Type I interferon-regulated gene expression and signaling in murine mixed glial cells lacking signal transducers and activators of transcription 1or 2 or interferon regulatory factor 9
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ABSTRACT: Type I interferons (IFN-I) are critical in antimicrobial and antitumor defense. Although IFN-I signal via the interferon-stimulated gene factor 3 (ISGF3) complex consisting of STAT1, STAT2 and IRF9, IFN-I can mediate significant biological effects via ISGF3-independent pathways. For example, absence of STAT1, STAT2 or IRF9 exacerbates neurological disease in transgenic mice with CNS-production of IFN-gamma. Here we determined the role of IFN-I-driven, ISGF3-independent signaling in regulating global gene expression in STAT1, STAT2 or IRF9-deficient murine mixed glial cell cultures (MGCs). Compared with WT, the expression of IFN-gamma-stimulated genes (ISGs) was reduced in number and magnitude in MGCs that lacked STAT1, STAT2 or IRF9. There were significantly fewer ISGs in the absence of STAT1 or STAT2 versus the absence of IRF9. The majority of ISGs regulated in the STAT1-, STAT2- or IRF9-deficient MGCs individually were shared with WT. However, only a minor number of ISGs were common to WT, STAT1-, STAT2- and IRF9-deficient MGCs. While signal pathway activation in response to IFN-gamma was rapid and transient in WT MGCs, this was delayed and prolonged and correlated with increased numbers of ISGs expressed at 12 h versus 4 h IFN-gamma exposure in all three IFN-I-signaling-deficient MGCs. In conclusion, (1) IFN-I can mediate ISG expression in MGCs via ISGF3-independent signaling pathways but with reduced efficiency, with delayed and prolonged kinetics and is more dependent on STAT1 and STAT2 than IRF9, and (2) signaling pathways not involving STAT1, STAT2 or IRF9 play a minor role only in mediating ISG expression in MGCs.
Project description:Type I Interferons (IFN-I) mediate cellular responses to virus infection. IFN-I induces IFN-stimulated gene (ISG) expression by phosphorylating STAT1 and STAT2, and together with interferon regulatory factor (IRF9), form the transcription complex ISGF3 that binds to the interferon-stimulated response element (ISRE) in ISG promoters. As a component of ISGF3, it is clear that STAT2 plays an essential role in the transcriptional responses to IFN-I with a strong dependence on STAT1. Previously, we showed that STAT2 also forms homodimers that interact with IRF9 (STAT2-IRF9) to activate transcription of ISRE-containing ISGs in response to IFN-I. Indeed, evidence is accumulating for the existence of a STAT1-independent IFN-I signaling pathway, where STAT2-IRF9 can substitute the role of ISGF3. Here, we provide further insight in the transcriptional regulation and the biological implications of STAT2-IRF9 dependent IFN-I signaling. In human STAT1 KO cells overexpressing human STAT2 (U3C-STAT2), we observed that in response to IFN-I, STAT2 homodimers interact with IRF9 to regulate ISG transcription. The IFN-I-induced phosphorylation profile of STAT2 in U3C-STAT2 was prolonged as compared to WT cells (2fTGH), which corresponded with the expression pattern of OAS2 that also depended on IRF9. Subsequent microarray analysis of IFN-I treated 2fTGH and U3C-STAT2 extended our initial observations and identified more than 60 known antiviral ISGs commonly up-regulated in both cell types. The expression profile of these ISGs was delayed and prolonged in U3C-STAT2 as opposed to the early and transient response in 2fTGH. Moreover, U3C-STAT2 were able to restore an antiviral response upon EMCV and VSV infection that was comparable to the response in 2fTGH. Together, our results strongly suggest that an alternative IFN-I-mediated, STAT2-IRF9 dependent signaling pathway exists that can generate an antiviral response without STAT1 and could be beneficial for example against viruses that directly block STAT1 and impair the formation of ISGF3.
Project description:Type I Interferons (IFN-I) mediate cellular responses to virus infection. IFN-I induce IFN stimulated gene (ISG) expression by phosphorylating STAT1 and STAT2, and together with interferon regulatory factor (IRF)9, form the transcription complex ISGF3 that binds to the interferon-stimulated response element (ISRE) in ISG promoters. As a component of ISGF3 it is clear that STAT2 plays an essential role in the transcriptional responses to IFN-I with a strong dependence on STAT1. Previously, we showed that STAT2 also forms homodimers that interact with IRF9 (STAT2-IRF9) to activate transcription of ISRE containing ISGs in response to IFN-I. Indeed, evidence is accumulating for the existence of a STAT1-independent IFN-I signaling pathway, where STAT2-IRF9 can substitute the role of ISGF3. Here, we provide further insight in the transcriptional regulation and the biological implications of STAT2-IRF9 dependent IFN-I signaling. In human STAT1 KO cells overexpressing human STAT2 (U3C-STAT2) we observed that in response to IFN-I STAT2 homodimers interact with IRF9 to regulate ISG transcription. The IFN-I-induced phosphorylation profile of STAT2 in U3C-STAT2 was prolonged as compared to WT cells (2fTGH), which corresponded with the expression pattern of OAS2 that also depended on IRF9. Subsequent microarray analysis of IFN-I treated 2fTGH and U3C-STAT2 extended our initial observations and identified more than 60 known antiviral ISGs commonly up-regulated in both cell types. The expression profile of these ISGs was delayed and prolonged in U3C-STAT2 as opposed to the early and transient response in 2fTGH. Moreover, U3C-STAT2 were able to restore an antiviral response upon EMCV and VSV infection that was comparable to the response in 2fTGH. Together, our results strongly suggest that an alternative IFN-I-mediated, STAT2-IRF9 dependent signaling pathway exists that can generate an antiviral response without STAT1 and could be beneficial for example against viruses that directly block STAT1 and impair the formation of ISGF3.
Project description:To further understand the role of phosphorylation in ISGF3- and STAT2/IRF9-mediated constitutive and long-term IFN-I-stimulated transcriptional responses, we performed RNA-Seq and ChIP-Seq, in combination with phosphorylation inhibition and anti-viral experiments. First, we identified a group of ISRE-containing ISGs that were commonly regulated in IFNα treated WT and STAT1-KO cells. Thus, in 2fTGH and Huh7.5 WT cells IFNα-inducible transcription and anti-viral activity relied on the recruitment of the ISGF3 components STAT1, STAT2 and IRF9 in a phosphorylation- and time-dependent manner. Likewise, in ST2-U3C and Huh-STAT1KO cells lacking STAT1, ISG expression correlated with DNA-binding of phosphorylated STAT2/IRF9. This pointed to a dominant role of classical ISGF3 and STAT2/IRF9, and not U-ISGF3 or U-STAT2/IRF9, in the regulation of early and prolonged ISG expression and viral protection, in WT and STAT1-KO cells. In addition, comparative experiments in U3C (STAT1-KO) cells overexpressing all ISGF3 components (ST1-ST2-IRF9-U3C), revealed a threshold-dependent role of U-ISFG3, and potentially U-STAT2/IRF9, in the regulation of constitutive and possibly long-term IFNα-treated ISG expression and anti-viral activity.
Project description:To further understand the role of phosphorylation in ISGF3- and STAT2/IRF9-mediated constitutive and long-term IFN-I-stimulated transcriptional responses, we performed RNA-Seq and ChIP-Seq, in combination with phosphorylation inhibition and anti-viral experiments. First, we identified a group of ISRE-containing ISGs that were commonly regulated in IFNα treated WT and STAT1-KO cells. Thus, in 2fTGH and Huh7.5 WT cells IFNα-inducible transcription and anti-viral activity relied on the recruitment of the ISGF3 components STAT1, STAT2 and IRF9 in a phosphorylation- and time-dependent manner. Likewise, in ST2-U3C and Huh-STAT1KO cells lacking STAT1, ISG expression correlated with DNA-binding of phosphorylated STAT2/IRF9. This pointed to a dominant role of classical ISGF3 and STAT2/IRF9, and not U-ISGF3 or U-STAT2/IRF9, in the regulation of early and prolonged ISG expression and viral protection, in WT and STAT1-KO cells. In addition, comparative experiments in U3C (STAT1-KO) cells overexpressing all ISGF3 components (ST1-ST2-IRF9-U3C), revealed a threshold-dependent role of U-ISFG3, and potentially U-STAT2/IRF9, in the regulation of constitutive and possibly long-term IFNα-treated ISG expression and anti-viral activity.
Project description:We investigated the transcriptional activation and cis-regulatory elements of effector ISGs in CD8+ murine dendritic cells (DCs) stimulated with IFN-beta. We analysed gene repression changes and characterized activated cis-regulatory regions. Binding of ISGF3 subunits (IRF9, Stat1, and Stat2) and other transcription factors, DNA motifs, and chromatin status were also determined.
Project description:The proposed ODE model describes dynamics of IFNalpha-induced signaling in Huh7.5 cells for a time scale up to 32 hours after stimulation with IFNalpha. The model consists of an IFN receptor model, formation/degradation and cytoplasmic/nuclear shuttling of STAT1-homodimers, STAT1-STAT2-heterodimers and STAT1-STAT2-IRF9 (ISGF3) complexes. On top, formation of feedback proteins STAT1, STAT2, IRF9, USP18, SOCS1, SOCS3 and IRF2 and corresponding influences on IFNalpha signaling dynamics was incorporated. The model was calibrated by dose response and time course measurements over 32 hours as well as time courses for USP18 inhibition and overexpression experiments. As a special focus, the model is able to describe dose-dependent sensitization and desensitization of IFNalpha signaling in form of double treatment experiments at 0h and 24h.
Project description:Virus infection induces the production of type I and type II interferons (IFN-I and IFN-II), cytokines that mediate the antiviral response. IFN-I (IFN-a and -b) induces the assembly of ISGF3 (interferon-stimulated gene factor 3), a multimeric transcriptional activation complex comprised of STAT1, STAT2 and IRF9. IFN-II (IFN-g) induces the homodimerization of STAT1 to form the GAF (gamma-activated factor) complex. ISGF3 and GAF bind specifically to distinct regulatory DNA sequences located upstream of IFN-I and II inducible genes, respectively, and activate the expression of distinct set of antiviral genes. The balance between the type I and type II IFN pathways plays a critical role in orchestrating the innate and adaptive immune systems. Here, we show that the phosphorylation of STAT1 by IKKε (IkB-related kinase epsilon) inhibits STAT1 homodimerization, and thus GAF formation, but does not disrupt ISGF3 formation. Therefore, virus and/or IFN-I activation of IKKε suppresses GAF-dependent transcription and promotes ISGF3-dependent transcription. In the absence of IKKε, GAF-dependent transcription is enhanced at the expense of ISGF3-mediated transcription, rendering cells less resistant to infection. We conclude that IKKε plays a critical role in regulating the balance between the IFN-I and IFN-II signaling pathways. ChIP-seq libraries were constructed with an antibody targeting STAT1 from bone marrow macrophages treated with interferon
Project description:The transcription factor STAT2 is essential for transcriptional activation downstream of the receptors for the innate IFNs -α/β (IFNAR) and -gamma (IFNLR). STAT2 is activated by tyrosine phosphorylation, associating with STAT1 and IRF9 to form the Interferon-Stimulated Gene Factor 3 (ISGF3) to effect gene transcription. Loss-of-function variants in STAT2 increase susceptibility to viral disease. Here a transcriptome study is reported on an individual with severe early-onset neuroinflammatory disease and an elevated IFN signature. The individual had a homozygous missense variant in STAT2 and symptoms consistent with a gain-of-function effect.
Project description:Type-I (e.g. IFN-alpha, IFN-beta) and type-II IFNs (IFN-gamma) have antiviral, antiproliferative, and immunomodulatory properties. Both types of IFN signal through the Jak/STAT pathway to elicit antiviral activity, yet IFN-gamma is thought to do so only through STAT1 homodimers while type-I IFNs activate both STAT1- and STAT2-containing complexes such as ISGF3. Here we show that ISGF3II - composed of phosphorylated STAT1, unphosphorylated STAT2, and IRF9 - also plays a role in IFN-gamma-mediated antiviral activity in humans. Using phosphorylated STAT1 as a marker for IFN signaling, western blot analysis of IFN-alpha2a treated human A549 cells revealed that pSTAT1 (Y701) levels peaked at 1h, decreased by 6h, and remained at low levels for up to 48h. Cells treated with IFN-gamma showed a biphasic pSTAT1 response with an early peak at 1-2h and a second peak at 15-24h. Gene expression microarray following IFN-gamma treatment for 24h indicated an induction of antiviral genes that are induced by ISGF3 and associated with a type-1 IFN response. Induction of these genes by autocrine type-I and type-III IFN signaling was ruled out using neutralizing antibodies to these IFNs in biological assays and by qRT-PCR. Despite the absence of autocrine IFNs, IFN-gamma treatment induced formation of ISGF3II. This novel transcription factor complex binds to ISRE promoter sequences, as shown by ChIP analysis of the PKR promoter. STAT2 and IRF9 knockdown in A549 cells reversed IFN-gamma-mediated ISRE induction and antiviral activity - implicating ISGF3II formation as a significant component of the cellular response and biological activity of IFN-gamma. Two treatments using three biological replicates each were performed using three million A549 cells. Each was seeded overnight in 10mL complete RPMI and treated. Three were treated with alpha-IFN and three treated with gamma-IFN for 24h. Control samples were left untreated.
Project description:The genome-wide distributions of STAT1, STAT2 and IRF9 in mock and interferon alpha (IFN) stimulated human cells was generated using high throughput sequencing to identify ISGF3 genomic occupancy. In combination, the nucleosome occupancy of 20 select IFN-stimulated gene regions were analyzed by direct selection MNase sequencing to determine the nucleosome positions and changes in nucleosome occupancy levels following IFN treatment over time. IFN stimulation resulted in decreased nucleosome positioning strength, with clear disruption over the course of IFN treatment followed by a return to steady state, and prominently at most ISGF3-bound regions.