 MAPK activation. 1692 32

The double-stranded RNA-dependent protein kinase PKR is a critical mediator of the antiproliferative and antiviral effects exerted by interferons. Not only is PKR an effector molecule on the cellular response to double-stranded RNA, but it also integrates signals in response to Toll-like receptor activation, growth factors, and diverse cellular stresses. In this review, we provide a detailed picture on how signaling downstream of PKR unfolds and what are the ultimate consequences for the cell fate. PKR activation affects both transcription and translation. PKR phosphorylation of the alpha subunit of eukaryotic initiation factor 2 results in a blockade on translation initiation. However, PKR cannot avoid the translation of some cellular and viral mRNAs bearing special features in their 5' untranslated regions. In addition, PKR affects diverse transcriptional factors such as interferon regulatory factor 1, STATs, p53, activating transcription factor 3, and NF-kappaB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IkappaB and NF-kappaB nuclear translocation has been intensively studied. At the cellular and organism levels PKR exerts antiproliferative effects, and it is a key antiviral agent. A point of convergence in both effects is that PKR activation results in apoptosis induction. The extent and strength of the antiviral action of PKR are clearly understood by the findings that unrelated viral proteins of animal viruses have evolved to inhibit PKR action by using diverse strategies. The case for the pathological consequences of the antiproliferative action of PKR is less understood, but therapeutic strategies aimed at targeting PKR are beginning to offer promising results.
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PMID:Impact of protein kinase PKR in cell biology: from antiviral to antiproliferative action. 1715 6

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