Cytomegalovirus Activates Interferon Immediate-Early Response Gene Expression and an Interferon Regulatory Factor 3-Containing Interferon-Stimulated Response Element-Binding Complex

Abstract

Interferon establishes an antiviral state in numerous cell types through the induction of a set of immediateearly response genes. Activation of these genes is mediated by phosphorylation of latent transcription factors of the STAT family. We found that infection of primary foreskin fibroblasts with human cytomegalovirus (HCMV) causes selective transcriptional activation of the alpha/beta-interferon-responsive ISG54 gene. However, no activation or nuclear translocation of STAT proteins was detected. Activation of ISG54 occurs independent of protein synthesis but is prevented by protein tyrosine kinase inhibitors. Further analysis revealed that HCMV infection induced the DNA binding of a novel complex, tentatively called cytomegalovirus-induced interferonstimulated response element binding factor (CIF). CIF is composed, at least in part, of the recently identified interferon regulatory factor 3 (IRF3), but it does not contain the STAT1 and STAT2 proteins that participate in the formation of interferon-stimulated gene factor 3. IRF3, which has previously been shown to possess no intrinsic transcriptional activation potential, interacts with the transcriptional coactivator CREB binding protein, but not with p300, to form CIF. Activating interferon-stimulated genes without the need for prior synthesis of interferons might provide the host cell with a potential shortcut in the activation of its antiviral defense.Alpha interferon (IFN-␣) and IFN-␤ are unique among the continuously growing superfamily of cytokines in their ability to confer resistance to viral infection (20,36). The synthesis of IFN-␣ and IFN-␤ is induced at the transcriptional level after a cell encounters virus or double-stranded RNA (dsRNA) (16,46). The subsequent secretion of the newly produced interferons and their binding to a common cell surface receptor results in the induction of a set of immediate-early response genes (12, 21, 24-26, 32, 44, 47). The activation of these interferon-stimulated genes (ISGs) represents the first step towards the development of an antiviral state. Control over ISGs is exerted by an IFN-␣/␤-activated transcription factor complex termed interferon-stimulated gene factor 3 (ISGF3), which binds to a common enhancer element referred to as the interferon-stimulated response element (ISRE) (10,14,23,27,43). ISGF3 is formed through the interaction of the DNA binding subunit ISGF3␥ (p48) and the regulatory component ISGF3␣ (14,28,48), which itself is composed of two members of the STAT (signal transducers and activators of transcription) family of transcription factors, STAT1 and STAT2 (14,15,43). Both STAT proteins become tyrosine phosphorylated in response to IFN-␣/␤ stimulation, which enables their nuclear translocation and DNA binding (8,10,13,41). Transcriptionally active STAT1 has been shown to be a requirement for the antiviral and antiproliferative effects of IFN-␣/␤ (5, 11, 31). The phosphorylation of STAT1 and STAT2 is mediated through the action of two related tyrosine kinases, Jak1 and Tyk2, which are enzymatic...

p38-dependent Activation of Interferon Regulatory Factor 3 by Lipopolysaccharide

“…U373 cells were stimulated for 6 h with 1 g/ml LPS in the presence of 100 g/ml cycloheximide, and nuclear extracts were subjected to electrophoretic mobility shift assays using the ISG15-ISRE as a probe. As anticipated, LPS induced the formation of a DNA binding complex whose migration is similar to that of the previously reported human cytomegalovirus-induced CIF complex (16), but is distinct from the IFN␣/␤-induced ISGF3 complex (Fig. 2A, lane 2).…”

Global modulation of cellular transcription by human cytomegalovirus is initiated by viral glycoprotein B

“…and T.C., unpublished data). Also compelling is the evidence that an indirect induction as a result of IFN production from HCMV-infected cells or gB-treated cells does not occur; neither experimental conditions require de novo synthesis for signaling to occur (3,9,23). Instead, gB seems to trigger IFN signaling through an unknown receptor and by incompletely characterized signaling mediators.…”

“…Instead, gB seems to trigger IFN signaling through an unknown receptor and by incompletely characterized signaling mediators. Whether or not viral gB-mediated signaling can induce cytomegalovirus-induced factor, a complex which can bind to IFN-response elements within the promoters of HCMV-stimulated ISGs, remains to be addressed (23). Ultimately, identification of the receptor that confers HCMV entry and signal transduction will be required to dissect the initial events in infection.…”

Cytomegalovirus InducesInterferon-Stimulated Gene Expression and Is Attenuated by Interferon in the DevelopingBrain

“…mCMV infection elicits an IFN response in infected animals through TLR3 and TLR9 by both MyD88-dependent and -independent mechanisms (16,51). Furthermore, infection of human cells with hCMV has been shown to induce IFN-stimulated gene expression, and this activation appears to occur by both IRF3-dependent and -independent mechanisms (15,33,65). A significant amount of antiviral gene expression is induced in hCMV-infected cells early after infection (6 to 8 hpi) and in the presence of the protein synthesis inhibitor cycloheximide, indicating that some gene expression is directly induced by hCMV rather than as a secondary consequence of IFN-␤ expression (7,15).…”