Translocation of enterohemorrhagic Escherichia coli effector Tir to the plasma membrane via host Golgi apparatus

Abstract

The translocated intimin receptor (Tir) is a canonical type III secretion system effector, secreted by the enterohemorrhagic Escherichia coli (E. coli). This receptor alters the regular cellular processing of host cells, to promote intracellular bacterial replication and evasion of the host immune system. Tir is translocated and integrated into the host cell plasma membrane, a process required for its pathogenic activity in these cells, however, the underlying mechanisms of how this occurs remain to be elucidated. The present study used immunofluorescence and immunoelectron microscopy to demonstrate that the Tir of enterohemorrhagic E. coli was localized to the plasma membrane and colocalized with the 58K Golgi protein of the host cells. Treatment with brefeldin A destroyed the Golgi structure, inhibited the formation of actin pedestal and blocked the localization of Tir on the host cell plasma membrane. The results of the present study suggested that Tir is translocated to the host plasma membrane in a Golgi‑dependent manner. It may mimic the activities of eukaryotic secretory proteins in order to make use of the Golgi apparatus for transportation and integration into the plasma membrane. These findings reveal a novel trafficking pathway for the translocation of bacterial secretory effectors to their specific subcellular compartments.

Revealing the mechanisms of membrane protein export by virulence-associated bacterial secretion systems

“…While evidence suggests that membrane insertion of translocon-type TMD-effectors is aided by the needle tip of the injectisome 28 , 29 , it is not clear at this point whether host proteins aid in membrane targeting and insertion of non-translocon type TMD-effectors. It is striking that most investigated type III-secreted TMD-effectors insert into the membrane that is directly targeted by the T3SS injectisome (e.g., Tir, SseF, SseG), however, the mechanism of membrane insertion may not involve lateral partitioning through the T3SS translocon as recent data for Tir suggest 30 but cytoplasmic intermediates 31 . Hence, in addition to playing a role in targeting discrimination, the intermediate hydrophobic density of TMS of TMD-effector proteins may also serve to prevent aggregation of these proteins in the host cell cytoplasm while being sufficient to mediate association of their TMD with the interface of lipid bilayers of host cells and subsequent membrane insertion.…”

The Salmonella transmembrane effector SteD hijacks AP1-mediated vesicular trafficking for delivery to antigen-loading MHCII compartments

“…Enterohemorrhagic E . coli (EHEC) Tir was also shown to localise at the Golgi network by immunofluorescence and immunoelectron microscopy [ 23 ]. Exposure of host cells to BFA prior to infection with EHEC prevented pedestal formation, suggesting that Tir, like SteD must first pass through the Golgi before reaching its site of action at the PM [ 23 ].…”

“…coli (EHEC) Tir was also shown to localise at the Golgi network by immunofluorescence and immunoelectron microscopy [ 23 ]. Exposure of host cells to BFA prior to infection with EHEC prevented pedestal formation, suggesting that Tir, like SteD must first pass through the Golgi before reaching its site of action at the PM [ 23 ]. NleA/EspI, another EHEC effector, contains two putative transmembrane domains and was shown by triton-dependent solubilisation following fractionation of infected host cells to integrate into membranes [ 24 ].…”

The Salmonella transmembrane effector SteD hijacks AP1-mediated vesicular trafficking for delivery to antigen-loading MHCII compartments

“…Enterohemorrhagic E. coli (EHEC) Tir was also shown to localise at the Golgi network by immunofluorescence and immunoelectron microscopy (23). Exposure of host cells to BFA prior to infection with EHEC prevented pedestal formation, suggesting that Tir, like SteD must first pass through the Golgi before reaching its site of action at the PM (23). NleA/EspI, another EHEC effector, contains two putative transmembrane domains and was shown by triton-dependent solubilisation following fractionation of infected host cells to integrate into membranes (24).…”

“…Tir, a conserved T3SS effector of pathogenic E. coli with a similar membrane topology to SteD, localises to the PM where it induces actin pedestals and enables tight attachment of extracellular bacteria by binding to the bacterial surface protein, Intimin (22). Enterohemorrhagic E. coli (EHEC) Tir was also shown to localise at the Golgi network by immunofluorescence and immunoelectron microscopy (23). Exposure of host cells to BFA prior to infection with EHEC prevented pedestal formation, suggesting that Tir, like SteD must first pass through the Golgi before reaching its site of action at the PM (23).…”