title: Induction of p21 by p53 following DNA damage inhibits both Cdk4 and Cdk2 activities.
abstract: DNA damage often activates the p53-p21 pathway and causes G(1)-phase arrest in mammalian cells. Although there is ample evidence that p21 induction by p53 leads to Cdk2 inhibition, it is unclear whether this checkpoint event also leads to Cdk4 inhibition. Diaminocyclohexane(trans-diacetato)(dichloro) platinum(IV) (DAP), a platinum-based coordination complex, is a DNA-damaging agent that is effective against a variety of tumor cells resistant to the parental drug cisplatin. Our previous studies established that treatment of human cancer cells with low effective concentrations of DAP specifically activates the G(1)-phase checkpoint and simultaneously inhibit Cdk4 and Cdk2 activities. Here we demonstrate that DAP treatment of human cancer cells activates the p53-p21 pathway without activating other known mechanisms that inhibit Cdk4 and Cdk2 activities. The induced p21 binds to both the Cdk4/cyclin D and Cdk2/cyclin E complexes and inhibits both of their kinase activities. Conversely, inhibition of p21 induction by cycloheximide or by p21 gene deletion prevents DAP-induced inhibition of Cdk4 and Cdk2 activities. Attenuated p53 expression and p21 induction also eliminates DAP-induced G(1)-phase arrest and inhibition of Cdk4 and Cdk2 activities. Together, these findings establish that activation of the p53-p21 pathway is responsible for the DAP-induced G(1)-phase checkpoint response and provide the first solid evidence that p21 induction by p53 during a DNA damage-induced G(1)-phase checkpoint response inhibits both Cdk4 and Cdk2 activities.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas, MD Anderson Cancer Center, Box 019, 1515 Holcombe Blvd, Houston, TX 77030, USA.
authors.forename: Guangan
authors.initials: G
authors.lastname: He
authors.forename: Zahid H
authors.initials: ZH
authors.lastname: Siddik
authors.forename: Zaifeng
authors.initials: Z
authors.lastname: Huang
authors.forename: Ruoning
authors.initials: R
authors.lastname: Wang
authors.forename: John
authors.initials: J
authors.lastname: Koomen
authors.forename: Ryuji
authors.initials: R
authors.lastname: Kobayashi
authors.forename: Abdul R
authors.initials: AR
authors.lastname: Khokhar
authors.forename: Jian
authors.initials: J
authors.lastname: Kuang
mesh_terms: D042846:CDC2-CDC28 Kinases / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D004249:DNA Damage / Q000502:physiology*; D016193:G1 Phase / Q000502:physiology; D006801:Humans; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; 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