HCMV-Encoded Chemokine Receptor US28 Mediates Proliferative Signaling Through the IL-6–STAT3 Axis

Abstract

US28 is a viral G protein (heterotrimeric guanosine triphosphate-binding protein)-coupled receptor encoded by the human cytomegalovirus (HCMV). In addition to binding and internalizing chemokines, US28 constitutively activates signaling pathways linked to cell proliferation. Here, we show increased concentrations of vascular endothelial growth factor and interleukin-6 (IL-6) in supernatants of US28-expressing NIH 3T3 cells. Increased IL-6 was associated with increased activation of the signal transducer and activator of transcription 3 (STAT3) through upstream activation of the Janus-activated kinase JAK1. We used conditioned growth medium, IL-6-neutralizing antibodies, an inhibitor of the IL-6 receptor, and short hairpin RNA targeting IL-6 to show that US28 activates the IL-6-JAK1-STAT3 signaling axis through activation of the transcription factor nuclear factor kappaB and the consequent production of IL-6. Treatment of cells with a specific inhibitor of STAT3 inhibited US28-dependent [(3)H]thymidine incorporation and foci formation, suggesting a key role for STAT3 in the US28-mediated proliferative phenotype. US28 also elicited STAT3 activation and IL-6 secretion in HCMV-infected cells. Analyses of tumor specimens from glioblastoma patients demonstrated colocalization of US28 and phosphorylated STAT3 in the vascular niche of these tumors. Moreover, increased phospho-STAT3 abundance correlated with poor patient outcome. We propose that US28 induces proliferation in HCMV-infected tumors by establishing a positive feedback loop through activation of the IL-6-STAT3 signaling axis.

Signal transducer and activator of transcription 3 (STAT3) and survivin induction by varicella-zoster virus promote replication and skin pathogenesis

“…Survivin also modulates cell proliferation; human cytomegalovirus was recently shown to mediate endothelial cell proliferation and angiogenesis associated with survivin expression (34,35). However, we observed no difference in expression of the Ki67 proliferation marker in VZV-infected and uninfected skin xenografts (36).…”

The Cell Biology of Cytomegalovirus: Implications for Transplantation

“…Multiple studies have demonstrated the presence of T cell reactivity to CMV in seronegative patients; this observation, although uncommon, may suggest that CMV infection of certain cell types (e.g. in association with some tumors) or with latency may fail to maintain serologic evidence of infection (155).…”

“…CMVinduced production of inflammatory cytokines such as IL-12, IL-18, TNF-a, and IFN-c by SMCs, macrophages and ECs may contribute to proatherosclerotic effects (170). Slinger et al showed that US28 of HCMV activates the IL-6-JAK1-STAT3 signaling axis through activation of the transcription factor NF-kB and the consequent production of IL-6 and cell proliferation of HCMV-infected tumor cells including glioblastoma (155).…”

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“…10 Other groups also described CMV viral material in glioma samples using similar methodology. 11,12 Mitchell et al found that a large percentage of GBM samples were positive for CMV immediate-early (IE)1, pp65 or glycoprotein B using IHC, ISH and polymerase chain reaction (PCR). 13 However, subsequent to these initial reports, other groups published reports of no detectable CMV protein or genomic material in glioma samples.…”