Characterization of a Membrane-Associated Estrogen Receptor in Breast Cancer Cells and Its Contribution to Hormone Therapy Resistance Using a Novel Selective Ligand.

•Novel specific ligand to membrane-associated estrogen receptor (mER) was prepared.•The mER specific ligand contributes to cell proliferation from outside of the cells.•The mER mediates both PI3K/akt and MAPK (Erk1/2) pathways.•The mER probably consists of sub-localized forms of nuclear ERα.•The mER signaling pathway may help generate hormone therapy resistance.