Activation of p34 cdc2 kinase by cyclin is negatively regulated by cyclic Amp-dependent protein kinase in Xenopus oocytes

Abstract

Microinjection of a bacterially expressed stable Δ90 sea urchin cyclin B into Xenopus prophase oocytes, in absence or presence of cycloheximide, provokes the activation of histone H1 kinase and the tyrosine dephosphorylation of p34 cdc2 Unexpectedly, when prophase oocytes are submitted to a treatment known to elevate the intracellular cAMP level (3-isobutyl-1-methylxanthine and cholera toxin), Δ90 cyclin has no effect and the oocytes remain blocked in prophase. This inhibition is reverted by the microinjection of the inhibitor of cAMP-dependent protein kinase. When Δ90 cyclin is microinjected into oocytes depleted of endogenous cyclins (cycloheximide-treated metaphase I) and in the presence of a high intracellular concentration of cAMP, p34 cdc2 kinase is tyrosine rephosphorylated. Altogether, our results indicate that in Xenopus oocyte, cAMP-dependent protein kinase (A-kinase) controls the formation of the cyclin B/p34 cdc2 complex which remains inactive and tyrosine phosphorylated.