title: Upregulation of p27 and its inhibition of CDK2/cyclin E activity following DNA damage by a novel platinum agent are dependent on the expression of p21.
abstract: The cisplatin analogue 1R,2R-diaminocyclohexane(trans-diacetato)(dichloro)platinum(IV) (DAP) is a DNA-damaging agent that will be entering clinical trials for its potent cytotoxic effects against cisplatin-resistant tumour cells. This cytotoxicity may reside in its ability to selectively activate G1-phase checkpoint response by inhibiting CDKs via the p53/p21 pathway. We have now evaluated the role of another CDK inhibitor p27 as a contributor to DAP-mediated inhibition of G1-phase CDK2 activity. Our studies in ovarian A2780 tumour cells demonstrate that p27 levels induced by DAP are comparable to or greater than those seen for p21. The induction of p27 is not through a transcriptional mechanism, but rather is due to a four-fold increase in protein stabilisation through a mechanism dependent on p21. Moreover, DAP-induced p21 promoted the selective increase of p27 in the CDK2 complex, but not in CDK4 complex, and this selective increase contributed to inhibition of the CDK2 kinase activity. The inhibited complex contained either p27 or p21, but not both, with the relative levels of cyclin E associated with p27 and p21 indicating that about 25% of the inhibition of CDK2 activity was due to p27 and 75% due to p21. This study provides the first evidence that p27 upregulation is directly attributable to activation of the p53/p21 pathway by a DNA-damaging agent, and promulgates p53/p21/p27 axis as a significant component of checkpoint response.
authors.affiliation: Department of Experimental Therapeutics, Unit 353, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA.
authors.forename: G
authors.initials: G
authors.lastname: He
authors.forename: J
authors.initials: J
authors.lastname: Kuang
authors.forename: Z
authors.initials: Z
authors.lastname: Huang
authors.forename: J
authors.initials: J
authors.lastname: Koomen
authors.forename: R
authors.initials: R
authors.lastname: Kobayashi
authors.forename: A R
authors.initials: AR
authors.lastname: Khokhar
authors.forename: Z H
authors.initials: ZH
authors.lastname: Siddik
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D015152:Blotting, Northern; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000031:analogs & derivatives* / Q000494:pharmacology; D019927:Cyclin E / Q000187:drug effects* / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000187:drug effects* / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000187:drug effects*; D018844:Cyclin-Dependent Kinases / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D005260:Female; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D009944:Organoplatinum Compounds; D010957:Plasmids; D018809:Proliferating Cell Nuclear Antigen / Q000187:drug effects* / Q000378:metabolism; D034741:RNA, Small Interfering; D014162:Transfection; D015854:Up-Regulation
chemical_list: C119451:(diaminocyclohexane)(diacetato)(dichloro)platinum; D000970:Antineoplastic Agents; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D009944:Organoplatinum Compounds; D018809:Proliferating Cell Nuclear Antigen; D034741:RNA, Small Interfering; C413374:p27 antigen; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D002945:Cisplatin