Salmonella type III effector SpvC, a phosphothreonine lyase, contributes to reduction in inflammatory response during intestinal phase of infection

Abstract

SummarySalmonella phosphothreonine lyase SpvC inactivates the dual-phosphorylated host mitogenactivated protein kinases (MAPK) through b-elimination. While SpvC can be secreted in vitro by both Salmonella pathogenicity island (SPI)-1 and SPI-2 type III secretion systems (T3SSs), translocation of this protein into the host cell cytosol has only been demonstrated by SPI-2 T3SS. In this study, we show that SpvC can be delivered into the host cell cytoplasm by both SPI-1 and SPI-2 T3SSs. Dephosphorylation of the extracellular signal-regulated protein kinases (ERK) was detected in an SPI-1 T3SS-dependent manner 2 h post infection. Using a mouse model for Salmonella enterocolitis, which was treated with streptomycin prior to infection, we observed that mice infected with Salmonella enterica serovar Typhimurium strains lacking the spvC gene showed pronounced colitis when compared with mice infected with the wild-type strain 1 day after infection. The effect of SpvC on the development of colitis was characterized by reduced mRNA levels of the pro-inflammatory cytokines and chemokines, and reduced inflammation with less infiltration of neutrophils. Furthermore, the reduction in inflammation by SpvC resulted in increased bacterial dissemination in spleen of mice infected with Salmonella. Collectively, our findings suggest that SpvC exerts as an antiinflammatory effector and the attenuation of intestinal inflammatory response by SpvC is involved in systemic infection of Salmonella.

Global Impact of Salmonella Pathogenicity Island 2-secreted Effectors on the Host Phosphoproteome

“…As for the ERK1/2, tyrosine phosphorylation at Tyr-205/Tyr-185 in ERK1/2 showed increased profiles (⌬ssaR/WT ϭ 0.54 and ⌬ssaR/WT ϭ 0.61) in RAW264.7 cells, although in HeLa cells the threonine phosphorylation site at Thr-190 on ERK2 showed the opposite trend (⌬ssaR/WT ϭ 1.96) ( Table I). This observation is consistent with the fact that an SPI2 phosphothreonine lyase SpvC dephosphorylates the threonine sites in ERK1/2 (47) to inactivate them, subsequently inducing antiinflammatory effect (48).…”

Impact ofSalmonella entericaType III Secretion System Effectors on the Eukaryotic Host Cell

“…Recently, it was demonstrated that SpvC is translocated into the host cell cytosol through T3SS1 when bacteria are grown under SPI1-inducing conditions [319]. This effector has phosphothreoninelyase activity [318,320].…”

“…SpvC specifically removes phosphate from threonine in the conserved activation loop motif TXY of ERK and inactivates this MAPK, and it is also active towards p38 and JNK in vitro [318,320]. Inactivation of MAPK is the proposed reason for the effect of SpvC in modulating host immune response by reducing inflammatory cytokines during the early stages of infection [319].…”

Subversion of MAPK signaling by pathogenic bacteria

“…Upon over expression, or in vitro, SpvC can target ERK1/2, p38 and JNK, 8,14 but in vivo, under physiological conditions, only ERK1/2 are dephosphorylated. 15 Genetic analyses show that SpvC is required for systemic infection in mice. 45 Inhibition of MAPK by SpvC reduces expression of pro-inflammatory cytokines (e.g., IL-8, TNFa) and diminishes inflammation and neutrophil infiltration at infection sites during early stages of infection.…”

“…45 Inhibition of MAPK by SpvC reduces expression of pro-inflammatory cytokines (e.g., IL-8, TNFa) and diminishes inflammation and neutrophil infiltration at infection sites during early stages of infection. 14,15 In addition to ERK inhibition, S. enterica employ the AvrA effector to block JNK signaling. AvrA is a SPI1 T3SS effector protein that is a close homologue of YopJ.…”