A role for Cdc2- and PP2A-mediated regulation of Emi2 in the maintenance of CSF arrest.
BACKGROUND
Vertebrate oocytes are arrested in metaphase II of meiosis prior to fertilization by cytostatic factor (CSF). CSF enforces a cell-cycle arrest by inhibiting the anaphase-promoting complex (APC), an E3 ubiquitin ligase that targets Cyclin B for degradation. Although Cyclin B synthesis is ongoing during CSF arrest, constant Cyclin B levels are maintained. To achieve this, oocytes allow continuous slow Cyclin B degradation, without eliminating the bulk of Cyclin B, which would induce release from CSF arrest. However, the mechanism that controls this continuous degradation is not understood.


RESULTS
We report here the molecular details of a negative feedback loop wherein Cyclin B promotes its own destruction through Cdc2/Cyclin B-mediated phosphorylation and inhibition of the APC inhibitor Emi2. Emi2 bound to the core APC, and this binding was disrupted by Cdc2/Cyclin B, without affecting Emi2 protein stability. Cdc2-mediated phosphorylation of Emi2 was antagonized by PP2A, which could bind to Emi2 and promote Emi2-APC interactions.


CONCLUSIONS
Constant Cyclin B levels are maintained during a CSF arrest through the regulation of Emi2 activity. A balance between Cdc2 and PP2A controls Emi2 phosphorylation, which in turn controls the ability of Emi2 to bind to and inhibit the APC. This balance allows proper maintenance of Cyclin B levels and Cdc2 kinase activity during CSF arrest.
Wu
Qiju
Q
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Guo
Yanxiang
Y
Yamada
Ayumi
A
Perry
Jennifer A
JA
Wang
Michael Z
MZ
Araki
Marito
M
Freel
Christopher D
CD
Tung
Jeffrey J
JJ
Tang
Wanli
W
Margolis
Seth S
SS
Jackson
Peter K
PK
Yamano
Hiroyuki
H
Asano
Maki
M
Kornbluth
Sally
S
D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D018076:DNA, Complementary; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044783:F-Box Proteins / Q000378:metabolism*; D015723:Gene Library; D006801:Humans; D008540:Meiosis; D019319:Okadaic Acid / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism*
D064199:Cdc20 Proteins; C577501:Cdc20 protein, Xenopus; D018797:Cell Cycle Proteins; D019926:Cyclin B; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; D044783:F-Box Proteins; C498166:FBXO43 protein, Xenopus; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins; D019319:Okadaic Acid; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D017231:Proto-Oncogene Proteins c-mos; D016203:CDC2 Protein Kinase; D010749:Phosphoprotein Phosphatases