An analysis of the effects of IR on cytokine mRNA and protein expression. (A) SDF-1 mRNA was significantly up-regulated in ECs exposed to radiation in both normoxic and hypoxic conditions (n = 4). (B) When examined over a time course ranging from 24 to 72 hours, 5 Gy IR significantly elevated SDF-1 mRNA expression over nonirradiated controls. The combination of 5 Gy IR and hypoxia resulted in the greatest up-regulation of SDF-1 mRNA expression at all time points. Maximal expression occurred at the 36-hour time point (n = 4). (C) SDF-1 protein expression was examined at 48 hours. Maximal expression was again seen with the combination of hypoxia and 5 Gy IR (n = 6). (D) To look at the effects of other proangiogenic HIF target genes, VEGF protein expression was examined at 48 hours showing maximal up-regulation with the combination of hypoxia and 5 Gy IR (n = 6).