Human Cytomegalovirus Immediate-Early 1 Protein Rewires Upstream STAT3 to Downstream STAT1 Signaling Switching an IL6-Type to an IFNγ-Like Response

Abstract

The human cytomegalovirus (hCMV) major immediate-early 1 protein (IE1) is best known for activating transcription to facilitate viral replication. Here we present transcriptome data indicating that IE1 is as significant a repressor as it is an activator of host gene expression. Human cells induced to express IE1 exhibit global repression of IL6- and oncostatin M-responsive STAT3 target genes. This repression is followed by STAT1 phosphorylation and activation of STAT1 target genes normally induced by IFNγ. The observed repression and subsequent activation are both mediated through the same region (amino acids 410 to 445) in the C-terminal domain of IE1, and this region serves as a binding site for STAT3. Depletion of STAT3 phenocopies the STAT1-dependent IFNγ-like response to IE1. In contrast, depletion of the IL6 receptor (IL6ST) or the STAT kinase JAK1 prevents this response. Accordingly, treatment with IL6 leads to prolonged STAT1 instead of STAT3 activation in wild-type IE1 expressing cells, but not in cells expressing a mutant protein (IE1dl410-420) deficient for STAT3 binding. A very similar STAT1-directed response to IL6 is also present in cells infected with a wild-type or revertant hCMV, but not an IE1dl410-420 mutant virus, and this response results in restricted viral replication. We conclude that IE1 is sufficient and necessary to rewire upstream IL6-type to downstream IFNγ-like signaling, two pathways linked to opposing actions, resulting in repressed STAT3- and activated STAT1-responsive genes. These findings relate transcriptional repressor and activator functions of IE1 and suggest unexpected outcomes relevant to viral pathogenesis in response to cytokines or growth factors that signal through the IL6ST-JAK1-STAT3 axis in hCMV-infected cells. Our results also reveal that IE1, a protein considered to be a key activator of the hCMV productive cycle, has an unanticipated role in tempering viral replication.

Human Cytomegalovirus Utilizes a Nontraditional Signal Transducer and Activator of Transcription 1 Activation Cascade via Signaling through Epidermal Growth Factor Receptor and Integrins To Efficiently Promote the Motility, Differentiation, and Polarization of Infected Monocytes

“…However, due to STAT1's well-established role in antiviral responses, the activation of STAT1 could potentially be a double-edged sword in that it promotes proviral monocyte biological changes but may also inhibit viral replication. This is illustrated in a study by Harwardt et al, in which the virus rewires STAT signaling in infected fibroblasts (103). In this study, HCMV IE1 binds to STAT3, depleting cytoplasmic stores of STAT3 that would become activated by JAK kinases following IFN signaling.…”

“…4C and E to G), rather than the traditional IFN-dependent pathway (Fig. 3) or the IE-induced rewiring of JAK/STAT signaling (103). Perhaps this unique regulation of STAT1 activation helps to overcome the hurdle of STAT1's potential antiviral activity while helping to regulate monocyte motility and differentiation.…”

Control of immune ligands by members of a cytomegalovirus gene expansion suppresses natural killer cell activation

“…The US12 family targets pro-inflammatory mediators, such as multiple members of the tumour necrosis factor receptor (TNFR) superfamily (TNFRSF8, TNFRSF12A, NGFR, LTBR), gp130 (IL6ST), the IL-6 receptor signaling receptor, pannexin-1 (PANX1) and the TLR4 ligand high-mobility group protein B1 (HMGB1) (Croft et al, 2013; Kanneganti et al, 2007; Park et al, 2004). IL6ST signaling may also have antiviral effects in the context of HCMV (Harwardt et al, 2016), which was suggested by the finding that disruption of gp130 STAT3 binding resulted in IFN-like signaling through STAT1(Costa-Pereira et al, 2002). …”

The Effects of IL10 and NK Cells on the Susceptibility to Mouse Cytomegalovirus in BALB/c Mice despite the Compensation of IFNγ

“…IFNγ inhibits the infection of cytomegalovirus, while IL18 can facilitate the secretion of IFNγ to control virus infections [21, 22]. Although IL10 is usually considered to be a suppressor for host immunity, it actually has a complicated role in MCMV infection [23, 24].…”

“…IFNγ can inhibit HCMV infection by regulating the expression of immediate early genes [21, 34]. The similar function of IFNγ also works in the process of MCMV infection [35, 36].…”