title: NF-κB mediates aberrant activation of HIF-1 in malignant lymphoma.
abstract: OBJECTIVE
  The goal of this study was to explore the molecular mechanisms of aberrant hypoxia inducible factor-1 (HIF-1) activation in lymphoma cells.
  
  
  METHODS
  We analyzed the expression of the α subunit of HIF-1 in three lymphoma cell lines and in normal CD19-positive B cells by Western blotting. To investigate the role of nuclear factor (NF)-κB in abnormal HIF-1α expression in lymphoma cells, we performed a reporter assay using HIF-1α promoter constructs that contained or lacked an NF-κB binding site. We also used a chromatin immunoprecipitation assay to assess whether NF-κB binds the HIF-1α promoter. In addition, we took advantage of NF-κB inhibitors. To analyze the function of HIF-1 in lymphoma cells, we established stable HIF-1α knockdown cells using short-hairpin RNA.
  
  
  RESULTS
  Malignant lymphoma cells, but not normal B cells, demonstrated constitutive expression of HIF-1α. Inhibitors of NF-κB, however, drastically suppressed this HIF-1α expression at both the messenger RNA and protein levels. Furthermore, we found that exposure of lymphoma cells to ionizing radiation clearly induced NF-κB activation and increased HIF-1α expression. Suppressing HIF-1α expression by short-hairpin RNA increased the sensitivity of lymphoma cells to ionizing radiation-induced cell death. In searching for downstream targets of the NF-κB/HIF-1 axis, we identified survivin, a member of the IAP family of anti-apoptotic proteins.
  
  
  CONCLUSIONS
  We found that aberrant activation of HIF-1 in malignant lymphoma cells was mediated, at least in part, by NF-κB activity. Our observations suggest that HIF-1 inhibition may be an effective strategy to improve the outcomes of lymphoma patients treated with radiation.
authors.affiliation: Department of Hematology and Oncology, University of Yamanashi, 1110 Shimokato, Chuo, Yamanashi, Japan.
authors.forename: Qiao
authors.initials: Q
authors.lastname: Qiao
authors.forename: Yumi
authors.initials: Y
authors.lastname: Nozaki
authors.forename: Kumi
authors.initials: K
authors.lastname: Sakoe
authors.forename: Norio
authors.initials: N
authors.lastname: Komatsu
authors.forename: Keita
authors.initials: K
authors.lastname: Kirito
mesh_terms: D017209:Apoptosis; D045744:Cell Line, Tumor; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000502:physiology*; D051034:Inhibitor of Apoptosis Proteins; D008223:Lymphoma / Q000378:metabolism / Q000473:pathology*; D008869:Microtubule-Associated Proteins / Q000235:genetics; D016328:NF-kappa B / Q000502:physiology*; D015398:Signal Transduction; D000077022:Survivin; D014158:Transcription, Genetic
chemical_list: C107489:BIRC5 protein, human; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D016328:NF-kappa B; D000077022:Survivin