Discontinuous induction of X-linked inhibitor of apoptosis in EA.hy.926 endothelial cells is linked to NF-κB activation and mediates the anti-inflammatory properties of low-dose ionising-radiation.
OBJECTIVE
This study aimed to characterize a link between X-linked inhibitor of apoptosis protein (XIAP) expression, apoptosis induction, Nuclear Factor kappa B (NF-κB) activity and the anti-inflammatory properties of low-dose ionising-radiation (LD-RT).


METHODS
EA.hy.926 endothelial cells (ECs) were irradiated with doses ranging from 0.3 to 3Gy, and subsequently stimulated by TNF-α, and XIAP expression was either detected by immunoblotting or TaqMan-PCR. Apoptosis was quantified by AnnexinV staining or by caspase 3/7 activity assays. NF-κB transcriptional activity was analysed by a luciferase reporter assay, secretion of Transforming Growth Factor beta 1 (TGF-β(1)) and adhesion of peripheral blood mononuclear cells (PBMC) to EC were quantified using ELISA and adhesion assays.


RESULTS
LD-RT of the activated EA.Hy.926 EC induces XIAP expression in a discontinuous manner with a relative maximum at 0.5Gy and 3Gy which parallels a discontinuity in apoptosis induction and caspase 3/7 activity. siRNA-mediated attenuation of XIAP resulted in an increased rate of apoptosis, a hampered NF-κB transcriptional activity and a diminished secretion of TGF-β(1). As compared to control-siRNA treated cells, adhesion of PBMC to EC was increased in XIAP depleted EA.Hy.926 EC.


CONCLUSIONS
The modulation of apoptosis, NF-κB activity and TGF-β(1) by XIAP in irradiated and subsequent stimulated EC contributes to an impaired PBMC/EC adhesion and to the anti-inflammatory properties of LD-RT.
Rödel
Franz
F
Department of Radiotherapy and Oncology, University of Frankfurt, Frankfurt am Main, Germany. franz.roedel@kgu.de
Frey
Benjamin
B
Capalbo
Gianni
G
Gaipl
Udo
U
Keilholz
Ludwig
L
Voll
Reinhard
R
Hildebrandt
Guido
G
Rödel
Claus
C
D000893:Anti-Inflammatory Agents / Q000378:metabolism*; D017209:Apoptosis / Q000502:physiology; D015153:Blotting, Western; D002460:Cell Line; D004307:Dose-Response Relationship, Radiation; D042783:Endothelial Cells / Q000378:metabolism*; D020869:Gene Expression Profiling; D006801:Humans; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D011839:Radiation, Ionizing; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism*
D000893:Anti-Inflammatory Agents; D016328:NF-kappa B; D051636:X-Linked Inhibitor of Apoptosis Protein