Effects of NF-κB1 (p50) targeted gene disruption on ionizing radiation-induced NF-κB activation and TNFα, IL-1α, IL-1β and IL-6 mRNA expression in vivo

Purpose: To investigate the role of the NF-κB1 (p50) gene in ionizing radiation (IR)-induced NF-κB activation and TNFα, IL-1α, IL-1β and IL-6 mRNA expression in vivo. Materials and methods: NF-κB activation was analysed by the gel shift/supershift assay and the levels of TNFα, IL-1α, IL-1β and IL-6 mRNA were measured using RNase protection assay (RPA). Various tissues from BALB/c, B6,129P-Nfkb1 (NF-κB1 or p50 gene knockout, p50^-/-) and B6,129PF2 (wild-type, p50^+/+) mice were analysed before or after exposure to a lethal dose (8.5 Gy) of total-body γ-irradiation. Results: Exposure of BALB/c mice to total-body IR selectively activated NF-κB in the spleen, mesenteric lymph nodes (LN) and bone marrow (BM). Gel supershift assay using polyclonal antibodies against NF-κB p50, p65 or c-Rel protein revealed that the NF-κB p50 subunit is a critical component of the NF-κB complexes activated by IR in vivo. Discretely augmented TNFα, IL-1α, IL-1β and IL-6 mRNA expression was found in the spleen, LN and BM after BALB/c mice received IR. However, mice lacking the p50 gene (p50^-/-) showed a significant reduction in IR-induced activation of NF-κB and increases in TNFα, IL-1α, IL-1β and IL-6 mRNA expression, as compared with that of wild-type mice (p50^+/+). Conclusions: The NF-κB p50 subunit is a critical component of the NF-κB complexes activated by IR and it plays an important role in mediating IR-induced TNFα, IL-1α, IL-1β and IL-6 mRNA expression in vivo.