Degradation of polyubiquitinated cyclin B is blocked by the MAPK pathway at the metaphase I arrest in starfish oocytes.
In the starfish ovary, maturing oocytes stimulated by 1-methyladenine undergo synchronous germinal vesicle breakdown and then arrest in metaphase of the first meiotic division (metaphase I). Immediately after spawning, an increase of intracellular pH (pH(i)) from approximately 7.0 to approximately 7.3 is induced by Na(+)/H(+) antiporter in oocytes, and meiosis reinitiation occurs. Here we show that an endogenous substrate of the proteasome, polyubiquitinated cyclin B, was stable at pH 7.0, whereas it was degraded at pH 7.3. When the MAPK pathway was blocked by MEK inhibitor U0126, degradation of polyubiquitinated cyclin B occurred even at pH 7.0 without an increase of the peptidase activity of the proteasome. These results indicate that the proteasome activity at pH 7.0 is sufficient for degradation of polyubiquitinated cyclin B and that the MAPK pathway blocks the degradation of polyubiquitinated cyclin B in the maturing oocytes in the ovary. Immediately after spawning, the increase in pH(i) mediated by Na(+)/H(+) antiporter cancels the inhibitory effects of the MAPK pathway, resulting in the degradation of polyubiquitinated cyclin B and the release of the arrest. Thus, the key step of metaphase I arrest in starfish oocytes occurs after the polyubiqutination of cyclin B but before cyclin B proteolysis by the proteasome.
Department of Biology, Ochanomizu University, 2-1-1 Ohtsuka, Tokyo 112-8610, Japan.
Eiko
E
Oita
Kaori
K
Harada
Kazuyoshi
K
Chiba
D000818:Animals; D002474:Cell-Free System; D019926:Cyclin B / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D020935:MAP Kinase Signaling System; D008677:Metaphase; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D025821:Polyubiquitin / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D013215:Starfish
D019926:Cyclin B; D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D025821:Polyubiquitin; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex