Estrogen receptor(ER) and hormone

1. Sex hormone is one class of hormones, which includes estrogen, androgen, and progestogen. Hormone are important for inter-cell signaling.
2. Estradiol (E2) is one of estrogen, which can enter cell freely and bind to its receptor.
3. Estrogen receptor (ER) is a group of receptor that can be activated by estrogen. There are two types of ER, ERα and ERβ, both of which can form a dimer after activated by hormone. So, there are ERα (αα) or ERβ (ββ) homodimers or ERαβ (αβ) heterodimer. ER-alpha mostly occurs in endometrium, breast cancer cells, ovarian stroma cells, and the hypothalamus, where ER-beta are found in kidney, brain, bone, heart, lungs, intestinal mucosa, prostate, and endothelial cells.
4. Without sex hormone, ER are largely located in cytosol. When it's bound by hormone, a numer of events "starting with migration of the receptor from the cytosol into the nucleus, dimerization of the receptor, and subsequent binding of the receptor dimer to specific sequences of DNA (called hormone response elements)" are triggered. The receptor/DNA complex can then recruit other factor to initiate/activate the transcription of downstream genes.