ER alpha Protein, Human

Estrogen receptor-alpha (ERα), also known as ESR1 or NR3A1, is a ligand-dependent nuclear transcription factor belonging to the nuclear receptor superfamily. Its protein structure comprises an N-terminal transcriptional activation domain (AF-1), a central DNA-binding domain (DBD), and a C-terminal ligand-binding domain (LBD containing AF-2). Upon estrogen binding to the LBD, the receptor undergoes conformational changes that promote dimerization and binding to estrogen response elements (EREs) in target gene promoters, thereby regulating gene transcription. ERα mediates estrogen's physiological effects on target tissues including breast, uterus, and bone, promoting cell proliferation, differentiation, and metabolic regulation. Clinically, ERα serves as the most critical molecular biomarker and therapeutic target in breast cancer, with approximately 70% of breast cancer patients being ERα-positive. Endocrine therapies such as tamoxifen and aromatase inhibitors significantly improve patient outcomes by blocking ERα signaling. Furthermore, ERα expression levels correlate with malignancy and treatment response in gynecological cancers including endometrial and ovarian cancers, while aberrant expression or mutations (e.g., Y537S, D538G) are associated with endocrine therapy resistance. Consequently, ERα testing has become the cornerstone for molecular subtyping of breast cancer and personalized treatment decision-making.