IONIZING-RADIATION INDUCES, VIA GENERATION OF REACTIVE OXYGEN INTERMEDIATES, INTERCELLULAR-ADHESION MOLECULE-1 (ICAM-1) GENE-TRANSCRIPTION AND NF-KAPPA-B-LIKE BINDING-ACTIVITY IN THE ICAM-1 TRANSCRIPTIONAL REGULATORY REGION

Ionizing radiation produces reactive oxygen intermediates in mammalian tissues and may serve as a model system for the investigation of the biologic effects of free radicals. We have previously shown that the a dhesion molecule ICAM-1 is induced by ionizing radiation, and here we have investigated the molecular mechanisms responsible. ICAM-1 mRNA an d cell surface expression was induced in HeLa and HaCaT cells after ex posure to ionizing radiation. This induction was blocked by preincubat ion with the antioxidants PDTC and N-acetyl cysteine. ICAM-1 promoter activity was assessed by transiently transfecting HeLa cells with CAT- reporter gene constructs containing sequential ICAM-1 5' deletions. IC AM-1 5' fragments -1162/+1 (relative to the transcription start site) and -277/+1 displayed increased promoter activity when cells were expo sed to ionizing radiation, but no induction was seen in a -182/+1 cons truct associating positions -277 to around -182 with inducibility by i onizing radiation. Nuclear extracts from HaCaT cells were tested in mo bility shift assays using an NF kappa B-like binding site of the ICAM- 1 5' region (positions -186/-177). There was marked enhancement of DNA -protein complex forming in extracts from irradiated versus untreated cells. Incubation of cells with antioxidants prior to irradiation prev ented the radiation-dependent increase in complex formation. We conclu de that reactive oxygen intermediates are involved in ICAM-1 induction by ionizing radiation. The ionizing radiation-induced, antioxidant-in hibitable binding at the ICAM-1 NF kappa B-like binding site is consis tent with the view that NF kappa B is a pro-oxidant transcription fact or.