NF-κB mediates aberrant activation of HIF-1 in malignant lymphoma

Objective The goal of this study was to explore the molecular mechanisms of aberrant hypoxia inducible factor-1 (HIF 1) activation in lymphoma cells Materials and Methods We analyzed the expression of the a 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)-kappa B in abnormal HIF-1 alpha expression in lymphoma cells, we performed a reporter assay using HIF-1 alpha promoter constructs that contained or lacked an NF-kappa B binding site We also used a chromatin immunoprecipitation assay to assess whether NF-kappa B binds the HIF- 1 alpha promoter In addition, we took advantage of NF-kappa B inhibitors To analyze the function of HIF-1 in lymphoma cells, we established stable HIF-1 alpha knockdown cells using short-hairpin RNA Results Malignant lymphoma cells, hut not normal B cells, demonstrated constitutive expression of HIF-1 alpha Inhibitors of NF-kappa B, however, drastically suppressed this HIF-1 alpha expression at both the messenger RNA and protein levels Furthermore, we found that exposure of lymphoma cells to ionizing radiation clearly induced NF-kappa B activation and Increased HIF-1 alpha expression Suppressing HIF-1 alpha 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-kappa B/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-kappa B activity Our observations suggest that HIF-1 inhibition may be an effective strategy to Improve the outcomes of lymphoma patients treated with radiation 2010 ISEH - Society for Hematology and Stem Cells Published by Elsevier Inc