Protease triggers dephosphorylation of cdc2 kinase during starfish oocyte maturation

We previously presented evidence that a Z-Phe-Ser-argininal-susceptible protease which is involved in oocyte maturation of the starfish, Asterina pectinifera is the proteasome (Takagi Sawada et al, Dev. Biol. 150, 414-418 (1992)). In the present study, we investigated the timing of the function of and the role of the protease in oocyte maturation using Z-Phe-Ser-argininal. By adding the inhibitor in maturing oocytes at various times after 1-methyladenine treatment, the inhibitory ability was markedly reduced in half the time required for germinal vesicle breakdown. Furthermore, the inhibitor potently blocked the activation of histone H1 kinase and the dephosphorylation of cdc2 kinase during oocyte maturation. These results indicate that the Z-Phe-Ser-argininal-susceptible protease, probably the proteasome, plays a key role in the step of the signal transduction pathway that triggers the dephosphorylation of cdc2 kinase in response to the maturation-inducing hormone.