Salmonella enterica serotype Typhimurium invades eukaryotic cells by re-arranging the host-cell cytoskeleton. However, the precise mechanisms by which Salmonella induces cytoskeletal changes remain undefined. IQGAP1 (IQ motif-containing GTPase-activating protein 1) is a scaffold protein that binds multiple proteins including actin, the Rho GTPases Rac1 and Cdc42 (cell division cycle 42), and components of the MAPK (mitogen-activated protein kinase) pathway. We have shown previously that optimal invasion of Salmonella into HeLa cells requires IQGAP1. In the present paper, we use IQGAP1-null MEFs (mouse embryonic fibroblasts) and selected well-characterized IQGAP1 mutant constructs to dissect the molecular determinants of Salmonella invasion. Knockout of IQGAP1 expression reduced Salmonella invasion into MEFs by 75%. Reconstituting IQGAP1-null MEFs with wild-type IQGAP1 completely rescued invasion. By contrast, reconstituting IQGAP1-null cells with mutant IQGAP1 constructs that specifically lack binding to either Cdc42 and Rac1 (termed IQGAP1ΔMK24), actin, MEK [MAPK/ERK (extracellular-signal-regulated kinase) kinase] or ERK only partially restored Salmonella entry. Cell-permeant inhibitors of Rac1 activation or MAPK signalling reduced Salmonella invasion into control cells by 50%, but had no effect on bacterial entry into IQGAP1-null MEFs. Importantly, the ability of IQGAP1ΔMK24 to promote Salmonella invasion into IQGAP1-null cells was abrogated by chemical inhibition of MAPK signalling. Collectively, these results imply that the scaffolding function of IQGAP1, which integrates Rac1 and MAPK signalling, is usurped by Salmonella to invade fibroblasts and suggest that IQGAP1 may be a potential therapeutic target for Salmonella pathogenesis.
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Research Article|
November 28 2011
Salmonella enterica serotype Typhimurium usurps the scaffold protein IQGAP1 to manipulate Rac1 and MAPK signalling
Hugh Kim;
Hugh Kim
*Department of Translational Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, U.S.A.
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Colin D. White;
Colin D. White
†Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02115, U.S.A.
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Zhigang Li;
Zhigang Li
‡Department of Laboratory Medicine, National Institutes of Health, Bethesda, MD 20892, U.S.A.
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David B. Sacks
David B. Sacks
1
‡Department of Laboratory Medicine, National Institutes of Health, Bethesda, MD 20892, U.S.A.
1To whom correspondence should be addressed (email david.sacks2@nih.gov).
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Publisher: Portland Press Ltd
Received:
March 07 2011
Revision Received:
July 18 2011
Accepted:
August 18 2011
Accepted Manuscript online:
August 18 2011
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2011 Biochemical Society
2011
Biochem J (2011) 440 (3): 309–318.
Article history
Received:
March 07 2011
Revision Received:
July 18 2011
Accepted:
August 18 2011
Accepted Manuscript online:
August 18 2011
Citation
Hugh Kim, Colin D. White, Zhigang Li, David B. Sacks; Salmonella enterica serotype Typhimurium usurps the scaffold protein IQGAP1 to manipulate Rac1 and MAPK signalling. Biochem J 15 December 2011; 440 (3): 309–318. doi: https://doi.org/10.1042/BJ20110419
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