%0 Journal Article
%T Activated ¦Á2-Macroglobulin Binding to Cell Surface GRP78 Induces T-Loop Phosphorylation of Akt1 by PDK1 in Association with Raptor
%A Uma Kant Misra
%A Salvatore Vincent Pizzo
%J PLOS ONE
%D 2014
%I Public Library of Science (PLoS)
%R 10.1371/journal.pone.0088373
%X PDK1 phosphorylates multiple substrates including Akt by PIP3-dependent mechanisms. In this report we provide evidence that in prostate cancer cells stimulated with activated ¦Á2-macroglobulin (¦Á2M*) PDK1 phosphorylates Akt in the T-loop at Thr308 by using Raptor in the mTORC1 complex as a scaffold protein. First we demonstrate that PDK1, Raptor, and mTOR co-immunoprecipitate. Silencing the expression, not only of PDK1, but also Raptor by RNAi nearly abolished Akt phosphorylation at AktThr308 in Raptor-immunoprecipitates of ¦Á2M*-stimulated prostate cancer cells. Immunodepleting Raptor or PDK from cell lysates of cells treated with ¦Á2M* drastically reduced Akt phosphorylation at Thr308, which was recovered by adding the supernatant of Raptor- or PDK1-depleted cell lysates, respectively. Studies of insulin binding to its receptor on prostate cancer cells yielded similar results. We thus demonstrate that phosphorylating the T-loop Akt residue Thr308 by PDK1 requires Raptor of the mTORC1 complex as a platform or scaffold protein.
%U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0088373