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Vol. 18, Issue 1, 119-128, January 2007
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*Department of Structural Analysis, National Cardiovascular Center Research Institute, Osaka 565-8565, Japan; Department of Pathology and Biology of Diseases, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan; and Institute of Molecular and Cellular Biosciences, University of Tokyo, Tokyo 113-0032, Japan
Submitted May 31, 2006;
Revised October 16, 2006;
Accepted October 19, 2006
Monitoring Editor: Martin A. Schwartz
We studied the spatiotemporal regulation of Akt (also called protein kinase B), phosphatidylinositol-3,4-bisphosphate [PtdIns(3,4)P2], and phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P3] by using probes based on the principle of fluorescence resonance energy transfer. On epidermal growth factor (EGF) stimulation, the amount of PtdIns(3,4,5)P3 was increased diffusely in the plasma membrane, whereas that of PtdIns(3,4)P2 was increased more in the nascent lamellipodia than in the plasma membrane of the central region. The distribution and time course of Akt activation were similar to that of increased PtdIns(3,4)P2 levels, which were most prominent in the nascent lamellipodia. Moreover, we found that upon EGF stimulation 3-phosphoinositide–dependent protein kinase-1 (PDK1) was also recruited to nascent lamellipodia in an Akt-dependent manner. Because PDK1 is known to activate Ral GTPase and because Ral is required for EGF-induced lamellipodial protrusion, we speculated that the PDK1–Akt complex may be indispensable for the induction of lamellipodia. In agreement with this idea, EGF-induced lamellipodia formation was promoted by the overexpression of Akt and inhibited by an Akt inhibitor or a Ral-binding domain of Sec5. These results identified the Akt–PDK1 complex as an upstream positive regulator of Ral GTPase in the induction of lamellipodial protrusion.
The online version of this contains supplemental material at MBC Online (http://www.molbiolcell.org). This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E06-05-0467) on November 1, 2006.
Address correspondence to: Michiyuki Matsuda (matsudam{at}path1.med.kyoto-u.ac.jp)
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