Lammer C, Wagerer S, Saffrich R, Mertens D, Ansorge W, Hoffmann I
FS 6 Angewandte Tumorvirologie (F0400), Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 242, Germany.
J Cell Sci. 1998 Aug;111 ( Pt 16):2445-53. doi: 10.1242/jcs.111.16.2445.
Cdc25 phosphatases play key roles in cell cycle progression by activating cyclin-dependent kinases. In human cells, cdc25 proteins are encoded by a multigene family, consisting of cdc25A, cdc25B and cdc25C. While cdc25A plays a crucial role at the G1/S phase transition, cdc25C is involved in the dephosphorylation and activation of the mitotic kinase, cdc2/cyclinB. In addition, cdc25C itself is regulated by cdc2/cyclinB which then creates a positive feedback loop that controls entry into mitosis. In this study we show that the activity of cdc25B appears during late S phase and peaks during G2 phase. Both in vitro and in vivo cdc25B is activated through phosphorylation during S-phase. Using a cell duplication, microinjection assay we show that ablation of cdc25B function by specific antibodies blocks cell cycle progression in Hs68 cells by inhibition of entry into mitosis. Cdc25B function neither plays a role in later stages of mitosis nor for the inititation of DNA replication. These results indicate that cdc25B is a mitotic regulator that might act as a 'starter phosphatase' to initiate the positive feedback loop at the entry into M phase.
Cdc25磷酸酶通过激活细胞周期蛋白依赖性激酶在细胞周期进程中发挥关键作用。在人类细胞中，cdc25蛋白由一个多基因家族编码，该家族由cdc25A、cdc25B和cdc25C组成。虽然cdc25A在G1/S期转换中起关键作用，但cdc25C参与有丝分裂激酶cdc2/细胞周期蛋白B的去磷酸化和激活。此外，cdc25C本身受cdc2/细胞周期蛋白B调控，进而形成一个控制进入有丝分裂的正反馈环。在本研究中，我们发现cdc25B的活性在S期后期出现，并在G2期达到峰值。在体外和体内，cdc25B在S期通过磷酸化被激活。使用细胞复制、显微注射试验，我们发现用特异性抗体消除cdc25B功能会通过抑制进入有丝分裂来阻断Hs68细胞的细胞周期进程。Cdc25B功能在有丝分裂后期以及DNA复制起始过程中均不起作用。这些结果表明，cdc25B是一种有丝分裂调节因子，可能作为一种“起始磷酸酶”在进入M期时启动正反馈环。
