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Langut Y, Edinger N, Flashner-Abramson E, Melamed-Book N, Lebendiker M, Levi-Kalisman Y, Klein S, Levitzki A. PSMA-homing dsRNA chimeric protein vector kills prostate cancer cells and activates anti-tumor bystander responses. Oncotarget 2018; 8:24046-24062. [PMID: 28445962 PMCID: PMC5421826 DOI: 10.18632/oncotarget.15733] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Accepted: 02/11/2017] [Indexed: 01/12/2023] Open
Abstract
The treatment of metastatic androgen-resistant prostate cancer remains a challenge. We describe a protein vector that selectively delivers synthetic dsRNA, polyinosinic/polycytidylic acid (polyIC), to prostate tumors by targeting prostate specific membrane antigen (PSMA), which is overexpressed on the surface of prostate cancer cells. The chimeric protein is built from the double stranded RNA (dsRNA) binding domain of PKR tethered to a single chain anti-PSMA antibody. When complexed with polyIC, the chimera demonstrates selective and efficient killing of prostate cancer cells. The treatment causes the targeted cancer cells to undergo apoptosis and to secrete toxic cytokines. In a bystander effect, these cytokines kill neighboring cancer cells that do not necessarily overexpress PSMA, and activate immune cells that enhance the killing effect. The strong effects of the targeted polyIC are demonstrated on both 2D cell cultures and 3D tumor spheroids.
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Affiliation(s)
- Yael Langut
- Department of Biological Chemistry, Unit of Cellular Signaling, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Nufar Edinger
- Department of Biological Chemistry, Unit of Cellular Signaling, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Efrat Flashner-Abramson
- Department of Biological Chemistry, Unit of Cellular Signaling, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Naomi Melamed-Book
- Department of Biological Chemistry, Unit of Bio-Imaging, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Mario Lebendiker
- The Protein Purification Facility, Wolfson Center for Applied Structural Biology, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Yael Levi-Kalisman
- The Center for Nanoscience and Nanotechnology, Silberman Institute for Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Shoshana Klein
- Department of Biological Chemistry, Unit of Cellular Signaling, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Alexander Levitzki
- Department of Biological Chemistry, Unit of Cellular Signaling, Silberman Institute of Life Sciences, Safra Campus, The Hebrew University of Jerusalem, Jerusalem, Israel
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Fros JJ, Pijlman GP. Alphavirus Infection: Host Cell Shut-Off and Inhibition of Antiviral Responses. Viruses 2016; 8:v8060166. [PMID: 27294951 PMCID: PMC4926186 DOI: 10.3390/v8060166] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2016] [Revised: 06/01/2016] [Accepted: 06/07/2016] [Indexed: 12/18/2022] Open
Abstract
Alphaviruses cause debilitating disease in humans and animals and are transmitted by blood-feeding arthropods, typically mosquitoes. With a traditional focus on two models, Sindbis virus and Semliki Forest virus, alphavirus research has significantly intensified in the last decade partly due to the re-emergence and dramatic expansion of chikungunya virus in Asia, Europe, and the Americas. As a consequence, alphavirus–host interactions are now understood in much more molecular detail, and important novel mechanisms have been elucidated. It has become clear that alphaviruses not only cause a general host shut-off in infected vertebrate cells, but also specifically suppress different host antiviral pathways using their viral nonstructural proteins, nsP2 and nsP3. Here we review the current state of the art of alphavirus host cell shut-off of viral transcription and translation, and describe recent insights in viral subversion of interferon induction and signaling, the unfolded protein response, and stress granule assembly.
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Affiliation(s)
- Jelke J Fros
- Nuffield Department of Medicine, Peter Medawar Building for Pathogen Research, University of Oxford, Oxford OX1 3SY, England, UK.
- Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen 6700 AB, The Netherlands.
| | - Gorben P Pijlman
- Laboratory of Virology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen 6700 AB, The Netherlands.
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Zhou F. Molecular mechanisms of viral immune evasion proteins to inhibit MHC class I antigen processing and presentation. Int Rev Immunol 2009; 28:376-93. [PMID: 19811316 DOI: 10.1080/08830180903013034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Viral products inhibit MHC class I antigen processing and presentation via three major pathways: inhibition of major histocompatibility complex (MHC) class I expression on cells, blockade of peptide trafficking and loading on MHC class I molecules, and inhibition of peptide generation in host cells. Viral products also interfere with IFN-gamma -mediated JAK/STAT signal transduction in cells. These results imply that viral proteins probably inhibit the function of IFN-gamma in MHC class I antigen presentation via inactivation of JAK/STAT signal transduction in host cells. Mechanisms of viral products to inhibit IFN-gamma -mediated MHC class I antigen presentation were summarized in this literature review.
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Affiliation(s)
- Fang Zhou
- University of Queensland Diamantina Institute for Cancer Immunology and Metabolic Medicine, Princess Alexandra Hospital, Brisbane QLD 4102, Australia.
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Ikegami T, Narayanan K, Won S, Kamitani W, Peters CJ, Makino S. Dual functions of Rift Valley fever virus NSs protein: inhibition of host mRNA transcription and post-transcriptional downregulation of protein kinase PKR. Ann N Y Acad Sci 2009; 1171 Suppl 1:E75-85. [PMID: 19751406 DOI: 10.1111/j.1749-6632.2009.05054.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Rift Valley fever virus (RVFV), which belongs to the genus Phlebovirus, family Bunyaviridae, is a negative-stranded RNA virus carrying a single-stranded, tripartite RNA genome. RVFV is an important zoonotic pathogen transmitted by mosquitoes and causes large outbreaks among ruminants and humans in Africa and the Arabian Peninsula. Human patients develop an acute febrile illness, followed by a fatal hemorrhagic fever, encephalitis, or ocular diseases. A viral nonstructural protein, NSs, is a major viral virulence factor. Past studies showed that NSs suppresses the transcription of host mRNAs, including interferon-beta mRNAs. Here we demonstrated that the NSs protein induced post-transcriptional downregulation of dsRNA-dependent protein kinase (PKR), to prevent phosphorylation of eIF2alpha and promoted viral translation in infected cells. These two biological activities of the NSs most probably have a synergistic effect in suppressing host innate immune functions and facilitate efficient viral replication in infected mammalian hosts.
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Affiliation(s)
- Tetsuro Ikegami
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas 77555-0438, USA.
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Ikegami T, Narayanan K, Won S, Kamitani W, Peters CJ, Makino S. Rift Valley fever virus NSs protein promotes post-transcriptional downregulation of protein kinase PKR and inhibits eIF2alpha phosphorylation. PLoS Pathog 2009; 5:e1000287. [PMID: 19197350 PMCID: PMC2629125 DOI: 10.1371/journal.ppat.1000287] [Citation(s) in RCA: 183] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 01/08/2009] [Indexed: 12/18/2022] Open
Abstract
Rift Valley fever virus (RVFV) (genus Phlebovirus, family Bunyaviridae) is a negative-stranded RNA virus with a tripartite genome. RVFV is transmitted by mosquitoes and causes fever and severe hemorrhagic illness among humans, and fever and high rates of abortions in livestock. A nonstructural RVFV NSs protein inhibits the transcription of host mRNAs, including interferon-β mRNA, and is a major virulence factor. The present study explored a novel function of the RVFV NSs protein by testing the replication of RVFV lacking the NSs gene in the presence of actinomycin D (ActD) or α-amanitin, both of which served as a surrogate of the host mRNA synthesis suppression function of the NSs. In the presence of the host-transcriptional inhibitors, the replication of RVFV lacking the NSs protein, but not that carrying NSs, induced double-stranded RNA-dependent protein kinase (PKR)–mediated eukaryotic initiation factor (eIF)2α phosphorylation, leading to the suppression of host and viral protein translation. RVFV NSs promoted post-transcriptional downregulation of PKR early in the course of the infection and suppressed the phosphorylated eIF2α accumulation. These data suggested that a combination of RVFV replication and NSs-induced host transcriptional suppression induces PKR-mediated eIF2α phosphorylation, while the NSs facilitates efficient viral translation by downregulating PKR and inhibiting PKR-mediated eIF2α phosphorylation. Thus, the two distinct functions of the NSs, i.e., the suppression of host transcription, including that of type I interferon mRNAs, and the downregulation of PKR, work together to prevent host innate antiviral functions, allowing efficient replication and survival of RVFV in infected mammalian hosts. The mosquito-borne bunyavirus Rift Valley fever virus (RVFV) devastates both humans and domestic animals; it causes abortions in ruminants and complications such as hemorrhage, encephalitis, or retinal vasculitis in humans. A major RVFV virulence factor, NSs, disables host cell mRNA synthesis. Here we describe our new evidence that showed NSs working in a second way; in addition to inhibiting host cell transcription, NSs kept translation active in infected cells. It is well-established that activated protein kinase PKR phosphorylates a translation factor, eIF2α, and then this phosphorylated eIF2α suppresses translation. We found that NSs decreased PKR abundance and prevented eIF2α phosphorylation in infected cells, allowing efficient viral translation and replication. In contrast, when cells were infected with an RVFV mutant lacking NSs in the presence of transcriptional inhibitors that mimic the transcription inhibition function of NSs, the PKR reduction did not occur and phoshorylated eIF2α was accumulated, resulting in the inhibition of virus gene expression and replication. Thus, NSs functions in two ways to help RVFV replicate in mammalian hosts: its newly identified PKR downregulation function secures efficient viral translation, and its host transcription inhibition function suppresses the expression of host innate antiviral functions.
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Affiliation(s)
- Tetsuro Ikegami
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Department of Pathology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Sealy Center for Vaccine Development, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Center for Biodefense and Emerging Infectious Diseases, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- * E-mail: (TI); (SM)
| | - Krishna Narayanan
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
| | - Sungyong Won
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
| | - Wataru Kamitani
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
| | - C. J. Peters
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Department of Pathology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Sealy Center for Vaccine Development, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Center for Biodefense and Emerging Infectious Diseases, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
| | - Shinji Makino
- Department of Microbiology and Immunology, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Sealy Center for Vaccine Development, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- Center for Biodefense and Emerging Infectious Diseases, The University of Texas Medical Branch at Galveston, Galveston, Texas, United States of America
- * E-mail: (TI); (SM)
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6
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Falsig J, van Beek J, Hermann C, Leist M. Molecular basis for detection of invading pathogens in the brain. J Neurosci Res 2008; 86:1434-47. [DOI: 10.1002/jnr.21590] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Puthenveetil S, Whitby L, Ren J, Kelnar K, Krebs JF, Beal PA. Controlling activation of the RNA-dependent protein kinase by siRNAs using site-specific chemical modification. Nucleic Acids Res 2006; 34:4900-11. [PMID: 16982647 PMCID: PMC1635244 DOI: 10.1093/nar/gkl464] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The RNA-dependent protein kinase (PKR) is activated by binding to double-stranded RNA (dsRNA). Activation of PKR by short-interfering RNAs (siRNAs) and stimulation of the innate immune response has been suggested to explain certain off-target effects in some RNA interference experiments. Here we show that PKR's kinase activity is stimulated in vitro 3- to 5-fold by siRNA duplexes with 19 bp and 2 nt 3′-overhangs, whereas the maximum activation observed for poly(I)•poly(C) was 17-fold over background under the same conditions. Directed hydroxyl radical cleavage experiments indicated that siRNA duplexes have at least four different binding sites for PKR's dsRNA binding motifs (dsRBMs). The location of these binding sites suggested specific nucleotide positions in the siRNA sense strand that could be modified with a corresponding loss of PKR binding. Modification at these sites with N2-benzyl-2′-deoxyguanosine (BndG) blocked interaction with PKR's dsRBMs and inhibited activation of PKR by the siRNA. Importantly, modification of an siRNA duplex that greatly reduced PKR activation did not prevent the duplex from lowering mRNA levels of a targeted message by RNA interference in HeLa cells. Thus, these studies demonstrate that specific positions in an siRNA can be rationally modified to prevent interaction with components of cellular dsRNA-regulated pathways.
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Affiliation(s)
| | | | | | - Kevin Kelnar
- Ambion, Inc.2130 Woodward, Austin, TX 78744, USA
| | | | - Peter A. Beal
- To whom correspondence should be addressed. Fax: +1 801 581 8433;
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8
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Ventoso I, Sanz MA, Molina S, Berlanga JJ, Carrasco L, Esteban M. Translational resistance of late alphavirus mRNA to eIF2alpha phosphorylation: a strategy to overcome the antiviral effect of protein kinase PKR. Genes Dev 2006; 20:87-100. [PMID: 16391235 PMCID: PMC1356103 DOI: 10.1101/gad.357006] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The double-stranded RNA-dependent protein kinase (PKR) is one of the four mammalian kinases that phosphorylates the translation initiation factor 2alpha in response to virus infection. This kinase is induced by interferon and activated by double-stranded RNA (dsRNA). Phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) blocks translation initiation of both cellular and viral mRNA, inhibiting virus replication. To counteract this effect, most viruses express inhibitors that prevent PKR activation in infected cells. Here we report that PKR is highly activated following infection with alphaviruses Sindbis (SV) and Semliki Forest virus (SFV), leading to the almost complete phosphorylation of eIF2alpha. Notably, subgenomic SV 26S mRNA is translated efficiently in the presence of phosphorylated eIF2alpha. This modification of eIF2 does not restrict viral replication; SV 26S mRNA initiates translation with canonical methionine in the presence of high levels of phosphorylated eIF2alpha. Genetic and biochemical data showed a highly stable RNA hairpin loop located downstream of the AUG initiator codon that is necessary to provide translational resistance to eIF2alpha phosphorylation. This structure can stall the ribosomes on the correct site to initiate translation of SV 26S mRNA, thus bypassing the requirement for a functional eIF2. Our findings show the existence of an alternative way to locate the ribosomes on the initiation codon of mRNA that is exploited by a family of viruses to counteract the antiviral effect of PKR.
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Affiliation(s)
- Iván Ventoso
- Departamento de Biología Molecular y Celular, Centro Nacional de Biotecnología/CSIC, Cantoblanco, E-28049 Madrid, Spain.
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Scumpia PO, Kelly KM, Reeves WH, Stevens BR. Double-stranded RNA signals antiviral and inflammatory programs and dysfunctional glutamate transport in TLR3-expressing astrocytes. Glia 2005; 52:153-62. [PMID: 15920723 DOI: 10.1002/glia.20234] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Astrocyte inflammation, reactive oxygen species (ROS) formation, and dysfunction form a common denominator shared by all the major neurodegenerative disorders. Viral infections are emerging as important events in the etiology of CNS damage involving astrocytes, but molecular understanding is incomplete. Double-stranded RNA (dsRNA) is a byproduct of viral replication and serves as the signature molecule for viral infection via Toll-like receptor 3 (TLR3) largely restricted to circulating peripheral dendritic cells. However, astrocytes are strategically located at the blood-brain barrier (BBB) and throughout brain tissues, making these cells ideal candidates as innate immunity sentinels within the CNS. We hypothesized that extracellular dsRNA, mimicked by polyinosinic-polycytidylic acid (Poly(I:C); PIC), initiates signaling of the double-edged sword of antiviral plus pathophysiological events in astrocytes. Using Western blot analysis and real-time qPCR, we determined that neonatal rat astrocyte cultures constitutively express TLR3 mRNA and protein, and that PIC dsRNA induced phosphorylation of eIF2alpha, as well as mRNA type I interferon (alpha/beta IFN)-response genes Mx1, PKR, and TLR3. Astrocyte TLR3 protein was downregulated after PIC treatment, however. PIC signaled degradation of IkappaBalpha with the consequence of upregulating iNOS, TNF-alpha, and IL-1beta mRNAs and proteins. In addition to antiviral protection events, dsRNA induced astrocyte dysfunction, evidenced by inhibiting EAAT1/GLAST transporter gene expression and attenuating L-glutamate uptake via sodium-dependent transport system X(AG)-, as well as inducing cytotoxicity. Anti-TLR3 blocking antibody attenuated PIC upregulation of TNF-alpha mRNA and iNOS activity. Extracellular PIC-induced events were prevented by 2-aminopurine, implicating PKR as an important downstream player in astrocyte dsRNA sensing pathways. The effects of plasma membrane impermeable poly(I:C) were dose-dependent (0-50 microM). In concert, these data provide evidence that dsRNA/TLR3-activated astrocytes initiate a battery of rapid innate pathogen-associated molecular pattern (PAMP) immune responses that are important for mounting antiviral defense in the CNS, yet also lead to pathophysiological events associated with the glutamate neurotoxicity of neurodegenerative diseases.
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Affiliation(s)
- Philip O Scumpia
- Department of Physiology and Functional Genomics, University of Florida College of Medicine, Gainesville, Florida 32610-0274, USA
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Stork J, Panaviene Z, Nagy PD. Inhibition of in vitro RNA binding and replicase activity by phosphorylation of the p33 replication protein of Cucumber necrosis tombusvirus. Virology 2005; 343:79-92. [PMID: 16154612 DOI: 10.1016/j.virol.2005.08.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/10/2005] [Accepted: 08/08/2005] [Indexed: 10/25/2022]
Abstract
Tombusviruses, which are small plus-strand RNA viruses of plants, require the viral-coded p33 replication co-factor for template selection and recruitment into replication in infected cells. As presented in the accompanying paper [Shapka, N., Stork, J., Nagy, P.D., 2005. Phosphorylation of the p33 replication protein of Cucumber necrosis tombusvirus adjacent to the RNA binding site affects viral RNA replication. J. Virol. 343, 65-78.], p33 can be phosphorylated in vitro at serine and threonine residues adjacent to its arginine-proline-rich RNA binding site. To test the effect of phosphorylation on p33 function, in this paper, we used phosphorylation-mimicking aspartic acid mutants of Cucumber necrosis virus (CNV) p33 and in-vitro-phosphorylated p33 in gel mobility shift experiments. We found that phosphorylation inhibited the ability of p33 to bind to the viral RNA. In contrast, the nonphosphorylation-mimicking alanine mutants of p33 bound to viral RNA as efficiently as the nonphosphorylated wild type p33 did. In vitro assays with purified CNV replicase preparations revealed that phosphorylation-mimicking mutants of p33 did not support the assembly of functional CNV replicase complexes in yeast, a model host. Based on these results, we propose that the primary function of reversible phosphorylation of p33 is to regulate the RNA binding capacity of p33, which could affect the assembly of new viral replicase complexes, recruitment of the viral RNA template into replication and/or release of viral RNA from replication. Thus, phosphorylation of p33 might help in switching the role of the viral RNA from replication to other processes, such as viral RNA encapsidation and cell-to-cell movement in infected hosts.
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Affiliation(s)
- Jozsef Stork
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, Lexington, KY 40546, USA
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Moschos SA, Bramwell VW, Somavarapu S, Alpar HO. Comparative immunomodulatory properties of a chitosan-MDP adjuvant combination following intranasal or intramuscular immunisation. Vaccine 2005; 23:1923-30. [PMID: 15734064 DOI: 10.1016/j.vaccine.2004.10.016] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Accepted: 10/18/2004] [Indexed: 11/24/2022]
Abstract
As the precise functions of adjuvants become clearer, opportunities are presented in their complementary use for the induction of tailored immune responses to subunit vaccines. Here we comparatively investigate the immunological outcome following intranasal or intramuscular immunisation with Helicobacter pylori urease admixed to a chitosan and muramyl di-peptide (MDP) combination. MDP appeared to limit the antigenicity of rUre by either administration route. Nasal administration of the combined adjuvant formulation resulted in an up-regulation of type I recall responses in splenocytes as opposed to adjuvantisation with chitosan alone. In contrast, intramuscular immunisation appeared to limit the responsiveness to the antigen when adjuvanted with chitosan and even more so when chitosan was combined with MDP, suggesting that the mechanism of adjuvantisation and adjuvant synergy differed depending on the immunisation route. Recognising the benefit of improved delivery of MDP intranasally due to the specific physiological effects of chitosan, we discuss the impact of the newly identified pathogen associated molecular pattern (PAMP) role of MDP with respect to the adjuvanticity of proposed chemical variants of this peptide adjuvant.
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Affiliation(s)
- Sterghios A Moschos
- Centre for Drug Delivery Research, Department of Pharmaceutics, The School of Pharmacy, 29-39 Brunswick Square, University of London, London, WC1N 1AX, UK
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Huang Y, Zuo Z. Isoflurane induces a protein kinase C alpha-dependent increase in cell-surface protein level and activity of glutamate transporter type 3. Mol Pharmacol 2005; 67:1522-33. [PMID: 15709112 DOI: 10.1124/mol.104.007443] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Glutamate transporters regulate extracellular concentrations of glutamate, an excitatory neurotransmitter in the central nervous system. We have shown that the commonly used anesthetic isoflurane increased the activity of glutamate transporter type 3 (excitatory amino acid transporter 3, EAAT3) possibly via a protein kinase C (PKC)-dependent pathway. In this study, we showed that isoflurane induced a time- and concentration-dependent redistribution of EAAT3 to the cell membrane in C6 glioma cells. This redistribution was inhibited by staurosporine, a pan PKC inhibitor, or by 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole (Go6976) at a concentration that selectively inhibits conventional PKC isozymes (PKC alpha, -beta, and -gamma). This isoflurane-induced EAAT3 redistribution was also blocked when the expression of PKC alpha but not PKC beta proteins was down-regulated by the respective antisense oligonucleotides. The isoflurane-induced increase of glutamate uptake by EAAT3 was abolished by the down-regulation of PKC alpha expression. Immunoprecipitation with an anti-EAAT3 antibody pulled down more PKC alpha in cells exposed to isoflurane than in control cells. Isoflurane also increased the phosphorylated EAAT3 and the redistribution of PKC alpha to the particulate fraction of cells. Consistent with the results in C6 cells, isoflurane also increased EAAT3 cell-surface expression and enhanced the association of PKC alpha with EAAT3 in rat hippocampal synaptosomes. Our results suggest that the isoflurane-induced increase in EAAT3 activity requires an increased amount of EAAT3 protein in the plasma membrane. These effects are PKC alpha-dependent and may rely on the formation of an EAAT3-PKC alpha complex. Together, these results suggest an important mechanism for the regulation of glutamate transporter functions and expand our understanding of isoflurane pharmacology at cellular and molecular levels.
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Affiliation(s)
- Yueming Huang
- Department of Anesthesiology, University of Virginia Health System, Charlottesville, 22908-0710, USA
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Lemaire PA, Lary J, Cole JL. Mechanism of PKR activation: dimerization and kinase activation in the absence of double-stranded RNA. J Mol Biol 2005; 345:81-90. [PMID: 15567412 DOI: 10.1016/j.jmb.2004.10.031] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2004] [Revised: 10/07/2004] [Accepted: 10/08/2004] [Indexed: 11/16/2022]
Abstract
The kinase PKR is a central component of the interferon antiviral pathway. PKR is activated upon binding double-stranded (ds) RNA to undergo autophosphorylation. Although PKR is known to dimerize, the relationship between dimerization and activation remains unclear. Here, we directly characterize dimerization of PKR in free solution using analytical ultracentrifugation and correlate self-association with autophosphorylation activity. Latent, unphosphorylated PKR exists predominantly as a monomer at protein concentrations below 2 mg/ml. A monomer sedimentation coefficient of s(20,w)(0)=3.58 S and a frictional ratio of f/f(0)=1.62 indicate an asymmetric shape. Sedimentation equilibrium measurements indicate that PKR undergoes a weak, reversible monomer-dimer equilibrium with K(d)=450 microM. This dimerization reaction serves to initiate a previously unrecognized dsRNA-independent autophosphorylation reaction. The resulting activated enzyme is phosphorylated on the two critical threonine residues present in the activation loop and is competent to phosphorylate the physiological substrate, eIF2alpha. Dimer stability is enhanced by approximately 500-fold upon autophosphorylation. We propose a chain reaction model for PKR dsRNA-independent activation where dimerization of latent enzyme followed by intermolecular phosphorylation serves as the initiation step. Subsequent propagation steps likely involve phosphorylation of latent PKR monomers by activated enzyme within high-affinity heterodimers. Our results support a model whereby dsRNA functions by bringing PKR monomers into close proximity in a manner that is analogous to the dimerization of free PKR.
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Affiliation(s)
- Peter A Lemaire
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269, USA
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Kim DH, Behlke MA, Rose SD, Chang MS, Choi S, Rossi JJ. Synthetic dsRNA Dicer substrates enhance RNAi potency and efficacy. Nat Biotechnol 2004; 23:222-6. [PMID: 15619617 DOI: 10.1038/nbt1051] [Citation(s) in RCA: 640] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2004] [Accepted: 11/01/2004] [Indexed: 02/07/2023]
Abstract
RNA interference (RNAi) is the process of sequence-specific post-transcriptional gene silencing triggered by double-stranded RNAs. In attempts to identify RNAi triggers that effectively function at lower concentrations, we found that synthetic RNA duplexes 25-30 nucleotides in length can be up to 100-fold more potent than corresponding conventional 21-mer small interfering RNAs (siRNAs). Some sites that are refractory to silencing by 21-mer siRNAs can be effectively targeted by 27-mer duplexes, with silencing lasting up to 10 d. Notably, the 27-mers do not induce interferon or activate protein kinase R (PKR). The enhanced potency of the longer duplexes is attributed to the fact that they are substrates of the Dicer endonuclease, directly linking the production of siRNAs to incorporation in the RNA-induced silencing complex. These results provide an alternative strategy for eliciting RNAi-mediated target cleavage using low concentrations of synthetic RNA as substrates for cellular Dicer-mediated cleavage.
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Bennett RL, Blalock WL, May WS. Serine 18 phosphorylation of RAX, the PKR activator, is required for PKR activation and consequent translation inhibition. J Biol Chem 2004; 279:42687-93. [PMID: 15299031 DOI: 10.1074/jbc.m403321200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is now apparent that the double-stranded (ds)RNA-dependent protein kinase, PKR, is a regulator of diverse cellular responses to stress. Recently, the murine dsRNA-binding protein RAX and its human ortholog PACT were identified as cellular activators of PKR. Previous reports demonstrate that following stress, RAX/PACT associates with and activates PKR resulting in eIF2alpha phosphorylation, consequent translation inhibition, and cell death via apoptosis. Although RAX/PACT is phosphorylated during stress, any regulatory role for this post-translational modification has been uncertain. Now we have discovered that RAX is phosphorylated on serine 18 in both human and mouse cells. The non-phosphorylatable form of RAX, RAX(S18A), although still able to bind dsRNA and associate with PKR, fails to activate PKR following stress. Furthermore, stable expression of RAX(S18A) results in a dominant-negative effect characterized by deficiency of eukaryotic initiation factor 2 alpha subunit phosphorylation, delay of translation inhibition, and failure to undergo rapid apoptosis following removal of interleukin-3. We propose that the ability of RAX to activate PKR is regulated by a sequential mechanism featuring RAX association with PKR, RAX phosphorylation at serine 18, and activation of PKR.
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Affiliation(s)
- Richard L Bennett
- University of Florida College of Medicine, Shands Cancer Center, Gainesville, Florida 32610, USA
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16
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Langland JO, Jacobs BL. Inhibition of PKR by vaccinia virus: role of the N- and C-terminal domains of E3L. Virology 2004; 324:419-29. [PMID: 15207627 DOI: 10.1016/j.virol.2004.03.012] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2003] [Revised: 01/12/2004] [Accepted: 03/17/2004] [Indexed: 01/27/2023]
Abstract
The process of eukaryotic translation initiation can be regulated by a highly conserved mechanism involving the phosphorylation of the translation initiation factor eIF2 on the alpha subunit. This mechanism is recognized as an efficient step in the host antiviral response. Vaccinia virus (VV), like many other viruses, encodes proteins to overcome this inhibitory process. The C-terminus of the vaccinia virus E3L is known to bind to double-stranded RNA (dsRNA) thereby sequestering the activator of this antiviral response. In this report, the N-terminus of E3L was found to be required for the additional regulation of eIF2alpha phosphorylation. This phosphorylation event did not lead to a global shutdown in protein synthesis. Because the N-terminus of E3L is required for full viral pathogenesis in mice, these results suggest an alternative role of eIF2alpha phosphorylation in regulating viral replication.
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Affiliation(s)
- Jeffrey O Langland
- Graduate Program in Microbiology, School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
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17
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Kirkegaard K, Taylor MP, Jackson WT. Cellular autophagy: surrender, avoidance and subversion by microorganisms. Nat Rev Microbiol 2004; 2:301-14. [PMID: 15031729 PMCID: PMC7097095 DOI: 10.1038/nrmicro865] [Citation(s) in RCA: 343] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Karla Kirkegaard
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California 94305, USA.
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18
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Langland JO, Jacobs BL. The role of the PKR-inhibitory genes, E3L and K3L, in determining vaccinia virus host range. Virology 2002; 299:133-41. [PMID: 12167348 DOI: 10.1006/viro.2002.1479] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Vaccinia virus encodes two regulators of the cellular antiviral response. The E3L gene is thought to act primarily by sequestering double-stranded RNA, whereas the K3L gene is thought to act as a competitive inhibitor of the double-stranded RNA-dependent protein kinase, PKR. The broad host range associated with vaccinia virus replication appears to be related to the presence of these genes. The E3L gene is required for replication in HeLa cells, but is not required for replication in BHK cells. On the contrary, the K3L gene is required for replication in BHK cells, but is dispensable for replication in HeLa cells. Our results suggest that these cell lines varied in the expression of endogenous activatable PKR and that replication of vaccinia virus in different cell lines led to altered levels of double-stranded RNA synthesis from the virus. Vaccinia virus was able to overcome these cellular variations by regulating PKR activity through the synthesis of either E3L or K3L. The results suggest that vaccinia virus has evolved a broad host range by maintaining both the E3L and the K3L genes.
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Affiliation(s)
- Jeffrey O Langland
- Department of Microbiology, Arizona State University, Tempe 85287-2701, USA
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19
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Donzé O, Abbas-Terki T, Picard D. The Hsp90 chaperone complex is both a facilitator and a repressor of the dsRNA-dependent kinase PKR. EMBO J 2001; 20:3771-80. [PMID: 11447118 PMCID: PMC125551 DOI: 10.1093/emboj/20.14.3771] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
PKR, a member of the eukaryotic initiation-factor 2alpha (eIF-2alpha) kinase family, mediates the host antiviral response and is implicated in tumor suppression and apoptosis. Here we show that PKR is regulated by the heat shock protein 90 (Hsp90) molecular chaperone complex. Mammalian PKR expressed in budding yeast depends on several components of the Hsp90 complex for accumulation and activity. In mammalian cells, inhibition of Hsp90 function with geldanamycin (GA) during de novo synthesis of PKR also interferes with its accumulation and activity. Hsp90 and its co-chaperone p23 bind to PKR through its N-terminal double-stranded (ds) RNA binding region as well as through its kinase domain. Both dsRNA and GA induce the rapid dissociation of Hsp90 and p23 from mature PKR, activate PKR both in vivo and in vitro and within minutes trigger the phosphorylation of the PKR substrate eIF-2alpha. A short-term exposure of cells to the Hsp90 inhibitors GA or radicicol not only derepresses PKR, but also activates the Raf-MAPK pathway. This suggests that the Hsp90 complex may more generally assist the regulatory domains of kinases and other Hsp90 substrates.
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Affiliation(s)
- O Donzé
- Département de Biologie Cellulaire, Université de Genève, Sciences III, 30 quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland.
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20
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Tian B, Mathews MB. Functional characterization of and cooperation between the double-stranded RNA-binding motifs of the protein kinase PKR. J Biol Chem 2001; 276:9936-44. [PMID: 11134010 DOI: 10.1074/jbc.m007328200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The interferon-inducible double-stranded RNA (dsRNA)-activated protein kinase PKR is regulated by dsRNAs that interact with the two dsRNA-binding motifs (dsRBMs) in its N terminus. The dsRBM is a conserved protein motif found in many proteins from most organisms. In this study, we investigated the biochemical functions and cytological activities of the two PKR dsRBMs (dsRBM1 and dsRBM2) and the cooperation between them. We found that dsRBM1 has a higher affinity for binding to dsRNA than dsRBM2. In addition, dsRBM1 has RNA-annealing activity that is not displayed by dsRBM2. Both dsRBMs have an intrinsic ability to dimerize (dsRBM2) or multimerize (dsRBM1). Binding to dsRNA inhibits oligomerization of dsRBM1 but not dsRBM2 and strongly inhibits the dimerization of the intact PKR N terminus (p20) containing both dsRBMs. dsRBM1, like p20, activates reporter gene expression in transfection assays, and it plays a determinative role in localizing PKR to the nucleolus and cytoplasm of the cell. Thus, dsRBM2 has weak or no activity in dsRNA binding, stimulation of gene expression, and PKR localization, but it strongly enhances these functions of dsRBM1 when contained in p20. However, dsRBM2 does not enhance the annealing activity of dsRBM1. This study shows that the dsRBMs of PKR possess distinct properties and that some, but not all, of the functions of the enzyme depend on cooperation between the two motifs.
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Affiliation(s)
- B Tian
- Department of Biochemistry and Molecular Biology and Graduate School of Biomedical Sciences, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103, USA
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21
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Brandt TA, Jacobs BL. Both carboxy- and amino-terminal domains of the vaccinia virus interferon resistance gene, E3L, are required for pathogenesis in a mouse model. J Virol 2001; 75:850-6. [PMID: 11134298 PMCID: PMC113981 DOI: 10.1128/jvi.75.2.850-856.2001] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2000] [Accepted: 10/10/2000] [Indexed: 11/20/2022] Open
Abstract
The vaccinia virus (VV) E3L gene is responsible for providing interferon (IFN) resistance and a broad host range to VV in cell culture. The E3L gene product contains two distinct domains. A conserved carboxy-terminal domain, which is required for the IFN resistance and broad host range of the virus, has been shown to bind double-stranded RNA (dsRNA) and inhibit the antiviral dsRNA-dependent protein kinase, PKR. The amino-terminal domain, while conserved among orthopoxviruses, is dispensable in cell culture. To study the role of E3L in whole-animal infections, WR strain VV recombinants either lacking E3L (VVDeltaE3L) or expressing an amino-terminal (VVE3LDelta83N) or carboxy-terminal (VVE3LDelta26C) truncation of E3L were constructed. Whereas wild-type VV had a 50% lethal dose of approximately 10(4) PFU after intranasal infection, and elicited severe weight loss and morbidity, VVDeltaE3L was apathogenic, leading to no death, weight loss, or morbidity. VVDeltaE3L was also apathogenic after intracranial injection. Although the amino-terminal domain of E3L is dispensable for infection of cells in culture, both the amino- and carboxy-terminal domains of E3L were required for full pathogenesis in intranasal infections. These results demonstrate that the entire E3L gene is required for pathogenesis in the mouse model.
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Affiliation(s)
- T A Brandt
- Department of Microbiology, Graduate Program in Molecular and Cellular Biology, Arizona State University, Tempe, Arizona 85287-2701, USA
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22
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Dorman NM, Lever AM. Investigation of RNA transcripts containing HIV-1 packaging signal sequences as HIV-1 antivirals: generation of cell lines resistant to HIV-1. Gene Ther 2001; 8:157-65. [PMID: 11313785 DOI: 10.1038/sj.gt.3301375] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2000] [Accepted: 10/25/2000] [Indexed: 11/09/2022]
Abstract
Based on the success of RNA decoy approaches using RRE and TAR sequences to inhibit HIV-1 replication, we studied the ability of HIV-1 packaging signal sequences to interfere with viral RNA encapsidation and formation of infectious particles. We made a variety of plasmid constructs in which the sequence context or number of repeats of the viral packaging signal was varied, and investigated the ability of these transcripts to inhibit replication of HIV-1 in stably transfected Jurkat T lymphocytes. We found that certain lines showed strong inhibition of HIV-1 replication, an effect that persisted at high input amounts of virus and significantly delayed viral replication for up to 4 weeks. An investigation of the mechanism of inhibition revealed that in these cell lines the packaging efficiency of the genomic HIV-1 transcript was unaffected. Further studies identified an antiviral effect on both HIV-1 and HIV-2 that did not correlate with decoy expression, and was substantially independent of CD4 expression or cellular proliferative capacity. Study of these resistant cell lines may lead to new insights into mechanisms of inhibition of HIV-1 replication.
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Affiliation(s)
- N M Dorman
- Department of Medicine, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 2QQ, UK
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23
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Abstract
Tropomyosin is a component protein of the thin filament system in striated muscle, regulating the interaction between actin and myosin. The 3' untranslated region of the alpha-striated tropomyosin gene (TM UTR) induces muscle differentiation when expressed in primary fibroblasts, but the mechanism has not been defined. We hypothesize that fibroblasts utilize resident proteins to effect this response, perhaps by TM UTR binding to protein(s). In order to facilitate identification of protein(s) involved in mediating this differentiation response, we investigated the potential for this sequence to bind to cellular protein utilizing electrophoretic mobility gel shifting analysis (EMSA) with and without UV cross-linking. Under very specific conditions (including pH, KCl, and Mg concentration and extent of phosphorylation of protein), the TM UTR is able to bind protein in cells that differentiate upon TM UTR expression. Protein binding is significantly more extensive in cytoplasmic than nuclear protein preparations. Secondary structure of the RNA probe facilitates protein binding. The molecular masses of bound proteins are approximately 42 and 115 kDa under basal conditions. EMSA analysis of extract from cultured skeletal muscle confirms that protein binding by the TM UTR occurs in this cell type, and is more extensive in less differentiated cells. The demonstration of highly regulated protein binding by the TM UTR raises the possibility that this sequence may cause differentiation by binding to endogenous proteins, and further that this sequence may play a role in normal differentiation. Identification of proteins bound by the TM UTR will be necessary to completely define the mechanism by which it causes differentiation.
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Affiliation(s)
- H L Fang
- Department of Pediatrics, Cardiology Division, Wayne State University, Children's Hospital of Michigan, 3901 Beaubien Boulevard, Detroit, Michigan, 48201, USA
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24
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Kim SH, Forman AP, Mathews MB, Gunnery S. Human breast cancer cells contain elevated levels and activity of the protein kinase, PKR. Oncogene 2000; 19:3086-94. [PMID: 10871861 DOI: 10.1038/sj.onc.1203632] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/1999] [Revised: 03/31/2000] [Accepted: 04/18/2000] [Indexed: 11/09/2022]
Abstract
PKR is a double-stranded (ds) RNA activated protein kinase whose expression is induced by interferon. Activated PKR phosphorylates its cellular substrate, eIF2, an essential initiation factor of translation. Prior evidence from a murine model system suggested that PKR may act as a tumor suppressor, but the evidence from human tumors is equivocal. To study PKR function in human breast cancer, PKR activity was measured in mammary carcinoma cell lines and nontransformed mammary epithelial cell lines. If PKR functioned as a tumor suppressor in this system, its activity would be higher in nontransformed cells than in carcinoma cells. On the contrary, PKR autophosphorylation and the phosphorylation of its substrate, the alpha-subunit of eIF2, is 7 - 40-fold higher in lysates prepared from breast carcinoma cell lines than in those from nontransformed epithelial cell lines. Correspondingly, a larger proportion of eIF2alpha is present in a phosphorylated state in carcinoma cell lines than in nontransformed cell lines. Protein synthesis is not inhibited by the high eIF2alpha phosphorylation in carcinoma cells, probably because they contain higher levels of eIF2B, the initiation factor that is inhibited by eIF2alpha phosphorylation. The dramatically lower PKR activity in nontransformed cell lines is partially due to lower PKR protein levels (2 - 4-fold) as well as to the presence of a PKR inhibitor. The nontransformed cells contain P58, a known cellular inhibitor of PKR that physically interacts with PKR and may be responsible for the low PKR activity in these cells. Taken together, these observations call into question the role of PKR as a tumor suppressor and suggest a positive regulatory role of PKR in growth control of breast cancer cells.
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Affiliation(s)
- S H Kim
- Department of Biochemistry and Molecular Biology, New Jersey Medical School, UMDNJ, 185, South Orange Avenue, Newark, NJ 07103, USA
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25
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Affiliation(s)
- C E Samuel
- Interdepartmental Graduate Program of Biochemistry and Molecular Biology, University of California at Santa Barbara, Santa Barbara, California, 93106, USA
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