Fig. 5.

IR induces cytotoxic IFNβ response. (A) Radiation-induced expression of IFNβ mRNA. IFNβ expression in D54, WiDr, SCC61, and HEK293 cells treated with or without 6 Gy IR was measured by qRT-PCR and normalized to GAPDH expression. Data are expressed as fold change relative to nonirradiated cells. (B) Radiation-induced activation of IFNβ promoter. HEK293 cells were transiently cotransfected with pGL3–Ifnβ and pRL–SV40. Firefly luciferase was normalized to Renilla luciferase and is expressed relative to nonirradiated cells at each collection time. (C) Type I IFN receptor (IFNAR1) is needed for cytotoxicity induced by IR. WT and IFNAR1^−/− MEFs were treated with the indicated doses of IR and collected 96 h post-IR. Viability was determined by methylene blue staining and extraction, followed by spectrophotometric quantification. Viability is shown relative to nonirradiated control cells. Data are represented as means with SDs for assays performed at least in triplicate.