AML1/RUNX1 phosphorylation by cyclin-dependent kinases regulates the degradation of AML1/RUNX1 by the anaphase-promoting complex

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) Cdkl and Cdk2. Furthermore, these residues can be phosphorylated in vitro by purified Cdkl/cyclin B and Cdk2/cyclin A. Mutant AML1 protein which cannot be phosphorylated at these sites (AML14A) is more stable than wild-type AMLL AML-4A is resistant to degradation mediated by Cdc20, one of the substrate-targeting subunits of the anaphase-promoting complex (APQ. However, Cdhl, another targeting subunit used by the APC, can mediate the degradation of AML14A. A phospho-mimic protein, AML14D, can be targeted by Cdc20 or Cdh1. These observations suggest that both Cdc20 and Cdhl can target AMLI for degradation by the APC but that AMLI phosphorylation may affect degradation mediated by Cdc20-APC to a greater degree.