Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression of the double-stranded RNA-activated protein kinase (PKR) is induced by interferons, with PKR activity playing a pivotal role in establishing the interferon-induced antiviral and antiproliferative states. PKR is directly regulated by physical association with the specific inhibitor, P58IPK, a cellular protein of the tetratricopeptide repeat (TPR) family, and K3L, the product of the corresponding vaccinia virus gene. P58IPK and K3L repress PKR activation and activity. To investigate the mechanism of P58IPK- and K3L-mediated PKR inhibition, we have used a combination of in vitro and in vivo binding assays to identify the interactive regions of these proteins. The P58IPK-interacting site of PKR was mapped to a 52-amino-acid aa segment (aa 244 to 296) spanning the ATP-binding region of the protein kinase catalytic domain. The interaction with PKR did not require the C-terminal DNA-J homology region of P58IPK but was dependent on the presence of the eukaryotic initiation factor 2-alpha homology region, mapping to the 34 aa within the sixth P58IPK TPR motif. Consistent with other TPR proteins, P58IPK formed multimers in vivo: the N-terminal 166 aa were both necessary and sufficient for complex formation. A parallel in vivo analysis to map the K3L-binding region of PKR revealed that like P58IPK , K3L interacted exclusively with the PKR protein kinase catalytic domain. In contrast, however, the K3L-binding region of PKR was localized to within aa 367 to 551, demonstrating that each inhibitor bound PKR in unique, nonoverlapping domains. These data, taken together, suggest that P58IPK and K3L may mediate PKR inhibition by distinct mechanisms. Finally, we will propose a model of PKR inhibition in which P58IPK or a P58IPK complex binds PKR and interferes with nucleotide binding and autoregulation, while formation of a PKR-K3L complex interferes with active-site function and/or substrate association.
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PMID:Interaction of the interferon-induced PKR protein kinase with inhibitory proteins P58IPK and vaccinia virus K3L is mediated by unique domains: implications for kinase regulation. 875 16

The interferon-induced double-stranded RNA-activated protein kinase, PKR, likely contributes to both the antiviral and the antiproliferative effects of interferon. We previously found that influenza virus avoids the translational inhibitory effects of activated PKR by activating a cellular inhibitory protein, termed P58IPK, based on its Mr of 58,000. P58IPK is a member of the tetratricopeptide family of proteins and possesses significant homology to the conserved J region of the DnaJ family of heat shock proteins. We earlier hypothesized that P58IPK was kept in an inactive state with its own inhibitor (termed I-P58IPK) in uninfected cells. We therefore attempted the purification and characterization of I-P58IPK. The following data suggest that we have identified the molecular chaperone, hsp40, as 1-P58IPK. (i) The MonoP-purified I-P58IPK protein reacted with hsp40 antibody. (ii) This preparation demonstrated high specific activity in an in vitro functional assay containing only purified recombinant and native components. (iii) Purified, recombinant hsp40 protein inhibited P58IPK in an identical in vitro assay. (iv) Finally, we demonstrate that hsp40 directly complexes with P58IPK, in vitro, suggesting the inhibition occurs through a direct interaction. Our data, taken together, provide evidence for a novel intersection between the heat shock and interferon pathways, and suggest that influenza virus regulates PKR activity through the recruitment of a cellular stress pathway.
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PMID:The molecular chaperone hsp40 regulates the activity of P58IPK, the cellular inhibitor of PKR. 899 Jan 67

The cellular response to environmental signals is largely dependent upon the induction of responsive protein kinase signaling pathways. Within these pathways, distinct protein-protein interactions play a role in determining the specificity of the response through regulation of kinase function. The interferon-induced serine/threonine protein kinase, PKR, is activated in response to various environmental stimuli. Like many protein kinases, PKR is regulated through direct interactions with activator and inhibitory molecules, including P58IPK, a cellular PKR inhibitor. P58IPK functions to represses PKR-mediated phosphorylation of the eukaryotic initiation factor 2alpha subunit (eIF-2alpha) through a direct interaction, thereby relieving the PKR-imposed block on mRNA translation and cell growth. To further define the molecular mechanism underlying regulation of PKR, we have utilized an interaction cloning strategy to identify a novel cDNA encoding a P58IPK-interacting protein. This protein, designated P52rIPK, possesses limited homology to the charged domain of Hsp90 and is expressed in a wide range of cell lines. P52rIPK and P58IPK interacted in a yeast two-hybrid assay and were recovered as a complex from mammalian cell extracts. When coexpressed with PKR in yeast, P58IPK repressed PKR-mediated eIF-2alpha phosphorylation, inhibiting the normally toxic and growth-suppressive effects associated with PKR function. Conversely, introduction of P52rIPK into these strains resulted in restoration of both PKR activity and eIF-2alpha phosphorylation, concomitant with growth suppression due to inhibition of P58IPK function. Furthermore, P52rIPK inhibited P58IPK function in a reconstituted in vitro PKR-regulatory assay. Our results demonstrate that P58IPK is inhibited through a direct interaction with P52rIPK which, in turn, results in upregulation of PKR activity. Taken together, our data describe a novel protein kinase-regulatory system which encompasses an intersection of interferon-, stress-, and growth-regulatory pathways.
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PMID:Regulation of interferon-induced protein kinase PKR: modulation of P58IPK inhibitory function by a novel protein, P52rIPK. 944 82

The interferon (IFN)-induced, double-stranded RNA-activated protein kinase (PKR) mediates the antiviral and antiproliferative actions of IFN, in part, via its translational inhibitory properties. Previous studies have demonstrated that PKR forms dimers and that dimerization is likely to be required for activation and/or function. In the present study we used multiple approaches to examine the modulation of PKR dimerization. Deletion analysis with the lambda repressor fusion system identified a previously unrecognized site involved in PKR dimerization. This site comprised amino acids (aa) 244 to 296, which span part of the third basic region of PKR and the catalytic subdomains I and II. Using the yeast two-hybrid system and far-Western analysis, we verified the importance of this region for dimerization. Furthermore, coexpression of the 52-aa region alone inhibited the formation of full-length PKR dimers in the lambda repressor fusion and two-hybrid systems. Importantly, coexpression of aa 244 to 296 exerted a dominant-negative effect on wild-type kinase activity in a functional assay. Due to its role as a mediator of IFN-induced antiviral resistance, PKR is a target of viral and cellular inhibitors. Curiously, PKR aa 244 to 296 contain the binding site for a select group of specific inhibitors, including the cellular protein P58IPK. We demonstrated, utilizing both the yeast and lambda systems, that P58IPK, a member of the tetratricopeptide repeat protein family, can block kinase activity by preventing PKR dimerization. In contrast, a nonfunctional form of P58IPK lacking a TPR motif did not inhibit kinase activity or perturb PKR dimers. These results highlight a potential mechanism of PKR inhibition and define a novel class of PKR inhibitors. Finally, the data document the first known example of inhibition of protein kinase dimerization by a cellular protein inhibitor. On the basis of these results we propose a model for the regulation of PKR dimerization.
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PMID:Double-stranded RNA-independent dimerization of interferon-induced protein kinase PKR and inhibition of dimerization by the cellular P58IPK inhibitor. 956 64

The interferon (IFN)-induced protein kinase (PKR) functions as a gatekeeper of mRNA translation initiation and is, therefore, a key mediator of the host IFN-induced antiviral defense system. Many viruses have invested countermeasures against PKR. Some apparently use more than one mechanism. The influenza virus can repress PKR activity through the use of at least two factors, the cellular P58IPK protein and the viral NS1 protein. The exact mode of action of the latter has not been established. Here, using a coprecipitation assay, we found that PKR could form a complex with NS1 in crude cell extracts prepared from influenza virus-infected HeLa cells. The NS1-PKR interaction was verified by using the yeast two-hybrid system and an in vitro binding assay. Deletion analysis mapped the NS1 binding site to the N-terminal 98 residues of PKR regulatory region. Furthermore, an NS1 mutant, which lacks PKR inhibitory activity, did not bind PKR. Finally, the functional role of NS1 in PKR inhibition was substantiated using an in vivo assay for PKR activity. These results support the role of NS1 in PKR modulation during viral infection that is mediated through a complex formation between the two proteins.
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PMID:Biochemical and genetic evidence for complex formation between the influenza A virus NS1 protein and the interferon-induced PKR protein kinase. 978 15

Tetratricopeptide repeats (TPRs) are loosely conserved 34-amino acid sequence motifs that have been shown to function as scaffolding structures to mediate protein-protein interactions. TPRs have been identified in a number of proteins with diverse functions and cellular locations. Recent studies suggest that individual TPR motifs can confer specificity in promoting homotypic and/or heterotypic interactions, often in a mutually exclusive manner. These features are best exemplified by the P58IPK protein, an influenza virus-activated cellular inhibitor of the PKR protein kinase, whose different TPR motifs mediate interactions with distinct proteins. P58IPK, which possesses cochaperone and oncogenic properties, represents a unique class of TPR proteins containing a J-domain. Here we review recent progress on the structural and functional characterization of P58IPK, and discuss the possible mechanisms by which P58IPK modulates PKR and induces tumorigenesis in view of present knowledge of TPR proteins and molecular chaperones.
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PMID:P58IPK, a novel cochaperone containing tetratricopeptide repeats and a J-domain with oncogenic potential. 1076 25

Tau protein aggregates are a recognized neuropathological feature in Alzheimer's disease as well as many other neurodegenerative disorders, known as tauopathies. The development of tau-targeting therapies is therefore extremely important but efficient strategies or protein targets are still unclear. Here, we performed a cell-based phenotypic screening under endoplasmic reticulum (ER) stress conditions and identified a small molecule, SB1617, capable of suppressing abnormal tau protein aggregation. By applying label-free target identification technology, we revealed that the transient enhancement of protein kinase-like endoplasmic reticulum kinase (PERK) signaling pathway through the inhibition of stress-responsive SB1617 targets, PDIA3 and DNAJC3, is an effective strategy for regulating proteostasis in tauopathies. The molecular mechanism and the promising efficacy of SB1617 were demonstrated in neuronal cells and a mouse model with traumatic brain injury, a tauopathy known to involve ER stress.
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PMID:Phenotypic Discovery of Neuroprotective Agents by Regulation of Tau Proteostasis via Stress-Responsive Activation of PERK Signaling. 3321 Apr 31