Mitogen-activated protein kinase (MAP kinase) activation in Xenopus oocytes: roles of MPF and protein synthesis.
Mitogen-activated protein kinase (MAP kinase) is a serine/threonine kinase whose enzymatic activity is thought to play a crucial role in mitogenic signal transduction and also in the progesterone-induced meiotic maturation of Xenopus oocytes. We have purified MAP kinase from Xenopus oocytes and have shown that the protein is present in metaphase II oocytes under two different forms: an inactive 41-kD protein able to autoactivate and to autophosphorylate in vitro, and an active 42-kD kinase resolved into two tyrosine phosphorylated isoforms on 2D gels. During meiotic maturation, MAP kinase becomes tyrosine phosphorylated and activated following the activation of the M-phase promoting factor (MPF), a complex between the p34cdc2 kinase and cyclin B. In vivo, MAP kinase activity displays a different stability in metaphase I and in metaphase II: protein synthesis is required to maintain MAP kinase activity in metaphase I but not in metaphase II oocytes. Injection of either MPF or cyclin B into prophase oocytes promotes tyrosine phosphorylation of MAP kinase, indicating that its activation is a downstream event of MPF activation. In contrast, injection of okadaic acid, which induces in vivo MPF activation, promotes only a very weak tyrosine phosphorylation of MAP kinase, suggesting that effectors other than MPF are required for the MAP kinase activation. Moreover, in the absence of protein synthesis, cyclin B and MPF are unable to promote in vivo activation of MAP kinase, indicating that this activation requires the synthesis of new protein(s).
Haccard
O
O
INRA/URA CNRS 1449, Université P. et M. Curie, Paris, France.
Jessus
C
C
Rime
H
H
Goris
J
J
Merlevede
W
W
Ozon
R
R
D000818:Animals; D004789:Enzyme Activation; D004988:Ethers, Cyclic / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D016200:Maturation-Promoting Factor / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1; D019319:Okadaic Acid; D009865:Oocytes / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism; D014982:Xenopus laevis
D004988:Ethers, Cyclic; D019319:Okadaic Acid; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D016200:Maturation-Promoting Factor; D019950:Mitogen-Activated Protein Kinase 1