Cloning, expression, and cellular localization of the oncogenic 58-kDa inhibitor of the RNA-activated human and mouse protein kinase

Molecular Characterization and Defense Functions of the Nile Tilapia (Oreochromis niloticus) DnaJ B9b and DnaJ C3a Genes in Response to Pathogenic Bacteria under High-Temperature Stress Conditions

DnaJ proteins or heat shock protein 40s (HSP40s) form one of the largest heat shock protein families. In this study, 2 cDNAs encoding Nile tilapia (Oreochromis niloticus) DnaJ proteins (On-DnaJ B9b and On-DnaJ C3a) were successfully cloned and characterized. The structures and organizations of these two genes are first reported in the present study. On-DnaJ B9b is approximately 2.1 kb long and contains 2 exons and 1 intron, while On-DnaJ C3a is approximately 12 kb long and contains 12 exons and 11 introns. Under normal conditions, On-DnaJ B9b mRNA is highly expressed in gonad and trunk kidney tissues, while On-DnaJ C3a transcripts are abundantly expressed in gills, intestine, liver, and trunk kidney tissues. Following pathogenic infections, the expression of both genes is induced in the liver, spleen and head kidney tissues of Nile tilapia that were infected with two virulent pathogenic bacteria, Streptococcus agalactiae and Flavobacterium columnare. Silencing of these two genes was first carried out, and the results clearly indicated their crucial roles under both heat and bacterial stress conditions. The fundamental knowledge obtained from this study indicates the characteristic basic biofunctions of heat shock proteins in the regulation of intracellular proteins during infection, which involve preventing protein aggregation, promoting protein refolding, and activating unfolded protein degradation.

Case Report: Homozygous DNAJC3 Mutation Causes Monogenic Diabetes Mellitus Associated With Pancreatic Atrophy

Introduction

DNAJC3, abundant in the pancreatic cells, attenuates endoplasmic reticulum stress. Homozygous DNAJC3 mutations have been reported to cause non-immune juvenile-onset diabetes, neurodegeneration, hearing loss, short stature, and hypothyroidism.

Case Description

We report a case of homozygous DNAJC3 mutation in two siblings of a consanguineous family. A 3-year-old boy presented with short stature and a thyroid nodule. Laboratory findings confirmed hypothyroidism. Subsequently, levothyroxine was administered. Growth hormone (GH) stimulation test results were within the normal limits. His stature was exceedingly short (80.5 cm) (-3.79 SDS). The patient developed sensorineural hearing loss at age 6 years; his intellectual functioning was impaired. Recombinant Human Growth Hormine (rhGH) treatment was postponed until the age of 6.9 years due to a strong family history of diabetes. At age 9 years, he developed an ataxic gait. Brain magnetic resonance imaging (MRI) revealed neurodegeneration. The patient developed diabetes at the age of 11 years-5 years after the initiation of rhGH treatment. Tests for markers of autoimmune diabetes were negative. Lifestyle modification was introduced, but insulin therapy was eventually required. Whole-exome-sequencing (WES) revealed a homozygous DNAJC3 mutation, which explained his clinical presentation. MRI revealed a small, atrophic pancreas. At the age of 17, his final adult height was 143 cm (-4.7 SDS). His elder brother, who had the same mutation, had a similar history, except that he had milder ataxia and normal brain MRI finding at the age of 28 years.

Conclusion

We propose that DNAJC3 mutation can be considered as a cause of maturity onset diabetes of the young. Patients with DNAJC3 mutations may possess a small atrophic pancreas.

Novel insights into diabetes mellitus due to DNAJC3-defect: Evolution of neurological and endocrine phenotype in the pediatric age group

BACKGROUND

A number of inborn errors of metabolism caused by abnormal protein trafficking that lead to endoplasmic reticulum storage diseases (ERSD) have been defined in the last two decades. One such disorder involves biallelic mutations in the gene encoding endoplasmic reticulum resident co-chaperone DNAJC3 (P58^IPK ) that leads to diabetes in the second decade of life, in addition to multiple endocrine dysfunction and nervous system involvement.

OBJECTIVE

The aim of this study was to define the natural history of this new form of diabetes, especially the course of abnormalities related to glucose metabolism.

METHODS

Whole-exome and Sanger sequencing was used to detect DNAJC3 defect in two patients. Detailed analysis of their clinical history as well as biochemical, neurological and radiological studies were carried out to deduce natural history of neurological and endocrine phenotype.

RESULTS

DNAJC3 defect led to beta-cell dysfunction causing hyperinsulinemichypoglycemia around 2 years of age in both patients, which evolved into diabetes with insulin deficiency in the second decade of life, probably due to beta cell loss. Endocrine phenotype involved severe early-onset growth failure due to growth hormone deficiency, and hypothyroidism of central origin. Neurological phenotype involved early onset sensorineural deafness discovered around 5 to 6 years, and neurodegeneration of central and peripheral nervous system in the first two decades of life.

CONCLUSION

Biallelic loss-of-function in the ER co-chaperone DNAJC3 leads to a new form of diabetes with early onset hyperinsulinemic hypoglycemia evolving into insulin deficiency as well as severe growth failure, hypothyroidism and diffuse neurodegeneration.

Deletion of endoplasmic reticulum stress-responsive co-chaperone p58IPK protects mice from diet-induced steatohepatitis

AIM

Activation of PKR-like endoplasmic reticulum kinase (PERK), an endoplasmic reticulum stress sensor, is a feature of non-alcoholic steatohepatitis (NASH), yet regulators of PERK signaling remain undefined in this context. The protein p58^IPK regulates PERK; however, its role in NASH has not been examined. The aim of this study was to assess the in vivo role of p58^IPK in the pathogenesis of dietary NASH.

METHODS

Parameters of hepatocyte cell death, liver injury, inflammation, fibrosis, indirect calorimetry and PERK activation were assessed in p58^IPK knockout (p58^ipk-/- ) mice and their wild-type littermate controls. All animals were fed a diet enriched in fat, fructose, and cholesterol (FFC) for 20 weeks.

RESULTS

Activation of PERK was attenuated in FFC-fed p58^ipk-/- mice. Accordingly, FFC-fed p58^ipk-/- mice showed a reduction in hepatocyte apoptosis and death receptor expression, with a significant reduction in serum alanine transaminase values. Correspondingly, macrophage accumulation and fibrosis were significantly lower in FFC-fed p58^ipk-/- mice.

CONCLUSION

We have shown that, in an in vivo dietary NASH model, p58^IPK mediates hepatocyte apoptosis and liver injury, likely through PERK phosphorylation. In the absence of p58^IPK , PERK phosphorylation and NASH are attenuated. Inhibition of hepatic p58^IPK could be a future target for NASH therapy.

Absence of BiP co-chaperone DNAJC3 causes diabetes mellitus and multisystemic neurodegeneration

Diabetes mellitus and neurodegeneration are common diseases for which shared genetic factors are still only partly known. Here, we show that loss of the BiP (immunoglobulin heavy-chain binding protein) co-chaperone DNAJC3 leads to diabetes mellitus and widespread neurodegeneration. We investigated three siblings with juvenile-onset diabetes and central and peripheral neurodegeneration, including ataxia, upper-motor-neuron damage, peripheral neuropathy, hearing loss, and cerebral atrophy. Exome sequencing identified a homozygous stop mutation in DNAJC3. Screening of a diabetes database with 226,194 individuals yielded eight phenotypically similar individuals and one family carrying a homozygous DNAJC3 deletion. DNAJC3 was absent in fibroblasts from all affected subjects in both families. To delineate the phenotypic and mutational spectrum and the genetic variability of DNAJC3, we analyzed 8,603 exomes, including 506 from families affected by diabetes, ataxia, upper-motor-neuron damage, peripheral neuropathy, or hearing loss. This analysis revealed only one further loss-of-function allele in DNAJC3 and no further associations in subjects with only a subset of the features of the main phenotype. Our findings demonstrate that loss-of-function DNAJC3 mutations lead to a monogenic, recessive form of diabetes mellitus in humans. Moreover, they present a common denominator for diabetes and widespread neurodegeneration. This complements findings from mice in which knockout of Dnajc3 leads to diabetes and modifies disease in a neurodegenerative model of Marinesco-Sjögren syndrome.

Deletion of P58(IPK), the Cellular Inhibitor of the Protein Kinases PKR and PERK, Causes Bone Changes and Joint Degeneration in Mice

OBJECTIVE

Protein kinase-like endoplasmic reticulum kinase (PERK) and protein kinase R (PKR) are implicated in endoplasmic reticulum stress-induced arthritis and pro-inflammatory cytokine-mediated cartilage degradation in vitro, respectively. We determined whether knockout of the cellular inhibitor of PERK and PKR, P58(IPK) causes joint degeneration in vivo and whether these molecules are activated in human osteoarthritis (OA).

MATERIALS AND METHODS

Sections of knee joints from P58(IPK)-null and wild-type mice aged 12-13 and 23-25 months were stained with toluidine blue and scored for degeneration using the osteoarthritis research society international (OARSI) system. Bone changes were assessed by radiology and high-resolution micro-computed tomography of hind limbs. Sections from the medial tibial plateaus of two human knees, removed in total knee replacement surgery for OA, were immunolabelled for phosphorylated PERK and PKR and P58(IPK).

RESULTS

Knockout mice exhibited narrower tibiae (p = 0.0031) and smaller epiphyses in tibiae (p = 0.0004) and femora (p = 0.0214). Older knockout mice had reduced total volume inside the femoral periosteal envelope (p = 0.023), reduced tibial (p = 0.03), and femoral (p = 0.0012) bone volumes (BV) and reduced femoral BV fraction (p = 0.025). Compared with wild-types, younger P58(IPK)-null mice had increased OARSI scores in medial femoral condyles (p = 0.035). Thirty four percent of null mice displayed severe joint degeneration with complete articular cartilage loss from the medial compartment and heterotopic chondro-osseous tissue in the medial joint capsule. Phosphorylated PERK and PKR were localized throughout human osteoarthritic tibial plateaus but, in particular, in areas exhibiting the most degeneration. There was limited expression of P58(IPK).

CONCLUSION

This study is the first to reveal a critical role for P58(IPK) in maintaining joint integrity in vivo, implicating the PKR and PERK stress signaling pathways in bony changes underlying the pathogenesis of joint degeneration.

Synthetic embryonic lethality upon deletion of the ER cochaperone p58(IPK) and the ER stress sensor ATF6α

The unfolded protein response (UPR) is activated as a consequence of alterations to ER homeostasis. It upregulates a group of ER chaperones and cochaperones, as well as other genes that improve protein processing within the secretory pathway. The UPR effector ATF6α augments-but is not essential for-maximal induction of ER chaperones during stress, yet its role, if any, in protecting cellular function during normal development and physiology is unknown. A systematic analysis of multiple tissues from Atf6α-/- mice revealed that all tissues examined were grossly insensitive to loss of ATF6α. However, combined deletion of ATF6α and the ER cochaperone p58(IPK) resulted in synthetic embryonic lethality. These findings reveal for the first time that an intact UPR can compensate for the genetic impairment of protein folding in the ER in vivo. The also expose a role for p58(IPK) in normal embryonic development.

Characterization of porcine P58IPK gene and its up-regulation after H1N1 or H3N2 influenza virus infection

BACKGROUND

The 58-kDa inhibitor of the interferon-induced double-stranded RNA-activated protein kinase (P58IPK) is a cellular protein that is activated during influenza virus infection. Although the function of human P58IPK has been studied for a long time, porcine P58IPK (pP58IPK) has little been studied except for its cloning.

OBJECTIVE

In this study, we aimed to investigate the characteristics of the pP58IPK gene, determine its subcellular localization, and find its expression change during H1N1 or H3N2 infection.

STUDY DESIGN

First, the sequence and structure of pP58IPK were analyzed. Second, pP58IPK gene was cloned into pEGFP-N1 and pEGFP-C1 vectors, respectively, which were transfected into cells to determine its subcellular localization. Third, Lung tissues of piglets from H1N1 infected, H3N2 infected and control groups were analyzed using histopathology, real-time PCR, and immunohistochemistry.

RESULTS

The sequence and structure of pP58IPK was highly similar to the counterpart of human. pP58IPK protein distributed only in the cytoplasm. Lung tissues of piglets infected by H1N1 or H3N2 appeared obvious pathological changes, and the expression of pP58IPK in both mRNA and protein level was up-regulated by approximate 1.5-fold in piglets infected by H1N1 or H3N2 comparing with control piglets.

CONCLUSIONS

We analyzed the characteristics of the pP58IPK gene, constructed a phylogenetic tree, determined its subcellular localization, and investigated its expression changes during H1N1 or H3N2 infection. The fundamental data accumulated in this study provides a potential medical model for investigating the function of P58IPK during influenza A viruses infection.

Nitric oxide: a regulator of eukaryotic initiation factor 2 kinases

Generation of nitric oxide (NO(•)) can upstream induce and downstream mediate the kinases that phosphorylate the α subunit of eukaryotic initiation factor 2 (eIF2α), which plays a critical role in regulating gene expression. There are four known eIF2α kinases (EIF2AKs), and NO(•) affects each one uniquely. Whereas NO(•) directly activates EIF2AK1 (HRI), it indirectly activates EIF2AK3 (PERK). EIF2AK4 (GCN2) is activated by depletion of l-arginine, which is used by nitric oxide synthase (NOS) during the production of NO(•). Finally EIF2AK2 (PKR), which can mediate inducible NOS expression and therefore NO(•) production, can also be activated by NO(•). The production of NO(•) and activation of EIF2AKs coordinately regulate physiological and pathological events such as innate immune response and cell apoptosis.

Orchestration of the activation of protein kinase R by the RNA-binding motif

The protein kinase R (PKR) constitutes part of the host antiviral response. PKR activation is regulated by the N-terminus of protein, which encodes tandem RNA-binding motifs (RBMs). The full capabilities of RBMs from PKR and other proteins have surpassed the narrow specificities initially determined as merely binding double-stranded RNA. Recognition of the increased affinity of the RBM for additional RNA species has established an immunological distinction by which PKR can detect exogenous RNAs, as well as identified PKR-mediated expression of specific endogenous genes. Furthermore, as RBMs also mediate interactions with other proteins, including PKR itself, this motif connects PKR to the broader RNA metabolism. Given the fundamental importance of protein-RNA interactions, not only in the innate immune response to intracellular pathogens, but also to coordinate the cellular replication machinery, there is considerable interest in the mechanisms by which proteins recognize and respond to RNA. This review appraises our understanding of how PKR activity is modulated by the RBMs.

Gene expression of Clonorchis sinensis metacercaria induced by gamma irradiation

Gamma-rays are a form of ionizing radiation and produce serious cellular damage to nuclei and organelles. Gamma irradiation induces the expressions of genes involved in DNA repair. Clonorchis sinensis resides in and provokes pathophysiologic changes in the bile ducts of mammals. The C. sinensis metacercariae are unsusceptible or resistant to gamma irradiation with LD50 of 16.5 Gy. Using the annealing control primer-based polymerase chain reaction (PCR) method, 19 genes were found to be up-regulated in C. sinensis metacercariae exposed to gamma rays. Contigs of up-regulated genes (URGs) were retrieved in a C. sinensis expressed sequence tag pool and extended by DNA-walking. Of the 13 URGs annotated putatively as functional genes, five URGs were associated with energy metabolism, six with protein processing, and the other two with DNA repair protein RAD23 and inhibitor of apoptosis protein. Four URGs were confirmed up-regulated by gamma irradiation by quantitative real-time PCR. One unknown gene, which was up-regulated to the greatest extent, might contribute to early recovery from gamma-irradiation-induced damage. The up-regulations of genes encoding DNA repair, protein processing, and energy metabolism proteins suggests that increases in gene products orchestrate DNA lesion repair and recover cellular functions in gamma-irradiated C. sinensis metacercariae.

Selective inhibition of eukaryotic translation initiation factor 2 alpha dephosphorylation potentiates fatty acid-induced endoplasmic reticulum stress and causes pancreatic beta-cell dysfunction and apoptosis

Free fatty acids cause pancreatic beta-cell apoptosis and may contribute to beta-cell loss in type 2 diabetes via the induction of endoplasmic reticulum stress. Reductions in eukaryotic translation initiation factor (eIF) 2alpha phosphorylation trigger beta-cell failure and diabetes. Salubrinal selectively inhibits eIF2alpha dephosphorylation, protects other cells against endoplasmic reticulum stress-mediated apoptosis, and has been proposed as a beta-cell protector. Unexpectedly, salubrinal induced apoptosis in primary beta-cells, and it potentiated the deleterious effects of oleate and palmitate. Salubrinal induced a marked eIF2alpha phosphorylation and potentiated the inhibitory effects of free fatty acids on protein synthesis and insulin release. The synergistic activation of the PERK-eIF2alpha branch of the endoplasmic reticulum stress response, but not of the IRE1 and activating transcription factor-6 pathways, led to a marked induction of activating transcription factor-4 and the pro-apoptotic transcription factor CHOP. Our findings demonstrate that excessive eIF2alpha phosphorylation is poorly tolerated by beta-cells and exacerbates free fatty acid-induced apoptosis. This modifies the present paradigm regarding the beneficial role of eIF2alpha phosphorylation in beta-cells and must be taken into consideration when designing therapies to protect beta-cells in type 2 diabetes.

Hijacking of the host-cell response and translational control during influenza virus infection

Influenza virus is a major public health problem with annual deaths in the US of 36,000 with pandemic outbreaks, such as in 1918, resulting in deaths exceeding 20 million worldwide. Recently, there is much concern over the introduction of highly pathogenic avian influenza H5N1 viruses into the human population. Influenza virus has evolved complex translational control strategies that utilize cap-dependent translation initiation mechanisms and involve the recruitment of both viral and host-cell proteins to preferentially synthesize viral proteins and prevent activation of antiviral responses. Influenza virus is a member of the Orthomyxoviridae family of negative-stranded, segmented RNA viruses and represents a particularly attractive model system as viral replication strategies are closely intertwined with normal cellular processes including the host defense and stress pathways. In this chapter, we review the parallels between translational control in influenza virus infected cells and in stressed cells with a focus on selective translation of viral mRNAs and the antagonism of the dsRNA and host antiviral responses. Moreover, we will discuss how the use of genomic technologies such as DNA microarrays and high through-put proteomics can be used to gain new insights into the control of protein synthesis during viral infection and provide a near comprehensive view of virus-host interactions.

Reovirus induces and benefits from an integrated cellular stress response

Following infection with most reovirus strains, viral protein synthesis is robust, even when cellular translation is inhibited. To gain further insight into pathways that regulate translation in reovirus-infected cells, we performed a comparative microarray analysis of cellular gene expression following infection with two strains of reovirus that inhibit host translation (clone 8 and clone 87) and one strain that does not (Dearing). Infection with clone 8 and clone 87 significantly increased the expression of cellular genes characteristic of stress responses, including the integrated stress response. Infection with these same strains decreased transcript and protein levels of P58(IPK), the cellular inhibitor of the eukaryotic initiation factor 2alpha (eIF2alpha) kinases PKR and PERK. Since infection with host shutoff-inducing strains of reovirus impacted cellular pathways that control eIF2alpha phosphorylation and unphosphorylated eIF2alpha is required for translation initiation, we examined reovirus replication in a variety of cell lines with mutations that impact eIF2alpha phosphorylation. Our results revealed that reovirus replication is more efficient in the presence of eIF2alpha kinases and phosphorylatable eIF2alpha. When eIF2alpha is phosphorylated, it promotes the synthesis of ATF4, a transcription factor that controls cellular recovery from stress. We found that the presence of this transcription factor increased reovirus yields 10- to 100-fold. eIF2alpha phosphorylation also led to the formation of stress granules in reovirus-infected cells. Based on these results, we hypothesize that eIF2alpha phosphorylation facilitates reovirus replication in two ways-first, by inducing ATF4 synthesis, and second, by creating an environment that places abundant reovirus transcripts at a competitive advantage for limited translational components.

Pancreatic beta-cell failure and diabetes in mice with a deletion mutation of the endoplasmic reticulum molecular chaperone gene P58IPK

The endoplasmic reticulum (ER) transmits apoptotic signals in the pancreas during ER stress, implicating ER stress-mediated apoptosis in the development of diabetes. P58(IPK) (DNAJC3) is induced during ER stress and functions as a negative feedback component to inhibit eIF-2alpha signaling and attenuate the later phases of the ER stress response. To gain insight into a more comprehensive role of P58(IPK) function, we generated deletion mutant mice that showed a gradual onset of glucosuria and hyperglycemia associated with increasing apoptosis of pancreatic islet cells. Lack of P58(IPK) had no apparent effect on the functional integrity of viable beta-cells. A set of genes associated with apoptosis showed altered expression in pancreatic islets from P58(IPK)-null mice, further substantiating the apoptosis phenotype. The data provide in vivo evidence to support the concept that P58(IPK) functions as a signal for the downregulation of ER-associated proteins involved in the initial ER stress response, thus preventing excessive cell loss by degradation pathways. Insulin deficiency associated with the absence of P58(IPK) mimics beta-cell failure associated with type 1 and late-stage type 2 diabetes. P58(IPK) function and activity may therefore provide a novel area of investigation into ER-mediated mechanistic and therapeutic approaches for diabetes.

XBP-1 regulates a subset of endoplasmic reticulum resident chaperone genes in the unfolded protein response

The mammalian unfolded protein response (UPR) protects the cell against the stress of misfolded proteins in the endoplasmic reticulum (ER). We have investigated here the contribution of the UPR transcription factors XBP-1, ATF6alpha, and ATF6beta to UPR target gene expression. Gene profiling of cell lines lacking these factors yielded several XBP-1-dependent UPR target genes, all of which appear to act in the ER. These included the DnaJ/Hsp40-like genes, p58(IPK), ERdj4, and HEDJ, as well as EDEM, protein disulfide isomerase-P5, and ribosome-associated membrane protein 4 (RAMP4), whereas expression of BiP was only modestly dependent on XBP-1. Surprisingly, given previous reports that enforced expression of ATF6alpha induced a subset of UPR target genes, cells deficient in ATF6alpha, ATF6beta, or both had minimal defects in upregulating UPR target genes by gene profiling analysis, suggesting the presence of compensatory mechanism(s) for ATF6 in the UPR. Since cells lacking both XBP-1 and ATF6alpha had significantly impaired induction of select UPR target genes and ERSE reporter activation, XBP-1 and ATF6alpha may serve partially redundant functions. No UPR target genes that required ATF6beta were identified, nor, in contrast to XBP-1 and ATF6alpha, did the activity of the UPRE or ERSE promoters require ATF6beta, suggesting a minor role for it during the UPR. Collectively, these results suggest that the IRE1/XBP-1 pathway is required for efficient protein folding, maturation, and degradation in the ER and imply the existence of subsets of UPR target genes as defined by their dependence on XBP-1. Further, our observations suggest the existence of additional, as-yet-unknown, key regulators of the UPR.

Death-associated protein 4 binds MST1 and augments MST1-induced apoptosis

The protein kinase MST1 is proapoptotic when overexpressed in an active form, however, its physiologic regulation and cellular targets are unknown. An overexpressed inactive MST1 mutant associates in COS-7 cells with an endogenous 761-amino acid polypeptide known as "death-associated protein 4" (DAP4). The DAPs are a functionally heterogeneous array of polypeptides previously isolated by Kimchi and colleagues (Kimchi, A. (1998) Biochim. Biophys. Acta 1377, F13-F33 in a screen for elements involved in the interferon gamma-induced apoptosis of HeLa cells. DAP4, which is encoded by a member of a vertebrate-only gene family, contains no identifiable domains, but is identical over its amino-terminal 488 amino acids to p52(rIPK), a putative modulator of protein kinase R. DAP4 is a widely expressed, constitutively nuclear polypeptide that homodimerizes through its amino terminus and binds MST1 through its carboxyl-terminal segment. MST1 is predominantly cytoplasmic, but cycles continuously through the nucleus, as evidenced by its rapid accumulation in the nucleus after addition of the Crm1 inhibitor, leptomycin B. Overexpression of DAP4 does not cause apoptosis, however, coexpression of DAP4 with a submaximal amount of MST1 enhances MST1-induced apoptosis in a dose-dependent fashion. DAP4 is not significantly phosphorylated by MST1 nor does it alter MST1 kinase activity in vivo or in vitro. MST1-induced apoptosis is suppressed by a dominant interfering mutant of p53. MST1 is unable to directly phosphorylate p53, however, DAP4 binds endogenous and recombinant p53. DAP4 may promote MST1-induced apoptosis by enabling colocalization of MST with p53.

Control of PERK eIF2alpha kinase activity by the endoplasmic reticulum stress-induced molecular chaperone P58IPK

P58(IPK) is an Hsp40 family member known to inhibit the interferon (IFN)-induced, double-stranded RNA-activated, eukaryotic initiation factor 2alpha (eIF2alpha) protein kinase R (PKR) by binding to its kinase domain. We find that the stress of unfolded proteins in the endoplasmic reticulum (ER) activates P58(IPK) gene transcription through an ER stress-response element in its promoter region. P58(IPK) interacts with and inhibits the PKR-like ER-localized eIF2alpha kinase PERK, which is normally activated during the ER-stress response to protect cells from ER stress by attenuating protein synthesis and reducing ER client protein load. Levels of phosphorylated eIF2alpha were lower in ER-stressed P58(IPK)-overexpressing cells and were enhanced in P58(IPK) mutant cells. In the ER-stress response, PKR-like ER kinase (PERK)-mediated translational repression is transient and is followed by translational recovery and enhanced expression of genes that increase the capacity of the ER to process client proteins. The absence of P58(IPK) resulted in increased expression levels of two ER stress-inducible genes, BiP and Chop, consistent with the enhanced eIF2alpha phosphorylation in the P58(IPK) deletion cells. Our studies suggest that P58(IPK) induction during the ER-stress response represses PERK activity and plays a functional role in the expression of downstream markers of PERK activity in the later phase of the ER-stress response.

Expression of human PKR protein kinase in transgenic mice

There is a large amount of evidence describing the expression, interaction, and mode of activation of the human interferon (IFN)-mediated double-stranded RNA-activated protein kinase (PKR) gene. Studies from Pkr-null mice have defined the kinase as a transducer of dsRNA signals that converge on transcription, translation, and apoptotic programs involved in the innate resistance to viral infection. In vitro studies also suggest that PKR may possess important cell growth regulatory and tumor suppressor properties. However, the study of Pkr-null mice has not fully elucidated the role that the kinase plays in these processes, in part because of apparent redundancies in PKR-dependent and PKR-independent regulatory pathways. To overcome such limitations and to begin to examine the role of PKR in a complex biologic system, we have generated transgenic mice overexpressing wild-type human (Hu) PKR. HuPKR was expressed and active in various tissues and associated with a small body phenotype. Spleen cells from transgenic mice were resistant to apoptosis when treated with the genotoxic agent actinomycin D and showed a decrease in proliferation in response to concanavalin A (ConA) compared with spleen cells from wild-type control mice. The initial characterization of this transgenic mouse line suggests it may be useful as a model for investigating biology and diseases relative to a number of scientific disciplines.

Proteome analysis of activated murine B-lymphocytes

Proteins extracted from murine B-lymphocytes after in vitro stimulation by lipopolysaccharide were separated by two-dimensional (2-D) polyacrylamide gel electrophoresis and analyzed by matrix assisted laser desorption/ionization mass spectrometry. Structural information on the protein entities from 153 spots was obtained. Since many of these spots occur as members of spot families, a smaller number --98 genes-- was found to be coding for the identified spots. The elucidated proteins belong to groups of functional categories; we found 26 enzymes, 36 regulatory proteins, 15 chaperones, 15 structural proteins, 4 immunoglobulins, 1 ribosomal and 1 histone protein. A comparison between expected and observed molecular masses yields a good correlation for the majority of the compared spot entities. This set of proteins now identified in the context of a lymphocyte 2-D gel pattern should advance further studies on lymphocyte functions.

Translational control of viral gene expression in eukaryotes

As obligate intracellular parasites, viruses rely exclusively on the translational machinery of the host cell for the synthesis of viral proteins. This relationship has imposed numerous challenges on both the infecting virus and the host cell. Importantly, viruses must compete with the endogenous transcripts of the host cell for the translation of viral mRNA. Eukaryotic viruses have thus evolved diverse mechanisms to ensure translational efficiency of viral mRNA above and beyond that of cellular mRNA. Mechanisms that facilitate the efficient and selective translation of viral mRNA may be inherent in the structure of the viral nucleic acid itself and can involve the recruitment and/or modification of specific host factors. These processes serve to redirect the translation apparatus to favor viral transcripts, and they often come at the expense of the host cell. Accordingly, eukaryotic cells have developed antiviral countermeasures to target the translational machinery and disrupt protein synthesis during the course of virus infection. Not to be outdone, many viruses have answered these countermeasures with their own mechanisms to disrupt cellular antiviral pathways, thereby ensuring the uncompromised translation of virion proteins. Here we review the varied and complex translational programs employed by eukaryotic viruses. We discuss how these translational strategies have been incorporated into the virus life cycle and examine how such programming contributes to the pathogenesis of the host cell.

Tissue specific expression of PKR protein kinase in aging B6D2F1 mice

A decline in the rate of protein synthesis is a common biochemical change observed with aging in a wide variety of cells and organisms. The double stranded RNA-dependent protein kinase PKR has been shown to phosphorylate eukaryotic initiation factor 2 alpha (eIF-2alpha), a well-characterized factor for down-regulating protein synthesis, in response to environmental stress conditions. Therefore, we were interested in evaluating the role of PKR in the aging process. Tissues from 2- and 20-month-old B6D2F1 male mice were evaluated by Western blot analysis. PKR was detected in all tissues of aging mice confirming its ubiquitous nature. Tissues examined from young mice showed little evidence of PKR expression, suggesting an age-associated up-regulation. P58(IPK), a cellular inhibitor of PKR, was expressed in tissues from both age groups but to a greater extent in tissues of aging mice suggesting an up-regulation to control PKR activity. Hyperphosphorylated eIF-2alpha was increased in selected tissues from older mice compared with tissues from younger mice indicating a possible correlation between PKR expression and kinase function. The data suggest that translational activity is slowing down in a tissue specific manner during the aging process in mice, possibly as the result of increased levels of PKR, and could be a factor in the reduction of the rate of protein synthesis during senescence seen in specific tissues of many organisms.

Inhibition of the double-stranded RNA-dependent protein kinase PKR by mammalian ribosomes

Previous evidence has shown that the majority of the interferon-inducible, double-stranded RNA-dependent protein kinase PKR is associated with ribosomes in vivo. Here we show that ribosomes are inhibitory for PKR activity since they compete with dsRNA for binding to PKR, inhibit the activation of the protein kinase by dsRNA, and prevent the phosphorylation of the PKR substrate eIF2alpha. We suggest that ribosomes constitute a reservoir of inactive PKR and that the protein kinase must be displaced from the ribosome by dsRNA in order to become activated.

Biochemical and genetic evidence for complex formation between the influenza A virus NS1 protein and the interferon-induced PKR protein kinase

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.

Using genetic means to dissect homologous and heterologous protein-protein interactions of PKR, the interferon-induced protein kinase

The interferon-induced protein kinase, PKR, is a pivotal component of interferon (IFN)-induced cellular antiviral and antiproliferative response. The identification and characterization of proteins, of both viral and cellular origins, that interact with PKR have proven to be a valuable probe for unraveling the cellular regulation and function of PKR. Several studies have demonstrated that PKR forms dimers and that dimerization is likely to be required for activation and/or catalytic function. It is therefore important to elucidate the mechanism of PKR dimer formation and the role of PKR effectors in modulating kinase dimerization. Herein we describe the use of the two genetic approaches, the lambda repressor fusion and the yeast two-hybrid systems, to detect and analyze homo- and heterotypic interactions with PKR. We also describe several biochemical methodologies commonly used in our laboratory to validate the genetic results. Although the examples in this article focus on PKR, the techniques can easily be adapted to investigate protein-protein associations in a variety of experimental systems. Finally, given the important role of PKR as a mediator of IFN-induced antiviral and antiproliferative effects, these studies may provide clues to the development of reagents that target PKR to enhance the therapeutic use of IFN in the treatment of disease.

Molecular mechanisms of interferon resistance mediated by viral-directed inhibition of PKR, the interferon-induced protein kinase

The interferon (IFN)-induced cellular antiviral response is the first line of defense against viral infection within an animal host. In order to establish a productive infection, eukaryotic viruses must first overcome the IFN-induced blocks imposed on viral replication. The double-stranded RNA-activated protein kinase (PKR) is a key component mediating the antiviral actions of IFN. This IFN-induced protein kinase can restrict viral replication through its ability to phosphorylate the protein synthesis initiation factor eukaryotic initiation factor-2 alpha-subunit and reduce levels of viral protein synthesis. Viruses, therefore, must block the function of PKR in order to avoid these deleterious antiviral effects associated with PKR activity. Indeed, many viruses have developed effective measures to repress PKR activity during infection. This review will focus primarily on an overview of the different molecular mechanisms employed by these viruses to meet a common goal: the inhibition of PKR function, uncompromised viral protein synthesis, and unrestricted virus replication. The past few years have seen exciting new advances in this area. Rather unexpectedly, this area of research has benefited from the use of the yeast system to study PKR. Other recent advances include studies on PKR regulation by the herpes simplex viruses and data from our laboratory on the medically important hepatitis C viruses. We speculate that IFN is ineffective as a therapeutic agent against hepatitis C virus because the virus can effectively repress PKR function. Finally, we will discuss briefly the future directions of this PKR field.

Regulation of interferon-induced protein kinase PKR: modulation of P58IPK inhibitory function by a novel protein, P52rIPK

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.

The double-stranded RNA-dependent protein kinase PKR: structure and function

This review describes the structure and function of the interferon (IFN)-inducible, double-stranded RNA-activated protein kinase PKR. This protein kinase has been studied extensively in recent years, and a large body of evidence has accumulated concerning its expression, interaction with regulatory RNA and protein molecules, and modes of activation and inhibition. PKR has been shown to play a variety of important roles in the regulation of translation, transcription, and signal transduction pathways through its ability to phosphorylate protein synthesis initiation factor eIF2, I-kappaB (the inhibitor of NF-kappaB), and other substrates. Expression studies involving both the wild-type protein and dominant negative mutants of PKR have established roles for the enzyme in the antiviral effects of IFNs, in the responses of uninfected cells to physiologic stresses, and in cell growth regulation. The possibility that PKR may function as a tumor suppressor and inducer of apoptosis suggests that this IFN-regulated protein kinase may be of central importance to the control of cell proliferation and transformation.

What happens inside lentivirus or influenza virus infected cells: insights into regulation of cellular and viral protein synthesis

Efficient manipulation of the regulatory mechanisms controlling host cell gene expression provides the means for productive infection by animal viruses. Upon infecting the host cell, viruses must: (i) bypass the cellular antiviral defense mechanisms to prevent the translational blocks imposed by the interferon pathway; and (ii) effectively "hijack" the host protein synthetic machinery into mass production of virion protein components. The multicomponent regulatory nature of cellular gene expression has provided the means of selecting for a diverse range of mechanisms utilized by animal viruses to ensure that replication efficiency is maintained throughout the virus life cycle. One important research component of the careful examination of gene regulation is those studies that focus on elucidating the mechanisms by which viruses control mRNA translation during host cell infection. Much of the work in our laboratory has focused on elucidating the strategies by which human immunodeficiency virus type 1 and influenza virus regulate protein synthesis during infection. Here we describe the ways in which these two distinctly different RNA viruses ensure the selective and efficient translation of their viral mRNAs in infected cells. These strategies include circumvention of the deleterious effects associated with activation of the interferon-induced protein kinase, PKR. Herein we describe our methodologies designed to elucidate the translational regulation in cells infected by these viruses. We conclude with a brief summary of new directions, utilizing these methods, taken toward understanding the translational control mechanisms imposed by these viral systems, and how our studies of virally infected cells have allowed us to identify growth-regulating components of normal, uninfected cells.

The molecular chaperone hsp40 regulates the activity of P58IPK, the cellular inhibitor of PKR

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.

The 58-kDa cellular inhibitor of the double stranded RNA-dependent protein kinase requires the tetratricopeptide repeat 6 and DnaJ motifs to stimulate protein synthesis in vivo

Double stranded RNA-dependent protein kinase (PKR) is a double stranded RNA-activated, interferon-induced serine-threonine kinase that participates in both the antiviral and antiproliferative properties of interferon. We previously found that influenza virus inhibited PKR function by recruiting or activating a cellular inhibitor termed P58(IPK). The present study was undertaken to complement our earlier analyses, which demonstrated that P58(IPK) efficiently inhibited PKR autophosphorylation and activity in vitro. We now report that P58(IPK) down-regulates PKR and, in turn, stimulates protein synthetic rates inside the cell. Using transfection analysis, we show that P58(IPK) stimulates translation of secreted embryonic alkaline phosphatase reporter gene mRNA. Furthermore, we found that at least two regions of the P58(IPK) molecule were required for PKR inhibitory activity in COS-1 cells: (i) the DnaJ similarity region at the carboxyl terminus (amino acids 391-504); and (ii) the tetratricopeptide repeat 6 (TPR6) domain (amino acids 222-255) located in the middle of the P58(IPK) protein and within the eukaryotic protein synthesis initiation factor 2alpha homology region. P58(IPK) variants lacking either one of these regions were unable to stimulate secreted embryonic alkaline phosphatase protein synthetic rates. Consistent with this data is the observation that the DeltaTPR6 mutant (the P58(IPK) variant lacking the TPR6 motif) failed to block PKR activity in vitro. Based on these data and our earlier in vitro functional and PKR-P58(IPK) binding analyses, a revised model of PKR regulation by P58(IPK) is presented.

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

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.