TABLE 1.

Characteristics of ERs.

ERs	ERα				ERβ		GPER
Identification	1969				1996		1997
Category			Nuclear steroid hormone superfamily				G protein-coupled receptor superfamily
Location	Cytoplasm, nucleus	Membrane (caveolae)		Cytoplasm, nucleus		Membrane (caveolae)	Membrane
Targets	ERE, non-ERE	PI3K, ERK		ERE, non-ERE		ND	AC/PKA, EGFR (PI3K, ERK)
References	(Caulin-Glaser et al., 1997; Lantin-Hermoso et al., 1997; Mendelsohn and Karas, 1999, 2005, 2010; Chambliss et al., 2000, 2010; Simoncini et al., 2000; McKenna and O’Malley, 2002; Florian et al., 2004; Lu et al., 2004; Levin, 2005; Osborne and Schiff, 2005; Pedram et al., 2006; Ueda and Karas, 2013; Ueda et al., 2018)			(Mendelsohn and Karas, 1999, 2005; Chambliss et al., 2002; McKenna and O’Malley, 2002; Patten et al., 2004; Fliegner et al., 2010)			(Haas et al., 2009; Prossnitz and Barton, 2011; Feldman and Limbird, 2017; Luo and Liu, 2020)

ER, estrogen receptor; GPER, G protein estrogen receptor; ERE, estrogen response element; AC, adenylate cyclase; PKA, protein kinase A; EGFR, epidermal growth factor receptor; PI3K, phosphoinositide 3-kinase; ERK, extracellular signal-regulated kinase; ND, not determined.