G-protein betagamma subunit-dependent phosphorylation of 62-kDa protein in the early signaling pathway of starfish oocyte maturation induced by 1-methyladenine.
In starfish oocytes, maturation is induced by a hormone, 1-methyladenine (1-MA), that binds to the receptors exposed to the outer surface of the plasma membrane. The signal of 1-MA stimulates the heterotrimeric G protein, resulting in dissociation of the betagamma subunit of G protein (Gbetagamma) from a pertussis toxin-sensitive Gi-type alpha subunit. To investigate the targets for Gbetagamma, we analyzed 1-MA- or Gbetagamma-dependent phosphorylation using in vivo and in vitro systems. A 62-kDa protein was phosphorylated immediately after 1-MA treatment in intact oocytes. In the cell-free preparations, the 62-kDa protein was also phosphorylated on serine residue(s) immediately after addition of 1-MA or Gbetagamma. The Gbetagamma-dependent phosphorylation of the 62-kDa protein was inhibited by wortmannin or LY294002, which are mechanistically different inhibitors of phosphatidylinositol 3-kinase (PI3K). LY294002 also inhibited Gbetagamma- as well as 1-MA-induced maturation of oocytes. Taken together, these results indicate that the 62-kDa protein functions downstream of Gbetagamma and PI3K in the early signaling pathway of 1-MA-induced starfish oocyte maturation. The phosphorylation of the 62-kDa protein may be required for the activation of maturation-promoting factor.
Nakano
T
T
Department of Biology, Ochanomizu University, 2-1-1 Ohtsuka, Tokyo, 112-8610, Japan.
Kontani
K
K
Kurosu
H
H
Katada
T
T
Hoshi
M
M
Chiba
K
K
D000225:Adenine / Q000031:analogs & derivatives* / Q000378:metabolism; D000730:Androstadienes / Q000378:metabolism; D000818:Animals; D002867:Chromones / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008845:Microinjections; D009025:Morpholines / Q000378:metabolism; D009865:Oocytes / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction; D013215:Starfish / Q000254:growth & development*; D013997:Time Factors; D000077191:Wortmannin
D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C008407:1-methyladenine; D019869:Phosphatidylinositol 3-Kinases; D019204:GTP-Binding Proteins; D000225:Adenine; D000077191:Wortmannin