The estrogen receptor (ER) is a ligand-activated enhancer protein that belongs to the steroid/nuclear receptor superfamily and functions as a signal transducer and transcription factor to modulate expression of target genes. Mammalian ER is encoded by two genes: alpha and beta (ER-alpha and ER-beta) which have three major functional domains including an N-terminus that modulates transcription in a gene- and cell-specific manner through Activation Function-1, a highly conserved central DBD through which ER interacts directly with the DNA helix, and the LBD that contains Activation Function-2. In human physiology, ERs not only play a central role in the control of sexual behavior and reproductive functions, but are also widely involved in the differentiation of several tissues and organs, the modulation of inflammation, and brain and cardiovascular functions. In response to ligand binding of 17beta-estradiol (E2) or other agonists, ER changes conformation and dissociates from hsp90, hsp70 and other proteins, so that ligand-occupied ER dimer has been formed to regulate target genes. Activated ER stimulates target gene expression by two mechanisms: genomic and non-genomic (non-genotropic) pathways. In the genomic pathway, ligand-occupied ER directly binds to a specific sequence in the promoters of target genes (specifically, the estrogen response element or ERE), resulting in enhanced transcription. In the non-genomic pathway, ER can indirectly associate with promoters through protein-protein interactions with other DNA-binding transcription factors. For example, ER-alpha interacts with Sp1 in response to estrogen stimulation to regulate the transcription of RARalpha, insulin-like growth factor-binding protein-4, transforming growth factor alpha, LDL receptor genes, and others.

Upon receipt, the positive control should be removed and stored at -20^° or -80^°C. The remainder of the kit can be stored for up to 6 months at 2-8^°C from the date of shipment. Opened Microplate Wells or reagents may be stored for up to 1 month at 2^° to 8^°C. Return unused wells to the pouch containing desiccant pack, reseal along entire edge. Note: The kit can be used within one year if the whole kit is stored at -20^°C upon receipt. Avoid repeated freeze-thaw cycles.