Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heparin can substitute for double-stranded (ds) RNA in the autophosphorylation and activation of the interferon-inducible, RNA-dependent elF-2 alpha protein kinase (PKR). We have used heparin oligosaccharides of defined lengths to examine the heparin-mediated activation of human PKR. Heparin oligosaccharide with 8 sugar residues was nearly as efficient as 16-residue heparin (Hep-16) in mediating the activation of PKR autophosphorylation, whereas 6-residue heparin was a poor activator. When examined in combination, Hep-16 and dsRNA did not act synergistically in activating PKR autophosphorylation. The RNA-binding activity of recombinant PKR, measured with adenovirus VA RNA, was competed by poly(rl):poly(rC) but not by Hep-16. When the catalytically inactive, histidine-tagged mutant PKR protein [His-PKR(K296R)] was examined as a substrate for purified wild-type PKR, the intermolecular phosphorylation of His-PKR(K296R) was efficiently catalyzed by dsRNA-activated PKR but not by heparin-activated PKR. However, elF-2 alpha phosphorylation was catalyzed by both heparin-and dsRNA-activated PKR. Preincubation of PKR with Hep-16 in the absence of ATP blocked subsequent autophosphorylation mediated either by Hep-16 or dsRNA, whereas preincubation with dsRNA either alone or in combination with Hep-16 did not impair subsequent autophosphorylation. Neither Hep-16 nor dsRNA caused a detectable degradation of PKR during preincubation or subsequent autophosphorylation of PKR. These results suggest that, while both dsRNA and heparin are capable of activating PKR autophosphorylation, the structural and functional basis of PKR activation differs for these two classes of polyanionic biomolecules.
...
PMID:Characterization of the heparin-mediated activation of PKR, the interferon-inducible RNA-dependent protein kinase. 866 26

The gene encoding the interferon-inducible, RNA-dependent protein kinase (PKR) was isolated as lambda phage and P1 phage clones from human genomic DNA libraries and characterized by Southern blot and nucleotide sequence analyses. Southern blot analyses were consistent with a single PKR gene, and genomic clones colocalized by fluorescence in situ hybridization to human chromosome 2p. Sequence analysis demonstrated that the human PKR gene consists of 17 exons and spans about 50 kb. The AUG translation initiation site for the 551-amino-acid PKR protein was located in exon 3; exon 17 was the largest exon and included the UAG translation termination site, AUUAAA polyadenylation signal, and putative C(A) 3' cleavage site. Two RNA-binding motifs, RI and RII, were present in exons 4 and 6, respectively, and the codon phasing of these exon junctions was conserved between them. The organization of the regulatory and catalytic subdomains of the PKR protein was remarkably preserved between the human and the mouse PKR genes; the amino acid junction positions for 13 of the 15 protein coding exons were exactly conserved.
...
PMID:Structural organization of the human gene (PKR) encoding an interferon-inducible RNA-dependent protein kinase (PKR) and differences from its mouse homolog. 881 37

Tumor necrosis factor alpha (TNF-alpha) is well-characterized for its necrotic action against tumor cells; however, it has been increasingly associated with an apoptosis-inducing potential on target cells. While the signaling events and the actual cytolytic mechanism(s) for both TNF-alpha-induced necrosis and apoptosis remain to be fully elucidated, we report here on (i) the ability of TNF-alpha to induce apoptosis in the promonocytic U937 cells, (ii) the discovery of a cross-talk between the TNF-alpha and the interferon signaling pathways, and (iii) the pivotal role of interferon-inducible, double-stranded RNA-activated protein kinase (PKR) in the induction of apoptosis by TNF-alpha. Our data from microscopy studies, trypan blue exclusion staining, and apoptotic DNA ladder electrophoresis revealed that a subclone derived from U937 and carrying a PKR antisense expression vector was resistant to TNF-alpha-induced apoptosis. Further, TNF-alpha initiated a generalized RNA degradation process in which the participation of PKR was required. Finally, the PKR gene is a candidate "death gene" since overexpression of this gene could bring about apoptosis in U937 cells.
...
PMID:An essential role for the interferon-inducible, double-stranded RNA-activated protein kinase PKR in the tumor necrosis factor-induced apoptosis in U937 cells. 890 2

The pkr gene encoding the interferon-inducible, RNA-dependent protein kinase was isolated as lambda phage and P1 phage clones from human genomic DNA and characterized by restriction mapping, Southern blot analysis, and nucleotide sequencing. The genomic nucleotide sequence, when compared to that of previously determined cDNA sequences, revealed 17 exons encoding the 551-amino-acid PKR protein. We report herein the sequence of the human PKR protein kinase deduced from genomic clones.
...
PMID:Mechanism of interferon action sequence of the human interferon-inducible RNA-dependent protein kinase (PKR) deduced from genomic clones. 892 13

The interferon-inducible double-stranded RNA protein kinase PKR controls protein synthesis through the phosphorylation of eukaryotic translation initiation factor (eIF)-2. In addition to its demonstrated role in translational control, several reports have suggested a transcriptional role for PKR. Here we report that PKR is involved in IFN- and dsRNA-signaling pathways by modulating the function of the signal transducer and activator of transcription STAT1. We also show that PKR associates with STAT1 in mouse and human cells. The association is not a kinase-substrate interaction since STAT1 phosphorylation is not modified by PKR in vitro or in vivo. In addition, the formation of the PKR-STAT1 complex is not dependent upon the enzymatic activity of PKR but does require the dsRNA-binding domain of PKR. Moreover, there is a concomitant decrease in PKR-STAT1 interaction and increase in STAT1 DNA binding in response to IFNs or dsRNA. These findings suggest that PKR plays an important role in IFN and dsRNA-signaling pathways by modulating the transcriptional function of STAT1.
...
PMID:Physical association between STAT1 and the interferon-inducible protein kinase PKR and implications for interferon and double-stranded RNA signaling pathways. 913 45

The RNA-regulated protein kinase, (PKR) is an interferon-inducible enzyme of widespread occurrence in eukaryotic organisms. This serine/threonine-specific protein kinase is activated by double-stranded RNA by a mechanism involving autophosphorylation. Once activated, the enzyme phosphorylates the alpha subunit of protein synthesis initiation factor eIF2, thereby inhibiting translation. Recent evidence suggests that there may be additional substrates, and that signal transduction and gene transcription pathways also may be regulated by the protein kinase. As well as being important in mediating the antiviral effects of interferons, PKR is implicated in regulating cell proliferation in uninfected cells and may have a tumour suppressor function under normal conditions. Studies using cell lines expressing inactive mutants of PKR and mice with homozygous disruptions of the PKR gene are leading to greater insights into the biological significance of this enzyme.
...
PMID:PKR--a protein kinase regulated by double-stranded RNA. 937 75

The interferon-inducible, double-stranded (ds) RNA-dependent serine/threonine protein kinase (PKR) plays a role in viral pathogenesis, cell growth, and differentiation and is implicated as a tumor suppressor gene. Expression of a trans-dominant negative, catalytically inactive mutant PKR protected NIH3T3 cells from apoptosis in response to either treatment with tumor necrosis factor alpha (TNF alpha), serum deprivation. In cells expressing mutant PKR, TNF alpha, but not dsRNA induced transcription from a nuclear factor kappa B-dependent promoter, demonstrating specificity for dsRNA in signaling through the PKR pathway. Serum or platelet-derived growth factor addition to serum-deprived mutant PKR-expressing cells induced transcription of the early response genes c-fos and c-jun, indicating that the immediate early response signaling was intact. Overexpression of wild-type PKR in a transient DNA transfection system was sufficient to induce apoptosis. TNF alpha-induced apoptosis correlated with increased phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2 alpha), the primary physiological substrate of the PKR. Furthermore, forced expression of a nonphosphorylatable S51A mutant eIF-2 alpha partially protected cells from TNF alpha-induced apoptosis, and expression of a S51D mutant eIF-2 alpha, a mutant that mimics phosphorylated eIF-2 alpha, was sufficient to induce apoptosis. Taken together, these studies identify a novel requirement for PKR in stress-induced apoptosis that is mediated through eIF-2 alpha phosphorylation.
...
PMID:Phosphorylation of eukaryotic translation initiation factor 2 mediates apoptosis in response to activation of the double-stranded RNA-dependent protein kinase. 944 91

The interferon-inducible, double-stranded (ds) RNA-dependent protein kinase (PKR) regulates protein synthesis initiation by phosphorylating the alpha-subunit of eukaryotic translation initiation factor 2 (eIF-2). The amino-terminal half of PKR contains two dsRNA binding domains, and the kinase domain resides in the carboxy-terminal half of the protein. PKR is a ribosomal-associated protein. In this report, we provide evidence that PKR contains three ribosome interaction sites, two that are localized in each of the dsRNA binding domains and one that is localized in the kinase domain. All three domains can associate with polysomes independently. The ribosome association of the dsRNA binding domains requires dsRNA binding activity. Ribosome interaction of either the individual or the combined dsRNA binding domains was disrupted by 0.1 M KCl. In contrast, the ribosome interaction of intact PKR and the isolated kinase domain was largely resistant to 0.5 M KCl. These results indicate that all three domains of PKR contribute to the high-affinity ribosomal association. After dissociation of polysomes with EDTA, both intact PKR and the isolated kinase domain were primarily associated with the 60S ribosomal subunit. Coexpression of the adenovirus VAI RNA, an RNA polymerase III gene product that binds and inactivates PKR, disrupted ribosomal association of intact PKR, but not of the isolated PKR kinase domain. The results support a model where VAI RNA induces a major conformational change in PKR to prohibit ribosome association of all interaction sites. In contrast, other inhibitors of PKR including vaccinia virus E3L and K3L gene products, and the HIV trans-activating response (TAR) element binding protein TRBP, did not disrupt ribosome association of PKR. The results suggest a novel mechanism by which viral RNAs may inactivate PKR through disrupting ribosome association.
...
PMID:Identification and requirement of three ribosome binding domains in dsRNA-dependent protein kinase (PKR). 975 71

Previous evidence has shown that the majority of the interferon-inducible, double-stranded RNA-dependent protein kinase PKR is associated with ribosomes in vivo. Here we show that ribosomes are inhibitory for PKR activity since they compete with dsRNA for binding to PKR, inhibit the activation of the protein kinase by dsRNA, and prevent the phosphorylation of the PKR substrate eIF2alpha. We suggest that ribosomes constitute a reservoir of inactive PKR and that the protein kinase must be displaced from the ribosome by dsRNA in order to become activated.
...
PMID:Inhibition of the double-stranded RNA-dependent protein kinase PKR by mammalian ribosomes. 980 Nov 45

PKR is an interferon-inducible, double-stranded (ds) RNA-activated serine/threonine protein kinase, and has been shown to play roles in viral pathogenesis, cell growth and apoptosis. We expressed PKR as a fusion protein with enhanced jellyfish green fluorescence protein (EGFP) in human embryonic kidney 293 cells to visualize the effect of PKR transfection. The EGFP-fusion construct with wild-type PKR showed both auto- and substrate-phosphorylation activities independent of dsRNA, indicating EGFP-PKR is constitutively active. The EGFP-construct with a mutant PKR with the first RNA binding domain deleted still possessed kinase activities. On the other hand, the EGFP-fusion with a catalytically inactive mutant of PKR with the substitution of K at 296 with R, which has been shown to have tumorigenic properties, did not possess kinase activities. Transfection of the constitutive active forms of EGFP-PKR constructs induced apoptosis in 293 cells without dsRNA, whereas the EGFP-fusion with the catalytically inactive mutant did not cause apoptosis but rather protected cells from Fas-induced cell death. In addition, Fas-stimulation increased endogenous PKR activities. These results constitute evidence that PKR is sufficient to induce apoptosis, and plays a role in Fas-mediated apoptosis.
...
PMID:Double-stranded RNA-activated protein kinase (PKR) fused to green fluorescent protein induces apoptosis of human embryonic kidney cells: possible role in the Fas signaling pathway. 999 Jan 39


<< Previous 1 2 3 4 5 6 7 Next >>

---