Rodier Geneviève, Coulombe Philippe, Tanguay Pierre-Luc, Boutonnet Christel, Meloche Sylvain
Institut de Recherche en Immunologie et Cancérologie, Université de Montréal, Montreal, Quebec, Canada.
EMBO J. 2008 Feb 20;27(4):679-91. doi: 10.1038/emboj.2008.6. Epub 2008 Jan 31.
The p27(Kip1) ubiquitin ligase receptor Skp2 is often overexpressed in human tumours and displays oncogenic properties. The activity of SCF(Skp2) is regulated by the APC(Cdh1), which targets Skp2 for degradation. Here we show that Skp2 phosphorylation on Ser64/Ser72 positively regulates its function in vivo. Phosphorylation of Ser64, and to a lesser extent Ser72, stabilizes Skp2 by interfering with its association with Cdh1, without affecting intrinsic ligase activity. Cyclin-dependent kinase (CDK)2-mediated phosphorylation of Skp2 on Ser64 allows its expression in mid-G1 phase, even in the presence of active APC(Cdh1). Reciprocally, dephosphorylation of Skp2 by the mitotic phosphatase Cdc14B at the M --> G1 transition promotes its degradation by APC(Cdh1). Importantly, lowering the levels of Cdc14B accelerates cell cycle progression from mitosis to S phase in an Skp2-dependent manner, demonstrating epistatic relationship of Cdc14B and Skp2 in the regulation of G1 length. Thus, our results reveal that reversible phosphorylation plays a key role in the timing of Skp2 expression in the cell cycle.
p27（Kip1）泛素连接酶受体Skp2在人类肿瘤中常过度表达，并具有致癌特性。SCF（Skp2）的活性受APC（Cdh1）调节，后者靶向Skp2进行降解。我们在此表明，Skp2在Ser64/Ser72位点的磷酸化在体内正向调节其功能。Ser64的磷酸化，以及程度较轻的Ser72的磷酸化，通过干扰Skp2与Cdh1的结合来稳定Skp2，而不影响其内在连接酶活性。细胞周期蛋白依赖性激酶（CDK）2介导的Skp2在Ser64位点的磷酸化使其在G1中期表达，即使在存在活性APC（Cdh1）的情况下也是如此。相反，有丝分裂磷酸酶Cdc14B在M期向G1期转变时对Skp2的去磷酸化促进了其被APC（Cdh1）降解。重要的是，降低Cdc14B的水平以Skp2依赖的方式加速了从有丝分裂到S期的细胞周期进程，证明了Cdc14B和Skp2在调节G1期长度中的上位关系。因此，我们的结果表明，可逆磷酸化在细胞周期中Skp2表达的时间调控中起关键作用。
