Haccard O, Jessus C, Cayla X, Goris J, Merlevede W, Ozon R
Institut National de la Recherche Agronomique/Unité Associeé du Centre National de la Recherche Scientifique 555, Université P. et M. Curie, Paris, France.
Eur J Biochem. 1990 Sep 24;192(3):633-42. doi: 10.1111/j.1432-1033.1990.tb19270.x.
We have characterized a serine/threonine protein kinase from Xenopus metaphase-II-blocked oocytes, which phosphorylates in vitro the microtubule-associated protein 2 (MAP2). The MAP2 kinase activity, undetectable in prophase oocytes, is activated during the progesterone-induced meiotic maturation (G2-M transition of the cell cycle). p-Nitrophenyl phosphate, a phosphatase inhibitor, is required to prevent spontaneous deactivation of the MAP2 kinase in crude preparations; conversely, the partially purified enzyme can be in vitro deactivated by the low-Mr polycation-stimulated (PCSL) phosphatase (also termed protein phosphatase 2A2), working as a phosphoserine/phosphothreonine-specific phosphatase and not as a phosphotyrosyl phosphatase indicating that phosphorylation of serine/threonine is necessary for its activity. S6 kinase, a protein kinase activated during oocyte maturation which phosphorylates in vitro ribosomal protein S6 and lamin C, can be deactivated in vitro by PCSL phosphatase. S6 kinase from prophase oocytes can also be activated in vitro in fractions known to contain all the factors necessary to convert pre-M-phase-promoting factor (pre-MPF) to MPF. Active MAP2 kinase can activate in vitro the inactive S6 kinase present in prophase oocytes or reactivate S6 kinase previously inactivated in vitro by PCSL phosphatase. These data are consistent with the hypothesis that the MAP2 kinase is a link of the meiosis signalling pathway and is activated by a serine/threonine kinase. This will lead to the regulation of further steps in the cell cycle, such as microtubular reorganisation and S6 kinase activation.
我们已对非洲爪蟾中期II阻滞卵母细胞中的一种丝氨酸/苏氨酸蛋白激酶进行了特性分析，该激酶可在体外使微管相关蛋白2（MAP2）磷酸化。在前期卵母细胞中无法检测到的MAP2激酶活性，在孕酮诱导的减数分裂成熟过程中（细胞周期的G2-M转换）被激活。对粗制品中的MAP2激酶而言，磷酸酶抑制剂对硝基苯磷酸是防止其自发失活所必需的；相反，部分纯化的酶可在体外被低分子量聚阳离子刺激的（PCSL）磷酸酶（也称为蛋白磷酸酶2A2）失活，该磷酸酶作为一种磷酸丝氨酸/磷酸苏氨酸特异性磷酸酶起作用，而非磷酸酪氨酸磷酸酶，这表明丝氨酸/苏氨酸的磷酸化对其活性是必需的。S6激酶是一种在卵母细胞成熟过程中被激活的蛋白激酶，可在体外使核糖体蛋白S6和核纤层蛋白C磷酸化，它可在体外被PCSL磷酸酶失活。前期卵母细胞中的S6激酶在已知含有将前促有丝分裂因子（pre-MPF）转化为MPF所需的所有因子的组分中也可在体外被激活。活性MAP2激酶可在体外激活前期卵母细胞中存在的无活性S6激酶，或使先前在体外被PCSL磷酸酶失活的S6激酶重新激活。这些数据与以下假设一致，即MAP2激酶是减数分裂信号通路的一个环节，并由一种丝氨酸/苏氨酸激酶激活。这将导致细胞周期后续步骤的调控，如微管重组和S6激酶激活。
