title: Hypoxia provokes base excision repair changes and a repair-deficient, mutator phenotype in colorectal cancer cells.
abstract: Regions of acute and chronic hypoxia exist within solid tumors and can lead to increased rates of mutagenesis and/or altered DNA damage and repair protein expression. Base excision repair (BER) is responsible for resolving small, non-helix-distorting lesions from the genome that potentially cause mutations by mispairing or promoting DNA breaks during replication. Germline and somatic mutations in BER genes, such as MutY Homolog (MUTYH/MYH) and DNA-directed polymerase (POLB), are associated with increased risk of colorectal cancer. However, very little is known about the expression and function of BER proteins under hypoxic stress. Using conditions of chronic hypoxia, decreased expression of BER proteins was observed because of a mechanism involving suppressed BER protein synthesis in multiple colorectal cancer cell lines. Functional BER was impaired as determined by MYH- and 8-oxoguanine (OGG1)-specific glycosylase assays. A formamidopyrimidine-DNA glycosylase (Fpg) Comet assay revealed elevated residual DNA base damage in hypoxic cells 24 hours after H2O2 treatment as compared with normoxic controls. Similarly, high-performance liquid chromatography analysis demonstrated that 8-oxo-2'-deoxyguanosine lesions were elevated in hypoxic cells 3 and 24 hours after potassium bromate (KBrO3) treatment when compared with aerobic cells. Correspondingly, decreased clonogenic survival was observed following exposure to the DNA base damaging agents H2O2 and MMS, but not to the microtubule interfering agent paclitaxel. Thus, a persistent downregulation of BER components by the microenvironment modifies and facilitates a mutator phenotype, driving genetic instability and cancer progression.
  
  
  CONCLUSIONS
  Aberrant BER is a contributing factor for the observed genetic instability in hypoxic tumor cells.
authors.affiliation: Princess Margaret Cancer Centre (University Health Network), Toronto, Ontario, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Norman
authors.initials: N
authors.lastname: Chan
authors.affiliation: Princess Margaret Cancer Centre (University Health Network), Toronto, Ontario, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Mohsin
authors.initials: M
authors.lastname: Ali
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: Gordon P
authors.initials: GP
authors.lastname: McCallum
authors.affiliation: Princess Margaret Cancer Centre (University Health Network), Toronto, Ontario, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Ramya
authors.initials: R
authors.lastname: Kumareswaran
authors.affiliation: Princess Margaret Cancer Centre (University Health Network), Toronto, Ontario, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Marianne
authors.initials: M
authors.lastname: Koritzinsky
authors.affiliation: Princess Margaret Cancer Centre (University Health Network), Toronto, Ontario, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Bradly G
authors.initials: BG
authors.lastname: Wouters
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy, University of Toronto, Ontario, Canada.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Wells
authors.affiliation: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: Steven
authors.initials: S
authors.lastname: Gallinger
authors.affiliation: Princess Margaret Cancer Centre (University Health Network), Toronto, Ontario, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada Rob.Bristow@rmp.uhn.on.ca.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Bristow
mesh_terms: D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology*; D045647:DNA Glycosylases / Q000378:metabolism; D004260:DNA Repair / Q000187:drug effects / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D008741:Methyl Methanesulfonate; D006861:Hydrogen Peroxide; D045647:DNA Glycosylases; C061738:mutY adenine glycosylase; C479058:oxoguanine glycosylase 1, human