ESR1 and breast cancer: Other studies on different cell lines found that a selective GPER-1 agonist inhibits nuclear ERs activity in human breast cancer cells (MCF-7) (Smith et al., 2016), whereas it was indicated to upregulate ERα expression in human breast cancer cells (SK-BR-3), human embryonic kidney cells (HEK293), and monkey kidney cells (COS7) (Kang et al., 2010).