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Lipopolysaccharide activates the expression of ISG15-specific protease UBP43 via interferon regulatory factor 3
Oxana Malakhova1, Michael Malakhov, Christopher Hetherington
1Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
Abstract:
UBP43 is a protease that specifically removes a ubiquitin-like protein, ISG15, from its targets. Highest levels of UBP43 expression are detected in macrophages and in cell lines of monocytic lineage. Macrophages are important in host defense against bacterial and viral infections. The lipopolysaccharide (LPS) of the bacterial cell wall can mimic bacteria and activate monocytes/macrophages to provoke inflammatory responses. Here, we report that LPS strongly activates UBP43 expression in macrophages, which is paralleled by changes in UBP43 protein levels. Two interferon regulatory factor (IRF) binding sites in the UBP43 promoter are responsible for the induction of UBP43 expression by LPS, as well as for basal UBP43 promoter activity. We have identified two members of the IRF family (IRF-2 and IRF-3) that specifically bind to these sites. IRF-3 plays a primary role in the LPS-inducible activation of the UBP43 gene and IRF-2 confers a basal transcriptional activity to the UBP43 promoter. Furthermore, we demonstrate that LPS treatment increases the amount of ISG15-conjugates in macrophages. Coordinated induction of ISG15 and UBP43 suggests that ISG15 conjugation is a dynamic process and that a critical balance of ISG15-modification should be maintained during innate immune response.
Insights
Lipopolysaccharide (LPS) activates the UBP43 protease in macrophages, which is crucial for removing ISG15. This coordinated regulation maintains a balance of ISG15 modification during the innate immune response.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- UBP43 is a protease that removes ISG15 (a ubiquitin-like protein) from targets.
- Macrophages are key immune cells involved in host defense, particularly against bacterial and viral infections.
- Lipopolysaccharide (LPS) from bacterial cell walls activates monocytes/macrophages, initiating inflammatory responses.
Purpose of the Study:
- To investigate the effect of LPS on UBP43 expression in macrophages.
- To identify the regulatory mechanisms controlling UBP43 gene induction by LPS.
- To understand the role of UBP43 and ISG15 conjugation in the innate immune response.
Main Methods:
- Analysis of UBP43 expression and protein levels in macrophages after LPS treatment.
- Promoter analysis to identify regulatory elements controlling UBP43 gene expression.
- Electrophoretic mobility shift assays (EMSAs) to identify transcription factors binding to the UBP43 promoter.
- Assessment of ISG15-conjugate levels in LPS-treated macrophages.
Main Results:
- LPS strongly activates UBP43 expression and protein levels in macrophages.
- Two interferon regulatory factor (IRF) binding sites in the UBP43 promoter are essential for LPS-inducible expression and basal activity.
- IRF-3 is the primary factor for LPS-induced UBP43 activation, while IRF-2 contributes to basal promoter activity.
- LPS treatment leads to increased ISG15-conjugates in macrophages.
Conclusions:
- LPS-induced UBP43 expression in macrophages is regulated by IRF-3 and IRF-2 binding to specific promoter sites.
- The coordinated induction of ISG15 and UBP43 suggests a dynamic regulation of ISG15 conjugation during innate immunity.
- Maintaining a balance of ISG15 modification is critical for effective innate immune responses.