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)

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

Eukaryotic initiation factor eIF-2B catalyses the exchange of guanine nucleotides on another translation initiation factor, eIF-2, which itself mediates the binding of the initiator Met-tRNA to the 40S ribosomal subunit during translation initiation. eIF-2B promotes the release of GDP from inactive [eIF-2.GDP] complexes, thus allowing formation of the active [eIF-2.GTP] species which subsequently binds the Met-tRNA. This guanine nucleotide-exchange step, and thus eIF-2B activity, are known to be an important control point for translation initiation. The activity of eIF-2B can be modulated in several ways. The best characterised of these involves the phosphorylation of the alpha-subunit of eIF-2 by specific protein kinases regulated by particular ligands. Phosphorylation of eIF-2 alpha leads to inhibition of eIF-2B. This mechanism is involved in the control of translation under a variety of conditions, including amino acid deprivation in yeast (Saccharomyces cerevisiae) where it causes translational upregulation of the transcription factor GCN4, and in virus-infected animal cells, where it involves a protein kinase activated by double-stranded RNA. There is now also growing evidence for direct regulation of eIF-2B. This appears likely to involve the phosphorylation of its largest subunit. Under certain circumstances eIF-2B may also be regulated by allosteric mechanisms. eIF-2B is a heteropentamer (subunits termed alpha, beta, gamma, delta and epsilon) and is thus more complex than most other guanine nucleotide-exchange factors. The genes encoding all five subunits have been cloned in yeast (exploiting the GCN4 regulatory system): all but the alpha appear to be essential for eIF-2B activity. However, this subunit may confer sensitivity to eIF-2 alpha phosphorylation. cDNAs encoding the alpha, beta, delta and epsilon subunits have been cloned from mammalian sources. There is substantial homology between the yeast and mammalian sequences. Attention is now directed towards understanding the roles of individual subunits in the function and regulation of eIF-2B.
...
PMID:The guanine nucleotide-exchange factor, eIF-2B. 789 25

Starvation of the yeast Saccharomyces cerevisiae for an amino acid signals increased translation of GCN4, a transcriptional activator of amino acid biosynthetic genes. We have isolated and characterized the GCD6 and GCD7 genes and shown that their products are required to repress GCN4 translation under nonstarvation conditions. We find that both GCD6 and GCD7 show sequence similarities to components of a high-molecular-weight complex (the GCD complex) that appears to be the yeast equivalent of translation initiation factor 2B (eIF-2B), which catalyzes GDP-GTP exchange on eIF-2. Furthermore, we show that GCD6 is 30% identical to the largest subunit of eIF-2B isolated from rabbit reticulocytes. Deletion of either GCD6 or GCD7 is lethal, and nonlethal mutations in these genes increase GCN4 translation in the same fashion described for defects in known subunits of eIF-2 or the GCD complex; derepression of GCN4 is dependent on short open reading frames in the GCN4 mRNA leader and occurs independently of eIF-2 alpha phosphorylation by protein kinase GCN2, which is normally required to stimulate GCN4 translation. Together, our results provide evidence that GCD6 and GCD7 are subunits of eIF-2B in S. cerevisiae and further implicate this GDP-GTP exchange factor in gene-specific translational control.
...
PMID:Evidence that GCD6 and GCD7, translational regulators of GCN4, are subunits of the guanine nucleotide exchange factor for eIF-2 in Saccharomyces cerevisiae. 844 23

Molecular genetic analyses in yeast are a powerful method to study gene regulation. Conservation of the mechanism and regulation of protein synthesis between yeast and mammalian cells makes yeast a good model system for the analysis of translation. One of the most common mechanisms of translational regulation in mammalian cells is the phosphorylation of serine-51 on the alpha subunit of the translation initiation factor elF2, which causes an inhibition of general translation. In contrast, in the yeast Saccharomyces cerevisiae phosphorylation of elF2 alpha on serine-51 by the GCN2 protein kinase mediates the translational induction of GCN4 expression. The unique structure of the GCN4 mRNA makes GCN4 expression especially sensitive to elF2 alpha phosphorylation, and the simple microbiological tests developed in yeast to analyze GCN4 expression serve as good reporters of elF2 alpha phosphorylation. It is relatively simple to express heterologous proteins in yeast, and it has been shown that the mammalian elF2 alpha kinases will functionally substitute for GCN2. Structure-function analyses of translation factors or translational regulators can also be performed by assaying for effects on general and GCN4-specific translation. Three tests can be used to study elF2 alpha phosphorylation and/or translational activity in yeast. First, general translation can be monitored by simple growth tests, while GCN4 expression can be analyzed using sensitive replicaplating tests. Second, GCN4 translation can be quantitated by measuring expression from GCN4-lacZ reporter constructs. Finally, isoelectric focusing gels can be used to directly monitor in vivo phosphorylation of elF2 alpha in yeast.
...
PMID:Using GCN4 as a reporter of eIF2 alpha phosphorylation and translational regulation in yeast. 912 54

In the yeast Saccharomyces cerevisiae, phosphorylation of translation initiation factor eIF2 by protein kinase GCN2 leads to increased translation of the transcriptional activator GCN4 in amino acid-starved cells. The GCN1 and GCN20 proteins are components of a protein complex required for the stimulation of GCN2 kinase activity under starvation conditions. GCN20 is a member of the ATP-binding cassette (ABC) family, most of the members of which function as membrane-bound transporters, raising the possibility that the GCN1/GCN20 complex regulates GCN2 indirectly as an amino acid transporter. At odds with this idea, indirect immunofluorescence revealed cytoplasmic localization of GCN1 and no obvious association with plasma or vacuolar membranes. In addition, a fraction of GCN1 and GCN20 cosedimented with polysomes and 80S ribosomes, and the ribosome association of GCN20 was largely dependent on GCN1. The C-terminal 84% of GCN20 containing the ABCs was found to be dispensable for complex formation with GCN1 and for the stimulation of GCN2 kinase function. Because ABCs provide the energy-coupling mechanism for ABC transporters, these results also contradict the idea that GCN20 regulates GCN2 as an amino acid transporter. The N-terminal 15 to 25% of GCN20, which is critically required for its regulatory function, was found to interact with an internal segment of GCN1 similar in sequence to translation elongation factor 3 (EF3). Based on these findings, we propose that GCN1 performs an EF3-related function in facilitating the activation of GCN2 by uncharged tRNA on translating ribosomes. The physical interaction between GCN20 and the EF3-like domain in GCN1 could allow for modulation of GCN1 activity, and the ABC domains in GCN20 may be involved in this regulatory function. A human homolog of GCN1 has been identified, and the portion of this protein most highly conserved with yeast GCN1 has sequence similarity to EF3. Thus, similar mechanisms for the detection of uncharged tRNA on translating ribosomes may operate in yeast and human cells.
...
PMID:Evidence that GCN1 and GCN20, translational regulators of GCN4, function on elongating ribosomes in activation of eIF2alpha kinase GCN2. 923 5

The interferon-induced, double-stranded RNA (dsRNA)-activated protein kinase, PKR, inhibits protein synthesis via phosphorylation of the alpha subunit of the translation initiation factor eIF2. A kinase insert region N-terminal of PKR kinase subdomain V, which is conserved among eIF2alpha kinases, has been proposed to determine substrate specificity of these kinases. To investigate the function of this kinase insert region, selective PKR mutants were generated, and kinase activities and eIF2alpha affinities were analyzed in vitro. The in vivo function was investigated by growth inhibitory assays in yeast and translational assays in COS cells. Among the 13 mutations, 5 lost kinase activity and 3 exhibited less than 30% of wild-type eIF2alpha binding activity. The deletion of the conserved sequence (amino acids 362-370) resulted in a protein that had no kinase activity and only about 25% of wild-type eIF2alpha binding, suggesting that this sequence is not only required for PKR kinase activity but also is important for substrate interaction. It was determined that the hydrophobicity of the conserved sequence of PKR is required for kinase activity but is not crucial for eIF2alpha binding. The amino acid residue Glu-367 in the conserved motif was shown to be directly involved in substrate binding but was not important for kinase activity. These results suggest that the activation of PKR is not a prerequisite for its binding to the substrate and that the conserved motif in subdomain V contributes to the interaction of PKR and eIF2alpha.
...
PMID:Mutations in the double-stranded RNA-activated protein kinase insert region that uncouple catalysis from eIF2alpha binding. 955 19

The human double-stranded RNA (dsRNA)-dependent protein kinase PKR inhibits protein synthesis by phosphorylating translation initiation factor 2alpha (eIF2alpha). Vaccinia virus E3L encodes a dsRNA binding protein that inhibits PKR in virus-infected cells, presumably by sequestering dsRNA activators. Expression of PKR in Saccharomyces cerevisiae inhibits protein synthesis by phosphorylation of eIF2alpha, dependent on its two dsRNA binding motifs (DRBMs). We found that expression of E3 in yeast overcomes the lethal effect of PKR in a manner requiring key residues (Lys-167 and Arg-168) needed for dsRNA binding by E3 in vitro. Unexpectedly, the N-terminal half of E3, and residue Trp-66 in particular, also is required for anti-PKR function. Because the E3 N-terminal region does not contribute to dsRNA binding in vitro, it appears that sequestering dsRNA is not the sole function of E3 needed for inhibition of PKR. This conclusion was supported by the fact that E3 activity was antagonized, not augmented, by overexpressing the catalytically defective PKR-K296R protein containing functional DRBMs. Coimmunoprecipitation experiments showed that a majority of PKR in yeast extracts was in a complex with E3, whose formation was completely dependent on the dsRNA binding activity of E3 and enhanced by the N-terminal half of E3. In yeast two-hybrid assays and in vitro protein binding experiments, segments of E3 and PKR containing their respective DRBMs interacted in a manner requiring E3 residues Lys-167 and Arg-168. We also detected interactions between PKR and the N-terminal half of E3 in the yeast two-hybrid and lambda repressor dimerization assays. In the latter case, the N-terminal half of E3 interacted with the kinase domain of PKR, dependent on E3 residue Trp-66. We propose that effective inhibition of PKR in yeast requires formation of an E3-PKR-dsRNA complex, in which the N-terminal half of E3 physically interacts with the protein kinase domain of PKR.
...
PMID:Inhibition of double-stranded RNA-dependent protein kinase PKR by vaccinia virus E3: role of complex formation and the E3 N-terminal domain. 981 17

Glycogen synthase kinase-3 is involved in diverse functions including insulin signalling and development. In a number of substrates, phosphorylation by glycogen synthase kinase-3 is known to require prior phosphorylation at a Ser in the +4 position relative to its own phosphorylation site. Here we have used synthetic peptides derived from a putative glycogen synthase kinase-3 site in the Drosophila translation initiation factor eIF2B epsilon to investigate the efficacy of residues other than Ser(P) as priming residues for glycogen synthase kinase-3beta and its Drosophila homologue Shaggy. Glycogen synthase kinase-3beta phosphorylated peptides with Ser(P) and Thr(P) in the priming position, but peptides with Tyr(P), Thr, Glu or Asp were not phosphorylated. The Vmax for the Thr(P) peptide was three times higher than that of the Ser(P) peptide. These data suggest that glycogen synthase kinase-3 is unique among phosphate-directed kinases. The priming site specificity of Shaggy is similar to that of mammalian glycogen synthase kinase-3beta. This unpredicted efficacy of Thr(P) in the priming position suggests that there may be other unidentified substrates for these kinases.
...
PMID:Phosphorylated seryl and threonyl, but not tyrosyl, residues are efficient specificity determinants for GSK-3beta and Shaggy. 1021 15

The interferon (IFN)-inducible double-stranded (ds) RNA-dependent protein kinase PKR plays a role in the regulation of gene expression through its capacity to phosphorylate the translation initiation factor eIF-2 and to inhibit protein synthesis. In addition to translational control, PKR has been implicated in the regulation of gene expression at the transcriptional level. In this regard, we have reported that PKR participates in IFN-and dsRNA-mediated signaling pathways by interacting with and modulating the transcriptional activity of the signal transducer and activator of transcription STAT1 [Wong, A.H.-T., Tam, N.W.N., Yang, Y.-L., Cuddihy, A.R., Li, S., Kirchhoff, S., Hauser, H., Decker, T. & Koromilas, A.E. (1997) EMBO J. 16, 1291-1304]. Here we report that the STAT1 protein is upregulated in cells lacking PKR (PKR-/-) and in cells expressing dominant negative PKR mutants. This upregulation is specific for STAT1 as increased expression is not observed for other STAT proteins. The inhibitory effect of PKR on STAT1 expression is exerted at the post-translational level because PKR-/- cells exhibit higher STAT1 protein stability than PKR+/+ cells.
...
PMID:Upregulation of STAT1 protein in cells lacking or expressing mutants of the double-stranded RNA-dependent protein kinase PKR. 1023 76

The tumor suppressor p53 is a multifunctional protein that plays a critical role in modulating cellular responses upon DNA damage or other stresses. These functions of p53 are regulated both by protein-protein interactions and phosphorylation. The double-stranded RNA activated protein kinase PKR is a serine/threonine kinase that modulates protein synthesis through the phosphorylation of translation initiation factor eIF-2alpha. PKR is an interferon (IFN)-inducible protein that is thought to mediate the anti-viral and anti-proliferative effects of IFN via its capacity to inhibit protein synthesis. Here we report that PKR physically associates with p53. The interaction of PKR with p53 is enhanced by IFNs and upon conditions that p53 acquires a wild type conformation. PKR/p53 complex formation in vitro requires the N-terminal regulatory domain of PKR and the last 30 amino acids of the C-terminus of human p53. In addition, p53 may function as a substrate of PKR since phosphorylation of human p53 on serine392 is induced by activated PKR in vitro. These novel findings raise the possibility of a functional interaction between PKR and p53 in vivo, which may account, at least in part, for the ability of each protein to regulate gene expression at both the transcriptional and the translational levels.
...
PMID:The double-stranded RNA activated protein kinase PKR physically associates with the tumor suppressor p53 protein and phosphorylates human p53 on serine 392 in vitro. 1034 43


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

---