Nuclear factor κB (NF-κB) is a pleiotropic transcription factor which is involved in the transcriptional regulation of several specific genes. Recent reports demonstrated that ionizing radiation in the dose range of 2-50 Gy results in expression of NF-κB in human KG-1 myeloid leukemia cells and human B-lymphocyte precursor cells; the precise mechanism involved and the significance are not yet known. The present report demonstrates that even lower doses of ionizing radiation, 0.25-2.0 Gy, are capable of inducing expression of NF-κB in EBV-transformed 244B human lymphoblastoid cells. These results are in a dose range where the viability of the cells remains very high. After exposure to137 Cs γ rays at a dose rate of 1.17 Gy/min, a maximum in expression of NF-κB was seen at 8 h after a 0.5-Gy exposure. Time-course studies revealed a biphasic time-dependent expression after 0.5-, 1- and 2-Gy exposures. However, for each time examined, the expression of NF-κB was maximum after the 0.5-Gy exposure. The expression of the p50 and p65 NF-κB subunits was also shown to be regulated differentially after exposures to 1.0 and 2.0 Gy.

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