Regulation of FOS by different compartmental stresses induced by low levels of ionizing radiation

We irradiated different cellular compartments and measured changes in expre ssion of the FOS gene at the mRNA and protein levels. [H-3]Thymidine and tr itiated water were used to irradiate the nucleus and the whole cell, respec tively. I-125-Concanavalin A binding was used to irradiate the cell membran e differentially. Changes in FOS mRNA and protein levels were measured usin g semi-quantitative RT-PCR and SDS-PAGE Western blotting, respectively, Irr adiation of the nucleus or the whole cell at a dose rate of 0.075 Gy/h caus ed no change in the level of FOS mRNA expression, but modestly (1.5-fold) i nduced FOS protein after 0.5 h, Irradiation of the nucleus at a dose rate o f 0.43 Gy/h induced FOS mRNA by 1.5-fold after 0.5 h, but there was no sign ificant effect after whole-cell irradiation. FOS protein was transiently in duced 2.5-fold above control levels 0.5 h after a 0.43-Gy/h exposure of the nucleus or the whole cell. Irradiation of the cell membrane at a dose rate of 1.8 Gy/h for up to 2 h caused no change in the levels of expression of FOS mRNA or protein, but a dose rate of 6.8 Gy/h transiently increased the level of FOS mRNA S-fold after 0.5 h, These data demonstrate the complexity of the cellular response to radiation-induced damage at low doses. The lac k of quantitative agreement between the transcript and protein levels for F OS suggests a role for posttranscriptional regulation. (C) 2000 by Radiatio n Research Society.