title: Differential modulation of paclitaxel-mediated apoptosis by p21Waf1 and p27Kip1.
abstract: The impact of the cyclin dependent kinase (CDK) inhibitors p21Waf1 and p27Kip1 on paclitaxel-mediated cytotoxicity was investigated in RKO human colon adenocarcinoma cells with the ecdysone-inducible expression of p21Waf1 or p27Kip1. Ectopic expression of p27Kip1 arrested cells at G1 phase, whereas p21Waf1 expression arrested cells at G1 and G2. Expression of p21Waf1 after paclitaxel treatment produced much greater resistance to paclitaxel than did expression of p27Kip1. We attributed this difference to the additional block at G2 induced by p21Waf1, which prevented cells from entering M phase and becoming paclitaxel susceptible. Expression of p21Waf1 inhibited p34cdc2 activity and markedly reduced paclitaxel-mediated mitotic arrest, from 87.5 to 23%. In contrast, p27Kip1 expression also inhibited p34cdc2 but reduced mitotic arrest only slightly, from 87. 4 to 74.5%. We concluded that the G2 block produced by p21Waf1, but not by p27Kip1, contributed to their unequal modulation of sensitivity to paclitaxel-mediated apoptosis in RKO cells, and there is no causal relationship between paclitaxel-mediated cytotoxicity and elevation of p34cdc2 activity.
authors.affiliation: Department of Experimental Therapeutics, Division of Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas, TX 77030, USA.
authors.forename: M
authors.initials: M
authors.lastname: Schmidt
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: B
authors.initials: B
authors.lastname: Liu
authors.forename: M
authors.initials: M
authors.lastname: Fang
authors.forename: J
authors.initials: J
authors.lastname: Mendelsohn
authors.forename: Z
authors.initials: Z
authors.lastname: Fan
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001483:Base Sequence; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000502:physiology*; D017931:DNA Primers; D016193:G1 Phase; D016195:G2 Phase; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D017239:Paclitaxel / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D017931:DNA Primers; D008869:Microtubule-Associated Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016203:CDC2 Protein Kinase; D017239:Paclitaxel