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In vitro GAP activity towards RhoA, Rac1 and Cdc42 is not a prerequisite for YopE induced HeLa cell cytotoxicity.
Umeå University, Faculty of Medicine, Molecular Biology.
Umeå University, Faculty of Medicine, Molecular Biology.
Umeå University, Faculty of Medicine, Molecular Biology.
Umeå University, Faculty of Medicine, Molecular Biology.
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2003 (English)In: Microbial Pathogenesis, ISSN 0882-4010, Vol. 34, no 6, 297-308 p.Article in journal (Refereed) Published
Abstract [en]

The YopE cytotoxin of Yersinia is an essential virulence determinant that is translocated into the eukaryotic target cell via a plasmid-encoded type III secretion system. YopE possess a GTPase activating protein activity that in vitro has been shown to down regulate RhoA, Rac1, and Cdc42. Translocated YopE induces de-polymerisation of the actin microfilament structure in the eukaryotic cell which results in a rounding up of infected cells described as a cytotoxic effect. Here, we have investigated the importance of different regions of YopE for induction of cytotoxicity and in vitro GAP activity. Sequential removal of the N- and C-terminus of YopE identified the region between amino acids 90 and 215 to be necessary for induction of cytotoxicity. Internal deletions containing the essential arginine at position 144 resulted in a total loss of cytotoxic response. In-frame deletions flanking the arginine finger defined a region important for the cytotoxic effect to amino acids 166–183. Four triple-alanine substitution mutants in this region, YopE166-8A, 169-71A, 175-7A and 178-80A were still able to induce cytotoxicity on HeLa cells although they did not show any in vitro GAP activity towards RhoA, Rac1 or Cdc42. A substitution mutant in position 206-8A showed the same phenotype, ability to induce cytotoxic response but no in vitro GAP activity. We speculate that YopE may have additional unidentified targets within the eukaryotic cell.

Place, publisher, year, edition, pages
2003. Vol. 34, no 6, 297-308 p.
URN: urn:nbn:se:umu:diva-4857DOI: 10.1016/S0882-4010(03)00063-9PubMedID: 12782482OAI: diva2:144116
Available from: 2005-11-24 Created: 2005-11-24Bibliographically approved
In thesis
1. Role of YopE and LcrH in effector translocation, HeLa cell cytotoxicity and virulence
Open this publication in new window or tab >>Role of YopE and LcrH in effector translocation, HeLa cell cytotoxicity and virulence
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In order to establish an extra-cellular infection the gram-negative bacteria Yersinia pseudotuberculosis uses a type III secretion system (T3SS) to translocate a set of anti-host effectors into eukaryotic cells. The toxins disrupt signalling pathways important for phagocytosis, cytokine production and cell survival. Secretion and translocation via this T3SS is strictly regulated on several levels. In this context, the function of YopE and LcrH during Yersinia infections has been analysed.

YopE is an essential translocated effector that disrupts the actin cytoskeleton of infected eukaryotic cells, by inactivating small GTPases through its GTPase activating protein (GAP) activity. However, cytotoxicity can be uncoupled from in vitro GAP activity towards the RhoA, Rac1 and Cdc42 GTPases. Furthermore, in vivo studies of the YopE GAP activity revealed that only RhoA and Rac1 are targeted, but this is not a pre-requisite for Yersinia virulence. Hence, YopE must target one or more additional GTPases to cause disease in mice.

YopE was the only Yersinia effector that blocks LDH release from infected cells. Moreover, translocated YopE could regulate the level of subsequent effector translocation by a mechanism that involved the YopE GAP function and another T3S component, YopK. Loss of translocation control elevated total T3S gene expression in the presence of eukaryotic cells. This indicated the existence of a regulatory loop for feedback control of T3S gene expression in the bacteria that originates from the interior of the eukaryotic cell after effector translocation is completed. This might represent the true virulence function of YopE.

Exoenzyme S (ExoS) of Pseudomonas aeruginosa has a YopE-like GAP domain with similar activity towards RhoA, Rac1 and Cdc42. However, ExoS is unable to complement hyper-translocation resulting from loss of YopE. This indicates a unique function for YopE in translocation control in Yersinia that might be dependent on correct intracellular localisation. It follows that the Membrane Localisation Domain in YopE was important for translocation control, but dispensable for cytotoxicity and blockage of LDH release.

YopD and its cognate chaperone LcrH are negative regulatory elements of the T3S regulon and together with YopB, are involved in the effector translocation process. Randomly generated point mutants in LcrH specifically effected stability and secretion of both the YopB and YopD substrates in vitro and prevented their apparent insertion as translocon pores in the membranes of infected cells. Yet, these mutants still produced stable substrates in the presence of eukaryotic cells and most could mediate at least partial effector translocation. Thus, only minimal amounts of the YopB and YopD translocator proteins are needed for translocation and the LcrH chaperone may regulate this process from inside the bacteria.

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Teknisk-naturvetenskaplig fakultet), 2005. 53 p.
Yersinia pseudotuberculosis, bacterial pathogenesis, YopE, LcrH, virulence, effector translocation, type III secretion, regulation
National Category
urn:nbn:se:umu:diva-646 (URN)91-7305-977-3 (ISBN)
Public defence
2005-12-16, 13:00 (English)
Available from: 2005-11-24 Created: 2005-11-24 Last updated: 2010-11-19Bibliographically approved

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