title: Hypoxia disrupts the Fanconi anemia pathway and sensitizes cells to chemotherapy through regulation of UBE2T.
abstract: OBJECTIVE
  Hypoxia is a common feature of the microenvironment of solid tumors which has been shown to promote malignancy and poor patient outcome through multiple mechanisms. The association of hypoxia with more aggressive disease may be due in part to recently identified links between hypoxia and genetic instability. For example, hypoxia has been demonstrated to impede DNA repair by down-regulating the homologous recombination protein RAD51. Here we investigated hypoxic regulation of UBE2T, a ubiquitin ligase required in the Fanconi anemia (FA) DNA repair pathway.
  
  
  METHODS
  We analysed UBE2T expression by microarray, quantitative PCR and western blot analysis in a panel of cancer cell lines as a function of oxygen concentration. The importance of this regulation was assessed by measuring cell survival in response to DNA damaging agents under normoxia or hypoxia. Finally, HIF dependency was determined using knockdown cell lines and RCC4 cells which constitutively express HIF1α.
  
  
  RESULTS
  Hypoxia results in rapid and potent reductions in mRNA levels of UBE2T in a panel of cancer cell lines. Reduced UBE2T mRNA expression is HIF independent and was not due to changes in mRNA or protein stability, but rather reflected reduced promoter activity. Exposure of tumor cells to hypoxia greatly increased their sensitivity to treatment with the interstrand crosslinking (ICL) agent mitomycin C.
  
  
  CONCLUSIONS
  Exposure to hypoxic conditions down-regulates UBE2T expression which correlates with an increased sensitivity to crosslinking agents consistent with a defective Fanconi anemia pathway. This pathway can potentially be exploited to target hypoxic cells in tumors.
authors: Ontario Cancer Institute and Campbell Family Institute for Cancer Research, University Health Network, Toronto, Canada.
authors: Chantal H M A
authors: CH
authors: Ramaekers
authors: Twan
authors: T
authors: van den Beucken
authors: Alice
authors: A
authors: Meng
authors: Shaqil
authors: S
authors: Kassam
authors: John
authors: J
authors: Thoms
authors: Robert G
authors: RG
authors: Bristow
authors: Bradly G
authors: BG
authors: Wouters
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002470:Cell Survival; D004260:DNA Repair; D015536:Down-Regulation; D005199:Fanconi Anemia / Q000188:drug therapy* / Q000209:etiology / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D000860:Hypoxia / Q000150:complications / Q000378:metabolism*; D009369:Neoplasms / Q000098:blood supply / Q000150:complications / Q000188:drug therapy; D012333:RNA, Messenger / Q000378:metabolism; D012016:Reference Values; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics; D014407:Tumor Cells, Cultured; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D012333:RNA, Messenger; C513404:UBE2T protein, human; D044763:Ubiquitin-Conjugating Enzymes