Expression of the estrogen receptor alpha (ERα) and the androgen receptor (AR) in CAMA-1, MCF-7, and MCF7-AR1 breast cancer cell lines at the protein level. Cell extracts were prepared during exponential proliferation in maintenance medium containing 10% fetal bovine serum. Immunoblots were performed as described in Materials and methods. (a) A representative immunoblot. (b) Relative expression of sex steroid receptors quantified to actin content. Each bar represents the mean ± standard error of the mean of four independent experiments. Double asterisk indicates P < 0.01 versus wild-type MCF-7 cells as determined by an analysis of variance followed by a Bonferroni post hoc test.