Modulation of Interferon Signaling Pathways by the Human Cytomegalovirus Immediate-Early 1 Protein
Final Report Abstract
Human cytomegalovirus (hCMV) is a leading cause of birth defects and of severe disease in immunocompromised patients. The pathogenesis of hCMV disease is commonly linked to adverse (innate) immune responses. At the molecular level, this is reflected by the fact that the virus alters expression of numerous immune regulatory host genes. Many of these genes are responsive to type I and/or type II interferons (IFNs) and subject to regulation by cellular signal transducer and activator of transcription (STAT) proteins. Our work has shown that the 72‐kDa immediate‐early 1 protein (IE1) of hCMV targets human STAT2 to block type I IFN‐ regulated anti‐viral signaling and gene expression. At the same time, IE1 activates pro‐inflammatory and immune‐stimulatory host genes normally controlled by type II IFN through a STAT1‐dependent mechanism. The completed project aimed to specify the molecular requirements underlying the differential effects of IE1 on STAT‐dependent IFN pathways. It was also designed to elucidate the impact the type II IFN‐like response to IE1 exerts on the course and outcome of hCMV infection. We identified a short motif between amino acids 410 and 420 in IE1 that serves as binding site for STAT2. This motif turned out to be required for all direct effects IE1 exerts on type I and type II IFN signaling. The same motif also confers binding to STAT3 resulting in disruption of signaling mediated by interleukin‐6 (IL6) and related cytokines. Unexpectedly, activation of type II IFN‐like signaling does not involve physical IE1‐STAT1 interaction but complex formation between IE1 and STAT3. In fact, IE1 proved to be sufficient and necessary to rewire upstream IL6‐type to downstream type II IFN‐like signaling, two pathways linked to opposing actions, resulting in repressed STAT3‐ and activated STAT1‐responsive genes. The type II IFN‐ like response mediated by IL6‐type cytokines in the presence of IE1 moderates rather than promotes hCMV replication, revealing an unanticipated temperance activity encoded in the viral protein. Finally, we designed a screening approach for compounds targeting viral IFN antagonists and identified two small molecule inhibitors of IE1 expression that potently inhibit hCMV replication. Our results provide important insights into the function of a viral key regulator of hCMV replication and devise a new anti‐viral strategy that may eventually contribute to reducing the huge health‐related and economic burden associated with this virus.
Publications
- (2013) Human cytomegalovirus IE1 protein disrupts interleukin‐6 signaling by sequestering STAT3 in the nucleus. J Virol. 87(19):10763‐76
Reitsma JM, Sato H, Nevels M, Terhune SS, Paulus C
(See online at https://doi.org/10.1128/JVI.01197-13) - (2016) Human cytomegalovirus immediate‐early 1 protein rewires upstream STAT3 to downstream STAT1 signaling switching an IL6‐type to an IFNγ‐like response. PLoS Pathog. 12(7):e1005748
Harwardt T, Lukas S, Zenger M, Reitberger T, Danzer D, Übner T, Munday DC, Nevels M, Paulus C
(See online at https://doi.org/10.1371/journal.ppat.1005748) - (2018) Modular cell‐based platform for high throughput identification of compounds that inhibit a viral interferon antagonist of choice. Antiviral Res. 150:79‐92
Vasou A, Paulus C, Narloch J, Gage ZO, Rameix‐Welti MA, Eléouët JF, Nevels M, Randall RE, Adamson CS
(See online at https://doi.org/10.1016/j.antiviral.2017.10.012)
