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Updated: Mar 28, 2026
NF-κB-dependent Luciferase Activation and Quantification of Gene Expression in Salmonella Infected Tissue Culture Cells
Published on: January 12, 2020
Salmonella Virulence Factor SsrAB Regulated Factor Modulates Inflammatory Responses by Enhancing the Activation of
Lei Lei1, Wenbiao Wang1, Chuan Xia1
1State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan 430072, China; and.
Abstract:
Effector proteins encoded by Salmonella pathogenicity islands play a key role in promoting bacterial intracellular survival, colonization, and pathogenesis. In this study, we investigated the function of the virulence-associated effector SrfA (SsrAB regulated factor) both in macrophages in vitro and in infected mice in vivo. SrfA was secreted into the cytoplasm during S. Typhimurium infection and disassociated IL-1R-associated kinase-1 (IRAK-1) from the IRAK-1-Toll interacting protein (Tollip) complex by interacting with Tollip. The released IRAK-1 was phosphorylated and subsequently activated the NF-κB signaling pathway, which enhanced the LPS-induced expression of inflammatory cytokines, such as IL-8, IL-1β, and TNF-α. The coupling of ubiquitin to endoplasmic reticulum degradation aa 183-219 domain of Tollip is the binding region for SrfA, and both the MDaa207-226 and CTaa357-377 regions of SrfA mediate binding to Tollip and NF-κB signaling activation. Deletion of SrfA in S. Typhimurium had no notable effects on its replication but impaired the induction of NF-κB activation in infected macrophages. The mice infected with srfA-deficient bacteria exhibited a decreased inflammatory response and an increased survival rate compared with those infected with wild-type S. Typhimurium. We conclude that SrfA is a novel Salmonella virulence effector that helps modulate host inflammatory responses by promoting NF-κB signaling activation.
Insights
Salmonella effector SrfA disrupts host immune complexes, activating NF-κB signaling and increasing inflammation. Deleting SrfA reduces inflammation and improves survival in infected mice, highlighting its role in Salmonella pathogenesis.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Salmonella pathogenicity islands encode effector proteins crucial for bacterial survival and pathogenesis.
- Understanding the function of these effectors is key to deciphering host-pathogen interactions.
Purpose of the Study:
- To investigate the role of the Salmonella virulence effector SrfA in host immune response modulation.
- To elucidate the molecular mechanism by which SrfA influences the NF-κB signaling pathway.
Main Methods:
- In vitro studies using macrophages and in vivo studies using infected mice.
- Investigated the interaction of SrfA with host proteins IRAK-1 and Tollip.
- Analyzed the impact of SrfA deletion on NF-κB activation and cytokine production.
- Assessed the effect of SrfA deficiency on host survival rates.
Main Results:
- SrfA dissociates IRAK-1 from the IRAK-1-Tollip complex, leading to IRAK-1 phosphorylation and NF-κB activation.
- SrfA enhances LPS-induced expression of inflammatory cytokines (IL-8, IL-1β, TNF-α).
- SrfA-deficient Salmonella impaired NF-κB activation in macrophages and reduced inflammatory responses in mice, increasing survival rates.
Conclusions:
- SrfA is a novel Salmonella effector that modulates host inflammatory responses by activating NF-κB signaling.
- SrfA's interaction with Tollip and subsequent modulation of the IRAK-1/Tollip complex is critical for its virulence function.
- Targeting SrfA could be a potential strategy to control Salmonella infections.
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