Fig. 6.

Radioresistant MCF-7 and ZR-751 cells show loss of ERα and PgR expression and gain in EGFR expression with a shift from ER to EGFR signalling pathways. A and B Expression profiles of signalling receptors, ERα, PgR, Her2 and EGFR in MCF-7 and MCF-7 RR cell lines using A IHC with MTS and B Western blot analysis. Ci SRB at 72 h and Cii scratch assay at 24 and 48 h showing the effects of the gefitinib in MCF-7 and RR cell lines. Ciii SRB assay showing the effect of tamoxifen in MCF-7 and RR cell lines at 72 h. D Levels of EGFR expression increased 96 and 120 h after ERα siRNA knockdown. Graphs document the relative intensity of EGFR normalised to the loading controls using 25 nM of ERα siRNA. Ei&ii SRB assay showing significant reduction in proliferation of the MCF-7 cells after 72 h treatment with either ERα siRNA (25 nM) or tamoxifen (0.05 μM), whereas no reduction in proliferation was seen in MCF-7 RR cells. Fi&ii SRB assay showing an additional reduction in MCF-7 proliferation following ERα knockdown or tamoxifen treatment when combined with radiation 24 h after transfection/tamoxifen treatment (2-way ANOVA with Holm-Sidak’s multiple comparisons test; data expressed as mean ± SEM, n = 3, ****p ≤ 0.0001; **p ≤ 0.01; *p ≤ 0.05)