scholarly journals Impact of Protein Kinase PKR in Cell Biology: from Antiviral to Antiproliferative Action

2006 ◽  
Vol 70 (4) ◽  
pp. 1032-1060 ◽  
Author(s):  
M. A. García ◽  
J. Gil ◽  
I. Ventoso ◽  
S. Guerra ◽  
E. Domingo ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Cell Fate ◽  
Cell Biology ◽  
Cellular Response ◽  
Nuclear Translocation ◽  
Receptor Activation ◽  
Initiation Factor ◽  
Viral Mrnas ◽  
Double Stranded Rna ◽  
Antiproliferative Action

SUMMARY 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-κB. In particular, how PKR triggers a cascade of events involving IKK phosphorylation of IκB and NF-κB 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.

scholarly journals Autophosphorylation sites participate in the activation of the double-stranded-RNA-activated protein kinase PKR.

1996 ◽  
Vol 16 (11) ◽  
pp. 6295-6302 ◽  
Author(s):  
D R Taylor ◽  
S B Lee ◽  
P R Romano ◽  
D R Marshak ◽  
A G Hinnebusch ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Mammalian Cells ◽  
Rna Binding ◽  
Initiation Factor ◽  
Double Stranded Rna ◽  
Catalytic Domains ◽  
Dependent Protein ◽  
Mutant Kinase

The interferon-induced RNA-dependent protein kinase PKR is found in cells in a latent state. In response to the binding of double-stranded RNA, the enzyme becomes activated and autophosphorylated on several serine and threonine residues. Consequently, it has been postulated that autophosphorylation is a prerequisite for activation of the kinase. We report the identification of PKR sites that are autophosphorylated in vitro concomitantly with activation and examine their roles in the activation of PKR. Mutation of one site, threonine 258, results in a kinase that is less efficient in autophosphorylation and in phosphorylating its substrate, the initiation factor eIF2, in vitro. The mutant kinase is also impaired in vivo, displaying reduced ability to inhibit protein synthesis in yeast and mammalian cells and to induce a slow-growth phenotype in Saccharomyces cerevisiae. Mutations at two neighboring sites, serine 242 and threonine 255, exacerbated the effect. Taken together with earlier results (S. B. Lee, S. R. Green, M. B. Mathews, and M. Esteban, Proc. Natl. Acad. Sci. USA 91:10551-10555, 1994), these data suggest that the central part of the PKR molecule, lying between its RNA-binding and catalytic domains, regulates kinase activity via autophosphorylation.

scholarly journals PERK (eIF2α kinase) is required to activate the stress-activated MAPKs and induce the expression of immediate-early genes upon disruption of ER calcium homoeostasis

2005 ◽  
Vol 393 (1) ◽  
pp. 201-209 ◽  
Author(s):  
Shun-Hsin Liang ◽  
Wei Zhang ◽  
Barbara C. Mcgrath ◽  
Peichuan Zhang ◽  
Douglas R. Cavener
Keyword(s):  
Protein Kinase ◽  
Er Stress ◽  
P38 Mapk ◽  
Cellular Response ◽  
Immediate Early Genes ◽  
Immediate Early ◽  
Initiation Factor ◽  
Secretory Cells ◽  
Global Changes ◽  
Early Genes

The eIF2α (eukaryotic initiation factor-2α) kinase PERK (doublestranded RNA-activated protein kinase-like ER kinase) is essential for the normal function of highly secretory cells in the pancreas and skeletal system, as well as the UPR (unfolded protein response) in mammalian cells. To delineate the regulatory machinery underlying PERK-dependent stress-responses, gene profiling was employed to assess global changes in gene expression in PERK-deficient MEFs (mouse embryonic fibroblasts). Several IE (immediate-early) genes, including c-myc, c-jun, egr-1 (early growth response factor-1), and fra-1 (fos-related antigen-1), displayed PERK-dependent expression in MEFs upon disruption of calcium homoeostasis by inhibiting the ER (endoplasmic reticulum) transmembrane SERCA (sarcoplasmic/ER Ca2+-ATPase) calcium pump. Induction of c-myc and egr-1 by other reagents that elicit the UPR, however, showed variable dependence upon PERK. Induction of c-myc expression by thapsigargin was shown to be linked to key signalling enzymes including PLC (phospholipase C), PI3K (phosphatidylinositol 3-kinase) and p38 MAPK (mitogen-activated protein kinase). Analysis of the phosphorylated status of major components in MAPK signalling pathways indicated that thapsigargin and DTT (dithiothreitol) but not tunicamycin could trigger the PERK-dependent activation of JNK (c-Jun N-terminal kinase) and p38 MAPK. However, activation of JNK and p38 MAPK by non-ER stress stimuli including UV irradiation, anisomycin, and TNF-α (tumour necrosis factor-α) was found to be independent of PERK. PERK plays a particularly important role in mediating the global cellular response to ER stress that is elicited by the depletion of calcium from the ER. We suggest that this specificity of PERK function in the UPR is an extension of the normal physiological function of PERK to act as a calcium sensor in the ER.

scholarly journals Binding and Nuclear Relocalization of Protein Kinase R by Human Cytomegalovirus TRS1

2006 ◽  
Vol 80 (23) ◽  
pp. 11817-11826 ◽  
Author(s):  
Morgan Hakki ◽  
Emily E. Marshall ◽  
Katherine L. De Niro ◽  
Adam P. Geballe
Keyword(s):  
Protein Kinase ◽  
Human Cytomegalovirus ◽  
Mammalian Cells ◽  
Rna Binding ◽  
Underlying Mechanism ◽  
Cellular Protein ◽  
Initiation Factor ◽  
Protein Kinase R ◽  
Double Stranded Rna

ABSTRACT The human cytomegalovirus (HCMV) TRS1 and IRS1 genes block the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α) and the consequent shutoff of cellular protein synthesis that occur during infection with vaccinia virus (VV) deleted of the double-stranded RNA binding protein gene E3L (VVΔE3L). To further define the underlying mechanism, we first evaluated the effect of pTRS1 on protein kinase R (PKR), the double-stranded RNA (dsRNA)-dependent eIF2α kinase. Immunoblot analyses revealed that pTRS1 expression in the context of a VVΔE3L recombinant decreased levels of PKR in the cytoplasm and increased its levels in the nucleus of infected cells, an effect not seen with wild-type VV or a VVΔE3L recombinant virus expressing E3L. This effect of pTRS1 was confirmed by visualizing the nuclear relocalization of PKR-EGFP expressed by transient transfection. PKR present in both the nuclear and cytoplasmic fractions was nonphosphorylated, indicating that it was unactivated when TRS1 was present. PKR also accumulated in the nucleus during HCMV infection as determined by indirect immunofluorescence and immunoblot analysis. Binding assays revealed that pTRS1 interacted with PKR in mammalian cells and in vitro. This interaction required the same carboxy-terminal region of pTRS1 that is necessary to rescue VVΔE3L replication in HeLa cells. The carboxy terminus of pIRS1 was also required for rescue of VVΔE3L and for mediating an interaction of pIRS1 with PKR. These results suggest that these HCMV genes directly interact with PKR and inhibit its activation by sequestering it in the nucleus, away from both its activator, cytoplasmic dsRNA, and its substrate, eIF2α.

scholarly journals Stress Granules Regulate Double-Stranded RNA-Dependent Protein Kinase Activation through a Complex Containing G3BP1 and Caprin1

mBio ◽  
2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Lucas C. Reineke ◽  
Nancy Kedersha ◽  
Martijn A. Langereis ◽  
Frank J. M. van Kuppeveld ◽  
Richard E. Lloyd
Keyword(s):  
Pattern Recognition ◽  
Innate Immunity ◽  
Protein Kinase ◽  
Antiviral Activity ◽  
Stress Granules ◽  
Initiation Factor ◽  
Dependent Protein Kinase ◽  
Α Subunit ◽  
Double Stranded Rna ◽  
Dependent Protein

ABSTRACT Stress granules (SGs) are dynamic cytoplasmic repositories containing translationally silenced mRNAs that assemble upon cellular stress. We recently reported that the SG nucleating protein G3BP1 promotes antiviral activity and is essential in double-stranded RNA-dependent protein kinase (PKR) recruitment to stress granules, thereby driving phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α). Here, we delineate the mechanism for SG-dependent PKR activation. We show that G3BP1 and inactive PKR directly interact with each other, dependent on both the NTF2-like and PXXP domains of G3BP1. The G3BP1-interacting protein Caprin1 also directly interacts with PKR, regulates efficient PKR activation at the stress granule, and is also integral for the release of active PKR into the cytoplasm to engage in substrate recognition. The G3BP1-Caprin1-PKR complex represents a new mode of PKR activation and is important for antiviral activity of G3BP1 and PKR during infection with mengovirus. Our data links stress responses and their resultant SGs with innate immune activation through PKR without a requirement for foreign double-stranded RNA (dsRNA) pattern recognition. IMPORTANCE Our previous work indicates that stress granules have antiviral activity and mediate innate immunity through functions of G3BP1; however, the mechanistic details of these functions were not resolved. We show that much of the antiviral activity of stress granules is contingent on the function of PKR in a complex with G3BP1 and Caprin1. The PKR-G3BP1-Caprin1 complex undergoes dynamic transitioning within and outside stress granules to accomplish PKR activation and translational repression. This mechanism appears to function distinctly from canonical pattern recognition of double-stranded RNA by PKR. Therefore, this mechanism bridges the stress response with innate immunity, allowing the cell to respond to many cellular stressors and amplify the pathogen pattern recognition systems of innate immunity.

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