Mutations of human DNA topoisomerase I at poly (ADP-ribose) binding sites: Modulation of camptothecin activity by ADP-ribose polymers

Cinzia Tesauro, Grazia Graziani, Barbara Arnò, Laura Zuccaro, Alessia Muzi, Ilda D'Annessa, Elettra Santori, Lucio Tentori, Carlo Leonetti, Paola Fiorani, Alessandro Desideri

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Background: DNA topoisomerases are key enzymes that modulate the topological state of DNA through the breaking and rejoining of DNA strands. Human topoisomerase I belongs to the family of poly(ADP-ribose)-binding proteins and is the target of camptothecin derived anticancer drugs. Poly(ADP-ribosyl)ation occurs at specific sites of the enzyme inhibiting the cleavage and enhancing the religation steps during the catalytic cycle. Thus, ADP-ribose polymers antagonize the activity of topoisomerase I poisons, whereas PARP inhibitors increase their antitumor effects. Methods: Using site-directed mutagenesis we have analyzed the interaction of human topoisomerase I and poly (ADP-ribose) through enzymatic activity and binding procedures. Results: Mutations of the human topoisomerase I hydrophobic or charged residues, located on the putative polymer binding sites, are not sufficient to abolish or reduce the binding of the poly(ADP-ribose) to the protein. These results suggest either the presence of additional binding sites or that the mutations are not enough perturbative to destroy the poly(ADP-ribose) interaction, although in one mutant they fully abolish the enzyme activity. Conclusions: It can be concluded that mutations at the hydrophobic or charged residues of the putative polymer binding sites do not interfere with the ability of poly(ADP-ribose) to antagonize the antitumor activity of topoisomerase I poisons.

Original languageEnglish
Article number71
JournalJournal of Experimental and Clinical Cancer Research
Issue number1
Publication statusPublished - 2014


  • Camptothecin
  • Cleavage
  • PARP inhibitors
  • PARylation
  • Religation rate
  • Topoisomerase I

ASJC Scopus subject areas

  • Cancer Research
  • Oncology


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