Distinct requirements for the Rad32(Mre11) nuclease and Ctp1(CtIP) in the removal of covalently bound topoisomerase I and II from DNA

Mol Cell. 2009 Jan 16;33(1):117-23. doi: 10.1016/j.molcel.2008.11.021.


For a cancer cell to resist treatment with drugs that trap topoisomerases covalently on the DNA, the topoisomerase must be removed. In this study, we provide evidence that the Schizosaccharomyces pombe Rad32(Mre11) nuclease activity is involved in the removal of both Top2 from 5' DNA ends as well as Top1 from 3' ends in vivo. A ctp1(CtIP) deletion is defective for Top2 removal but overproficient for Top1 removal, suggesting that Ctp1(CtIP) plays distinct roles in removing topoisomerases from 5' and 3' DNA ends. Analysis of separation of function mutants suggests that MRN-dependent topoisomerase removal contributes significantly to resistance against topoisomerase-trapping drugs. This study has important implications for our understanding of the role of the MRN complex and CtIP in resistance of cells to a clinically important group of anticancer drugs.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Camptothecin / pharmacology
  • Cell Nucleolus / drug effects
  • Cell Nucleolus / enzymology
  • Cell Nucleolus / radiation effects
  • DNA Topoisomerases, Type I / metabolism*
  • DNA Topoisomerases, Type II / metabolism*
  • DNA, Fungal / metabolism*
  • DNA-Binding Proteins / metabolism*
  • Etoposide / analogs & derivatives
  • Etoposide / pharmacology
  • Exodeoxyribonucleases / metabolism*
  • Gamma Rays
  • Methyl Methanesulfonate / pharmacology
  • Mutant Proteins / metabolism
  • Mutation / genetics
  • Protein Binding / drug effects
  • Schizosaccharomyces / cytology
  • Schizosaccharomyces / drug effects
  • Schizosaccharomyces / enzymology*
  • Schizosaccharomyces / radiation effects
  • Schizosaccharomyces pombe Proteins / metabolism*


  • Ctp1 protein, S pombe
  • DNA, Fungal
  • DNA-Binding Proteins
  • Mutant Proteins
  • Rad50 protein, S pombe
  • Schizosaccharomyces pombe Proteins
  • TOP 53
  • Etoposide
  • Methyl Methanesulfonate
  • Exodeoxyribonucleases
  • Mre11 protein, S pombe
  • DNA Topoisomerases, Type I
  • DNA Topoisomerases, Type II
  • Camptothecin