Analysis of MCF-10A Cells for ERα, ERβ, and EGFR. Nuclear proteins extracted from MCF-10A cells that were exposed to differing culture conditions were analyzed by Western blotting for the presence of ERα, ERβ, and EGFR. Numbers in parentheses indicate the number of passages in that particular type of medium. Proteins (42 μg/lane) were electrophoresed onto two 12% Tris-HCl gels (lanes 1-8 and 9-16 respectively) and transferred onto nitrocellulose membranes. Membranes were probed with antibodies directed against ERα (a and b), stripped and re-probed with antibodies directed against ERβ (c and d), and stripped a second time and re-probed with antibodies directed against EGFR (e and f). Results shown are those from one experiment.