Akt/protein kinase B isoforms are differentially regulated by epidermal growth factor stimulation.
Overexpression of epidermal growth factor receptor (EGFR) in certain cancers is well established. There is growing evidence that epidermal growth factor (EGF) activates Akt/protein kinase B (PKB) in a phosphoinositide 3-OH kinase (PI3K)-dependent manner, but it is not yet clear which Akt isoforms are involved in this signal transduction pathway. We investigated the functional regulation of three Akt isoforms, Akt1/PKBalpha, Akt2/PKBbeta, and Akt3/PKBgamma, in esophageal cancer cells where EGFR is frequently overexpressed. Upon EGF simulation, phosphorylation of Akt1 at the Ser-473 residue was remarkably induced. This result was corroborated by in vitro Akt kinase assays using glycogen synthase kinase 3beta as the substrate. PI3K inhibitors, wortmannin or LY294002, significantly blocked the Akt kinase activity induced by EGF. Akt2 activity was evaluated by electrophoretic mobility shift assays. Robust activation of Akt2 by EGF was observed in some cell lines in a PI3K-dependent manner. EGF-induced Akt3 activation was demonstrated by Ser-472 phosphorylation of Akt3 but in a restrictive fashion. In aggregate, EGF-mediated activation of Akt isoforms is overlapping and distinctive. The mechanism by which EGFR recruits the PI3K/Akt pathway was in part differentially regulated at the level of Ras but independent of heterodimerization of EGFR with either ErbB2 or ErbB3 based upon functional dissection of pathways in esophageal cancer cell lines.
Okano
J
J
Division of Gastroenterology, Howard Hughes Medical Institute, Cancer Center, and Department of Genetics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Gaslightwala
I
I
Birnbaum
M J
MJ
Rustgi
A K
AK
Nakagawa
H
H
D000730:Androstadienes / Q000494:pharmacology; D015139:Blotting, Southern; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D019281:Dimerization; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism*; D004938:Esophageal Neoplasms / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006801:Humans; D008024:Ligands; D009025:Morpholines / Q000494:pharmacology; D015513:Oncogene Proteins / Q000737:chemistry*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011233:Precipitin Tests; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry*; D011518:Proto-Oncogene Proteins / Q000737:chemistry*; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry / Q000378:metabolism; D020893:Receptor, ErbB-3 / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D000077191:Wortmannin; D018631:ras Proteins / Q000737:chemistry / Q000378:metabolism
D000730:Androstadienes; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002867:Chromones; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D008024:Ligands; D009025:Morpholines; D015513:Oncogene Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3; D012694:Serine; D014443:Tyrosine; D000077191:Wortmannin; D018631:ras Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C494921:AKT2 protein, human; C491754:AKT3 protein, human