The B56α Regulatory Subunit of Protein Phosphatase 2A Is a Target for Regulation by Double-Stranded RNA-Dependent Protein Kinase PKR

Xu, Zeyuan; Williams, Bryan R.G.

doi:10.1128/mcb.20.14.5285-5299.2000

Cited by 112 publications

(98 citation statements)

References 63 publications

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“…Our results suggest that MKK6 has an increased affinity for activated PKR. This observation is in accord with previous observations showing that specific PKR-interacting proteins preferentially recognize activated PKR (28). Moreover, the finding that MKK6 and PKR physiologically interact with each other after dsRNA stimulation in cells supports the idea that this association is important for dsRNA signaling.…”

Section: Fig 3 Physical Interaction Between Pkr and Mkk6 A Anti-psupporting

confidence: 82%

“…Some of these mechanisms mediated by PKR in response to dsRNA might be attributed either to protein-protein interaction or to the phosphorylation of substrates other than eIF2␣. Accordingly, PKR has been shown to interact constitutively or in a stimulus-dependent manner with a number of proteins, which may serve as PKR substrates, thus regulating protein translation and transcriptional activity (3,4,14,15,(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). A role for PKR in transcriptional activity in the inflammatory response was suggested by the observation that PKR-null primary fibroblasts and mice had defects in the activation of p38 mitogen-activated protein kinase (MAPK) and downstream proinflammatory gene expression in response to different stimuli (29).…”

Section: Expression Of Kinase-inactive Pkr (K296r) In Cells Inhibitedmentioning

confidence: 99%

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Protein Kinase R (PKR) Interacts with and Activates Mitogen-activated Protein Kinase Kinase 6 (MKK6) in Response to Double-stranded RNA Stimulation

Silva¹,

Whitmore²,

Xu³

et al. 2004

Journal of Biological Chemistry

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105

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The double-stranded RNA (dsRNA)-activated protein kinase R (PKR) has been invoked in different signaling pathways. In cells pre-exposed to the PKR inhibitor 2-aminopurine or in PKR-null cells, the activation of p38 mitogen-activated protein kinase (MAPK) following dsRNA stimulation is attenuated. We found that the p38 MAPK activator MKK6, but not its close relatives MKK3 or MKK4, exhibited an increased affinity for PKR following the exposure of cells to poly(rI:rC), a dsRNA analog. In vitro kinase assays revealed that MKK6 was efficiently phosphorylated by PKR, and this could be inhibited by 2-aminopurine. Expression of kinase-inactive PKR (K296R) in cells inhibited the poly(IC)-induced phosphorylation of MKK3/6 detected by phosphospecific antiserum but did not affect the poly(IC)-induced gel migration retardation of MKK3.This suggests that poly(IC)-mediated in vivo activation of MKK6, but not MKK3, is through PKR. Consistent with this observation, PKR was capable of activating MKK6 as assessed in a coupled kinase assay containing the components of the p38 MAPK pathway. Our results indicate that the interaction of MKK6 and PKR provides a mechanism for regulating p38 MAPK activation in response to dsRNA stimulation. Double-stranded RNAs (dsRNA) 1 formed during virus infection can be potent stimulating agents triggering cellular responses through distinct targets and pathways. DsRNA-dependent interferon synthesis as well as NF-B activation may require the binding of dsRNA with cellular membrane component(s) that includes Toll-like receptor 3 (TLR-3) (1). However, other dsRNA sensor cellular components have also been implicated in the activation of cellular pathways triggered by dsRNA (2-4).The dsRNA-dependent protein PKR is a serine/threonine kinase, the expression of which is induced by interferons. This enzyme is activated in response to dsRNA of viral or synthetic origin, most notably the synthetic polyribonucleotide duplex, poly(rI):poly(rC) (pIC), and also by cytokines and cellular stress signals (5). Once activated, PKR functions as one of the mediators of antiviral and antiproliferative activities of interferons (6 -12). PKR has two double-stranded RNA-binding motifs located in the NH 2 -terminal domain (5, 13), which bind pIC or viral dsRNA intermediates generated during a viral infection and also permit the recruitment of other dsRNA-binding domain-containing proteins (14, 15). The carboxyl-terminal half of PKR harbors the kinase catalytic domain (9). On binding dsRNA, PKR dimerizes and undergoes autophosphorylation at multiple sites (5, 16). The direct antiviral activity of PKR is a consequence of the phosphorylation and activation of its major substrate eukaryotic translation initiation factor eIF2␣, thereby inhibiting protein synthesis and impeding virus multiplication (6,10,12).In addition to playing a role in protein synthesis inhibition, PKR also functions in other biological processes including apoptosis, transcriptional regulation, and cell growth, independent of the phosphorylation of eIF2␣ (5). ...

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Section: Fig 3 Physical Interaction Between Pkr and Mkk6 A Anti-psupporting

confidence: 82%

Section: Expression Of Kinase-inactive Pkr (K296r) In Cells Inhibitedmentioning

confidence: 99%

Protein Kinase R (PKR) Interacts with and Activates Mitogen-activated Protein Kinase Kinase 6 (MKK6) in Response to Double-stranded RNA Stimulation

Silva¹,

Whitmore²,

Xu³

et al. 2004

Journal of Biological Chemistry

Self Cite

105

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“…37,38 While serine phosphorylation of a PP2A regulatory subunit (B56 a) by the dsRNA-dependent protein kinase (PKR) has been established, this phosphorylation event promotes PP2A function. 39 Thus, the question remained if PKC a can negatively regulate PP2A. Such a relationship is particularly important, considering that Bcl2 appears to be necessary for PKC a-mediated cytoprotection in REH cells.…”

Section: Discussionmentioning

confidence: 99%

“…24 Thus, at least one mechanism as to how PKC a may suppress mitochondrial PP2A activity involves the regulation of PP2A/B56 a expression. Since phosphorylation of PP2A can regulate its activity, [37][38][39] it will be important to determine if PKC a can phosphorylate any of the PP2A subunits. This possibility is currently under investigation.…”

Section: Pkc a Overexpression Suppresses Mitochondrial Pp2a Activitymentioning

confidence: 99%

PKC α mediates chemoresistance in acute lymphoblastic leukemia through effects on Bcl2 phosphorylation

et al. 2004

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“…Interestingly, this regulatory ERK site is conserved in all of the known B56 family members except B56␣. Although ERK may not regulate B56␣ function negatively, phosphorylation of this particular B56 isoform by the double-stranded RNA-activated protein kinase (PKR) has been suggested to affect PP2A function positively (19). PKR activation is associated with growth inhibition and cell death (20 -23).…”

mentioning

confidence: 99%

PKR Regulates B56α-mediated BCL2 Phosphatase Activity in Acute Lymphoblastic Leukemia-derived REH Cells

Ruvolo

Kurinna

Karanjeet

et al. 2008

Journal of Biological Chemistry

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Protein phosphatase 2A (PP2A) is a heterotrimer comprising catalytic, scaffold, and regulatory (B) subunits. There are at least 21 B subunit family members. Thus PP2A is actually a family of enzymes defined by which B subunit is used. The B56 family member B56␣ is a phosphoprotein that regulates dephosphorylation of BCL2. The stress kinase PKR has been shown to phosphorylate B56␣ at serine 28 in vitro, but it has been unclear how PKR might regulate the BCL2 phosphatase. In the present study, PKR regulation of B56␣ in REH cells was examined, because these cells exhibit robust BCL2 phosphatase activity. PKR was found to be basally active in REH cells as would be predicted if the kinase supports B56␣-mediated dephosphorylation of BCL2. Suppression of PKR promoted BCL2 phosphorylation with concomitant loss of B56␣ phosphorylation at serine 28 and inhibition of mitochondrial PP2A activity. PKR supports stress signaling in REH cells, as suppression of PKR promoted chemoresistance to etoposide. Suppression of PKR promoted B56␣ proteolysis, which could be blocked by a proteasome inhibitor. However, the mechanism by which PKR supports B56␣ protein does not involve PKR-mediated phosphorylation of the B subunit at serine 28 but may involve eIF2␣ activation of AKT. Phosphorylation of serine 28 by PKR promotes mitochondrial localization of B56␣, because wild-type but not mutant S28A B56␣ promoted mitochondrial PP2A activity. Cells expressing wildtype B56␣ but not S28A B56␣ were sensitized to etoposide. These results suggest that PKR regulates B56␣-mediated PP2A signaling in REH cells.Protein phosphatase 2A (PP2A) 2 is an important regulator of apoptosis and may be a tumor suppressor (1-4). How PP2A might function as a tumor suppressor is not clear, as the enzyme on the one hand is required for cell survival but on the other is active in processes responsible for cell death (2-7). An explanation for this paradox is that PP2A is not a single enzyme but rather a family of protein phosphatase isoforms (3,4,8,9). PP2A is a heterotrimer composed of a catalytic (C) subunit, a scaffold (A) subunit, and a regulatory (B) subunit. The C and A subunits form a catalytic complex that interacts with one of at least 21 diverse B subunit members from three major families (i.e. B55, B56, and PR72/130; see Refs. 2, 3, and 9). It is becoming evident that the function of PP2A relies on the B subunit because the various B subunit proteins determine substrate specificity and PP2A complex subcellular localization (2, 3, 7, 10 -13). The recent crystal structure of PP2A supports this premise (4, 13-15). Thus the PP2A family of protein phosphatase isoforms can best be defined by its regulatory B subunit.PP2A function is regulated both negatively and positively by post-translational modification (4, 16 -18). Phosphorylation of B56␥ by ERK at serine 337 inhibits PP2A function (13, 18). Interestingly, this regulatory ERK site is conserved in all of the known B56 family members except B56␣. Although ERK may not regulate B56␣ function negatively, phosphory...

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The B56α Regulatory Subunit of Protein Phosphatase 2A Is a Target for Regulation by Double-Stranded RNA-Dependent Protein Kinase PKR

Cited by 112 publications

References 63 publications

Protein Kinase R (PKR) Interacts with and Activates Mitogen-activated Protein Kinase Kinase 6 (MKK6) in Response to Double-stranded RNA Stimulation

Protein Kinase R (PKR) Interacts with and Activates Mitogen-activated Protein Kinase Kinase 6 (MKK6) in Response to Double-stranded RNA Stimulation

PKC α mediates chemoresistance in acute lymphoblastic leukemia through effects on Bcl2 phosphorylation

PKR Regulates B56α-mediated BCL2 Phosphatase Activity in Acute Lymphoblastic Leukemia-derived REH Cells

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