Mice deficient in STAT1 but not STAT2 or IRF9 develop a lethal CD4+ T-cell-mediated disease following infection with lymphocytic choriomeningitis virus

Interferon (IFN) signaling is crucial for antiviral immunity. While type I IFN signaling is mediated by STAT1, STAT2, and IRF9, type II IFN signaling requires only STAT1. Here, we studied the roles of these signaling factors in the host response to systemic infection with lymphocytic choriomeningitis virus (LCMV). In wild-type (WT) mice and mice lacking either STAT2 or IRF9, LCMV infection was nonlethal, and the virus either was cleared (WT) or established persistence (STAT2 knockout [KO] and IRF9 KO). However, in the case of STAT1 KO mice, LCMV infection was lethal and accompanied by severe multiorgan immune pathology, elevated expression of various cytokine genes in tissues, and cytokines in the serum. This lethal phenotype was unaltered by the coabsence of the gamma interferon (IFN-γ) receptor and hence was not dependent on IFN-γ. Equally, the disease was not due to a combined defect in type I and type II IFN signaling, as IRF9 KO mice lacking the IFN-γ receptor survived infection with LCMV. Clearance of LCMV is mediated normally by CD8(+) T cells. However, the depletion of these cells in LCMV-infected STAT1 KO mice was delayed, but did not prevent, lethality. In contrast, depletion of CD4(+) T cells prevented lethality in LCMV-infected STAT1 KO mice and was associated with a reduction in tissue immune pathology. These studies highlight a fundamental difference in the role of STAT1 versus STAT2 and IRF9. While all three factors are required to limit viral replication and spread, only STAT1 has the unique function of preventing the emergence of a lethal antiviral CD4(+) T-cell response.     

干扰素的信号传导和抗病毒效应机制

干扰素是一种具有抗病毒、抗增殖和免疫调节功能的细胞因子,它在宿主天然免疫防御中起着重要的作用。干扰素诱导的信号通路除了最初的Jak-Stat途径以外,很多新发现的信号途径对于干扰素反应也是必需的。干扰素反应最终导致抗病毒的效应蛋白通路,包括2′,5′-寡聚腺苷酸合成酶、蛋白激酶、ISG15等途径。这些效应蛋白通过抑制病毒转录、降解病毒RNA、抑制翻译和修饰蛋白的功能来控制病毒复制的过程。     

Acetylation-dependent signal transduction for type I interferon receptor

Cytokine-activated receptors initiate intracellular signaling by recruiting protein kinases that phosphorylate the receptors on tyrosine residues, thus enabling docking of SH2 domain-bearing activating factors. Here we report that in response to type 1 interferon (IFNalpha), IFNalpha receptors recruit cytoplasmic CREB-binding protein (CBP). By binding to IFNalphaR2 within the region where two adjacent proline boxes bear phospho-Ser364 and phospho-Ser384, CBP acetylates IFNalphaR2 on Lys399, which in turn serves as the docking site for interferon regulatory factor 9 (IRF9). IRF9 interacts with the acetyl-Lys399 motif by means of its IRF homology2 (IH2) domain, leading to formation of the ISGF3 complex that includes IRF9, STAT1, and STAT2. All three components are acetylated by CBP. Remarkably, acetylation within the DNA-binding domain (DBD) of both IRF9 and STAT2 is critical for the ISGF3 complex activation and its associated antiviral gene regulation. These results have significant implications concerning the central role of acetylation in cytokine receptor signal transduction.