Fig. 2.

Paracrine factors produced in response to estrogen expand ERα⁻ breast CSCs. (A) Immunofluorescence of sorted cytospun MCF7 cells for ERα (green) and ESA/EpCAM (red) expression, counterstained for nuclei with DAPI (blue). (B) Cytometric plots of ERα expression in CD44⁺/CD24⁺/ESA⁺ cells (red, bulk), and in CD44⁺/CD24⁻/ESA⁺ stem-like cells (green), which comprise 2% of the culture. (C) Average percentage of CD44⁺/CD24⁻/ESA⁺ cells in ERα⁻ SUM149, SUM159, and BT20 cultures following treatment with conditioned media from either ethanol (EtOH) or E2-pretreated MCF7. MCF7 cells are shown for reference, *P < 0.0001, n = 4 biological replicates. Data are mean ± SEM. (D) Tumorsphere-forming potential of SUM149 or SUM159 cultures described in C; n = 4 biological replicates. Data are mean ± SEM.