Cyclin A Potentiates Maturation-Promoting Factor Activation in the Early Xenopus Embryo via Inhibition of the Tyrosine Kinase That Phosphorylates CDC2

• Published in: The Journal of cell biology 1992-09, Vol.118 (5), p.1109-1120
• Main Authors: Devault, Alain, Fesquet, Didier, Cavadore, Jean-Claude, Garrigues, Anne-Marie, Labbé, Jean-Claude, Lorca, Thierry, Picard, André, Philippe, Michel, Dorée, Marcel
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Biological and medical sciences; CDC2 Protein Kinase - metabolism; Cell cycle; Cell differentiation, maturation, development, hematopoiesis; Cell physiology; Cellular biology; Cyclins; Cyclins - metabolism; Eggs; Embryos; Enzyme Activation; Ethers, Cyclic - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Interphase; Maturation-Promoting Factor - metabolism; Mitosis; Models, Biological; Molecular and cellular biology; Molecular Sequence Data; Okadaic Acid; Oocytes; Phosphatases; Phosphorylation; Protein-Tyrosine Kinases - antagonists & inhibitors; Protein-Tyrosine Kinases - metabolism; Tyrosine - metabolism; Vanadates; Vanadates - pharmacology; Xenopus
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.118.5.1109

We have produced human cyclin A in Escherichia coli and investigated how it generates H1 kistone kinase activity when added to cyclin-free extracts prepared from parthenogenetically activated Xenopus eggs. Cyclin A was found to form a major complex with cdc2, and to bind cdk2/Eg1 only poorly. No lag phase was detected between the time when cyclin A was added and the time when H1 histone kinase activity was produced in frog extracts, even in the presence of 2 mM vanadate, which blocks cdc25 activity. Essentially identical results were obtained using extracts prepared from starfish oocytes. We conclude that formation of an active cyclin A-cdc2 kinase during early development escapes an inhibitory mechanism that delays formation of an active cyclin B-cdc2 kinase. This inhibitory mechanism involves phosphorylation of cdc2 on tyrosine 15. Okadaic acid (OA) activated cyclin B-cdc2 kinase and strongly reduced tyrosine phosphorylation of cyclin B-associated cdc2, even in the presence of vanadate. 6-dimethylaminopurine, a reported inhibitor of serine-threonine kinases, suppressed OA-dependent activation of cyclin B-cdc2 complexes. This indicates that the kinase(s) which phosphorylate(s) cdc2 on inhibitory sites can be inactivated by a phosphorylation event, itself antagonized by an OA-sensitive, most likely type 2A phosphatase. We also found that cyclin B- or cyclin A-cdc2 kinases can induce or accelerate conversion of the cyclin B-cdc2 complex from an inactive into an active kinase. Cyclin B-associated cdc2 does not undergo detectable phosphorylation on tyrosine in egg extracts containing active cyclin A-cdc2 kinase, even in the presence of vanadate. We propose that the active cyclin A-cdc2 kinase generated without a lag phase from neo-synthesized cyclin A and cdc2 may cause a rapid switch in the equilibrium of cyclin B-cdc2 complexes to the tyrosine-dephosphorylated and active form of cdc2 during early development, owing to strong inhibition of the cdc2-specific tyrosine kinase(s). This may explain why early cell cycles are so rapid in many species.