NF-kappaB and AP-1 are responsible for inducibility of the IL-6 promoter by ionizing radiation in HeLa cells.
OBJECTIVE
To investigate the mechanisms leading to initiation by ionizing radiation of IL-6 transcription in HeLa cells.


METHODS
HeLa cells were irradiated with X-rays at a dose rate of approximately 1 Gy/min or treated with TPA (100 ng/ml). Transient transfection analysis with truncated IL-6 promoter CAT constructs was used to identify the radiation-sensitive region within the IL-6 promoter/enhancer.


RESULTS
For basal expression of the IL-6 gene in unirradiated control cells the presence of the binding site for the nuclear factor kappa B (NF-kappaB) and the multiple response elements (MRE) were necessary. After deletion of either the activator protein (AP)-1 or the MRE site, radiation-induced IL-6 promoter CAT activity was significantly reduced, whereas after deletion of the NF-kappaB site it was completely abolished. Maximal radiation-induced 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 constitutive, 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 in X-ray-inducible IL-6 expression in HeLa cells. The fact that IL-6 promoter activity was dramatically enhanced in the presence of the MRE and distal AP-1 binding motif is indicative of a cooperative mode of transcriptional activation involving all three transcription factor systems. These data provide new insights into the prodromal events of radiation-induced inflammation of epithelial cells and putatively the cutaneous radiation syndrome.
Beetz
A
A
Institute of Radiobiology, Federal Armed Forces Medical Academy, Munich, Germany.
Peter
R U
RU
Oppel
T
T
Kaffenberger
W
W
Rupec
R A
RA
Meyer
M
M
van Beuningen
D
D
Kind
P
P
Messer
G
G
D001665:Binding Sites / Q000235:genetics; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004742:Enhancer Elements, Genetic / Q000528:radiation effects; D006367:HeLa Cells; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics*; D016328:NF-kappa B / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000528:radiation effects*; D011836:Radiation Tolerance / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D015533:Transcriptional Activation / Q000528:radiation effects; D014162:Transfection
D017931:DNA Primers; D015850:Interleukin-6; D016328:NF-kappa B; D018808:Transcription Factor AP-1; D015500:Chloramphenicol O-Acetyltransferase