title: Distinct, constitutively active MAPK phosphatases function in Xenopus oocytes: implications for p42 MAPK regulation In vivo.
abstract: Xenopus oocyte maturation requires the phosphorylation and activation of p42 mitogen-activated protein kinase (MAPK). Likewise, the dephosphorylation and inactivation of p42 MAPK are critical for the progression of fertilized eggs out of meiosis and through the first mitotic cell cycle. Whereas the kinase responsible for p42 MAPK activation is well characterized, little is known concerning the phosphatases that inactivate p42 MAPK. We designed a microinjection-based assay to examine the mechanism of p42 MAPK dephosphorylation in intact oocytes. We found that p42 MAPK inactivation is mediated by at least two distinct phosphatases, an unidentified tyrosine phosphatase and a protein phosphatase 2A-like threonine phosphatase. The rates of tyrosine and threonine dephosphorylation were high and remained constant throughout meiosis, indicating that the dramatic changes in p42 MAPK activity seen during meiosis are primarily attributable to changes in MAPK kinase activity. The overall control of p42 MAPK dephosphorylation was shared among four partially rate-determining dephosphorylation reactions, with the initial tyrosine dephosphorylation of p42 MAPK being the most critical of the four. Our findings provide biochemical and kinetic insight into the physiological mechanism of p42 MAPK inactivation.
authors.affiliation: Department of Molecular Pharmacology and Program in Cancer Biology, Stanford University School of Medicine, Stanford, California 94305-5332, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Sohaskey
authors.forename: J E
authors.initials: JE
authors.lastname: Ferrell
mesh_terms: D000818:Animals; D004789:Enzyme Activation; D007700:Kinetics; D048369:MAP Kinase Kinase 1; D008540:Meiosis; D008845:Microinjections; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D009865:Oocytes; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology; D014981:Xenopus
chemical_list: D019319:Okadaic Acid; D013912:Threonine; D014638:Vanadates; D014443:Tyrosine; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases