Akt-PDK1 complex mediates epidermal growth factor-induced membrane protrusion through Ral activation.
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.
Yoshizaki
Hisayoshi
H
Department of Structural Analysis, National Cardiovascular Center Research Institute, Osaka 565-8565, Japan.
Mochizuki
Naoki
N
Gotoh
Yukiko
Y
Matsuda
Michiyuki
M
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000187:drug effects; D002522:Chlorocebus aethiops; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D031541:Fluorescence Resonance Energy Transfer; D047468:Immunoprecipitation; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism*; D041681:NIH 3T3 Cells; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011554:Pseudopodia / Q000187:drug effects*; D020725:ral GTP-Binding Proteins / Q000378:metabolism*; D020726:ral Guanine Nucleotide Exchange Factor / Q000378:metabolism*
D009097:Multienzyme Complexes; D018129:Phosphatidylinositol Phosphates; C060980:phosphatidylinositol 3,4-diphosphate; D020726:ral Guanine Nucleotide Exchange Factor; D004815:Epidermal Growth Factor; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578564:Pdpk1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020725:ral GTP-Binding Proteins