Sustained elevation of NF‐κB DNA binding activity in radiation‐induced lung damage in rats

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Abstract
Purpose: To characterize the cellular distribution and DNA binding activity of the nuclear factor kappaB (NF‐κB) in a model of radiation‐induced lung damage in the rat. Materials and methods: The right lung of Fischer rats was irradiated with a single dose of 20 Gy. The cellular distributions of NF‐κB proteins and mRNA were detected with immunohistochemistry and in‐situ hybridization respectively. The DNA binding activity of NF‐κB, nuclear and cytoplasmic levels of NF‐κB proteins, and kinase activity towards IkappaBalpha (IκBα) were determined using electrophoretic mobility shift assays (EMSA), Western blots and kinase assays, respectively. The mRNA level of interleukin 6 (IL‐6) was determined using quantitative room temperature polymerase chain reaction. Results: There was a continuous elevation of NF‐κB DNA binding activity in the rat lung after ionizing irradiation over 6 months. The irradiated lung tissue exhibited an increased kinase activity towards IκBα and a selective loss of nuclear IκBα. The NF‐κB–DNA binding complex switched from p50–p65 heterodimers in normal lung tissue to p50 homodimers in irradiated lung tissue. The increased level of IL‐6 mRNA suggests transcriptional activation of NF‐κB‐dependent genes in the irradiated rat lung. Conclusions: The DNA binding activity of NF‐κB is continuously activated after irradiation of the rat lung by loss of nuclear IκBα. This might play a role in sustaining chronic inflammation and hyperproliferation of mesenchymal cells after irradiation.
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