SipA, SopA, SopB, SopD, and SopE2 Contribute toSalmonella entericaSerotype Typhimurium Invasion of Epithelial Cells

Abstract

The centisome 63 type III secretion system (T3SS-1) encoded by Salmonella pathogenicity island 1 (SPI1) mediates invasion of epithelial cells by Salmonella enterica serotype Typhimurium. Characterization of mutants lacking individual genes has revealed that T3SS-1 secreted proteins (effectors) SopE2 and SopB are required for invasion while the SipA protein accelerates entry into cells. Here we have revisited the question of which T3SS-1 effectors contribute to the invasion of epithelial cells by complementing a strain lacking all of the effector genes that are required to cause diarrhea in a calf (a sipA sopABDE2 mutant). Introduction of either the cloned sipA, the cloned sopB, or the cloned sopE2 gene increased the invasiveness of the sipA sopABDE2 mutant for nonpolarized HT-29 cells. However, a contribution of sopA or sopD to invasion was not apparent when invasion assays were performed with the nonpolarized colon carcinoma cell lines T84 and HT-29. In contrast, introduction of either the sopA, the sopB, the sopD, or the sopE2 gene increased the invasiveness of the sipA sopABDE2 mutant for polarized T84 cells. Furthermore, introduction of a plasmid carrying sipA and sopB increased the invasiveness of the sipA sopABDE2 mutant for polarized T84 cells significantly compared to the introduction of plasmids carrying only sipA or sopB. We conclude that SipA, SopA, SopB, SopD, and SopE2 contribute to S. enterica serotype Typhimurium invasion of epithelial cells in vitro.

SopB activates the Akt-YAP pathway to promote Salmonella survival within B cells

“…SopB is an inositol phosphate phosphatase that plays an important role in cell invasion and enteropathogenesis and is involved in protecting epithelial cells from apoptosis through Akt activation [16–19,44]. Likewise, SopB promotes the accumulation of PI(3,4)P2/PI(3,4,5)P3 at the cell membrane, which leads to Akt recruitment and activation by PDK1 and mTORC2.…”

“…SPI-1 is required for invasion during oral infection, and the effectors encoded in this pathogenicity island are involved in cytoskeleton rearrangements of epithelial cells to promote the entry of Salmonella via macropinocytosis [16,17]. SopE/SopE2 and the inositide phosphate phosphatase SopB are some of the effector proteins responsible for the induction of macropinocytosis.…”

“…SopE/SopE2 and the inositide phosphate phosphatase SopB are some of the effector proteins responsible for the induction of macropinocytosis. SopB is also involved in host cell survival through activation of the Akt signaling pathway [16,18,19]. Additional functions have recently been described for SPI-1, including activation of the host innate immune system and induction of cell death [20,21].…”

SipA, SopA, SopB, SopD and SopE2 effector proteins of Salmonella enterica serovar Typhimurium are synthesized at late stages of infection in mice

“…Four independent extractions for each sample were added together to minimize differences in protein recovery from sample to sample. The proteins were then boiled for 5-10 min, and an aliquot of each sample was separated by SDS-PAGE (10 % gel) (Raffatellu et al, 2005). Finally, effector proteins were immunodetected using mouse anti-FLAG M2-peroxidase (HRP) mAbs (Sigma).…”

Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

“…Similar cooperation occurs between Salmonella type III effector proteins to orchestrate bacterial entry into intestinal epithelial cells, an essential step in the development of enteritis. A large number of type III effector proteins working in concert are required to achieve maximal levels of Salmonella bacterial uptake (Raffatellu et al, 2005). These proteins cause a complex series of actin cytoskeletal changes, which result in the transient formation of localized host-cell surface membrane ruffles that engulf the invading bacteria.…”