FIG. 1.

IR differentially regulates protein synthesis in transformed and nontransformed cells. (A) Established cell lines with increasing transformation, from immortalized breast epithelial cells (MCF10A) to highly transformed breast cancer cells (BT474), were propagated under identical conditions and either left untreated or treated with 8 Gy IR (the highest tolerated dose for MCF10A cells), and protein-synthetic activity was measured 24 h later in the surviving fraction by [³⁵S]methionine/cysteine incorporation and determination of protein specific activity. The data are presented as the ratio of treated to untreated specific activities of protein labeling plus standard errors of the mean. (B and C) Protein synthesis rates of MCF10A cells (B) and BT474 cells (C) with increasing IR doses. The rates were measured by [³⁵S]methionine/cysteine incorporation and determination of protein specific activity. The data presented were derived from the mean of at least three independent experiments.