The Experts below are selected from a list of 102 Experts worldwide ranked by ideXlab platform
Curt M. Horvath - One of the best experts on this subject based on the ideXlab platform.
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A Point Mutation, E95D, in the Mumps Virus V Protein Disengages STAT3 Targeting from STAT1 Targeting
Journal of Virology, 2009Co-Authors: Mamta Puri, Ken Lemon, W. Paul Duprex, Bertus K. Rima, Curt M. HorvathAbstract:Mumps virus, like other paramyxoviruses in the Rubulavirus genus, encodes a V Protein that can assemble a ubiquitin ligase complex from cellular components, leading to the destruction of cellular signal transducer and activator of transcription (STAT) Proteins. While many V Proteins target the interferon-activated STAT1 or STAT2 Protein, mumps virus V Protein is unique in its ability to also target STAT3 for ubiquitin modification and proteasome-mediated degradation. Here we report that a single amino acid substitution in the mumps virus V Protein, E95D, results in defective STAT3 targeting while maintaining the ability to target STAT1. Results indicate that the E95D mutation disrupts the ability of the V Protein to associate with STAT3. A recombinant mumps virus carrying the E95D mutation in its P and V Proteins replicates normally in cultured cells but fails to induce targeting of STAT3. Infection with the recombinant virus results in the differential regulation of a number of cellular genes compared to wild-type mumps virus and increases cell death in infected cells, producing a large-plaque phenotype.
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Enabled interferon signaling evasion in an immune-competent transgenic mouse model of parainfluenza virus 5 infection
Virology, 2007Co-Authors: Thomas Kraus, Lily Garza, Curt M. HorvathAbstract:Parainfluenza virus 5 (PIV5 or SV5) infects several mammalian species but is restricted from efficient replication in mice. In humans, PIV5 evades IFN signaling by targeting STAT1 for proteasomal degradation in a STAT2-dependent reaction. In contrast, cell culture experiments have demonstrated that the divergent murine STAT2 Protein fails to support STAT1 targeting. Expression of human STAT2 in mouse cells can overcome the species restriction to enable PIV5-induced STAT1 degradation and subsequent IFN antagonism. Here, we describe a transgenic mouse that ubiquitously expresses human STAT2. PIV5 infection induces STAT1 degradation leading to enhanced virus replication and Protein expression in the cells from the transgenic mouse but not from the non-transgenic littermates. Importantly, intranasal inoculation with PIV5 results in increased viral load in the lungs of the transgenic mice compared to wild-type littermates. These transgenic mice provide a small animal model to study the role of innate immune evasion in paramyxovirus pathogenesis.
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a hybrid irf9 STAT2 Protein recapitulates interferon stimulated gene expression and antiviral response
Journal of Biological Chemistry, 2003Co-Authors: Thomas Kraus, Jean Patrick Parisien, Curt M. HorvathAbstract:Abstract Type I interferon (IFN) signaling induces the heterotrimeric transcription complex, IFN-stimulated gene factor (ISGF) 3, which contains STAT1, STAT2, and the DNA binding subunit, interferon regulatory factor (IRF) 9. Because IRF9 is targeted to the nucleus in the absence of IFN stimulation, the potential of IRF9 Protein for gene regulation was examined using a GAL4 DNA binding domain fusion system. GAL4-IRF9 was transcriptionally active in reporter gene assays but not in the absence of cellular STAT1 and STAT2. However, the inert IRF9 Protein was readily converted to a constitutively active ISGF3-like activator by fusion with the C-terminal transcriptional activation domain of STAT2 or the acidic activation domain of herpesvirus VP16. The IRF9 hybrids are targeted to endogenous ISGF3 target loci and can activate their transcription. Moreover, expression of the IRF9-STAT2 fusion can recapitulate the type I IFN biological response, producing a cellular antiviral state that protects cells from virus-induced cytopathic effects and inhibits virus replication. The antiviral state generated by regulated IRF9-STAT2 hybrid Protein expression is independent of autocrine IFN signaling and inhibits both RNA and DNA viruses.
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The V Protein of human parainfluenza virus 2 antagonizes type I interferon responses by destabilizing signal transducer and activator of transcription 2
Virology, 2001Co-Authors: Jean Patrick Parisien, Jason J. Rodriguez, Brian M. Sullivan, Anne Moscona, Griffith D. Parks, Robert A. Lamb, Curt M. HorvathAbstract:Abstract Type I interferon (IFN) induces antiviral responses through the activation of the ISGF3 transcription factor complex that contains the subunit Proteins STAT1, STAT2, and p48/ISGF3γ/IRF9. The ability of some human paramyxoviruses to overcome IFN actions by specific proteolysis of STAT Proteins has been examined. Infection of cells with type 2, but not type 1 or type 3 human parainfluenza virus (HPIV) leads to a loss of cellular STAT2 Protein. Expression of a single HPIV2 Protein derived from the V open reading frame blocks IFN-dependent transcriptional responses in the absence of other viral Proteins. The loss of IFN response is due to V-Protein-induced proteolytic degradation of STAT2. Expression of HPIV2 V causes the normally stable STAT2 Protein to be rapidly degraded, and this proteolytic activity can be partially alleviated by proteasome inhibition. No V-Protein-specific effects on STAT2 mRNA levels were observed. The results indicate that the V Protein of HPIV2 is sufficient to recognize and target a specific cellular transcription factor for destruction by cellular machinery.
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Interferon regulatory factor subcellular localization is determined by a bipartite nuclear localization signal in the DNA-binding domain and interaction with cytoplasmic retention factors
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: Jean Patrick Parisien, Curt M. HorvathAbstract:The transduction of type I interferon signals to the nucleus relies on activation of a Protein complex, ISGF3, involving two signal transducers and activators of transcription (STAT) Proteins, STAT1 and STAT2, and the interferon (IFN) regulatory factor (IRF) Protein, p48/ISGF3γ. The STAT subunits are cytoplasmically localized in unstimulated cells and rapidly translocate to the nucleus of IFN-stimulated cells, but the p48/ISGF3γ Protein is found in both the nucleus and the cytoplasm, regardless of IFN stimulation. Here, we demonstrate that p48 is efficiently and constitutively targeted to the nucleus. Analysis of the subcellular distribution of green fluorescent Protein-p48 fragments indicates that p48 contains a bipartite nuclear retention signal within its amino-terminal DNA-binding domain. This signal is preserved in two other IRF Proteins involved in immune responses, ICSBP and IRF4. Mutations to clustered basic residues within amino acids 50–100 of p48 or IRF4 disrupt their nuclear accumulation, and DNA-binding ability is not required for nuclear targeting. This is the only example of a nuclear localization signal for any ISGF3 component and assigns a second function to the IRF DNA-binding domain. We also demonstrate that the nuclear distribution of p48 is dramatically altered by coexpression of the STAT2 Protein, indicating that STAT2 forms a cytoplasmic complex with p48, overriding the intrinsic p48 nuclear targeting. Retention by STAT2 may serve to regulate the activity of free p48 and/or guarantee that cytoplasmic pools of preassociated STAT2:p48 are available for rapid activation of the IFN response. These findings suggest that analogous mechanisms may exist for regulating the distribution of other IRF Proteins.
James E Darnell - One of the best experts on this subject based on the ideXlab platform.
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function of STAT2 Protein in transcriptional activation by alpha interferon
Molecular and Cellular Biology, 1996Co-Authors: Sajjad A Qureshi, Stewart Leung, Ian M Kerr, George R Stark, James E DarnellAbstract:Alpha interferon (IFN-alpha)-induced transcriptional activation requires the induction of a complex of DNA-binding Proteins, including tyrosine-phosphorylated Stat1 and STAT2, and of p48, a Protein which is not phosphorylated on tyrosine and which comes from a separate family of DNA-binding Proteins. The isolation and characterization of U6A cells, which lack STAT2, have allowed the introduction of normal and mutant forms of STAT2 so that various functions of the STAT2 Protein can be examined. As reported earlier, Stat1, which is the second target of tyrosine phosphorylation in IFN-alpha-treated cells, is not phosphorylated in the absence of STAT2. We show that all mutations that block STAT2 phosphorylation also block Stat1 phosphorylation. These include not only the mutations of Y-690 and SH2 domain residues that are involved in tyrosine phosphorylation but also short deletions at the amino terminus of the Protein. Two mutants of STAT2 that are not phosphorylated on tyrosine can act as dominant negative Proteins in suppressing wild-type STAT2 phosphorylation, most likely by competition at the receptor-kinase interaction site(s). We also show that the COOH-terminal 50 amino acids are required for transcriptional activation in response to IFN-alpha. Mutants lacking these amino acids can be phosphorylated, form IFN-stimulated gene factor 3, and translocate to the nucleus but cannot stimulate IFN-alpha-dependent transcription. Seven acidic residues are present in the deleted COOH-terminal residues, but 24 acidic residues still remain in the 100 carboxy-terminal amino acids after deletion. Thus, transcriptional activation is unlikely to depend on acidic amino acids alone.
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Role of STAT2 in the alpha interferon signaling pathway.
Molecular and Cellular Biology, 1995Co-Authors: Stewart Leung, Sajjad A Qureshi, Ian M Kerr, James E Darnell, George Stark StarkAbstract:We have isolated U6A, a mutant cell line which lacks the STAT2 subunit of the transcription factor interferon (IFN)-stimulated gene factor 3 (ISGF3). The response of U6A cells to IFN-alpha is almost completely defective, but the response to IFN-gamma is normal. Complementation of U6A cells with a cDNA encoding STAT2 restores the IFN-alpha response, proving that STAT2 is required in this pathway. Binding of IFNs to their receptors triggers tyrosine phosphorylation and activation of the receptors, JAK family kinases, STAT1, and STAT2. In IFN-alpha-treated U6A cells, phosphorylation of the essential tyrosine kinases TYK2 and JAK1 is normal, but the phosphorylation of STAT1 is weak. A mutant STAT2 Protein in which the phosphorylated tyrosine at position 690 is changed to phenylalanine does not restore normal phosphorylation of STAT1 in response to IFN-alpha. The dependence of STAT1 phosphorylation on the presence of STAT2 but not vice versa (T. Improta, C. Schindler, C. M. Horvath, I. M. Kerr, G. R. Stark, and J. E. Darnell, Jr., Proc. Natl. Acad. Sci. USA 91:4776-4780, 1994) indicates that in the formation of ISGF3, these two Proteins may be phosphorylated sequentially in response to IFN-alpha and that phosphorylated STAT2 may be required to allow unphosphorylated STAT1 to bind to the activated IFN-alpha receptor.
Sajjad A Qureshi - One of the best experts on this subject based on the ideXlab platform.
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function of STAT2 Protein in transcriptional activation by alpha interferon
Molecular and Cellular Biology, 1996Co-Authors: Sajjad A Qureshi, Stewart Leung, Ian M Kerr, George R Stark, James E DarnellAbstract:Alpha interferon (IFN-alpha)-induced transcriptional activation requires the induction of a complex of DNA-binding Proteins, including tyrosine-phosphorylated Stat1 and STAT2, and of p48, a Protein which is not phosphorylated on tyrosine and which comes from a separate family of DNA-binding Proteins. The isolation and characterization of U6A cells, which lack STAT2, have allowed the introduction of normal and mutant forms of STAT2 so that various functions of the STAT2 Protein can be examined. As reported earlier, Stat1, which is the second target of tyrosine phosphorylation in IFN-alpha-treated cells, is not phosphorylated in the absence of STAT2. We show that all mutations that block STAT2 phosphorylation also block Stat1 phosphorylation. These include not only the mutations of Y-690 and SH2 domain residues that are involved in tyrosine phosphorylation but also short deletions at the amino terminus of the Protein. Two mutants of STAT2 that are not phosphorylated on tyrosine can act as dominant negative Proteins in suppressing wild-type STAT2 phosphorylation, most likely by competition at the receptor-kinase interaction site(s). We also show that the COOH-terminal 50 amino acids are required for transcriptional activation in response to IFN-alpha. Mutants lacking these amino acids can be phosphorylated, form IFN-stimulated gene factor 3, and translocate to the nucleus but cannot stimulate IFN-alpha-dependent transcription. Seven acidic residues are present in the deleted COOH-terminal residues, but 24 acidic residues still remain in the 100 carboxy-terminal amino acids after deletion. Thus, transcriptional activation is unlikely to depend on acidic amino acids alone.
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Role of STAT2 in the alpha interferon signaling pathway.
Molecular and Cellular Biology, 1995Co-Authors: Stewart Leung, Sajjad A Qureshi, Ian M Kerr, James E Darnell, George Stark StarkAbstract:We have isolated U6A, a mutant cell line which lacks the STAT2 subunit of the transcription factor interferon (IFN)-stimulated gene factor 3 (ISGF3). The response of U6A cells to IFN-alpha is almost completely defective, but the response to IFN-gamma is normal. Complementation of U6A cells with a cDNA encoding STAT2 restores the IFN-alpha response, proving that STAT2 is required in this pathway. Binding of IFNs to their receptors triggers tyrosine phosphorylation and activation of the receptors, JAK family kinases, STAT1, and STAT2. In IFN-alpha-treated U6A cells, phosphorylation of the essential tyrosine kinases TYK2 and JAK1 is normal, but the phosphorylation of STAT1 is weak. A mutant STAT2 Protein in which the phosphorylated tyrosine at position 690 is changed to phenylalanine does not restore normal phosphorylation of STAT1 in response to IFN-alpha. The dependence of STAT1 phosphorylation on the presence of STAT2 but not vice versa (T. Improta, C. Schindler, C. M. Horvath, I. M. Kerr, G. R. Stark, and J. E. Darnell, Jr., Proc. Natl. Acad. Sci. USA 91:4776-4780, 1994) indicates that in the formation of ISGF3, these two Proteins may be phosphorylated sequentially in response to IFN-alpha and that phosphorylated STAT2 may be required to allow unphosphorylated STAT1 to bind to the activated IFN-alpha receptor.
Nancy C. Reich - One of the best experts on this subject based on the ideXlab platform.
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Tracking STAT nuclear traffic
Nature Reviews Immunology, 2006Co-Authors: Nancy C. ReichAbstract:Accurate cellular localization is crucial for the effective function of most signalling molecules and nuclear translocation is central to the function of transcription factors. The passage of large molecules between the cytoplasm and nucleus is restricted, and this restriction affords a mechanism to regulate transcription by controlling the access of transcription factors to the nucleus. In this Review, we focus on the signal transducer and activator of transcription (STAT) family of transcription factors. The regulation of the nuclear trafficking of STAT-family members is diverse. Some STAT Proteins constitutively shuttle between the nucleus and cytoplasm, whereas others require tyrosine phosphorylation for nuclear localization. In either case, the regulation of nuclear trafficking can provide a target for therapeutic intervention. The signal transducer and activator of transcription (STAT) transcription factors are activated by direct tyrosine phosphorylation in response to cytokines, growth factors and other hormones. Tyrosine phosphorylation promotes the formation of STAT dimers that can bind specific DNA targets. Passage of large Proteins between cytoplasmic and nuclear compartments occurs through nuclear pore complexes and is regulated by interaction with transporter Proteins of the karyopherin-β family. Individual STAT Proteins have diversified with distinct nuclear trafficking regulation. Cellular localization of a particular STAT is dependent or independent of tyrosine phosphorylation. Cellular localization of STAT1 is integrated with its ability to bind DNA. The nuclear localization and nuclear-export signals of STAT1 have co-evolved with the DNA-binding domain. The regulation of STAT1 nuclear trafficking is conditional based on its state of tyrosine phosphorylation. A specific member of the importin-α family of adaptor molecules, importin-α5, recognizes a conditional nuclear-localization signal of the STAT1 phosphorylated dimer. STAT2 is distinct among the STATs in that it constitutively interacts with the transcription factor interferon-regulatory factor 9 (IRF9). The constitutive nuclear-localization signal of IRF9 is responsible for nuclear localization of the unphosphorylated STAT2–IRF9 complex. STAT2 has a nuclear-export signal located in its carboxyl terminus that is responsible for export of the unphosphorylated or phosphorylated STAT2 Protein. STAT3 is imported to the nucleus independent of tyrosine phosphorylation and dependent on recognition by the importin-α3 adaptor. The constitutive nuclear-localization signal of STAT3 is located in the coiled-coil domain, a distance from the DNA-binding domain. Individual STATs have evolved distinct nuclear trafficking properties, and these distinguishing features may reflect their physiological roles. Understanding the molecular aspects that regulate their nuclear trafficking may provide an avenue to promote or inhibit STAT function. The passage of transcription factors in and out of the nucleus must be regulated for their proper function. Surprisingly, regulation of nuclear trafficking among members of the signal transducer and activator of transcription (STAT) family differs, revealing specific targets for therapeutic intervention.
Stewart Leung - One of the best experts on this subject based on the ideXlab platform.
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function of STAT2 Protein in transcriptional activation by alpha interferon
Molecular and Cellular Biology, 1996Co-Authors: Sajjad A Qureshi, Stewart Leung, Ian M Kerr, George R Stark, James E DarnellAbstract:Alpha interferon (IFN-alpha)-induced transcriptional activation requires the induction of a complex of DNA-binding Proteins, including tyrosine-phosphorylated Stat1 and STAT2, and of p48, a Protein which is not phosphorylated on tyrosine and which comes from a separate family of DNA-binding Proteins. The isolation and characterization of U6A cells, which lack STAT2, have allowed the introduction of normal and mutant forms of STAT2 so that various functions of the STAT2 Protein can be examined. As reported earlier, Stat1, which is the second target of tyrosine phosphorylation in IFN-alpha-treated cells, is not phosphorylated in the absence of STAT2. We show that all mutations that block STAT2 phosphorylation also block Stat1 phosphorylation. These include not only the mutations of Y-690 and SH2 domain residues that are involved in tyrosine phosphorylation but also short deletions at the amino terminus of the Protein. Two mutants of STAT2 that are not phosphorylated on tyrosine can act as dominant negative Proteins in suppressing wild-type STAT2 phosphorylation, most likely by competition at the receptor-kinase interaction site(s). We also show that the COOH-terminal 50 amino acids are required for transcriptional activation in response to IFN-alpha. Mutants lacking these amino acids can be phosphorylated, form IFN-stimulated gene factor 3, and translocate to the nucleus but cannot stimulate IFN-alpha-dependent transcription. Seven acidic residues are present in the deleted COOH-terminal residues, but 24 acidic residues still remain in the 100 carboxy-terminal amino acids after deletion. Thus, transcriptional activation is unlikely to depend on acidic amino acids alone.
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Role of STAT2 in the alpha interferon signaling pathway.
Molecular and Cellular Biology, 1995Co-Authors: Stewart Leung, Sajjad A Qureshi, Ian M Kerr, James E Darnell, George Stark StarkAbstract:We have isolated U6A, a mutant cell line which lacks the STAT2 subunit of the transcription factor interferon (IFN)-stimulated gene factor 3 (ISGF3). The response of U6A cells to IFN-alpha is almost completely defective, but the response to IFN-gamma is normal. Complementation of U6A cells with a cDNA encoding STAT2 restores the IFN-alpha response, proving that STAT2 is required in this pathway. Binding of IFNs to their receptors triggers tyrosine phosphorylation and activation of the receptors, JAK family kinases, STAT1, and STAT2. In IFN-alpha-treated U6A cells, phosphorylation of the essential tyrosine kinases TYK2 and JAK1 is normal, but the phosphorylation of STAT1 is weak. A mutant STAT2 Protein in which the phosphorylated tyrosine at position 690 is changed to phenylalanine does not restore normal phosphorylation of STAT1 in response to IFN-alpha. The dependence of STAT1 phosphorylation on the presence of STAT2 but not vice versa (T. Improta, C. Schindler, C. M. Horvath, I. M. Kerr, G. R. Stark, and J. E. Darnell, Jr., Proc. Natl. Acad. Sci. USA 91:4776-4780, 1994) indicates that in the formation of ISGF3, these two Proteins may be phosphorylated sequentially in response to IFN-alpha and that phosphorylated STAT2 may be required to allow unphosphorylated STAT1 to bind to the activated IFN-alpha receptor.