title: p21Cip1 and p27Kip1 induce distinct cell cycle effects and differentiation programs in myeloid leukemia cells.
abstract: The cyclin-dependent kinase (Cdk) inhibitors p21(Cip1) and p27(Kip1) have been proposed to exert redundant functions in cell cycle progression and differentiation programs, although nonoverlapping functions have also been described. To gain further insights into the relevant mechanisms and to detect possible functional differences between both proteins, we conditionally expressed p21(Cip1) and p27(Kip1) in K562, a multipotent human leukemia cell line. Temporal ectopic expression of either p21(Cip1) or p27(Kip1) arrested proliferation, inhibited Cdk2 and Cdk4 activities, and suppressed retinoblastoma phosphorylation. However, whereas p21(Cip1) arrested cells in both G(1) and G(2) cell cycle phases, p27(Kip1) blocked the G(1)/S-phase transition. Furthermore, although both p21(Cip1) and p27(Kip1) associated with Cdk6, only p27(Kip1) significantly inhibited its activity. Most importantly, each protein promoted differentiation along a distinct pathway; p21(Cip1) triggered megakaryocytic maturation, whereas p27(Kip1) resulted in the expression of erythroid markers. Consistently, p21(Cip1) and p27(Kip1) were rapid and transiently up-regulated when K562 cells are differentiated into megakaryocytic and erythroid lineages, respectively. These findings demonstrate distinct functions of p21(Cip1) and p27(Kip1) in cell cycle regulation and differentiation and indicate that these two highly related proteins possess unique biological activities and are not functionally interchangeable.
authors.affiliation: Grupo de Biología Molecular del Cáncer, Departamento de Biología Molecular y Unidad de Biomedicina-Consejo Superior de Investigaciones Científicas, Universidad de Cantabria, 39011 Santander, Spain.
authors.forename: María J
authors.initials: MJ
authors.lastname: Muñoz-Alonso
authors.forename: Juan C
authors.initials: JC
authors.lastname: Acosta
authors.forename: Carlos
authors.initials: C
authors.lastname: Richard
authors.forename: M Dolores
authors.initials: MD
authors.lastname: Delgado
authors.forename: John
authors.initials: J
authors.lastname: Sedivy
authors.forename: Javier
authors.initials: J
authors.lastname: León
mesh_terms: D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics; D002454:Cell Differentiation / Q000502:physiology*; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D007951:Leukemia, Myeloid / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
chemical_list: C493956:CDKN1A protein, human; C436291:CDKN1B protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D047908:Intracellular Signaling Peptides and Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27