ISG15 Regulates Peritoneal Macrophages Functionality against Viral Infection

Abstract

Upon viral infection, the production of type I interferon (IFN) and the subsequent upregulation of IFN stimulated genes (ISGs) generate an antiviral state with an important role in the activation of innate and adaptive host immune responses. The ubiquitin-like protein (UBL) ISG15 is a critical IFN-induced antiviral molecule that protects against several viral infections, but the mechanism by which ISG15 exerts its antiviral function is not completely understood. Here, we report that ISG15 plays an important role in the regulation of macrophage responses. ISG15−/− macrophages display reduced activation, phagocytic capacity and programmed cell death activation in response to vaccinia virus (VACV) infection. Moreover, peritoneal macrophages from mice lacking ISG15 are neither able to phagocyte infected cells nor to block viral infection in co-culture experiments with VACV-infected murine embryonic fibroblast (MEFs). This phenotype is independent of cytokine production and secretion, but clearly correlates with impaired activation of the protein kinase AKT in ISG15 knock-out (KO) macrophages. Altogether, these results indicate an essential role of ISG15 in the cellular immune antiviral response and point out that a better understanding of the antiviral responses triggered by ISG15 may lead to the development of therapies against important human pathogens.

Differential Induction of Apoptosis, Interferon Signaling, and Phagocytosis in Macrophages Infected with a Panel of Attenuated and Nonattenuated Poxviruses

“…Recently, we reported that the phagocytic capacity of macrophages is highly regulated by IFN (35). Latex beads are a common substrate used in biochemical studies to study phagocytosis in macrophages (28).…”

ISG15 Is a Critical Microenvironmental Factor for Pancreatic Cancer Stem Cells

“…Appreciating that other pathways may also be modulated by ISG15, we are currently investigating whether the AKT-PI3K and mTOR/S6K pathways, both of which have been shown to be important in PDAC (44,45), are also affected by free ISG15. Along these lines, previous work from our laboratory has shown a direct link between AKT signaling and ISG15 in macrophages (11). We have reported that ISG15 plays an important role in the regulation of macrophage functions as ISG15 À/À macrophages display reduced activation, phagocytic capacity, and programmed cell death activation in response to vaccinia virus infection.…”

“…Since its discovery in 1979 (10), ISG15 has been extensively studied as an anti-viral protein (11)(12)(13), but we now appreciate that ISG15 has many other functions, including ISGylation, a ubiquitinlike modification process whereby ISG15 can be covalently linked to cytoplasmic and nuclear proteins (14). Like ubiquitin, ISG15 coupling to target proteins involves the ISG15-specific E1-like activating enzyme (UbE1L), the conjugating E2 enzyme, and the ligating E3 enzymes (15,16).…”

ISG15 Is Counteracted by Vaccinia Virus E3 Protein and Controls the Proinflammatory Response against Viral Infection

“…Also, it is important to underscore that free ISG15 becomes secreted and the lack of secreted ISG15 is associated with severe mycobacterial disease in both mice and humans (37). Furthermore, we recently reported the importance of ISG15 in regulating macrophage activity (38), indicating that ISG15 is a crucial molecule in the regulation of the immune response. Additional studies to understand the biological functions of unconjugated intracellular and/or extracellular ISG15 and of ISGylation may help our knowledge of innate immunity and on how viruses have developed strategies to subvert it.…”