Reassessment of Estrogen Receptor Expression in Human Breast Cancer Cell Lines

Human breast cancer cell (BCC) lines are used extensively in biomedical research and are classified as estrogen receptor (ER)-positive or ER-negative. We used flow cytometry (FCM), reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting (WB) to assess ER expression in human BCC lines reported as being ER-positive (MCF7, T-47D, ZR-75-1) or ER-negative (MDA-MB-231, SK-BR-3, MDA-MB-453, HCC1954) to determine the validity of this classification. ER was assessed in permeablized, fixed cells by FCM using two monoclonal anti-ERα antibodies and a polyclonal anti-ERβ antibody, in parallel with RT-PCR and WB. All of the cell lines expressed ERα and ERβ. Indirect immunofluorescence indicated that it was membrane and cytoplasmic ER that was being detected by FCM. Down-regulation by fulvestrant confirmed it was ER. These results demonstrate the importance of reassessing the ER status of human BCC lines that are used widely in biomedical research.