title: Extracellular superoxide production by Enterococcus faecalis promotes chromosomal instability in mammalian cells.
abstract: OBJECTIVE
  We investigated whether Enterococcus faecalis, a Gram-positive intestinal commensal that produces extracellular superoxide, could promote chromosomal instability (CIN) in mammalian cells.
  
  
  METHODS
  We measured the ability of E faecalis to promote CIN using hybrid hamster cells (A(L)N) containing human chromosome 11.
  
  
  RESULTS
  E faecalis promoted CIN in A(L)N cells with average mutant fractions per 10(5) survivors (+/-SD) of 72.3 +/- 6.7 at 1 x 10(9) cfu mL(-1) compared with 22.2 degrees +/- 4.5 for the no bacteria control. Gamma-irradiation at 2 Gray similarly resulted in 74.7 +/- 5.7 mutant clones per 10(5) survivors. Deletions in chromosome 11 consistent with CIN were verified in 80% of mutant clones. E faecalis-treated A(L)N cells were protected from CIN by superoxide dismutase, gamma-tocopherol, and cyclooxygenase-2 (COX-2) inhibitors. In a dual-chamber tissue culture model designed to mimic stromal-epithelial cell interactions, macrophages pretreated with E faecalis grown on permeable supports increased mutant fractions 2.5-fold for A(L)N cells. COX-2 was up-regulated by superoxide from E faecalis and mutant fractions decreased when COX-2 was silenced using short interfering RNA. Escherichia coli, a Gram-negative commensal that produces negligible extracellular superoxide, only modestly promoted CIN in this model.
  
  
  CONCLUSIONS
  These findings indicate that macrophage COX-2 is induced by superoxide from E faecalis and promotes CIN in mammalian cells through diffusible factors. This mechanism links the oxidative physiology of E faecalis to propagation of genomic instability through a bystander effect, and offers a novel theory for the role of commensal bacteria in the etiology of sporadic colorectal cancer.
authors.affiliation: The Muchmore Laboratories for Infectious Disease Research, Department of Veterans Affairs Medical Center, University of Oklahoma Health Sciences Center, Oklahoma City, USA.
authors.forename: Xingmin
authors.initials: X
authors.lastname: Wang
authors.forename: Mark M
authors.initials: MM
authors.lastname: Huycke
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D024201:Bystander Effect / Q000187:drug effects; D002470:Cell Survival; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D043171:Chromosomal Instability; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics*; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D006224:Cricetinae; D051546:Cyclooxygenase 2 / Q000096:biosynthesis* / Q000378:metabolism; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D013293:Enterococcus faecalis / Q000378:metabolism*; D004790:Enzyme Induction; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000382:microbiology* / Q000528:radiation effects; D004926:Escherichia coli / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005720:Gamma Rays; D006801:Humans; D015227:Lipid Peroxidation; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism / Q000382:microbiology*; D009154:Mutation; D010587:Phagocytosis; D013481:Superoxides / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D052246:Cyclooxygenase 2 Inhibitors; D013481:Superoxides; D051546:Cyclooxygenase 2