title: Oncogenic KRAS sensitises colorectal tumour cells to chemotherapy by p53-dependent induction of Noxa.
abstract: BACKGROUND
  Oxaliplatin and 5-fluorouracil (5-FU) currently form the backbone of conservative treatment in patients with metastatic colorectal cancer. Tumour responses to these agents are highly variable, but the underlying mechanisms are poorly understood. Our previous results have indicated that oncogenic KRAS in colorectal tumour cells sensitises these cells to chemotherapy.
  
  
  METHODS
  FACS analysis was used to determine cell-cycle distribution and the percentage of apoptotic and mitotic cells. A multiplexed RT-PCR assay was used to identify KRAS-controlled apoptosis regulators after exposure to 5-FU or oxaliplatin. Lentiviral expression of short-hairpin RNAs was used to suppress p53 or Noxa.
  
  
  RESULTS
  Oncogenic KRAS sensitised colorectal tumour cells to oxaliplatin and 5-FU in a p53-dependent manner and promoted p53 phosphorylation at Ser37 and Ser392, without affecting p53 stabilisation, p21 induction, or cell-cycle arrest. Chemotherapy-induced expression of the p53 target gene Noxa was selectively enhanced by oncogenic KRAS. Suppression of Noxa did not affect p21 induction or cell-cycle arrest, but reduced KRAS/p53-dependent apoptosis after exposure to chemotherapy in vitro and in tumour xenografts. Noxa suppression did not affect tumour growth per se, but strongly reduced the response of these tumours to chemotherapy.
  
  
  CONCLUSIONS
  Oncogenic KRAS determines the cellular response to p53 activation by oxaliplatin or 5-FU, by facilitating apoptosis induction through Noxa.
authors.affiliation: Department of Surgery, University Medical Center Utrecht, The Netherlands.
authors.forename: M T
authors.initials: MT
authors.lastname: de Bruijn
authors.forename: D A E
authors.initials: DA
authors.lastname: Raats
authors.forename: F J H
authors.initials: FJ
authors.lastname: Hoogwater
authors.forename: W J
authors.initials: WJ
authors.lastname: van Houdt
authors.forename: K
authors.initials: K
authors.lastname: Cameron
authors.forename: J P
authors.initials: JP
authors.lastname: Medema
authors.forename: I H M
authors.initials: IH
authors.lastname: Borel Rinkes
authors.forename: O
authors.initials: O
authors.lastname: Kranenburg
mesh_terms: D000818:Animals; D017209:Apoptosis; D002453:Cell Cycle / Q000187:drug effects; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics*; D005472:Fluorouracil / Q000008:administration & dosage*; D016158:Genes, p53; D011905:Genes, ras; D045325:HCT116 Cells; D006801:Humans; D008297:Male; D051379:Mice; D009944:Organoplatinum Compounds / Q000008:administration & dosage*; D000077150:Oxaliplatin; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D009944:Organoplatinum Compounds; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D000077150:Oxaliplatin; D005472:Fluorouracil