NF-kappaB promotes cell survival against external stress such as radiation. We examined whether NF-kappaB decoy transfection enhances the antiproliferative effects of radiation on vascular smooth muscle cells (VSMCs) in vitro. The irradiation induced activation or nuclear translocation of NF-kappaB p65 in VSMCs was confirmed by immunofluorescence. NF-kappaB decoy transfection resulted in inhibition of the radiation-induced NF-kappaB activation in VSMCs and the subsequent reduction of transcription and translocation of ICAM, iNOS, and TNF-alpha, downstream molecules under the control of NF-kappaB. By using MTT assay, NF-kappaB decoy augmented the antiproliferative effects of radiation, where the effect of low dose radiation (2 and 8-Gy) of the cells transfected with NF-kappaB decoy was equivalent to the high dose (16-Gy) irradiated non-transfected cells at 48 h after irradiation: 1.06+/-0.16, 1.11+/-0.22, 1.20+/-0.25, respectively. The decrease in proliferation and survival of the radiation treated cells by flow cytometry analysis showed that NF-kappaB inhibition did not show any additive effects on the cell cycle of the irradiated VSMCs, while apoptosis was significantly increased after NF-kappaB decoy transfection in the irradiated VSMCs (apoptosis fraction: 13.33+/-2.08% vs. 26.29+/-7.43%, for radiation only vs. radiation+NF-kappaB decoy transfection, P < 0.05). In addition, at 48 h, NF-kappaB decoy transfection dose dependently (10 microM vs. 20 microM) inhibited proliferation of 16Gy-irradiated VSMCs, and showed greater antiproliferative efficacy than 100 microM sulfasalazine, a specific NF-kappaB inhibitor. These results indicate that NF-kappaB inhibition reduces proliferation and survival of irradiated VSMCs, likely by increased apoptosis rather than additive cell cycle arrest and suggest the possibility of adjunctive gene therapy using NF-kappaB decoy to improve efficacy and to decrease the adverse effects of intracoronary radiation therapy.
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