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PROJECT #2 |
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TIFs: Topoisomerase Interacting Factors. |
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P53 Dependence of Topoisomerase I Recruitment in vivo
Abstract DNA damage is attended by rapid recruitment of endogenous type I topoisomerase (topo I) into covalent cleavage complexes with genomic DNA in vivo. We demonstrate that the recruitment is dependent upon the presence of a wild type tumor suppressor protein p53. In addition, topo I and p53 physically interact at arrested topo I-genomic DNA covalent complexes in vivo, suggesting that p53 directly stimulates topo I activity and damage to the genome of the afflicted cell. The p53 dependence of topo I is conditional since topo I recruitment following DNA damage can be partially restored if p53 mutant cells are artificially held in G1. In addition, topo I deployment after DNA damage is greater in G1 cells compared to S phase cells. These results show that topo I activation following DNA damage is dependent upon the cell cycle in a way that is very different from that observed with DNA replication dependent, camptothecin mediated DNA breaks. The data suggest that p53 activates topo I which inflicts additional genomic damage after the initial UV damage events. Topoisomerases therefore may contribute to the p53 commitment to apoptosis and topo I might assist in elimination of DNA damaged cells as part of the cellular proofreading function inherent in the p53 pathway.
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