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

PURPOSE: To characterize the cellular distribution and DNA binding activity of the nuclear factor kappaB (NF-KappaB) in a model of radiation-induced lung damage in the rat. MATERIAL AND METHODS: The right lung of Fischer rats was irradiated with a single dose of 20 Gy. The cellular distributions of NF-KappaB proteins and mRNA were detected with immunohistochemistry and in-situ hybridization respectively. The DNA binding activity of NF-KappaB, nuclear and cytoplasmic levels of NF-KappaB proteins, and kinase activity towards IkappaBalpha (IKappaBAlpha) 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-KappaB DNA binding activity in the rat lung after ionizing irradiation over 6 months. The irradiated lung tissue exhibited an increased kinase activity towards IKappaBAlpha and a selective loss of nuclear IKappaBAlpha. The NF-KappaB-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-KappaB-dependent genes in the irradiated rat lung. CONCLUSIONS: The DNA binding activity of NF-KappaB is continuously activated after irradiation of the rat lung by loss of nuclear IKappaBAlpha. This might play a role in sustaining chronic inflammation and hyperproliferation of mesenchymal cells after irradiation.