Visit our Expo - Redox and Inflammation signaling 2012

Session X : Cell death in cancer Poster X, 103
Dual action of roscovitine on human MCF-7 breast cancer cells: induction of G2 arrest
via inhibition of CDKs and initiation of apoptosis by activation of site-specific
phosphorylation of wt p53 protein
Józefa W*sierska-G+dek, Carmen Ranftler and Marieta Gueorguieva
Cell Cycle Regulation Group, Division: Institute of Cancer Research, Department of
Medicine I, Medical University of Vienna, Borschkegasse 8 a, A-1090 Vienna, Austria.
E-mail: Jozefa.Gadek-Wesierski@meduniwien.ac.at
Exposure of MCF-7 cells to roscovitine (ROSC), a potent CDK inhibitor, resulted in a strong
inhibition of cell proliferation. Detailed analysis revealed that ROSC arrested MCF-7 cells in
G2 phase of the cell cycle and induced apoptosis. Cell cycle arrest preceded the main wave of
apoptosis. The cell cycle block was attributable to the inactivation of CDK2 and CDK1. Postincubation
of G2 arrested cells for 24h in a drug-free medium did not diminish the number of
the G2 cell population indicating that ROSC-mediated cell cycle arrest was prolonged. ROSC
induced wt p53 tumor suppressor protein in MCF-7 cells in a time- and dose-dependent
manner. ROSC increased p53 steady-state. The half-life of wt p53 protein increased
approximately forty-fold after exposure of MCF-7 cells to ROSC for 15h. At 4h after ROSC
administration a strong phosphorylation of serine at position 46 was observed. The onset of
Ser-46-p53 phosphorylation preceded the induction of apoptosis. P-Ser-46-p53
transcriptionally upregulated p53AIP1 protein, a component of mitochondria. Surprisingly,
the reconstitution with human caspase-3 did not sensitize MCF-7 cells to the action of ROSC.
Our results unequivocally show that ROSC simultaneously inhibits CDK2 and CDK1 and
activates a kinase catalyzing the phosphorylation of p53 protein at Ser46.
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