An analysis of the effects of HIF-1α siRNA on genes up-regulated by low-dose radiation therapy. (A) HIF-1α mRNA expression was examined with real time qRT-PCR after silencing with HIF-1α siRNA to demonstrate effective HIF-1α knockdown. An 85% reduction in HIF-1α mRNA expression was achieved (n = 4). (B) SDF-1 mRNA levels with and without HIF-1α silencing. There was an overall reduction in SDF-1 expression in hypoxia. However, 5 Gy IR exposure still effected a relative increase versus nonradiated samples despite HIF-1α blockade (n = 4).