ISG15 governs mitochondrial function in macrophages following vaccinia virus infection.

Sara Baldanta,Jesús Vázquez,Emilio Camafeita,José Antonio Enríquez,Mercedes Fernández-Escobar,Rebeca Acín-Perez,Manuel Albert,Inmaculada Jorge,Susana Guerra,Deborah J Lenschow

doi:10.1371/journal.ppat.1006651

Abstract

The interferon (IFN)-stimulated gene 15 (ISG15) encodes one of the most abundant proteins induced by interferon, and its expression is associated with antiviral immunity. To identify protein components implicated in IFN and ISG15 signaling, we compared the proteomes of ISG15-/- and ISG15+/+ bone marrow derived macrophages (BMDM) after vaccinia virus (VACV) infection. The results of this analysis revealed that mitochondrial dysfunction and oxidative phosphorylation (OXPHOS) were pathways altered in ISG15-/- BMDM treated with IFN. Mitochondrial respiration, Adenosine triphosphate (ATP) and reactive oxygen species (ROS) production was higher in ISG15+/+ BMDM than in ISG15-/- BMDM following IFN treatment, indicating the involvement of ISG15-dependent mechanisms. An additional consequence of ISG15 depletion was a significant change in macrophage polarization. Although infected ISG15-/- macrophages showed a robust proinflammatory cytokine expression pattern typical of an M1 phenotype, a clear blockade of nitric oxide (NO) production and arginase-1 activation was detected. Accordingly, following IFN treatment, NO release was higher in ISG15+/+ macrophages than in ISG15-/- macrophages concomitant with a decrease in viral titer. Thus, ISG15-/- macrophages were permissive for VACV replication following IFN treatment. In conclusion, our results demonstrate that ISG15 governs the dynamic functionality of mitochondria, specifically, OXPHOS and mitophagy, broadening its physiological role as an antiviral agent.

Highlights

The type I interferon (IFN) signaling system is activated following viral infection, resulting in upregulation of interferon-stimulated genes (ISGs) that have diverse functions in the antiviral innate immune response
We found that Interferon-stimulated gene 15 product (ISG15) modulates macrophage polarization, which has been shown to be dependent on cellular metabolism [31], suggesting that the antiviral effect of ISG15 may be due to the fine regulation of its polarization
To investigate the role of ISG15 and ISGylation in macrophages, we evaluated the presence of ISGylated proteins in total extracts from ISG15+/+ and ISG15-/- bone marrow derived macrophages (BMDM) infected or not with vaccinia virus (VACV), or pre-treated or not with IFN

Summary

Introduction

The type I interferon (IFN) signaling system is activated following viral infection, resulting in upregulation of interferon-stimulated genes (ISGs) that have diverse functions in the antiviral innate immune response. ISGylation has been shown to occur in a cotranslational process favoring modification of viral proteins in infected cells, which in turn obstructs virus assembly or function [3,4,5]. Several viral proteins can be conjugated to ISG15, such as the non-structural NS1 protein from influenza A/B virus and the human immunodeficiency virus (HIV) Gag protein [7], which inhibits specific viral functions or virion assembly and blocks viral progression [8, 9]. ISG15 expression has been shown to disrupt the process of virus-budding via different mechanisms such as by blocking the endosomal sorting complexes required for transport (ESCRT machinery in HIV-infected cells) [11], or by inhibiting Nedd E3 ubiquitin ligase activity in the case of Ebola and other enveloped viruses [12]

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Conclusion