Type-I interferon/Caspase-4/Gasdermin-D pathway is involved in the extracellular release of unconjugated Interferon stimulated gene 15 (ISG15) protein from Lipopolysaccharide primed human macrophages 2490

Abstract Description Interferon-stimulated gene 15 (ISG15) plays diverse roles in innate immunity. It functions intracellularly through ISGylation, a process in which ISG15 attaches covalently to target proteins, modulating their activity. In its unconjugated form, free ISG15 is also released from immune cells to confer its cytokine-like activity for pro-inflammatory response, and immune cell activation. Despite its significance, the mechanisms underlying free ISG15 release is yet to be characterized. Bacterial lipopolysaccharide (LPS) is a major factor involved in septicemia due to exaggerated systemic inflammation. In that regard, whether extracellular LPS triggers ISGylation in immune cells is unknown. Additionally, ISG15 release from LPS primed immune cells has yet to be reported. Our study with human THP-1 macrophages demonstrated extracellular LPS promoting robust ISGylation and ISG15 release in immune cells. Further study revealed type-I interferon (IFN) mediated activation of non-canonical inflammasome pathway triggering ISG15 release from macrophages. Specifically, IFN released from LPS primed THP-1 macrophages acted via its autocrine/paracrine action to promote ISG15 release via caspase-4 mediated cleavage of pore-forming protein Gasdermin D (GSDMD), which then translocate to the plasma membrane to facilitate extracellular release of ISG15. Thus, our studies have identified IFN/Caspase4/GSDMD pathway as a critical regulator of ISG15 release from immune cells. Topic Categories Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)