Classically, the mechanism of action of oestrogen was singularly attributed to the binding of nuclear oestrogen receptor (ER) and subsequently activation of target genes over the course of several hours.
In a variety of experimental tissues and human breast cancers, binding of the oestrogen conjugates was demonstrable, but it appeared nonspecific (i.e., rarely displaceable by competitor) and unrelated to oestrogen receptor (RE) status of the tissue as determined biochemically by assay with dextran-coated charcoal.
The mechanism occurred through competitive inhibition of oestrogen following the selective binding of oestrogen receptors (ERα) on the hypothalamus and pituitary [ 52].
Gata-3 binds to the promoter of FoxA1, a forkhead factor that is required for chromatin binding of oestrogen receptor [ 2, 5].
MEK ERK activation in breast cancer cell lines occurs after binding of oestrogen to its receptor (Collins and Webb, 1999), stimulation by insulin (Griffiths et al, 1998) or binding of growth factors like EGF or PDGF (Whitmarsh and Davis, 1996).
Although binding of oestrogen to LBD is essential for complete activation of ER α, phosphorylation by extracellular signal-activated kinases is thought to play a role in oestrogen-dependent and oestrogen-independent activity of ER α (Ali et al, 1993; Le Goff et al, 1994).
Tamoxifen is a selective OR modulator that blocks the binding of oestrogen to its nuclear receptor, is cytostatic in action (O'Regan and Jordan, 2002) and has been shown to reduce cell proliferation in IBC (Clarke et al, 1993) and in normal breast epithelium (Bernardes et al, 1999) as determined, using Ki67 nuclear antigen immunohistochemistry.
The drug blocks the binding of oestrogens to the human oestradiol receptors (ER), which are specific proteins in the human breast cell.
In the activation process, the first step, binding of oestrogens to ER and subsequent binding to ERE, induces the synthesis of GAL4ff protein and in the second step Gal4ff protein induces synthesis of GFP.
Unlike Tam, AFPep did not inhibit binding of oestradiol (E2) to oestrogen receptor (ER).
