Biggs Joseph R, Peterson Luke F, Zhang Youhong, Kraft Andrew S, Zhang Dong-Er
Division of Oncovirology, Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Rd., MEM-L51, La Jolla, CA 92037, USA.
Mol Cell Biol. 2006 Oct;26(20):7420-9. doi: 10.1128/MCB.00597-06. Epub 2006 Aug 5.
AML1 (RUNX1) regulates hematopoiesis, angiogenesis, muscle function, and neurogenesis. Previous studies have shown that phosphorylation of AML1, particularly at serines 276 and 303, affects its transcriptional activation. Here, we report that phosphorylation of AML1 serines 276 and 303 can be blocked in vivo by inhibitors of the cyclin-dependent kinases (CDKs) Cdk1 and Cdk2. Furthermore, these residues can be phosphorylated in vitro by purified Cdk1/cyclin B and Cdk2/cyclin A. Mutant AML1 protein which cannot be phosphorylated at these sites (AML1-4A) is more stable than wild-type AML1. AML-4A is resistant to degradation mediated by Cdc20, one of the substrate-targeting subunits of the anaphase-promoting complex (APC). However, Cdh1, another targeting subunit used by the APC, can mediate the degradation of AML1-4A. A phospho-mimic protein, AML1-4D, can be targeted by Cdc20 or Cdh1. These observations suggest that both Cdc20 and Cdh1 can target AML1 for degradation by the APC but that AML1 phosphorylation may affect degradation mediated by Cdc20-APC to a greater degree.
AML1（RUNX1）调控造血、血管生成、肌肉功能和神经发生。先前的研究表明，AML1的磷酸化，尤其是丝氨酸276和303位点的磷酸化，会影响其转录激活。在此，我们报告，细胞周期蛋白依赖性激酶（CDK）Cdk1和Cdk2的抑制剂可在体内阻断AML1丝氨酸276和303的磷酸化。此外，这些残基在体外可被纯化的Cdk1/细胞周期蛋白B和Cdk2/细胞周期蛋白A磷酸化。在这些位点不能被磷酸化的突变型AML1蛋白（AML1-4A）比野生型AML1更稳定。AML-4A对后期促进复合物（APC）的底物靶向亚基之一Cdc20介导的降解具有抗性。然而，APC使用的另一个靶向亚基Cdh1可介导AML1-4A的降解。一种磷酸模拟蛋白AML1-4D可被Cdc20或Cdh1靶向。这些观察结果表明，Cdc20和Cdh1均可靶向AML1使其被APC降解，但AML1磷酸化可能在更大程度上影响Cdc20-APC介导的降解。
