Estrogen Receptor Mediates the Radiosensitivity of Triple-Negative Breast Cancer Cells

Abstract

BACKGROUND This study aimed to evaluate differences in the radiosensitivities of triple-negative breast cancer (TNBC) and luminal-type breast cancer cells and to investigate the effects of estrogen receptor (ER) expression on the biological behaviors of the cells. MATERIAL AND METHODS Colony-forming assays were performed to detect differences in radiosensitivities in breast cancer cell lines. Gene transfection technology was used to introduce the expression of ERα in TNBC cells to compare the difference in radiosensitivity between the TNBC cells and ERα transfected cells. CCK-8 assays were used to observe changes in the proliferation of TNBC cells after ERα transfection. Immunofluorescence was used to detect the number of γH2AX foci in nuclei. Flow cytometry was used to detect changes in cell cycle distribution and apoptosis. Western blotting was used to detect changes in autophagy-associated proteins. RESULTS The radioresistance of the TNBC cell line MDA-MB-231 (231 cells) was greater than that of ERα-positive luminal-type breast cancer cell line MCF-7. Moreover, 231 cell proliferation and radioresistance decreased after ERα transfection. Interestingly, ERα-transfected 231 cells showed increased double-stranded breaks and delayed repair compared with 231 cells, and ERα-transfected 231 cells showed increased G2/M phase arrest and apoptosis after irradiation compared with those in 231 cells. ERα transfection in 231 cells reduced autophagy-related protein expression, suggesting that autophagy activity decreased in 231 ER-positive cells after irradiation. CONCLUSIONS TNBC cells were more resistant to radiation than luminal-type breast cancer cells. ERα expression may have major roles in modulating breast cancer cell radiosensitivity.

Figure 1

(A) Survival curves of 231 and MCF-7 cells. (B) Expression levels of endogenous HER2 and ERα in MCF-7 and 231 cells.

Figure 2

(A) Agarose gel electrophoresis of the ERα amplification fragment. (B) Electrophoresis of the double-enzyme digested recombinant plasmid.

Figure 3

(A) Identification of ERα protein expression in stably transfected cell lines. (B) Growth curves of MDA-MB-231, ER231, and pBabe231 cells.

Figure 4

Survival of MDA-MB-231, ER231 and MCF-7 cells after exposure to different doses of radiation.

Figure 5

Changes in the number of γH2AX foci in each nucleus in 231 and ER231 cells after irradiation.

Figure 6

The cell cycle distributions of 231 and ER231 cells at different times after single-dose irradiation.

Figure 7

(A) Early-stage apoptosis in 231 and ER231 cells at different times after irradiation. (B) Late-stage apoptosis in 231 and ER231 cells at different times after irradiation.

Figure 8

Expression of autophagy-associated proteins in 231 and ER231 cells after irradiation.