Enhanced antiviral and antiproliferative properties of a STAT1 mutant unable to interact with the protein kinase PKR (original) (raw)
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EMBO reports, 2003
Stat1 (signal transducer and activator of transcription 1) regulates transcription in response to the type I interferons IFN-α and IFN-β, either in its dimerized form or as a subunit of the interferon-stimulated gene factor 3 (Isgf3) complex (consisting of Stat1, Stat2 and interferon-regulating factor 9). Full-length Stat1-α and the splice variant Stat1-β, which lacks the carboxyl terminus and the Ser727 phosphorylation site, are found in all cell types. IFN-induced phosphorylation of Stat1-α on Ser727 occurs in the absence of the candidate kinase, protein kinase C-δ. When expressed in Stat1-deficient cells, Stat1-β and a Stat1-S727A mutant both restored the formation of Stat1 dimers and of the Isgf3 complex on treatment with IFN-β. By contrast, only Stat1-α restored the ability of IFN-β to induce high levels of transcription from target genes of Stat1 dimers and Isgf3 and to induce an antiviral state. Our data suggest an important contribution of the Stat1 C terminus and its phosphorylation at Ser727 to the transcriptional activities of the Stat1 dimer and the Isgf3 complex.
Immunity, 2013
Gene regulation by cytokine-activated transcription factors of the signal transducer and activator of transcription (STAT) family requires serine phosphorylation within the transactivation domain (TAD). STAT1 and STAT3 TAD phosphorylation occurs upon promoter binding by an unknown kinase. Here, we show that the cyclin-dependent kinase 8 (CDK8) module of the Mediator complex phosphorylated regulatory sites within the TADs of STAT1, STAT3, and STAT5, including S727 within the STAT1 TAD in the interferon (IFN) signaling pathway. We also observed a CDK8 requirement for IFN-g-inducible antiviral responses. Microarray analyses revealed that CDK8-mediated STAT1 phosphorylation positively or negatively regulated over 40% of IFN-gresponsive genes, and RNA polymerase II occupancy correlated with gene expression changes. This divergent regulation occurred despite similar CDK8 occupancy at both S727 phosphorylationdependent and -independent genes. These data identify CDK8 as a key regulator of STAT1 and antiviral responses and suggest a general role for CDK8 in STAT-mediated transcription. As such, CDK8 represents a promising target for therapeutic manipulation of cytokine responses.
A novel anti-viral role for STAT3 in IFN-α signalling responses
Cellular and molecular life sciences : CMLS, 2017
The cytokine, Interferon (IFN)-α, induces a wide spectrum of anti-viral mediators, via the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. STAT1 and STAT2 are well characterised to upregulate IFN-stimulated gene (ISG) expression; but even though STAT3 is also activated by IFN-α, its role in anti-viral ISG induction is unclear. Several viruses, including Hepatitis C and Mumps, reduce cellular STAT3 protein levels, via the promotion of ubiquitin-mediated proteasomal degradation. This viral immune evasion mechanism suggests an undiscovered anti-viral role for STAT3 in IFN-α signalling. To investigate STAT3's functional involvement in this Type I IFN pathway, we first analysed its effect upon the replication of two viruses, Influenza and Vaccinia. Viral plaque assays, using Wild Type (WT) and STAT3-/- Murine Embryonic Fibroblasts (MEFs), revealed that STAT3 is required for the inhibition of Influenza and Vaccinia replication. Furthermore, STAT3 shRN...
1996
Tyrosine phosphorylation and activation of the transcription factor Stat5 occur in response to stimuli like granulocyte-macrophage colony-stimulating factor, interleukin-3, or erythropoietin that stimulate both proliferation and differentiation of hematopoietic cells. It is unclear whether Stat5 is part of a proliferative response or part of the events leading to cellular differentiation. Here we report that agents promoting differentiation but not proliferation of hematopoietic cells, like phorbol ester or both types of interferons (IFNs), activate Stat5 in promonocytic U937 cells. Both IFN types caused tyrosine phosphorylation and DNA binding of predominantly one Stat5 isoform (Stat5a) despite expression of both Stat5a and Stat5b proteins. Monocytic differentiation of U937 cells led to a strong decrease in IFN-␥-mediated activation of Stat5 but not of Stat1. Transactivation of Stat5-target genes occurred in response to IFN-␥, which activates both Stat5 and Stat1, but not in response to granulocyte-macrophage colony-stimulating factor, which activates only Stat5. Tyrosine phosphorylation of Stat5 is not generally part of the IFN response. IFN-␥ did not cause Stat5 activation in HeLa cells, despite the expression of both Stat5 isoforms at similar levels. By contrast, IFN-␣ caused tyrosine phosphorylation and DNA binding of exclusively the b isoform of Stat5, and activated Stat5b formed a DNA binding activity previously found in HeLa cells and designated IFN-␣ activation factor 2. Taken together, our results demonstrate that ligand binding of IFN receptors leads to an isoform-specific activation of Stat5 in a restricted number of cell lineages. Moreover, they suggest that Stat5 might be part of the differentiation response of myeloid cells.
Journal of Interferon & Cytokine Research, 1999
We determined whether selective activation of components of the Jak-Stat pathway by different type I interferons (IFN) occurs in human myocardial fibroblasts that exhibit much higher sensitivity to the antiviral effects of IFN-b than of IFN-a. Similar levels of activation of the Tyk2 kinase and the Stat3 transcription factor were induced in response to either IFN-b or IFN-a treatment. However, activation of the Jak1 tyrosine kinase was detectable only in IFN-b-treated but not IFN-a-treated cells. Consistent with this, tyrosine phosphorylation of Stat1 and Stat2 and formation of the IFN-stimulated gene factor 3 (ISGF3) complex occurred to a much higher degree in response to IFN-b stimulation. These findings demonstrate that differential activation of distinct components of the Jak-Stat pathway by different type I IFN can occur. Furthermore, they strongly suggest that such selective activation accounts for the occurrence of differences in the antiviral properties of distinct type I IFN in certain cell types.
Global changes in STAT target selection and transcription regulation upon interferon treatments
Genes & Development, 2005
The STAT (signal transducer and activator of transcription) proteins play a crucial role in the regulation of gene expression, but their targets and the manner in which they select them remain largely unknown. Using chromatin immunoprecipitation and DNA microarray analysis (ChIP–chip), we have identified the regions of human chromosome 22 bound by STAT1 and STAT2 in interferon-treated cells. Analysis of the genomic loci proximal to these binding sites introduced new candidate STAT1 and STAT2 target genes, several of which are affiliated with proliferation and apoptosis. The genes on chromosome 22 that exhibited interferon-induced up- or down-regulated expression were determined and correlated with the STAT-binding site information, revealing the potential regulatory effects of STAT1 and STAT2 on their target genes. Importantly, the comparison of STAT1-binding sites upon interferon (IFN)- and IFN- treatments revealed dramatic changes in binding locations between the two treatments. The IFN- induction revealed nonconserved STAT1 occupancy at IFN-induced sites, as well as novel sites of STAT1 binding not evident in IFN--treated cells. Many of these correlated with binding by STAT2, but others were STAT2 independent, suggesting that multiple mechanisms direct STAT1 binding to its targets under different activation conditions. Overall, our results reveal a wealth of new information regarding IFN/STAT-binding targets and also fundamental insights into mechanisms of regulation of gene expression in different cell states.
Activated Ras/MEK Inhibits the Antiviral Response of Alpha Interferon by Reducing STAT2 Levels
Journal of Virology, 2009
The ability of interferon (IFN) to induce the expression of antiviral genes, and therefore suppress viral infection, is dependent on the activity of cellular suppressors. The Ras/MEK pathway is one of these cellular suppressors, since the activation of Ras/MEK permits viral replication in the presence of alpha IFN (IFN-␣). Here, we have investigated the mechanism by which activated Ras/MEK inhibits the IFN-␣ response. We found that the induction of antiviral proteins in response to IFN-␣ was impaired in Ras-transformed NIH 3T3 (RasV12) cells. The inhibition of the Ras/MEK pathway restored the IFN-mediated induction of antiviral genes, indicating that activated Ras interrupts the IFN pathway upstream of antiviral gene transcription.