title: PDK1 is required for the hormonal signaling pathway leading to meiotic resumption in starfish oocytes.
abstract: Meiotic resumption is generally under the control of an extracellular maturation-inducing hormone. It is equivalent to the G2-M phase transition in somatic cell mitosis and is regulated by cyclin B-Cdc2 kinase. However, the complete signaling pathway from the hormone to cyclin B-Cdc2 is yet unclear in any organism. A model system to analyze meiotic resumption is the starfish oocyte, in which Akt/protein kinase B (PKB) plays a key mediator in hormonal signaling that leads to cyclin B-Cdc2 activation. Here we show in starfish oocytes that when PDK1 activity is inhibited by a neutralizing antibody, maturation-inducing hormone fails to induce cyclin B-Cdc2 activation at the meiotic G2-M phase transition, even though PDK2 activity becomes detectable. These observations assign a novel role to PDK1 for a hormonal signaling intermediate toward meiotic resumption. They further support that PDK2 is a molecule distinct from PDK1 and Akt, and that PDK2 activity is not sufficient for the full activation of Akt in the absence of PDK1 activity.
authors.affiliation: Laboratory of Cell and Developmental Biology, Graduate School of Bioscience, Tokyo Institute of Technology, Nagatsuta, Midoriku, Yokohama 226-8501, Japan.
authors.forename: Daisaku
authors.initials: D
authors.lastname: Hiraoka
authors.forename: Sawako
authors.initials: S
authors.lastname: Hori-Oshima
authors.forename: Takeshi
authors.initials: T
authors.lastname: Fukuhara
authors.forename: Kazunori
authors.initials: K
authors.lastname: Tachibana
authors.forename: Eiichi
authors.initials: E
authors.lastname: Okumura
authors.forename: Takeo
authors.initials: T
authors.lastname: Kishimoto
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000378:metabolism; D016203:CDC2 Protein Kinase / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D004789:Enzyme Activation; D006133:Growth Substances / Q000378:metabolism*; D008540:Meiosis / Q000502:physiology*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*; D013215:Starfish
chemical_list: D000906:Antibodies; D019926:Cyclin B; D006133:Growth Substances; D011518:Proto-Oncogene Proteins; D064413:3-Phosphoinositide-Dependent Protein Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D016203:CDC2 Protein Kinase