title: Involvement of Ca2+-dependent proteasome in the degradation of both cyclin B1 and Mos during spontaneous activation of matured rat oocytes.
abstract: In matured rat oocytes, spontaneous activation from the metaphase-II (MII) stage occurred after collection from the oviducts. It is well known that the mitogen-activated protein kinase (MAPK) pathway and p34(cdc2) kinase play an important role in the arrest at MII in other species. However, there is no information about the difference in these factors among strains of rats. In the present study, in spontaneously activated oocytes from the Wistar rat, the Mos protein level and the activity of MAPK kinase (MEK)/MAPK were decreased at 120 min (13.8, 25.7, and 19.3, respectively, P<0.05), whereas Sprague-Dawley (SD) oocytes, which were not spontaneously activated, had a high level of Mos protein and MEK/MAPK activity (75.9, 76.2, and 87.9, respectively, P<0.05). Phosphorylation of MAPK in the SD oocytes was significantly suppressed by MEK inhibitor, U0126 at 60 min; this treatment decreased p34(cdc2) kinase activity via cyclin B1 degradation in a time-dependent manner. The treatment with proteasome inhibitor, MG132 or Ca2+-chelator, BAPTA-AM, overcame the spontaneous degradation of both Mos and cyclin B1 in a dose-dependent manner in Wistar oocytes. More than 90% of Wistar oocytes treated with BAPTA-AM were arrested at MII until 120 min. In conclusion, SD oocytes carrying Mos/MEK/MAPK, maintained a high activity of p34(cdc2) kinase by stabilizing cyclin B1, thus involved in their meiotic arrest. In contrast, Wistar oocytes had a relatively low cytostatic factor activity; rapid decrease of Mos/MEK/MAPK failed to stabilize both cyclin B1 and Mos, and these oocytes were likely to spontaneously activate.
authors.affiliation: Section of Molecular Genetics, Center for Brain Experiment, National Institute for Physiological Sciences, Okazaki, Aichi 444-8787, Japan. jito@vasci.umass.edu
authors.forename: Junya
authors.initials: J
authors.lastname: Ito
authors.forename: Masayuki
authors.initials: M
authors.lastname: Shimada
authors.forename: Shinichi
authors.initials: S
authors.lastname: Hochi
authors.forename: Masumi
authors.initials: M
authors.lastname: Hirabayashi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D049109:Cell Proliferation; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D005260:Female; D007976:Leupeptins / Q000494:pharmacology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D017232:Oncogene Proteins v-mos / Q000378:metabolism*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013997:Time Factors; D000095043:Cyclin-Dependent Kinase-Activating Kinase
chemical_list: C534701:Ccnb1 protein, rat; D019926:Cyclin B; D056744:Cyclin B1; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D017232:Oncogene Proteins v-mos; D018844:Cyclin-Dependent Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D002118:Calcium; D000095043:Cyclin-Dependent Kinase-Activating Kinase