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)

Interferon-induced proteins have been previously implicated in the regulation of cell growth. In an attempt to provide evidence for the involvement of these proteins in differentiation, the effect of transforming growth factor beta 1 (TGF-beta) and EGTA on the expression and activity of (2'-5') oligoadenylate synthetase (2-5A synthetase) and double-stranded RNA activated protein kinase (PKR) during myogenesis of rat primary skeletal muscle cultures or the myogenic cell line L8 was studied. Both TGF-beta and EGTA inhibited the fusion of myoblasts and reduced significantly the level of the muscle-specific proteins, acetylcholine receptors, and creatine kinase activity in rat primary muscle cultures. Likewise, TGF-beta exhibited a similar inhibitory effect on the fusion of L8 cells and the level of creatine kinase activity in these cells. The kinetics of 2-5A synthetase activity in both types of cells during differentiation was then established. In both types, a transient increase in activity was observed followed by a decrease thereafter. However, while the peak activity in primary muscle cultures appeared after 24 h in culture, it was observed only on the third day in L8 cells grown in differentiation medium (DM). Treatment of primary cultures with either TGF-beta or EGTA reduced the amount of 1.7-kb 2-5A synthetase-specific RNA transcripts and decreased significantly the level of 2-5A synthetase activity compared to that in untreated cultures. Western blot analysis of 2-5A synthetase proteins in untreated primary muscle cultures showed that the major species synthesized in these cells was the 43-kDa isoform of the enzyme. However, the 71-kDa isoform was clearly visible after 72 h in culture. Both TGF-beta and EGTA abrogated the appearance of all forms of 2-5A synthetase. Similarly, in L8 cells grown in DM, TGF-beta down-regulated the expression of 2-5A synthetase and reduced the level of enzymatic activity. Western blot analysis revealed the presence of the 71-kDa isoform as the major species of 2-5A synthetase in L8 cells; however, the 43-kDa isoform was also visible on the third day in DM. TGF-beta treatment resulted in a reduced amount of 2-5A synthetase proteins. The kinetics of PKR activity in L8 cells grown in DM was similar to that observed with 2-5A synthetase. Furthermore, TGF-beta strongly reduced the level of PKR activity in differentiating L8 cells.
...
PMID:Interruption of myogenesis by transforming growth factor beta 1 or EGTA inhibits expression and activity of the myogenic-associated (2'-5') oligoadenylate synthetase and PKR. 762 37

Plant virus or viroid infection stimulates the phosphorylation of a plant-encoded protein of M(r) 68,000 to 70,000 (now termed pPKR) that is associated with double-stranded RNA-stimulated protein kinase activity. Using various biochemical and immunological comparisons, we have demonstrated that this plant protein is an analog of the mammalian PKR enzymes. pPKR is both cytosolic and ribosome associated, similar to mammalian PKR, and appears to be capable of phosphorylating exogenous histones. Monoclonal anti-serum to the human PKR as well as antiserum to a conserved double-stranded RNA-binding domain present on mammalian PKR demonstrated cross-reactivity with pPKR. Likewise, polyclonal antiserum to the pPKR detected the mouse and human PKR in western blot analysis. Northern blot analysis of a mammalian PKR cDNA detected a specific 2.5-kb transcript present in plant poly (A)+ RNA.
...
PMID:Identification of a plant-encoded analog of PKR, the mammalian double-stranded RNA-dependent protein kinase. 763 Sep 44

The double-stranded RNA (dsRNA)-activated protein kinase, now called PKR, was first discovered by virtue of its ability to phosphorylate translation initiation factor eIF-2 and inhibit its activity. Recent studies have shown that expression of inactive mutants of PKR in cultured cells causes them to acquire characteristics typical of transformed cells. These and other findings indicate that PKR plays a role in the normal control of cell growth and differentiation. It seems likely that, in addition to eIF-2, PKR has other substrates including the protein I-kappa B, which regulates the transcription of certain genes. Indeed, it now seems likely that PKR mediates the regulation of selected genes by dsRNA.
...
PMID:PKR: a new name and new roles. 763 21

RNA-dependent protein kinase is a M(r) 68,000 protein in human cells (p68 kinase) or a M(r) 65,000 protein in murine cells (p65 kinase). p65/p68 is a serine/threonine kinase induced by interferon treatment and generally activated by double-stranded RNAs. Once activated, the known function of this kinase is inhibition of protein synthesis through phosphorylation of the eukaryotic initiation factor 2. Here we have investigated the potential for tumorigenicity in mice of murine NIH 3T3 clones expressing human p68 kinase, either the wild-type or a mutant inactive kinase with a single amino acid substitution in the invariant lysine-296 in the catalytic domain II. Expression of the mutant p68 kinase was correlated with a malignant transformation phenotype, giving rise to the production of large tumors of at least 1 cm in diameter within 7-12 days in all inoculated mice. In contrast, no tumor growth was observed for several weeks in mice inoculated with NIH 3T3 cell clones expressing either the wild-type recombinant p68 kinase or only the endogenous p65 kinase, the murine analogue of the p68 kinase. These results suggest that functional p65/p68 kinase (recently called PKR), by a still undefined mechanism, may also act as a tumor suppressor. Consequently, one of the pathways by which interferon inhibits tumor growth might be through its capacity to induce the enhanced expression of this kinase.
...
PMID:Tumor suppressor function of the interferon-induced double-stranded RNA-activated protein kinase. 767 39

The interferon-induced RNA-dependent protein kinase (PKR) is postulated to have an important regulatory role in the synthesis of viral and cellular proteins. Activation of the enzyme requires the presence of a suitable activator RNA and is accompanied by an autophosphorylation of PKR. Active PKR phosphorylates the alpha subunit of protein synthesis eukaryotic initiation factor 2, resulting in an inhibition of translation initiation. The mechanism of autophosphorylation is not well understood. Here we present evidence that the autophosphorylation of human PKR can involve intermolecular phosphorylation events, i.e., one PKR protein molecule phosphorylating a second PKR molecule. Both wild-type PKR and the point mutant PKR(K296R) synthesized in vitro were phosphorylated, even though PKR(K296R) was deficient in kinase catalytic activity. Phosphorylation of both wild-type PKR and PKR(K296R) was inhibited in the presence of 2-aminopurine. Furthermore, purified human recombinant PKR(K296R) was a substrate for the purified wild-type human PKR kinase. This intermolecular phosphorylation of mutant PKR(K296R) by wild-type PKR was dependent on double-stranded RNA and was inhibited by 2-aminopurine. Finally, PKR mRNA was capable of mediating an autoactivation of wild-type PKR kinase autophosphorylation in vitro.
...
PMID:Mechanism of interferon action: evidence for intermolecular autophosphorylation and autoactivation of the interferon-induced, RNA-dependent protein kinase PKR. 769 78

The mouse TIK protein, a serine/threonine kinase, was originally isolated from a murine pre-B cell expression library by its ability to bind anti-phosphotyrosine antibodies (Icely et al., J. Biol. Chem. 266, 16073-16077, 1991). The 67 kDa protein was found to have an associated autophosphorylation activity when incubated with ATP. Our results show that TIK is actually the mouse interferon-induced, dsRNA-dependent protein kinase, PKR. We demonstrate that the TIK message is interferon-inducible in mouse L-cells and in vitro transcription and translation of the TIK cDNA produces a protein that is capable of binding double-stranded RNA. The in vitro synthesized TIK protein migrated as a 65 kDa protein on SDS-PAGE when incubated with ATP, but migrated as a 60 kDa protein when incubated with an inhibitor of PKR, 2-aminopurine. We further show that proteolytic digestion of TIK with Staphylococcus aureus V8 protease results in a cleavage pattern identical to that obtained by V8 digestion of authentic PKR. Antiserum to TIK specifically recognized PKR. Cloned TIK had inhibitory activity for replication of EMCV but not VSV. From these observations we conclude that TIK kinase is the mouse interferon-induced, double-stranded RNA-dependent kinase, PKR.
...
PMID:The mouse antiphosphotyrosine immunoreactive kinase, TIK, is indistinguishable from the double-stranded RNA-dependent, interferon-induced protein kinase, PKR. 769 35

The levels and subcellular distribution of the interferon-inducible double-stranded RNA-dependent protein kinase PKR have been measured in human Daudi cells and stably transfected mouse NIH 3T3 cells expressing the human protein kinase. Immunofluorescence of intact cells and quantitative immunoblotting of cell extracts indicate that PKR occurs in both the cytoplasm and the cell nucleus, with staining specifically in the nucleolus. The ratio of cytoplasmic to nuclear PKR is approximately 5:1 in control cells; in response to interferon treatment the protein kinase is induced severalfold in the cytoplasm whereas the level in the nucleus does not increase significantly. Analysis of individual transfected cells by confocal microscopy reveals a pattern of distribution of PKR similar to that in Daudi cells, with immunostaining of cytoplasm and nucleoli. Similar results are observed whether cells expressing wild-type PKR or a catalytically inactive mutant form of the kinase are analyzed, but untransfected 3T3 cells are not stained by the antibody used. Two-dimensional isoelectric focusing analysis of PKR in whole cell extracts reveals the presence of multiple forms with different pI values whereas similar analysis of the nuclear fraction indicates only one predominant species with a relatively basic pI. These results suggest that PKR may have a role in the cell nucleus as well as the cytoplasm and that the subcellular distribution of the protein kinase may be related to post-translational modifications.
...
PMID:Nuclear localization of the interferon-inducible protein kinase PKR in human cells and transfected mouse cells. 773 57

Adenoviruses use virus-associated RNA I (VAI RNA) to counteract the cellular antiviral response mediated by the interferon-induced, double-stranded-RNA-activated protein kinase PKR. VAI RNA is a highly structured small RNA which consists of two long duplex regions connected at the center by a complex, short stem-loop. This short stem-loop and the adjacent base-paired regions, referred to as the central domain, bind to PKR and inactivate it. Currently it is not known whether binding of VAI RNA to PKR is dependent solely on the secondary (and tertiary) structure of the central domain or whether nucleotide sequences in the central domain are also critical for this interaction. To address this question, 54 VAI mutants with single-base substitution mutations in the central domain of the RNA were constructed, and their capacities to inhibit the autophosphoryation of PKR in vitro were determined. It was found that although about half of the mutants inhibited PKR activity as efficiently as the wild type, a significant number of mutants lost the inhibitory activity substantially, without a perceptible change in their secondary structures. These results indicate that, in addition to secondary structure, at least some nucleotides in the central domain may be critical for the efficient function of VAI RNA.
...
PMID:Effect of single-base substitutions in the central domain of virus-associated RNA I on its function. 776 91

The double-stranded (ds) RNA-activated protein kinase, DAI (also known as PKR), contains an RNA-binding domain comprising two tandem repeats of a motif, the dsRBM, which is shared with a number of other proteins that interact with structured RNAs. We have expressed the entire domain and the first copy of the motif in Escherichia coli and purified the two proteins, p20 and p10, to apparent homogeneity in order to study their interactions with RNA and with the intact kinase enzyme. Both p20 and p10 bound preferentially to structured RNA molecules. Competition assays showed that in both cases the order of affinity is dsRNA > VA RNA > tRNA, but the isolated motif bound much less tightly than the entire domain. Measurement of the dissociation constants for dsRNA by quantitative gel mobility shift analysis gave apparent Kd values of 4 x 10(-9) M and 3.8 x 10(-7) M for p20 and p10, respectively. The binding of p20 molecules to dsRNA appeared to be cooperative. Multiple complexes were formed between the intact domain and dsRNA, saturating at a density of about one p20 molecule/11.25 base-pairs (or one turn) of duplex, whereas p10 achieved only about half of this packing density. The apparent Kd for the p20-VA RNA interaction was estimated as 3.5 x 10(-7) M and at least three complexes were detected, but no distinct complexes were visualized for the interaction between p10 and VA RNA. Both p20 and p10 inhibited autophosphorylation of intact DAI, probably by binding the dsRNA activator. Once activated, DAI could phosphorylate both p10 and p20, suggesting that intermolecular phosphorylation can occur.
...
PMID:Functional characterization of the RNA-binding domain and motif of the double-stranded RNA-dependent protein kinase DAI (PKR). 777 74

2-5A antisense (2-5A-AS) molecules are chimeric oligonucleotides that cause 2-5A-dependent RNase (RNase L) to catalyze the selective cleavage of RNA in human cells. These composite nucleic acids consist of a 5'-monophosphorylated, 2',5'-linked oligoadenylate known as 2-5A (an activator of RNase L) covalently attached to antisense 3',5'-oligodeoxyribonucleotides. Here, we characterize the targeted cleavage of the double-stranded RNA-dependent protein kinase (PKR) mRNA by purified, recombinant human RNase L. A 2-5A-AS chimera, which contains complementary sequence to PKR mRNA, and unmodified 2-5A, which causes general RNA decay, were about 20- and 40-fold more active, respectively, than 2-5A-AS chimeras in which the DNA domains are not complementary to sequences in PKR mRNA. Directed cleavage was efficient because each 2-5A-AS chimera targeted many RNA molecules. Moreover, RNase L caused the catalytic cleavage of the RNA target (kcat of approximately 7 s-1). The precise sites of PKR mRNA cleavage caused by 2-5A-AS were mapped, using a primer extension assay, to phosphodiester bonds adjacent to the 3' terminus of the chimera binding site (5' on the RNA target) as well as within the chimera's oligonucleotide binding site itself. The selectivity of this approach is shown to be provided by the antisense arm of the chimera, which places the RNA target in close proximity to the RNase.
...
PMID:Catalytic cleavage of an RNA target by 2-5A antisense and RNase L. 779 90


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---