E-selectin gene induction by ionizing radiation is independent of cytokine induction

The mechanism of the x-ray-mediated inflammatory response in normal tissues is unknown. To determine whether leukocyte infiltration into irradiated tissue is regulated by adhesion molecule expression, we quantified the synthesis of glycoproteins that participate in inflammation. We found that E-selectin is synthesized in a time-dependent manner following exposure to doses as low as 0.5 Gy. Northern blot analysis demonstrated that E-selectin mRNA expression increased at 2 h after x-irradiation and increased expression required no de novo protein synthesis. Transcription of the promoter region of E-selectin (-578 to +35) was transiently induced following x-irradiation, whereas deletion of the NFkB binding site eliminated x-ray induction. Electrophoretic mobility gel shift analysis confirmed increased binding of nuclear proteins from irradiated endothelial cells to the NFkB binding sequence from the E-selectin promoter. Nuclear protein binding to the NFkB binding sequence was altered by antibodies to the p50 and p65 components of NFkB. These data demonstrate that E-selectin expression does not require cytokine synthesis, but involves NFkB activation.