title: PDK1 mediates growth factor-induced Ral-GEF activation by a kinase-independent mechanism.
abstract: Ras proteins transduce extracellular signals to intracellular signaling pathways by binding to and promoting the activation of at least three classes of downstream signaling molecules: Raf kinases, phosphoinositide-3-kinase (PI3-K) and Ral guanine nucleotide exchange factors (Ral-GEFs). Previous work has demonstrated that epidermal growth factor (EGF) activates Ral-GEFs, at least in part, by a Ras-mediated redistribution of the GEFs to their target, Ral-GTPases, in the plasma membrane. Here we show that Ral-GEF stimulation by EGF involves an additional mechanism, PI3-K-dependent kinase 1 (PDK1)-induced enhancement of Ral-GEF catalytic activity. Remarkably, this PDK1 function is not dependent upon its kinase activity. Instead, the non-catalytic N-terminus of PDK1 mediates the formation of an EGF-induced complex with the N-terminus of the Ral-GEF, Ral-GDS, thereby relieving its auto-inhibitory effect on the catalytic domain of Ral-GDS. These results elucidate a novel function for PDK1 and demonstrate that two Ras effector pathways cooperate to promote Ral-GTPase activation.
authors.affiliation: Department of Biochemistry, Tufts University School of Medicine, Boston, MA 02111, USA.
authors.forename: Xuejun
authors.initials: X
authors.lastname: Tian
authors.forename: Gabriel
authors.initials: G
authors.lastname: Rusanescu
authors.forename: Weimin
authors.initials: W
authors.lastname: Hou
authors.forename: Brian
authors.initials: B
authors.lastname: Schaffhausen
authors.forename: Larry A
authors.initials: LA
authors.lastname: Feig
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D019556:COS Cells; D002461:Cell Line, Transformed; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020725:ral GTP-Binding Proteins; D020726:ral Guanine Nucleotide Exchange Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D064413:3-Phosphoinositide-Dependent Protein Kinases; D004815:Epidermal Growth Factor; D020558:GTP Phosphohydrolases; D010455:Peptides; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011993:Recombinant Fusion Proteins; D020725:ral GTP-Binding Proteins; D020726:ral Guanine Nucleotide Exchange Factor; C578562:PDPK1 protein, human; C492198:RALA protein, human