Expression of Oestrogen Receptor and Transforming Growth Factor-α in MCF-7 Cells after Exposure to Fractionated Irradiation

Abstract

The expression of critical growth controlling genes was studied in MCF-7 cells after exposure to cumulative radiation doses of 20 and 60 Gy yielding cell lines called MCF-IR-1 and MCF-IR-3, respectively. The irradiated cell lines exhibited increased plating efficiencies but no differences in growth rates. MCF-IR-1/-IR-3 cells showed a reduced oestrogen responsiveness as indicated by their diminished response to tamoxifen-induced growth arrest and 17β-oestradiol (E₂)-induced growth stimulation. The reduced expression of oestrogen receptor (ER) was determined by quantitative immune peroxidase staining of single cells and by total cellular E₂ binding. There was also a radiation dose-dependent increase in the radiosensitivity of MCF-IR-3 cells as determined by the radiobiological parameters α, β, and D¯ (mean inactivation dose). Using RNA protection assays the irradiated cell lines produced steady-state ER mRNA at reduced levels while the levels of TGF-α were unchanged in MCF-IR-1 cells but increased 2·8-fold in MCF-IR-3 cells. A similar pattern was seen for TGF-α protein. While the current analyses cannot differentiate between radiation-induced altered gene expression or cell selection the results demonstrate that reduced ER expression and increased TGF-α expression are associated with the survival of MCF-7 cells after fractionated irradiation in vitro. In contrast, the MCF-IR cells were found to be more radiosensitive in acute survival experiments.