Fig. 5.

EGFRvIII decreased the expression of ER and PgR in estrogen-independent, tamoxifen-resistant breast cancer cells. Immunoblot analysis of the ERα and PgR expression of breast cancer cells expressing EGFRvIII in comparison to parental cells. Whole cell lysates (25 μg) from MCF-7/wt, MCF-7/vIII, MDA-MB-361/wt, and MDA-361/vIII cells were electrophoresed on SDS-PAGE, transferred onto nitrocellulose membranes, and immunoblotted with anti-ERα or anti-PgR antibodies. GAPDH was used as a loading control. Protein bands were detected using a chemiluminescence detection system. Estrogen-dependent, tamoxifen-sensitive MCF-7/vIII cells did not have altered ERα protein levels, but did not have increased PgR expression in comparison to MCF-7/wt cells. Conversely, estrogen-independent, tamoxifen-resistant MDA-MB-361/vIII cells had decreased levels of ERα and PgR protein levels in comparison to MDA-MB-361/wt cells.