title: Topoisomerase I function during Escherichia coli response to antibiotics and stress enhances cell killing from stabilization of its cleavage complex.
abstract: OBJECTIVE
  To explore the role of topoisomerase I in gene activation and increased RecA levels during the bacterial SOS response, as well as the effect of antibiotic treatment and stress challenge on cell killing initiated by trapped topoisomerase I cleavage complex.
  
  
  METHODS
  A mutant Escherichia coli strain with a ΔtopA mutation was used to investigate the role of topoisomerase I function in the SOS response to trimethoprim and mitomycin C. Induction of the recA and dinD1 promoters was measured using luciferase reporters of these promoters fused to luxCDABE. An increase in the RecA level following trimethoprim treatment was quantified directly by western blotting. The effect of stress challenge from trimethoprim and acidified nitrite treatments on cell killing by topoisomerase I cleavage complex accumulation was measured by the decrease in viability following induction of recombinant mutant topoisomerase I that forms a stabilized cleavage complex.
  
  
  RESULTS
  Topoisomerase I function was found to be required for efficient transcriptional activation of the recA and dinD1 promoters during the E. coli SOS response to trimethoprim and mitomycin C. The role of topoisomerase I in the SOS response was confirmed with quantitative western blot analysis of RecA following trimethoprim treatment. The bactericidal effect from topoisomerase I cleavage complex accumulation was shown to be enhanced by stress challenge from trimethoprim and acidified nitrite.
  
  
  CONCLUSIONS
  Bacterial topoisomerase I function is actively involved in the SOS response to antibiotics and stress challenge. Cell killing initiated by the topoisomerase I cleavage complex would be enhanced by antibiotics and the host response. These findings provide further support for bacterial topoisomerase I as a therapeutic target.
authors.affiliation: Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY 10595, USA.
authors.forename: I-Fen
authors.initials: IF
authors.lastname: Liu
authors.forename: Jeanette H
authors.initials: JH
authors.lastname: Sutherland
authors.forename: Bokun
authors.initials: B
authors.lastname: Cheng
authors.forename: Yuk-Ching
authors.initials: YC
authors.lastname: Tse-Dinh
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D019677:Artificial Gene Fusion; D015153:Blotting, Western; D004264:DNA Topoisomerases, Type I / Q000172:deficiency / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects* / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics; D017353:Gene Deletion; D017930:Genes, Reporter; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D050296:Microbial Viability / Q000187:drug effects; D016685:Mitomycin / Q000494:pharmacology; D009573:Nitrites / Q000494:pharmacology; D011938:Rec A Recombinases / Q000096:biosynthesis / Q000235:genetics; D014295:Trimethoprim / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D009573:Nitrites; C087483:dinD protein, E coli; D016685:Mitomycin; D014295:Trimethoprim; D008156:Luciferases; D011938:Rec A Recombinases; D004264:DNA Topoisomerases, Type I