NF-kappa B and AP-1 are responsible for inducibility of the IL-6 promoter by ionizing radiation in HeLa cells

Purpose: To investigate the mechanisms leading to initiation by ionizing ra diation of IL-6 transcription in HeLa cells. Materials and methods: HeLa cells were irradiated with X-rays at a dose rat e of approximately 1 Gy/min or treated with TPA (100 ng/ml). Transient tran sfection analysis with truncated IL-6 promoter CAT constructs was used to i dentify the radiation-sensitive region within the IL-6 promoter/enhancer. Results: For basal expression of the IL-6 gene in unirradiated control cell s the presence of the binding site for the nuclear factor kappa B (NF-kappa B) and the multiple response elements (MRE) were necessary. After deletion of either the activator protein (AP)-1 or the MRE site, radiation-induced I L-6 promoter CAT activity was significantly reduced, whereas after deletion of the NF-kappaB site it was completely abolished. Maximal radiation-induc ed IL-6 promoter CAT activity was observed when the AP-1, NF-kappaB and MRE motifs were present. In electrophoretic mobility shift analyses (EMSA), X- ray-inducible activity was found for NF-kappaB and AP-1 at the MRE constitu tive, but no inducible activities were detectable. The nuclear factor IL-6 (NF-IL6) element showed no specific radiation-responsive activity. Conclusions : These results demonstrate that NF-kappaB plays a major role i n X-ray-inducible IL-6 expression in HeLa cells. The fact that IL-6 promote r activity was dramatically enhanced in the presence of the MRE and distal AP-1 binding motif is indicative of a cooperative mode of transcriptional a ctivation involving all three transcription factor systems. These data prov ide new insights into the prodromal events of radiation-induced inflammatio n of epithelial cells and putatively the cutaneous radiation syndrome.