HSV Infection Induces Production of ROS, which Potentiate Signaling from Pattern Recognition Receptors: Role for S-glutathionylation of TRAF3 and 6

Abstract

The innate immune response constitutes the first line of defense against infections. Pattern recognition receptors recognize pathogen structures and trigger intracellular signaling pathways leading to cytokine and chemokine expression. Reactive oxygen species (ROS) are emerging as an important regulator of some of these pathways. ROS directly interact with signaling components or induce other post-translational modifications such as S-glutathionylation, thereby altering target function. Applying live microscopy, we have demonstrated that herpes simplex virus (HSV) infection induces early production of ROS that are required for the activation of NF-κB and IRF-3 pathways and the production of type I IFNs and ISGs. All the known receptors involved in the recognition of HSV were shown to be dependent on the cellular redox levels for successful signaling. In addition, we provide biochemical evidence suggesting S-glutathionylation of TRAF family proteins to be important. In particular, by performing mutational studies we show that S-glutathionylation of a conserved cysteine residue of TRAF3 and TRAF6 is important for ROS-dependent activation of innate immune pathways. In conclusion, these findings demonstrate that ROS are essential for effective activation of signaling pathways leading to a successful innate immune response against HSV infection.

Author Summary

Herpes simplex virus (HSV) type 1 and 2 are important human pathogens, which can give rise to severe diseases during both primary and recurrent infections. In addition to activating “classical” innate and adaptive immune responses, many infections stimulate other cellular activities such as and production of reactive oxygen species (ROS). However, there is little knowledge on the cross-talk between ROS and the innate antiviral response. In this article we show that HSV infection leads to production of ROS, and that ROS play a critical role in activation of innate immune responses to these viruses. At the mechanistic level, we show that ROS stimulate glutathionylation (a protein modification) of the signaling molecules TRAF3 and 6, which promotes redox-sensitive signaling. Our data support the idea that the innate immune system not only detects specific HSV molecules but also senses the cellular oxidative stress level, and integrates this into the innate immune response to infections.