The phosphoinositol-3-kinase-protein kinase B/Akt pathway is critical for Pseudomonas aeruginosa strain PAK internalization

Department of Medicine, University of California, San Francisco, San Francisco, CA 94143, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 06/2005; 16(5):2577-85. DOI: 10.1091/mbc.E04-08-0717
Source: PubMed


Several Pseudomonas aeruginosa strains are internalized by epithelial cells in vitro and in vivo, but the host pathways usurped by the bacteria to enter nonphagocytic cells are not clearly understood. Here, we report that internalization of strain PAK into epithelial cells triggers and requires activation of phosphatidylinositol 3-kinase (PI3K) and protein kinase B/Akt (Akt). Incubation of Madin-Darby canine kidney (MDCK) or HeLa cells with the PI3K inhibitors LY294002 (LY) or wortmannin abrogated PAK uptake. Addition of the PI3K product phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] to polarized MDCK cells was sufficient to increase PAK internalization. PtdIns(3,4,5)P3 accumulated at the site of bacterial binding in an LY-dependent manner. Akt phosphorylation correlated with PAK invasion. The specific Akt phosphorylation inhibitor SH-5 inhibited PAK uptake; internalization also was inhibited by small interfering RNA-mediated depletion of Akt phosphorylation. Expression of constitutively active Akt was sufficient to restore invasion when PI3K signaling was inhibited. Together, these results demonstrate that the PI3K signaling pathway is necessary and sufficient for the P. aeruginosa entry and provide the first example of a bacterium that requires Akt for uptake into epithelial cells.

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    • "Studies on the involvement of mTOR in actin regulation have shown that knockdown of rictor resulted in defective actin cytoskeleton rearrangement [12,13]. Moreover, ERK and Akt signaling molecules are regulated by mTORC2, and these molecules seem to be implicated in actin regulation, as exemplified by the necessity for ERK in the cell entry of Francisella novicida [7] and Chlamydia pneumoniae [23], and for Akt in the internalization of Pseudomonas aeruginosa [24]. Downstream effectors of mTORC1, such as the 70 kDa ribosomal S6 kinase (p70S6K), known to be important in cell growth, have been recently reported to also regulate the actin cytoskeleton [11]. "
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