Human herpesviruses-encoded dUTPases: a family of proteins that modulate dendritic cell function and innate immunity

Abstract

We have previously shown that Epstein-Barr virus (EBV)-encoded dUTPase can modulate innate immune responses through the activation of TLR2 and NF-κB signaling. However, whether this novel immune function of the dUTPase is specific for EBV or a common property of the Herpesviridae family is not known. In this study, we demonstrate that the purified viral dUTPases encoded by herpes simplex virus type 2 (HSV-2), human herpesvirus-6A (HHV-6A), human herpesvirus-8 (HHV-8) and varicella-zoster virus (VZV) differentially activate NF-κB through ligation of TLR2/TLR1 heterodimers. Furthermore, activation of NF-κB by the viral dUTPases was inhibited by anti-TLR2 blocking antibodies (Abs) and the over-expression of dominant-negative constructs of TLR2, lacking the TIR domain, and MyD88 in human embryonic kidney 293 cells expressing TLR2/TLR1. In addition, treatment of human dendritic cells and PBMCs with the herpesviruses-encoded dUTPases from HSV-2, HHV-6A, HHV-8, and VZV resulted in the secretion of the inflammatory cytokines IL-1β, IL-6, IL-8, IL-12, TNF-α, IL-10, and IFN-γ. Interestingly, blocking experiments revealed that the anti-TLR2 Ab significantly reduced the secretion of cytokines by the various herpesviruses-encoded dUTPases (p < 0.05). To our knowledge, this is the first report demonstrating that a non-structural protein encoded by herpesviruses HHV-6A, HHV-8, VZV and to a lesser extent HSV-2 is a pathogen-associated molecular pattern. Our results reveal a novel function of the virus-encoded dUTPases, which may be important to the pathophysiology of diseases caused by these viruses. More importantly, this study demonstrates that the immunomodulatory functions of dUTPases are a common property of the Herpesviridae family and thus, the dUTPase could be a potential target for the development of novel therapeutic agents against infections caused by these herpesviruses.

Herpesviruses dUTPases: A New Family of Pathogen-Associated Molecular Pattern (PAMP) Proteins with Implications for Human Disease

“…Furthermore, it has been shown that IL-17 serum levels were significantly increased in patients with SLE and positively correlated with SLE Disease Activity Index (SLEDAI) scores [118]. In line with these findings, extensive studies by our group have demonstrated that the EBV dUTPase activates TLR2 in human immune cells [7,27,29] and induces the production of pro-inflammatory T H 1/T H 17 cytokines [7,27,29,30], which have been implicated in the pathogenesis of SLE [113,114]. …”

“…We have demonstrated that the EBV-dUTPase triggers NF-κB activation through engagement of TLR2 homodimers, while the dUTPases expressed by HSV-2, HHV-6A, HHV-8, and VZV require ligation of the TLR2/1 heterodimer complex to activate NF-κB [7,27]. We have also demonstrated that these viral dUTPases are capable of differentially inducing the secretion of the pro-inflammatory T H 1/T H 17 cytokines IL-1β, IL-6, IL-8, IL-12p70, TNF-α, and IFN-γ as well as the anti-inflammatory cytokine IL-10 ( p < 0.001) in human primary immune cells [7,25,26,27].…”

“…We have also demonstrated that these viral dUTPases are capable of differentially inducing the secretion of the pro-inflammatory T H 1/T H 17 cytokines IL-1β, IL-6, IL-8, IL-12p70, TNF-α, and IFN-γ as well as the anti-inflammatory cytokine IL-10 ( p < 0.001) in human primary immune cells [7,25,26,27]. These differences in the ability of the herpesviruses dUTPases to induce NF-κB activation and cytokine secretion may reflect differences in intrinsic properties of each viral protein including binding affinities of the dUTPases to TLR2 or TLR2/TLR1 and the overall structure of the dUTPases.…”

“…Moreover, exosomes have been implicated in the pathogenesis of RA and SLE [119]. EBV-dUTPase stimulation of human dendritic cells and macrophages in the microenvironment would result in the increased expression and secretion of T H 1/T H 17 proinflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8) as well as the anti-inflammatory cytokine IL-10 [7,25,27,29]. The production of IL-17 by T H 17 cells promotes chronic inflammation, which is enhanced by IL-8-mediated recruitment of neutrophils and macrophages to the site of inflammation.…”

“…Sequencing analyses have demonstrated the presence of an additional conserved motif (motif 6) of unknown function in the herpesviruses’ dUTPases that is absent in the homotrimeric dUTPases [5]. Although the human β herpesviruses (human cytomegalovirus, HCMV; human herpesvirus 6A and B, HHV-6; human herpesvirus 7, HHV-7) contain putative genes encoding a dUTPase, studies with HCMV (UL72) [6] and HHV-6A (U45) [7] have shown that these genes do not encode for a protein with functional dUTPase activity. This is not surprising since examination of the protein expressed by these viruses revealed that they lack the five conserved motifs typical of homotrimeric and monomeric dUTPases.…”