Salmonella Effector SpvB Inhibits NF-κB Activity via KEAP1-Mediated Downregulation of IKKβ

Abstract

Bacterial pathogens have a broad arsenal of genes that are tightly regulated and coordinated to facilitate adaptation to alter host inflammatory response and prolong intracellular bacterial survival. Salmonella enterica serovar Typhimurium utilizes a type III secretion system (T3SS) to deliver effector molecules into host cells and regulate signal transduction pathways such as NF-κB, thereby resulting in salmonellosis. SpvB, a pSLT-encoded cytotoxic protein secreted by Salmonella pathogenicity island-2 T3SS, is associated with enhanced Salmonella survival and intracellular replication. In this report, we characterized the effects of SpvB on NF-κB signaling pathway. We showed that SpvB has a potent and specific ability to prevent NF-κB activation by targeting IκB kinase β (IKKβ). Previous studies from our laboratory showed that SpvB decreases Nrf2 through its C-terminal domain. Here we further demonstrated that KEAP1, a cytoplasmic protein that interacts with Nrf2 and mediates its proteasomal degradation, is involved in SpvB-induced downregulation of IKKβ expression and phosphorylation. Reduction of KEAP1 by small-interfering RNA prevented the suppression of IKKβ and its phosphorylation mediated by SpvB. These findings revealed a novel mechanism by which Salmonella modulates NF-κB activity to ultimately facilitate intracellular bacterial survival and proliferation and delay host immune response to establish infection.

NLRP6 induces RIP1 kinase-dependent necroptosis via TAK1-mediated p38MAPK/MK2 phosphorylation in S. typhimurium infection

“…Cells were then transfected with the experimental reporter plasmid pNF-κB-Luc (Firefly luciferase, Clontech, Mountain View, CA, USA), pIL8-Luc and the internal control plasmid pRL-TK (Renilla luciferase, Clontech), as well as other plasmids as described in the figure legend and our previous study. 42 When appropriate, cells were treated with PMA (79346, MilliporeSigma), TNF-α (300-01A, PeproTech) or IL-1β (200-01B, PeproTech). Enzyme activity was measured using the Dual Luciferase reporter assay kit (E1910, Promega) according to the manufacturer’s instructions.…”

The ERK-p38MAPK-STAT3 Signalling Axis Regulates iNOS Expression and Salmonella Infection in Senescent Cells

“…For this, we adopted the Salmonella Typhimurium-senescent cell infection model, which has been described previously and shows reduced bacterial infection in senescent cells (Fernandes et al, 2021). In this study, we have used two host cell lines: HeLa, which is commonly used to study Salmonella pathogenesis and host responses to its infection (Takemura et al, 2021;Yang et al, 2021) and HepG2 (Hannemann et al, 2013), a human hepatocyte cell line as the liver is a primary target of the bacterium during the systemic disease, Typhoid (Watson and Holden, 2010). Since persistent DNA damage is the major trigger of cellular senescence, a DNAdamage induced senescent cell model was used.…”

Delivering the pain: an overview of the type III secretion system with special consideration for aquatic pathogens

“…The resulting p651–38 fragment then interferes with p65/ RPS3 interactions to hinder the transcription of NF-κB and NF-κB signalling [ 83 ]. Likewise, the effector SpvB secreted by the Salmonella pathogenicity island-2 (SPI-2) T3SS of Salmonella enterica serovar Typhimurium has been shown to promote the expression of the E3 ligase KEAP1 [ 84 ]. KEAP1 acts as a repressor for IKKb which is in turn a promoter of NF-kB, therefore this effector proteins allows the bacterium to supress the NF-kB-dependent signalling pathway associated with the immune response [ 84 ].…”