Cyclin B/cdc2 induces c-Mos stability by direct phosphorylation in Xenopus oocytes.
The c-Mos proto-oncogene product plays an essential role during meiotic divisions in vertebrate eggs. In Xenopus, it is required for progression of oocyte maturation and meiotic arrest of unfertilized eggs. Its degradation after fertilization is essential to early embryogenesis. In this study we investigated the mechanisms involved in c-Mos degradation. We present in vivo evidence for ubiquitin-dependent degradation of c-Mos in activated eggs. We found that c-Mos degradation is not directly dependent on the anaphase-promoting factor activator Fizzy/cdc20 but requires cyclin degradation. We demonstrate that cyclin B/cdc2 controls in vivo c-Mos phosphorylation and stabilization. Moreover, we show that cyclin B/cdc2 is capable of directly phosphorylating c-Mos in vitro, inducing a similar mobility shift to the one observed in vivo. Tryptic phosphopeptide analysis revealed a practically identical in vivo and in vitro phosphopeptide map and allowed identification of serine-3 as the largely preferential phosphorylation site as previously described (Freeman et al., 1992). Altogether, these results demonstrate that, in vivo, stability of c-Mos is directly regulated by cyclin B/cdc2 kinase activity.
Castro
A
A
Centre de Recherche de Biochimie Macromoléculaire, Centre National de la Recherche Scientifique Unité Propre de Recherche 1086, 34293 Montpellier cedex 5, France. castro@crbm.cnrs-mop.fr
Peter
M
M
Magnaghi-Jaulin
L
L
Vigneron
S
S
Galas
S
S
Lorca
T
T
Labbé
J C
JC
D000818:Animals; D015153:Blotting, Western; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D019926:Cyclin B / Q000378:metabolism*; D004795:Enzyme Stability; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D009865:Oocytes / Q000378:metabolism*; D010449:Peptide Mapping; D010766:Phosphorylation; D011233:Precipitin Tests; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D014981:Xenopus / Q000378:metabolism*; D029867:Xenopus Proteins / Q000378:metabolism
D019926:Cyclin B; D011994:Recombinant Proteins; D025801:Ubiquitin; D029867:Xenopus Proteins; D017231:Proto-Oncogene Proteins c-mos; D016203:CDC2 Protein Kinase; D020928:Mitogen-Activated Protein Kinases