title: P21Waf1/Cip1 dysfunction in neuroblastoma: a novel mechanism of attenuating G0-G1 cell cycle arrest.
abstract: In normal cells in which DNA has been damaged, p53 induces the expression of p21(Waf1/Cip1); p21, in turn, binds to cyclin-dependent kinase 2 (cdk2) and inhibits its function. Inhibition of cdk2 results in cell cycle arrest in G(0)-G(1). Although p53 is transcriptionally active and induces p21 expression in neuroblastoma (NB) cells, the G(0)-G(1) checkpoint is attenuated. Here we report that the mechanism that mediates this defect in NB cells is the inability of p21 to bind to, or inhibit the activity of cdk2. However, when recombinant p21 protein was added to NB cell extracts in vitro, the protein inhibited the activity of cdk2. This finding suggests that endogenous p21 protein in NB cells is inactive and may be bound either to a protein complex or in a conformation that precludes its binding to cdk2. The dysfunction of p21 in NB cells represents a novel mechanism by which the G(0)-G(1) cell cycle checkpoint can be inactivated. This mechanism may be important in regulating the growth of NB and potentially other types of tumors. Cdk inhibitors currently being developed for clinical use may be useful therapy for tumors such as NB in which endogenous cdk inhibitors are defective.
authors.affiliation: Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Pamela P
authors.initials: PP
authors.lastname: McKenzie
authors.forename: Mary K
authors.initials: MK
authors.lastname: Danks
authors.forename: Richard W
authors.initials: RW
authors.lastname: Kriwacki
authors.forename: Linda C
authors.initials: LC
authors.lastname: Harris
mesh_terms: D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000502:physiology*; D002648:Child; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase; D005822:Genetic Vectors; D006801:Humans; D009447:Neuroblastoma / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D014162:Transfection
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases