title: NPM phosphorylation stimulates Cdk1, overrides G2/M checkpoint and increases leukemic blasts in mice.
abstract: An elevated level of nucleophosmin (NPM) is often found in actively proliferative cells including human tumors. To identify the regulatory role for NPM phosphorylation in proliferation and cell cycle control, a series of mutants targeting the consensus cyclin-dependent kinase (CDK) phosphorylation sites was created to mimic or abrogate either single-site or multi-site phosphorylation. Simultaneous inactivation of two CDK phosphorylation sites at Ser10 and Ser70 (NPM-AA) induced G(2)/M cell cycle arrest, phosphorylation of Cdk1 at Tyr15 (Cdc2(Tyr15)) and increased cytoplasmic accumulation of Cdc25C. Strikingly, stress-induced Cdk1(Tyr15) and Cdc25C sequestration was suppressed by expression of a phosphomimetic NPM mutant created on the same CDK sites (S10E/S70E, NPM-EE). Further analysis revealed that phosphorylation of NPM at both Ser10 and Ser70 was required for proper interaction between Cdk1 and Cdc25C. Moreover, NPM-EE directly bound to Cdc25C and prevented phosphorylation of Cdc25C at Ser216 during mitosis. Finally, NPM-EE overrided stress-induced G(2)/M arrest and increased leukemia blasts in a NOD/SCID xenograft model. Thus, these findings reveal a novel function of NPM on regulation of cell cycle progression, in which phosphorylation of NPM controls cell cycle progression at G(2)/M transition through modulation of Cdk1 and Cdc25C activities.
authors.affiliation: Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Du
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhou
authors.forename: Suzette
authors.initials: S
authors.lastname: Pike
authors.forename: Qishen
authors.initials: Q
authors.lastname: Pang
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002455:Cell Division; D049109:Cell Proliferation; D016195:G2 Phase; D015151:Immunoblotting; D047468:Immunoprecipitation; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D008940:Mitotic Index; D009687:Nuclear Proteins / Q000378:metabolism*; D000090243:Nucleophosmin; D010766:Phosphorylation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000378:metabolism* / Q000473:pathology*
chemical_list: C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D000090243:Nucleophosmin; D016203:CDC2 Protein Kinase