Intra-macrophage expression of ArtAB toxin gene in Salmonella

Abstract

Salmonella entericasubspeciesentericaserovar Typhimurium (S. Typhimurium) definitive phage type 104 (DT104),S. Worthington, andS. bongoriproduce ArtAB toxin, which catalyses ADP-ribosylation of pertussis toxin-sensitive G protein. ArtAB gene (artAB) is encoded on a prophage inSalmonella, and prophage induction by SOS-inducing agents is associated with increases in ArtAB productionin vitro. However, little is known about the expression ofartAB in vivo. Here, we showed a significant increase inartABtranscription of DT104 within macrophage-like RAW264.7 cells. Intracellular expression of ArtAB was also observed by immunofluorescence staining. The induced expression ofartABin DT104 andS. bongoriwas enhanced by treatment of RAW264.7 cells with phorbol 12-myristate 13-acetate (PMA), which stimulates the production of reactive oxygen species (ROS); however, such induction was not observed inS. Worthington. Upregulation ofoxyR, a major regulator of oxidative stress, andcI,a repressor of prophage induction, was observed inS. Worthington within RAW264.7 cells treated with PMA but not in the DT104 strain. Although the expression ofoxyRwas increased,artABwas upregulated inS. bongori,which lacks thecIgene in the incompleteartAB-encoded prophage. Taken together, oxidative stress plays a role in the production ofartABtoxins in macrophages, and high expression levels ofoxyRandcIare responsible for the low expression ofartAB. Therefore, strain variation in the level ofartABexpression within macrophages could be explained by differences in the oxidative stress response of bacteria and might be reflected in its virulence.