Bachmann Malte, Kosan Christian, Xing Pei Xiang, Montenarh Mathias, Hoffmann Ingrid, Möröy Tarik
Institut für Zellbiologie (Tumorforschung), IFZ, Universitätsklinikum Essen, Virchowstrasse 173, D-45122 Essen, Germany.
Int J Biochem Cell Biol. 2006 Mar;38(3):430-43. doi: 10.1016/j.biocel.2005.10.010. Epub 2005 Nov 8.
The proto-oncogene Pim-1 encodes a serine-threonine kinase which is a downstream effector of cytokine signaling and can enhance cell cycle progression by altering the activity of several cell cycle regulators among them the G1 specific inhibitor p21(Waf), the phosphatase Cdc25A and the kinase C-TAK1. Here, we demonstrate by using biochemical assays that Pim-1 can interact with the phosphatase Cdc25C and is able to directly phosphorylate the N-terminal region of the protein. Cdc25C is functionally related to Cdc25A but acts specifically at the G2/M cell cycle transition point and can be inactivated by C-TAK1-mediated phosphorylation. Immuno-fluorescence experiments showed that Pim-1 and Cdc25C co-localize in the cytoplasm of both epithelial and myeloid cells. We find that phosphorylation by Pim-1 enhances the phosphatase activity of Cdc25C and in transfected cells that are arrested in G2/M by bleomycin, Pim-1 can enhance progression into G1. Therefore, we propose that Pim-1 activates Cdc25C by a direct phosphorylation and can thereby assume the function of a positive cell cycle regulator at the G2/M transition.
原癌基因Pim-1编码一种丝氨酸-苏氨酸激酶，它是细胞因子信号传导的下游效应器，可通过改变几种细胞周期调节因子的活性来促进细胞周期进程，这些调节因子包括G1特异性抑制剂p21（Waf）、磷酸酶Cdc25A和激酶C-TAK1。在此，我们通过生化分析证明，Pim-1可与磷酸酶Cdc25C相互作用，并能够直接磷酸化该蛋白的N端区域。Cdc25C在功能上与Cdc25A相关，但在G2/M细胞周期转换点发挥特异性作用，并且可被C-TAK1介导的磷酸化作用失活。免疫荧光实验表明，Pim-1和Cdc25C在上皮细胞和髓样细胞的细胞质中共定位。我们发现，Pim-1介导的磷酸化作用增强了Cdc25C的磷酸酶活性，在因博来霉素而停滞于G2/M期的转染细胞中，Pim-1可促进细胞进入G1期。因此，我们提出Pim-1通过直接磷酸化作用激活Cdc25C，从而在G2/M转换过程中发挥正向细胞周期调节因子的功能。
