title: New alternative phosphorylation sites on the cyclin dependent kinase 1/cyclin a complex in p53-deficient human cells treated with etoposide: possible association with etoposide-induced apoptosis.
abstract: Cell cycle arrest is a major cellular response to DNA damage preceding the decision to repair or die. Many malignant cells have non-functional p53 rendering them more "aggressive" in nature. Arrest in p53-negative cells occurs at the G2M cell cycle checkpoint. Failure of DNA damaged cells to arrest at G2 results in entry into mitosis and potential death through aberrant mitosis and/or apoptosis. The pivotal kinase regulating the G2M checkpoint is Cdk1/cyclin B whose activity is controlled by phosphorylation. The p53-negative myeloid leukemia cell lines K562 and HL-60 were used to determine Cdk1 phosphorylation status during etoposide treatment. Cdk1 tyrosine 15 phosphorylation was associated with G2M arrest, but not with cell death. Cdk1 tyrosine 15 phosphorylation also led to suppression of nuclear cyclin B-associated Cdk1 kinase activity. However cell death, associated with broader tyrosine phosphorylation of Cdk1 was not attributed to tyrosine 15 alone. This broader phosphoryl isoform of Cdk1 was associated with cyclin A and not cyclin B. Alternative phosphorylations sites were predicted as tyrosines 4, 99 and 237 by computer analysis. No similar pattern was found on Cdk2. These findings suggest novel Cdk1 phosphorylation sites, which appear to be associated with p53-independent cell death following etoposide treatment.
authors.affiliation: Centre for Haematology, Institute of Cell and Molecular Sciences, Barts and The London School of Medicine and Dentistry, Queen Mary's University of London, 4 Newark Street, London, E1 2AT, UK.
authors.forename: Karen
authors.initials: K
authors.lastname: Higginbottom
authors.forename: Ulrike
authors.initials: U
authors.lastname: Jahnke
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Newland
authors.forename: Finbarr E
authors.initials: FE
authors.lastname: Cotter
authors.forename: Paul David
authors.initials: PD
authors.lastname: Allen
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D016203:CDC2 Protein Kinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology; D019925:Cyclin A / Q000235:genetics / Q000378:metabolism*; D019926:Cyclin B / Q000378:metabolism; D005047:Etoposide / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D020014:K562 Cells; D046912:Multiprotein Complexes / Q000378:metabolism; D010766:Phosphorylation; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D019925:Cyclin A; D019926:Cyclin B; D046912:Multiprotein Complexes; D016159:Tumor Suppressor Protein p53; D005047:Etoposide; D016203:CDC2 Protein Kinase